Process Description
Purpose
The purpose of the Catalytic Reformer Unit is to convert paraffins and naphthenes present in the feed naphtha to aromatic compounds to meet anti-knock specifications when blended into gasoline.
Importance
Catalytic Reformer units are highly important for refineries to produce motor gasoline products with good anti-knock properties that meet local regulations for the sale of gasoline. Therefore, the loss of or sub-optimal operation of a Catalytic Reformer unit can result in a large loss of revenue to an operating company.
Major Equipment
The Catalytic Reformer process consists of two main sections: the Reactor Section and the Stabilizer Section.
The Reactor Section consists of:
- Feed Surge Drum, D-201
- Reactor Feed Pumps, P-201A/B
- Reactor Feed/Effluent Heat Exchangers, E-201 & E-202
- Reactor Feed Heater & Reactor Reheaters, F-201
- Catalytic Reformer Reactor, R-201
- Reactor Effluent Air Cooler, E-203
- Reactor Effluent Separator, D-202
- Recycle Compressor, K-201
The Stabilizer Section consists of:
- Stabilizer Feed/Bottoms Heat Exchanger, E-204
- Stabilizer Feed Preheater, E-205
- Stabilizer Column, T-202
- Overhead Condenser, E-208
- Stabilizer Reflux Drum, D-204
- Stabilizer Reflux Pumps, P-202A/B
- Stabilizer Reboiler, E-206
- Product Cooler, E-207
Process Overview: Reactor Section
Hydrotreated naphtha, with low sulfur and nitrogen content, is received from battery limit and fed to the Feed Surge Drum, D-201, and pumped from D-201 by Reactor Feed Pumps, P-201A/B, to Reactor Feed/Effluent Heat Exchanger No. 1, E-201. The design feed flow is 20.0 MBPD of hydrotreated naphtha. Recycle gas from Recycle Compressor, K-201, is combined with the naphtha feed prior to entering E-201. The concentration of hydrogen in the recycle gas is 84.4 volume % and the design flow is 4.684 MMSCF/H.
The feed/recycle gas mixture is preheated in E-201 from 149 DEG F to 437 DEG F using warm reactor effluent from the Stabilizer Feed Preheater, E-205, and Reboiler, E-206. The feed naphtha in the mixture is completely vaporized in E-201. The feed mixture from E-201 is further heated to 775 DEG F in Reactor Feed/Effluent Heat Exchanger No. 2, E-202, using hot effluent from Catalytic Reforming Reactor, R-201. The preheated mixture is sent to the Reactor Feed Heater/Reheater, F-201.
F-201 is a gas-fired process heater with three individual radiant sections, each with its own set of burners, which share a common stack. The first radiant section serves to preheat the feed mixture from E-202 to the design outlet conditions of 995 DEG F and 405 PSIG. The outlet from the feed heating radiant section is sent to the first bed of the Catalytic Reforming Reactor, R-201. The other two radiant sections of F-201 reheat the outlet streams from the 1st and 2nd beds of R-201 since the temperature decrease across the beds of R-201.
Process Overview: Reactor Beds
Catalytic Reforming Reactor, R-201 consists of three fixed-bed reactors employing conventional naphtha reforming catalysts. The solid particles of the three reactor beds are porous which increases the available surface area for the feed/hydrogen mixture to contact the active metal catalysts within the particles. The reforming reaction takes place completely in the gas phase and results in the conversion of paraffinic and naphthenic hydrocarbons in the feed to their aromatic counterparts. As a consequence of reforming the carbon structure of the feed hydrocarbons into unsaturated ringed aromatics, hydrogen is produced by the reaction. A large amount of catalyst and high temperature are required because the reaction rate is very low. The reforming reaction also absorbs heat so that the temperature of the stream decreases as more reforming takes place. In order to keep the reaction rates sufficiently high, the stream must be reheated twice in the reheating sections of Reactor Feed Heater/Reheater, F-201. After each reheat of the reacting stream, the stream is introduced into the next fixed-bed section.
