SULPHUR RECOVERY UNIT

CONTENTS                                                                                                                 PAGE

1.0       INTRODUCTION                                                                      -                       01 - 13

Block Diagram                                                                                  

General Layout and Fire Safety System Layout                                       

Capacity                                                                    

Design Flexibility

Feed Specifications                                                

Product Specifications                                                                    

Utility Specifications                                                                        

Effluents

Underground Layout of Liquid Effluent Streams

RWWTP system in SRU                                                                    

2.0       PROCESS DESIGN                                                                 -                       14 - 37            

Theory of Operation

Process Description

Schematic Diagram

ACID Gas Feed Distribution

H₂S Absorption and Locat Regeneration

Locat Cooling

Compression of Oxidizing Air

Sulphur Melting and Separation

Sulphur Storage and Forming

Chemical Requirements

Common Facilities

3.0       OPERATING PARAMETERS                                                   -                       38 - 54

Operating Variables

Equipment Parameters

4.0       GENERAL INFORMATION                                                      -                       55 - 63

Sulphur Recovery Unit

Frequent Problems Observed in SRU

Procedures for SRU

ALARMS AND TRIP SETTINGS                                               -                       64 - 70

5.0       MODIFICATIONS AND SCHEMATICS                                    -                       71 - 79

            Major innovations/ In-house modifications

            Guidelines for Horizontal Steam Condensate Transfer Pump

SECTION – 1

INTRODUCTION

INTRODUCTION

The SRU of Hazira Plant consists of 6 Trains which came up in phases – Tr. 61, 62, 63 (Phase I); Tr. 64, 65 (Phase II) and Tr 66 (Phase III). In addition to these, there is one Incinerator (Tr. 60), which came up with Phase I.

1.1. CAPACITY

The SRU is designed to treat 35,000 NM³/Hr of acid gas originating from the Gas Sweetening Unit. Each train is capable of treating up to 7000 NM³/Hr of acid gas with a hydrogen sulfide concentration ranging between 0.3 and 5.2 mole percent i.e. 3000 to 52000 ppm of H₂S. The sulphur production will range between 0.7 and 12.2 metric tons per day per train. Under normal circumstances four trains will operate at full capacity while two remains on stand by / under maintenance.

1.2. DESIGN FLEXIBILITY

Each train may be operated down to a guaranteed turndown of 40%. In the unlikely situation where a malfunction occurs in one train while the spare train is undergoing annual or scheduled maintenance, the acid gas would be automatically diverted to a stand by thermal incinerator which would oxidize the hydrogen sulfide and hydrocarbons before expelling them into the atmosphere. The incinerator is designed for a maximum of 7000 NM³/Hr.

The operation of each train is completely independent of the others. The 6 trains may be operated in one of the following two modes:

•       Operate five trains at reduced capacity with one train as hot stand by / under annual turnaround.

•       Operate 4 trains at full capacity while one train remains as hot stand by and other under annual turnaround.

A discussion on each mode of operation follows:

Operating 5 trains, each at reduced capacity, is advantageous for a system, which experience frequent changes in feed flow rate or composition. These changes can more easily be handled when spread over 5 trains than 4 trains. Another advantage is the ease in which 4 of the 5 operating trains can increase their capacities up to 100 % when the running train experiences a shutdown. In this situation, the switchover from 5 trains operation to a 4 train operation will be quick and uninterrupted.

Operating in this mode, however, results in a higher chemical consumption and utility consumption, especially power. For instance, five air blowers would be operating regardless of operating capacity instead of 4. The additional power consumption attributed only to the air blowers is about 600 KW. The drawbacks outweigh the benefits and a 5 train operation, although possible for operating flexibility, is not recommended due to economic considerations. Also at lower acid gas flow, acid gas spargers tend to choke.

Operating 4 trains while the other two remain as hot stand by / under turnaround is more economically and technically acceptable. Its technical drawbacks have been addressed and relieved by the provision of a stand by thermal incinerator, which will take up any flow fluctuations that cannot be handled by the 4 operating trains or handle the total flow from one train in the event of a train shut down. During a sudden train shutdown, acid gas would be diverted to the thermal incinerator until the stand by train is ready to accept feed gas. This situation should last for about 10 minutes or less. But nowadays GPCB has advised to run the incinerator for minimum possible period and its run time with reasons and amount of gas incinerated be logged down in a separate register.

Since sulfur is stored in its molten form, the sulfur system of the stand by train will remain ‘hot’ to prevent plugging due to solidification of stagnant sulfur  in lines.

It is recommended to operate the SRU with 4 trains operating and 2 trains as spare with its molten sulfur system remaining ‘hot’. Out of the two spare trains one can be taken for annual maintenance / turnaround activity.

1.3 FEED SPECIFICATIONS:

The acid gas composition will vary with the variation in sour gas throughput, arrival pressure and temperature at Hazira.

The acid gas has the following properties:

1.4 PRODUCT SPECIFICATIONS:

Sulfur produced by the SRU is a consequence of meeting an environmentally acceptable gaseous effluent.

The sulfur is expected to have the following characteristics:-

1.5 UTILITY SPECIFICATIONS:-

1.5.1       ELECTRICAL POWER:

SERVICE                                        VOLTAGE            PHASE   FREQ.CPS  

                                                                                                    (Hertz, Hz)

a. Motors up to 160 kw                          415 V                     3         50

b. Motors of 161 kw and above             6.6 KV                    3         50

c. Lighting Distribution                           240 V                     3         50

d. Instruments                                       110 V DC – for interlocks

                                                                    110 V DC - through inverter (no break)

                                                                            Voltage variation: + / - 6 %

                                                                            Frequency variation: + / - 3 %

1.5.2       STEAM:

1.5.3       INSTRUMENT AIR:

1.5.4       PLANT AIR:

1.5.5       COOLING WATER:

1.5.6       BOILER FEED WATER (BFW):

Demineralised and deaerated water, suitable for production of H. P. steam.

Pressure          : 5 kg/cm²

Temperature    : 70 ⁰C

1.5.7       DEMINERALISED WATER:

Same as boiler feed water, except for de-aeration.

Pressure          : 5 kg/cm²

Temperature   : 40 ⁰C

1.5.8       CONDENSATE:

Steam condensate will be flashed to steam header pressure thus making condensate available at 4.5 kg/cm² at B/L at grade.

1.5.9       INERT GAS  (CO₂ + N₂):

1.5.10  FUEL GAS:

* This condition will also occur at the time of LPG plant shutdown.

