An all-oxygen combustion system with bypass air release and its process method

Abstract

The present invention relates to an all-oxygen combustion system with bypass air release and its process principle, which includes a grate cooler (5), a rotary kiln (4), a smoke chamber (3), a precalciner (2), a preheater (1) and a waste heat boiler (7) arranged in sequence along the gas path, and also includes a tertiary air duct (6) connected between the precalciner (2) and the rotary kiln (4); it further includes a kiln tail flue gas circulation system (8), a bypass air release system (9), an oxygen supply system (10) and a carbon dioxide capture and purification system (11); the present invention can realize the co-disposal of waste in a cement kiln and the enrichment of carbon dioxide in all-oxygen combustion, reduce the harmful components in the cement kiln system through the bypass air release system, ensure the normal and stable operation of the system, realize the enrichment of carbon dioxide at the same time, combine the cooling, circulation of the high-temperature flue gas of the whole system with all-oxygen supply, basically no air enters the system, and the nitrogen amount entering the system is reduced to the greatest extent, and the generation of NOx can be reduced significantly.

Description

Technical Field

[0001] The present invention relates to an all-oxygen combustion system with bypass air release and its process method. Background Art

[0002] According to the raw material characteristics and calcination process system of the cement industry itself, the cement kiln is an ideal place for disposing of waste. In particular, the cement kiln system with a preheating and pre-calcination system is more suitable for co-disposal of waste. However, most waste contains elements harmful to the calcination of cement clinker, such as potassium, sodium, sulfur, chlorine, etc. These elements are likely to form eutectic compounds in the cyclone tubes in the high-temperature sections of the decomposition furnace, smoke chamber, and preheater, resulting in material blockage and crust formation, affecting the normal operation of the cement kiln system. A bypass air release system is designed in the smoke chamber to extract harmful elements in the high-temperature gaseous state to the bypass air release system, reducing the impact of harmful elements. Generally, the extracted flue gas is cooled by mixing with air, and harmful elements form solids at low temperatures and are discharged from the system along with the dust collected by the dust collector. The waste gas is purified and then discharged into the atmosphere.

[0003] The existing cement combustion system cannot effectively, quickly, and at low cost capture carbon dioxide. A large amount of carbon dioxide is discharged outward, which not only pollutes the environment but also leads to a relatively high nitrogen content in the flue gas, and then a large amount of NOx is generated, thus having an adverse impact on the normal operation of the system. Therefore, it is urgently needed to be solved. Summary of the Invention

[0004] Aiming at the current situation of the above-mentioned prior art, the technical problem to be solved by the present invention is to provide an all-oxygen combustion system with bypass air release and its process method, which can reduce the harmful components in the cement kiln system to ensure the normal and stable operation of the system, and at the same time, can greatly reduce the amount of nitrogen entering the system to significantly reduce the generation of NOx, and can efficiently enrich carbon dioxide to achieve zero emissions of carbon dioxide and reduce the capture cost.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows: An all-oxygen combustion system with bypass air bleed, including a grate cooler, a rotary kiln, a smoke chamber, a precalciner, a preheater, and a waste heat boiler arranged in sequence along the gas path, further including a tertiary air duct connected between the precalciner and the rotary kiln, characterized in that it further includes a kiln tail flue gas circulation system, a bypass air bleed system, an oxygen supply system, and a carbon dioxide capture and purification system; the kiln tail flue gas circulation system includes a first dust collector and a first circulation fan, the air inlet of the first dust collector is connected to the air outlet of the waste heat boiler, the air outlet of the first dust collector is connected to the air inlet of the first circulation fan, and the air outlet of the first circulation fan is formed with a first pipeline, a second pipeline, and a third pipeline arranged in parallel; the bypass air bleed system includes a smoke chamber extraction duct, a mixing chamber, a second dust collector, and a second circulation fan; both ends of the smoke chamber extraction duct are internally communicated with the smoke chamber and the mixing chamber respectively, the air inlet of the second dust collector is connected to the air outlet of the mixing chamber, the air outlet of the second dust collector is connected to the air inlet of the second circulation fan, and the air outlet of the second circulation fan is connected to the interior of the front chamber of the grate cooler; the end of the first pipeline is connected to the mixing chamber, the end of the second pipeline is connected in parallel with the air outlet of the oxygen supply system and then connected to the interior of the front chamber of the grate cooler, and the end of the third pipeline is connected to the air inlet of the carbon dioxide capture and purification system.

