Feed coal preheating and drying and semicoke cooling coupled low-rank coal pyrolysis system and method

Abstract

The invention relates to a feed coal preheating and drying and semicoke cooling coupled low-rank coal pyrolysis system and method. The low-rank coal pyrolysis system comprises a low-rank coal pyrolysis device, an air fan, an air secondary heat supplementing device and a cyclone dust collector, the low-rank coal pyrolysis device is sequentially provided with a coal direct drying section, a low-temperature pyrolysis section, a medium-high-temperature pyrolysis section and a semicoke indirect cooling section from top to bottom; the lower part of the semicoke indirect cooling section is provided with an air inlet, and the upper part is provided with a hot air outlet which is connected with the hot air inlet of the coal direct drying section through a hot air pipeline; and the hot air pipeline is provided with an air secondary heat supplementing device. In the feed coal drying and semicoke cooling process, air is adopted as carrier gas for heat exchange, sufficient recovery of semicoke heat is achieved, the recovered heat is used for drying and preheating the feed coal, and comprehensive utilization of the heat is achieved; the process characteristics of coal drying preheating, pyrolysis and semicoke cooling are fully considered, an economical and reasonable heat exchange form is adopted, the process is simple, the heat recovery efficiency is high, and the productivity of the pyrolysis device is high.

Description

Technical Field

[0001] The present invention relates to the technical field of low-rank coal quality improvement, and in particular to a low-rank coal pyrolysis system and method that couples raw coal preheating and drying with semi-coke cooling. Background Art

[0002] Low-rank coal boasts vast reserves, relatively shallow depths, and economical mining. According to statistics, global geological reserves of low-rank coal are staggering (approximately 4 trillion tons), accounting for over 40% of the world's total coal reserves. In my country, the development and utilization of high-quality coal varieties (such as bituminous and anthracite) is nearing saturation. In contrast, the large-scale development and utilization of low-rank coal is still in its early stages.

[0003] Currently, internally heated vertical furnaces are commonly used to upgrade low-rank coal. This process involves injecting a mixture of coal gas and air into the furnace for combustion to achieve coal dry distillation. Although this method can produce a large amount of coal gas, its quality is unsatisfactory, with ineffective components such as nitrogen accounting for more than 50%. Most of this low-quality coal gas is sent to power plants for combustion and power generation, and cannot be further processed into high-value-added chemicals. In recent years, a process has been developed using externally heated vertical furnaces to achieve low-temperature pyrolysis of coal, solving the problem of low coal gas quality. However, the main problems with externally heated vertical furnaces are poor overall heat transfer efficiency, low output, and large overall equipment investment.

[0004] The Chinese patent application with application publication number CN105018120A discloses "a continuous dry distillation process and device for low-rank pulverized coal". The low-rank pulverized coal first enters the material buffer bin through a double-sealed feeding device, and is then sent to an externally heated continuous dry distillation refractory furnace. After the dry distillation process is completed in the furnace, the raw gas is collected by a gas collecting device and a gas collecting cavity, and is discharged by a gas collecting system. The furnace charge after dry distillation is discharged in an orderly manner through a special discharge device. It realizes the continuous operation of low-rank pulverized coal as raw material in an externally heated continuous dry distillation furnace, which not only ensures the rapid discharge of raw gas, but also increases the light oil production and the calorific value of coal gas. In addition, during the coke discharge process, the discharge of powdered coke can be evenly and continuously controlled, and the quality of semi-coke can also be flexibly adjusted according to needs. However, since the furnace body of the device is entirely made of refractory bricks, the heat transfer efficiency is reduced to a certain extent, thereby limiting the unit production capacity and increasing the overall investment cost.

