CN103666611B - System and method for preparing alternative natural gas - Google Patents
System and method for preparing alternative natural gas Download PDFInfo
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- CN103666611B CN103666611B CN201210350983.2A CN201210350983A CN103666611B CN 103666611 B CN103666611 B CN 103666611B CN 201210350983 A CN201210350983 A CN 201210350983A CN 103666611 B CN103666611 B CN 103666611B
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 124
- 238000000034 method Methods 0.000 title claims abstract description 43
- 239000003345 natural gas Substances 0.000 title claims abstract description 29
- 239000007789 gas Substances 0.000 claims abstract description 149
- 238000006243 chemical reaction Methods 0.000 claims abstract description 47
- 239000002994 raw material Substances 0.000 claims abstract description 44
- 239000000203 mixture Substances 0.000 claims abstract description 9
- 238000002156 mixing Methods 0.000 claims abstract description 3
- 239000002918 waste heat Substances 0.000 claims description 26
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 21
- 238000000926 separation method Methods 0.000 claims description 10
- 239000007788 liquid Substances 0.000 claims description 9
- 238000007670 refining Methods 0.000 claims description 8
- 230000029936 alkylation Effects 0.000 claims description 7
- 238000005804 alkylation reaction Methods 0.000 claims description 7
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 4
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 3
- 239000001569 carbon dioxide Substances 0.000 claims description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 239000000047 product Substances 0.000 description 44
- 239000003245 coal Substances 0.000 description 11
- 239000000463 material Substances 0.000 description 7
- 238000005265 energy consumption Methods 0.000 description 6
- 238000002309 gasification Methods 0.000 description 6
- 230000008901 benefit Effects 0.000 description 5
- 239000003054 catalyst Substances 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- 239000000376 reactant Substances 0.000 description 3
- 239000002253 acid Substances 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 239000012895 dilution Substances 0.000 description 2
- 239000012495 reaction gas Substances 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 229910002090 carbon oxide Inorganic materials 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000003085 diluting agent Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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Abstract
The invention provides a system and a method for preparing an alternative natural gas. The system comprises a main methanation part and a refined methanation part, wherein the main methanation part comprises three methanation reactors connected in series; the refined methanation part comprises two or three methanation reactors connected in series. The method comprises the following steps: (1) raising the temperature of a raw material gas, subsequently respectively feeding the raw material gas into a first methanation reactor, a second methanation reactor and a third methanation reactor to be reacted, partially compressing a product at the bottom of the third methanation reactor after heat exchange, mixing the product as a circulation gas with the raw material gas, subsequently feeding into the first methanation reactor, and feeding a part of the mixture into a fourth methanation reactor; (2) feeding a product at the bottom of the fourth methanation reactor into a fifth methanation reactor after heat exchange, and generating an SNG (Synthetic Natural Gas) product gas from the bottom of the fifth or a sixth methanation reactor. By adopting the system and the method, the reaction depth of methanation reaction is increased, and an alternative natural gas product with high methane content and heat value can be obtained.
Description
Technical Field
The invention relates to the field of coal-based substitute natural gas, in particular to a system and a method for preparing substitute natural gas.
Background
Coal-based Substitute Natural Gas (SNG) is becoming a new hotspot in the field of coal chemical industry. Under the situation that natural gas reserves in China are limited and the capacity cannot meet the demand, the coal-based SNG is an effective supplement means for natural gas resources in China.
The core process of coal-based SNG is methanation technology. More specifically, the coal gasification product containing hydrogen and carbon oxides is subjected to methanation reaction on a metal catalyst, so that the coal gasification product containing more than 94% of methane and having a higher calorific value of more than 31.4MJ/Nm is obtained3And (3) producing methane-rich gas. The methanation process mainly comprises the following reactions:
（I）CO+3H2→CH4+H2O △H0 298=-206Kj/mol
(II)CO2+4H2→CH4+2H2O △H0 298=-165Kj/mol
the methanation reaction is a strongly exothermic reaction, with each 1% conversion of CO causing an adiabatic temperature rise of 74 ℃; every 1 percentage point of CO2The conversion caused an adiabatic temperature rise of 60 ℃. The methanation reaction is also a reaction with the volume greatly reduced, the methanation reaction of CO, the volume of the product is only half of that of the reactant, and CO2The volume of the product is only 60 percent of that of the reactant. Thus, lower reaction temperatures and higher back pressures favor CO and CO2The methanation reaction equilibrium is shifted towards the product. Generally, after the synthesis gas from the coal gasification unit passes through the shift conversion and acid gas removal unit, the concentration of CO in the synthesis gas is about 20%, and the adiabatic temperature rise caused by the whole reaction of CO exceeds 1000 ℃, which is unacceptable for a methanation catalyst and a reactor.
