A gradient combustion deep self-denitrification decomposition furnace system and process with tertiary air-carrying material

Abstract

The present invention discloses a gradient combustion depth self-denitrification decomposition furnace system and process with tertiary air carrying material, the decomposition furnace is composed of a furnace bottom cone, a strong oxygen-poor zone column, a first venturi throat, an oxygen-poor combustion zone column, a second venturi throat and a burnout zone column from bottom to top; the raw material feeding point is divided into a lower material distribution point, a middle material distribution point and a tertiary air distribution point, the lower material distribution point is located at the lower part of the strong oxygen-poor zone column, the middle material distribution point is located at the lower part of the oxygen-poor combustion zone column, and the tertiary air distribution point is located at the entrance of the tertiary air upper branch pipe; the tertiary air lower branch pipe is connected to the first venturi throat, and the height between the tertiary air lower branch pipe and the top of the kiln tail smoke chamber is greater than 10m, and the tertiary air upper branch pipe is connected to the lower part of the burnout zone column, so that a gradient combustion environment of strong oxygen-poor zone-oxygen-poor combustion zone-oxygen-rich burning zone is formed in the decomposition furnace. The present invention breaks through the height limit of the raw material feeding point, prolongs the denitrification time of the strong oxygen-poor zone, realizes the improvement of self-denitrification efficiency, and realizes the full decomposition of raw materials in the decomposition furnace at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of cement burning, and in particular to a gradient combustion deep self-denitrification decomposition furnace system and process with tertiary air-carrying materials. Background Art

[0002] In recent years, my country's annual cement production has exceeded 2 billion tons, accounting for more than 50% of the world's total production. As a traditional high-energy-consuming and high-emission industry, the cement industry faces arduous tasks in reducing pollution and carbon emissions. Nitrogen oxides are gases produced when fossil fuels and air burn at high temperatures, and are highly toxic. Nitrogen oxide emissions affect air quality and have serious harm to human living environment and health. The cement industry is the third largest emitter of nitrogen oxides after thermal power generation and automobile exhaust. Denitrification in the cement industry is generally based on staged combustion, supplemented by SNCR or SCR technology. The use of SNCR technology or SCR technology alone requires the consumption of a large amount of ammonia water, which increases carbon emissions in the ammonia water manufacturing process. At the same time, ammonia escape will cause an increase in pollutants and energy consumption.

[0003] Fuel combustion self-denitrification technology is a combustion technology that uses the control of fuel combustion characteristic parameters to inhibit the generation of NOx through the intermediate products formed during the combustion process without adding an external denitrification reducing agent. After self-denitrification, the NOx in the flue gas is greatly reduced, which reduces the amount of reducing agent used in the subsequent SNCR and SCR denitrification links, reduces the denitrification cost, and indirectly reduces the carbon emissions generated by the electricity consumption in the production process of reducing agent ammonia water, achieving synergy in pollution reduction and carbon reduction.

[0004] At present, the fuel combustion self-denitrification technology includes air staged combustion technology and fuel staged combustion technology. Air staged combustion technology uses the three-stage air feeding into the decomposition furnace to form an oxygen-poor combustion zone in the column section of the decomposition furnace, which can suppress the NOx produced by the combustion of the decomposition furnace fuel itself. However, the excess oxygen coefficient of the formed oxygen-poor combustion zone is still high, and the overall denitrification effect is poor. Fuel staged combustion technology uses the fuel feeding into the decomposition furnace to form an oxygen-poor combustion zone in the cone of the decomposition furnace, which can effectively reduce the NOx in the flue gas out of the rotary kiln, but the reduction is generally only about 30%. The main reason for limiting the improvement of denitrification efficiency is the insufficient denitrification reaction time. The residence time of the denitrification reaction is short, and it is difficult to suppress the combustion of the decomposition furnace fuel itself to produce NOx.

[0005] The denitrification reaction under reducing atmosphere is mainly: CO+NO→N2+CO2

[0006] H2+NO→N2+H2O

[0007] Chinese patent publication number CN108167860A discloses a gradient combustion self-denitrification process method for a firing system, which forms a gradient combustion environment of extremely oxygen-poor zone-oxygen-poor combustion zone-oxygen-rich burnout zone in the decomposition furnace to realize the self-denitrification function of the decomposition furnace. Among them: the excess air coefficient of the extremely oxygen-poor zone is 0.1-0.5, the excess air coefficient of the oxygen-poor combustion zone is 0.5-1.0, and the excess air coefficient of the oxygen-rich burnout zone is above 1.0. By forming a gradient combustion atmosphere, the combustion intermediate products are used to reduce the NOx generated in the rotary kiln, and the generation of NOx in the decomposition furnace is suppressed. Under the premise of not affecting the burnout of the fuel, the concentration of NOx in the flue gas discharged from the furnace is reduced.

[0008] Chinese patent publication number CN111750670A discloses a zoned combustion self-denitrification system and process with a reduction furnace and a decomposition furnace, which is characterized in that a reduction furnace is arranged between the kiln tail smoke chamber and the decomposition furnace, and a gradient combustion environment is formed in the combined combustion space of the reduction furnace and the decomposition furnace. Since the reduction furnace is relatively independent of the decomposition furnace, the denitrification reaction time in the strong reduction zone can be extended by increasing the height of the reduction furnace, thereby improving the self-denitrification efficiency. However, in this system, the reduction furnace is an offline furnace type. When abnormal fluctuations occur in the decomposition furnace, the risk of raw materials short-circuiting into the kiln is greater than that of an online decomposition furnace.