1.6    EFFLUENTS:

1.6.1       GASEOUS EFFLUENT:

The purpose of the SRU is to remove Hydrogen Sulphide from the acid gas prior to expelling it into the atmosphere.

In order for the effluent to be environmentally acceptable it must contain no more than 10 ppm (v) H₂S. It has recently been revised by GPCB to 30 ppm of H₂S. The expected characteristics of the gaseous effluent are given below:

1.6.2     LIQUID EFFLUENT :

The liquid effluent is a waste stream, which will be sent directly to the open drain chemical sewer. The characteristics are as follows:

There are three Liquid Effluent streams in SRU. The detailed layout is at Fig. 1.3.

a)     Storm Water – Goes to open storm water channel.

b)     Plant Floor Wash – Contains some LOCAT chemicals and sulphur particles. It goes to OWS through RWWTP (Fig. 1.4) for treatment.

c)      Spent LOCAT – It goes to SCTP for treatment and disposal.

- o -

SRU PLANT

SEWAGE

(FLOOR WASH)

Fig. 1.4

SECTION 2

PROCESS DESIGN

2.   PROCESS DESIGN

The Locat unit will reduce the H₂S by 99.9 % from 5.2 % to 10 ppmv. The Locat unit works by contacting the H₂S with a liquid phase catalytic reagent, which absorbs the H₂S and converts it to elemental sulphur and H₂O. Details of the theory and operation of the Locat unit designed for this application are contained in the following sections.

2.1   THEORY OF OPERATION :

The Locat process brings about the following reactions to produce solid elemental sulphur from hydrogen sulphide gas.

Absorption:

H₂S (Gas) + H₂O (Liquid)  à  H₂S (Liquid) + H₂O (Liquid)      ---------     (1)

First Ionization:

H₂S (Liquid)    à  H⁺  +  HS ^-           -------------------------------------------     (2)

Second Ionization:

HS^-      à   H⁺   +   S  ⁼                        -------------------------------------------     (3)

Oxidation by Metal ions (Fe⁺⁺⁺):

S ⁼  +  2 Fe⁺⁺⁺           à   S ^o (Solid)  +     2 Fe⁺⁺      -----------------------------   (4)

Overall Reaction:

  H₂S (Gas) +  2 Fe⁺⁺⁺           à     2 H ⁺   +    S ^o   +     2 Fe⁺⁺   ---------------  (5)

The metal ions must then be deoxidized in the regeneration part of the process using oxygen from either ambient air (anaerobic process) or the process gas itself (aerobic process).

Absorption:

O₂ (Gas)  +  2 H₂O  à    O₂ (Liquid)  +  2 H₂O   --------------------------        (6)

Regeneration of Metal Ions:

½ O₂ (Liquid)  +    H₂O  +     2 Fe⁺⁺   à   2 (OH) ^-   +    2 Fe⁺⁺⁺     --------    (7)

Overall Reaction:

½ O₂ (Gas)  +  H₂O   +    2 Fe⁺⁺     à   2 (OH) ^-   +    2 Fe⁺⁺⁺      ------------  (8) 

Now, adding equations (5) and (8) together gives

H₂S (Gas) +  ½ O₂ (Gas)  +  H₂O   à   S ^o  (Solid)  + 2 H₂O (Liquid)  --- (9)

Or,    H₂S (Gas) +  ½ O₂ (Gas)  à   S ^o  (Solid)  +   H₂O (Liquid)  ----   (10)

In this overall reaction, the metal serves to transport electrons from the absorber side of the reaction to the regeneration side, and it is necessary to supply at least two metal ions per atom of sulphur made. In this sense, the metal ions are a reagent. However, they are not used up in the overall reaction and serve as a catalyst for the reaction of H₂S and oxygen. Because of this dual function, the metal ion concentrate, ARI-310 solution is described as a catalytic reagent.

The auotcirculation LO-CAT^R unit addressed in this manual utilizes the differential density between two aerated liquid phases at different aeration rates to circulate ARI-310 solution from the oxidizer section to the absorber section of the vessel. The solution absorbs H₂S and small amounts of CO₂ and is returned to the oxidizer. Air is introduced in the oxidizer section of the vessel, whose oxygen is absorbed into the solution. This absorbed oxygen regenerates the catalyst.

Equation (10) indicates that there is no net production of H⁺ ions of OH^- ions and that the pH of the solution is not changed by the basic reaction. However, several competing side reactions do go on to a limited extent, and require the addition of KOH, or other alkaline material to maintain the pH of the solution high enough to give good H₂S absorption.

The side reactions are less clearly defined from a chemical standpoint, but may be represented by the following generalized reaction:

2HS + 2O₂             S₂O₃ + H₂O

When this is combined with the ionization reactions, it is apparent that there is a net production of H+ ions whenever S₂O₃ is produced. This would lead to a decrease in the pH of the solution, and to prevent this, it is necessary to add an alkaline reagent such as KOH either continuously or intermittently to control the pH of the solution.

Usually pH values in the mildly alkaline range between 7.5 and 8.5 are satisfactory for most applications.

The exact pH required will vary with the type of absorber and absorber efficiency required.

Operation at an excessively high pH will encourage the formation of thiosulphate ions even though a larger fraction of the dissolved H₂S will be in the form of S ions at high pH values. Operation at abnormally low pH will prevent absorption of the H₂S.

The process gas streams contain CO₂, which will also be absorbed by the circulating catalyst to form carbonic acid, which also reduces the pH of the solution. To prevent this form happening, it is necessary to further buffer the solution with an alkaline reagent such as KOH. As a general rule, a concentration of 10 wt% KOH is required in the circulating solution for a gas stream containing 1 atmos partial pressure of CO₂. This will give a solution pH of between 7.5 and 8.5. Batch or continuous make up will be required to overcome the withdrawal losses from the system.

It is apparent that the formation of sulphate and thiosulphate and the addition of alkaline reagents to control the pH will lead to increasing concentrations of dissolved salts in the ARI-310 solution with time.

Small units have been designed to remove the solid sulphur as a 50-wt% cake. The sulphur is handled at about 50-wt% with the remaining 50% consisting of the catalyst solution. Thus, for each pound of sulphur removed from the system, approximately on pound of solution will also be removed. This rate of removal substantially exceeds the rate necessary to purge by-product salts, and constitutes a significant loss of catalyst from the system.

