Process for producing gas by pulverized coal composite riser staged pyrolysis gasification

Abstract

The application provides a pulverized coal composite riser staged pyrolysis gasification process for producing gas, wherein 0-3mm pulverized coal is sent into the middle part of a composite riser through a conveyor and rapidly mixed with high-temperature gasification coal gas and circulating ash and slag which are lifted upwards, so that hydrogen-assisted rapid pyrolysis and gas-phase tar cracking reactions occur, and then gas-solid staged separation is carried out at the top of the composite riser; the first-stage separated coarse semi-coke and ash are sent back to the bottom of the composite riser through a fluidized bed return feeder, and gasification calcination reactions are carried out at 800-1100 DEG C with oxidants and steam, high-temperature gasification coal gas and part of the ash flow upwards to form a circulation, and part of the ash is discharged; the second-stage separated high-temperature fine semi-coke and ash are sent to a gas flow bed which is communicated with the lower part of the riser and the fluidized bed return feeder through the return feeder, and melting gasification reactions occur at 1300-1600 DEG C, liquid slag vertically falls into the fluidized bed return feeder to be rapidly cooled and solidified, and generated high-temperature gasification gas flows into the lower part of the riser from the lower part of the gas flow bed, thereby providing heat and a hydrogen atmosphere for the pyrolysis of the pulverized coal.

Description

1. Technical Field

[0001] This invention provides a staged pyrolysis gasification process for producing fuel gas using pulverized coal composite riser pipes, which belongs to the field of coal chemical industry. 2. Background Technology

[0002] Gasification is a leading technology for the clean and efficient utilization of coal for energy. Methane content and calorific value are key indicators, but controlling methane content and tar is a trade-off. Based on the gasification method, it is mainly divided into fixed-bed / moving-bed lump coal gasification technology, fluidized-bed pulverized coal gasification technology, and entrained gasification technology. Other methods under development include hydrogenation gasification, nuclear-powered coal gasification, and underground gasification. Fixed-bed / moving-bed coal gasification technology uses lump coal, air, and steam to produce gas. It produces gas with high methane and calorific value, is a mature technology, and offers efficient and rational utilization of heat in a cascade manner. It requires less equipment investment and has lower gasification costs. However, its disadvantages include high tar content in the gas, which can easily cause pipeline blockage and secondary pollution from phenol-containing wastewater; high residual carbon content in ash (10%–30%); and the requirement for high-quality lump coal permeability. Strict coal type restrictions result in high raw material costs for many enterprises, low gasification capacity, and persistently high production costs. Fluidized bed gasification technology for pulverized coal involves continuous gasification using pulverized coal, oxygen, and steam. It directly uses various inexpensive pulverized coals as raw materials, has moderate gasification capacity, high gasification efficiency, low environmental pollution, relatively high equipment investment, and low gasification production cost. However, its disadvantages include low methane content and calorific value in the fuel gas, large fly ash content with high residual carbon content (20%–30%), and high residual carbon content in the slag (7–15%), leading to problems with gasification and sludge discharge. Entrained flow gasification technology uses fine pulverized coal to continuously gasify at high temperatures using oxygen and steam. It has high gasification capacity and efficiency, but also high equipment investment and relatively high residual carbon content in the ash and slag (2–7%). However, its disadvantages include almost no methane in the fuel gas, low calorific value, high requirements for pulverized coal fineness, high grinding energy consumption, high reaction temperature (around 1400℃), short reaction time (a few seconds), inability to preheat the feed pulverized coal, high oxygen consumption, and unreasonable energy utilization, especially for coal-water slurry feed, which has high oxygen consumption and low carbon utilization efficiency.

[0003] The reactivity of coal varies depending on the stage of conversion. The first 80% to 90% is relatively easy to gasify, while the last 10% to 20% is difficult to gasify. Current coal gasification technologies often treat coal as a single substance and attempt to convert it completely through a single process. Therefore, the last 10% to 20% of the difficult-to-gasify residual carbon determines the harsh overall gasification reaction conditions (high temperature, high pressure, long residence time). There is an urgent need to develop low-energy-consumption staged gasification technologies and equipment based on the reaction characteristics of each stage of coal gasification, which can meet the feeding requirements of fluidized beds and achieve the gasification effect of entrained flow beds.

