Comprehensive system for carrying out waste heat recovery and denitration treatment on kiln tail waste flue gas of cement kiln

Abstract

The utility model discloses a comprehensive system for carrying out waste heat recovery and denitration treatment on kiln tail waste flue gas of a cement kiln. The comprehensive system comprises a bypass ventilation pretreatment system, wherein the bypass exhaust pretreatment system comprises a high-temperature waste heat exchanger, a flue gas cooling unit, a first dust removal unit, a second dust removal unit and an exhaust fan; the cooling unit consists of a quenching fan and a quenching chamber; the second dust removal unit is composed of a bag dust collector and a dust conveying mechanism; the bypass exhaust pretreatment system comprises a high-temperature waste heat exchanger, a flue gas cooling unit, a first dust removal unit, a second dust removal unit and an exhaust fan; the cooling unit consists of a quenching fan (202) and a quenching chamber; the second dust removal unit is composed of a bag dust collector and a dust conveying mechanism; according to the invention, the problems of efficient waste heat utilization and denitration treatment of two flue gases at the kiln tail are comprehensively solved.

Description

Technical Field

[0001] This utility model relates to the field of waste heat utilization and flue gas denitrification technology, and more specifically, to a comprehensive system for waste heat recovery and denitrification treatment of waste flue gas from cement kiln tail. Background Technology

[0002] Currently, the technology for utilizing waste heat from cement kiln flue gas is mature and has been widely applied in the construction of waste heat power generation projects. For the utilization of waste heat from cement kiln tail flue gas, this involves installing a waste heat boiler at the outlet of the primary preheater at the kiln tail to recover the waste heat from the flue gas and generate low-pressure steam for power generation. With increasingly stringent environmental protection requirements, some regions have begun to require denitrification treatment of cement kiln tail exhaust gas. Based on the temperature characteristics of the flue gas at the outlet of the primary preheater at the cement kiln tail, which is generally 260~320℃, SCR (Selective Catalytic Reduction) technology is used for denitrification. SCR denitrification technology uses a catalyst to catalytically reduce NOx in the flue gas to produce harmless N2 and H2O. Therefore, currently, a waste heat boiler and a denitrification tower are generally required at the cement kiln tail to meet the functions of waste heat utilization and flue gas denitrification, respectively.

[0003] Furthermore, with the research and development efforts of cement industry design and research institutions, and the active practice of cement plants, cement calcination technology has made significant progress. Cement kilns are becoming increasingly powerful, and their applicability to fuels and raw materials is also improving. Regarding fuels, some cement plants have begun to use high-sulfur coal. In terms of fuel substitution, the use of coal for calcination is reduced by co-firing textile waste, waste plastics, waste tires (rubber granules), carbon black, dried sludge, and biomass. Regarding the harmless treatment of solid waste, municipal solid waste, industrial solid waste, medical waste, waste incineration ash, organic polluted soil, and chemical waste are added to the raw material system to reduce the hazards and high costs associated with treating these substances through other methods. The advancements in cement calcination technology have made a significant contribution to improving the economic efficiency of cement plants and to environmental protection. However, after adding the aforementioned substances to the cement calcination system, under high-temperature conditions, they volatilize into gaseous harmful substances containing alkali, sulfur, and chlorine. These substances repeatedly circulate in the cement kiln and preheating system, gradually accumulating and ultimately affecting the quality of clinker and the safe operation of the preheater. Specifically, volatile components containing harmful substances such as alkali, sulfur, and chlorine rise into the preheater system along with the kiln gas. As the gas rises to the higher level of the preheater, when the temperature of the material and gas inside the preheater is lower than the melting points of alkali, sulfur, and chlorine, they condense on the surface of the raw meal particles. They then enter the lower level of the preheater with the raw meal and finally return to the kiln, where they volatilize again in the rotary kiln firing system or other high-temperature zones. These volatile components thus undergo multiple volatilization and condensation processes between the kiln and the preheater, causing a gradual accumulation and increase of harmful components in the raw meal within the preheater and kiln. If these substances are not removed, they will affect the quality of the clinker and cause scaling and blockage in the preheater system, affecting normal cement production. Currently, industry research institutions are focusing on bypass ventilation technology as a key research direction for solving these problems. Its basic principle is to add an exhaust port at a certain point at the kiln tail to forcibly extract the high-temperature, dusty, hot flue gas rich in inorganic salt compounds or their ionic forms, such as chlorine, potassium, sodium, and sulfur, from the kiln system, thereby reducing the atmosphere of these harmful substances in the firing and preheating systems. Practice has proven that bypass ventilation technology is an important measure to ensure normal cement production. Because the bypass ventilation flue gas temperature reaches 1000℃, it has waste heat utilization value. However, its high temperature, high dust, high alkali content, easy scaling, and excessive NOx levels necessitate addressing the safety and stability of waste heat utilization, as well as environmentally friendly treatment of harmful substances.

