CN101597527B - Method for making synthetic natural gas by utilizing coke oven gas - Google Patents

Abstract

A method for producing synthetic natural gas from coke oven gas, which is to add carbon source to coke oven gas after rough desulfurization, so that the volume percentage of coke oven gas satisfies the stoichiometric ratio of (H ₂ -3CO)/CO ₂ 4 , compressed and boosted to 0.5-5.4MPa, the fine desulfurization enters the methanation reactor, and the methanation reaction is carried out under the action of the Ni-based catalyst to obtain artificial natural gas, and then to prepare liquefied natural gas. The invention optimizes the stoichiometric ratio of H ₂ , CO and CO ₂ in the coke oven gas by adding carbon to the coke oven gas, thereby improving the yield of synthetic natural gas. The process for producing synthetic natural gas of the present invention is suitable for coking plants of tens to hundreds of tons, so that _H2 , CO, _CO2 and supplemented _CO2 in the coke oven gas can be fully utilized, which is helpful for improving resource utilization and Strengthening environmental protection has practical significance.

Description

A method for producing synthetic natural gas from coke oven gas

technical field

The invention relates to a method for producing synthetic natural gas, in particular to a method for producing synthetic natural gas by using coke oven gas.

Background technique

China is a large coke producing country, with a production capacity of about 300 million tons/year, and about 60 billion Nm ³ of coke oven gas exhausted per year. In addition to being used as civil fuel, power generation, and methanol synthesis, a large part of the coke oven gas is directly burned in the torch, which wastes resources and pollutes the environment. Benzene, naphthalene, tar and other components contained in coke oven gas have been recovered in the chemical production department, and the remaining components are H ₂ 54-59%, CH ₄ 24-28%, N ₂ 3-6%, CO ₂ 1.4- 2.5%, CO 5-8%, O ₂ 0.3-0.7%, and a small amount of impurity sulfide. Its resources are characterized by CH ₄ content of about 1/4 and H ₂ content of nearly 60%.

With the implementation of the domestic sustainable development strategy and the implementation of environmental protection policies, the domestic demand for natural gas is increasing day by day. It is estimated that the demand for natural gas in China will reach 100-110 billion m ³ in 2010, while the output in the same period can only reach 90-95 billion m ³ ; in 2020, the demand for natural gas in China will reach 200 billion m ³ , and the output in the same period can only reach 140-160 billion m ³ . Therefore, in order to solve the contradiction between the supply and demand of natural gas in my country, in addition to sufficient existing domestic resources, it is also necessary to expand the supply of resources through multiple channels and methods. Synthetic natural gas is one of the effective channels.

In recent years, there have been many patents related to the technology of synthesizing artificial natural gas (SNG) and liquefied natural gas (LNG) from coke oven gas in China: CN1935956A, CN1952082A, CN1952083A, CN1952084A and US4318997 all disclose the use of coke oven The method of producing artificial natural gas by multi-stage catalytic methanation of natural gas has the obvious disadvantage that _H2 in coke oven gas is not fully utilized due to insufficient carbon source.

CN101100622A discloses a method for supplementing carbon into coke oven gas and producing synthetic natural gas by using multi-stage catalytic methanation reaction and PSA separation technology. Although this method makes full use of the H ₂ resources in the coke oven gas, it also has the disadvantages of long process, large investment, and low recovery and utilization rate of CH ₄ and heat energy.

Contents of the invention

The object of the present invention is to provide a method for producing synthetic natural gas by utilizing coke oven gas. The method optimizes the stoichiometric ratio of _H2 , CO and _CO2 in coke oven gas by adding carbon to the coke oven gas to improve the synthetic natural gas. The yield of natural gas.

The purpose of the present invention is achieved through the following technical solutions:

A method for producing synthetic natural gas from coke oven gas, comprising the following steps:

a). The coke oven gas undergoes rough desulfurization to remove most of the inorganic sulfur and part of the organic sulfur;

b). Add carbon source to the coke oven gas after crude desulfurization, so that the volume percentage of the gas in the coke oven gas satisfies the stoichiometric ratio of (H ₂ -3CO)/CO ₂ ≈ 4, and the mixed gas is compressed and boosted to 0.5～5.4MPa;

c). Refined desulfurization of the compressed mixed gas, so that the total sulfur in it is ≤0.1ppm;

d). The purified mixed gas enters the methanation reactor, and is subjected to a methanation reaction under the action of a Ni-based catalyst to obtain artificial natural gas with a light hydrocarbon content of 80-95%;

e). Deep decarbonization and deep dehydration of the artificial natural gas produced;

f). After the removal of impurities, the artificial natural gas is subjected to cryogenic separation to prepare liquefied natural gas with a calorific value of about 8500Kcal/Nm ³ (35530KJ/Nm ³ ).

The supplementary carbon source mentioned in the present invention can be CO ₂ , CO, water gas or a mixture thereof. These supplementary carbon sources can be supplied by the exhaust gas of the decarbonization process of the fertilizer plant or the methanol plant, or can be supplied by the exhaust gas of the desulfurization process of the fertilizer plant or the methanol plant, and can also be recovered from the flue gas discharged from the boiler.

