Cement kiln oxygen-enriched combustion system and method based on circulating flue gas classification

Abstract

The invention discloses a cement kiln oxygen-enriched combustion system and method based on circulating flue gas classification, and aims to reduce the carbon emission intensity in the cement production industrial process. The system comprises an oxygen generation subsystem, a flue gas purification and compression (CPU) subsystem, a cement firing subsystem and a coal / raw material grinding subsystem, wherein the cement firing subsystem comprises a cyclone preheater, a decomposing furnace, a rotary kiln, a grate cooler, a medium and low temperature SCR (Selective Catalytic Reduction), a heat exchanger, a dust remover, a desulfurizing tower and the like. According to the method, a technical path of dry flue gas circulation is adopted, and circulating flue gas is fed in a staged manner, so that the combustion / decomposition reaction temperature in a decomposing furnace and a rotary kiln is ensured, meanwhile, the flue gas flow velocity of an inlet of a cyclone preheater under the air and oxygen-enriched atmosphere is approximately the same, and the system has relatively high operation flexibility and economical efficiency. The system is also provided with a medium and low temperature SCR and a desulfurization tower, so that the design and operation difficulty of a CPU system is reduced, and CO2 carbon capture in the cement production industry is realized at low cost.

Description

Technical Field

[0001] The present invention relates to an oxygen-enriched combustion process for a cement kiln based on circulating flue gas staging, belonging to the technical fields of energy conversion and industrial production. Background Art

[0002] As the most representative carbon capture technology during combustion, oxygen-enriched combustion realizes the effective enrichment of CO2 through multiple cycles of flue gas, and uses a relatively mature flue gas compression and purification process to achieve near-zero emissions of CO2 from a cement kiln. In recent years, this technology has received extensive attention in the industry due to its excellent capture effect and good economy.

[0003] However, due to the relatively large specific heat capacity of CO2, in order to achieve a combustion temperature similar to that in an air atmosphere in the oxygen-enriched combustion system of a cement kiln, the oxygen concentration at the inlets of the decomposition furnace and the rotary kiln is generally above 26%. Due to the increase in oxygen concentration, the total flue gas flow rate of the system decreases, and the operating wind speed of components such as the cyclone preheater also decreases accordingly, resulting in a large-scale modification of the original combustion device in an air atmosphere. Therefore, after adopting oxygen-enriched combustion, it is necessary to carry out a large-scale transformation of the original cement clinker burning system, or be forced to increase the output of the original cement production line, deviating from the designed optimal operating conditions. The present application proposes an oxygen-enriched combustion process route for a cement kiln based on circulating flue gas staging, and by feeding the circulating flue gas in stages, it can achieve CO2 carbon capture in the cement production industry at low cost. Summary of the Invention

[0004] Objects of the Invention: The object of the present invention is to provide an oxygen-enriched combustion system for a cement kiln based on circulating flue gas staging with near-zero emissions; another object of the present invention is to provide an oxygen-enriched combustion method for a cement kiln based on circulating flue gas staging.

[0005] Technical Solution: An oxygen-enriched combustion system for a cement kiln based on circulating flue gas staging according to the present invention, the system includes a cement burning subsystem, an oxygen production subsystem, a raw material grinding system, and a coal grinding system. The cement burning subsystem includes a cyclone preheater group, a decomposition furnace connected to the cyclone preheater group, a rotary kiln connected to the decomposition furnace, and a grate cooler connected to the rotary kiln. The cyclone preheater group includes several stages of serially connected cyclone preheaters. According to the feeding sequence, the outlet of the uppermost cyclone preheater is connected to a circulating flue gas fan group for driving the directional flow of the circulating flue gas; the air inlet of the lowermost cyclone preheater is connected to the grate cooler; the grate cooler is divided into a first cooling zone, a second cooling zone, and a third cooling zone.

[0006] The air inlets of the first cooling zone are respectively connected to the circulating flue gas fan group and the outlet of the oxygen production subsystem, and the outlet of the first cooling zone is respectively connected to the air inlet of the rotary kiln and the air inlet of the decomposition furnace.

[0007] Among them, the outlets of the circulating flue gas fan group and the oxygen production subsystem are respectively connected to the inlet of the decomposition furnace and the inlet of the rotary kiln;

[0008] The inlet of the second cooling zone is connected to the outlet of the circulating flue gas fan group, and the outlet of the second cooling zone is connected to the inlet of the lowest-stage cyclone preheater;

[0009] Normal temperature air is introduced into the inlet of the third cooling zone, and the outlet is respectively connected to the raw material grinding system and the coal grinding system.

