Cement kiln system transformed from online calciner and method for preparing cement clinker

Abstract

The present invention relates to a cement kiln system transformed from an online decomposition furnace and a method for preparing cement clinker. The present invention creatively integrates a CO2 self-enrichment type cement kiln and an online cement kiln into the same system, and the system can be switched to a CO2 self-enrichment type cement kiln or an online cement kiln as needed. When the cement kiln is used as a CO2 self-enrichment type cement kiln, the CO2 self-enrichment process can be realized in the decomposition furnace to ensure that the CO2 concentration of the flue gas at the outlet of the first and second cyclone preheaters is greater than 50%, thereby improving the problem of low CO2 concentration and difficult purification of the flue gas at the kiln tail in the prior art, and can greatly reduce the investment cost and operating cost of subsequent CO2 capture and purification in the flue gas. Moreover, the present invention does not require the redesign of the rotary kiln and the cooler, and is suitable for the transformation of most existing cement kiln systems, greatly simplifying the process flow and reducing the transformation cost, and can also be used for the design of a new cement production line.

Description

Technical Field

[0001] The invention belongs to the technical field of cement production equipment, and in particular relates to a cement kiln system transformed from an online decomposition furnace and a method for preparing cement clinker. Background Art

[0002] As a major greenhouse gas, the large-scale emission of CO2 has aggravated the global greenhouse effect. All countries in the world are generally faced with the arduous task of achieving carbon emission reduction and mitigating global climate change. In order to better develop the global economy and protect the natural environment, countries around the world have successively formulated strategic goals for carbon emission reduction.

[0003] There have been many reports on carbon emission reduction technology research at home and abroad, but these studies are mainly aimed at industries such as electricity, coal and steel, and there are relatively few reports on carbon emission reduction technology related to the cement industry. At present, the carbon emission reduction technology solutions adopted by the cement industry are pre-combustion capture and post-combustion capture. Among them, pre-combustion capture refers to the pretreatment of fuel before combustion to separate the carbon in the fuel. Due to the characteristics of cement clinker production process, a significant disadvantage of pre-combustion CO2 capture is that it can only separate the CO2 produced by fuel combustion, while about 60% of the CO2 produced by raw material calcination is discharged with the flue gas, and this part of CO2 is not treated at all. In addition, compared with other CO2 capture technologies, the pre-combustion capture technology has very harsh conditions for hydrogen combustion in the clinker calcination process, and special design of the rotary kiln burner is required. Therefore, this technology is less feasible in the cement industry and can be excluded. Post-combustion capture technology in the cement industry mainly refers to capturing or separating CO2 from post-combustion flue gas. The main technologies include absorption, adsorption, membrane absorption and mineral carbonization. Since the flue gas from the cement industry kiln has low pressure, large volume flow, low CO2 concentration, and contains a large amount of dust and N2, the above methods all have problems such as low carbon capture efficiency, small capture flow, complex system, large equipment investment or high operating cost.

[0004] Therefore, there is an urgent need to develop a cement kiln system with a simple system, small equipment investment, low operating cost and CO2 enrichment function. Summary of the invention

[0005] In order to improve the above technical problems, the present invention provides a cement kiln system transformed from an online decomposition furnace, the system comprising a first row of cyclone preheaters, a second row of cyclone preheaters, a decomposition furnace, a smoke chamber, a rotary kiln, a cooler, a heat exchanger, and a switching component;

[0006] The air inlets of the first and second cyclone preheaters are connected to the decomposition furnace, and the discharge ports of the first and second cyclone preheaters are connected to the smoke chamber; the decomposition furnace is connected to the smoke chamber, and the smoke chamber is connected to the rotary kiln; the rotary kiln is connected to the cooler;

[0007] The cooler is provided with a tertiary air duct, which is provided with a switching component. The tertiary air duct is divided into two paths through the switching component. One path is that the tertiary air duct is connected to the heat exchanger, and the heat exchanger is connected to the decomposition furnace through a pipeline; the other path is that the tertiary air duct is directly connected to the decomposition furnace without passing through the heat exchanger.

