CN110938481A

CN110938481A - LNG preparation process for quality-divided utilization of low-rank coal

Info

Publication number: CN110938481A
Application number: CN201911175046.6A
Authority: CN
Inventors: 张宏伟; 吕彬峰; 金飞伟; 马倩; 李佳春; 潘建波
Original assignee: Zhejiang Tianlu Environmental Technology Co Ltd
Current assignee: Zhejiang Tianlu Environmental Technology Co Ltd
Priority date: 2019-11-26
Filing date: 2019-11-26
Publication date: 2020-03-31

Abstract

The invention discloses an LNG preparation process for utilizing low-rank coal according to quality, which utilizes volatile components and coal quality in the low-rank coal to obtain CO and H required by LNG synthetic raw materials₂The LNG is prepared by the method, the impurities in the LNG are few, the quality is high, the volatile components in low-rank coal are fully and effectively utilized, the LNG is prepared from abundant raw materials and is low in cost, the production cost is greatly saved, high-value upgraded coal and coal tar are produced, the comprehensive utilization direction of national coal is met, and the energy is provided for corresponding processes through coupling of a methane synthesis process and a liquefaction process, coupling among specific steps of the methane synthesis process, and coupling of the methane synthesis process and other coal processing processes.

Description

LNG preparation process for quality-divided utilization of low-rank coal

Technical Field

The invention relates to the technical field of low-rank coal quality-based utilization, in particular to an LNG preparation process for low-rank coal quality-based utilization.

Background

China is a country rich in coal, poor in oil and less in gas, and the coal consumption accounts for more than 60% of the primary energy consumption, so that the energy structure mainly based on coal is difficult to change in a long period of time. From the ascertained coal mine quality, the proportion of low-rank coal in the coal in China is very large, so that the reasonable and efficient utilization of the low-and-medium-rank coal to produce high-quality chemical products is very important. In recent years, the continuous development of technologies such as coal gasification, coal pyrolysis, coal gas purification, coal gas separation and the like makes the clean and efficient utilization of medium-low-grade coal more and more important.

Natural gas is a highly efficient clean energy source. In recent years, with the successive construction and use of national grade fuel gas transportation projects such as Shanxi gas import Jing and Xiqidong gas transportation, the demand of natural gas is increased explosively. According to prediction, in 2015, the demand of Chinese natural gas reaches 1700 hundred million Nm 3-2100 hundred million Nm3, while the yield of the natural gas at the same time can only reach 1400 hundred million Nm3, and the supply and demand gaps are about 300 hundred million Nm 3-700 hundred million Nm 3. In order to solve the problem of contradiction between supply and demand of natural gas in China, other alternative ways are required to be found besides the domestic resources are established and natural gas resources in other countries in the world are actively utilized.

High-quality coal such as anthracite is used for preparing LNG, the yield of LNG is high, but the production cost is high. And many middle-low rank coals in China have poor quality, high ash content and high water content, and LNG is prepared by utilizing the low rank coals, so that the production cost of the LNG can be reduced. The raw coal gas is obtained by pyrolyzing low rank coal, which is generally carried out in the presence of a large amount of oxygen (or air), wherein a part of low rank coal is reacted with oxygen to supply heat and produce a large amount of CO₂. Due to CO₂Can not be combusted, belongs to ineffective gas, and has over high nitrogen content due to aerobic combustion, thereby reducing H in the crude gas₂And CO energy density, so that the calorific value of the crude gas is reduced, and the crude gas produced by pyrolysis has other economic values except for return combustion. The biggest problem of the coal gasification process is that chemical components contained in coal are not fully utilized, and the molecules of the chemical components cannot be completely broken into CO and H₂And then the LNG is chemically synthesized. The low-rank coal gasification reduction and reforming technology and the LNG synthesis technology can reserve chemical components in coal to the maximum extent in the form of LNG.

Disclosure of Invention

In view of the above, the present invention provides a LNG preparation process for low-rank coal quality-based utilization, which aims at overcoming the defects of the prior art, and provides an LNG preparation process for low-rank coal quality-based utilization, wherein purified gas is reacted in at least 5 reactors connected in series to synthesize methane, and then a liquefaction process is combined to obtain an LNG product, so that the process has the advantages of low raw material cost, substantial production cost saving, less impurities in the prepared LNG, high quality, full and effective utilization of volatile components in low-rank coal, coupling of methane synthesis process and liquefaction process, coupling of specific steps of the methane synthesis process, coupling of the methane synthesis process and other coal processing processes, and energy supply for corresponding processes.

In order to solve the technical problems, the invention provides the following technical scheme:

the LNG preparation process for quality-divided utilization of low-rank coal comprises the following steps:

(1) preparing upgraded coal and rich gas from low-rank coal through a gasification reduction process, wherein the upgraded coal and/or the rich gas are/is prepared to contain CO and CO₂And H₂Adding the purified gas into the first reactor, and preheating the purified gas so that the temperature of the purified gas is 150-;

(2) enabling the purified gas obtained in the step (1) to become a first methane synthesis material, and enabling the first methane synthesis material to enter a second reactor, wherein in the second reactor, in the environment with a first high-temperature-resistant methane catalyst, carbon monoxide, carbon dioxide and hydrogen of the first methane synthesis material react to synthesize methane, and a first methane material flow is obtained;

(3) enabling the first methane material flow to become a second methane synthetic material to enter a third reactor, and enabling carbon monoxide, carbon dioxide and hydrogen of the second methane synthetic material to react in the third reactor in the presence of a second high-temperature-resistant methane catalyst to synthesize methane to obtain a second methane material flow;

(4) separating the second methane material flow by a first gas-water separation device to obtain condensate with water as a main component and a gas-phase material, wherein the gas-phase material becomes a third methane synthetic material;

(5) the third methane synthetic material enters a fourth reactor, and in the fourth reactor, in the environment with a third high-temperature resistant methane catalyst, carbon monoxide, carbon dioxide and hydrogen of the third methane synthetic material react to synthesize methane, so that a third methane material flow is obtained, and a methane product flow is obtained;

(6) separating the methane product stream obtained in the step (5) by a second gas-water separation device to obtain a raw LNG stream;

(7) and introducing the original LNG material flow into a liquefaction process, and producing methane with volume percentage not less than 90% by using a cryogenic liquefaction process to obtain the product LNG.

