A deep self-denitration cement clinker calcination system with an online reduction furnace and a process thereof

Abstract

This invention discloses a deep self-denitrification cement clinker calcination system and process with an online reduction furnace. The system includes an online reduction furnace located between the kiln tail flue and the decomposition furnace. The online reduction furnace has a raw meal feeding point one and a fuel feeding point. The raw meal feeding point one is located at the bottom of the online reduction furnace, and the fuel feeding point is located below the raw meal feeding point one. The height of the online reduction furnace is greater than 10m. A tertiary air lower branch pipe connects to the bottom of the online reduction furnace, and a tertiary air upper branch pipe connects to the bottom of the decomposition furnace. A second raw meal feeding point is located at the inlet of the tertiary air upper branch pipe. The bottom outlet of the final stage cyclone separator is connected to both raw meal feeding points one and two, creating a combined gradient combustion environment of a strong oxygen-deficient zone and an oxygen-rich combustion zone within the online reduction furnace and the decomposition furnace. This invention overcomes the height limitation of the raw meal feeding point, extends the denitrification time in the strong oxygen-deficient zone, improves self-denitrification efficiency, and simultaneously achieves complete decomposition of the raw meal.

Description

Technical Field

[0001] This invention relates to the field of cement calcination technology, and in particular to a deep self-denitrification cement clinker calcination system and process with an online reduction furnace. Background Technology

[0002] The cement industry is the third largest emitter of nitrogen oxides after thermal power generation and vehicle exhaust. Denitrification in the cement industry generally relies on staged combustion, supplemented by SNCR or SCR technologies. However, solely using SNCR or SCR technologies requires the consumption of large amounts of ammonia water, increasing carbon emissions from the ammonia water production process. Furthermore, ammonia escape leads to increased pollutants and energy consumption.

[0003] Fuel combustion self-denitrification technology is a combustion technology that inhibits NOx formation by controlling fuel combustion characteristic parameters and utilizing intermediate products formed during combustion, without adding external denitrification reducing agents. After self-denitrification, flue gas NOx is significantly reduced, decreasing the amount of reducing agent used in subsequent SNCR and SCR denitrification processes, thus lowering denitrification costs. Simultaneously, it indirectly reduces carbon emissions from the electricity consumption of the ammonia water production process, achieving a synergistic effect of pollution reduction and carbon reduction.

[0004] Currently, fuel combustion-based denitrification technologies include air-staged combustion and fuel-staged combustion. Air-staged combustion utilizes tertiary air feeding into the decomposer to create an oxygen-deficient combustion zone in the decomposer column, suppressing NOx generated by the combustion of fuel itself. However, the excess oxygen coefficient in this oxygen-deficient combustion zone remains high, resulting in poor overall denitrification efficiency. Fuel-staged combustion utilizes staged fuel feeding into the decomposer to create an oxygen-deficient combustion zone in the decomposer cone, effectively reducing NOx in the rotary kiln flue gas. However, the reduction is generally only around 30%, and the main reason limiting denitrification efficiency is the insufficient denitrification reaction time; the residence time of the denitrification reaction is short, and it is difficult to suppress NOx generated by the combustion of fuel itself in the decomposer.

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

[0006] H2 + NO → N2 + H2O

[0007] Chinese Patent Publication No. CN108167860A discloses a gradient combustion self-denitrification process for a calcination system. This process creates a gradient combustion environment within the decomposition furnace, consisting of an extremely oxygen-deficient zone, an oxygen-deficient combustion zone, and an oxygen-rich burnout zone, thereby achieving self-denitrification in the decomposition furnace. Specifically, the excess air coefficient in the extremely oxygen-deficient zone is 0.1~0.5, in the oxygen-deficient combustion zone it is 0.5~1.0, and in the oxygen-rich burnout zone it is above 1.0. By creating this gradient combustion atmosphere, the combustion intermediates are used to reduce NOx generated in the rotary kiln, while simultaneously suppressing NOx generation within the decomposition furnace. This reduces the NOx concentration in the flue gas without affecting fuel burnout.

[0008] Chinese Patent Publication No. CN111750670A discloses a zoned combustion self-denitrification system and process with a reduction furnace and a decomposition furnace. Its key feature is the placement of a reduction furnace between the kiln tail flue and the decomposition furnace, creating a gradient combustion environment within the combined combustion space of the reduction and decomposition furnaces. 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, and the risk of raw material short-circuiting into the kiln is greater than in an online decomposition furnace when abnormal fluctuations occur within the decomposition furnace.

[0009] Cement raw meal is preheated by a preheater system, undergoes gas-solid separation in a cyclone separator, and then fed into a decomposition furnace for high-temperature decomposition. In an online gradient combustion decomposition furnace system, increasing the height of the strong oxygen-deficient zone and extending the denitrification reaction time in the strong oxygen-deficient zone can improve the self-denitrification efficiency. However, in the existing system, the raw meal entering the furnace from the cyclone separator is fed into the decomposition furnace by gravity. If the strong oxygen-deficient zone is increased, the feeding point of the raw meal entering the furnace needs to be raised accordingly. This means that the position of the cyclone separator also needs to be raised accordingly, and increasing the height of the cyclone separator requires increasing the total height of the preheater tower, resulting in a significant increase in investment costs. Especially for energy-saving and environmental protection technology upgrades of existing old production lines, if the height of the lower cyclone separator is significantly increased, the entire cyclone separator sequence needs to be raised accordingly, increasing the load on the preheater tower equipment, and requiring corresponding modifications to the civil engineering pile foundations and the plane support beams of each layer, resulting in a very high overall cost.