[0009] The cement raw meal is preheated by the preheater system, and gas-solid separation is carried out in the cyclone. The separated raw meal is fed into the decomposition furnace for high-temperature decomposition. In the linear gradient combustion decomposition furnace system, increasing the height of the strong oxygen-depleted zone and extending the denitrification reaction time in the strong oxygen-depleted zone can improve the self-denitrification efficiency. However, in the existing system, the raw meal entering the furnace from the cyclone is fed into the decomposition furnace by gravity descent. When the strong oxygen-depleted zone is raised, the feeding point on the raw meal entering the furnace needs to be raised accordingly. This means that the position of the cyclone also needs to be raised accordingly, and increasing the height of the cyclone requires raising the total height of the preheater tower, resulting in a substantial increase in investment costs.

[0010] In addition, in the existing online gradient combustion decomposition furnace system, the temperature control under gradient combustion is mainly achieved through stepped material distribution. When the height of the strong reduction zone increases, the height of the upper material distribution point is correspondingly increased, and the decomposition time of the raw material entering the furnace from the upper material distribution point is relatively shortened, which can easily cause insufficient decomposition of this part of the raw material in the furnace, which is not conducive to energy saving and consumption reduction.

[0011] In summary, the problems existing in the prior art are:

[0012] (1) Self-denitrification during the combustion process can reduce the amount of ammonia water used for denitrification in the SNCR or SCR system, reduce carbon emissions caused by ammonia water consumption, and achieve pollution reduction and carbon reduction. However, the self-denitrification efficiency of the decomposition furnace is still limited and needs to be further improved.

[0013] (2) In the off-line gradient combustion decomposition furnace system, the use of an independent reduction furnace can increase the denitrification reaction time, but there is a risk of the decomposition furnace raw material short-circuiting into the kiln from the bottom.

[0014] (3) In the existing online gradient combustion decomposition furnace system, due to the limitation of the total height of the tower of the kiln tail preheater system, it is difficult to significantly increase the height of the strong reduction zone and improve the denitrification efficiency.

[0015] (4) In the existing online gradient combustion decomposition furnace system, when the height of the strong reduction zone increases, the decomposition time of the raw material entering the furnace from the upper material distribution point is relatively shortened, and there is a problem of insufficient decomposition of the raw material. Summary of the invention

[0016] One of the purposes of the present invention is to provide a gradient combustion deep self-denitrification decomposition furnace system with tertiary air carrying material. The deep self-denitrification decomposition furnace system of the present invention sets a feeding point on the tertiary air upper branch pipe, and uses the tertiary air to carry raw material into the burnout zone of the gradient combustion decomposition furnace, thereby breaking through the height limitation of the raw material feeding point, extending the denitrification time in the strong oxygen-deficient zone, and realizing improved self-denitrification efficiency; in addition, the CO2 partial pressure in the high-temperature tertiary air is low, and the tertiary air carries the raw material while preheating and predecomposing the raw material, so that the raw material is fully decomposed in the decomposition furnace.

[0017] Another object of the present invention is to provide a deep self-denitrification process using the above-mentioned deep self-denitrification decomposition furnace system for gradient combustion.

[0018] The present invention is implemented as follows: a gradient combustion depth self-denitrification decomposition furnace system with tertiary air carrying material, comprising a rotary kiln, a kiln tail smoke chamber connected to the kiln tail of the rotary kiln, a decomposition furnace connected to the kiln tail smoke chamber, a decomposition furnace fuel feeding point, a decomposition furnace raw material feeding point, a tertiary air lower branch pipe, a tertiary air upper branch pipe and a secondary final cyclone;

[0019] The decomposition furnace is composed of a furnace bottom cone, a strong oxygen-poor zone column, a first venturi throat, an oxygen-poor combustion zone column, a second venturi throat and a burnout zone column connected in sequence from bottom to top; the raw material feeding point of the decomposition furnace is divided into a lower material distribution point of the decomposition furnace, a middle material distribution point of the decomposition furnace and a tertiary air distribution point, the lower material distribution point of the decomposition furnace is located on the lower side of the strong oxygen-poor zone column, the middle material distribution point of the decomposition furnace is located on the lower side of the oxygen-poor combustion zone column, the tertiary air distribution point is located at the entrance of the tertiary air upper branch pipe, and the tertiary air upper branch pipe is a pipe lifted vertically upward; the fuel feeding point of the decomposition furnace is located below the lower material distribution point of the decomposition furnace, and the lower material pipe at the bottom outlet of the secondary and final cyclone is respectively connected to the lower material distribution point of the decomposition furnace, the middle material distribution point of the decomposition furnace and the tertiary air distribution point;

[0020] The tertiary air lower branch is connected to the first venturi throat, the height between the tertiary air duct lower branch and the top of the kiln tail smoke chamber is greater than 10m, the tertiary air upper branch is connected to the lower side of the burnout zone column, the decomposition furnace area below the tertiary air lower branch is a strong oxygen-depleted zone, the area between the tertiary air upper branch and the tertiary air upper branch is an oxygen-depleted combustion zone, and the area above the tertiary air upper branch is an oxygen-rich combustion zone, so that a gradient combustion environment of strong oxygen-depleted zone-oxygen-depleted combustion zone-oxygen-rich combustion zone is formed in the decomposition furnace.

