Decomposing furnace control method based on low-NOX full-system oxygen-fuel combustion and method and system for preparing cement clinker

Abstract

The invention discloses a decomposing furnace control method based on low-NOX full-system oxygen-fuel combustion and a method and system for preparing cement clinker, kiln-out flue gas and lifting air are introduced into the bottom of a decomposing furnace, and the lifting air comes from flue gas which is discharged from an air outlet in the top end of a preheater and is subjected to heat exchange through a cooling area in the middle of a grate cooler; the concentration of O2 in the lifting air is lower than 5%, the concentration of CO2 in the lifting air is higher than 70%, and the temperature is 500-900 DEG C; tertiary air is introduced into the decomposing furnace above the lifting air, the tertiary air comes from mixed gas obtained after industrial oxygen and flue gas exhausted from an air outlet in the top end of a preheater are subjected to heat exchange through a cooling area at the head of a grate cooler, and the concentration of O2 in the mixed gas is larger than 30%; the decomposition furnace is arranged between the lifting air inlet and the tertiary air inlet, the peroxidation coefficient is smaller than 0.5, a reduction area is formed, the average temperature in the reduction area is 800-1200 DEG C, and self-removal of NOX in the flue gas discharged out of the kiln and lifting of materials below the tertiary air inlet are achieved; and a burnout area is formed above the tertiary air inlet.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas carbon capture, and particularly to a control method for a precalciner based on all-oxygen combustion of the whole system, a method for preparing cement clinker, and a system therefor. X Background Art

[0002] All-oxygen combustion of the whole system is based on the existing industrial kiln system, using high-purity oxygen to replace combustion-supporting air, and at the same time adopting flue gas circulation to adjust the medium flow rate and heat transfer characteristics of the whole kiln system, enriching all CO2 of fuel combustion and raw material decomposition, and obtaining CO2 flue gas with a volume concentration of more than 80%, so as to achieve permanent sequestration or resource utilization of CO2 after capture and purification at a relatively small cost, and realize large-scale industrial CO2 enrichment and emission reduction. Existing analyses have shown that compared with other carbon capture methods, the all-oxygen combustion technology has advantages in terms of investment cost, operation cost, CO2 emission reduction cost, large-scale and compatibility with existing technologies.

[0003] The all-oxygen combustion technology is a research hotspot in the field of carbon emission reduction in the international cement industry. However, compared with traditional air combustion, there are problems such as difficult control of the combustion flame under high O2 concentration and increased NO generated during combustion at high temperatures. X After the oxygen concentration increases, the highest flame temperature in the burning zone will rise rapidly, and the combustion temperature under all-oxygen conditions can reach above 2500 °C. The thermal NO in the rotary kiln will X double, increasing the load of flue gas denitrification in the production line.

[0004] Chinese Patent Publication No. CN112500001A discloses a low-energy-consumption carbon enrichment cement production system and a method for producing cement clinker, proposing to divide the kiln head cooler into zones, using the circulating flue gas in the medium temperature section as the lifting air, and recycling the heat of the clinker out of the kiln to the preheater system; Chinese Patent Publication No. CN115867515A discloses a system and method for producing cement clinker by all-oxygen combustion, proposing to control the temperature of the rotary kiln wall surface by using the lifting air from the grate cooler. Although the above patents disclose the lifting air process of all-oxygen combustion, they do not involve the problem of NO X emission reduction in flue gas under all-oxygen combustion. Chinese Patent Publication No. CN108167860A discloses a gradient combustion self-denitrification process method for a firing system, proposing to form a gradient combustion environment of an extremely oxygen-deficient zone - an oxygen-deficient combustion zone - an oxygen-rich burnout zone in the precalciner, and reducing the NO in the rotary kiln through the oxygen-deficient reducing atmosphere X , but this process is applicable to the air combustion condition. Under the all-oxygen combustion condition, the flue gas volume out of the rotary kiln is greatly reduced, and there is a problem that the oxygen-deficient zone cannot normally lift the raw material due to too low air volume out of the kiln, resulting in furnace bottom collapse. Summary of the Invention ​

[0005] In order to solve the problems of high NO concentration in the flue gas discharged from the kiln during the clinker burning process under the condition of all-oxygen combustion and great difficulty in denitrification, the present invention proposes a control method for a precalciner based on low-NO all-system all-oxygen combustion, a method and a system for preparing cement clinker. By moving the position of the tertiary air in the precalciner upward and introducing the lifting air from the grate cooler into the furnace bottom, and spraying the fuel into the mixture of the flue gas discharged from the kiln and the lifting air, an oxygen-deficient combustion environment is established at the lower part of the precalciner. The fuel gasifies in the oxygen-deficient combustion environment to generate reducing gases, forming a reduction zone, so as to achieve self-removal of NO in the flue gas discharged from the kiln. X At the same time, due to the reduction of the flue gas volume discharged from the kiln under the all-oxygen condition and the upward movement of the tertiary air, a single flue gas discharged from the kiln is not sufficient to lift the materials in the reduction zone. Part of the lifting air from the grate cooler is introduced into the reduction zone at the furnace bottom to regulate the air volume in the reduction zone, which can prevent the problem of raw material collapse caused by insufficient air volume at the furnace bottom. X The present invention is realized as follows. A control method for a precalciner based on low-NO all-system all-oxygen combustion includes the following steps: X The flue gas discharged from the kiln and the lifting air are introduced into the bottom of the precalciner. The lifting air comes from the flue gas discharged from the top air outlet of the preheater and cooled by the middle cooling zone of the grate cooler. The O2 concentration in the lifting air is lower than 5%, the CO2 concentration is higher than 70%, and the temperature is 500-900°C.