[0010] In addition, in existing online denitrification decomposition furnace systems, the temperature control of the strong reduction zone is mainly achieved through upper and lower material distribution. When the height of the strong reduction zone increases, the height of the upper material distribution point increases accordingly. The decomposition time of the raw material entering the furnace from the upper material distribution point is relatively shortened, which can easily lead to 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 with existing technologies are:

[0012] (1) The self-denitrification process of combustion can reduce the amount of ammonia water used for denitrification in SNCR or SCR systems, 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 offline gradient combustion decomposition furnace system, the use of an independent reduction furnace can improve the denitrification reaction time, but there is a risk that the raw material of the decomposition furnace will be short-circuited into the kiln from the bottom.

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

[0015] (4) In the existing online gradient combustion decomposition furnace system, when the height of the strong reduction zone increases, the decomposition time of raw materials entering the furnace from the upper distribution point is relatively shortened, resulting in insufficient decomposition of raw materials.

[0016] Therefore, for online decomposition furnace systems, it is necessary to develop a method that allows sufficient reaction time for deep reduction of NOx in the flue gas exiting the kiln, without increasing the overall height of the preheater tower, thereby improving the system's self-denitrification efficiency while remaining economically feasible. Summary of the Invention

[0017] One objective of this invention is to provide a deep self-denitrification cement clinker calcination system with an online reduction furnace. This system adds an online reduction furnace between the decomposition furnace and the kiln tail flue gas chamber, creating a strong reducing atmosphere within the furnace to fully remove NOx from the kiln exhaust gas. Furthermore, by setting a raw material feeding point on the upper branch pipe of the tertiary air system, the raw material is first fed into the pipe by gravity, and then carried into the decomposition furnace by the tertiary air, thus overcoming the height limitation of the raw material feeding point. Additionally, the low CO2 partial pressure in the high-temperature tertiary air allows the tertiary air to preheat and pre-decompose the raw material while carrying it, achieving full decomposition of the raw material within the decomposition furnace.

[0018] Another object of the present invention is to provide a deep self-denitrification cement clinker calcination process using the above-described system with an online reduction furnace.

[0019] The present invention is implemented as follows: a deep self-denitrification cement clinker calcination system with an online reduction furnace includes a rotary kiln, a kiln tail smoke chamber connected to the kiln tail of the rotary kiln, a decomposition furnace, a tertiary air duct and a secondary final stage cyclone separator, wherein the tertiary air duct is divided into a tertiary air lower branch pipe and a tertiary air upper branch pipe.

[0020] It also includes an online reduction furnace, which is located between the kiln tail flue and the decomposition furnace. The bottom inlet of the online reduction furnace is connected to the outlet of the kiln tail flue, and the top outlet of the online reduction furnace is connected to the bottom inlet of the decomposition furnace. The online reduction furnace is equipped with a raw material feeding point and a fuel feeding point. The raw material feeding point is located at the bottom of the online reduction furnace, and the fuel feeding point is located below the raw material feeding point. The height of the online reduction furnace is greater than 10m.

[0021] The tertiary air lower branch pipe is connected to the lower part of the online reduction furnace, and the connection point is located below the first raw material feeding point; the tertiary air upper branch pipe is connected to the lower part of the decomposition furnace, and the tertiary air upper branch pipe is a vertically upward lifting pipe, with a second raw material feeding point at the inlet of the tertiary air upper branch pipe; the bottom outlet of the secondary final stage cyclone is connected to the first and second raw material feeding points respectively through a discharge pipe;

[0022] The online reduction furnace is a strongly oxygen-deficient zone, while the decomposition furnace is an oxygen-rich combustion zone, creating a combined gradient combustion environment of strongly oxygen-deficient zone and oxygen-rich combustion zone in the online reduction furnace and the decomposition furnace.

[0023] The gradient combustion environment is achieved through the coordinated operation of fuel fed into the online reduction furnace, tertiary air fed into the online reduction furnace and the decomposition furnace, and raw materials. Fuel is fed into the online reduction furnace from the bottom; tertiary air is fed into the online reduction furnace from the bottom, and tertiary air is fed into the decomposition furnace from the bottom; the raw materials exiting the final stage cyclone separator are divided into two paths. The first path of raw materials slides down the feed pipe under gravity to raw material feeding point one and enters the online reduction furnace, while the second path of raw materials slides down the feed pipe under gravity to raw material feeding point two and enters the upper branch pipe of the tertiary air, and then enters the decomposition furnace along with the tertiary air under pneumatic lifting.

