A segmented low-rank coal pyrolysis method and device

Abstract

The present invention discloses a segmented low-rank coal pyrolysis method and device, the pyrolysis method comprising: spraying the mixed coal gas mixed with tar, steam and dust at the coal gas outlet of the dry distillation section to achieve dust removal and primary cooling, and then performing secondary cooling to separate tar and low-temperature coal gas; using a part of the low-temperature coal gas as a cooling medium to recover the sensible heat of semi-coke in the cooling section of the pyrolysis furnace; the coal gas discharged from the coal gas outlet of the cooling section is sent back to the dry distillation section of the pyrolysis furnace after dust removal and heating, and is used to successively dry and dry distill the raw coal. A vertical pipe pretreatment device is provided at the coal gas outlet of the dry distillation section of the pyrolysis furnace, a spray water nozzle is provided inside the vertical pipe pretreatment device, a water seal tank is provided at the bottom, and a screw conveyor is provided at the bottom of the water seal tank to discharge the dust deposited by the spraying. The present invention has higher heat utilization efficiency, can improve the quality of semi-coke, the output and quality of pyrolysis coal gas, and the pyrolysis device operates stably and reliably.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-rank coal pyrolysis, and relates to a segmented low-rank coal pyrolysis method and device. Background Art

[0002] After pyrolysis of low-rank coal, semi-coke can be obtained, also known as lignite or upgraded coal, which is widely used in fields such as calcium carbide, metallurgy, and blast furnace injection. Low-rank coal has a high volatile matter content and can produce a large amount of tar and coal gas as by-products. The low-rank coal pyrolysis process using gas as the heating medium can be divided into direct heat exchange and indirect heat exchange according to the form of heat exchange. Direct heat exchange has the characteristics of fast heat transfer speed and high heat exchange efficiency, and is more widely used. This pyrolysis process requires a large amount of fuel to heat the gas to increase its temperature, and then pass it into the pyrolysis device to exchange heat with the low-rank coal.

[0003] Low-rank coal pyrolysis devices are divided into moving beds, rotary furnaces, belt furnaces, etc. according to the furnace type. Among them, the internal heating moving bed, which uses high-temperature gas as the heat carrier and direct gas-solid contact, has the advantages of simple structure, no power components, and low operating costs, and is the most widely used in industry. The traditional moving bed directly introduces air and gas into the furnace, and uses the high-temperature flue gas generated after combustion to heat the material. The material undergoes drying and pyrolysis in the furnace, and the semi-coke is discharged from the furnace after being sprayed with water or cooled by inert gas at the bottom of the furnace. Due to the uneven combustion reaction in the furnace, the quality of the semi-coke is unstable, and the tar is easy to crack, resulting in a low tar yield. It is currently facing a technical upgrade.

[0004] The new moving bed adopts the drying, distillation or cooling segmented form: in the drying section, the raw material exchanges heat with the gas to remove moisture and preheat; in the distillation section, high-temperature coal gas is used as a heat carrier for gas-solid heat exchange to improve the quality of coal gas products; in the cooling section, the residual gas from the drying section is introduced to recover the semi-coke waste heat, and the gas after heat exchange returns to the drying section for preheating and drying of the raw material, realizing heat recovery. The segmented moving bed can effectively improve the heat utilization efficiency, but there are still the following problems:

[0005] (1) Low-rank coal pyrolysis equipment is generally in continuous production. The solid (coal or semi-coke) in the furnace flows downward continuously. The gas composition in direct contact with the solid should be as consistent as possible. Different gas atmospheres are used for distillation and cooling, which is likely to cause gas cross-talk and affect the coal gas quality.

