WO2018032944A1

WO2018032944A1 - Comprehensive utilization process for selective catalytic oxidative conversion of tail gas from fischer-tropsch synthesis

Info

Publication number: WO2018032944A1
Application number: PCT/CN2017/094219
Authority: WO
Inventors: 李蒙; 蒯平宇; 马永明; 田文堂; 王大祥
Original assignee: 武汉凯迪工程技术研究总院有限公司
Priority date: 2016-08-19
Filing date: 2017-07-25
Publication date: 2018-02-22
Also published as: CN106221720A; CN106221720B

Abstract

A comprehensive utilization process for selective catalytic oxidative conversion of a tail gas from Fischer-Tropsch synthesis. The process comprises: conditioning a raw gas for Fischer-Tropsch synthesis, feeding the raw gas into a Fischer-Tropsch synthesis reactor, then performing a Fischer-Tropsch synthesis reaction to obtain a liquid hydrocarbon product and a tail gas; feeding the tail gas into a gas separation device to separate and to extract hydrogen from the tail gas, collecting a portion of a separated tail gas obtained after hydrogen extraction for use as a recycled tail gas, transporting the recycled tail gas into a selective catalytic oxidative conversion reactor, allowing, under the effect of a catalyst, a light hydrocarbon in the recycled tail gas to undergo selective catalytic oxidation with an oxidizing agent, and be converted into hydrogen and carbon monoxide; and returning the hydrogen and carbon monoxide to mix with the raw gas for Fischer-Tropsch synthesis, and to enter the Fischer-Tropsch synthesis reactor again to produce a liquid hydrocarbon product. The process lowers the depth of raw gas conversion and the scale of conversion equipment, increases the utilization rate and carbon efficiency of Fischer-Tropsch synthesis raw material, and improves the economics of a Fischer-Tropsch system.

Description

Comprehensive utilization process of selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas

Technical field

The invention relates to a comprehensive process for converting and utilizing Fischer-Tropsch synthesis tail gas, in particular to a comprehensive utilization process of selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas.

Background technique

Fischer-Tropsch synthesis is a process in which a synthesis gas produced by converting carbonaceous resources such as natural gas, coal, biomass, etc. is produced by a catalyst to produce a liquid hydrocarbon product. The tail gas generated in the process mainly includes H ₂ , CO, CO ₂ and low carbon hydrocarbons. . Among them, the low-carbon hydrocarbon component is mainly CH ₄ and further contains a part of low-carbon olefin. At present, there are two main technical methods for the utilization of Fischer-Tropsch synthesis tail gas: one is to separate and recover high calorific value gases such as H ₂ and CH ₄ in the exhaust gas as fuel for power generation or heat supply; the other is to exhaust gas. The conversion of low- and medium-carbon hydrocarbons (mainly methane) into syngas as Fischer-Tropsch synthesis feed gas enters the synthesis unit to further synthesize oil products, which improves the carbon efficiency and oil yield of the raw materials while reducing the environmental pollution caused by tail gas emissions.

The Chinese invention patent with the publication number CN102730637A discloses a low-carbon exhaust Fischer-Tropsch synthesis tail gas comprehensive utilization process, which converts the non-recycled tail gas into a hydrogen-rich gas after the Fischer-Tropsch synthesis reaction, and further purifies the high-purity hydrogen gas through further purification. And the process of using it.

The Chinese invention patent with the publication number CN102703108A discloses a process for the Fischer-Tropsch synthesis and tail gas utilization, which separates the hydrogen and methane of the Fischer-Tropsch synthesis tail gas by a pressure swing adsorption technique, and undergoes reforming to obtain a high hydrogen to carbon ratio. The syngas is mixed with the Fischer-Tropsch synthesis feed gas and converted into a synthesis reactor to produce oil after the conversion purification process, thereby realizing the recycling of the Fischer-Tropsch synthesis tail gas. The main purpose of the method is to reduce the load of the conversion process, thereby improving the production efficiency and economy of the Fischer-Tropsch synthesis apparatus, but the method places high demands on the purity of hydrogen and methane.

Chinese Patent Publication No. 104150441A discloses a method for converting Fischer-Tropsch synthesis tail gas into Fischer-Tropsch synthesis feed gas, which converts Fischer-Tropsch synthesis tail gas into saturated hydrocarbon by catalytic hydrogenation, and then reforms two stages by steam reforming. Conversion and conversion yields a suitable hydrogen and carbon ratio Fischer-Tropsch and synthetic feed gas, but this process requires the tail gas to pass through a hydrogenation and shifting process, which is not only cumbersome in process but also reduces the economics of the plant.