[0006] Preferably, a first control valve is further provided on the first pipeline, a second control valve is further provided on the second pipeline, and a third control valve is further provided on the third pipeline.

[0007] Preferably, a condensation water remover is further provided between the air outlet of the first dust collector and the air inlet of the first circulation fan.

[0008] Preferably, a high-temperature resistant air valve is further provided on the smoke chamber extraction duct.

[0009] A process method of an all-oxygen combustion system with bypass air bleed, characterized by including the following steps:

[0010] S1: The hot flue gas extracted from the smoke chamber by the bypass air bleed system sequentially enters the mixing chamber, the second dust collector, and the second circulation fan; the circulating flue gas in the first pipeline is mixed with the hot flue gas extracted from the smoke chamber in the mixing chamber to form low-temperature mixed flue gas, which enters the second dust collector, and then is introduced into the front chamber of the grate cooler through the second circulation fan; the second pipeline converges with the oxygen supply system to form a gas mainly composed of CO 2 , O 2 , and together with the low-temperature mixed flue gas from the bypass air bleed system, is blown into the front chamber of the grate cooler. By exchanging heat with the high-temperature clinker introduced into the grate cooler by the rotary kiln, a hot gas mainly composed of CO 2 , O 2 is formed and enters the rotary kiln and the precalciner respectively for fuel combustion in the rotary kiln and the precalciner.

[0011] S2: In the rotary kiln and the precalciner, fuel burns and carbonates in the cement raw meal decompose to form flue gas with a higher carbon dioxide concentration, which enters the preheater and exchanges heat with the raw meal fed into the preheater. The preheated raw meal is sent to the precalciner for carbonate decomposition. At the same time, the high-temperature flue gas is preheated and absorbed by the raw meal to form medium- and low-temperature flue gas, which is then discharged from the preheater and enters the waste heat boiler.

[0012] S3: The kiln tail recycle flue gas consists of two parts. One part is formed by mixing the low-temperature flue gas from the bypass air extraction system of the smoke chamber and the flue gas in the first pipeline after the waste gas at the outlet of the preheater is cooled. The other part of the flue gas is the flue gas in the second pipeline after the waste gas at the outlet of the preheater is cooled. The two-way flue gas and the pure oxygen provided by the oxygen supply system enter the front chamber of the grate cooler together; the flue gas in the third pipeline after the waste gas at the outlet of the preheater is sent to the carbon dioxide capture and purification system. This part of the flue gas is flue gas with a high carbon dioxide concentration, and its capture and purification are carried out. Compared with the capture and purification of flue gas in a conventional cement kiln system, the capture efficiency is higher and the cost is lower.

[0013] S4: By adjusting the recycle flue gas and the proportion of pure oxygen, the oxygen content in the mixed flue gas entering the front chamber of the grate cooler is controlled at 21 - 35%, and the carbon dioxide content is controlled at 40 - 75%. This not only meets the relatively high carbon dioxide concentration in the flue gas but also ensures the oxygen amount required for fuel combustion in the precalciner and the rotary kiln, further ensuring the fuel combustion rate and high burnout rate, and providing a guarantee for the stable and reliable thermal process system of the cement kiln system.