[0021] The gradient combustion environment is achieved by the graded feeding and coordination of the fuel, tertiary air and raw meal into the decomposition furnace. The fuel into the decomposition furnace is fed from the cone at the bottom of the decomposition furnace; the tertiary air duct into the furnace is divided into two upper and lower branches, the tertiary air of the lower branch of the tertiary air is fed from the lower part of the oxygen-poor combustion zone, and the tertiary air of the upper branch of the tertiary air is fed from the lower part of the oxygen-rich burnout zone; the raw meal out of the secondary final cyclone is divided into three routes to enter the decomposition furnace, the first route of raw meal slides down the down pipe under the action of gravity to the middle distribution point of the decomposition furnace and enters the decomposition furnace, the second route of raw meal slides down the down pipe under the action of gravity to the lower distribution point of the decomposition furnace and enters the decomposition furnace, the third route of raw meal slides down the down pipe under the action of gravity to the tertiary air distribution point and enters the upper branch of the tertiary air, and enters the decomposition furnace with the tertiary air under the action of air force.

[0022] Preferably, the height of the position where the tertiary air upper branch pipe enters the decomposition furnace is higher than the height of the bottom outlet of the secondary and final cyclone, so that the raw material is carried upward.

[0023] Preferably, the tertiary air lower branch pipe is connected to the side of the upper expansion section of the first Venturi throat.

[0024] Preferably, a lower branch pipe valve is provided on the tertiary air lower branch pipe, and an upper branch pipe valve is provided on the tertiary air upper branch pipe. The air distribution ratio of the tertiary air upper and lower branches can be adjusted by the opening of the upper and lower branch pipe valves.

[0025] Preferably, a two-stage dividing valve is arranged on the discharge pipe at the bottom outlet of the secondary and final cyclone, so that the raw material exiting the secondary and final cyclone is respectively connected to the lower dividing point of the decomposition furnace, the middle dividing point of the decomposition furnace and the tertiary air dividing point through the discharge pipe, and the dividing ratio of the three dividing points is adjusted by the opening of the dividing valve arranged on the discharge pipe.

[0026] Preferably, the fuel feeding point of the decomposition furnace is located at the cone at the bottom of the furnace or at the lower side of the column in the strong oxygen-deficient zone.

[0027] The above-mentioned deep self-denitrification decomposition furnace system is used to carry out a gradient combustion deep self-denitrification process. The process adopts a gradient combustion environment of a strong oxygen-poor zone-oxygen-poor combustion zone-oxygen-rich burnout zone formed in the decomposition furnace, and the height of the strong oxygen-poor zone is greater than 10m. The gradient combustion environment is achieved by feeding the fuel into the decomposition furnace, the tertiary air into the decomposition furnace, and the raw material into the decomposition furnace in stages. The fuel is fed into the decomposition furnace from the bottom, a part of the tertiary air is fed from the bottom of the oxygen-poor combustion zone, and a part of the tertiary air is carried down from the discharge pipe of the secondary and final cyclone. Part of the raw meal reaching the tertiary air distribution point moves upward and is fed from the bottom of the oxygen-rich burnout zone, part of the raw meal that slides down from the discharge pipe of the next-to-last stage cyclone to the lower distribution point of the decomposition furnace is fed from the lower part of the strong oxygen-depleted zone, and part of the raw meal that slides down from the discharge pipe of the next-to-last stage cyclone to the middle distribution point of the decomposition furnace is fed from the lower part of the oxygen-depleted combustion zone. The excess air coefficient of the strong oxygen-depleted zone is controlled to be 0.1-0.5, the excess air coefficient of the oxygen-depleted combustion zone is controlled to be 0.5-1.0, and the excess air coefficient of the oxygen-rich burnout zone is above 1.0.

[0028] Preferably, the average cross-sectional wind speed in the strong oxygen-deficient zone is 3 to 8 m / s, and the gas residence time is greater than 1.5 s.

[0029] Preferably, the tertiary air component is air, and the temperature in the tertiary air main pipe is 850-1100°C; when the tertiary air upper branch pipe carries material, the opening of the upper branch pipe valve is greater than 20%, the average wind speed in the pipe is greater than 10m / s, the material distribution ratio increases with the increase of the air volume of the tertiary air upper branch pipe, and the material-air mass ratio is controlled to be less than 3.0 to prevent material collapse caused by insufficient tertiary air supporting capacity.

[0030] Preferably, the temperature of the raw material entering the calciner is lower than 850°C.

[0031] The present invention has the following advantages and beneficial effects:

[0032] 1. The present invention sets a feeding point on the tertiary air upper branch pipe, and uses the tertiary air to carry the raw meal into the burnout zone of the gradient combustion decomposition furnace, thereby breaking through the height limitation of the raw meal feeding point, and the height of the strong oxygen-poor zone can be raised to more than 10m, which greatly prolongs the residence time of the flue gas in the strong oxygen-poor zone, prolongs the denitrification time in the strong oxygen-poor zone, and further fully removes the NOx in the kiln flue gas in this area, thereby improving the self-denitrification efficiency and reducing the total investment cost; the CO2 partial pressure in the high-temperature tertiary air is low, and the tertiary air can preheat and pre-decompose the raw meal while carrying the raw meal, so that the raw meal can be fully decomposed in the decomposition furnace, saving energy and reducing consumption.