The drying process removes most of moisture in the low-rank coal to obtain dried low-rank coal and waste gas, and the dried low-rank coal enters a gasification reduction process to react to obtain high-temperature rich gas and upgraded coal with a certain temperature. The oxygen source in the oxygen-free or micro-oxygen environment adopted by the gasification reduction process is mainly divided into the following cases: (1) the air carried in the gaps between the raw material low-rank coal and the materials; (2) a small amount of mixed air is leaked from a feed inlet, a discharge outlet and the like of the gasification reduction process; (3) under the explosion limit value, O accounting for 5 percent of the coal by mass can be slightly introduced into the gasification reduction process₂Or (air), and further preferably, O in an amount of 3% by mass of the coal is introduced₂Or (air), is beneficial to improving the temperature of the gasification reduction reaction, preventing coking and the like, and simultaneously ensures the safety and stability of the whole gasification reduction process reaction; the dried low-rank coal is preferably subjected to gasification reduction reaction in an oxygen-free environment, so that the condition that the dried low-rank coal and oxygen are subjected to combustion reaction in the reaction process of the gasification reduction process to generate a large amount of incombustible CO is avoided₂Thereby ensuring CO in the obtained high-temperature rich gas₂The volume percentage of (A) is small, which is beneficial to the subsequent preparation of rich gas with high energy density, the process steps are few, and the operation is simple and easy, so that the reaction can be safely carried out.

The high-temperature rich gas contains CO and H₂、CO₂Hydrocarbons, dust,Coal tar, naphthalene, water vapor, unsaturated hydrocarbons, sulfur-containing compounds and the like, and impurities such as solid dust, tar, naphthalene, water vapor and the like are removed through a purification process, so that purified rich gas is obtained. Resources such as coal tar, waste water and the like can be recovered in the purification process, and especially the coal tar is an important byproduct of low-rank coal. And treating the purified rich gas through a desulfurization process and a first compression process in sequence to obtain reforming conversion feed gas. The desulfurization process comprises a coarse desulfurization process and a coarse desulfurization process, and most of sulfur-containing compounds in the purified rich gas are removed primarily through the coarse desulfurization process, so that H is obtained₂S removal to 20mg/Nm³The following; and then the gas pressure is increased by the first compression process, the sulfur-containing compounds in the purified rich gas are continuously removed by the fine desulfurization process, the total sulfur in the purified rich gas is reduced to be below 0.1ppm, the catalyst poisoning in the subsequent process caused by the sulfur-containing compounds is prevented, and the requirements of the catalyst of the subsequent reforming conversion process and the catalyst of the LNG synthesis process on the sulfur content are met. In addition, during the fine desulfurization process, dechlorinating agent and purifying agent of decarbonylation metal compound can be added simultaneously to remove these harmful substances, so as to prevent the poisoning and deactivation of LNG synthesis catalyst.

The reforming conversion raw material gas mainly comprises CO and CO₂、H₂And hydrocarbons, CO and H being well known₂Can be directly used as a primary raw material for chemical synthesis, and hydrocarbons can be reformed to generate CO and H₂Therefore, part of the hydrocarbons in the reforming conversion raw material gas is reformed and converted by the reforming conversion process to obtain the gas containing CO and H₂Reforming reformed gas of (1), CO and H in the reforming reformed gas after reforming₂The total volume percentage is increased, which is beneficial to improving the amount of the subsequent LNG synthetic raw materials.

The effective component in LNG synthesis gas required by LNG synthesis is H₂、CO、CO₂The requirement for the hydrogen-carbon ratio in the LNG syngas is expressed as follows: r ═ H₂-CO₂)/(CO+CO₂) Wherein, the hydrogen-carbon ratio R value of the LNG synthetic gas is 3.0 in theory, and the optimal value is 2.95-3.05. The R value of the hydrogen-carbon ratio in the reformed conversion gas prepared by the method can not just meet the R value of 2.95-3.05, so the decarbonization is utilized to supplementAdjusting the hydrogen-carbon ratio of the reformed and converted gas to adjust the R value of the hydrogen-carbon ratio of the LNG synthesis gas to 2.95-3.05 in one or more of a carbon process, a transformation and conversion process and a hydrogen supplement process, so that upgraded coal and/or rich gas are prepared from low-rank coal through a gasification reduction process, wherein the upgraded coal and/or the rich gas are prepared to contain CO and CO₂And H2, thereby entering a methane synthesis process to synthesize methane; the purge gas is added to the first reactor and preheated such that the temperature of the purge gas is 150-.

Preferably, carbon dioxide-rich gas is introduced into the second reactor and/or the third reactor, and the hydrogen-carbon ratio of the carbon dioxide-rich gas is (2.9-3.5): 1 and the volume percentage of carbon dioxide is not less than 5%, so that the reaction temperature is 200-500 ℃ when methane is synthesized.

Preferably, the purified gas is introduced into the second reactor and/or the third reactor so that the reaction temperature is 200-500 ℃ when methane is synthesized.

Further, feeding carbon dioxide-rich gas into the second reactor, the third reactor, the fourth reactor and/or the fifth reactor, wherein the carbon dioxide-rich gas has a hydrogen-carbon ratio of (2.9-3.5): 1 and the volume percentage of the carbon dioxide is not less than 5 percent, and the reaction temperature is 200-500 ℃.

Further, introducing hydrogen-rich gas into the second reactor, the third reactor, the fourth reactor, the fifth reactor and/or the sixth reactor, wherein the volume percentage of hydrogen in the hydrogen-rich gas is not less than 50%.

Preferably, in step (5), the third methane stream enters a fifth reactor, and in the fifth reactor, in the presence of a fourth high temperature resistant methane catalyst, the carbon monoxide, the carbon dioxide and the hydrogen of the third methane stream react to synthesize methane, so as to obtain a fourth methane stream with a carbon monoxide volume fraction content of less than 3%, thereby obtaining the methane product stream.

Further, in the step (5), the third methane material flow or the fourth methane material flow enters a sixth reactor, in the sixth reactor, in an environment with a fifth high temperature resistant methane catalyst, the carbon monoxide, the carbon dioxide and the hydrogen of the third methane material flow or the fourth methane material flow react to synthesize methane, and a fifth methane material flow with the carbon monoxide volume fraction content of less than 1% is obtained, so that the methane product material flow is obtained.