The Fischer-Tropsch synthesis of liquid hydrocarbons from syngas (H ₂ and CO) can be expressed as follows:

CO+2H ₂ =[-CH ₂ -]+H ₂ O, ΔH=-167kJ/mol

It can be seen that the hydrogen to carbon ratio plays a decisive role in the yield of the product. In theory, the product yield will reach the maximum when the hydrogen to carbon ratio is 2.0, and it is also the highest carbon efficiency. The low-carbon hydrocarbon components in the Fischer-Tropsch synthesis tail gas are mainly methane, and the methane reforming process for syngas is methane steam reforming, methane selective catalytic oxidation and methane carbon dioxide reforming. These processes can be described by the following reaction equations. :

Methane steam reforming

CH ₄ +H ₂ O=CO+3H ₂ , ΔH _298.5k = 206kJ/mole;

Selective catalytic oxidation of methane

CH ₄ +1/2O ₂ =CO+2H ₂ , ΔH _298.5k =-35.5kJ/mole;

Methane carbon dioxide reforming

CH ₄ +CO ₂ =2CO+2H ₂ , ΔH _298.5k =247kJ/mole

It can be seen that the hydrogen-carbon ratio of the synthesis gas obtained by steam reforming and carbon dioxide reforming cannot directly meet the requirements of Fischer-Tropsch synthesis, and the synthesis gas obtained by selective catalytic oxidation can achieve the yield and carbon efficiency of the Fischer-Tropsch synthesis reaction. maximum.

The steam reforming and carbon dioxide reforming reactions of methane are all strong endothermic reactions, and the reactor with complicated structure is required to provide the heat required for the reaction by indirect heating. Due to the limitation of the heat transfer performance of the reactor and the relatively low catalytic activity of the reforming catalyst, the space velocity of the reactor is generally from 5,000 to 10,000 hr ^-1 . Therefore, the reactor is bulky and the equipment cost is high. The selective catalytic oxidation reaction can be carried out under the action of a suitable catalyst, and the self-heating reaction operation can be realized by utilizing the moderate exothermic property of the reaction itself. The reactor is insulated and eliminates the need to provide indirect heat of reaction. The reaction rate is not affected by the heat transfer rate of the equipment. The highly active catalyst can be operated at a space velocity of 500000 to 1000000 hr ^-1 and the reaction product is close to the thermodynamic equilibrium composition. Compared with the catalytic reforming process, the simple adiabatic reactor has a simple structure and a small volume, which can greatly reduce equipment investment.

Summary of the invention

The object of the present invention is to provide a process for comprehensive utilization of a simple catalytic selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas. The process converts the Fischer-Tropsch synthesis tail gas into synthesis gas as a Fischer-Tropsch synthesis feed gas and further produces the oil product, which improves the production efficiency and economy of the Fischer-Tropsch synthesis device while reducing the carbon emissions of the entire system.

In order to achieve the above object, the present invention provides a comprehensive utilization of a selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas The process comprises the steps of converting the tail gas after the Fischer-Tropsch synthesis reaction into a synthesis gas by a selective catalytic oxidation process, and synthesizing the synthesis gas as a raw material gas of the Fischer-Tropsch synthesis reaction, which comprises the following steps:

1) After the raw material gas is quenched and tempered, it is sent to a Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch synthesis reaction to obtain a liquid hydrocarbon product, water and tail gas;

2) The tail gas generated in step 1) enters the gas separation device, and the hydrogen gas is separated and extracted from the tail gas, and the purity of the hydrogen gas is 80 to 99%;

3) Collecting step 2) Part of the gas in the separated tail gas after hydrogen extraction is sent as a circulating tail gas to the selective catalytic oxidation conversion reactor, and under the action of the catalyst, the low-carbon hydrocarbons in the circulating tail gas are selectively catalyzed by the oxidant. The oxidation reaction is converted into hydrogen and carbon monoxide, and is sent to the step 1) to be mixed with the Fischer-Tropsch synthesis feed gas, and then into the Fischer-Tropsch synthesis reactor to produce a liquid hydrocarbon product;

4) Step 3) Separate the uncollected gas from the exhaust gas as the exhaust gas, directly discharge or send it to combustion for heating or power generation.

Further, in the step 1), the raw material gas refers to a synthesis gas containing carbon monoxide and hydrogen formed by conversion of natural gas or coal or biomass, and the molar ratio of hydrogen to carbon monoxide in the raw material gas is 0.1 to 2.5, and the amount of hydrogen and carbon monoxide gas is And the amount of gas which is effective syngas, the raw gas is a synthesis gas whose effective synthesis gas accounts for 50% or more of the total gas volume.

Further, in the step 1), the Fischer-Tropsch synthesis reaction temperature is 160 to 350 ° C, the pressure is 2 to 5 MPa (A), and the catalyst is an iron group or a cobalt group.

Still further, in the step 2), the gas separation device is a pressure swing adsorption device or a membrane separation device or other industrial device for gas separation.

