Low-rank coal pyrolysis system and control method thereof

Abstract

The invention provides a low-rank coal pyrolysis system and a control method thereof. The low-rank coal pyrolysis system comprises a through-flow type rotary dryer, a pyrolysis furnace, a dust remover, a waste heat recovery device, a venturi tower and a purification recovery device, and a dried coal outlet of the through-flow type rotary dryer is connected with a product inlet of the pyrolysis furnace; a raw gas outlet of the pyrolyzing furnace is connected with a gas inlet of the venturi tower through the dust remover and the waste heat recovery device in sequence, a flue gas outlet of the pyrolyzing furnace is communicated with a flue gas recovery port of the cross-flow rotary dryer to recover flue gas to dry raw material coal, and a tower bottom outlet of the venturi tower is connected with the ammonia water purification and recovery device to recover coal tar; and a coal gas outlet of the venturi tower is communicated with the coal gas purification and recovery device. According to the low-rank coal pyrolysis system provided by the invention, on one hand, waste heat of raw gas can be recycled, and on the other hand, raw materials can be conveniently dried, so that the pyrolysis efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of low-temperature coal pyrolysis technology, and in particular to a low-rank coal pyrolysis system and its control method. Background Technology

[0002] In my country's coal resources, low-rank coal reserves and production account for more than 55% of the national total. Low-rank coal is characterized by high volatile matter content and high reactivity. Scientific conversion based on its coal structure is of significant strategic importance for achieving the clean and efficient utilization of my country's coal resources. Employing low-rank coal low-temperature pyrolysis (dry distillation) technology can yield medium- and high-value-added oil and gas products, as well as high-carbon semi-coke products, enabling the graded utilization of low-rank coal and improving energy efficiency and economic value.

[0003] In traditional low-rank coal low-temperature pyrolysis processes, the high-temperature raw coal gas produced by pyrolysis is cooled down by a direct cooling tower, and the waste heat of the raw coal gas cannot be recovered.

[0004] Traditional low-temperature pyrolysis processes for low-rank coal generally involve directly feeding the coal into the pyrolysis furnace for production. However, due to the high moisture content of low-rank pulverized coal (25%–60%), the pyrolysis furnace suffers from high energy consumption and low production efficiency.

[0005] Therefore, it is necessary to optimize and improve the pyrolysis process for low-rank coal. Summary of the Invention

[0006] The main objective of this invention is to provide a low-rank coal pyrolysis system and its control method, which aims to recover the waste heat of raw coal gas on the one hand, and facilitate the drying of raw materials on the other.

[0007] To achieve the above objectives, the present invention provides a low-rank coal pyrolysis system, comprising a through-flow rotary dryer, a pyrolysis furnace, a dust collector, a waste heat recovery device, a venturi tower, and a purification and recovery device, wherein... The dry coal outlet of the through-flow rotary dryer is connected to the product inlet of the pyrolysis furnace. The raw coal gas outlet of the pyrolysis furnace is connected to the coal gas inlet of the Venturi tower via a dust collector and a waste heat recovery device. The flue gas outlet of the pyrolysis furnace is connected to the flue gas recovery port of the through-flow rotary dryer to recover flue gas for drying raw coal. The bottom outlet of the Venturi tower is connected to an ammonia water purification and recovery device to recover coal tar. The coal gas outlet of the Venturi tower is connected to the coal gas purification and recovery device.

[0008] Preferably, the pyrolysis furnace is an externally heated pyrolysis furnace.

[0009] Preferably, the heat source of the pyrolysis furnace is an external gas burner installed on both sides of it.

[0010] Preferably, the gas pipeline of the external gas burner is connected to the gas purification and recovery device.

[0011] Preferably, the flue gas outlet of the through-flow rotary dryer is connected to a flue gas purification device, and a temperature measuring device is installed on the pipeline between the flue gas outlet of the through-flow rotary dryer and the flue gas purification device.

[0012] Preferably, the ammonia water purification and recovery device is a tar ammonia water separation tank. A recovery port for recovering the upper layer of ammonia water inside the tar ammonia water separation tank is provided above the tar ammonia water separation tank. The recovery port is connected to the spray port of the Venturi tube tower through a recovery pipeline to spray ammonia water. An ammonia water circulation pump is installed on the recovery pipeline.

[0013] Preferably, the waste heat recovery device is a waste heat boiler; the dust collector is a cyclone dust collector.