[0006] The tertiary air is introduced into the precalciner above the lifting air. The tertiary air comes from the mixture of industrial oxygen and the flue gas discharged from the top air outlet of the preheater and cooled by the head cooling zone of the grate cooler. The O2 concentration in the mixture is greater than 30%. X Fuel and raw materials are fed between the inlet of the lifting air and the inlet of the tertiary air in the precalciner. The excess oxygen coefficient is less than 0.5 to form a reduction zone, so that the average temperature in the reduction zone is 800-1200°C, realizing self-removal of NO in the flue gas discharged from the kiln and lifting the materials below the inlet of the tertiary air. Raw materials are fed above the inlet of the tertiary air to form a burnout zone.

[0007] In the above technical solution, preferably, the flue gas at the top outlet of the precalciner first goes up and then down, and the lifting air is introduced into the downward pipeline to adjust the outlet temperature of the precalciner.

[0008] In the above technical solution, preferably, the lifting air swirls into the precalciner. Along the flow direction of the lifting air, the lifting air first contacts the raw materials and then contacts the fuel.

[0009] In the above technical solution, preferably, the wind speed at the bottom of the precalciner is maintained between 30 and 50 m / s. X In the above technical solution, preferably, the flue gas at the top outlet of the precalciner first goes up and then down, and the lifting air is introduced into the downward pipeline to adjust the outlet temperature of the precalciner.

[0010] In the above technical solution, preferably, the lifting air swirls into the precalciner. Along the flow direction of the lifting air, the lifting air first contacts the raw materials and then contacts the fuel.

[0011] In the above technical solution, preferably, the wind speed at the bottom of the precalciner is maintained between 30 and 50 m / s.

[0012] In the above technical solution, preferably, the wind speed at the bottom of the precalciner is maintained between 30 and 50 m / s.

[0013] In the above technical solution, preferably, the O2 concentration in the industrial oxygen is greater than 80%.

[0014] A method for preparing cement clinker by low-NOx all-system oxy-fuel combustion, comprising the following steps:

[0015] Feed the raw meal into the preheater, where the raw meal exchanges heat with the flue gas and undergoes gas-solid separation in the preheater to preheat the raw meal to the decomposition temperature;

[0016] Feed the preheated raw meal into the decomposition furnace; a decomposition reaction occurs in the decomposition furnace to obtain hot raw meal; and a large amount of flue gas is generated and enters the preheater, and the low-temperature flue gas after heat exchange is discharged from the outlet of the cyclone at the top of the preheater;

[0017] The hot raw meal enters the rotary kiln and is calcined to form clinker; the clinker is cooled in the grate cooler to obtain cement clinker;

[0018] Part of the low-temperature flue gas discharged from the outlet of the cyclone at the top of the preheater is used as recycled flue gas and enters the head cooling zone and the middle cooling zone of the grate cooler respectively;

[0019] The cooling medium in the head cooling zone of the grate cooler is a mixture of industrial oxygen and recycled flue gas, the cooling medium in the middle cooling zone is recycled flue gas, and the cooling medium in the tail cooling zone is air;

[0020] The high-temperature gas discharged from the head cooling zone is used as secondary air and tertiary air respectively. The secondary air is fed into the rotary kiln, and the tertiary air is fed into the decomposition furnace. The recycled flue gas discharged from the middle cooling zone is fed into the decomposition furnace as lift air;

[0021] The decomposition furnace is controlled by the above decomposition furnace control method.

[0022] In the above technical solution, preferably, there is no air leakage between the head cooling zone, the middle cooling zone, and the tail cooling zone of the grate cooler.

[0023] In the above technical solution, preferably, the CO2 concentration in the low-temperature flue gas discharged from the outlet of the top cyclone is greater than 70%.

[0024] A low-NO X A system for preparing cement clinker by all-system oxy-fuel combustion to implement the method for preparing cement clinker by low-NOx all-system oxy-fuel combustion, comprising a preheater, a decomposition furnace, a kiln tail smoke chamber, a rotary kiln, and a grate cooler connected in sequence;

[0025] The grate cooler is divided into three zones from the clinker inlet to the outlet, namely the head cooling zone, the middle cooling zone, and the tail cooling zone in sequence. The outlet of the top cyclone of the preheater is respectively connected to the air inlets of the head cooling zone and the middle cooling zone, and an industrial oxygen inlet is provided at the air inlet of the head cooling zone; characterized in that:

[0026] The calciner is provided with a tertiary air inlet, a lifting air inlet, a raw material feeding point and a fuel feeding point. The lifting air inlet is located below the tertiary air inlet; the secondary air intake of the head cooling zone of the grate cooler is communicated with the rotary kiln, the tertiary air intake is communicated with the tertiary air inlet of the calciner through a pipeline, and the lifting air intake of the middle cooling zone is communicated with the lifting air inlet of the calciner through a pipeline; at least 2 raw material feeding points are provided, at least one of the raw material feeding points is located between the lifting air inlet and the tertiary air inlet, and at least one of the raw material feeding points is located above the tertiary air inlet; the height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet; the fuel feeding point is located between the lifting air inlet and the tertiary air inlet, so that the fuel is sprayed into the mixture of the flue gas from the kiln and the lifting air; a reduction zone is formed between the lifting air inlet and the tertiary air inlet in the calciner, and a burnout zone is formed above the tertiary air inlet.

[0027] In the above technical solution, preferably, the outlet of the cyclone at the top of the preheater is connected to a high-temperature fan, and the outlet of the high-temperature fan is divided into two paths, one path is connected to the carbon capture system, and the other path is connected to the air inlets of the head cooling zone and the middle cooling zone of the grate cooler.

[0028] In the above technical solution, preferably, the outlet at the top of the calciner is provided with a pipeline that first goes up and then goes down, and the lifting air intake of the middle cooling zone is also communicated with the downpipe through a pipeline.