Further, in the step 3), the oxidant that selectively catalyzes the oxidation reaction is an oxygen-rich gas.

Further, in the step 3), the molar ratio of the oxygen in the oxidant of the selective catalytic oxidation reaction to the lower hydrocarbon in the recycle tail gas is 0.3 to 0.7.

Further, in the step 3), the molar ratio of oxygen to low hydrocarbons is from 0.5 to 0.6.

Further, in the step 3), the molar ratio of hydrogen to carbon monoxide is 1.4 to 2.1.

Further, in the step 2), the hydrogen purity is 85 to 95%.

Still further, in the step 1), the water is directly discharged outside the device.

The beneficial effects of the invention are:

The method of the present invention directly converts Fischer-Tropsch synthesis tail gas into a suitable Fischer-Tropsch by selective catalytic oxidation Compared with the conventional reforming, the synthesis of the desired hydrogen-carbon ratio of the raw material gas reduces the depth of the feed gas conversion and the scale of the conversion equipment, and improves the utilization rate and carbon efficiency of the Fischer-Tropsch synthesis raw materials. It also improves the economics of the Fischer-Tropsch system; at the same time, the traditional reforming requires external heat supply, and a large amount of heat released by the selective catalytic oxidation reaction can be used as a heat source, and the energy cost can be reduced without introducing an additional heat source from the outside. Compared with the catalytic reforming process, the adiabatic reactor has a simple structure and a small volume, which can greatly reduce equipment investment.

DRAWINGS

1 is a schematic flow chart of a comprehensive utilization process of a selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to the present invention.

detailed description

In order to better explain the present invention, the main contents of the present invention will be further clarified below with reference to specific embodiments, but the content of the present invention is not limited to the following embodiments.

Comparative example:

This comparative example describes a process of Fischer-Tropsch synthesis that does not convert the Fischer-Tropsch synthesis tail gas.

The biomass gasifier produces a crude syngas of 101,253 Nm ³ /h. After quenching and tempering, the tempering gas used for Fischer-Tropsch synthesis is 90000 Nm ³ /h.

After the tempering gas enters the Fischer-Tropsch synthesis unit, it produces 13464.1 Kg/h of hydrocarbon fuel and emits 9140.2 Nm ^{3 /} h of Fischer-Tropsch tail gas.

The gas composition of each unit in the comparative example is shown in Table 1.

Table 1: Composition of each unit gas in the comparative example

Example 1

This example uses the same raw material gas as the comparative example, and the main process operating conditions are set as follows:

1) Fischer-Tropsch synthesis reactor operating temperature is 220 ° C;

2) Fischer-Tropsch synthesis reactor operating pressure is 2.8MPa (A);

3) The purity of the separated and extracted hydrogen gas is 90%;

4) Separating 5% of the tail gas as a recycle tail gas;

5) The selective catalytic oxidation reforming reactor operating temperature is 750 ° C;

6) The selective catalytic oxidation reforming reactor operating pressure is 1.0 MPa (A);

According to the above setting conditions, the main logistics data and performance parameters of the process in the implementation process of the present invention will be specifically described with reference to the accompanying drawings:

1) The volume ratio of H ₂ /CO in the fresh synthesis gas required for the Fischer-Tropsch synthesis reactor is 2.2, and the effective synthesis gas (H ₂ + CO) accounts for 95% of the total gas;

2) The amount of liquid hydrocarbon products that can be produced per hour is 13577.2Kg/h, which is 0.84% more than that when the exhaust gas is not separated from the same working conditions;

3) The volume ratio of H ₂ /CO in the synthesis gas produced by the selective catalytic oxidation reforming reactor is 1.5, and the effective synthesis gas (H ₂ + CO) accounts for 76% of the total gas;

4) The CO ₂ emission per hour is 689.2 Kg/h, which is 4.1% less than the CO ₂ emission when the exhaust gas is not separated from the same working conditions;

5) The output of 20bar by-product steam per hour is 1173.8Kg/h, which is 1.7% more than the exhaust gas of the same working condition.

Example 2

1) Fischer-Tropsch synthesis reactor operating temperature is 220 ° C;

2) Fischer-Tropsch synthesis reactor operating pressure is 2.8MPa (A);

3) The purity of the separated and extracted hydrogen gas is 90%;

4) Separating 20% of the tail gas as a recycle tail gas;

2) The amount of liquid hydrocarbon product that can be produced per hour is 13929.9Kg/h, which is 3.53% more than the exhaust gas of the same working condition;

3) The volume ratio of H ₂ /CO in the synthesis gas produced by the selective catalytic oxidation reforming reactor is 1.5, and the effective synthesis gas (H ₂ + CO) accounts for 74% of the total gas;

4) The CO ₂ emission per hour is 597.5Kg/h, which is 16.9% less CO ₂ emission than when the exhaust gas is not separated from the same working conditions;

5) The production of 20bar by-product steam per hour is 5132.8Kg/h, which is 7.4% more than the exhaust gas of the same working condition.