[0024] Preferably, the height of the tertiary air branch pipe entering the decomposition furnace is higher than the height of the bottom outlet of the secondary final stage cyclone, so that the raw material is carried upward.

[0025] Preferably, the tertiary air lower branch pipe is connected to the bottom side of the column of the online reduction furnace, and the tertiary air upper branch pipe is connected to the bottom of the column of the decomposition furnace.

[0026] Preferably, a lower branch pipe valve is provided on the tertiary air lower branch pipe, and a main pipe valve is provided on the tertiary air duct. The air distribution ratio of the upper and lower branches of the tertiary air duct can be adjusted by the opening degree of the two valves.

[0027] Preferably, a material distribution valve is provided on the discharge pipe at the bottom outlet of the secondary cyclone, so that the raw material exiting the secondary cyclone is connected to raw material feeding point one and raw material feeding point two respectively through the discharge pipe. The material distribution ratio of the two raw material feeding points is adjusted by the opening of the material distribution valve provided on the discharge pipe.

[0028] Preferably, the fuel feeding point is located at the bottom cone of the online reduction furnace or at the bottom of the column of the online reduction furnace.

[0029] The above system is used for the deep self-denitrification cement clinker calcination process with an online reduction furnace. This process adopts a combined gradient combustion environment of strong oxygen-deficient zone and oxygen-rich combustion zone in the online reduction furnace and the decomposition furnace, and the height of the online reduction furnace is greater than 10m. The gradient combustion environment is achieved by the coordinated operation of fuel entering the online reduction furnace, tertiary air entering the online reduction furnace and the decomposition furnace, and raw materials. Fuel entering the online reduction furnace is fed from the bottom of the online reduction furnace, a portion of tertiary air is fed from the lower part of the online reduction furnace, and a portion of tertiary air carries a portion of raw materials that slides down from the feed pipe of the secondary cyclone separator to the second raw material feeding point and moves upward to be fed from the lower part of the decomposition furnace. A portion of raw materials that slides down from the feed pipe of the secondary cyclone separator to the first raw material feeding point is fed from the lower part of the online reduction furnace. The excess air coefficient of the online reduction furnace is controlled to be 0.1~0.5, and the excess air coefficient of the decomposition furnace is greater than 1.0.

[0030] Preferably, the average cross-sectional wind speed inside the online reduction furnace is 3~8m / s, and the gas residence time is greater than 1.5s.

[0031] Preferably, the tertiary air component is air, and the temperature inside the tertiary air duct is 850~1100℃.

[0032] Preferably, when the tertiary air supply branch pipe is carrying material, the opening degree of the main valve is greater than 20%, the average wind speed in the tertiary air supply branch pipe is greater than 10m / s, the material distribution ratio increases with the increase of the tertiary air volume, and the material-to-air mass ratio is controlled to be less than 3.0 to prevent material collapse due to insufficient material support capacity of the tertiary air supply.

[0033] The present invention has the following advantages and beneficial effects:

[0034] 1. This invention adds an online reduction furnace between the decomposition furnace and the kiln tail flue gas chamber. A strong reducing atmosphere is created within the online reduction furnace to fully remove NOx from the kiln exhaust gas. Because the online reduction furnace raises the position of the decomposition furnace, it is difficult to directly feed raw materials from the secondary final stage cyclone separator into the decomposition furnace. This invention addresses this by setting a raw material feeding point on the upper branch pipe of the tertiary air. The raw materials are first fed into the upper branch pipe by gravity, and then carried into the decomposition furnace by the tertiary air. This overcomes the height limitation of the raw material feeding point, allowing the height of the online reduction furnace to be increased to over 10m. This significantly extends the residence time of flue gas in the strong oxygen-deficient zone, thus prolonging the denitrification time in this zone and further ensuring the full removal of NOx from the kiln exhaust gas in this area. This improves self-denitrification efficiency and reduces total investment costs. Furthermore, the low CO2 partial pressure in the high-temperature tertiary air allows the tertiary air to preheat and pre-decompose the raw materials while carrying them, achieving full decomposition of the raw materials within the decomposition furnace, resulting in energy saving and consumption reduction.

[0035] 2. This invention achieves a combined gradient combustion environment of strong oxygen-deficient zone and oxygen-rich combustion zone within the online reduction furnace and decomposition furnace by coordinating the fuel fed into the online reduction furnace, the tertiary air fed into the online reduction furnace and the raw materials fed into the decomposition furnace. The raw materials are fed in an upper and lower distribution technology to regulate the temperature distribution within the decomposition furnace. By controlling the temperature within the bottom cone of the decomposition furnace, the problem of high-temperature scaling in the cone of the decomposition furnace is solved. By increasing the temperature of the decomposition furnace, the denitrification reaction rate is increased, and the burnout of the fuel within the decomposition furnace is improved. This achieves self-denitrification function without affecting the normal operation of the calcination system.

