Method and system for coupling RTC dry gas and ethylene device and improvement of ethylene device

Abstract

The invention belongs to the field of ethylene production devices, and discloses a method and a system for coupling RTC dry gas and an ethylene device and transformation of the ethylene device. The system comprises an ethylene rectifying tower unit, an original propylene refrigeration unit, a newly added propylene refrigeration unit, a cold box unit and an RTC ethylene-rich C2 gas feeding pipeline. According to the invention, the newly added cold box unit and the newly added propylene refrigeration unit are used for recovering cold energy in circulating ethane and a liquid-phase ethylene product of a modified system, so that the temperature and the operation difficulty of RTC dry gas entering an ethylene rectifying tower are reduced, the yield of the ethylene product is increased, and the influence degree on an original ethylene device is minimum; the investment cost and the construction period can be saved.

Description

Technical Field

[0001] The invention belongs to the field of ethylene production devices, and more specifically, relates to a method and system for coupling RTC dry gas with an ethylene device and the transformation of an ethylene device. Background Art

[0002] The heavy oil efficient catalytic cracking (RTC) process overcomes the disadvantage of the heavy oil catalytic cracking (DCC) process, which has poor selectivity for inferior heavy raw materials, and has been successfully applied in industry. The RTC process will produce a part of dry gas as a by-product, mainly including hydrogen, methane, ethane, ethylene, propylene, propane and other components. In order to realize the resource utilization of ethylene and other products, the dry gas produced by the RTC device can be concentrated.

[0003] The location where the concentrated dry gas enters the ethylene unit needs to be comprehensively analyzed in combination with the dry gas composition, land occupation and investment, so as to minimize the impact on the original ethylene unit. The existing technology is to obtain ethane-rich gas by concentrating the coking dry gas and directly send it to the ethane cracking furnace for cracking; the existing technology is to perform non-clear separation before the concentrated dry gas enters the ethylene unit, so that the dry gas containing light components such as ethylene and methane enters the demethanizer of the ethylene unit for separation and recovery; the existing technology is to receive the concentrated ethylene-rich gas in the third stage of the compressor of the cracking unit, which greatly increases the operating temperature and pressure of the ethylene distillation tower, increasing the difficulty of operation.

[0004] After concentration, RTC dry gas can be obtained as ethylene-rich carbon digas with a high ethylene concentration. If the composition is appropriate and the impurity content is within the allowable range, it can directly enter the ethylene distillation tower system for separation and purification to obtain polymerization-grade ethylene. It will not affect other main separation processes except the ethylene distillation tower system, nor will it affect the production and operation of the cracking furnace.

[0005] However, after the ethylene-rich carbon dioxide gas enters the ethylene distillation tower, the load of the ethylene distillation system will increase, especially the load of the top condenser of the ethylene distillation tower (1.56 times the original load). The refrigerant used in the top condenser of the ethylene distillation tower is -40℃ propylene refrigerant, which is the largest refrigerant user of the propylene refrigeration compressor of the ethylene plant, and the temperature is relatively low, usually accounting for 60-70% of the total power of the propylene refrigeration compressor. If the refrigeration is to rely on the original ethylene plant, after the RTC dry gas is introduced into the ethylene distillation tower, the propylene refrigeration machine system of the existing device needs to be adaptively modified, which increases the investment and the modification period is relatively long. In addition, the operating temperature of the ethylene distillation tower is relatively low. Receiving carbon dioxide-rich RTC dry gas at room temperature or above room temperature will affect the gas-liquid balance in the tower, resulting in increased difficulty in operation. In severe cases, it will cause the products of the top and bottom of the tower to be unqualified, resulting in local parking and material loss.

[0006] Therefore, how to energy couple RTC dry gas with ethylene plants will be a critical research content and direction, which will have a great impact on the scope of capacity expansion and transformation of ethylene plants, construction investment, land occupation, and operational stability of the plants. Summary of the invention

[0007] The purpose of the present invention is to address the defects of the prior art and propose a method and system for coupling RTC dry gas with an ethylene device and the transformation of an ethylene device. The present invention utilizes a newly added cold box unit and a newly added propylene refrigeration unit to recover the cold in the circulating ethane and liquid ethylene products of the transformed system, reduces the temperature and operation difficulty of the RTC dry gas entering the ethylene distillation tower, increases the production of ethylene products and minimizes the impact on the original ethylene device, thereby saving investment costs and construction period.

[0008] In order to achieve the above-mentioned object, the first aspect of the present invention provides a system for coupling RTC dry gas with an ethylene device, the system comprising an ethylene rectification tower unit, an original propylene refrigeration unit, an additional propylene refrigeration unit, a cold box unit and an RTC ethylene-rich carbon two gas feed pipeline;

[0009] The ethylene distillation tower unit comprises an ethylene distillation tower, an ethylene distillation tower condenser subunit and an ethylene distillation tower reboiler subunit; the ethylene distillation tower is provided with a C2 feed port, a liquid ethylene product outlet, an ethylene distillation tower bottom ethane outlet and an RTC ethylene-rich carbon two gas feed port;

[0010] The pipeline of the liquid ethylene product outlet is connected to the gaseous ethylene product pipeline through the cold box unit; the ethane outlet at the bottom of the ethylene distillation tower is connected to the first ethane circulation pipeline and the second ethane circulation pipeline; the first ethane circulation pipeline is connected to the cracking furnace through the cold box unit; the RTC ethylene-rich carbon digas feed pipeline is connected to the RTC ethylene-rich carbon digas feed port through the cold box unit;

[0011] The cold box unit is used to realize the recovery of the coldness of the liquid ethylene product and part of the ethane obtained by the ethylene distillation tower using the propylene refrigerant from the newly added propylene refrigeration unit;

[0012] The original propylene refrigeration unit and the newly added propylene refrigeration unit simultaneously provide cooling capacity for the ethylene distillation tower condenser subunit and provide a heat source for the ethylene distillation tower reboiler subunit.

