Energy-saving tunnel kiln with flue gas circulation

Abstract

The application discloses a flue gas circulation energy-saving tunnel kiln, which comprises, from the kiln head to the kiln tail, a preheating zone, a sintering zone and a cooling zone arranged in sequence, wherein the preheating zone is located at the side of the kiln head sealing door, the upstream side of the preheating zone is provided with a circulating flue gas outlet, the downstream side of the sintering zone is provided with a fresh air inlet, the downstream side of the cooling zone is provided with a circulating flue gas inlet, the hot air zone is located at the side of the kiln tail sealing door, the downstream side of the hot air zone is provided with a cold air inlet, and the upstream side of the hot air zone is provided with a hot air outlet. The tunnel kiln is provided with the flue gas circulation heat exchange technology, meets the more stringent environmental protection emission standard, can realize one-time continuous sintering, has the characteristics of high efficiency and energy saving, can effectively improve the product qualified rate, and realizes large-scale continuous production of green and red bricks and tiles.

Description

Technical Field

[0001] This invention relates to tunnel kilns. More specifically, this invention relates to an energy-saving tunnel kiln with flue gas recirculation. Background Technology

[0002] As a type of continuous kiln, tunnel kilns have advantages over other types of kilns, such as shorter firing time, higher output, better product quality, better working conditions, and longer continuous service life. Tunnel kilns are now widely used for firing red bricks and tiles. Currently, China has mature technology for producing red bricks and tiles using tunnel kilns. However, there are still problems such as large ventilation volume inside the kiln, and the oxygen content in the flue gas is generally higher than 17%, resulting in a large amount of waste gas treatment, difficulty in meeting environmental protection standards, and high energy consumption.

[0003] Current tunnel kilns use a single channel, with fresh air for cooling and heat exchange. All fresh air becomes flue gas after passing through the tunnel kiln and is directly discharged. To meet the heat exchange requirements, the ventilation volume is huge. However, the calcination inside the kiln does not require such a large amount of air. This results in excessively high oxygen content in the flue gas. Most of the air is directly discharged, which inevitably takes away most of the heat. At the same time, the huge amount of flue gas to be treated makes the flue gas treatment facilities for tunnel kilns enormous, increasing investment and making it difficult to meet environmental protection requirements.

[0004] When firing blue bricks, the bricks and tiles that turn blue after reduction firing must be cooled in an oxygen-free reducing atmosphere to prevent them from re-oxidizing and turning red. The temperature inside the kiln must reach a safe temperature of 300-400℃ before they can be cooled to air and removed from the kiln. Current tunnel kilns have a high oxygen-air excess coefficient, which makes it impossible to achieve a reducing atmosphere in the cooling zone inside the kiln, so they can only produce red bricks. Tunnel kilns for firing blue bricks and tiles are very rare and have a complex structure. Existing tunnel kilns have limited oxygen-free cooling methods, making it difficult to achieve continuous production of blue bricks and tiles. Summary of the Invention

[0005] This invention provides a flue gas recirculation energy-saving tunnel kiln, which meets stricter environmental protection emission standards through flue gas recirculation heat exchange technology, can carry out continuous firing in one go, has the characteristics of high efficiency and energy saving, can effectively improve the product qualification rate, and realize large-scale continuous production of blue and red bricks and tiles.

[0006] To achieve these and other advantages according to the present invention, a flue gas recirculation energy-saving tunnel kiln is provided, comprising, sequentially arranged from the kiln head to the kiln tail:

[0007] The preheating zone is located on the side of the kiln head closed door, and a circulating flue gas outlet is provided on the upstream side of the preheating zone;

[0008] The firing zone has a fresh air inlet on its downstream side;

[0009] The cooling zone has a circulating flue gas inlet on its downstream side;

[0010] A hot air belt is located at the side of the kiln tail closing door, and a cold air inlet is arranged at the downstream side of the hot air belt, and a hot air outlet is arranged at the upstream side of the hot air belt;

[0011] The first circulating heat preservation pipeline is provided outside the kiln, a circulating fan is arranged on the first circulating heat preservation pipeline, an air inlet of the circulating fan is communicated with the circulating flue gas outlet, an air outlet of the circulating fan is communicated with the circulating flue gas inlet, and the air outlet of the circulating fan is further communicated with a flue gas inlet of a flue gas treatment facility through a flue gas treatment pipeline, and a flue gas outlet of the flue gas treatment facility is communicated with a smoke stack.