[0036] 3. This invention improves denitrification efficiency without reducing fuel combustion speed or complete raw material decomposition, and has no adverse effects on cement clinker production. It boasts advantages such as a rational system process, high reliability, and strong adaptability, thereby reducing environmental governance costs for enterprises. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the deep self-denitrification cement clinker calcination system with an online reduction furnace provided in Embodiment 1 of the present invention;

[0038] Figure 2 This is a schematic diagram of the raw material feeding point provided in Embodiment 1 of the present invention;

[0039] Figure 3 This is a schematic diagram of the structure of the deep self-denitrification cement clinker calcination system with an online reduction furnace provided in Embodiment 2 of the present invention.

[0040] In the picture:

[0041] g1 - Kiln exhaust gas; g2 - Tertiary air; g3 - Decomposition furnace exhaust gas; G - Low temperature flue gas; M1 - Raw material entering the online reduction furnace; M2 - Raw material entering the decomposition furnace; F1 - Pulverized coal at the kiln head; F2 - Pulverized coal at the kiln tail; K - Clinker; A - Strong oxygen-deficient zone; B - Oxygen-enriched combustion zone;

[0042] 1-Preheater; 101-First-stage cyclone separator; 102-Second-stage cyclone separator; 103-Third-stage cyclone separator; 104-Fourth-stage cyclone separator; 105-Fifth-stage cyclone separator; 106-Distribution valve;

[0043] 2-Online reduction furnace; 201-Fuel feeding point; 202-Raw material feeding point one;

[0044] 3-Decomposition furnace;

[0045] 4-Tertiary air duct; 401-Main valve; 402-Raw material feeding point two; 403-Tertiary air upper branch pipe; 404-Lower branch pipe valve; 405-Tertiary air lower branch pipe; 406-Emergency discharge port;

[0046] 5-Kiln tail smoke chamber; 6-Rotary kiln; 7-Cooler; 8-Kiln head burner;

[0047] The dashed line with an arrow indicates the airflow direction; the solid line with an arrow indicates the flow direction of raw material or pulverized coal. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0049] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0050] This embodiment uses a five-stage preheater as an example for illustration. This embodiment of the invention provides a deep self-denitrification cement clinker calcination system with an online reduction furnace, including a rotary kiln 6, a kiln tail smoke chamber 5 connected to the kiln tail of the rotary kiln 6, a decomposition furnace 3, a tertiary air duct 4, a fourth-stage cyclone separator 104, and an online reduction furnace 2. The tertiary air duct 4 is divided into a tertiary air lower branch pipe 405 and a tertiary air upper branch pipe 403.

[0051] The online reduction furnace 2 is located between the kiln tail flue chamber 5 and the decomposition furnace 3. The bottom inlet of the online reduction furnace 2 connects to the outlet of the kiln tail flue chamber 5, and the top outlet of the online reduction furnace 2 connects to the bottom inlet of the decomposition furnace 3. The online reduction furnace 2 is equipped with a raw material feeding point 202 and a fuel feeding point 201. The raw material feeding point 202 is located at the lower part of the column of the online reduction furnace 2. Raw materials are fed into the lower part of the column of the online reduction furnace 2, and the temperature inside the furnace bottom cone is controlled by the heat absorption of raw material decomposition, preventing the problem of crusting caused by excessively high temperatures inside the furnace bottom cone due to fuel combustion. The fuel feeding point 201 is located below the raw material feeding point 202. In this embodiment, the fuel feeding point 201 is located at the furnace bottom cone of the online reduction furnace 2, allowing the NOx in the flue gas g1 exiting the kiln to fully react with the reducing gas. The height of the online reduction furnace 2 is greater than 10m, extending the denitrification reaction time in the strongly oxygen-deficient zone A.

[0052] The tertiary air lower branch pipe 405 is connected to the bottom side of the column of the online reduction furnace 2, and the connection point is located below the raw material feeding point 202. The tertiary air enhances the dispersion and lifting of the raw material entering the online reduction furnace 2. The opening of the lower branch pipe valve 404 controls the tertiary air entering the online reduction furnace 2, controlling the excess air coefficient in the strongly oxygen-deficient zone. The tertiary air upper branch pipe 403 is connected to the bottom of the column of the decomposition furnace 3. The tertiary air upper branch pipe 403 is a vertically upward-lifting pipe to meet the oxygen requirements for fuel combustion. A raw material feeding point 402 is set at the inlet of the tertiary air upper branch pipe 403. The bottom outlet of the fourth-stage cyclone 104 is connected to the raw material feeding points 202 and 402 respectively through the discharge pipe. The distribution of raw material at the raw material feeding points 202 and 402 reduces the amount of raw material fed from the bottom of the online reduction furnace 2, thereby increasing the temperature at the bottom of the online reduction furnace 2.

[0053] The online reduction furnace 2 contains a strongly oxygen-deficient zone A, and the decomposition furnace 3 contains an oxygen-rich combustion zone C, thus creating a combined gradient combustion environment of strongly oxygen-deficient zone A and oxygen-rich combustion zone C within the online reduction furnace 2 and the decomposition furnace 3.