[0029] In the above technical solution, more preferably, a first loop air regulating valve is provided on the pipeline between the lifting air intake of the middle cooling zone of the grate cooler and the downpipe, and a second loop air regulating valve is provided on the pipeline between the lifting air intake and the lifting air inlet of the calciner.

[0030] In the above technical solution, preferably, a tertiary air regulating valve is provided on the pipeline between the tertiary air intake of the head cooling zone of the grate cooler and the tertiary air inlet of the calciner.

[0031] In the above technical solution, preferably, a distributing valve is provided on the feeding pipe at the raw material feeding point of the calciner to regulate the distribution ratio of each raw material feeding point, so that the average temperature in the reduction zone of the calciner is 800 - 1200 °C.

[0032] In the above technical solution, preferably, a first constriction is provided at the tertiary air inlet of the calciner, and a second constriction is provided at the lifting air inlet.

[0033] In the above technical solution, preferably, the head cooling zone and the middle cooling zone of the grate cooler are located in the first section of the grate cooler, the tail cooling zone is located in the second section of the grate cooler, an intermediate roller crusher for reducing the air leakage between the two sections is provided between the first section and the second section of the grate cooler, and a partition wall for reducing the air leakage between the head cooling zone and the middle cooling zone is provided in the middle of the first section of the grate cooler.

[0034] The advantages and positive effects of the present invention are as follows:

[0035] (1) By moving the inlet position of the tertiary air of the precalciner upward and introducing the lifting air from the grate cooler into the bottom of the precalciner, the fuel is sprayed into the mixture of the flue gas from the kiln and the lifting air, so as to establish an oxygen-deficient combustion environment in the lower part of the precalciner. The fuel gasifies in the oxygen-deficient combustion environment to generate reducing gases, forming a reduction zone, and realizing the self-removal of NO in the flue gas from the kiln. X Meanwhile, since the air volume of the flue gas from the kiln decreases under the all-oxygen condition and the inlet position of the tertiary air moves upward, the single flue gas from the kiln is not sufficient to lift the materials in the reduction zone. Part of the lifting air from the grate cooler is introduced into the reduction zone at the bottom of the furnace to regulate the air volume in the reduction zone, which can avoid the problem of raw meal collapse caused by insufficient air volume at the bottom of the furnace.

[0036] (2) The present invention realizes the self-removal of NO in the flue gas from the kiln under the all-oxygen combustion condition, and at the same time can prevent the problem of raw meal collapse caused by insufficient air volume at the bottom of the furnace, ensuring the stable operation of the system. X Brief Description of the Drawings Brief Description of the Drawings

[0037] Figure 1 is a schematic diagram of a system for preparing cement clinker by all-oxygen combustion of the whole system provided in Embodiment 2 of the present invention; X is a top view of the lifting air entering the furnace with a double-inlet structure provided in Embodiment 2 of the present invention;

[0038] Figure 2 is a top view of the lifting air entering the furnace with a double-inlet structure provided in Embodiment 2 of the present invention;

[0039] Figure 3 is a top view of the lifting air entering the furnace with a single-inlet structure provided in Embodiment 3 of the present invention.

[0040] In the figure: A - industrial oxygen; B - recycled flue gas; C - air; g2 - secondary air; g3 - tertiary air; g4 - lifting air; g41 - the first path of lifting air; g42 - the second path of lifting air; g5 - air leaving the air cooling zone; F1 - fuel entering the rotary kiln; F2 - fuel entering the precalciner; R - raw meal; K - cement clinker;

[0041] 1 - grate cooler; 101 - the first section of the grate cooler; 102 - the second section of the grate cooler; 103 - intermediate roller crusher; 104 - partition wall; 1a - head cooling zone; 1b - middle cooling zone; 1c - tail cooling zone;

[0042] 2 - Rotary kiln; 3 - Calciner; 301 - Reduction zone; 302 - Burnout zone; 303 - Downcomer; 304 - Burner; 305 - Feeding box; 306 - Lifting air inlet; 4 - Preheater; 401 - First - stage cyclone; 402 - Second - stage cyclone; 403 - Third - stage cyclone; 404 - Fourth - stage cyclone; 405 - Fifth - stage cyclone; 5 - Kiln tail flue chamber; 6 - High - temperature fan; 903 - Tertiary air regulating valve; 904 - First - path recirculating air regulating valve; 905 - Second - path recirculating air regulating valve; 906 - Material distributing valve;

[0043] The dotted line with an arrow represents the air flow direction; the solid line with an arrow represents the material flow direction. Specific implementation mode

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0046] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" 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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0047] Embodiment 1

[0048] Under the condition of oxy - fuel combustion, the O2 concentration of the secondary air entering the kiln is greater than 30%, and the flue gas volume leaving the kiln is less than 0.3 Nm 3 / kg. clinker, while under the normal air - fuel combustion condition, the flue gas volume leaving the kiln is generally 0.4 - 0.45 Nm 3 / kg of clinker, so the air volume of the flue gas leaving the kiln is reduced by more than 25% compared with the conventional air combustion condition. With the increase in the O2 concentration of the secondary air entering the kiln and the increase in the combustion flame temperature, the NOx in the rotary kiln will increase. If a reduction zone can be created in the precalciner to reduce the NOx in the flue gas leaving the kiln, the NOx emission of the flue gas will be reduced. Therefore, it is necessary to design a low-NOx type precalciner. However, for a low-NOx type precalciner, the raw meal entering the furnace mainly moves upward through the flue gas in the tail gas chamber of the kiln to lift the raw meal at the bottom of the furnace. The decrease in the air volume of the tail gas chamber of the kiln easily leads to insufficient momentum for lifting the raw meal and causes material collapse. Therefore, it is necessary to add a lifting air flow g4 at the bottom of the precalciner. The lifting air flow g4 is located below the raw meal feeding point and can supplement the function of lifting the raw meal. When the O2 content in the lifting air flow g4 is less than 5%, after the lifting air flow g4 enters the reduction zone 301, it can still ensure that the excess oxygen coefficient in the reduction zone is less than 0.5, thus not reducing the denitrification effect in the reduction zone.

