CN113150849A

CN113150849A - Improved process for producing LNG (liquefied Natural gas) from coke-oven gas

Info

Publication number: CN113150849A
Application number: CN202110581830.8A
Authority: CN
Inventors: 杨皓; 史保金; 罗国林; 李江波; 宋尉源
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-05-26
Filing date: 2021-05-26
Publication date: 2021-07-23

Abstract

The invention relates to an improved process for producing LNG (liquefied natural gas), wherein the coke-oven gas is prepared by separating methane, hydrocarbon part above carbon 2 and other component gases in the coke-oven gas by using a pressure swing adsorption device as raw materials for producing LNG, wherein the raw materials comprise 10-15% of hydrogen, 10-18% of carbon dioxide, 54-68% of methane, 2-3% of carbon monoxide, 1% of hydrogen-carbon ratio: 1.2-1: 2.1; removing total sulfur, total phosphorus and total chlorine which are all lower than 0.1ppm, sending to methanation, converting hydrogen into methane in the methanation process, reducing the concentration of hydrogen in outlet gas to be less than or equal to 100ppm, sending to a carbon dioxide removing device for decarburization to an anti-freezing and anti-blocking degree after heat recovery and cooling to 20-50 ℃, and then sending to LNG for liquefaction after removing harmful components in other liquefaction processes.

Description

Improved process for producing LNG (liquefied Natural gas) from coke-oven gas

Technical Field

The invention relates to the fields of metallurgy, energy conservation and environmental protection, and discloses a method for effectively reducing the emission of gas wastes and reducing resource consumption.

Background

The coke oven gas containing methane is a raw material for producing LNG.

CN101280235A of Duwenguang, Tai Yuan Cheng science and technology Co., Ltd, discloses a method for producing liquefied natural gas by using coke oven gas as raw material, which comprises pretreating coke oven gas to deeply purify the impurities such as tar, naphthalene and benzene, and purifying the impuritiesAfter compression and desulfurization, methanation reaction is carried out, and CH-containing is obtained through a cryogenic separation process₄More than 85% of liquefied natural gas products and the rest of non-condensable gas are subjected to PSA (pressure swing adsorption) separation technology to obtain hydrogen with the purity of more than 99%, and the rest of desorbed gas can be used as artificial fuel gas.

CN103773524A of Kawasaki force of Mitsubishi engineering technology Limited company announced a method for producing liquefied natural gas, wherein coke oven gas is used for introducing carbon monoxide and carbon dioxide for methanation to produce LNG; in order to avoid concentration of inert gas such as nitrogen in the non-condensable gas when the non-condensable gas is circulated, it is preferable to recycle 70% or less of the total amount of the non-condensable gas, or to provide a hydrogen separation step of selectively separating hydrogen in the circulating non-condensable gas, and to recycle a part or all of the hydrogen selectively separated in the hydrogen separation step. Wherein the hydrogen separation step can use H₂PSA, membrane separation devices, and the like. Further, the remaining non-condensable gas and the by-product gas remaining after the separation of hydrogen can be effectively used as fuel. Further, it is preferable to use them as a fuel for a coke oven. In addition, it is natural that hydrogen selectively separated in the hydrogen separation step can be recovered as a product.

CN105713686A of Yanghao, Ningping and the like announces a process for producing civil fuel gas by using a coke oven and a methanation process, coke oven gas produced in the coke oven production process is completely used as a raw material I for synthesizing methane, 3.5MPa steam by-produced in the methanation process is used for generating power and reducing the pressure to 0.3MPa, a part of steam, coke and pure oxygen are fixed bed to produce carbon monoxide and hydrogen which are used as a raw material II for synthesizing methane, the raw material I and the raw material II are mixed for methanation to prepare the civil fuel gas, and the synthetic gas is directly compressed to be used as compressed civil fuel gas or is further decarbonized and dehydrated to prepare LNG; the rest steam of the methanation byproduct, coke and air gas produced by the oxygen-enriched air fixed bed are used as coke oven fuel instead of coke oven gas.

Methanation is an important step in the process of producing LNG from coke oven gas, and an important purpose of methanation of coke oven gas is to reduce the concentration of harmful carbon dioxide in the liquefaction of LNG to a harmless level (to prevent freezing and blocking of carbon dioxide). The amount of carbon monoxide and carbon dioxide added to increase the utilization rate of hydrogen is limited by the extent to which the carbon dioxide is reduced to harmless extent after methanation. Usually, the methanation process is rich in hydrogen, and if the carbon dioxide is excessive, the excessive carbon dioxide needs to be removed before methanation and then sent for methanation.

The high-concentration hydrogen reacts with carbon monoxide, and the methanation catalyst has short service life due to excessive reaction heat.

Generally, flash steam obtained after LNG liquefaction is prepared through methanation of coke-oven gas contains low-concentration hydrogen, the actual low-concentration hydrogen is extremely difficult to utilize, and a compression separation device is required to recycle the hydrogen.

A large amount of carbon dioxide is introduced in the methanation process, so that the reaction heat can be reduced, and the catalyst deactivation process is slowed down. Excess CO_XThe source allows the full use of the low concentration hydrogen.