[0014] S5: The oxygen supply system divides the oxygen into two paths. One path converges with the flue gas in the second pipeline at the outlet of the first recycle fan to form a cooling gas mainly composed of CO 2 、O 2 and enters the front chamber of the grate cooler; the other path converges with the flue gas at the outlet of the second recycle fan to form a cooling gas mainly composed of CO 2 、O 2 and enters the front chamber of the grate cooler. The two paths of gas entering the front chamber of the grate cooler are separately introduced, and there is a difference in the oxygen content, that is, the oxygen content in the fuel combustion gas entering the rotary kiln and the precalciner is adjusted through the oxygen supply ratio, which provides convenience for the clinker calcination in a high carbon dioxide concentration environment.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] The present invention can realize the coordinated disposal of waste in the cement kiln and the enrichment of carbon dioxide in oxy-fuel combustion. The harmful components in the cement kiln system are reduced through the bypass air extraction system, ensuring the normal and stable operation of the system, and at the same time realizing the enrichment of carbon dioxide.

[0017] The present invention combines the cooling, circulation of high-temperature flue gas in the whole system with the supply of pure oxygen. Basically, no air enters the system, which minimizes the amount of nitrogen entering the system and can significantly reduce the generation of NOx.

[0018] The present invention can achieve the enrichment of carbon dioxide in the flue gas at the kiln tail, and the carbon dioxide concentration in the flue gas can reach ≥80%. It can greatly improve the efficiency of carbon dioxide capture and purification and reduce the cost of carbon dioxide capture and purification.

[0019] The present invention can achieve the complete capture of high-concentration carbon dioxide and realize the zero emission of carbon dioxide in the cement kiln system.

[0020] The present invention combines the co-disposal in cement kilns, bypass air release, oxy-fuel combustion, flue gas circulation, and carbon dioxide capture to achieve the green and low-carbon development of the cement industry. Description of the Drawings

[0021] Figure 1 is the process flow chart of the present invention;

[0022] Figure 2 is the installation position diagram of the first control valve, the second control valve, and the third control valve of the present invention;

[0023] Figure 3 is the installation position diagram of the condensate water remover of the present invention;

[0024] Figure 4 is the installation position diagram of the high-temperature resistant air valve of the present invention. Detailed Embodiments

[0025] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains. The "first", "second" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "comprising" or "including" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left", "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0026] To keep the following description of the embodiments of the present invention clear and concise, the detailed descriptions of known functions and known components are omitted in the present invention.

[0027] As Figure 1As shown in the figure, an all-oxygen combustion system with bypass air bleed includes a grate cooler 5, a rotary kiln 4, a smoke chamber 3, a decomposition furnace 2, a preheater 1, and a waste heat boiler 7 arranged in sequence along the gas path. It also includes a tertiary air duct 6 connected between the decomposition furnace 2 and the rotary kiln 4. It further includes a kiln tail flue gas circulation system 8, a bypass air bleed system 9, an oxygen supply system 10, and a carbon dioxide capture and purification system 11. The kiln tail flue gas circulation system 8 includes a first dust collector 12 and a first circulation fan 13. The air inlet of the first dust collector 12 is connected to the air outlet of the waste heat boiler 7, the air outlet of the first dust collector 12 is connected to the air inlet of the first circulation fan 13, and the air outlet of the first circulation fan 13 forms a first pipeline 13-1, a second pipeline 13-2, and a third pipeline 13-3 arranged in parallel. The bypass air bleed system 9 includes a smoke chamber extraction duct 9-1, a mixing chamber 9-2, a second dust collector 9-3, and a second circulation fan 9-4. Both ends of the smoke chamber extraction duct 9-1 are internally connected to the smoke chamber 3 and the mixing chamber 9-2 respectively. The air inlet of the second dust collector 9-3 is connected to the air outlet of the mixing chamber 9-2, the air outlet of the second dust collector 9-3 is connected to the air inlet of the second circulation fan 9-4, and the air outlet of the second circulation fan 9-4 is connected to the interior of the front chamber 5-1 of the grate cooler 5. The end of the first pipeline 13-1 is connected to the mixing chamber 9-2, the end of the second pipeline 13-2 is connected in parallel with the air outlet of the oxygen supply system 10 and then connected to the interior of the front chamber 5-1 of the grate cooler 5, and the end of the third pipeline 13-3 is connected to the air inlet of the carbon dioxide capture and purification system 11.