[0005] Chinese invention patent publication number CN112625720B discloses a "cross-flow mixed coal pyrolysis method and apparatus." The vertical pyrolysis furnace comprises a drying unit located in the upper section, a pyrolysis unit located in the middle section, and a cooling unit located in the lower section. The furnace utilizes a multi-layer longitudinal gas distribution and collection structure, combining gas-solid cross-flow and counter-flow, achieving uniform heat exchange and primary dust reduction. The dusty and oily high-temperature coal gas produced by pyrolysis is brought into contact with the medium-temperature material in the drying and retorting transition section for heat exchange, achieving secondary dust removal and condensing a portion of the heavy tar. The dried coal is then carried into the retorting section for secondary pyrolysis. The coal gas released from the pyrolysis unit has a moderate temperature, low dust content, and high light oil content, significantly reducing the workload and equipment investment of the gas purification system and improving the quality of the coal gas and tar products. However, the process involves direct contact between the coal and gas throughout the entire process, with numerous gas circulation loops, making the process complex and difficult to control. Summary of the Invention

[0006] The present invention provides a low-rank coal pyrolysis system and method that couples raw coal preheating and drying with semi-coke cooling. During the process of raw coal drying and semi-coke cooling, air is used as a carrier gas for heat exchange, thereby fully recovering the heat of the semi-coke. The recovered heat is used to dry and preheat the raw coal, thereby achieving comprehensive utilization of heat. The process characteristics of coal drying and preheating, pyrolysis and semi-coke cooling are fully considered, and an economical and reasonable heat exchange form is adopted, resulting in a simple process, high heat recovery efficiency and high production capacity of the pyrolysis device.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A low-rank coal pyrolysis system that couples raw coal preheating and drying with semi-coke cooling comprises a low-rank coal pyrolysis device, an air blower, an air secondary heat generator and a cyclone dust collector; the low-rank coal pyrolysis device is provided with a coal direct drying section, a low-temperature pyrolysis section, a medium-high temperature pyrolysis section and a semi-coke indirect cooling section in sequence from top to bottom; the low-temperature pyrolysis section, the medium-high temperature pyrolysis section and the semi-coke indirect cooling section are provided with multiple continuous material discharge channels; a high-temperature exhaust gas inlet is provided at the lower part of the medium-high temperature pyrolysis section and is connected to a high-temperature exhaust gas input pipe, and a low-temperature exhaust gas outlet is provided at the upper part of the low-temperature pyrolysis section and is connected to a low-temperature exhaust gas output pipe; an air inlet is provided at the lower part of the semi-coke indirect cooling section and is connected to the air blower through the air input pipe, and a hot air outlet is provided at the upper part of the semi-coke indirect cooling section; multiple hot air inlets are provided on one side of the coal direct drying section and are connected to the hot air outlet of the semi-coke indirect cooling section through a hot air pipe, and an air secondary heat generator is provided on the hot air pipe; multiple humid air outlets are provided on the other side of the coal direct drying section and are connected to a cyclone dust collector through a humid air pipe.

[0009] The air secondary heat recovery device is a heat exchanger, a burner or a gas mixer; the heat exchanger is further provided with a high-temperature medium inlet and a high-temperature medium outlet after heat exchange; the burner is provided with a combustion medium inlet and an exhaust gas outlet, an air-exhaust gas mixer is provided on the hot air pipe, and the exhaust gas outlet of the burner is connected to the exhaust gas inlet of the air-exhaust gas mixer; the gas mixer is further provided with a high-temperature medium inlet.

[0010] The air outlet of the cyclone dust collector is connected to the air inlet of the air cooler through a circulating air duct, and the air outlet of the air cooler is connected to the air inlet of the air blower.

[0011] The semi-coke indirect cooling section consists of a cooling section outer shell, semi-coke cooling tubes and air baffles; the cooling section outer shell is provided with an air inlet and a hot air outlet; the cooling section shell is provided with semi-coke cooling tubes as a material discharge channel; multiple layers of air baffles are provided along the height direction in the cooling section shell to form a serpentine air flow channel.

[0012] The semi-coke cooling tube array is composed of a plurality of parallel semi-coke cooling tubes, each of which has a diameter of For circular tubes, the center distance between adjacent semi-coke cooling tubes is 200 to 700 mm.

[0013] The multiple semi-coke cooling tubes constituting the semi-coke cooling tube array are arranged in the form of n rows × m columns, and the semi-coke cooling tubes in two adjacent rows are aligned or staggered.

[0014] The distance between two adjacent layers of air deflectors is 400 to 1600 mm.

[0015] A furnace top silo is provided at the top of the direct coal drying section; a coke pusher and a semi-coke conveying device are provided at the bottom of the semi-coke indirect cooling section.

