CN1319915C - Energ ysaving method for producing ethyl benzene by benzene and dry gas hydrocarbonization - Google Patents

Abstract

The invention discloses an energy-saving method for producing ethylbenzene by alkylating benzene and dry gas, which is characterized in that: the inter-stage quenching mode of the alkylation reactor is improved, benzene and dry gas jointly participate in the inter-stage quenching of the reactor; the side line of the coarse separation tower Recycle benzene to reduce the load of benzene tower, improve the separation sequence of polyethylbenzene tower and diethylbenzene tower, increase the number of theoretical plates of propylbenzene tower to reduce the energy consumption of separation, realize the separation between benzene tower and ethylbenzene tower through the middle reboiler of benzene tower Heat integration, the ethylbenzene tower adopts a double-tower process to obtain high-grade ethylbenzene products; the heat exchange network is optimized and integrated, and the pinch technology is used to optimize the design of the heat exchange network to obtain an optimized heat recovery network. Referring to the similar ethylbenzene plant of 6×10 ⁴ t/a, the comprehensive energy saving of this scheme is 24GJ/h, and the unit energy consumption of the product is reduced from the original level by 3.2GJ/t. This invention is especially suitable for the existing benzene and dry gas alkylation Ethylbenzene production process has undergone energy-saving transformation, and the energy consumption of the ethylbenzene plant designed based on this scheme is the lowest level of similar domestic plants.

Description

Energy-saving method for producing ethylbenzene by alkylation of benzene and dry gas

technical field

The invention belongs to the technical field of petroleum refining and petrochemical industry, and in particular relates to an energy-saving method for producing ethylbenzene by alkylating benzene and dry gas.

Background technique

Ethylbenzene is mainly used to produce styrene monomer, which can be obtained by dehydrogenating ethylbenzene. Ethylbenzene is an important industrial raw material. The strong market demand for styrene continues to drive the production scale of ethylbenzene. The production methods of ethylbenzene mainly include the synthesis of benzene and ethylene alkylation, and the separation of C ₈ aromatic fractions in petroleum refining, of which the former accounts for 90%, while the latter only accounts for 10%. Since the 1930s, a variety of unique methods for producing ethylbenzene by alkylation have been developed, most of which use high-concentration ethylene as raw material, resulting in high raw material cost of ethylbenzene. The sources of ethylene raw materials in my country are severely restricted by petroleum resources, so it is of great significance to seek ways to produce ethylbenzene cheaply. With the development of the petrochemical industry, the direct use of low-concentration ethylene catalytic cracking dry gas as a raw material for the production process of ethylbenzene synthesis has been extensively and in-depth researched. These technologies are mainly published in relevant domestic and foreign patents. Foreign patents include : US Patent US2,939,890; US3,691,245; US3,702,886; US3,848,012; US4,107,224; US4,459,026; British Patent BP827,830; . Chinese patents include: PetroChina Fushun Petrochemical Branch, Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Sinopec Luoyang Petrochemical Engineering Company CN90109803.5; CN92106016.5; CN93115960.1; CN96100371.5; CN97116471.1; CN03156679.0; CN200410021102.8, Mobil Petroleum Co., Ltd. CN93112744.0, Elef Ato Chemical Co., Ltd. CN93108241.2, Tianjin Xintianjin Technology Development Co., Ltd. CN00131924.8, Shanghai Petrochemical Research Institute CN02155114.6, ABB Lammers Global Co., Ltd. CN99804925.5, etc. The relevant contents such as reaction and separation, energy saving and consumption reduction described in the above related patents are important references of the present invention.

The alkylation process of benzene and ethylene includes aluminum trichloride method, BF ₃ -Al ₂ O ₃ method and solid phosphoric acid method. According to the reaction phase, it can be divided into two types: liquid-phase alkylation method and gas-phase alkylation method. The traditional AlCl3 liquid-phase alkylation process has been gradually replaced by the improved AlCl3 process developed by Monsanto Company of the United States, that is, the BF ₃ -Al ₂ O ₃ high-pressure homogeneous alkylation process. In the 1970s, the alkylation process using ZSM-5 as a catalyst jointly developed by Mobil and Badger was a major change in the production of ethylbenzene. The newly developed processes are mainly the Y-type molecular sieve catalyst and its related liquid-phase alkylation process developed by Unocal in the 1980s; and the catalytic distillation ethylbenzene technology jointly developed by CD-Tech and Lummus in the early 1990s.

