CN103980948A - Coal powder pyrolysis and gasification method - Google Patents

Abstract

The invention discloses a pulverized coal pyrolysis and gasification method, which integrates and recovers the sensible heat of the synthesis gas from the high-temperature gasification of the semi-coke through the pyrolysis of the pulverized coal in the entrained bed and the gasification of the semi-coke in the entrained bed. All the pulverized coal enters the entrained bed pulverized coal pyrolysis furnace, and the tar generated by pulverized coal pyrolysis is further pyrolyzed at high temperature to generate low molecular hydrocarbons (such as methane) and coke; the semi-coke generated by pulverized coal pyrolysis enters the entrained bed The gasifier generates high temperature syngas. The synthesis gas generated by this method is rich in methane (methane content 2-15v%), low in tar content (less than 10ppm), high cold gas efficiency of the device (greater than 80%), wide adaptability of raw materials, and can be applied to coal-based natural gas and Gas and other fields.

Description

A kind of pulverized coal pyrolysis and gasification method

technical field

The invention relates to a coal gasification method, in particular to a method for efficiently preparing methane-rich synthesis gas or fuel gas by coupling entrained bed pulverized coal pyrolysis and entrained bed semi-coke gasification.

technical background

Coal accounts for two-thirds of the primary energy consumed in my country, and for a long time to come, coal will still play the leading role in energy supply. Coal chemical industry uses coal as raw material, and converts coal into gaseous fuel, liquid fuel, coke and chemicals through chemical processing, including gasification, coking, liquefaction and other utilization routes of coal.

Coal pyrolysis is a very complicated process, and chemical reactions can be generally divided into two categories: cracking and polycondensation. Coal pyrolysis is an extremely important intermediate process of coal processing and conversion, such as combustion, gasification, coking, liquefaction and other processes. Without hydrogenation and oxygen, partial gasification and liquefaction of coal can be realized to produce gas and tar. The pyrolysis and graded conversion of coal improves the efficiency of the coal utilization process and is beneficial to the removal of pollutants in the coal. It is one of the hotspots in the development of new coal technologies. Representative foreign processes include COED and Garrett processes in the United States. Zhejiang University put forward the high-efficiency power generation technology of coal graded conversion, and Dalian University of Technology put forward the lignite upgrading technology.

The development of coal gasification technology has a history of more than 150 years, forming three technical schools of fixed bed, fluidized bed and entrained bed. Entrained bed coal gasification technology has become the main direction of gasification technology development because of its large-scale, high efficiency, and strong adaptability to coal types. It is a hotspot in gasification technology research. The entrained bed gasifier adopts the method of liquid slagging, and the temperature of the high-temperature syngas exiting the gasifier is above 1300°C. The high-temperature sensible heat recovery methods of the syngas mainly include waste heat boiler, water quenching and chemical heat recovery. Chemical heat recovery is to recover the sensible heat of the high-temperature syngas in the first stage of the gasifier through the pyrolysis of coal to absorb energy. For example, the E-gas gasification technology of Phillips66 Company uses the method of injecting part of the coal-water slurry into the second stage. TPRI (Xi'an Thermal Engineering Research Institute) and MHI adopt the method of injecting part of the pulverized coal in the second stage, and East China University of Science and Technology proposes a coupling method of entrained-flow gasification and fixed-bed pyrolysis on the basis of multi-nozzle opposed gasification technology.

However, currently commercialized entrained-bed coal gasifiers that use chemical heat to recover sensible heat from high-temperature syngas only inject part of coal-water slurry or pulverized coal into the second stage, and there is still room for further improvement in energy conversion efficiency. The tar generated during the coal pyrolysis process is easy to condense and stick to the heat exchanger, semi-coke separator or subsequent synthesis gas treatment device during the process of cooling the high-temperature gas to recover heat, which affects the long-term stable operation of the coal gasification device. The pyrolysis of tar in the gasifier needs to be further considered.

Contents of the invention

In view of the above problems, in order to further improve the energy conversion efficiency of the entrained bed coal gasifier and solve the problem of tar pyrolysis, the present invention proposes a coupling of entrained bed pulverized coal pyrolysis and entrained bed semi-coke gasification to efficiently prepare methane-rich syngas Or the gas method.

