CN115228264A

CN115228264A - Coal-to-liquid tail gas treatment system and method

Info

Publication number: CN115228264A
Application number: CN202210950428.7A
Authority: CN
Inventors: 梁鹏; 王伟林; 张俊才; 刘鹏; 张玮; 张磊
Original assignee: Shanxi Lu'an Mining Industry Group Co ltd; Shandong University of Science and Technology
Current assignee: Shanxi Lu'an Mining Industry Group Co ltd; Shandong University of Science and Technology
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2022-10-25

Abstract

The invention provides a coal-to-liquid tail gas treatment system and method, and belongs to the technical field of waste gas treatment. The system comprises a tail gas inlet pipe and a catalytic reactor which are sequentially connected, and further comprises a carbon dioxide absorption device and a dehydration device which are sequentially arranged on the tail gas inlet pipe, and a washing device is further connected to the downstream of the catalytic reactor. And the tail gas is subjected to carbon dioxide and water removal through the carbon dioxide absorption device and the dehydration device, enters the catalytic reactor for catalytic oxidation, finally enters the washing device for washing, and is discharged. According to the system and the method, the carbon dioxide and water in the tail gas are removed by arranging the carbon dioxide removing device, the dehydrating device and the washing device, the hydrothermal inactivation of the catalyst is avoided, and the purification efficiency of the tail gas is improved; meanwhile, the heat value is greatly improved, the volume of the catalytic oxidation device for treating the VOCs waste gas is obviously reduced, the device investment is reduced, the energy is better utilized, and the carbon dioxide emission is less.

Description

Coal-to-liquid tail gas treatment system and method

Technical Field

The invention relates to the technical field of waste gas treatment, in particular to a coal-to-liquid tail gas treatment system.

The invention also relates to a coal-to-liquid tail gas treatment method.

Background

More than 85 percent (volume ratio) of tail gas of the reaction for preparing oil by indirect coal liquefaction (FT synthesis) is carbon dioxide, 10 percent (volume ratio) of tail gas is water, and the rest is mainly combustible gas such as methane, carbon monoxide, hydrogen, ethane, ethylene and the like, and trace nitrogen, oxygen, hydrogen sulfide and the like. Because the environmental protection is increasingly strict and the treatment of VOCs in tail gas discharged by reaction is required, the scheme adopted at present is to add oxygen or air into the tail gas in a gathering way for catalytic oxidation reaction, all organic components and hydrogen are converted into carbon dioxide and water and then discharged, but because the oxygen content is too low, the combustion is insufficient or even cannot be carried out.

As shown in figure 1, in the conventional coal-to-liquids tail gas treatment device, tail gas is preheated by a first heat exchanger 19, enters a catalytic reactor 21 through a reactor inlet pipe 20 (a combustion-supporting gas inlet pipe 30 is arranged on the reactor inlet pipe 20), is subjected to catalytic reaction through a honeycomb ceramic heat accumulator 22 and an oxidation catalyst 23, enters the first heat exchanger 19 through a reactor outlet pipe 24 for heat exchange, and is discharged through a discharge outlet pipe 29 after being cooled.

The main problems at present are as follows:

1) Too high a carbon dioxide content in the gas results in low combustible concentrations that are detrimental to the oxidation of the VOCs. Higher temperatures are required for combustion and the exhaust gas is preheated, inefficient carbon dioxide increases the energy consumption for preheating.

2) The high water content in the exhaust results in the noble metal catalysts (VOCs oxidation catalysts) being susceptible to hydrothermal deactivation. That is, at high temperature and in the presence of water vapor, noble metals are easily agglomerated and lose activity. The catalyst is expensive, after hydrothermal deactivation, not only the replacement cost needs to be paid, but also the shutdown is needed, and the start-stop cost of the coal-to-liquid device is very high.

3) Since carbon dioxide and water occupy too much volume, the tail gas treatment equipment (VOCs catalytic oxidation) is bulky, the gas heating value is low, and additional heat supply is required to maintain the operation of the unit.