[0033] 2. The present invention realizes the formation of a gradient combustion environment of strong oxygen-poor zone-oxygen-poor combustion zone-oxygen-rich burnout zone in the decomposition furnace by feeding fuel, tertiary air and raw meal into the decomposition furnace in stages. The raw meal staged feeding technology is used to regulate the temperature distribution in the decomposition furnace. By controlling the temperature inside the cone of the decomposition furnace, the problem of high temperature and easy crusting in the cone of the decomposition furnace is solved. By increasing the temperature of the oxygen-poor combustion zone of the decomposition furnace, the combustion speed of the fuel is increased, and the burnout degree of the fuel in the decomposition furnace is increased. The self-denitrification function of gradient combustion is realized without affecting the normal operation of the firing system.

[0034] 3. The present invention can improve the efficiency of self-denitrification without reducing the combustion speed of the decomposition furnace fuel and the complete decomposition of the raw material, and has no adverse effect on the cement clinker production process. It has the advantages of reasonable system process, good reliability, strong adaptability, etc., and can reduce the environmental protection management cost of enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a structural schematic diagram of a depth gradient combustion decomposition furnace system provided in Example 1 of the present invention;

[0036] Figure 2 is a schematic structural diagram of a raw material feeding point of a decomposition furnace provided in the first embodiment of the present invention;

[0037] Figure 3 It is a schematic diagram of the structure of the deep gradient combustion decomposition furnace system provided in the second embodiment of the present invention.

[0038] In the figure:

[0039] g1-kiln flue gas; g2-tertiary air; g3-calciner flue gas; M1-first-way raw material; M2-second-way raw material; M3: third-way raw material; F-coal powder;

[0040] A-strong oxygen-poor zone; B-oxygen-poor combustion zone; C-oxygen-rich burnout zone;

[0041] 1-calciner; 11-furnace bottom cone; 12-strong oxygen-poor zone column; 13-first venturi throat; 14-oxygen-poor combustion zone column; 15-second venturi throat; 16-burnout zone column; 17-calciner lower material distribution point; 18-calciner middle material distribution point; 19-calciner fuel feeding point;

[0042] 2- tertiary air main pipe; 21- tertiary air lower branch pipe; 22- tertiary air upper branch pipe; 23- lower branch pipe valve; 24- upper branch pipe valve; 25, tertiary air material distribution point;

[0043] 3-secondary final cyclone; 31-upper dispensing valve; 32-lower dispensing valve;

[0044] 4-kiln tail smoke chamber; 5-rotary kiln;

[0045] The dotted line with arrow is the direction of airflow; the solid line with arrow is the direction of raw meal or coal powder flow. DETAILED DESCRIPTION

[0046] 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 and accompanying drawings. 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.

[0047] 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.

[0048] An embodiment of the present invention provides a gradient combustion depth self-denitrification decomposition furnace system with tertiary air carrying material, including a rotary kiln 5, a kiln tail smoke chamber 4 connected to the kiln tail of the rotary kiln 5, a decomposition furnace 1 connected to the kiln tail smoke chamber 4, a decomposition furnace fuel feeding point 19, a decomposition furnace raw material feeding point, a tertiary air lower branch pipe 21, a tertiary air upper branch pipe 22 and a secondary and final cyclone 3.

[0049] The decomposition furnace 1 is composed of a furnace bottom cone 11, a strong oxygen-poor zone column 12, a first venturi throat 13, an oxygen-poor combustion zone column 14, a second venturi throat 15 and a burnout zone column 16 connected in sequence from bottom to top; the raw material feeding point of the decomposition furnace is divided into a decomposition furnace lower material distribution point 17, a decomposition furnace middle material distribution point 18 and a tertiary air distribution point 25, the decomposition furnace lower material distribution point 17 is located on the lower side of the strong oxygen-poor zone column 12, the decomposition furnace middle material distribution point 18 is located on the lower side of the oxygen-poor combustion zone column 14, and the tertiary air distribution point 25 is located at the entrance of the tertiary air upper branch pipe 22. The decomposition furnace fuel feeding point 19 is located below the decomposition furnace lower material distribution point 17, so that the NOx in the kiln flue gas can fully react with the reducing gas. Raw materials are fed into the lower material distribution point 17 of the decomposition furnace, and the temperature in the furnace bottom cone 11 is controlled by the heat absorption of the raw materials decomposition, so as to prevent the problem of crusting caused by excessive temperature in the furnace bottom cone 11 caused by fuel combustion. The feed pipe at the bottom outlet of the secondary and final cyclone 3 is respectively connected to the lower material distribution point 17 of the decomposition furnace, the middle material distribution point 18 of the decomposition furnace, and the tertiary air distribution point 25. The material distribution at the middle distribution point and the upper distribution point reduces the amount of raw materials fed from the lower material distribution point of the decomposition furnace 1, and increases the temperature of the lower part of the decomposition furnace 1.