[0006] (2) The high-temperature coal gas introduced into the dry distillation section consumes a lot of heat, while the semi-coke in the cooling section has a lot of waste heat that can be used. After the waste heat recovered from the semi-coke is used to dry and preheat the raw coal, the exhaust temperature is too high, and a large amount of cooling is required to reduce its temperature to the process temperature required by the cooling section. Therefore, the sensible heat of the semi-coke has not been effectively utilized, and there is still room for improvement in heat utilization efficiency. Summary of the invention

[0007] Purpose of the invention: The first purpose of the present invention is to provide a segmented low-rank coal pyrolysis method with higher heat utilization efficiency and capable of ensuring coal gas quality; the second purpose of the present invention is to provide a pyrolysis device that can realize the segmented low-rank coal pyrolysis method and can operate continuously for a long period of time.

[0008] Technical solution: A segmented low-rank coal pyrolysis method of the present invention comprises: spraying the mixed coal gas containing tar, steam and dust at the coal gas outlet of the distillation section to achieve dust removal and primary cooling, and then performing secondary cooling to separate the tar and low-temperature coal gas; using a part of the low-temperature coal gas as a cooling medium to recover the sensible heat of semi-coke in the cooling section of the pyrolysis furnace; and sending the coal gas discharged from the coal gas outlet of the cooling section back to the distillation section of the pyrolysis furnace after dust removal and heating, so as to successively dry and distill the raw coal.

[0009] Furthermore, another part of the low-temperature coal gas is used as fuel to heat the coal gas discharged from the coal gas outlet of the cooling section, and the remaining part of the low-temperature coal gas is used as the coal gas product.

[0010] Furthermore, the coal gas discharged from the coal gas outlet of the cooling section is heated to above 850°C.

[0011] Furthermore, in the upper part of the dry distillation section of the pyrolysis furnace, the raw coal is heated to above 100°C to remove all moisture.

[0012] Furthermore, the low temperature coal gas cools the semi-coke to below 80°C.

[0013] The present invention provides a pyrolysis device for realizing the segmented low-rank coal pyrolysis method, comprising a pyrolysis furnace with a dry distillation section and a cooling section, wherein a vertical tube type pretreatment device is provided at the coal gas outlet of the dry distillation section, a spray water nozzle is provided inside the vertical tube type pretreatment device, a water seal tank is provided at the bottom, a screw conveyor is provided at the bottom of the water seal tank for discharging the dust deposited by the spraying, and a water outlet pipe of the water seal tank is connected to an oil-water separation tank of a tar recovery system; the coal gas outlet after pretreatment at the top of the vertical tube type pretreatment device is connected to a coal gas cooling device, and ... The gas cooling device is used to separate tar and low-temperature coal gas. The tar is stored in the tar storage tank. A part of the low-temperature coal gas is led to the cooling section of the pyrolysis furnace through the gas fan as a cooling medium, and the remaining part is stored in the gas storage cabinet. A purified gas fan is connected between the gas cooling device and the gas storage cabinet; the gas outlet of the cooling section is sequentially connected to a dust collector, a circulating gas fan and a gas heating device. The coal gas discharged from the gas outlet of the cooling section is heated by the gas heating device and then sent to the distillation section of the pyrolysis furnace for drying and distilling the raw coal in turn.

[0014] Furthermore, the gas heating equipment adopts a thermal storage gas heating furnace or a high-temperature gas heat exchanger. When a thermal storage gas heating furnace is used, the thermal storage gas heating furnace is connected to a gas storage cabinet through a combustion gas fan, and an air fan is also connected to the thermal storage gas heating furnace.

[0015] Furthermore, a number of porous cloth gas folds are arranged at intervals in the middle of the distillation section, and the high-temperature coal gas enters the furnace through the porous cloth gas folds to achieve uniform gas distribution and ensure uniform heat exchange between the gas and solid phases; a number of finned material guide folds are arranged at the lower part of the distillation section to increase the disturbance of the semi-coke in the furnace, strengthen the heat conduction process between the particles, and completely precipitate the volatile matter in the pores of the material.

[0016] Furthermore, the distance between the gas outlet of the cooling section and the gas outlet of the carbonization section is more than 15 m.