Chinese patent CN87105054 "Process of Alkylation of Dilute Ethylene to Ethylbenzene and Zeolite Catalyst Used therein" discloses the preparation of a catalyst for the alkylation of benzene and catalytic cracking dry gas to synthesize ethylbenzene. Chinese patent CN93112744.0 "production of ethylbenzene" adopts ZSM-5 molecular sieve catalyst to carry out alkylation reaction of ethylene to benzene in the gas phase to synthesize ethylbenzene. Chinese patent CN99124797 "method and equipment for producing ethylbenzene by catalytic distillation of benzene and refinery dry gas" pretreats the raw refinery dry gas, and then makes benzene and ethylene in solid in the catalytic distillation tower The gas-liquid-solid three-phase alkylation reaction is carried out on the surface of the catalyst, and the reaction product mixture is distilled and separated at the same time. Chinese patent CN00131924.8 "Process of Catalyzing Dry Gas to Produce Ethylbenzene" uses an absorbent to absorb ethylene in the dry gas to obtain a fulvene solution, which then enters the reactor for liquid-phase homogeneous reaction with benzene.

PetroChina Fushun Petrochemical Company, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, and Sinopec Luoyang Petrochemical Engineering Company have jointly developed catalytic cracking dry gas production of ethylbenzene technology, and in 1993, the first production set was built in Fushun Petroleum Plant No. 2 of PetroChina Fushun Petrochemical Company A dry gas ethylbenzene plant with a capacity of 3×10 ⁴ t/a. Existing similar ethylbenzene production devices are constantly undergoing energy-saving and consumption-reducing technological transformation. The latest Chinese patents are CN200410021102.8 and CN03156679.0. After energy analysis, it is found that there is still room for further energy-saving and consumption-reduction.

Contents of the invention

The purpose of the present invention is to provide an energy-saving method for the production of ethylbenzene by alkylation of benzene and dry gas, which uses dry gas and recycled benzene to participate in the inter-section chilling of the reactor, makes full use of the reaction heat, and maintains the temperature rise of the catalyst bed at 30-50°C , the outlet temperature of the reactor reaches the peak value, and no raw material preheating furnace is needed. Double-effect rectification is realized by adjusting the pressure of the benzene tower and the ethylbenzene tower. The column condenser is thermally integrated with the benzene column intermediate reboiler. The technological route improvement of the separation sequence of the tower system and the optimization of the operation parameters of the single tower, 10 ⁴ kg/hr circulating benzene was produced from the side line of the crude separation tower to reduce the load of the benzene tower, and the separation sequence of the polyethylbenzene tower-diethylbenzene tower was improved to reduce the separation Energy consumption, increasing the number of theoretical plates in the propylbenzene tower from 20 to 30; the ethylbenzene tower adopts a double-tower process to obtain superior ethylbenzene products, the first ethylbenzene tower performs non-clear segmentation to obtain superior ethylbenzene products, and the second The ethylbenzene tower is clearly divided to obtain the first-grade ethylbenzene; the thermal pinch technology is used to obtain the distribution of the heat flow of the process system along the temperature level, and the optimization scheme of the heat exchange network is finally obtained by adjusting the logistics matching. The energy consumption of similar devices designed based on this scheme is the lowest in China.

The technical scheme of the invention includes three aspects: improvement of the process flow of the alkylation reaction, heat integration of the benzene tower-ethylbenzene tower, and improvement of the process heat recovery heat exchange network.

(1) Reaction part (see accompanying drawing 1)

(1) Improving the direct quenching method between the reactor stages, using dry gas and circulating benzene to participate in the interstage quenching of the reactor. The dry gas and circulating benzene are equally divided into four feeds, wherein the main feed stream of dry gas and circulating benzene enters the top of the reactor, and the dry gas and circulating benzene quench feed enters the reactor in three side streams.