[0010] Furthermore, the cyclone preheater group includes at least four stages of serially connected cyclone preheaters. Among them, in the feeding order, the uppermost-stage cyclone preheater is connected to the circulating flue gas fan group, and the lowermost-stage cyclone preheater is connected to the grate cooler.

[0011] Furthermore, a partition chamber is arranged between the second cooling zone and the third cooling zone of the grate cooler. A part of the flue gas at the outlet of the second cooling zone enters the partition chamber and keeps it at a slightly positive pressure.

[0012] Furthermore, in the air inlet order, the circulating flue gas fan group includes a medium and low temperature SCR denitration device, a flue gas heat exchanger, a dust collector, a desulfurization tower, and a water eliminator connected in sequence.

[0013] Furthermore, the oxygen production subsystem is an air separation device using the cryogenic method or an oxygen production device using electrolytic water.

[0014] On the other hand, the present invention provides a method for oxygen-enriched combustion of a cement kiln using the above system, including the following steps:

[0015] (1) The flue gas discharged from the cyclone preheater group is processed by the circulating flue gas fan group to obtain circulating flue gas;

[0016] (2) Oxygen is mixed with a part of the circulating flue gas to obtain a mixed gas; after the mixed gas is mixed with coal, it is respectively introduced into the decomposition furnace and the rotary kiln. The flue gas discharged from the decomposition furnace is introduced into the lowermost-stage cyclone preheater in the cyclone preheater group;

[0017] (3) A mixed gas of oxygen and circulating flue gas is introduced into the inlet of the first cooling zone, and the outlet is respectively connected to the inlet of the rotary kiln and the inlet of the decomposition furnace. A part of the mixed gas after heat exchange with high-temperature clinker enters the rotary kiln, and a part enters the decomposition furnace;

[0018] Circulating flue gas is introduced into the inlet of the second cooling zone. The circulating flue gas after heat exchange with high-temperature clinker enters the inlet of the lowermost-stage cyclone preheater for raw material heat exchange;

[0019] Normal temperature air is introduced into the inlet of the third cooling zone to further cool the clinker. A part of the air after heat exchange enters the raw material grinding system for raw material drying, and a part enters the coal grinding system for coal drying;

[0020] (4) Steps (2) and (3) have no sequential order. The flue gas generated in the cyclone preheater group in these two steps is discharged into the flue gas and circulated through the above steps (1)-(3).

[0021] Furthermore, all raw materials, coal, and clinker particles in the cement firing subsystem are transported using recycled flue gas.

[0022] Furthermore, all air leakage points and main rotating components in the cement firing subsystem, including the rotating components of the rotary kiln, movable holes of the dust collector, etc., are sealed with positive pressure using recycled flue gas to reduce the leakage of air and increase the CO2 concentration in the tail flue gas.

[0023] Furthermore, by controlling the amount of recycled flue gas entering the first cooling zone, the oxygen concentration in the mixed gas entering the decomposition furnace and the rotary kiln is maintained between 26% and 32%.

[0024] Furthermore, by controlling the amount of recycled flue gas entering the second cooling zone, the oxygen concentration in the mixed gas entering the decomposition furnace and the rotary kiln is maintained between 21% and 24%.

[0025] In the above technical solution, a cement kiln oxy-fuel combustion process route with staged recycled flue gas is proposed. The recycled flue gas is fed in stages, which not only guarantees the combustion / decomposition reaction temperature in the decomposition furnace and the rotary kiln, but also makes the flue gas flow velocity at the inlet of the cyclone preheater under air and oxy-fuel atmospheres approximately the same. The system has high operating flexibility and economy. This process also reduces the design and operation difficulty of the flue gas purification and compression (CPU) subsystem by setting up medium and low temperature SCR and desulfurization towers, and realizes CO2 capture in the cement production industry at low cost.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: 1) CO2 capture and utilization in the cement production process are realized; 2) High-concentration O2 combustion is adopted in the decomposition furnace and the rotary kiln, which guarantees the combustion temperature and raw meal decomposition rate in the decomposition furnace and the rotary kiln; 3) Through staged recycled flue gas, a flue gas volume similar to that under the air atmosphere is achieved in the cyclone preheater, reducing the transformation amount of the original air combustion cement production line for the oxy-fuel combustion process. Description of the Drawings

