Dust removal system and method for low-rank coal pyrolysis raw gas

Abstract

The invention belongs to the technical field of coal chemical industry, oil shale and biomass pyrolysis, and particularly relates to a low-rank coal pyrolysis raw gas dust removal system and method, the low-rank coal pyrolysis raw gas dust removal system is characterized by comprising a pyrolysis device, a filtering dust removal device, a high-temperature dust fluidization device and a high-temperature compressed gas supply device, a plurality of filtering bodies are arranged in each filtering bin, and the filtering bin is divided into a dust gas side and a purified gas side through the filtering bodies. In a filtering and dust removing device composed of a plurality of independent filtering bins, each filtering bin completes purification of pyrolysis raw gas in a state circulation mode. The invention has the advantages that the dust isolation layer with a certain thickness is arranged on the surface of the filter body in advance, and the filter bin is not subjected to back-blowing dust removal when being put into use, so that viscous substances in raw gas are prevented from being in direct contact with the surface of the filter body, the viscous substances are prevented from adhering and blocking the filter body, and the service life of the filter body is prolonged. The dust removal device can continuously, stably and efficiently operate.

Description

Technical Field

[0001] This invention belongs to the fields of coal chemical industry, oil shale and biomass pyrolysis technology, and particularly relates to a dust removal system and method for raw coal gas from low-rank coal pyrolysis. Background Technology

[0002] my country is rich in coal but lacks oil resources. While coal resources are relatively abundant, most are currently used directly for power generation. With my country's rapid economic growth, the demand for fuel oil is constantly increasing. The pyrolysis and upgrading process of pulverized coal (or oil shale) extracts high-value-added, hydrogen-rich coal tar before coal combustion or gasification. This is of great significance for the comprehensive utilization of coal resources, reducing nitrogen oxide and sulfide emissions in waste gas, increasing the added value of coal, and thus increasing the source of raw materials for fuel oil production. Although there are many pulverized coal pyrolysis processes, they all currently suffer from high dust content in the oil and gas produced. When the pyrolysis gas condenses, dust enters the oil and water, forming water-in-oil emulsions, making it difficult to separate oil, water, and solids (dust). Furthermore, the high-value-added coal tar produced by pyrolysis cannot be recycled, becoming sludge that easily causes blockages in equipment, pipelines, and valves, hindering long-term stable operation and restricting the development of pulverized coal pyrolysis coal tar extraction technology.

[0003] Currently, common dry dust removal technologies for high-temperature raw coal gas include granular bed dust collectors, cyclone separators, electrostatic precipitators, ceramic tube dust collectors, and bag filters. Among these, granular bed dust collectors and cyclone separators have relatively low dust removal efficiency and cannot meet the final requirements for raw coal gas dust removal and purification; they are only used as pre-dust collectors. Because the temperature of pyrolysis raw coal gas is 400~550℃ or higher, the dust removal efficiency of electrostatic precipitators decreases significantly at such high temperatures, also failing to meet requirements. Ceramic tube dust collectors and bag filters have high dust removal efficiency, but because pyrolysis raw coal gas contains easily precipitated sticky substances such as tar, these sticky substances easily clog the ceramic filter elements and filter bags, making regeneration and maintenance difficult. Even with high-pressure backflushing cleaning, it is difficult to remove the already adhered sticky substances.

[0004] Chinese utility model patent CN210699208U discloses a large-flow, anti-clogging composite pulse bag filter. A circulating pre-coating device, located at the bottom of the bag filter, includes a mixing chamber, a spray pipe, an electric valve, a venturi tube, and a pre-coating pipe. An external pre-coating powder supply system pre-feeds pre-coating powder to the bag filter via the circulating pre-coating device, coating the inner walls of the ash hopper, buffer chamber, middle chamber, and upper chamber, as well as the surfaces of the buffer plates and filter bag assemblies, with a layer of pre-coating powder. The pre-coating powder and compressed air used here are typically at room temperature. The tar and other viscous substances in the flue gas do not need to be retained as valuable products; therefore, there is no need to consider the reduced tar yield caused by excessive tar precipitation due to condensation during pre-coating filtration. However, for pyrolysis raw coal gas at temperatures of 400℃~550℃ or higher, tar is an important low-rank coal pyrolysis product. Therefore, while effectively removing dust, it is crucial to minimize tar precipitation in the raw coal gas. Conventional pre-spraying techniques, using pre-sprayed dust layers at room temperature and compressed air at room temperature, can lead to the precipitation of large amounts of high-value tar during filtration due to the cooling of the high-temperature raw coal gas. This not only severely impacts tar product yield but also renders the pre-spraying technology ineffective or with minimal results, ultimately causing the filter dust collector to fail. Therefore, maintaining the condensation and precipitation of tar from the raw coal gas during filtration is critical. Summary of the Invention