[0050] The tertiary air lower branch pipe 21 is connected to the side of the upper expansion section of the first venturi throat 13 to strengthen the mixing of the tertiary air and the rising flue gas in the strong oxygen-poor zone and promote the combustion of coal powder in the oxygen-poor combustion zone. The height between the tertiary air lower branch pipe 21 and the top of the kiln tail smoke chamber 4 is greater than 10m, which prolongs the denitrification reaction time of the strong oxygen-poor zone A. The tertiary air upper branch pipe 22 is connected to the lower side of the burnout zone column 16 to meet the amount of oxygen required for fuel burnout. The area of ​​the decomposition furnace 1 below the tertiary air lower branch pipe 21 is the strong oxygen-poor zone A, the area between the tertiary air upper branch pipe 22 and the tertiary air upper branch pipe 22 is the oxygen-poor combustion zone B, and the area above the tertiary air upper branch pipe 22 is the oxygen-rich burnout zone C, so that a gradient combustion environment of the strong oxygen-poor zone A-oxygen-poor combustion zone B-oxygen-rich burnout zone C is formed in the decomposition furnace 1.

[0051] The gradient combustion environment is achieved by the graded feeding and coordination of the fuel, tertiary air and raw meal into the decomposition furnace. The fuel into the decomposition furnace is fed from the bottom cone 11 of the decomposition furnace 1; the tertiary air duct into the furnace is divided into two upper and lower branches, the tertiary air of the lower branch 21 of the tertiary air is fed from the lower part of the oxygen-poor combustion zone B, and the tertiary air of the upper branch 22 of the tertiary air is fed from the lower part of the oxygen-rich burnout zone C; the raw meal out of the secondary final cyclone 3 is divided into three routes to enter the decomposition furnace 1, the first route of raw meal M1 slides down along the lower pipe under the action of gravity to the middle distribution point 18 of the decomposition furnace and enters the decomposition furnace 1, the second route of raw meal M2 slides down along the lower pipe under the action of gravity to the lower distribution point 17 of the decomposition furnace and enters the decomposition furnace 1, the third route of raw meal M3 slides down along the lower pipe under the action of gravity to the tertiary air distribution point 25 and enters the upper branch 22 of the tertiary air, and enters the decomposition furnace 1 with the tertiary air under the action of air force.

[0052] The height of the position where the tertiary air upper branch pipe 22 enters the decomposition furnace 1 is higher than the height of the bottom outlet of the secondary and final cyclone 3, and the raw material is carried upward.

[0053] The tertiary air lower branch pipe 21 is provided with a lower branch pipe valve 23, and the tertiary air upper branch pipe 22 is provided with an upper branch pipe valve 24. The air distribution ratio between the tertiary air upper branch pipe 22 and the tertiary air lower branch pipe 21 can be adjusted by the opening of the upper branch pipe valve 24 and the lower branch pipe valve 23.

[0054] A two-stage dividing valve is arranged on the discharge pipe at the bottom outlet of the secondary and final cyclone 3, so that the raw material exiting the secondary and final cyclone 3 is respectively connected to the lower dividing point 17 of the decomposition furnace, the middle dividing point 18 of the decomposition furnace and the tertiary air dividing point 25 through the discharge pipe. The three dividing points adjust the dividing ratio by the opening of the dividing valve arranged on the discharge pipe, thereby controlling the temperature in the decomposition furnace 1, preventing the problem of high-temperature crusting on the furnace wall, and at the same time reducing the amount of raw material fed from the lower dividing point, thereby increasing the temperature of the lower part of the decomposition furnace 1.

[0055] The decomposition furnace fuel feeding point 19 is located at the furnace bottom cone 11 or at the lower side of the column 12 in the strong oxygen-deficient zone A.

[0056] The above-mentioned deep self-denitrification decomposition furnace system is used to carry out a gradient combustion deep self-denitrification process. The process adopts a gradient combustion environment of strong oxygen-poor zone A-oxygen-poor combustion zone B-oxygen-rich burnout zone C formed in the decomposition furnace 1, and the height of the strong oxygen-poor zone A is greater than 10m. The gradient combustion environment is achieved by feeding the fuel into the decomposition furnace, the tertiary air into the decomposition furnace, and the raw material into the decomposition furnace in stages; the fuel into the furnace is fed from the bottom of the decomposition furnace 1, the tertiary air component is air, the temperature in the tertiary air main pipe 2 is 850-1100°C, when the tertiary air upper branch pipe 22 carries material, the opening of the upper branch pipe valve 24 is greater than 20%, the average wind speed in the pipe is greater than 10m / s, the material distribution ratio increases with the increase of the air volume of the tertiary air upper branch pipe, and the material-gas mass ratio is controlled to be less than 3.0 to prevent the problem of material collapse due to insufficient tertiary air supporting capacity; a part of the tertiary air It is fed from the lower part of the oxygen-depleted combustion zone B, a part of the tertiary wind carries part of the raw material that slides down from the downpipe of the next-to-last cyclone 3 to the tertiary wind distribution point 25, moves upward and is fed from the bottom of the oxygen-rich burnout zone C, part of the raw material that slides down from the downpipe of the next-to-last cyclone 3 to the lower distribution point 17 of the decomposition furnace is fed from the lower part of the strong oxygen-depleted zone A, and part of the raw material that slides down from the downpipe of the next-to-last cyclone 3 to the middle distribution point 18 of the decomposition furnace is fed from the lower part of the oxygen-depleted combustion zone B, the temperature of the raw material entering the decomposition furnace 1 is lower than 850°C, the excess air coefficient of the strong oxygen-depleted zone A is controlled to be 0.1-0.5, the average cross-sectional wind speed in the strong oxygen-depleted zone A is 3-8m / s, the gas residence time is greater than 1.5s, the excess air coefficient of the oxygen-depleted combustion zone B is 0.5-1.0, and the excess air coefficient of the oxygen-rich burnout zone C is above 1.0.