[0016] A low-rank coal pyrolysis method that couples raw coal preheating and drying with semi-coke cooling includes the following steps:

[0017] 1) Raw coal with a temperature of 20-35°C and a moisture content of 8%-22% enters the coal direct drying section through the furnace top hopper and is directly contacted with the hot air output from the semi-coke indirect cooling section to achieve drying and preheating. After drying and preheating, the raw coal temperature rises to 50-110°C and the moisture content is reduced to 6%-17%.

[0018] 2) The dried and preheated raw coal enters the low-temperature pyrolysis section and the medium-high-temperature pyrolysis section in sequence under the action of gravity. The low-temperature pyrolysis section and the medium-high-temperature pyrolysis section use the high-temperature exhaust gas generated after combustion as the heat source to pyrolyze the raw coal and remove the remaining moisture, tar and volatile matter in the raw coal. The temperature of the high-temperature semi-coke after high-temperature pyrolysis is 550-700°C.

[0019] 3) After high-temperature pyrolysis, the hot semi-coke enters the semi-coke indirect cooling section, where it undergoes indirect heat exchange with the air entering the outer shell of the cooling section in the semi-coke cooling tubes. The temperature of the cooled semi-coke drops to 80-180°C. The coke is discharged at a speed controlled by a coke pusher and then transported to the outside by a semi-coke conveyor.

[0020] 4) The air is pressurized to 1-3 kPa by the air blower and then enters the semi-coke indirect cooling section. It flows in the air flow channel formed by the semi-coke cooling tubes and the air baffles, and indirectly exchanges heat with the high-temperature semi-coke in the semi-coke cooling tubes.

[0021] 5) After heat exchange, the hot air heated to 80-110°C is supplied by the secondary air heater and the temperature is controlled at 90-120°C after the hot air flow is replenished. It enters the coal direct drying section through multiple hot air inlets and directly contacts and exchanges heat with the raw coal after entering the furnace. The temperature of the moist air after drying and preheating the raw coal is 60-90°C and enters the cyclone dust collector for dust removal.

[0022] The low-rank coal pyrolysis method that couples raw coal preheating and drying with semi-coke cooling also includes step 6): the air after dust removal is recycled, first entering an air cooler to be cooled to 30-40°C, and removing condensed water therein, and then being pressurized by an air fan and sent back to the semi-coke indirect cooling section.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The low-rank coal pyrolysis device adopts a four-section structure consisting of a coal direct drying section, a low-temperature pyrolysis section, a medium-high temperature pyrolysis section, and a semi-coke indirect cooling section. The direct drying section is a process of direct heat transfer between the medium and the coal, while the low-temperature pyrolysis section, the medium-high temperature pyrolysis section, and the semi-coke indirect cooling section are processes of indirect heat transfer between the medium and the coal or semi-coke.

[0025] 2) During the process of drying the raw coal and cooling the semi-coke, air is used as the carrier gas for heat exchange to fully recover the heat of the semi-coke. The recovered heat is used to dry and preheat the raw coal, achieving comprehensive heat utilization;

[0026] 3) The present invention fully considers the process characteristics of coal drying and preheating, pyrolysis and semi-coke cooling, adopts an economical and reasonable heat exchange form, has a simple process, high heat recovery efficiency, and high pyrolysis device production capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the low-rank coal pyrolysis system with coupled coal preheating and drying and semi-coke cooling according to the present invention. Figure 1 .

[0028] Figure 2 This is a schematic diagram of the structure of the low-rank coal pyrolysis system with coupled coal preheating and drying and semi-coke cooling according to the present invention. Figure 2 .

[0029] Figure 3 It is a structural schematic diagram of the semi-coke indirect cooling section of the low-rank coal pyrolysis device described in the present invention.

[0030] Figure 4 yes Figure 3 Top view of .

[0031] Figure 5 yes Figure 3 Main cross-sectional view.