4) The catalytic oxidation is difficult to achieve complete 100% conversion, although the treatment effect is still good, the smell threshold of some components is high, and a certain peculiar smell exists after the catalytic oxidation, namely, a small amount of unconverted hydrogen sulfide and organic ammonia can be generated, so that the surrounding environment is influenced.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a coal-to-liquids tail gas treatment system and a method, and the system and the method remove carbon dioxide and water in tail gas by arranging a carbon dioxide removal device, a dehydration device and a washing device, avoid hydrothermal inactivation of a catalyst and improve the purification efficiency of the tail gas; meanwhile, the heat value is greatly improved, the volume of the catalytic oxidation device for treating the VOCs waste gas is obviously reduced, the device investment is reduced, the energy is better utilized, and the carbon dioxide emission is less.

In order to achieve the above purpose, the invention adopts the following technical scheme:

the utility model provides a coal liquifaction tail gas processing system, is including the tail gas admission pipe and the catalytic reactor that connect gradually, still including locating in proper order carbon dioxide absorbing device and dewatering device on the tail gas admission pipe, catalytic reactor low reaches still is connected with washing device.

Firstly, the carbon dioxide is separated in advance, which is very beneficial to the oxidation reaction of VOCs and energy conservation; secondly, the water in the tail gas is separated in advance, the method is very favorable in the aspects of energy consumption and prolonging the service life of the catalyst, and meanwhile, the volume and the device for treating the waste gas are reduced, the gas heat value is improved, and the energy consumption is reduced; and finally, the washing unit after catalytic combustion can absorb the generated carbon dioxide while removing peculiar smell, and the washing liquid can be recycled to the carbon dioxide absorption device to be used as absorption liquid for absorbing the carbon dioxide.

In the present invention, the washing liquid composition and concentration may be preferably selected to be the same as those of the absorbing liquid in the carbon dioxide absorbing device. Therefore, preferably, the waste liquid outlet of the washing device is communicated with the absorption liquid inlet of the carbon dioxide absorption device for recycling the washing liquid of the washing device; and an absorption liquid outlet of the carbon dioxide absorption device is communicated with a coal inlet of an entrained flow gasifier of front-end coal gasification equipment for preparing the coal oil. The front-stage process of coal indirect liquefaction reaction is a coal gasification section, and the waste absorption liquid (containing calcium carbonate, sodium carbonate and the like) can be used as a fluxing agent of an entrained flow gasifier after being concentrated, and particularly for high-ash-melting-point coal, the ash melting point of the coal can be reduced so as to facilitate slag tapping operation.

The washing liquid and the absorption liquid are recycled, so that the whole process of the invention does not generate solid waste.

Preferably, the dewatering device is at least one set of dewatering tanks; the lower part and the upper part of the dehydration tank are respectively provided with a dry air inlet and a dry air outlet; and the top and the bottom of the dehydration tank are respectively provided with a tail gas inlet and a tail gas outlet.

Preferably, the outlet of the catalytic reactor is in communication with the scrubbing device via a heat exchange device.

Further, the heat exchange device comprises a plurality of groups of heat exchangers connected in series, preferably a first heat exchanger and a second heat exchanger which are connected in series, the tail gas outlet is communicated with the inlet of the catalytic reactor through the first heat exchanger, and the dry air inlet is communicated with an external dry air source through the second heat exchanger.

Preferably, a combustion air inlet is arranged between the first heat exchanger and the inlet of the catalytic reactor.

The invention also provides a coal-to-liquid tail gas treatment method based on the system, wherein the tail gas is subjected to carbon dioxide and water removal through the carbon dioxide absorption device and the dehydration device, enters the catalytic reactor for catalytic oxidation, finally enters the washing device for washing, and is then emptied.

Preferably, the heat generated by catalytic oxidation in the catalytic reactor is cooled by a heat exchange device, and simultaneously, the tail gas entering the catalytic reactor is preheated, and the dry air entering the dehydration device is preheated.