[0013] According to the present invention, preferably, the ethylene distillation tower unit further comprises a boiler in the ethylene distillation tower.

[0014] According to the present invention, preferably, the ethylene distillation tower is connected to the C2 hydrogenation system via the C2 feed port.

[0015] According to the present invention, preferably, the second ethane circulating pipeline liquid is directly connected to the cracking furnace.

[0016] According to the present invention, preferably, the cold box unit comprises 4-6 heat exchangers, preferably the cold box unit comprises four heat exchangers, namely a first heat exchanger, a second heat exchanger, a third heat exchanger and an ethylene product vaporizer;

[0017] The pipeline of the liquid-phase ethylene product outlet is connected to the gas-phase ethylene product pipeline through the cold side inlet of the first heat exchanger, the cold side outlet of the first heat exchanger, the second heat exchanger, the cold side inlet of the ethylene product vaporizer, the cold side outlet of the ethylene product vaporizer and the third heat exchanger in sequence;

[0018] The first ethane circulation pipeline is connected to the cracking furnace through the cold side inlet of the first heat exchanger, the cold side outlet of the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence;

[0019] The RTC ethylene-rich carbon digas feed pipeline is connected to the RTC ethylene-rich carbon digas feed port of the ethylene rectification tower through the third heat exchanger and the second heat exchanger in sequence.

[0020] According to the present invention, preferably, the newly added propylene refrigeration unit comprises a two-stage propylene refrigeration compressor, a water cooler, a first buffer tank, an interstage tank, a second buffer tank, and optionally a third buffer tank;

[0021] The two-stage propylene refrigeration compressor is provided with a connecting pipeline of a primary outlet and a connecting pipeline of a secondary outlet; the connecting pipeline of the primary outlet is connected to the first hot side inlet of the ethylene product vaporizer; the connecting pipeline of the secondary outlet is connected to the second hot side inlet of the ethylene product vaporizer through the water cooler and the first buffer tank in sequence;

[0022] The first hot side outlet of the ethylene product vaporizer is divided into two pipelines, one pipeline is connected to the secondary inlet of the two-stage propylene refrigeration compressor;

[0023] The second hot side outlet of the ethylene product vaporizer is connected to the interstage tank, and the interstage tank is provided with a tank top outlet and a tank bottom outlet; the pipeline of the tank top outlet is connected to the hot side inlet of the ethylene distillation tower reboiler subunit together with another pipeline of the first hot side outlet of the ethylene product vaporizer;

[0024] The hot side outlet of the ethylene rectification tower reboiler subunit is connected to the first hot side inlet of the first heat exchanger. Optionally, the hot side outlet of the ethylene rectification tower reboiler subunit is connected to the first hot side inlet of the first heat exchanger through the third buffer tank; the pipeline of the tank bottom outlet is connected to the second hot side inlet of the first heat exchanger;

[0025] The first hot side outlet of the first heat exchanger and the second hot side outlet of the first heat exchanger are both connected to the cold side inlet of the ethylene distillation tower condenser subunit; the cold side outlet of the ethylene distillation tower condenser subunit is connected to the first-stage inlet of the two-stage propylene refrigeration compressor through the second buffer tank.

[0026] According to the present invention, preferably, the ethylene distillation tower is further provided with a tower top outlet, a tower top reflux port, a tower bottom outlet and a tower bottom reflux port;

[0027] The ethylene rectification tower condenser subunit is a high-load condenser, and the ethylene rectification tower reboiler subunit is a high-load reboiler (in the present invention, the load is determined by the RTC dry gas feed amount);

[0028] The hot side inlet of the high-load condenser is connected to the tower top outlet, the hot side outlet of the high-load condenser is connected to the tower top reflux tank of the ethylene distillation tower, the tank bottom material outlet of the tower top reflux tank is connected to the tower top reflux port through a reflux pump; the cold side inlet of the high-load reboiler is connected to the tower bottom outlet; the cold side outlet of the high-load reboiler is connected to the tower bottom reflux port;

[0029] or,

[0030] The ethylene rectification tower condenser subunit includes an original condenser and a newly added condenser; the ethylene rectification tower reboiler subunit includes an original reboiler and a newly added reboiler; the original propylene refrigeration unit provides cooling capacity for the original condenser and a heat source for the original reboiler; the pipeline of the tank top outlet is connected to the hot side inlet of the newly added reboiler together with another pipeline of the first hot side outlet of the ethylene product vaporizer; the first hot side outlet of the first heat exchanger and the second hot side outlet of the first heat exchanger are both connected to the cold side inlet of the newly added condenser;

[0031] The hot side inlets of the original condenser and the newly added condenser are both connected to the tower top outlet; the hot side outlets of the original condenser and the newly added condenser are both connected to the tower top reflux tank of the ethylene distillation tower, and the tank bottom material outlet of the tower top reflux tank is connected to the tower top reflux port through a reflux pump; the cold side inlets of the original reboiler and the newly added reboiler are both connected to the tower bottom outlet; the cold side outlets of the original reboiler and the newly added reboiler are both connected to the tower bottom reflux port.

[0032] A second aspect of the present invention provides a method for modifying an ethylene device, the method for modifying an ethylene device is used to obtain the system for coupling the RTC dry gas with the ethylene device, comprising the following steps:

[0033] Set up an RTC ethylene-rich carbon digas feed port in the ethylene distillation tower; set up a cold box unit, a new propylene refrigeration unit and an RTC ethylene-rich carbon digas feed pipeline;

[0034] Connecting the RTC ethylene-rich carbon digas feed pipeline to the RTC ethylene-rich carbon digas feed port through the cold box unit;

[0035] The ethane outlet at the bottom of the ethylene distillation tower is connected to the first ethane circulation pipeline and the second ethane circulation pipeline respectively; the first ethane circulation pipeline liquid is connected to the cracking furnace through the cold box unit;

[0036] Connecting the pipeline of the liquid-phase ethylene product outlet of the ethylene rectification tower to the gas-phase ethylene product pipeline through the cold box unit;

[0037] Using propylene refrigerant from the newly added propylene refrigeration unit to recover the cold of the liquid ethylene product and part of the ethane obtained in the ethylene distillation tower in the cold box unit;

[0038] The original propylene refrigeration unit of the ethylene distillation tower and the newly added propylene refrigeration unit simultaneously provide cooling capacity for the condenser subunit of the ethylene distillation tower and provide a heat source for the reboiler subunit of the ethylene distillation tower.