Further, in the first high temperature resistant methane catalyst, the second high temperature resistant methane catalyst, the third high temperature resistant methane catalyst, the fourth high temperature resistant methane catalyst and the fifth high temperature resistant methane catalyst, the content of nickel is 10-40% and increases in sequence.

Preferably, the first methane synthesis material enters a first heat exchanger for heating, and enters the second reactor after being heated.

Preferably, the first methane material flow flows out from the outlet of the second reactor, and after the first methane material flow passes through the first waste boiler to recover heat, the first methane material flow enters the first heat exchanger to exchange heat and reduce the temperature to 150-500 ℃, and the first heat exchanger is coupled with the second reactor to heat the first methane synthetic material.

Preferably, the second methane material flow flows out from the outlet of the third reactor, the second methane material flow enters a second heat exchanger for cooling after passing through a second waste boiler for heat exchange and heat recovery, and then enters a first gas-water separation device after passing through a third heat exchanger, a fourth heat exchanger or a first condenser for heat exchange, the second heat exchanger and the first condenser are coupled with the fourth reactor for heating the third methane synthetic material, the third heat exchanger is coupled with the first reactor for heating the purified gas, and the fourth heat exchanger is coupled with the second reactor for heating the first methane synthetic material.

Preferably, the methane product stream enters the second gas-water separation device after being cooled by the deoxygenated water preheater and the second condenser.

And finally, the methane product stream is liquefied to obtain crude LNG and LNG purge gas, and the LNG purge gas is rich in hydrogen, so that the raw materials can be recycled, and the effective utilization rate of the raw materials is improved.

Preferably, the liquefaction process comprises a decarburization process and a liquefaction process, wherein the decarburization process comprises the steps that LNG liquefied raw material gas enters an absorption device, after decarburization, entrained solution is separated by a demister on the upper part of the absorption device and flows out, then the LNG liquefied raw material gas enters a cooling device, is cooled to be less than 40 ℃, and then water is separated by a gas-liquid separation device to obtain raw material gas which is sent to the liquefaction process; the liquefaction process comprises the steps that raw material gas enters a refrigeration heat exchanger, flows into a low-pressure rectifying device after precooling, is further cooled, then flows back to the refrigeration heat exchanger, is continuously cooled to minus 156 ℃ to minus 160 ℃, flows into a high-pressure rectifying device for rectification, hydrogen components in the raw material gas are distilled out from the top of a tower to form a hydrogen-rich material flow, first rectifying gas containing carbon monoxide, nitrogen and methane flows out from the lower part of the high-pressure rectifying device, flows into a low-pressure rectifying tower through throttling and pressure reduction, the carbon monoxide and the nitrogen in the first rectifying gas form a carbon monoxide-rich material flow, the carbon monoxide-rich material flow is distilled out from the upper part of the low-pressure rectifying tower, and the rest material forms second rectifying gas and flows out from the lower part of the low-pressure rectifying device.

Further, in the absorption device, the NG liquefies CO in the feed gas₂The components are absorbed by the active MDEA complex solution.

Preferably, the hydrogen-rich stream, passing through the refrigeration heat exchanger, is reheated to 20-40 ℃ and exits.

And further, reheating the low carbon monoxide-rich material flow to 20-40 ℃ by a refrigeration heat exchanger and then flowing out.

Preferably, the method further comprises a deamination process and a demercuration process, wherein the deamination process and the demercuration process are connected in series to sequentially remove ammonia and mercury in the feed gas, wherein the deamination process comprises the step that the feed gas enters a deamination device and then contacts desalted water sprayed from the upper part of the deamination device, so that ammonia in the feed gas is removed; the demercuration process comprises the steps that the deaminated feed gas enters a demercuration tower, and under the action of sulfur-carrying activated carbon, mercury in the feed gas is absorbed, so that the mercury content in the feed gas is removed to be less than or equal to 0.1 mu g/m 3.

Preferably, the TSA dehydration process is further included, the TSA dehydration process comprises a dehydration link, a heating link, a cooling link and a gas-liquid separation link, the dehydration link comprises a first dehydration link, a second dehydration link and a third dehydration link, the raw material gas flows through the first dehydration link after dehydration, then the rich liquid flows through the heating link after heating, the second dehydration link carries out dehydration, then the rich liquid flows through the cooling link after cooling, the rich liquid flows through the third dehydration link, and the rich liquid flows through the gas-liquid separation link after dehydration.

Preferably, the second rectification gas flow returns to the refrigeration heat exchanger for cooling, is further throttled to about 0.015MPa after being subcooled to-156 ℃ to-160 ℃, flows out of the refrigeration heat exchanger, and flows into an LNG storage tank for storage.

The LNG is prepared by gasifying anthracite coal into synthesis gas and then preparing LNG in an industrialized mode, the unit cost price of the anthracite coal is about 1200 plus 1500 yuan/t, about 0.294 ton of LNG is prepared from 1 ton of coal, the unit cost price of the low-rank coal is 80-100 yuan/t, the volatile content of the low-rank coal is 20-55 wt%, and the yield of LNG prepared from the volatile components in the low-rank coal is 15% based on 1 ton of the low-rank coal. As shown in table 1 below, the unit cost price of LNG prepared from low-rank coal is much lower than that of LNG prepared from anthracite coal, so that the LNG prepared by the method of the present invention greatly reduces the cost expenditure of raw materials. In addition, in the process for preparing LNG by using low-rank coal, byproduct upgraded coal and coal tar can be obtained, and the unit price of the upgraded coal is 500-; the unit price of the coal tar is 2000-2500 yuan/t, and the product value of the upgraded coal and the coal tar is high.

TABLE 1 comparison table of unit cost and price of LNG prepared from anthracite and low-rank coal

Based on the technical scheme, on one hand, the method in the inventionThe coal quality and the volatile components are obtained by gasifying and reducing the low-rank coal, so that CO and H required by LNG synthetic raw materials are obtained₂The LNG is prepared by the method, the impurities in the LNG are few, the quality is high, the volatile components in low-rank coal are fully and effectively utilized, the LNG is prepared from abundant raw materials and is low in cost, the production cost is greatly saved, high-value upgraded coal and coal tar are produced, the comprehensive utilization direction of national coal is met, and on the other hand, the energy can be provided for corresponding processes through coupling of a methane synthesis process and a liquefaction process, coupling among specific steps of the methane synthesis process, and coupling of the methane synthesis process and other coal processing processes.