[0012] A cold air fan is further arranged outside the kiln, and an air outlet of the cold air fan is communicated with the cold air inlet.

[0013] A fresh air fan is further arranged outside the kiln, an air inlet of the fresh air fan is communicated with the hot air outlet, and an air outlet of the fresh air fan is communicated with the fresh air inlet, and a first air curtain is formed by being sprayed into the kiln.

[0014] A wind curtain fan is further arranged outside the kiln, an air inlet of the wind curtain fan is communicated with the hot air outlet, and an air outlet of the wind curtain fan is communicated with a wind curtain air inlet, a second air curtain is formed by being sprayed into the kiln, and the upstream side of the second air curtain is the cooling belt, and the downstream side of the second air curtain is the hot air belt.

[0015] A drying chamber, a drying air fan and a dehumidification air fan are further arranged outside the kiln, the drying chamber is arranged in parallel with the tunnel kiln, the drying chamber is provided with an air inlet and an air outlet, an air inlet of the drying air fan is communicated with the hot air outlet, an air outlet of the drying air fan is communicated with the air inlet of the drying chamber, the air outlet of the drying chamber is communicated with the air inlet of the dehumidification air fan, and an air outlet of the dehumidification air fan is communicated with a dehumidification smoke stack.

[0016] The air volume ratio of the drying air fan to the fresh air fan is a drying coefficient, and is controlled to be 2-7.

[0017] Preferably, a heat exchanger is further arranged on the first circulating heat preservation pipeline, and the heat exchanger is provided with a flue gas inlet, a flue gas outlet, a cold air inlet and a hot air outlet.

[0018] The flue gas outlet of the circulating flue gas is communicated with the flue gas inlet of the heat exchanger, and the air inlet of the circulating fan is communicated with the flue gas outlet of the heat exchanger.

[0019] The air outlet of the fresh air fan is communicated with the cold air inlet of the heat exchanger, and the fresh air inlet is communicated with the hot air outlet of the heat exchanger.

[0020] Preferably, the cross section of the sintering belt is larger than that of the preheating belt, the cooling belt and the hot air belt, and a bypass air duct is formed at the side or top of the sintering belt.

[0021] Preferably, the new air is air or oxygen-enriched air, which is sprayed into the kiln through the new air inlet during internal combustion baking; the new air is mixed with fuel to generate hot air, which is sprayed into the kiln through the new air inlet during external combustion baking; and the fuel is sprayed into the kiln through the new air inlet along with the new air during mixed internal and external combustion baking.

[0022] Preferably, movable cutoff doors are arranged between the preheating zone, the firing zone, the cooling zone, and the hot air zone, and when the kiln car is running, all the fans stop running, and all the movable cutoff doors are opened simultaneously or sequentially, and when the kiln car stops, all the movable cutoff doors are closed simultaneously, and the preheating zone, the firing zone, the cooling zone, and the hot air zone form four independent spaces, and all the fans start running.

[0023] The downstream side of the preheating zone is further provided with a high-temperature flue gas inlet.

[0024] The new air inlet on the downstream side of the firing zone is replaced by a hot air inlet, and the upstream side of the firing zone is further provided with a hot flue gas outlet.

[0025] The upstream side of the cooling zone is further provided with a high-temperature flue gas outlet.

[0026] The air curtain fan and the air curtain air inlet are cancelled.

[0027] The second circulating heat preservation pipeline is further arranged outside the kiln, and the second circulating heat preservation pipeline is in communication with the high-temperature flue gas inlet and the high-temperature flue gas outlet, respectively.

[0028] The air outlet of the new air fan is in communication with the hot air inlet.

[0029] The flue gas inlet of the flue gas treatment facility is in communication with the hot flue gas outlet.

[0030] The oxygen content in the flue gas treatment pipeline is an oxygen index, and the control range is 0-17%.

