A direct-fired pulverizing system for drying high-moisture raw coal by using flue gas waste heat

Abstract

The present application is a kind of direct-fired pulverizing system for drying high-moisture raw coal by using flue gas waste heat, comprising raw coal bunker, coal feeder, primary air fan and secondary air fan, the primary air fan and the secondary air fan are connected with air preheater, a plurality of spiral hollow shafts are arranged on the raw coal bunker, the inlet of the spiral hollow shaft is connected with mixed flue pipe, the other end of the mixed flue pipe is connected with hot furnace flue and cold furnace flue, and the outlet of the spiral hollow shaft is connected with flue gas flue. The present application has reasonable design and flexible adjustment, the stirring effect of raw coal bunker can be realized by adjusting the rotating speed of the spiral hollow shaft, the mixed flue gas temperature can be controlled by controlling the ratio of cold and hot flue gas, and the drying effect of raw coal with different moisture content can be adapted to meet the drying requirements of raw coal. In addition, the hot secondary air of the air preheater dries the coal powder in the coal mill, reducing the load of the unit.

Description

Technical Field

[0001] This invention relates to the field of coal-fired power generation technology, and in particular to a direct-fired pulverizing system that utilizes waste heat from flue gas to dry high-moisture raw coal. Background Technology

[0002] With rising coal prices, large coal-fired power generating units have begun to use a large proportion of low-quality coal, among which high-moisture lignite is widely used. However, due to the high moisture content of lignite, the drying capacity of the pulverizing system is required to be high. For most blending units, the drying capacity of the pulverizing system limits the blending ratio of high-moisture lignite. Therefore, modifying the original pulverizing system to improve its drying capacity is the main way to solve this problem.

[0003] Currently, modifications to the pulverizing system mainly include increasing the capacity of the coal mill and modifying the air preheater (changing the area of ​​the primary and secondary air chambers) to improve the primary air temperature at the coal mill inlet. However, due to spatial constraints, increasing the area of ​​the primary air chamber still cannot meet the drying requirements for a large proportion of lignite blended in, thus restricting the coal mill's drying process and affecting the unit's load-bearing capacity. Furthermore, for pulverizing systems with a large proportion of lignite blended in, the high moisture content and viscosity of the raw coal make it highly susceptible to coal blockage in the feeder pipe and coal chute. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provide a direct-fired pulverizing system that utilizes waste heat from flue gas to dry high-moisture raw coal.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas, comprising a boiler, an air preheater, a dust collector, an induced draft fan, a desulfurization tower, and a chimney connected to the boiler outlet. The air preheater, dust collector, induced draft fan, and desulfurization tower are sequentially installed on the pipe connecting the boiler and the chimney.

[0006] It also includes a raw coal bunker, a coal feeder, a primary air fan, and a secondary air fan. Both the primary and secondary air fans are connected to an air preheater. The raw coal bunker is located above the coal feeder, and a coal feed pipe connects the raw coal bunker and the coal feeder. Several spiral hollow shafts are arranged on the raw coal bunker. The inlet of each spiral hollow shaft is connected to a mixing flue pipe, and the other end of the mixing flue pipe is connected to both the hot furnace flue and the cold furnace flue. The outlet of each spiral hollow shaft is connected to a waste flue. Hot flue fans are arranged on the hot furnace flue, and hot flue fan outlet regulating dampers and hot flue fan inlet regulating dampers are installed at both the outlet and inlet of the hot flue fans. The end of the hot furnace flue away from the mixing flue pipe is connected to the hot flue gas extraction port at the bottom of the screen-type superheater on the boiler. A cold flue gas fan is arranged on the cold furnace flue gas duct. A cold flue gas fan inlet regulating valve is arranged at the inlet of the cold flue gas fan, and a cold flue gas fan outlet regulating valve is arranged at the outlet of the cold flue gas fan. The end of the cold furnace flue gas duct away from the mixing flue pipe is connected to the extraction port in front of the desulfurization tower. An exhaust flue gas fan is arranged on the exhaust flue gas duct. An exhaust flue gas fan inlet regulating valve is arranged at the inlet of the exhaust flue gas fan, and an exhaust flue gas fan outlet regulating valve is arranged at the outlet of the exhaust flue gas fan. The end of the exhaust flue gas duct away from the spiral hollow shaft is connected to the burnout tuyer of the boiler.

[0007] It also includes a coal mill, which is equipped with a separator. A coal drop pipe connects the separator and the coal feeder. A pulverized coal pipe is connected to the outlet of the coal mill, and the other end of the pulverized coal pipe is connected to the burner of the boiler.

[0008] Several layers of spiral hollow shafts are distributed vertically, with two spiral hollow shafts in each layer. The spiral hollow shafts are rotatably installed on the raw coal bunker, and spiral fins are installed on the spiral hollow shafts.