[0039] A third aspect of the present invention provides a method for coupling RTC dry gas with an ethylene device, the method using the system for coupling RTC dry gas with an ethylene device, comprising the following steps:

[0040] S1: Cooling the RTC ethylene-rich carbon digas through the cold box unit and then sending it to the ethylene distillation tower; sending C2 to the ethylene distillation tower; obtaining the top gas at the top of the ethylene distillation tower, producing the liquid ethylene product at the side line of the tower, and obtaining ethane and the bottom reflux liquid logistics at the bottom of the tower;

[0041] S2: using the propylene refrigerant from the newly added propylene refrigeration unit to recover the cold of the liquid ethylene product and part of the ethane in the cold box unit; obtaining the gaseous ethylene product and sending it out of the boundary area, and returning the ethane after the cold is recovered to the cracking furnace for cyclic cracking;

[0042] The tower bottom reflux liquid phase stream is sent to the ethylene rectification tower reboiler subunit, and heated by the original propylene refrigeration unit and the newly added propylene refrigeration unit to obtain a tower bottom heated stream;

[0043] The tower top gas is sent to the condenser subunit of the ethylene distillation tower, and condensed by the original propylene refrigeration unit and the newly added propylene refrigeration unit to obtain the tower top condensate flow.

[0044] According to the present invention, preferably, in step S1:

[0045] The RTC ethylene-rich carbon digas is an RTC dry gas that has been concentrated and impurities removed, wherein, based on the total molar amount of the RTC ethylene-rich carbon digas, the ethylene content is 60-80 mol%, the ethane content is 25-40 mol%, the methane content is 0.01-0.1 mol%, the acetylene content is <1 ppm, the carbon three content is <0.1 mol%, and the water content is <1 ppm;

[0046] The temperature of the RTC ethylene-rich carbon digas is 8-60°C and the pressure is 1.8-2.8MPaG;

[0047] The temperature of the RTC ethylene-rich carbon digas after cooling is -10 to -5°C;

[0048] The C2 comes from the carbon dihydrogenation system.

[0049] According to the present invention, preferably, in step S2,

[0050] The liquid-phase ethylene product is sequentially passed through the first heat exchanger, the second heat exchanger, the ethylene product vaporizer and the third heat exchanger of the cold box unit to recover cold; the liquid-phase ethylene product is a polymerization-grade ethylene product with a purity of 99.94-99.96 mol%;

[0051] A portion of the ethane is sequentially passed through the first heat exchanger, the second heat exchanger and the third heat exchanger of the cold box unit to recover cold and then returned to the cracking furnace for cyclic cracking; the remaining portion of the ethane is directly returned to the cracking furnace for cyclic cracking; preferably, the ratio of the ethane recovered by the cold box unit to the ethane directly returned to the cracking furnace is 1:(0.8-1.2);

[0052] The process flow of recovering the cold of the liquid ethylene product and part of the ethane in the cold box unit by using the propylene refrigerant from the newly added propylene refrigeration unit comprises:

[0053] The propylene refrigerant at the primary outlet of the two-stage propylene refrigeration compressor and the propylene refrigerant at the secondary outlet of the two-stage propylene refrigeration compressor flowing through the water cooler and the first buffer tank are heat exchanged with the liquid-phase ethylene product after the cooling capacity is recovered by the first heat exchanger and the second heat exchanger in the ethylene product vaporizer to obtain a vaporized ethylene product, a cooled primary propylene refrigerant and a cooled secondary propylene refrigerant; the vaporized ethylene product is recovered by the third heat exchanger to obtain a gas-phase ethylene product and sent out of the boundary area;

[0054] The cooled secondary propylene refrigerant is sent into the interstage tank to obtain the tank top outlet material and the tank bottom outlet material; the cooled primary propylene refrigerant is divided into two parts, one part is used together with the tank top outlet material as the heat source of the ethylene rectification tower reboiler subunit to obtain a further cooled propylene refrigerant; the remaining part is refluxed to the secondary inlet of the two-stage propylene refrigeration compressor; preferably, the ratio of the cooled primary propylene refrigerant used as the heat source of the ethylene rectification tower reboiler subunit to the cooled primary propylene refrigerant refluxed to the secondary inlet of the two-stage propylene refrigeration compressor is (1.1-1.5):1;

[0055] The further cooled propylene refrigerant and the tank bottom outlet material are heat exchanged with the liquid ethylene product and a portion of ethane in the first heat exchanger to obtain the liquid ethylene product with recovered cold, the ethane with recovered cold and the further cooled propylene refrigerant;

[0056] After the re-cooled propylene refrigerant is used to provide cooling for the ethylene rectification tower condenser subunit, the propylene refrigerant after providing cooling is sent to the first inlet of the two-stage propylene refrigeration compressor through the second buffer tank; the ethane with recovered cooling is returned to the cracking furnace for cyclic cracking after the cooling is recovered through the second heat exchanger and the third heat exchanger;

[0057] Preferably, the temperature of the propylene refrigerant at the primary outlet is 30-40°C, the temperature of the propylene refrigerant at the secondary outlet is 80-100°C, and the temperature of the propylene refrigerant at the secondary outlet after flowing through the water cooler and the first buffer tank is 35-45°C.

[0058] According to the present invention, preferably, the cooled primary propylene refrigerant is divided into two parts, one part is used together with the tank top outlet material as the heat source of the newly added reboiler;

[0059] The re-cooled propylene refrigerant is used to provide cooling capacity for the newly added condenser.