The entrained bed pulverized coal pyrolysis furnace adopts pulverized coal (particle size less than 100 microns). Small-sized coal is easy to heat and the temperature inside and outside the particles is relatively uniform. The resistance of volatile matter to diffuse is small, and the escape speed is fast. The entrained bed pulverized coal pyrolysis furnace adopts the entrained bed reactor, and the pulverized coal is conveyed by dense phase pneumatically and a small amount of gas is used to realize the dispersion of the pulverized coal, which strengthens the mixing process in the pyrolysis furnace and improves the pulverized coal Heating rate, pyrolysis produces less polymer products and high volatile matter precipitation rate; the heat carrier of the entrained bed pulverized coal pyrolysis furnace is the high-temperature synthesis gas from the first stage, which is mainly composed of H ₂ , CO, CO ₂ and water vapor. During the coal heating process, the intermolecular bridge breaks to generate a large number of free radicals, which can combine with hydrogen to generate small molecular weight alkanes and aromatic compounds, which is beneficial to the pyrolysis of tar; the entrained bed pulverized coal pyrolysis furnace operates at high temperature, The pyrolysis of tar can be enhanced by prolonging the residence time of materials in the pyrolysis furnace, and the content of tar in the synthesis gas is less than 10PPM.

The specific technical scheme is as follows:

A pulverized coal pyrolysis and gasification method, the gasification furnace (1) used in the method is divided into two sections, the first section is an entrained bed semi-coke gasification furnace (101), and the semi-coke powder (S13 ) for high-temperature entrained-bed gasification; the second stage is an entrained-bed pulverized-coal pyrolysis furnace (102), which recovers the high-temperature synthesis gas from the entrained-bed semi-coke gasifier (101) through pyrolysis of pulverized coal (S1) to absorb energy Sensible heat;

The method comprises the steps of:

The pulverized coal (S1) enters the entrained bed pulverized coal pyrolysis furnace (102) through the nozzle by dense-phase pneumatic conveying, and a small amount of gas (S2) is passed through the nozzle to realize the dispersion of the pulverized coal (S1) in the pulverized coal pyrolysis furnace (102) , strengthen the heat and mass transfer process in the pyrolysis furnace; the high-temperature synthesis gas rich in _H2 from the entrained bed semi-coke gasifier (101) makes the pulverized coal (S1) pyrolyzed to generate gas, tar or semi-coke, said The tar is further pyrolyzed at high temperature to generate low molecular hydrocarbons (such as methane) and coke; the semi-coke and its methane-rich synthesis gas (S3) generated after the pyrolysis of pulverized coal (S1) exit the gasifier (1) and enter The waste heat boiler (2) recovers sensible heat; the temperature of the synthesis gas (S5) entering the waste heat boiler (2) is adjusted through the chilling medium (S4), and the boiler feed water (S16) enters the high-pressure steam (S17) through the waste heat boiler (2); The residence time of pulverized coal (S1) in the entrained bed pulverized coal pyrolysis furnace (102) is 2 to 20 seconds to ensure that the tar generated by pyrolysis can be further pyrolyzed, so that the tar content in the synthesis gas is less than 10ppm, which will not affect Operation of equipment such as waste heat boiler (2) and semi-coke filter (3).

The semi-coke powder (S13) enters the entrained-bed semi-coke gasification furnace (101) through the dense-phase pneumatic conveying through the nozzle, and the nozzle is passed into the gasification agent (S14) to realize the semi-coke powder (S13) in the entrained-bed semi-coke gasifier ( The dispersion and gasification reaction in 101) generate rich CO and H ₂ Syngas; said rich CO and H ₂ Syngas enters the entrained bed pulverized coal pyrolysis furnace (102), molten ash (S15) Exiting the gasifier (1); the residence time of the semi-coke powder (S13) in the entrained-bed semi-coke gasifier (101) is 2 to 10 seconds;

The synthesis gas (S6) exiting the waste heat boiler (2) enters the semi-coke filter (3), the filtered synthesis gas (S7) goes downstream for further processing, and the recovered semi-coke (S8) enters the semi-coke storage tank (4);

The semi-coke powder (S9) in the semi-coke storage tank (4) enters the semi-coke lock hopper (5), and under the action of inert gas (nitrogen or carbon dioxide, etc.) (S10), the semi-coke powder in the semi-coke lock hopper (5) is The coke powder (S11) is pressurized and activated and enters the semi-coke powder feeding tank (6), and under the action of the gasification agent (S12), the semi-coke powder in the semi-coke powder feeding tank (6) is subjected to dense-phase air pressure. delivery and activation.

The particle size of the pulverized coal (S1) and semi-coke powder (S13) is less than 100 microns.

The gas (S2) is an inert gas or carbon dioxide, or a small amount of recycled synthesis gas after compression.