[0028] As Figure 2 shown, a first control valve 14 is further provided on the first pipeline 13-1, a second control valve 15 is further provided on the second pipeline 13-2, and a third control valve 16 is further provided on the third pipeline 13-3. The first control valve 14, the second control valve 15, and the third control valve 16 are used to respectively adjust the flue gas flow rates in the first pipeline 13-1, the second pipeline 13-2, and the third pipeline 13-3, so as to reduce the high-temperature flue gas of the bypass air bleed system 9 and ensure that the cooling flue gas volume entering the grate cooler 5 is appropriate and the oxygen concentration and carbon dioxide concentration in the flue gas are reasonably stable.

[0029] As Figure 3 shown, a condensate water remover 17 is further provided between the air outlet of the first dust collector 12 and the air inlet of the first circulation fan 13 to remove the moisture in the flue gas at the outlet of the preheater 1, thereby increasing the carbon dioxide content in the flue gas and further reducing the flue gas temperature. Since the waste or alternative fuel contains more water and hydrogen, the water vapor content in the kiln tail flue gas of the cement kiln system is often relatively large. Installing the condensate water remover 17 can reduce the water vapor content in the flue gas, and through flue gas circulation, the water vapor content in the pre-combustion gas of the furnace is also reduced.

[0030] As Figure 4As shown, a high-temperature resistant air valve 18 is also provided on the flue gas extraction pipe 9-1 of the smoke chamber, which can adjust the bypass air discharge amount according to the harmful component data in cooperation with the second circulation fan 9-4; when the harmful components are low and bypass air discharge is not required, the bypass air discharge system 9 is closed by closing the high-temperature resistant air valve 18 without affecting the normal operation of the system.

[0031] A process method of an all-oxygen combustion system with bypass air discharge includes the following steps:

[0032] S1: The hot flue gas extracted from the smoke chamber 3 by the bypass air discharge system 9 sequentially enters the air mixing chamber 9-2, the second dust collector 9-3, and the second circulation fan 9-4; the circulating flue gas in the first pipeline 13-1 is mixed with the hot flue gas extracted from the smoke chamber 3 in the air mixing chamber 9-2 to form low-temperature mixed flue gas, which enters the second dust collector 9-3, and then is introduced into the front chamber 5-1 of the grate cooler 5 through the second circulation fan 9-4; the second pipeline 13-2 converges with the oxygen supply system 10 to form a gas mainly composed of CO 2 , O 2 . The gas enters the front chamber 5-1 of the grate cooler 5 together with the low-temperature mixed flue gas from the bypass air discharge system 9, and exchanges heat with the high-temperature clinker introduced into the grate cooler 5 by the rotary kiln 4 to form a hot gas mainly composed of CO 2 , O 2 . The hot gas enters the rotary kiln 4 and the decomposition furnace 2 respectively for fuel combustion in the rotary kiln 4 and the decomposition furnace 2.

[0033] S2: Fuel combustion in the rotary kiln 4 and the decomposition furnace 2 and decomposition of carbonate in the cement raw material form flue gas with a higher carbon dioxide concentration, which enters the preheater 1 and exchanges heat with the raw material fed into the preheater 1. The preheated raw material is sent to the decomposition furnace 2 for carbonate decomposition. At the same time, the high-temperature flue gas is preheated and absorbed by the raw material to form medium and low-temperature flue gas, which is discharged from the preheater 1 and enters the waste heat boiler 7.

[0034] S3: The kiln tail circulating flue gas consists of two parts. One part is formed by mixing the low-temperature flue gas from the smoke chamber bypass air discharge system 9 and the flue gas in the first pipeline 13-1 after the waste gas at the outlet of the preheater 1 is cooled. The other part of the flue gas is the flue gas in the second pipeline 13-2 after the waste gas at the outlet of the preheater 1 is cooled. The two-way flue gas and the pure oxygen provided by the oxygen supply system 10 enter the front chamber 5-1 of the grate cooler 5 together; the flue gas in the third pipeline 13-3 after the waste gas at the outlet of the preheater 1 is cooled is sent to the carbon dioxide capture and purification system 11. This part of the flue gas is flue gas with a high carbon dioxide concentration, and its capture and purification are carried out. Compared with the capture and purification of flue gas in a common cement kiln system, the capture efficiency is higher and the cost is lower.