The feed temperature to each of the three catalyst beds of R-201 is 995 DEG F. The maximum reforming of feed takes place in the first reactor bed and its design outlet temperature is 816 DEG F. Less conversion takes place in the 2nd and 3rd reactor beds and their design outlet temperatures are 896 DEG F and 943 DEG F., respectively.
In addition to the reforming reactions, there are other unwanted reactions occurring to lesser extents in catalyst beds of R-201 due the high temperatures. These are coking (carburization) of the hydrocarbons and hydrocracking (cleaving larger hydrocarbons into smaller ones).
Coking results in a slow laydown of solid carbon on the catalyst and blocks the active sites on the catalyst particles. This results in a decreased conversion of feed to aromatics over time. To minimize the rate of coke formation, the partial pressure of hydrogen in the combined reactor feed is kept very high by recycling produced make gas which is rich in hydrogen.
Hydrocracking is unavoidable owing to the nature of the catalyst materials and the high temperature of the reactor beds. The rate of hydrocracking is minimized by keeping the reactor temperatures as low as possible while still maintaining good conversion to aromatics. The hydrocracking reaction gives off heat and its effect on the outlet temperature is more dominant in the last reactor since the heat-absorbing aromatics conversion reaction (reforming) is less in each subsequent reactor bed. The hydrocracking reaction also causes lighter hydrocarbons (methane, ethane, propane, butane and pentane; C1 to C5) to be produced from the naphtha feed which primarily consists of hexane and heavier (C6 through C11) hydrocarbons. These light hydrocarbons are generally not suitable as gasoline components, so they need to be separated from the product reformate in the downstream Stabilizer section.
The outlet stream from the 3rd reactor bed of R-201 is sent to Reactor Feed/Effluent Heat Exchanger No. 2, E-202 to preheat the mixed reactor feed. The outlet of R-201 operates at 379 PSIG.
Process Overview: Reactor Effluent Cooling
The effluent from the bottom of Catalytic Reforming Reactor, R-201 at 943 DEG F is sent to Reactor Feed/Effluent Heat Exchanger No. 2, E-202, to preheat the feed from Reactor Feed/Effluent Heat Exchanger No. 1, E-201. The outlet of the reactor effluent side of E-202 at design is 525 DEG F. After E-202, the reactor effluent is sent to Stabilizer section to provide heat to preheat the Stabilizer Column, T-202, feed in Stabilizer Feed Preheater, E-205, and to reboil the Stabilizer column through Stabilizer Reboiler, E-206.
The reactor effluent streams from the Stabilizer section are combined and sent to E-201. The temperature of the reactor outlet stream at the inlet of E-201 is 542 DEG F. The reactor outlet stream leaves E-201 at 228 DEG F and is sent to Reactor Effluent Air Cooler, E-203. A large portion of the hydrocarbons in the reactor effluent condenses in E-201.
E-203 cools and condenses the remainder of the reactor effluent. The normal outlet temperature of E-203 is 120 DEG F. Most of the hydrogen remains in the vapor phase at the outlet of E-203 and is separated from the condensed unstabilized reformate in Reactor Effluent Separator, D-202.
D-202 normally operates at 375 PSIG. The separated gas from D-202 is sent to the Recycle Compressor, K-201, for compression so it can be recycled back to reactor to inhibit coke formation. A portion of the hydrogen-rich compressed gas (termed “make gas”) is taken off to battery limits for use elsewhere in the refinery’s hydrogen system. The normal gas flow to K-201 is 5.800 MMSCF/H and has a hydrogen concentration of 84.4 volume %.
The unstabilized reformate liquid from D-202 is sent to the Stabilizer Feed Preheater, E-205. Its design flow rate is 18.9 MBPD.
Process Overview: Recycle Compressor
The Recycle Compressor, K-201, is a centrifugal type that is used to compress hydrogen-rich gas from Reactor Effluent Separator, D-202. K-201 discharges most of its flow to Reactor Feed/Effluent Heat Exchanger, E-201. A portion of the compressed gas from K-201 is “make gas” and is sent to the hydrogen system at battery limit. The hydrogen concentration of the recycle gas is 84.4 volume %.