Larger systems, like the ONGC SRU, which utilizes a sulphur melter, do not involve the discharge of any waste water with the sulphur product, and therefore, require a purge stream after the concentration of dissolved solids in the system has built up to a level of 15 to 30-wt%. The same requirement may hold true for a system in which some of the sulphur-containing solution is diverted to a filter and then returns to the absorber / oxidizer vessel. Some of the dissolved solids will be removed with the liquid in the filter cake; periodic checks should be made to ensure that the thiosulphates concentration in the circulating solution does not exceed 15 to 30-wt%. Suspended solids concentrations of 0 to 1 wt% should be maintained during normal operating conditions.

The satisfactory methods for monitoring the concentration of the solution are available. The most straightforward involves performing chemical tests for total metal content, and adjusting the addition rate as required to hold the concentration within predefined limits. The second method, which is much simpler to use, involves the measurement of the Redox Potential with an electronic instrument much as a pH probe. The redox potential measures the activity of the solution with respect to a fixed reference. This is not the same as the concentration of the metal ions, but rather the product of the concentration and the effective oxidation. Maintaining a redox potential value between –100 and –250 mv in the absorber / oxidizer assures that there is reasonable amount of active catalyst in the system.

If neither of these means is available, catalyst can be added at a constant rate based upon an assumed rate of loss plus a safety factor. Sulphur is formed as a granular solid within the aqueous system and must be removed by a liquid-solid separation technique such as settling or filtration. In general, the sulphur will be formed in the absorber and will be wetted with scrubbing solution. Because sulphur has nearly twice the density of water, it settles relatively rapidly. Two exceptions to this rule may be encountered.

(1)   The sulphur formed during the initial operation with fresh                                    catalyst solution is likely to be extremely fine in particle size, and difficult to either filter or settle. This is corrected by allowing the concentration of sulphur to build up to 1.0 to 1.5 grams per litre of solution, which results in growth of the particles to a manageable size of around 25 microns.

(2)   Sulphur particles may become attached to minute air bubbles and float to the surface of the solution rather than sinking to the bottom. Ordinarily, these floating particles will eventually be wetted by the solution and behave in the normal fashion provided there is no place in the system where floating material may accumulate and cause plugging.

It has been found in some cases that sulphur particles are produced, which have hydrophobic surfaces and are not easily wetted by the aqueous catalyst solution. This unwetted sulphur forms froth and is difficult to remove as slurry. In order to ensure that this problem does not occur, any one of the numbers of wetting agents may be added to the system.

Another problem that has occurred occasionally involves biological attack on the organic materials in the solution. This is unlikely to occur ay pH levels 9. ARI-400 Biochem is added to the solution and serves as a bacterial growth inhibitor.

Water is created by the sulphur reactions which form sulphur, but ordinarily, sulphur, must be added to the system to replace losses by evaporation into the oxidizing air and process gas stream. This is true even if the incoming gas streams are saturated with water before entering the LOCAT^R process. This is because the reaction generates about 3500 Btu per pound of sulphur produced (enough to evaporate 3.5 lb. Of water), while the amount of water produced by the reaction is only a little more than ½ lb. per lb. sulphur produced.

2.2.           PROCESS DESCRIPTION (Fig 2.1):

The Sulphur Recovery Unit consists of 6 identical SRU trains (61, 62, 63, 64, 65, 66) and one common facilities train including incinerator (60). The following discussion will be associated with Train 61.

2.2.1       ACID GAS FEED DISTRIBUTION (Fig 2.2):

Acid gas from the Amine Gas Sweetening Unit enters the South battery limits of the SRU through a 24” pipeline header. The pipeline is sized to handle acid gas from both Phase I and Phase II of Gas Sweetening Unit. Another header from GSU Phase III enters SRU at South – East corner and joins the earlier header near train 66 making the whole system floating, giving the flexibility of treating acid gas from any phase to any SRU train.

In the event flow to one of the operating trains is choked, the pressure of the acid gas header will increase and Pressure Controller 60-PIC-1102 will open control valve 60 – PV-1108, sending the appropriate amount of acid gas to the incinerator in order to maintain pressure in the header. Pressure Controller 60-PIC-1102 is set at a higher pressure than the normal operating pressure of the acid gas sent to the incinerator.

A high flow alarm 60-FAH-1110 on the incinerator line warns operators when the acid gas rate to the incinerator is approaching the design rate of 7000 NM³/Hr. This is required since the incinerator is designed to handle gas to the equivalent of only one train or 7000 NM3/Hr. Spectacle blinds and block-off valves are provided at the branch connections of each one of SRU trains.

Flow to each train is controlled by a flow controller 61-FIC-1101 which is reset by the acid gas header pressure (60-PIC-1101). This allows equal distribution of acid gas to all operating trains regardless of acid gas pressure fluctuations.

Each unit is designed to process amine unit off gas at approximately 1.0 Kg/Cm² pressure and at a rate of 7000 NM³/Hr. The feed gas H₂S concentration is to be reduced from a maximum of 5.2 mole % to 10 ppm (v).

Feed gas enters Unit 61 through flow control valve 61-FV-1101 and in to the feed gas knock out drum, which removes any condensate entering the unit. This condensate is removed on level control / manually and sent off to the MDEA Sump Storage tank (60- V-654). Low level switch 61-LSL-1101 will automatically close 61-LV-1101 to prevent the acid gas from entering 60-V-654. The scrubbed acid gas continues to the oxidizer / absorber (61-V-602).

                                                        SRU AREA

2.2.2.     HYDROGEN SULFIDE ABSORPTION AND LO-CAT SOLUTION REGENERATION:

Absorption of H₂S is accomplished by contacting the sour gas with basic solution of ARI-310 catalytic reagent in the center well of the liquid full Absorber / Oxidizer 61-V-602. The process gas is introduced into each of the four (4) absorber sections through four (4) 8” process gas sparger assemblies. Process gas leaves the absorber section of the vessel through a perforated gas-liquid distributor plate at the top of the center well is mixed with spent air from the oxidizer section of the vessel and is finally vented to the atmosphere through the Cooling Tower 61-X-601. An H₂S analyzer located in the discharge neck of 61-X-601 will activate an alarm when the H₂S concentration reaches 15 ppm.

Circulating Lo-cat solution is introduced into the absorber section of the vessel by spilling over the center well wall through the gas-liquid distributor plate, as can be seen from the figure-2.3 &2.4. The absorption volume required to obtain the design H₂S removal is maintained by providing enough liquid in the system to allow circulation (this will be explained further below). Circulating liquid leaves the absorber section of the main process vessel by under flowing the center well wall, through the settler section and into the oxidizer section of the vessel.