Detailed Description

The present invention is further illustrated by the following examples, which are not intended to limit the invention to these embodiments. It will be appreciated by those skilled in the art that the present invention encompasses all alternatives, modifications and equivalents as may be included within the scope of the claims.

In the present invention, the raw materials and equipment used are commercially available or commonly used in the art, unless otherwise specified. The methods in the following examples are conventional in the art unless otherwise specified. The terms "first," "second," and the like in the present disclosure are used for distinguishing between descriptions and not to imply or imply relative importance.

Preparation example

The invention discloses an LNG preparation process for quality-based utilization of low-rank coal, which comprises the following process steps;

The raw material low-rank coal can be pulverized coal or lump coal, and when the low-rank coal adopts the lump coal, the pulverized coal with smaller granularity can be obtained by crushing and screening the oversize lump coal. The pulverized coal is preferably used as a raw material, on one hand, the pulverized coal does not need to be crushed and screened, so that the process steps are saved, the heating area is large during drying, the drying efficiency is high, and on the other hand, the pulverized coal is low in price compared with lump coal. Pulverized coal having a particle size of less than 20mm is preferably used, and pulverized coal having a particle size of less than 6mm is still more preferably used. The low-rank coal generally has 20-55% of volatile components, about 3-15% of tar, 30-60% of fixed carbon, 10-40% of water and the balance of other impurities such as dust. The low-rank coal has low coalification degree but contains abundant oil and gas resources, and the volatile components in the low-rank coal are very beneficial to extracting the synthesis gas, so that the low-rank coal with the volatile components between 30% and 55% is preferred.

The drying process can only remove most of the free water in the low-rank coal, but not remove the bound water in the low-rank coal, so that the low-rank coal is treated by the drying process to obtain the dried low-rank coal and waste gas, the dried low-rank coal still contains a certain amount of moisture, and the residual moisture can be gasified to form steam in the subsequent gasification reduction process.

The drying process can be one-stage or multi-stage, because if the water content of the low-rank coal after the first-stage drying process still does not meet the process requirement, multi-stage drying such as secondary drying, tertiary drying and the like can be adopted to continue further drying until the water content of the dried low-rank coal meets the process condition. The low-rank coal dried by the drying process enters the gasification reduction process for reaction, and for one-step optimization process, a gasification feeding process can be added before the dried low-rank coal enters the gasification reduction process, so that the dried low-rank coal can rapidly enter the gasification reduction process, the surface area of the material is increased, and the gasification reduction reaction can be accelerated.

Wherein, the gasification reduction process is a chemical reaction process for heating the dried low-rank coal under the condition of no oxygen or micro oxygen. The dried low-rank coal enters a gasification reduction process, under the heating of heating media such as flue gas and the like, additives and other substances are not needed to be added in the reaction process, the temperature is generally 350-800 ℃, and the pressure is less than or equal to 30Kpa, a complex chemical reaction process is carried out, so that solid carbon and high-temperature rich gas are obtained, wherein the solid carbon is upgraded coal, and the volatile matter in the upgraded coal is 8-15 wt%. The high-temperature rich gas comprises CO and H₂、CO₂Hydrocarbon, coal tar, naphthalene, halide, dust, sulfur compounds, and the like.

Wherein, the gasification reduction process can be one-stage or multi-stage. When the primary gasification reduction process is adopted, the reaction temperature of the gasification reduction process is 350-800 ℃, the volatile content in the upgraded coal is 8-15 wt%, and the reaction temperature of the gasification reduction process is further preferably 400-750 ℃; still more preferably 450-700 ℃. When the multistage gasification reduction process is adopted, the multistage gasification reduction process mainly has the main function of continuously gasifying certain amount of high-boiling-point oily substances (such as similar asphalt and the like) which cannot be gasified in a certain retention time and cannot be separated out or the temperature cannot reach the polycondensation reaction conditions of phenolic compounds, aromatic hydrocarbon compounds and the like in the previous stage gasification reduction process, and continuously reacting and gasifying, so that the gas yield and the quality of upgraded coal are improved. The unit price of the upgraded coal is generally 500-.

The high-temperature rich gas obtained from the gasification reduction process enters a purification process so as to obtain purified rich gas. The purification process comprises a dust removal process, a tar removal process and the like. The rich gas sequentially passes through a dust removal process and a tar removal process to contain CO and H₂And a purified rich gas of hydrocarbons. The high-temperature rich gas contains a large amount of dust, coal tar, water vapor, sulfur-containing compounds and the like; firstly, a dust removal device and the like are used for removing dust, so that the temperature of rich gas is prevented from being reduced in the dust removal process, and the coal tar, water vapor and the like are condensed into liquid and adhered with a large amount of dust to cause the blockage of a subsequent process pipeline and the reduction of the dust removal effect; the rich gas should contain a large amount of substances which are easy to solidify or crystallize, such as naphthalene and tar, and if the substances are not removed as much as possible, the substances will cause harm to the subsequent processes and even endanger the safety of the whole device. Therefore, tar in the rich gas is removed to be less than or equal to 1mg/Nm by using the tar removing process³For example, a cooling tower is adopted to cool the gaseous coal tar in the rich gas and simultaneously condense a large amount of substances such as water vapor and naphthalene, and the byproduct coal tar can be obtained by separating oil from water after cooling the obtained oil-water mixture. The unit price of the coal tar is 2000-2500 yuan/t, and the value of the coal tar rich in yield is higher. Further preferably, the purification process further comprises a naphthalene removal process, and the gas left after the treatment by the tar removal process enters naphthalene removalThe process is to remove the naphthalene in the rich gas to less than or equal to 4mg/Nm³. The naphthalene removing process comprises light tar naphthalene washing, anthracene oil naphthalene removing and regenerating, and rich oil naphthalene washing and regenerating. In the process, high-temperature volatile matters are cooled step by step to respectively obtain coal tar with different temperature distillation ranges like diesel oil, gasoline, light gasoline and the like, and the coal tar with the distillation range like the light gasoline is the light coal tar. Because the light coal tar is rich in raw materials, the light coal tar is preferably used for washing naphthalene, and qualified synthesis gas can be obtained. Further preferably, the purification process further comprises a hydrogenation process, wherein the hydrogenation process can select whether to hydrogenate according to the content of unsaturated hydrocarbons in the rich gas, and the rich gas prepared in the invention contains a certain amount of olefins and simultaneously prevents the problem that reforming conversion of the olefins is easy to cause carbon deposition, so the hydrogenation process needs to be arranged. The hydrogenation process is mainly realized by a hydrogenation catalyst, wherein a certain amount of hydrogen is introduced into common cobalt-molybdenum hydrogenation catalysts and iron-molybdenum hydrogenation catalysts, and olefins are converted into alkanes under the action of the catalysts.

