A boiler coal combustion energy-saving device

Abstract

The present invention relates to the technical field of coal-fired boilers, and specifically to a coal-saving device for boilers. Through a smoke-dividing pipe, high-temperature flue gas can be shunted into a heat exchange cavity inside the workbench to heat a steam heater. The steam heater can keep the pulverized coal at an ambient temperature between 150°C and 300°C all the time, ensuring effective preheating of the pulverized coal without spontaneous combustion, which helps the pulverized coal to rapidly react with oxygen and burn after entering the combustion furnace, and at the same time reduces the generation of nitrogen oxides. The coal-scattering plate of this device has a stepped structure, so that the pulverized coal is continuously disturbed during the falling process, preventing the pulverized coal from caking or dispersing the caked pulverized coal; and the first vibrator can generate mechanical impact force, which not only helps to prevent the formation of new caking, but also effectively disperses the caked pulverized coal, greatly reducing the phenomenon of pulverized coal caking, improving the fluidity and combustion efficiency of the pulverized coal. At the same time, this design can also reduce the risk of equipment blockage, improving the operation stability and reliability of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired boilers, and particularly relates to a coal-saving device for a boiler. Background Art

[0002] A coal-fired boiler is a boiler with coal as the fuel. It refers to a thermal energy power device that releases heat by burning coal in the furnace and heats the heat medium water or other organic heat carriers (such as heat-conducting oil, etc.) to a certain temperature (or pressure). Coal-fired boilers are mainly classified according to their uses, and they are divided into coal-fired water boilers (supplying boiling water), coal-fired hot water boilers (for heating and bathing), coal-fired steam boilers (supplying steam), coal-fired heat-conducting oil boilers (for cooking and drying), etc.

[0003] During the use of existing coal-fired boilers, lumpy coal is directly pushed into the coal-fired boiler for combustion. During the combustion process, the contact between the lumpy coal and the combustion air inside the coal-fired boiler is limited, reducing the combustion efficiency of the coal-fired boiler for coal and increasing the energy consumption during the combustion process of the coal-fired boiler. By burning pulverized coal, the contact area between the pulverized coal and air can be effectively increased, and the combustion efficiency of the coal-fired boiler for coal can be improved.

[0004] Existing boiler pulverized coal adding devices usually cannot preheat the pulverized coal while effectively preventing the pulverized coal from caking, and cannot ensure the combustion efficiency and combustion stability. The caked pulverized coal will cause local overheating or cooling due to uneven distribution during combustion, affecting the combustion efficiency and heat exchange effect. The un-preheated pulverized coal directly enters the combustion chamber with a relatively low temperature, resulting in difficult ignition, incomplete combustion, and poor stability, which will affect the normal operation of the boiler, causing the boiler to go out or burn unevenly, thereby reducing the combustion efficiency. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a coal-saving device for a boiler to solve the problems existing in the above background art.

[0006] To achieve the above purpose, the embodiments of the present invention provide the following technical solutions:

[0007] A coal-fired energy-saving device for a boiler, comprising a coal-fired boiler, an inlet pipe and an exhaust pipe are respectively arranged on the coal-fired boiler, a workbench is arranged on one side of the coal-fired boiler, a heat exchange chamber is arranged inside the workbench, a steam heater is arranged on the workbench, the exhaust pipe is communicated with the heat exchange chamber through a smoke dividing pipe, the heat exchange chamber is used for heating the steam heater, and a through cavity is arranged in the middle of the steam heater; a coal spreading plate for preventing coal powder caking is arranged in a penetrating manner in the cavity, the coal spreading plate is inclined, both ends of the coal spreading plate extend out of the steam heater, one end of the coal spreading plate is connected to the steam heater through a hinge shaft, a first vibrator for driving the coal spreading plate to vibrate is arranged at the bottom of the other end of the coal spreading plate and is installed on the workbench, and a stepped structure is arranged in an array on the surface of the coal spreading plate; one end of the workbench is provided with a diversion box through a connecting block, an opening is arranged at the top of one end of the diversion box, a screening frame is movably installed at the opening, a second vibrator for driving the screening frame to vibrate is arranged on the top of the diversion box, and the screening frame is located below the end of the coal spreading plate with the hinge shaft; a Venturi feeder communicated with the inlet pipe is arranged at one end of the diversion box far away from the screening frame.

