CN102021054A - New process for synthesizing natural gas by methanation of coke oven gas - Google Patents

Abstract

The invention belongs to the technical field of application of coke oven gas, and specifically relates to a new process for producing synthetic natural gas by methanation of coke oven gas. After the coke oven gas diluted with circulating gas passes through the methanation reactor bed, a certain proportion of The coke oven gas and circulating gas enter the methanation reactor, the gas composition of the inlets of the methanation reactors at all levels is CO+CO ₂ <7%, the temperature at the inlets of the methanation reactors at each level is controlled at 220°C to 400°C, and in the last stage The stage reactors exchange heat through heat exchangers. Adopting this process can protect the environment and save energy. Technically, the methanation reaction process of the present invention can sharply reduce the number of heat exchangers in the process and make full use of the heat generated in the reaction; The raw material gas composition of the first-stage methanation reactor; at the same time, the temperature of the outlet gas of the methanation reactor is effectively controlled. It is beneficial to the choice of reactor material, the circulating gas volume is reduced, the energy consumption is reduced, and thus the cost is reduced.

Description

A new process for producing synthetic natural gas by methanation of coke oven gas

technical field

The invention belongs to the application technical field of coke oven gas, and in particular relates to a new process for producing synthetic natural gas through methanation of coke oven gas.

Background technique

The annual production capacity of coke in my country is 360 million tons, 324 million tons in 2008 and 345 million tons in 2009, one-third of the production capacity is in iron and steel complexes, and two-thirds are in independent coking enterprises . Calculated on the basis of about 400 m ³ coke oven gas by-product per ton of coke, the annual by-product gas volume of independent enterprises is more than 100 billion m ³ , and besides self-use, civil and commercial fuels, the coke oven gas released every year exceeds 20 billion m ³ . Using coke oven gas methanation to produce synthetic natural gas has the function of turning waste into treasure.

The typical composition of coke oven gas is as follows:

name CH ₄ N ₂ CO ₂ CO H ₂ C ₂ H ₆ Coke oven gas (mol%) 26.9 4.1 2.1 7.2 57.6 2.1

The chemical equation for the reaction of _H2 with CO and _CO2 is:

CO + 3H ₂ = CH ₄ + H ₂ O -206.2KJ

And CO ₂ + 4H ₂ = CH ₄ + 2H ₂ O-165.0KJ

The reaction is a strong exothermic reaction, which will generate a high temperature. At present, the main methanation process is multi-stage heat exchange after the methanation reactor, and the heat recovery rate is low, such as:

(1) CRG double methanation process

The process flow is shown in Figure 1. The naphtha or liquefied petroleum gas is purified and preheated, and then enters the two-stage methanation reactor with the participation of circulating gas. The whole reaction is a low exothermic reaction, and the reaction is at a lower temperature and Under the condition of steam-to-material ratio, synthetic natural gas containing more than 98% methane can be obtained, and the reaction requires multi-stage heat exchange.

(2) Lurgi coal-to-substitute natural gas process

The process flow is shown in Figure 2. The raw coal enters the methanation process after gasification and CO conversion to adjust the H ₂ /CO ratio. In order to adjust the temperature of the methanation furnace, the method of partial circulation of product gas is adopted to control the CO content in the raw material gas entering the methanation furnace at about 4.3%, and the maximum temperature of the methanation furnace is kept below 450°C. hot.

(3) ICI one-pass methanation process

ICI Company develops a high-temperature-resistant methanation catalyst and adopts a gas-pass methanation process, as shown in Figure 3. The gas circulation is removed, the process flow is simplified, and the first methanation furnace is operated at a high temperature of nearly 750°C, so that heat exchange is required after each stage of the reactor.

If the generated hot gas continues to be used as a heat source to heat the appropriate proportion of raw material gas and circulating gas, and conducts centralized heat exchange after the last reactor, it is bound to save equipment investment and reduce energy loss, and improve heat utilization. A gas mixture mainly containing CH ₄ , H ₂ and N ₂ with high calorific value can be obtained, and then the synthetic natural gas that meets the national natural gas standard GB 17820 1999 can be obtained through separation technology.

Contents of the invention

The present invention is aimed at the above technical problems, and provides a method that can effectively control the temperature of the reaction inlet and the concentration of CO and CO ₂ to obtain synthetic natural gas with high calorific value, so that the heat generated by the reaction can be used more efficiently, and the circulation volume can be reduced. And it is beneficial to protect the environment and develop new energy, a new process of using coke oven gas methanation to produce synthetic natural gas.