[0008] According to an embodiment of the present invention, the switching component is selected from a valve.

[0009] According to an embodiment of the present invention, the valve is selected from a gate valve or a butterfly valve.

[0010] According to an embodiment of the present invention, the valve comprises a first valve, a second valve and a third valve; the first valve and the third valve are arranged on the tertiary air duct, and the second valve is arranged on the pipe connecting the heat exchanger and the decomposition furnace;

[0011] The first valve is arranged on the tertiary air duct connecting the cooler and the heat exchanger, the second valve is arranged on the pipeline connecting the heat exchanger and the decomposition furnace; the third valve is arranged on the tertiary air duct connecting the cooler and the decomposition furnace.

[0012] According to an embodiment of the present invention, the first valve is valve B, the second valve is valve C, and the third valve is valve A.

[0013] According to an embodiment of the present invention, the air inlet of the lowest cyclone separator of the first row of cyclone preheaters and the second row of cyclone preheaters is connected to the decomposition furnace;

[0014] The discharge ports of the lowest-stage cyclone separators of the first row of cyclone preheaters and the second row of cyclone preheaters are connected to the smoke chamber.

[0015] Furthermore, the feed inlets of the first-row cyclone preheaters and the penultimate-stage cyclone separators of the second-row cyclone preheaters are both connected to the decomposition furnace through pipelines.

[0016] According to an embodiment of the present invention, the discharge ports of the penultimate cyclone separators of the first row of cyclone preheaters and the second row of cyclone preheaters are both connected to the decomposition furnace via a pipeline, and the pipeline may or may not contain a branch;

[0017] When the pipeline does not contain branches, the first row of cyclone preheaters and the second row of cyclone preheaters feed the decomposition furnace at a single point; when the pipeline contains branches, the first row of cyclone preheaters and the second row of cyclone preheaters feed the decomposition furnace at multiple points; the conveying pipelines connecting the discharge ports of the penultimate cyclone separators of the first row of cyclone preheaters and the second row of cyclone preheaters to the decomposition furnace all include a conveying trunk and a conveying branch, and the number of the conveying branches is more than 2; the conveying branches are connected in parallel, and a dividing valve is provided at the connection between the conveying trunk and the conveying branch; the dividing valve can adjust the amount of material entering each conveying branch from the conveying trunk, thereby realizing multi-point feeding of the decomposition furnace.

[0018] According to an embodiment of the present invention, the number of stages of the first row of cyclone preheaters and the second row of cyclone preheaters is selected from 3 to 7.

[0019] According to an embodiment of the present invention, the heat exchanger is provided with more than one gas inlet and more than one gas outlet;

[0020] One of the gas outlets is connected to a waste heat utilization or treatment system; the waste heat utilization or treatment system includes a waste heat boiler for power generation, material drying or other waste heat utilization or treatment device;

[0021] The cooler is selected from a grate cooler, a single-drum cooler, and a multi-drum cooler.

[0022] According to an embodiment of the present invention, the first row of cyclone preheaters and the second row of cyclone preheaters are provided with a raw meal feeding inlet, which is arranged at the inlet air duct of the topmost first-stage cyclone separator of the first row of cyclone preheaters and the second row of cyclone preheaters, or at the inlet air duct of the topmost second-stage cyclone separator of the first row of cyclone preheaters and the second row of cyclone preheaters.

[0023] According to an embodiment of the present invention, a fuel inlet is provided on the decomposition furnace, and the number of the fuel inlets is more than one.