[0031] The carbon monoxide content in the first circulating heat preservation pipeline and the second circulating heat preservation pipeline is a reduction index, and the control range during firing is 0-7.5%.

[0032] Preferably, a heat exchanger is further arranged on the flue gas treatment pipeline, which is provided with a flue gas inlet, a flue gas outlet, a cold air inlet, and a hot air outlet.

[0033] The hot flue gas outlet is in communication with the flue gas inlet of the heat exchanger, and the flue gas inlet of the flue gas treatment facility is in communication with the flue gas outlet of the heat exchanger.

[0034] The air outlet of the new air fan is in communication with the cold air inlet of the heat exchanger, and the hot air inlet is in communication with the hot air outlet of the heat exchanger.

[0035] Preferably, the reduction index is controlled in the range of 1.0-7.5% during the firing of the green bricks.

[0036] Preferably, a third circulating heat preservation pipeline is further arranged outside the kiln, which is in communication with the air outlet of the circulating fan and the hot air inlet, and a flow regulating valve is further arranged on the third circulating heat preservation pipeline.

[0037] Preferably, inward protruding strips are arranged on the top and side walls of the preheating zone and the cooling zone to form a corrugated structure.

[0038] Preferably, a boiler is arranged on the top of the firing zone, and the boiler exhaust pipe is in contact with the flue gas of the firing zone for heat exchange.

[0039] The present application at least includes the following beneficial effects:

[0040] The tunnel kiln of the present application meets the more stringent environmental protection emission standards through the flue gas circulation heat exchange technology, can perform one-time continuous firing, has the characteristics of high efficiency and energy saving, can effectively improve the product qualification rate, and realizes large-scale continuous production of green and red bricks.

[0041] The tunnel kiln of the present application is divided into four parts, including a preheating zone, a firing zone, a cooling zone and a hot air zone. The preheating zone and the cooling zone adopt circulating flue gas heat exchange, the firing zone adopts independent combustion of fresh air, and the hot air zone adopts fresh air cooling to provide hot air for the calcination of the firing zone and the drying of the drying chamber. The present application adopts circulating flue gas heat exchange to solve the contradiction between the large demand for heat exchange air and the small demand for calcination air through a special structure, effectively reduces the amount of flue gas discharged, and has significant energy saving and environmental protection effects. At the same time, when the circulating flue gas adopts a reducing atmosphere, it can realize large-scale continuous production of antique green bricks, solving the current industry problem.

[0042] The present application adopts circulating flue gas to complete heat exchange and adopts fresh air with high oxygen content to complete combustion. The two systems can be completely independent, thereby meeting the requirement of flue gas heat exchange in the cooling process using a reducing atmosphere for green bricks, producing antique green bricks, and realizing the step change of products between red and green through the control of oxygen content and reducing atmosphere in the circulating flue gas.

[0043] Other advantages, objects and features of the present application will be partly embodied in the following description, and partly understood by those skilled in the art through research and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The figure is a structural schematic diagram of one technical solution of the present application;

[0045] Figure 2 The figure is a structural schematic diagram of one technical solution of the present application;

[0046] Figure 3 This is a schematic diagram of the structure of one technical solution of the present invention;

[0047] Figure 4 This is a schematic diagram of the structure of one technical solution of the present invention;

[0048] Figure 5 This is a schematic diagram of the structure of one technical solution of the present invention. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0050] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0051] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods, and the reagents and materials mentioned are commercially available. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "setting" should be interpreted broadly. For example, they can refer to fixed connection or setting, detachable connection or setting, or integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0052] like Figure 1 As shown, this invention provides a flue gas recirculation energy-saving tunnel kiln, defined by the kiln car entering the tunnel kiln as the kiln head position and upstream, including the following sequentially arranged from the kiln head to the kiln tail:

[0053] Preheating zone 1 is located on the side of the kiln head closed door, and a circulating flue gas outlet is provided on the upstream side of the preheating zone 1;

[0054] The firing zone 2 has a fresh air inlet on its downstream side;

[0055] Cooling zone 3 has a circulating flue gas inlet on its downstream side;