In order to remove the reaction heat quickly and ensure that the reaction temperature is not too high, the reaction can be carried out in a multi-section adiabatic reactor, all or most of fresh raw material gas enters a first methanation reactor, and the temperature rise of the first methanation reactor is controlled by circulating methane-rich gas cooled at the outlet of one reactor, so that process condensate water is possibly generated, the energy loss is caused, and the energy recovery rate is reduced. The subsequent reactor controls the reaction exotherm by taking the reactor outlet product gas upstream of the reactor as a diluent gas stream, which is then mixed with the remainder of the fresh feed gas. The waste heat boiler is arranged at the outlet of the reactor to generate high-pressure steam to recover heat, so that the comprehensive energy consumption is reduced.
For example, the known process known under the name CRG comprises a methanation unit provided with a first and a second methanation reactor, which are respectively fed with fresh feed gas in suitable proportions, and two further methanation reactors. And the reaction gas at the outlet of the first methanation reactor passes through a steam superheater and a high-pressure waste heat boiler and then is mixed with the rest fresh raw material gas to be injected into a second methanation reactor. The reaction gas at the outlet of the second methanation reactor is divided into two gas flows by a high-pressure waste heat boiler. One air flow is led to a downstream reactor, the other air flow passes through a gas cooler and enters a liquid separation tank, and a large amount of process condensate is separated, boosted through a compressor, recycled to an air inlet of the first methanation reactor after passing through a gas preheater.
The common characteristics of the prior art are that the circulating gas is reduced from high temperature to low temperature and then is increased to high temperature, a large amount of process condensate is discharged in the middle, which means that a large amount of energy is lost, the process heat recovery rate is low, and the energy consumption of the device is high. Another disadvantage is the need to increase the number of cold exchange equipment, increase equipment investment and ultimately decrease process economics. Another common feature is that the number of reactors in the circulation section is only two or less, and the fresh raw gas treatment capacity of the first methanation reactor directly connected with the circulation compressor is most or all, which means that the circulation gas amount required for controlling the reaction temperature rise is very large, and the molar ratio of the circulation gas to the fresh gas is as high as 3 or more, which has the defect that the volume of the methanation reactor is larger along with the larger volume of the methanation reactor, and more catalyst filling amount is required.
For another example, the patent numbers are: CN101560423A entitled "a method and apparatus for producing substitute natural gas", said "adding steam at the inlet of at least a first reactor, preferably also at the inlet of a second reactor of a methanation unit, thanks to which the compressor of the recirculation loop is much smaller than the compressors required by the prior art; the fresh feed gas is parallelly introduced into the reactor, the aim of reducing the power of the compressor is achieved by sacrificing the amount of generated steam and adding a large amount of steam, and the comparison of the energy consumption conversion value of the high-pressure superheated steam and the electric power of the compressor shows that the method of adding the steam is not economical, the reaction balance is moved to the direction of reactants, and the comprehensive energy consumption of the methanation device is increased. The parallel introduction of fresh feed gas into the reactor is difficult to ensure the heat value requirement of SNG and the concentration requirement of CH 4.
Disclosure of Invention
In order to solve the problems that the energy loss is large, the power of a compressor is high, the size of a methanation reactor is large and the scale of a single series of devices is limited in the process of preparing the substitute natural gas by using the coal gasification synthesis gas in the prior art, the invention provides a system and a method for preparing the substitute natural gas. The method can increase the reaction depth of the methanation reaction and obtain the substitute natural gas product with higher methane content and calorific value. In addition, any material flow except fresh raw materials and methane-rich gas of products produced by the process is not mixed in the system, so that the process flow and the configuration of an external system are simplified.