[0057] The present invention is further described in detail below.

[0058] Example 1

[0059] See also Figure 1 and Figure 2 This embodiment provides a gradient combustion depth self-denitrification decomposition furnace system with tertiary air carrying material. The decomposition furnace 1 is divided into a strong oxygen-poor zone A, an oxygen-poor combustion zone B and an oxygen-rich burnout zone C from bottom to top according to the high and low excess oxygen coefficients. The strong oxygen-poor zone A is the area of ​​the decomposition furnace 1 below the tertiary air lower branch pipe 21, and the excess air coefficient of this area is 0.1-0.5; the oxygen-poor combustion zone B is the area between the tertiary air lower branch pipe 21 and the tertiary air upper branch pipe 22, and the excess air coefficient of this area is 0.5-1.0; the oxygen-rich burnout zone C is the area above the tertiary air upper branch pipe 22, and the excess air coefficient of this area is above 1.0.

[0060] The kiln flue gas g1 is the flue gas generated by the combustion of fuel in the rotary kiln 5, with a temperature of 900-1300°C, a NOx concentration of generally 500-1500ppm, and an O2 concentration of less than 10%. The kiln flue gas g1 passes through the kiln tail smoke chamber 4 and flows upward into the strong oxygen-depleted zone A, which is composed of the furnace bottom cone 11 and the strong oxygen-depleted zone column 12. The coal powder F is sprayed from the furnace bottom cone 11 and mixed with the kiln flue gas g1. The coal powder F releases volatiles in the high-temperature oxygen-deficient airflow, and the volatiles undergo pyrolysis reactions to produce reducing gases CO, H2 and aromatic organic matter CxHy. The reducing gases undergo oxidation-reduction reactions with NOx to reduce NOx to N2. The height of the strong oxygen-depleted zone A is more than 10m, the average cross-sectional wind speed is 3-8m / s, and the gas residence time is greater than 1.5s, so that the NOx in the kiln flue gas g1 can be fully removed in this area.

[0061] In this embodiment, a double series preheater is used, two secondary and final stage cyclones 3 are provided, and the tertiary air is inletted from both sides.

[0062] The composition of tertiary air g2 is air with a temperature of 850-1100℃, which provides oxygen for the fuel. After passing through the tertiary air main pipe 2, the tertiary air g2 is divided into two routes. The first route of tertiary air enters the tertiary air lower branch pipe 21, which is connected to the lower part of the oxygen-depleted combustion zone B; the second route of tertiary air enters the tertiary air upper branch pipe 22 and is connected to the lower part of the oxygen-rich burnout zone C. An upper branch pipe valve 24 is provided on the tertiary air upper branch pipe 22, and a lower branch pipe valve 23 is provided on the tertiary air lower branch pipe 21. When the tertiary air upper branch pipe 22 carries material, the opening of the upper branch pipe valve 24 is greater than 20%, the average wind speed in the pipe is greater than 10m / s, and the material distribution ratio increases with the increase of the air volume of the tertiary air upper branch pipe. The material-gas mass ratio is controlled to be less than 3.0 to prevent the problem of material collapse due to insufficient tertiary air supporting capacity.

[0063] The raw material entering the decomposition furnace 1 flows downward from the bottom outlet after being separated by the secondary final cyclone 3, and is divided into three paths by the upper dividing valve 23 and the lower dividing valve 24. The first path of raw material M1 slides down along the lower material pipe under the action of gravity to the lower dividing point 17 of the decomposition furnace and enters the decomposition furnace 1, the second path of raw material M2 slides down along the lower material pipe under the action of gravity to the middle dividing point 18 of the decomposition furnace and enters the decomposition furnace 1, and the third path of raw material M3 slides down along the lower material pipe under the action of gravity to the tertiary air dividing point 25 and enters the tertiary air upper branch pipe 22, and enters the decomposition furnace 1 with the tertiary air under the action of air force.

[0064] See also Figure 2 The first raw material M1 moves upwards under the influence of the smoke from the rotary kiln 5. The second raw material M2 moves upwards under the influence of the smoke from the kiln g1 and the combustion-supporting air from the lower branch pipe 21 of the tertiary air. The third raw material M3 moves upwards under the influence of the combustion-supporting air from the upper branch pipe 22 of the tertiary air, enters the decomposition furnace 1, and moves upwards with the wind in the furnace. The three raw materials flowing into the furnace all flow out from the outlet of the decomposition furnace 1 along with the smoke from the decomposition furnace g3.