(2) The main feed stream of dry gas and circulating benzene is preheated to a suitable reaction temperature of 330-360°C, and the quenching feed stream of dry gas and circulating benzene is preheated to a suitable quenching temperature of 250-280°C. Because the temperature level of the dry air stream is increased, the mixing and cooling of high-temperature circulating benzene due to the low dry gas temperature is avoided, and the heat of the alkylation reaction is fully used to heat the reactant stream and the chilled feed stream.

(3) Maintain the temperature rise of the catalyst bed at 30-50°C, and the temperature of the alkylation reaction product at the outlet of the reactor reaches 390-400°C, which can meet the needs of preheating dry gas and circulating benzene as the main feed, so there is no need for a raw material preheating furnace, Save the equivalent heating load of 0.5-0.6GJ/ton of ethylbenzene. Both the reactant stream and the chilled stream can be preheated to the required temperature by recovering the reaction heat of the hydrocarbonated product stream.

(2) Separation part

(1) Referring to attached drawing 2, the circulating benzene is extracted from the liquid phase sideline between the 5th and 10th theoretical plates of the crude separation tower, and the output is 10 ⁴ to 1.5×10 ⁴ kg/hr, the temperature is 114°C, and the benzene The content is more than 99.5% (Mass), meeting the requirement of circulating benzene. The temperature at the bottom of the column was 124.3°C. The load of the benzene tower is correspondingly reduced through the side line extraction of the crude separation tower, and the reflux flow of the benzene tower is reduced by 14%, thereby reducing the load of the benzene tower reboiler.

(2) Referring to accompanying drawing 3, the material from the bottom of the ethylbenzene tower first enters the propylbenzene tower, and the overhead distills propylbenzene, and the still liquid at the bottom of the tower is mixtures such as diethylbenzene and high boilers. The still liquid of the propylene benzene tower enters the diethylbenzene tower, diethylbenzene distills out from the top of the tower, and the still liquid at the bottom of the tower is a high boiler. By changing the separation sequence of polyethylbenzene tower → propylbenzene tower to propylbenzene tower → diethylbenzene tower sequence, under the condition of ensuring the product quality and recovery rate of propylbenzene and diethylbenzene, due to the less gasification and condensation of propylbenzene Once, reduce the energy consumption of this separation sequence by 23%.

(3) Referring to accompanying drawing 4, increase the theoretical plate number of propylene tower to 30, under the premise of guaranteeing product quality, operating reflux ratio is down to 5～6 (Mass), propylene tower reboiler load reduces 74%.

(4) Referring to accompanying drawing 5, realize double-effect rectification by adjusting benzene tower and ethylbenzene tower pressure, benzene tower is provided with intermediate reboiler, ethylbenzene tower condenser and benzene tower intermediate reboiler carry out thermal integration. The pressure at the top of the benzene tower is 1.34MPa (absolute pressure), and the temperature of the oil gas at the top of the benzene tower is 192°C. The pressure at the top of the ethylbenzene tower is 0.73-0.78MPa (absolute pressure), and the temperature of the oil gas at the top of the ethylbenzene tower is 229-233°C. The middle reboiler of the benzene tower draws out the liquid phase from the 46th theoretical plate, returns to the gas-liquid two-phase at the 47th theoretical plate, and heats the reflux material in the middle section from 216°C to 221°C. The oil gas at the top of the ethylbenzene tower is used as the heat source of the intermediate reboiler of the benzene tower, and no saturated steam will be generated. Control the heat load of the intermediate reboiler to not exceed one-third of the total heating load of the whole tower, and reduce the heat load drop of the bottom reboiler of the benzene tower by 30%.