The sulfides are liable to cause poisoning and deactivation of the reforming conversion catalyst and the LNG synthesis catalyst, and thus the sulfides in the purified rich gas need to be removed before the reforming conversion process. The purified rich gas enters a coarse desulfurization process for treatment, and H in the purified rich gas is removed₂S removal to 20mg/Nm³The following. The coarse desulfurization process adopts wet coarse desulfurization, the wet flue gas desulfurization technology is a gas-liquid reaction, the reaction speed is high, the desulfurization efficiency is high and generally higher than 90%, the technology is mature, and the application range is wide. The wet desulphurization technology is mature, the production operation is safe and reliable, and the wet desulphurization technology always occupies the dominant position in a plurality of desulphurization technologies, and accounts for more than 80 percent of the total installed capacity of desulphurization. Therefore, the wet desulphurization firstly removes a large amount of H in the rich gas₂And (4) removing the S.

The reforming conversion feed gas contains H₂、CO、CO₂And hydrocarbons, the hydrocarbons being primarily saturated hydrocarbons, the hydrocarbons being inert to the synthesis of LNG, but the hydrocarbons being convertible by a reforming conversion process to H required for the synthesis of LNG₂And CO, so that the amount of raw material gas for LNG synthesis is increased, the waste of resources is reduced, and the utilization rate of low-rank coal is improved.

The main reaction mechanism is as follows:

(1)CmHn+mH₂O＝mCO+1/2(n+2m)H₂main reaction, endothermic reaction

(2)

Side reactions, endothermic reactions

With CH₄For example, the main reaction equation is CH₄+H₂O→CO+3H₂Generation of H₂The molar ratio of CO to CO is 3:1, and the ratio is large, so that the method is very favorable for preparing reforming conversion gas. During the reforming conversion process, the reforming conversion raw material gas contains H₂In the presence of O (water vapor), certain side reactions are accompanied, mainly CO and H₂O (steam) shift conversion to H₂The reaction of (1).

The pure oxygen reforming conversion is to introduce pure oxygen into the reforming conversion raw material gas, and the main reaction mechanism is as follows: CH (CH)₄+1/2O₂→CO+2H₂Generation of H₂And CO in a molar ratio of 2:1, which is favorable for preparing the reformed gas. Hydrocarbons other than methane with methane and O₂The reaction mechanism of (3) is similar.

Generally, in actual production processes, steam catalytic reforming conversion and non-catalytic reforming conversion or a combination of both are generally used.

(1) The hydrogen-carbon ratio of reformed gas obtained by adopting the first-stage steam deep reforming conversion is about 1.98;

(2) the hydrogen-carbon ratio of the reformed gas obtained by adopting the first-stage steam shallow reforming conversion and the second-stage pure oxygen autothermal reforming conversion is about 1.31-1.98.

(3) The reformed gas obtained by reforming and converting the steam pure oxygen has a hydrogen-carbon ratio of about 1.31.

The effective component in LNG synthesis gas required by LNG synthesis is H₂、CO、CO₂The requirement for the hydrogen-carbon ratio in the LNG syngas is expressed as follows: r ═ H₂-CO₂)/(CO+CO₂) Wherein the hydrogen-carbon ratio of the LNG synthesis gas is R ═ (H)₂-CO₂)/(CO+CO₂) The theoretical value is 3.0, and the optimal value is 2.9-3.1. LNG synthesis gasContains a certain amount of CO₂Can increase the catalytic activity of the synthetic LNG catalyst, reduce the thermal effect of the reaction, make the catalytic temperature easy to control, reduce the thermal inactivation of the catalyst caused by overtemperature, thereby prolonging the service life of the catalyst, but, CO₂The content of (A) must be appropriate. If CO is present₂If the content of (b) is too high, the water content in the product will increase, thus reducing the compression capacity of the compressor and increasing the energy consumption of the gas compression and rectification processes. CO 2₂The optimum content in the LNG synthesis gas is adjusted according to the catalyst used for LNG synthesis and the LNG synthesis operation temperature.

The main chemical reaction formula for synthesizing LNG is as follows:

since the LNG synthesis process is exothermic and thus there are many side reactions, it is preferable to introduce a carbon dioxide-rich gas into the second reactor and/or the third reactor, the carbon dioxide-rich gas having a hydrogen-to-carbon ratio of (2.9 to 3.5): 1 and the volume percentage of carbon dioxide is not less than 5%, so that the reaction temperature is 200-500 ℃ when methane is synthesized. Preferably, the purified gas is introduced into the second reactor and/or the third reactor so that the reaction temperature is 200-500 ℃ when methane is synthesized. Further, feeding carbon dioxide-rich gas into the second reactor, the third reactor, the fourth reactor and/or the fifth reactor, wherein the carbon dioxide-rich gas has a hydrogen-carbon ratio of (2.9-3.5): 1 and the volume percentage of the carbon dioxide is not less than 5 percent, and the reaction temperature is 200-500 ℃. Further, introducing hydrogen-rich gas into the second reactor, the third reactor, the fourth reactor, the fifth reactor and/or the sixth reactor, wherein the volume percentage of hydrogen in the hydrogen-rich gas is not less than 50%.

