GAS TERMINAL

PHASE-I & PHASE-II

SECTION-I

GENERAL

1.1 INTRODUCTION

Hazira onshore terminal project of ONGC is a facility to receive the two-phase flow gas stream of south Bassein-Hazira gas pipeline. Gas & condensate are separated here and they flow to the down stream units of the complex.

1.2 GAS ARRIVAL CONDITION

The gas arrival condition at the terminal inlet at various flow rates are as follows:

1.3 STREAM FACTOR

The number of streams days per year   365

1.4 UTILITIES SPECIFICATION

Note: Cooling water will be available after LPG plant is commissioned. Shut-off pressure of cooling water re circulation pump is 8.5 kg/cm²abs. Service water is supplied for cooling purpose till then.

1.5 UTILITIES CONSUMPTION

Notes:   1.   Service water includes 5.0 m3/hr. of cooling water.

2.      Not a regular consumption item.

3.      Steam & inert gas are envisaged to be available from Hazira gas processing complex

1.6 LIST OF EQUIPMENTS

1.7 ALARMS/TRIPS SET POINTS

NOTE: PLEASE REFER VENDOR DOCUMENTS FOR ALARMS/TRIP SETTINGS FOR PACKAGE ITEMS

EMERGENCY SHUT DOWN SYSTEM

      On operation of emergency shut down push button, following valves should close:

1. 310 MOV- 1
2. 310 MOV-60
3. 310 MOV-53
4. 310 MOV-53
5. 310 MOV –54
6. 320 PV- 5A
7. 320 PV-5B
8. 320 PV-6B
9. 320 FV-20A
10. 320 FV-20B
11. PUMPS 310-P-1A/B IN CASE RUNNING
12. 310 MOV –34 VALVES SHOULD CLOSE
13. 310 MOV – 36 VALVES SHOULD CLOSE

SECTION -2

Process Description

(Phase-I)

2.1 GENERAL

The Hazira Onshore terminal begins at the point where the South Bassein -Hazira Pipeline ends and ends at the distribution outlet points for the gas and condensate streams. The terminal has facilities for receiving the two-phase flow, separating into Condensate and gas streams, condensate stabilization and distribution and gas distribution.

The two-phase flow is received in the Slug Catcher, where the gas and condensate streams are separated. The gas is filtered, metered and sent to the GSU plants for further processing.

The separated condensate from the Slug Catcher is metered and sent to the CFU plants for further treatment.

2.2 WET GAS RECEIVING FACILITIES

The two phase flow receiving section of the terminal is provided with the following main systems:

a) Pig receiving trap

b) Pressure reducing valves station

c) Slug catcher

The detailed description of the various equipments and some of the important parameters are described below.

2.2.1 PIG RECEIVEING  TRAP

The pig-receiving trap is a facility to recover the pig when scraping the Line and to remove the foreign matters and residual solids, entrained by the pig itself.

At the terminal inlet point of the South Bassein Hazira pipeline downstream of the terminal main valve, is located the Pig receiving trap 310AR-l. The pig receiving trap is a 40 inches diameter and 7.0 feet long, approximately, horizontal barrel. Provided with motor operated inlet and outlet valves. The pressurization bypass, drains and vents complete the connections to perform the pig receiving operation.

A pig signal indicator 310 XX-l mounted in the mainline, approximately 2 kms from the terminal battery limit is used to alert the operator about the arrival of the pig. Another pig signal indicator 310XX-24 mounted at the trap inlet acknowledges the arrival of the pig at the trap.

The main terminal valve, 310 MOV-l, Pig trap inlet and outlet & Valves can be operated both locally as well as from the control room to manage with the receipt of the pigs.

During the normal operation, the terminal inlet valve 310MOVl and pig receiving trap bypass valve 310MOV-3 are kept open and the trap inlet and outlet valves 310 MOV2 & 310 MOV4, the drain valve and vent valve kept closed. The trap is kept in depressurized condition.

When the pig is to be received; the receiving trap is pressurized by opening the bypass valves of the inlet valve 310 MOV2. When the trap is pressurized to the operating pressure, as indicated by the pressure indicator 310 PI.2 the inlet and outlet valves 310 MOV2 & 4 are opened and flow established through the trap.

When the pig signal 310 XXI is actuated, the operator is alerted about the approach of the pig. The operator should now reduce the gas flow through the main line and increase the flow through the receiver trap by throttling the trap bypass valve to 75% of the initial opening. Immediately after the actuation of the pig signal 310XX-2, the trap inlet and outlet valves are closed and normal flow established through the bypass valve.              

After isolating the pig barrel, the drain valve is opened, gradually to drain the condensate into the condensate blow down drum 310-V-3. The pig trap pressure will start falling it is an indication that the trap is drained of liquid. The drain is closed the vent valve is opened to Elevated flare, to depressurize the trap.

The manhole cover should be opened carefully only after ascertaining that the Atrap is completely depressurized. The trap contents are emptied out arid the pig is then retrieved. It is necessary to clean the pig trap and inspect the gaskets before bottling up the trap. The pig-receiving trap should be restored to the same condition as before the launching of the pig operation. Pig indicator switches to be reset in the field.

The residual solids and foreign matter collected as are result of the pig operation have a tendency to catch fire when exposed to the atmosphere for a long time. This is perhaps, because of the heat generated due to the oxidation of nascent iron in the waste. The waste material should be properly disposed off, as is done with hydrocarbon wastes.

There are a number of precautions that need to be taken at the terminal, during the pig operation.

i) Checking and pressure testing of pig receiving trap

ii) Testing and recalibration of the pig signal sensors and the safety valve mounted on the  receiving trap.

iii) Keeping the Slug Catcher condensate level low to receive the pipeline hold up liquid.

iv) Maintaining the gas distribution to consumers at a reduced level because as the line is filled with the condensates pushed by the pig, the plants downstream would remain without gas until the pig arrives.

v) Taking care during condensate drain from trap to blow

down drum at the time of depressurization. To avoid freeze up in the blow down system the electric heating elements on the pipe should be energized.

vi) Complete depressurization of receiving trap before the manhole is opened.

Vii) Proper disposal of foreign and residual matter collected in the trap during the pig operation.

The frequency of pig operation depends upon a number of factors.

i) Gas/condensate flow rate

ii) wax content in the condensate

iii) Hydrogen Sulphide content in the gas

It is necessary to monitor the pipeline efficiency to at the frequency of the pig operation.

2.2.2 PRESSURE-REDUCING VALVES STATION

A pressure reducing valves station is mounted as a bypass to the main gas pipeline, between the terminal inlet valve and the slug catcher. The purpose of the pressure-reducing device is to maintain the pressure inside the arrival terminal within the range allowed for which the terminal piping is designed.

The gas pressure at the terminal inlet at various gas flow rates is given in earlier section. The terminal arrival pressures have been worked out based on a constant pressure of 1500 psia at the South Bassein 'A' platform. It is apparent from the valves that up to a gas flow rate of 7.0 MMSCMD, the terminal inlet pressures can exceed the working pressure allowed by the terminal piping class.

For the operation of the pressure reducing station, a high/low pressure switch, 310 PXHL1 is provided. In the presence of low flow rates, the gas pressure at the terminal inlet will exceed the design pressure and the motor driven valve 310 MOV9 in the main line will be closed, and the gas will be diverted through the pressure reducing valves station. When the flow rate tends to increase up to valves exceeding 10-11 MMSCMD, the design flow of the valves, the low: pressure Switch, set pressure 94 Kg/cm2 absolute is actuated and the motor operated valve. 310 MOV9 will be opened to allow the two-phase flow directly to the Slug Catcher.

The pressure-reducing device consists of two control valves, 310-PV-2A/2B, 10 inches diameter each together sized for a total gas flow\v rate of approx. 10 MMSCMD.

In addition, a 3 inches control valve 310-PV-2 is provided for control at very low flow rates. Pressure indicator controller 310-PIC-2, set pressure 96 Kg/cm2 absolute actuates these control valves. The pipe line is protected against malfunctioning of the pressure indicator controller by three pressure high switches, 310-PXSH 2,3 & 4 set pressure 98 Kg/cm2 absolute two operating and one standby and pressure relief safety valves 310-PSV 2 & 3 set pressure 99 Kg/cm2 absolute. The actuation of the pressure high switches will trigger closure of the terminal inlet valve 310 MOV-l.

2.2.3 SLUG CATCHER

This is a gas liquid separator cum liquid reservoir. The slug catcher has been sized so as to allow the separation of condensate from the gas coming from the sub-sea pipeline, which gets pushed during the pigging of the sub-sea pipeline. The main inlet line to slug catcher is provided with isolation valve 310 MOV-10.

Slug catcher is made up of 48 Fingers of 48" dia and a length of 490 m. It is split into two 24-pipe sectors fully self-sufficient for 50% running in the event of maintenance of one of the two sectors. To get a greater efficiency in the two areas of separation and storage, two different slopping has been adopted, 5 % for the separation area: 0.5% for the storage area.

The feed pipes to the slug catcher, are sized so that the, gas is shared uniformly among the different fingers and there is a progressive decrease in the flow speed, thus facilitating the separation of liquid from gas.

The separation area has been sized so as to allow the thorough separation of the condensate slugs entrained by the gas at the design flow 21.2 MMSCMD.

The storage area has been sized so as to recover the pipe-line hold up (max.), resulting from the. Pigging of the line during a flow rate of 2.85 MMSCMD.

A storage volume of 22,000 M3 has been provided. There are three headers of gas coming out of the slug catcher, having different diameters and connected to each other so as to balance the pressure and convey the separated gas flows towards the common outlet. The branch connections from each finger to the headers are sized so as to contain the, outlet gas speed within the low values that prevent liquid entrainment. The header connecting lines are counts sloping (in respect of the gas flow), so that the liquid that might have been entrained by the gas is allowed to go back into the fingers. The three headers have been positioned along the length of the fingers and are connected as follows with the fingers:

A. PRIMARY RISERS HEADER

This is close to the inlet side of the slug catcher. It allows the separated gas to come out during normal running.

B. SECONDARY  RISERS HEADER

Positioned approx. in the center the storage area, it diverts small quantities of gas coming with the, liquid during normal running. Also it acts as the escape line of the gas left in this area during the arrival of the condensate batch during pigging of the line.

C. EQUALIZING RISERS HEADER

Positioned in the end point of the storage area (near condensate draining). This is to balance the pressures in the liquid phase. Also it acts as escape line of the gas, left in the fingers during pigging of the line.

The two headers, secondary and Equalizing mentioned in B&C above permit the removal of gas left with the liquid in the fingers. Also they prevent liquid agitation and Entrainment produced by counter current flow of gas and liquid towards the primary gas header.

The three headers (Primary, Secondary and Equalizing) of each of the Slug catcher valves join together. They are connected to the main gas outlet line (30") through isolation valves 310-MOV-51 & 310-MOV-52 for the purpose of isolation on gas outlet side.

It may be noted that during the pig arrival time when the line is filled with liquid, the flow through Slug Catcher is reduced by cutting down on downstream consumers. This is to bring down the velocity of two phases as it enters the Slug catcher and reduce chances of liquid carryover condensate collection from slug catcher is through headers which are connected through branch pipes to the lowest point in the fingers of the Slug Catcher, so that it can be completely emptied out.

The liquid outlet lines of each of the slug catcher valves is provided with motorized valves 310-MOV-53 & 310-MOV-54 for isolation purpose. Their downstream side is connected to the common condensate header (8") going to metering & each of. The slug catcher valves are provided with following liquid level indications.