The sulfur created by the reaction forms in the absorber section of the vessel. Since the density of solid sulfur is approximately twice that of water, the formed sulfur will settle down into the settler section of the vessel. A small amount of fine sulfur particles will continuously circulate with the liquid catalyst solution but this will equilibrate at a low enough concentration to not interfere with H₂S removal.

The reduced solution from the absorber section of the vessel underflows the center well wall and enters the oxidizer section.

As the reduced solution proceeds through the oxidizing section, it is regenerated by contact with air. The injection of air also serves the purpose of providing the driving force necessary to circulate the Lo-cat solution by lowering the bulk density of the oxidizing section.

The solution is completely regenerated by the time it reaches the top of the oxidizer section. Regenerated solution spills over the top wall of the absorber center wells and proceeds downward making counter current contact with upward flowing acid gas bubbles, thus completing the oxidation / regeneration cycle.

It is very important that the oxidizer airflow be maintained at all times. If the air supply is interrupted while the acid gas continues to flow into 61-V-602, the most apparent consequence is the breakthrough of H₂S to the atmosphere. A less apparent consequence is the over reduction of the Locat solution. Excessive over-reduction may result in the change out of the entire charge since it will reach a point where it will no longer be regenerable. The auto circulation system circulates catalyst solution between the oxidizer, absorber and settler sections of

_{ABSORBER INTERNALS}

Fig. 2.3

the vessel without the use of a circulating pump. The driving force for liquid circulation is provided by the difference in density between the aerated catalyst solution in the absorber and oxidizer sections of the vessel. The density of an aerated solution decreases with increasing superficial gas velocity. The superficial gas velocity in the oxidizer section of the vessel is set at about twice that in the center well absorber section of the vessel. Consequently, there is a tendency for the liquid level in the oxidizer section of the vessel to rise higher than the level in the absorber section. If the total liquid volume in the vessel is sufficient to provide a liquid level higher than the center well baffle, the aerated liquid in the oxidizer section of the vessel will spill over the center well baffle into the absorber section of the vessel. As a result, liquid catalyst circulation is achieved.

The oxidizer section has been designed with sufficient superficial gas velocity to assure adequate agitation for mixing gas and liquid in the oxidizer as well as providing a driving force for circulating liquid through the oxidizer and absorber sections of the vessel. The oxidation volume require to regenerate the catalyst solution at design H₂S load is provided for with the level controller – water make up system which also takes care of the net loss of water experienced by the process. Demineralised water on flow control is added either to the absorber / oxidizer to the recirculating sulfur slurry line or a combination of both. D M water is added on flow control (61-FIC-1204), which is reset by level (61-LIC-1204).

The system has been designed to provide sufficient catalyst circulation over the entire expected range of process gas flow rates. Liquid flows up flow co-current to the airflow in the annular oxidizer section and down flow counter current to the process gas flow in the center well absorber section. Since circulation is accomplished by spilling liquid over the center well baffle, it is critical to the operation of the system that the liquid catalyst level be maintained higher than the top of the center well baffle.

2.2.3.     LO-CAT SOLUTION COOLING (Refer Fig 2.5):

The reactions occurring in the process are exothermic, resulting in a net gain of heat by the Locat solution. During winter months and / or times of low H₂S concentration in the feed, the heat gain is more than compensated by the heat losses to ambient. However, during summer months and / or times of high H₂S concentration in the feed, the heat gain will result in Locat solution temperatures greater than the recommended 50 ⁰C. it is during these times that a heat removal system is necessary.

In order to maintain the solution at 50 ⁰C, 165.2 M³/Hr of Locat solution is withdrawn from the top of 61-V-602, sent to the Locat solution cooler (61-E-602) and returned to the top of 61-V-602. Cooling water in 61-E-602 cools the Locat solution down to 45 ⁰C. The cooling loop provided maintains the bulk of the Locat solution at a temperature no higher than 50

Fig. 2.4   LOCAT REGENERATION

⁰C during the worst possible situations (high H₂S in feed gas and high ambient temperature).

As currently H₂S ppm in acid gas is around 8000 ppm, cooling of Locat solution is not required and the system is isolated.

2.2.4.     COMPRESSION OF OXIDIZING AIR (Ref Fig 2.6):

Air for reoxidation of the catalyst solution is provided by two centrifugal air blowers (61-B-601 A/B). The air enters the blowers through the inlet air filter and silencer and is compressed to approximately 2.1 Kg / cm² (a). A low pressure alarm 61-PSL-1103 warns operators when the pressure drops below 0.9 Kg / cm² (g). The hot compressed air is sent to a water cooled exchanger 61-E-601, where it is cooled to 50 ⁰C using cooling water. The cooled air proceeds to the air K.O. drum where condensed water is removed. Condensate-free air continues to the absorber / oxidizer where it is diverted into four (4) air sparging assemblies, and evenly distributed throughout the oxidizer section of 61-E-602. The air sparging assemblies are located just above the bottom of the absorber center wells.

In the event the air blowers fail or excessive resistance is experienced in the air spargers of 61-V-602, the flow rate of air will drop below the design requirements. When the flow rate drops to 11200 Kg / Hr, 61-FSLL-1211 will activate an alarm and will also shut down the acid gas flow to unit 61.

2.2.5       SULFUR MELTING AND SEPARATION (refer fig 2.7):

Sulfur particles produced in the absorber section of 61-V-602 drop out into the settling section. The sulfur particles are about two times the density of water and rely on gravity and on the centrifugal force resulting from the circulation of Locat solution to settle out into the cone section of 61-V-602.

Sulfur will accumulate in the cone section to about a concentration of approximately 10-wt%. A continuously operating scraper prevents bridging of sulfur off the inside walls of the cone. An air blast sparger ring directs air jets towards the wall of the cone to prevent sulfur bridging in the lower section of the cone (below the scraper). An adjustable timer has been incorporated with the air blast valve to provide a series of pulsating air jets.

Sulfur is withdrawn from the bottom cone of the settler section 61-V-602 and pumped to the sulfur melter section of the unit by one of the two mono type progressive cavity positive displacement pumps (61-P-601 A/B). Demineralised water make-up is added to the sulfur slurry upstream of 61-P-601 A/B. This is done in order to wash the sulfur and produce a better quality sulfur product. As was mentioned earlier, this water make-up can either be added directly to the absorber / oxidizer or just upstream of the sulfur slurry pumps. The rate of water added upstream of 61-P-601 A/B is controlled by manually adjusting the ball valve downstream of 61-FI-1201.

