CHEVRONTEXACO PETROLEUM COMPANY
GUATEMALA REFINERY
GENERAL DESCRIPTION OF THE CATALYTIC REFORMER UNIT
DESCRIPTION OF PROCESS
Catalytic Reforming Unit – Section 400
S. R. Naphtha Debutanizer The catalytic reformer debutanizer, DA-404, is designed to fractionate the straight run naphtha from the Crude Unit (Section 100), thus essentially removing propanes and butanes overhead. The debutanizer overhead is treated with caustic to eliminate any residual hydrogen sulfide and mercaptans in this stream. The straight run naphtha bottoms (via FA-407) is sent to the Naphtha Hydrotreater (Section 200) where it is treated in preparation for catalytic reforming charge. The catalytic reformer is designed to upgrade the straight run naphtha from the naphtha hydrotreater and produce the following products or process streams:
a. Stabilized gasoline (product to gasoline storage tanks FB-506A & B, and FB-507)
b. LPG (product to LPG storage tanks FA-501A & B)
c. H2 rich gas to naphtha hydrotreater (feed gas to hydrotreater)
d. Off-gas to low pressure fuel gas header
The straight run naphtha flows under flow control (FRC-105) from the discharge of pump GA-102 (S.R. naphtha debutanizer pump) to the tube side of EA-414 where it is preheated by the debutanizer bottoms in the shell side of this exchanger. The naphtha then flows to the S.R. naphtha debutanizer, DA-404, on feed tray #13. The net overhead vapors (consisting primarily of butanes and propanes) are totally condensed and cooled to 100°F by cooling water in the shellside of EA-416, and then collected in the debutanizer overhead accumulator, FA-404. Part of this liquid as reflux is pumped by GA-406 and returned to the top tray of the naphtha debutanizer which is under temperature control (TIC-407). The remainder of this stream pumped by GA-406 (under level control LC-409) is then treated with a 10% solution of NaOH in the caustic settler, FA-408, water washed in settler (FA-409) and sent to the reboiled absorber, DA-402.
The tower bottom is under level control (LC-408) and flows to the debutanizer bottoms accumulator, FA-407. Liquid from this accumulator flows to the shellside of EA-414, where it preheats the incoming feed to the debutanizer to approximately 228°F, and then enters the suction of GA-407. This material is then sent to the naphtha hydrotreater as charge stock under flow control (FRC-415) to exchanger EA-201A, B, C, and D. Reboil heat to this tower (DA-404) is supplied by the catalytic reformer effluent (from reactor DC-403). This material exchanges heat in the tube side of EA-415 where it vaporizes part of the tower bottoms liquid in the shellside to approximately 350°F and then is returned to the tower underneath tray #26.
Caustic Treating Several commercial caustic drums are placed on the grating in the lined concrete sump which is then filled to the desired water level to make a 50% (wt.) caustic solution. The caustic transfer pump, GA-411, is used to recycle this solution within this sump until the concentration reaches 50% NaOH. This solution is pumped to the fresh caustic storage tank, FB-401, by GA-411 and cooling water is added to produce the desired concentration (Design is 10% NaOH). The tank contents are mixed thoroughly by recycling through pump GA-410 back to the tank.
Reactor Section The catalytic reformer is designed to process low-octane naphtha in the presence of hydrogen and a platinum catalyst to produce high-octane gasoline. By-products of the reaction are light hydrocarbons and hydrogen-rich gas. The hydrogen-rich gas supplies the necessary hydrogen for the naphtha hydrotreater and kerosene hydrotreater.
The catalytic reformer charge is pumped from the naphtha surge tank, FA-405, under flow control (FRC-401) to the shellside of the feed-effluent exchanger EA-403. A controlled amount of hydrogen-rich gas at approximately 600 psig, from compressors GB-401A and GB-401B operating in parallel mixes with this charge stream before preheating against a portion of reactor effluent in EA-403. The preheated catalytic reformer charge and H2 is further heated to approximately 643°F in the naphtha feed-reactor effluent exchangers (EA-401A, B, and C) by exchange with another portion of reactor effluent (DC-403) prior to final heating to reaction conditions (approximately 975°F) in the preheater section of BA-401.