[0032] Figure: 1. Furnace top silo 2. Coal direct drying section 3. Low-temperature pyrolysis section 4. Medium- and high-temperature pyrolysis section 5. Semi-coke indirect cooling section 501. Air inlet (for the semi-coke indirect cooling section) 502. Hot air outlet 503. Cooling section outer shell 504. Semi-coke cooling pipe 505. Air baffle 6. Coke pusher 7. Semi-coke conveyor 8. Air blower 9. Air secondary reheater 10. Cyclone dust collector 11. Air cooler

[0033] A. Raw coal B. Coal after drying and preheating C. High-temperature semi-coke D. Air-cooled semi-coke E. Transported semi-coke F. Air G. Air after semi-coke heat exchange H. Air after secondary heating I. Moisturized air after drying J. High-temperature exhaust gas K. Low-temperature exhaust gas L. Circulating air after dust removal M. Condensate DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0035] like Figure 1 As shown, the low-rank coal pyrolysis system of the present invention, which couples raw coal preheating and drying with semi-coke cooling, comprises a low-rank coal pyrolysis device, an air blower 8, an air secondary heat supplement device 9 and a cyclone dust collector 10; the low-rank coal pyrolysis device is provided with a coal direct drying section 2, a low-temperature pyrolysis section 3, a medium-high temperature pyrolysis section 4 and a semi-coke indirect cooling section 5 in sequence from top to bottom; the low-temperature pyrolysis section 3, the medium-high temperature pyrolysis section 4 and the semi-coke indirect cooling section 5 are provided with a plurality of continuous feeding channels; the lower part of the medium-high temperature pyrolysis section 4 is provided with a high-temperature exhaust gas inlet connected to the high-temperature exhaust gas input pipeline, and the low-temperature pyrolysis section 3 ... semi-coke indirect cooling section 5. A low-temperature exhaust gas outlet is provided at the upper part of section 3 and is connected to the low-temperature exhaust gas output pipe; an air inlet 501 is provided at the lower part of the semi-coke indirect cooling section 5 and is connected to the air fan 8 through an air input pipe, and a hot air outlet 502 is provided at the upper part of the semi-coke indirect cooling section 5; a plurality of hot air inlets are provided on one side of the coal direct drying section 2, which are connected to the hot air outlet 502 of the semi-coke indirect cooling section 5 through a hot air pipe, and an air secondary heat replenisher 9 is provided on the hot air pipe; a plurality of humid air outlets are provided on the other side of the coal direct drying section 2 and are connected to the cyclone dust collector 10 through a humid air pipe.

[0036] The air secondary heat recovery device 9 is a heat exchanger, a burner or a gas mixer; the heat exchanger is further provided with a high-temperature medium inlet and a high-temperature medium outlet after heat exchange; the burner is provided with a combustion medium inlet and an exhaust gas outlet, an air-exhaust gas mixer is provided on the hot air pipe, and the exhaust gas outlet of the burner is connected to the exhaust gas inlet of the air-exhaust gas mixer; the gas mixer is further provided with a high-temperature medium inlet.

[0037] like Figure 2 As shown, the air outlet of the cyclone dust collector 10 is connected to the air inlet of the air cooler 11 through a circulating air duct, and the air outlet of the air cooler 11 is connected to the air inlet of the air blower 8.

[0038] like Figure 3-Figure 5 As shown, the semi-coke indirect cooling section 5 consists of a cooling section outer shell 503, semi-coke cooling tubes and air deflectors 505; an air inlet 501 and a hot air outlet 502 are provided on the cooling section outer shell 503; semi-coke cooling tubes are provided in the cooling section shell 503 as a material discharge channel; multiple layers of air deflectors 505 are provided in the cooling section shell 503 along the height direction to form a serpentine air flow channel.

[0039] The semi-coke cooling pipe array is composed of a plurality of parallel semi-coke cooling pipes 504, each of which has a diameter of The center distance between adjacent semi-coke cooling tubes 504 is 200 to 700 mm.

[0040] The multiple semi-coke cooling tubes 504 constituting the semi-coke cooling tube array are arranged in the form of n rows×m columns, and the semi-coke cooling tubes in two adjacent rows are aligned or staggered.

[0041] The distance between two adjacent layers of air deflectors 505 is 400 to 1600 mm.

[0042] A furnace top silo 1 is provided at the top of the coal direct drying section 2; a coke pusher 6 and a semi-coke conveying device 7 are provided at the bottom of the semi-coke indirect cooling section 5.