[0017] Furthermore, a conveyor belt is provided on the top of the pyrolysis furnace for conveying raw coal into the furnace; and a scraper is provided at the bottom of the pyrolysis furnace for discharging semi-coke products out of the furnace.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) The low-rank coal pyrolysis process generally includes three stages: drying, distillation and cooling. Drying and distillation require heat consumption, while cooling requires heat release. The present invention combines the drying and distillation processes into one heat exchange process, uses circulating high-temperature coal gas as a heat carrier, and efficiently couples the two heat exchange processes, which can not only reduce the overall energy consumption of the pyrolysis device, but also increase the output of pyrolysis coal gas. Specifically:

[0020] Low-temperature coal gas is used as the cooling medium to recover the sensible heat of semi-coke to achieve dry quenching. At the same time, the obtained medium-temperature coal gas is heated again for the pyrolysis process, which can save overall heat consumption. Compared with other gas dry quenching processes, the process flow is simpler and the heat utilization efficiency is higher (the sensible heat of semi-coke is directly used in the distillation stage, reducing about 40% of the heat required for heating the high-temperature gas medium); in addition, because circulating high-temperature coal gas is used as the heat carrier, the atmosphere of the distillation and cooling gases is consistent, which is beneficial to improving the quality of the coal gas; low-temperature gas directly cools the semi-coke, completely avoiding contact with water, and the semi-coke quality is higher.

[0021] Therefore, the present invention not only achieves higher heat utilization efficiency and reduces the energy consumption of unit semi-coke product by about 10%, but also improves the quality of semi-coke and the output and quality of pyrolysis coal gas.

[0022] (2) The coal gas separated from the pyrolysis device contains tar gas, steam, dust, etc. The dust is easily deposited or adhered to the pipe wall, causing blockage of the pipeline and equipment, and the water condensed from the gas is difficult to handle, which will restrict the long-term operation of the segmented low-rank coal pyrolysis device. To this end, the present invention sets a vertical pipe pretreatment device at the coal gas outlet of the dry distillation section. The coal gas is directly led out of the furnace after being cooled and dusted by water spraying. The hot water, tar and dust after spraying flow into the water seal tank. The water seal tank is isolated from the coal gas and can be cleaned online, ensuring that the pyrolysis device can operate for a long period of time.

[0023] The present invention pre-treats dusty and oily coal gas by arranging a tubular pre-treatment device, thereby avoiding the blockage of pipelines and equipment, facilitating online cleaning, and having stable operation and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a process flow chart of a segmented low-rank coal pyrolysis device provided by an embodiment of the present invention;

[0025] Figure 2 is a schematic structural diagram of a pyrolysis furnace in an embodiment of the present invention;

[0026] Figure 3 2 is a schematic diagram of the structure of a porous cloth air folding plate according to an embodiment of the present invention;

[0027] Figure 4 2 is a schematic structural diagram of a finned material guide folding plate according to an embodiment of the present invention;

[0028] Figure 5 It is a structural schematic diagram of a vertical tube pretreatment device in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] Attached Figures 1 to 5 The reference numerals in the figures are as follows:

[0031] 1. Conveyor belt; 2. Pyrolysis furnace dry distillation section; 3. Pyrolysis furnace cooling section; 4. Gas fan; 5. Scraper; 6. Dust collector; 7. Circulating gas fan; 8. Regenerative gas heating furnace; 9. Air fan; 10. Combustion gas fan; 11. Desulfurization tower; 12. Gas storage cabinet; 13. Purification gas fan; 14. Tar storage tank; 15. Gas cooling device; 16. Vertical pipe pretreatment device; 17. Dry distillation section gas outlet; 18. Porous cloth gas folding plate; 19. Finned guide folding plate; 20. Pre-treated gas outlet; 21. Spray water nozzle; 22. Screw conveyor.