[0056] A hot air zone 4 is located at the side of the kiln tail closing door, and a cold air inlet is arranged at the downstream side of the hot air zone 4, and a hot air outlet is arranged at the upstream side of the hot air zone 4;

[0057] The first circulating heat preservation pipeline 5 is arranged outside the kiln, and a circulating fan 6 is arranged on the first circulating heat preservation pipeline 5, the air inlet of the circulating fan 6 is communicated with the circulating flue gas outlet, the air outlet of the circulating fan 6 is communicated with the circulating flue gas inlet, and the air outlet of the circulating fan 6 is further communicated with the flue gas inlet of the flue gas treatment facility 7 through the flue gas treatment pipeline, and the flue gas outlet of the flue gas treatment facility 7 is communicated with the exhaust flue 8;

[0058] A cold air fan 9 is further arranged outside the kiln, and the air outlet of the cold air fan 9 is communicated with the cold air inlet;

[0059] A fresh air fan 10 is further arranged outside the kiln, the air inlet of the fresh air fan 10 is communicated with the hot air outlet, the air outlet of the fresh air fan 10 is communicated with the fresh air inlet, and the first air curtain is formed by being sprayed into the kiln;

[0060] A wind curtain fan 11 is further arranged outside the kiln, the air inlet of the wind curtain fan 11 is communicated with the hot air outlet, the air outlet of the wind curtain fan 11 is communicated with the wind curtain air inlet, and the second air curtain is formed by being sprayed into the kiln, and the upstream side of the second air curtain is the cooling zone 3 and the downstream side is the hot air zone 4;

[0061] A drying chamber 12, a drying fan 13 and a dehumidification fan 14 are further arranged outside the kiln, the drying chamber 12 is arranged in parallel with the tunnel kiln, the drying chamber 12 is provided with an air inlet and an air outlet, the air inlet of the drying fan 13 is communicated with the hot air outlet, the air outlet of the drying fan 13 is communicated with the air inlet of the drying chamber 12, the air outlet of the drying chamber 12 is communicated with the air inlet of the dehumidification fan 14, and the air outlet of the dehumidification fan 14 is communicated with the dehumidification flue 15;

[0062] The air volume ratio of the drying fan 13 to the fresh air fan 10 is a drying coefficient, and is controlled to be 2-7.

[0063] In the above technical solution, the tunnel kiln is connected to the drying chamber 12, the brick billets are placed on the kiln cars, and multiple kiln cars are connected in series in the drying chamber 12 for drying, which ensures that the moisture of the brick billets entering the kiln is reduced to within 5%, effectively controls the moisture content of the circulating flue gas, is convenient to operate, and the kiln car platform adopts a two-layer platform design. Ventilation channels are arranged in the two-layer platform. During calcination, hot air is directly sprayed into the ventilation channels in the two-layer platform and then returns to the brick stacks placed in the upper layer. This is beneficial to ventilation in the kiln and is more suitable for the firing of medium and high-end products such as plaza bricks. After drying, the kiln cars pass through the preheating zone 1, the firing zone 2, the cooling zone 3, and the hot air zone 4 of the calcining kiln in sequence. The drying coefficient is an important indicator for measuring the drying efficiency of the drying chamber 12 and is also an important indicator for measuring the thermal efficiency of the calcining kiln. The present technology can provide better cooling for the finished bricks by increasing the hot air zone 4, and the provided hot air does not contain flue gas, so that the drying air in the drying chamber 12 does not contain sulfur, and the dust content can easily meet the standard and can be directly discharged, which also meets more stringent environmental protection requirements, and reduces the air handling volume, which is beneficial to reducing costs.

[0064] In the preheating zone 1 of the tunnel kiln, flue gas preheating is used. The circulating flue gas and the brick billets on the kiln cars in the preheating zone 1 exchange heat and dry in countercurrent. Preheating with flue gas circulation can increase the air speed in the kiln without increasing the oxygen content, which is beneficial to the heat exchange between the flue gas and the brick billets. Under the condition of meeting the heat exchange requirement, the oxygen content can be effectively controlled to be very low or even to reach a reducing atmosphere.