(5) See accompanying drawing 6. Since the ethylbenzene tower cannot separate ethylbenzene from m-xylene and p-xylene in the current process, if the content of m-xylene and p-xylene in the feed to the ethylbenzene tower is high, the superior product cannot be obtained; the dual-tower process can obtain Superior grade ethylbenzene product. The first ethylbenzene tower conducts non-clear segmentation to obtain the superior grade of ethylbenzene, and the second ethylbenzene tower performs clear segmentation to obtain the first-grade ethylbenzene product. The liquid in the benzene tower enters the first ethylbenzene tower by self-pressure, and the feeding position of the first ethylbenzene tower is the 43rd theoretical plate. Grade ethylbenzene storage tank, the kettle liquid is a mixture of ethylbenzene, polyethylbenzene and high boilers, which enters the second ethylbenzene tower by self-pressure; the feeding position of the second ethylbenzene tower is the 30th theoretical plate, and the second ethylbenzene The ethylbenzene product (first-class product) distilled from the top of the benzene tower enters the first-class product ethylbenzene storage tank, and the still liquid enters the propylbenzene tower after being pressurized for subsequent separation. The operating pressure at the top of the first ethylbenzene tower is 0.53-0.55MPa (absolute pressure), the number of theoretical plates is 100, the operating reflux ratio is 12-13 (Mass), the temperature at the top of the tower is 212-214°C, and the recovery rate of ethylbenzene at the top of the tower is 79.5%, the xylene content of ethylbenzene products can be controlled below 1000PPM, reaching the standard of superior products. The operating pressure at the top of the second ethylbenzene tower is 0.35-0.45MPa (absolute pressure), the number of theoretical plates is 100, the feeding position is the 30th theoretical plate, the operating reflux ratio is controlled above 20 (Mass), and the temperature at the top of the tower is 190-202 °C, the recovery rate of ethylbenzene at the top of the tower is 99.5%, and the xylene content of the ethylbenzene product can be controlled below 1500PPM, reaching the first-grade product standard.

(3) Heat exchange network part (see accompanying drawing 7)

(1) The alkylation reaction product stream is used for preheating dry gas feed, circulating benzene feed, anti-alkylation feed and generating saturated steam, raising the grade of steam from 0.4MPa (gauge pressure) to 1.0MPa ( Gauge pressure), the amount of steam generated is 0.55GJ/ton of ethylbenzene.

(2) The oil gas at the top of the crude separation tower is used to preheat the dry gas feed, and the dry gas is heated from 40°C to 90°C to fully recover low-grade heat, and the recovered heat is 0.15GJ/ton of ethylbenzene.

(3) The ethylbenzene product of the ethylbenzene tower first preheats the fresh benzene feed, and heats the fresh benzene from 40°C to 140°C, fully recovers the waste heat, and recovers 0.14GJ/ton of ethylbenzene.

The effects and benefits of the present invention are to greatly reduce the unit consumption of ethylbenzene by dry process, save energy, and improve the grade of products; similar devices designed based on the above-mentioned series of schemes can greatly reduce energy consumption. The technology has good controllability and stability, and is beneficial to the transformation of existing devices.

Description of drawings

Figure 1: Partial process flow diagram of the alkylation reactor.

Figure 2: Process flow chart of the side line extraction process of the coarse separation tower.

Figure 3: Propylene tower-diethylbenzene tower process flow chart.

Figure 4: Diagram of optimized operating conditions for the propane column.

Figure 5: Flow chart of heat integration process of benzene tower and ethylbenzene tower.

Figure 6: Process flow chart of ethylbenzene refining twin towers.

Figure 7: Process flow chart of heat exchange network.

Attached drawings 1 to 7 are marked as follows:

