Decomposing furnace gradient combustion and fuel gasification coupled ammonia-free self-denitration system and process

Abstract

The invention relates to a decomposing furnace gradient combustion and fuel gasification coupled ammonia-free self-denitration system and process, the system comprises a decomposing furnace, a tertiary air pipe, a gasification furnace and a cyclone separator, a tertiary air lower branch pipe is connected with the bottom of an ascending cylinder of the decomposing furnace or a cone of the decomposing furnace, and a tertiary air upper branch pipe is connected with a descending cylinder of the decomposing furnace; an air inlet of the gasification furnace is connected with the kiln tail smoke chamber, an air outlet of the gasification furnace is connected with an air inlet of the cyclone separator, and an air outlet of the cyclone separator is connected with the middle of the ascending cylinder of the decomposing furnace through a reducing gas pipe; the space, between the tertiary air lower branch pipe and the reducing gas air pipe, in the decomposing furnace is a main combustion area, the space, between the reducing gas air pipe and the tertiary air upper branch pipe, in the decomposing furnace is a reducing area, the space, between the tertiary air upper branch pipe and the outlet of the decomposing furnace, in the decomposing furnace is a burnout area, and a gradient combustion environment with the main combustion area, the reducing area and the burnout area combined is formed. According to the invention, the self-denitration efficiency is improved, and the combustion speed of the fuel of the decomposing furnace and the complete decomposition of the raw material are not reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of flue gas denitration in cement industry, and particularly relates to a kind of decomposition furnace gradient combustion and fuel gasification coupled ammonia-free self-denitration system and process. BACKGROUND

[0002] Nitrogen oxide is a gas produced when fossil fuels and air are burned at high temperatures, which has strong toxicity. Nitrogen oxide emissions affect air quality and have serious harm to human living environment and health. The cement industry is the third largest nitrogen oxide emitter after thermal power generation and automobile exhaust. NO x in cement kiln flue gas is mainly produced during fuel combustion in the rotary kiln and the decomposition furnace. The type of NO x in the cement rotary kiln is mainly thermal NO x , i.e. the NO x produced by the oxidation of N2 in the combustion air at high temperature. When the combustion process, the higher the flue gas temperature, the faster the generation rate of thermal NO x . The calcination temperature of cement clinker is generally as high as 1350-1450℃, and the concentration of NO x in the kiln flue gas is often high, generally 800-1500 ppm. The kiln flue gas after the rotary kiln passes through the kiln tail smoke chamber into the decomposition furnace, which is important to reduce the concentration of NO x in the kiln flue gas and improve the overall self-denitration efficiency.

[0003] The decomposition furnace realizes the functions of raw material decomposition and fuel combustion. The fuel in the decomposition furnace accounts for about 60% of the total fuel in the firing system, and the combustion temperature is generally 900-1100℃, and the generation of thermal NO x can be ignored, and fuel NO x is the main NO x generated by combustion in the decomposition furnace. Fuel NO x is mainly related to the N content in the fuel and the combustion atmosphere, and when the N content in the fuel is high, fuel NO x is often high. The commonly used fuel in the decomposition furnace is coal powder, and the fuel NO x produced by coal powder combustion includes two parts: NO x generated by N in the volatile matter and NO x generated by N remaining in the coke. During the combustion process, the volatile matter is released quickly, followed by the combustion of coke.

[0004] Fuel combustion self-denitration technology is a technology that uses control of fuel combustion characteristic parameters to inhibit NO xCombustion technology. With the improvement of environmental protection requirements, the operation cost of cement enterprises for denitrification is further increased. It is urgent for the cement industry to improve the self-denitrification efficiency of fuel combustion, reduce the operation cost of denitrification, and reduce secondary pollution. Through the reduction of intermediate products in the combustion process, NO x x is reduced, which is a source reduction environmental protection management method and is beneficial to the reduction of the overall operation cost of denitrification. Chinese Patent Publication No. CN111750671A discloses a decomposition furnace partition combustion self-denitrification system and process. Part of the fuel is combusted in the strong reduction zone with a peroxide coefficient less than 0.8 to produce CO, and the thermal NO x in the kiln flue gas is reduced. Under the condition of oxygen deficiency, the coke is difficult to ignite and burn. When sufficient oxygen is encountered in the burnout zone, the coke continues to burn, and the N in the coke will continue to generate NO x . The burnout zone has no reducing atmosphere, so that the concentration of NO x is raised again in the burnout zone, resulting in the gradual release of fuel NO x in the decomposition furnace and difficulty in deep removal. It cannot meet the NO x emission standard, and needs to be combined with SNCR and other end treatment methods to further reduce the concentration of NO x by spraying ammonia. However, ammonia escape caused by ammonia spraying will cause secondary pollution.

[0005] In summary, the existing technology has the following problems:

[0006] (1) The existing decomposition furnace fuel combustion self-denitrification technology can reduce most of the thermal NO x generated in the rotary kiln, but cannot reduce the fuel NO x generated by the combustion of fuel in the decomposition furnace.