[0024] The present invention also provides a method for preparing cement clinker using the cement kiln system transformed from the online calciner, the method for preparing cement clinker comprising:

[0025] The raw meal is added to the first row of cyclone preheaters and the second row of cyclone preheaters respectively, and the raw meal exchanges heat with the flue gas in the cyclone preheaters;

[0026] The raw meal preheated by the first and second cyclone preheaters enters the calciner through one or more points;

[0027] The hot raw material decomposed by the decomposition furnace leaves the decomposition furnace and enters the penultimate cyclone separator of the first and second cyclone preheaters respectively. After gas-solid separation, it enters the rotary kiln through the smoke chamber and is calcined in the rotary kiln to form clinker. The clinker enters the cooler from the outlet of the rotary kiln and is then cooled by the cooler to obtain cement clinker.

[0028] The kiln gas formed in the rotary kiln enters the decomposition furnace; the kiln gas formed in the rotary kiln and the flue gas formed in the decomposition furnace are discharged from the outlets of the top cyclone separators of the first and second rows respectively after gas-solid heat exchange in the first and second rows of cyclone preheaters;

[0029] The tertiary air is divided into two paths by the switching component, and any one of the following paths is selected by adjusting the switching component: one path is that the tertiary air enters the heat exchanger through the tertiary air duct, the mixed gas of circulating flue gas and oxygen or oxygen enters the heat exchanger, the tertiary air exchanges heat with the mixed gas of circulating flue gas and oxygen or oxygen through the heat exchanger, the mixed gas of circulating flue gas and oxygen or oxygen after the heat exchange enters the decomposition furnace, and the tertiary air after the heat exchange enters the waste heat utilization or treatment system; the other path is that the tertiary air in the tertiary air duct enters the decomposition furnace without passing through the heat exchanger, that is, the tertiary air directly enters the decomposition furnace through the tertiary air duct.

[0030] According to the implementation scheme of the present invention, the tertiary air is divided into two paths through a valve, and any one of the following paths is selected by adjusting the valve: one path is that the third valve is closed, the first valve and the second valve are opened, the tertiary air enters the heat exchanger through the tertiary air duct, the mixed gas of circulating flue gas and oxygen or oxygen enters the heat exchanger, the tertiary air and the mixed gas of circulating flue gas and oxygen or oxygen exchange heat through the heat exchanger, the mixed gas of circulating flue gas and oxygen or oxygen after the heat exchange enters the decomposition furnace, and the decomposition furnace is oxygen-enriched combustion, and at this time the system is a CO2 self-enrichment type cement kiln; the other path is that the third valve is opened, the first valve and the second valve are closed, and the tertiary air in the tertiary air duct directly enters the decomposition furnace, and at this time the system is an online cement kiln.

[0031] According to the implementation scheme of the present invention, in terms of gas flow direction, the air is cooled by the cooler to cool the high-temperature clinker, and the air after heat exchange is divided into the following three routes: the first route of high-temperature air is used as secondary air to directly enter the rotary kiln for fuel combustion; the second route of air is divided into two situations: when the third valve is fully closed and the first valve and the second valve are fully opened, the system acts as a CO2 self-enrichment cement kiln, and the tertiary air exchanges heat with the mixed gas of circulating flue gas and oxygen or oxygen through the heat exchanger, and the mixed gas of circulating flue gas and oxygen or oxygen after the heat exchange enters the decomposition furnace, and the tertiary air after the heat exchange enters the waste heat utilization or treatment system; when the third valve is fully opened and the first valve and the second valve are fully closed, the system acts as an online cement kiln, and the tertiary air directly enters the decomposition furnace for fuel combustion, and the mixed gas of circulating flue gas and oxygen or oxygen is no longer supplied to the decomposition furnace; the third route of air with a higher temperature enters the waste heat utilization or treatment system, for example, enters the waste heat boiler to generate electricity, and the flue gas after power generation is treated by the waste air and discharged into the atmosphere through the chimney.

[0032] According to an embodiment of the present invention, the air outlets of the cooling machine are the first route, the second route, and the third route; or the first route is the only route, and the second route and the third route are combined.

[0033] According to an embodiment of the present invention, the second and third air outlets are combined so that the second and third air outlets share one air outlet pipe.