[0060] According to the present invention, preferably, the bottom heating stream is refluxed to the bottom of the ethylene distillation tower;

[0061] According to the present invention, preferably, the tower top condensate stream is sent to the tower top reflux tank to obtain the tank bottom material and reflux to the tower top of the ethylene distillation tower through the reflux pump.

[0062] The beneficial effects of the technical solution of the present invention are as follows:

[0063] The present invention utilizes the newly added cold box unit and the newly added propylene refrigeration unit to recover the cold in the circulating ethane and liquid ethylene products of the modified system of the present invention, reduces the temperature of the RTC dry gas entering the ethylene distillation tower, improves the operating difficulty of the ethylene distillation tower, reduces the power of the newly added propylene refrigeration compressor by 20-40%, and thus reduces the comprehensive energy consumption of the modified system. Moreover, the system and method of the present invention have no effect on most of the equipment of the original ethylene device, can greatly shorten the period of modification and construction, and can save investment costs.

[0064] For the system in which the RTC dry gas enters the ethylene distillation tower without cooling in Comparative Example 1 of the present invention, if the purity of the ethylene product and the ethylene recovery rate in the RTC dry gas are to be ensured to be the same as those of the present invention, the load of the top condenser of the ethylene distillation tower of the system may be 5 times the total load of the condenser subunits of the ethylene distillation tower under the coupled system of the present invention, and the load of the bottom reboiler of the ethylene distillation tower of the system may be 8 times the total load of the reboiler subunits of the ethylene distillation tower under the coupled system of the present invention.

[0065] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0067] Figure 1 A schematic diagram of a system for coupling RTC dry gas and an ethylene device provided in Example 1 of the present invention is shown.

[0068] Figure 2 A schematic diagram showing a system in which a cold box unit of a system of coupling RTC dry gas and an ethylene device provided in Example 1 of the present invention utilizes a newly added propylene refrigeration unit to recover cold energy.

[0069] The following are the descriptions of the reference numerals:

[0070] 1-ethylene distillation tower; 2-original condenser; 2-1-newly added condenser; 3-original reboiler; 3-1-newly added reboiler; 4-boiler in ethylene distillation tower; 5-tower top reflux tank; 6-reflux pump; 7-first heat exchanger; 8-second heat exchanger; 9-third heat exchanger; 10-ethylene product vaporizer; 11-two-stage propylene refrigeration compressor; 12-water cooler; 13-first buffer tank; 14-interstage tank; 15-second buffer tank; 16-RTC ethylene-rich carbon digas feed pipeline; 17-C2 feed port; 18-liquid ethylene product outlet; 19-ethylene distillation tower bottom ethane outlet; 20-RTC ethylene-rich C2 gas feed inlet; 21-first ethane circulation pipeline; 22-second ethane circulation pipeline; 24-gas phase ethylene product pipeline; 25-third buffer tank; 26-primary outlet; 27-secondary outlet; 28-secondary inlet; 29-tank top outlet; 30-tank bottom outlet; 31-primary inlet; 32-ethane after cold recovery; 33-liquid phase ethylene product after cold recovery by the first heat exchanger and the second heat exchanger; 34-vaporized ethylene product; 35-tank top outlet material; 36-tank bottom outlet material; 37-liquid phase ethylene product; 38-a portion of ethane; 39-liquid phase logistics refluxed from the bottom of the tower; 40-tower top gas. DETAILED DESCRIPTION

[0071] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0072] Example 1

[0073] This embodiment provides a system for coupling RTC dry gas with an ethylene device, such as Figure 1 , 2 As shown, the system includes an ethylene distillation tower unit, an original propylene refrigeration unit, an additional propylene refrigeration unit, a cold box unit and an RTC ethylene-rich carbon two gas feed pipeline 16;

[0074] The ethylene distillation tower unit comprises an ethylene distillation tower 1, an original condenser 2, a newly added condenser 2-1, an ethylene distillation tower mid-boiler 4, an original reboiler 3 and a newly added reboiler 3-1; the ethylene distillation tower 1 is provided with a C2 feed port 17, a liquid ethylene product outlet 18, an ethylene distillation tower bottom ethane outlet 19 and an RTC ethylene-rich carbon two gas feed port 20;

[0075] The ethylene distillation tower 1 is connected to a carbon two hydrogenation system (not shown) via the C2 feed port 17;

[0076] The ethane outlet 19 at the bottom of the ethylene distillation tower is connected to a first ethane circulation pipeline 21 and a second ethane circulation pipeline 22; the second ethane circulation pipeline liquid 22 is directly connected to the cracking furnace (not shown);

[0077] The cold box unit is used to realize the recovery of the coldness of the liquid ethylene product and part of the ethane obtained by the ethylene distillation tower 1 using the propylene refrigerant from the newly added propylene refrigeration unit; the cold box unit includes four heat exchangers, namely, a first heat exchanger 7, a second heat exchanger 8, a third heat exchanger 9 and an ethylene product vaporizer 10;

[0078] The pipeline of the liquid-phase ethylene product outlet 18 is connected to the gas-phase ethylene product pipeline 24 through the cold side inlet of the first heat exchanger 7, the cold side outlet of the first heat exchanger 7, the second heat exchanger 8, the cold side inlet of the ethylene product vaporizer 10, the cold side outlet of the ethylene product vaporizer 10 and the third heat exchanger 9 in sequence; the gas-phase ethylene product pipeline 24 is connected outside the boundary area.

[0079] The first ethane circulation pipeline 21 is connected to the cracking furnace through the cold side inlet of the first heat exchanger 7, the cold side outlet of the first heat exchanger 7, the second heat exchanger 8, and the third heat exchanger 9 in sequence;

[0080] The RTC ethylene-rich carbon digas feed pipeline 16 is connected to the RTC ethylene-rich carbon digas feed port 20 of the ethylene distillation tower 8 through the third heat exchanger 9 and the second heat exchanger in sequence.