[0065] In the firing zone 2 of the tunnel kiln, independent calcination is used. The firing zone 2 sprays as much new air as possible to increase the oxygen content in the firing zone 2. By controlling the amount of new air in the firing zone 2, the oxygen content in the flue gas can be controlled to be in a reducing atmosphere or an oxidizing atmosphere, so that the product appearance is blue or red, and color control can also be achieved.

[0066] In the cooling zone 3 of the tunnel kiln, flue gas cooling is used. The circulating flue gas and the bricks on the kiln cars in the cooling zone 3 exchange heat in countercurrent. All the flue gas is circulated and cooled without adding new air. The air volume for preheating and cooling does not affect the calcination air volume. The circulating flue gas volume can be increased to improve the thermal efficiency of the kiln.

[0067] In the hot air zone 4 of the tunnel kiln, cold air heat exchange is used. All the air entering the hot air zone 4 is cold air, which is pure air. The fired bricks continue to exchange heat and cool in the hot air zone 4, generating hot air. After heat exchange, the hot air is supplied to the drying chamber 12 for drying brick billets, or to the firing zone 2 for new air into the kiln for calcination, ensuring that the finished brick temperature is low, and the heat is utilized to the maximum extent to achieve the purpose of energy saving.

[0068] The flue gas circulation technology based on the present technical solution can greatly reduce the flue gas emission, reduce the flue gas treatment capacity, and reduce the heat carried away by unnecessary flue gas emission. It can achieve more stringent energy-saving standards.

[0069] In another technical solution, as shown in Figure 2 The first circulating heat preservation pipeline 5 is further provided with a heat exchanger 20, which is provided with a flue gas inlet, a flue gas outlet, a cold air inlet and a hot air outlet.

[0070] The circulating flue gas outlet is communicated with the flue gas inlet of the heat exchanger 20, and the air inlet of the circulating fan 6 is communicated with the flue gas outlet of the heat exchanger 20.

[0071] The air outlet of the fresh air fan 10 is communicated with the cold air inlet of the heat exchanger 20, and the fresh air inlet is communicated with the hot air outlet of the heat exchanger 20.

[0072] In the above technical solution, when the heat exchanger 20 is a boiler, steam or hot water can be supplied externally, and the heat exchanger 20 can also be used as a heater of a power generation boiler; when the heat exchanger 20 is a gas heat exchanger, the fresh air is heated by the heat exchanger 20, so that the inlet air temperature of the cooling zone 3 is controlled, the heat entering the kiln is reduced, the outlet temperature of the circulating flue gas is indirectly reduced, and the brick billets in the preheating zone 1 are prevented from being heated by the flue gas with too high temperature, so that the brick billets are not damaged due to large temperature difference.

[0073] In another technical solution, the cross section of the firing zone 2 is larger than that of the preheating zone 1, the cooling zone 3 and the hot air zone 4, and a bypass air duct is formed on the side or top of the firing zone 2.

[0074] In the above technical solution, the cross section of the firing zone 2 is enlarged on the side, and the cross section of the ventilation duct is increased. The bypass air duct is added on the side or top of the brick stack in the firing zone 2, so that the circulating flue gas passes through the bypass air duct as much as possible and passes through the middle of the brick stack as little as possible, thereby reducing the oxygen content in the fresh air.

[0075] In another technical solution, when internal combustion firing is performed, the fresh air is air or oxygen-enriched air, which is injected into the kiln through the fresh air inlet; when external combustion firing is performed, the fresh air is mixed with fuel to generate hot air, which is injected into the kiln through the fresh air inlet; when internal combustion and external combustion mixed firing is performed, the fuel is injected into the kiln through the fresh air inlet together with the fresh air.

[0076] In the above technical solution, the oxygen content in the firing zone 2 is increased, and the fuel is fully mixed and combusted when the oxygen content is high, so as to improve the combustion efficiency.