[0005] The purpose of this invention is to provide a dust removal system and method for low-rank coal pyrolysis raw gas, which overcomes the shortcomings of the prior art. By making full use of the high-temperature dust collected by the dust removal system itself and the purified pyrolysis gas resources, the system achieves continuous and stable operation of a high-efficiency separation system for dust and tar-containing gas in low-rank coal pyrolysis raw gas, making it easier to recover and utilize the high-value coal tar produced by pyrolysis and reducing the adhesion of tar to the filter medium.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One technical solution: A dust removal system for raw coal gas from low-rank coal pyrolysis, comprising a pyrolysis unit, a filtration and dust removal unit, a high-temperature dust fluidization unit, and a high-temperature compressed gas supply unit. The filtration and dust removal unit consists of multiple independent filter chambers, each containing multiple filter elements that divide the chamber into a dust-gas side and a clean-gas side. The dust-gas side is connected to the raw coal gas outlet of the pyrolysis unit, and a raw coal gas inlet valve is installed at the dust-gas side inlet. The clean-gas side is connected to the clean coal gas outlet, and a clean coal gas outlet valve is installed at the clean coal gas outlet. A dust hopper is located at the bottom of the filter chamber. The high-temperature dust fluidization unit is located in the dust hopper and includes a fluidized nozzle. The inlet of the fluidized nozzle is connected to the high-temperature compressed gas supply unit. The fluidized nozzle is a hollow cavity with multiple holes or slits on its surface, and the holes or slits on the surface of the fluidized nozzle are buried in the dust collected at the bottom of the dust hopper. The high-temperature compressed gas supply unit contains a gas compressor and a gas heating unit, which is a hot air heat exchanger.

[0008] Furthermore, the gas source of the high-temperature compressed gas supply device is purified pyrolysis gas or inert gas, wherein the inert gas is any one of nitrogen, steam, or CO2.

[0009] Furthermore, the hot air heat exchanger is installed inside the hot air supply duct of the externally heated rotary kiln, and the hot air heat exchanger is a plate heat exchanger or a tubular heat exchanger.

[0010] Furthermore, the clean gas outlet is connected to a gas cooling and purification device via a pipeline.

[0011] Furthermore, the outlet of the gas cooling and purification device is connected to the inlet of the high-temperature compressed gas supply device via a pyrolysis gas return pipe.

[0012] Technical Solution Two: A method for dust removal from raw pyrolysis gas of low-rank coal, wherein in a filtration and dust removal device composed of multiple independent filter chambers, each filter chamber completes the purification of the raw pyrolysis gas in a state-cycle manner, and the specific steps are as follows:

[0013] 1) Pre-coating: With the gas inlet valve of an independent filter chamber in the dust removal device closed, high-temperature compressed gas is used to fluidize the dust in the ash hopper at the bottom of the filter chamber, raising the dust. Under the action of the induced draft fan, the dust is adsorbed on the outer surface of the filter body of the filter chamber, forming a dust isolation layer of a certain thickness.

[0014] 2) Standby: Stop the fluidization treatment of dust in the ash hopper with high-temperature compressed gas and wait for it to be put into online use;

[0015] 3) Filtration: When the filter chamber to be put into use receives the commissioning instruction, the raw coal gas inlet valve of the filter chamber is opened. The raw coal gas enters the filter chamber from the inlet valve and passes through the dust isolation layer under the action of the induced draft fan. The dust in the raw coal gas is blocked outside the dust isolation layer. The raw coal gas after dust removal enters the clean gas side and is discharged.

[0016] 4) Dust removal: When the filter chamber resistance reaches the set value or the dust on the surface of the filter body needs to be removed according to the set cycle, close the raw coal gas inlet valve and the clean coal gas outlet valve, and backflush the high-temperature compressed gas from the clean gas side to the inside of the filter body.

[0017] 5) Settling: After a period of settling, open the clean gas outlet valve. The dust isolation layer attached to the surface of the filter body and the dust on the dust isolation layer fall into the ash hopper below. Repeat steps 1) to 5.

[0018] Furthermore, the high-temperature compressed gas supply device outputs compressed gas pressure of not less than 0.1 MPa and compressed gas temperature of not less than 450°C.

[0019] Furthermore, the tar content in the dust collected does not exceed 5%, and the particle size is 200 mesh.