It is an object of the present invention to provide a system for producing substitute natural gas.
The method comprises the following steps: a main methanation part and a refined methanation part; the main methanation part comprises three methanation reactors connected in parallel in series, and the refined methanation part comprises two or three methanation reactors connected in series;
a main methanation part: the feed gas pipeline is divided into three parts which are respectively connected with the inlets of the first methanation reactor, the second methanation reactor and the third methanation reactor, and the outlet of the first methanation reactor is connected with the first high-temperature high-pressure waste heat boiler and then is combined with the feed gas pipeline of the second methanation reactor to be connected with the inlet of the second methanation reactor; the outlet of the second methanation reactor is connected with the second high-temperature high-pressure waste heat boiler, and then is merged with a feed gas pipeline of a third methanation reactor to enter the inlet of the third methanation reactor; the outlet of the third methanation reactor is sequentially connected with a superheater, a third high-temperature high-pressure waste heat boiler, a second raw material heat exchanger and a fifth reaction inlet heat exchanger and then divided into two parts, wherein one part is connected with the top of the fourth methanation reactor of the refined methanation part, and the other part is connected with a compressor and then is combined with a raw material inlet pipeline at the top of the first methanation reactor;
refining the methanation part: and the outlet of the fourth methanation reactor is connected with a boiler feed water heat exchanger, a first desalted water heat exchanger, an intermediate liquid separation tank and a fifth reverse inlet heat exchanger and then connected with the inlet of a fifth methanation reactor, the outlet of the fifth methanation reactor is used for producing SNG product gas, or is connected with the inlet of a sixth methanation reactor, and the outlet of the sixth methanation reactor is used for producing SNG product gas.
Another object of the present invention is to provide a method for producing substitute natural gas.
The method comprises the following steps:
(1) heating the raw material gas, then respectively feeding the raw material gas into a first methanation reactor, a second methanation reactor and a third methanation reactor for reaction, and mixing a product at the bottom of the first methanation reactor with the raw material gas after heat exchange and then feeding the mixture into the top of the second methanation reactor; the product at the bottom of the second methanation reactor is mixed with the feed gas after heat exchange and then enters the top of the third methanation reactor; after heat exchange, partial product at the bottom of the third methanation reactor is compressed to be used as circulating gas to be mixed with feed gas, and then the mixture is sent into the first methanation reactor, and partial product is sent into the fourth methanation reactor;
(2) and (3) conveying the product at the bottom of the fourth methanation reactor into a fifth methanation reactor after heat exchange, conveying the SNG product into a sixth methanation reactor before or after heat exchange at the bottom of the fifth methanation reactor, and collecting the SNG product gas at the bottom of the sixth methanation reactor.
Heating the raw material gas in the step (1) to 250-350 ℃;
the temperature of the bottom product of the third methanation reactor is not lower than 200 ℃ after heat exchange, part of the bottom product is compressed to be used as circulating gas to be mixed with feed gas and then sent into the first methanation reactor, and part of the bottom product is sent into the fourth methanation reactor;
the flow rate of the raw material gas entering the first methanation reactor is 2-35% of the total raw material gas molar flow rate;
the feed gas entering the second methanation reactor has a flow rate of 10% to 60% of the molar flow rate entering the second and third methanation reactors.
The molar flow ratio of the circulating gas to the raw gas of the first methanation reactor is 1-3.
The temperature of the circulating gas is 200-300 ℃.
The outlet temperatures of the first methanation reactor, the second methanation reactor and the third methanation reactor are 620-700 ℃.
20-70% of the molar flow of the bottom product of the third alkylation reactor enters the fourth alkylation reactor.
The main composition ranges of the raw materials are as follows:
hydrogen gas: 60% -90%, carbon monoxide: 5% -30%, carbon dioxide: 0 to 10 percent.
The pressure in all the methanation reactors mentioned above is 20bar to 65 bar.