[0049] Specifically, based on low NO X The control method of the precalciner for all-oxygen combustion of the whole system includes the following steps:

[0050] The flue gas leaving the kiln and the lifting air flow g4 are introduced into the bottom of the precalciner 3. The lifting air flow g4 comes from the flue gas discharged from the top air outlet of the preheater 4 and heat-exchanged in the middle cooling zone of the grate cooler. The O2 concentration in the lifting air flow is lower than 5%, the CO2 concentration is higher than 70%, and the temperature is 500 - 900 °C;

[0051] The tertiary air flow g3 is introduced above the lifting air flow g4 into the precalciner. The tertiary air flow g3 comes from the mixture of industrial oxygen A and the flue gas discharged from the top air outlet of the preheater and heat-exchanged in the head cooling zone 1a of the grate cooler. The O2 concentration in the mixture is greater than 30%;

[0052] Fuel and raw meal are fed between the inlet 306 of the lifting air flow and the inlet of the tertiary air flow into the precalciner, with the excess oxygen coefficient less than 0.5, to form a reduction zone 301, so that the average temperature in the reduction zone is 800 - 1200 °C, realizing the self-removal of NO in the flue gas leaving the kiln and the lifting of the material below the inlet of the tertiary air flow; raw meal is fed above the inlet of the tertiary air flow to form a burnout zone 302. X

[0053] As a preferred implementation mode, the flue gas at the top outlet of the precalciner 3 first goes up and then down, and the lifting air flow is introduced into the downward pipeline 303 to adjust the outlet temperature of the precalciner 3 and avoid the blocking of the final-stage cyclone separator of the preheater 4 due to crust formation.

[0054] As a preferred embodiment, the lifting air g4 swirls into the decomposition furnace 3. Along the flow direction of the lifting air, the lifting air first contacts the raw meal and then contacts the fuel. On the one hand, the lifting air is relatively close to the raw meal, which is beneficial to the lifting of the raw meal. On the other hand, the temperature of the lifting air g4 is 500 - 900 °C, which is relatively lower than the temperature of the flue gas leaving the kiln (1000 - 1200 °C). The lifting air is relatively far from the fuel, so it will not reduce the temperature of the fuel feeding area and will not reduce the fuel gasification rate.

[0055] As a preferred embodiment, the air velocity at the bottom of the decomposition furnace 3 is maintained between 30 - 50 m / s to ensure the lifting of the materials at the bottom of the decomposition furnace.

[0056] As a preferred embodiment, the O2 concentration in the industrial oxygen A is greater than 80%, and it comes from the oxygen production system.

[0057] Example 2

[0058] Please refer to Figure 1 , the embodiment of the present invention provides a system for preparing cement clinker by all - oxygen combustion in the whole system with low NO X The system includes a preheater 4, a decomposition furnace 3, a kiln tail smoke chamber 5, a rotary kiln 2, and a grate cooler 1 connected in sequence.

[0059] The preheater 4 can adopt a two - to seven - stage preheater. In this embodiment, a five - stage preheater is taken as an example for illustration. The raw meal R fed into the preheater 4 is fed through the outlet air duct of the second - stage cyclone. After gas - solid heat exchange, it enters the first - stage cyclone 401 driven by the air flow. After gas - solid separation in the first - stage cyclone 401, the material is fed into the outlet air duct of the third - stage cyclone 403 through the discharge pipe of the first - stage cyclone 401. In the above - mentioned manner, it enters the second - stage cyclone 402, the third - stage cyclone 403, and the fourth - stage cyclone 404 in sequence. The raw meal after gas - solid separation in the fourth - stage cyclone 404 enters the decomposition furnace 3, and the raw meal decomposition is completed in the decomposition furnace. The decomposed hot raw meal enters the fifth - stage cyclone 405 along with the air flow. After gas - solid separation, it is fed into the kiln tail smoke chamber 5 and enters the rotary kiln 2 for calcination to produce clinker, and then is cooled by the grate cooler 1 to obtain cement clinker K.

[0060] The grate cooler 1 is divided into three zones from the clinker inlet to the outlet, namely the head cooling zone 1a, the middle cooling zone 1b, and the tail cooling zone 1c in sequence. The head cooling zone 1a and the middle cooling zone are located in the first section 101 of the grate cooler, and the tail cooling zone 1c is located in the second section 102 of the grate cooler. The air outlets of the cyclones at the top of the preheater are respectively connected to the air inlets of the head cooling zone 1a and the middle cooling zone, and an industrial oxygen inlet is provided at the air inlet of the head cooling zone 1a. Under the condition of all-oxygen combustion, the flue gas discharged from the air outlets of the cyclones at the top of the preheater 4 is low-temperature flue gas, and the CO2 concentration in the low-temperature flue gas is greater than 70%, which is denoted as CO2 recycle flue gas. A mixture of industrial oxygen A and CO2 recycle flue gas, that is, O2 / CO2 mixture gas, is introduced into the air inlet of the head cooling zone 1a, only CO2 recycle flue gas is introduced into the air inlet of the middle cooling zone 1b, and air C is introduced into the air inlet of the tail cooling zone 1c. Then, from the clinker inlet to the outlet of the grate cooler are successively the O2 / CO2 mixture gas cooling zone, the recycle flue gas cooling zone, and the air cooling zone. The air outlets of the cyclones at the top of the preheater 4 are connected to the air inlets of the O2 / CO2 mixture gas cooling zone and the recycle flue gas cooling zone. A mixture of industrial oxygen A and CO2 recycle flue gas is introduced into the air inlet of the O2 / CO2 mixture gas cooling zone, only CO2 recycle flue gas is introduced into the air inlet of the recycle flue gas cooling zone, and air C is introduced into the air inlet of the air cooling zone.