[0007] (2) The fuel used in the decomposition furnace is coal powder. After pyrolysis of coal powder, volatile matter and coke are generated. Under the condition of oxygen deficiency, the coke is difficult to ignite and burn. The coke will continue to burn in the burnout zone, the N in the coke will continue to generate NO x , resulting in the gradual release of fuel NO x in the decomposition furnace and difficulty in deep removal.

[0008] (3) The existing decomposition furnace fuel combustion self-denitrification technology can reduce the NO x in the flue gas out of the decomposition furnace, but basically cannot meet the emission requirements, and still needs to be combined with SNCR or SCR and other end treatment methods to further reduce the concentration of NO x by spraying ammonia. However, ammonia escape caused by ammonia spraying will cause secondary pollution. SUMMARY

[0009] To address the problems existing in the prior art, this invention provides an ammonia-free self-denitrification system and process that couples gradient combustion and fuel gasification in a decomposition furnace. This invention utilizes a staged design for tertiary air, gasifier flue gas, fuel, and raw materials to create a gradient combustion environment within the decomposition furnace, combining a main combustion zone, a reduction zone, and a burnout zone with different peroxide coefficients. This allows for the early release of NO from the fuel in the decomposition furnace. x The gasifier and cyclone separator decouple the volatiles and coke in the fuel. The fuel is degassed in the gasifier to produce reducing gas and coke. The coke then enters the main combustion zone of the decomposition furnace for further combustion, releasing NO. x The reducing gas enters the decomposition furnace, which not only reduces the thermal NO in the flue gas exiting the rotary kiln, but also... x At the same time, it reduced the NO produced by fuel combustion in the decomposition furnace. x It achieves deep self-denitrification, eliminating NO without spraying ammonia water. x Emissions met standards, solving the problem of fuel-based NO x This technology addresses the problem of gradual release of nitrogen oxides in the decomposer, which makes deep denitrification difficult. It improves self-denitrification efficiency without reducing the combustion rate of fuel or the complete decomposition of raw materials. This is of great significance for the promotion and application of efficient and low-cost denitrification technology for cement kiln flue gas.

[0010] The present invention is implemented as follows: an ammonia-free self-denitrification system coupling gradient combustion and fuel gasification in a decomposition furnace includes a preheater, a rotary kiln, a kiln tail flue connected to the kiln tail, a decomposition furnace, a tertiary air duct, a gasifier, and a cyclone separator. A decomposition furnace fuel feeding point is set on the decomposition furnace, and the tertiary air duct includes a tertiary air lower branch pipe and a tertiary air upper branch pipe.

[0011] The decomposition furnace comprises a decomposition furnace cone, an ascending column, a gooseneck tube, and a descending column connected in sequence. The tertiary air downpipe is connected to the bottom of the ascending column or the decomposition furnace cone, and the tertiary air uppipe is connected to the descending column.

[0012] The gasifier inlet is connected to the kiln tail flue, the gasifier outlet is connected to the cyclone separator inlet, the gasifier outlet gas is reducing gas with a CO volume fraction greater than 10,000 ppm; the cyclone separator outlet is connected to the middle of the decomposition furnace's ascending column via a reducing gas duct, and the cyclone separator discharge port is connected to the bottom of the decomposition furnace's ascending column.

[0013] The space inside the decomposition furnace between the tertiary air lower branch pipe and the reducing gas duct is the main combustion zone, the space inside the decomposition furnace between the reducing gas duct and the tertiary air upper branch pipe is the reduction zone, and the space inside the decomposition furnace from the tertiary air upper branch pipe to the decomposition furnace outlet is the burnout zone. A gradient combustion environment combining the main combustion zone, reduction zone, and burnout zone is formed in the space of the decomposition furnace.

[0014] Preferably, the length of the reduction zone is greater than 5m, and the height of the burnout zone is greater than 5m, providing combustion space for the combustion of the reducing gas.

[0015] Preferably, the gasifier includes a gasifier fuel feeding point, a gasifier air inlet, a gasifier air outlet, and a gasifier slag discharge port. The gasifier fuel feeding point is located at the lower part of the gasifier, the gasifier air inlet and the gasifier slag discharge port are located at the bottom of the gasifier, and the gasifier slag discharge port is connected to the bottom of the ascending column of the decomposition furnace.

[0016] Preferably, the gasifier air inlet is connected to the kiln tail flue through the gasifier air inlet pipe, and a gasifier air inlet branch pipe is provided on the gasifier air inlet pipe. The air entering the gasifier air inlet branch pipe is low-temperature air or low-temperature flue gas with low oxygen content.

[0017] Preferably, a raw material feeding point for the decomposition furnace is provided in the main combustion zone. The raw material feeding point for the decomposition furnace includes an upper raw material feeding point and a lower raw material feeding point. The lower raw material feeding point is located on the decomposition furnace cone or at the bottom of the decomposition furnace ascending column, and is located above the air inlet of the tertiary air lower branch pipe. The upper raw material feeding point is located in the middle of the decomposition furnace ascending column, and is located below the air outlet of the gasifier outlet pipe.