The total flow of gas through K-201 is 5.800 MMSCF/H with 4.684 MMSCF/H recycled to E-201 and 1.116 MMSCF/H taken off as make gas. The discharge pressure of K-201 is normally 429 PSIG.
K-201 is driven by Recycle Compressor Turbine, KT-201, which uses high pressure steam from battery limit as the motive fluid. KT-201 exhausts to the medium pressure steam header at battery limit. K-201/KT-201 normally operate at 5,478 RPM.
Process Overview: Stabilizer Section
Condensed, unstabilized reformate collected in Reactor Effluent Separator, D-202, contains a fairly significant fraction of dissolved hydrogen and light gases such as methane and ethane owing to the elevated pressure of the Reactor Section. It also contains lighter hydrocarbons such as propane, butane and pentane produced by hydrocracking in the reforming reactor beds. As such, the reformate cannot be sent directly to storage for use as a gasoline blending stock. To remove these light gases and lighter hydrocarbons (i.e. to stabilize the treated product) the liquid is sent to the Stabilizer Column, T-202, where it undergoes distillation to separate out the lighter gas components as a product overhead gas and a lighter hydrocarbon as a light top product. The stabilized reformate product is sent off to storage.
Process Overview: Stabilizer Column Feed
The cool, unstabilized reformat from Reactor Effluent Separator, D-202, is heated from 120 DEG F to 339 DEG F in Stabilizer Feed/Bottoms Heat Exchanger, E-204, using hot stabilized reformate from the bottom of the Stabilizer Column T-202/Reboiler E-206. The flow rate of unstabilized reformate from D-202 is 18.9 MBPD. The feed to Stabilizer Column, T-202, is further heated to 370 DEG F in Stabilizer Feed Preheater, E-205, using warm reactor effluent from Feed/Effluent Exchanger No. 2, E-202.
Heated, unstabilized reformate from E-205 enters T-202 onto tray 15. T-202 operates at 155 PSIG which is much lower than the pressure in D-202. Because of the lower pressure and high temperature, the feed reformate flashes into a vapor fraction and a liquid fraction as it enters T-202. The vapor fraction mainly contains hydrogen, methane, ethane and lighter hydrocarbons that were dissolved in the reformate leaving D-202. The vapor fraction flows up through the top section of T-202 where a portion of recoverable lighter hydrocarbons will be washed down T-202 by reflux. The liquid fraction of the feed entering T-202 will fall through the bottom section of T-202 where vapor generated by Stabilizer Reboiler, E-206, will strip any unflashed hydrogen and methane and will vaporize lighter hydrocarbons that are undesirable as a gasoline blending stock.
Process Overview: Stabilizer Column Bottoms
Reformate leaving the bottom-most tray of Stabilizer Column, T-202, is routed into the Stabilizer Reboiler, E-206, which is a kettle-type reboiler. Warm reactor effluent from Feed/Effluent Exchanger No. 2, E-202, is used to vaporize lighter components reaching the bottom of T-202. Unvaporized, stabilized reformate from the boiling side of E-206 spills over an internal weir and is collected in a sump and taken off to as product to Stabilizer Feed/Bottoms Heat Exchanger, E-204. The vapor generated in E-206 is returned to the base of T-202 and continues up through the trays in the column.
The hot product leaves the sump of E-206 at 437 DEG F and is cooled to 170 DEG F in E-204 and continues through Product Cooler, E-207, and sent to storage. E-207 uses cooling water as its cooling fluid. The product is cooled down to 94 DEG F in E-207.
Process Overview: Stabilizer Column Overhead
Vapor leaves the top of Stabilizer Column, T-202, at 225 DEG F and flows through Overhead Condenser, E-208, which is cooled using cooling water. The process stream leaves E-208 at 100 DEG F. Most of the light gases stripped from the feed remain as vapor leaving E-208 and are separated from the liquid in Stabilizer Reflux Drum, D-204. A small portion of the gases still dissolve in the overhead liquid, but after they are refluxed to T-202 they will recycle back up the top of T-202 and through E-208 until they are completely removed in D-204.