Example 3

1) Fischer-Tropsch synthesis reactor operating temperature is 220 ° C;

2) Fischer-Tropsch synthesis reactor operating pressure is 2.8MPa (A);

3) The purity of the separated and extracted hydrogen gas is 90%;

4) Separating 60% of the tail gas as a recycle tail gas;

2) The amount of liquid hydrocarbon products that can be produced per hour is 14996.1Kg/h, which is 11.4% more than that when the tail gas is not separated from the same working conditions;

3) The volume ratio of H _{2 /} CO in the synthesis gas produced by the selective catalytic oxidation reforming reactor is 1.5, and the effective synthesis gas (H ₂ + CO) accounts for 63% of the total gas;

4) The CO ₂ emission per hour is 326.2Kg/h, which is 54.6% less CO ₂ emission than when the exhaust gas is not separated from the same working conditions;

5) The by-product per hour production of 20bar steam increases by 17186.8Kg/h, which is 24.7% more than the exhaust gas in the same working condition;

Other parts not described in detail are prior art. While the above-described embodiments have been described in detail, the present invention is only a part of the embodiments of the present invention, but not all of the embodiments, and other embodiments may be obtained without inventiveness according to the embodiments. All belong to the scope of protection of the present invention.

Claims

A comprehensive utilization process for selective catalytic oxidation conversion of Fischer-Tropsch synthesis tail gas, which converts exhaust gas after Fischer-Tropsch synthesis reaction into synthesis gas by selective catalytic oxidation technology, and uses synthesis gas as raw material gas for Fischer-Tropsch synthesis reaction Another step in the production of oil is characterized in that it comprises the following steps:

1) After the raw material gas is quenched and tempered, it is sent to a Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch synthesis reaction to obtain a liquid hydrocarbon product, water and tail gas;

2) The tail gas generated in step 1) enters the gas separation device, and the hydrogen gas is separated and extracted from the tail gas, and the purity of the hydrogen gas is 80 to 99%;

3) Collecting step 2) Part of the gas in the separated tail gas after hydrogen extraction is sent as a circulating tail gas to the selective catalytic oxidation conversion reactor, and under the action of the catalyst, the low-carbon hydrocarbons in the circulating tail gas are selectively catalyzed by the oxidant. The oxidation reaction is converted into hydrogen and carbon monoxide, and is sent to the step 1) to be mixed with the Fischer-Tropsch synthesis feed gas, and then into the Fischer-Tropsch synthesis reactor to produce a liquid hydrocarbon product;

4) Step 3) Separate the uncollected gas from the exhaust gas as the exhaust gas, directly discharge or send it to combustion for heating or power generation.
The process for comprehensively utilizing the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 1, wherein in the step 1), the feed gas refers to a synthesis of carbon monoxide and hydrogen formed by conversion of natural gas or coal or biomass. The molar ratio of hydrogen to carbon monoxide in the feed gas is 0.1 to 2.5, and the sum of hydrogen and carbon monoxide gas is the gas volume of the effective synthesis gas, which is a synthesis gas in which the effective synthesis gas accounts for 50% or more of the total gas volume.
The process for comprehensively utilizing the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 1 or 2, wherein in the step 1), the Fischer-Tropsch synthesis reaction temperature is 160 to 350 ° C, and the pressure is 2 to 5 MPa ( A) The catalyst is iron or cobalt based.
The process for comprehensively utilizing the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 1 or 2, wherein in the step 2), the gas separation device is a pressure swing adsorption device or a membrane separation device or other gas. Separated industrial unit.
The comprehensive utilization process of the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 1 or 2, wherein in the step 3), the oxidant for selectively catalyzing the oxidation reaction is an oxygen-rich gas.
The comprehensive utilization process of the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 5, characterized in that In the step 3), the molar ratio of the oxygen in the oxidant of the selective catalytic oxidation reaction to the lower hydrocarbon in the recycle tail gas is 0.3 to 0.7.
The process for comprehensively utilizing the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 6, wherein in the step 3), the molar ratio of oxygen to low carbon hydrocarbon is 0.5 to 0.6.
The process for comprehensively utilizing the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 5, wherein in the step 3), the molar ratio of hydrogen to carbon monoxide is 1.4 to 2.1.
The comprehensive utilization process of the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 1 or 2, wherein in the step 2), the purity of the hydrogen gas is 85 to 95%.
The process for comprehensively utilizing the selective catalytic oxidation conversion Fischer-Tropsch synthesis tail gas according to claim 1 or 2, wherein in the step 1), the water is directly discharged from the apparatus.