[0004] For the high-temperature and hazardous flue gas from the outlet of the primary preheater at the kiln tail of cement kilns, and the flue gas from the emerging bypass venting technology, the industry currently considers waste heat recovery and denitrification measures separately for these two gases, significantly increasing project investment. Therefore, the industry urgently needs a low-cost technical route and method for unified waste heat recovery and flue gas denitrification for both types of flue gas. Utility Model Content

[0005] In response to the above situation, this utility model provides a comprehensive system for waste heat recovery and denitrification treatment of waste gas from cement kiln tail. This system can comprehensively solve the problems of efficient waste heat utilization and denitrification treatment of the two types of flue gas from the kiln tail. Compared with building waste heat boilers and denitrification systems for the two types of flue gas separately, it can greatly reduce the total investment of the project.

[0006] Specifically, this utility model patent is achieved through the following technical solution:

[0007] A comprehensive system for waste heat recovery and denitrification treatment of waste gas from cement kiln tail, the comprehensive system comprising a kiln tail preheater system and a unified waste heat recovery and denitrification system for kiln tail gas; a bypass venting pretreatment system is provided between the kiln tail preheater system and the unified waste heat recovery and denitrification system for kiln tail gas; wherein:

[0008] The bypass venting pretreatment system includes a high-temperature waste heat exchanger, a flue gas cooling unit, a first dust removal unit, a second dust removal unit, and an exhaust fan; the cooling unit consists of a quench fan and a quench chamber; the second dust removal unit consists of a bag dust collector and an ash conveying mechanism.

[0009] The high-temperature waste heat exchanger converts the flue gas output from the kiln tail preheater system 100 at 900℃~1100℃ into flue gas at 450~550℃ and delivers it to the flue gas cooling unit.

[0010] The flue gas cooling unit cools the 500°C flue gas to 180°C~210°C using a quench fan and a quench chamber, and then delivers the flue gas to the cyclone separator.

[0011] The first dust removal unit removes large particles from the cooling flue gas through a cyclone separator to obtain the first dust removal flue gas; the kiln tail preheater system recovers large dust particles from the first dust removal flue gas.

[0012] The second dust removal unit removes harmful substances from the first dust removal flue gas using a bag dust collector to obtain the second dust removal flue gas; the ash conveying mechanism recovers harmful substances from the second dust removal flue gas.

[0013] The exhaust fan pressurizes and delivers the second dust removal flue gas to the high-temperature waste heat exchanger;

[0014] The high-temperature waste heat exchanger heats the second dust removal flue gas to 300~400℃ and sends it to the kiln tail flue gas unified waste heat recovery and denitrification system.

[0015] Furthermore, the kiln tail preheater system includes a staged preheater group consisting of a stage 1 preheater, a stage 2 preheater, a stage 3 preheater, a stage 4 preheater, and a stage 5 preheater, a decomposition furnace, a flue chamber, and a cement production equipment unit; wherein: the kiln tail preheater system provides two flue gas resources; one route passes through the stage 1 preheater of the staged preheater group to transport high-temperature flue gas to the unified waste heat recovery and denitrification system for kiln tail flue gas, and the other route passes through the flue chamber to transport bypass venting flue gas to the bypass venting pretreatment system.