D-204 separates the vapor, hydrocarbon liquid and liquid water phases leaving E-208. The vapor is taken off to the fuel gas system at battery limit. The design rate of light gas is 16.9 MSCFH. D-204 normally operates at 150 PSIG. This assures hexane and heavier hydrocarbons will be minimized in the light liquid product produced from D-204.
Part of the hydrocarbon liquid collected in D-204, which mainly consists of propane, butane and pentane, is refluxed back to T-202. Stabilizer Reflux Pumps, P-202A/B, are used to pump the reflux back up to the top of T-202. The balance of the produced light liquid product is taken off to storage. The design flow rate of reflux is 9.00 MBPD. The flow rate of light liquid to storage is 2.83 MBPD.
Normally, the amount of water reaching D-204 from the reactor section is very small. This water is collected in the boot of D-204 and taken off to the sour water treating unit.
Instrumentation
Basic Controls: Feed System
LIC-201 controls the level of feed distillate in the Feed Surge Drum, D-201, by adjusting the opening of the feed supply valve LV-201.
PIC-201 controls the pressure of the nitrogen blanket of D-201 by adjusting the nitrogen supply valve PV-201A or the vent to flare valve PV-201B via a split-range control. When the output of PIC-201 is 50% both valves are closed. When the output moves to 100%, PV-201A fully opens and PV-201B stays closed. When the output moves to 0%, PV-201A stays closed and PV-201B fully opens.
HS-201A/B are switches that control the motors of Reactor Feed Pumps, P-201A/B, respectively. If a motor trips, the respective switch will move to the STOP state.
FIC-201 controls the flow of feed from P-201A/B to Reactor Feed/Effluent Heat Exchanger No. 1, E-201, via FV-201 on the discharge line from the pumps. It is assumed a local minimum flow controller protects the pumps against damage from dead-heading the pumps by closure of FV-201.
TI-201 indicates the temperature of the feed drawn from D-201.
AI-201 indicates the Research Octane Number (RON) of the feed.
Basic Controls: Feed Heating
HIC-203 is used to adjust the opening of the hydrogen supply valve HV-203. This line is used to pressure up the reactor loop with hydrogen at startup. HV-203 is normally closed.
PI-203 indicates the pressure of the supply hydrogen.
FI-203 indicates the hydrogen flow through HV-203 to Reactor Feed/Effluent Heat Exchanger No. 1, E-201.
HIC-204 is used to adjust the nitrogen supply valve HV-204. This is normally used during startup and shutdown to sweep hydrogen and oxygen out of the Reactor Section.
PI-204 indicates the pressure of the supply nitrogen.
FI-204 indicates the nitrogen flow through HV-204 to Reactor Feed/Effluent Heat Exchanger No. 2, E-201. PI-206 indicates the pressure of the mixed feed to E-201.
PAH-206 indicates the same and is an independent sensor for the protective system of the Reactor Feed Heater F-201.
TI-206 indicates the temperature of the mixed feed to E-201.
TI-207 indicates the outlet temperature of the mixed feed from E-201.
TI-208 indicates the outlet temperature of the mixed feed from Reactor Feed/Effluent Exchanger No. 2, E-202.
TI-219 indicates the outlet temperature of the reactor effluent leaving E-202.
HIC-218 is used to bypass some hot reactor effluent around E-202 with HV-218. This bypass is normally 70% open and can be adjusted to provide more or less heat to the Stabilizer Feed Preheater, E-205, and Stabilizer Reboiler, E-206.
TI-220 indicates the mixed temperature of the reactor effluent downstream of leaving E-202 and HV-218.
TI-223 indicates the mixed temperature of the reactor effluent returning from the Stabilizer heat exchangers E-205 and E-206.
TI-224 indicates the outlet temperature of the reactor effluent leaving E-201.
Basic Controls: F-201
TIC-210 controls the combined outlet temperature of Reactor Feed Heater & Reactor Reheaters, F-201, “Feed Heater” coil by adjusting the setpoint of the fuel gas flow controller FIC-210. The setpoint of TIC-210 tracks its PV when in MANUAL mode. The protective system for F-201 will lock TIC-210 in MANUAL mode if the trip is active.
