CN-121975558-A - Process and device for preparing LNG and co-producing carbon dioxide from coke oven gas

CN121975558ACN 121975558 ACN121975558 ACN 121975558ACN-121975558-A

Abstract

The invention discloses a process and a device for preparing LNG and co-producing carbon dioxide by coke oven gas, and belongs to the field of chemical industry. The invention divides the coke oven gas subjected to fine desulfurization into two paths, wherein the first path directly enters a methanation section, the second path enters a CO conversion tower to convert CO into CO 2 through a water gas shift reaction, H 2 is generated at the same time, the converted gas is cooled by a heat exchanger I2 or a steam boiler and then enters an alcohol amine decarbonization tower, CO 2 is partially or almost completely removed by spraying an alcohol amine solution, the alcohol amine solution is heated and regenerated to obtain high-purity CO 2 serving as a chemical raw material, the decarbonized gas and the first path gas are converged and then enter the methanation section, and CH 4 is generated by the reaction of H 2 and CO 2 in three methanation reactors connected in series and parallel. The device comprises a main pipeline, a CO conversion tower, a heat exchanger, an alcohol amine decarbonization tower, an alcohol amine regeneration tower, a methanation reactor and the like. The invention avoids large-gas circulation and a compressor, saves cost, coproduces higher-purity CO 2 , can flexibly regulate and control the content and temperature rise of CO/CO 2 , and prevents the temperature from flying.

Inventors

LI WEIFENG
LI QUANQUAN
WU JINGCHUAN
XIAO JIAYU
LI XUEWEI

Assignees

重庆赛迪热工环保工程技术有限公司

Dates

Publication Date: 20260505
Application Date: 20260112

Claims (10)

