SWS Operating Manual Rev 02

Essar Refinery Integrated Management System

SOUR WATER STRIPPER UNIT (5100) OPERATING MANUAL

Prepared By: Reviewed By: Approved By

SIC AM HOD

Version No. Revision Date

00 02 05.06.11

Doc. No. Doc. type Page no.

EOL/SRU/SWS/RD/001 Operating Manual Page 1 of 73


INDEXS.NO.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

DESCRIPTIONINTRODUCTION PROCESS DESCRIPTION BATTERY LIMIT CONDITIONS KEY FEATURES OF MAIN EQUIPMENT OPERATING VARIABLE AND PROCESS CONTROL SAFETY INTERLOCKS AND ALARMS ANALYTICAL CONTROL PRECOMMISSIONING PROCEDURE COMMISSIONING PROCEDURE SHUT DOWN PROCEDURE TROUBLE SHOOTING MAINTENANCE DOS AND DONTS SAFETY EMERGENCY SHUT DOWN PROCEDURE UTILITY CONSUMPTION ANNEXURES

PAGE NUMBER3 5 8 9 14 16 18 19 40 43 45 48 50 51 54 58 59


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1. INTRODUCTION1.1 OBJECTIVEThe Sour Water Stripping Unit (5100) processes sour water generated in the following units: Crude Distillation Unit (1000) Vacuum Distillation Unit (1100) Amine Regeneration Unit (1200) Saturated Gas Separation Unit (1300) Visbreaker Unit (2000) Naphtha Hydrotreater Unit (3000) Unsaturated Gas Separation Unit (3500) Diesel Hydrodesulphurization Unit (4000) Sulphur Recovery Unit (5000) The Hydrogen Sulphide (H2S) and Ammonia (NH3) present in the sour water are stripped off and are routed to the Sulphur Recovery Unit (5000). The stripped water is partially routed to the Crude desalters of the Crude Distillation Unit (1000). The remaining stripped water is sent to the Waste Water Treatment Plant (8400).

1.2 SECTIONS OF SWSThe SWS unit consists of three sections. They are as follows: The degassing section. Sour water stripping section. Low pressure condensate collection section.

1.3 FEED SPECIFICATIONThe design of the unit is based on the refinery crude mix of 70% Arabian Light and 30% Arabian Heavy. The Unit receives sour water feed from the above said units. The unit is designed to process 185030 kg/hr of sour water. The feed quantity comes to 169467 kg/hr of sour water if the deferred units are not considered. The feed quantity from the individual units and their constituents are listed below.


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TOTAL SOUR WATER(kg/hr) CDU VDU ARU SGU VBU NHT UGS HDS SRU DCU* DGH* DNH* TOTAL

H2S

NH3

SALTS

HCS

H2

N2

SO2

CO2

29546 67888 5510 216 13624 850 25578 21255 5000 7413 8051 99 185030

41.36 71.57 24.59 1.68 9.42 0.38 28.43 167 8.15 186.1 20.40 559.0 8

0.35 8.37 38.12 48.55 83 5.09 93.0 20.40 296.8 8

4.71 6.67 11.38

0.08 0.08

0.03 0.03

0.08 0.08

0.1 0.10

0.08 0.89 0.97

* Deferred units.

1.4 PRODUCT SPECIFICATIONThe stripped water produced in the unit is required to meet the following specifications: H2S: maximum 10 ppm wt. NH3: maximum 100 ppm wt.

1.5 TURNDOWN AND OVERDESIGN REQUIREMENTSThe unit is capable of operating at 50% of its hydraulic design capacity. It is also capable of operating at 110% of its hydraulic design capacity. The overdesign on the stripper including the overhead system is based on 10% overdesign on the reboiler duty.


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2. PROCESS DESCRIPTIONThe SWS unit consists of three sections. They are as follows: The degassing section. Sour water stripping section. Low pressure condensate collection section.

2.1 DEGASSING SECTIONThe sour water from CDU/VDU/SGU/VBU/NHT and UGS are collected in the Sour water buffer vessel (75V-001) located in the Visbreaker Unit (VBU). From there it is routed to the Sour water collecting vessel (51V-201) at a pressure of 4 kg/cm2g and temperature of 40C. The sour water line from DHDS joins the sour water line from VBU to 51V-201. The sour water flashes from 4 kg/cm2g to 0.2 kg/cm2g on entering the collecting vessel as a result of which, the lighter hydrocarbons present in the sour water get separated and are routed to the H 2S flare header. The pressure in this vessel is floating on the flare pressure. Fuel gas is used for blanketing purpose. Liquid hydrocarbons present in the sour water are skimmed off and are pumped by the Slop oil Pump (51P-201) to the Wet slop tank in PIT.