1. Alkylation reactor 2. Chilled dry gas preheater 3. Main feed dry gas preheater 4. Chilled cycle benzene preheater 5. Main cycle benzene preheater 6. Crude separation tower 7. Benzene Tower 8. Coarse fractionation tower top condensing cooler 9. Absorption tower feed cooler 10. Crude fractionation tower reflux tank 11. Crude fractionation tower side line circulating benzene preheater 12. Circulating benzene buffer tank 13. Crude fractionation tower reflux pump 14. Benzene tower feed pump 15. Reactant - benzene tower feed preheater 16. Benzene tower top condensation cooler 17. Benzene circulating evaporator 18. Benzene tower reflux tank 19. Topping benzene cooler 20. B Benzene tower feed pump 21. Benzene tower reboiler 22. Propylene tower 23. Diethylbenzene tower 24. Propylene tower overhead condensing cooler 25. Propylene tower reflux tank 26. Propylene tower reflux pump 27. C Benzene cooler 28. Propylene tower reboiler 29. Diethylbenzene tower top condensation cooler 30. Diethylbenzene tower reflux tank 31. Diethylbenzene tower cooler 32. Diethylbenzene tower benzene tower reflux pump 33. Diethylbenzene tower reboiler 34. High boiler pump tank 35. Propylene tower 36. Propylene tower top condensation cooler 37. Propylene tower reflux tank 38. Propylene tower reflux pump 39. Propylene cooler 40 .Propylbenzene tower reboiler 41.Benzene tower 42.Ethylbenzene tower 43.Benzene tower top condensation cooler 44.Circulating benzene evaporation 45.Benzene tower reflux tank 46.Top benzene cooler 47.Ethylbenzene tower feed Pump 48. Benzene tower reboiler 49. Benzene tower intermediate reboiler 50. Ethylbenzene tower feed tank 51. Ethylbenzene tower top condensation cooler 52. Ethylbenzene tower reflux tank 53. Ethylbenzene tower reflux pump 54. Ethylbenzene cooler 55. Ethylbenzene tower reboiler 56. Polyethylbenzene tower feed pump 57. First ethylbenzene tower 58. Second ethylbenzene tower 59. Ethylbenzene tower feed tank 60. First ethylbenzene tower Tower top condensing cooler 61. First ethylbenzene tower reflux tank 62. First ethylbenzene tower reflux pump 63. First ethylbenzene tower ethylbenzene cooler 64. First ethylbenzene tower reboiler 65. Second ethylbenzene Tower top condensing cooler 66. Second ethylbenzene tower reflux tank 67. Second ethylbenzene tower reflux pump 68. Second ethylbenzene tower ethylbenzene cooler 69. Second ethylbenzene tower reboiler 70. Polyethylbenzene Tower feed pump 71. Quenching dry gas preheater 72. Main feed dry gas preheater 73. Main feed circulation benzene preheater 74. Chilling circulation benzene preheater 75. Circulation benzene evaporator 76. Reaction product-anti-alkylation feed heat exchanger 77. Reaction product-benzene tower feed No.2 heat exchanger 78. Reaction product-steam generator 79. Reaction product-benzene tower feed No.1 heat exchanger 80 .Reaction product-dry gas heat exchanger 81. Oil gas at the top of crude separation tower-dry gas heat exchanger 82. Ethylbenzene product-fresh benzene heat exchanger 83. Circulating benzene feed splitter 84. Chilled dry gas feed shunt.

Detailed ways:

Specific embodiments of the present invention will be described in detail below in conjunction with technical solutions and accompanying drawings.

Referring to a similar ethylbenzene plant with a production capacity of 6×10 ⁴ t/a, the comprehensive energy saving of the device in this scheme can reach 24GJ/h, and the unit energy consumption of the product is reduced from the original level by 3.2GJ/t (76×10 ⁴ kcal/t). The matching structure of energy recovery is optimized, and the 2t/h generated steam level is increased from 0.4MPa (gauge pressure) to 1.0MPa (gauge pressure). It can produce not only first-class ethylbenzene but also high-grade ethylbenzene, and the output of high-grade ethylbenzene can reach 4.8×10 ⁴ t/a. The invention is particularly suitable for energy-saving transformation of the existing process of producing ethylbenzene by alkylation of benzene and dry gas.

(1) The reaction part is detailed as follows:

After being washed with water, the catalytic dry gas enters the chilled dry gas preheater for heat exchange to 260°C and is divided into four paths, one of which is heated to 360°C by the main feed dry gas preheater and then enters the hydrocarbon as the main feed dry gas from the top The other three routes are used as chilled dry gas to enter the alkylation reactor from the stage; the circulating benzene is heated to 260°C by the chilled circulating benzene preheater and then divided into four routes, and one route is preheated by the main feed circulating benzene After the reactor is heated to 360°C, it enters the alkylation reactor as the main feed circulating benzene from the top, and the other three routes enter the alkylation reactor as chilling circulation benzene from the interstage; the inlet temperature of each stage of the alkylation reactor is controlled at 360-370 °C, the corresponding outlet temperature is maintained at 390-400 °C.