Concrete technical scheme of the present invention is as follows:

A new process of using coke oven gas methanation to produce synthetic natural gas. The coke oven gas diluted with circulating gas passes through the bed of the methanation reactor, then is mixed with coke oven gas and circulating gas, and sent to the methanation reactor to make each The gas composition at the inlet of the first-stage methanation reactor is CO+CO ₂ <7%. The inlet temperature of the first-stage methanation reactor is controlled at 220°C to 400°C, and heat is exchanged through the heat exchanger at the last stage of the reactor.

The methanation reactors for feeding coke oven gas and circulating gas are two or more stages, preferably, the methanation reactors are 2-7 stages.

The coke oven gas and circulating gas are mixed and then enter the primary methanation reactor, so that CO+CO ₂ in the inlet gas composition is <7%, and the inlet temperature is controlled at 220°C-400°C, preferably 225°C-300°C.

After the primary methanation reactor, add circulating gas and coke oven gas, and mix with reaction gas, so that CO+CO ₂ in the inlet gas composition is <7%, and the inlet temperature is controlled at 220°C to 400°C, preferably 225°C ~300°C.

The circulating gas entering the second or more stages is preheated or not; the methanation reactor can be two or more stages, and centralized heat exchange is carried out after the last stage reactor.

A new process of using coke oven gas methanation to produce synthetic natural gas. After the coke oven gas diluted with circulating gas passes through the methanation reactor bed, a certain proportion of coke oven gas and circulating gas enters the methanation reactor. The composition of the gas entering the inlets of the methanation reactors at all levels is CO+CO ₂ <7%.

This process makes full use of the heat generated in the reaction process, effectively controls the concentration of CO+CO ₂ in the raw material gas, the gas circulation volume is small, and effectively controls the outlet gas temperature of the methanation reactor, which is beneficial to the methanation reaction. And the choice of reactor material reduces the number of heat exchangers and improves heat exchange efficiency.

The positive effect of the invention is embodied in that a new method for recycling and utilizing exhaust gas from the coke oven gas industry is created, the environment is protected, and energy is saved. Technically, the methanation reaction process of the present invention can sharply reduce the number of heat exchangers in the process and make full use of the heat generated in the reaction; secondly, it can well control the composition of the feed gas entering the methanation reactors at all levels; At the same time, the temperature of the outlet gas of the methanation reactor is effectively controlled. It is beneficial to the choice of reactor material, the circulating gas volume is reduced, the energy consumption is reduced, and thus the cost is reduced.

the

Description of drawings

Fig. 1 is a process flow diagram of CRG double methanation in the background technology of the present invention.

Fig. 2 is a process flow chart of the Lurgi coal-to-substitute natural gas in the background technology of the present invention.

Fig. 3 is the process flow chart of the methanation of ICI company in the background technology of the present invention.

Fig. 4 is a flow chart of the methanation reaction process for synthesizing natural gas from coke oven gas in Example 1 of the present invention.

Fig. 5 is a flow chart of the methanation reaction process for synthesizing natural gas from coke oven gas in Example 2 of the present invention.

Fig. 6 is a flow chart of the methanation reaction process for synthesizing natural gas from coke oven gas in Example 3 of the present invention.

Fig. 7 is a flow chart of the methanation reaction process for synthesizing natural gas from coke oven gas in Example 4 of the present invention.

Among them, R1——methanation reactor 1, R2——methanation reactor 2, R3——methanation reactor 3, R4——methanation reactor 4, R5——methanation reactor 5, E1——change Heater 1, B1——heat exchanger 2, E2——heat exchanger 3, P——compressor.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments, but it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples.

Embodiment one:

As shown in Figure 4: The coke oven gas composition (vol%) is: H ₂ 57.6, CH ₄ 26.9, CO 7.2, CO ₂ 2.1, N ₂ 4.1, C ₂ H ₆ 2.1, and the amount of raw gas after purification is 1000 kmol/ h (22400 Nm ³ /h).