[0054] The gradient combustion environment is achieved through the coordinated operation of fuel entering the online reduction furnace 2, tertiary air entering the online reduction furnace 2 and the decomposition furnace 3, and raw materials. Fuel entering the online reduction furnace 2 is fed from the bottom of the online reduction furnace 2; tertiary air entering the online reduction furnace 2 is fed from the bottom of the online reduction furnace 2, and tertiary air entering the decomposition furnace 3 is fed from the bottom of the decomposition furnace 3; the raw materials exiting the fourth-stage cyclone 104 are divided into two paths. The first path of raw materials slides down the feed pipe under gravity to the raw material feeding point 1 202 and enters the online reduction furnace 2. The second path of raw materials slides down the feed pipe under gravity to the raw material feeding point 2 402 and enters the upper branch pipe of the tertiary air 403, and is then lifted by pneumatic force and enters the decomposition furnace 3 along with the tertiary air.

[0055] The height of the tertiary air branch pipe 403 entering the decomposition furnace 3 is higher than the height of the bottom outlet of the fourth-stage cyclone 104, and the raw material is carried upward.

[0056] The tertiary air down branch pipe 405 is equipped with a down branch pipe valve 404, and the tertiary air pipe 4 is equipped with a main pipe valve 401. The air distribution ratio of the tertiary air up branch pipe 403 and the tertiary air down branch pipe 405 can be adjusted by the opening of the main pipe valve 401 and the down branch pipe valve 404.

[0057] A material distribution valve 106 is installed on the feed pipe at the bottom outlet of the fourth-stage cyclone 104, so that the raw material exiting the fourth-stage cyclone 104 is connected to raw material feeding point 1 202 and raw material feeding point 2 402 respectively through the feed pipe. The material distribution ratio of the two raw material feeding points is adjusted by the opening of the material distribution valve 106 on the feed pipe, thereby controlling the temperature inside the online reduction furnace 2 and the decomposition furnace 3, preventing the problem of high temperature scaling on the furnace wall, and reducing the amount of raw material fed from raw material feeding point 1 202, thereby increasing the temperature of the online reduction furnace 2.

[0058] The fuel feeding point 201 is located at the bottom cone of the online reduction furnace 2 or at the bottom of the column of the online reduction furnace 2.

[0059] The above system is used for the deep self-denitrification cement clinker calcination process with an online reduction furnace. This process employs a combined gradient combustion environment within the online reduction furnace 2 and the decomposition furnace 3, creating a strong oxygen-deficient zone A and an oxygen-rich combustion zone C. The height of the online reduction furnace 2 is greater than 10m. This gradient combustion environment is achieved through the coordinated operation of fuel fed into the online reduction furnace 2, tertiary air fed into both the online reduction furnace 2 and the decomposition furnace 3, and raw materials. Fuel is fed into the online reduction furnace 2 from the bottom. The tertiary air is composed of air, and the temperature inside the tertiary air duct 4 is 850~1100℃. When the tertiary air upper branch pipe 403 is carrying material, the opening degree of the main valve 401 is greater than 20%, the average wind speed inside the tertiary air upper branch pipe 403 is greater than 10m / s, and the material distribution ratio is... The amount of tertiary air increases with the increase of tertiary air volume. The material-to-gas mass ratio is controlled to be less than 3.0 to prevent material collapse due to insufficient material support capacity of tertiary air. Part of the tertiary air is fed in from the bottom of the online reduction furnace 2. Part of the tertiary air carries some raw material that has slid down from the feed pipe of the fourth-stage cyclone 104 to the raw material feeding point 202 and moves upward to be fed in from the bottom of the decomposition furnace 3. Part of the raw material that has slid down from the feed pipe of the fourth-stage cyclone 104 to the raw material feeding point 202 is fed in from the bottom of the online reduction furnace 2. The excess air coefficient of the online reduction furnace 2 is controlled to be 0.1~0.5, the average cross-sectional wind speed in the online reduction furnace 2 is 3~8m / s, the gas residence time is greater than 1.5s, and the excess air coefficient of the decomposition furnace 3 is greater than 1.0.

[0060] The present invention will now be described in further detail.

[0061] Example 1

[0062] Please see Figure 1 and Figure 2 This embodiment provides a deep self-denitrification cement clinker calcination system with an online reduction furnace. The system mainly consists of a preheater 1, an online reduction furnace 2, a decomposition furnace 3, a tertiary air duct 4, a kiln tail smoke chamber 5, a rotary kiln 6, a cooler 7, and a kiln head burner 8.

[0063] A kiln head burner 8 is installed on the rotary kiln 6; the kiln tail flue chamber 5, the rotary kiln 6, and the cooler 7 are connected in sequence. The raw material preheating and pre-decomposition system includes a decomposition furnace 3 and a preheater 1; the bottom air inlet of the preheater 1 is connected to the outlet air pipe of the decomposition furnace 3, and the top air outlet of the preheater 1 discharges low-temperature flue gas G; the top feed inlet of the preheater 1 is used for feeding raw material M, and the bottom discharge outlet of the preheater is connected to the kiln tail flue chamber 5.