[0020] Furthermore, the thickness of the dust isolation layer is not less than 1 mm.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1) The present invention pre-sets a dust isolation layer of a certain thickness on the surface of the filter body, and does not back-flushing clean it during the use of the filter chamber, thereby avoiding direct contact between the sticky substances in the raw coal gas and the surface of the filter body, thus preventing the sticky substances from sticking and clogging the filter body, and enabling the dust removal device to operate continuously, stably and efficiently.

[0023] 2) This invention uses clean pyrolysis gas as the backflushing cleaning medium and high-temperature dust screening gas. The gas entering the filter chamber has the same composition as the raw coal gas processed by the filter dust collector, which will not reduce the quality of the pyrolysis gas.

[0024] 3) This invention uses high-temperature compressed gas as the backflushing cleaning medium and high-temperature dust screening gas, which can ensure that the backflushing cleaning has sufficient power and the fluidization power of the dust in the ash hopper, resulting in more thorough cleaning, better filter regeneration effect, and better dust screening effect.

[0025] 4) This invention uses high-temperature compressed gas as the backflushing cleaning medium and high-temperature dust screening gas, which can ensure that the filter body and high-temperature dust have sufficient temperature, and avoid the large amount of tar in the raw coal gas from being released due to the temperature drop when it is put back into use, thereby reducing the risk of increasing the proportion of sticky substances in the raw coal gas and increasing the sticky substances to stick and clog the filter body.

[0026] 5) The present invention uses high-temperature dust collected in the ash hopper by a filtration and dust removal device, and obtains high-temperature dust for use as a dust isolation layer on the surface of the filter body through compressed coal gasification screening. This can avoid the problem of a large amount of tar precipitation in the raw coal gas caused by the temperature drop in the filter chamber and the low temperature of the dust isolation layer on the surface of the filter body due to the direct use of room temperature dust. Attached Figure Description

[0027] Figure 1 A schematic diagram of the system process flow in this embodiment of the invention, wherein the high-temperature compressed gas is an inert gas;

[0028] Figure 2 A process flow diagram of a system embodiment in which purified pyrolysis gas is used as a high-temperature compressed gas in this invention.

[0029] Figure 3 A schematic diagram of the compressed gas heating unit structure in a hot air duct according to an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of the filter chamber and high-temperature dust fluidization device in this embodiment of the invention;

[0031] Figure 5 A schematic diagram of the working cycle of the filter chamber in an embodiment of the present invention.

[0032] In the diagram: 1-Dust removal and filtration device, 2-High-temperature dust fluidization device, 3-High-temperature compressed gas supply device, 4-Pyrolysis device, 5-Gas cooling and purification device, 6-Pyrolysis gas return pipe, 11-Filter chamber, 12-Filter body, 13-Dust gas side, 14-Clean gas side, 15-Raw gas inlet valve, 16-Clean gas outlet valve, 17-Ash hopper, 21-High-temperature compressed gas inlet, 22-Fluidized nozzle, 31-Gas compressor, 32-Gas heating unit. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] The components of the embodiments of the invention described and shown in the accompanying drawings can typically be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0036] See Figure 1 This is a schematic diagram of an embodiment of a low-rank coal pyrolysis raw coal gas dust removal system according to the present invention. It includes a pyrolysis device 4, a filtration and dust removal device 1, a high-temperature dust fluidization device 2, and a high-temperature compressed gas supply device 3. The filtration and dust removal device 1 consists of multiple independent filter chambers 11. Each filter chamber 11 is equipped with multiple filter elements 12, which divide the filter chamber 11 into two parts: a dust gas side 13 and a clean gas side 14. The dust gas side is connected to the raw coal gas outlet of the pyrolysis device 4, and a raw coal gas inlet valve 15 is installed at the dust gas side inlet. The clean gas side 14 is connected to the clean coal gas outlet. A clean coal gas outlet valve 16 is installed at the gas outlet, and an ash hopper 17 is located at the bottom of the filter chamber 11. A high-temperature dust fluidization device 2 is installed in the ash hopper 17, including a fluidized bed nozzle 22. The high-temperature compressed gas inlet 21 of the fluidized bed nozzle 22 is connected to a high-temperature compressed gas supply device 3. The fluidized bed nozzle 22 is a hollow cavity with multiple holes or slits on its surface, and the holes or slits on the surface of the fluidized bed nozzle 22 are buried in the dust collection ash at the bottom of the ash hopper 17. The high-temperature compressed gas supply device 3 is equipped with a gas compressor 31 and a gas heating unit 32, which is a hot air heat exchanger. The hot air heat exchanger is located in the heating air duct of the externally heated rotary kiln and can be a plate heat exchanger or a tubular heat exchanger. The gas source of the high-temperature compressed gas supply device 3 can be purified pyrolysis gas or inert gas, and the inert gas can be any one of nitrogen, steam, or CO2. The high-temperature compressed gas supply device 3 outputs compressed gas with a pressure of not less than 0.1 MPa and a temperature of not less than 450℃.