[0016] Furthermore, the unified waste heat recovery and denitrification system for kiln tail flue gas includes a denitrification tower, a kiln tail waste heat boiler, a kiln tail high-temperature fan, an ash conveying unit, and connecting pipes and ash conveying pipes between the various devices. Specifically, the unified waste heat recovery and denitrification system for kiln tail flue gas connects the outlet flue gas of the first-stage preheater of the staged preheater group with the outlet flue gas of the second dust removal unit of the high-temperature waste heat exchanger, and performs flue gas merging. At this point, the pipeline is divided into two paths: one enters the gas inlet of the denitrification tower, and the other enters the inlet of the kiln tail high-temperature fan. The kiln tail waste heat boiler recovers the waste heat from the outlet flue gas of the denitrification tower, converting it into low-temperature flue gas of approximately 180-200°C, which is then pressurized by the kiln tail high-temperature fan and discharged into the subsequent process system at the kiln tail. The unified waste heat recovery and denitrification system for kiln tail flue gas generates low-pressure steam of 0.8-1.2 MPa from the waste heat of the flue gas and inputs it into power generation equipment.

[0017] Beneficial effects

[0018] 1. This utility model, by adding a high-temperature waste heat exchanger, maximizes the recovery of heat from the bypass flue gas, improves the waste heat recovery rate, and can generate economic benefits.

[0019] 2. In this utility model, the bypass flue gas is cooled to 500°C after heat exchange in the high-temperature waste heat exchanger. This temperature setting takes into account both the maximum recovery of waste heat and the fact that harmful substances in the flue gas are less likely to condense at this temperature, thus reducing the harm to downstream equipment.

[0020] 3. The quench chamber of this utility model rapidly reduces the temperature of the bypass flue gas from 500°C to 200°C, causing harmful substances in the flue gas to condense and mix with the flue gas dust, thus reducing the harm to downstream equipment.

[0021] 4. After the bypass venting flue gas of this utility model passes through the bypass venting pretreatment system, a large amount of harmful substances become solid and are mixed with dust. After secondary dust collection, the harmful dust is collected and removed, resulting in flue gas with low content of harmful substances and low dust concentration.

[0022] 5. By rationally setting up the bypass venting pretreatment system, the bypass venting flue gas is not discharged separately, but enters the subsequent kiln tail flue gas unified waste heat recovery and denitrification system, and finally returns to the kiln tail flue gas process in the cement process for unified discharge.

[0023] 6. This utility model achieves the purpose of recovering waste heat from two types of waste gas resources in the cement kiln tail system and uniformly treating them by setting up a denitrification tower and a waste heat boiler at the kiln tail. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a comprehensive system for waste heat recovery and denitrification treatment of waste flue gas from cement kiln tail.

[0025] Figure label:

[0026] 100. Kiln tail preheater system; 101. Stage preheater group; 102. Decomposition furnace; 103. Smoke chamber;

[0027] 200. Bypass venting pretreatment system; 201. High-temperature waste heat exchanger; 202. Quenching fan; 203. Quenching chamber; 204. Cyclone separator; 205. Bag dust collector; 206. Ash conveyor zipper; 207. Exhaust fan;

[0028] 300. Unified waste heat recovery and denitrification system for kiln tail flue gas; 301. Denitrification tower; 302. Waste heat boiler at kiln tail; 303. High-temperature fan at kiln tail; 304. Ash conveying system. Detailed Implementation

[0029] The following is in conjunction with the appendix Figure 1 The present invention will be further described below.

[0030] This utility model provides a comprehensive system for waste heat recovery and denitrification treatment of waste flue gas from cement kiln tail. The main objectives are: first, to remove harmful substances such as potassium, sulfur, and chlorine from the cement kiln tail preheater system to meet the safety requirements of cement production process and the requirements for producing high-quality cement; second, to further recover the waste heat of high-temperature flue gas to obtain greater economic benefits; and third, to minimize the total investment of the project.

