CHAPTER-4 UTILITY SYSTEM DESCRIPTIION The different utility systems provided in Hydrogen Generation Unit for its smooth operation are described in this chapter. They include 1. Service water 2. Cooling water 3. DM water 4. Boiler feed water 5. Plant air 6. Instrument air 7. HP steam 8. MP steam 9. LP steam 10. Reformer fuel 11. Nitrogen 12. Closed blowdown 13. Flare 14. Chemical injection i. Hydrazine ii. Amine iii. TSP 4.1 SERVICE WATER (REFER P & ID : U-10) Service water is received through a 3 header into the unit through hydrocracker unit from Raw Water Treatment Plant. Block valves with a spectacle blind and ¾ drain have been provided at the battery limit in service water header. Local pressure gauge has been provided in service water header. 4.2 COOLING WATER (REFER P & ID : U-6) Cooling water to the unit is supplied from the process-cooling tower. A 18 tap off from the hydrocracker header feeds the unit header. Block valves with spectacle blind and a ¾ drain is provided at the unit battery limit. Pressure (PI-3601), temperature (TI-3601) and flow indicators (FI-3601) are provided in the DCS control panel. Local pressure and local temperature gauges have also been provided on the cooling water supply header. In case of low pressure in the header an alarm sounds in the control room. Cooling water return header 18 is also provided with block valves with spectacle blind and a ¾ drain at the battery limit. Pressure (PI-3602) and temperature (TI-3602) indications are provided on the cooling water return header in the control room. Local pressure and temperature gauges are provided on the cooling water return header. CHAPTER-4 1/10
4.3 DM WATER ( REFER P & ID : P-9 ) DM water is supplied from DM Water Plant. A 8 header feeds the DM water to the hydrocarbon unit. Block valves with a spectacle blind and ¾ drain is provided at the battery limit. Flow indicator (FIC-0902) indicates the total quantity of DM water flow to the unit. Pressure (PI-0909) and temperature (TI-0901) indicators are provided on the DCS control panel. Local pressure and temperature gauges are also provided on the DM water header. A ½ line at the downstream of flow meter is taken for routing DM water for chemical preparation. 4.4 BOILER FEED WATER SYSTEM The entire boiler feed water requirement of all the process units will be met from the deaerator located in Hydrogen Unit and FCC units. In the event of any unit under shut down the other deaerator will cater to the total BFW requirement of all the process units. A 4 line from HP BFW pump discharge charges the HP BFW header. Block valve with spectacle blind and a ¾ drains are provided on the HP BFW header at the unit battery limit. Flow control (FIC-0905) indicates the quantity of HP BFW export to the HP BFW header. A 6 line from MP BFW pump discharge is routed to the MP BFW header. Block valves with spectacle blind and a ¾ drain is provided on the MP BFW header at the unit battery limit. Flow meter (FI-0901) indicates the quantity of MP BFW header. 4.5 PLANT AIR (REFER P & ID : U-10) Plant air header is charged from the utilities section. A 3 line from this header is provided for meeting the plant air requirement of the hydrogen unit. Block valves with spectacle blind and a ¾ bleeders are provided on the plant airline at the battery limit. Local pressure gauge is provided in the plant air header. 4.6 INSTRUMENT AIR (REFER P & ID : U-10) The instrument air header is charged from the air compressor house of the utilities section. A 3 line from the main header is provided for receiving instrument air into the hydrogen unit. Block valves with spectacle blind and ¾ drain is provided on the instrument air header at the battery limit. Local pressure gauge is provided on the instrument header at the battery limit. 4.7 HP STEAM (REFER P & ID : U-1) Hydrogen unit is a net exporter of HP steam during operation. 10 line is laid from the unit to the HP steam header. Block valves with spectacle blind and a ¾ drain are CHAPTER-4 2/10