[0004] Coal combined circulating fluidized bed staged gasification process (CN102965157A), 0-6mm pulverized coal and a small amount of limestone are sent into the entrained bed reactor of the combined circulating fluidized bed in the middle part to mix with the gasification gas and circulating ash to be lifted upward for hydrogenation pyrolysis, after gas-solid separation, the high-temperature coarse semi-coke separated in the first stage is returned to the bottom of the circulating fluidized bed to react with the oxidant and steam at 800-1100℃ to generate gasification gas, which flows upward together with the circulating ash to form material circulation; the high-temperature fine semi-coke separated in the second stage is sent to the gas flow bed communicated with the lower part of the fluidized bed in Y type, and reacts at 1200-1600℃ to generate high-temperature gas and liquid slag which flow out of the gas flow bed in the same direction, the high-temperature gas rises into the circulating fluidized bed to provide heat for the gasification of the fluidized bed; the liquid slag flows downward to the circulating ash layer of the turbulent fluidized bed and is solidified into solid ash slag after heat exchange. At present, the process has realized industrial application, the gasification gas of the staged pyrolysis of pulverized coal is rich in methane, the heat value is as high as 1400Kcal / Nm 3 , but does not contain tar, and there is no secondary pollution of phenolic wastewater and the up-and-down phenomenon of the fluidized bed gasification, which achieves the effect of the gas flow bed gasification. However, when the liquid slag of the gas flow bed flows downward to the turbulent fluidized bed, there are problems of poor flow and solidification blockage, which directly affect the long-period safe and stable operation of the combined circulating fluidized bed; at the same time, although the residual carbon content in the discharged gasification ash is greatly reduced, it still contains part of semi-coke, which has not yet reached the target of less than 2%, and it is urgent to further calcine to reduce the residual carbon content, so as to realize clean and efficient energy utilization of coal. 3. Summary

[0005] The purpose of the present application is to overcome the deficiencies of the existing staged pyrolysis gasification technology of pulverized coal, and to provide a pulverized coal composite riser staged pyrolysis gasification process for producing fuel gas, which can realize that the fuel gas is rich in methane but does not contain tar, and there is no secondary pollution of phenolic wastewater and the up-and-down phenomenon of the fluidized bed gasification; and can make the liquid slag of the fly ash gas flow bed melt gasification vertically fall, and quickly mix and cool in the fluidized bed with hundreds of times of large and medium particle coke slag, without the hidden dangers of poor flow and solidification blockage, to ensure the long-period safe and stable operation of the gasification device; at the same time, the gasification slag can be discharged by calcination, to further reduce the residual carbon content of the gasification slag to less than 2%, and solve the problem of high-value utilization of the gasification slag.

[0006] The technical scheme of the present application is: firstly, realizing secondary pollution free of tar and phenol-containing wastewater by hydrogenation high-temperature rapid pyrolysis of pulverized coal and high-temperature cracking of gas-phase tar; secondly, reducing oxygen consumption, solving the problem of upflowing in fluidized bed gasification process, and achieving low-cost and low-severity operation of fluidized bed gasification and carbon conversion efficiency and gasification effect of entrained flow bed by circulating fluidized gasification of large and medium particle semi-coke and ash in riser and entrained flow bed gasification of small particle semi-coke; thirdly, solving the problems of poor flow and solidification blockage of high-temperature gasification melt slag of entrained flow bed by using more than 100 times of fluidized large and medium particle semi-coke and ash to rapidly mix, cool and solidify; and finally, solving the problem of high carbon residue content of fluidized bed gasification discharge slag by further gasification and calcination of returned large and medium particle semi-coke and ash.

[0007] The feature is that the pulverized coal with a size of 0-3 mm is sent into the riser reactor of the composite riser circulating fluidized bed through a conveyor and rapidly mixes with the upwardly rising high-temperature gasification gas and circulating ash at the lower part of the riser reactor, and the hydrogenation rapid pyrolysis and gas-phase tar cracking step-by-step reaction occurs while the upwardly rising, and the gas is sent out as product gas after gas-solid separation at the top of the composite riser; the large and medium particle semi-coke and ash separated in the first stage are sent back to the ladder turbulent bed at the bottom of the composite riser through a fluidized bed return feeder, and are gasified and calcined with the oxidant and steam at 800-1100℃ to form a cycle of the upwardly flowing high-temperature gasification gas and part of the ash, and part of the calcined slag is discharged; the high-temperature fine semi-coke separated in the second stage is sent to the entrained flow bed connected with the lower part of the riser reactor and the fluidized bed return feeder through the return feeder, and the melt gasification reaction occurs at 1200-1600℃, the liquid slag vertically falls into the fluidized bed return feeder to rapidly cool and granulate, and the generated high-temperature gasification gas flows into the lower part of the riser reactor from the lower part of the entrained flow bed to provide heat and hydrogenation atmosphere for the hydrogenation rapid pyrolysis of the pulverized coal.

[0008] The gasification temperature of the large and medium particle semi-coke and ash in the ladder turbulent bed is 800-950℃, and the calcination temperature of the discharged ash is 900-1100℃.