[0027] Figure 1Schematic diagram of the system structure of the present invention; in the figure, 1. Cyclone preheater group; C1. The topmost cyclone preheater; C2. The second-stage cyclone preheater; C3. The third-stage cyclone preheater; C4. The fourth-stage cyclone preheater; C5. The bottommost cyclone preheater; 2. Calciner; 3. Rotary kiln; 301. The first rotary kiln zone; 302. The first rotary kiln zone; 4. Grate cooler; 401. The first cooling zone; 402. The second cooling zone; 403. The third cooling zone; 5. Circulating flue gas fan group; 501. Medium and low temperature SCR denitration device; 502. Flue gas heat exchanger; 503. Dust collector; 504. Desulfurization tower; 505. Water eliminator; 6. Cooler;

[0028] Figure 2 Schematic flow diagram of the present invention;

[0029] Figure 3 Effect of flue gas recirculation rate on the outlet temperature of the calciner in the embodiment;

[0030] Figure 4 Effect of flue gas recirculation rate on the outlet temperature of the rotary kiln in the embodiment. Specific implementation manner

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] The oxy-fuel combustion system for cement kilns provided by the embodiment of the present invention includes an oxygen production subsystem, a flue gas purification and compression subsystem, a cement firing subsystem, a raw material grinding system, and a coal grinding system. Among them, the oxygen production subsystem, the flue gas purification and compression subsystem, the raw material grinding system, and the coal grinding system are prior arts. The embodiment of the present invention improves the existing cement firing subsystem. The solid material flow in the cement firing subsystem remains unchanged, and mainly the gas material flow is changed. By grading the circulating flue gas, a flue gas volume similar to that in the air atmosphere is achieved in the cyclone preheater, reducing the modification amount of the oxy-fuel combustion process to the original air combustion cement production line.

[0033] Such as Figure 1As shown in the figure, the cement firing subsystem includes a cyclone preheater bank 1, a decomposition furnace 2, a rotary kiln 3, a grate cooler 4, a circulating flue gas fan bank 5, and a cooler 6. Among them, the cyclone preheater bank 1 is connected to the decomposition furnace 2, the rotary kiln 3 is connected to the decomposition furnace 2, the grate cooler 4 is connected to the rotary kiln 3. The cyclone preheater bank 1 includes several stages of serially connected cyclone preheaters. In the embodiment of the present invention, 5-stage cyclone preheaters are used as an example for illustration. According to the feeding order, the outlet of the uppermost cyclone preheater C1 is connected to the circulating flue gas fan bank 5; the air inlet of the lowermost cyclone preheater C5 is connected to the grate cooler 4; the grate cooler 4 is divided into a first cooling zone 401, a second cooling zone 402, and a third cooling zone 403. The air inlet of the first cooling zone 401 is respectively connected to the circulating flue gas fan bank 5 and the outlet of the oxygen production subsystem. The outlet of the first cooling zone 401 is respectively connected to the air inlet of the rotary kiln 3 and the air inlet of the decomposition furnace 2; among them, the outlets of the circulating flue gas fan bank 5 and the oxygen production subsystem are also respectively connected to the air inlet of the decomposition furnace 2 and the air inlet of the rotary kiln 3; the air inlet of the second cooling zone 402 is connected to the outlet of the circulating flue gas fan bank 5, and the outlet of the second cooling zone 402 is connected to the air inlet of the lowermost cyclone preheater C5; the air inlet of the third cooling zone 403 is fed with normal temperature air, and the outlet is respectively connected to the raw material grinding system and the coal grinding system.

[0034] The circulating flue gas fan bank 5 includes a medium and low temperature SCR denitration device 501, a flue gas heat exchanger 502, a dust collector 503, a desulfurization tower 504, and a water eliminator 505 connected in sequence.

[0035] As Figure 2 shown, the embodiment of the present invention provides a method for oxy-fuel combustion in a cement kiln, including:

[0036] The flue gas discharged from the cyclone preheater bank is processed by the circulating flue gas fan bank to obtain circulating flue gas;

[0037] Oxygen is mixed with a part of the circulating flue gas to obtain a mixed gas; the mixed gas is mixed with coal and then respectively fed into the decomposition furnace and the rotary kiln. The flue gas discharged from the decomposition furnace is fed into the lowermost cyclone preheater in the cyclone preheater bank;

[0038] The inlet of the first cooling zone is fed with a mixed gas of oxygen and circulating flue gas, and the outlet is respectively connected to the air inlet of the rotary kiln and the air inlet of the decomposition furnace. A part of the mixed gas after heat exchange with high-temperature clinker enters the rotary kiln, and a part enters the decomposition furnace;

[0039] The inlet of the second cooling zone is fed with circulating flue gas. The circulating flue gas after heat exchange with high-temperature clinker enters the inlet of the lowermost cyclone preheater for raw material heat exchange;

[0040] The inlet of the third cooling zone is fed with normal temperature air to further cool the clinker. A part of the air after heat exchange enters the raw material grinding system for raw material drying, and a part enters the coal grinding system for coal drying;

[0041] The flue gas generated in the cyclone preheater group is discharged, and the flue gas is circulated through the above steps.