[0034] Compared with the prior art, the present invention has the following advantages and effects:

[0035] 1. The present invention creatively integrates the CO2 self-enrichment type cement kiln and the online cement kiln into the same system, and the system can be switched to the CO2 self-enrichment type cement kiln or the online cement kiln as needed.

[0036] 2. When the cement kiln is used as a CO2 self-enrichment type cement kiln, the CO2 self-enrichment process can be realized in the decomposition furnace to ensure that the CO2 concentration of the flue gas at the outlet of the first and second cyclone preheaters is greater than 50% (the CO2 concentration of the flue gas at the outlet of the cyclone preheater of a conventional production line is about 25-35%), thereby improving the problem of low CO2 concentration in the flue gas at the outlet of the cyclone preheater and difficulty in purification in the prior art, and can greatly reduce the investment cost and operating cost of subsequent CO2 capture and purification in the flue gas.

[0037] 3. The present invention does not require redesign of the rotary kiln and cooler, and is suitable for transformation of most existing cement kiln systems, greatly simplifying the process flow and reducing the transformation cost. It can also be used for the design of new cement production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1This is a diagram of a cement kiln system transformed from an inline decomposition furnace in an embodiment of the present invention. Among them, 1-raw meal feed inlet of the A-row cyclone preheater, 2-raw meal feed inlet of the B-row cyclone preheater, 3-material distribution valve, 4-decomposition furnace, 5-fuel inlet of the decomposition furnace, 6-smoke chamber, 7-rotary kiln, 8-fuel inlet of the rotary kiln, 9-cooler; 10-tertiary air duct, 11-valve B, 12-valve C, 13-valve A, 14-heat exchanger, 1401-gas inlet, 1402-gas outlet, 15-smoke outlet of the A-row cyclone preheater, 16-smoke outlet of the B-row cyclone preheater, 17-fan. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] like Figure 1As shown, the cement kiln system transformed from an inline decomposition furnace comprises an A-row cyclone preheater, a B-row cyclone preheater, a decomposition furnace (4), a smoke chamber (6), a rotary kiln (7), a cooler (9), a heat exchanger (14), a valve A (13), a valve B (11), a valve C (12), and a material dividing valve (3). The A-row cyclone preheater and the B-row cyclone preheater are provided with raw material feeding inlets, and the raw material feeding inlet (1) of the A-row cyclone preheater and the raw material feeding inlet (2) of the B-row cyclone preheater are respectively provided at the inlet air ducts of the first-stage cyclone separators at the top of the A-row cyclone preheater and the B-row cyclone preheater. The air inlets of the lowest cyclone separators of the A-row cyclone preheaters and the lowest cyclone separators of the B-row cyclone preheaters are both connected to the decomposition furnace (4) through pipelines; the discharge ports of the second-to-last cyclone separators of the A-row cyclone preheaters and the B-row cyclone preheaters are both connected to the decomposition furnace (4) through pipelines; the feed ports of the last cyclone separators of the A-row cyclone preheaters and the B-row cyclone preheaters are both connected to the decomposition furnace (4) through pipelines; and the discharge ports of the last cyclone separators of the A-row cyclone preheaters and the B-row cyclone preheaters are both connected to the smoke chamber (6) through pipelines. The decomposition furnace (4) is connected to a smoke chamber (6), and the smoke chamber (6) is connected to a rotary kiln (7); the rotary kiln (7) is connected to a cooler (9); a tertiary air duct (10) is provided on the cooler (9); a valve A (13) and a valve B (11) are provided on the tertiary air duct (10), and a valve C (12) is provided on a pipeline connecting a heat exchanger (14) and the decomposition furnace (4). The tertiary air duct (10) is divided into two paths by a valve, one path is the tertiary air duct (10) connected to the heat exchanger (14), and the heat exchanger (14) is connected to the decomposition furnace (4) through a pipeline; the other path is the tertiary air duct (10) directly connected to the decomposition furnace (4) without passing through the heat exchanger (14). The valve B (11) is arranged on the tertiary air duct (10) connecting the cooler (9) and the heat exchanger (14), and the valve C (12) is arranged on the pipeline connecting the heat exchanger (14) and the decomposition furnace (4); the valve A (13) is arranged on the tertiary air duct (10) connecting the cooler (9) and the decomposition furnace (4). The discharge ports of the penultimate cyclone separators of the A-row cyclone preheaters and the B-row cyclone preheaters are both connected to the decomposition furnace (4) through pipelines; the conveying pipelines connecting the discharge ports of the penultimate cyclone separators of the A-row cyclone preheaters and the B-row cyclone preheaters and the decomposition furnace (4) each include a conveying trunk and a conveying branch, and the number of the conveying branches of the A-row and the B-row are both two; each conveying branch is connected in parallel, and a material dividing valve (3) is arranged at the connection between the conveying trunk and the conveying branch; the material dividing valve (3) can adjust the amount of material entering each conveying branch from the conveying trunk, thereby realizing multi-point feeding of the decomposition furnace. The decomposition furnace (4) is provided with a fuel inlet (5) for the decomposition furnace, and the number of the fuel inlets is 4, so that the fuel can be fed at multiple points. The rotary kiln (7) is provided with a fuel inlet (8) for the rotary kiln. The cooler (9) is selected from a grate cooler, a single-cylinder cooler, a multi-cylinder cooler, etc.