Disclosure of Invention

The invention relates to an improved process for producing LNG (liquefied natural gas), wherein the coke-oven gas is separated from methane, hydrocarbon part with more than 2 carbon atoms and other component gases by a pressure swing adsorption device and is used as an LNG manufacturing raw material. Other non-methane gas is used for conveying hydrogen, nitrogen and carbon monoxide to the utilization system. The LNG production raw material gas comprises 10-15% of hydrogen, 10-18% of carbon dioxide, 54-68% of methane, 2-3% of carbon monoxide and a hydrogen-carbon ratio of 1: 1.2-1: 2.1, and is gas generated in the regeneration process of a pressure swing adsorption device.

The gas can be subjected to methanation only if the total sulfur, the total phosphorus and the total chlorine of the gas are removed to be lower than 0.1ppm, so that the catalyst is not poisoned in the methanation process. The methanation process converts all hydrogen into methane, the outlet concentration of the hydrogen is reduced to be below 100ppm, the process almost fully utilizes low-concentration hydrogen, and the excessive carbon dioxide can reduce the intensity of the methanation reaction, thereby prolonging the service life of the catalyst. And (3) recovering heat of the methanation outlet gas, cooling to 20-50 ℃, sending the methanation outlet gas to a decarbonization device to remove carbon dioxide to an anti-freezing and anti-blocking degree, and then removing harmful components in other liquefaction processes to carry out LNG liquefaction.

The methanation process is mainly different from other processes in that the methanation process is placed before the surplus carbon dioxide is removed, and hydrogen and CO are_XIs much lower than the equivalent reaction ratio. LNG productionThe amount is also higher than that of the decarburization pre-process.

After methanation, a decarbonization device is arranged to separate carbon dioxide, so that freezing blockage prevention is realized, and the separated carbon dioxide can be directly used as a high-grade liquid carbon dioxide raw material due to low sulfur, low phosphorus and low chlorine.

Drawings

FIG. 1 is a schematic process flow diagram of the present invention.

Fig. 2 is a flow diagram of a general process for manufacturing LNG.

Fig. 3 is a flow diagram of a conventional flow LNG manufacturing process.

Detailed Description

Example 1 Coke oven gas 35000NM³Adopting a pressure swing adsorption device to separate methane, hydrocarbon parts above carbon 2 and other component gases in the LNG as LNG manufacturing raw materials, wherein 11% of hydrogen, 18% of carbon dioxide, 68% of methane, 3% of carbon monoxide and a hydrogen-carbon ratio of 1:1.9 in the manufactured raw material gas; removing total sulfur, total phosphorus and total chlorine which are all lower than 0.1ppm, sending to methanation, completely converting hydrogen into methane in the methanation process, sending the hydrogen content of outlet gas to 30ppm, cooling to 20-50 ℃ through heat recovery, sending to a carbon dioxide removing device for decarburization to 5ppm, and then sending to LNG for liquefaction through removing harmful components in other liquefaction processes, wherein the separated carbon dioxide can be directly used as a high-grade liquid carbon dioxide raw material.

Example 2 Coke oven gas 35000NM³Adopting a pressure swing adsorption device to separate methane, hydrocarbon parts above carbon 2 and other component gases in the LNG as LNG manufacturing raw materials, and preparing 14% of hydrogen, 16% of carbon dioxide, 58% of methane, 2% of carbon monoxide and 1:1.3 of hydrogen-carbon ratio in the raw material gases; removing total sulfur, total phosphorus and total chlorine which are all lower than 0.1ppm, sending to methanation, completely converting hydrogen into methane in the methanation process, sending the outlet gas with the hydrogen content of 50ppm, cooling to 20-50 ℃ through heat recovery, sending to a carbon dioxide removing device for decarburization to 5ppm, and then sending to LNG for liquefaction through removing harmful components in other liquefaction processes, wherein the separated carbon dioxide can be directly used as a high-grade liquid carbon dioxide raw material.

Example 3 Coke oven gas 35000NM³The methane, the hydrocarbon part with more than 2 carbon atoms and other component gases in the crude oil are separated by a pressure swing adsorption deviceThe LNG production raw material comprises 15% of hydrogen, 18% of carbon dioxide, 58% of methane, 3% of carbon monoxide and a hydrogen-carbon ratio of 1:1.4 in the production raw material gas; removing total sulfur, total phosphorus and total chlorine which are all lower than 0.1ppm, sending to methanation, completely converting hydrogen into methane in the methanation process, sending the outlet gas with the hydrogen content of 80ppm to a decarbonization device for decarbonization to 2ppm after heat recovery and cooling to 20-50 ℃, sending to an LNG for liquefaction after removing harmful components in other liquefaction processes, and directly using the separated carbon dioxide as a high-grade liquid carbon dioxide raw material.

Claims

1. An improved process for producing LNG by using coke oven gas is characterized in that: the coke oven gas is firstly separated by a pressure swing adsorption device from methane, hydrocarbon part above carbon 2 and other component gases as LNG manufacturing raw materials, 10-15% of hydrogen, 10-18% of carbon dioxide, 54-68% of methane, 2-3% of carbon monoxide, 1% of hydrogen-carbon ratio: 1.2-1: 2.1; removing total sulfur, total phosphorus and total chlorine which are all lower than 0.1ppm, sending to methanation, converting hydrogen into methane in the methanation process, reducing the concentration of hydrogen in outlet gas to be less than or equal to 100ppm, sending to a carbon dioxide removing device for decarburization to an anti-freezing and anti-blocking degree after heat recovery and cooling to 20-50 ℃, and then sending to LNG for liquefaction after removing harmful components in other liquefaction processes.