[0061] A tertiary air inlet, a lifting air inlet 306, a raw meal feeding point, and a fuel feeding point are provided on the decomposition furnace 3. The lifting air inlet 306 is located below the tertiary air inlet. The secondary air extraction opening in the O2 / CO2 mixture gas cooling zone of the grate cooler is communicated with the air inlet of the rotary kiln. The tertiary air extraction opening in the O2 / CO2 mixture gas cooling zone of the grate cooler is communicated with the tertiary air inlet of the decomposition furnace through a pipeline. The high-temperature gas discharged from the O2 / CO2 mixture gas cooling zone is respectively used as secondary air g2 and tertiary air g3. The lifting air extraction opening in the recycle flue gas cooling zone of the grate cooler is communicated with the lifting air inlet 306 of the decomposition furnace through a pipeline, and the CO2 recycle flue gas discharged from the recycle flue gas cooling zone is used as lifting air g4. At least 2 raw meal feeding points are provided at the raw meal feeding point of the decomposition furnace, and at least one raw meal feeding point is located between the lifting air inlet 306 and the tertiary air inlet, and at least one raw meal feeding point is located above the tertiary air inlet; the height of the lifting air inlet of the decomposition furnace is below the raw meal feeding point below the tertiary air inlet to realize the lifting of the material below the tertiary air inlet and prevent material collapse; the fuel feeding point of the decomposition furnace is located between the lifting air inlet 306 and the tertiary air inlet so that the fuel is sprayed into the mixture gas of the flue gas from the kiln and the lifting air; a reduction zone 301 is formed between the lifting air inlet 306 and the tertiary air inlet in the decomposition furnace to realize the self-removal of NO X from the flue gas from the kiln, and a burnout zone 302 is formed above the tertiary air inlet.

[0062] The high-temperature gas exiting the O2 / CO2 mixed gas cooling zone is respectively used as the secondary air g2 and the tertiary air g3. The secondary air intake of the grate cooler is connected to the intake of the rotary kiln, and the tertiary air intake of the grate cooler is connected to the tertiary air inlet of the decomposition furnace through a pipeline. Both the secondary air g2 and the tertiary air are the heat-exchanged O2 / CO2 mixed gas. The heat at the outlet of the O2 / CO2 mixed gas cooling zone is recovered and utilized, and then they enter the rotary kiln 2 and the decomposition furnace 3 respectively to provide a combustion-supporting environment. The CO2 recycle flue gas exiting the recycle flue gas cooling zone serves as the lifting air. The lifting air is the heat-exchanged CO2 recycle flue gas. The concentration of CO2 in the lifting air is higher than 70% and the concentration of O2 is lower than 5%. The temperature of the lifting air is higher than 500 °C. The lifting air is introduced into the lower part of the decomposition furnace, so that the fuel is sprayed into the mixed gas of the flue gas exiting the kiln and the lifting air, thereby creating an oxygen-deficient combustion environment in the lower part of the decomposition furnace. The fuel gasifies to produce reducing gas in the oxygen-deficient combustion environment, forming a reduction zone 301, achieving the self-removal of NO X from the flue gas exiting the kiln. At the same time, the air volume in the reduction zone 301 is regulated to prevent raw meal collapse caused by insufficient air volume at the furnace bottom.

[0063] As a preferred embodiment, as Figure 2 shown, in this embodiment, the lifting air enters the furnace in a double-inlet form. There are two lifting air inlets 306, two feeding boxes 305 and two burners 304 arranged on the decomposition furnace 3. The two lifting air inlets are arranged centrosymmetrically, the two burners 304 are arranged axially symmetrically, and the two feeding boxes are arranged axially symmetrically. Seen Figure 2 from the side, the two streams of lifting air swirl into the decomposition furnace respectively. Seen along the flow direction of the lifting air, each stream of lifting air first contacts the raw meal in its adjacent downstream and then contacts the fuel in its adjacent downstream. On the one hand, the lifting air is closer to the raw meal, which is beneficial to lifting the raw meal; on the other hand, the temperature of the lifting air is 500 - 900 °C, which is relatively lower than the temperature of the flue gas exiting the kiln (1000 - 1200 °C). The lifting air is relatively farther from the fuel and will not reduce the temperature in the fuel feeding area and the fuel gasification rate.

[0064] As a preferred embodiment, a pipeline that first goes up and then goes down is arranged at the top outlet of the decomposition furnace 3. The lifting air intake of the grate cooler recycle flue gas cooling zone is also connected to the downward pipeline 303 through a pipeline. The lifting air intake of the grate cooler is connected to the lifting air inlet of the decomposition furnace and the downward pipeline through pipelines respectively. The first stream of lifting air g41 is introduced into the lower part of the decomposition furnace to achieve the self-removal of NO X from the flue gas exiting the kiln. At the same time, the air volume in the reduction zone 301 is regulated to prevent raw meal collapse caused by insufficient air volume at the furnace bottom; the second stream of lifting air g42 is introduced into the downward pipeline 303 at the outlet of the decomposition furnace to adjust the outlet temperature of the decomposition furnace and avoid the clogging of the last-stage cyclone separator of the preheater due to crust formation.