[0037] In this embodiment, the clean coal gas outlet is connected via a pipeline to a coal gas cooling and purification device 5, which includes, but is not limited to, vertical pipe coolers, horizontal pipe coolers, and primary coolers. The outlet of the coal gas cooling and purification device 5 is connected via a pyrolysis coal gas return pipe 6 to the inlet of a high-temperature compressed gas supply device 3, thus enabling reuse.

[0038] The pyrolysis unit 4 is a conventional coal chemical, oil shale and biomass pyrolysis equipment in this field, which can produce raw coal gas.

[0039] This invention discloses a method for dust removal from raw pyrolysis gas of low-rank coal. In a filtration and dust removal device 1 composed of multiple independent filter chambers 11, each filter chamber 11 completes the purification of the raw pyrolysis gas through a state cycle. The specific steps are as follows:

[0040] 1) Pre-coating: Before the system of this invention is put into use, a portion of the purified ambient temperature pyrolysis gas passes through the gas compressor 31, and the pressure is increased to not less than 0.1 MPa. Then, it enters the gas heating unit 32 through the compressed gas pipeline. In the gas heating unit 32, the purified pyrolysis gas is heated to above 450°C. With the raw coal gas inlet valve 15 of a certain independent filter chamber 11 of the dust removal device 1 closed, the dust in the ash hopper 17 at the bottom of the filter chamber 11 is fluidized by high temperature compressed gas, and the dust is lifted up. Under the suction of the induced draft fan, the dust is adsorbed on the outer surface of the filter body 12 of the filter chamber 11, forming a dust isolation layer of a certain thickness.

[0041] 2) Standby: Stop the fluidization treatment of dust in ash hopper 17 with high-temperature compressed gas and wait for it to be put into online use; the filter chamber 11 in use will not be back-flushed during the filtration and dust removal process, so as to maintain a sufficiently thick dust isolation layer on the surface of the filter body 12.

[0042] 3) Filtration: When the filter chamber 11 receives the commissioning instruction, the raw coal gas inlet valve 15 of the filter chamber 11 is opened. The raw coal gas enters the filter chamber 11 through the inlet valve 15 and passes through the dust isolation layer 7 under the action of the induced draft fan. The thickness of the dust isolation layer 7 is not less than 1mm. The dust in the raw coal gas is blocked outside the dust isolation layer, and the dust-removed raw coal gas enters the clean gas side 14 and is discharged. When the raw coal gas passes through the dust isolation layer, the dust in the raw coal gas will be adsorbed on the dust isolation layer and cannot penetrate the dust isolation layer to directly contact the surface of the filter body 12. Therefore, the problem of sticky substances in the raw coal gas sticking and clogging the filter body 12 is fundamentally eliminated. As the filter body 12 in the filter chamber 11 continuously filters and removes dust from the raw coal gas, the gas pressure difference between the dust side 13 and the clean gas side 14 will gradually increase.

[0043] 4) Dust removal: When the resistance between the dust side 13 and the clean gas side 14 of the filter chamber 11 reaches the set value or the dust on the surface of the filter body 12 needs to be removed according to the set cycle, close the raw coal gas inlet valve 15 and the clean coal gas outlet valve 16, and backflush high-temperature compressed gas from the clean gas side 14 to the inside of the filter body 12.

[0044] 5) Settling: After a period of settling, open the clean gas outlet valve 16. The dust isolation layer attached to the surface of the filter body 12 and the dust on the dust isolation layer fall into the ash hopper 17 below. Repeat steps 1) to 5) in this cycle to achieve continuous, stable and efficient dust removal of raw coal gas.