FIC-210 controls the fuel gas flow to F-201’s “Feed Heater” coil via FV-210. It is normally in CASCADE mode and receives its setpoint from TIC-210. When it is in AUTOMATIC or MANUAL mode, it will initialize the output of TIC-210 to maintain bumpless control when placed into CASCADE mode. When in MANUAL mode, the setpoint of FIC-210 will track its PV. The protective system for F-201 will lock FIC-210 in MANUAL mode with an output of 0% if the trip is active.
TIC-213/FIC-213 and TIC-216/FIC-216 are functionally configured the same as TIC-210/FIC-210. These control the outlet temperatures of the Reheater No. 1 and Reheater No. 2 coils of F-201, respectively.
Basic Controls: Catalytic Reforming Reactor
TAH-210 is an independent sensor of the outlet temperature of the “Feed Heater” coil of Reactor Feed Heater & Reheaters, F-201, for the protective system of F-201.
PI-210 indicates the pressure of the feed to Catalytic Reforming Reactor, R-201. PAH-210 indicates the same and is an independent sensor for the protective system of the F-201.
TI-211A/B/C indicate the top bed temperatures of R-201. They indicate at the same bed depth but vary radially by 120 degrees. TAH-211A/B/C indicate the same and are independent sensors for the protective system of F-201.
TI-212 indicates the outlet temperature from the top bed of R-201.
PDI-211 indicates the pressure drop across the top bed of R-201.
The middle and bottom beds of R-201 are instrumented identically to the top bed.
PI-218 indicates the outlet pressure from the bottom bed of R-201.
Basic Controls: Cooling and Separation
HS-210A/B are switches that control the motors of the fans of Reactor Effluent Air Cooler, E-203. If a motor trips, the respective switch will move to the STOP state.
TIC-228 controls the outlet temperature from E-203 by adjusting the louvers at the top of the cells of E-203. The louvers affect the air flow through each cell. Normally both fans are in service.
LIC-225 controls the level of unstabilized reformate in Reactor Effluent Separator, D-202, by adjusting the setpoint of the unstabilized reformate flow controller FIC-225. The setpoint of LIC-225 tracks its PV when in MANUAL mode.
LAH-225 is an independent sensor of the level of liquid in D-202 and is used to protect the Recycle Compressor, K-201, from damage in case of high level.
FIC-225 controls the flow of unstabilized reformate to Stabilizer Feed/Bottoms Heat Exchanger, E-205, via FV-225. It is normally in CASCADE mode. When it is in CASCADE mode it receives its setpoint from LIC-225. When it is in AUTOMATIC or MANUAL mode, it will initialize the output of LIC-225 to maintain bumpless control when placed into CASCADE mode. When in MANUAL mode, the setpoint of FIC-225 will track its PV.
TI-225 indicates the temperature of the unstabilized reformate leaving D-202.
PIC-225A controls the pressure of D-202 by adjusting the opening of control valve PV-225A.
PIC-225B indicates the same PV as PIC-225A and controls the pressure of D-202 in the event the Recycle Compressor, K-201, is not operating. PIC-225B adjusts the position of control valve PV-225B which vents gas from D-202 directly to flare. The setpoint of PIC-225B is normally 75 PSIG higher than PIC-225A. PIC-225B can be used to manually depressure the Reactor Section in case of an emergency. It is also used to vent the Reactor Section as needed during startup and shutdown.
Basic Controls: Recycle Compressor
TI-226 indicates the temperature of the gas from Reactor Effluent Separator, D-202, to Recycle Compressor, K-201.
FIC-226 controls the flow of gas through K-201 as measured at its suction by adjusting the setpoint of SIC-227. When in MANUAL mode, the setpoint of FIC-226 will track its PV.
PI-227 indicates K-201’s discharge pressure.
TI-227 indicates K-201’s discharge temperature. TAH-227 indicates the same and is an independent sensor for the protective system of the K-201.
AI-227 indicates the concentration of hydrogen in the recycle gas leaving K-201 in units of volume %.
HIC-227 is a hand controller that is used to adjust the opening of the gas valve HV-227. HV-227 should normally be 100% open when the compressor is operating.