[0065] As a preferred embodiment, a first constriction is provided at the inlet of the tertiary air of the precalciner, and a second constriction is provided at the inlet 306 of the lifting air, enhancing the gas-solid mixing and turbulent flow effect, preventing the material from settling and accumulating, and further ensuring the system stability.

[0066] As a preferred embodiment, a tertiary air regulating valve 903 is provided on the pipeline between the tertiary air extraction opening of the grate cooler and the tertiary air inlet of the precalciner. A first-stage circulating air regulating valve 904 is provided on the pipeline between the lifting air extraction opening of the grate cooler and the downstream pipeline 303, and a second-stage circulating air regulating valve 905 is provided on the pipeline between the lifting air extraction opening of the grate cooler and the lifting air inlet 306 of the precalciner, for distributing the air volume leading to the reduction zone 301 at the bottom of the precalciner and the downstream pipeline, realizing adjustable air volume. Both the first-stage circulating air regulating valve 904 and the second-stage circulating air regulating valve 905 are selected as high-temperature gate valves.

[0067] As a preferred embodiment, a distributing valve 906 is provided on the feeding pipe at the raw meal feeding point of the precalciner, regulating the distributing ratio of each raw meal feeding point, so that the average temperature in the reduction zone of the precalciner is 800 - 1200 °C.

[0068] As a preferred embodiment, the flue gas discharged from the air outlet at the top of the preheater 4 is low-temperature flue gas, and the CO2 concentration in the low-temperature flue gas is greater than 70%. The air outlet of the cyclone at the top of the preheater 4 is connected to the high-temperature fan 6. The outlet of the high-temperature fan 6 is divided into two paths. One path is connected to the carbon capture system, and the other path is used as circulating flue gas B and then divided into two branches to be connected to the grate cooler. A flue gas circulation volume regulating valve, a bag filter and a circulating fan can be sequentially arranged on the pipeline where this circulating flue gas B is located. The flue gas circulation volume regulating valve is used to adjust the circulating air volume of the circulating flue gas B, and the bag filter is used to reduce the dust concentration in the circulating fan to 100 mg / m 3 below; The waste gas from the high-temperature fan 6 is divided into two parts. One part enters the next carbon capture process, and the other part can be circulated and returned to the grate cooler under the induced draft of the circulating fan, serving as CO2 circulating flue gas.

[0069] Specifically, the outlet of the circulating fan is divided into two branches. One branch is connected to the air inlet of the O2 / CO2 mixed gas cooling zone of the grate cooler, and the other branch is connected to the air inlet of the circulating flue gas cooling zone of the grate cooler. An industrial oxygen inlet is provided on the branch connected to the air inlet of the O2 / CO2 mixed gas cooling zone of the grate cooler, and an oxygen concentration regulating valve is provided upstream of the industrial oxygen inlet on this branch, so that industrial oxygen A and CO2 circulating flue gas are mixed and enter the O2 / CO2 mixed gas cooling zone of the grate cooler.

[0070] The cooling medium of the grate cooler is divided into three levels. The first level is the O2 / CO2 mixed gas, the second level is the CO2 recycled flue gas, and the third level is air. By adding a level of CO2 recycled flue gas between the O2 / CO2 mixed gas and air, the direct cross-draft between the O2 / CO2 mixed gas and air is blocked, reducing the reduction of CO2 concentration in the waste gas due to cross-draft and enhancing the CO2 enrichment effect. At the same time, the second-level CO2 recycled flue gas is the lifting air, used as the heat transfer medium for transferring the heat of high-temperature clinker to raw meal. The CO2 recycled flue gas absorbs the heat of high-temperature clinker and transfers the heat of the CO2 recycled flue gas to raw meal through the preheater at the kiln tail, thereby reducing the heat consumption of the cement production system.

[0071] As a preferred implementation mode, the grate cooler is divided into two sections. The O2 / CO2 mixed gas cooling area and the recycled flue gas cooling area are located in the first section of the grate cooler, and the air cooling area is located in the second section of the grate cooler. An intermediate roller crusher for reducing cross-draft between the two sections is arranged between the first section and the second section of the grate cooler. A partition wall 104 for reducing cross-draft between the O2 / CO2 mixed gas cooling area and the recycled flue gas cooling area is arranged in the middle of the first section of the grate cooler. The partition wall is located between the tertiary air intake and the lifting air intake.

[0072] In summary, the oxygen for combustion in the decomposer 3 mainly comes from the tertiary air. To remove NO from the kiln exit flue gas X the lifting air from the grate cooler is introduced into the furnace bottom, and the fuel is sprayed into the mixed gas of the kiln exit flue gas and the lifting air, thereby establishing an oxygen-deficient combustion environment in the lower part of the decomposer. The fuel gasifies to produce reducing gases in the oxygen-deficient combustion environment, forming a reduction zone 301 to achieve self-removal of NO in the kiln exit flue gas. X At the same time, under the all-oxygen condition, the air volume at the kiln exit decreases, and the tertiary air moves upward. The single kiln exit flue gas is not sufficient to lift the materials in the reduction zone. Part of the lifting air from the grate cooler is introduced into the reduction zone at the furnace bottom to regulate the air volume in the reduction zone, which can prevent the problem of raw meal collapse caused by insufficient air volume at the furnace bottom.

[0073] Embodiment 3

[0074] As Figure 3 shown, different from Embodiment 2, the lifting air inlet to the furnace in this embodiment is in a single-inlet form. One lifting air inlet 306, one feeding box 305 and two burners 304 are arranged on the decomposer 3. The two burners are arranged axially symmetrically. From Figure 3 the perspective of the reduction zone, the raw meal feeding box is located between the lifting air inlet and the burner. The lifting air swirls into the decomposer. Looking along the flow direction of the lifting air, the lifting air first contacts the raw meal and then the fuel. On the one hand, the lifting air is relatively close to the raw meal, which is beneficial to lifting the raw meal; on the other hand, the temperature of the lifting air is 500 - 900 °C, which is lower than the temperature of the flue gas in the smoke outlet chamber (1000 - 1200 °C). The lifting air is relatively far from the fuel and will not reduce the temperature in the fuel feeding area or the fuel gasification speed.