The invention is realized by the following technical scheme:
the fresh raw gas is divided into three parts with unequal flow rates and is sent to three adiabatic methanation reactors which are arranged in series, part of the fresh raw gas is mixed with the circulating gas before entering the first methanation reactor, more specifically, is mixed with part of the product gas from the outlet of the third methanation reactor, the product gas at the outlet of the third methanation reactor passes through a superheater, a high-pressure waste heat boiler and a cooling heat exchanger, the temperature is divided into two parts at a temperature of not lower than 200 ℃, one part of the cooled product gas enters a fourth, a fifth or/and a sixth methanation reactor which are connected in series at the downstream, the other part of the cooled product gas is directly mixed with part of the fresh raw gas as the circulating gas through a circulating compressor, the second and the third methanation reactors respectively receive the product gas of respective upstream reactors as dilution gas, the dilution gas is mixed with the fresh raw gas in proper proportion and then enters the second and the third methanation reactors, the other part of the product methane-rich gas at the outlet of the third methanation reactor enters a, sequentially passes through a fourth alkylation reactor and a heat exchanger and then enters an intermediate liquid separation tank to separate out condensate. And then, the methane-rich gas is subjected to heat exchange, methanation reaction refining and final cooling to obtain a product to replace natural gas.
Specifically, the method comprises the following steps:
the fresh raw material gas is preheated and then divided into three parts according to a certain proportion and is sent to three heat-insulating methanation reactors which are connected in series, and the circulation gas quantity is reduced and the power of a circulation compressor is reduced by reducing the quantity of the fresh raw material gas entering the first methanation reactor. In a preferable scheme, the fresh feed gas entering the first methanation reactor accounts for 10-30% of the total feed gas flow, 10-60% of the rest fresh feed gas is mixed with the methane-rich gas cooled by the high-pressure waste heat boiler at the outlet of the first methanation reactor and then enters the second methanation reactor, and the rest fresh feed gas is mixed with the methane-rich gas at the outlet of the second methanation reactor and then enters the third methanation reactor. A high-pressure waste heat boiler is arranged behind the first methanation reactor and the second methanation reactor respectively for recovering reaction heat, and a superheater and the high-pressure waste heat boiler are arranged behind the third methanation reactor for recovering heat.
According to another aspect of the invention, the product methane-rich gas of the three methanation reactors which are used as the main methanation reaction part and are arranged in series is sent to the refining part, except for part of the product methane-rich gas used for circulation, and the substitute natural gas product with the methane content of more than 94% v is obtained through deep methanation reactions in the two or three methanation reactors which are connected in series.
According to another aspect of the invention, the gas circulation is carried out as follows: after passing through a superheater, a third high-pressure waste heat boiler, a second raw material preheater and a five-reaction inlet heat exchanger, the methane-rich gas produced at the outlet of the third methanation reactor is kept at a temperature of more than 200 ℃, and no process condensate is produced at the temperature. The product methane-rich gas is divided into two parts, the circulating gas is directly sent into a circulating compressor, and the compressed circulating gas is mixed with fresh raw material gas and enters a first methanation reactor. Preferably, the mole fraction of the recycle gas in the product gas is 20-70%.
The invention has the following advantages:
no process condensate is generated in the recycling process of the circulating gas, energy is saved compared with the prior art, and more high-grade superheated steam can be generated by the saved energy. For example, implement the prior art and canProduction of SNG (1.77X 10)5Nm3The amount of superheated steam is 507t/h, but the method of the invention can generate 558t/h of the same-grade superheated steam, and on the other hand, any reactor of the invention does not need to consume externally added steam, so the comprehensive energy consumption is further reduced, and the economic benefit is stronger.
The other advantage is that the main methanation part composed of three parallel reactors in series and heat exchange and recycle gas compression is relatively separated from the refining part composed of two or three reactors in series and corresponding heat exchange and liquid separation equipment, the main reaction part can select higher reaction temperature and reactor temperature rise, which not only can reduce the recycle gas quantity needed by the first methanation reactor and further reduce the actual feeding quantity of the second and third methanation reactors, but also utilizes the characteristic of reduced methanation volume to mix the outlet material flow of the first methanation reactor which is smaller than the mixed feed gas volume at the inlet with the second part of fresh raw materials, and mix the outlet material flow of the second methanation reactor which is smaller than the mixed feed gas volume at the inlet of the second methanation reactor with the third part of fresh raw materials, so that the volume of a single reactor, the filling quantity of the catalyst and the total reactor volume and the catalyst quantity are reduced, this is advantageous for increasing the scale of the single-stage methanation apparatus. On the other hand, two or three methanation reactors connected in series with the refining part can select lower reaction temperature and reaction temperature rise, and can increase the reaction depth of methanation reaction to obtain a substitute natural gas product with higher methane content and calorific value.