FI-227 indicates the flow of recycle gas through HV-227 to Reactor Feed/Effluent Heat Exchanger No. 1, E-201. Its process value is sent to the low-flow trip instrument FAL-227 which is used for the Feed Heater & Reactor Reheaters, F-201, interlock I-210.
FI-222 indicates the make gas flow from the outlet line of Recycle Compressor, K-201, to the hydrogen system at battery limit via control valve PV-225A.
SIC-227 controls the shaft speed of K-201/KT-201 via SV-227 which is the admission steam valve on Recycle Compressor Turbine, KT-201. SIC-227 is normally in CASCADE mode. When it is in CASCADE mode it receives its setpoint from FIC-226 which controls the flow of gas through Recycle Gas Compressor, K-201. When SIC-227 is in AUTOMATIC or MANUAL mode, it will initialize the output of FIC-226 to maintain bumpless control when placed into CASCADE mode.
SAH-227 is an independent sensor of the compressor/turbine shaft speed and will trip K-201 on high speed.
XI-227 is a switch that indicates any trouble from the mechanical monitoring system of the compressor. XA-227 is a switch that indicates a serious mechanical problem has been detected with the compressor and is tied into the protective system of the compressor I-228.
XA-228 is a switch that both indicates the state of the Recycle Compressor Interlock I-228 and acts a hand switch to manually trip the compressor and to reset the interlock once all other trip inputs are clear.
HIC-228 is a hand controller that is used to adjust the opening of KT-201’s trip valve XV-228. XV-228 should normally be 100% open when the compressor is operating. HIC-228 is locked in manual with a 0% output when the K-101 interlock I-228 is tripped.
FI-228 measures the high pressure steam flow to KT-201.
Basic Controls: Stabilizer Feed
TI-229 indicates the Stabilizer feed outlet temperature of Stabilizer Feed/Bottoms Exchanger, E-204.
TI-250 indicates the stabilized product reformate outlet temperature of E-204.
TIC-230 controls the Stabilizer feed outlet temperature from Stabilizer Feed Preheater, E-205. TIC-230 adjusts the position of control valve TV-230 to control the flow rate of hot reactor effluent from Reactor Feed/Effluent Heat Exchanger No. 2, E-202, going through E-205.
TI-221 indicates the outlet temperature of E-205 on the reactor effluent side.
Basic Controls: Stabilizer Bottom
PDI-235 indicates the pressure drop across the trays of the bottom (stripping) section of Stabilizer Column, T-202.
TI-234 indicates the temperature of Tray 15.
TI-235 indicates the temperature of Tray 10.
TIC-236 is used to control the temperature of Tray 4 by adjusting the position of control valve TV-236 which controls the flow rate of hot reactor effluent from Reactor Feed/Effluent Heat Exchanger No. 2, E-202, going through Stabilizer Reboiler, E-206. TIC-236 is locked in manual with a zero output when Reboiler Interlock I-236 has been tripped.
XA-236 is a switch that both indicates the state of the Reboiler Interlock I-236 and acts a hand switch to manually trip the Reboiler and to reset the interlock once all other trip inputs are clear.
LI-237 indicates the liquid level in the bottom of T-202.
TI-237 indicates the temperature of the bottoms liquid going to E-206.
LIC-239 controls the level of the product sump of E-206 by adjusting the setpoint of the product flow controller FIC-251. The setpoint of LIC-239 tracks its PV when in MANUAL mode.
TI-238 indicates the temperature of hot stabilized reformate going to Stabilizer Feed/Bottoms Heat Exchanger, E-204.
TI-222 indicates the temperature of the reactor effluent leaving the tubes of Stabilizer Reboiler, E-206.
PDIC-221 controls the pressure drop across E-206/TV-236 by adjusting the position of control valve PDV-221. Normally, PDV-221 is only slightly open and most of the reactor effluent from E-202 is routed through Stabilizer Feed Preheater, E-205, and E-206. In case the demand for reactor effluent flow is reduced by TIC-230 (E-205) of TIC-236 (E-206) then PDIC-221 will open PDV-221. By keeping the pressure drop across E-205 and E-206 regulated to a consistent value, the likelihood of temperature variations in the Stabilizer Column, T-201, is reduced.