[0081] The original propylene refrigeration unit provides cooling capacity for the original condenser 2 and provides a heat source for the original reboiler 3 .

[0082] The newly added propylene refrigeration unit includes a two-stage propylene refrigeration compressor 11, a water cooler 12, a first buffer tank 13, an interstage tank 14, a second buffer tank 15 and a third buffer tank 25;

[0083] The two-stage propylene refrigeration compressor 11 is provided with a connecting pipeline of a primary outlet 26 and a connecting pipeline of a secondary outlet 27; the connecting pipeline of the primary outlet 26 is connected to the first hot side inlet of the ethylene product vaporizer 10; the connecting pipeline of the secondary outlet 27 is connected to the second hot side inlet of the ethylene product vaporizer 10 through the water cooler 12 and the first buffer tank 13 in sequence;

[0084] The first hot side outlet of the ethylene product vaporizer 10 is divided into two pipelines, one pipeline is connected to the secondary inlet 28 of the two-stage propylene refrigeration compressor;

[0085] The second hot side outlet of the ethylene product vaporizer 10 is connected to the interstage tank 14, and the interstage tank 14 is provided with a tank top outlet 29 and a tank bottom outlet 30; the pipeline of the tank top outlet 29 and another pipeline of the first hot side outlet of the ethylene product vaporizer 10 are connected to the hot side inlet of the newly added reboiler 3-1;

[0086] The hot side outlet of the newly added reboiler 3-1 is connected to the first hot side inlet of the first heat exchanger 7 through the third buffer tank 25; the pipeline of the tank bottom outlet 30 is connected to the second hot side inlet of the first heat exchanger 7;

[0087] The first hot side outlet of the first heat exchanger 7 and the second hot side outlet of the first heat exchanger 7 are both connected to the cold side inlet of the newly added condenser 2-1; the cold side outlet of the newly added condenser 2-1 is connected to the first-stage inlet 31 of the two-stage propylene refrigeration compressor 11 through the second buffer tank 15.

[0088] The ethylene distillation tower is also provided with a top outlet, a top reflux port, a bottom outlet and a bottom reflux port; the hot side inlets of the original condenser 2 and the newly added condenser 2-1 are both connected to the top outlet; the hot side outlets of the original condenser 2 and the newly added condenser 2-1 are both connected to the top reflux tank 5 of the ethylene distillation tower, and the tank bottom material outlet of the top reflux tank 5 is connected to the top reflux port through a reflux pump 6; the cold side inlets of the original reboiler 3 and the newly added reboiler 3-1 are both connected to the bottom outlet; the cold side outlets of the original reboiler 3 and the newly added reboiler 3-1 are both connected to the bottom reflux port.

[0089] The method for coupling RTC dry gas with an ethylene device using the above system comprises the following steps:

[0090] S1: The RTC ethylene-rich carbon dioxide gas (temperature is 42°C, pressure is 1.8-2.8MPaG) is sent to the ethylene distillation tower 1 (corresponding to a tray temperature of -25°C) after passing through the third heat exchanger 9 (reduced to 0.34°C), and the second heat exchanger 8 is cooled (reduced to -6.7°C); C2 from the carbon dioxide hydrogenation system is sent to the ethylene distillation tower 1; the top gas is obtained at the top of the ethylene distillation tower, and a liquid ethylene product is produced from the side line of the tower (the liquid ethylene product is a polymerization-grade ethylene product with a purity of 99.95mol% and a flow rate of 41t / h), and ethane and a bottom reflux liquid logistics are obtained at the bottom of the tower;

[0091] The RTC ethylene-rich carbon digas is RTC dry gas that has been concentrated and impurities removed, and based on the total molar amount of the RTC ethylene-rich carbon digas, the ethylene content is 68.5 mol%, the ethane content is 31.3 mol%, the methane content is 0.1 mol%, the acetylene content is <1 ppm, the carbon three content is 0.1 mol%, and the water content is <1 ppm;

[0092] The refrigerant of the original condenser 2 is the -40°C propylene refrigerant provided by the original propylene refrigeration unit, the heat source of the boiler 4 in the ethylene distillation tower is the ethylene refrigerant of the ethylene refrigeration system, and the heat source of the original reboiler 3 is the propylene refrigerant of the original propylene refrigeration unit;

[0093] S2: using the propylene refrigerant from the newly added propylene refrigeration unit to recover the cold of the liquid ethylene product and part of the ethane in the cold box unit; wherein:

[0094] The liquid ethylene product is sequentially passed through the first heat exchanger 7, the second heat exchanger 8, the ethylene product vaporizer 10 and the third heat exchanger 9 of the cold box unit to recover cold energy;

[0095] A portion of the ethane is sequentially passed through the first heat exchanger 7, the second heat exchanger 8 and the third heat exchanger 9 (heated to 30° C.) of the cold box unit to recover cold and then returned to the cracking furnace for cyclic cracking; the remaining portion of the ethane is directly returned to the cracking furnace for cyclic cracking; the ratio of the ethane recovered by the cold box unit and the ethane directly returned to the cracking furnace is 1:1;

[0096] The process flow of the propylene refrigerant of the newly added propylene refrigeration unit in the cold box unit includes:

[0097] The propylene refrigerant (35.5°C) at the primary outlet 26 of the two-stage propylene refrigeration compressor and the propylene refrigerant (outlet temperature is 82.6°C, 40°C after water cooling) at the secondary outlet 28 of the two-stage propylene refrigeration compressor flowing through the water cooler 12 and the first buffer tank 13 are heat exchanged with the liquid-phase ethylene product 33 after the cold is recovered by the first heat exchanger 7 and the second heat exchanger 8 in the ethylene product vaporizer 10 to obtain a vaporized ethylene product 34, a cooled primary propylene refrigerant and a cooled secondary propylene refrigerant; the vaporized ethylene product is recovered by the third heat exchanger 9 (superheated to 30°C) to obtain a gas-phase ethylene product and sent out of the boundary area;