In the LNG synthesis process, the pressure is about 2.5MPa generally, the part of steam can be used as a byproduct of the LNG synthesis tower of the device and can be used as a source of steam for steam reforming conversion in the reforming conversion process, and waste heat wastewater is recycled, so that the process cost is saved. Preferably, in step (5), the third methane stream enters a fifth reactor, and in the fifth reactor, in the presence of a fourth high temperature resistant methane catalyst, the carbon monoxide, the carbon dioxide and the hydrogen of the third methane stream react to synthesize methane, so as to obtain a fourth methane stream with a carbon monoxide volume fraction content of less than 3%, thereby obtaining the methane product stream. Further, in the step (5), the third methane material flow or the fourth methane material flow enters a sixth reactor, in the sixth reactor, in an environment with a fifth high temperature resistant methane catalyst, the carbon monoxide, the carbon dioxide and the hydrogen of the third methane material flow or the fourth methane material flow react to synthesize methane, and a fifth methane material flow with the carbon monoxide volume fraction content of less than 1% is obtained, so that the methane product material flow is obtained. Further, in the first high temperature resistant methane catalyst, the second high temperature resistant methane catalyst, the third high temperature resistant methane catalyst, the fourth high temperature resistant methane catalyst and the fifth high temperature resistant methane catalyst, the content of nickel is 10-40% and increases in sequence. Preferably, the first methane synthesis material enters a first heat exchanger for heating, and enters the second reactor after being heated.

And (4) feeding the crude LNG obtained from the LNG synthesis process into an LNG rectification process to obtain a product LNG. Preferably, the liquefaction process comprises a decarburization process and a liquefaction process, wherein the decarburization process comprises the steps that LNG liquefied raw material gas enters an absorption device, after decarburization, entrained solution is separated by a demister on the upper part of the absorption device and flows out, then the LNG liquefied raw material gas enters a cooling device, is cooled to be less than 40 ℃, and then water is separated by a gas-liquid separation device to obtain raw material gas which is sent to the liquefaction process; the liquefaction process comprises the steps that raw material gas enters a refrigeration heat exchanger, flows into a low-pressure rectifying device after precooling, is further cooled, then flows back to the refrigeration heat exchanger, is continuously cooled to minus 156 ℃ to minus 160 ℃, flows into a high-pressure rectifying device for rectification, hydrogen components in the raw material gas are distilled out from the top of a tower to form a hydrogen-rich material flow, first rectifying gas containing carbon monoxide, nitrogen and methane flows out from the lower part of the high-pressure rectifying device, flows into a low-pressure rectifying tower through throttling and pressure reduction, the carbon monoxide and the nitrogen in the first rectifying gas form a carbon monoxide-rich material flow, the carbon monoxide-rich material flow is distilled out from the upper part of the low-pressure rectifying tower, and the rest material forms second rectifying gas and flows out from the lower part of the low-pressure rectifying device.

Preferably, the TSA dehydration process is further included, the TSA dehydration process comprises a dehydration link, a heating link, a cooling link and a gas-liquid separation link, the dehydration link comprises a first dehydration link, a second dehydration link and a third dehydration link, the raw material gas flows through the first dehydration link after dehydration, then the rich liquid flows through the heating link after heating, the second dehydration link carries out dehydration, then the rich liquid flows through the cooling link after cooling, the rich liquid flows through the third dehydration link, and the rich liquid flows through the gas-liquid separation link after dehydration. The rich solution is formed after the dehydration solvent absorbs water, and the dehydration solvent comprises diethylene glycol and triethylene glycol.

Preferably, the second rectification gas flow returns to the refrigeration heat exchanger for cooling, is further throttled to about 0.015MPa after being subcooled to-160 ℃ -160 ℃, flows out of the refrigeration heat exchanger, and flows into an LNG storage tank for storage.

The methanation catalyst comprises a first high-temperature-resistant methane catalyst, a second high-temperature-resistant methane catalyst, a third high-temperature-resistant methane catalyst, a fourth high-temperature-resistant methane catalyst and a fifth high-temperature-resistant methane catalyst, and comprises 20-75% by mass of alumina as a carrier, 10-90% by mass of nickel oxide as an active component, and 5-25% by mass of rare earth metal oxide and alkaline earth metal oxide, wherein the rare earth metal comprises Nd, La and Gd, and the alkaline earth metal comprises Be and Sr. Preferably, the content of the nickel oxide of the active component is increased from the first high-temperature-resistant methane catalyst, the second high-temperature-resistant methane catalyst to the third high-temperature-resistant methane catalyst in sequence, and the content of the nickel oxide of the active component is increased from the fourth high-temperature-resistant methane catalystLa of active component added to fifth high-temperature-resistant methane catalyst₂O₃The content of (a) increases in turn.

Since many side reactions occur during the LNG synthesis process, these side reactions generate a large amount of inert gas and accumulate in the process, which affects the normal operation of the LNG synthesis process, and must be continuously discharged, this discharged gas is called LNG purge gas. The LNG purge gas comprises H as the main component₂、CO、H₂O and CH₄In the presence of an inert gas, wherein H₂And CH₄The volume percentage content is about 90 percent. Recovery of H in LNG purge gas by pressure swing adsorption technology₂And the double purposes of increasing the LNG yield and saving energy and reducing emission can be achieved. Recovery of H in LNG purge gas by pressure swing adsorption or the like₂In supplementing the reformed gas, H recovered from the subsequent LNG purge gas may also be recovered₂As recycle gas to supplement the second compression process in the machine with additional recovered H₂It can also be used as fuel for combustion and heat supply. Or purifying H without pressure swing adsorption₂And directly introducing the LNG purge gas serving as a circulating gas into a second compression process to be used as a part of raw material for LNG synthesis. In addition, the

At present, anthracite is basically gasified into synthesis gas to produce LNG in industrialized production, the unit cost of the anthracite is about 1500 yuan/t, 0.294 ton of LNG is restricted to 1 ton of coal, the unit cost of the low-rank coal as the raw material is 80-100 yuan/t, the volatile content in the low-rank coal is 20-55 wt%, and the yield of LNG produced by using the volatile components in the low-rank coal is 15% based on 1 ton of low-rank coal. As shown in table 1 below, the unit cost price of LNG prepared from low-rank coal is much lower than that of LNG prepared from anthracite coal, so that the LNG prepared by the method of the present invention greatly reduces the cost expenditure of raw materials. In addition, in the process for preparing LNG by using low-rank coal, byproduct upgraded coal and coal tar can be obtained, the unit price of the upgraded coal is 500-600 yuan/t, the unit price of the coal tar is 2000-2500 yuan/t, and the value of the product rich in yield is high.