Sulfur slurry exiting 61-P-601 A/B proceeds to the sulfur melter 61-E-603, 61-PSH-1203 and 61-PSL-1202 alarm in the control room when the sulfur slurry pressure is either too high (possible restriction problems downstream) or too low (malfunction of 61-PV-1307 or 61-P-601 A/B). The sulfur melter is a vertical exchanger with the sulfur slurry flowing downward in the tube section. Low pressure steam, which has been desuperheated, is the heat source and is introduced into the shell side of the sulfur melter through 61-TV-1305.

Temperature controller 61-TIC-1305 maintains the temperature of the LO-cat / molten sulfur exiting the sulfur melter at 125 ⁰C by adjusting 61-TV-1305. Condensed steam gravity flows to condensate separator 61-V-606 from which it is removed on level control through 61-LV-1305. Steam condensate proceeds to the condensate steam heater. The sulfur melter is fully insulated and is equipped with a melting coil (for start-up) and a jacketed bonnet on the discharge side. The hot molten sulfur / Lo-cat solution proceeds through a jacketed line to the molten sulfur separator. Molten sulfur settles to the bottom of 61-V-603 and is removed on interface level control (61-LIC-1306), through 61-LV-1306 to the sulfur surge tank (61-V-604). Low level switch 61-LSLL-1306 will close 61-LV –1306 when the sulfur level drops too low. This prevents contamination of the molten sulfur with Lo-cat solution. A high level switch61-LSHH-1302 will shut down 61-P-601 A/B in the event the sulfur level approaches the top of the vessel. High and low temperature alarms on 61-V-603 will warn operators of possible malfunction of 61-E-603. Hot Lo-cat solution exits the top of 61-V-603 and returns to the cooling tower (61-X-601), which is located on top of 61-V-602. In returning, it goes through 61-PV-1307 which maintains a pressure of 4.0 Kg / cm² (g) in the melting section.            

2.2.6       SULPHUR STORAGE AND SULPHUR FORMING (refer Fig.  2.8):

Liquid sulfur exiting the sulfur separator, flows to the sulfur surge tank (61-V-604) where it is stored the storage capacity of this tank is about 7 days.

The sulfur surge tank is fully jacketed and insulated. An internal coil is provided to speed up start-up if sulfur has been allowed to solidify within the tank.

Liquid sulfur is pumped from 61-V-604 by sulfur transfer pumps 61-P-603 A / B, to the sulfur forming system 61-X-602. There are three sulfur forming units (61 / 62 / 63 – X – 602). The liquid sulfur header feeding the sulfur forming units is completely integrated with all the 6 surge drums of SRU trains. Molten sulfur from any of the 6 surge drums can be processed by any of the three sulfur forming units (61 / 62 / 63 – X – 602). From surge drum through P – 603, molten sulfur proceeds to sulfur former where it enters the rotoformer, which drops molten sulfur onto a rotating stainless steel belt. The belt transports the flakes across a cooling section where the sulfur solidifies and cools. Cooling water is sprayed to the opposite (bottom) side of the belt providing the heat sink required for solidifying and cooling the sulfur flakes. Cooling water returns to the sewer system and serves as cooling water blow down for the Hazira Cooling Pastilles Conveyor (61-X-603), which transports sulfur flakes to the Bagging Hopper (61-X-604). The sulfur flakes are automatically fed into 25 Kg sulfur bags, weighed & sewed.

Nowadays, sulfur bagging is being done manually. Afterwards the bags are weighed and stored in the godowns.

Fig. 2.8

2.2.7.     CHEMICAL REQUIREMENTS:

Chemical make-up is normally required in order to maintain the Lo-cat solution at its most desirable chemical composition. The Lo-cat process uses the following make-up chemicals:

ARI - 310M                      Surfactant

ARI - 310C                       Biochem

     KOH

The addition of these chemicals on a regular basis has been provided for in the process design. However, chemical addition should be governed by the chemical composition of the circulating Lo-cat solution.

2.2.7.1.                      ARI- 310M / ARI – 350:

The iron in ARI-310 is held in solution by a mixture of chelating agents. A small amount of the Type A chelate is destroyed by oxidation and should be replaced on a continuous basis. ARI 310M make-up solution is a special mixture of stabilized Type A chelate.

ARI – 310M dosing pumps (61-P-605 A/B) transfers ARI – 310M solution from ARI – 310M dosing tank (61-T-601) to the Chemical Header. A no-flow switch 61-FSL-1601 warns the operators when the flow of ARI – 310M in the chemical supply header is interrupted.

2.2.7.2.                      KOH SOLUTION:

KOH solution is added to the process to maintain the required pH for H₂S absorption.

KOH solution Dosing Pumps (61-P-604 A/B) transfer KOH solution from the KOH solution Dosing Tank (61-T-602) to 61-V-602. A no-flow switch 61-FISL-1602 warns operators when the flow of KOH solution to 61-V-602 is interrupted.

2.2.7.3.         ARI 310 CONCENTRATE (ARI 310 C):

The catalyst used in the LO-CATR process is a chemically caged iron complex. The concentrate contains 18000 ppm free iron.

ARI-310 Dosing Pumps (61-P-607 A/B), transfer ARI-310 solution from ARI-310 Tank (61-T-605) to the Chemical Header.

A no-flow switch 61-FSL-1703 warns operators when the flow of ARI-310 to the chemical supply header is interrupted.

The dosing pump rate is manually adjustable to control chemical addition. A graduated level gauge on 61-T-605 is used to verify the rate of chemical addition.

2.2.7.4.        SURFACTANT (ARI 600S):

The sulfur particles sometimes agglomerate and entrap air bubbles. Dosages of 10 ppm per day of surfactant are ordinarily sufficient to provide adequate settling if the system is free of hydrocarbons. Larger doses are required if oil or other organics are absorbed in the circulating solution. Alkyl Aryl Sulfonate is the surfactant used.

Surfactant Dosing Pumps (61-P-606 A/B) transfers surfactant from Surfactant Tank (61-T-604) to the Chemical Header.

A no-flow switch 61-FISL-1704 warns operators when the flow of surfactant to the chemical supply header is interrupted.

The dosing pump rate is manually adjustable to control chemical addition. A graduated level gauge on 61-T-604 is used to verify the rate of chemical addition.

2.2.7.5.       BIOCHEM (ARI – 400):

Biochem is required to prevent biological degradation of the catalyst solution. Very small dosages of 10 ppm per day are usually adequate to suppress biological oxidation. ARI-400 Biochem^R , which serves as a bacterial growth inhibitor, is the recommended Biochem for this application.