provided at the unit battery limit. Pressure (PI-3103), temperature (TI-3102) indicators are provided on the HP steam header. Flow meter FI-3102 indicates the quantity of steam export/import from to the unit. The saturated HP steam from steam drum is used for 1. Vaporization/pre heating of feed Naphtha in E-214A/B 2. Vaporization of fuel naphtha in E-220 3. Pre heating of fuel gas in E-221 During start up of the unit, saturated HP steam is also used for heating nitrogen in Hydro-Desulphurisation section (in E-230) and in reformer and shift section (in E-232). The balance saturated HP steam is superheated in the waste heat coil (E-203). Major part of super heated HP steam is consumed for reaction purpose in the reformer. The surplus HP steam after quenching with BFW is exported into the refinery HP steam header. 4.8 MP STEAM (REFER P & ID : U-1) MP steam is consumed for tracing and steams jacketing of reformer fuel lines, for maintaining the necessary superheat of reformer fuel and prevent condensation of naphtha. A 4 line is laid from the MP steam header. Block valves with spectacle blind and a ¾ drain is provided on the MP steam header at battery limit. A flow meter (FI- 3103) is provided with a totaliser on the MP steam line in the unit. 4.9 LP STEAM (REFER P & ID : U-1) LP steam is used in deaerator, preheating the combustion air during winter, for process vents, purging of equipment and lines carrying liquid and hose stations. A 8 line is laid from the refinery LP steam header into the hydrogen unit. Block valves with a spectacle blind and a ¾ drain is provided at the unit battery limit. Pressure (PI- 3105) and temperature (TI-3105) indicators on the LP steam are provided in the control room. Local pressure gauge is also provided on the LP steam line at the battery limit. 4.10 REFORMER FUEL (REFER P & ID: U-4) The reformer furnace fuel consists of 1. PSA purge gas 2. Vaporized Naphtha 3. Refinery fuel gas About 60% of reformer furnace fuel requirement is met from the low pressure PSA purge gas or synthesis gas. Balance heat requirement is met from vaporized Naphtha CHAPTER-4 3/10
and Refinery fuel gas. Reformer burners are of dual gas firing type. Burners can perform on 100% vaporized Naphtha also. Vaporized Naphtha and fuel gas mixture is routed through central pipe to the burner tip and the PSA purge gas through annular space to the burner tip. The fuel gas systems are discussed separately. 4.10.1 PSA PURGE GAS/SYNTHESIS GAS (REFER P & ID:P-10 & P-6) PSA purge gas generated during regeneration of PSA adsorption system is the primary fuel to the Reformer furnace. During regeneration of PSA adsorber the caloric value of PSA purge gas generated is varying. The PSA purge gas is routed to the PSA purge gas vessel V-320, where it is uniformity mixed in the vessel through the inlet pipe to minimize variations in flow and composition. The PSA purge gas from the vessel is routed to the reformer through a 30 line. The PSA off gas is routed to the burners through branch lines from the main header through 16 purge gas headers on both sides of the reformer twin cells. The purge gas vessel pressure is maintained at 0.25 KG/CM 2 G by PIC-1007, which releases excess pressure to flare or high point vent. A 6 /16 synthesis gas header from vessel V-203 also meets the PSA purge gas header at the downstream of FIC-1005 to supply the synthesis gas as fuel during shutdown of the PSA unit. Synthesis gas flow to the reformer is controlled by FIC-1007. Double block (UV- 0601, PV-0602) and bleed valves (UV-0603) are provided on the PSA purge gas supply line to the reformer which will cut off PSA purge gas in the event of reformer trip activated by interlocks and shut down system. In case of low pressure in the PSA purge gas, PIC-0602 sounds an alarm in the control room and in case of low low pressure, cuts off the PSA off gas to the burners. The PSA off gas is distributed to the 216 burners through 16 branch lines on both sides of the twin cell reformer. From the 16 branch line PSA off gas is supplied to the burners in all 6 rows through 3 /2 lines. Pressure gauges are provided on the branch lines to the burners in each row to check the PSA off gas pressure locally. 4.10.2 FUEL GAS AND VAPORIZED NAPHTHA FUEL (REFER P & ID : U-3) The balance fuel requirement of the reformer after burning PSA off gas shall be met from fuel gas and vaporized naphtha. Over and above the PSA off gas and available fuel, the heat requirement of the reformer furnace shall be met from vaporized naphtha. 4.10.3 FUEL GAS (REFER P & ID : U-3) Refinery fuel gas pressure is maintained by AVU. A 6 line from the header supplies fuel gas to hydrogen unit. Block valves with spectacle blind and a ¾ drain is provided at the unit battery limit. A pressure (PI-3304) indicator is provided on the fuel gas header to indicate the fuel gas supply pressure to the unit. A knock out pot is provided to separate any liquid/condensate carry over along with the fuel gas. Pressure controller (PIC-3303) maintains the fuel gas pressure at the outlet of fuel CHAPTER-4 4/10