Water is injected into the hydrogen naphtha charge to the heater, BA-401, using pump GA-403, which takes suction from the calibrated tank HA-401. A 33% solution of ethylene dichloride in naphtha is also injected at the same time using GA-403. This solution is fed from the calibrated tank HA-402. For production of 90 octane product at design charge rate the amount of water injection should be 0.032 GPH and for the ethyline dichloride solution, 1.0 GPH.
From the preheater BA-401, the mixture of hydrocarbons and hydrogen (all vapor) flows into the top of the first reactor DC-401, where part of the reaction occurs. The reaction in the first reactor is quite endothermic; therefore, the temperature drops approximately 122°F from the inlet to the outlet of DC-401.
From DC-401, the mixture flows through the first fired reheater BA-402, where it is reheated back to the required reaction temperature, and thence to the second reactor DC.-402. Again the reaction is endothermic and the temperature drops approximately 42°F from the inlet to the outlet of the reactor.
From DC-402, the mixture flows through the second fired reheater BA-403, where it is again heated back up to the required reactor temperature, and thence to the third reactor DC-403. As in the other two reactors the reaction is endothermic and is accompanied by a temperature drop of approximately 11°F form the inlet to the outlet of this, the last reactor.
After leaving the last reactor (DC-403), the reactor effluent is split into three streams. Part of the effluent material flows to the tube side of the DA-401 stabilizer reboiler EA-405, where it gives up some of its heat to supply the heat requirements of the stabilizer DA-401. From the tube side of EA-405, this material flows to the tube side of EA-403.
Another portion of the reactor effluent material flows to the tube side of the S.R. Naphtha Debutanizer Reboiler, EA-415, where it gives up some of its heat to supply the heat requirements of the debutanizer, DA-404. From the tube side of EA-415 this material joins the reactor effluent material from EA-405 and flows to the tube side of EA-403, where the combined stream is cooled against the naphtha and hydrogen reactor feed stream.
The main part of the reactor DC-403 effluent flows directly to the tube side of EA-401A, B, and C, where it gives up most of its heat to the reactor feed stream from EA-403. Downstream of EA-401A, B, and C tube side, this effluent stream is joined by the effluent from the tube side of EA-403, and the combined stream then flows through the tube side of the reactor effluent cooler EA-402A and B, where the material is cooled to approximately 100°F by cooling water.
From the tube side of EA-402A and B the effluent flows into the flash drum, FA-401, where the liquid and vapor phases are separated. The vapor from this flash drum is rich in hydrogen and is used as recycle gas for the reactor system. This gas flows form the top of FA-401 to the suction of the recycle gas compressor GB.-401A and B, where it is compressed and pumped into the charge naphtha stream upstream of EA-403. The suction line to the recycle gas compressors is fitted with a steam jacket to vaporize any entrained liquid, and therefore, obviate a compressor suction knock-out drum.
The excess hydrogen-rich gas produced in the catalytic reformer is released under pressure control (PRC-404) from the discharge of the catalytic reformer recycle compressor GB-401A and B to the naphtha hydrotreater reactor (DC-201) inlet line.
Fractionation Section The feed to the reboiled absorber DA-402 comes from two places. One is the liquid propane-butane stream from FA-421, which has been caustic and water washed. The other is the liquid leaving the flash drum, FA-401, under level control (LC-402). These two streams then combine and enter the shellside of EA-409A and B, where the feed is preheated to approximately 250°F by heat exchange with hot stabilized gasoline in the tube side before entering the reboiled absorber on feed tray #19.