Biochem dosing pumps (61-P-608 A/B) transfers Biochem from Biochem tank (61-T-603) to Chemical Header.

2.2.7.6.       DEFOAMER:

Foaming can sometimes occur within the absorber / oxidizer. Both the surfactant and Biochem have a tendency to cause foaming if used in excess as do some organic materials contained in the process stream.

In the event foaming occurs defoamer would be injected directly into the absorber / oxidizer in ½ to 1 liter dosages. The recommended defoamer is NALCO 5740, which is ‘air blown’ into 61-V-602 as follows:

•       Close block valve down stream of 60-LG-1808.

•       Make sure air supply is closed.

•       Fill 60-LG-1808 with one (1) litre of defoamer by opening vent on  1”-CA-60-60-1814-A2K and filling 60-LG-1808 and 60-T-650. Close filling valve and vent.

      Open air supply valve until pressure reaches 5.0 kg/cm². Close air supply line.

•       Open valve leading to unit to be dosed.

•       For Tr 61, 61 and 63 individual lines with valves are there. For Tr 64, 65 and 66 one common line with valve has been provided. Individual valves (located near P-602) in each train (64, 65 & 66) is to be opened in addition to the common valve.

•       Open valve immediately downstream of 60 – LG - 1808.

•       “Run” air until all of defoamer has reached its destination.

Defoamer is available from the Defoamer Tank (60-T-650). One Defoaming Tank supplies all six SRU trains.

2.2.7.7.         GNFC CHEMICAL:

Train 64 is under trial run with GNFC chemicals. The equivalent GNFC chemicals to ARI chemicals are –

G101 N  –  ARI 310C

G202 C  – ARI 350 (Previously ARI 310M)

G302 S  –  ARI 600 (Surfactant)

Rest all chemicals viz. KOH, Biochem and Defoamer are same.

2.2.8.               COMMON FACILITIES:

The common facilities of the SRU unit can be identified by the number 60 preceding equipment and instrument tag numbers. Unit 60 as it is more commonly referred to consists of the following:

•       Defoamer storage and injection system. (Discussed in section 2.2.7.6)

•       KOH solution preparation and storage.

•       ARI 310 M storage

•       Locat solution tank.

•       Chemical transfer

•       DM water handling

•       Steam tempering

•       Acid gas incinerator

•       MDEA drain handling

2.2.8.1              DEFOAMER STORAGE AND INJECTION SYSTEM

           Refer to section 2.2.7.6

2.2.8.2               KOH SOLUTION PREPARATION AND STORAGE:

Under full load condition, two batch of KOH solution are to be prepared every day but it varies depending on number of trains running and dosing rate required.

Solid KOH feeder (60-X-661) delivers KOH flakes from a KOH hopper to the KOH Solution Preparation Tank (60-T-652). This tank is provided with a mixer and a sump type pump (60-P-652). As KOH flakes are added to the preparation tank, the KOH solution pump circulates KOH solution through the preparation tank. This is required to remove the heat of solution, which is produced during the mixing process. The automatic feeder limits the rate of KOH flakes to reduce the possibility of boiling over of the solution. If the temperature of the solution rises beyond 80⁰C, an alarm (60-TAH-1829) will be activated, warning the operator of a possible malfunction. Cooling water runs through the shell side of 60-E-651 to cool the KOH solution. After the KOH solution has cooled, the batch is transferred to the KOH solution storage tank (60-T-653). This tank has a capacity of 15 M3 and can hold up to 3 batches of solution.

The individual KOH solution dosing tanks (61/62/63/64/65/66-T-602) are topped off on a daily basis using the KOH solution transfer / unloading pumps (60-T-653 A/B). Over filling of  (61/62/63/64/65/66-T-602) is prevented by an automatic shut down of 60-P-653 A/B when a high level switch 61-LSH-1608 is activated. These pumps can also be used to unload KOH solution from tanker trucks.

2.2.8.3    ARI-310 M STORAGE:

ARI-310-M is stored in ARI-310 M storage tank (60-T-651) of 20 M3 capacity located in the common facilities area. ARI-310-M transfer pumps (60-P-651A/B) transfer ARI-310-M, as needed, each of the 6 SRU trains. A high level switch 61-LSH-1607 on the dosing tank prevents over filling by shutting down 60-P651 A/B. The ARI-310 M storage tank is filled periodically using air operated, portable diaphragm pumps.

2.2.8.4    LO-CAT SOLUTION TANK:

The Locat solution tanks (60 T-654 A/B are 1000 M³ epoxy coated carbon steel tanks which are empty under normal conditions. In the event of a problem in the Absorber / Oxidizer vessel on any of the 6 SRU trains, the Locat solution will be transferred to the Locat solution tank. Locat solution filling pumps (60-P-654 A/B for 60-T-654 and 60 P-654 C for 60-T-654 A) are used to transfer the solution back to the absorber after the problems have been corrected.

Generally one tank is used to store reusable fresh Locat solution. In the other tank, blown down Locat from any of the trains is kept. The spent LOCAT is then sent to SCTP for treatment and disposal.

During initial Start-up, the Locat solution filling pumps are also used to mix the initial charge of chemicals and to fill the absorber vessels of each of the six SRU trains.

2.2.8.5    D M WATER HANDLING SYSTEM:

D M water is available from the ONGC offsite at a SRU battery limits pressure of 1.0 kg/cm². For most purpose this water is acceptable at the delivered pressure. However, if used as make-up water to absorber, the pressure of the available DM water is too low. For this reason a DM water surge drum and DM water supply pumps have been provided.

DM water enters the Demineralised Water Drum 60-V-62 on level control through 60-LV-1903. The Demineralised Water Drum operates at atmospheric pressure and is vented to the atmosphere. The D. M. water supply pumps (60-P-655 A/B/C) boost the D M water pressure to 6.5 Kg/cm² (g). Low-level switch 60-LSL-1926 automatically shuts down 60-P-655 A/B/C in the event of a low level in 60-V-652 to prevent damage to the pumps. High pressure D M water proceeds to the High Pressure D M Water Supply Header where it is distributed to all high pressure D M Water users.

2.2.8.6. STEAM TEMPERING:

Steam is available at ONGC off sites at the following conditions:

4.5 Kg / cm² (g)                 155 ⁰C

5.0 Kg / cm2 (g)                 156 ⁰C

5.5 Kg / cm2 (g)                 180 ⁰C

Since steam is used mainly for sulphur melting and as a heat source for jacketed lines and equipment, the maximum temperature allowable is 155 ⁰C. if the temperature is higher, there is an increased risk of molten sulphur plugging problems due to the increased viscosity experienced above 155 ⁰C.