[0098] The cooled secondary propylene refrigerant is sent to the interstage tank 14 to obtain the tank top outlet material 35 and the tank bottom outlet material (-2.4°C) 36; the cooled primary propylene refrigerant is divided into two parts, one part is used together with the tank top outlet material 35 as the heat source of the newly added reboiler 3-1 to obtain a further cooled propylene refrigerant (-3.1°C); the remaining part is refluxed to the secondary inlet 28 of the two-stage propylene refrigeration compressor; the ratio of the cooled primary propylene refrigerant used as the heat source of the newly added reboiler 3-1 to the cooled primary propylene refrigerant refluxed to the secondary inlet 28 of the two-stage propylene refrigeration compressor is 1.3:1;

[0099] The further cooled propylene refrigerant (-3.1°C) and the tank bottom outlet material (-2.4°C) 36 are heat exchanged with the liquid ethylene product 37 and a portion of ethane 38 in the first heat exchanger 7 to obtain the liquid ethylene product with recovered cold, the ethane with recovered cold and the further cooled propylene refrigerant;

[0100] After the re-cooled propylene refrigerant is used to provide -40°C cooling capacity for the newly added condenser 2-1, the propylene refrigerant with the provided cooling capacity is sent to the first-stage inlet 31 of the two-stage propylene refrigeration compressor through the second buffer tank 15; the ethane with recovered cooling capacity is returned to the cracking furnace for cyclic cracking after the cooling capacity is recovered through the second heat exchanger 8 and the third heat exchanger 9;

[0101] The tower bottom reflux liquid phase stream 39 is sent to the ethylene rectification tower reboiler subunit, and heated by the original propylene refrigeration unit and the newly added propylene refrigeration unit to obtain a tower bottom heated stream;

[0102] The tower top gas 40 is sent to the condenser subunit of the ethylene distillation tower, and condensed by the original propylene refrigeration unit and the newly added propylene refrigeration unit to obtain a tower top condensate stream. The tower top condensate stream is sent to the tower top reflux tank 5 to obtain a tank bottom material and reflux to the top of the ethylene distillation tower through the reflux pump 6.

[0103] In this embodiment:

[0104] The original condenser load remains unchanged at 10.9MW, and the load of the newly added condenser 2-1 is 6.2MW;

[0105] The original condenser load remains unchanged at 6.2MW, and the load of the newly added reboiler 3-1 is 4.0MW;

[0106] The power of the compressor of the original propylene refrigeration unit remains unchanged, and the power of the two-stage propylene refrigeration compressor 11 of the newly added propylene refrigeration unit is 2061kW;

[0107] The power of the water cooler 12 is 2.6 kW.

[0108] Comparative Example 1

[0109] This comparative example provides a method for feeding RTC dry gas into the system described in Example 1 to obtain polymerization-grade ethylene. The difference between this comparative example and Example 1 is only that:

[0110] The RTC ethylene-rich carbon digas (temperature of 42° C., pressure of 1.8-2.8 MPaG) is directly fed into the ethylene distillation tower 1 (corresponding to a tower plate temperature of -23° C.).

[0111] Such a large temperature difference between the RTC ethylene-rich carbon digas (42°C) and the corresponding plate (-23°C) of the ethylene distillation tower 1 will cause a large amount of vaporization of the liquid phase on the plate, which is not conducive to gas-liquid mass transfer, and the temperature in the tower will also fluctuate greatly, which is obviously not conducive to maintaining the stability of operation. However, in Example 1, the temperature difference between the RTC ethylene-rich carbon digas (-6.7°C) entering the ethylene distillation tower 1 and the corresponding plate (-25°C) of the ethylene distillation tower 1 is greatly reduced, reducing the difficulty of operating the ethylene distillation tower.

[0112] The total load of the ethylene distillation column condenser subunit is 84.1MW;

[0113] The total load of the ethylene distillation column reboiler subunit is 76.7MW;

[0114] The power of the compressor of the original propylene refrigeration unit remains unchanged, and the power of the two-stage propylene refrigeration compressor 11 of the newly added propylene refrigeration unit is 2926 kW; compared with comparative example 1, the power consumption of Example 1 is reduced by 865 kW.

[0115] The power of the water cooler 12 is 5.6kW

[0116] The purity and flow rate of the liquid ethylene product obtained are the same as those in Example 1.

[0117] Compared with comparative example 1, the comprehensive energy consumption reduction in example 1 is equivalent to 6.3 kg standard oil / ton of ethylene product (the energy conversion coefficient refers to "GB30250-2013 Energy Consumption Limits per Unit Product of Ethylene Plant").

[0118] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A system for coupling RTC dry gas with an ethylene device, characterized in that: The system includes an ethylene rectification tower unit, an original propylene refrigeration unit, a newly added propylene refrigeration unit, a cold box unit and an RTC ethylene-rich carbon two gas feed pipeline; The ethylene distillation tower unit comprises an ethylene distillation tower, an ethylene distillation tower condenser subunit and an ethylene distillation tower reboiler subunit; the ethylene distillation tower is provided with a C2 feed port, a liquid ethylene product outlet, an ethylene distillation tower bottom ethane outlet and an RTC ethylene-rich carbon two gas feed port; The pipeline of the liquid ethylene product outlet is connected to the gaseous ethylene product pipeline through the cold box unit; the ethane outlet at the bottom of the ethylene distillation tower is connected to the first ethane circulation pipeline and the second ethane circulation pipeline; the first ethane circulation pipeline is connected to the cracking furnace through the cold box unit; the RTC ethylene-rich carbon digas feed pipeline is connected to the RTC ethylene-rich carbon digas feed port through the cold box unit; The cold box unit is used to realize the recovery of the coldness of the liquid ethylene product and part of the ethane obtained by the ethylene distillation tower using the propylene refrigerant from the newly added propylene refrigeration unit; The original propylene refrigeration unit and the newly added propylene refrigeration unit simultaneously provide cooling capacity for the ethylene distillation tower condenser subunit and provide a heat source for the ethylene distillation tower reboiler subunit.