[0018] Preferably, the fuel feeding point of the decomposition furnace is located below the raw material feeding point of the decomposition furnace. The fuel fed from the fuel feeding point of the decomposition furnace is completely burned in sufficient air, and all the nitrogen in the fuel is released to generate fuel-type NO. x .

[0019] Preferably, the tertiary air entering the decomposition furnace through the upper branch pipe flows tangentially along the cross-section of the decomposition furnace. After entering the decomposition furnace, the tertiary air evenly covers the cross-section of the decomposition furnace, which is conducive to the complete combustion of unburned reducing gas.

[0020] Preferably, both the lower and upper branches of the tertiary air supply are equipped with tertiary air valves.

[0021] Preferably, the preheater has 5 to 7 stages, with the last stage cyclone feed pipe of the preheater connected to the kiln tail flue; and the penultimate stage cyclone feed pipe connected to the raw material feeding point of the decomposition furnace.

[0022] This invention also provides an ammonia-free self-denitrification process coupling gradient combustion and fuel gasification in a decomposer furnace, as follows:

[0023] Fuel is fed into the decomposer fuel feed point, and the tertiary air distribution ratio is adjusted to control the oxygen coefficient in the main combustion zone to 1.0-1.1, meeting the oxygen demand for fuel combustion and ensuring that all nitrogen in the fuel is released to produce NO. x ;

[0024] Fuel is fed into the gasifier from the fuel feeding point. The air volume entering the gasifier is adjusted to control the oxygen coefficient inside the gasifier to be less than 0.5. Under oxygen-deficient conditions, the fuel undergoes pyrolysis and gasification, producing a large amount of reducing gas and coke. After gas-solid separation by a cyclone separator, the reducing gas enters the reduction zone of the decomposition furnace to reduce NO in the kiln flue gas. x NO produced by fuel combustion in the main combustion zone x The coke enters the main combustion zone and burns;

[0025] Adjusting the proportion of the tertiary air distribution controls the oxygen coefficient in the burnout zone to be greater than 1.0-1.2, ensuring that the reducing gases are completely burned.

[0026] Preferably, the air entering the gasifier is a mixture of flue gas from the kiln tail flue and low-temperature air or low-temperature flue gas with low oxygen content.

[0027] Preferably, the feeding ratio of raw materials in the decomposition furnace is adjusted to control the temperature in the main combustion zone at 850-1200℃ and the temperature in the reduction zone at 850-1100℃.

[0028] Preferably, the wind velocity at the bottom constriction of the decomposition furnace is greater than 20 m / s.

[0029] The present invention has the following advantages and beneficial effects:

[0030] 1. This invention utilizes the characteristics of the cement production line's calcination process to develop an ammonia-free self-denitrification system that couples gradient combustion in a decomposition furnace with fuel gasification. Through the staged design of tertiary air, gasifier flue gas, fuel, and raw materials, a gradient combustion environment combining a main combustion zone, a reduction zone, and a burnout zone with different peroxide coefficients is formed within the decomposition furnace. This allows for the early release of NO from the fuel in the decomposition furnace. x The reducing gas produced by fuel gasification in the gasifier enters the decomposition furnace, which not only reduces the thermal NO in the flue gas exiting the rotary kiln, but also... x At the same time, it reduced the NO produced by fuel combustion in the decomposition furnace. x It achieves deep self-denitrification, eliminating NO without spraying ammonia water. x Emissions met standards, solving the problem of fuel-based NO x This invention addresses the problem of gradual release of nitrogen oxides in the decomposition furnace, which makes deep removal difficult. It improves self-denitrification efficiency without reducing the combustion rate of fuel or the complete decomposition of raw materials. This invention has no adverse effects on the cement clinker production process and boasts advantages such as a rational system process, high reliability, and strong adaptability, thereby reducing environmental governance costs for enterprises.

[0031] 2. This invention decouples volatiles and coke in fuel by setting up a gasifier and a cyclone separator. The fuel is degassed in the gasifier with lean oxygen to obtain reducing gas and coke, which then enter the cyclone separator for gas-solid separation. The coke then enters the main combustion zone of the decomposition furnace for further combustion, releasing NO. xThe reducing gas enters the reduction zone of the decomposition furnace to reduce NO in the rotary kiln flue gas. x NO produced by fuel combustion in the decomposition furnace x This reduces NO production generated during fuel combustion in the aerobic environment of the burnout zone. x To avoid NO x The concentration rises again in the burnout zone, thus achieving the NO requirement without spraying ammonia. x Emission standards have solved the problem of reducing NO through ammonia injection. x The concentration of ammonia leads to escape and causes secondary pollution.