–Level gauges                   310-LG-6/7

-High-level alarms             310-LSH-14/17

-Very high level alarms     310-LSXHH-13/16

-Low-level alarm        310-LSXL-15/18

-Low level alarm        31U-LSXL-15A/18A

The very high alarm 310-LSXH-13/16 will close the slug catcher inlet shut down valve 310 MOV10 low level alarms 310-LSXL-15/18 will close the condensate outlet line motorized valve 310-MOV 43,54 respectively; low level alarm 310-LSXL15 A/18A will, close the shut down valve, 10SDV-102 located on the condensate line from slug catcher to condensate surge drum in LPG plant.

The slug catcher has been sized so as to allow the of condensate from the gas the sub-sea pipeline two phase flow as well as the storage of the total condensate left in the sub-sea pipeline which gets pushed during the pigging of the sub-sea pipeline. The main inlet line to slug catcher is provided with isolation valve 310-MOV-10.

2.3 WET GAS  HANDLING AND DISTRIBUTION

Ref. P & ID's 2035-02-310AO-I01,102

Separated gas leaves the slug catcher through a 30” pipeline. The gas then passes through the Natural Gas Filters MS-1/2/3 out of which two are normally in line and one is a standby.

These filters are cyclone type moisture separators designed to remove entrained moisture from the gas. These are provided with gas inlet-side motorized valves MOV 15/17/19 and MOV 16/18/20 on gas outlet side. Each vessel is provided. With a safety valve PSV 4 / 5 / 6 for protection from overpressure.

Liquid withdrawal from the filters is through. The On- Off action or a high/low level switch LSXHL2/4/6 which Operates the control valves LSV 2/4/6. Liquid from all the three filters combines and joins the main condensate header. Additionally a very high/ very low level Switch is provided LSXHL 1/3/5. In case of very low liquid level it closes the shutdown valve MOV 70/71/72 in the liquid outlet line and gives alarm. In case of very high level it gives only alarm. Filter is provided with differential pressure indicators PDI 1/2/3 with high differential pressure alarms PDSH 1/3/5. For further detail on equipment refer vendor’s document.

After filtration the gas passes through a metering skid. It consist of three flow measurement devices each having an inlet isolation valve MOV-24/26/28, a flow straighter, orifice meter, temperature and pressure sensors for compensation and an outlet isolation valve MOV-25/27/29. Each metering bank is provided with a flow computer with facility for telemeter also.

            Downstream of the metering facility is provided a 2" diameter branch line with a pressure-reducing valve, 310PV-21A to supply gas to pressurize the blow down vessel, 310-V-3.

            Further, two branch connections of 30" diameter each are provided for future installation of gas sweetening facility.

            The gas distribution to various consumers are as follows:

-5.0 MMSCMD feed to Hazira LPG plant and Kribhco fertilizer plant

-16.2 MMSCMD feed to HBJ pipeline.

            The Source gas to the Kribhco fertilizer plant can be the lean gas from LPG plant or directly from the terminal. In order to supply the gas directly from the terminal to the KRIBHCO fertilizer plant, a gas preheating and pressure reduction facility is provided, as the Ferti1izer plant requires gas at a pressure of 43.0 kg/cm2 Absolute.

            For preheating the gas two hot water heat exchangers 310-E-1/2 are provided one running and the other standby. They pre-heat the gas so as to guarantee, downstream from the pressure reduction system a minimum temperature of 50°C to enable the correct operation of control valve and avoid the separation of water in liquid state. Water separation could give rise to hydrates formation with consequent partial obstruction of the gas flow section. Downstream temperature is controlled by TIC-2, which operates the selected hot water control valve 310-TV-2A, 2B / 2C, 2D and by diverting the hot water flow to the exchanger bypass. Control valve can be selected using the switch HS-2/3.

            Exchangers are provided with inlet block valve MOVs 30/32 and outlet block valves MOV-31/33 on gas side.

Pressure reduction system installed downstream of preheater consists of total 3 Nos control valves installed in parallel, each with inlet block valves MOV 34/36/61 and MOV-35/37/62 outlet. Two control valves are of 6” size and third are of 2'1 size for very low flow rate. Anyone of the three is used for control purpose. Control is through the downstream pressure controller PIC-14. A high-pressure switch PSXH8 is also provided which shuts down the exchanger inlet MOV’s 30 & 32 and gives alarm. Downstream piping is provided with a set of two safety valves PSV-7 & 8 to protect from over pressurization as the downstream piping is of 400 # pressure rating only.

            To knock out drums 310-V-1/2 one operating and one standby are installed immediately downstream the pressure reduction to separate the condensate formed due to temp. drop caused by expansion of gas. Each K.O. drum is provided with inlet MOV 39/41 and outlet MOV-40/42. Vessel is fitted with safety valve for protecting from overpressure. Withdrawal of liquid is from bottom through an On-Off type high/low level switch LSXHL 7/9 which operates the liquid outlet control valve LSV-7/9. A very low/very high-level switch with alarm is also provided LSXHL 8/10, which also shuts down the liquid outlet line MOV 73/74 in case of very low level. Liquid goes to the terminal blow down system. There is also a provision to divert the liquid to the condensate stabilization facility, which will come in future. The gas after knocking off the liquid is sent to the fertilizer.

            A 2” diameter branch line, downstream of the KOD is taken to the terminal fuel gas system. A 16 ” diameter tapping is provided in the gas line, for supply of feed stock to a future petrochemical plant. Other tipping in the lines are for consumers not immediately foreseen.

-Take water in drinking water network at different user points ensuring that all the lines are sufficiently clean.

- Drain the tank

-Start feeding the drinking water tank.

-Switch on the electrolyser after carefully following all vendor instructions.

-Dose chlorine into the drinking water. Check the chlorine content. Residual content

should not exceed 0. 5 ppm.

-Fill drinking water tank with chlorinated drinking water.

-Open drinking water system isolation valve and charge drinking water into the network.

B. NORMAL OPERATION

-Regularly check drinking water tank level.

-Chlorine dosing should be done regularly to maintain desired chlorine content.

-Check regularly free chlorine in drinking water.

            This will directly give the amount of calories delivered to the fertilizer plant.

Process Description

(Phase-II)

3.1 GENERAL

        The gas is supplied in the existing 36”pipeline and 42" pipeline. The following main equipments are provided at this terminal:

-Pig receiver

-Pressure reducing valves

-Slug catcher

-Filtering unit

-Metering unit

           The pig-receiving trap makes it possible to recover the pig when scraping the line and to remove any foreign matters and residual solids entrained by the pig itself.

             There are pressure controllers downstream of the pig receiving stations. The sour gas (42") pipeline has downstream pressure control valve to vary input depending on HBJ requirement.

3.2 SLUG CATCHER

            Downstream of the control valves is the slug catcher, which has existing 48 fingers and new 6 fingers. During normal operation phase-I slug catcher (24 –fingers) separate condensate from 25MMSCMD sour gas from the 42" line. Phase-ll slug catcher (24 fingers) separate gas and condensates from 36" line. ,Suitable inter-connections have been envisaged in the existing line to hook up with the new line from offshore.

             However, during pigging of the 42" line, all the 48 fingers. will be lined up to receive the liquid hold up in the 231 km line. During this time the 3.6 lines shall be lined up to the 6 new fingers to separate gas and condensate. Each finger is 498 mts long. Refer to attached drwg.

              Slug catcher consists of condensate storage section, separating section, primary riser, and secondary riser and equalizing riser.

             Gas and condensate from pig receiver is fed to slug catcher separation section where the gas is separated. The separated gas goes to gas filtering unit through Primary risers. Condensate, which is removed from gas, is stored in slug catcher and for further separations of any entrained gas. The separated gas from primary riser, secondary riser and equalizing riser combines together and goes to filtering unit through 26"-P-O4-1219-D17A. Slug catcher-III has 6 fingers.

            Condensates, which are collected, each finger go to condensate header (16"-P-O4- 1215-D 17 A) and further go to condensate metering unit. Slug catcher has a level indicator, level switches. When the level of slug catcher is low, LSL-1202 is energized and closes MOV-1201.

3.3 GAS FILTERING UNIT

          The gas from slug catcher is sent for filtration in which any condensate entrained along with the gas is separated. Sour gas from Ph- I slug catcher is sent for to existing filtration unit (31 0-MS-1/2/3) and sweet gas from Ph-II / Ph-III slug catcher is sent to new filtration unit (O4-MS-402/403/404). For normal operation, two filters will be operated to cover the 25MMSCMD of sour gas and one is standby.

            New filtration unit has three filters. Each filter can treat max. 580,000SCMH (13.92 MMSCMD) sweet gas to remove 99% of 10 u (micron) solid particles. For normal operation, two filters are operated to cover sour gas. Sweet gas which is removed of solid particles goes to the metering unit and then goes to DPD unit.

          Each filter is equipped with liquid automatic discharge, which is controlled by the liquid level inside the filter itself. The condensate from sweet and sour gas are metered separately.

         Gas filter separate gas from condensate or particle with principle of centrifuge.

Gas filter has 200-2" dia cyclones. Feed is injected tangentially into the upper part of the cylindrical section and develops a strong swirling motion within the cyclone. Liquid containing the fine-particle fraction is discharged out through the under flow.

            Gas filters equipped with differential pressure gauge to monitor the any leakage. The liquid coming out of the filters will be sent to a single collecting line, connected both with the line conveying the condensates to the blow down and with the feeding line of the stabilization plant. The condensates from sweet and sour gas are metered separately. Provision is kept for mixing the sweet gas condensate in the sour condensate, after which it goes to the sour condensate fractionation unit.

3.4 METERING UNIT

            There are four sweet gas-metering units and one condensate metering unit. Sweet gas from gas filtering unit goes to sweet gas metering unit to measure the flow rate with compensation of pressure and temperature. Each metering unit consists of flow meter, pressure gauge and temperature gauge. Condensates from Phase-II/Phase-III slug catcher feed to condensate metering unit and measure the condensate flow rate. After then, go to condensate fractionation unit.

4.       PREPRATION FOR START-UP

4.1          GENERAL

4.2          UTILITIES

4.3          PRIMARY VERIFICATION

4.4          START-UP CHECK LIST

4.1 GENERAL

          Once that all commissioning activities and the leak proof tests have been accomplished the preparation of the unit for initial start-up can be started. This phase consists of cleaning up and washing truly all of the vessels, lines and equipments, in a manner to eliminate all of the substances (pieces of iron, welding electrodes, etc.) which otherwise, could create important troubles while unit is operating.

          Much of the work involved in this section is performed only on the initial start- up. However, some of these items must be performed following times such as when the units are down for major overhaul or inspection.

             During this phase the following points have to be carried out for the Units.

4.2 UTILITIES

a) Air:              When air is available blow all the air lines clear. After dry air is available blow all instrument air lines free of dirt and moisture prior to testing the instruments.

b) Water:        Flush all water lines until lines are clear and free of dirt, welding slag, etc. Do this with enough open drains and opened flanges to be sure each line is clear before commissioning any instrumentation.

c) Steam:       After steam is available blow all steam lines clear before starting to pressure up the system.

Gradually bring the system up to operating pressure. After activating the steam headers then blow the steam tracing, jacketing and heating lines clear and activate them.

Flush through all vents, drains and other side connection. Flush bypasses, alternately with their main channels. All control valves should be blocked and by-passed until the major part of the foreign matter has been removed from their systems. Then remove the valve itself from the line and flush through the opening thus created. Flow meter and restriction orifices should not be installed until the lines are clean. Provide ample top venting during the draining operation, or whenever the level is being lowered in a vessel, to avoid pulling a vacuum on the equipment.