[0014] Preferably, a temperature measuring device for measuring the temperature of raw coal gas is installed at the gas outlet of the waste heat boiler, and a flow control device is installed at the feed water inlet of the waste heat boiler. The flow control device and the temperature measuring device are electrically connected to control the temperature of the raw coal gas at the gas outlet above the tar dew point temperature.

[0015] This invention also proposes a control method for the above-mentioned low-rank coal pyrolysis system, comprising the following steps: Wet raw coal is continuously fed into a through-flow rotary dryer. After being heated and dried to a moisture content of less than 12%, the raw coal is sent into a pyrolysis furnace. The dried raw coal enters the pyrolysis furnace for continuous dry distillation. The raw coal gas produced by the pyrolysis furnace is discharged into the dust collector, and the solid furnace charge semi-coke after dry distillation is continuously discharged. The high-temperature raw coal gas discharged from the pyrolysis furnace enters the dust collector to remove dust particles larger than 10μm, and then is sent to the waste heat recovery device. After dust removal, the high-temperature raw coal gas enters the waste heat recovery device, exchanges heat with the heat recovery medium, and is then sent into the Venturi tube tower. The raw coal gas in the Venturi tube tower is cooled and washed with circulating ammonia water. The mixture of ammonia water, tar and dust is discharged from the bottom of the tower into the ammonia water purification and recovery device, and the coal gas enters the coal gas purification and recovery device. After the mixture in the ammonia water purification and recovery device settles, the upper layer of ammonia water is sent to a venturi tower for circulating cooling and washing of raw coal gas, while the lower layer of coal tar is recovered as a product.

[0016] Preferably, the outlet raw coal gas temperature of the waste heat recovery device is controlled by interlocking with the inlet flow rate of the heat exchange medium to keep the outlet raw coal gas temperature above the tar dew point temperature; the through-flow rotary dryer directly exchanges heat with the hot flue gas discharged from the pyrolysis furnace to recover and utilize the flue gas; the heat source of the pyrolysis furnace is supplied by the burner, and the heat is provided by burning the self-produced purified coal gas to provide heat for the dry distillation of the raw coal in the pyrolysis furnace.

[0017] The low-rank coal pyrolysis system proposed in this invention has the following beneficial effects: 1. By combining the dust collector, venturi tower and waste heat recovery device, the waste heat of the high-temperature raw coal gas generated by the pyrolysis of low-rank coal can be effectively recovered and utilized, solving the problem that the waste heat of raw coal gas cannot be recovered when the traditional process cools down the coal gas through a direct cooling tower. 2. A through-flow rotary dryer is used for continuous drying of low-rank raw coal, which effectively utilizes the waste heat of flue gas from the external heating pyrolysis furnace and solves the problems of high energy consumption and low production efficiency in traditional low-rank coal pyrolysis processes. 3. The through-flow rotary dryer operates independently of the pyrolysis furnace. The operating load of the through-flow rotary dryer can be flexibly adjusted according to the moisture content of the low-rank raw coal, thus solving the problem of moisture fluctuation in the coal fed into the furnace. 4. This low-rank coal pyrolysis system has the advantages of simple structure and stable and reliable operation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the low-rank coal pyrolysis system of the present invention; Figure 2 This is a schematic flowchart of the control method for the low-rank coal pyrolysis system of the present invention.

[0019] In the diagram, 1-through-flow rotary dryer, 2-pyrolysis furnace, 3-external gas burner, 4-dust collector, 5-waste heat boiler, 6-Venturi tube tower, 7-tar-ammonia-water separation tank, 8-ammonia-water circulation pump, 9-temperature measuring device, 10-flue gas purification device, 11-gas purification and recovery device.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] It should be noted that in the description of this invention, the terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] This invention proposes a low-rank coal pyrolysis system.

[0024] Reference Figure 1 In this preferred embodiment, a low-rank coal pyrolysis system includes a through-flow rotary dryer 1, a pyrolysis furnace 2, a dust collector 4, a waste heat recovery device, a venturi tower 6, and a purification and recovery device, wherein... The dry coal outlet of the through-flow rotary dryer 1 is connected to the product inlet of the pyrolysis furnace 2. The raw coal gas outlet of the pyrolysis furnace 2 is connected to the coal gas inlet of the venturi tower 6 via the dust collector 4 and the waste heat recovery device. The flue gas outlet of the pyrolysis furnace 2 is connected to the flue gas recovery port of the through-flow rotary dryer 1 to recover the flue gas for drying the raw coal. The bottom outlet of the venturi tower 6 is connected to the ammonia water purification and recovery device to recover coal tar. The coal gas outlet of the venturi tower 6 is connected to the coal gas purification and recovery device 11.