[0042] By switching the valve, the system can be switched to any of the following three situations:

[0043] The first case: valve A (13) is fully closed, valve B (11) and valve C (12) are fully open, and the system is a CO2 self-enrichment type cement kiln.

[0044] The tertiary air enters the heat exchanger (14) through the tertiary air duct (10), and the oxygen enters the heat exchanger (14) through the gas inlet (1401). The tertiary air and the oxygen exchange heat in the heat exchanger (14). The oxygen after the heat exchange enters the decomposition furnace (4). The tertiary air after the heat exchange enters the waste heat utilization or treatment system through the gas outlet (1402) provided on the heat exchanger (14).

[0045] The raw meal is fed into the A-row cyclone preheater and the B-row cyclone preheater respectively. The raw meal is heat-exchanged with the flue gas for multiple times through the cyclone separator and the connecting air duct, and finally the raw meal can be preheated to 700-800°C. The preheated raw meal passes through the penultimate cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater and enters the decomposition furnace (4). The combustion of fuel in the decomposition furnace (4) releases a large amount of heat for decomposition of raw materials. The decomposition-completed hot raw materials leave the decomposition furnace (4). The raw materials leaving the decomposition furnace (4) enter the rotary kiln (7) after gas-solid separation in the A-row cyclone preheater and the lowest-level cyclone separator in the B-row cyclone preheater. The raw materials are calcined in the rotary kiln (7) to form clinker. The clinker enters the cooler (9) from the outlet of the rotary kiln (7) and is then cooled to 65°C+ambient temperature by the cooler (9). The kiln gas generated in the rotary kiln (7) enters the decomposition furnace (4). The decomposition furnace (4) is oxygen-enriched combustion. The kiln gas generated in the rotary kiln (7) and the flue gas generated by the combustion of fuel and decomposition of raw materials in the decomposition furnace (4) are discharged from the decomposition furnace. (4) The outlets enter the lowest cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater respectively, and after completing gas-solid separation with the hot raw meal, enter the penultimate cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater. The raw meal is preheated multiple times in the cyclone separator and the connecting air duct, and finally leaves from the flue gas outlet (15) of the A-row cyclone preheater and the flue gas outlet (16) of the B-row cyclone preheater. The flue gas temperature at the outlet of the A-row and the B-row cyclone preheater is 300-400°C, and the CO2 concentration in the flue gas is greater than 50%. After a series of processes such as drying, purification, capture and purification, the CO2 concentration can reach more than 99%, and then it is recycled or sealed. The air at ambient temperature is passed through a cooler (9) to cool the high-temperature clinker entering the cooler (9) from the outlet of the rotary kiln. After the heat exchange is completed, the air is divided into three paths: the first path of air enters the rotary kiln (7) as high-temperature secondary air (900-1200°C) for fuel combustion, the second path of air is high-temperature tertiary air (800-1000°C), the tertiary air enters the heat exchanger (14) through the tertiary air duct (10), oxygen enters the heat exchanger (14), oxygen and tertiary air exchange heat through the heat exchanger (14), the oxygen after the heat exchange is completed enters the decomposition furnace (4), and the tertiary air after the heat exchange is completed enters the waste heat utilization or treatment system. The third path of air (250-450°C) enters the waste heat boiler for power generation or other waste heat utilization or treatment systems, and the flue gas after power generation or other waste heat utilization and treatment systems is discharged into the atmosphere through the chimney after being treated by the waste air.