The gasification agent (S12) is oxygen or oxygen-enriched air, and contains at least one of water vapor or carbon dioxide.

The medium for the pulverized coal (S1) and semi-coke powder (S13) to be transported by dense phase pneumatic force is nitrogen or carbon dioxide.

The operating pressure of the gasifier (1) is 0.1-10.0 MPa, the operating temperature of the entrained-bed semi-coke gasifier (101) is 1200-1600°C, and the synthesis gas from the entrained-bed pulverized coal pyrolysis furnace (102) is (S3) temperature is 600-1200 degreeC.

The entrained-bed semi-coke gasification furnace (101) and the entrained-bed pulverized coal pyrolysis furnace (102) can be integrated into one device, or two separate devices can be connected through a conduit.

The temperature of the synthesis gas (S5) entering the waste heat boiler (2) is less than 900° C., and the temperature is adjusted by the quenching medium (S4); the quenching medium (S4) is circulating syngas or quenching water.

The tube side of the waste heat boiler (2) uses boiler feed water (S16) or high-pressure steam (S17), and the shell side uses synthesis gas and semi-coke (S5); the temperature of the synthesis gas (S6) exiting the waste heat boiler (2) is 200 ~400°C.

This process is integrated through the pyrolysis of entrained bed pulverized coal and entrained bed semi-coke gasification, the generated synthesis gas is rich in methane (methane content 2-15v%), the tar content is low (less than 10ppm), and the cold gas efficiency of the device is high (greater than 80%), wide adaptability of raw materials, can be used in coal-to-natural gas and fuel gas and other fields.

Description of drawings

Fig. 1 is a schematic flow chart of pulverized coal pyrolysis and gasification method.

Symbol Description

1 gasifier; 101 entrained-bed semi-coke gasifier; 102 entrained-bed pulverized coal pyrolysis furnace; 2 waste heat boiler;

3 semi-coke filter; 4 semi-coke storage tank; 5 semi-coke lock bucket; 6 semi-coke feeding tank;

S1 pulverized coal and carrier gas; S2 pulverized coal diffused gas; S3 pulverized coal pyrolysis furnace synthesis gas; S4 chilling medium; S5 waste boiler synthesis gas; S6 waste boiler synthesis gas; S7 semi-coke filter synthesis gas ; S8 semi-coke out of the filter; S9 out of the semi-coke storage tank; S10 pressurization and activation of gas from the pulverized coal lock hopper; S11 semi-coke out of the pulverized coal lock hopper; Semi-coke gasification furnace semi-coke and carrier gas; S14 gasification agent; S15 molten ash; S16 boiler feed water; S17 steam.

Detailed ways

The following are examples of the present invention, providing detailed implementation and specific operation process, the purpose of which is only to better understand the content of the present invention. The scope of protection of the invention is therefore not restricted by the examples given.

See Figure 1. The core content of the integration of entrained bed pulverized coal pyrolysis and semi-coke gasification is to recover the high sensible heat of semi-coke gasification through pulverized coal pyrolysis, and all the pulverized coal enters the entrained bed pulverized coal pyrolysis furnace. The synthetic gas after pyrolysis is rich in methane and low in tar content, which improves the cold gas efficiency of the device.

The gasifier (1) is divided into two sections, the first section is an entrained bed semi-coke gasification furnace (101), which performs high-temperature entrained gasification of the semi-coke powder (S13) generated in the second section; the second section is an entrained bed pulverized coal thermal The pyrolysis furnace (102) recovers the sensible heat of the high-temperature syngas from the entrained-bed semi-coke gasifier (101) by absorbing energy through pyrolysis of pulverized coal (S1).

All the pulverized coal (S1) enters the entrained bed pulverized coal pyrolysis furnace (102) through the nozzle by dense phase pneumatic conveying, and a small amount of gas (S2) is fed into the nozzle to realize the pulverized coal in the entrained bed pulverized coal pyrolysis furnace (102). dispersion. The high-temperature synthesis gas rich in _H2 from the entrained-bed semi-coke gasifier (101) makes the pulverized coal pyrolyze to generate gas, tar and semi-coke, etc., and the tar is further pyrolyzed at high temperature to generate low-molecular hydrocarbons (such as methane ) and coke. The semi-coke and the methane-rich synthesis gas (S3) generated after the pyrolysis of pulverized coal (S1) exit the gasifier and enter the waste heat boiler (2).