[0043] The low-rank coal pyrolysis method of the present invention, which couples raw coal preheating and drying with semi-coke cooling, comprises the following steps:

[0044] 1) Raw coal with a temperature of 20-35°C and a moisture content of 8%-22% enters the coal direct drying section 2 through the furnace top hopper 1, and is directly contacted with the hot air output from the semi-coke indirect cooling section 5 to achieve drying and preheating. After drying and preheating, the raw coal temperature rises to 50-110°C, and the moisture content is reduced to 6%-17%.

[0045] 2) The dried and preheated raw coal enters the low-temperature pyrolysis section 3 and the medium-high temperature pyrolysis section 4 in sequence under the action of gravity. The low-temperature pyrolysis section 3 and the medium-high temperature pyrolysis section 4 use the high-temperature exhaust gas generated after combustion as the heat source to pyrolyze the raw coal, removing the remaining moisture, tar and volatile matter in the raw coal. The high-temperature semi-coke temperature after high-temperature pyrolysis is 550-700°C.

[0046] 3) The hot semi-coke after high-temperature pyrolysis enters the semi-coke indirect cooling section 5, where it undergoes indirect heat exchange with the air entering the cooling section outer shell 503 in the semi-coke cooling tubes, reducing the temperature of the cooled semi-coke to 80-180°C. The coke is discharged at a controlled speed by the coke pusher 6, and then transported to the outside by the semi-coke conveyor 7.

[0047] 4) The air is pressurized to 1-3 kPa by the air blower 8 and then enters the semi-coke indirect cooling section 5. It flows in the air flow channel formed by the semi-coke cooling tubes and the air baffles 505, and indirectly exchanges heat with the high-temperature semi-coke in the semi-coke cooling tubes.

[0048] 5) After heat exchange, the hot air heated to 80-110°C passes through the air secondary reheater 9 to replenish heat and hot air flow, and the temperature is controlled at 90-120°C. It enters the coal direct drying section 2 through multiple hot air inlets, and directly contacts and exchanges heat with the raw coal after entering the furnace; the temperature of the moist air after drying and preheating the raw coal is 60-90°C, and enters the cyclone dust collector 10 for dust removal.

[0049] The low-rank coal pyrolysis method of the present invention, which couples raw coal preheating and drying with semi-coke cooling, also includes step 6): the air after dust removal is recycled, first entering the air cooler 11 to be cooled to 30-40°C, and the condensed water therein is removed, and then pressurized by the air fan 8 and sent back to the semi-coke indirect cooling section 5.

[0050] The low-rank coal pyrolysis device described in the present invention is designed as a four-section structure consisting of a coal direct drying section 2, a low-temperature pyrolysis section 3, a medium-high temperature pyrolysis section 4 and a semi-coke indirect cooling section 5. The coal direct drying section 2 adopts a direct heat transfer method between hot air and raw coal, and the low-temperature pyrolysis section 3, the medium-high temperature pyrolysis section 4 and the semi-coke indirect cooling section 5 all adopt an indirect heat transfer method between air / high temperature exhaust gas and semi-coke / coal.

[0051] The present invention uses air as carrier gas for heat exchange during the process of coal drying and preheating and semi-coke cooling, thereby fully recovering the heat of the semi-coke and using this heat to dry and preheat the raw coal entering the furnace, thereby achieving comprehensive utilization of the system's heat.

[0052] As a specific embodiment, the low-rank coal pyrolysis device of the present invention is equipped with, from top to bottom, a furnace top silo 1, a coal direct drying section 2, a low-temperature pyrolysis section 3, a medium-high temperature pyrolysis section 4, a semi-coke indirect cooling section 5, a coke pusher 6, and a semi-coke conveyor 7. In the coal direct drying section 2, the raw coal and hot air undergo a direct heat exchange process; in the low-temperature pyrolysis section 3 and the medium-high temperature pyrolysis section 4, the coal and exhaust gas undergo an indirect heat exchange process; and in the semi-coke indirect cooling section 5, the semi-coke and ambient temperature air undergo an indirect heat exchange process.

