CN110862841B

CN110862841B - Method for preparing natural gas from coal water slurry

Info

Publication number: CN110862841B
Application number: CN201911213293.0A
Authority: CN
Inventors: 潘建波; 陈锋江; 何巍; 舒文华; 杨军兵; 吕彬峰
Original assignee: Zhejiang Tianlu Environmental Technology Co ltd
Current assignee: Zhejiang Tianlu Environmental Technology Co ltd
Priority date: 2019-12-02
Filing date: 2019-12-02
Publication date: 2023-01-20
Anticipated expiration: 2039-12-02
Also published as: CN110862841A

Abstract

The invention discloses a method for preparing natural gas from coal water slurry, which comprises the following steps of (1) preparing the coal water slurry by crushing and grinding low-rank coal, heating the coal water slurry to 800-1300 ℃ under the condition of no oxygen or micro oxygen, and preparing the coal water slurry containing CO and H ₂ The synthesis gas of (2); (2) Removing sulfur in the synthesis gas through a pre-desulfurization process to obtain pre-desulfurized synthesis gas; (3) Converting all unsaturated hydrocarbons of the pre-desulfurized syngas to corresponding saturated hydrocarbons by a hydrogenation process while converting organic sulfur to H ₂ S, obtaining hydrogenated synthesis gas; according to the method, the low-rank coal is prepared into the coal water slurry through crushing and grinding steps, and further, the coal water slurry is prepared by using part or all of upgraded coal and then prepared to contain CO and H ₂ The synthetic gas prepared by the method has less impurities and high quality, fully and effectively utilizes coal substances in low-rank coal, and accords with the national coal comprehensive utilization direction.

Description

Method for preparing natural gas from coal water slurry

Technical Field

The invention relates to the technical field of clean utilization of coal substances, in particular to a method for preparing natural gas from coal water slurry.

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 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 quality of coal mines, the proportion of low-rank 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 particularly important. In recent years, the development of coal gasification, coal pyrolysis, coal gas purification, coal gas separation and other technologies has led to more and more attention being paid to the clean and efficient utilization of middle-low-grade coal.

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. It is predicted that the demand of natural gas in China will reach 1700 billion Nm 3-2100 billion Nm3 in 2015, while the yield of natural gas in the same period can only reach 1400 billion Nm3, and the supply and demand gap is about 300 billion Nm 3-700 billion Nm3. 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.

The low-rank coal in China has poor quality, high ash content and high water content, the low-rank coal is generally utilized from pyrolysis gasification to crude coal gas and quality-improved coal, the pyrolysis is generally carried out under the condition of a large amount of oxygen (or air), and part of the low-rank coal is used for supplying heat through oxygen reaction and generates a large amount of CO during the pyrolysis ₂ . Due to CO ₂ Can not be combusted, belongs to ineffective gas, and has over high nitrogen content due to aerobic combustion, thereby reducing H in the crude gas ₂ And 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. And due to aerobic pyrolysis, the quantity of upgraded coal is reduced, even the upgraded coal cannot be obtained, the quantity of natural gas prepared by the upgraded coal is reduced, the effective coal resources in the low-rank coal are greatly wasted, and the utilization rate of the low-rank coal is low.

Disclosure of Invention

In view of the above, the present invention provides a method for preparing natural gas from coal water slurry, which prepares coal water slurry by utilizing low-rank coal according to quality, and prepares coal water slurry containing CO and H under the condition of no oxygen or micro oxygen ₂ The synthetic gas is subjected to a pre-desulfurization process, a hydrogenation process, a desulfurization process, a transformation process, a methane synthesis process and a liquefaction process, so that coal substances in the low-rank coal are converted into natural gas, the prepared natural gas has less impurities and high quality, and the coal substances in the low-rank coal are fully and effectively utilized.

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

a method for preparing natural gas from coal water slurry comprises the following steps,

(1) The low-rank coal is prepared into water-coal-slurry through the steps of crushing and grinding, the water-coal-slurry is heated to 800-1300 ℃ under the condition of no oxygen or micro oxygen, and the water-coal-slurry is prepared to contain CO and H ₂ The synthesis gas of (2);

(2) Removing sulfur in the synthesis gas through a pre-desulfurization process to obtain pre-desulfurized synthesis gas;

(3) Converting all unsaturated hydrocarbons of the pre-desulfurized syngas to the corresponding saturated hydrocarbons by means of a hydrogenation process, while converting organic sulfur to H ₂ S, obtaining hydrogenated synthesis gas;

(4) Removing sulfur in the hydrogenated synthesis gas through a desulfurization process to obtain desulfurized synthesis gas;

(5) And (2) subjecting the desulfurized synthesis gas to a shift conversion process to obtain shift conversion gas, wherein the molar ratio of hydrogen to CO in the shift conversion gas is (3-10): 1;

(6) And removing carbon dioxide in the converted gas through a decarburization process to obtain natural gas synthetic gas, so that the hydrogen-carbon ratio in the natural gas synthetic gas is (2.95-3.05): 1;

(7) The natural gas synthesis gas is subjected to a methane synthesis process in which at least 4 methanation reactors are connected in series, so that carbon monoxide, carbon dioxide and hydrogen in the desulfurized synthesis gas react in the presence of a methanation catalyst to synthesize methane, and a methane product material flow is obtained;

(8) And (3) introducing the methane product 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 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 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 synthesis gas and upgraded coal with a certain temperature.

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 synthesis gas are obtained, wherein the solid carbon is upgraded coal, and the volatile component in the upgraded coal is 8-15wt%. The high-temperature synthesis gas comprises CO and H ₂ 、CO ₂ Hydrocarbons, coal tar, naphthalene, halides, dust, and sulfur-containing compounds.

Wherein, the gasification reduction process can be one-stage or multi-stage. When the primary gasification reduction process is adopted, the temperature mainly aims to obtain most high-temperature synthesis gas, the subsequent gas production amount, the yield of the upgraded coal and the temperature of the primary upgraded coal are directly influenced by the temperature, the reaction temperature of the gasification reduction process is 350-800 ℃, the volatile content in the upgraded coal is 8-15wt%, and the reaction temperature of the gasification reduction process is further preferably 400-750 ℃; still more preferably 450 to 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.

Besides ensuring reasonable temperature of the gasification reduction process, certain retention time in the gasification reduction process is ensured, the retention time is too short, volatile components are not completely escaped for gasification, and the quality of upgraded coal is influenced more while the gas yield is influenced; the residence time is too long, and although the product is guaranteed, the yield cannot be kept up to, so that maintaining a reasonable residence time for the gasification reduction reaction is critical to the yield and quality of the product. Due to different varieties of raw material low-rank coal, the retention time of materials in the general gasification reduction process is 30min-4h.

The method preferably adopts a two-stage gasification reduction process, the materials dried by the drying process enter a first-stage gasification reduction process and then enter a second-stage gasification reduction process, the dried low-rank coal enters the first-stage gasification reduction process to obtain first-stage gas and first-stage solid, the first-stage solid enters the second-stage gasification reduction process to be continuously gasified to obtain second-stage gas and second-stage solid, and the second-stage solid is upgraded coal; the feeding temperature of the primary gasification reduction process is 80-120 ℃, the gas outlet temperature is 180-550 ℃, the reaction temperature is 450-650 ℃, and the discharging temperature is 350-600 ℃; the feeding temperature of the secondary gasification reduction process is 350-600 ℃, the discharging temperature is 450-750 ℃, the reaction temperature is 550-800 ℃, and the gas outlet temperature is 450-700 ℃. When the two-stage gasification reduction process is adopted, the aim is to completely gasify most of volatile matters, so that a large amount of gas can be obtained, and upgraded coal with lower volatile matters can be obtained, wherein the volatile matter content in the upgraded coal is 3-8wt%.

Preferably, the coal water slurry also contains upgraded coal, and the upgraded coal is prepared from low-rank coal through a gasification reduction process. Further, in the coal water slurry, the mass ratio of the upgraded coal to the low-rank coal is (1-10): 1.

heating the water-coal-slurry to 800-1300 ℃ under the condition of no oxygen or micro oxygen, gasifying the water in the water-coal-slurry into steam, and mixing low-rank coal or upgraded coal in the water-coal-slurry with H ₂ The reaction of O (water vapor) is endothermic and the reaction equation is C + H ₂ O＝CO+H ₂ The upgraded coal obtained after the gasification reduction process reaction is the upgraded coal with temperature. Preferably, in step 1, steam preheated to 800-1300 ℃ is introduced. Preferably, the coal water slurry is heated by a resistance wire to prepare the synthesis gas at the temperature of 800-1300 ℃. Further, the resistance wire contains nickel and chromium.

The particle size of the low rank coal and upgraded coal also affects syngas generation, preferably, the upgraded coal is subjected to a pulverization process such that the upgraded coal has a particle size between 100 mesh and 300 mesh. Preferably, the low-rank coal is subjected to a crushing process so that the particle size of the low-rank coal is between 100 and 300 meshes.

To facilitate the generation of syngas by allowing water vapor to adhere to the upgraded coal particles and within the interstices thereof, it is preferred that the water vapor pass through electrodes to which a DC voltage in excess of 10KV is applied to charge the water vapor.

The upgraded coal with small granularity is preferably the upgraded coal with small granularity, the upgraded coal with large strength can be directly sold, and the upgraded coal with small granularity is easy to cause dust, cannot be transported conveniently and is easy to cause environmental pollution.

The main impurity gas in the synthesis gas is CO ₂ 、H ₂ S, COS and other impurities, and a small amount of dust. The pre-desulfurization process, the hydrogenation process and the desulfurization process are required to remove relevant impurities to obtain the purified desulfurized synthesis gas. Preferably, before the synthesis gas enters the pre-desulfurization process, the particulate matters in the synthesis gas are removed through a dust removal process. Preferably, the pre-desulfurization process comprises the use of a filtration device loaded with a composition comprising an adsorbent material and the pre-desulfurization catalyst. Preferably, the pre-desulfurization process comprises using a pre-desulfurization solution, wherein the synthesis gas enters from the lower part of the first desulfurization device and is in countercurrent contact with the pre-desulfurization solution sprayed from the upper part of the first desulfurization device, so that hydrogen sulfide in the synthesis gas is removed, and the pre-desulfurization solution comprises a PDS catalyst. Further, the pre-desulfurization process comprises a second desulfurization device using at least one of a resistance wire and a pre-desulfurization catalyst, wherein the resistance wire comprises nickel and chromium, the pre-desulfurization catalyst comprises at least one of basic copper carbonate, copper oxide, copper hydroxide, basic zinc carbonate, zinc oxide and zinc hydroxide, the synthesis gas is introduced into the second desulfurization device, and the resistance wire heats the synthesis gas to 200-500 ℃ so that H in the synthesis gas is generated ₂ S is decomposed into elemental sulfur, and the elemental sulfur is filtered outAfter sulphur, the pre-desulphurised synthesis gas is obtained. Preferably, the desulfurization process comprises using a desulfurization solution, wherein the hydrogenated synthesis gas enters from the lower part of a third desulfurization device and is in countercurrent contact with the desulfurization solution sprayed from the upper part of the third desulfurization device, so that hydrogen sulfide in the hydrogenated synthesis gas is removed, and the desulfurization solution contains an NHD solvent. Further, in the desulfurization process, pressurized gas is introduced so that the pressure is 0.2 to 1.0MPa, and the temperature is maintained at 20 to 30 ℃.

The effective component in the natural gas and the synthetic gas is H ₂ 、CO、CO ₂ The requirement for the hydrogen-carbon ratio in the natural gas and the synthetic gas has the following expression: r = (H) ₂ -CO ₂ )/(CO+CO ₂ ) Wherein, the hydrogen-carbon ratio R of the natural gas and the synthetic gas is 3.0 in theory, and 2.95-3.05 in optimal value. And the R value of the hydrogen-carbon ratio in the prepared converted gas can not just meet the R value of 2.95-3.05, so the R value of the hydrogen-carbon ratio in the obtained natural gas and synthetic gas is adjusted to 2.95-3.05 by adjusting the hydrogen-carbon ratio of the converted gas through one or more of a decarburization carbon-supplementing process, a transformation conversion process and a hydrogen-supplementing process. Preferably, in the step (3), the converted gas is firstly subjected to a conversion process to obtain converted gas, and the converted gas is subjected to a decarburization carbon supplementing process to obtain natural gas synthesis gas. Because of CO + H in the upgrading coal gasification process ₂ 1, too high in trans-CO content, by a shift conversion reaction:

can increase H ₂ Volume percent of CO, volume percent of CO reduction, if CO is caused ₂ The surplus is easy to remove. The converted gas obtained after the quality-improved coal gasification contains a certain amount of unreacted H ₂ O (water vapour), using the H contained in the reformed gas ₂ O (water vapour) or externally supplemented H ₂ O (water vapor) can directly carry out conversion reaction under certain conditions. The choice of conversion process is determined according to the R value of converted gas, and the R value is generally close to 2.95-3.05The R value is directly and rapidly adjusted through a subsequent decarburization carbon supplementing process without adopting a conversion process; when the R value is far less than 2.95-3.05, a conversion process is added so as to increase the R value.

Preferably, the shift conversion process is to pass CO in the converted gas through H ₂ Conversion of O into H ₂ And CO ₂ The process of (1).

Preferably, in the decarbonization and carbon supplement process in the step (3), when the hydrogen-carbon ratio R value of the converted gas is greater than 3.1, CO is introduced ₂ So that the R value is adjusted to 2.95-3.05; when the hydrogen-carbon ratio R value of the converted gas is less than 2.95, removing CO ₂ So that the R value is adjusted to 2.95-3.05. When the R value of the converted gas is more than 3.1, the converted gas represents more hydrogen and less carbon, and CO is introduced into the whole converted gas through a carbon supplementing process ₂ Or CO of high purity ₂ And obtaining the natural gas synthetic gas meeting the standard. When the R value of the reformed gas is less than 2.95, the reformed gas represents less hydrogen and more carbon, and a part of CO in the reformed gas is removed by pressure swing adsorption or solution absorption ₂ The R value range of the natural gas and the synthetic gas is adjusted to be 2.95-3.05.

Preferably, the decarbonization process comprises the use of decarbonization liquid, the hydrogenated synthesis gas enters from the lower part of a decarbonization device and is in countercurrent contact with decarbonization liquid sprayed from the upper part of the decarbonization device, so that carbon dioxide in the hydrogenated synthesis gas is removed, and the decarbonization liquid contains NHD solvent. Furthermore, in the decarburization process, pressurized gas is introduced so that the pressure is 0.3 to 1.0MPa.

And finally, producing methane with the volume percentage not less than 90% by a cryogenic liquefaction process through a liquefaction process to obtain the LNG synthesis gas product, so that the natural gas product is obtained, the impurities are few, the quality is high, and the requirement of natural gas quality index is met.

Based on the technical scheme, the method comprises the steps of crushing and grinding low-rank coal to obtain the coal water slurry, and then carrying out gasification reduction under the oxygen-free or micro-oxygen condition to obtain the coal water slurry containing CO and H ₂ The synthesis gas is further obtained by gasifying and reducing part or all of the low-rank coal to obtain upgraded coal, and the upgraded coal has less volatile components and less impuritiesAnd then the upgraded coal is prepared into coal water slurry and gasified to prepare raw materials CO and CO required by natural gas synthesis ₂ And H ₂ When the gas is used, the prepared natural gas has less impurities and high quality, fully and effectively utilizes coal substances in low-rank coal, and accords with the national coal comprehensive utilization direction.

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.

(5) And (2) subjecting the desulfurized synthesis gas to a conversion process to obtain a conversion gas, wherein the molar ratio of hydrogen to CO in the conversion gas is (3-10): 1;

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 a low degree of coalification, but is preferably low-rank coal having a fixed carbon content of 40% to 60%.

The drying process can only remove most of the free water in the low-rank coal, but cannot 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 and changed into steam in the subsequent gasification reduction process. If the low-rank coal contains a large amount of moisture, the heat consumption in the gasification reduction reaction process is large, so the technical scheme of the invention firstly treats the low-rank coal through a drying process and removes a part of moisture in the low-rank coal. The drying medium of the drying process can be flue gas or water vapor, and the drying can be divided into direct drying and indirect drying. When flue gas is used as a drying medium, although the drying efficiency of the flue gas in direct contact with low-rank coal is the highest, the volume percentage of oxygen in the drying process environment is strictly controlled to be below an explosion limit when the flue gas is used for drying so as to prevent deflagration, and the efficiency of flue gas indirect drying is not ideal, so that steam drying is preferred for production safety and drying efficiency. The direct drying of the steam can easily cause the steam to be mixed into the low-rank coal, thereby not only causing the consumption of reaction coal resources, but also reducing the drying efficiency, and therefore, the drying mode of indirectly drying the low-rank coal by the steam is adopted to prevent the moisture in the steam from entering the low-rank coal. In addition, if the pressure of the steam is too high in the drying process, the temperature caused by the steam is too high, so that partial volatile components in the low-rank coal can escape out in the drying process, on one hand, the escape of the volatile components can bring potential safety hazards, and on the other hand, the gas yield of a subsequent gasification reduction process can be influenced, therefore, the drying steam pressure is not too high in the drying process, the drying effect can be guaranteed, and the volatile components in the low-rank coal can be prevented from being gasified. Therefore, preferably, the drying process adopts indirect drying by using water vapor, the pressure of the water vapor is 0.3-1.5Mpa, the temperature of the water vapor is 105-250 ℃, the water content in the low-rank coal can be reduced to the maximum extent under the process condition, even the water content in the low-rank coal discharged from a discharge port of the drying process can be reduced to below 7wt%, most of the water escapes from the low-rank coal along with dust such as coal dust and enters the waste gas generated after drying in the form of water vapor, and the temperature of the outlet material of the drying process is 50-150 ℃; still further preferably, when the pressure of the water vapor is 0.6-1.2Mpa and the temperature of the water vapor is 120-200 ℃, the water content of the dried low-rank coal is reduced to below 6wt%, and the temperature of the outlet material of the drying process is 80-130 ℃.

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. In addition, the multistage drying process can be arranged in series or in parallel, the drying effect can be enhanced when the multistage drying process is connected in series, and the treatment capacity of the drying process can be increased when the multistage drying process is connected in parallel, so that the multistage drying process can be adjusted according to the actual situation according to the requirement of the actual production process and the design of the multistage drying process of being connected in series or in parallel or being connected in series and in parallel at the same time, as long as the same technical effect can be achieved, and particularly, when the feeding amount of the drying process is calculated by 20-30t/h of low-rank coal, a one-level steam drying process can be adopted; when the feeding amount of the drying process is calculated by a low level of 50-70t/h, a secondary steam drying process can be adopted, so that the method is more economical and reasonable.

The low-rank coal dried by the drying process enters the gasification reduction process to react, and 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 is 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 process of complex chemical reaction is carried out under the pressure of less than or equal to 30Kpa, so as to obtain solid carbon and high-temperature synthesis gas, wherein the solid carbon is upgraded coal, and the volatile components in the upgraded coal are 8-15wt%. The high-temperature synthesis gas comprises CO and H ₂ 、CO ₂ Hydrocarbon, coal tar, naphthalene, halide, dust, sulfur compounds, and the like.

Preferably, the coal water slurry also contains upgraded coal, and the upgraded coal is prepared from low-rank coal through a gasification reduction process.

Wherein, the gasification reduction process can be one-stage or multi-stage. When the primary gasification reduction process is adopted, the temperature mainly aims to obtain most high-temperature synthesis gas, the subsequent gas production amount, the yield of the upgraded coal and the temperature of the primary upgraded coal are directly influenced by the temperature, the reaction temperature of the gasification reduction process is 350-800 ℃, the volatile content in the upgraded coal is 8-15wt%, 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.

Heating the water-coal-slurry to 800-1300 ℃ under the condition of no oxygen or micro oxygen, gasifying the water in the water-coal-slurry into steam, low-rank coal in the water-coal-slurry or upgraded coal and H ₂ The reaction of O (water vapor) is endothermic and the reaction equation is C + H ₂ O＝CO+H ₂ . Preferably, the coal water slurry is heated by a resistance wire so as to react at the temperature of 800-1300 ℃. Further, the resistance wire contains nickel and chromium. Preferably, the steam is preheated to 800-1300 ℃ before reacting with the upgraded coal. Syngas is produced continuously by continuously introducing steam so that upgraded coal reacts with the steam.

Because most of volatile components, tar and the like are gasified and removed in the gasification reduction process stage, the content of coal substances in the obtained upgraded coal is high, and therefore, the content of impurity gas in the synthesis gas obtained by utilizing the upgraded coal is less. Therefore, the substance content in the synthesis gas can be controlled by adjusting the content of the upgraded coal in the coal water slurry; preferably, in the coal water slurry, the mass ratio of the upgraded coal to the low-rank coal is (1-10): 1.

the upgraded coal is preferably upgraded coal with a small particle size, the upgraded coal with a large strength can be sold directly, the upgraded coal with a small particle size is easy to cause dust, cannot be transported conveniently and easily causes environmental pollution, and the synthesis gas is preferably prepared by using the pulverized upgraded coal with a small particle size obtained by screening the upgraded coal.

The main impurity gas in the synthesis gas is CO ₂ 、H ₂ S, COS and other impurities, and a small amount of dust. And removing impurities such as deacidified gas and a small amount of dust in the synthesis gas by a purification process to obtain the purified synthesis gas. The purification process comprises a physical absorption method, a chemical absorption method and a physical and chemical absorption method. Physical absorption processes include low temperature natural gas scrubbing, the polyethylene glycol dimethyl ether process, the N-2 methylpyrrolidone process, and the like. Among them, the physical absorption method is more economical and mature, and is widely applied to industrial production, and the representative methods include a low-temperature natural gas scrubbing method (Rectisol) and a polyethylene glycol dimethyl ether method (NHD). The low-temperature natural gas washing process takes cold natural gas as an absorption solvent and utilizes natural gas to treat acid gas (CO) at low temperature ₂ 、H ₂ S, COS, etc.) and is a physical absorption method for removing acid gases from syngas. The low-temperature natural gas washing process is the most economic gas purification technology with high purification degree which is recognized at home and abroad at present, and has the characteristics that other desulfurization and decarburization technologies cannot be replaced, such as: high quality of purified gas, high purification degree, selective absorption of CO ₂ 、H ₂ The characteristics of S and CO, cheap and easily obtained solvent, low operation cost, stable and reliable production operation and the like. Therefore, the purification process is preferably a low temperature natural gas wash process to remove acid gases from the synthesis gas.

Preferably, before the synthesis gas enters the pre-desulfurization process, the particulate matters in the synthesis gas are removed through a dust removal process. Preferably, the pre-desulfurization process comprises the use of a filtration device loaded with a composition comprising an adsorbent material and the pre-desulfurization catalyst. Preferably, the pre-desulfurization process comprises using a pre-desulfurization solution, the syngas being removed from the first streamAnd the lower part of the sulfur device enters and is in countercurrent contact with pre-desulfurization liquid sprayed from the upper part of the first desulfurization device, so that hydrogen sulfide in the synthesis gas is removed, and the pre-desulfurization liquid comprises a PDS catalyst. Further, the pre-desulfurization process comprises a second desulfurization device using at least one of a resistance wire and a pre-desulfurization catalyst, wherein the resistance wire comprises nickel and chromium, the pre-desulfurization catalyst comprises at least one of basic copper carbonate, copper oxide, copper hydroxide, basic zinc carbonate, zinc oxide and zinc hydroxide, the synthesis gas is introduced into the second desulfurization device, and the resistance wire heats the synthesis gas to 200-500 ℃ so that H in the synthesis gas is generated ₂ And decomposing S into elemental sulfur, and filtering to remove the elemental sulfur to obtain the pre-desulfurized synthesis gas. Preferably, the desulfurization process comprises using a desulfurization solution, wherein the hydrogenated synthesis gas enters from the lower part of a third desulfurization device and is in countercurrent contact with the desulfurization solution sprayed from the upper part of the third desulfurization device, so that hydrogen sulfide in the hydrogenated synthesis gas is removed, and the desulfurization solution contains an NHD solvent. Further, in the desulfurization process, pressurized gas is introduced so that the pressure is 0.2 to 1.0MPa, and the temperature is maintained at 20 to 30 ℃.

The R value of the hydrogen-carbon ratio in the converted gas obtained after the purification process usually cannot meet the requirement that the R value of the raw gas for natural gas synthesis is 2.95-3.05, so the R value needs to be adjusted.

The effective component in the gas required for natural gas synthesis is H ₂ 、CO、CO ₂ The following expression is required for the hydrogen-carbon ratio in natural gas synthesis gas:

R＝(H ₂ -CO ₂ )/(CO+CO ₂ ) Wherein, the hydrogen-carbon ratio R of the natural gas and the synthetic gas is = (H) ₂ -CO ₂ )/(CO+CO ₂ ) The theoretical value is 3.0, and the optimal value is 2.95-3.05.

The natural gas synthetic gas contains a certain amount of CO ₂ Can increase the catalytic activity of the catalyst for synthesizing natural gas, reduce the heat effect of reaction, make the catalytic temperature easy to control, reduce the thermal deactivation of the catalyst caused by overtemperature, thus prolong the service life of the catalyst, but CO ₂ The content of (c) must be appropriate. If CO is present ₂ If 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 2 ₂ The optimal content in the natural gas synthetic gas is adjusted according to the catalyst used for natural gas synthesis and the natural gas synthesis operation temperature.

Preferably, the decarbonization process comprises the use of decarbonization liquid, the hydrogenated synthesis gas enters from the lower part of a decarbonization device and is in countercurrent contact with decarbonization liquid sprayed from the upper part of the decarbonization device, so that carbon dioxide in the hydrogenated synthesis gas is removed, and the decarbonization liquid contains NHD solvent. Further, in the decarburization process, pressurized gas is introduced so that the pressure is 0.3 to 1.0MPa. The aim is to remove carbon dioxide from the desulphurised synthesis gas.

When the R value of the natural gas synthetic gas is more than 3.1, the natural gas synthetic gas represents more hydrogen and less carbon, at the moment, the circulating gas quantity of a natural gas synthetic loop is large, the power consumption of a circulating gas compressor is large, the purge gas quantity of natural gas is also large, and a plurality of raw materials are used for preparing useful H through multiple processes ₂ 、CO、CO ₂ And methane and the like are sent into a fuel system along with the purge gas of the natural gas to be burnt, so that serious resource waste is caused, and the consumption of raw materials is increased. When the R value of the natural gas synthetic gas is less than 2.95, the requirement of natural gas synthesis cannot be met. Therefore, the R value of the converted air needs to be adjusted.

The R value of the converted gas can be realized by one or more of a decarburization carbon supplementing process, a change conversion process and a hydrogen supplementing process.

The decarbonization and carbon supplement process comprises a decarbonization process and a carbon supplement process, namely removing CO ₂ And make-up of CO ₂ The process of (1). The converted gas is treated by a decarburization carbon-supplementing process to obtain natural gas synthesis gas with the R value of 2.95-3.05. When the R value of the converted gas is more than 3.1, the converted gas represents more hydrogen and less carbon, and CO is introduced into the converted gas through a carbon supplementing process ₂ Or CO of high purity ₂ And obtaining the natural gas synthetic gas meeting the standard. When the R value of the converted gas is less than 2.95, the converted gas represents more carbon and less hydrogen, and a part of CO in the converted gas is removed by a decarburization process ₂ So that the R value range value of the natural gas and the synthetic gas is adjustedIs 2.95-3.05.

Removal of CO industrially ₂ There are many methods, and they can be broadly classified into two categories: one is solvent absorption and the other is Pressure Swing Adsorption (PSA). The solvent absorption method includes physical absorption method, chemical absorption method and physical-chemical absorption method, the physical absorption method includes low temperature natural gas washing method, polyethylene glycol dimethyl ether method, propylene carbonate method; chemical absorption, in general like NaOH, KOH, ba (OH) ₂ The alkali liquor with stronger equialkalinity can effectively absorb CO ₂ Gas, the principle of which is due to CO ₂ The gas is dissolved in water to generate carbonic acid, and a small part of hydrogen ions generated by ionization of the carbonic acid react with hydroxide ions in the alkali liquor to generate water, so that CO can be removed ₂ . The PSA method utilizes the characteristic that the adsorbent has different adsorption capacities, adsorption speeds and adsorption forces to adsorbates under different partial pressures and has selective adsorption to each component of a separated gas mixture under a certain pressure to remove impurity components in raw gas by pressure adsorption and remove the impurities by decompression so as to regenerate the adsorbent ₂ The new technology has wide prospect. In addition, the process works to remove CO ₂ And can be recycled.

When the R value of the converted gas is less than 2.95, H can also be supplemented by a hydrogen supplementing process ₂ The method replaces the decarburization process to adjust the R value of the converted gas so that the R value is between 2.95 and 3.05. Adding a proper amount of outside H ₂ Or H of high purity ₂ Introducing into converted gas to make R value in the range of 2.95-3.05, so as to save decarbonization process and reduce technological process. Here H ₂ Or H of high purity ₂ Can be purchased directly from the outside, and can also recover purified H from the natural gas purge gas remaining after the subsequent natural gas synthesis process ₂ Preferably, purified H from natural gas purge gas is used ₂ And the reformed gas and the converted gas enter a subsequent compression process, so that the resource recycling is realized, and the process cost expenditure is saved.

Before the converted gas is subjected to the decarburization carbon supplementing process to obtain the natural gas synthesis gas, the converted gas is subjected to a conversion process to obtain converted gas. When the R value of the hydrogen-carbon ratio in the converted gas is generally less than 2.05, the converted gas represents more carbon and less hydrogen, and the components cannot meet the requirements of synthesizing natural gas. Carbon is excessive and hydrogen is insufficient, and the optimization focuses on how to obtain more hydrogen. The converted gas is subjected to a conversion process to obtain converted gas, the converted gas is subjected to a decarburization carbon supplement process to obtain natural gas synthetic gas, and the hydrogen-carbon ratio R value of the natural gas synthetic gas is adjusted to be 2.95-3.05.

A certain amount of H ₂ Introducing O (water vapor) into the converted gas to perform conversion reaction to obtain converted gas. The main reactions in the shift conversion process are:

thermal effect of this reaction H ₂ Depending on the state of O, an endothermic reaction is obtained in the case of liquid water, and an exothermic reaction is obtained in the case of steam. The change reaction is a reversible reaction whose equilibrium constant decreases with increasing pressure. The converted gas is treated by the conversion process to obtain the converted gas, and H can be increased ₂ Volume percent of CO, while increasing CO ₂ Therefore, the shift conversion process is generally followed by a decarburization process for removing CO ₂ . The transformation conversion process is used for increasing the effective component H ₂ At the same time, the CO is increased ₂ Volume percent, but CO ₂ Is easy to remove, and a great amount of CO in the shift gas is obtained after the shift conversion process ₂ Can be treated by a decarburization carbon supplementing process. Determining the choice of the conversion process according to the R value of the converted gas, and directly and quickly adjusting the R value through the subsequent decarburization carbon-supplementing process without adopting the conversion process when the R value is generally close to 2.95-3.05; when the R value is far less than 2.95-3.05, the conversion process is added to increase the R value, and the R value is adjusted by the decarburization carbon-supplementing process after reuse. Because the prepared converted gas contains a certain amount of unreacted H ₂ O (water vapor), and does not need to supplement H externally when changing ₂ O (water vapor) can directly carry out conversion reaction under certain conditions.

The natural gas synthesis gas obtained from the decarburization carbon supplementing process is firstly compressed by a compression process, so that the pressure of the subsequent natural gas synthesis compression process is favorably 40-50kg, and the temperature is 200-350 ℃. Because the pressure of the gas treated by the compression process is 40-50kg, the natural gas is synthesized by adopting a low-pressure method. In order to realize isobaric natural gas synthesis, save a natural gas synthesis gas compressor and compression power consumption, and reduce investment cost and production cost, the production and purification of the natural gas synthesis gas are generally carried out under low pressure. The natural gas synthetic gas enters a natural gas synthesis process, a catalyst required by natural gas synthesis is added, and crude natural gas and natural gas purge gas are obtained after reaction. The natural gas synthesis catalyst can be generally divided into a zinc-chromium catalyst, a copper-based catalyst, a palladium-based catalyst, a molybdenum-based catalyst and the like, and the copper-zinc-aluminum-based catalyst is commonly used in industrial production. The purity of the crude natural gas in the invention is about 95%. The main chemical reaction formula of the synthetic natural gas is as follows:

the main chemical reaction formula of the synthetic natural gas is as follows:

because of the exothermicity in the natural gas synthesis process, a plurality of side reactions are generated, the side reactions generate a large amount of inert gases and are accumulated in the system continuously, the normal operation of the natural gas synthesis process is influenced, and the discharged gases are required to be discharged continuously, and the discharged gases are called natural gas purge gases. The main component of the natural gas purge gas is H ₂ 、CO、H ₂ O and CH ₄ In the presence of an inert gas, wherein H ₂ And CH ₄ The volume percentage content is about 90 percent.

The invention at least adopts a methane synthesis process with 4 methanation reactors connected in series, so that in the presence of a methanation catalyst, carbon monoxide, carbon dioxide and hydrogen in the desulfurized synthesis gas react to synthesize methane to obtain a methane product material flow, thereby reducing the consumption of methaneThe discharge of the natural gas purge gas fully utilizes H in the natural gas purge gas which needs to be discharged originally ₂ And the dual purposes of increasing the yield of natural gas, saving energy and reducing emission can be achieved.

And then, analyzing the obtained composition analysis of the synthetic gas and the natural gas through a comparative experiment, thereby analyzing the technical progress of preparing the natural gas from the coal water slurry which is used by the low-rank coal according to the quality.

Experimental example 1

In the embodiment 1, the low-rank coal adopts pulverized coal with the granularity of less than 20 mm;

in example 1, the slurry formation rate of the coal-water slurry is not less than 55%, specifically 58%, the coal-water slurry is sprayed from the top in the gasification furnace, and during the falling process, the coal-water slurry is heated to 800-1300 ℃, specifically about 1000 ℃, so that the low-rank coal in the coal-water slurry reacts with water to generate synthesis gas comprising carbon monoxide and hydrogen.

Experimental example 2

Experimental example 2 referring to Experimental example 1, except that in Experimental example 2, coal water slurry is heated by a resistance wire under the condition of no oxygen or micro oxygen, so that synthesis gas is prepared at the temperature of 800-1300 ℃. Specifically, upgraded coal is reacted with steam at a temperature of about 1000 ℃ to obtain syngas.

Experimental example 3

Experimental example 3 referring to Experimental example 1, except that the pre-desulfurization process in Experimental example 3 includes a second desulfurization device using at least one of a resistance wire including nickel and chromium and a pre-desulfurization catalyst including at least one of basic copper carbonate, copper oxide, copper hydroxide, basic zinc carbonate, zinc oxide, and zinc hydroxide, the syngas is passed into the second desulfurization device, the resistance wire heats the syngas to 200-500 ℃, such that H in the syngas is ₂ And decomposing S into elemental sulfur, and filtering to remove the elemental sulfur to obtain the pre-desulfurization synthesis gas. The specific second desulfurization device comprises a resistance wire and a pre-desulfurization catalyst.

Comparative example 1

The method for preparing natural gas from the synthesis gas by using the low-rank coal in a quality-divided manner comprises the following steps:

(1) Heating low-rank coal at 400-600 ℃ by isolating air to obtain byproducts of semi-coke, coal tar and synthesis gas, wherein the synthesis gas comprises CH ₄ 28-40% of the total carbon content, and CO content10-15％，H ₂ 25-40% of CO ₂ Content 5-10%, C ₂ H ₆ Content of 2-8%, C ₂ H ₄ Content 1-4%, C ₃ H ₆ 0.5-3% of C ₃ H ₈ Content of 0.4-2.5%, C ₄ H ₈ 0.2-2% of H ₂ S content 2000-6000ppm and NH ₃ The content is 300-800ppm;

(2) Through the spray washing purification process adopted by the washing purification unit 2, the pretreated synthesis gas is further purified, ammonia and sulfide in the synthesis gas are removed, so that the load of a subsequent desulfurization process is reduced, and the pre-desulfurized synthesis gas is obtained;

(3) All unsaturated hydrocarbons in the coal gas are converted into corresponding saturated hydrocarbons through the hydrogenation unit 3, and organic sulfur is simultaneously converted into H ₂ S, obtaining hydrogenated synthesis gas;

(4) The fine desulfurization unit 4 adopts a dry desulfurization process, solid ZnO is used for desulfurization, and H in the feed gas is removed ₂ S content is reduced to<0.1ppm, obtaining the desulfurized synthesis gas;

(5) Passing the desulfurized gas through a pre-conversion unit 5, and pre-converting the desulfurized gas by using a hydrocarbon steam pre-conversion catalyst with high nickel content, wherein the NiO content in the catalyst is 48-68%, and the Al content in the catalyst is 48-68% ₂ O ₃ 15-36% of La, 1.2-4.8% of MgO and ₂ O ₃ 1.2-4.8% of CaO, 5-12% of CaO and K ₂ 0.5-1.2% of O and 1.5-4.5% of graphite; the unit leads higher hydrocarbon with more than C2 in coal gas to carry out pre-conversion reaction to generate methane under the conditions of 1.5-3.5MPa of pressure, 400-800 ℃ of temperature and 2-4 of water-carbon ratio; wherein the coal gas after the pre-conversion reaction comprises the following components: CH (CH) ₄ 30-50% of CO, 13-18% of H2, 30-60% of CO ₂ 10-15% and containing a small amount of water vapor and other impurity gases;

(6) Passing the pre-converted gas through a methanation unit 6, and adopting a methanation catalyst with low nickel content, wherein the components of the methanation catalyst comprise NiO content of 12-24%, al2O3 content of 32-74%, mgO content of 1.2-4.8%, la2O3 content of 1.2-4.8%, caO content of 5-12%, K2O content of 0.5-1.2% and graphite content of 1.5-4.5%; through methanation catalystEffective components in raw material gas: h2, CO and CO ₂ Methanation reaction is carried out, so that the concentration of the generated methane can reach 75-90%;

(7) And introducing the gas after the methanation reaction into a pressure swing adsorption unit 7, and producing high-concentration methane, namely a product LNG and high-purity hydrogen through a pressure swing adsorption process.

TABLE 1 analysis table of composition of synthesis gas produced in test examples 1-3 and comparative example 1 ^*

Note: 1. the content is volume percentage content;

2. others include other alkanes and ammonia.

From the results in Table 1, we analyzed the composition of the obtained synthesis gas and we obtained that first a coal water slurry was heated to 800-1300 ℃ in the absence of oxygen or micro-oxygen to produce a mixture containing CO and H ₂ The content of methane in the synthesis gas can be completely reserved, and the expression is that the amount of methane in the synthesis gas obtained in the experimental examples 1-3 is not obviously reduced, but is slightly increased; secondly, the sulfur content in the gas after pre-desulfurization can be obviously reduced by using resistance wire heating in the gasification furnace, and is reduced from 4200ppm of experimental example 1 to 62ppm of experimental example 2.

TABLE 2 analysis of composition of pre-desulfurized Synthesis gas produced in test examples 1 to 3 and comparative example 1 ^*1

Composition of	Experimental example 1	Experimental example 2	Experimental example 3	Comparative example 1
					CH ₄	38.36	39.04	38.26	26.56
H ₂	26.25	28.33	27.35	25.86
					CO	24.84	23.02	24.24	14.5
CO ₂	6.66	6.26	6.54	17.96
					N ₂	1.52	1.25	1.42	1.34
H ₂ O	1.68	1.56	1.62	6.58
					Others	0.69	0.54	0.57	7.2
Sulfur content	36.8ppm	4.6ppm	16.2ppm	139.4ppm

Note: 1. the content is volume percentage content;

2. others include other alkanes and ammonia.

From the results of Table 2, analyzing the composition of the resulting pre-desulfurized syngas, we can obtain that, first, upgraded coals from Experimental examples 1, 2 and 3 were prepared to contain CO and H by reacting with steam under oxygen-free or micro-oxygen conditions ₂ So that in the pre-desulphurised synthesis gas, H ₂ CO, all higher than control 1 and the amount of carbon dioxide was significantly lower in the synthesis gas of experimental example 1, experimental example 2 and experimental example 3 than in control 1, and secondly, we found that in the pre-desulphurised synthesis gas of experimental example 3 the sulphur content was significantly reduced, whereby the pre-desulphurisation process included the use of resistance wire contributing to H ₂ S is ionized to elemental sulfur, which is reflected in the pre-desulfurized syngas with a significant reduction in sulfur content.

The product natural gas is obtained from the crude natural gas obtained from the natural gas synthesis process through a liquefaction process, the recovery rate is about 99.5%, the obtained natural gas has few impurities, the quality is high, and the quality index of the natural gas is required.

In conclusion, in the method, the low-rank coal is prepared into the coal water slurry through the steps of crushing and grinding, and then is gasified and reduced under the oxygen-free or micro-oxygen condition to prepare the coal water slurry containing CO and H ₂ The synthesis gas is further prepared into raw materials of CO and CO required by natural gas synthesis by gasifying and reducing part or all of low-rank coal to obtain upgraded coal with less volatile components and less impurities, preparing the upgraded coal into water-coal slurry and gasifying the water-coal slurry ₂ And H ₂ When the natural gas is used, the prepared natural gas has less impurities and high quality, fully and effectively utilizes coal substances in low-rank coal, and 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. A method for preparing natural gas from coal water slurry is characterized by comprising the following steps,

(1) The low-rank coal is prepared into the coal water slurry through the steps of crushing and grinding, the coal water slurry is heated to 800-1300 ℃ under the condition of no oxygen or micro oxygen, and the coal water slurry containing CO and H is prepared ₂ The synthesis gas of (2);

(3) Converting all unsaturated hydrocarbons of the pre-desulfurized syngas to corresponding saturated hydrocarbons by a hydrogenation process while converting organic sulfur to H ₂ S, obtaining hydrogenated synthesis gas;

(8) Introducing the methane product material flow into a liquefaction process, and producing methane with volume percentage not less than 90% by a cryogenic liquefaction process to obtain a product LNG;

heating by using a resistance wire to enable the coal water slurry to prepare the synthesis gas at the temperature of 800-1300 ℃; the resistance wire contains nickel and chromium;

the synthesis gas enters from the lower part of a first desulfurization device and is in countercurrent contact with a pre-desulfurization solution sprayed from the upper part of the first desulfurization device, so that hydrogen sulfide in the synthesis gas is removed, wherein the pre-desulfurization solution comprises a PDS catalyst;

the pre-desulfurization process comprises a second desulfurization device using at least one of a resistance wire and a pre-desulfurization catalyst, wherein the resistance wire comprises nickel and chromium, the pre-desulfurization catalyst comprises at least one of basic copper carbonate, copper oxide, copper hydroxide, basic zinc carbonate, zinc oxide and zinc hydroxide, the synthesis gas is introduced into the second desulfurization device, the resistance wire heats the synthesis gas to 200-500 ℃, and H in the synthesis gas is enabled to be at least one of H and Cr ₂ And decomposing S into elemental sulfur, and filtering to remove the elemental sulfur to obtain the pre-desulfurized synthesis gas.

2. The method according to claim 1, wherein the coal-water slurry further comprises upgraded coal, and the upgraded coal is low-rank coal prepared by a gasification reduction process.

3. The method according to claim 2, wherein in the coal-water slurry, the mass ratio of the upgraded coal to the low-rank coal is (1-10): 1.

4. the method as claimed in claim 1, wherein in step 1, steam preheated to 800-1300 ℃ is introduced.

5. The method of claim 1, wherein the pre-desulfurization process comprises using a filtration device loaded with a composition comprising an adsorbent material and the pre-desulfurization catalyst.

6. The method of claim 1, wherein the particulate matter in the syngas is removed by a dust removal process prior to entering the pre-desulfurization process.