HIC-251 controls the flow of cooling water to Product Cooler, E-207, by adjustment of HV-251.
TI-251 indicates the temperature of the reformate product leaving E-207 for storage.
FIC-251 controls the flow of product reformate to storage via FV-251. It is normally in CASCADE mode. When it is in CASCADE mode it receives its setpoint from LIC-239. When it is in AUTOMATIC or MANUAL mode, it will initialize the output of LIC-239 to maintain bumpless control when placed into CASCADE mode. When in MANUAL mode, its setpoint will track its PV.
AI-250A indicates the Research Octane Number (RON) of the reformate product to storage.
AI-250B indicates the concentration of pentane in the reformate product to storage in mole %.
Basic Controls: Stabilizer Top
TI-231 indicates the temperature of the vapor leaving the top of Stabilizer Column, T-202.
PI-231 indicates the pressure at the top of T-202. PAH-231 indicates the same and is an independent sensor for the protective system of T-202.
TI-232 indicates the temperature of Tray 22.
TI-233 indicates the temperature of Tray 18.
PDI-232 indicates the pressure drop across the trays of the top (rectifying) section of T-202.
FIC-231 controls the flow of reflux to T-202 via FV-231. It is normally in AUTOMATIC mode. When it is in CASCADE mode it receives its setpoint from LIC-240A. This operating mode may be used during startup and shutdown when no overhead product draw from Reflux Drum D-204 to storage is desired. When FIC-231 is in AUTOMATIC or MANUAL mode, it will initialize the output of LIC-240A to maintain bumpless control when placed into CASCADE mode. When in MANUAL mode, the setpoint of FIC-231 will track its PV.
HIC-240 controls the flow of cooling water to Overhead Condenser, E-208, by adjusting the position of HV-240. The flow of cooling water will affect the condensing rate in E-208.
TI-240 indicates the outlet temperature from E-208.
Basic Controls: Reflux Drum
PIC-240 controls the pressure of Stabilizer Reflux Drum, D-204, by adjusting the opening of PV-240 on the line from D-204 to the fuel gas system.
FI-240 indicates the flow of gas through PV-240 to the fuel gas system.
LIC-240B controls the hydrocarbon level of D-204 by adjusting the setpoint of light top product flow controller FIC-241. Normally LIC-240B is in AUTOMATIC mode and FIC-241 is in CASCADE mode. The setpoint of LIC-240B tracks its PV when in MANUAL mode.
LIC-240A shares the same PV with LIC-240B and controls the hydrocarbon level of D-204 by adjusting the setpoint of reflux flow controller FIC-231. Normally LIC-240A is in MANUAL mode and FIC-231 is in AUTOMATIC mode. The setpoint of LIC-240A tracks its PV when in MANUAL mode. LIC-240A may be used during startup and shutdown when no overhead product draw from D-204 to storage is desired.
LIC-240A should normally not be placed in AUTOMATIC mode when LIC-240B is also in AUTOMATIC mode because the two controllers will fight each other for control of the hydrocarbon level of D-204 if they have approximately the same setpoint. However, LIC-240A can be placed into service in cascade with FIC-231 (reflux) with a much higher setpoint than LIC-240B in order to dump any excess light product from D-204 back into T-202 in case LIC-240B cannot control the level of D-204. This approach can be used to protect against tripping the Stabilizer Reboiler’ s heat input on high level in D-204.
LAH-240 indicates the top liquid level of D-204 and is an independent sensor for the protective system of the Stabilizer Column.
LIC-241 controls the level of the water boot of D-204 by discharging the water through LV-241 and on to the sour water treater.
HS-240A/B are switches that control the motors of Stabilizer Reflux Pumps, P-202A/B, respectively. If a motor trips, the respective switch will move to the STOP state.
Interlocks
There are three protective interlock systems in the Catalytic Reformer Unit as follows:
- I-210 – Reactor Feed Heater & Reheaters, F-201, and Catalytic Reforming Reactor, R-201, Protective System
- I-228 – Recycle Compressor, K-201, Protective System
- I-236 – Stabilizer Column, T-202, and Reboiler, E-206, Protective System
Each system is described below.