[0042] Specifically, a medium- and low-temperature SCR catalytic denitration device, a flue gas heat exchanger, a bag filter, and an alkali liquor desulfurization device are sequentially added at the outlet of the first-stage preheating cyclone C1. While realizing the cascade utilization of flue gas energy, it reduces the contents of NOx, SOx, and soot entering the CPU subsystem, alleviates the anti-corrosion requirements of the compressor and pipelines in the CPU system, and reduces the overall investment and operation and maintenance costs of the system.

[0043] Compared with the prior art, three gas injection points are set in the embodiment of the present invention: gas injection point A, gas injection point B, and gas injection point C. The grate cooler is divided into a first cooling zone, a second cooling zone, and a third cooling zone, and the air distribution strategy is modified according to its heat matching with the overall system. After the same thermal calculation, the material flow in the three cooling zones and the gas injection points are optimized. The specific process is as follows:

[0044] Oxygen-rich gas and recycled flue gas are introduced into the inlet of the first cooling zone, and the outlet is respectively connected to the inlet of the rotary kiln and the tertiary air duct. A part of the mixed gas after heat exchange with high-temperature clinker enters the rotary kiln as secondary air, and a part enters the decomposition furnace as tertiary air through the tertiary air duct.

[0045] Recycled flue gas is introduced into the inlet of the second cooling zone. The recycled flue gas after heat exchange with high-temperature clinker enters the inlet of the lowest-stage cyclone preheater C5, that is, enters the cyclone preheater C5 through gas injection point C for raw material heat exchange, improving the thermal energy utilization rate of the system. At the same time, a partition chamber is arranged between the second cooling zone and the third cooling zone. A part of the flue gas at the outlet of the second cooling zone enters the partition chamber and keeps it slightly positive pressure to prevent the air in the third cooling zone from entering the second cooling chamber, solving the air leakage problem.

[0046] Normal-temperature air is introduced into the inlet of the third cooling zone to further cool the clinker. A part of the air after heat exchange enters the raw material grinding system for raw material drying, and a part enters the coal grinding system for coal drying.

[0047] After the recycled flue gas, oxygen, and coal are mixed, a part enters the second rotary kiln through gas injection point A, and another part enters the second rotary kiln through gas injection point B.

[0048] In the prior art, the injection points of gas are only in the precalciner and the rotary kiln. Compared with the existing patents (such as CN119554882A), since the specific heat capacities of high-concentration CO2 and H2O in the recycled flue gas are greater than that of N2, in order to reach the same combustion temperature, it is necessary to increase the O2 concentration in the mixed gas at the inlets of the precalciner and the rotary kiln. However, the increase in the O2 concentration will reduce the total flue gas volume, resulting in a decrease in the flow rate at the inlet of the cyclone preheater, disrupting the original process and causing a decline in the separation efficiency of the cyclone preheater. To solve this problem, in the traditional solutions (as shown in CN119554882A), after adopting oxygen-enriched combustion, it is necessary to carry out large-scale transformation on the original cement clinker burning system, or be forced to increase the output of the original cement production line, deviating from the designed optimal operating conditions. In this project, by setting the second cooling zone of the grate cooler and introducing a part of the recycled flue gas at the inlet of the lowest-stage cyclone preheater, the flue gas flow rate at the inlet of the cyclone preheater is increased, enabling the existing cement production line to meet the requirements of both air and oxygen-enriched combustion conditions without large-scale technical transformation.