Precaution

During washing and cleaning period, remove or block the diaphragms, the flow meters and the control valves. Do not forget to put back the items that have been removed or blocked during the cleaning operation, back in service.

d) Lubrication:           Lubrication of the motors, machu1ery and valves must be done respecting me maI1ufacturer's instructions.

e) Control System and Instrumentation:      Check the links between the control room and each control instrument. Then, after the instrument air lines have been blown free of dirt and moisture check the lines for leaks then test all instruments for mechanical condition and calibration to insure that all are operable and accurate. All instrumentation required for operation which has not yet been installed should now be placed in position. All instruments must be Checked, calibrated and commissioned for operation.

-Flow indicators, controllers and recorders - Orifice plates shall be installed only after the lines have been flushed and blown free, check them for correctness of bore and where tapered bores are used, check and see that they are installed in the proper direction of flow. This should be observed by an experienced operator. Calibrate the flow instruments and mark their coefficients adjacent to each instrument prior to the initial operation.

-Alarms  - Check all electrically operated alarms to see that they are in working order and test each alarm by simulating the alarm condition to insure that the signal activated corresponds to the proper alarm mechanism in the plant, and that the alarm horns can be heard by the operators.

4.3 PRIMARY VERIFICATION

a)     Hydro testing

Make sure that installation which has to be put in service has already been tested hydrostatical during the construction period. If for any reason it becomes necessary for operator to carry out this test, the following points have to be respected. The hydrostatic pressure is the highest pressure at which an item may be subjected under any circumstances. Before testing a line, all the vessel having a lower test pressure than that of the line, must be blinded off.

b)  Vessels

Before closing any vessel, make sure that its interior has been inspected for cleanliness and proper fixation of internal equipments.

c)  Prepare the following materials necessary for washing and cleaning:

     - The flanges equipped with the fast connecting hook -up

      - The isolating and the blind flanges

     -  Strainers for occasional filtration at a precise point of a line

     -  Fire hoses

d)   Water Flushing

Process lines can be flushed with water through established circuits from vessels which are filled with water for this purpose. Water may be admitted to any vessels through temporary hose connections and flushing should be downwards or horizontal with the water exit at a low point.

e)  Temperature Indicators. Controllers and Recorders

Check all temperature indicators and recorders and insure that all points in the recorder and indicators correspond to the proper thermocouple in the plant and at the proper controller reacts to the simulated conditions in the plant. Check all controllers and DP cells for calibration.

t)  Pressure and Level Controllers

Check service and preset tile pressure and level instruments by Simulating operating conditions. This can be done in most instances in conjunction with tightness testing and water washing. Safety valves are preset at the shop prior to installation. Therefore, take care and do not exceed the setting of these safety valves when doing tightness test or simulating operating pressures. Check and see that each instrument gives the proper signal and results in the proper response from the controller.

g) Unit Shutdown System

Test the entire emergency shutdown system. The ESD valves are closed by de-energizing solenoid operated valves which close off the instrument air supply and vent the air from the valve opening mechanism. Hence, these valves are normally open during operation and the solenoid valves arenom1ally energized during normal operation. Since these valves and trips can be activated from the central control room and several process cut -off check that each of them activates the correct valves and trips, and the correct response is obtained at each point.

h) Piping Review

A complete review of process piping and instrument diagrams must be done to ensure that piping is complete and installed as designed. All vent, relief, and drain system must be checked.

i) General Instructions

-During winter, if there is a risk of freezing, don't let any 'equipment full of water without flow circulation.

-Have an open vent at the top of the equipment during fill up or draining.

-During the pressure test, use a foaming product to check for leakage around the flanges.

-Check the valve packers

4.4 START-UP CHECK LIST

Before admitting the process gas to any section of the unit or proceeding with other start-up operations. The following checks must be carried out.

-All fire-fighting systems are pressurized and ready for operation.

-All safety equipments are at their place and operational.

-Unit is ready for start-up.

--Testing equipments should be available and operational.

-All valves are operational.

-All instrumentation and control systems are linked.

-Instrument air is available and delivered to all instruments.

-Emergency shut-down systems are operational.

-All blinds must be in correct position.

-All relief and block valves are in service and positioned correctly.

-Sewer system is ready to use.

-Electrical power is on to all boards

-All pressure instruments are in Operation.

-Check that the flare is operational and its plots are lighted.

4.5 NORMAL START-UP

During the course of operation the plant, it will be necessary to start-up all or portions of the plant after shutting down for various reasons. . After each maintenance turn around, the plant will have to be brougl1t up from a depressurized, ambient temperature state. Portions of the plant will have to be restarted after a shutdown due to a mechanical malfunction or an operating problem.

            The following normal start-up is recommended with the Understanding that the judgment of the operators should dictate which of these steps are required and in what order based on the nature of the preceding shutdown. The initial start- up instructions previously described should be referred to for specific details.

In this procedure, it has been assumed that the plant has been shutdown for a short -duration to allow maintenance on an equipment item or because of any interruption to the feed supply.

         The unit at this stage assumed to have been fully precommissioned if necessary in accordance with precommissioning Instructions, has been purged of air and repressurized  to normal operating conditions.

         It is assumed that all the utility system have been fully commissioned and are available to the unit. That all instruments have been checked and are ready to function in the automatic mode.

         All piping all equipment in the unit should be lined up, and internal block valves and isolation valves should be opened as necessary.

Commission the process gas feed loop and condensate feed loop

Slowly establish a flow to gas filters by opening the by-pass valve on 04- MOV-1301.

Slowly establish a flow to gas metering unit and condensate metering unit by opening 2" by-pass valves on inlet MOVs.

Establish a level in the slug catcher (04-LI-1201)

Establish a level of gas filter (04-MS-402)

Check that the pressure controls in pressure reducing valve and 22-FIC- 1601, 22-P!C-1604, 22-PIC-1605 and ensure that there is a adequate gas/condensate flow.

When the pressure control is all right, the output of the system should be slowly increased up to design levels depend on the downstream .of slow.

SECTION-5

OPERATING PROCEDURES

5.1 General

            This section covers operating procedures for start up, normal operation and shutdown of the terminal process facilities. Steps to be taken during emergencies in the terminal such as power failure, are also covered, One of the hazards most frequently encountered during start up and shutoff of units is accidental mixing of air and hydrocarbons to form and explosive mixture, Other hazards primarily associated with start-up/shut down are pressure, vacuum., thermal and mechanical shocks. These can result in fires, explosions, destructive pressure, surges and other damages to the unit as well as injury to personnel.

            It is essential that the operation crew realize the potential hazards involved in the start up and shut down operations and eliminate them by diligently following the procedures outlined below:

5.2 PREPARATIONS FOR START UP

Prior to commissioning of the process units, it Should be established that all preparatory work have been successfully completed and all equipments are ready to function. 'I'he following  preparatory work have to be taken up:

-The system is checked for mechanical completion and against P&ID.

-Isolate instruments and remove control valves and

-Inspect equipment intervals. Clear the vessel of construction debris and clean the vessels.

-Fix the manhole.

-Provide water hose connection vessels and flush with water.

-The water through the drain point.

-Provide air hose connection and dry the vessels with plant air and then with instrument air. Check the dew point of air.

-Box up individual loOps, slug catcher and equipment

-Pressurize individually each loop and equipment with air and leak test Progressively at higher pressures upto 6.0 kg/cm2g. the pressure drop should not exceed 0.1 kg/cm2 in 24 hrs..

-Connect up different loops remove isolation from equipments and slug catcher, replace control valves and instruments. Pressure test the entire system at 6.0  kg/cm2g. The pressure drop should not again exceed 0.1 kg/cm2 in 24 hrs. Depressurize the system.

-Purge the system with inert gas. Analyze the gas at different points/pockets fro oxygen. the oxygen at all points should not exceed 0.5%.

-While purging the System with inert gas, it is preferable to include the flare header such that the flare header system is also inertised. After flare header is freed of oxygen, maintain inert gas flow through the flare header by allowing a small purge gas through the header from the terminal inlet side of the flare header.

-In the mean time the fuel gas system will be flushed and dried, purged with inert gases. Kept ready for charging with fuel gas.

5.3 SEQUENCE OF START UP

         The sequence of start-up activities for Commissioning of the terminal shall be as follows :

-Commission all utility systems.

-Charge fuel gas system with gas through the modified connection.

-Start the hot water boilers and commission the Natural Gas, Condensate and Fuel gas heaters.

-Using LPG try the pilot burners of the flare and the condensate burning system and later put it off.

-Keep the Terminal including the flare header inertised.

-Charge pipeline gas/condensate to the slug catcher and vent the inert gas to flare. Increase the gas pressure in progressive

-Check for gas leakage from flange joints at each step.

-Charge gas in to gas filters and kribhco pressure reducing system

-Take gas from the Terminal and charge the fuel gas system. Cutoff LPG fuel gas system.

-Ignite the flare and burning system pilot burners. Use fuel gas as purge gas for the flare header.

-Taking gas from the Terminal, pressurize the blow down drum.

-Commission the liquid handling system and condensate burning system.

5.4   COMMISSIONING:

        Before commissioning of the sub-sea South Basin –Hazira pipeline is checked for mechanical completion. The pipeline pigged and drained of water. Further, it is dried with Methanol and filled with inert gas. The pipeline then, is changed with hydrocarbon gas/condensate from the South Basin platform. The detailed description of commissioning procedure is beyond the scope of this manual.

        After all the preparatory work in the terminal for startup, is completed and the terminal is ready, in all respects, for receiving the hydrocarbon gas/condensate, the isolation blind at the terminal battery limit is of MOV 1, is reversed to the open position, By gradually opening the bypass valves of MOV 1, hydrocarbon gas/condensate is allowed to flow into the terminal, Bypassing the pig receiver, the gas condensate is led through the bypass of MOV 3, and through the motorized valves 310 MOV 9, into the slug catcher, During this operation, care is to be taken that the hydrocarbon liquid does not freeze due to sudden pressure reduction. The operation of pressurizing the slug catcher with hydrocarbon gas/liquid to the operating pressure is carried on gradually so that ambient heat loss offsets the temperature drop due to pressure reduction and the hydrocarbon liquid does not approach the freezing point of the mixture.

            As the pressure in the slug catcher approaches the terminal operating pressure, as indicated by 310 PI3/4, the bypass valves of the motor driven valves, MOV 1 & 3 are closed and the motor driven valves are opened to divert the hydrocarbon gas/condensate flow through the main line.

           When the pressure in the slug catcher reaches the operating pressure, the slug catcher pressure reducing/control system takes over to maintain the pressure inside the terminal within the range allowed within the piping class. When the pressure equals or exceeds 95 kg/cm2 absolute, the motor driven valve, MOV 9, on the main line would close and the flow is diverted through the pressure control valve, 310 PV23, (for low flows) and the controller, 310 PIC-2 controls the downstream pressure, if because of malfunction or failure of the valve, PV-2C, the pressure downstream tends to increase, the pressure switch, PSXH 2/3/4 (2 out of 3 being in operation) would close the motor driven valve, terminal inlet.

            Along-with the gas, condensate also into the terminal and the liquid level in the slug catcher builds up.

            Gas from the slug catcher is filtered, before; it passes to the pressure reducing station for supply to Kribhco. Three filters MS 1/2/3 are provided for gas filtrations. While two will be normally in operation at the gas condensate flow, at the pipeline design conditions, at low flows, only one filter would be sufficient.

           Open the bypass valves of the MOV-15, and gradually pressurize the gas filter, MS-1. Adequate care is taken during pressurizations that the temperature of the gas does not drop very low to cause liquid condensation and condensate freezing. When the gas filter pressure approaches the normal operating pressure, as indicated by 310 PI 8, the motor driven valve bypass is closed and the 310 MOV-15 opened by using the hand switch 310 HS-15. Gas is withdrawn from the filter by opening 310 MOV-16. This is done by operating the hand switch 310-HS-16.