[0077] In another technical solution, as shown in Figure 3 The preheating zone 1, the firing zone 2, the cooling zone 3 and the hot air zone 4 are all provided with movable stop doors 19. When the kiln car is running, all the fans stop running, all the movable stop doors 19 are opened at the same time or in sequence, and when the kiln car stops, all the movable stop doors 19 are closed at the same time. The preheating zone 1, the firing zone 2, the cooling zone 3 and the hot air zone 4 form four independent spaces, and all the fans start running.

[0078] The high-temperature flue gas inlet is further arranged on the downstream side of the preheating zone 1.

[0079] The fresh air inlet on the downstream side of the firing zone 2 is replaced by a hot air inlet, and a hot flue gas outlet is further arranged on the upstream side of the firing zone 2.

[0080] A high-temperature flue gas outlet is further arranged on the upstream side of the cooling zone 3.

[0081] The air curtain fan 11 and the air curtain air inlet are cancelled.

[0082] The second circulating heat preservation pipeline 16 is further arranged outside the kiln, and the second circulating heat preservation pipeline 16 is in communication with the high-temperature flue gas inlet and the high-temperature flue gas outlet respectively.

[0083] The air outlet of the fresh air fan 10 is changed to be in communication with the hot air inlet.

[0084] The flue gas inlet of the flue gas treatment facility 7 is changed to be in communication with the hot flue gas outlet.

[0085] The oxygen content in the flue gas treatment pipeline is an oxygen index, and the control range is 0-17%.

[0086] The carbon monoxide content in the first circulating heat preservation pipeline 5 and the second circulating heat preservation pipeline 16 is a reduction index, and the control range during firing is 0-7.5%.

[0087] In the above technical solution, the kiln is divided into sections by arranging the kiln head sealing door, the kiln tail sealing door and the movable cutoff door 19, and each set of double-layer kiln door is spaced apart by a distance of one kiln car, so that the kiln can be better sealed, and the air volume and the oxygen content and the carbon monoxide content can be more easily controlled. The second circulating heat preservation pipeline 16 is arranged, the circulating flue gas and the fresh air are operated separately, and completely independently, so that the oxygen content is not limited by the circulating air volume, and the oxygen content can be independently controlled without affecting the reduction control of the circulating flue gas. When the firing zone 2 independently burns, the oxygen index is controlled to independently control the oxygen content of the exhaust flue gas, so that the air excess coefficient is as low as possible, the heat carried away by the exhaust flue gas is reduced, and the treatment amount of the flue gas is reduced, and the equipment investment is reduced.

[0088] In the cooling zone 3, the flue gas is in a reducing atmosphere, the reduction index is controlled to independently control the carbon monoxide content in the circulating flue gas, the reduction ability of the circulating flue gas is controllable, and the bricks are cooled in a certain degree of reducing atmosphere after firing, so as to achieve the purpose of producing green bricks.

[0089] In actual production, the oxygen content and the reduction atmosphere in the circulating flue gas can be controlled to realize the step change between red and green products, and the specific mode is as follows:

[0090] The ratio of oxygen to reducing gas in the circulating flue gas is controlled. When the reducing gas exceeds 0.5% and the oxygen is less than 1%, the surface of the brick is more than 80% blue. When the reducing gas is less than 0.5% and the oxygen is less than 1%, the surface of the brick will show partial blue, with an area ratio of less than 80%. As the ratio changes, the blue and red colors will change in a stepwise manner. Of course, this color is also related to the cooling rate. The faster the cooling rate, the higher the proportion of red.

[0091] In another technical solution, such as Figure 4 As shown, the flue gas treatment pipeline is also equipped with a heat exchanger 20, which has a flue gas inlet, a flue gas outlet, a cold air inlet, and a hot air outlet;

[0092] The hot flue gas outlet is now connected to the flue gas inlet of the heat exchanger 20, and the flue gas inlet of the flue gas treatment facility 7 is now connected to the flue gas outlet of the heat exchanger 20.

[0093] The air outlet of the fresh air unit 10 is now connected to the cold air inlet of the heat exchanger 20, and the hot air inlet is now connected to the hot air outlet of the heat exchanger 20.