[0064] Raw material M is preheated in preheater 1. The raw material is fed through a pipe into the outlet duct of the second-stage cyclone separator 102 for gas-solid heat exchange, and then enters the first-stage cyclone separator 101 under the influence of airflow. After gas-solid separation in the first-stage cyclone separator 101, the material is fed from the discharge pipe of the first-stage cyclone separator 101 into the outlet duct of the third-stage cyclone separator 103. This process is repeated sequentially through the second-stage cyclone separator 102, the third-stage cyclone separator 103, and the fourth-stage cyclone separator 104. After gas-solid separation in the fourth-stage cyclone separator 104, the raw material enters the online reduction furnace 2 and the tertiary air branch pipe 403, where it undergoes decomposition in the decomposition furnace 3 (calcium carbonate in the raw material decomposes into calcium oxide). The decomposed raw material then enters the fifth-stage cyclone separator 105 with the airflow, and after gas-solid separation, it is fed into the kiln tail flue chamber 5. After passing through the kiln tail smoke chamber 5, the raw material enters the rotary kiln 6 for calcination, where it is sintered into clinker. The clinker exiting the kiln is cooled by the cooler 7 to produce clinker product K.

[0065] The online reduction furnace 2 is located between the kiln tail smoke chamber 5 and the decomposition furnace 3. The lower inlet of the online reduction furnace 2 is connected to the outlet of the kiln tail smoke chamber 5, and the top outlet of the online reduction furnace 2 is connected to the bottom inlet of the decomposition furnace 3; the online reduction furnace 2 is equipped with a raw material feeding point 202 and a fuel feeding point 201.

[0066] The tertiary air upper branch pipe 403 is connected to the bottom of the column of the decomposition furnace 3. The tertiary air upper branch pipe 403 is a vertically upward lifting pipe. A raw material feeding point 402 is set at the inlet of the tertiary air upper branch pipe 403. The raw material moves upward into the decomposition furnace 3 under the carrying of the tertiary air.

[0067] Fuel is injected into the online reduction furnace 2, and the tertiary air entering the online reduction furnace 2 is controlled by the opening of the lower branch valve 404, so that the online reduction furnace 2 has a strongly oxygen-deficient atmosphere with an excess air coefficient of 0.1~0.5. One stream of tertiary air enters the online reduction furnace 2, and the other stream enters the decomposition furnace 3, which has an oxygen-rich atmosphere with an excess air coefficient of 1.0 or higher.

[0068] Powdered coal F1 at the kiln head is burned in the rotary kiln 6, providing heat for clinker calcination. The temperature of the flue gas g1 exiting the kiln is 900~1300℃, the NOx concentration is generally 500~1500ppm, and the O2 concentration is less than 10%. The flue gas g1 exiting the kiln passes through the kiln tail flue chamber 5 and flows upward into the online reduction furnace 2. Powdered coal F2 from the kiln tail is injected into the online reduction furnace 2 and mixes with the flue gas g1 exiting the kiln. The powdered coal F2 from the kiln tail releases volatiles in the high-temperature, oxygen-deficient flow. The pyrolysis of the volatiles produces reducing gases CO, H2, and aromatic organic compounds CxHy. The reducing gases undergo a redox reaction with NOx, reducing NOx to N2. The height of the online reduction furnace 2 is more than 10m, the average cross-sectional wind speed is 3~8m / s, and the gas residence time is greater than 1.5s, ensuring that NOx in the flue gas g1 exiting the kiln is fully removed within the furnace. The unburned portion of the pulverized coal F2 at the kiln tail moves upward with the flue gas exiting the online reduction furnace 2 into the decomposition furnace 3, where it continues to burn.

[0069] Tertiary air g2 is composed of air at a temperature of 850~1100℃, providing oxygen for the fuel. After passing through the tertiary air main pipe 4, tertiary air g2 splits into two paths. The first path enters the lower tertiary air branch pipe 405, which connects to the bottom of the column of the online reduction furnace 2. The second path enters the upper tertiary air branch pipe 403 and connects to the bottom of the column of the decomposition furnace 3. A lower branch pipe valve 404 is installed on the lower tertiary air branch pipe 405, and a main pipe valve 401 is installed on the tertiary air pipe 4. When the upper tertiary air branch pipe 403 is carrying material, the opening degree of the main pipe valve 401 is greater than 20%, the average air velocity inside the upper tertiary air branch pipe 403 is greater than 10m / s, and the material distribution ratio increases with the increase of the tertiary air volume, controlling the material-to-air mass ratio to be less than 3.0 to prevent material collapse due to insufficient material support capacity of the tertiary air.

[0070] After being separated by the fourth-stage cyclone separator 104, the raw material flows downward from the bottom and is divided into two streams by the distribution valve 106. The first stream of raw material slides down the feed pipe under gravity to the raw material feeding point 1 202 and enters the online reduction furnace 2. The second stream of raw material slides down the feed pipe under gravity to the raw material feeding point 2 402 and enters the tertiary air upper branch pipe 403, and is then lifted by pneumatic force and enters the decomposition furnace 3 along with the tertiary air.