[0032] 3. In this invention, the upper branch pipe of the tertiary air of the decomposition furnace is connected to the lower column of the decomposition furnace, and the high-temperature tertiary air is introduced to the lower column of the decomposition furnace. The furnace capacity of the decomposition furnace can be increased according to the site space, ensuring that the space of the secondary reduction zone and the combustion zone is sufficient, and guaranteeing the denitrification effect and fuel combustion degree. Attached Figure Description

[0033] Figure 1 This is a system schematic diagram of Embodiment 1 of the present invention;

[0034] Figure 2 This is a schematic diagram of the connection between the branch pipe of the tertiary air duct and the decomposition furnace in this invention.

[0035] In the picture:

[0036] A - Cooling air; B - Flue gas exiting the preheater;

[0037] a-Raw material; b-Cooked material;

[0038] 1-Decomposition furnace, 101-Bottom narrowing of decomposition furnace, 102-Decomposition furnace cone, 103-Upward column of decomposition furnace, 104-Gooseneck tube, 105-Downward column of decomposition furnace;

[0039] 1a - Main combustion zone, 1b - Reduction zone, 1c - Burnout zone;

[0040] 2-Gasifier, 201-Gasifier fuel feeding point, 202-Gasifier ash discharge port;

[0041] 3-Tertiary air duct, 301-Tertiary air lower branch pipe, 302-Tertiary air upper branch pipe, 303-Tertiary air valve;

[0042] 401 - Lower feeding point of raw materials for the decomposition furnace; 402 - Upper feeding point of raw materials for the decomposition furnace.

[0043] 5 - Fuel feeding point for the decomposition furnace;

[0044] 6-Reducing gas duct; 601-Reducing gas valve;

[0045] 7-Preheater, 701-Final stage cyclone separator, 702-Pinus stage cyclone separator, 703-Electric material distribution valve, 704-First stage cyclone separator;

[0046] 8-Kiln tail flue chamber; 9-Rotary kiln; 10-Cooler; 11-Rotary kiln burner; 12-Slag discharge pipe; 1201-Unloading valve; 13-Gasifier inlet pipe; 1301-Gasifier inlet branch pipe; 14-Cyclone separator;

[0047] The dashed line with arrows indicates the airflow direction, and the solid line with arrows indicates the material flow direction. 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. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0049] Example 1

[0050] Please see Figure 1 The present invention provides an ammonia-free self-denitrification system that couples gradient combustion in a decomposition furnace with fuel gasification, including a preheater 7, a rotary kiln 9, a kiln tail smoke chamber 8 connected to the kiln tail of the rotary kiln, a decomposition furnace 1, a tertiary air duct 3, a gasifier 2, a cyclone separator 14, and a cooler 10; the decomposition furnace 1 and the tertiary air duct 3 are both lined with refractory materials.

[0051] The decomposition furnace 1 comprises a decomposition furnace cone 102, an ascending column 103, a gooseneck tube 104, and a descending column 105 connected in sequence. The ascending column 103 and the descending column 105 are connected via the gooseneck tube 104. The decomposition furnace 1 is equipped with a raw material feeding point and a fuel feeding point 5. The tertiary air duct 3 includes a tertiary air lower branch pipe 301 and a tertiary air upper branch pipe 302. The tertiary air lower branch pipe 302 is connected to the bottom of the ascending column 103 or the decomposition furnace cone 102, and the tertiary air upper branch pipe 302 is connected to the descending column 105.

[0052] The gasifier 2 includes a fuel feeding point 201, an air inlet, an air outlet, and a slag discharge port 202. The fuel feeding point 201 is located on the lower side of the gasifier. The air inlet and slag discharge port 202 are located at the bottom of the gasifier 2. The air inlet is connected to the kiln tail flue chamber 8, and the slag discharge port 202 is connected to the bottom of the ascending column 103 of the decomposition furnace. The air outlet is connected to the air inlet of the cyclone separator 14. The gasifier outlet gas is reducing gas with a CO volume fraction greater than 10,000 ppm. The discharge port of the cyclone separator 14 is connected to the bottom of the ascending column 103 of the decomposition furnace, and the air outlet of the cyclone separator 14 is connected to the middle of the ascending column 103 of the decomposition furnace through a reducing gas duct 6.

[0053] The high-temperature clinker discharged from rotary kiln 9 falls onto the grate of cooler 10. Under the action of cooling air A blown into the grate below cooler 10, the high-temperature clinker is cooled to a suitable temperature, and the resulting low-temperature clinker is transported to the clinker silo. After cooling the high-temperature clinker, cooling air A produces high-temperature secondary air and tertiary air. The secondary air enters rotary kiln 9, and the tertiary air enters decomposition furnace 1 through tertiary air duct 3.