[0065] The above-mentioned multi-stage material distribution technology is used to control the temperature distribution in the decomposition furnace 1. By controlling the temperature in the bottom cone 11 of the decomposition furnace 1, the problem of high temperature and easy crusting in the bottom cone 11 of the decomposition furnace 1 is solved, and by increasing the temperature of the column 14 in the oxygen-poor combustion zone in the decomposition furnace 1, the combustion speed of the fuel is increased, and the burnout degree of the fuel in the decomposition furnace 1 is increased. While realizing the gradient combustion self-denitrification function, it does not affect the normal operation of the burning system, and achieves the purpose of energy saving and consumption reduction.

[0066] In this system, in order to achieve a height of more than 10m in the strong oxygen-poor zone A and a gas residence time greater than 1.5s, so that the NOx in the kiln flue gas g1 can be fully removed in this area, the height of the tertiary wind lower branch pipe 21 and the height of the decomposition furnace distribution point 18 in the raw material entering the decomposition furnace 1 need to be raised upwards compared with the conventional decomposition furnace 1 system. Furthermore, the position of the distribution point on the decomposition furnace also needs to be raised upwards. However, under the conventional production line feeding method, the raw material flowing into the furnace downpipe is gravity-dropping, so the height of the distribution point on the decomposition furnace cannot be higher than the bottom discharge port height of the secondary and final cyclone 3, so the temperature of the oxygen-rich burnout zone C is difficult to control by upper distribution. In the present invention, a combined feeding method is proposed in which the third-way raw material M3 is first fed into the tertiary wind upper branch pipe 22 by gravity-dropping through the downpipe, and then the raw material is fed into the upper part of the decomposition furnace 1 by the tertiary wind pneumatic lifting method, which breaks through the limitation of the position of the secondary and final cyclone 3 on the position of the upper distribution point entering the furnace. The height H2 of the tertiary air upper branch pipe 22 from the furnace bottom is higher than the height H1 of the bottom outlet of the secondary and final cyclone tube 3 from the furnace bottom, and the raw material is carried upward, so that the upper material distribution point entering the furnace moves upward.

[0067] After the third raw material M3 is fed into the tertiary air upper branch pipe 22, since the temperature of the tertiary air is higher than the decomposition temperature of calcium carbonate (above 850°C), and the tertiary air is composed of air with a very low CO2 concentration (less than 1%), the third raw material M3 is preheated and heated in the tertiary air upper branch pipe 22 under high temperature and low CO2 partial pressure, and a decomposition reaction occurs: CaCO3→CaO+CO2. This solves the problem of shortened decomposition time and reduced decomposition rate of raw materials in the decomposition furnace 1 caused by the elevated position of the upper material feeding point, and achieves full decomposition of raw materials in the decomposition furnace 1.

[0068] Example 2

[0069] See also Figure 3 , which is different from the embodiment 1, there is one secondary and final cyclone 3 for the raw materials entering the furnace, and the tertiary air is fed from one side. The system is suitable for a cement clinker production line using a single series preheater.

[0070] In summary, the present invention sets a feeding point at the entrance of the tertiary air upper branch pipe 22, and uses the tertiary air to carry the raw material into the oxygen-rich burnout zone C of the gradient combustion decomposition furnace 1, thereby breaking through the limitation on the height of the feeding point into the decomposition furnace, and the height of the strong oxygen-depleted zone A can be increased to more than 10m, which greatly prolongs the residence time of the flue gas in the strong oxygen-depleted zone A, prolongs the denitrification time of the strong oxygen-depleted zone A, and further fully removes the NOx in the kiln flue gas in this area, thereby improving the self-denitrification efficiency; in addition, the CO2 partial pressure in the high-temperature tertiary air is low, and the tertiary air carries the raw material while preheating and predecomposing the raw material, so that the raw material is fully decomposed in the decomposition furnace 1. By feeding the fuel into the decomposition furnace, the tertiary air into the decomposition furnace and the raw meal into the decomposition furnace in stages, a gradient combustion environment of strong oxygen-depleted zone A-oxygen-depleted combustion zone B-oxygen-rich burnout zone C is formed in the decomposition furnace 1. The raw meal staged feeding technology is used to regulate the temperature distribution in the decomposition furnace. By controlling the temperature inside the decomposition furnace cone, the problem of high temperature and easy crusting in the decomposition furnace cone is solved. By increasing the temperature of the oxygen-depleted combustion zone B of the decomposition furnace, the combustion speed of the fuel is increased, and the burnout degree of the fuel in the decomposition furnace is increased. While realizing the gradient combustion self-denitrification function, the normal operation of the firing system is not affected.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, 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 gradient combustion depth self-denitrification decomposition furnace system with tertiary air carrying material, comprising a rotary kiln, a kiln tail smoke chamber connected to the kiln tail of the rotary kiln, a decomposition furnace connected to the kiln tail smoke chamber, a decomposition furnace fuel feeding point, a decomposition furnace raw material feeding point, a tertiary air lower branch pipe, a tertiary air upper branch pipe and a secondary final cyclone; characterized in that: The decomposition furnace is composed of a furnace bottom cone, a strong oxygen-poor zone column, a first venturi throat, an oxygen-poor combustion zone column, a second venturi throat and a burnout zone column connected in sequence from bottom to top; the raw material feeding point of the decomposition furnace is divided into a lower material distribution point of the decomposition furnace, a middle material distribution point of the decomposition furnace and a tertiary air distribution point, the lower material distribution point of the decomposition furnace is located on the lower side of the strong oxygen-poor zone column, the middle material distribution point of the decomposition furnace is located on the lower side of the oxygen-poor combustion zone column, and the tertiary air distribution point is located at the entrance of the tertiary air upper branch pipe; the fuel feeding point of the decomposition furnace is located below the lower material distribution point of the decomposition furnace, and the lower material pipe at the bottom outlet of the secondary and final cyclone is respectively connected with the lower material distribution point of the decomposition furnace, the middle material distribution point of the decomposition furnace and the tertiary air distribution point; The tertiary air lower branch is connected to the first venturi throat, the height between the tertiary air duct lower branch and the top of the kiln tail smoke chamber is greater than 10m, the tertiary air upper branch is connected to the lower side of the burnout zone column, the decomposition furnace area below the tertiary air lower branch is a strong oxygen-depleted zone, the area between the tertiary air upper branch and the tertiary air upper branch is an oxygen-depleted combustion zone, and the area above the tertiary air upper branch is an oxygen-rich combustion zone, so that a gradient combustion environment of strong oxygen-depleted zone-oxygen-depleted combustion zone-oxygen-rich combustion zone is formed in the decomposition furnace.