[0049] In one embodiment, after thermodynamic simulation by Aspen Plus software, under the conditions of air atmosphere, oxygen-enriched atmosphere with two cooling zones, and oxygen-enriched atmosphere with three cooling zones, the heat recovery efficiencies of the grate cooler are 74.05%, 75.86%, and 79.56% respectively. The design of the grate cooler with three cooling zones is beneficial to improving the energy utilization efficiency of the system. Among them, the condition of the oxygen-enriched atmosphere with three cooling zones is the situation of the three gas injection points and the three cooling zones in the embodiment of the present invention. The condition of the air atmosphere with two cooling zones is that after the high-temperature zone of the grate cooler is cooled by air, the heat-exchanged air enters the precalciner and the rotary kiln respectively to participate in combustion. After the low-temperature zone of the grate cooler is cooled by air, the heat-exchanged air enters the fuel / raw material mill system for raw material drying. The condition of the oxygen-enriched atmosphere with two cooling zones is that high-purity oxygen is mixed with the recycled flue gas. After the high-temperature zone of the grate cooler is cooled by the above mixed gas, the heat-exchanged gas enters the precalciner and the rotary kiln respectively to participate in combustion. After the low-temperature zone of the grate cooler is cooled by air, the heat-exchanged air enters the fuel / raw material mill system for raw material drying.

[0050] Change the original air powder feeding to recycled flue gas powder feeding. At the same time, for all the air leakage points and main rotating components in the system, such as the head and tail of the rotary kiln, the manhole doors and ash discharge holes of the dust collector, etc., use the recycled flue gas for positive pressure air sealing to reduce the leakage of air and increase the CO2 concentration in the tail flue gas.

[0051] In this embodiment, a dry-process cement production line with a daily output of 5500t is used as a reference object. In this system, raw meal is first preheated by high-temperature flue gas in a cyclone preheater, then further heated and decomposed in a decomposition furnace and enters a rotary kiln. After a series of chemical reactions, it is sent to a grate cooler for cooling, and finally the product clinker is obtained. The flue gas flows against the direction of the raw meal flow, successively passing through the rotary kiln, the decomposition furnace, and the cyclone preheater, and finally is dust-removed and discharged into the atmosphere. The cryogenic method is used for air separation to produce oxygen, and the inlet oxygen purity is 95%.

[0052] During oxy-fuel combustion, the equivalent oxygen concentration at the furnace inlet mainly affects the combustion effect in the kiln. The higher the concentration, the better the fuel combustion effect. However, too high a concentration will also cause the temperature in the system to rise, which will have a certain impact on the decomposition of raw meal and the clinker burning reaction. According to the results of pilot-scale tests, when the mixed oxygen concentration is higher than 30%, the temperature will rise rapidly; when the oxygen concentration is lower than 26%, the flame temperature is not sufficient to support the decomposition of calcium carbonate in the decomposition furnace. At the same time, too high an oxygen concentration will also cause the total gas volume in the system to differ greatly from that in the air atmosphere, affecting the gas flow rate in the decomposition furnace and the cyclone separator.

[0053] Referring to the pilot-scale test data of China National Building Materials Group, in the embodiment of the present invention, an oxygen concentration of 26%-30% is selected to compare the influence of different oxygen concentrations on the kiln head temperature. During the calculation process, the temperature of the decomposition furnace is maintained at 900°C, and the flue gas circulation ratio is automatically adjusted with the change of the oxygen concentration. The relevant results are as Figure 3 shown. The results show that when the equivalent oxygen concentration at the furnace inlet is 30%, the temperature at the kiln head of the rotary kiln can reach 1450°C, meeting the requirements for clinker burning.

[0054] The proportion of flue gas circulation in the cement kiln is mainly used to control the heat distribution in the furnace and the component concentration in the flue gas. By adjusting the flue gas circulation ratio, the temperature in the furnace can be controlled while ensuring that the oxygen concentration remains at 30%. In order to study the influence of the flue gas circulation mode on the system, the oxygen supply purity is set at 95%, the air leakage coefficient is taken as 5%, the mixed oxygen concentration is set at 30%, and the temperature of the decomposition furnace is 900°C. The results are as Figure 4 shown. Under the above working conditions, when the flue gas circulation ratio is between 0.46 and 0.47, the temperature at the kiln head of the rotary kiln can reach the set value of 1450°C.