[0009] The operation state of the fluidized bed return feeder is turbulent flow, the return air is steam, oxidant or mixture of the two, and the oxidant is air, oxygen or oxygen-enriched air.

[0010] The features of the present application are described in detail in the embodiments. 4. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings are used to illustrate the present application. Figure 1 The accompanying drawings are used to illustrate the present application.

[0012] The drawings are illustrated as follows:

[0013] 1. composite riser circulating fluidized bed 2. gas distributor 3. gas inlet pipe 4. pulverized coal feeding port 5. first stage gas-solid separator 6. fluidized bed return feeder 7. second stage gas-solid separator 8. entrained flow bed 9. coal gas outlet 10. turbulent fluidized bed 11. riser reactor 12. return feeder 13. high temperature gasification gas return pipe 14. first stage return pipe 15. calcination fluidized bed 16. calcination gasification agent feeding port 17. slag discharge port 18. entrained flow bed gasification agent inlet

[0014] The process features of the present application will be described in detail below in combination with the drawings and examples. 5. DETAILED DESCRIPTION

[0015] In Example 1, 0-3mm pulverized coal fed from the pulverized coal feeding port (4) is rapidly mixed with gasification coal gas and circulating ash at the lower part of the riser reactor (11) of the composite riser circulating fluidized bed (1), and the upwardly rising pulverized coal is subjected to rapid pyrolysis and gas phase tar cracking reactions in stages, and the gas is separated from the semi-coke in the composite riser at the top, and is discharged as product gas from the coal gas outlet (9); the high temperature large and medium particle semi-coke separated by the first stage gas-solid separator (5) is returned to the step turbulent bed (10) at the bottom of the composite riser through the fluidized bed return feeder (6) and the first stage return pipe (14), and is subjected to gasification reaction with oxygen and steam fed through the gas inlet pipe (3) at 1000-1100°C on the gas distributor (2), and the generated high temperature gasification coal gas flows upward together with part of the ash to form a material circulation; the high temperature fine semi-coke and ash separated by the second stage gas-solid separator (7) is fed to the entrained flow bed (8) through the return feeder (12), and the entrained flow bed (8) is in communication with the lower part of the riser reactor (11) and the fluidized bed return feeder (6), and the high temperature fine semi-coke and ash is subjected to melting gasification reaction with the oxygen and steam mixture fed through the entrained flow bed gasification agent inlet (18) at 1300-1600°C, and the liquid slag falls vertically into the fluidized bed return feeder (6) to be rapidly cooled and solidified, the return air of the fluidized bed return feeder is a mixture of steam and oxygen, and the generated high temperature gasification gas flows obliquely downward from the lower part of the entrained flow bed (8) through the high temperature gasification gas return pipe (13) into the lower part of the riser reactor (11), thereby providing heat and a hydrogen atmosphere for the high temperature rapid pyrolysis of the pulverized coal; the discharged ash in the step turbulent bed (10) is subjected to calcination and separation by oxygen fed through the calcination gasification agent feeding port in the calcination fluidized bed (15), and the gasification ash without semi-coke is discharged through the slag discharge port (17). In this way, the problem of up and down flow in the fluidized bed gasification is solved, and high methane content fuel gas without tar is obtained, thereby ensuring long period safe and stable operation of the gasification device. The industrial demonstration application results of 100 tons / day Shenmu pulverized coal composite riser staged pyrolysis oxygen gasification are as follows: carbon conversion rate 99.5%, methane content in the fuel gas 8.5%, heat value 2850 Kcal / Nm 3 , no tar, and the discharged gasification slag residual carbon content 1.2%, and no slag flow circulation and solidification blockage during long period operation of the gasification device.