[0053] As an embodiment, in the low-rank coal pyrolysis system of the present invention, the air as carrier gas heat exchange route adopts an open design; the air flow path is the air blower 8, the semi-coke indirect cooling section 5, the air secondary reheater 9 and the coal direct drying section 2. Among them, the air inlet of the air blower 8 draws air from the atmosphere, the air outlet of the air blower 8 is connected to the air inlet of the semi-coke indirect cooling section 5, the hot air outlet of the semi-coke indirect cooling section 5 is connected to the air inlet of the air secondary reheater 9 through a hot air pipe, the hot air outlet (or high-temperature mixed gas outlet) of the air secondary reheater 9 is connected to multiple hot air inlets of the coal direct drying section 2 through hot air pipes, the multiple humid air outlets of the coal direct drying section 2 are connected to the air inlet of the cyclone dust collector 10, and the air outlet of the cyclone dust collector 10 is connected to the atmosphere.

[0054] As another example, in the low-rank coal pyrolysis system of the present invention, air as the carrier gas for heat exchange adopts a closed-loop design. The air flow path for one cycle is, in order, through the air blower 8, the semi-coke indirect cooling section 5, the air secondary reheater 9, the direct coal drying section 2, the cyclone separator 10, the air cooler 11, and finally the air blower 8. Among them, the air inlet of the air fan 8 is connected to the air outlet of the air cooler 11 through a pipeline, the air outlet of the air fan is connected to the air inlet of the semi-coke indirect cooling section 5, the hot air outlet of the semi-coke indirect cooling section 5 is connected to the air inlet of the air secondary heat exchanger 9 through a hot air pipeline, the hot air outlet (or high-temperature mixed gas outlet) of the air secondary heat exchanger is connected to each hot air inlet of the coal direct drying section 2 through a hot air pipeline, the multiple wet and cold air outlets of the coal direct drying section 2 are connected to the air inlet of the cyclone dust collector 10 through a pipeline, the air outlet of the cyclone dust collector 10 is connected to the air inlet of the air cooler 11, and the air outlet of the air cooler 11 is connected to the air inlet of the air fan 8, thereby realizing the closed-loop circulation of the carrier gas.

[0055] The semi-coke indirect cooling section 5 includes an air inlet 501, a cooling section outer shell 503, a semi-coke cooling tube array (composed of multiple semi-coke cooling tubes 504), air baffles 505, and a hot air outlet 502. The air inlet 501 and hot air outlet 502 are positioned on opposite sides of the cooling section outer shell 503. Multiple layers of air baffles 505 are positioned within the cooling section outer shell 503 to form a serpentine air flow channel. The semi-coke cooling tube array serves as a channel for semi-coke flow, discharge, and heat exchange.

[0056] The air secondary heat recovery device 8 can adopt the following equipment: 1) a heat exchanger, which uses other heat media as a heat source to perform secondary heating on the hot air after the semi-coke heat exchange; 2) a burner and a mixer, which directly mixes the hot flue gas formed after the combustion of combustible gases such as coal gas with the hot air after the semi-coke heat exchange to achieve secondary heating of the hot air; 3) a mixer, which directly mixes other high-temperature gases into the hot air after the semi-coke heat exchange.

[0057] As a specific embodiment, in the semi-coke indirect cooling section 5, the semi-coke cooling pipe array is composed of a plurality of vertical semi-coke cooling pipes, and the diameter of the semi-coke cooling pipe 504 is The center-to-center distance between adjacent semi-coke cooling tubes is 515mm. The semi-coke cooling tubes are arranged in 8 rows and 16 / 14 columns (16 columns and 14 columns are arranged alternately), with adjacent rows of semi-coke cooling tubes staggered. Five layers of air baffles are evenly distributed within the cooling section's outer shell, with each layer spaced 480mm apart.

[0058] like Figure 1 As shown in FIG. 1 , as an example, the low-rank coal pyrolysis process of coupling raw coal preheating and drying with semi-coke cooling is as follows:

[0059] 1) Raw coal A, at a temperature of 25°C and a moisture content of 18%, enters the direct coal drying section 2 through the furnace top hopper 1. It comes into direct contact with secondary heated air H, achieving drying and preheating of the raw coal. After heat exchange, the dried and preheated coal B reaches a temperature of 70°C and a moisture content of 8%.