1. A process for preparing LNG and CO-producing carbon dioxide from coke oven gas is characterized in that the coke oven gas subjected to fine desulfurization is divided into two paths, the first path is directly fed into a methanation section, the second path of coke oven gas fed into a CO conversion tower is subjected to water gas shift reaction to convert CO in the components into CO 2 , H 2 is produced simultaneously, the content of CO is reduced, the coke oven gas coming out of the CO conversion tower is cooled down by a heat exchanger I or a steam boiler and then fed into an alcohol amine decarbonization tower, CO 2 in the coke oven gas is partially or almost completely removed by adopting a method of spraying alcohol amine solution to the gas, and the decarbonized coke oven gas and the coke oven gas which is not decarbonized in the first path are converged and then fed into the methanation section together; the methanation section comprises a main pipeline connected into coke oven gas and a plurality of methanation reactors which are arranged in sections along the airflow direction in the main pipeline, wherein a plurality of branch pipes are arranged on the main pipeline at intervals along the airflow direction, inlets of the methanation reactors are connected with the branch pipes in a one-to-one correspondence manner to form parallel connection of the inlets of the methanation reactors, outlets of the methanation reactors positioned at the front section in the airflow direction are connected with inlets of methanation reactors positioned at the adjacent rear section in series to form series connection among the methanation reactors, and gas in the main pipeline flows through each branch pipe according to the flow direction, and then a diversion part enters the methanation reactor of the corresponding section to react with CO and CO 2 to generate CH 4 .
2. The process for preparing LNG and CO-producing carbon dioxide from coke oven gas according to claim 1, wherein the alcohol amine solution in the alcohol amine decarbonization tower is heated by a heat exchanger II and then enters an alcohol amine regeneration tower for regeneration, the regeneration temperature is 105-125 ℃, CO 2 and the regenerated alcohol amine solution are obtained, the regenerated alcohol amine solution is cooled by the heat exchanger III and then enters the alcohol amine decarbonization tower, and CO 2 is collected and stored as chemical raw materials or is further processed and then reused.
3. The process for producing LNG and CO-producing carbon dioxide from coke oven gas according to claim 1, wherein the outlet of the methanation reactor is connected with a steam generator, and the produced steam is used for the water gas shift reaction in the CO conversion tower.
4. The process for preparing LNG and CO-producing carbon dioxide from coke oven gas according to claim 1, wherein the water gas shift reaction temperature in the CO conversion tower is 200-300 ℃, the outlet is provided with a CO content detector, and the reaction progress of the water gas shift reaction is controlled by adjusting the reaction temperature, the reaction airspeed and the catalyst loading, so that the CO content in the coke oven gas is adjusted.
5. The process for producing LNG and co-producing carbon dioxide from coke oven gas according to claim 1, wherein the first path and the second path are respectively provided with a flow regulating valve, and the flow ratio of the two paths of gas is regulated according to the requirement.
6. The process for producing LNG and co-producing carbon dioxide from coke oven gas according to claim 1, wherein each branch pipe in the methanation section is provided with a flow control valve, each methanation reactor is provided with a thermocouple for monitoring the temperature of the bed, and the gas flow is regulated according to the temperature to prevent the temperature from flying.
7. The process for preparing LNG and CO-producing carbon dioxide from coke oven gas according to claim 1, wherein the alcohol amine solution in the alcohol amine decarbonization tower is a mixed solution of any one or more of MEA, DEA, DIPA, MDEA, and the content of CO 2 in the coke oven gas is controlled by adjusting the spraying amount and the gas flow rate.
8. The process for preparing LNG and CO-producing carbon dioxide from coke oven gas according to claim 1, wherein three methanation reactors are arranged in the methanation section, a first methanation reactor, a second methanation reactor and a third methanation reactor are respectively arranged along the airflow direction and are all adiabatic fixed beds, the second methanation reactor utilizes the H 2 rich in the first methanation reactor to react with residual CO and CO 2 to generate CH 4 , and the third methanation reactor utilizes the H 2 rich in the second methanation reactor to react with residual CO and CO 2 to generate CH 4 .
9. The device for preparing LNG and CO-producing carbon dioxide from coke oven gas is characterized by comprising a main pipeline, a CO conversion tower, a heat exchanger I, an alcohol amine decarbonization tower, a heat exchanger II, an alcohol amine regeneration tower, a heat exchanger III, a first-stage methanation reactor, a second-stage methanation reactor and a third-stage methanation reactor; The main pipeline is divided into two paths, the first path is directly connected to the methanation section, the second path is connected with a make-up steam pipeline, the CO conversion tower is connected to the second path and is used for converting CO into CO 2 , and the CO conversion tower, the heat exchanger I and the alcohol amine decarbonization tower are sequentially connected in series; The alcohol amine decarbonization tower, the heat exchanger II, the alcohol amine regeneration tower and the heat exchanger III are sequentially connected in series to form an alcohol amine regeneration loop for regeneration and recycling of alcohol amine; The top of the alcohol amine decarbonization tower is connected with the first path and then is connected with a main pipeline of the methanation section, three branch pipes are arranged on the main pipeline of the methanation section along the air flow direction at intervals, the inlets of the first-stage methanation reactor, the second-stage methanation reactor and the third-stage methanation reactor are connected with the three branch pipes in a one-to-one correspondence manner to form parallel connection of the inlets of the three methanation reactors, and meanwhile, the outlet of the first-stage methanation reactor is connected with the inlet of the second-stage methanation reactor, and the outlet of the second-stage methanation reactor is connected with the inlet of the three methanation reactors to form serial connection of the three methanation reactors.
10. The device for producing LNG and CO-producing carbon dioxide from coke oven gas according to claim 9 is characterized in that outlets of the first-stage methanation reactor, the second-stage methanation reactor and the third-stage methanation reactor are further connected with a steam generator, the steam generator is connected with a water vapor supplementing pipeline, a CO content detector is arranged at an outlet of the CO conversion tower, flow control valves are arranged at inlet ends of the CO conversion tower, the first-stage methanation reactor, the second-stage methanation reactor and the third-stage methanation reactor and used for adjusting gas proportions, and thermocouples are arranged on the first-stage methanation reactor, the second-stage methanation reactor and the third-stage methanation reactor and used for monitoring bed temperature and realizing reaction load balance.