Preferably, the washing liquid waste liquid in the washing device enters the carbon dioxide absorption device for recycling.

Optionally, the amount of the washing liquid in the washing device is 1/5-1/30 of the amount of the absorption liquid in the carbon dioxide absorption device; preferably, the dosage of the washing liquid in the washing device is 1/10 to 1/20 of the dosage of the absorption liquid in the carbon dioxide absorption device.

Compared with the prior art, the system has a simple structure, carbon dioxide and water in the tail gas are removed by arranging the carbon dioxide removing device, the dehydrating device and the washing device, the hydrothermal inactivation of the catalyst is avoided, and the purification efficiency of the tail gas is improved; meanwhile, the heat value is greatly improved, the volume of the catalytic oxidation device for treating the VOCs waste gas is obviously reduced, the device investment is reduced, the energy is better utilized, and the carbon dioxide emission is less. Furthermore, the invention also utilizes the heat of the catalytic oxidation device to preheat tail gas and dehydrate dry gas, and has the advantage of energy conservation.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present invention, the following brief descriptions of the embodiments and the drawings used in the background art will be provided, and it should be understood that the following drawings only illustrate some embodiments of the present invention, and therefore should not be taken as limiting the scope of the present invention.

FIG. 1 is a schematic diagram of a coal-to-liquids tail gas treatment system in the prior art;

fig. 2 is a schematic structural diagram of a system in embodiment 1 of the present invention.

Reference numerals:

1. tail gas inlet pipe; 2. a carbon dioxide absorption tank; 3. an absorption liquid outlet; 4. an absorption tank exhaust pipe; 5. 6, a tail gas inlet; 7. 8, a dewatering tank; 9. 10, a tail gas inlet; 11. a dry air inlet; 13. a dry air outlet; 15. drying the tail gas pipe; 16. a drying air inlet pipe; 17. an outlet pipe of the second heat exchanger; 18. a second heat exchanger; 19. a first heat exchanger; 20. a reactor inlet tube; 21. a catalytic reactor; 22. a honeycomb ceramic heat accumulator; 23. an oxidation catalyst; 24. a reactor outlet pipe; 25. a heat exchanger connecting pipe; 26. an inlet pipeline of the washing tower; 27. a washing tower; 28. a waste liquid outlet; 29. a discharge outlet pipe; 30. and a combustion supporting gas inlet pipe.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention and are not to be construed as limiting the present invention.

In the description of the present invention, it is to be understood that the terms "upstream", "downstream", "upper", "lower", "top", "bottom", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature "under," "beneath," and "under" a second feature may be directly under or obliquely under the second feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

Example 1

As shown in fig. 2, a coal-to-liquids tail gas treatment system comprises a tail gas inlet pipe 1 and a catalytic reactor 21 which are connected in sequence, wherein a carbon dioxide absorption tank 2 and

dehydration tanks

7 and 8 are arranged before the tail gas inlet pipe 1 enters the catalytic reactor 21, and a washing tower 27 is connected to the downstream of the catalytic reactor 21.

In this embodiment, the bottom of the carbon dioxide absorption tank 2 is provided with an absorption liquid outlet 3; a honeycomb ceramic heat accumulator 22 and an oxidation catalyst 23 are sequentially arranged in the catalytic reactor 21 from top to bottom; the washing tower 27 is provided with a waste liquid outlet 28 at the lower part and a discharge outlet pipe 29 at the upper part.

The lower parts and the upper parts of the

dewatering tanks

7 and 8 are respectively provided with

dry air inlets

11 and 12 and

dry air outlets

13 and 14; the top and the bottom of the

dewatering tanks

7 and 8 are respectively provided with tail gas inlets 5 and 6 and tail gas outlets 9 and 10. CO removal from carbon dioxide absorber 2 ₂ Exhaust pipe for tail gas passing through absorption tank4 are respectively communicated with tail gas inlets 5 and 6.