[0054] The space within the decomposition furnace between the tertiary air lower branch pipe 301 and the reducing gas duct 6 is the main combustion zone 1a; the space between the reducing gas duct 6 and the tertiary air upper branch pipe 302 is the reduction zone 1b; and the space from the tertiary air upper branch pipe 302 to the decomposition furnace outlet is the burnout zone 1c. This creates a gradient combustion environment combining the main combustion zone, reduction zone, and burnout zone within the decomposition furnace space. In the main combustion zone 1a, the flue gas exiting the rotary kiln mixes with the tertiary air in the tertiary air lower branch pipe 301. A tertiary air valve 303 is installed on the tertiary air lower branch pipe 301 to adjust the tertiary air distribution volume and control the oxygen coefficient in the main combustion zone 1a to be 1.0-1.1. The commonly used fuel in the decomposition furnace 1 is pulverized coal. To ensure sufficient space for fuel combustion, the fuel feeding points 5 are located at the decomposition furnace cone 102 or the bottom constriction 101 of the decomposition furnace, and the number of fuel feeding points 5 is 1 to 4. Fuel is injected from fuel feed point 5 in the decomposition furnace to ensure the heat required for raw material decomposition. This fuel is completely burned in sufficient air, causing all the nitrogen in the fuel to be released prematurely to produce NO. x To prevent excessively high combustion temperatures in the main combustion zone of the decomposition furnace, which could lead to crust formation, raw material feeding points are set up within the main combustion zone. These points include an upper raw material feeding point 402 and a lower raw material feeding point 401. The lower raw material feeding point 401 is located on the decomposition furnace cone 102 or at the bottom of the ascending column 103, and above the air inlet of the tertiary air branch pipe 301. The upper raw material feeding point 402 is located in the middle of the ascending column 103 and below the air outlet of the gasifier outlet pipe 6. The fuel feeding point 5 is located below the lower raw material feeding point 401. The gas temperature in the main combustion zone 1a is controlled to be 850–1200°C by adjusting the distribution of raw material at the lower and upper raw material feeding points 401 and 402. The wind speed at the bottom constriction section 101 of the decomposition furnace is controlled to be greater than 20 m / s to prevent raw materials from short-circuiting through the bottom of the decomposition furnace into the kiln tail smoke chamber 8 and affecting the quality of cement clinker.

[0055] Within reduction zone 1b, the flue gas from the rotary kiln, the flue gas from the main combustion zone, and the flue gas from the cyclone separator are mixed. Gasifier 2 is an oxygen-deficient environment; fuel pyrolysis and gasification produce coke and large amounts of CO and C. x H yThe reducing gases produced, such as coke and reducing gases, have a CO volume fraction greater than 10,000 ppm at the gasifier outlet. The resulting coke and reducing gases enter cyclone separator 14. After gas-solid separation, the coke enters the main combustion zone 1a for further combustion and heating, releasing NO. x The reducing gas enters the decomposition furnace 1 through the reducing gas duct 6, forming a reduction zone. Under the catalytic action of the raw materials, gases such as CO reduce NO in the kiln flue gas. x NO released prematurely during fuel combustion within the main combustion zone 1a x To control the temperature in the reduction zone at 850-1100℃, the feed distribution at the feeding point 402 on the raw material in the decomposition furnace can be adjusted. By setting up the gasifier 2 and the cyclone separator 14 to decouple the volatile matter and coke in the fuel, the NO produced by the combustion of fuel in the aerobic environment of the burnout zone is reduced. x To avoid NO x The concentration rises again in the burnout zone, thus achieving the NO requirement without spraying ammonia. x Emission standards have solved the problem of reducing NO through ammonia injection. x The concentration of ammonia leads to escape and causes secondary pollution.

[0056] The burnout zone 1c is located within the downward column 105 of the decomposition furnace. This is to ensure the NO content in the reduction zone... x The removal effect is that there is an excess of reducing gases such as CO in the flue gas exiting the gasifier, requiring further combustion. A tertiary air valve 303 is installed on the tertiary air upper branch pipe 302 to regulate the tertiary air distribution volume. Within the combustion zone 1c, the tertiary air distribution ratio is adjusted to control the oxygen coefficient in the combustion zone to be greater than 1.0-1.2, ensuring complete combustion of the gas exiting the gasifier. The tertiary air upper branch pipe 302 of the decomposition furnace is connected to the decomposition furnace lower column 105, leading the high-temperature tertiary air to the decomposition furnace lower column 105. The furnace capacity of the decomposition furnace can be increased according to the site space to ensure sufficient space in the reduction zone 1b and the combustion zone 1c, guaranteeing the denitrification effect and fuel combustion degree.

[0057] In a preferred embodiment, the burnout zone height is greater than 5m to provide combustion space for the combustion of reducing gas; the length of the reduction zone is greater than 5m.

[0058] Furthermore, in an oxygen-deficient environment, the fuel fed into the gasifier will tend to convert nitrogen-containing compounds such as HCN into nitrogen (N2) during gasification, thus inhibiting the production of nitrogen (NO). x The gasifier ash discharge port 202 is connected to the ascending column 103 of the decomposition furnace through the ash discharge pipe 12. The ash discharge pipe 12 is equipped with a discharge valve 1201, and large pieces of difficult-to-burn substances in the fuel fall into the bottom of the gasifier and enter the main combustion zone of the decomposition furnace for continued combustion.