The semi-coke powder (S13) is conveyed by dense-phase pneumatics into the entrained-bed semi-coke gasifier (101) through the nozzle, and the nozzle is passed through the gasification agent (S13) to realize the semi-coke powder in the entrained-bed semi-coke gasifier (101). The dispersion and gasification reaction occurs to generate syngas rich in CO and _H2 . The generated high-temperature synthesis gas enters the entrained bed pulverized coal pyrolysis furnace (S102), and the molten ash (S13) is discharged out of the gasifier (1).

The waste heat boiler (2) further recovers the sensible heat of the pyrolyzed semi-coke and its methane-rich synthesis gas (S3). The temperature of the synthesis gas (S5) fed to the waste heat boiler (2) is regulated by means of a chilling medium (S4). Boiler feed water (S16) enters the waste heat boiler (2) to produce medium and high pressure steam (S17).

The synthesis gas (S6) exiting the waste heat boiler (2) enters the semi-coke filter (3), the filtered synthesis gas (S7) goes downstream for further processing, and the recovered semi-coke (S8) enters the semi-coke storage tank (4).

The semi-coke powder (S9) in the semi-coke storage tank (4) enters the semi-coke lock hopper (5), and under the action of inert gas (nitrogen or carbon dioxide, etc.) (S10), the semi-coke powder in the semi-coke lock hopper (5) is The coke powder is pressurized and activated.

The semi-coke powder (S11) in the semi-coke powder lock hopper (4) enters the semi-coke powder feeding tank (6), and under the action of an inert gas (nitrogen or carbon dioxide, etc.) (S10), the semi-coke powder feeding tank (6) The semi-coke powder inside is subjected to dense-phase pneumatic conveying and activation.

The arrangement of nozzles of pulverized coal pyrolysis furnace and gasifier of the present invention is preferably the arrangement of multi-nozzle impingement flow (ZL98110616.1).

The waste heat boiler of the present invention adopts a convection boiler type.

The semi-coke separator of the present invention can be ceramic filter, cyclone separator and other types.

Example 1

For the production of synthesis gas by the gasification technology of entrained bed pulverized coal pyrolysis and semi-coke gasification, the sensible heat in the high-temperature gasification synthesis gas of semi-coke is recovered by means of pulverized coal pyrolysis. The content of CH ₄ in the syngas is high, and the system The cold gas has high efficiency and can be widely used in the preparation of methane-rich synthesis gas or fuel gas with high calorific value. Table 1 shows the properties of raw coal. The pressure of the gasifier is 4.0MPa, and the processing capacity of a single gasifier is greater than 1000 tons (dry basis coal) per day.

Table 1 Properties of raw coal

In this embodiment, the gasifier consists of two stages: an entrained bed pulverized coal pyrolysis furnace and an entrained bed semi-coke gasifier. All pulverized coal is transported into the entrained bed pulverized coal pyrolysis furnace through N ₂ , and the synthetic gas circulation volume for pulverized coal dispersion is about 8000Nm ³ /h. After the pulverized coal enters the pyrolysis furnace, it is fully mixed with the high-temperature synthesis gas (about 1300°C) from the semi-coke gasifier, and is pyrolyzed into low-molecular hydrocarbons and coke mainly composed of methane. Part of the coke and the H in the synthesis gas ₂ O and CO ₂ undergo a gasification reaction. The synthesis gas and coke at the outlet of the pulverized coal pyrolysis furnace are separated after cooling down, and all the coke is transported to the entrained semi-coke gasifier through _N2 for gasification reaction. In order to improve the gasification efficiency, the entrained semi-coke gasifier adds A certain amount of water vapor is used as gasification agent. Table 2 compares the gasification conditions and process indicators between the gasification method of this embodiment and the traditional pulverized coal gasification method.

Table 2 Gasification conditions and process indicators

*In the calculation of specific oxygen consumption and specific coal consumption, each mole of methane is converted according to 3.12 moles of _H2 or CO.

It can be seen from Table 2 that the specific coal consumption and specific oxygen consumption of the gasification device are reduced by 3.82% and 28.19%, respectively, and the cold gas efficiency is increased by 3.46% by adopting the coupling process of entrained-bed semi-coke gasification and entrained-bed pulverized coal pyrolysis Percentage points, the gasification process performance of the coupling process is better than that of the current entrained bed pulverized coal gasification process.