The bottom of the catalytic reactor 21 is provided with a reactor outlet pipe 24 which is communicated with a washing tower 27 through a first heat exchanger 19 and a second heat exchanger 18 which are connected in series; the first heat exchanger 19 is communicated with the second heat exchanger 18 through a heat exchanger connecting pipe 25; the second heat exchanger 18 is communicated with the washing tower 27 through a washing tower inlet pipeline 26.

The tail gas outlets 9 and 10 converge on the dry tail gas pipe 15 and are communicated with the inlet of the catalytic reactor 21 through a first heat exchanger 19, and a combustion-supporting gas inlet pipe 30 is arranged on a reactor inlet pipe 20 between the first heat exchanger 19 and the inlet of the catalytic reactor 21.

One end of the drying air inlet pipe 16 is connected with an external drying air source, and the other end of the drying air inlet pipe is communicated with the drying

air inlets

11 and 12 through a second heat exchanger 18 and a second heat exchanger outlet pipe 17.

The invention also provides a coal-to-liquid tail gas treatment method based on the system, wherein the tail gas is subjected to CO removal through the carbon dioxide absorption tank 2 ₂ In a preferred embodiment of the present embodiment, potassium carbonate may be used in the carbon dioxide absorption tank 2, pure carbon dioxide may be obtained by a hot potash method, potassium carbonate may be reused, or carbon dioxide may be neutralized by an alkaline solution such as sodium carbonate or calcium carbonate. CO in tail gas after carbon dioxide removal ₂ Can be reduced to mg/m ³ And (4) stages.

The tail gas coming out of the carbon dioxide absorption tank 2 enters

dehydration tanks

7 and 8 for dehydration, water absorption materials such as water absorption molecular sieves of 3A, 4A, 13X and the like or silica gel and the like can be used in the

dehydration tanks

7 and 8, desorption is carried out after adsorption saturation, and the

dehydration tanks

7 and 8 are switched to be used. Of course, in other embodiments, other dehumidification methods such as a desiccant wheel may be used.

In this embodiment, the

dehydration tanks

7 and 8 are further dehydrated by the preheated dry air. The water content in the dehydrated tail gas can be reduced to 0.05-0.2%, thus greatly avoiding the hydrothermal deactivation of the catalyst and improving the purification efficiency of the waste gas.

The tail gas of carbon dioxide and water is removed, the heat value is greatly improved, the volume and device investment of a catalytic oxidation device for treating VOCs waste gas are obviously reduced, the energy is better utilized, and the carbon dioxide emission is less. Wherein, the floor area and the device investment can be saved by more than 80 percent.

The dehydrated tail gas enters the catalytic reactor 21 for catalytic oxidation, and finally enters the washing tower 27, the washing tower 27 absorbs carbon dioxide and a trace amount of acid gases (including hydrogen sulfide, carbonyl sulfide and other odor gases) generated by combustion, and carbon dioxide generated after catalytic combustion of carbon monoxide, hydrocarbons and the like in the tail gas is absorbed in the washing tower 27, so that carbon emission is further reduced, and odor removal is facilitated.

The heat generated by catalytic oxidation in the catalytic reactor 21 is cooled by the first heat exchanger 19 and the second heat exchanger 18, the temperature of the gas at the inlet of the first heat exchanger 19 is about 300 ℃, the tail gas entering the catalytic reactor 21 is heated, the temperature of the gas at the inlet of the second heat exchanger 18 is about 200 ℃, the gas belongs to low-grade heat, the gas can just exchange heat to dry air and serve as a desorption medium (80-120 ℃) of water, and the energy can be fully and reasonably utilized.

Example 2

Substantially identical to the system in example 1, except that the waste liquid outlet 28 of the washing column 27 is communicated with the absorbing liquid inlet of the carbon dioxide absorbing tank 2. The composition and concentration of the washing liquid are selected to be consistent with those of the absorption liquid in the carbon dioxide absorption tank 2, and after the washing tower 27 absorbs carbon dioxide generated by combustion and a trace amount of acid gas (including hydrogen sulfide, carbonyl sulfide and other odor gases), the gas is discharged through the discharge outlet pipe 29, and the washing liquid discharged outside enters the carbon dioxide absorption tank 2 through the washing liquid discharge pipe 28 for previous carbon dioxide absorption.