gas knock out pot. The flow of fuel gas to the reformer is controlled by FIC-3301. The set point of FIC-3301 is calculated after deducting the heat duty of PSA off gas from total heat input HIC-3302 and the calorific value of fuel gas given by HIC- 3301. The maximum limit of set point to FIC-3301 corresponds to 3000 KG/HR fuel gas. The fuel gas is preheated to 200 C in E-221 against saturated HP steam. The pressure (PI-3301) and temperature (TI-3301) indications at the outlet of fuel gas pre heater E-221 are indicated in the control room. In case of pressure and temperature at the outlet of E-221 being high or low, corresponding alarm sounds in the control room. In the event of trip of reformer or low pressure in vaporized naphtha fuel gas mixture shut down circuit activates the control valve FV-3301 to close and isolates the fuel gas. 4.10.4 NAPHTHA FUEL (REFER P & ID : U-3) The liquid naphtha is received in the naphtha feed surge drum V-205 from off sites under level control. The feed surge drum pressure is maintained by nitrogen at 3.0 KG/CM 2 G. A 2 line from the feed naphtha line with isolation with block valves and a spectacle blind routes the fuel naphtha to the evaporator E-220. The fuel naphtha is vaporized and heated to 200 C in E-220 fuel naphtha evaporator against saturated HP steam. The vapor naphtha is routed through a fuel naphtha knock vessel before routing to the reformer along with the hot fuel gas. The pressure controller (PIC-3305) at fuel naphtha knock out pot maintains the pressure by controlling the liquid naphtha flow to the evaporator. The flow of liquid naphtha to evaporator E-220 is indicated by FI-3304. In the event of pressure, temperature fluctuation at fuel naphtha knock out drum, it sounds corresponding low/high alarm in the control room. The outlet line from the fuel naphtha and fuel gas vaporizer are MP steam traced up to the first floor of the reformer and from there they are jacketed with MP steam. The set point in the vaporized naphtha flow controller FIC-3302 is calculated after subtracting the heat duty of PSA off gas to reformer and fuel gas to reformer from the reformer heat duty HIC-3302. In the event of low or no vaporized naphtha consumption in the reformer, the vaporized naphtha is cooled in fuel naphtha cooler E-222 and recycled back to feed surge drum V-205. The recycle flow of vapor naphtha is controlled by FIC-3303. Fuel naphtha circulation shall be continued in order to maintain the stand by fuel to the reformer furnace. 4.11 NITROGEN (REFER P & ID : U-7) Nitrogen is used as inert gas in hydrogen unit for purging of lines and equipment and during start up. Nitrogen is supplied from the Nitrogen Plant through a 4 line. Block valves with spectacle blind and a ¾ drain is provided on the nitrogen line at the battery limit. A flow meter (FI-3701) with totaliser is provided on the header to indicate the nitrogen consumption in the unit control room. CHAPTER-4 5/10
Nitrogen connections are provided from the 4 nitrogen header at the following. To Naphtha feed surge drum V-205 for continuous purging through 1½ line. To DMDS vessel V-211 and DMDS barrel through ¾ line. To hose station near V-214 through 1 line. To compressor KA-203-A through 1 line. To compressor KA-203-B through 1 line. To hose station near KA-203A/B through 1 line. To compressor KA-207 through 1 line. To hose station near RB-201 and RB-202A through 1 line. To hose station near RB-204 and RB-205 through 1 line. To fuel naphtha recycle pot V-224 through 1½ line. To start up knock out pot for HDS V-206 through 1½ line. To suction of start up nitrogen compressor for shift section KA-205 through 1½ line. Near compressor KA-205 through 1 line. To hose station near pre-reformer through 1 line. To pre-reformer feed pre-heater E-202 inlet through 3 for purging. To PSA vessels through 2 line for purging of PSA vessels. 4.12 CLOSED BLOW DOWN SYSTEM (REFER P & ID : U-9) An underground closed blow down system has been provided in the hydrogen system for draining light liquid hydrocarbons from different equipment and lines. The drains of the following equipment and lines are connected to the under ground 6 CBD header. P-208 fuel naphtha recycle pump casing. P-201A/B naphtha feed pump casing. V-205 feed naphtha surge drum outlet line. Suction lines of naphtha feed pumps P-201A/B. Feed naphtha supply line from off sites at battery limit. Feed naphtha pumps discharge line. Outlet of DMDS vessel V-211. Shell side of feed naphtha evaporator E-214A/B. Shell side of feed naphtha super heater E-215. Drain of naphtha circulation line from start up knock out pot for HDS, V- 206 to V-205. Drain from boot of vessel V-205. Outlet of fuel naphtha recycle pot V-224. Outlet of fuel naphtha evaporator E-220. CHAPTER-4 6/10