[0055] Finally, it should be noted that the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. An oxygen-enriched combustion system for a cement kiln based on staged recycle flue gas, the system comprising a cement firing subsystem, an oxygen generation subsystem, a raw material grinding system and a coal grinding system, the cement firing subsystem including a cyclone preheater bank, a decomposition furnace connected to the cyclone preheater bank, a rotary kiln connected to the decomposition furnace, and a grate cooler connected to the rotary kiln, characterized in that, The cyclone preheater group includes several stages of cyclone preheaters connected in series. In the feeding order, a circulating flue gas fan group is connected to the outlet of the uppermost cyclone preheater, and the circulating flue gas fan group is used to drive the directional flow of the circulating flue gas; the air inlets of the lowermost cyclone preheater are respectively connected to the decomposition furnace and the grate cooler; the grate cooler is divided into a first cooling zone, a second cooling zone and a third cooling zone. The air inlets of the first cooling zone are respectively connected to the outlet of the circulating flue gas fan group and the oxygen production subsystem, and the outlets of the first cooling zone are respectively connected to the air inlet of the rotary kiln and the air inlet of the decomposition furnace. Among them, the outlets of the circulating flue gas fan group and the oxygen production subsystem are also respectively connected to the air inlet of the decomposition furnace and the air inlet of the rotary kiln. The air inlet of the second cooling zone is connected to the outlet of the circulating flue gas fan group, and the outlet of the second cooling zone is connected to the air inlet of the lowermost cyclone preheater. Normal temperature air is introduced into the air inlet of the third cooling zone, and the outlet is respectively connected to the raw material grinding system and the coal grinding system.

2. The oxygen-enriched combustion system for a cement kiln based on staged recycle flue gas according to claim 1, wherein The cyclone preheater group includes at least four stages of cyclone preheaters connected in series. Among them, in the feeding order, the uppermost cyclone preheater is connected to the circulating flue gas fan group, and the lowermost cyclone preheater is connected to the grate cooler.

3. The oxygen-enriched combustion system for a cement kiln based on staged recycle flue gas according to claim 1, wherein A partition chamber is arranged between the second cooling zone and the third cooling zone of the grate cooler. Part of the flue gas at the outlet of the second cooling zone enters the partition chamber and keeps it slightly positive pressure.

4. The oxygen-enriched combustion system for a cement kiln based on staged recycle flue gas according to claim 1, wherein In the air inlet order, the circulating flue gas fan group includes a medium and low temperature SCR denitration device, a flue gas heat exchanger, a dust collector, a desulfurization tower and a water remover connected in sequence.

5. The oxygen-enriched combustion system for a cement kiln based on staged recycle flue gas according to claim 1, wherein The oxygen production subsystem is an air separation device using the cryogenic method or an oxygen production device using electrolytic water.

6. A method for oxygen-enriched combustion in a cement kiln using the system according to claim 1, characterized in that, It includes the following steps: (1) The flue gas discharged from the cyclone preheater group is processed by the circulating flue gas fan group to obtain circulating flue gas. (2) Oxygen and a part of the circulating flue gas are mixed to obtain a mixed gas; after the mixed gas is mixed with coal, it is respectively introduced into the decomposition furnace and the rotary kiln, and the flue gas discharged from the decomposition furnace is introduced into the lowermost cyclone preheater in the cyclone preheater group. (3) The mixed gas of oxygen and circulating flue gas is introduced into the inlet of the first cooling zone, and the outlet is respectively connected to the air inlet of the rotary kiln and the air inlet of the decomposition furnace. After heat exchange with the high-temperature clinker, a part of the mixed gas enters the rotary kiln, and a part enters the decomposition furnace. The circulating flue gas is introduced into the inlet of the second cooling zone, and the circulating flue gas after heat exchange with the high-temperature clinker enters the inlet of the lowermost cyclone preheater for raw material heat exchange. Normal temperature air is introduced into the inlet of the third cooling zone to further cool the clinker. Part of the air after heat exchange enters the raw material grinding system for raw material drying, and part enters the coal grinding system for coal drying. (4) Steps (2) and (3) have no sequential order, and the flue gas generated in the cyclone preheater group in the two steps is discharged into the flue gas and circulated through the above steps (1)-(3).

7. The method for oxygen-enriched combustion in a cement kiln according to claim 6, characterized in that, All raw materials, coal and clinker particles in the cement firing subsystem are transported by circulating flue gas.

8. The method for oxygen-enriched combustion in a cement kiln according to claim 6, characterized in that, By controlling the amount of circulating flue gas entering the first cooling zone, the oxygen concentration in the mixed gas entering the decomposition furnace and the rotary kiln is maintained between 26% and 32%.

9. The method for oxygen-enriched combustion in a cement kiln according to claim 6, wherein By controlling the amount of circulating flue gas entering the second cooling zone, the oxygen concentration in the mixed gas entering the decomposition furnace and the rotary kiln is maintained between 21% and 24%.

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