Document eZjEzkDNgNMbr9Xm7KqpGNo9

PED ORIENTATION PROGRAM ETHYLENE UNIT LAKE CHARLES CHEMICAL PLANT The Lummus-designed ethylene unit was brought on stream In February 1968 after a record-low startup period of nine days. The nameplate capacity was 500 MM pounds per year ethylene using ethane feedstock. Subsequent debottlenecking, including addition of a new cracking heater, has elevated capacity to 650 MM pounds per year using both ethane and propane feedstock. The technology employs Lummus* "SRT" high severity cracking heaters to maximize ethylene yield. The primary feedstock is ethane, although supplemental quantities of propane are charged during periods when ethane is in short supply. PROCESS DESCRIPTION The following is a brief description of the processing sequence as shown on the overall process flow diagram. Reaction chemistry is represented typically as follows: C2H6 C2H4 + H2 C3H8 H?a C2H4 + CH4 A. Cracking and Quench Ethane and propylene-propane recycle are cracked in tubular heaters in the presence of dilution steam to an outlet temperature of 1,560F. The heater effluents are cooled to 600F in transfer line exchangers which generate high pressure steam at 650 psig. The effluents from the transfer line exchangers are combined and directed to the quench tower. By direct contact water cooling, the greater part of the dilution steam and some heavier hydrocarbons are condensed. Net overhead vapor at 110F flows to the compressor system. Quench water plus condensed steam is separated from the condensed hydrocarbons in a quench water surge drum which is operated at 180F. The circulating hot water is used to preheat the ethane furnace feed and further cooled in the air-cooled quench water coolers and against cooling water. Condensed dilution steam is sent to the process water stripper, where it is stripped of dissolved gases and light hydrocarbons, vaporized against 200 psig steam, and reused as heater dilution steam. B. Charge Compression and Acid Gas Removal The quench tower overhead vapors are compressed in four centrifugal compressor stages to a pressure of 535 psig, with interstage cooling to 110F. Between the third and fourth stages, the gas is treated for acid gas removal in the caustic and water wash tower. The fourth SAL CC3C1C1** PROCESS DESCRIPTION (CONTINUED) B. Charge Compression and Acid Gas Removal (Continued) stage discharge is cooled with water and with propylene refrigerant to 60F. Liquid condensate is separated and the vapor is sent to the desiccant dryers. Interstage hydrocarbon and water condensates from the first three stages are sent back to the quench water surge drum. Fourth stage condensate is recycled to the third stage discharge drum. 1. Drying and Feed Chilling The final compressor discharge gas at 60F and 525 psig is dried in packed bed dryers using activated alumina before passing to the low temperature recovery section. Three dryers are provided. Two are on stream in series, while the third is regenerated. Both regeneration and cooling of the dryers are accomplished using hydrogen-rich offgas on a once-through basis. A regeneration heater and a cooler are provided for the regeneration operation. The dried gas at 60F is progressively chilled and partially condensed, with condensate removal at -30F, -*95F, -145'F, and -185F. The remaining vapor is the hydrogen-rich offgas. The condensates are fed to the demethanizer. The chilling is achieved with propylene and ethylene refrigeration, vaporizing feed and recycle ethane and reheating hydrogen and methane offgas streams. An expander is used on the hydrogen-rich offgas to provide the lowest level refrigeration. The hydrogen-rich offgas and the methane-rich offgas are sent to fuel after reheating in the chilling train and against liquid propylene refrigerant. 2. Demethanization and Deethanizatlon The demethanizer, which operates at 445 psig, has a bottoms temperature of 31F and an overhead temperature of -113F. The column is reboiled with propylene refrigerant, and reflux is condensed with ethylene refrigerant. The demethanizer overhead is the methane offgas, which is sent to fuel after reheating in the chilling train and against liquid propylene refrigerant. The demethanizer bottoms flow to the deethanizer where C2's are separated from the Cj and heavier fraction. The deethanizer operates at 395 psig with !6F and !82F overhead and bottoms temperature, respectively. The reboiler utilizes low pressure steam and reflux is condensed with propylene refrigeration. The bottoms product is sent to the depropanizer and the overhead flows to the acetylene removal system. SAL JC0C1C150 PROCESS DESCRIPTION (CONTINUED) B. Charge Compression and Acid Gas Removal (Continued) 3. Acetylene Removal and Ethylene Fractionation The deethanizer overhead vapor, after feed-effluent exchange and preheat, is sent to the acetylene converter. Acetylene is hydrogenated over a