404 kmol/h (9049.6 Nm ³ /h) coke oven gas is passed into methanation reactor one R1, the circulation ratio is 2.1, the concentration of CO+CO ₂ is 3.0%, the inlet temperature is 280°C, and the reactor outlet The temperature is 456°C. After passing through methanation reactor-R1, the outlet gas is mixed with 848.4 kmol/h (19004.2 Nm ³ /h) of coke oven gas. At this time, the concentration of CO+CO ₂ participating in the reaction is 3.4%. The inlet temperature of the second methanation reactor R2 is about 300°C. After the reaction gas comes out, heat exchanger 1, heat exchanger 2 B1, and heat exchanger 3 E2 are used for centralized heat exchange, and the other part is preheated by compressor P A certain temperature makes it mix with the coke oven gas at the inlet of R1, and the temperature is 280°C, and the rest is output as product gas.

Embodiment two:

The present embodiment utilizes the methanation process of coke oven gas to synthesize natural gas as shown in Figure 5:

The composition (vol%) of the purified coke oven gas is: H ₂ 57.6, CH ₄ 26.9, CO 7.2, CO ₂ 2.1, N ₂ 4.1, C ₂ H ₆ 2.1. The purified raw gas volume is 1000 kmol/h (22400 Nm3/h).

208.33 kmol/h (4446.60 Nm ³ /h) of coke oven gas is passed into methanation reactor one R1, the circulation ratio is 1.325, the concentration of CO+CO ₂ is 4.0%, and the inlet temperature is 250°C. After passing through methanation reactor-R1, the outlet gas is mixed with 64.58 kmol/h (1446.60 Nm ³ /h) of recycle gas and 343.75 kmol/h (7730.98 Nm ³ /h) of coke oven gas. The concentration of CO+CO2 participating in the reaction is 4%, the inlet temperature of the second R2 into the methanation reactor is about 250°C, the outlet temperature of the reactor is about 485°C, and the outlet gas after passing through the second R2 of the methanation reactor is at a temperature of 288.12 The circulating gas of kmol/h (6453.89 Nm3/h) and the coke oven gas of 447.92 kmol/h (10033.41 Nm3/h) are mixed. The concentration of CO+CO ₂ is 3%. After the reaction gas comes out, heat exchanger 1, heat exchanger 2 B1, and heat exchanger 3 E2 are used for centralized heat exchange, and part of the gas is used as a part of the circulating gas to directly enter the methanation Reactor 2 R2 and methanation reactor 3 R3, the other part is preheated by compressor P to a certain temperature to make it mix with the coke oven gas at the inlet of methanation reactor 1 R1, and the temperature is 250°C, and the rest is output as product gas.

Embodiment three:

In this embodiment, the methanation reaction process of using coke oven gas to synthesize natural gas is shown in Figure 6:

The composition (vol%) of the purified coke oven gas is: H ₂ 57.6, CH ₄ 26.9, CO 7.2, CO ₂ 2.1, N ₂ 4.1, C ₂ H ₆ 2.1. The purified raw gas volume is 1000 kmol/h (22400 Nm ³ /h).

Feed 135.87 kmol/h (3043.49 Nm ³ /h) coke oven gas into methanation reactor one R1, the circulation ratio is 1.657, the concentration of CO+CO ₂ is 3.5%, and the inlet temperature is 280°C. After passing through methanation reactor-R1, the outlet gas is mixed with 38.72 kmol/h (867.33 Nm ³ /h) of recycle gas and 201.09 kmol/h (4504.42 Nm ³ /h) of coke oven gas. The inlet temperature of the second methanation reactor R2 is about 280°C, the concentration of CO+CO ₂ participating in the reaction is 3.5%, and the outlet temperature of the reactor is about 485°C. 60.33 kmol/h (1351.39 Nm ³ /h) of recycle gas and 312.50 kmol/h (7000 Nm ³ /h) of coke oven gas are mixed. At this time, the inlet temperature of R3 into the methanation reactor 3 is about 280°C. The concentration of CO+CO ₂ participating in ^the reaction is 3.5%, and the outlet temperature of the reactor is about 485 °C. Nm ³ /h) coke oven gas is mixed. At this time, the inlet temperature of R4 into the methanation reactor 4 is about 280°C, and the concentration of CO+CO2 participating in the reaction is 2.5%. E1, Heat Exchanger 2 B1, Heat Exchanger 3 E2 conduct centralized heat exchange, and make part of the gas directly enter Methanation Reactor 2 R2, Methanation Reactor 3 R3 and Methanation Reactor 4 R4 as part of the cycle gas, The other part is preheated to a certain temperature by compressor P to make it mix with the coke oven gas at the inlet of methanation reactor-R1, and the temperature is 280°C, and the rest is output as product gas.