[0060] 2) After drying and preheating, coal B enters the low-temperature pyrolysis section 3 and the medium-high temperature pyrolysis section 4 in sequence under the action of gravity for pyrolysis; the high-temperature exhaust gas J generated after combustion enters from the bottom of the medium-high temperature pyrolysis section 4 as a heat source, and the remaining moisture, tar and volatile matter in the coal are removed through pyrolysis. The low-temperature exhaust gas K after pyrolysis is discharged from the top of the low-temperature pyrolysis section 3; the temperature of the high-temperature semi-coke C after high-temperature pyrolysis is 650°C.

[0061] 3) After pyrolysis, the high-temperature semi-coke C enters the multiple semi-coke cooling tubes 504 of the semi-coke indirect cooling section 5, where it is cooled by indirect heat exchange with room-temperature air. After air cooling, the temperature of the semi-coke D drops to 80°C. The coke discharge speed is controlled by the coke pusher 6, and the semi-coke E after coking is delivered to the outside by the semi-coke conveying device 7.

[0062] 4) The air F is pressurized to 2 kPa by the air blower 8, and then enters the air inlet 501 of the semi-coke indirect cooling section 5. The normal temperature air flows along the air flow channel of the semi-coke indirect cooling section 5, is deflected by the air deflector 505 to increase the residence time, and indirectly exchanges heat with the high-temperature semi-coke C. After the semi-coke heat exchange, the temperature of the air G is within 80°C.

[0063] 5) After the heat exchange with the semi-coke, the air G enters the air secondary reheater 9 to supplement the heat and hot air flow. The temperature of the air H after the secondary reheating is within 115°C. It enters the coal direct drying section 2 through multiple hot air inlets to exchange heat with the raw coal A. The temperature of the moist air I after drying is 90°C. It is discharged into the atmosphere after dust removal by the cyclone dust collector 10.

[0064] For the closed-loop carrier gas circulation scheme, the dried moist air I passes through the cyclone dust collector 10 to remove dust. The circulating air L after dust removal enters the air cooler 11 to be cooled to 35°C, and part of the condensed water M is separated. It is then pressurized by the air blower 8 and re-enters the semi-coke indirect cooling section 5 to form a closed-loop circulation.

[0065] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A low-rank coal pyrolysis system that couples raw coal preheating and drying with semi-coke cooling, characterized in that: It includes a low-rank coal pyrolysis device, an air blower, an air secondary heat replenisher and a cyclone dust collector; the low-rank coal pyrolysis device is provided with a coal direct drying section, a low-temperature pyrolysis section, a medium-high temperature pyrolysis section and a semi-coke indirect cooling section in sequence from top to bottom; the low-temperature pyrolysis section, the medium-high temperature pyrolysis section and the semi-coke indirect cooling section are provided with multiple continuous feeding channels; a high-temperature exhaust gas inlet is provided at the lower part of the medium-high temperature pyrolysis section and is connected to a high-temperature exhaust gas input pipe, and a low-temperature exhaust gas outlet is provided at the upper part of the low-temperature pyrolysis section and is connected to a low-temperature exhaust gas output pipe; an air inlet is provided at the lower part of the semi-coke indirect cooling section and is connected to an air blower through an air input pipe, and a hot air outlet is provided at the upper part of the semi-coke indirect cooling section; multiple hot air inlets are provided on one side of the coal direct drying section and are connected to the hot air outlet of the semi-coke indirect cooling section through a hot air pipe, and an air secondary heat replenisher is provided on the hot air pipe; multiple humid air outlets are provided on the other side of the coal direct drying section and are connected to a cyclone dust collector through a humid air pipe.

2. The low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling according to claim 1 is characterized in that: The air secondary heat recovery device is a heat exchanger, a burner or a gas mixer; the heat exchanger is further provided with a high-temperature medium inlet and a high-temperature medium outlet after heat exchange; the burner is provided with a combustion medium inlet and an exhaust gas outlet, an air-exhaust gas mixer is provided on the hot air pipe, and the exhaust gas outlet of the burner is connected to the exhaust gas inlet of the air-exhaust gas mixer; the gas mixer is further provided with a high-temperature medium inlet.