All the liquid drains from the above sources are collected in an under ground CBD header and is sent to the underground CBD vessel V-239. The liquid level in CBD vessel is indicated (LI-3901) in the control room. In case the level increases highlevel alarm LAH-3902 sounds in the control room and the CBD pump P-209 starts and the liquid is pumped out to one of the stop tanks. The pump stops when the liquid level falls to low level and an alarm LAL-3902 sounds in the control room. The CBD vessel is provided with fuel gas purge. Utility connection is also provided with fuel gas purge. Utility connection is also provided for flushing purpose. 4.13 FLARE (REFER P & ID : U-8) The Hydrogen unit is provided with a 30 flare header to collect all the inflammable gases from different sources through separate lines. All the gases are collected into the flare header and sent to the flare knock out drum V- 238 before routing to the outlet, OHCU flare knock out drum and from there to the 54 main flare for dispersing them to the main flare. Any liquid/condensate entering the drum is separated in the knock out drum. The following are the various sources of gases into the flare header. SAFETY VALVE DISCHARGE TAG NO. LOCATION PSV-0155 Naphtha feed surge drum V-205 PSV-0253 Naphtha feed evaporator E-214B outlet line. PSV-0254 Naphtha feed evaporator E-214A outlet line. PSV-0351 HDS start up compressor KA-204 outlet line. PSV-0353 Hydrogenerator reactor RB-201 PSV-0362 Sulfur absorber RB-202A PSV-0363 Sulfur absorber RB-202B PSV-0359/0360 HDS start up knock out pot V-206 outlet line. PSV-0757/0758/0759 Shell side outlet of waste heat boiler E-206 PSV-0852 MT shift reactor RB-204 PSV-0856 LT shift reactor RB-205 PSV-0861 1 st process condensate separator V-202 PSE-0963 DM water pre heater E-211 shell side. PSV-1053/1054 Synthesis gas inlet to PSA unit. PSV-1056/1057 PSA off gas surge drum V-320 outlet. PSV-1060 Hydrogen rich gas from catalytic reformer knock out pot PSV-1061/1062 Synthesis gas header to PSA off gas fuel line. PSV-3354 Fuel gas preheat coil E-221. PSV-3357 Fuel gas knock out pot V-223. PSV-3358 Fuel naphtha knock out drum V-222. PSV-3370 Fuel naphtha recycle pot V-224. PSV-3451 Hydrogen emergency buffer vessel V-232. PSV-3453 Recycle hydrogen compressor KA-203A discharge line. PSV-3454 Recycle hydrogen compressor KA-203B discharge line. CHAPTER-4 7/10
PSV-3455/3456 Emergency hydrogen line to E-202, pre-reformer feed preheat coil. PSV-3464/3465 Hydrogen compressor KA-206 discharge line. PSV-3469/3470/3471/3472 Hydrogen compressors suction header. PSV-3473/3474 Hydrogen recycle compressor for reformer and shift KA-207 discharge line. PSV-2103 to 3003 PSA absorber vessel V-320 to V-330 Excess gas released from the system through pressure control valves for maintaining the system pressure as well routing to the flare. The following are the list of control valves releasing gases to flare. PIC-0102 Naphtha feed surge drum V-205 PIC-0304 Start up knock out pot for HDS V-206 PIC-1005 Hydrogen product header from PSA vessels PIC-1008/PIC-1001 Synthesis gas header to PSA inlet PIC-1007 PSA off gas to reformer fuel ex. V-320 System depressurization/purging will be done during startup/shut down/equipment handing over through the above control valves. In some cases the depressurization is done through PSV bye- pass lines. There is provision to purge the 30 flare header continuously with fuel gas at both the extreme ends in the unit. For purging there is also provision for LP steam/n2 purging of flare header at both the extreme ends. A high level alarm LAH-3601 sounds in the control in case of high level in the flare knock out drum V-238. 4.14 CHEMICAL INJECTION ( REFER P & ID : U-2) The chemical injection system in hydrogen unit consists of chemicals required for preparation of boiler feed water and for maintaining the residual phosphate level in steam drum water. The chemicals used in preparation of boiler feed water are to maintain ph and oxygen content. The chemicals used for BFW treatment are 1) Amine/Moropholine to maintain the ph of the boiler feed water in deaerator. 2) Hydrazine to remove the residual oxygen in the deaerator. 3)... Tri-Sodium Phosphate to maintain the residual phosphate level in boiler feed water with in a range to avoid scaling on the surface of the steam generation system. 4.14.1 AMINE/MOROPHOLINE INJECTION Amine/Moropholine solution is received in drums as 100% solution. It is unloaded from the drum to the Amine/Moropholine dozing vessel through a hand operated loading pump. Amine/Moropholine solution is prepared by adding DM water through 1½ in line from DM water supply line into Amine/Moropholine dozing vessel V-209. Dosing vessel is provided with a level gauge for verifying the level CHAPTER-4 8/10