[0046] The second situation: valve A (13) is fully closed, valve B (11) and valve C (12) are fully open, and the system is a CO2 self-enrichment type cement kiln.

[0047] The flow direction of materials and gases is the same as that in the first case, except that a portion of the flue gas discharged from the outlet of the A-row cyclone preheater or the B-row cyclone preheater or the outlet of both the A-row and B-row cyclone preheaters is used as circulating flue gas, and the mixed gas of circulating flue gas and oxygen enters the heat exchanger (14) through the gas inlet (1401), and the tertiary air exchanges heat with the mixed gas of circulating flue gas and oxygen in the heat exchanger (14). The mixed gas of circulating flue gas and oxygen after the heat exchange enters the decomposition furnace (4), and oxygen-enriched combustion is performed in the decomposition furnace (4).

[0048] The flue gas temperature at the outlet of the cyclone preheaters of columns A and B is 300-400°C, and the CO2 concentration in the flue gas is >50%.

[0049] The third situation: valve A (13) is fully open, valve B (11) and valve C (12) are fully closed, and the system is an online cement kiln at this time.

[0050] The raw meal is fed into the A-row cyclone preheater and the B-row cyclone preheater respectively. The raw meal is heat-exchanged with the flue gas for many times through the cyclone separator and the connecting air duct, and finally the raw meal can be preheated to 700-800°C. The preheated raw meal enters the decomposition furnace (4) from the penultimate cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater. The combustion of fuel in the decomposition furnace (4) releases a large amount of heat for the decomposition of the raw meal. The hot raw meal after decomposition leaves the decomposition furnace (4) and passes through the lowest cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater after gas-solid separation, and then enters the rotary kiln (7) through the smoke chamber (6). The raw meal is calcined in the rotary kiln (7) to form clinker. The clinker enters the cooler (9) from the outlet of the rotary kiln (7), and then is cooled to 65°C + ambient temperature through the cooler (9).