[0008] Preferably, a smoke dividing pipe communicated with the heat exchange chamber is arranged at one end of the workbench, an exhaust pipe communicated with the heat exchange chamber is arranged at the other end of the workbench, and heat exchange fins for heating the steam heater are arranged inside the heat exchange chamber.

[0009] Preferably, the steam heater has a pressurizing function, a water inlet pipe and a pressure relief valve are respectively arranged on the steam heater, and a display screen is also arranged on the steam heater.

[0010] Preferably, a storage box is arranged above the end of the coal spreading plate where the first vibrator is arranged at the bottom, a feeding hopper is arranged at the bottom of the storage box, and a control valve is arranged at the bottom of the feeding hopper.

[0011] Preferably, the bottom plate of the diversion box is inclined, and the horizontal height of the end of the bottom plate of the diversion box close to the screening frame is higher than the horizontal height of the end close to the feeder.

[0012] Preferably, the feeder comprises an inner shell and an outer shell, a cavity is arranged between the inner shell and the outer shell, and the end of the diversion box is communicated with the cavity between the inner shell and the outer shell.

[0013] Preferably, the same end of the inner shell and the outer shell is closed by an annular plate, the other end of the outer shell is connected to the inlet pipe through a funnel-shaped structure, the inside of the inner shell is communicated with the cavity between the inner shell and the outer shell through a funnel-shaped structure, a fan is arranged at the end of the inner shell far away from the inlet pipe, a fan blade is arranged inside the fan, and a pipe communicated with the outside is arranged on the side wall of the fan.

[0014] Preferably, a plurality of coal dispersion columns are arranged on each of the stepped structures, the screening frame includes a screening mesh, and coal dispersion columns are also arranged on the screening mesh.

[0015] Preferably, heat insulation curtains are respectively arranged at both ends of the cavity of the steam heater.

[0016] The beneficial effects of the embodiments of the present invention are as follows:

[0017] 1. Through the flue gas distribution pipe, the high-temperature flue gas discharged from the internal of the coal-fired boiler to the exhaust pipe can be shunted into the heat exchange cavity inside the workbench. A steam heater is arranged on the top of the workbench. By means of the steam heater, the preheating temperature of the pulverized coal can be controlled, so that the pulverized coal is always in an ambient temperature between 150°C and 300°C, ensuring that the pulverized coal is effectively preheated without spontaneous combustion, which helps the pulverized coal to quickly react with oxygen and burn after entering the combustion furnace, and at the same time reduces the generation of nitrogen oxides.

[0018] 2. The coal dispersion plate of the device has a stepped structure, which can increase the flow path of the pulverized coal on the coal dispersion plate, so that the pulverized coal is continuously disturbed during the falling process. This kind of disturbance can break the weak bonding formed between the pulverized coal particles, prevent the pulverized coal from caking or disperse the caked pulverized coal; the inclined angle uses the gravity to make the pulverized coal slide downward. During the sliding process, the pulverized coal will continuously impact the surface and steps of the coal dispersion plate, further crushing the caking; and the first vibrator can generate mechanical impact force to further disturb the pulverized coal particles and make them separate from each other. Vibration not only helps to prevent the formation of new caking, but also can effectively disperse the already caked pulverized coal, greatly reducing the phenomenon of pulverized coal caking, improving the fluidity and combustion efficiency of the pulverized coal. At the same time, this design can also reduce the risk of equipment blockage and improve the operation stability and reliability of the system.

[0019] 3. The device is convenient for preheating the pulverized coal on the coal dispersion plate, and the display screen can accurately display various values such as the pressure and temperature inside, which is convenient for controlling the steam heater to better preheat the pulverized coal.