The crude desulfurization and fine desulfurization purification technologies in the present invention can refer to the methods in the current coke oven gas methanol production process. Crude desulfurization adopts wet oxidation method for desulfurization. H _{2 S} in the coke oven gas after this process is ≤20mg/Nm ³ , and the removal rate of organic sulfur is not less than 50%. Fine desulfurization adopts dry desulfurization, so that the total sulfur in it is ≤0.1ppm, and other impurities meet the requirements of methanation.

The methanation reaction of the present invention adopts a water-cooled tubular methanation reactor. Water passes through the tube side of the reactor. The Ni-based catalyst uses _Al2O3 as a carrier and is installed in the shell side of the reactor. The reaction gas passes through the shell side _of the reactor. pass in the process. The reaction pressure of the methanation reaction is 0.5-5.4MPa, and the temperature is 250-400°C. The reaction heat released by the reaction heats the cooling water into medium and high pressure steam, which can be recovered as the power of the compressor.

The invention also installs a water pump on the water inlet pipe before the water-inlet-cooled tubular methanation reactor, which can speed up the flow rate of water, control the reaction temperature of the catalyst bed, and prevent the catalyst from overheating.

The deep decarburization of the present invention adopts the MDEA method, and the deep dehydration adopts the molecular sieve method. The impurity CO ₂ ≤ 100ppm, H ₂ O ≤ 0.1ppm, and total sulfur ≤ 0.1ppm in the artificial natural gas after the two-step process. At the same time, the CO ₂ gas separated from the deep decarburization process is recycled as a carbon source for carbon replenishment, and the regenerated tail gas from the deep dehydration process is externally supplied as fuel gas.

The present invention utilizes the cryogenic separation method to remove the _N in artificial natural gas to produce high-quality clean energy and chemical raw materials—liquefied natural gas. At the same time, the coke oven gas methanation reaction and cryogenic separation in the present invention are both It is completed under the same pressure level, the methanation process does not set a circulation loop, and the H ₂ ≤ 1% and CO ₂ ≤ 1% in the reactor after passing through the methanation reactor once, and CO can not be detected, can reach the process index.

The process for producing synthetic natural gas from coke oven gas of the present invention is suitable for matching with coking plants of tens to hundreds of tons, so that _H2 , CO, _CO2 and supplemented _CO2 in coke oven gas can be fully utilized, which is beneficial to improving resources Utilization rate and strengthening environmental protection have practical significance.

The process for producing synthetic natural gas from coke oven gas of the present invention effectively utilizes the CO ₂ waste gas that produces the greenhouse effect, so that H ₂ , CO, and CO ₂ in the coke oven gas can be fully chemically reacted, and the methane recovery rate is close to 98%. The heat energy generated by the reaction can produce high-grade steam of 4.0-10.0MPa, which is used as the power of the compressor. Therefore, the present invention objectively reduces _CO2 emissions and rationally utilizes resources, and is an energy project that reduces emissions, saves energy, and utilizes resources rationally.

The process for producing synthetic natural gas from coke oven gas of the present invention completes the methanation reaction of coke oven gas and the cryogenic separation of natural gas at the same pressure level. The methanation does not have a circulation loop, and light hydrocarbons can be produced after one pass of the methanation reaction. For artificial natural gas with a content greater than 90%, the released _CO can be recycled, and the regenerated tail gas can be used as fuel gas. Compared with the PSA separation process, the recovery rate _of CH in cryogenic separation is high. The present invention has a short process flow and low investment Province.

The coke oven gas production process of the present invention adopts a water-cooled tubular methanation reactor, and a water pump is provided on the water inlet pipe, which can speed up the flow rate of water and ensure that the catalyst bed is not overheated; There are rough desulfurization and fine desulfurization processes to ensure that the total sulfur of raw gas is ≤0.1ppm. The use of these two measures can prolong the service life of the catalyst, increase the methanation conversion yield, and lower the production cost.

Detailed ways

A specific example of using coke oven gas to produce synthetic natural gas is given below, and the gas balance table of the process in this example is shown in Table 1.

Table 1 Coke oven gas to produce synthetic natural gas gas balance table

component 1 2 3 4 5 6 7 8 9 10 CO,% 7.50 7.10 7.10 0 0 0 0 0 H ₂ ,% 57.50 54.42 54.42 1.23 1.23 0 1.93 14.09 CO ₂ ,% 2.80 100.00 100.00 8.00 8.00 0.20 0 0 0 0 CH ₄ , % 24.50 23.19 23.19 83.64 83.81 91.60 0 14.32 O ₂ ,% 6.50 0.47 0.47 0 0 0 0 0 N ₂ ,% 4.60 4.35 4.35 9.53 9.55 2.47 96.90 70.65 Ar,% 0.40 0.38 0.38 0.83 0.83 0.87 1.17 0.94 C ₂ H ₆ ,% 1.87 1.77 1.77 3.88 3.89 4.29 0 0 C ₃ H ₈ ,% 0.22 0.21 0.21 0.46 0.46 0.51 0 0 C ₄ H ₁₀ ,% 0.11 0.11 011 0.23 0.23 0.26 0 0 H ₂ S 5.6g/ ^Nm3 20mg/ ^Nm3 ≤0.1ppm organic sulfur 6000mg/ ^Nm3 3000mg/ ^Nm3 ∑, Nm ³ /h 23500 1305.33 22.67 24828 24828 1137 11314.33 10189.02 148.73 976.19 P, MPa 5.35 5.10 5.05 T, ℃ 40 40 40 40 40 40