[0009] The end of the hollow spiral shaft extends from the side wall of the raw coal bunker, and a No. 1 gear is installed at the extended end. The No. 1 gear meshes with a No. 2 gear, and an electric motor that drives the hollow spiral shaft to rotate is installed on the No. 2 gear.

[0010] The mixing flue pipe is rotatably connected to the spiral hollow shaft, and the mixing flue pipe and the spiral hollow shaft are sealed by a sealing ring.

[0011] The hot primary air preheated by the air preheater is supplied to the burner, and the hot secondary air preheated by the air preheater is supplied to the coal mill.

[0012] The beneficial effects of this invention are as follows: The invention is rationally designed and flexibly adjustable. By adjusting the rotational speed of the hollow spiral shaft, the coal falling from the raw coal bunker can be agitated. By controlling the ratio of hot and cold flue gas, the mixed flue gas temperature can be controlled, adapting to the drying effect of raw coal with different moisture contents and meeting the drying requirements of raw coal. Furthermore, the hot secondary air from the air preheater dries the pulverized coal in the coal mill, reducing the unit's load. This invention uses waste heat from the flue gas to heat the raw coal, solving the problem of coal blockage in the coal mill pipe and coal chute caused by high moisture content in the raw coal. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the present invention;

[0014] Figure 2 This is a schematic diagram showing the connection between the spiral fins and the hollow spiral shaft.

[0015] In the diagram: 1-Coal mill; 2-Separator; 3-Coal chute; 4-Coal feeder; 5-Coal feed pipe; 6-Hollow spiral shaft; 7-Exhaust flue; 8-Pulverized coal pipe; 9-Burner; 10-Combustion vent; 11-Exhaust flue fan outlet regulating valve; 12-Exhaust flue fan; 13-Exhaust flue fan inlet regulating valve; 14-Mixing flue pipe; 15-Raw coal bunker; 16-Hot flue fan outlet regulating valve; 17-Hot flue fan 18-Hot flue gas fan inlet regulating valve; 19-Hot flue gas extraction port; 20-Hot primary air; 21-Air preheater; 22-Dust collector; 23-Induced draft fan; 24-Desulfurization tower; 25-Chimney; 26-Secondary air fan; 27-Primary air fan; 28-Cold flue gas fan inlet regulating valve; 29-Cold flue gas fan; 30-Cold flue gas fan outlet regulating valve; 31-Hot secondary air; 32-Spiral fins; 33-Boiler

[0016] The following will describe in detail, with reference to the accompanying drawings, embodiments of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0018] like Figures 1 to 2 As shown, a direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas includes a boiler 33, an air preheater 21, a dust collector 22, an induced draft fan 23, a desulfurization tower 24, and a chimney 25 connected to the outlet of the boiler 33. The air preheater 21, dust collector 22, primary air fan 27, secondary air fan 26, induced draft fan 23, and desulfurization tower 24 are sequentially installed on the pipe connecting the boiler 33 and the chimney 25. The primary air fan 27 and secondary air fan 26 are both connected to the air preheater 21. The system also includes a raw coal bunker 15, arranged above a coal feeder 4. A coal feed pipe 5 connects the raw coal bunker 15 and the coal feeder 4. Several spiral feeders are arranged on the raw coal bunker 15. Hollow shafts 6 are arranged in several layers, with two hollow spiral shafts 6 distributed in each layer. The hollow spiral shafts 6 are rotatably mounted on the raw coal bunker 15. The ends of the hollow spiral shafts 6 extend from the side wall of the raw coal bunker 15, and a first gear is installed at the extended end. The first gear meshes with a second gear, and a motor that drives the hollow spiral shafts 6 to rotate is installed on the second gear. The mixing flue pipe 14 is rotatably connected to the hollow spiral shafts 6, and the mixing flue pipe 14 and the hollow spiral shafts 6 are sealed by a sealing ring. The sealing ring is a lip seal used for shaft sealing connection, which ensures the rotatable connection between the mixing flue pipe 14 and the hollow spiral shafts 6 while achieving a seal between them.

[0019] The coal feeder 4 is a scraper-type coal feeder. The hot primary air 20 preheated by the air preheater 21 is supplied to the burner 9, and the hot secondary air 31 preheated by the air preheater 21 is supplied to the coal mill 1.