2. The gradient combustion deep self-denitrification decomposition furnace system with tertiary air carrying material according to claim 1 is characterized in that: The height of the position where the tertiary air upper branch pipe enters the decomposition furnace is higher than the height of the bottom outlet of the secondary and final stage cyclone.

3. The gradient combustion deep self-denitrification decomposition furnace system with tertiary air carrying material according to claim 1 is characterized in that: The tertiary air lower branch pipe is connected to the side surface of the upper expansion section of the first venturi throat pipe.

4. The gradient combustion deep self-denitrification decomposition furnace system with tertiary air carrying material according to claim 1 is characterized in that: The tertiary air lower branch pipe is provided with a lower branch pipe valve, and the tertiary air upper branch pipe is provided with an upper branch pipe valve.

5. The gradient combustion deep self-denitrification decomposition furnace system with tertiary air carrying material according to claim 1 is characterized in that: A two-stage material distribution valve is arranged on the discharge pipe at the bottom outlet of the secondary and final cyclone, so that the raw material out of the secondary and final cyclone is respectively connected to the lower material distribution point of the decomposition furnace, the middle material distribution point of the decomposition furnace and the tertiary air material distribution point through the discharge pipe.

6. The gradient combustion deep self-denitrification decomposition furnace system with tertiary air carrying material according to claim 1 is characterized in that: The fuel feeding point of the decomposition furnace is located at the cone at the bottom of the furnace or at the lower side of the column in the strong oxygen-deficient zone.

7. A gradient combustion deep self-denitrification process with tertiary air-carrying material based on the system according to any one of claims 1 to 6, characterized in that: The process adopts a gradient combustion environment of strong oxygen-depleted zone-oxygen-depleted combustion zone-oxygen-rich burnout zone formed in the decomposition furnace, and the height of the strong oxygen-depleted zone is greater than 10m. The gradient combustion environment is achieved by feeding the fuel into the decomposition furnace, the tertiary air into the decomposition furnace and the raw material into the decomposition furnace in stages. The fuel into the furnace is fed from the bottom of the decomposition furnace, a part of the tertiary air is fed from the lower part of the oxygen-depleted combustion zone, a part of the tertiary air carries part of the raw material that slides down from the down pipe of the next-to-last cyclone to the tertiary air distribution point upward and is fed from the bottom of the oxygen-rich burnout zone, a part of the raw material that slides down from the down pipe of the next-to-last cyclone to the lower distribution point of the decomposition furnace is fed from the lower part of the strong oxygen-depleted zone, and a part of the raw material that slides down from the down pipe of the next-to-last cyclone to the middle distribution point of the decomposition furnace is fed from the lower part of the oxygen-depleted combustion zone. The excess air coefficient of the strong oxygen-depleted zone is controlled to be 0.1-0.5, the excess air coefficient of the oxygen-depleted combustion zone is 0.5-1.0, and the excess air coefficient of the oxygen-rich burnout zone is above 1.

0.

8. The gradient combustion deep self-denitrification process with tertiary air carrying material according to claim 7 is characterized in that: The average cross-sectional wind speed in the strong oxygen-deficient zone is 3-8 m / s, and the gas residence time is greater than 1.5 s.

9. The gradient combustion deep self-denitrification process with tertiary air carrying material according to claim 7, characterized in that: The tertiary air component is air, and the temperature in the tertiary air main pipe is 850-1100°C; when the tertiary air upper branch pipe carries material, the opening of the upper branch pipe valve is greater than 20%, the average wind speed in the pipe is greater than 10m / s, the material distribution ratio increases with the increase of the air volume of the tertiary air upper branch pipe, and the material-air mass ratio is controlled to be less than 3.

0.

10. The gradient combustion deep self-denitrification process with tertiary air carrying material according to claim 7, characterized in that: The temperature of the raw material entering the calciner is lower than 850°C.

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