[0020] 4. The pulverized coal of this device enters the cavity between the inner shell and the outer shell of the feeder through the diversion box. Since the fan drives the fan blades to rotate, the fan can transport the external combustion-supporting gas or other gases to the inside of the boiler through the feed pipe. Due to the Venturi effect, when the fan drives the gas into the boiler, a negative pressure will be formed between the inner shell and the outer shell, driving the pulverized coal to mix with the gas driven by the fan, and then entering the boiler through the feed pipe. Due to the negative pressure formed by the Venturi effect, the diversion box opening at the screening frame will suck in the external gas into the diversion box, which can prevent a large amount of pulverized coal suspension from forming when the pulverized coal falls onto the screening frame, facilitating the suction of all the pulverized coal into the diversion box and into the feeder, avoiding the explosion caused by the contact between the pulverized coal suspension floating outside and static electricity, and improving the safety of the working environment.

[0021] 5. By setting the coal dispersion column in this device, when the first vibrator and the second vibrator work, the coal dispersion column can help the pulverized coal to be more evenly distributed on the coal dispersion plate. The mechanical energy generated by vibration is transmitted to the pulverized coal through the coal dispersion column, making it spread more evenly, reducing the phenomena of accumulation and segregation; at the same time, it can further prevent the pulverized coal from caking and fully break up the caked pulverized coal, ensuring the fluidity of the pulverized coal and the stability during combustion. Brief Description of the Drawings

[0022] Figure 1 is the schematic diagram of the overall structure of the present invention Figure 1 ;

[0023] Figure 2 is the schematic diagram of the overall structure of the present invention Figure 2 ;

[0024] Figure 3 is the cross-sectional view of the steam heater and the diversion box;

[0025] Figure 4 is the cross-sectional view of the feeder;

[0026] Figure 5 is Figure 3 the enlarged view of the partial structure of

[0027] In the figure: 1, coal-fired boiler; 2, feed pipe; 3, exhaust pipe; 4, flue gas distribution pipe; 5, workbench; 6, heat exchange cavity; 7, heat exchange fins; 8, steam heater; 9, water inlet pipe; 10, pressure relief valve; 11, display screen; 12, flue gas outlet pipe; 13, storage tank; 14, hopper; 15, coal dispersion plate; 16, stepped structure; 17, coal dispersion column; 18, first vibrator; 19, diversion box; 20, screening frame; 21, second vibrator; 22, feeder; 23, fan; 24, outer shell; 25, inner shell; 26, fan blades. Detailed Embodiment

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] Embodiment 1

[0030] A coal-fired energy-saving device for boilers, as Figures 1-5 shown, includes a coal-fired boiler 1, an inlet pipe 2 and an exhaust pipe 3 are respectively arranged on the coal-fired boiler 1, a workbench 5 is arranged on one side of the coal-fired boiler 1, a heat exchange chamber 6 is arranged inside the workbench 5, a steam heater 8 is arranged on the workbench 5, the exhaust pipe 3 is communicated with the heat exchange chamber 6 through a smoke dividing pipe 4, the heat exchange chamber 6 is used to heat the steam heater 8, and a through cavity is arranged in the middle of the steam heater 8; a coal dispersing plate 15 for preventing coal powder caking is arranged in a penetrating manner in the cavity, the coal dispersing plate 15 is inclined, both ends of the coal dispersing plate 15 extend out of the steam heater 8, one end of the coal dispersing plate 15 is connected to the steam heater 8 through a hinge shaft, a first vibrator 18 for driving the coal dispersing plate 15 to vibrate is arranged at the bottom of the other end of the coal dispersing plate 15 and is installed on the workbench 5, and a stepped structure 16 is arranged in an array on the surface of the coal dispersing plate 15; one end of the workbench 5 is provided with a diversion box 19 through a connecting block, an opening is arranged at the top of one end of the diversion box 19, a screening frame 20 is movably installed at the opening, a second vibrator 21 for driving the screening frame 20 to vibrate is arranged on the top of the diversion box 19, and the screening frame 20 is located below the end of the coal dispersing plate 15 with the hinge shaft; a Venturi feeder 22 communicated with the inlet pipe 2 is arranged at one end of the diversion box 19 away from the screening frame 20.