Claims (9)

1. A pulverized coal pyrolysis and gasification method is characterized in that, the gasifier (1) used in the method is divided into two sections, and one section is an entrained bed semi-coke gasifier (101), and the second section generates The semi-coke powder (S13) is subjected to high-temperature entrained-bed gasification; the second stage is an entrained-bed pulverized coal pyrolysis furnace (102), and the entrained-bed semi-coke gasification furnace ( 101) sensible heat of the high-temperature syngas; The method comprises the steps of: The pulverized coal (S1) enters the entrained bed pulverized coal pyrolysis furnace (102) through the nozzle by dense-phase pneumatic conveying, and a small amount of gas (S2) is passed through the nozzle to realize the dispersion of the pulverized coal (S1) in the pulverized coal pyrolysis furnace (102) , strengthen the heat and mass transfer process in the pyrolysis furnace; the high-temperature synthesis gas rich in _H2 from the entrained bed semi-coke gasifier (101) makes the pulverized coal (S1) pyrolyzed to generate gas, tar or semi-coke, said The tar is further pyrolyzed at high temperature to generate low molecular hydrocarbons and coke; the semi-coke and its methane-rich synthesis gas (S3) generated after the pyrolysis of pulverized coal (S1) go out of the gasifier (1) and enter the waste heat boiler (2 ) to recover sensible heat; adjust the temperature of the synthesis gas (S5) entering the waste heat boiler (2) through the chilling medium (S4), and the boiler feed water (S16) enters the high-pressure steam (S17) through the waste heat boiler (2); the pulverized coal (S1) The residence time in the entrained bed pulverized coal pyrolysis furnace (102) is 2 to 20 seconds; The semi-coke powder (S13) enters the entrained-bed semi-coke gasification furnace (101) through the dense-phase pneumatic conveying through the nozzle, and the nozzle is passed into the gasification agent (S14) to realize the semi-coke powder (S13) in the entrained-bed semi-coke gasifier ( The dispersion and gasification reaction in 101) generate rich CO and H ₂ Syngas; said rich CO and H ₂ Syngas enters the entrained bed pulverized coal pyrolysis furnace (102), molten ash (S15) Exiting the gasifier (1); the residence time of the semi-coke powder (S13) in the entrained-bed semi-coke gasifier (101) is 2 to 10 seconds; The synthesis gas (S6) exiting the waste heat boiler (2) enters the semi-coke filter (3), the filtered synthesis gas (S7) goes downstream for further processing, and the recovered semi-coke (S8) enters the semi-coke storage tank (4); The semi-coke powder (S9) in the semi-coke storage tank (4) enters the semi-coke lock hopper (5), and under the action of the inert gas (S10), the semi-coke powder (S11) in the semi-coke lock hopper (5) is removed. The pressurized and activated semi-coke powder enters the semi-coke powder feeding tank (6), and under the action of the gasification agent (S12), the semi-coke powder in the semi-coke powder feeding tank (6) is subjected to dense-phase pneumatic conveying and activation. 2. The method according to claim 1, characterized in that the particle size of the pulverized coal (S1) and semi-coke powder (S13) is less than 100 microns. 3. The method according to claim 1, characterized in that the gas (S2) is an inert gas or carbon dioxide, or a small amount of recycled synthesis gas after being compressed. 4. The method according to claim 1, characterized in that the gasification agent (S12) is oxygen or oxygen-enriched air, and at least one of water vapor or carbon dioxide is additionally contained. 5 . The method according to claim 1 , characterized in that, the medium for the pulverized coal ( S1 ) and semi-coke powder ( S13 ) to be conveyed by dense-phase pneumatics is nitrogen or carbon dioxide. 6. The method according to claim 1, characterized in that the operating pressure of the gasifier (1) is 0.1-10.0 MPa, and the operating temperature of the entrained semi-coke gasifier (101) is 1200-1600°C , the temperature of the synthesis gas (S3) exiting the entrained bed pulverized coal pyrolysis furnace (102) is 600-1200°C. 7. The method according to claim 1, characterized in that, the entrained bed semi-coke gasifier (101) and the entrained bed pulverized coal pyrolysis furnace (102) can be integrated in one device, or two separate The middle of the equipment is connected by a conduit. 8. The method according to claim 1, characterized in that, the temperature of the synthesis gas (S5) entering the waste heat boiler (2) is less than 900°C, and the temperature is regulated by a quenching medium (S4); the quenching medium (S4) is circulating syngas or chilled water. 9. The method according to claim 1, characterized in that, the tube side of the waste heat boiler (2) uses boiler feed water (S16) or high-pressure steam (S17), and the shell side uses syngas and semi-coke (S5); The temperature of the synthesis gas (S6) exiting the waste heat boiler (2) is 200-400°C.