(2) The separation part is detailed as follows:

The first point:

The liquid phase is extracted from the 5th to 10th theoretical plate of the crude fractionation column, and the extracted product is pressurized and preheated as circulating benzene, and then mixed with the circulating benzene extracted from the benzene tower to the circulating benzene buffer tank. The output of the side stream is controlled to be 10 ⁴ kg/hr, the output temperature is 114-115°C, and the benzene content of the side stream product is 99.5% (Mass). Maintain the operating pressure of the crude separation tower at 0.55MPa (absolute pressure), and after the side line is withdrawn, the temperature at the bottom of the tower rises to 124.3°C. Since the feed amount of the benzene tower is reduced by 10 ⁴ kg/hr, the reflux flow of the benzene tower is reduced by 7000kg/hr, and the corresponding benzene tower reboiler load is reduced by 3.2GJ/hr.

Second point:

The mixture of polyethylbenzene and high boilers at the bottom of the ethylbenzene column enters the propylbenzene column by self-pressure, and the feed position is the seventh theoretical plate, the number of theoretical plates of the propylbenzene column is 20, the control column pressure is 0.43MPa (absolute pressure), and the reflux Ratio 20 (Mass), the tower top temperature is 225 ℃, and the purity of the propylbenzene product distilled from the tower top is 93% (Mass), and the recovery rate is 99.6% (Mass), and the propylbenzene is used as a product delivery device. The liquid in the propylbenzene tower enters the diethylbenzene tower by self-pressure, the feed position is the 22nd theoretical plate, the number of theoretical plates of the diethylbenzene tower is 30, the control tower pressure is 0.18MPa (absolute pressure), and the reflux ratio is 4 (Mass). The temperature at the top of the tower is 209° C. The purity of diethylbenzene product distilled from the top of the tower is 99% (Mass), and the recovery rate is 99.5% (Mass). Diethylbenzene enters the absorption tower as an absorbent, and high boilers are discharged from the system. Since both propylbenzene and diethylbenzene are vaporized and condensed only once, the reboiler loads of the propylbenzene tower and the diethylbenzene tower are reduced to 9.51GJ/hr and 1.15GJ/hr respectively. The consumption is reduced by 3.1GJ/hr.

Third point:

Through theoretical analysis, it can be seen that the theoretical plate number and reflux ratio of the propylene benzene column have not reached a suitable match. The number of theoretical plates of the propane column was increased from 20 to the appropriate number of theoretical plates of 30. Under the premise of ensuring product quality, the operating reflux ratio was correspondingly reduced from 20 (Mass) to the appropriate operating reflux ratio of 5 (Mass), and the propene column was optimized. operating conditions, so that the propylene tower reboiler load can be reduced by 6.84GJ/hr.

fourth point:

The feed to the benzene tower comes from the crude fractionation tower hydrocarbonate liquid and the reverse hydrocarbonate reactor reverse hydrocarbonate liquid, and the feed positions are respectively at the 45th and 49th theoretical plates; the pressure at the top of the benzene tower is 1.34MPa (absolute pressure); The oil and gas at the top of the tower first pass through the circulating benzene evaporator and generate corresponding low-pressure steam, and then enter the condensing cooler at the top of the benzene tower; After the cooler is cooled, the obtained liquid phase flows into the benzene tower reflux tank, and is pumped into the top of the benzene tower as reflux by the benzene tower reflux pump, and the obtained gas phase is transported to the crude separation tower; a part of the benzene tower kettle liquid is heated and vaporized by the benzene tower reboiler and returned In the tower, the other part is conveyed to the feed tank of the ethylbenzene tower by pressure; the circulating benzene is extracted from the side line of the benzene tower. The liquid phase is derived from the 46th theoretical plate of the benzene tower and enters the intermediate reboiler of the benzene tower. The temperature of the liquid phase is 216°C, the flow rate is 7×10 ⁴ kg/hr, and the gas-liquid mixing temperature after reboiling is 221°C. The 47th theoretical plate returns to the tower; the heat load of the middle reboiler of the benzene tower is about 7GJ/hr, and the load of the bottom reboiler of the benzene tower is 15.5GJ/hr. The feed to the ethylbenzene tower enters the ethylbenzene tower from the feed tank of the ethylbenzene tower in two ways, and the feeding position is at the 40th theoretical plate; the oil and gas at the top of the ethylbenzene tower enters the steam generator after being condensed by the intermediate reboiler 1.0MPa (absolute pressure) steam is generated, and part of the oil and gas is fully condensed and returned to the top of the ethylbenzene tower as reflux, and the other part enters the ethylbenzene product tank after cooling, and the liquid in the ethylbenzene tower enters the subsequent separation process by self-pressure. The pressure at the top of the ethylbenzene tower is 0.73MPa (absolute pressure), the temperature of the oil gas at the top of the tower is 229°C, and the load of the reboiler is 24GJ/hr. The output of ethylbenzene at the top of the tower is 7.556×10 ³ kg/hr, the recovery rate of ethylbenzene is 99.5%, and the xylene content of the ethylbenzene product can be controlled below 1500PPM, reaching the first-grade product standard. By adding an intermediate reboiler, the heat integration of the benzene tower and the ethylbenzene tower can be realized, and the heat carrier equivalent can be saved by 5.5GJ/hr.