The following comparative experiments were conducted to analyze the composition of the raw LNG stream and the purity of methane in the product gas LNG, thereby analyzing the technological progress of the method of the present invention in the production of LNG.

Experimental example 1

In experimental example 1, 4 adiabatic methane synthesis reactors (R1, R2, R3 and R4, respectively) were used, four-five reactors were connected in series, R1 preheated the purge gas so that the temperature of the purge gas was 150 ℃ and 500 ℃, specifically about 250 ℃, and the internal carriers of R2, R3 and R4 were ceramic and consisted of: al (Al)₂O₃: 56.5 percent; MgO: 22.5 percent; ni: 18.5 percent; la: 1.0 percent; ce: 1.0 percent; ba: 0.5% of catalyst, with the first gas-water separation device as a boundary, in the stage of carrying out methane synthesis in R2 and R3, in R4, the content of CO in the product is reduced, so that the quality of the product is improved. The total gas amount of purified gas is 1000kmol/h, under the condition of 3.0MPa, the temperature of R1 outlet gas is about 250 ℃, the purified gas enters R2, the temperature of R2 outlet gas is reduced to 260 ℃ after heat recovery and enters R3, the temperature of R3 outlet gas is about 350 ℃, the temperature of R3 outlet gas is recovered and enters a first gas-water separation device for gas-liquid separation, the outlet gas of the first gas-water separation device is heated to 150-phase-enriched gas by coupling, specifically about 280 ℃, the outlet gas enters R4 and R4, the temperature of the heat recovery and the temperature of the outlet gas is reduced to about 100-phase-enriched gas 120 ℃, the outlet gas enters a second gas-water separation device for gas-liquid separation, and the original LNG material flow is obtained; and introducing the original LNG material flow into a liquefaction process, and producing methane with the volume percentage not less than 90% by a cryogenic liquefaction process to obtain the product LNG.

Experimental example 2

Experimental example 2 referring to experimental example 1, except that 5 adiabatic methane synthesis reactors (R1, R2, R3, R4, and R5, respectively) were used, five reactors were connected in series, and reactor R5 was added after the first gas-water separation device, so that the CO content in the raw LNG stream of the product was reduced, the quality of the product was improved, and quality control was performed, with the aim of reducing the CO content in the raw LNG stream; recovering heat of gas at an outlet of the R4, cooling to 260 ℃, entering the R5, recovering heat of gas at an outlet of the R5, cooling to about 100-120 ℃, entering a second gas-water separation device, and performing gas-liquid separation to obtain an original LNG material flow; and introducing the original LNG material flow into a liquefaction process, and producing methane with the volume percentage not less than 90% by a cryogenic liquefaction process to obtain the product LNG.

Experimental example 3

Experimental example 3 referring to experimental example 1, except that in the methane synthesis reactors R2, R3 of experimental example 3, carbon dioxide-rich gas was introduced so that the carbon-hydrogen ratio of the carbon dioxide-rich gas was (2.9-3.5) when the methane synthesis reactors R2, R3 were performing methane synthesis reaction: 1, the volume percentage of carbon dioxide in the carbon dioxide-rich gas is about 5 percent, so that when the methane is synthesized, the temperature is controlled below 500 ℃, and the optimized temperature is controlled between 250 ℃ and 350 ℃.

Experimental example 4

Experimental example 4 referring to experimental example 1, except that in the methane synthesis reactors R2, R3 of experimental example 4, a carbon dioxide-rich gas and a hydrogen-rich gas were introduced, respectively, so that the carbon dioxide-rich gas had a hydrogen-to-carbon ratio of (2.9-3.5) when the methane synthesis reactors R2, R3 were subjected to methane synthesis reaction: 1, the volume percentage of carbon dioxide in the carbon dioxide-rich gas is about 5%, the content of hydrogen in the hydrogen-rich gas is higher than 50%, so that the temperature is accurately controlled when the methane is synthesized, specifically, the temperature is controlled below 500 ℃, the temperature is optimally controlled to be between 250 ℃ and 350 ℃, when the temperature is higher than the optimal temperature, the carbon dioxide-rich gas is introduced to reduce the temperature of the reaction due to more moisture in the product, and when the temperature is lower than the optimal temperature, the hydrogen-rich gas is introduced to improve the temperature of the reaction.

Experimental example 5

Experimental example 5 referring to experimental example 1, except that in the methane synthesis reactor R4 of experimental example 4, hydrogen-rich gas was introduced so that the concentration of CO in the raw LNG stream was reduced after the methane synthesis reaction in the methane synthesis reactor R4 was performed.

Experimental example 6

Experimental example 6 referring to experimental example 1, except that a reactor R5 was further provided after the methane synthesis reactor R4 of experimental example 6, and hydrogen-rich gas was introduced into R4 and R5, so that the concentration of CO in the raw LNG stream was reduced after the methane synthesis reactions in the methane synthesis reactors R4 and R5 were carried out.

Comparative example 1

The process of comparative example 1 used 2 adiabatic methane synthesis reactors (R1, R2, respectively). Two reactorsThe series connection, built-in carrier is pottery, and the composition is: al2O 3: 56.5 percent; MgO: 22.5 percent; ni: 18.5 percent; la: 1.0 percent; ce: 1.0 percent; ba: 0.5% of catalyst. The total gas amount of the purified fresh feed gas is 1000kmol/h, and the synthesis of natural gas from coke oven gas is carried out under the pressure condition of 3.0 MPa. Adjusting the temperature of the feed gas to 260 ℃, feeding the feed gas into R1, adjusting the temperature of the gas at the outlet of R1 to 650 ℃, recovering the heat of the gas at the outlet of R1, cooling the recovered heat to 260 ℃, feeding the recovered heat into R2, adjusting the temperature of the gas at the outlet of R2 to about 304 ℃, cooling the recovered heat to 140 ℃, and separating the recovered heat in a separator S1 to obtain 187kmol/h of condensate, wherein the volume of the condensate consists of CH₄1.0％、H₂0.1％、N₂0.1％、H₂98.8% of O and less than 0.1% of others, the condensate being pumped at 180kmol/h before being fed to R1. After cooling and separation of the reaction product, methane is obtained.