          Before taking the Kribhco pressure reducing station on line, the hot water circuit of the gas heater, 310 E-1/2 is established. Commission the hot water boilers with LPG from bottles and circulate hot water through the gas heater, 310 E-1.

          When the temperature of the heater comes up, gradually open the rotor driven valve, 310 MOV-30, by operating the hand switch, 310 HS 30 and pressurize the gas heater. When the gas gets heated, open the MOV 31, by operating the hand switch, HS 31 and let the gas pass to the pressure reducing station. Set the pressure indicator controller, 310 PK-14 at 44 kg/cm a and Operate motor operating valves MOV34 and MOV 35 and pressure the Knock out pot V 1, through the control valve, PV 14A, to the set pressure.

Let the PIC control the downstream pressure. Open the knock out drum downstream motor operated valve MOV 40 and let the gas pass into the 16 ” diameter line, 16"-310-P-66-1413-V, connected to Kribhco and other consumers. Open the isolation valve in the 2" diameter branch line, leading to the fuel gas system. Slowly pressurize the fuel gas header and commission the fuel gas system as described in Section 3.8.

        Charge the fuel gas into the flare pilot gas line. Ignite the pilots. Commission the flare as detailed in Section 3.10. Changeover the purge gas for the flare header from inert gas to fuel gas.

            Through the 2 ” diameter branch line, on the gas main stream, downstream of the gas heaters, pressurize the blow down vessel to its Operating pressure of 40 kg/cm2a by opening the pressure valve, 310 PV 21 A. when the blowdown drum pressure reaches the operating pressure, put the split range controller, PIC 21 an auto operation. The drum pressure will be maintained by releasing the excess pressure to flare through PV 21. Drain condensate from the slug catcher and gas filter blow down drum and commission the blow down system.

            Light the pilots of the burn pit, after changing the pilot gas header of the burning system with fuel gas. Pressurize the condensate flash drum V 4 and V 8 to 6 kg/cm2a and 4 kg/cm2 respectively with fuel gas from the main gas stream through the lines Place the pressure indicator controllers,

320 PIC 5A and 320 PIC 6A an auto operation to control maintain the pressures of flash drum V 4 and V 8, respectively. Commission the gas burners of the burning system such that the excess gas from K.O. drum, V 4, is burnt in the gas burners. The excess gas from the K. O. drum, V 8, passes to the elevated flare.

            Changeover the heating gas to water boilers from LPG to fuel gas and stabilize the operation of the hot water heaters.

            During this period, it is likely that the gas filters, MS-1, would have built up liquid level. Drain the liquid to the blow down vessel through the filter drain line. Ensure that the electric tracing on the drain line are energized and the liquid does not freeze on sudden release of pressure.

When the liquid builds up in the blow down drum, start the pump and Pump the liquid to knock out drum V-4. Put the level indicator controller 320 LIC-4, on auto operation. when the level in V-4 goes up, transfer the liquid to V-8 and then send the liquid to the condensate burners. Commission the condensate burners, make sure that the condensate heater and pressure reduction system is isolated.

                  Till the time, some condensate level builds up in slug catcher the operation of the condensate handling and burning system has to be carried out as a batch operation and adequate care should be taken to that the operation is stable and safe. when the Hazira terminal Unit systems are commissioned, and in stable operation, the terminal is in a position to supply gas to Kribhco fertilizer plant.

            As soon as, Kribhco indicates its willingness to accept the gas, reverse the Spectacle blind in the 16" diameter line, at the Kribhco end; operate the motor operated valve, MOV 60 and the ball valve VB 61 and start supplying gas to the Kribhco fertilizer. Before taking gas, in the Kribhco line, it is necessary to ensure that the line is properly flushed and Cleaned, dried and Purged with nitrogen such that

the oxygen in the pipeline gas does not exceed 0.5%. Slowly pressurize the line to the operating pressure, before the gas is supplied, to avoid sudden gas cooling and condensate formation.

             Gradually pressurize the metering line, to the Kribhco line operating pressure through the bypass of MOV 43. when the line pressure reaches the operating pressure close the bypass gate and plug valves and open the motor operated valve MOV 43 and MOV 44. Check the Quantity of gas supplied to the fertilizer, after calibrating the flow, temperature and Pressure instruments in the metering line. Record the gas supplied to the fertilizer plant.

            An analyzer is provided in the gas supply line to Kribhco fertilizer plant. Commission the analyzers as per the vendor-operating manual. Maintain a record of the gas analysis, supplied to the fertilizer plant.

          Meanwhile, the condensate level in the slug catcher will gradually keep rising. When adequate hydrocarbon condensate has built up in the slug catcher, the condensate handling system should be commissioned.

          Start hot water to the condensate heater, and establish hot water circulation in the heater shell, when the temperature of the heater comes up to the operating point, operate the motor operated valves, MOV 53 and 54 and allow condensate flow to the heater tubes through the condensate metering bypass line; Set the temperature indicator controller, 310 TIC 21 on auto operation allow the controller to regulate hot water through the heater to control the condensate outlet temperature.

          Set the pressure indicator controller 310 PV 7, at 43 kg/an a, and open the upstream and downstream ball valves and slowly allow condensate to pass to the condensate burning system.

Liquid enters the flash drum, 320 V-4 in the condensate burning system

through the level control valves 320-LV-4A. level indicator controller,

320 LIC-4, regulates the flow of condensate to the flash drum to maintain

      Liquid level in the drum. Hydrocarbon liquid flashes in the drum, V-4, to generate vapor. The vapor passes into the fuel gas header. Readjust the set point on 320 pic-7 on the fuel gas line from the fuel gas mainstream, such that vapor generated in V-4 is  mainly utilized as fuel gas and gas from the main gas stream is used to make up the short fall in fuel gas requirement. Let 320 PIC-5 maintall1 the fuel gas header pressure and release only the excess fuel gas generated from V-4 to the burning system,

         Let the hydrocarbon liquid pass under level control, from the flash drum V-4 to flash drum V-8, which is maintained at 4.0 kg/cm2a. Some vapor will be generated due to hydrocarbon condensate flashing at a lower pressure. Close the globe valve, VD 06, on the condensate drum V-8, through which fuel gas was passed to flash drum V-8, maintain the drum pressure. Let the controller, 320 PIC 6 control the drum pressure and release the excess vapor to elevated flare.

            Set the flow indicator controller,  320 PIC 20, at the expected condensate flow rate into the terminal. Through the control valve, 320 Fl 20A, allow liquid to pass from the flash drum V-4 to the condensate burners. Atomize and ignite condensate in the burners as described in the Section 3.11.Adjust the set point of FIC 20 such that the condensate level in slug catcher does not rise.

             When the operation of the condensate handling system is steady, the condensate metering system may be commissioned. Calibrate the flow, temperature and pressure, indicating instruments in the metering line.

             Remove the spectacle blind located upstream of ball valve VB 01. Operate 310 MOV 56 and 310 MOV 59 and allow hydrocarbon condensate to flow into the metering line. Release purge gas through the high vent and let the liquid fill up the lines. Close the vent valve. Close the bypass connection, thus allowing condensate to pass through the metering line. Let the flow, temperature and pressure measurement valves stabilize. Record the measured valves periodically and maintain a record.

5.5  Normal operation:

               The following steps should be carried out periodically for normal operation of the terminal:

-Keep a reword of the gas pressure in the slug catcher and Kribhco supply pressure. If the former pressure is tending to rise or the latter pressure tending to fall, change over the pressure reducing control valves, 2A/B/C and 14 A/B/C respectively or take one or more valves in line for control purpose.

-Check the condensate in the slug catcher. Reset the flow indicator controller, 320 FIC 20 to keep the level if for controlling the level.

- Check the flash drum V-4 and V-8 for presence of water interface. Drain the water, if present. Water is likely to be present in the drums initially if the terminal is not dried, if dehydration of gas is not done properly.

-Check auto open/closure of condensate valves on the filter and ensure that the level of liquid in the vessel is low.

-Check auto start/stop of blowdown  pumps and ensure that the liquid level in the blow down vessel is low.

-Establish a routine for checking and recalibration of instruments and interlock system.

-Conduct such1 other routine checks as are necessary for the, safe operation of the terminal.

5.6 EMERGENCY PROCEDURE:

5.6.1 GENERAL

           The Hazira terminal operates 365 days a year. So it is important to take adequate steps during emergencies to protect the terminal and to keep in running. In the event that the shutdown becomes inevitable, the procedures outlined herein attempt to overcome the

Hazards of a quick shutdown as much possible.

            Emergency can result from equipment failure and from interruption in utilities or feed supply. Certain features have been incorporated in the terminal to minimize the likelihood of an emergency, these include emergency power, spare pumps, isolation of equipments which can not be used in case of equipment failure.

          Operators should be thoroughly familiar with emergency procedures. Obviously any written procedures cannot cover all the details or problems, which might arise in a emergency, as the nature and degree of emergency, vary from time to time. Good judgment must be exercised in such cases. Under emergency conditions, actions are to be taken fast as per guidelines below.

5.6.2 LOSS OF  MAIN ELECTRICAL POWER :

          Power requirement for the terminal is supplied by the GSEB. Apart from this there is an emergency diesel power generating station, which automatically comes on line, in the event of failure of power supply from the State Electricity Board. When terminal main power supply fails, all equipments running on Power including the air compressors and service water pump will trip. As the diesel power generator will auto start on power failure, power supply will be restored to the terminal within few seconds. On restoration of power restart the service water pumps, air compressor and the hot water generation Unit, and bring the terminal to the stead state.

          If, however the diesel generator, does not auto start, then the following steps should be taken:

-Shut off the condensate burners and close the flow control Valve, FV 20 A/B.

-Close the motor operated valves, MOV 53 and 54 on the condensate line at the outlet of the slug catcher.

-The gas supply to Kribhco pressure reducing station may be reduced to avoid condensate formation and freezing due to failure of hot water system. If, however, the temperature of gas goes very low, shut off gas supply to Kribhco fertilizer plant by closing MOV 60. Inform the fertilizer plant if gas supply is to be suspended.

-Simultaneously take steps to start the DG manually. If the DG set starts on manual operation within less than quarter of an hour, the power supply to the terminal is resumed. Start the service water pump, air Compressor and hot water generation Unit and resume gas supply to Kribhco fertilizer after obtaining their approval. The condensate burning may also be resumed.

- If the DG set fails to start on manual operation within stipulated time, arrangements for a longer duration. Press the emergency push button to close the motor operated valves MOV 1, 34, 36, 53, 54, 60 and 61 and control valves FV 20A/B and PV 1 A/B. Ensure that the fuel gas header is supplied gas from gas mainstream to header purge.

-Operate such other isolation valves to bring the terminal to a safe shutdown.

-The plant may be restarted when the power supply is resumed.

5.6.3 LOSS OF SERVICE WATER

         Service water to the terminal may fail due to overload trip of the Pump motor or mechanical breakdown of the pump.

         When the service water header pressure goes down, the low pressure switch, 320 PSL 31, will actuate & start the stand by pump , in the even the stand by pump fails to start automatically, start the pump on manual mode  and restore service water to plant.

         The air compressor of the terminal will trip on cooling water flow. However instrument air surge capacity is adequate to operate the plant for about half an hour. As soon as service water is resumed make arrangements to restart the air compressor and steady the operations.

5.6.4  INSTRUMENT AIR COMPRESSOR FALIURE

           Instrument air compressor can fail due to overload tripping of the motor or due to any of the interlock devices Such as high discharge air temperature, low cooling water flow etc. As soon as the trip alarm comes on the panel, start the stand by compressor after ensuring that the system is safe and operatable.