2. The system of coupling RTC dry gas with ethylene device according to claim 1, wherein: The ethylene distillation tower unit also includes a boiler in the ethylene distillation tower; The ethylene distillation tower is connected to the carbon two hydrogenation system through the C2 feed port; The second ethane circulating pipeline liquid is directly connected to the cracking furnace.

3. The system of coupling RTC dry gas with ethylene device according to claim 1, wherein: The cold box unit includes 4-6 heat exchangers, preferably the cold box unit includes four heat exchangers, namely a first heat exchanger, a second heat exchanger, a third heat exchanger and an ethylene product vaporizer; The pipeline of the liquid-phase ethylene product outlet is connected to the gas-phase ethylene product pipeline through the cold side inlet of the first heat exchanger, the cold side outlet of the first heat exchanger, the second heat exchanger, the cold side inlet of the ethylene product vaporizer, the cold side outlet of the ethylene product vaporizer and the third heat exchanger in sequence; The first ethane circulation pipeline is connected to the cracking furnace through the cold side inlet of the first heat exchanger, the cold side outlet of the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence; The RTC ethylene-rich carbon digas feed pipeline is connected to the RTC ethylene-rich carbon digas feed port of the ethylene distillation tower through the third heat exchanger and the second heat exchanger in sequence.

4. The system of coupling RTC dry gas with ethylene device according to claim 3, wherein: The newly added propylene refrigeration unit includes a two-stage propylene refrigeration compressor, a water cooler, a first buffer tank, an interstage tank, a second buffer tank, and optionally a third buffer tank; The two-stage propylene refrigeration compressor is provided with a connecting pipeline of a primary outlet and a connecting pipeline of a secondary outlet; the connecting pipeline of the primary outlet is connected to the first hot side inlet of the ethylene product vaporizer; the connecting pipeline of the secondary outlet is connected to the second hot side inlet of the ethylene product vaporizer through the water cooler and the first buffer tank in sequence; The first hot side outlet of the ethylene product vaporizer is divided into two pipelines, one pipeline is connected to the secondary inlet of the two-stage propylene refrigeration compressor; The second hot side outlet of the ethylene product vaporizer is connected to the interstage tank, and the interstage tank is provided with a tank top outlet and a tank bottom outlet; the pipeline of the tank top outlet is connected to the hot side inlet of the ethylene distillation tower reboiler subunit together with another pipeline of the first hot side outlet of the ethylene product vaporizer; The hot side outlet of the ethylene rectification tower reboiler subunit is connected to the first hot side inlet of the first heat exchanger. Optionally, the hot side outlet of the ethylene rectification tower reboiler subunit is connected to the first hot side inlet of the first heat exchanger through the third buffer tank; the pipeline of the tank bottom outlet is connected to the second hot side inlet of the first heat exchanger; The first hot side outlet of the first heat exchanger and the second hot side outlet of the first heat exchanger are both connected to the cold side inlet of the ethylene distillation tower condenser subunit; the cold side outlet of the ethylene distillation tower condenser subunit is connected to the first-stage inlet of the two-stage propylene refrigeration compressor through the second buffer tank.

5. The system of coupling RTC dry gas with ethylene device according to claim 4, wherein: The ethylene distillation tower is also provided with a tower top outlet, a tower top reflux port, a tower bottom outlet and a tower bottom reflux port; The ethylene rectification tower condenser subunit is a high-load condenser, and the ethylene rectification tower reboiler subunit is a high-load reboiler; The hot side inlet of the high-load condenser is connected to the tower top outlet, the hot side outlet of the high-load condenser is connected to the tower top reflux tank of the ethylene distillation tower, the tank bottom material outlet of the tower top reflux tank is connected to the tower top reflux port through a reflux pump; the cold side inlet of the high-load reboiler is connected to the tower bottom outlet; the cold side outlet of the high-load reboiler is connected to the tower bottom reflux port; or, The ethylene distillation tower condenser subunit includes an original condenser and a newly added condenser; The ethylene distillation tower reboiler subunit includes an original reboiler and a newly added reboiler; The original propylene refrigeration unit provides cooling capacity for the original condenser and heat source for the original reboiler; the pipeline of the tank top outlet and another pipeline of the first hot side outlet of the ethylene product vaporizer are connected to the hot side inlet of the newly added reboiler; the first hot side outlet of the first heat exchanger and the second hot side outlet of the first heat exchanger are both connected to the cold side inlet of the newly added condenser; The hot side inlets of the original condenser and the newly added condenser are both connected to the tower top outlet; the hot side outlets of the original condenser and the newly added condenser are both connected to the tower top reflux tank of the ethylene distillation tower, and the tank bottom material outlet of the tower top reflux tank is connected to the tower top reflux port through a reflux pump; the cold side inlets of the original reboiler and the newly added reboiler are both connected to the tower bottom outlet; the cold side outlets of the original reboiler and the newly added reboiler are both connected to the tower bottom reflux port.

6. A method for modifying an ethylene device, the method being used to obtain a system for coupling RTC dry gas and an ethylene device as claimed in any one of claims 1 to 5, characterized in that: The method comprises the following steps: Set up an RTC ethylene-rich carbon digas feed port in the ethylene distillation tower; set up a cold box unit, a new propylene refrigeration unit and an RTC ethylene-rich carbon digas feed pipeline; Connecting the RTC ethylene-rich carbon digas feed pipeline to the RTC ethylene-rich carbon digas feed port through the cold box unit; The ethane outlet at the bottom of the ethylene distillation tower is connected to the first ethane circulation pipeline and the second ethane circulation pipeline respectively; the first ethane circulation pipeline liquid is connected to the cracking furnace through the cold box unit; Connecting the pipeline of the liquid-phase ethylene product outlet of the ethylene rectification tower to the gas-phase ethylene product pipeline through the cold box unit; Using propylene refrigerant from the newly added propylene refrigeration unit to recover the cold of the liquid ethylene product and part of the ethane obtained in the ethylene distillation tower in the cold box unit; The original propylene refrigeration unit of the ethylene distillation tower and the newly added propylene refrigeration unit simultaneously provide cooling capacity for the condenser subunit of the ethylene distillation tower and provide a heat source for the reboiler subunit of the ethylene distillation tower.