[0031] Through the flue gas diversion pipe 4, the high-temperature flue gas discharged from the interior of the coal-fired boiler 1 to the exhaust pipe 3 can be diverted into the heat exchange chamber 6 inside the workbench 5. A steam heater 8 is provided at the top of the workbench 5. The high-temperature flue gas entering the interior of the heat exchange chamber 6 transfers heat to the steam heater 8. After being heated by the high-temperature flue gas, the coal plate 15 penetrating through the interior of the steam heater 8 can be baked by the high temperature generated by the steam heater 8. Since the coal plate 15 is inclined, and a first vibrator 18 is provided at one end thereof, and the other end is connected to the steam heater 8 through a hinge shaft. Therefore, when the first vibrator 18 drives the coal plate 15 to vibrate, the pulverized coal sprinkled on the coal plate 15 can move along the inclined angle in the direction of the diversion box 19. By converting the heat of the high-temperature flue gas through the steam heater 8, it is possible to avoid the heat of the high-temperature flue gas being too high, resulting in the combustion of the pulverized coal. Moreover, through the steam heater 8, the preheating temperature of the pulverized coal can be controlled, so that the pulverized coal is always in an ambient temperature between 150°C and 300°C, ensuring the effective preheating of the pulverized coal on the premise of not self-igniting, which helps the pulverized coal to react with oxygen and burn rapidly after entering the combustion furnace, and at the same time reduces the generation of nitrogen oxides;

[0032] Since during the preheating process of the pulverized coal, it usually causes the pulverized coal to adhere to each other to form coal blocks, which will affect the transportation and combustion of the pulverized coal and may cause equipment blockage or unstable operation. The coal plate 15 has a stepped structure 16, which can increase the flow path of the pulverized coal on the coal plate 15, so that the pulverized coal is continuously disturbed during the falling process. This kind of disturbance can break the weak bond formed between the pulverized coal particles, prevent the pulverized coal from caking or disperse the caked pulverized coal; the inclined angle makes the pulverized coal slide downward by the action of gravity. During the sliding process, the pulverized coal will continuously impact the surface and steps of the coal plate 15, further breaking the lumps; and the first vibrator 18 can generate mechanical impact force, further disturbing the pulverized coal particles, making them separate from each other. Vibration not only helps to prevent the formation of new lumps, but also effectively disperses the already caked pulverized coal, greatly reducing the phenomenon of pulverized coal caking, improving the fluidity and combustion efficiency of the pulverized coal. At the same time, this design can also reduce the risk of equipment blockage, improving the operation stability and reliability of the system;

[0033] The pulverized coal passing through the coal plate 15 falls into the screening frame 20 on the diversion box 19. By the operation of the second vibrator 21, the screening frame 20 can be driven to vibrate, further dispersing the caked pulverized coal. After screening, the pulverized coal enters the Venturi feeder 22 through the diversion box 19, and after being mixed with gas, it enters the combustion furnace of the boiler, realizing the efficient and clean combustion of the pulverized coal and meeting the environmental protection requirements.

[0034] One end of the workbench 5 is provided with a smoke dividing pipe 4 communicating with the heat exchange chamber 6, and the other end of the workbench 5 is provided with a smoke outlet pipe 12 communicating with the heat exchange chamber 6. Inside the heat exchange chamber 6, there are heat exchange fins 7 for heating the steam heater 8.

[0035] The smoke dividing pipe 4 can guide the high-temperature flue gas in the smoke exhaust pipe 3 into the heat exchange chamber 6 of the workbench 5. Since there are heat exchange fins 7 in the heat exchange chamber 6, the high temperature in the flue gas can be transferred to the steam heater 8 to heat the steam heater 8. The flue gas after temperature conversion is discharged from the smoke outlet pipe 12 out of the heat exchange chamber 6 and enters the subsequent heat exchange process.

[0036] The steam heater 8 has a pressurizing function. An inlet water pipe 9 and a pressure relief valve 10 are respectively arranged on the steam heater 8, and a display screen 11 is also arranged on the steam heater 8.

[0037] The inlet water pipe 9 on the steam heater 8 is convenient for injecting water into the interior of the steam heater 8. Through the heat exchange fins 7, the high temperature in the flue gas can be transferred to the steam heater 8. After the steam heater 8 is heated, steam is formed inside it. The pressure relief valve 10 can control the pressure inside the steam heater 8 to ensure that the steam heater 8 can generate a temperature range between 150°C and 300°C, which is convenient for preheating the pulverized coal on the pulverized coal plate 15. The display screen 11 can accurately display various values such as the pressure and temperature inside, which is convenient for controlling the steam heater 8 to better preheat the pulverized coal.