          The instrument air surge capacity is adequate for safe operation of the terminal for about half an hour. If the Standby compressor cannot be started within the time, shut down the terminal as described above. Rectify the air compressors and restart. In the event of total loss of instrument air following are consequences:

-All the pneumatic control valves move to their fail safe position.

-All the MOV Operation from control room is lost. However local operation of MOV’s thru' hydraulic system is possible.

             For MOV-l, N2 backup is available from N2 cylinders.

5.6.5  INSTRUMENT POWER FAILURE

           There are two different types of instrument power provided in the terminal, a 230V AC power and a 48-volt t DC power. The former power is supplied to the main control panel, the computer module and the gas detection panel in the control room and to the water heater panel and the flare ignition panel other local panels in the utilities areas. The 48 V DC power is supplied to the logic cabinets I & II to the main control panel for alarm/shut down.

           The 230V AC power source is the Gujarat electricity board. This power is backed a terminal emergency diesel generator Power. The instrument power system is provided with one Uninterrupted power Supply system UPS, which comprise of a rectifier,  battery back-up, and inverter. The whole rectifier & inverter combination has one static bypass Switch provision.

          The battery source through an inventor provides Uninterrupted instrument AC power supply for a limited duration to the instrument panel in the event of failure of power from the GEB as well as from the emergency generator. The 48V DC power is supplied from the UPS System through rectifiers.

         The battery is kept on trickle charge normally. Only on main power failure the reserve power from the batteries is utilized, and the instrument power supply is maintained with out interruption for a limited duration.

          In the event of UPS system fault the instrument power supply is maintained thru' the static bypass switch provided in the UPS.

               This change over however would cause momentary interruption in instrument power supply.In the event of failure of UPS system also the instrument power 230V AC supply to central control room panel and micro processor along with CRT and printer is lost.

           The UPS supply failure will also affect the following:

1. All the local panels.

2. Plant emergency supply to area lightings.

3. All the control valve due to loss of signal from controllers shall go to fail

4. All the controllers’ indication shall be lost.

5. Semi graphic indications & annunciators will be lost.

6. Gas detection and fire alarm system by rendered non-functional

7. 48V, DC system is also lost since it is from UPS

           Consequently the terminal shut down would take place. Thereafter ensuring that the terminal has shutdown situation the subsequent action to be taken as 1. Start-up of emergency diesel engine for emergency power supply. With the return of instrument power supply resume the terminal start-up as per the procedures outlines earlier. This section may need revision/updating as gained during commissioning.

6.0    OPERATING PARAMETERS

6.1         GENERAL

6.2         OPERATING CONTROL POINTS

6.3          SLUG CATCHER

6.4         GAS FILTER

6.1 GENERAL

          Any changes in the operation of the field treating units will directly affect the operation of the plant. Likewise, changes in the different units within the plant will mutually affect the, other units and ultimately require offsetting adjustments, Other changes which affect the plant and require adjustments are the effects of seasonal changes, ambient temperatures, the changes called by the intensity of the sun's rays & the effect of rail or wind. These cause temperatures to vary, resulting in changes in stream densities and viscosities. Tower operation often displays cyclical effects due to day-vs-night temperature changes. All of these require adjustments in operation in order to produce products of a constant specification. However, excessively frequent operational adjustments or extremely large corrections and undesirable as they will cause upsets which, in turn, will not allow operations to stabilize. Change pressures and temperatures carefully and deliberately to avoid equipment damage and operational upsets. Make small changes incrementally to avoid over controlling or oscillating around control point always employ elaborate precautions to avoid air-hydrocarbon mixtures in explosive ranges. Conform that the flare system are in continuous operation, to protect the plant by providing a rapid means of disposal of flammable materials at all times. Regular inspections and preventive maintenance are proven procedures for achieving peak operating efficiency and long trouble-free runs. Inspect all units at frequent intervals and check the levels in all vessels, which have liquid levels.

             Normally, temperatures are the most dependable data in the plant. However thermocouple calibrations are subject to drift ; therefore, before making drastic changes based on what may be incorrectly reported temperatures, check the local mounted temperature indicators. If required the thermocouples and other temperature instrumentation can be recalibrated.

6.2 OPERATING CONTROL POINTS

             In normal operation, the following parameters should be regularly inspected:

-Slug catcher gas flow and pressure of 310-PI-1

-Slug catcher level (04-LI-1201)

-Differential pressure of 04-PDI-1301/ 04-PDI-1302/ 04-PDI-1303.

-Pressure of HBJ line

-Temperature of HBJ line

6.2.1       FEED COMPOSITIONS

MATERIAL BALANCE

25 MMSCM Sour Gas

6..2.2 UTILITY SPECIFICATION

6.2.2.1            STEAM

6.2.2.2            PLANT AIR

OIL CONTENT                      OIL FREE

NOTE: IF THIS GAS IS NOT SUITABLE FOR BLANKETING, FUEL GAS MAY BE USED.

6.3       Slug catcher

            Depend on the slug catcher gas flow rate, the arrival gas pressure is vary. As the gas flow increase, the arrival gas pressure is reduced, Pressure reducing valve of downstream of pig receiver control the pressure of slug catcher to 79.5 kg/cm2a.

          Pressure reducing valve control the pressure of slug catcher constantly. The variation of slug catcher pressure influence on sweet gas composition gas flow rate and condensate flow rate and composition. This affect the downstream unit  such as DPD, CFU and GSU.

          The level of slug catcher should be controlled constantly. If the level of slug catcher is increased, entrained liquid will be increased.

6.4 GAS FILTERS

-Differential pressure of gas filter

         With increasing of sweet gas flow rate, the differential pressure of gas filter will increase. The deferential pressure of gas filter indicate the removal of condensate and efficiency of gas filter.

        Take care of leakage of gas filters or plugging of gas filters. If the, differential pressure is increased without change-: of flow rate, operator should check bottom level of gas filter and PDI gauge. The level and PDI gauge is OK gas filter should be out of service and should be cleaned.

        The level of gas filter is automatically controlled by level Switch.

SHUTDOWN   PROCEDURES

7.0       SHUTDOWNPROCEDURE

Basically, this part facilities are not totally shutdown except for utilities failure. When equipments and instrumentation have a some trouble and need maintenance, standby equipment and instrument will be used during maintenance period. In case of shutdown of condensate metering, condensate can be stored in the slug catcher during short duration.

7.1       EMERGENCY SHUTDOWN PROCEDURE

             Emergency can result due to failure of equipment, interruption of utilities or feed supply and fire. Most common emergencies are due to failure of utilities. The failure of utilities will be indicated in the control room by appropriate alarms. In case of any failure of the utilities, the plant should be shutdown in a safe manner.

               In case of power failures all motor operated valves are stuck in their position. So depend on the downstream unit the slug catcher and related unit should be ready for shutdown.

                a) Instrument Air Failure in case of instrument air failures, all automatic shutdown valves are closed and all control valves will be fail position. In case of instrument failure, all level control valves of gas filters will be closed and all valves of HBJ gas line will be closed. Operator should be taken following action.

-Slowly close the 3l0-MOV-9 (slug catcher inlet MOV).

-Close all MOV's on gas filter inlet line.

-Close all MOV's on gas filtering unit.

-If the level of slug catcher is below the 30%, close the 04-MOV-1201 and close 04-MOV -1501 on condensate filtering unit. When the pressure of instrument air is normal condition~ start the entire system according to start -up procedure.

b) Action During Emergency Shutdown

1. High high level in slug catcher

04-LSHH-1204 will be activated automatically operator should be close the 310-HS-IO to close 310-MOV-10,

2. low level in slug catcher

04-LSL-1202 will be activated  operator should be push 04-PB-120IB button to close  04-MOV-1201.

3. Pressure high high (22-PSHH-1609) or

Pressure high high (22-PSHH-161 0) or

Flow high high (22-FSHH-1607) on LPG line.

22-PSHH-1609 or 22-PSHH-1610 will be activated and

Close 22-SDV-1601 automatically

Close 22-PV-I601 automatically

Close 22-PV -1602 automatically

Operator should be taken following actions.

-If one of two control valve (22-PV-1604, 22-PV -1605) is close, open another control valve.

-If all control valve on HBJ line is opened, increase the flow through HBJ line.

-If all three control valves onHB] line are closed, open PV –1601 and flow through the 22-FV-1601.

4. 22-FSHH-1606 or 22-PSHH-1606 activated.

        If  22-FSHH-1606 or 22-PSHH-1606 will be activated 22-FV-1601 will be closed.

       Operator should be taken following actions.

-If the 22-PV-1604 and 22-PV-1605 is closed

Push BPS-1605: start-up by-pass of22-PSLL-1618,

Push BPS-1606: start-up by-pass of 22-TSLL--I608, then open 22-PV-1604 manually.

-If the 22-PV -1605 is closed,

Push BPS-1607 start-up by-pass of 22-PSLL-1617

Push BPS-1608 start-up by-pass of22-TSLL-1618 then open 22-PV~1605 manually.

-If the process is normal condition. Service the 22-FV-1601

-Push BPS-1603 start-up by-pass switch of 22-PSLL-1619

Push BPS-1604: start-up by-pass switch of 22-TSLL-1609 " then open 22-FV-1601. ;

          When process condition is stable, put 22-FIL -1601 in auto control mode.

5. 22-PSHH-1621 or 22-FSHH-1605 on 22-PV-1604 or 22-PSHH-1620 or 22-FSHH-1604 on 22-PV-1605.

If one of two (22-PV-1604, 22-PV-1605) is closed by flow high high switch activation or pressure high high switch activation.

Operator should be pushed another start-up by-pass switch and open another control on manually.

OPERATING PROCEDURE

FOR

GAS METERING STATION

A Brief Introduction to Custody Transfer

The custody transfer measurement of gas being supplied to GAIL for their HBJ line is being done through the Gas Metering Station (GMS) W.E.F 11^th April 2003. The Gas Quantity measurement is done through the twelve 12” Turbine meter runs (Old & New) having an overall designed capacity to measure 40 MMSCMD this is with an operating philosophy of 10 meter runs in operations and 2 standby. Presently around 33 MMSCMD of gas is being measured & supplied through this station. The Gas Quality is monitored through the online analyzers deployed in the station.

The fundamental criteria for Custody Transfer Measurement is that the measurements have to be in conformity with all physical, conventional and legal aspects of the “Metering” fully known and understood by both the “Seller” and the “Buyer”. Secondly the two parties must agree to the quantity of the product that is measured and agree to pay money based on the measurement. The Gas Metering Station ensures Accurate & Repeatable measurement by means of the following:

•      The various sections of the metering station have been designed in accordance to their relevant standards. The piping, straight lengths upstream & downstream of TFM, location of flow straigteners, PTs & TTs are in accordance to AGA Report no.7. The choice of the type of Flow straightener in each meter run is in accordance to ISO-5167. The Turbine meters are designed in accordance to ISO-9951. The Gas sampling system is in accordance to ISO-10715. The selection of standard calibration gas for the Gas chromatographs is in accordance to ISO-6974. The flow computation & compressibility calculations in the Flow computers are in accordance to AGA 8. The physical properties of individual gas components and determination of calorific value of gas by the Gas Chromatograph is in accordance to ISO-6976.

•      The New Turbine meters have been calibrated at high pressure testing facilities of Pigsar, Germany while the Old Turbine meters have been calibrated at Air testing facilities of FCRI, Kerela and Proved Jointly by ONGC & GAIL at our Proving Station.

•     The calibration of P & T Transmitters deployed in the New Meter runs have been carried out by M/S NMI, Netherlands, while P & T & DP Transmitters deployed in the old meter runs have been carried out by FCRI, Kerela and witnessed by M/S NMI, Netherlands. The Flow Computers have been checked and verified by M/S NMI, Netherlands.