[0025] In this embodiment, the pyrolysis furnace 2 is an externally heated pyrolysis furnace. The waste heat recovery device is a waste heat boiler 5; the dust collector 4 is a cyclone dust collector. The heat source for the pyrolysis furnace 2 is an external gas burner 3 installed on both sides of it. The gas pipeline of the external gas burner 3 is connected to the gas purification and recovery device 11, that is, the gas used by the external gas burner 3 is self-produced gas, thereby reducing the overall production cost.

[0026] Furthermore, the flue gas outlet of the through-flow rotary dryer 1 is connected to a flue gas purification device 10, and a temperature measuring device is installed on the pipe between the flue gas outlet of the through-flow rotary dryer 1 and the flue gas purification device 10. The temperature of the flue gas after use at the flue gas outlet of the through-flow rotary dryer 1 is controlled above the dew point (105-110°C) before being sent into the flue gas purification device 10.

[0027] Specifically, in this embodiment, the ammonia water purification and recovery device is a tar ammonia water separation tank 7. A recovery port for recovering the upper layer of ammonia water inside the tar ammonia water separation tank 7 is provided above the tar ammonia water separation tank 7. The recovery port is connected to the spray port of the Venturi tube tower 6 through a recovery pipeline to spray ammonia water. An ammonia water circulation pump 8 is installed on the recovery pipeline.

[0028] Furthermore, a temperature measuring device 9 for measuring the temperature of raw coal gas is installed at the gas outlet of the waste heat boiler 5, and a flow control device is installed at the feed water inlet of the waste heat boiler 5. The flow control device and the temperature measuring device 9 are electrically connected to control the temperature of the raw coal gas at the gas outlet above the tar dew point temperature.

[0029] The working principle of this low-rank coal pyrolysis system is as follows.

[0030] 1. Low-rank raw coal with high moisture content (wet raw coal) is continuously fed into the through-flow rotary dryer 1, where it directly exchanges heat with the hot flue gas discharged from the heating system of the pyrolysis furnace 2 in a countercurrent manner. After the raw coal is heated and dried to a moisture content of less than 10%, it is fed into the pyrolysis furnace 2. 2. The dried raw coal enters pyrolysis furnace 2 for continuous dry distillation, and the raw coal gas produced by pyrolysis is discharged in a centralized manner; the solid furnace charge (semi-coke) after dry distillation is continuously discharged and recycled as semi-coke product.

[0031] 3. The heat source of the pyrolysis furnace 2 is supplied by two external burners symmetrically arranged on the left and right. The heat is provided by burning the purified coal gas produced by the furnace itself to provide heat for the dry distillation of the raw coal in the pyrolysis furnace 2. The heated flue gas (about 290°C) is discharged from the pyrolysis furnace 2 and enters the through-flow rotary dryer 1 for waste heat utilization to provide heat for drying the raw coal. The temperature of the flue gas after utilization is controlled above the dew point (105-110°C) and then sent to the flue gas purification device 10.

[0032] 4. The high-temperature raw coal gas discharged from the pyrolysis furnace 2 first enters the dust collector 4 to remove dust particles with a diameter >10μm, creating conditions for the recovery of waste heat from the high-temperature raw coal gas; then it is sent to the waste heat boiler 5 system.

[0033] 5. The high-temperature raw coal gas, after being scavenged by a cyclone separator, enters the waste heat boiler 5, exchanges heat with the heat recovery medium, and is then sent to the venturi tower 6. To prevent tar precipitation in the raw coal gas, the outlet temperature of the raw coal gas in the waste heat boiler 5 is interlocked with the inlet flow rate of the heat exchange medium, keeping the outlet temperature of the raw coal gas in the waste heat boiler 5 above the tar dew point temperature.

[0034] 6. The raw coal gas entering the Venturi tower 6 is cooled and washed with circulating ammonia water. The raw coal gas containing dust and tar is washed and cooled under the action of the Venturi effect. The mixture of ammonia water, tar and a small amount of dust is discharged from the bottom of the tower and the coal gas enters the subsequent coal gas purification and recovery device 11.