[0032] Example 1

[0033] like Figure 1 and Figure 2 As shown, Example 1 provides a segmented low-rank coal pyrolysis device, including a pyrolysis furnace, a dust collector 6, a regenerative coal gas heating furnace 8, a coal gas cooling device 15 and a vertical pipe pretreatment device 16, wherein the pyrolysis furnace has a pyrolysis furnace retorting section 2 and a pyrolysis furnace cooling section 3, and a conveyor belt 1 is provided at the top of the pyrolysis furnace retorting section 2 for conveying raw coal into the furnace. A scraper 5 is provided at the bottom of the pyrolysis furnace cooling section 3 for discharging semi-coke products out of the furnace.

[0034] The vertical pipe pretreatment device 16 is arranged at the gas outlet 17 of the dry distillation section. Figure 5 The vertical tube pretreatment device 16 is provided with a plurality of spray water nozzles 21, a water seal tank is provided at the bottom, a screw conveyor 22 is provided at the bottom of the water seal tank, and is used to discharge the dust deposited by the spraying. The water seal tank outlet pipe is connected to the oil-water separation tank of the tar recovery system. The vertical tube pretreatment device 16 can realize gas-liquid separation and online cleaning, and ensure the long-term operation of the pyrolysis device.

[0035] The gas cooling device 15 is connected to the pretreated gas outlet 20 at the top of the vertical pipe pretreatment device 16. The gas cooling device 15 is a prior art and is used to separate tar and low-temperature gas, wherein the tar is stored in the tar storage tank 14, and a part of the low-temperature gas is led to the pyrolysis furnace cooling section 3 as a cooling medium through the gas blower 4, and the remaining part is stored in the gas storage cabinet 12. A purified gas blower 13 is connected between the gas cooling device 15 and the gas storage cabinet 12.

[0036] The dust collector 6 and the regenerative gas heating furnace 8 are sequentially connected to the gas outlet of the cooling section, and a circulating gas blower 7 is arranged between the dust collector 6 and the regenerative gas heating furnace 8. The regenerative gas heating furnace 8 is connected to the gas storage cabinet 12 through the combustion gas blower 10, and the regenerative gas heating furnace 8 is also connected to the air blower 9. The combustion gas blower 10 and the air blower 9 respectively introduce the gas and air required for combustion into the regenerative gas heating furnace 8, and the combustion tail gas discharged from the regenerative gas heating furnace 8 is connected to the desulfurization tower 11 and discharged after desulfurization. The gas discharged from the gas outlet of the cooling section is heated by the regenerative gas heating furnace 8 and then sent to the pyrolysis furnace dry distillation section 2, which is used to dry and dry distill the raw coal in turn.

[0037] A plurality of porous cloth air folding plates 18 are arranged in the middle of the dry distillation section. The structure of the porous cloth air folding plates 18 is as follows: Figure 3 As shown, the end face is a pentagon, and the gas can enter the furnace through the bottom and side holes. The total area of ​​the side holes is smaller than the bottom. Under certain pressure conditions, the lateral flow rate of the gas is higher than the longitudinal flow rate, and the gas can simultaneously achieve vertical and longitudinal contact with the material in the furnace, which can enhance heat exchange. The high-temperature coal gas enters the middle of the dry distillation section through the porous cloth gas folding plate 18 to achieve uniform gas distribution and ensure uniform heat exchange between the gas and solid phases.

[0038] A plurality of finned guide folding plates 19 are provided at the lower part of the dry distillation section. The structure of the finned guide folding plates 19 is as follows: Figure 4 The finned material guide folding plate 19 adds longitudinal fins on the side to disturb the longitudinal flow of semi-coke, change the pores and contact surfaces between particles, strengthen the heat conduction process between particles, make the semi-coke particle dry distillation process more uniform, and make the volatile matter in the material pores completely precipitate, so as to improve the product quality.