In addition, the process flow of the invention does not mix any material flow except fresh raw materials and methane-rich gas of products produced by the process, thereby simplifying the process flow and the configuration of an external system.
All the advantages mentioned above make the method and apparatus of the present invention have higher economic benefit, lower comprehensive energy consumption and smaller equipment size compared with the traditional technical method. The invention is particularly suitable for preparing Substitute Natural Gas (SNG) from coal gasification synthesis gas.
Drawings
FIG. 1 is a schematic diagram of a system for producing substitute natural gas according to the present invention
Description of reference numerals:
101 a first feed heat exchanger; 102 a second feed heat exchanger; 103 a first high-temperature high-pressure waste heat boiler; 104 a second high-temperature high-pressure waste heat boiler; 105 a superheater; 106 a third high-temperature high-pressure waste heat boiler; 107 five reverse inlet heat exchangers; 108 boiler feed water heat exchanger; 109 a first demineralized water heat exchanger; 110 a second demineralized water heat exchanger; 201 a first methanation reactor; 202 a second methanation reactor; 203 a third methanation reactor; 204 a fourth alkylation reactor; 205 a fifth methanation reactor; 206 sixth alkylation reactor; 301 a compressor; 401 intermediate liquid separation tank;
1, raw material gas; 17, circulating gas; 24SNG product gas
Detailed Description
The present invention will be further described with reference to the following examples.
Example (b):
as shown in fig. 1, a system for producing substitute natural gas,
the method comprises the following steps: a main methanation part and a refined methanation part; the main methanation part comprises three methanation reactors connected in parallel in series, and the refined methanation part comprises two or three methanation reactors connected in series;
a main methanation part: the feed gas pipeline is divided into three parts which are respectively connected with the inlets of the first methanation reactor 201, the second methanation reactor 202 and the third methanation reactor 203, and the outlet of the first methanation reactor 201 is connected with the first high-temperature high-pressure waste heat boiler 103 and then is connected with the inlet of the second methanation reactor 202 together with the feed gas pipeline of the second methanation reactor; the outlet of the second methanation reactor is connected with a second high-temperature high-pressure waste heat boiler 104, and then is merged with a feed gas pipeline of a third methanation reactor to enter the inlet of a third methanation reactor 203; the outlet of the third methanation reactor 203 is sequentially connected with a superheater 105, a third high-temperature high-pressure waste heat boiler 106, a second raw material heat exchanger 102 and a five-reaction inlet heat exchanger 107 and then divided into two parts, one part is connected with the top of a fourth methanation reactor 204 of the refined methanation part, and the other part is connected with a compressor 301 and then is combined with a raw material inlet pipeline at the top of the first methanation reactor 201;
refining the methanation part: the outlet of the fourth methanation reactor 204 is connected with the boiler feed water heat exchanger 108, the first desalted water heat exchanger 109, the intermediate liquid separation tank 104 and the five reverse inlet heat exchanger 107 and then connected with the inlet of the fifth methanation reactor 205, the outlet of the fifth methanation reactor 205 is connected with the second desalted water heat exchanger 110 and then connected with the inlet of the sixth methanation reactor 206, and the outlet of the sixth methanation reactor 206 is connected with the first raw material heat exchanger 101 and then produces SNG product gas.