•     Moreover, M/S NMI, Netherlands, who command esteemed authority in the international field of gas measurement have inspected, checked & validated each and every aspect of the Gas Metering Station that has an influence over the fiscal measurement, after the system was installed and commissioned.

•      All agreed eternal data (preset values) & various alarm limits have been entered in the Flow computers, Gas Chromatographs & supervisory computers jointly by ONGC & GAIL.

•     All secondary measurement instruments like PTs, TTs, and GCs are periodically validated / calibrated jointly by ONGC & GAIL.

The endeavor is to achieve the highest standards in Gas measurements giving top priority to maintain the sanctity of measurement.

A Brief Description of Gas Metering Station

The Gas Metering Station compromises of the following: (Please refer Figure-1)

1.      Old metering station (5 old 12” Turbine meter runs + 1 new 12” Turbine meter run)

2.      New metering station (6 new 12” Turbine meter runs)

3.      Meter Proving section

4.      Analyzer Section (Two Gas Chromatographs, a Hydrocarbon Dew Point, a Water Dew Point and a H2S analyzer)

The Gas Quantity measurement is being done through the twelve 12” Turbine meter runs (Old & New) having an overall designed capacity to measure 40 MMSCMD this is with an operating philosophy of 10 meter runs in operations and 2 standby. Presently around 33 MMSCMD of gas is being measured & supplied through this station.

The Gas Quality is being monitored through the online analyzers we have two Gas Chromatographs, a HCDP analyzer, a Water DP analyzer and a H2S analyzer.

A Meter proving section is used for proving the Turbine meters against a Master meter.

Gas Routing

Configuration of individual Meter runs

An individual meter run in Old or New metering stations consists of the following parts between their inlet & outlet 30”collecting header (Please refer Figure-2):

1.            30” Inlet collecting header.

2.            First inlet isolation, manually operated, ball valve, with a by 2” pass line.

3.            Second inlet manually operated (old meter runs–Gate valve, new meter runs–Ball Valve) valve.

4.            Spectacle blind (present only in New Metering Station).

5.            Dry Gas Vertical Cartridge Filter with DP transmitter, switch & gauge.

6.            Flow meter inlet spool piece with tube bundle flow straightener.

7.            Instromet make 12” G-4000 Turbine Meter with pressure transmitter.

8.            Flow meter outlet spool with Temperature Transmitter & Gauge and Pressure Gauge.

9.            Flow control valve (old meter runs – 8” FCV (ball valve) with pneumatic actuator, new meter run – 10” FCV (butterfly valve) with electric actuator).

10.       1” Vent line.

11.       Outlet isolation, manually operated Ball valve.

12.       30” Outlet collecting header.

The Meter runs broadly have three sections - the flow conditioning section, flow measuring section & the flow balancing section between the inlet & outlet isolation valves.

The flow conditioning section has a vertical gas filter for ensuring clean gas entering the Turbine meter. Its filtering media are pleated polyester needle felt cartridges reinforced by SS mesh capable of filtering 98% of dust particles >3 micron and 99% of dust particles > 5 micron. This is followed by the minimum requisite straight length of >10D (flow meter inlet spool) in the upstream of the Turbine meter to kill if any swirls are generated to insignificant levels, this is further assisted by a flow straightener installed at a distance of 5D upstream of Turbine meter. This is a bundle of 19 SS tubes of around 600-mm length having an OD around 57 mm. The gas now attains a uniform laminar flow profile before entering the Turbine meter. A straight length > 5D downstream of Turbine meter (flow meter outlet spool) is also given to avoid any introduction of disturbances in the flow profile

The flow measuring section has a 12” G-4000 Instromet make Turbine meter, the no. of revolutions of the turbine wheel is measured by a HF sensor probes mounted on the Turbine meter, the Pressure is measured through the designated tapping on the Turbine meter and  the Temperature is measured from the tapping ~2D downstream of Turbine meter.  These three signals are digitally transmitted to the respective flow computer for flow quantity computation. The forth input required for flow computation is the gas composition, which is given by the Gas Chromatograph.

The flow balancing section has a control valve serving two purposes. Firstly it is sized such that it allows the flow through the meter run upto 90% of Qmax, this is to safeguard the Turbine meter against over speeding and its probably damage. Secondly it balances the flow through each meter run in its corresponding Old or New metering station.

Configuration of Meter Prover run

The Proving section consists of the following (Please refer Figure-3):

A.     A 30” manifold consisting of three 30” ball valves for taking the proving meter run in or off line.

B.     An 18” control valve (marked as “B” in figure-3) to create a DP forcing a part of the flow through the proving line along with a DP transmitter to reflect of the control valve’s response.

C.    The 12” meter run  for Proving, having the following configuration:

1.            First inlet isolation, manually operated, 12” ball valve.

2.            Dry Gas Vertical Cartridge Filter with DP transmitter, switch & gauge.

3.            First Flow meter inlet spool piece with tube bundle flow straightener.

4.            Instromet make 12” G-4000 Turbine Master Meter with pressure transmitter.

5.            Flow meter outlet spool piece with Temperature Transmitter & Gauge and Pressure Gauge

6.            Intermediate isolation 12” ball valve.

7.            Second Flow meter inlet spool piece with tube bundle flow straightener.

8.            Space for the Meter Under Test (MUT) with a DP transmitter

9.            Flow meter outlet spool.

10.       Flow control valve (10” FCV (butterfly valve) with electric actuator).

11.       1” Vent line.

12.       Outlet isolation, manually operated 12” Ball valve.

Since gas measurement at high pressure and varying operating conditions is a complex exercise, many aspects have to be accurately measured. The major contribution of inaccuracy and uncertainty in gas measurement will come from the gas meter itself. In order to establish the required confidence level in the instrument, a meter prover has been installed.

A 12” Master (Turbine) Meter will be used as the proving element since all operating meters in the station have the same size. This “Master” was tested and approved by the Dutch metrological institute “NMI”. The different tested flow points (established with natural gas at approximately 60 bars) are entered into a computer system with the corresponding error, or deviation from the zero error point, for compensation. The intermediate flow points and corresponding deviations are calculated using a polynomial. Pressure, differential pressure and operating temperature are accurately measured for compensation of possible differences in operating conditions between “Master” meter and “MUT” (meter under test). The primary data acquisition and transfer is established by a separate and fully independent PLC.

Dry Gas Filters

Each meter run has a vertical Dry Gas Filter for ensuring clean gas entering the Turbine meter. The capacities of these filters are to handle a maximum of 4 MMSCMD of gas. The filtering media are pleated polyester needle felt cartridges reinforced by SS mesh capable of filtering 98% of dust particles >3 micron and 99% of dust particles > 5 micron.

In the Old Metering Station the Dry Gas Filters has bolted type Top cover and the each filter houses three Filter elements however, in the New Metering Station the Top cover are Quick closure type and each filter houses two Filter elements.

A filter DP gauge & switch and a DP transmitter is provided in each Dry Gas Filter to monitor the health of the filter elements. In due course of operation the filter DP increases when clogged by dust particles, this is normally a slow and gradual process. However, it also varies with the rate of gas flow through the meter run i.e. at higher flow there is a higher DP registered. Under normal condition say when the flow is around 3 MMSCMD per meter run the filter DP is around 275 to 300 mBar.

The vendor prescribes the max permissible filter DP as 500 mBar. Accordingly Alarms settings in the supervisory computer for DP Hi alarm is set at 400 mBar and DP HiHi alarm at 450 mBar.

In case the flow through any of the Old or New Metering Station increases more than 20.0 MMSCMD i.e. more than 4.0 MMSCMD per individual meter run and the filter DP increases more than 500 mBar, this may result in rupturing of the filter elements and these ruptured pieces may even damage the Turbine meters.

Presently the maximum gas available in the downstream of DPD is normally less than    34 MMSCMD and this is generally distributed more or less equally between the DPD 1&2 and DPD-3 units. Therefore under normal conditions, the situation where the quantity of gas through either Old or New metering station is exceeding more than 20 MMSCMD does not arise.

However, under certain abnormal conditions such a situation may arise, i.e. whenever there is an imbalance in the flow distribution among DPD 1&2 and DPD-3 units (i.e. more gas is processed in one compared to the other) to the extent that flow through either Old or New metering station increases more than 20 MMSCMD.

As the inlet to DPD-1&2 and DPD-3 units is floating on common header, whenever some DPD units in either DPD 1&2 or DPD-3 are under shut down due to operational requirement (due to maintenance jobs, safety checks, etc) or whenever sudden tripping of one or more running DPD units in either DPD 1&2 or DPD-3 occurs, the gas preferentially re-routes on its own through the other DPD units leading to the above situation.

So whenever such a situation is envisaged or if it suddenly arises priority must be given to safeguard the filters in the Gas Metering Station and this can only be achieved by reducing flow through the meter runs in question. The possible methods being as follows:

A.     By reducing gas through respective DPD units.

B.     By taking the 6^th standby meter run in line in order to redistributes the flow through 6 meter runs instead of the previously 5 meter runs.

Based on the operational situation and the time envisaged to carry out the action any of the two methods may be used to reduce the flows through the meter runs in question below 4 MMSCMD. Sometimes the situation may even demand to use combination of the either methods or even reducing the gas throughput for sometime. In any case the priority should be to safeguard the filters.

Even though the gas entering the metering station is expected to be dry and free of any liquid particle still each of the Dry Gas Filter is provided with a drain point which is lined up to the OWS sump. The OWS sump has two pumps to pump out the liquid in the sump to the OWS plant’s OWS grid.

In the eventuality of any upset of process parameters in the upstream plants (GSU, GDU or DPD) if any liquid is carried over then it would be knocked out in the filter, the indication of the liquid presence in filters is reflected in increase of filter DP. The entrapped liquid must be immediately drained to OWS sump to avoid any possibility of carryover of the liquid particles through the filter to the Turbine meters.

Liquids are incompressible and would hit the Turbine blades as a stone causing damage; hence we must always ensure that any liquid entrapped in the filter must be drained out to the OWS sump.

Turbine Meter

The gas enters the turbine meter through a specially designed flow straightener, which imposes an evenly distributed pattern on flow, impinging on the turbine wheel. The contraction of the flow in the annular slot increases gas velocity in order to exert a higher torque on the turbine wheel. The blades of the rotor are positioned under an angle of 30°C to 45°C.

The gas flow drives the turbine wheel with a speed proportional to the velocity of the gas. The total volume of the gas passing through the meter per unit time is equal to the velocity of the gas multiplied by the area of the annular slot, and every revolution of the turbine wheel is equivalent to a certain fixed volume passing through.

The number of revolution of Turbine meter blade per unit volume is called the “K” factor which depends on the geometry of the meter. This “K” factor is fed into the respective flow computer of the meter run where that particular Turbine meter in is installed. The no. of revolutions of the turbine wheel is measured by a HF sensor probes mounted on the Turbine meter, the Pressure is measured through the designated tapping on the TFM and  the temperature from the tapping ~2D D/S of Turbine meter. These three signals are digitally transmitted to the respective flow computer for flow quantity computation. The forth input required is the gas composition which is given by the GC.

All the meter runs in the Gas Metering Station have 12” G 4000, Instromet make Turbine meters installed having the following specifications:

Configurations of Analyzer section

Gas Chromatographs

There are two dual stream Gas Chromatographs (Make – Encal, Instromet) installed which are used to measure component concentrations in the gas, calculate heating value, relative density & to provide the required information to the flow-computers for the Supercompressibility calculations. These are NMI certified having an Accuracy better than ± 0.2%, Repeatability better than ± 0.05%.