[0071] Please see Figure 2 Raw material M1 entering the online reduction furnace moves upward under the influence of the flue gas g1 exiting the kiln. Raw material M2 entering the decomposition furnace moves upward under the influence of the combustion air in the tertiary air branch pipe 403, enters the decomposition furnace 3, and moves upward with the air inside the furnace. Both raw materials entering the furnace flow out of the decomposition furnace 3 outlet with the flue gas g3 exiting the decomposition furnace.

[0072] The upper and lower material distribution technology is used to regulate the temperature distribution inside the decomposition furnace 3. By controlling the temperature inside the bottom cone of the decomposition furnace 3, the problem of high temperature and easy scaling in the cone of the decomposition furnace 3 is solved. By increasing the temperature of the decomposition furnace 3, the denitrification reaction rate is increased, and the combustion degree of the fuel inside the decomposition furnace 3 is improved. While realizing the self-denitrification function, it does not affect the normal operation of the calcination system, thus achieving the purpose of energy saving and consumption reduction.

[0073] In this system, to achieve an online reduction furnace 2 height of over 10m and a gas residence time greater than 1.5s, ensuring sufficient NOx removal from the flue gas g1 exiting the kiln in this region, the height of the decomposition furnace 3 needs to be increased. Furthermore, the feed distribution point of the decomposition furnace 3 also needs to be raised. However, under conventional production line feeding methods, the material flow in the furnace feed pipe is gravity-driven downwards, therefore the feed distribution point height of the decomposition furnace 3 cannot be higher than the outlet height of the fourth-stage cyclone 104. Consequently, the temperature of the oxygen-enriched combustion zone B is difficult to control through upward feed distribution. This invention proposes a feeding method where the raw material M2 entering the decomposition furnace is first fed into the tertiary air upper branch pipe 403 via gravity-driven downward flow through the feed pipe, and then fed into the decomposition furnace 3 by tertiary air force lifting. This method overcomes the limitation imposed by the position of the fourth-stage cyclone 104 on the position of the raw material entering the decomposition furnace 3. The height H2 of the tertiary air branch pipe 403 entering the decomposition furnace 3 from the furnace bottom is higher than the height H1 of the bottom outlet of the fourth-stage cyclone 104 from the furnace bottom, carrying the raw material upwards and realizing the upward shift of the upper furnace entry point position.

[0074] After the raw meal M2 is fed into the tertiary air upper branch pipe 403, the temperature of the tertiary air is higher than the decomposition temperature of calcium carbonate (above 850℃). Simultaneously, the tertiary air is composed of air with a very low CO2 concentration (less than 1%). Under this high temperature and low CO2 partial pressure, the raw meal M2 entering the decomposition furnace is preheated and decomposed within the tertiary air upper branch pipe 403: CaCO3 → CaO + CO2. This solves the problem of shortened decomposition time and reduced decomposition rate of the raw meal in decomposition furnace 3 caused by raising the position of the raw meal inlet, thus achieving complete decomposition of the raw meal within decomposition furnace 3.

[0075] Example 2

[0076] Please see Figure 3 Unlike Example 1, in some older production line upgrade projects, due to limited space, it is impossible to install tertiary air branch pipes. Tertiary air duct 4 does not have tertiary air branch pipes 405, and there is no connecting pipe between tertiary air duct 4 and the online reduction furnace 2. All tertiary air enters the decomposition furnace 3 and does not enter the online reduction furnace 2. An emergency discharge port 406 is installed at the bottom of the bend where the tertiary air duct rises upwards, used for cleaning up accumulated material in the tertiary air duct after a collapse accident caused by abnormal system operation or sudden shutdown.