[0035] 7. The ammonia and tar mixture discharged from the bottom of the Venturi tube tower 6 is sent to the tar-ammonia separation tank 7. After separation by gravity sedimentation, the upper layer of ammonia is sent to the Venturi tube tower 6 through the ammonia circulation pump 8 to circulate and cool the raw coal gas, while the lower layer of coal tar is recovered as a product.

[0036] The low-rank coal pyrolysis system proposed in this invention has the following beneficial effects: 1. By combining the dust collector 4, the venturi tower 6 and the waste heat recovery device, the waste heat of the high-temperature raw coal gas generated by the pyrolysis of low-rank coal can be effectively recovered and utilized, solving the problem that the waste heat of raw coal gas cannot be recovered when the traditional process cools down the coal gas through a direct cooling tower. 2. A through-flow rotary dryer 1 is used for continuous drying of low-rank raw coal, which effectively utilizes the waste heat of flue gas from the external heating pyrolysis furnace 2, and solves the problems of high energy consumption and low production efficiency in traditional low-rank coal pyrolysis processes. 3. The through-flow rotary dryer 1 operates independently of the pyrolysis furnace 2. The operating load of the through-flow rotary dryer 1 can be flexibly adjusted according to the moisture content of the low-rank raw coal, thus solving the problem of moisture fluctuation in the coal fed into the furnace. 4. This low-rank coal pyrolysis system has the advantages of simple structure and stable and reliable operation.

[0037] This invention also proposes a control method for a low-rank coal pyrolysis system.

[0038] Reference Figure 2 In this preferred embodiment, a control method based on the above-mentioned low-rank coal pyrolysis system includes the following steps: Step S10: The wet raw coal is continuously fed into the through-flow rotary dryer 1. After the raw coal is heated and dried to a moisture content of less than 10%, it is fed into the pyrolysis furnace 2. In step S20, the dried raw coal enters the pyrolysis furnace 2 for continuous dry distillation. The raw coal gas generated by the pyrolysis in the pyrolysis furnace 2 is discharged into the dust collector 4, and the solid furnace charge semi-coke after dry distillation is continuously discharged. In step S30, the high-temperature raw coal gas extracted from the pyrolysis furnace 2 enters the dust collector 4 to remove dust particles larger than 10μm, and then is sent to the waste heat recovery device. In step S40, the high-temperature raw coal gas after dust removal enters the waste heat recovery device, exchanges heat with the heat recovery medium, and is then sent into the Venturi tower 6. In step S50, the raw coal gas in Venturi tower 6 is cooled and washed with circulating ammonia water. The mixture of ammonia water, tar and dust is discharged from the bottom of the tower into the ammonia water purification and recovery device, and the coal gas enters the coal gas purification and recovery device 11. In step S60, after the mixture in the ammonia water purification and recovery device settles, the upper layer of ammonia water is sent to the Venturi tube tower 6 for circulating cooling and washing of the raw coal gas, and the lower layer of coal tar is recovered as a product.

[0039] Specifically, in step S10, the through-flow rotary dryer 1 and the hot flue gas discharged from the pyrolysis furnace 2 undergo direct countercurrent heat exchange to recover and utilize the flue gas, thereby realizing the utilization of waste heat from the flue gas of the pyrolysis furnace 2 and reducing the overall production cost.

[0040] In step S20, the heat source of the pyrolysis furnace 2 is supplied through a burner, which provides heat for the dry distillation of raw coal in the pyrolysis furnace 2 by burning the self-produced purified coal gas, thereby facilitating the use of self-produced coal gas and reducing production costs.

[0041] In step S40, the outlet raw gas temperature of the waste heat recovery device is controlled above the tar dew point temperature by interlocking the outlet raw gas temperature with the inlet flow rate of the heat exchange medium.

[0042] The control method proposed in this invention combines a high-temperature cyclone dust collector 4, a venturi tower 6, and a waste heat boiler 5 to effectively recover and utilize the waste heat from the high-temperature raw coal gas generated during the pyrolysis of low-rank coal. This solves the problem of unrecoverable waste heat from raw coal gas in traditional processes that rely on direct cooling towers for temperature reduction. Furthermore, the continuous drying of low-rank raw coal using a through-flow rotary dryer 1 effectively utilizes the waste heat from the flue gas of the externally heated pyrolysis furnace 2, addressing the issues of high energy consumption and low production efficiency in traditional low-rank coal pyrolysis processes.