locally and a vent line. Dosing vessel is also provided with a mixer for uniform mixing of the solution. About 1 to 2 % of Amine/Moropholine solution in DM water is prepared. The total capacity of the vessel is 950 Liters. The capacity of pumps can be adjusted from 0 to 100%. The rated capacity of the pump is 20 litre/hr. The Amine/Moropholine solution is pumped by the reciprocating pumps P- 205A/B into the deaerator through 1½ line. In the pumps discharge line PSV-3253 and PSV-3254 are provided to protect the pumps against high discharge pressure. Based on the continuous production of M 3 /HR of boiler feed water, the consumption of Amine/Moropholine shall be 6300 KG/HR as 100% solution. The dosing rate work out to be approximately 4.4 PPM as 100% Amine/Moropholine. The amount of Amine/Moropholine required to prepare the given concentration of solution can be calculated by the following equations H= (WXR)/(A-R) H= Quantity of Amine/Moropholine to be diluted with DM water. W= Quantity of DM water R= Concentration of Amine/Moropholine required. A= Concentration of available Amine/Moropholine. 4.14.2 HYDRAZINE INJECTION Hydrazine injection solution is available in 200 litre drums as solution of 50% strength. It is also available in 5/10 litre containers. Hydrazine is unloaded from the drums/containers using hand operated unloading pump into hydrazine solution vessel V-210. It is diluted with DM water through a 1½ line tapped off from DM water supply line. The amount of DM water required for dilution of hydrazine hydrate depends on the concentration of hydrazine and the concentration of the hydrazine solution to be prepared for injection into deaerator. Generally a 1 to 2% concentration of hydrazine is prepared in DM water. The hydrazine solution vessel is provided with a gauge glass for verifying the level locally and also an atmospheric vent. An agitator is provided for uniform mixing of the solution during preparation. Hydrazine dosing pumps P-206A/B takes suction from vessel V-210 and discharges into deaerator V-204 through a 1½ in line. The capacity of the hydrazine solution vessel in 950 litre. The rated capacity of the hydrazine dosing pump is 10 litre/hr. The dosing rate can be varied from 0 to 100% of the rated capacity. Based on the continuous production of 180 M 3 /HR of boiler feed water, the consumption of hydrazine as N2H4 shall be 180 KG/Year. The dosing rate of hydrazine works out to be approximately 0.125 PPM as N2H4. Safety valves PSV- 3255 and PSV-3256 are provided in the discharge lines of the pumps for protecting the pumps against high discharge pressure. The amount of hydrazine required to prepare the given concentration of hydrazine solution can be calculated by the following equation. H= (WXR)/(A-R) CHAPTER-4 9/10
H= Quantity of Hydrazine to be diluted with DM water. W= Quantity of DM water R= Concentration of Hydrazine required. A= Concentration of available Hydrazine 4.14.3 PHOSPHATE INJECTION Trisodium phosphate is available in solid powder from in 50 KGS. Bags. TSP dosing varies as per quantity of water in steam drum and the residual phosphate content as PO4 and alkalinity. A solution of 1 to 2% of PO4 strength in DM water is prepared in vessel V-208. The vessel is provided with an agitator for uniform mixing of the solution during preparation. The DM water is supplied through 1½ tap off line from DM water supply line to the vessel V-208. A gauge glass is provided in the vessel for verifying the level locally. The phosphate dosing pumps P-204A/B takes the suction from vessel V-208 and discharge into steam drum V-201. Safety valves PSV-3251 and PSV-3252 are provided in the discharge lines of pumps to protect against high discharge pressure. The rated capacity of phosphate dosing pumps P-204A/B is 10 litre/hr. The phosphate-dosing rate can be varied from 0 to 100% of the rated capacity. Based on the continuous production of 85 MT/HR of HP steam the consumption of phosphate, as PO4 would be 240 KG/HR. The dosing rate of phosphate as PO4 works out to be approximately 0.19 PPM. CHAPTER-4 10/10