[0077] In summary, this invention, by setting a raw material feeding point in the tertiary air branch pipe 403, utilizes the tertiary air to carry the raw material into the oxygen-enriched combustion zone of the decomposition furnace 3, thereby overcoming the height limitation of the raw material feeding point in the decomposition furnace 3. The height of the online reduction furnace 2 can be increased to over 10m, significantly extending the residence time of flue gas in the online reduction furnace 2, thus prolonging the denitrification time in the online reduction furnace 2. This further ensures that NOx in the flue gas g1 exiting the kiln is fully removed in this area, achieving improved self-denitrification efficiency. In addition, the CO2 partial pressure in the high-temperature tertiary air is low, and the tertiary air preheats and pre-decomposes the raw material while carrying it, achieving full decomposition of the raw material in the decomposition furnace 3. By coordinating the fuel fed into the online reduction furnace 2, the tertiary air fed into the online reduction furnace 2 and the decomposition furnace 3, and the raw materials, a combined gradient combustion environment of strong oxygen-deficient zone A and oxygen-rich combustion zone C is formed in the online reduction furnace 2 and the decomposition furnace 3. The raw materials adopt the upper and lower feeding technology to regulate the temperature distribution in the decomposition furnace 3. By controlling the temperature in the bottom cone of the decomposition furnace 3, the problem of high temperature and easy scaling in the cone of the decomposition furnace 3 is solved. By increasing the temperature of the decomposition furnace 3, the denitrification reaction rate is increased, and the combustion degree of the fuel in the decomposition furnace 3 is improved. While achieving the self-denitrification function, the normal operation of the calcination system is not affected.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 deep self-denitrifying cement clinker calcination system with an online reduction furnace, comprising a rotary kiln, a kiln tail flue connected to the kiln tail, a decomposition furnace, tertiary air ducts, and a secondary and final stage cyclone separator, wherein the tertiary air ducts are divided into a lower tertiary air branch pipe and an upper tertiary air branch pipe; characterized in that: It also includes an online reduction furnace, which is located between the kiln tail flue and the decomposition furnace. The bottom inlet of the online reduction furnace is connected to the outlet of the kiln tail flue, and the top outlet of the online reduction furnace is connected to the bottom inlet of the decomposition furnace. The decomposition furnace is located above the online reduction furnace. The online reduction furnace is provided with a raw material feeding point and a fuel feeding point. The raw material feeding point is located at the bottom of the online reduction furnace, and the fuel feeding point is located below the raw material feeding point. The height of the online reduction furnace is greater than 10m. The tertiary air lower branch pipe is connected to the lower part of the online reduction furnace, and the connection point is located below the first raw material feeding point; the tertiary air upper branch pipe is connected to the lower part of the decomposition furnace, and the tertiary air upper branch pipe is a vertically upward lifting pipe, with a second raw material feeding point at the inlet of the tertiary air upper branch pipe; the bottom outlet of the secondary final stage cyclone is connected to the first and second raw material feeding points respectively through a discharge pipe; The online reduction furnace is a strongly oxygen-deficient zone, while the decomposition furnace is an oxygen-rich combustion zone. Through the coordinated operation of the fuel entering the online reduction furnace, the tertiary air entering the online reduction furnace and the decomposition furnace, and the raw materials, a combined gradient combustion environment of strongly oxygen-deficient zone and oxygen-rich combustion zone is formed in the online reduction furnace and the decomposition furnace.

2. The deep self-denitrification cement clinker calcination system with an online reduction furnace as described in claim 1, characterized in that, The height of the tertiary air branch pipe entering the decomposition furnace is higher than the height of the bottom outlet of the secondary final stage cyclone.

3. The deep self-denitrification cement clinker calcination system with an online reduction furnace as described in claim 1, characterized in that, The tertiary air lower branch pipe is connected to the bottom side of the column of the online reduction furnace, and the tertiary air upper branch pipe is connected to the bottom of the column of the decomposition furnace.

4. The deep self-denitrification cement clinker calcination system with an online reduction furnace as described in claim 1, characterized in that, A branch valve is installed on the tertiary air duct, and a main valve is installed on the tertiary air duct.

5. The deep self-denitrification cement clinker calcination system with an online reduction furnace as described in claim 1, characterized in that, A material distribution valve is installed on the discharge pipe at the bottom outlet of the secondary cyclone, so that the raw material exiting the secondary cyclone is connected to raw material feeding point one and raw material feeding point two respectively through the discharge pipe.

6. The deep self-denitrification cement clinker calcination system with an online reduction furnace as described in claim 1, characterized in that, The fuel feeding point is located at the bottom cone of the online reduction furnace or at the bottom of the column of the online reduction furnace.

7. A deep self-denitrification cement clinker calcination process with an online reduction furnace based on the system described in any one of claims 1 to 6, characterized in that, This process employs a combined gradient combustion environment, creating a strong oxygen-deficient zone and an oxygen-rich combustion zone within the online reduction furnace and the decomposition furnace, with the online reduction furnace having a height greater than 10m. This gradient combustion environment is achieved through the coordinated operation of fuel fed into the online reduction furnace, tertiary air fed into both the online reduction and decomposition furnaces, and raw materials. Fuel is fed into the online reduction furnace from the bottom, a portion of the tertiary air is fed into the online reduction furnace from the lower part, and a portion of the tertiary air carries raw materials that have slid down from the feed pipe of the secondary cyclone separator to raw material feeding point two, moving upwards to be fed into the decomposition furnace from the lower part. A portion of the raw materials that have slid down from the feed pipe of the secondary cyclone separator to raw material feeding point one are fed into the online reduction furnace from the lower part. The excess air coefficient of the online reduction furnace is controlled to be 0.1~0.5, and the excess air coefficient of the decomposition furnace is greater than 1.

0.

8. The deep self-denitrification cement clinker calcination process with an online reduction furnace as described in claim 7, characterized in that, The average cross-sectional wind speed inside the online reduction furnace is 3~8m / s, and the gas residence time is greater than 1.5s.

9. The deep self-denitrification cement clinker calcination process with an online reduction furnace as described in claim 7, characterized in that, The tertiary air component is air, and the temperature inside the tertiary air duct is 850~1100℃.

10. The deep self-denitrification cement clinker calcination process with an online reduction furnace as described in claim 7, characterized in that, When the tertiary air supply branch pipe is carrying material, the opening degree of the main valve is greater than 20%, the average wind speed in the tertiary air supply branch pipe is greater than 10m / s, the material distribution ratio increases with the increase of the tertiary air volume, and the material-to-air mass ratio is controlled to be less than 3.0.

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