Table 2 table of analysis of composition of raw LNG stream produced in test examples 1-6 and comparative example 1

Composition of

Experimental example 1

Experimental example 2

Experimental example 3

Experimental example 4

Experimental example 5

Experimental example 6

Comparative example 1

CH₄

95.77％

97.38％

94.74％

95.64％

95.44％

94.91％

85.54％

H₂

1.49％

1.21％

1.06％

0.92％

2.33％

2.86％

5.3％

CO

0.16％

Not detected out

0.46％

0.32％

Not detected out

0.53％

CO₂

0.26％

0.06％

1.86％

0.86％

Not detected out

0.48％

N₂

1.89％

1.97％

1.88％

1.87％

1.85％

H₂O

0.42％

0.38％

0.40％

0.38％

0.36％

0.38％

6.3％

Note that the raw LNG stream has a composition content in volume percent.

Table 3 comparison of purity of methane in LNG as product gas produced in test examples 1 to 6 and comparative example 1

Name (R)

Experimental example 1

Experimental example 2

Experimental example 3

Experimental example 4

Experimental example 5

Experimental example 6

Comparative example 1

Methane

99.026％

99.137％

99.118％

99.124％

99.057％

99.010％

85.54％

Note that the methane purity in LNG is the volume percent content of methane.

From the results shown in tables 2 and 3, we can obtain CO and H required for obtaining LNG synthesis feedstock by gasifying and reducing low-rank coal to obtain volatile components, and then reforming and converting hydrocarbons and the like in the volatile components₂The LNG is prepared, and the impurities in the LNG are less and the quality is high; the LNG preparation process has higher methane synthesis efficiency; the LNG preparation process of the invention fully and effectively utilizes the volatile components in the low-rank coal, has rich raw materials for manufacturing LNG and lower cost, greatly saves the production cost, and also has rich high-value upgraded coal and coal tar, thereby conforming to the national coal comprehensive utilization direction; according to the method disclosed by the invention, the prepared LNG has few impurities and high quality, and the volatile components in the low-rank coal are fully and effectively utilized.

In summary, the method of the invention obtains coal quality and volatile components by gasification reduction of low-rank coal, and then reforms and converts hydrocarbons and the like in the volatile components to obtain CO and H required by LNG synthetic raw materials₂The LNG prepared by the method has less impurities and high quality, fully and effectively utilizes the volatile components in the low-rank coal, and the raw materials for preparing the LNG are richThe cost is low, the production cost is greatly saved, high-value upgraded coal and coal tar are rich, and the method accords with the national coal comprehensive utilization direction.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. The LNG preparation process for quality-divided utilization of low-rank coal is characterized by comprising the following steps of:

2. The LNG production process of claim 1 wherein in step (5) the third methane stream is passed to a fifth reactor wherein carbon monoxide, carbon dioxide and hydrogen of the third methane stream are reacted in the presence of a fourth refractory methane catalyst to synthesize methane and produce a fourth methane stream having a carbon monoxide volume fraction of less than 3% to produce the methane product stream.

3. The LNG production process of claim 1 or 2 wherein in step (5) the third methane stream or the fourth methane stream enters a sixth reactor where carbon monoxide, carbon dioxide and hydrogen of the third methane stream or the fourth methane stream react in the presence of a fifth refractory methane catalyst to synthesize methane to produce a fifth methane stream having a carbon monoxide volume fraction content of less than 1% to produce the methane product stream.

4. The LNG production process according to claim 1, wherein a carbon dioxide-rich gas is introduced into the second reactor and/or the third reactor, wherein the carbon dioxide-rich gas has a hydrogen-to-carbon ratio of (2.9-3.5): 1 and the volume percentage of carbon dioxide is not less than 5%, so that the reaction temperature is 200-500 ℃ when methane is synthesized.

5. The LNG production process as claimed in claim 1, wherein the purified gas is introduced into the second reactor and/or the third reactor so that the reaction temperature is 200-500 ℃ when methane is synthesized.

6. The LNG production process according to claim 2, wherein carbon dioxide-rich gas is introduced into the second reactor, the third reactor, the fourth reactor and/or the fifth reactor, wherein the carbon dioxide-rich gas has a hydrogen-to-carbon ratio of (2.9-3.5): 1 and the volume percentage of the carbon dioxide is not less than 5 percent, and the reaction temperature is 200-500 ℃.

7. The LNG production process according to claim 3, characterized in that hydrogen rich gas, in which the volume percentage of hydrogen is not less than 50%, is fed into the second reactor, the third reactor, the fourth reactor, the fifth reactor and/or the sixth reactor.

8. The LNG production process according to claim 1, wherein the liquefaction process comprises a decarbonization process and a liquefaction process, wherein the decarbonization process comprises introducing LNG liquefied raw material gas into an absorption device, decarbonizing, separating entrained solution by a demister at the upper part of the absorption device, discharging, introducing into a cooling device, cooling to less than 40 ℃, separating water by a gas-liquid separation device, obtaining raw material gas, and introducing into the liquefaction process; the liquefaction process comprises the steps that raw material gas enters a refrigeration heat exchanger, flows into a low-pressure rectifying device after precooling, is further cooled, then flows back to the refrigeration heat exchanger, is continuously cooled to minus 156 ℃ to minus 160 ℃, flows into a high-pressure rectifying device for rectification, hydrogen components in the raw material gas are distilled out from the top of a tower to form a hydrogen-rich material flow, first rectifying gas containing carbon monoxide, nitrogen and methane flows out from the lower part of the high-pressure rectifying device, flows into a low-pressure rectifying tower through throttling and pressure reduction, the carbon monoxide and the nitrogen in the first rectifying gas form a carbon monoxide-rich material flow, the carbon monoxide-rich material flow is distilled out from the upper part of the low-pressure rectifying tower, and the rest material forms second rectifying gas and flows out from the lower part of the low-pressure rectifying device.

9. The LNG production process of claim 8 wherein in the absorption unit the CO in the NG liquefaction feed gas₂The components are absorbed by the active MDEA complex solution.

10. The LNG production process of claim 8 wherein the hydrogen-rich stream, passing through the refrigeration heat exchanger, is reheated to 20-40 ℃ and bled.