[0051] The kiln gas generated in the rotary kiln (7) enters the decomposition furnace (4), and the kiln gas generated by the combustion of fuel and the decomposition of raw materials in the decomposition furnace (4) respectively enters the lowest cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater from the outlet of the decomposition furnace (4), and enters the penultimate cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater after completing gas-solid separation with the hot raw materials. The raw materials are preheated multiple times in the cyclone separator and the connecting air duct, and finally leave from the outlet of the highest cyclone separator of the A-row cyclone preheater and the B-row cyclone preheater. The outlet flue gas temperature of the A-row cyclone preheater and the B-row cyclone preheater is 300-400°C, and the CO2 concentration in the flue gas is 25-35%. After passing through the waste heat boiler for power generation, the drying raw material mill and the flue gas treatment system, it is discharged into the atmosphere. The air at ambient temperature is passed through a cooler (9) to cool the high-temperature clinker entering the cooler (9) from the outlet of the rotary kiln (7). After the heat exchange is completed, the air is divided into three paths: the first path of air enters the rotary kiln (7) as high-temperature secondary air (900-1200°C) for fuel combustion, the second path of air is tertiary air (800-1000°C), and the tertiary air enters the decomposition furnace (4) through the tertiary air duct (10) to provide fuel combustion in the decomposition furnace (4). The third path of air (250-450°C) enters the waste heat boiler for power generation or other waste heat utilization or treatment systems. After power generation is completed or the flue gas from other waste heat utilization and treatment systems is discharged into the atmosphere through a chimney after being treated by the waste air.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. The cement kiln system transformed from an online calciner is characterized by: The system includes a first row of cyclone preheaters, a second row of cyclone preheaters, a decomposition furnace, a smoke chamber, a rotary kiln, a cooler, a heat exchanger, and a switching component; The air inlets of the lowest cyclone separators of the first and second cyclone preheaters are connected to the decomposition furnace; the discharge ports of the lowest cyclone separators of the first and second cyclone preheaters are connected to the smoke chamber; the discharge ports of the second to last cyclone separators of the first and second cyclone preheaters are connected to the decomposition furnace through pipelines; the decomposition furnace is connected to the smoke chamber, the smoke chamber is connected to the rotary kiln; the rotary kiln is connected to the cooler; The cooler is provided with a tertiary air duct, and the tertiary air duct is provided with a switching component. The tertiary air duct is divided into two paths by the switching component. One path is that the tertiary air duct is connected to the heat exchanger, and the heat exchanger is connected to the decomposition furnace through a pipeline; the other path is that the tertiary air duct is directly connected to the decomposition furnace without passing through the heat exchanger; The switching component is selected from a valve; The valves include a first valve, a second valve, and a third valve; The first valve is arranged on the tertiary air duct connecting the cooler and the heat exchanger, the second valve is arranged on the pipeline connecting the heat exchanger and the decomposition furnace; the third valve is arranged on the tertiary air duct connecting the cooler and the decomposition furnace.

2. The cement kiln system transformed from an online calciner according to claim 1, characterized in that: The valve is selected from a gate valve or a butterfly valve.

3. The cement kiln system transformed from an online calciner according to claim 1, characterized in that: The pipeline may or may not contain branches; When the pipeline does not include a branch, the first row of cyclone preheaters and the second row of cyclone preheaters feed the decomposition furnace at a single point; When the pipeline includes branches, the first row of cyclone preheaters and the second row of cyclone preheaters feed the decomposition furnace at multiple points; the conveying pipelines connecting the discharge ports of the penultimate cyclone separators of the first row of cyclone preheaters and the second row of cyclone preheaters to the decomposition furnace all include a conveying trunk and a conveying branch, and the number of the conveying branches is more than 2; the conveying branches are connected in parallel, and a dividing valve is provided at the connection between the conveying trunk and the conveying branch; the dividing valve adjusts the amount of material entering each conveying branch from the conveying trunk.

4. The cement kiln system transformed from an online calciner according to claim 1, characterized in that: The number of stages of the first row of cyclone preheaters and the second row of cyclone preheaters is selected from 3 to 7.

5. The cement kiln system transformed from an online calciner according to claim 1, characterized in that: The heat exchanger is provided with one or more gas inlets and one or more gas outlets; One of the gas outlets is connected to a waste heat utilization or treatment system; the waste heat utilization or treatment system includes a waste heat boiler for power generation and material drying; The cooler is selected from a grate cooler, a single-drum cooler, and a multi-drum cooler.

6. The cement kiln system transformed from an online calciner according to claim 1, characterized in that: The first row of cyclone preheaters and the second row of cyclone preheaters are provided with raw material feeding inlets, which are arranged at the inlet air duct of the top first-stage cyclone separator of the first row of cyclone preheaters and the second row of cyclone preheaters, or at the inlet air duct of the top second-stage cyclone separator of the first row of cyclone preheaters and the second row of cyclone preheaters.

7. The cement kiln system transformed from an online calciner according to claim 1, characterized in that: The decomposition furnace is provided with a fuel inlet, and the number of the fuel inlets is more than one.