The separation of individual components in the GCs is achieved using high purity Helium gas as carrier gas in the micro columns. The respective component concentrations are measured based on the principle of difference in solubility of gas and using the principle of difference in heat capacitance of different component by the Thermal conductivity detectors.

Gas chromatography is used to measure the major component concentrations in the gas in order to:

•       Monitor the gas quality.

•    Calculate the gas Calorific Value.

•    to provide the required information to the flow-computers for the Supercompressibility calculations

H2S Analyzer

There is one dual stream H2S Analyzer (Make – Galvanic Applied Sciences). It has Repeatability better than ± 2% span.

The measurement is derived by the optical measurement of lead acetate impregnated paper tape discoloring reaction when in contact with H2S in the gas.

Water Dew Point Analyzer

There is one dual stream Water Dew point analyzer (Make - Michell Instruments). It has Accuracy better than ± 1°C.

The measurement is derived from the electrical resistance variation of aluminum oxide crystals in contact with humidity.

Hydrocarbon Dew Point analyzer

There is one dual stream Hydrocarbon Dew point analyzer (Make - Michell Instruments). It has Accuracy better than ± 0.5°C condensation temperature measurement.

The measurement principle is based on the patented technique by Shell research, it involves detecting the formation of condensate through a secondary effect, a reduction in scattered light intensity is observed when a red LED light is reflected from a conical depression in a cooled probe surface.

The Gas Chromatographs and all the Analyzers are configured in such a way that they analyze the gas from Old metering station inlet header and New metering station inlet header in their respective alternate analysis cycles.

Gas Flow Measurement

The equation of state derived from Boyle’s Law reminds us that gases are compressible and their volume depends on pressure, temperature and component concentrations.

PV = ZRT

Since the aim is to measure gas, one wishes to establish a “known gas volume” independent and irrespective from any operating variables. So a cubic meter at agreed “Normal”,  “Standard” or Base conditions was created.

Vb = VL * Pabs * Tb * Zb

                  Pb      T      Z

Compressibility and Super compressibility factors

The ideal gas law: For all gases or mixtures of gases, the volume of the gas varies with temperature and pressure. The equation of state relating the volume, pressure, temperature and mass of the gas is PV =nRT where P is pressure absolute, V is volume and T is Temperature. R is the Universal gas constant and n is the number of moles of gases.

Deviation from the ideal gas law: The pressure-volume relationships deviate from the ideal gas law at all pressures. The deviation from the ideal gas law is a result of the interaction of the gas molecules. Since gas molecules do occupy space and do exert forces on other molecules, they do deviate from the ideal gas law. The lighter gases -those with low molecular weights, such as hydrogen and helium follow the ideal gas relationships more closely than other real gases. All gases obey the ideal gas law at zero pressure absolute but they will deviate as the pressure departs from absolute zero. Equation of state is modified to account for the deviation of real gases from the ideal gas law:                                                     PV = ZnRT

Where Z is a dimensionless factor relating the real gas characteristics to the ideal or perfect gas relationship and can be less than or greater than 1.0. Z for an ideal gas equals 1.0. Z is not a constant for any gas, but is a function of pressure, temperature and molecular structure. Because the deviation factor Z is less than 1.0 for most gases, if a gas is compressed, the resulting volume occupied by the gas is less than predicted by the ideal gas law, thus, Z has become known as the " Compressibility factor”.

To emphasize that the natural gas is more compressible than predicted by the ideal gas law, the term "super compressibility” is used. For turbine meter or ultrasonic meter calculations, deviation from the ideal gas law is accounted for by applying a factor equal to the ratio of compressibility factors. This factor is known as the "Supercompressibility ratio" S = Zb / Zf Where b: base conditions, f: flowing conditions

The Supercompressibility (Z and ZN) calculation in our Flow computers is being done according to AGA-8, which considers the full gas composition for a broader range of pressures and temperatures.

Instrumentation for Flow Measurement

Primary Measurement Instrument - Turbine meter

The gas flow drives the turbine wheel with a speed proportional to the velocity of the gas. The total volume of the gas passing through the meter per unit time is equal to the velocity of the gas multiplied by the area of the annular slot, and every revolution of the turbine wheel is equivalent to a certain fixed volume passing through. The no. of revolutions of the turbine wheel is measured by a HF sensor probes mounted on the Turbine meter and sent directly to the respective Flow computer.

Secondary Measurement Instruments

The flow meter is only part of a measurement system. Other elements include secondary instrumentation, the data acquisition and transmission system and the computer network that distributes the data.

The Absolute Pressure Transmitter of every meter run measures and transmits the operating gas pressure to the respective Flow computer using the latest technology in signal transfer; “Smart” digital data transfer via a FSK (Frequency Shift Keying) signal in accordance with the “HART”© protocol.

The Temperature Transmitter of every meter run measures and transmits the operating gas temperature to the respective Flow computer using a “class A” platinum resistance where 0°C = 100 Ohm ± 75 mΩ. The resistance measurement is digitally converted to a temperature indication and subsequently transferred to the flow computer via the “HART”© protocol.

Note: Both P & T transmitters are connected in parallel on two wires to the same 24 VDC power supply. The flow computer will access the data via the transmitter polling address (Pressure = address 1 and Temperature = address 2), thereby reducing any uncertainity caused during the signal transmitting.

The gas composition analyzed by the Gas Chromatographs is used to provide the required information to the Flow computers for the Supercompressibility calculations.  The analysis from the Old Metering station inlet header is sent to the flow computers of meter runs in Old metering station and similarly the analysis from the New Metering station inlet header is sent to the flow computers of meter runs in New metering station.

The flow-computer, the heart of the metrological system, converts the received “VL” information into “Vb” as instantaneous flow rate and integrated in a number of totalizers using the received information for pressure, temperature and the gas quality information.

The Supervisory Computer (SVC) receives, distributes, stores, monitors, displays and reports all required information to complete the fiscal gas measurement. The information from the GCs is distributed to all Flow-computers. All flow-computer totalizers are registered and reported. The system consists of two identical PC’s running in parallel as hot stand-by. One is designated as “back-up” while the other will be “duty”. Digital information is provided by a dual PLC also operating in a hot stand-by mode.

Gas Metering Station - Field Operations

To ensure smooth operation of the Gas Metering Station and accurate measurement, the shift engineer must bear in mind the following points:

Gas Metering Station Field area

1.      Carry out visual inspection of all the meter runs to check for any possible leakage or valve passing, etc.

2.      Check and ensure no gas is passing through the 6” vent line in inlet headers, 1” vent line in meter runs or from vent of Dry Gas Filter’s PSV.

3.      Check for any abnormal sound in the meter runs this may be possibly due to damaged filter elements, improper fitted gaskets, loose flow straightener, damage of turbine meter, some foreign material stuck up in the meter run or any other reason. In any case it is advised to take the matter seriously, investigate, identify the source and eliminate the cause. Till such time the meter run in question may be taken off line and the standby meter taken in line.

4.      To check & ensure that all isolation valves of the meter runs in operation are fully open as partially open valves introduces disturbances in the gas flow profile leading to inaccurate measurement.

5.      Check & Monitor the dry gas filters DP of all meter runs in operation.

6.      Check readings of all field instrument, those used for Fiscal measurement and those used for monitoring the operation of the metering station.

7.      Special care should be taken for the instruments bearing impact on the fiscal measurement. In case they are not working or even suspected to be faulty i.e. under-reading or over-reading measurements,  then immediately the matter is to be reported to concerned authorities for rectification and first the standby meter run is to be taken in line and then the meter run in question is to be taken in standby. This is to ensure that at no point gas goes unmeasured or with inaccurate measurement.

Gas Metering Station Analyzer section

1.      Check pressure of Helium cylinder. There are four cylinders (one in line & one stand by for each of the two GCs). If the pressure is around 20 bar remind Gen shift personnel for replacing the cylinder.

2.      Check pressures of standard calibration gas cylinders for GCs.

3.      Check 5% Acetic acid soln level in the H2S analyzers, its level should be up to the recommended level marked by a red line in the container. Also check the availability of Lead acetate paper. In case of shortage of any of the two, Co-Gen instrumentation is to be immediately informed for replenishment.

Ensure that instrument air is always lined up to the H2S, Water and Hydrocarbon Dew Point analyzer, as it is required for their operation.

Recommended Procedure to take a metering run (Old or New) in line

1.      Ensure that all the individual portions of the meter run configuration has been boxed up and ready to be taken in line.

2.      In case the meter run has been opened up for maintenance then ensure the meter run is IG purged.

3.      Ensure that all the instruments (PT, TT, DPT & Turbine meter’s HF/LF signal) are lined up and are in working condition, their instrumentation wiring connection have been made, and all requisite signals are being received by the Flow computers / supervisory computer at the control room.

4.      Start to pressurize the meter run through the 2” bypass line of the first inlet ball valve of the meter run.

•      Special care should be taken to pressurize the meter run very very slowly. Any sudden increase in pressure or flow may damage the Filter cartridges or the Turbine meters.

•     Never pressurize by directly opening the 12” inlet isolation valve.

•       Never pressurize by opening the 12” outlet isolation valve as it is not at all recommended to allow the flow through the Turbine meter in the reverse direction.

5.      Carry out leak checks if no leaks observed then slowly increase the pressure to operating pressure. This step may be skipped if the meter run was not under any maintenance and was previously as standby. However, a visual inspection of the meter run is advisable.

6.      Once the meter run is at the operating pressure and ready to be taken in operation then proceed to open the outlet isolation valve.

7.      Now the flow through this meter run would have been established and measurement started.

Special care should be taken to ensure that all isolation valves are fully open. Any partial open valves cause disturbances in the flow profile leading to inaccurate flow measurements.

Recommended Procedure to take a metering run (Old or New) off-line (standby)

1.      First close the 12” Outlet ball valve.

2.      The flow through the meter run would have stopped, Ensure the same from control room.

3.      Then close the first 12” inlet isolation ball valve.

Gas Metering Station - Control room Operations

The control room building has a Control room housing the Supervisory computers & Control panels, a MCC room, a UPS room & a Battery room. The main power supply for the Gas Metering Station is received and distributed from the panels in the MCC room. Then there are two redundant UPS (make-Tata Libert) along with a battery bank capable of supplying backup power, required for the control system, for 30 minutes.

In the control room we have the Supervisory computers (SVCs) and the Control Panels. The Supervisory computer (SVCs) acts as “Master” and regulates the flow of requisite data between the SVCs, Flow computers, Control units of all the analyzers & the PLCs. They serve the purpose of monitoring & controlling the station, storing historical data and also generating various reports. Then there are four Control Panels. The first Control Panel houses the 24V DC power supply unit, Modicon & SAIA PLCs. The second Control Panel has the GPS clock, Control units of GC, HC, H2O analyzer and the ticket printer. The third Control Panel has the flow computers & a Black box (data sharer). While in the fourth Control panel the HC & H2S detector panels have been housed.

Elaborate description on the Measurement, Monitoring & Control system installed in the control room has been given in the Installation, Maintenance & Operation Manual Volume-II, under Tab-8 - chapter on “Function Design Specification” (FDS).

It may be noted that certain changes in the display screens of SVCs have been done after commissioning of the system in order to provide more information useful to monitor the station. Presently the submission of As- Built FDS is pending, however, this chapter gives detailed information for better understanding of the various features of the system.

Apart from thorough understanding of the system the following points may also be borne in mind during control room operations:

1.      Due to the fiscal implications involved the system is designed such that the Supervisory computer’s (SVC) software allows access to various levels (screens on SVC) based on authorizations i.e. one has to log in using a user name & Password. In order to disallow usage of the system by any unauthorized person. If the control room is left unattended due to some reason then one must log out from their access level. The access level for the shift engineer’s operation is - user name “Operator” and the password has been given to shift engineers.