[0016] In Example 2, the 0-3mm pulverized coal added from the pulverized coal adding port (4) is rapidly mixed with the gasification coal gas and the circulating ash at the lower part of the riser reactor (11) of the composite riser circulating fluidized bed (1), and the fast pyrolysis and the gas phase tar cracking step-by-step reaction occur while being lifted upward, and the gas is separated from the coal gas at the top of the composite riser, and the gas is sent out as product gas from the coal gas outlet (9); the high-temperature large and medium particle semicoke separated by the first stage gas-solid separator (5) is sent back to the step turbulent bed (10) at the bottom of the composite riser through the fluidized bed return feeder (6) and the first stage return pipe (14), and the gasification reaction occurs at 1000-1100℃ on the gas distributor (2) with the air and the steam added through the gas inlet pipe (3), the generated high-temperature gasification coal gas flows upward together with part of the ash to form the material circulation; the high-temperature fine semicoke and the ash separated by the second stage gas-solid separator (7) are sent to the entrained flow bed (8) in communication with the lower part of the riser reactor (11) and the fluidized bed return feeder (6) through the return feeder (12), and the melting gasification reaction occurs at 1200-1400℃ with the air and the steam mixture sent from the entrained flow bed gasification agent inlet (18), the liquid slag falls vertically into the fluidized bed return feeder (6) to be rapidly cooled and solidified, the return air of the fluidized bed return feeder is steam, and the generated high-temperature gasification gas flows into the lower part of the riser reactor (11) from the high-temperature gasification gas return pipe (13) at the lower part of the entrained flow bed (8) to provide heat and hydrogen atmosphere for the high-temperature fast pyrolysis of the pulverized coal; the discharged ash in the step turbulent bed (10) is calcined and sorted in the calcination fluidized bed (15) by the air sent from the calcination gasification agent feeding port (16), and the ash without semicoke is discharged through the ash discharge port (17). In this way, the problem of up and down of the fluidized bed gasification is solved, the fuel gas with high methane content and without tar is obtained, and the long-period safe and stable operation of the gasification device is ensured. The industrial demonstration application results of 100 tons / day Shenmu pulverized coal composite riser step pyrolysis air gasification are as follows: the carbon conversion rate is 99%, the methane content in the fuel gas is 4.2%, the heat value is 1400 Kcal / Nm 3 , the tar is not contained, the residual carbon content of the discharged gasification ash is 1.5%, and the long-period operation of the gasification device is not blocked by the molten slag and solidified.

[0017] In Example 3, the oxygen in Example 1 is replaced by oxygen-enriched air, the return air is replaced by steam, and the others are the same.

[0018] The process for preparing gas by pulverized coal composite lifting pipe staged pyrolysis and gasification provided by the present application realizes the staged pyrolysis and gasification of pulverized coal at different positions and under different conditions in the same equipment and the calcination of residual slag according to the pyrolysis and gasification reaction characteristics of coal and its chemical group components, and has low oxygen consumption, high gasification efficiency and low residual carbon content in ash; the synthesis gas is rich in methane, can adapt to the feeding requirements of the fluidized bed, achieve the gasification effect of the gas flow bed, eliminate tar in the gasification process, not produce phenol water, solve the difficult problem of vomiting and diarrhea in the fluidized bed gasification process; has large gasification intensity, small equipment volume, low steel consumption and greatly reduced fixed investment; has low feeding particle size requirement and does not need much crushing energy consumption; has simple operation, convenient start and stop, good continuity and strong coal adaptability; realizes the internal partial desulfurization in the reactor, simplifies the purification process; the high-temperature gas and liquid ash generated in the gas flow bed simultaneously supply heat for the circulating fluidized bed, the liquid ash is converted into solid ash and discharged, the phenomena of poor flow and solidification blockage of molten slag are eliminated, the ash discharge process is simple and the operation is stable.

Claims

1. A staged pyrolysis gasification process for producing fuel gas using pulverized coal composite riser pipes, characterized by: Pulverized coal (0-3mm) is fed into the lower part of the riser reactor of the composite riser circulating fluidized bed via a conveyor. It is rapidly mixed with the upward-rising high-temperature gasified coal gas and circulating ash. Simultaneously, rapid hydrogen pyrolysis and gas-phase tar cracking occur in stages during the upward movement. At the top of the composite riser, gas-solid separation is performed, with the gas being sent out as product gas. The large and medium-sized semi-coke particles and ash separated in the first stage are returned to the stepped turbulent bed at the bottom of the composite riser via a fluidized bed return feeder, where they react with oxidants and steam at 800-1100℃. In the gasification and calcination reaction, the generated high-temperature gasified coal gas and some ash slag flow upward to form a circulation, while some calcined slag is discharged externally. The high-temperature fine semi-coke separated in the second stage is sent to the fluidized bed connected to the lower part of the riser reactor and the fluidized bed return feeder through the return feeder. It undergoes a melting and gasification reaction at 1200-1600℃. The liquid slag falls vertically into the fluidized bed return feeder for rapid cooling and granulation. The generated high-temperature gasified gas flows obliquely downward from the middle and lower part of the fluidized bed into the lower part of the riser reactor, providing heat and hydrogen atmosphere for the high-temperature hydrogen-induced rapid pyrolysis of pulverized coal.

2. The pulverized coal composite riser staged pyrolysis gasification process for producing fuel gas according to claim 1, characterized in that... The gasification temperature of large and medium-sized semi-coke and ash in the stepped turbulent bed is 800-950℃, and the calcination temperature of the discharged ash is 900-1100℃.

3. The pulverized coal composite riser staged pyrolysis gasification process for producing fuel gas according to claim 1, characterized in that... The fluidized bed return feeder operates in a turbulent state, and the return air is water vapor, oxidant, or a mixture of the two. The oxidant is air, oxygen, or oxygen-enriched air.

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