[0039] The pipeline interfaces of the pyrolysis furnace from bottom to top are respectively the cooling section gas inlet, the cooling section gas outlet, the distillation section gas inlet and the distillation section gas outlet. The cooling section gas outlet is more than 15m away from the distillation section gas outlet 17. This can prevent the gas from the cooling section from entering the distillation section and being exported through the distillation section gas outlet 17, which is the common gas cross-talk phenomenon in other devices. The upper and lower fans of the segmented pyrolysis device are not easy to interfere with each other, and the production operation flexibility is large.

[0040] In some embodiments, the above-mentioned regenerative gas heating furnace 8 can be replaced by a high-temperature gas heat exchanger, which can also achieve the effect of gas heating.

[0041] Example 2

[0042] Taking long flame coal pyrolysis as an example, a segmented low-rank coal pyrolysis method provided in Example 2 is exemplified below. This method adopts a segmented low-rank coal pyrolysis device described in Example 1.

[0043] The raw coal enters the furnace directly through the conveyor belt 1, and directly contacts the rising pyrolysis gas in the furnace at the upper part of the pyrolysis furnace retorting section 2. After the temperature of the raw coal rises to above 100°C and the moisture is completely removed, the solid material continues to descend in the furnace to the middle of the pyrolysis furnace retorting section 2, and directly contacts the high-temperature coal gas entering the furnace to undergo a pyrolysis reaction. The high-temperature coal gas enters the furnace through a number of porous cloth gas deflectors 18, achieving uniform gas distribution and ensuring uniform heat exchange between the gas and solid phases.

[0044] In the middle of the pyrolysis furnace retorting section 2, the material temperature rises to 600-700°C and a pyrolysis reaction occurs, and the volatile matter is precipitated in the form of gas. Under the action of the induced draft fan, the gas flows upward through the upper part of the pyrolysis furnace retorting section 2 to dry the raw coal, and then flows into the vertical tube pretreatment device 16. After spray pretreatment, the gas is discharged. The gas outlet temperature is about 80°C, and it continues to be condensed to 40°C through the gas cooling device 15 to recover the tar in the gas. A part of the obtained low-temperature coal gas is sent to the pyrolysis furnace cooling section 3 through the gas fan 4 as a cooling medium, another part is used as fuel for the heat storage gas heating furnace 8, and the remaining part is used as a coal gas product.

[0045] The semi-coke that has completed the pyrolysis reaction continues to descend to the lower part of the pyrolysis furnace distillation section 2, where a finned material guide folding plate 19 is provided to increase the disturbance of the semi-coke in the furnace, strengthen the heat conduction process between the particles, and completely precipitate the volatile matter in the pores of the material. Then the semi-coke enters the pyrolysis furnace cooling section 3 through the material discharge channel, exchanges heat with the low-temperature coal gas (about 40°C) from the coal gas blower 4, and the sensible heat of the semi-coke is recovered by the coal gas. The coal gas discharged from the pyrolysis furnace cooling section 3 has a temperature of about 400°C and a low water content. After cyclone dust removal, it enters the regenerative coal gas heating furnace 8 to continue to heat up to above 850°C, and then enters the pyrolysis furnace distillation section 2 for recycling.

[0046] After cooling, the temperature of the semi-coke drops below 80°C. After being replaced with a small amount of nitrogen, it can be directly discharged from the furnace. The moisture content and volatility of the semi-coke are both less than 3%, which has a high quality. The regenerative gas heating furnace 8 can heat the 400°C gas from the cooling section 3 of the pyrolysis furnace to 850°C by burning a small amount of gas. The exhaust flue gas can meet the emission standards after desulfurization.

[0047] In summary, the present invention uses the coal gas precipitated from low-rank coal raw materials as a circulating heat carrier, which can maximize the recovery and utilization of the waste heat in the cooling section. Compared with the traditional pyrolysis scheme, it can increase the coal gas output and quality, improve the quality of semi-coke, improve the overall heat utilization efficiency, reduce the energy consumption per unit of lignite product, and at the same time, the system operation is more stable and reliable.