7. A method for coupling RTC dry gas with an ethylene device, characterized in that: The method adopts the system of coupling RTC dry gas and ethylene device according to any one of claims 1 to 5, comprising the following steps: S1: Cooling the RTC ethylene-rich carbon digas through the cold box unit and then sending it to the ethylene distillation tower; sending C2 to the ethylene distillation tower; obtaining the top gas at the top of the ethylene distillation tower, producing the liquid ethylene product at the side line of the tower, and obtaining ethane and the bottom reflux liquid logistics at the bottom of the tower; S2: using propylene refrigerant from the newly added propylene refrigeration unit to recover the cold of the liquid ethylene product and part of the ethane in the cold box unit; The gas phase ethylene product is obtained and sent out of the boundary area, and the ethane after the cold is recovered is returned to the cracking furnace for cyclic cracking; The tower bottom reflux liquid phase stream is sent to the ethylene rectification tower reboiler subunit, and heated by the original propylene refrigeration unit and the newly added propylene refrigeration unit to obtain a tower bottom heated stream; The tower top gas is sent to the condenser subunit of the ethylene distillation tower, and condensed by the original propylene refrigeration unit and the newly added propylene refrigeration unit to obtain the tower top condensate flow.

8. The method for coupling RTC dry gas with an ethylene device according to claim 7, wherein: In step S1: The RTC ethylene-rich carbon digas is an RTC dry gas that has been concentrated and impurities removed, wherein, based on the total molar amount of the RTC ethylene-rich carbon digas, the ethylene content is 60-80 mol%, the ethane content is 25-40 mol%, the methane content is 0.01-0.1 mol%, the acetylene content is <1 ppm, the carbon three content is <0.1 mol%, and the water content is <1 ppm; The temperature of the RTC ethylene-rich carbon digas is 8-60°C and the pressure is 1.8-2.8MPaG; The temperature of the RTC ethylene-rich carbon digas after cooling is -10 to -5°C; The C2 comes from the carbon dihydrogenation system.

9. The method for coupling RTC dry gas with an ethylene device according to claim 7, wherein: In step S2, The liquid-phase ethylene product is sequentially passed through the first heat exchanger, the second heat exchanger, the ethylene product vaporizer and the third heat exchanger of the cold box unit to recover cold; the liquid-phase ethylene product is a polymerization-grade ethylene product with a purity of 99.94-99.96 mol%; A portion of the ethane is sequentially passed through the first heat exchanger, the second heat exchanger and the third heat exchanger of the cold box unit to recover cold and then returned to the cracking furnace for cyclic cracking; the remaining portion of the ethane is directly returned to the cracking furnace for cyclic cracking; preferably, the ratio of the ethane recovered by the cold box unit to the ethane directly returned to the cracking furnace is 1:(0.8-1.2); The process flow of recovering the cold of the liquid ethylene product and part of the ethane in the cold box unit by using the propylene refrigerant from the newly added propylene refrigeration unit comprises: The propylene refrigerant at the primary outlet of the two-stage propylene refrigeration compressor and the propylene refrigerant at the secondary outlet of the two-stage propylene refrigeration compressor flowing through the water cooler and the first buffer tank are heat exchanged with the liquid-phase ethylene product after the cooling capacity is recovered by the first heat exchanger and the second heat exchanger in the ethylene product vaporizer to obtain a vaporized ethylene product, a cooled primary propylene refrigerant and a cooled secondary propylene refrigerant; the vaporized ethylene product is recovered by the third heat exchanger to obtain a gas-phase ethylene product and sent out of the boundary area; The cooled secondary propylene refrigerant is sent into the interstage tank to obtain the tank top outlet material and the tank bottom outlet material; the cooled primary propylene refrigerant is divided into two parts, one part is used together with the tank top outlet material as the heat source of the ethylene rectification tower reboiler subunit to obtain a further cooled propylene refrigerant; the remaining part is refluxed to the secondary inlet of the two-stage propylene refrigeration compressor; preferably, the ratio of the cooled primary propylene refrigerant used as the heat source of the ethylene rectification tower reboiler subunit to the cooled primary propylene refrigerant refluxed to the secondary inlet of the two-stage propylene refrigeration compressor is (1.1-1.5):1; The further cooled propylene refrigerant and the tank bottom outlet material are heat exchanged with the liquid ethylene product and a portion of ethane in the first heat exchanger to obtain the liquid ethylene product with recovered cold, the ethane with recovered cold and the further cooled propylene refrigerant; After the re-cooled propylene refrigerant is used to provide cooling for the ethylene rectification tower condenser subunit, the propylene refrigerant after providing cooling is sent to the first inlet of the two-stage propylene refrigeration compressor through the second buffer tank; the ethane with recovered cooling is returned to the cracking furnace for cyclic cracking after the cooling is recovered through the second heat exchanger and the third heat exchanger; Preferably, the temperature of the propylene refrigerant at the primary outlet is 30-40°C, the temperature of the propylene refrigerant at the secondary outlet is 80-100°C, and the temperature of the propylene refrigerant at the secondary outlet after flowing through the water cooler and the first buffer tank is 35-45°C.

10. The method for coupling RTC dry gas with an ethylene device according to claim 9, wherein: The cooled primary propylene refrigerant is divided into two parts, and one part is used together with the material at the tank top outlet as the heat source of the newly added reboiler; Using the re-cooled propylene refrigerant to provide cooling capacity for the newly added condenser; Reflux the heated bottom stream to the bottom of the ethylene distillation tower; The tower top condensate flow is sent to the tower top reflux tank to obtain the tank bottom material and reflux to the tower top of the ethylene distillation tower through the reflux pump.

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