LP steam entering the SRU facility is first reduced in pressure to 4.5kg/cm² by 60-pv-1915. the steam then proceeds to the first stage desuperheater (60 – X - 662) which reduces the steam temperature to 155 ^oC. High pressure DM water is injected into 60 - X - 662 to control the steam temp. Jacketed steam lines down stream of the sulphur preconditioner require steam at a lower temp. than what is produced by the first stage desuperheater. The required temp. is 130 ⁰C which corresponds to a saturated pressure of 1.8 kg/cm². A second stage desuperheater (61 – X - 611) produces steam at the required conditions.

Tempered steam produced by the first stage desuperheater is reduced in pressure by 61 PV 1916 and continues to 61 X 611 where high pressure DM water is injected to produce a steam at the desired conditions. DM water addition is controlled by 61 TIC 1916, which modulates 61 TV 1916.

2.2.8.7. ACID GAS INCINERATOR:

Acid gas from the Acid Gas Distribution system proceeds to the Incinerator System when acid gas header pressure increases beyond the set pressure.

Acid gas enters the Incinerator Scrubber 60 – V 653 which removes any condensate entering the unit.

The condensate is removed on level control and sent off to the MDEA Sump Storage Tank (60 – V 654). Low level switch 60 – LSL 2227 will automatically close 60 – LV 2227 to prevent the acid gas from entering 60 – V 654. The scrubbed acid gas continues to the acid gas incinerator 60 – X 651.

Acid gas is introduced into the annular space between muffle blocks and the burner corbel where it is mixed at the flame burst. Additional air is also introduced at this location to reach optimum excess air.

The incinerator has been designed considering the acid gas composition, normal composition for fuel gas (minimum of LHV) and the residence time of the fuel gas in order to guarantee the perfect combustion of the wastes.

The resultant gases are chemically inert. The operative temperature in the combustion chamber (800 ^oC) is maintained constant by the regulation of the fuel gas.

The quantity of fuel gas burnt varies depending on the waste sent to the incinerator. The residence time is greater than one second. Flue gas will be sent to the stack after quenching with air. Air quench flow rate will be a maximum of 36200 m³/hr.

2.2.8.8.          MDEA DRAINS HANDLING:

Sour MDEA condensate from the feed gas knockout drum 61 V 601 and from    the incinerator scrubber 60 V 653 is collected in the MDEA sump storage tank 60 V 654. MDEA sump transfer pump 60 P 658 is activated by level switch 60 – LSH / L-1928. When the level is high transferring the sour MDEA condensate offsite to the amine sump 30 – V 307. The amine sump is looked after by others and is located within the gas sweetening unit. When the level drops to a low setting, 60 LSL 1928 shuts down 60 P 658. The cycle repeats itself when the level in 60 V 654 rises to a high level set point.

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SECTION      :          3

OPERATING   PARAMETERS

3.    OPERATING   PARAMETERS

3.1.       OPERATING VARIABLES:

3.1.1. VARIABLES AFFECTING ABSORPTION AND OXIDATION                              EFFICIENCY:                    

Variables that affect absorption and oxidation efficiency are:

A.     pH

B.     Gas rate

C.    H₂S concentration

D.    Lo-cat solution concentration rate / Iron concentration

E.     Oxidizer air rate

F.     Lo-cat solution temperature

A.     pH:

The pH of the circulating solution should be kept between 7.5 and 8.5 by the rate of addition of potassium hydroxide (KOH). Operating at the high end of the pH range has the following effects:

1.      Maximum H₂S absorption

2.      Maximum catalyst life by –

a.      Reduced biological activity

b.      Reduced catalyst oxidation rate

3.      Increased chemical costs by –

a.      Increased Thiosulfate (K₂S₂O₃) production

b.      Increased losses with purged stream

Initial operation at a high pH level is recommended. This can be reduced as a function of time, consistent with good Hydrogen Sulfide absorption efficiency and catalyst life.

B.    ACID GAS RATE:

The flow of process gas at the design H₂S level can vary from 40% to 100% of the design flow rate without a significant loss of oxidation efficiency. Uniform distribution of both gas and catalyst solution will suffer at lower gas rates. This may cause a loss of oxidation efficiency.

Operating excursions at flow rates higher than design are possible without a significant effect on the catalyst system. H₂S oxidation efficiency will likely decrease during these periods.

C.    H₂S RATE:

The design H₂S rate, 553.5 Kg/Hr, is the basis for setting all operating parameters and is a product of gas flow and H₂S concentration. The operating parameter would be the same if the design gas rate were cut in half and the H₂S level doubled.         

If the H₂S increases significantly when operating at the design flow rate, it will be necessary to increase the iron concentration, the oxidizer air rate, and the sulphur slurry rate.

The iron circulation can be increased by operating at the same rate with higher iron concentration.

Operating at higher catalyst concentration will increase catalyst losses with the purge stream and catalyst losses due to oxidation of the catalyst chelants. Conversely, if the H₂S concentration decreases significantly while operating at design low rates, savings in operating costs can be realized by operating at lower iron circulation rates by reducing catalyst concentration. The sulphur slurry rate should also be reduced.

D.    LO-CAT CIRCULATION RATE – IRON CONCENTRATION:

As indicated in the preceding discussion, these two variables are interconnected and any combination of concentration & solution circulation rates within equipment design limitations that give the desired iron circulation rate are acceptable. However, with an auto circulation system, it is difficult to vary the Lo-cat solution circulation rate. The design catalyst concentration for this application is 500 ppm iron, which was selected to give the optimum trade-off between electrical costs, chemical costs and capital costs.

Directionally, it is more desirable to maintain or reduce the catalyst concentration as the H₂S flow rate varies. This will have the following beneficial effects:

1.      Reduce catalyst concentrate consumption directly proportional to the reduction in catalyst concentration.

2.      Reduce potassium hydroxide (KOH) consumption almost directly proportional to the reduction in catalyst concentration. Some KOH is lost in the production of potassium thiosulfate (K₂S₃O₂).

3.      A slight reduction in make-up catalyst addition. This should be changed reluctantly and only after review of the weekly catalyst analysis.

The disadvantage of operating at a low iron concentration is lack of iron reservoir, which could lead to complete failure of the catalyst system of an operation upset.

5. OXIDIZER AIR RATE:

The Oxidizer air rate has been set to pr­ovide the oxygen required for the design quantity of H₂S. Running with a highly oxidized catalyst has no adverse effect except for a possible increase in thiosulphate production.