Claims

1. A segmented low-rank coal pyrolysis method, characterized in that: include: The mixed coal gas containing tar, steam and dust at the coal gas outlet of the distillation section is sprayed to achieve dust removal and primary cooling, and then secondary cooling is performed to separate the tar and low-temperature coal gas; a part of the low-temperature coal gas is used as a cooling medium to recover the sensible heat of semi-coke in the cooling section of the pyrolysis furnace; the coal gas discharged from the coal gas outlet of the cooling section is sent back to the distillation section of the pyrolysis furnace after dust removal and heating, and is used to successively dry and distill the raw coal.

2. The segmented low-rank coal pyrolysis method according to claim 1, characterized in that: Another part of the low-temperature coal gas is used as fuel to heat the coal gas discharged from the coal gas outlet of the cooling section, and the remaining part of the low-temperature coal gas is used as coal gas product.

3. The segmented low-rank coal pyrolysis method according to claim 1, characterized in that: The coal gas discharged from the coal gas outlet of the cooling section is heated to above 850°C.

4. The segmented low-rank coal pyrolysis method according to claim 1, characterized in that: In the upper part of the pyrolysis furnace retorting section, the raw coal is heated to above 100°C to remove all moisture.

5. The segmented low-rank coal pyrolysis method according to claim 1, characterized in that: The low-temperature coal gas cools the semi-coke to below 80°C.

6. A pyrolysis device for implementing the segmented low-rank coal pyrolysis method according to claim 1, characterized in that: The utility model comprises a pyrolysis furnace with a dry distillation section and a cooling section. A vertical tube type pretreatment device is arranged at a gas outlet of the dry distillation section. A spray water nozzle is arranged inside the vertical tube type pretreatment device. A water seal tank is arranged at the bottom. A screw conveyor is arranged at the bottom of the water seal tank for discharging dust deposited by the spraying. The water outlet pipe of the water seal tank is connected to an oil-water separation tank of a tar recovery system. The pretreated gas outlet at the top of the vertical tube type pretreatment device is connected to a gas cooling device. The gas cooling device is used to separate tar and low-temperature gas. The tar is stored in the tar storage tank. A part of the low-temperature gas is led to the cooling section of the pyrolysis furnace as a cooling medium through a gas blower, and the remaining part is stored in a gas storage cabinet. A purified gas blower is connected between the gas cooling device and the gas storage cabinet. A dust collector, a circulating gas blower and a gas heating device are sequentially connected to the gas outlet of the cooling section. The gas discharged from the gas outlet of the cooling section is heated by the gas heating device and then sent to the dry distillation section of the pyrolysis furnace for drying and dry distilling the raw coal in sequence.

7. The pyrolysis device according to claim 6, characterized in that: The gas heating equipment adopts a regenerative gas heating furnace or a high-temperature gas heat exchanger. When a regenerative gas heating furnace is adopted, the regenerative gas heating furnace is connected to a gas storage cabinet through a combustion gas blower, and an air blower is also connected to the regenerative gas heating furnace.

8. The pyrolysis device according to claim 6, characterized in that: Several porous cloth gas folding plates are arranged at intervals in the middle of the distillation section. High-temperature coal gas enters the furnace through the porous cloth gas folding plates to achieve uniform gas distribution and ensure uniform heat exchange between gas and solid phases. Several finned material guide folding plates are arranged at the lower part of the distillation section to increase the disturbance of the semi-coke in the furnace, strengthen the heat conduction process between the particles, and completely precipitate the volatile matter in the pores of the material.

9. The pyrolysis device according to claim 6, characterized in that: The distance between the gas outlet of the cooling section and the gas outlet of the distillation section is more than 15m.

10. The pyrolysis device according to claim 6, characterized in that: A conveyor belt is provided on the top of the pyrolysis furnace to transport raw coal into the furnace; a scraper is provided at the bottom of the pyrolysis furnace to discharge semi-coke products out of the furnace.

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