[0020] The mixing flue duct 14 is connected to the inlet of the spiral hollow shaft 6, and the exhaust flue duct 7 is connected to the outlet of the spiral hollow shaft 6. The mixing flue duct 14 is connected to the hot furnace flue duct and the cold furnace flue duct. A hot flue fan 17 is arranged on the hot furnace flue duct. A hot flue fan inlet regulating valve 18 is arranged at the inlet of the hot flue fan 17, and a hot flue fan outlet regulating valve 16 is arranged at the outlet of the hot flue fan 17. The hot furnace flue is taken from the hot flue exhaust port 19 at the bottom of the screen superheater. The cold furnace flue... A cold flue fan 29 is arranged on the upper part of the boiler 33. A cold flue fan inlet regulating valve 28 is arranged at the inlet of the cold flue fan 29. The cold flue gas is taken from the flue gas outlet in front of the desulfurization tower 24. A waste flue fan 12 is arranged on the waste flue duct 7. A waste flue fan inlet regulating valve 13 is arranged at the inlet of the waste flue fan 12. A waste flue fan outlet regulating valve 11 is arranged at the outlet of the waste flue fan 12. The end of the waste flue duct 7 away from the spiral hollow shaft 6 is connected to the burnout tuyer 10 of the boiler 33.

[0021] Spiral fins 32 are arranged on the hollow spiral shaft 6. Mixed flue gas passes through the hollow spiral shaft 6, and the mixed flue gas transfers heat to the hollow spiral shaft 6 and the spiral fins 32. During the falling process, the coal in the raw coal bunker 15 comes into contact with the hollow spiral shaft 6 and the spiral fins 32, and obtains heat from the hollow spiral shaft 6 and the spiral fins 32 to be heated. The hollow spiral shaft 6 and the spiral fins 32 can rotate. During the falling process, the coal in the raw coal bunker 15 is disturbed by the spiral fins 32, which promotes the heat exchange effect. The heated raw coal is transported to the coal drop pipe 3 by the coal feeder 4, and then enters the coal mill 1. It is then heated by the hot secondary air 31 and ground by the coal mill 1 to be ground into coal powder. Then, the raw coal is separated into coarse powder by the separator 2. The qualified coal powder is sent to the burner 9 through the coal powder pipe 8 for combustion.

[0022] The flue gas passing through the spiral hollow shaft 6 is a mixture of cold and hot furnace flue gas. The cold furnace flue gas is drawn from the flue in front of the desulfurization tower 24 by the cold flue gas fan 29. The amount of cold flue gas drawn can be controlled by the cold flue gas fan inlet regulating valve 28 and the cold flue gas fan outlet regulating valve 30 of the cold flue gas fan 29. The hot furnace flue gas is drawn from the hot flue gas extraction port 19 at the bottom of the screen superheater by the hot flue gas fan 17. The amount of hot flue gas drawn can be controlled by the hot flue gas fan inlet regulating valve 18 and the hot flue gas fan outlet regulating valve 16 of the cold flue gas fan 17.

[0023] The "cold" in cold smoke extraction and the "hot" in hot smoke extraction are relative terms. The hot smoke extracted by hot smoke fan 17 has a temperature of 800-900℃, while the cold smoke extracted by cold smoke fan 29 has a temperature of 100-140℃. The temperature of the raw coal is lowered by mixing the cold and hot smoke. The raw coal is heated while ensuring that it does not burn due to excessive temperature. The mixing ratio of cold and hot smoke is adjusted according to the moisture content of the raw coal. If the moisture content of the raw coal is too high, the proportion of hot smoke is increased, and vice versa.

[0024] Because the raw coal is heated and disturbed during its descent within the raw coal bunker 15, it is dried, reducing the moisture content and viscosity of the raw coal. This significantly reduces the risk of blockage in the coal feed pipe 5 and coal drop pipe 3 due to excessive moisture causing the raw coal to stick together. Furthermore, the heating within the raw coal bunker 15 saves heat taken from the secondary hot air 31, thereby increasing the output of the coal mill 1. Since most of the heat for heating the raw coal is taken from the flue gas before the desulfurization tower 24, for conventional coal-fired units, the heat in this part of the flue gas is no longer utilized. For large coal-fired units, the flue gas volume is large, resulting in significant waste heat. The pulverizing system described in this invention, which utilizes waste heat from flue gas to heat high-moisture raw coal, can recover some of the waste heat, improving the unit's economic efficiency.

[0025] This invention features a reasonable design and flexible adjustment. By adjusting the rotational speed of the hollow spiral shaft 6, the coal falling into the raw coal bunker 15 can be agitated. Controlling the hot and cold flue gas ratio allows for control of the mixed flue gas temperature, adapting to the drying effect of raw coal with different moisture contents and meeting the drying requirements. Furthermore, the hot secondary air 31 from the air preheater 21 dries the pulverized coal in the coal mill 1, reducing the unit's load. This invention uses waste heat from the flue gas to heat the raw coal, solving the problem of coal blockage in the coal mill pipe 5 and the coal falling pipe 3 caused by high moisture content in the raw coal.