[0059] The reducing gas duct 6 is also equipped with a reducing gas valve 601 to regulate the air volume entering the decomposition furnace 1.

[0060] The gasifier inlet is connected to the kiln tail flue chamber 8 via the gasifier inlet pipe 13, and a gasifier inlet branch pipe 1301 is installed on the gasifier inlet pipe 13. The air entering the gasifier inlet branch pipe 1301 can be low-temperature air or low-temperature flue gas with low oxygen content. Because the flue gas temperature exiting the rotary kiln is relatively high, when the oxygen content in the flue gas is high, the fuel is easily combusted in the gasifier, which leads to a reduction in the amount of reducing gas. In order to reduce the temperature of the air entering the gasifier or reduce its oxygen content, low-temperature air or low-temperature flue gas with low oxygen content can be introduced to ensure that the fuel gasification produces sufficient reducing gas and guarantees denitrification efficiency.

[0061] The number of air inlets in the tertiary air upper branch pipe 302 entering the downward column 105 of the decomposer is 1 to 2. When there is 1 air inlet, the tertiary air enters in a tangential swirling flow along the cross-section of the decomposer; when there are 2 air inlets, the two air inlets are centrally symmetrical, such as... Figure 2 As shown, the tertiary air enters the decomposition furnace and evenly covers the cross-section of the furnace, which is conducive to the complete combustion of unburned reducing gases.

[0062] The preheater has 5 to 7 stages. The feed pipe of the last stage cyclone 701 is connected to the kiln tail flue chamber 8. The feed pipe of the penultimate stage cyclone 702 is connected to the feed point 402 and the feed point 401 of the raw material feeder in the decomposition furnace. The feed pipe of the penultimate stage cyclone 702 is equipped with an electric feed valve 703 to ensure stable and uniform material distribution.

[0063] In summary, this invention, through a staged design of tertiary air, gasification furnace flue gas, fuel, and raw materials, creates a gradient combustion environment within the decomposition furnace that combines a main combustion zone, a reduction zone, and a burnout zone with different oxygen permeability coefficients. This allows for the early release of NO from the fuel within the decomposition furnace. x The gasifier and cyclone separator decouple the volatiles and coke in the fuel. The fuel is degassed in the gasifier to produce reducing gas and coke. The coke then enters the main combustion zone of the decomposition furnace for further combustion, releasing NO. x The reducing gas enters the decomposition furnace, which not only reduces the thermal NO in the flue gas exiting the rotary kiln, but also... x At the same time, it reduced the NO produced by fuel combustion in the decomposition furnace. x It achieves deep self-denitrification, eliminating NO without spraying ammonia water. x Emissions met standards, solving the problem of fuel-based NO x This invention addresses the problem of gradual release and difficulty in deep denitrification in the decomposition furnace, improving self-denitrification efficiency without reducing the combustion rate of fuel or the complete decomposition of raw materials. Simultaneously, the gasifier can be used with alternative fuels, which are first gasified before entering the decomposition furnace for reduction and combustion, reducing the impact of poorly combustible alternative fuels on the decomposition furnace. This invention has no adverse effects on the cement clinker production process and boasts advantages such as a rational system process, high reliability, and strong adaptability, thereby reducing environmental governance costs for enterprises.

[0064] Example 2

[0065] The ammonia-free self-denitrification process using the above-mentioned system, which couples gradient combustion in the decomposer with fuel gasification, is as follows:

[0066] Raw meal a, after being crushed, pre-homogenized, ground, and homogenized, enters preheater 7 to complete preheating and gas-solid separation. Flue gas B exiting the preheater enters the flue gas treatment system. Material exiting the preheater enters decomposition furnace 1 for pre-decomposition, then enters rotary kiln 9 via kiln tail flue chamber 8. Fuel fed into the rotary kiln is sent to kiln head burner 11 to provide heat. The pre-decomposed raw meal undergoes rapid decomposition and a series of solid-phase reactions in rotary kiln 9 to generate cement clinker. The high-temperature clinker discharged from rotary kiln 9 falls onto the grate of cooler 10, spreading along the entire length of the grate to form a material bed of a certain thickness. Under the action of cooling air A blown into the grate below cooler 10, the high-temperature clinker is cooled to a suitable temperature, resulting in low-temperature clinker that is transported to the clinker silo. After cooling the high-temperature clinker, the high-temperature secondary air obtained by cooling air A enters rotary kiln 9; the tertiary air enters decomposition furnace 1 via tertiary air duct 3.

[0067] Within the decomposition furnace 1, a gradient combustion environment is formed by the graded design of tertiary air, gasification furnace flue gas, fuel, and raw materials, which combines the main combustion zone 1a, reduction zone 1b, and burnout zone 1c with different peroxide coefficients.