3. The low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling according to claim 1 is characterized in that: The air outlet of the cyclone dust collector is connected to the air inlet of the air cooler through a circulating air duct, and the air outlet of the air cooler is connected to the air inlet of the air blower.

4. The low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling according to claim 1 is characterized in that: The semi-coke indirect cooling section consists of a cooling section outer shell, semi-coke cooling tubes and air baffles; the cooling section outer shell is provided with an air inlet and a hot air outlet; the cooling section shell is provided with semi-coke cooling tubes as a material discharge channel; multiple layers of air baffles are provided along the height direction in the cooling section shell to form a serpentine air flow channel.

5. The low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling according to claim 4 is characterized in that: The semi-coke cooling tube array is composed of a plurality of parallel semi-coke cooling tubes, each of which has a diameter of For circular tubes, the center distance between adjacent semi-coke cooling tubes is 200 to 700 mm.

6. The low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling according to claim 4 is characterized in that: The multiple semi-coke cooling tubes constituting the semi-coke cooling tube array are arranged in the form of n rows × m columns, and the semi-coke cooling tubes in two adjacent rows are aligned or staggered.

7. The low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling according to claim 4 is characterized in that: The distance between two adjacent layers of air deflectors is 400 to 1600 mm.

8. The low-rank coal pyrolysis system coupled with raw coal preheating and drying and semi-coke cooling according to claim 1 is characterized in that: A furnace top silo is set at the top of the coal direct drying section; a coke pusher and a semi-coke conveying device are set at the bottom of the semi-coke indirect cooling section.

9. A low-rank coal pyrolysis method with coupled raw coal preheating and drying and semi-coke cooling, which is implemented based on the low-rank coal pyrolysis system with coupled raw coal preheating and drying and semi-coke cooling as described in any one of claims 1 to 8; characterized in that: The steps include: 1) Raw coal with a temperature of 20-35°C and a moisture content of 8%-22% enters the coal direct drying section through the furnace top hopper and is directly contacted with the hot air output from the semi-coke indirect cooling section to achieve drying and preheating. After drying and preheating, the raw coal temperature rises to 50-110°C and the moisture content is reduced to 6%-17%. 2) The dried and preheated raw coal enters the low-temperature pyrolysis section and the medium-high-temperature pyrolysis section in sequence under the action of gravity. The low-temperature pyrolysis section and the medium-high-temperature pyrolysis section use the high-temperature exhaust gas generated after combustion as the heat source to pyrolyze the raw coal and remove the remaining moisture, tar and volatile matter in the raw coal. The temperature of the high-temperature semi-coke after high-temperature pyrolysis is 550-700°C. 3) After high-temperature pyrolysis, the hot semi-coke enters the semi-coke indirect cooling section, where it undergoes indirect heat exchange with the air entering the outer shell of the cooling section in the semi-coke cooling tubes. The temperature of the cooled semi-coke drops to 80-180°C. The coke is discharged at a speed controlled by a coke pusher and then transported to the outside by a semi-coke conveyor. 4) The air is pressurized to 1-3 kPa by the air blower and then enters the semi-coke indirect cooling section. It flows in the air flow channel formed by the semi-coke cooling tubes and the air baffles, and indirectly exchanges heat with the high-temperature semi-coke in the semi-coke cooling tubes. 5) After heat exchange, the hot air heated to 80-110°C is supplied by the secondary air heater and the temperature is controlled at 90-120°C after the hot air flow is replenished. It enters the coal direct drying section through multiple hot air inlets and directly contacts and exchanges heat with the raw coal after entering the furnace. The temperature of the moist air after drying and preheating the raw coal is 60-90°C and enters the cyclone dust collector for dust removal.

10. The low-rank coal pyrolysis method of coupling raw coal preheating and drying with semi-coke cooling according to claim 9, characterized in that: The method also includes step 6): the air after dust removal is recycled, first entering an air cooler to be cooled to 30-40° C., and the condensed water therein is removed, and then pressurized by an air blower and re-sent to the semi-coke indirect cooling section.

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