In some alternative embodiments, the amount of the washing liquid in the washing tower 27 is 1/5 to 1/30 of the amount of the absorption liquid in the carbon dioxide absorption tank 2; in some more preferred embodiments, the amount of the washing liquid in the washing column 27 may be 1/10 to 1/20 of the amount of the absorbing liquid in the carbon dioxide absorbing tank 2.

Example 3

In substantial conformity with the system in embodiment 2, the absorption liquid outlet 3 of the absorption tank 2 excluding carbon dioxide is communicated with the coal inlet of the entrained flow gasifier of the front end coal gasification facility for producing oil from coal through a concentration device. The front-stage process of coal indirect liquefaction reaction is a coal gasification section, and waste absorption liquid (containing calcium carbonate, sodium carbonate and the like) is concentrated and then poured on a coal inlet of an entrained flow gasifier, so that the absorption liquid can be used as a fluxing agent of the entrained flow gasifier, and particularly for high ash fusion point coal, the ash fusion point of the coal can be reduced to facilitate slag tapping operation. Through the recycling of the washing liquid and the absorption liquid, the whole process of the embodiment does not generate solid waste.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.

Claims

1. The utility model provides a coal liquifaction tail gas processing system, is including the tail gas admission pipe and the catalytic reactor that connect gradually, its characterized in that still including locating in proper order carbon dioxide absorbing device and dewatering device on the tail gas admission pipe, catalytic reactor low reaches still is connected with washing device.

2. The system of claim 1, wherein the waste liquid outlet of the scrubbing device is in communication with the absorption liquid inlet of the carbon dioxide absorption device; and an absorption liquid outlet of the carbon dioxide absorption device is communicated with a coal inlet of front-end coal gasification equipment for preparing the coal oil.

3. The system of claim 1, wherein the dewatering device is at least one set of dewatering tanks; the lower part and the upper part of the dehydration tank are respectively provided with a dry air inlet and a dry air outlet; and the top and the bottom of the dehydration tank are respectively provided with a tail gas inlet and a tail gas outlet.

4. A system according to claim 3, wherein the outlet of the catalytic reactor is in communication with the scrubbing means via heat exchange means.

5. The system of claim 4, wherein the heat exchange means comprises several banks of heat exchangers in series.

6. The system of claim 5, wherein the heat exchange device comprises a first heat exchanger and a second heat exchanger connected in series, the tail gas outlet is communicated with the inlet of the catalytic reactor through the first heat exchanger, and the drying air inlet is communicated with an external drying air source through the second heat exchanger.

7. The system of claim 6, wherein a combustion air inlet is provided between the first heat exchanger and the inlet of the catalytic reactor.

8. The coal-to-liquid tail gas treatment method based on the system of any one of claims 1 to 7, characterized in that the tail gas is subjected to carbon dioxide and water removal through the carbon dioxide absorption device and the dehydration device, enters a catalytic reactor for catalytic oxidation, finally enters a washing device for washing, and then is discharged.

9. The method of claim 8, wherein heat generated by catalytic oxidation in the catalytic reactor is cooled by a heat exchange device, and simultaneously the tail gas entering the catalytic reactor is preheated, and the dry air entering the dehydration device is preheated.

10. The method according to claim 9, wherein the washing liquid waste liquid in the washing device enters the carbon dioxide absorption device for recycling;

preferably, the washing liquid in the washing device and the absorption liquid in the carbon dioxide absorption device have the same composition and concentration;

preferably, the dosage of the washing liquid in the washing device is 1/5-1/30 of the dosage of the absorption liquid in the carbon dioxide absorption device;

more preferably, the amount of the washing liquid in the washing device is 1/10 to 1/20 of the amount of the absorbing liquid in the carbon dioxide absorbing device.