[0043] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A low-rank coal pyrolysis system, characterized in that, The device comprises a through-flow rotary dryer, a pyrolysis furnace, a dust remover, a waste heat recovery device, a venturi tower and a purification recovery device, wherein, the drying coal outlet of the through-flow rotary dryer is connected with the product inlet of the pyrolysis furnace, the raw coal gas outlet of the pyrolysis furnace is connected with the coal gas inlet of the venturi tower through the dust remover and the waste heat recovery device in sequence, the flue gas outlet of the pyrolysis furnace is communicated with the flue gas recovery port of the through-flow rotary dryer to recover flue gas to dry raw coal, the tower bottom outlet of the venturi tower is connected with the ammonia water purification recovery device to recover coal tar, and the coal gas outlet of the venturi tower is communicated with the coal gas purification recovery device.

2. The low-rank coal pyrolysis system of claim 1, wherein, The pyrolysis furnace is an external heating pyrolysis furnace.

3. The low-rank coal pyrolysis system of claim 2, wherein, The heat source of the pyrolysis furnace is an external coal gas burner installed on both sides of the pyrolysis furnace.

4. The low-rank coal pyrolysis system of claim 3, wherein, The coal gas pipeline of the external coal gas burner is communicated with the coal gas purification recovery device.

5. The low-rank coal pyrolysis system of claim 1, wherein, The flue gas purification device is connected with the flue gas discharge port of the through-flow rotary dryer, and a temperature measuring device is installed on the pipeline between the flue gas discharge port of the through-flow rotary dryer and the flue gas purification device.

6. The low-rank coal pyrolysis system of claim 1, wherein, The ammonia water purification recovery device is a tar-ammonia water separation tank, the upper part of the tar-ammonia water separation tank is provided with a recovery port for recovering the upper layer ammonia water in the tank, the recovery port is communicated with the spraying port of the venturi tower through a recovery pipeline to spray ammonia water, and an ammonia water circulating pump is installed on the recovery pipeline.

7. The low-rank coal pyrolysis system of any one of claims 1 to 6, wherein, The waste heat recovery device is a waste heat boiler, and the dust remover is a cyclone dust remover.

8. The low-rank coal pyrolysis system of claim 7, wherein, A temperature measuring device for measuring the temperature of raw coal gas is installed at the coal gas outlet of the waste heat boiler, a flow control device is installed at the water inlet of the waste heat boiler, and the flow control device and the temperature measuring device are electrically connected to control the temperature of raw coal gas at the coal gas outlet to be higher than the tar dew point temperature.

9. A control method for a low-rank coal pyrolysis system according to any one of claims 1 to 8, characterized by, The device comprises the following steps: wet raw coal is continuously fed into the through-flow rotary dryer, the raw coal is heated and dried to a water content of less than 10%, and then fed into the pyrolysis furnace; the dried raw coal is continuously dry distillation in the pyrolysis furnace, the raw coal gas generated by pyrolysis is discharged into the dust remover, and the solid coke after dry distillation is continuously discharged; the high-temperature raw coal gas discharged from the pyrolysis furnace is sent into the dust remover to remove dust with a particle size greater than 10 μm, and then sent into the waste heat recovery device; the dust-removed high-temperature raw coal gas is sent into the waste heat recovery device, and exchanged with heat recovery medium, and then sent into the venturi tower; the raw coal gas in the venturi tower is cooled and washed by circulating ammonia water, the mixture of ammonia water, tar and dust is discharged from the bottom into the ammonia water purification recovery device, and the coal gas enters the coal gas purification recovery device; after the mixture in the ammonia water purification recovery device is settled, the upper layer ammonia water is fed into the venturi tower for circulating cooling and washing of raw coal gas, and the lower layer coal tar is recovered as a product.

10. The method of claim 9, wherein the low-rank coal pyrolysis system is controlled by the controller to: The temperature of raw coal gas at the outlet of the waste heat recovery device is interlocked with the flow of heat exchange medium at the inlet to control the temperature of raw coal gas at the outlet of the waste heat boiler to be higher than the tar dew point temperature; the hot flue gas discharged from the through-flow rotary dryer and the pyrolysis furnace is directly countercurrently exchanged to recover and utilize the flue gas; the heat source of the pyrolysis furnace is supplied by the burner, the purified coal gas produced by the burner is used for heating, and the dry distillation of raw coal in the pyrolysis furnace is provided with heat.

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