[0026] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any improvements made using the inventive concept and technical solution of the present invention, or direct application to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas, comprising a boiler (33), an air preheater (21), a dust collector (22), an induced draft fan (23), a desulfurization tower (24), and a chimney (25) connected to the outlet of the boiler (33), wherein the air preheater (21), the dust collector (22), the induced draft fan (23), and the desulfurization tower (24) are sequentially installed on the pipe connecting the boiler (33) and the chimney (25), characterized in that, It also includes a raw coal bunker (15), a coal feeder (4), a primary air fan (27), and a secondary air fan (26). The primary air fan (27) and the secondary air fan (26) are both connected to the air preheater (21). The raw coal bunker (15) is located above the coal feeder (4). A coal feed pipe (5) connects the raw coal bunker (15) and the coal feeder (4). Several spiral hollow shafts (6) are arranged on the raw coal bunker (15). The inlet of the spiral hollow shaft (6) is connected to a mixing flue pipe (14). The other end of the mixing flue pipe (14) is connected to a hot furnace flue and a cold furnace flue. The outlet of the spiral hollow shaft (6) is connected to a waste flue (7). A hot flue fan (17) is arranged on the hot furnace flue. A hot flue fan outlet regulating valve (16) is arranged at the outlet of the hot flue fan (17). A hot flue fan inlet regulating valve is arranged at the inlet of the hot flue fan (17). The end of the hot furnace flue away from the mixing flue pipe (14) is connected to the hot flue gas extraction port (19) at the bottom of the screen superheater on the boiler (33). A cold flue gas fan (29) is arranged on the cold furnace flue. A cold flue gas fan inlet regulating valve (28) is arranged at the inlet of the cold flue gas fan (29). A cold flue gas fan outlet regulating valve (30) is arranged at the outlet of the cold flue gas fan (29). The end of the cold furnace flue away from the mixing flue pipe (14) is connected to the extraction port in front of the desulfurization tower (24). A waste flue gas fan (12) is arranged on the waste flue gas flue (7). A waste flue gas fan inlet regulating valve (13) is arranged at the inlet of the waste flue gas fan (12). A waste flue gas fan outlet regulating valve (11) is arranged at the outlet of the waste flue gas fan (12). The end of the waste flue gas flue (7) away from the spiral hollow shaft (6) is connected to the burnout tuyer (10) of the boiler (33). The flue gas inside the spiral hollow shaft (6) is a mixture of cold and hot furnace flue gas. The cold furnace flue gas is drawn from the flue in front of the desulfurization tower (24) by the cold flue gas fan (29). The amount of cold flue gas drawn can be controlled by the cold flue gas fan inlet regulating valve (28) and the cold flue gas fan outlet regulating valve (30) of the cold flue gas fan (29). The hot furnace flue gas is drawn from the hot flue gas extraction port (19) at the bottom of the screen superheater by the hot flue gas fan (17). The amount of hot flue gas drawn can be controlled by the hot flue gas fan inlet regulating valve (18) and the hot flue gas fan outlet regulating valve (16) of the hot flue gas fan (17). The temperature of the hot flue gas drawn by the hot flue gas fan (17) is 800-900℃, and the temperature of the cold flue gas drawn by the cold flue gas fan (29) is 100-140℃. It also includes a coal mill (1), a coal feeder (4) which is a scraper feeder, a primary air (20) preheated by an air preheater (21) which supplies the burner (9), and a secondary air (31) preheated by an air preheater (21) which supplies the coal mill (1).

2. The direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas according to claim 1, characterized in that, A separator (2) is installed on the coal mill (1). A coal drop pipe (3) is connected between the separator (2) and the coal feeder (4). A pulverized coal pipe (8) is connected to the outlet of the coal mill (1). The other end of the pulverized coal pipe (8) is connected to the burner (9) of the boiler (33).

3. The direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas according to claim 2, characterized in that, Several hollow spiral shafts (6) are distributed in several layers, with two hollow spiral shafts (6) distributed in each layer. The hollow spiral shafts (6) are rotatably installed on the raw coal bunker (15), and spiral fins (32) are installed on the hollow spiral shafts (6).

4. The direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas according to claim 3, characterized in that, The end of the spiral hollow shaft (6) extends from the side wall of the raw coal bunker (15), and a No. 1 gear is installed at the extended end. The No. 1 gear meshes with the No. 2 gear, and an electric motor that drives the spiral hollow shaft (6) to rotate is installed on the No. 2 gear.

5. The direct-fired pulverizing system for drying high-moisture raw coal using waste heat from flue gas according to claim 4, characterized in that, The mixing flue pipe (14) is rotatably connected to the spiral hollow shaft (6), and the mixing flue pipe (14) and the spiral hollow shaft (6) are sealed by a sealing ring.

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