The coke oven gas sent by the chemical production and recovery of the coking plant, the gas composition is shown in the component 1 in Table 1. After the rough desulfurization by the wet oxidation method, it is mixed with _CO2 gas (including external decarbonization waste gas) accounting for 5.65% of the coke oven gas volume. (Component 2) is mixed with CO ₂ gas ₍ component 3) produced in the deep decarburization process. The composition of the mixed gas is shown in Table 1. CO ₂ =4.14, H ₂ S decreased from 5.6g/Nm ³ to 20mg/Nm ³ , organic sulfur decreased from 600mg/Nm ³ to 300mg/Nm ³ . After the mixed gas is compressed by the compressor, the pressure is increased to 5.35MPa, and the fine desulfurization is carried out by dry method to obtain the reaction gas with total sulfur ≤ 0.1ppm shown in component 5 in Table 1, and enter the water-cooled tubular methanation reactor. Contact with the Ni catalyst supported on the Al ₂ O ₃ carrier at a temperature of 300-400°C, where H ₂ , CO, and CO ₂ complete the methanation reaction due to the action of the Ni catalyst. The reaction heat generated during the methanation reaction is taken away by the flowing cooling water to generate medium-high pressure steam to ensure that the catalyst bed is not overheated, and the medium-high pressure steam is returned as the power of the compressor. The gas composition of the methanation process is shown in component 6 in Table 1, wherein the light hydrocarbon content is 88.21%, the _H2 content is 1.23%, the _CO2 content is 0.20%, and the CO content cannot be detected, and artificial natural gas is obtained. After deep decarburization of artificial natural gas by MDEA method, it can be seen from component 7 that the CO ₂ content cannot be measured, and the released CO ₂ is returned as carbon replenishing gas for recycling. Next, artificial natural gas is dehydrated through molecular sieves to remove impurities such as H ₂ O and then sent to the cold box. The regeneration tail gas (component 10 in Table 1) generated by dehydration is used as fuel gas. The artificial natural gas passed into the cold box undergoes cryogenic separation to separate N ₂ (component 9 in Table 1) and vent it to make liquefied natural gas (component 8 in Table 1) as a high-quality clean energy or chemical raw material.

In addition, the intermediate product artificial natural gas (component 6) of this embodiment can also be directly made into high-quality compressed natural gas for vehicles.

Claims (8)

1. method of utilizing coke(oven)gas to produce synthetic natural gas may further comprise the steps:

A). coke(oven)gas is removed most inorganic sulfurs and part organosulfur through thick desulfurization;

B). mend carbon source in the coke(oven)gas after thick desulfurization, make the volume percent of gas in the coke(oven)gas satisfy (H ₂-3CO)/CO ₂=4.14 stoichiometric ratio boosts to 0.5～5.4MPa with the gas mixture compression;

C). the smart desulfurization of the gas mixture after the compression makes total sulfur≤0.1ppm wherein;

D). the gas mixture after the purification gets into water-cooled tubulation methanator; Water passes through from tube side, and the Ni series catalysts is contained in the shell side, and reaction gas passes through from shell side; Under catalyst action; With reaction pressure 0.5～5.4MPa, temperature is carried out methanation reaction for 250～400 ℃, obtains the artificial Sweet natural gas of lighter hydrocarbons content 80～95%;

E). the artificial Sweet natural gas that will process carries out depth decarburization and deep dehydration;

F). the artificial natural gas via low temperature separation process after the removal of impurities prepares natural gas liquids.

2. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 is characterized in that said additional carbon source is CO ₂, CO, water-gas or their mixture.

3. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 and 2 is characterized in that described carbon source from fertilizer plant or Methanol Plant decarbonization process waste gas, perhaps from fertilizer plant or Methanol Plant desulfurization process waste gas.

4. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 and 2 is characterized in that described carbon source is from the boiler smoke that reclaims.

5. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 is characterized in that the desulfurization of described thick desulfurization employing wet oxidation process, and dry desulfurization is adopted in smart desulfurization.

6. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 is characterized in that being equipped with on the water inlet pipe before water-cooled tubulation methanator the water pump that helps to accelerate water flow velocity.

7. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 is characterized in that described depth decarburization adopts the MDEA method, and deep dehydration adopts sieve method.

8. the method for utilizing coke(oven)gas to produce synthetic natural gas according to claim 1 is characterized in that the CO that is told by the depth decarburization operation ₂Gas returns as benefit carbon carbon source and recycles.