The fresh raw material gas is from coal or other materials and is subjected to conventional steps of gasification, transformation, acid gas removal, deep desulfurization and the like. After being preheated to 250-350 ℃ by a first raw material preheater and a second raw material preheater, fresh raw material gas is divided into three parts which respectively enter three adiabatic methanation reactors which are arranged in series and in parallel. The three reactors were operated at atmospheric pressure of 25-35 bar and outlet temperature of 600-660 ℃. The raw gas entering the first methanation reactor accounts for 30% of the total raw gas molar flow, 60% (mole fraction) of the residual fresh raw gas is mixed with the methane-rich gas at the outlet of the first methanation reactor and then enters the second methanation reactor, and the residual fresh raw gas is mixed with the methane-rich gas at the outlet of the second methanation reactor and then enters the third methanation reactor. And a high-pressure waste heat boiler is respectively arranged behind the first methanation reactor and the second methanation reactor to recover reaction heat, and a superheater and a third high-temperature high-pressure waste heat boiler are arranged behind the third methanation reactor to recover heat.
And (2) after the methane-rich gas at the outlet of the third methanation reactor passes through a superheater, a third high-temperature high-pressure waste heat boiler, a second raw material preheater and a heat exchanger, the temperature of the cooled methane-rich gas is reduced to more than 200 ℃, process condensate water is not generated at the temperature, the cooled methane-rich gas is divided into two streams, the circulating gas directly enters a circulating compressor, the circulating gas is mixed with the raw material gas after compression and enters the first methanation reactor, and the mole fraction of the circulating gas in the methane-rich product gas is 60%. And the other stream of cooled methane-rich product gas is sent into a refining part and firstly enters a fourth methanation reactor, the temperature of the reaction refined methane-rich product gas is between 400 and 500 ℃, the temperature of the reaction refined methane-rich product gas is reduced to about 120 ℃ after passing through a boiler water supply heat exchanger and a first desalted water heat exchanger, according to the characteristics that water is generated by methanation reaction and the reaction generated water is not beneficial to moving towards the product direction of the methanation reaction, a middle liquid separation tank is arranged to separate a large amount of condensed water, the refined methane-rich gas after water separation enters a fifth methanation reactor through a fifth reverse inlet heat exchanger, the methane-rich gas at the outlet of the fifth methanation reactor enters a sixth methanation reactor after passing through a second desalted water heat exchanger, and the methane-rich gas at the outlet of the sixth methanation reactor passes through a first raw material heat exchanger to obtain a final product SNG with the methane content of over 94 percent.
Wherein,
the temperature of the fresh feed gas is 40 ℃, the molar flow rate is 30000Kmol/h, and the gas flow rate of the fresh feed gas of the three adiabatic methanation reactors arranged in parallel is 3000Kmol/h, 16800Kmol/h and 10200 Kmol/h. The outlet temperatures of the three adiabatic methanation reactors arranged in parallel are all 600-660 ℃, and superheated steam 550t/h with the temperature of 100bar and 500 ℃ can be generated. Taking 44% of cooled material flow of the product gas at the outlet of the third methanation reactor 203 as circulating gas, taking the circulating gas and the material flow 6 as inlet gas of the first methanation reactor, and obtaining the SNG with 7918Kmol/h after the residual methane-rich product gas passes through the methanation reactors connected in series.
Claims (8)
1. A system for producing substitute natural gas, the system comprising:
a main methanation part and a refined methanation part; the main methanation part comprises three methanation reactors connected in parallel in series, and the refined methanation part comprises two or three methanation reactors connected in series;
a main methanation part: the feed gas pipeline is divided into three parts which are respectively connected with the inlets of the first methanation reactor, the second methanation reactor and the third methanation reactor, and the outlet of the first methanation reactor is connected with the first high-temperature high-pressure waste heat boiler and then is combined with the feed gas pipeline of the second methanation reactor to be connected with the inlet of the second methanation reactor; the outlet of the second methanation reactor is connected with the second high-temperature high-pressure waste heat boiler, and then is merged with a feed gas pipeline of a third methanation reactor to enter the inlet of the third methanation reactor; the outlet of the third methanation reactor is sequentially connected with a superheater, a third high-temperature high-pressure waste heat boiler, a second raw material heat exchanger and a fifth reaction inlet heat exchanger and then divided into two parts, wherein one part is connected with the top of the fourth methanation reactor of the refined methanation part, and the other part is connected with a compressor and then is combined with a raw material inlet pipeline at the top of the first methanation reactor;
refining the methanation part: and the outlet of the fourth methanation reactor is connected with a boiler feed water heat exchanger, a first desalted water heat exchanger, an intermediate liquid separation tank and a fifth reverse inlet heat exchanger and then connected with the inlet of a fifth methanation reactor, the outlet of the fifth methanation reactor is used for producing SNG product gas, or is connected with the inlet of a sixth methanation reactor, and the outlet of the sixth methanation reactor is used for producing SNG product gas.