The function of the reboiled absorber is to strip light ends (H2, C1, and C2) from the feed, while at the same time absorb, by means of a lean oil stream, propanes, butanes, and heavier material to produce a rich absorber bottoms stream.
Stabilizer bottoms from GA-404 preheats the absorber feed in EA-409 as described above. This stabilizer bottoms then splits into two streams. One portion, combined with some of the bottoms from the depropanizer DA-403 under flow control, FRC-406, becomes the net debutanized gasoline product from this section and is cooled to 100°F in the shellside of EA-406 against cooling water before going to storage under level control, LC-405 in DA-401.
The other part of the stabilizer bottoms stream is cooled to 100°F in the shellside of EA-407 and is used as lean oil entering the top of the absorber DA-402, under flow control, FRC-404.
The off-gas from the top of the absorber passes through pressure controller PRC-401, which maintains the proper pressure in the tower and then is joined by the surplus butane portion of the depropanizer bottoms stream before going to the fuel gas system.
Heat to the absorber for reboiling is supplied by saturated steam (145 psig) in the tube side of absorber reboiler EA-408, and controlled by TRC-406 measuring the temperature of the vapor above tray #21.
The rich absorber bottoms stream is pressured out of the tower bottom under level control (LC-403) to the feed tray #15 of the stabilizer DA-401.
Water may be present in the feed to the absorber as a result of water washing the C3 – C4 stream or injection of water into the reactor feed stream. This water is drawn off from the absorber through water draw-off pot, HA-408. An interface in the pot will show water in the lower layer which is drawn off to sewer under level control, LC-416.
In the stabilizer tower DA-401 two streams are obtained form this column. The overhead is essentially propanes and butanes. The bottom product is debutanized gasoline which is combined with butane from the depropanizer bottoms for Reid vapor pressure control, cooled, and pumped to gasoline storage tanks (FB-506A and B) located outside of battery limits. The overhead vapor enters the shellside of EA-404 where it is totally condensed in the stabilizer accumulator FA-402 to 110°F by cooling water. Liquid from this drum is pumped by GA-402, part of the stream returning to the tower as reflux liquid under temperature control TIC-404, while net overhead liquid is fed to the depropanizer, DA-403 under level control (LC-404) to produce LPG.
Reboil heat to the stabilizer is provided by a slipstream of reactor effluent from the third stage reactor (Catalytic Reforming Unit) entering the tube side of EA-405 and returning to EA-403. Stabilizer bottoms liquid enters the shellside of the exchanger EA-405 heated and partially vaporized from approximately 331°F to 355°F, and returns to the tower DA-401 underneath the bottom tray #26.
The feed to the depropanizer, DA-403, is net overhead liquid (propanes and butanes as described above) from the stabilizer tower and is pumped to the downcomer of the 16th tray in DA-403. The overhead vapors (propanes) from the depropanizer are totally condensed in the shellside of the condenser, EA-411, with cooling water to approximately 100°F. Liquid from the depropanizer accumulator flows to the suction of GA-405. This pumps is used for both DA-403 reflux and net overhead LPG product. The reflux is pumped back to the top tray of tower DA-403 under flow control (FRC-409) and the net product is pumped to the LPG dryers, PA-401 A and B. From the LPG dryers the liquid is then sent (under level control LC-406) to LPG storage tanks FA-501A and B located outside the battery limits.
Reboil heat to the depropanizer is provided by low pressure saturated steam (50 psig) entering the tube side of Ea-410 heating and partially vaporizing the butanes in the shellside of this reboiler, which are returned to the tower below the bottom tray #32. The steam flow is controlled by TIC-405 which measures the temperature of vapor above tray #26.
A slipstream of depropanizer bottoms (i.e. butanes) is blended with debutanized gasoline for Reid vapor pressure specifications, and the remainder is vaporized in the butane vaporizer by low pressure saturated steam (45 psig), flowing (under LC-407) to the low pressure fuel gas drum, FA-304.