[0035] S4: By adjusting the circulating flue gas and the proportion of pure oxygen, the oxygen content in the mixed flue gas entering the front chamber 5-1 of the grate cooler 5 is controlled at 21-35%, and the carbon dioxide content is controlled at 40-75%. This not only meets the requirement of a relatively high carbon dioxide concentration in the flue gas but also ensures the amount of oxygen required for fuel combustion in the decomposition furnace 2 and the rotary kiln 4, further guaranteeing the fuel combustion rate and high burnout rate, and providing assurance for the stable and reliable thermal regime of the cement kiln system.

[0036] S5: The oxygen supply system 10 divides the oxygen into two paths. One path merges with the flue gas in the second pipeline 13-2 at the outlet of the first circulation fan 13 to form a cooling gas mainly composed of CO 2 , O 2 , which enters the front chamber 5-1 of the grate cooler 5. The other path merges with the flue gas at the outlet of the second circulation fan 9-4 to form a cooling gas mainly composed of CO 2 , O 2 , which enters the front chamber 5-1 of the grate cooler 5. The two paths of gas entering the front chamber 5-1 of the grate cooler 5 are introduced separately, and there is a difference in the oxygen content, that is, the oxygen content in the fuel combustion gas entering the rotary kiln and the decomposition furnace is adjusted by the oxygen supply ratio, which provides convenience for the clinker calcination in a high carbon dioxide concentration environment.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. However, such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An all-oxygen combustion system with bypass air extraction, comprising a grate cooler (5), a rotary kiln (4), a smoke chamber (3), a precalciner (2), a preheater (1) and a waste heat boiler (7) arranged in sequence along the gas path, and also comprising a tertiary air duct (6) connected between the precalciner (2) and the rotary kiln (4). Characterized in that it further comprises a kiln tail flue gas circulation system (8), a bypass air extraction system (9), an oxygen supply system (10) and a carbon dioxide capture and purification system (11); the kiln tail flue gas circulation system (8) comprises a first dust collector (12) and a first circulation fan (13), the air inlet of the first dust collector (12) is connected to the air outlet of the waste heat boiler (7), the air outlet of the first dust collector (12) is connected to the air inlet of the first circulation fan (13), and the air outlet of the first circulation fan (13) is formed with a first pipeline (13-1), a second pipeline (13-2) and a third pipeline (13-3) arranged in parallel; the bypass air extraction system (9) comprises a smoke chamber extraction duct (9-1), a mixing chamber (9-2), a second dust collector (9-3) and a second circulation fan (9-4); both ends of the smoke chamber extraction duct (9-1) are internally communicated with the smoke chamber (3) and the mixing chamber (9-2) respectively, the air inlet of the second dust collector (9-3) is connected to the air outlet of the mixing chamber (9-2), the air outlet of the second dust collector (9-3) is connected to the air inlet of the second circulation fan (9-4), and the air outlet of the second circulation fan (9-4) is connected to the interior of the front chamber (5-1) of the grate cooler (5); the end of the first pipeline (13-1) is connected to the mixing chamber (9-2), the end of the second pipeline (13-2) is connected in parallel with the air outlet of the oxygen supply system (10) and then connected to the interior of the front chamber (5-1) of the grate cooler (5), and the end of the third pipeline (13-3) is connected to the air inlet of the carbon dioxide capture and purification system (11). A first control valve (14) is further arranged on the first pipeline (13-1), a second control valve (15) is further arranged on the second pipeline (13-2), and a third control valve (16) is further arranged on the third pipeline (13-3). A high-temperature resistant air valve (18) is further arranged on the smoke chamber extraction duct (9-1).

2. An all-oxygen combustion system with bypass air extraction according to claim 1, Characterized in that a condensate water remover (17) is further arranged between the air outlet of the first dust collector (12) and the air inlet of the first circulation fan (13).