2. A method of producing substitute natural gas using the system of claim 1, the method comprising:
(1) the method comprises the following steps of heating a raw material gas, then respectively feeding the raw material gas into a first methanation reactor, a second methanation reactor and a third methanation reactor for reaction, and mixing a product at the bottom of the first methanation reactor with the raw material gas after heat exchange by a first high-temperature high-pressure waste heat boiler, and then feeding the mixture into the top of the second methanation reactor; the bottom product of the second methanation reactor is subjected to heat exchange by a second high-temperature high-pressure waste heat boiler, mixed with the feed gas and then enters the top of the third methanation reactor; after heat exchange of the bottom product of the third methanation reactor sequentially through the superheater, the third high-temperature high-pressure waste heat boiler, the second raw material heat exchanger and the five-reaction inlet heat exchanger, part of the bottom product is compressed to be used as circulating gas to be mixed with the raw material gas, and then the mixture is sent into the first methanation reactor, and part of the bottom product is sent into the fourth methanation reactor;
(2) the bottom product of the fourth methanation reactor is sent into a fifth methanation reactor after heat exchange through a boiler water supply heat exchanger, a first desalted water heat exchanger, an intermediate liquid separation tank and a five-reverse inlet heat exchanger, the bottom of the fifth methanation reactor is sent into a sixth methanation reactor before or after heat exchange, and the bottom of the sixth methanation reactor is sent out SNG product gas;
heating the raw material gas in the step (1) to 250-350 ℃;
the temperature of the bottom product of the third methanation reactor is not lower than 200 ℃ after heat exchange, part of the bottom product is compressed to be used as circulating gas to be mixed with feed gas and then sent into the first methanation reactor, and part of the bottom product is sent into the fourth methanation reactor;
the temperature of the circulating gas is 200-300 ℃.
3. The method of producing substitute natural gas according to claim 2, wherein:
the flow rate of the raw material gas entering the first methanation reactor is 2-35% of the total raw material gas molar flow rate;
the feed gas entering the second methanation reactor has a flow rate of 10% to 60% of the molar flow rate entering the second and third methanation reactors.
4. The method of producing substitute natural gas according to claim 2, wherein:
the molar flow ratio of the circulating gas to the raw gas of the first methanation reactor is 1-3.
5. The method of producing substitute natural gas according to claim 2, wherein:
the outlet temperatures of the first methanation reactor, the second methanation reactor and the third methanation reactor are 620-700 ℃.
6. The method of producing substitute natural gas according to claim 2, wherein:
20-70% of the molar flow of the bottom product of the third alkylation reactor enters the fourth alkylation reactor.
7. The method for producing substitute natural gas according to any one of claims 2 to 6, wherein:
the main composition range of the raw materials is as follows:
hydrogen gas: 60% -90%, carbon monoxide: 5% -30%, carbon dioxide: 0 to 10 percent.
8. The method of producing substitute natural gas according to claim 7, wherein:
the pressure of the methanation reactor is 20-65 bar.
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| GB201503606D0 (en) * | 2015-03-03 | 2015-04-15 | Johnson Matthey Davy Technologies Ltd | Process |
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| CN104830391A (en) * | 2015-05-15 | 2015-08-12 | 西南化工研究设计院有限公司 | Methanation device and process for synthesizing high-quality natural gas produced by coal |
| CN105112111A (en) * | 2015-09-24 | 2015-12-02 | 中国石化工程建设有限公司 | Integration process and equipment for loop-free methanation of coal-based syngas to prepare natural gas |
| CN106118773B (en) * | 2016-07-16 | 2019-04-02 | 中国科学院山西煤炭化学研究所 | A kind of synthesis gas methanation process that hydrogen converts completely |
| JP6786054B2 (en) * | 2017-12-18 | 2020-11-18 | 株式会社豊田中央研究所 | Methane production equipment and methane production method using it |
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