   If the H₂S rate should increase significantly, a higher oxidizer air rate will   be required.

6. LO-CAT SOLUTION TEMPERATURE:

The Lo-Cat solution temperature in 61-V-602 should be kept between 16⁰C and 50⁰C. Excessive thiosulphate production will result if the temperature is allowed to increase beyond 50^OC. The situation can be corre­cted by commissioning the Lo-cat solution cooling 1oop.Lo-cat solution temperatures below 16⁰C are not expected.

3.1.2. COMBlNED EFFECT OF OPERATING VARIABLES:-

The combined effect of the operating variables is best measured by the Redox potential. The following ranges of Redox potential have significance:

The highly oxidized condition represents a "safe" operating condition with more capacity to oxidize H2S than is required. This is not likely to cause any damage to the catalyst or the equipment, but may result in more thiosulphate by product than is necessary. For short periods of time no corrective action need be taken. However, operation at potentials above +50 mv should be avoided by decreasing oxidizer air rate. This can be accomplished by venting some air to the   atmosphere.

Abnormally low Redox potential (less than -250 mv) indicate catalyst deficiency. This can be due to:

a)  Increase in H2S rate concentration and/or

b)     Low iron content in the catalyst

In turn, low iron content can be due to:

                                                              i.      Insufficient catalyst make-up and/or

                                                            ii.      Catalyst loss

And, further, catalyst loss is to:

i.                    Leakage and/or

ii.                  Damage to catalyst       

If the redox potential is abnormally low, immediate action should be taken. By adding large amount of catal­yst the redox potential should come back up to operating range. The process gas should be checked for H₂S load, and if there has been no increase, the 1ow redox potent­ial was most likely due to low iron content. Check reco­rded data to see that catalyst addition rates were at the design levels. If so, low iron content was probably due to catalyst loss. If no sign of leakage is evident, biological activity may have destroyed some of the cata­lyst. If redox potential begins to drop again have the circulating solution checked for bacteria count. Under no circumstances should the redox potential be allowed to drop -300 mv.

3.1.3. SULPHUR SLURRY-The Sulphur slurry concentration should he in accordance with the following table:

Note: When the train is standby and the slurry concentration ii nil then the P-601 to be either stopped or the melter temperature to be reduced less than 65 ^oC to avoid locat degradation.

3.1.4.     MOLTEN SULPHUR:

The molten sulphur temperature existing in the sulphur melter (61-E-603), within the molten sulphur separator (61-V-603) and sulphur surge tank (61-V-604) should be in accordance with the following table.

The molten sulphur feeding the sulphur forming system must be 125 - 135 ⁰C. Check the operation of the sulphur preconditioner if out of this range.

NOTE:  Chances of polysulphide formation is high when the temperature is above 126 ^oC in melter.

3.1.5. CHEMICAL TREATMENT:

1. Biochem:

The pressure, temperature and pH in the locat system operation may be conducive to biological growth. To prevent such growth the locat solution may require additional Biochem addition.

2. Surfactant:

Should non-wetted sulphur froth appear on the liquid / gas interfaces of the Absorber / Oxidizer (61-V-602), a "shot" of surfactant may be added.

3. Defoamer:

Level control problems in 61-V-602 may be due to foa­ming. If foaming is a problem, add 1 lit "shot" of defoamer using the air pressurizing system provided with 60-T-650.

3.1.6.     LOCAT PARAMETERS:

3.2.         EQUIPMENT PARAMETERS:

Equipment operating parameters under normal conditions will be discussed in the following section. The same sequ­ence will be followed as for Section- 2 : Process Description.

3.2.1. ACID GAS FEED DISTRIBUTION:

Acid gas enters each SRU train at temperature of 45 - 50 ⁰C and a pressure ranging between 0.8 - 1.0 Kg/Cm ² (g). The normal flow is 7000 NM³/Hr., but can be as low as 2,800 NM³/Hr. (Based on a 40% turndown for the Gas Sweetening Unit). The temperature and pressure are a function of the operating conditions of the gas sweetening unit and of the acid flow gas rate.

Hydrogen sulphide concentration in the feed varies between 0.3 – 5.2 mole %. Operating parameters for the acid gas feed distribution system are as follows:

3.2.2   HYDROGEN SULFIDE ABSORPTION AND LO-CAT SOLUTION                            REGENERATION:

Lo-cat auto circulation vessel 61-V-602 operates normally at 45 - 50 ⁰C and under a very slight positive pressure. Feed to 61-V-602 consists of oxidizing air, acid gas and hot locat solution from the sulphur melting system.

Operating parameters for the Hydrogen Sulfide Absorption and locat solution regeneration system are as follows:

3.2.3.     LOCAT SOLUTION COOLING:

The locat solution cooling system cools locat solution from 50^oC to 45^oC in order to remove the heat of reaction generated by the process. The operating parameters are as follows:

3.2.4       COMPRESSION OF OXIDIZING AIR:

Air required for oxidizing (regenerating) the Locat solution is supplied to the absorber / oxidizer at 0.9 – 1.1 Kg/Cm ² (g) and 50 ⁰C. It is recommended to maintain the minimum airflow rate to absorber at 1.3 times of acid gas flow. The operating parameters are as follows:

3.2.5   SULPHUR MELTING AND SEPARATION:

Sulphur slurry from 61-V-602 is melted in 61-E-603 and decanted in 61-V-603. Molten sulphur exits 61-E-603 at 126 ⁰C.

Operating parameters for the sulphur melting and separation system is as follows:

3.2.6       sulphur storage and sulphur forming:

Sulphur storage capacity is approximately 7 days at maximum sulphur production rate of one train. Normally all Phase I trains are lined up to one Surge Drum (61/62/63 V 604) and Phase II & III trains to another (64/65/66 V 604). The sulphur forming system is run as and when required basis producing up to 12.20 MT/day of solidified in the form of flakes.

Operating parameters for the sulphur storage and sulphur forming system are as follows:

3.2.7.     CHEMICAL DOSING SYSTEM:

Operating parameters of the chemical dosing system are as follows:

3.2.8.     COMMON FACILITIES:

The common facilities associated with the sulphur recovery unit consist of chemical storage, chemical preparation and utility treatment systems.

Operating parameters for the common facilities are as follows:

3.2.9.     MDEA SUMP AND STORAGE:

Operating parameters for the MDEA Sump and Storage system are as follows:

3.2.10.INCINERATOR:

Operating parameters for the Incinerator system are as follows:

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SECTION:     4

GENERAL   INFORMATION