2.      One of the SVC is kept as “Duty” and the other as “Backup”. It may be noted that the SVC which is on “Duty” is the master and the one which is “Backup” is standby to the “Duty” SVC. All reports (Daily & Snapshot) should be printed only from “Duty” SVC. The reason may be best understood if one understands the following flow of data.

Gas Flow Quantity:    The flow quantities which are computed in the Flow computers are transferred to the SVCs after a designated period. If for some reason if the SVC is shutdown for a few hours within a particular “Day” then whenever it comes alive it communicates with the flow computers and updates its flow quantities by adding the quantities for the period it was not alive in the figure for the next designated time. Hence the Flow quantities for the “Day” are same in both the SVCs.

Gas Composition:     The gas composition is communicated to the SVCs by GCs after analysis and depending on the “priority” selected the “Duty” SVC sends the “in use” gas composition data to the respective Flow computers for compressibility calculation which is further used for computation of Flow quantities. (Term “Priority” & “in use” explained further below)

Gas NCV:                  The Gas NCV (ideal) is computed by the GCs and sent to the SVCs where it is converted to NCV (real) and then these are averaged over the period “Day” in the SVCs. As there is always a difference in timings of receiving the data from GCs by the respective SVCs, the Daily Average NCVs in the “Duty” & “Backup” SVCs are slightly different.

For the purpose of Custody transfer we must consider the NCV from the Master i.e. “Duty” SVC.

Some of the configuration may be changed depending on the operational requirements through “Maintenance” available in both SVCs. The relevant options in this are as follows: Click “Maintenance” then “Options” then we have a pop up window having the following options:

Duty/Backup

Printer

Existing GC & New GC

Existing PID & New PID

Existing Control & New Control

3.      The health status of all components of the entire system may be checked from the Display screen “System Overview”. In the SVC. If any of the components were faulty then those components would turn red in colour. In such case the matter should be immediately reported to concerned section for rectification. Such failures of components are also indicated by an audiovisual Alarm in the SVC.

4.      The various readings of the Gas Metering Station like pressures & temperatures of inlet collecting headers & of all individual meter runs, DPs of all filters in operation, current, hourly & daily average gas composition data from GC and the gas quality (H2S, HC & Water DP) data from the analyzers, Gas quantity totals – current, hourly, daily etc can be monitored through the various Display pages on the SVCs. The method to display various screens on the SVC is by simply pressing the requisite soft buttons for the desired display screen.

5.      If and when the alarm condition occurs, the system generates an audio sound along with the following display indications on the SVC screens:

a)     The “Alarm” written on the right top corner of all the SVC screens turns red.

b)     The respective alarm string is displayed in the active alarm window on most of the display screens of SVCs.

c)      The “Alarm Summary” display screen has a list of all possible alarms along with their set point value of the Limits against the ones which are user defined. Those alarms, which are in alarm condition, are accompanied with a message “Alarm” in red colour and “Unack” in Yellow colour.

To acknowledge the alarm simply press the “Ack all” soft button on the “Alarm Summary” display screen this would silences the audio alarm and then the message “Unack” in Yellow colour disappears. Once the alarm condition is normalized the message “Alarm” in red colour disappears and the message “Normal” in green colour appears.

•     In case of DPSH alarms of Filters these have to be reset by pressing the “Reset DPSH” soft button on the “Alarm Summary” display screen.

6.      The Control panel for the detectors has a total of 28 (27 LEL+1H2S) detector control units, 16 in the first row, 12 in the second row and 4 spare slots in the second row. There is a display screen on the left side of each row. Each detector is designated a channel no. i.e 1 to 16 in the first row and similarly 1 to 12 in the second row (13 to 16 are spare slots). Against each detector its tag no. and its location in the field is displayed.

If and when the alarm condition occurs, detection system generates an audio sound locally in the panel along with the glowing of the red LED in the corresponding detector’s control unit, a hooter in the field along with the alarm audio-visual indications on the SVC screens.

To acknowledge the hooter select the respective channel on the display screen for the detector sensing alarm condition using the Up or Down buttons on the left side of display screen then press “Reset”. This will silence the audio alarms.

A faster method is to inhibit the detector sensing the alarm condition - irrespective of the channel selected in the display screen simply press both the “Reset” button and the “Inhibit” button corresponding to the detector sensing alarm condition, at same time.

Investigate the cause around the location of the detector sensing the alarm condition and take appropriate actions.

7.      The Printer kept inside the control panel is the “Ticket Printer” connected to the Flow Computers through a sharer called the Black box. It is configured to print out the 24 hrs Day-Quantity for each of the twelve Flow Computers every day at 0500 hrs called the Ticket. This Ticket is an important document for Custody transfer records. It must be ensured that the Ticket printer is ready with requisite paper for printing at 0500hrs.

8.      To manually print reports from SVC: The most important thing is to print reports only from “Duty” SVC.  On the “Duty” SVC’s, go to either of the display pages “Existing Totals “ of “New Totals” then go to “Reports”, a pop up window would appear which would have an the following options to choose from:

“Daily report”           It prints the 10 page daily report. One should choose the date for which the report is desired.

“Monthly Report”     It prints the 10 page monthly report. One should choose the month for which the report is desired.

“Snapshot”              It prints the 2 page snapshot report having current instantaneous values on one page and previous day’s (24hrs) values on the other page. This report can be printed for only the present day.

9.      To prepare the morning DPR in the designated format, the following methods may be used.

a)     From the 2 Page “Snapshot” Report from “Duty” SVC.

b)     From the 10 Page “Daily” Report from “Duty” SVC.

c)      From the “Duty” SVC’s display screens of “Previous Day Totals” of Existing Metering Station & “Previous Day Totals” of New Metering Station.

d)     The Day quantity can also available on the print out of the Ticket Printer.

SEMI-RICH

GAS

TO IPCL

INTRODUCTION

The Gandhar petrochemical complex of Indian petrochemicals corporation ltd. (IPCL) in Dahej is based on natural gas as feedstock. The partial requirement of gas for IPCL’s plant would be supplied from ONGC, Hazira. Accordingly, two pipelines are being laid from Hazira to Dahej : a 26 “ line to carry Semi-Rich gas from Hazira to Dahej and a 24 “ dia line for returning Lean gas from Dahej to Hazira after recovery of C2/C3 from the semi rich gas.

1.0.0       DEFINITION

Commissioning is defined as the activity of filling a pipeline with gas to be transported through it and bringing the line to its normal operating condition.

1.0.1       PURPOSE

Charging a cross-country pipeline with inflammable natural gas is a critical operation and has to be planned and executed carefully and systematically. The purpose of this document is to describe in details the procedure to be followed for commissioning of the twin gas pipelines between Hazira and Dahej. This document will facilitate proper planning and execution of the commissioning activities in a safe and systematic manner.

      2.0.0  SYSTEM DESCRIPTION

The Hazira Dahej pipelines consists of twin gas pipelines along with terminal facilities and associated systems. For both the pipelines gas is received from the plants at the required pipeline pressure and no further compression is required. A brief description of the system is given below

      2.1.0 PIPELINES

There are two parallel pipelines laid in the same trench with a minimum gap of 500 mm between them.

2.1.1 SEMI RICH GAS PIPELINE

A 26” NB pipeline starting from a tap off downstream of the LPG plant of ONGC, Hazira and at the other end connected to the Gandhar Dahej  semi rich gas pipeline at Dahej downstream of the turbine flow meter.

Design basis: MATERIAL BALANCE: 16 MMSCM Sweet Gas

INSTALLATION, OPERATION

AND

MAINTENANCE

OF

FLARE SYSTEM

FUS TIP AND PILOTS

The Airoil Flaregas 'FUS' Tip is a smokeless flare tip suitable for USE with a wide range of gasses. The steam is injected directly into the root of the flame by means of numerous nozzles positioned around the top of the tip, so that the jetting effect also draws in the surrounding air to produce more rapid and clean combustion a center steam jet is also provided.

The scope of this center jet is to achieve a better smokeless flaring mixing the flare gas before to take combustion. Moreover the center jet will keep cool the flare tip body and it will help in case of back combustion.

This tip employs the same well-proven flame stabilization techniques used on other tips to ensure complete flame stability under even severe wind condition.

The tip is provided with a wind shield. The purpose of above shield is to create a turbulent zone to flare gas exit and stabilizing the root of the flame. Flame stabilizers and ignition pilots are provided to maintain satisfactory combustion.

Detailed instructions on the lighting sequence are give later.

The tip is internally insulated with high temperature fine grain cast able three off forced pilot 1200 equally spaced are fitted on flare tip. Flare tip is made in high alloy steel.

The flare tip is provided with 3 continuous pilot burners

The air adjusters are situated at the base of each pilot and should be set approximately 6 mm open. The method of ignition the pilots is described fully under the section dealing with the ignition panel. Each pilot is fitted with a K-type thermocouple 6.35 mm dia. The thermocouple is connected to the temperature relay on control panel at ground. Each thermocouple will give via the temperature relay the following signal:

Red light: Pilot off

Green signal: .Pilot on

Free contacts are available for remote control room.

NOTE:

Since steam is not available for the first year of flare operation, .it is recommended that the external steam manifold will not installed. Flare tip is equipped with a special wind shield suitable: for such conditions. During this, period smoke flame is possible.

INTEGRAL GAS SEAL

The Airoil Flaregas Integral Seal is of the venturi type. These rely on a momentary increase in the gas velocity near the tip to create a turbulent flow condition and prevent the ingress of air into the stack.

GUY ROPES

•       The flare system is supported by three set of zinc coated wire ropes. Each set, positioned at different level will include 3 ropes equi spaced at 120°.

•       During the erection the initial tension of the ropes has to be checked with a dynamometer.

•       Tolerance on initial tension value from 0 to 10 %

•       We recommend to check periodically the initial tension of the wire ropes, at least after the first year from the erection.

•       Initial tension during erection

•       Wire ropes at first level (Elevation 21 mts.)

•       The initial tension of the ropes is 40.000 Newton at +2loc The tension will increase by 509 Newton per each reduction of one degree centigrade.

Example: if the temperature is +10°C the reduction .is (+21)-(+10)=+11°C

(509xll) + 40.000 = 45.599 Newton

The tension will decrease by 509 Newton per each increase of one degree centigrade.

Example: if the temperature is +35 degree the increase is (+35)-(+21)= +14°C 40.000- (509x 14) = 32.874 Newton.

Wire ropes at second level (Elevation 40 mts.)

•       The initial tension of the ropes is 55.000 Newton at 21°C

•       The tension will increase by 322 Newton per each reduction of one degree centigrade.

Example: if the temperature is 10°C the reduction is (+21)-(+10)= +11  degree C

(322x11)+55.000= 58.542 Newton

DESCRIPTION OF THE FLARE SYSTEM

•       The flare system is designed to permit continuous And emergency Relief of gas from the plant and to burn this gas in a safe and Clean manner.

•       The flare system will be suitable to burn 305.305 Kg/hr of max flow rate.

•       The main safety relief devices are the elevated flares which are able to handle the maximum relief of the emergency case.

•       The elevated flare consists of a guy-supported structure with an overall height of 70 m stack, is fitted with a 30” FUS flare tip.

•       The design ideas of the tip are explained in the technical memo attached to these instructions.

•       The elevated flare is, however, intended for continuous use.

•       FUS flare tip is equipped with three forced draft pilot and steam smoke suppression device (to be fitted when steam will be available).

•       The attached drawing list gives details of all part drawings which should be considered as forming part of these.

•       Each pilot is fitted with a CR/AL thermocouple K-Type -given the following signals: