CN109207220B

CN109207220B - Methanation process for preparing synthetic natural gas from coal-based synthetic gas

Info

Publication number: CN109207220B
Application number: CN201710514081.0A
Authority: CN
Inventors: 吴�琳; 朱艳芳; 张�杰; 吴学其; 徐本刚; 蔡进; 黄先亮; 王金利
Original assignee: China Petroleum and Chemical Corp; Research Institute of Nanjing Chemical Industry Group Co Ltd
Current assignee: China Petroleum and Chemical Corp; Research Institute of Sinopec Nanjing Chemical Industry Co Ltd
Priority date: 2017-06-29
Filing date: 2017-06-29
Publication date: 2020-10-30
Anticipated expiration: 2037-06-29
Also published as: CN109207220A

Abstract

A novel methanation process for preparing synthetic natural gas from coal-based synthesis gas. Methane synthesis gas from a coal gas purification section is subjected to fine desulfurization to obtain fresh gas, and the fresh gas sequentially passes through four heat-insulating methanation reactors connected in series; the fresh gas is cooled through the outlet of the first methane synthesis reactor and then is divided into a gas A and a gas B, the gas A enters a circulating compressor for pressure increase and then returns to the inlet of the first methane synthesis reactor as a circulating gas to be mixed with the fresh gas to form a raw material gas, and the gas B sequentially enters the second methane synthesis reactor, the third methane synthesis reactor and the fourth methane synthesis reactor for methane synthesis reaction; the inlet of the first methane synthesis reactor is provided with a back-off pneumatic valve, so that fresh gas can be automatically discharged before entering the first methane synthesis reactor.

Description

Methanation process for preparing synthetic natural gas from coal-based synthetic gas

Technical Field

The invention relates to methanation technologies of city coal gas methanation and coal-to-Synthetic Natural Gas (SNG), belongs to the technical field of new energy, and particularly provides a novel methanation process for preparing synthetic natural gas from coal-based synthetic gas.

Background

The resources in China are characterized by being relatively rich in coal, lack of oil and little gas, and the ascertained reserves of natural gas are less than 1% of the total amount of the world. The coal-based natural gas can be used as a supplement for natural gas gaps in China, and the development of the coal-based natural gas is an effective way for solving the contradiction between supply and demand of natural gas in China. In coal chemical engineering projects, the energy efficiency conversion rate of coal-based natural gas can reach 60% at most, unit heat value water consumption is lowest, and the heat value of the coal-based natural gas is 17.8% -21% higher than the lowest heat value specified by national natural gas quality standards. The product indexes of carbon dioxide, hydrogen sulfide, total sulfur and the like are higher than the national standard.

The coal-based natural gas has good economic benefit in the high oil price era, solves the problem of clean utilization of coal resources, relieves the current situation of shortage of oil and gas resources in China, maintains the energy safety of China, and realizes CO₂The method has important significance for emission reduction and environmental protection.

The adiabatic temperature rise per 1% CO methane synthesis in a syngas clean-up methane synthesis reaction reaches 73 deg.C per 1% CO₂The adiabatic temperature rise for methane synthesis is about 60 ℃, assuming feed gas composition H₂30%、CO 6.6%、CO₂3.6%、CH₄59.8%, product gas composition H₂10.2%、CO 1.3%、CO₂3.2%、CH₄85.3%, the reaction was carried out in an adiabatic reactor with an adiabatic temperature rise of about 270 ℃. If the CO content rises to 10%, the adiabatic temperature rise can reach about 400 ℃. Therefore, the temperature rise of the coal-to-SNG methane synthesis reaction is very significant. The existing methanation technology of coal-based SNG generally uses a circulation technology to control temperature, once a circulation compressor is stopped, a large amount of fresh gas immediately enters a reactor to bring about rapid temperature rise in a short time, the temperature can rapidly rise by more than 150 ℃, and in order to relieve the temperature rise caused by strong heat release and prevent potential safety hazards, the traditional method adopts nitrogen gas replacement, but the effect is poor.

Disclosure of Invention

The invention aims to provide a novel methanation process for preparing synthetic natural gas from coal-based synthetic gas.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: the methanation process for preparing the synthetic natural gas from the coal-based synthetic gas comprises the following process steps: methane synthesis gas from a coal gas purification section is subjected to fine desulfurization to obtain fresh gas, and the fresh gas sequentially passes through four adiabatic methanation reactors connected in series; the fresh gas is cooled through the outlet of the first methane synthesis reactor and then is divided into a gas A and a gas B, the gas A enters a circulating compressor for pressure increase and then returns to the inlet of the first methane synthesis reactor as a circulating gas to be mixed with the fresh gas to form a raw material gas, and the gas B sequentially enters the second methane synthesis reactor, the third methane synthesis reactor and the fourth methane synthesis reactor for methane synthesis reaction; a reverse discharge pneumatic valve is arranged at the inlet of the first methane synthesis reactor; carrying out water separation treatment on outlet gas of the second methane synthesis reactor, cooling and water separating the outlet gas of the second methane synthesis reactor, then carrying out heat exchange with the outlet gas of the second methane synthesis reactor, and feeding the dry gas after water separation into the third methane synthesis reactor; the dry content of methane in the gas at the outlet of the fourth methane synthesis reactor is more than 96 percent, and then the synthetic natural gas SNG meeting the requirements is obtained through cooling and dehydration.

In the above process, the first methane synthesis reactor is a heat pipe heat transfer radial bed methanation reactor.

The temperature of the inlet of each methane synthesis reactor is 250-350 ℃, the pressure is 1-8 MPa, and the volume space velocity calculated by dry gas in the reactor is 5000h^-1~30000h^-1。

The inlet temperature of the first methane synthesis reactor is 250-300 ℃, the outlet temperature of the first methane synthesis reactor is 600-700 ℃, the inlet temperature of the second, third and fourth methane synthesis reactors is 250-300 ℃, the outlet temperature of the second methane synthesis reactor is 600-700 ℃, the outlet temperature of the third methane synthesis reactor is 400-500 ℃, and the outlet temperature of the fourth methane synthesis reactor is 250-350 ℃; the temperature of the gas entering the compressor is 30-80 ℃.

The reactors for carrying out the methane synthesis reaction are adiabatic reactors.

The methane synthesis catalyst takes nickel as a main active component and takes one or two of pseudo-boehmite, alumina, magnesia and magnesia-alumina spinel as a carrier.

The catalyst takes nickel as a main active component, is assisted by a first auxiliary agent and a second auxiliary agent, and adopts a precipitation method to prepare an active matrix. The first auxiliary agent is transition metal element, including one or two of La, Ce, Zr, Ti, etc. The content is 0.1-5% of the mass of Ni; the second auxiliary agent is one or two of dispersing agents such as triethyl hexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, cellulose derivatives, polyacrylamide, Guel gum, glycol, polyethylene glycol, fatty acid polyglycol ester, glycerol and the like, and the second auxiliary agent is used as a dispersing agent instead of conventional water during precipitation, wherein the using amount of the second auxiliary agent is 0.01-1% of that of Ni.

The catalyst carrier is composed of alumina and composite salt of aluminum and magnesium, wherein the alumina is gamma-Al₂O₃or-Al₂O₃Or alpha-Al₂O₃In the form of a complex salt of aluminium and magnesium MgAl₂O₄The morphology exists.

The first methane synthesis reactor adopts a radial bed reactor, and a reverse-discharging pneumatic valve is arranged at an inlet. The radial bed reactor has simple structure and small bed pressure drop, can take away reaction heat in time, homogenize the bed temperature, improve the conversion rate of reactants, avoid a catalyst from generating an overheated area and prolong the service life of the catalyst; the method has the advantages that the small-flow reverse-discharging technology is adopted, the bed layer can be prevented from being blown over, namely, the pneumatic valve is arranged in front of the inlet of the first methane synthesis reactor, once the circulating compressor is stopped, fresh gas is immediately and safely discharged from the pneumatic valve in front of the inlet of the first methane synthesis reactor, and the temperature of the reactor is prevented from being further influenced by the high-concentration CO fresh gas.

The invention has the following advantages:

1. the methanation process for preparing the synthetic natural gas from the coal-based synthetic gas adopts a small-flow reverse discharge technology to prevent a bed layer from being blown over, namely a pneumatic valve is arranged in front of an inlet of a first methane synthesis reactor, once a circulating compressor is stopped, fresh gas is immediately and safely discharged from the pneumatic valve in front of the inlet of the first methane synthesis reactor, and the temperature of the reactor is prevented from being continuously influenced by the high-concentration CO fresh gas;

2. and (3) carrying out water separation treatment on outlet gas of the second methane synthesis reactor, namely cooling and water separating the outlet gas of the second methane synthesis reactor, then carrying out heat exchange with the gas per se, and feeding the dry gas after water separation into an inlet of the third methane synthesis reactor. The process can freely adjust the water separation amount according to the content of the required product gas, and further improve the content of methane in the product gas;

3. the first methane synthesis reactor is a radial bed reactor, has simple structure and small bed pressure drop, can take away reaction heat in time, homogenizes the bed temperature, improves the conversion rate of reactants, avoids a catalyst from generating an overheating area, and prolongs the service life of the catalyst.

Drawings

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

In the figure, R1-a first methane synthesis reactor, R2-a second methane synthesis reactor, R3-a third methane synthesis reactor, R4-a fourth methane synthesis reactor, P1-a recycle compressor, E1-a gas-gas heat exchanger, E2-a water cooler, F1-an inverse discharge pneumatic valve and v 1-a liquid separation tank.

Detailed Description

The present invention is explained in detail by the following examples in conjunction with the accompanying drawings.

Example 1

According to the process flow shown in figure 1, the pressure is 1.0MPa, and the space velocity is 10000h^-1The composition (vol%) of the fresh gas A is: h₂67.08，CH₄9.2，CO 21.17，CO₂2.05，N₂0.5. Fresh gas and circulating gas are mixed to form feed gas, the feed gas enters an inlet of a first methane synthesis reactor, the temperature of the gas inlet is 280 ℃, and the temperature after reaction is 680 ℃. The reaction temperature zone of the first methane synthesis reactor bed layer is 670-680 ℃ from top to bottom, and the first methane synthesis reactor outlet gas is divided into two streams: a part of gas enters a circulating compressor P1 to be used as circulating gas after being pressurized and then returns to the inlet of the first methane synthesis reactor to be mixed with the fresh gas A to form feed gas; and the other gas enters a second methane synthesis reactor R2, the temperature is raised to 420 ℃ after reaction, the temperature of the two-reaction gas is raised to 280 ℃ after the two-reaction gas is subjected to heat exchange of E1 gas, the two-reaction gas is cooled and water-distributed by an E2 water cooler and then subjected to heat exchange by E1, the temperature of the two-reaction gas enters a third methane synthesis reactor R3 inlet and is raised to 285 ℃ after reaction, the three-reaction gas is cooled to about 150 ℃ after the heat exchange of the three-reaction gas cooler, the three-reaction gas enters a four-reaction R4 inlet, condensed water is removed by a product gas liquid-distributing tank, and the three-reaction gas is cooled to 40 ℃ by.

Example 2

According to the process flow shown in figure 1, the pressure is 5.5MPa, and the space velocity is 20000h^-1Fresh gas composition (vol%) of：H₂69.5，CH₄8.21，CO 19.84，CO₂1.95，N₂0.5. Fresh gas and circulating gas are mixed to form raw material gas, the raw material gas enters an inlet of the first methane synthesis reactor, the temperature of the gas inlet is 280 ℃, and the temperature after reaction is 695 ℃. The reaction temperature zone of the bed layer of the first methane synthesis reactor is 680-695 ℃ from top to bottom, and the gas outlet of the first methane synthesis reactor is divided into two streams: a part of gas enters a circulating compressor P1 to be used as circulating gas after being pressurized and then returns to the inlet of the first methane synthesis reactor to be mixed with the fresh gas A to form feed gas; and the other gas enters a second methane synthesis reactor R2, the temperature is raised to 430 ℃ after reaction, the temperature of the two-reaction gas is raised to 280 ℃ after the two-reaction gas is subjected to heat exchange of E1 gas, the two-reaction gas is cooled and water-distributed by an E2 water cooler and then subjected to heat exchange by E1, the temperature of the two-reaction gas enters a third methane synthesis reactor R3 inlet and is raised to 285 ℃ after reaction, the three-reaction gas is cooled to about 160 ℃ after the heat exchange of the three-reaction gas cooler, the three-reaction gas enters a four-reaction R4 inlet, condensed water is removed by a product gas liquid-distributing tank, and the three-reaction gas is cooled to 40 ℃ by.

Example 3

According to the process flow shown in figure 1, the pressure is 8MPa, and the space velocity is 30000h^-1Has a fresh gas composition (vol%) of: h₂68.5，CH₄8.82，CO 20.23，CO₂1.95，N₂0.5. Fresh gas and circulating gas are mixed to form raw material gas, the raw material gas enters an inlet of a first methane synthesis reactor, the temperature of the gas inlet is 280 ℃, and the temperature after reaction is 685 ℃. The reaction temperature zone of the bed layer of the first methane synthesis reactor is 675-685 ℃ from top to bottom, and the gas outlet of the first methane synthesis reactor is divided into two paths: a part of gas enters a circulating compressor P1 to be used as circulating gas after being pressurized and then returns to the inlet of the first methane synthesis reactor to be mixed with the fresh gas A to form feed gas; the other gas enters a second methane synthesis reactor R2, the temperature is raised to 430 ℃ after reaction, the two-reaction gas is subjected to heat exchange by E1 gas, cooled by an E2 water cooler, subjected to water diversion, subjected to heat exchange by E1, enters a third methane synthesis reactor R3 inlet at the temperature of 280 ℃, the temperature is raised to 285 ℃ after reaction, the three-reaction gas is subjected to heat exchange by a cooler, cooled to about 160 ℃, enters a four-reaction R4 inlet, is subjected to product gas liquid separation tank to remove condensed water, and then passes through a product gas final coolerAnd reducing the temperature to 40 ℃ to obtain 96% SNG and conveying the SNG to a pipe network.

Example 4

According to the process flow shown in figure 1, the pressure is 8MPa, and the space velocity is 30000h^-1Has a fresh gas composition (vol%) of: h₂68.5，CH₄8.82，CO 20.23，CO₂1.95，N₂0.5. Fresh gas and circulating gas are mixed to form raw material gas, the raw material gas enters an inlet of a first methane synthesis reactor, the temperature of the gas inlet is 280 ℃, and the temperature after reaction is 685 ℃. The reaction temperature zone of the bed layer of the first methane synthesis reactor is 675-685 ℃ from top to bottom, and the gas outlet of the first methane synthesis reactor is divided into two paths: a part of gas enters a circulating compressor P1 to be used as circulating gas after being pressurized and then returns to the inlet of the first methane synthesis reactor to be mixed with the fresh gas A to form feed gas; the other stream enters a second methane synthesis reactor R2, the recycle compressor is stopped for 5 minutes, a small flow dump valve is started, and the temperature of the first methane synthesis reactor rises from 685 ℃ to 700 ℃. Device stopping and opening N₂And (4) replacement, so that potential safety hazards caused by overtemperature are avoided.

Claims

1. A methanation process for preparing synthetic natural gas from coal-based synthetic gas is characterized by comprising the following steps: the method comprises the following technical processes: methane synthesis gas from a coal gas purification section is subjected to fine desulfurization to obtain fresh gas, and the fresh gas sequentially passes through four adiabatic methanation reactors connected in series; the fresh gas is cooled through the outlet of the first methane synthesis reactor and then is divided into a gas A and a gas B, the gas A enters a circulating compressor for pressure increase and then returns to the inlet of the first methane synthesis reactor as a circulating gas to be mixed with the fresh gas to form a raw material gas, and the gas B sequentially enters the second methane synthesis reactor, the third methane synthesis reactor and the fourth methane synthesis reactor for methane synthesis reaction; a reverse discharge pneumatic valve is arranged at the inlet of the first methane synthesis reactor; carrying out water separation treatment on outlet gas of the second methane synthesis reactor, cooling and water separating the outlet gas of the second methane synthesis reactor, then carrying out heat exchange with the outlet gas of the second methane synthesis reactor, and feeding the dry gas after water separation into the third methane synthesis reactor; the dry content of methane in the gas at the outlet of the fourth methane synthesis reactor is more than 96 percent, and then the synthetic natural gas SNG meeting the requirements is obtained through cooling and dehydration.

2. The methanation process for preparing synthetic natural gas from coal-based synthesis gas according to claim 1, characterized in that: the first methane synthesis reactor is a heat pipe heat transfer radial bed methanation reactor.

3. The methanation process for preparing synthetic natural gas from coal-based synthesis gas according to claim 1, characterized in that: the volume space velocity calculated by dry gas in the reactor is 5000h^-1~30000h^-1The pressure is 1-8 MPa.

4. The methanation process for preparing synthetic natural gas from coal-based synthesis gas according to claim 1, characterized in that the inlet temperature of the first methane synthesis reactor is 250 ℃ to 300 ℃, the outlet temperature is 600 ℃ to 700 ℃, the inlet temperature of the second, third and fourth methane synthesis reactors is 250 ℃ to 300 ℃, the outlet temperature of the second methane synthesis reactor is 500 ℃ to 650 ℃, the outlet temperature of the third methane synthesis reactor is 400 ℃ to 500 ℃, and the outlet temperature of the fourth methane synthesis reactor is 250 ℃ to 350 ℃.

5. The methanation process for preparing synthetic natural gas from coal-based synthesis gas according to claim 1, characterized in that the temperature of gas A entering a recycle compressor is 30-80 ℃.

6. The methanation process for preparing synthetic natural gas from coal-based synthesis gas according to claim 1, characterized in that the methane synthesis catalyst uses nickel as a main active component and one or two of pseudo-boehmite, alumina, magnesia and magnesia-alumina spinel as a carrier.

7. The methanation process for preparing synthetic natural gas from coal-based synthetic gas according to claim 6, characterized in that the catalyst uses nickel as a main active component, and first and second auxiliary agents are added, and a precipitation method is adopted to prepare an active matrix; the first auxiliary agent is a transition metal element, and comprises one or two of La, Ce, Zr and Ti, and the content of the first auxiliary agent is 0.1-5% of the mass of Ni; the second auxiliary agent is one or two of dispersing agents such as triethyl hexyl phosphoric acid, sodium dodecyl sulfate, methyl amyl alcohol, cellulose derivatives, polyacrylamide, Guel gum, glycol, polyethylene glycol, fatty acid polyglycol ester, glycerol and the like, and the second auxiliary agent is used as a dispersing agent instead of conventional water during precipitation, wherein the using amount of the second auxiliary agent is 0.01-1% of that of Ni.

8. The methanation process for preparing synthetic natural gas from coal-based synthesis gas according to claim 6, characterized in that the catalyst carrier is composed of alumina and composite salt of aluminum and magnesium, wherein the alumina is gamma-Al₂O₃or-Al₂O₃Or alpha-Al₂O₃In the form of a complex salt of aluminium and magnesium MgAl₂O₄The morphology exists.