[0075] Example 4

[0076] A method for preparing cement clinker by low-NOx full-system and full-oxygen combustion, comprising the following steps:

[0077] Feed the raw meal into the preheater, where the raw meal exchanges heat with the flue gas and undergoes gas-solid separation in the preheater, and the raw meal is preheated to the decomposition temperature.

[0078] The preheated raw meal enters the decomposition furnace through the raw meal feeding point between the lifting air inlet 306 and the tertiary air inlet and the raw meal feeding point above the tertiary air inlet respectively; a decomposition reaction occurs in the decomposition furnace to obtain hot raw meal; and a large amount of flue gas is generated and enters the preheater, and the low-temperature flue gas after heat exchange is discharged from the air outlet of the top cyclone of the preheater, and the CO2 concentration in the low-temperature flue gas discharged from the air outlet of the top cyclone of the preheater is greater than 70%.

[0079] The hot raw meal enters the rotary kiln 2 and is calcined in the rotary kiln to form clinker; the clinker is cooled in the grate cooler to obtain cement clinker.

[0080] The low-temperature flue gas enters the high-temperature fan 6, and then is divided into two paths. One path enters the carbon capture system, and the other path can reduce the dust concentration in the flue gas to 100 mg / m 3 Then enter the circulation fan, and then is divided into two branches, and enters the O2 / CO2 mixture cooling zone and the circulation flue gas cooling zone of the grate cooler as circulation flue gas (clinker cooling gas) respectively.

[0081] The cooling medium in the O2 / CO2 mixture cooling zone is a mixture of industrial oxygen A and CO2 circulation flue gas, that is, O2 / CO2 mixture, the cooling medium in the circulation flue gas cooling zone is CO2 circulation flue gas, and the cooling medium in the air cooling zone is air; there is no air leakage between the O2 / CO2 mixture cooling zone, the circulation flue gas cooling zone and the air cooling zone.

[0082] The high-temperature gas discharged from the O2 / CO2 mixture cooling zone is used as secondary air g2 and tertiary air respectively to recover the heat at the outlet of the O2 / CO2 mixture cooling zone. The secondary air g2 is introduced into the rotary kiln 2, and the tertiary air is introduced into the decomposition furnace through the tertiary air inlet to form a burnout zone 302 above the tertiary air inlet; the CO2 circulation flue gas discharged from the circulation flue gas cooling zone of the grate cooler is used as lifting air, and a part of it is introduced into the bottom of the decomposition furnace to maintain the wind speed at the second constriction between 30 and 50 m / s. At the same time, the fuel of the decomposition furnace is sprayed into the mixture of the flue gas from the kiln and the lifting air to form a reduction zone 301 between the lifting air inlet 306 and the tertiary air inlet, so that the average temperature in the reduction zone is 800-1200 °C, and the NO in the flue gas from the kiln is realized XSelf-removal is achieved while lifting the materials below the inlet of the tertiary air; a part of it is introduced into the downward pipeline 303 at the outlet of the precalciner, avoiding the problem that all the lifting air composed of the recycled CO2 flue gas is introduced into the furnace from the bottom of the precalciner, resulting in an increase in the CO2 partial pressure in the flue gas in the precalciner and raising the raw meal decomposition temperature to 950 °C or even above 1000 °C; at the same time, the temperature at the outlet of the precalciner is adjusted to prevent the outlet temperature of the precalciner from being too high and causing the fouling and blockage of the last-stage cyclone in the preheater; the air g5 coming out of the air cooling zone is directly discharged from the system.

[0083] 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 of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A decomposition furnace control method based on low NO X complete system and all-oxygen combustion, characterized in that It includes the following steps: The flue gas from the kiln outlet and the lifting air are introduced into the bottom of the precalciner. The lifting air comes from the flue gas discharged from the top air outlet of the preheater and heat-exchanged in the middle cooling zone of the grate cooler. The O2 concentration in the lifting air is lower than 5%, the CO2 concentration is higher than 70%, and the temperature is 500-900°C; The tertiary air is introduced into the precalciner above the lifting air. The tertiary air comes from the mixture of industrial oxygen and the flue gas discharged from the top air outlet of the preheater and heat-exchanged in the head cooling zone of the grate cooler. The O2 concentration in the mixture is greater than 30%; Between the lifting air inlet and the tertiary air inlet of the decomposition furnace, the excess oxygen coefficient is less than 0.5, forming a reduction zone, so that the average temperature in the reduction zone is 800-1200 °C, realizing the self-removal of NO in the flue gas from the kiln and the lifting of the materials below the tertiary air inlet; above the tertiary air inlet, a burnout zone is formed. X Self-removal and the lifting of the materials below the tertiary air inlet; above the tertiary air inlet, a burnout zone is formed.

2. The decomposition furnace control method for all-oxygen combustion of the whole system according to claim 1, characterized in that: X ​ The flue gas at the top outlet of the precalciner first goes up and then down. The lifting air is introduced into the downcomer pipe to adjust the temperature at the outlet of the precalciner.

3. The decomposition furnace control method for all-oxygen combustion of the entire system according to claim 1, characterized in that: X ​ The lifting air swirls into the precalciner. Along the flow direction of the lifting air, the lifting air first contacts the raw meal and then contacts the fuel.

4. The precalciner control method for all-oxygen combustion of the entire system according to claim 1, characterized in that: X ​ The air velocity at the bottom of the precalciner is maintained between 30 and 50 m / s.