Interlocks: Reactor Feed Heater Trip
I-210 – Reactor Feed Heater & Reheaters F-201 and Catalytic Reforming Reactor R-201 Protective System.
This interlock protects the Reactor Feed Heater & Reheaters, F-201, and the Catalytic Reforming Reactor, R-201, against operation under conditions that will cause damage to the equipment. The inputs to the interlock are:
- FAL-227 – Recycle gas flow (trips at 100% of computed flow)
- PAH-206 – E-201 inlet pressure (trips at 490 PSIG)
- TAH-210/213/216 – F-201 outlet temperatures (trips at 1250 DEG F)
- PAH-210 – F-201 outlet pressure (trips at 490 PSIG)
- TAH-211A/B/C – R-201 top bed temperatures (trips at 1250 DEG F)
- TAH-214A/B/C – R-201 middle bed temperatures (trips at 1250 DEG F)
- TAH-217A/B/C – R-201 bottom bed temperatures (trips at 1250 DEG F)
- I-228 Recycle Compressor trip (XA-228 in the TRIP state)
The status of the interlock is indicated on switch XA-210. XA-210 not only indicates the status of the interlock but is also used to reset the interlock if it is in the TRIP state and all trip inputs are clear. Additionally, switching XA-210 to the TRIP state will manually activate the interlock.
When activated, interlock I-210 will:
- Lock naphtha Lock all three F-201 fuel gas flow controllers FIC-210/213/216 in MANUAL mode with an output of 0%
- Lock all three F-201 outlet temperature controllers TIC-210, TIC-213 and TIC-216 in MANUAL mode
- feed flow controller FIC-201 in MANUAL mode with an output of 0%
- Set XA-210 to the TRIP state
- Generate an audible alarm on the DCS
Interlocks: Recycle Compressor Trip
I-228 – Recycle Compressor K-201 Protective System.
This interlock protects the Recycle Compressor, K-201, and its Recycle Compressor Turbine, KT-201, against operation under conditions which will damage it. The inputs to the interlock are:
- TAH-227 – K-201 discharge temperature (trips at 280 DEG F)
- XA-227 – K-201 trouble (trips on TRIP state)
- LAH-225 – D-202 high liquid level (trips at 95%)
- SAH-227 – K-201/KT-201 shaft speed (trips at 8,500 RPM)
The status of the interlock is indicated on switch XA-228. XA-228 not only indicates the status of the interlock but is also used to reset the interlock if it is in the TRIP state and all trip inputs are clear. Additionally, switching XA-228 to the TRIP state will manually activate the interlock.
When activated, interlock I-228 will:
- Lock KT-201 steam trip valve hand controller HIC-228 in MANUAL mode with an output of 0%
- Lock K-201 speed controller SIC-227 in MANUAL mode with an output of 0%
- Lock K-201 suction flow controller FIC-226 in MANUAL mode
- Active Interlock I-210 (see above)
- Set XA-228 to the TRIP state
- Generate an audible alarm on the DCS
Interlocks: Stabilizer Reboiler Trip
I-236 – Stabilizer Column T-202 and Reflux Drum D-204 Protective System.
This interlock protects the Stabilizer Column against operation under conditions which will cause a large release to flare (via pressure safety valve opening) and protects the Reflux Drum from causing a potentially unsafe condition in the downstream fuel gas unit due to carryover of liquid in the light overhead gas to the fuel gas system. The inputs to the interlock are:
- PAH-231 – T-202 top pressure (trips at 180 PSIG)
- LAH-240 – D-104 high liquid level (trips at 90%)
The status of the interlock is indicated on switch XA-236. XA-236 not only indicates the status of the interlock but is also used to reset the interlock if it is in the TRIP state and all trip inputs are clear. Additionally, switching XA-236 to the TRIP state will manually activate the interlock.
When activated, interlock I-236 will:
- Lock T-202 Tray 4 temperature controller TIC-236 in MANUAL mode with an output of 0%.
- Set XA-236 to the TRIP state
- Generate an audible alarm on the DCS