Embodiment four:

In this embodiment, the methanation reaction process of synthesizing natural gas from coke oven gas is shown in Figure 7:

The composition (vol%) of the purified coke oven gas is: H ₂ 57.6, CH ₄ 26.9, CO 7.2, CO ₂ 2.1, N ₂ 4.1, C ₂ H ₆ 2.1. The purified raw gas volume is 1000 kmol/h (22400 Nm ³ /h).

Feed 62.62 kmol/h (1042.69 Nm ³ /h) of coke oven gas into methanation reactor one R1, the circulation ratio is 1.657, the concentration of CO+CO ₂ is 3.5%, and the inlet temperature is 280°C. The reactor outlet temperature After passing through the methanation reactor-R1, the outlet gas is mixed with 22.54 kmol/h (504.90 Nm ³ /h) of recycle gas and 120.85 kmol/h (2707.04 Nm ³ /h) of coke oven gas. The inlet temperature of the methanation reactor R2 is about 250°C, the concentration of CO+CO ₂ participating in the reaction is 4.0%, the outlet temperature of the reactor is about 485°C, and the outlet gas after passing through the methanation reactor R2 is 38.77 The circulating gas of kmol/h (868.45 Nm ³ /h) and the coke oven gas of 207.86 kmol/h (4656.06 Nm ³ /h) are mixed, and the inlet temperature of the third R3 of the methanation reactor is 250 ℃, the concentration of CO+CO ₂ participating in the reaction is 4.0%, the outlet temperature of the reactor is about 485℃, the outlet gas after passing through the methanation reactor 3 R3 and the circulation of 66.68 kmol/h (1493.63 Nm ³ /h) Gas and 357.53 kmol/h (8008.67 Nm ³ /h) coke oven gas are mixed. At this time, the inlet temperature of the methanation reactor 4 R4 is about 250°C, and the concentration of CO+CO ₂ participating in the reaction is 4.0%. The outlet gas after passing through methanation reactor 4 R4 is mixed with 339.25 kmol/h (7599.20 Nm ³ /h) of recycle gas and 251.15 kmol/h (5625.76 Nm ³ /h) of coke oven gas. The inlet temperature of reactor five R5 is about 280°C, and the concentration of CO+ _CO2 participating in the reaction is 2.5%. After the reaction gas comes out, heat exchanger one R1, heat exchanger two B1 and heat exchanger three E2 are used for centralized exchange. heat, and make a part of the gas directly enter the second R2 methanation reactor, the third R3 methanation reactor and the fourth R4 methanation reactor as the circulating gas, and the other part is preheated by the compressor P to a certain temperature to make it react with methanation The temperature of the coke oven gas at the inlet of device 1 R1 is 280°C after mixing, and the rest is output as product gas.

Claims (6)

1. A new process for producing synthetic natural gas by methanation of coke oven gas, characterized in that: after the coke oven gas diluted by circulating gas passes through the methanation reactor bed, it is mixed with coke oven gas and circulating gas, and then fed into methane The gas composition of the inlets of the methanation reactors at each level is CO+CO ₂ <7%. heat exchanger. 2. The new process for producing synthetic natural gas by methanation of coke oven gas according to claim 1, characterized in that: the methanation reactors for coke oven gas and recycle gas are two or more stages. 3. The new process for producing synthetic natural gas by methanation of coke oven gas according to claim 1, characterized in that: the mixed coke oven gas and circulating gas enter the primary methanation reactor, so that the methanation reactor The inlet gas composition is CO+CO ₂ <7%, and the inlet temperature of the methanation reactor is controlled at 220°C-400°C, preferably 225°C-300°C. 4. The new process of utilizing coke oven gas methanation to produce synthetic natural gas according to claim 1, characterized in that: after the first-stage methanation reactor, recycle gas and coke oven gas are added, and mixed with reaction gas, The CO+CO ₂ in the inlet gas composition of the methanation reactor should be <7%, and the inlet temperature should be controlled at 220°C-400°C, preferably 225°C-300°C. 5. The new process for producing synthetic natural gas by methanation of coke oven gas according to claim 1, characterized in that: the circulating gas entering the second or more stages is preheated or not. 6. The new process for producing synthetic natural gas by methanation of coke oven gas according to claim 1, characterized in that concentrated heat exchange is performed after the last reactor.

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