[0094] In the above technical solution, the exhaust gas is directly discharged in the firing zone 2. The high temperature of the exhaust gas will take away a lot of heat. The heat is effectively recovered through the heat exchanger 20 and the hot air temperature is further increased to achieve the purpose of energy saving. The energy of the heat exchanger 20 can be connected to fresh air for external heating, or it can absorb energy from hot water or steam boilers and supply heat to the outside.

[0095] In another technical solution, the reduction index is controlled within the range of 1.0 to 7.5% when firing blue bricks.

[0096] In the above technical solution, when firing blue bricks, the reduction index is controlled between 1.0 and 7.5%, so that the bricks are reduced and cooled during the cooling process after firing, thus realizing the firing of blue bricks in a tunnel kiln.

[0097] In another technical solution, such as Figure 5 As shown, a third circulating heat preservation pipe 17 is also provided outside the kiln. The third circulating heat preservation pipe 17 is connected to the air outlet of the circulating fan 6 and the hot air inlet, respectively. A flow regulating valve 18 is also provided on the third circulating heat preservation pipe 17.

[0098] In the above technical solution, a portion of flue gas is added to the firing zone 2 to reduce the oxygen content during firing in the firing zone 2, thereby reducing the generation of nitrogen oxides and meeting higher environmental protection requirements.

[0099] In another technical solution, the top and side walls of the preheating zone 1 and the cooling zone 3 are provided with inward protruding strips to form a corrugated structure.

[0100] In the above technical solution, the kiln side wind resistance is increased, so that more wind passes through the gaps between the brick billets, and invalid ventilation is reduced.

[0101] In another technical solution, a boiler is arranged on the top of the firing zone 2, and the boiler is in contact with the flue gas of the firing zone 2 to exchange heat.

[0102] In the above technical solution, the heat taken away by the exhaust flue gas is reduced, and the heat of the flue gas is recovered.

[0103] The number of devices and the processing scale described herein are used to simplify the description of the present application. The application, modification and change of the present application are obvious to those skilled in the art.

[0104] Although the embodiments of the present application have been disclosed as above, it is not limited to the application and the modification and change of the present application are obvious to those skilled in the art. Therefore, the present application is not limited to the specific details and the figures shown and described herein, and the general concept defined by the claims and the equivalent scope.

Claims

1. A flue gas recirculation energy-saving tunnel kiln, characterized in that, Including those arranged sequentially from the kiln head to the kiln tail: The preheating zone is located on the side of the kiln head closed door, and a circulating flue gas outlet is provided on the upstream side of the preheating zone; The firing zone has a fresh air inlet on its downstream side; The cooling zone has a circulating flue gas inlet on its downstream side; A hot air belt is located on the side of the kiln tail closed door. A cold air inlet is provided on the downstream side of the hot air belt, and a hot air outlet is provided on the upstream side. The kiln is equipped with a first circulating insulation pipe, and a circulating fan is installed on the first circulating insulation pipe. The air inlet of the circulating fan is connected to the circulating flue gas outlet, and the air outlet of the circulating fan is connected to the circulating flue gas inlet. The air outlet of the circulating fan is also connected to the flue gas inlet of the flue gas treatment facility through a flue gas treatment pipe. The flue gas outlet of the flue gas treatment facility is connected to the exhaust chimney. A cold air fan is also installed outside the kiln, and the air outlet of the cold air fan is connected to the cold air inlet; A fresh air fan is also installed outside the kiln. The air inlet of the fresh air fan is connected to the hot air outlet, and the air outlet of the fresh air fan is connected to the fresh air inlet, which sprays into the kiln to form the first air curtain. An air curtain fan is also installed outside the kiln. The air inlet of the air curtain fan is connected to the hot air outlet, and the air outlet of the air curtain fan is connected to the air curtain inlet. The air is sprayed into the kiln to form a second air curtain. The upstream side of the second air curtain is the cooling zone, and the downstream side is the hot air zone. A drying chamber, a drying fan, and an exhaust fan are also provided outside the kiln. The drying chamber and the tunnel kiln are arranged side by side. The drying chamber is provided with an air inlet and an air outlet. The air inlet of the drying fan is connected to the hot air outlet. The air outlet of the drying fan is connected to the air inlet of the drying chamber. The air outlet of the drying chamber is connected to the air inlet of the exhaust fan. The air outlet of the exhaust fan is connected to the exhaust chimney. The air volume ratio between the drying fan and the fresh air fan is the drying coefficient, which is controlled between 2 and 7. The cross-section of the firing zone is larger than that of the preheating zone, cooling zone, and hot air zone, and a bypass air duct is formed on the side or top of the firing zone; A boiler is installed at the top of the firing zone, and the boiler pipes exchange heat with the flue gas in the firing zone.