palladium catalyst in the packed bed reactor. Hydrogen offgas after enrichment, methanation, and drying over molecular sieves is injected into the converter feed to provide the hydrogen requirements. Two vessels are provided, one is on stream while the other is on standby. A fired heater is provided for regeneration. The converter effluent is used to preheat the feed and sent to the ethylene fractionator. The feed to the ethylene fractionator consists of ethylene, ethane, and unreacted hydrogen and methane from the acetylene removal system. The tower operates at 285 psig with overhead and bottoms temperatures of -20F and 21F, respectively. Condensing and reboiling are done by propylene refrigeration. The ethylene product is withdrawn as a side stream from the tower, and unreacted hydrogen and methane from the acetylene removal system are recycled from the reflux drum to the charge compressor. The liquid ethylene product is vaporized and delivered to the battery limits at 600 psig and 225 psig. The fresh ethane feed is dried over molecular sieves, combined with the bottoms ethane product from the ethylene fractionator, and vaporized against demethanizer feed. The total ethane vapor stream is superheated against propylene refrigerant and circulating quench water and then charged to the cracking heaters. 4. Fractionation of Propane and Heavier Components The depropanizer, operating at 160 psig with 77F and 228F overhead and bottoms temperatures, respectively, receives feed from the deethanizer bottoms. Steam and propyiene are the reboiling and condensing mediums, respectively. The overhead vapor product is recycled to the cracking furnace.* The bottoms product con taining C4 and heavier is sent to the debutanizer. The debutanizer operates at 65 psig with 119F top and 249F bottom temperatures. Cooling water is the reflux condensing medium, while steam is used for reboiling. The overhead liquid is the mixed product which is sent to battery limits, and the bottoms is the light aromatic distillate product which is cooled to 120F and sent to battery limits. *The C-j overhead is now being sold as product and Is not recycled to the furnaces. SAL JCCCICI^I PROCESS DESCRIPTION (CONTINUED) B. Charge Compression and Acid Gas Removal (Continued) 5- Propylene Refrigeration The propylene refrigeration system is a closed, multistage system using a centrifugal compressor. It provides refrigeration at four levels: -35F, -5F, 37F, and 60F. The compressor effluent is cooled and condensed against cooling water and subcooled against various produce and process streams. Interstage condensing at the various levels is obtained from reboiling the demethanizer and the ethylene fractionator and also from the vaporization of the liquid ethane feed and ethylene product. 6. Ethylene Refrigerat ion The ethylene refrigeration system is a closed, multistage system using a centrifugal compressor. The ethylene system has three levels of refrigeration: -150F., -100F, and -65F. The compressor effluent is desuperheated against propylene refrigerant and then condensed against the lowest level propylene refrigerant. SAL 0CCC11^2 This sheet Is CONFIDENTIAL and should not be distributed outside Continental Oil Company. Spec. No. 07-5100 ETHYLENE rest Ethylene, Wt. % Other Hydrocarbons, Wt. % Propylene, ppm Acetylene, ppm Carbon Dioxide, ppm Carbon Monoxide, ppm Hydrogen, ppm Oxygen, ppm Sulfur, ppm Water, ppm Specification 99.8 min. 0.2 max. 65 max. 20 max. 350 max. 10 max. 10 max. 5 max. 2 max. 5 max. Test Method By difference 1 . 251 1.251 1 . 252 1.253 1.254 1.255 1.254 1.256 - 12-15-73 S rA L 0CCC1C153 This sheet is CONFIDENTIAL and should not be distributed outside Continental Oil Company. Spec. No. 07-5122 Propane-Propylene Test Distribution Ctt's and lower, wt.% Propylene, wt.% Propane, wt.X Ci+'s and higher, vt.% Sulfur, ppm wt. Specification 2.5 max. 65 rain. 55 max. 3 max. 10 max. Typical Property 1.2 79.5 18.5 0.8 <1 Test Method GC 1.256 5-01-77 0OC01C154 Test Distribution C3's and lower, wt.% Butanes, wt.% Butenes, wt.% 1,3 Butadiene, wt.% 1,2 Butadiene, wt.% C4 Acetylenes, wt.% C5 and higher, wt.% Peroxides, ppm as H2O2 Sulfur, ppm Antioxidant (TBC) ppm This sheet is CONFIDENTIAL and should not be distributed outside Continental Oil Company. Spec. No. 07-5142 BUTADIENE Specification 2.0 max. 65.0 min. 2.0 max. 1.0 max. 10 max. 10 max. a Typical Property 1.2 12.0 14.0 71.3 0.2 1.2 0.1 <1 <1 100 Test Method GC ASTM D-1022 MOD 1.256 LC-EU-8 This sheet is CONFIDENTIAL and should not be distributed outside Conoco Inc. Spec. No. 07-5180 Light Aromatic Distillate Test Benzene, Wt. Z Ct+'s and Lower, Wt. Z 90% Evaporation Point, F Specification 40.0 min. 3.0 max. 400 max. Typical Property 48.6 1.5 340 Test Method GC GC ASIM D-86 10-15-79 ^0010156 ETHYLENE UK) IT AT LAKE CHARLES PLAK1T rino o o f.2 O C<1l V Z - U 8 5 3 -OH wo S4L o^cnicise t <c I i i 5 A L ZC0010159