Fifth:

The liquid in the benzene tower enters the first ethylbenzene tower from the 43rd theoretical plate by self-pressure, and part of the ethylbenzene (high-grade product) is distilled from the top of the first ethylbenzene tower, and enters the high-grade ethylbenzene storage tank. It is a mixture of ethylbenzene, polyethylbenzene and high boilers, and enters the second ethylbenzene tower by self-pressure; the feeding position of the second ethylbenzene tower is the 30th theoretical plate, and the ethylbenzene product is distilled from the top of the second ethylbenzene tower (First-class product) enters the first-class product ethylbenzene storage tank, and the still liquid enters the propylbenzene tower for subsequent separation after being pressurized. The operating pressure at the top of the first ethylbenzene tower is 0.53MPa (absolute pressure), the number of theoretical plates is 100, the operating reflux ratio is 13 (Mass), the temperature at the top of the tower is 212 ° C, the recovery rate of ethylbenzene at the top of the tower is 79.5%, and the ethylbenzene product The content of xylene can be controlled below 1000PPM, reaching the standard of superior products. The operating pressure at the top of the second ethylbenzene tower is 0.35-0.45 MPa (absolute pressure), the number of theoretical plates is 100, the feeding position is the 30th theoretical plate, the operating reflux ratio is 20 (Mass), and the temperature at the top of the tower is 190-202°C. The recovery rate of ethylbenzene at the top of the tower is 99.5%, and the xylene content of the ethylbenzene product can be controlled below 1500PPM, reaching the first-grade product standard.

(3) The heat exchange network part is described in detail as follows:

First, the alkylation product from the alkylation reactor passes through the reaction product-main feed circulation benzene heat exchanger, the reaction product-main feed dry gas heat exchanger, and the main feed dry gas and main feed circulation benzene are transferred from 260 °C is preheated to 360 °C, and the temperature of the hydrocarbonated product is correspondingly lowered to 370 °C. Then, the hydrocarbonated product passes through the reaction product-anti-alkylated feed heat exchanger to heat the anti-alkylated feed from 185°C to 260°C, and the temperature of the alkylated product drops to 348°C accordingly. The fresh benzene is preheated from 40°C to 140°C by the ethylbenzene product stream through the ethylbenzene product-fresh benzene heat exchanger, which makes full use of the heat of the ethylbenzene product at the top of the ethylbenzene tower, and can recover 1.05GJ/hr. The circulating benzene is heated from 177°C to 181°C by the oil gas at the top of the benzene tower through the circulating benzene evaporator, and then the vaporized circulating benzene is heated from 181°C to 260°C by the hydrocarbonated product through the reaction product-chilling circulating benzene heat exchanger, The temperature of the hydrocarbonated product dropped accordingly to 294°C. Then, the hydrocarbonated product passes through the reaction product-chilled dry gas heat exchanger to preheat the chilled dry gas from 120°C to 260°C. Then, the hydrocarbonated product passes through the reaction product-benzene tower feed No.2 heat exchanger to preheat the benzene tower feed from 120°C to 140°C, and the temperature of the hydrocarbonated product drops to 200°C accordingly. Then, the hydrocarbonated product passes through the reaction product-steam generator to generate 1.0 MPa (absolute pressure) saturated steam, and the temperature of the hydrocarbonated product drops to 190° C. correspondingly. Then, the hydrocarbonated product passes through the reaction product-benzene tower feed No.1 heat exchanger, the temperature of the benzene tower feed is raised from 140°C to 170°C, and the temperature of the hydrocarbonated product is correspondingly reduced to 165°C. The dry gas is preheated from 40°C to 90°C through the oil-gas-dry gas heat exchanger at the top of the crude fractionation tower. The dry gas preheater makes full use of the low-grade heat of the crude oil gas stream at the top of the crude fractionation tower, and can recover 1.17GJ/ hr. The hydrocarbonated product finally passes through the reaction product-dry gas heat exchanger to preheat the dry gas from 90°C to 120°C, and the temperature of the hydrocarbonated product drops to 140°C accordingly.