[0038] One end of the first vibrator 18 is arranged above the bottom of the pulverized coal plate 15, and a storage box 13 is arranged above it. A feed hopper 14 is arranged at the bottom of the storage box 13, and a control valve is arranged at the bottom of the feed hopper 14.

[0039] A large amount of pulverized coal is stored inside the storage box 13. The pulverized coal falls onto the upper part of the pulverized coal plate 15 through the feed hopper 14. Since a control valve is arranged at the bottom of the feed hopper 14, it is convenient for the feed hopper 14 to control the falling speed of the pulverized coal onto the pulverized coal plate 15 and the amount of pulverized coal falling, better controlling the preheating effect of the pulverized coal, avoiding that too much pulverized coal cannot achieve the best preheating effect, and controlling the amount of pulverized coal can control the amount of pulverized coal entering the combustion chamber, ensuring the stable and efficient operation of the boiler, reducing pollutant emissions at the same time, and improving the overall economic efficiency.

[0040] The bottom plate of the diversion box 19 is inclined, and the horizontal height of the end of the bottom plate of the diversion box 19 close to the screening frame 20 is higher than the horizontal height of the end close to the feeder 22. The sieved pulverized coal is convenient to slide on the inclined bottom plate of the diversion box 19 towards the feeder 22.

[0041] The feeder 22 includes an inner housing 25 and an outer housing 24. There is a cavity between the inner housing 25 and the outer housing 24. The end of the diversion box 19 is connected to the cavity between the inner housing 25 and the outer housing 24. The same end of the inner housing 25 and the outer housing 24 is closed by an annular plate. The other end of the outer housing 24 is connected to the feed pipe 2 through a funnel-shaped structure. The interior of the inner housing 25 is connected to the cavity between the inner housing 25 and the outer housing 24 through a funnel-shaped structure. A fan 23 is provided at one end of the inner housing 25 away from the feed pipe 2. A fan blade 26 is provided inside the fan 23. A pipe communicating with the outside is provided on the side wall of the fan 23.

[0042] The pulverized coal enters the cavity between the inner housing 25 and the outer housing 24 of the feeder 22 through the diversion box 19. Since the fan 23 drives the fan blade 26 to rotate, the fan 23 can transport the external combustion-supporting gas or other gases to the inside of the boiler through the feed pipe 2. Due to the Venturi effect, when the fan 23 drives the gas into the boiler, a negative pressure will be formed between the inner housing 25 and the outer housing 24, driving the pulverized coal to mix with the gas driven by the fan 23, and then entering the boiler through the feed pipe 2. Due to the negative pressure formed by the Venturi effect, the opening of the diversion box 19 at the screening frame 20 will suck in the external gas into the diversion box 19, which can prevent a large amount of pulverized coal suspension from forming when the pulverized coal falls onto the screening frame 20, facilitating all the pulverized coal to be sucked into the diversion box 19 and enter the feeder 22, avoiding the floating of the pulverized coal suspension in the external environment and contact with static electricity, resulting in explosion, and improving the safety of the working environment.

[0043] Heat insulation curtains are respectively provided at both ends of the cavity of the steam heater 8. By providing the heat insulation curtains, the heat inside it can be better suppressed in the cavity of the steam heater 8, facilitating the effective preheating of the pulverized coal on the coal spreading plate 15, avoiding excessive heat dissipation, and reducing the preheating effect of the pulverized coal.

[0044] Embodiment 2

[0045] On the basis of Embodiment 1, a plurality of coal spreading columns 17 are provided on each of the stepped structures 16. The screening frame 20 includes a screening mesh, and coal spreading columns 17 are also provided on the screening mesh.

[0046] By providing the coal spreading columns 17, when the first vibrator 18 and the second vibrator 21 work, the coal spreading columns 17 can help the pulverized coal to be more evenly distributed on the coal spreading plate 15, and the mechanical energy generated by vibration is transmitted to the pulverized coal through the coal spreading columns 17, making it spread more evenly, reducing the phenomena of accumulation and segregation; at the same time, it can further prevent the pulverized coal from caking and fully break up the caked pulverized coal, ensuring the fluidity of the pulverized coal and the stability during combustion.