[0045] The dust collected in this invention is obtained by screening high-temperature dust collected from raw coal gas, with a tar content of no more than 5% and a particle size of 200 mesh sieve undersize. This composition is consistent with the dust in the subsequently processed raw coal gas, exhibiting good compatibility. When initially adding dust to the filtration and dust removal device 1, powdered material meeting these conditions must be selected. The powdered material is first pre-sprayed onto the surface of the filter media in each filter chamber, and then the pre-sprayed filter chambers are put into normal filtration. During operation of the filtration and dust removal device 1, the dust collected in the ash hopper originates from dust blown down from the surface of the filter media. As the dust removal system continues to operate, the remaining dust collected in the ash hopper, except for the amount retained for pre-spraying, should be discharged and transported out, thus continuously renewing the dust collected in the ash hopper.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dust removal system for raw coal gas from low-rank coal pyrolysis, characterized in that, It includes a pyrolysis device, a filtration and dust removal device, a high-temperature dust fluidization device, and a high-temperature compressed gas supply device. The filtration and dust removal device consists of multiple independent filter chambers. Each filter chamber is equipped with multiple filter elements, which divide the filter chamber into two parts: a dust gas side and a clean gas side. The dust gas side is connected to the raw coal gas outlet of the pyrolysis device, and a raw coal gas inlet valve is installed at the dust gas side inlet. The clean gas side is connected to the clean coal gas outlet, and a clean coal gas outlet valve is installed at the clean coal gas outlet. An ash hopper is provided at the bottom of the filter chamber. The high-temperature dust fluidization device is installed in the ash hopper and includes a fluidized nozzle. The inlet of the fluidized nozzle is connected to a high-temperature compressed gas supply device. The fluidized nozzle is a hollow cavity with multiple holes or slits on its surface. The holes or slits on the surface of the fluidized nozzle are buried in the dust collection ash at the bottom of the ash hopper. The high-temperature compressed gas supply device is equipped with a gas compressor and a gas heating unit, the gas heating unit being a hot air heat exchanger.

2. The dust removal system for low-rank coal pyrolysis raw coal gas according to claim 1, characterized in that, The gas source for the high-temperature compressed gas supply device is purified pyrolysis gas or inert gas, wherein the inert gas is any one of nitrogen, steam, or CO2.

3. The dust removal system for low-rank coal pyrolysis raw coal gas according to claim 1, characterized in that, The hot air heat exchanger is installed inside the hot air supply pipeline of the externally heated rotary kiln. The hot air heat exchanger is a plate heat exchanger or a tubular heat exchanger.

4. The dust removal system for low-rank coal pyrolysis raw gas according to claim 1, characterized in that, The clean gas outlet is connected to a gas cooling and purification device via a pipeline.

5. A dust removal system for low-rank coal pyrolysis raw coal gas according to claim 4, characterized in that, The outlet of the gas cooling and purification device is connected to the inlet of the high-temperature compressed gas supply device via a pyrolysis gas return pipe.

6. A method for dust removal from raw coal gas after pyrolysis of low-rank coal, characterized in that, In the filtration and dust removal device composed of multiple independent filter chambers, each filter chamber completes the purification of pyrolysis raw coal gas through a state cycle. The specific steps are as follows: 1) Pre-coating: With the gas inlet valve of an independent filter chamber in the dust removal device closed, high-temperature compressed gas is used to fluidize the dust in the ash hopper at the bottom of the filter chamber, raising the dust. Under the action of the induced draft fan, the dust is adsorbed on the outer surface of the filter body of the filter chamber, forming a dust isolation layer of a certain thickness. 2) Standby: Stop the fluidization treatment of dust in the ash hopper with high-temperature compressed gas and wait for it to be put into online use; 3) Filtration: When the filter chamber to be put into use receives the commissioning instruction, the raw coal gas inlet valve of the filter chamber is opened. The raw coal gas enters the filter chamber from the inlet valve and passes through the dust isolation layer under the action of the induced draft fan. The dust in the raw coal gas is blocked outside the dust isolation layer. The raw coal gas after dust removal enters the clean gas side and is discharged. 4) Dust removal: When the filter chamber resistance reaches the set value or the dust on the surface of the filter body needs to be removed according to the set cycle, close the raw coal gas inlet valve and the clean coal gas outlet valve, and backflush the high-temperature compressed gas from the clean gas side to the inside of the filter body. 5) Settling: After a period of settling, open the clean gas outlet valve. The dust isolation layer attached to the surface of the filter body and the dust on the dust isolation layer fall into the ash hopper below. Repeat steps 1) to 5.

7. A method for dust removal from raw coal gas after low-rank coal pyrolysis according to claim 7, characterized in that, The high-temperature compressed gas supply device outputs compressed gas with a pressure of not less than 0.1 MPa and a temperature of not less than 450°C.

8. A method for dust removal from raw coal gas after pyrolysis of low-rank coal according to claim 7, characterized in that, The dust ash has a tar content of no more than 5% and a particle size of 200 mesh.

9. A method for dust removal from raw coal gas after pyrolysis of low-rank coal according to claim 7, characterized in that, The thickness of the dust isolation layer is not less than 1 mm.

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