8. A method for preparing cement clinker using a cement kiln system transformed from an online calciner according to any one of claims 1 to 7, characterized in that: The method for preparing cement clinker comprises: The raw meal is added to the first row of cyclone preheaters and the second row of cyclone preheaters respectively, and the raw meal exchanges heat with the flue gas in the cyclone preheaters; The raw meal preheated by the first and second cyclone preheaters enters the calciner through one or more points; The hot raw material decomposed by the decomposition furnace leaves the decomposition furnace and enters the penultimate cyclone separator of the first and second cyclone preheaters respectively. After gas-solid separation, it enters the rotary kiln through the smoke chamber and is calcined in the rotary kiln to form clinker. The clinker enters the cooler from the outlet of the rotary kiln and is then cooled by the cooler to obtain cement clinker. The kiln gas formed in the rotary kiln enters the decomposition furnace; the kiln gas formed in the rotary kiln and the flue gas formed in the decomposition furnace are discharged from the outlets of the top cyclone separators of the first and second rows respectively after gas-solid heat exchange in the first and second rows of cyclone preheaters; The tertiary air is divided into two paths by the switching component, and any one of the following paths is selected by adjusting the switching component: one path is that the tertiary air enters the heat exchanger through the tertiary air duct, the mixed gas of circulating flue gas and oxygen or oxygen enters the heat exchanger, the tertiary air exchanges heat with the mixed gas of circulating flue gas and oxygen or oxygen through the heat exchanger, the mixed gas of circulating flue gas and oxygen or oxygen after the heat exchange enters the decomposition furnace, and the tertiary air after the heat exchange enters the waste heat utilization or treatment system; the other path is that the tertiary air in the tertiary air duct directly enters the decomposition furnace.

9. The method for preparing cement clinker according to claim 8, characterized in that: The tertiary air is divided into two paths by a valve, and any one of the following paths is selected by adjusting the valve: one path is that the third valve is closed, the first valve and the second valve are opened, the tertiary air enters the heat exchanger through the tertiary air duct, the mixed gas of circulating flue gas and oxygen or oxygen enters the heat exchanger, the tertiary air exchanges heat with the mixed gas of circulating flue gas and oxygen or oxygen through the heat exchanger, and the mixed gas of circulating flue gas and oxygen or oxygen after the heat exchange enters the decomposition furnace, and oxygen-enriched combustion is performed in the decomposition furnace. At this time, the system is a CO2 self-enrichment type cement kiln; the other path is that the third valve is opened, the first valve and the second valve are closed, and the tertiary air in the tertiary air duct directly enters the decomposition furnace. At this time, the system is an online cement kiln.

10. The method for preparing cement clinker according to claim 8 or 9, characterized in that: In terms of gas flow direction, the air cools the high-temperature clinker through the cooler, and the air after heat exchange is divided into the following three routes: the first route of high-temperature air is used as secondary air to directly enter the rotary kiln for fuel combustion; the second route of air is divided into two situations: when the third valve is fully closed and the first valve and the second valve are fully open, the system acts as a CO2 self-enrichment cement kiln, and the tertiary air exchanges heat with the mixed gas of circulating flue gas and oxygen or oxygen through the heat exchanger, and the mixed gas of circulating flue gas and oxygen or oxygen exiting the heat exchanger enters the decomposition furnace, and the tertiary air exiting the heat exchanger enters the waste heat utilization or treatment system; when the third valve is fully open and the first valve and the second valve are fully closed, the system acts as an online cement kiln, and the tertiary air directly enters the decomposition furnace for fuel combustion; the third route of air enters the waste heat utilization or treatment system.

11. The method for preparing cement clinker according to claim 10, characterized in that: The air outlets of the cooling machine are the first route, the second route and the third route; or the first route is the only air outlet and the second route and the third route are combined air outlets.

12. The method for preparing cement clinker according to claim 11, characterized in that: The second and third air outlets are combined so that the second and third air outlets share one air outlet pipe.

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