Claims (1)

1. An energy-saving method for the production of ethylbenzene by alkylation of benzene and dry gas, including the improvement of the process of the alkylation reaction, the recovery of recycled benzene from the side line of the crude separation tower, the separation sequence of the propylbenzene tower and the diethylbenzene tower, and the appropriate theory for designing the propylbenzene tower Number of plates, benzene tower-ethylbenzene tower heat integration, ethylbenzene tower adopts double-tower process, process heat recovery and heat exchange network improvement, characterized in that: 1). Improvement of the alkylation reaction process: improve the direct quenching method between the reactor stages, and use dry gas and circulating benzene to participate in the quenching between the reactor stages. The main feed temperature of dry gas and circulating benzene is 330-360°C, The gas and circulating benzene quench the feed stream temperature at 250-280°C, maintain the temperature rise of the catalyst bed at 30-50°C, and the temperature of the alkylation reaction product at the reactor outlet reaches 390-400°C, without the need for a raw material preheating furnace; 2). Extraction of circulating benzene from the side line of the crude separation tower: 10 ⁴ ~ 1.5×10 ⁴ kg/hr of circulating benzene is extracted from the liquid phase side line at the 5th to 10th theoretical plates of the crude separation tower; 3). Using propylbenzene tower-diethylbenzene tower separation sequence: using propylbenzene tower-diethylbenzene tower separation sequence, under the condition of ensuring the product quality and recovery rate of propylbenzene and diethylbenzene; 4). The suitable number of theoretical plates for the design of the propylene tower: the suitable number of theoretical plates for the design of the propylene tower is 30, and the operating reflux ratio is correspondingly designed to be a suitable reflux ratio of 5-6Mass; 5). Benzene tower-ethylbenzene tower heat integration: the pressure at the top of the benzene tower is 1.34MPa, the absolute pressure at the top of the ethylbenzene tower is 0.73-0.78MPa, and the oil gas at the top of the ethylbenzene tower is used as the heat source for the intermediate reboiler of the benzene tower; The benzene column is extracted from the liquid phase of the 46th theoretical plate, and returns to the gas-liquid two-phase at the 47th theoretical plate through the intermediate reboiler; the heat load of the intermediate reboiler is controlled not to exceed one-third of the total heating load of the entire tower; 6). The ethylbenzene tower adopts a double-tower process: ethylbenzene is refined using a double-tower process. The first ethylbenzene tower performs non-clear segmentation to obtain the superior grade of ethylbenzene, and the second ethylbenzene tower performs clear segmentation to obtain the first-grade ethylbenzene; The absolute operating pressure at the top of the first ethylbenzene tower is 0.53-0.55MPa, the recovery rate of ethylbenzene at the top of the tower is 79.5%, and the xylene content of the ethylbenzene product can be controlled below 1000PPM; the absolute operating pressure at the top of the second ethylbenzene tower is 0.35 ~0.45MPa, the recovery rate of ethylbenzene at the top of the tower is 99.5%, and the content of xylene in ethylbenzene products is controlled below 1500PPM; 7). Improvement of heat exchange network for process heat recovery: the grade of steam generated in the stream of alkylation reaction product is raised from gauge pressure 0.4MPa to gauge pressure 1.0MPa; The gas is heated from 40°C to 90°C; the ethylbenzene product of the ethylbenzene tower first preheats the fresh benzene feed, and the fresh benzene is heated from 40°C to 140°C.

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