5. According to claim 1, the control method of the decomposition furnace for all-oxygen combustion of the whole system is characterized in that: X ​ The O2 concentration in the industrial oxygen is greater than 80%.

6. A method for preparing cement clinker by low-NOx full-system and full-oxygen combustion, characterized in that, It includes the following steps: The raw meal is fed into the preheater. The raw meal exchanges heat and undergoes gas-solid separation with the flue gas in the preheater, and the raw meal is preheated to the decomposition temperature; The preheated raw meal is fed into the precalciner; The decomposition reaction occurs in the precalciner to obtain hot raw meal; and a large amount of flue gas is generated and enters the preheater. The low-temperature flue gas after heat exchange is discharged from the air outlet of the cyclone at the top of the preheater; The hot raw meal enters the rotary kiln and is calcined to produce clinker; the clinker is cooled in the grate cooler to obtain cement clinker; Part of the low-temperature flue gas discharged from the air outlet of the cyclone at the top of the preheater is used as recycled flue gas and enters the head cooling zone and the middle cooling zone of the grate cooler respectively; The cooling medium in the head cooling zone of the grate cooler is the mixture of industrial oxygen and recycled flue gas, the cooling medium in the middle cooling zone is recycled flue gas, and the cooling medium in the tail cooling zone is air; The high-temperature gas discharged from the head cooling zone is used as the secondary air and the tertiary air respectively. The secondary air is introduced into the rotary kiln, and the tertiary air is introduced into the precalciner. The recycled flue gas discharged from the middle cooling zone is used as the lifting air and introduced into the precalciner; The precalciner is controlled by the control method described in any one of claims 1-5.

7. The method for preparing cement clinker by low-NOx full-system oxy-fuel combustion according to claim 1, characterized in that: There is no air leakage between the head cooling zone, the middle cooling zone and the tail cooling zone of the grate cooler.

8. The method for preparing cement clinker by low-NOx full-system oxy-fuel combustion according to claim 1, characterized in that: The CO2 concentration in the low-temperature flue gas discharged from the air outlet of the top cyclone is greater than 70%.

9. A low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, which is used to implement the method described in any one of claims 6 or 7, and includes a preheater, a decomposition furnace, a kiln tail flue gas chamber, a rotary kiln, and a grate cooler connected in sequence; The grate cooler is divided into three zones from the clinker inlet to the outlet, namely the head cooling zone, the middle cooling zone and the tail cooling zone in sequence. The air outlets of the top cyclone of the preheater are respectively connected to the air inlets of the head cooling zone and the middle cooling zone, and an industrial oxygen inlet is arranged at the air inlet of the head cooling zone; characterized in that: The decomposition furnace is provided with a tertiary air inlet, a lifting air inlet, a raw material feeding point and a fuel feeding point. The lifting air inlet is located below the tertiary air inlet; the secondary air extraction opening in the head cooling zone of the grate cooler is communicated with the rotary kiln, the tertiary air extraction opening is communicated with the tertiary air inlet of the decomposition furnace through a pipeline, and the lifting air extraction opening in the middle cooling zone is communicated with the lifting air inlet of the decomposition furnace through a pipeline; at least 2 raw material feeding points are provided, at least one of the raw material feeding points is located between the lifting air inlet and the tertiary air inlet, and at least one of the raw material feeding points is located above the tertiary air inlet; the height of the lifting air inlet is below the raw material feeding point below the tertiary air inlet; the fuel feeding point is located between the lifting air inlet and the tertiary air inlet, so that the fuel is sprayed into the mixed gas of the flue gas from the kiln and the lifting air; a reduction zone is formed between the lifting air inlet and the tertiary air inlet in the decomposition furnace, and a burnout zone is formed above the tertiary air inlet.

10. According to claim 9, the low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: The outlet of the cyclone at the top of the preheater is connected to a high-temperature fan. The outlet of the high-temperature fan is divided into two paths, one path is connected to the carbon capture system, and the other path is connected to the air inlets of the head cooling zone and the middle cooling zone of the grate cooler.

11. According to claim 9, the low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: The outlet at the top of the decomposition furnace is provided with a pipeline that first goes up and then goes down. The lifting air extraction opening in the middle cooling zone is also communicated with the downward pipeline through a pipeline.

12. According to claim 11, the low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: A first-stage circulating air regulating valve is provided on the pipeline between the lifting air extraction opening in the middle cooling zone of the grate cooler and the downward pipeline, and a second-stage circulating air regulating valve is provided on the pipeline between the lifting air extraction opening and the lifting air inlet of the decomposition furnace.

13. According to claim 9, the low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: A tertiary air regulating valve is provided on the pipeline between the tertiary air extraction opening in the head cooling zone of the grate cooler and the tertiary air inlet of the decomposition furnace.

14. According to claim 9, the low NO X System for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: A distributing valve is provided on the feeding pipe at the raw material feeding point of the decomposition furnace to regulate the distribution ratio of each raw material feeding point, so that the average temperature in the reduction zone of the decomposition furnace is 800-1200 °C.

15. According to claim 9, the low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: A first constriction is provided at the tertiary air inlet of the decomposition furnace, and a second constriction is provided at the lifting air inlet.

16. According to claim 1, the low NO X A system for preparing cement clinker by all-oxygen combustion of the whole system, characterized in that: The head cooling zone and the middle cooling zone of the grate cooler are located in the first section of the grate cooler, the tail cooling zone is located in the second section of the grate cooler, an intermediate roller crusher for reducing the air leakage between the two sections is provided between the first section and the second section of the grate cooler, and a partition wall for reducing the air leakage between the head cooling zone and the middle cooling zone is provided in the middle of the first section of the grate cooler.

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