Description

Process and device for preparing LNG and co-producing carbon dioxide from coke oven gas Technical Field The invention belongs to the technical field of chemical industry, and relates to a process and a device for preparing LNG and co-producing carbon dioxide from coke oven gas. Background Coke Oven Gas (COG) is a by-product Gas generated when coal is subjected to high-temperature carbonization (air heating is isolated) in a Coke Oven to produce Coke, belongs to an important industrial Gas and chemical raw material, and mainly comprises hydrogen (H 2, 50-60%), methane (CH 4, 20-30%) and carbon monoxide (CO, 5-8%), contains a small amount of nitrogen, carbon dioxide, oxygen and the like, and also contains a large amount of impurity components such as tar, benzene, naphthalene, ammonia, hydrocyanic acid, organic sulfur, inorganic sulfur and the like. The composition of the coke oven gas shows that the contents of hydrogen, carbon monoxide and methane in the coke oven gas are higher, so that the coke oven gas has higher resource utilization value. China is the country with the largest world coke yield, however, the theoretical recovery amount of coke oven gas in China is just over half, which indicates that nearly half of coke oven gas is still underutilized. A large amount of coke oven gas is directly combusted and discharged into the atmosphere, which not only causes great waste of high-value energy sources, but also brings serious environmental pollution risks. At present, in order to fully utilize coke oven gas resources, the international society sequentially provides a plurality of comprehensive utilization ways, such as a methanol production way, a hydrogen production way, a natural gas production way and the like, wherein H 2 in the coke oven gas reacts with CO and CO 2 as raw materials to generate CH 4 with high heat value, the CH 4 content is improved, and the methanation process for preparing synthetic natural gas becomes one of main ways of clean and efficient resource utilization of the coke oven gas, and the reaction is mainly as follows: (1), (2), As can be seen from the chemical reaction equation, methanation reaction belongs to a strong exothermic reaction, which may cause the exothermic rate of the reaction to exceed the heat dissipation capacity, so that the temperature in the reactor is rapidly increased, the catalyst is deactivated by sintering, side reactions are aggravated, even the reaction equipment is damaged, and serious consequences such as safety accidents are caused. At present, two solutions are generally adopted for solving the problem: A. The circulating adiabatic fixed bed process is simple to operate and easy to control the temperature, but in order to remove the reaction heat, high-rate gas recirculation is needed to control the temperature of the reactor, so that the volume of the methanation reactor is greatly increased, and meanwhile, the high-rate gas recirculation is needed to be provided with a high-power gas compressor (usually one-on-one), so that the equipment investment is obviously increased, the running power consumption is increased, and the equipment maintenance cost is also increased. B. A one-stage isothermal bed reactor was developed. The isothermal bed reactor can remove heat generated by the reaction in real time through a built-in heat exchange device (such as a coil pipe and a jacket) or an external circulating coolant, keep the temperature of a bed layer uniform, ensure the reaction to be always in an optimal temperature window, and avoid side reactions (such as carbon deposition generation) increase caused by temperature rise of an adiabatic bed, thereby prolonging the service life of the catalyst and reducing the safety risk. Meanwhile, the isothermal bed reactor does not need to reenter a large amount of circulating gas into the reactor inlet, so that energy consumption and investment are saved, but the existing large-scale industrial application still has a bottleneck due to the problems of complex internal structure, high processing difficulty and the like of the isothermal bed reactor. Therefore, a one-stage methanation process which can effectively control the temperature rise of a methanation reactor and does not need a large amount of circulating gas is needed, so that the investment cost and the operation energy consumption are reduced while the production requirement is met. Disclosure of Invention In view of the above, the invention aims to solve the above-mentioned shortcomings and provide a process and a device for preparing LNG and co-producing carbon dioxide from coke oven gas. In order to achieve the above purpose, the present invention provides the following technical solutions: A process for preparing LNG and CO-producing carbon dioxide from coke oven gas comprises dividing the coke oven gas subjected to fine desulfurization into two paths, wherein the first path directly enters a methanation section, the second path of coke oven gas e