2.2 SOUR WATER STRIPPING SECTIONThe sour water feed pumps (51P-202A/S) pump the sour water from the collecting vessel (51V-201) to the sour water stripper column (51C-201). The sour water is preheated from 40C to 68-70C against the stripped water from the column bottom in the feed/bottom exchanger (51E-201). The sour water stripper column contains 28 trays. Except tray no.6 (which is a chimney tray) all the trays are valve trays. The sour water stripper consists of a washing section (trays 1to 6) and a stripping section (trays 7 to 28). The sour water flow controller to the column is cascaded with the level controller on 51V-201. The sour water enters the stripper column on the 7 th tray. Two vertical thermosyphon type reboilers (51E-202A/B) are provided for heating the column bottom liquid. The stripped water enters the bottom of the reboilers on the tube side and the vapours generated leave the reboiler at the top. Low pressure Steam (LP steam) is used as the heating medium. The flow of LP steam to the reboilers is controlled by a flow controller which is cascaded with the sour water feed controller. The LP steam flow is controlled on ratio with the feed flow. The condensate generated in the reboilers is separated by traps whose downstream is connected to the LP condensate knock out vessel (51V-301).


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A part of the liquid collected in tray no.6 (chimney tray) is pumped by the circulating reflux water pumps (51P-204A/S) to circulating water air coolers (51EA202A/B), where it is cooled from 98C to 65C before entering in the top of the column to wash the overhead gas. The temperature of the overhead gas is controlled by changing the angle of the Fin fan blades (pitch control). The flow of reflux water is controlled by a flow controller. There is a provision for routing the stripped water from the stripped water cooler (51E-203) downstream to the chimney tray. The stripped water from the column bottom, at a temperature of 118C, is pumped by the stripped water bottom pumps (51P-203A/S) to the feed/bottom exchanger (51E-201) and then to the stripped water air coolers (51EA-201A/B/C/D). The stripped water is cooled to a temperature of around 65C at the outlet of the air coolers. It is then cooled to 40C at the outlet of the stripped water trim cooler (51E203). Sea cooling water is used as the cooling medium in 51E-203. The stripped water is then routed partially to the Desalters of the Crude Distillation Unit (CDU). The rest of the stripped water is routed to the Waste Water Treatment Plant (8400) for further treatment. The bottom level controller of 51C-201 controls the stripped water flow to WWTP. A start-up/recycle line is provided for routing the stripped water from the outlet of 51E-203 to 51V-201. This line is used during internal circulation of the plant during start-up/shutdown and also during low throughput of SWS. The stripper top pressure is maintained at 0.9 kg/cm 2g by a pressure controller which is cascaded with the SWS acid gas flow controllers located in the two trains of the Sulphur Recovery Unit (SRU). There is a second pressure controller which vents the overhead gas to the H2S flare in case of a high pressure build-up due to SWS acid gas cut-off in SRU. The stripper overhead line to SRU is steam jacketed in order to avoid plugging due to ammonium salts deposition. In case of a pressure build-up which could not be controlled by the flare pressure controller, two PSVs (51PSV-019A/S) are provided with a set point of 3.5 kg/cm 2g to protect the column.

2.3 LOW PRESSURE CONDENSATE COLLECTION SECTIONThe Low pressure condensate from the SWS reboilers (51E-202A/B) is routed to the LP condensate flash vessel (51V-301). The vessel also receives low pressure condensate from the ARU reboilers (12E-202A/B/C/D) via the condensate collection vessel (12V-203). It also receives condensate from the LP condensate flash drum (50V-009). The LP condensate produced in DHDS is also routed to this vessel. The vessel is provided with condensate overhead condensers (51EA-301A/B). The


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condensate from 51V-301 is pumped with condensate pumps (51P-301A/S) to the Refinery LP condensate system on level control.


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3. BATTERY LIMIT CONDITIONSS.NO. SERVICE TEMPERATURE (C) DESIGN OPERATING PRESSURE (kg/cm 2g) DESIGN OPERATING

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Sour Water Acid gas to SRU Stripped water to CDU Stripped water to WWTP Fuel Gas Low Pressure Steam Demineralized Water Sea Cooling Water Supply Sea Cooling Water Return Sweet Cooling Water Supply Sweet Cooling water Return Service Water Instrument Air Plant Air Nitrogen

150 245 100 65 65 65 65 65 65 65 65

40 90 40 40 Ambient 190

SWS Operating Manual Rev 02

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