[0047] The above embodiments are only exemplary embodiments of the present invention and are not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the present invention.

Claims

1. A coal-fired boiler energy-saving device, comprising a coal-fired boiler (1), wherein a feed pipe (2) and an exhaust pipe (3) are respectively arranged on the coal-fired boiler (1), and it is characterized in that, On one side of the coal-fired boiler (1), there is a workbench (5). Inside the workbench (5), there is a heat exchange chamber (6). On the workbench (5), there is a steam heater (8). The exhaust pipe (3) is connected to the heat exchange chamber (6) through a smoke distribution pipe (4). The heat exchange chamber (6) is used to heat the steam heater (8). The middle of the steam heater (8) has a through cavity. Inside the cavity, there is a coal dispersion plate (15) for preventing coal powder caking. The coal dispersion plate (15) is inclined. Both ends of the coal dispersion plate (15) extend out of the steam heater (8). One end of the coal dispersion plate (15) is connected to the steam heater (8) through a hinge shaft. At the bottom of the other end of the coal dispersion plate (15), there is a first vibrator (18) installed on the workbench (5) for driving the coal dispersion plate (15) to vibrate. On the surface of the coal dispersion plate (15), there is an array of stepped structures (16). One end of the workbench (5) is provided with a diversion box (19) through a connecting block. At the top of one end of the diversion box (19), there is an opening. A screening frame (20) is movably installed at the opening. At the top of the diversion box (19), there is a second vibrator (21) for driving the screening frame (20) to vibrate. The screening frame (20) is located below the end of the coal dispersion plate (15) with the hinge shaft. At the end of the diversion box (19) away from the screening frame (20), there is a Venturi feeder (22) connected to the feed pipe (2). The steam heater (8) has a pressurizing function. An inlet pipe (9) and a pressure relief valve (10) are respectively arranged on the steam heater (8). A display screen (11) is also arranged on the steam heater (8). On each of the stepped structures (16), there are a plurality of coal dispersion columns (17). The screening frame (20) includes a screening net, and the screening net is also provided with coal dispersion columns (17).

2. The boiler coal-fired energy-saving device according to claim 1, characterized in that, One end of the workbench (5) is provided with a smoke distribution pipe (4) connected to the heat exchange chamber (6). The other end of the workbench (5) is provided with an outlet smoke pipe (12) connected to the heat exchange chamber (6). Inside the heat exchange chamber (6), there are heat exchange fins (7) for heating the steam heater (8).

3. The boiler coal-fired energy-saving device according to claim 2, wherein, Above one end of the bottom of the coal dispersion plate (15) where the first vibrator (18) is arranged, there is a storage box (13). At the bottom of the storage box (13), there is a feed hopper (14). At the bottom of the feed hopper (14), there is a control valve.

4. The boiler coal-fired energy-saving device according to claim 3, wherein The bottom plate of the diversion box (19) is inclined. The horizontal height of the end of the bottom plate of the diversion box (19) close to the screening frame (20) is higher than the horizontal height of the end close to the feeder (22).

5. The boiler coal-fired energy-saving device according to claim 4, characterized in that, The feeder (22) includes an inner housing (25) and an outer housing (24). There is a cavity between the inner housing (25) and the outer housing (24). The end of the diversion box (e19) is connected to the cavity between the inner housing (25) and the outer housing (24).

6. The coal-fired energy-saving device for a boiler according to claim 5, characterized in that One end of the inner housing (25) and the outer housing (24) is closed by an annular plate. The other end of the outer housing (24) is connected to the feed pipe (2) through a funnel-shaped structure. The interior of the inner housing (25) communicates with the cavity between the inner housing (25) and the outer housing (24) through a funnel-shaped structure. A blower (23) is provided at one end of the inner housing (25) away from the feed pipe (2). A fan blade (26) is provided inside the blower (23). A pipe communicating with the outside is provided on the side wall of the blower (23).

7. The coal-fired energy-saving device for a boiler according to claim 1, wherein Heat insulation curtains are respectively provided at both ends of the cavity of the steam heater (8).

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