2. The flue gas recirculation energy-saving tunnel kiln as described in claim 1, characterized in that, The first circulating insulation pipeline is also equipped with a heat exchanger, which has a flue gas inlet, a flue gas outlet, a cold air inlet, and a hot air outlet; The circulating flue gas outlet is now connected to the flue gas inlet of the heat exchanger, and the air inlet of the circulating fan is now connected to the flue gas outlet of the heat exchanger. The air outlet of the fresh air unit is now connected to the cold air inlet of the heat exchanger, and the fresh air inlet is now connected to the hot air outlet of the heat exchanger.

3. The flue gas recirculation energy-saving tunnel kiln as described in claim 1 or 2, characterized in that, During internal combustion roasting, the fresh air is air or oxygen-enriched air, which is injected into the kiln through the fresh air inlet; during external combustion roasting, the fresh air is mixed with the fuel and then burned to generate hot air, which is injected into the kiln through the fresh air inlet; during mixed internal and external combustion roasting, the fuel is injected into the kiln along with the fresh air through the fresh air inlet.

4. The flue gas recirculation energy-saving tunnel kiln as described in claim 1, characterized in that, Movable shut-off doors are installed between the preheating zone, firing zone, cooling zone, and hot air zone. When the kiln car moves, all the fans stop running and all the movable shut-off doors open simultaneously or in sequence. When the kiln car stops, all the movable shut-off doors close simultaneously. The preheating zone, firing zone, cooling zone, and hot air zone form four independent spaces, and all the fans start running. A high-temperature flue gas inlet is also provided on the downstream side of the preheating zone; A hot flue gas outlet is also provided on the upstream side of the firing zone; A high-temperature flue gas outlet is also provided on the upstream side of the cooling zone; The air curtain fan and air curtain inlet have been removed. A second circulating insulation pipe is also installed outside the kiln, which is connected to the high-temperature flue gas inlet and the high-temperature flue gas outlet respectively. The flue gas inlet of the flue gas treatment facility is now connected to the hot flue gas outlet. The oxygen content in the flue gas treatment pipeline is measured by the oxygen index, with a control range of 0-17%. The carbon monoxide content in the first and second circulating insulation pipes is the reduction index, and the range during firing is controlled at 0~7.5%.

5. The flue gas recirculation energy-saving tunnel kiln as described in claim 4, characterized in that, The flue gas treatment pipeline is also equipped with a heat exchanger, which has a flue gas inlet, a flue gas outlet, a cold air inlet, and a hot air outlet; The hot flue gas outlet is now connected to the flue gas inlet of the heat exchanger, and the flue gas inlet of the flue gas treatment facility is now connected to the flue gas outlet of the heat exchanger. The air outlet of the fresh air unit is now connected to the cold air inlet of the heat exchanger, and the fresh air inlet on the downstream side of the firing zone is now connected to the hot air outlet of the heat exchanger.

6. The flue gas recirculation energy-saving tunnel kiln as described in claim 4 or 5, characterized in that, The reduction index should be controlled within the range of 1.0 to 7.5% when firing blue bricks.

7. The flue gas recirculation energy-saving tunnel kiln as described in claim 4, characterized in that, A third circulating insulation pipe is also installed outside the kiln. The third circulating insulation pipe is connected to the air outlet of the circulating fan and the fresh air inlet on the downstream side of the firing zone. A flow regulating valve is also installed on the third circulating insulation pipe.

8. The flue gas recirculation energy-saving tunnel kiln as described in claim 1, characterized in that, The top and side walls of the preheating zone and cooling zone are provided with inwardly protruding strips, forming a corrugated structure.

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