[0068] The space inside the decomposition furnace between the tertiary air branch pipe 301 and the reducing gas duct 6 is the main combustion zone 1a. Fuel is fed into the decomposition furnace from the fuel feeding point 5. The oxygen distribution ratio of the tertiary air is adjusted to control the oxygen permeability coefficient in the main combustion zone 1a to be 1.0-1.1, meeting the oxygen demand for fuel combustion and ensuring that all N in the fuel is released in advance to produce NO. x Adjusting the raw material ratio at the feeding point 401 of the decomposition furnace controls the temperature in the main combustion zone 1a to be between 850-1200℃.

[0069] The space inside the decomposition furnace between the reducing gas duct 6 and the tertiary air branch duct 302 is the reduction zone 1b. Fuel is fed into the gasifier 2, and the airflow into the furnace is adjusted to control the oxygen coefficient inside the furnace to be less than 0.5. Under oxygen-deficient conditions, the fuel undergoes pyrolysis and gasification, producing a large amount of reducing gas and coke. After gas-solid separation by the cyclone separator 14, the reducing gas enters the reduction zone 1b of the decomposition furnace, reducing NO in the rotary kiln flue gas. x NO produced by fuel combustion in the main combustion zone x The coke enters the main combustion zone 1a for combustion. The raw material ratio at the feeding point 402 of the raw material fed into the decomposition furnace is adjusted to control the temperature in the reduction zone at 850-1100℃.

[0070] The space inside the decomposition furnace between the tertiary air branch pipe 303 and the outlet of decomposition furnace 1 is the burnout zone 1c. Adjusting the tertiary air distribution ratio controls the oxygen coefficient of the burnout zone to be greater than 1.0-1.2, ensuring complete combustion of the gas exiting the gasifier.

[0071] Because the flue gas temperature at the rotary kiln exit is relatively high, when the oxygen content in the flue gas is high, the fuel is easily combusted in the gasifier, leading to a reduction in the amount of reducing gas. In order to reduce the temperature of the air entering the gasifier or reduce its oxygen content, the air entering the gasifier 2 can be a mixture of flue gas introduced from the kiln tail flue chamber 8 and low-temperature air or low-temperature flue gas with low oxygen content, so that the fuel gasification produces sufficient reducing gas and ensures denitrification efficiency.

[0072] Since the sintering temperature of cement clinker in a rotary kiln is generally 1350–1450℃, the NO content in the rotary kiln flue gas is high. x The concentration is often high, generally 800–1500 ppm; O2 content is low, generally below 5%; and CO2 content is high, between 15% and 25%. NO produced during fuel combustion in the main combustion zone... x Concentration approximately 100-500 ppm. CO content in the reduction zone is 1-3%. NO at the decomposition furnace outlet. x The content can be controlled to be no higher than 50 ppm or lower, which can be controlled by the type of fuel fed into gasifier 2. The O2 content at the decomposition furnace outlet is less than 3%, and the CO content is less than 1000 ppm.

[0073] Controlling the air velocity at the bottom constriction of the decomposition furnace to be greater than 20 m / s can suspend the raw materials inside the decomposition furnace and prevent material collapse caused by short circuits.

[0074] In summary, this invention, through a staged design of tertiary air, gasification furnace flue gas, fuel, and raw materials, creates a gradient combustion environment within the decomposition furnace that combines a main combustion zone, a reduction zone, and a burnout zone with different oxygen permeability coefficients. This allows for the early release of NO from the fuel within the decomposition furnace. x By setting up a gasifier and a cyclone separator, the volatile matter and coke in the fuel are decoupled. The fuel is degassed in the gasifier with lean oxygen to obtain reducing gas and coke, which then enter the cyclone separator for gas-solid separation. The coke enters the main combustion zone of the decomposition furnace for further combustion, releasing NO. x The reducing gas enters the reduction zone of the decomposition furnace to reduce NO in the rotary kiln flue gas. x NO produced by fuel combustion in the decomposition furnace x It achieves deep self-denitrification, eliminating NO without spraying ammonia water. x Emissions met standards, solving the problem of fuel-based NO x This invention addresses the problem of gradual release of nitrogen oxides in the decomposition furnace, which makes deep removal difficult. It improves self-denitrification efficiency without reducing the combustion rate of fuel or the complete decomposition of raw materials. This invention has no adverse effects on the cement clinker production process and boasts advantages such as a rational system process, high reliability, and strong adaptability, thereby reducing environmental governance costs for enterprises.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A denitrification system coupling gradient combustion and fuel gasification in a decomposer, comprising a preheater, a rotary kiln, a kiln tail flue connected to the kiln tail, a decomposer, a tertiary air duct, a gasifier, and a cyclone separator, wherein a fuel feeding point for the decomposer is provided on the decomposer, and the tertiary air duct includes a lower tertiary air branch pipe and an upper tertiary air branch pipe; characterized in that: The decomposition furnace includes a decomposition furnace cone, an upward column, a gooseneck tube, and a downward column connected in sequence. The tertiary air down branch pipe is connected to the bottom of the upward column of the decomposition furnace or the decomposition furnace cone, and the tertiary air up branch pipe is connected to the downward column of the decomposition furnace. The gasifier inlet is connected to the kiln tail flue, the gasifier outlet is connected to the cyclone separator inlet, the gasifier outlet gas is reducing gas with a CO volume fraction greater than 10,000 ppm; the cyclone separator outlet is connected to the middle of the decomposition furnace's ascending column via a reducing gas duct, and the cyclone separator discharge port is connected to the bottom of the decomposition furnace's ascending column. The space inside the decomposition furnace between the tertiary air lower branch pipe and the reducing gas duct is the main combustion zone, the space inside the decomposition furnace between the reducing gas duct and the tertiary air upper branch pipe is the reduction zone, and the space inside the decomposition furnace from the tertiary air upper branch pipe to the decomposition furnace outlet is the burnout zone. A gradient combustion environment combining the main combustion zone, reduction zone, and burnout zone is formed in the space of the decomposition furnace.

2. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1, characterized in that, The reduction zone has a length of more than 5m and a burnout zone height of more than 5m, providing combustion space for the combustion of reducing gas.

3. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1, characterized in that, The gasifier includes a fuel feeding point, an air inlet, an air outlet, and a slag discharge port. The fuel feeding point is located at the bottom of the gasifier, while the air inlet and slag discharge port are located at the bottom of the gasifier. The slag discharge port is connected to the bottom of the ascending column of the decomposition furnace.

4. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1 or 3, characterized in that, The gasifier air inlet is connected to the kiln tail flue through the gasifier air inlet pipe. A gasifier air inlet branch pipe is provided on the gasifier air inlet pipe. The air entering the gasifier air inlet branch pipe is low-temperature air or low-temperature flue gas with low oxygen content.

5. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1, characterized in that, The main combustion zone is equipped with a raw material feeding point for the decomposition furnace. The raw material feeding point for the decomposition furnace includes an upper raw material feeding point and a lower raw material feeding point. The lower raw material feeding point is located on the decomposition furnace cone or at the bottom of the decomposition furnace ascending column, and is located above the air inlet of the tertiary air lower branch pipe. The upper raw material feeding point is located in the middle of the decomposition furnace ascending column, and is located below the air outlet of the gasifier outlet pipe.

6. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 5, characterized in that, The fuel feeding point of the decomposition furnace is located below the raw material feeding point of the decomposition furnace. The fuel fed from the fuel feeding point of the decomposition furnace is completely burned in sufficient air, and all the nitrogen in the fuel is released to generate fuel-type NO. x .

7. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1, characterized in that, The tertiary air entering the decomposition furnace through the upper branch pipe flows tangentially along the cross-section of the decomposition furnace.

8. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1, characterized in that, Both the lower and upper branches of the tertiary air supply are equipped with tertiary air valves.

9. The ammonia-free self-denitrification system coupled with gradient combustion and fuel gasification in a decomposition furnace according to claim 1, characterized in that, The preheater has 5 to 7 stages. The feed pipe of the last stage cyclone in the preheater is connected to the kiln tail smoke chamber; the feed pipe of the second to last stage cyclone is connected to the raw material feeding point of the decomposition furnace.

10. A denitrification process without ammonia, coupled with gradient combustion and fuel gasification in a decomposition furnace, characterized in that, The self-denitrification system according to any one of claims 1 to 9 is used, and the process is as follows: Fuel is fed into the decomposer fuel feed point, and the tertiary air distribution ratio is adjusted to control the oxygen coefficient in the main combustion zone to 1.0-1.1, meeting the oxygen demand for fuel combustion and ensuring that all nitrogen in the fuel is released to produce NO. x ; Fuel is fed into the gasifier from the fuel feeding point. The air volume entering the gasifier is adjusted to control the oxygen coefficient inside the gasifier to be less than 0.

5. Under oxygen-deficient conditions, the fuel undergoes pyrolysis and gasification, producing a large amount of reducing gas and coke. After gas-solid separation by a cyclone separator, the reducing gas enters the reduction zone of the decomposition furnace to reduce NO in the kiln flue gas. x NO produced by fuel combustion in the main combustion zone x The coke enters the main combustion zone and burns; Adjusting the proportion of the tertiary air distribution controls the oxygen coefficient in the burnout zone to be greater than 1.0-1.2, ensuring that the reducing gases are completely burned.

11. The ammonia-free self-denitrification process coupled with gradient combustion and fuel gasification in a decomposer according to claim 10, characterized in that, The air entering the gasifier is a mixture of flue gas from the kiln tail flue and low-temperature air or low-temperature flue gas with low oxygen content.

12. The ammonia-free self-denitrification process coupled with gradient combustion and fuel gasification in a decomposer according to claim 10, characterized in that, Adjust the feeding ratio of raw materials in the decomposition furnace to control the temperature in the main combustion zone at 850-1200℃ and the temperature in the reduction zone at 850-1100℃.

13. The ammonia-free self-denitrification process coupled with gradient combustion and fuel gasification in a decomposer according to claim 10, characterized in that, The air velocity at the bottom constriction of the decomposition furnace is greater than 20 m / s.

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