3. A process method of an all-oxygen combustion system with bypass air extraction according to claim 1, Characterized in that it comprises the following steps: S1: The hot flue gas extracted by the bypass air extraction system (9) from the smoke chamber (3) sequentially enters the air mixing chamber (9-2), the second dust collector (9-3), and the second circulation fan (9-4); the circulated flue gas in the first pipeline (13-1) is mixed with the hot flue gas extracted from the smoke chamber (3) in the air mixing chamber (9-2) to form low-temperature mixed flue gas, which enters the second dust collector (9-3), and then is introduced into the front chamber (5-1) of the grate cooler (5) through the second circulation fan (9-4); the second pipeline (13-2) converges with the oxygen supply system (10) to form a gas mainly composed of CO 2 , O 2 . The gas is blown into the front chamber (5-1) of the grate cooler (5) together with the low-temperature mixed flue gas from the bypass air extraction system (9). By exchanging heat with the high-temperature clinker introduced into the grate cooler (5) from the rotary kiln (4), a hot gas mainly composed of CO 2 , O 2 is formed and enters the rotary kiln (4) and the decomposition furnace (2) respectively for fuel combustion in the rotary kiln (4) and the decomposition furnace (2); S2: Fuel combustion in the rotary kiln (4) and the precalciner (2) and decomposition of carbonate in the cement raw meal form flue gas with a higher carbon dioxide concentration and enter the preheater (1) and exchange heat with the raw meal fed into the preheater (1). The preheated raw meal is sent to the precalciner (2) for carbonate decomposition. At the same time, the high-temperature flue gas is preheated and absorbed by the raw meal to form medium and low-temperature flue gas, which is then discharged from the preheater (1) and enters the waste heat boiler (7). S3: The circulating flue gas at the kiln tail consists of two parts. One part is formed by the mixing of the low-temperature flue gas from the bypass air extraction system (9) of the smoke chamber and the flue gas in the first pipeline (13-1) after the waste gas at the outlet of the preheater (1) is cooled. The other part of the flue gas is the flue gas in the second pipeline (13-2) after the waste gas at the outlet of the preheater (1) is cooled. The two-way flue gas and the pure oxygen provided by the oxygen supply system (10) enter the front chamber (5-1) of the grate cooler (5) together; the flue gas in the third pipeline (13-3) after the waste gas at the outlet of the preheater (1) is cooled is sent to the carbon dioxide capture and purification system (11). This part of the flue gas is the flue gas with a high carbon dioxide concentration. Compared with the capture and purification of the flue gas in the ordinary cement kiln system, the capture efficiency is higher and the cost is lower. S4: By adjusting the proportion of the circulating flue gas and pure oxygen, the oxygen content in the mixed flue gas entering the front chamber (5-1) of the grate cooler (5) is controlled at 21-35%, and the carbon dioxide content is controlled at 40-75%. This not only meets the relatively high carbon dioxide concentration in the flue gas but also ensures the oxygen required for fuel combustion in the decomposition furnace (2) and the rotary kiln (4), further ensuring the fuel combustion rate and high burnout rate, and providing a guarantee for the stable and reliable thermal regime of the cement kiln system. S5: The oxygen supply system (10) divides oxygen into two paths. One path merges with the flue gas in the second pipeline (13-2) at the outlet of the first circulation fan (13) to form a cooling gas mainly composed of CO 2 , O 2 , and enters the front chamber (5-1) of the grate cooler (5). The other path merges with the flue gas at the outlet of the second circulation fan (9-4) to form a cooling gas mainly composed of CO 2 , O 2 , and enters the front chamber (5-1) of the grate cooler (5). The two paths of gas entering the front chamber (5-1) of the grate cooler (5) are separately introduced, and there is a difference in oxygen content, that is, the oxygen content in the fuel combustion gas entering the rotary kiln and the decomposition furnace is adjusted through the oxygen supply ratio, which provides convenience for the clinker calcination in a high carbon dioxide concentration environment.

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