[0031] like Figure 1 As shown, this utility model provides a comprehensive system for waste heat recovery and denitrification treatment of waste gas from the tail of a cement kiln. The comprehensive system includes a kiln tail preheater system 100 and a unified waste heat recovery and denitrification system for kiln tail flue gas 300. A bypass venting pretreatment system 200 is provided between the kiln tail preheater system 100 and the unified waste heat recovery and denitrification system for kiln tail flue gas 300.

[0032] The kiln tail preheater system 100 includes a staged preheater group 101, a decomposition furnace 102, a flue gas chamber 103, and a cement production equipment unit. The staged preheater group consists of a first-stage preheater, a second-stage preheater, a third-stage preheater, a fourth-stage preheater, and a fifth-stage preheater. The first-stage preheater is located at the highest point of the cement kiln tail preheater system, followed by the second-stage preheater, the third-stage preheater, the fourth-stage preheater, the fifth-stage preheater, the decomposition furnace 102, and the flue gas chamber 103. Currently, most cement kilns use a dual-series system from the first-stage preheater 101 to the fifth-stage preheater 102. The flue gas outlet of the first-stage preheater 101 is connected to the flue gas inlet of the unified waste heat recovery and denitrification system 300 at the kiln tail, and further, it is connected to the flue gas inlet of the denitrification tower 301. In addition, the flue gas outlet of the first-stage preheater 101 is also connected to the flue gas outlet of the bypass venting pretreatment system 200, and further connected to the clean flue gas outlet of the high-temperature waste heat exchanger 201 for merging, and together they enter the kiln tail flue gas unified waste heat recovery and denitrification system 300. An opening is made in the upper part of the smoke chamber 103 to lead out the bypass venting flue gas, which is connected to the bypass venting flue gas inlet of the high-temperature waste heat exchanger 201.

[0033] In this invention, after the bypass venting flue gas passes through the bypass venting pretreatment system 200, a large amount of harmful substances become solid, mixed with dust. After secondary dust collection, the harmful dust is collected and removed, resulting in flue gas with low harmful substance content and low dust concentration. The bypass venting pretreatment system, by adding a high-temperature waste heat exchanger, maximizes the recovery of heat from the bypass venting flue gas, improving the waste heat recovery rate. Simultaneously, through reasonable configuration of the equipment in the bypass venting pretreatment system 200, the bypass venting flue gas is not discharged separately, but instead enters the subsequent unified waste heat recovery and denitrification system 300 for kiln tail flue gas, and finally returns to the unified discharge process of the cement process kiln tail flue gas. Specific details are as follows:

[0034] The bypass venting pretreatment system 200 consists of a high-temperature waste heat exchanger 201, a quench fan 202, a quench chamber 203, a cyclone separator 204, a bag filter 205, an ash conveyor 206, an exhaust fan 207, and connecting flue gas ducts and ash conveying ducts between these devices. According to the bypass venting flue gas flow path, the bypass venting flue gas flows through the high-temperature waste heat exchanger 201, the quench chamber 203, the cyclone separator 204, the bag filter 205, the ash conveyor 206, and the exhaust fan 207, respectively. Flue gas connecting ducts and necessary flue gas valves are installed between these devices. Among them:

[0035] The high-temperature waste heat exchanger 201 recovers heat from the approximately 1000°C bypass exhaust gas drawn from the upper part of the flue gas chamber 103. Since this portion of the flue gas contains a high amount of harmful substances, to minimize damage to the high-temperature waste heat exchanger 201, the outlet flue gas temperature after heat exchange with the high-temperature heat exchanger 201 should not be too low; otherwise, the condensation of harmful substances in the flue gas will cause corrosion and other damage to the high-temperature heat exchanger. This invention sets the flue gas outlet temperature of the high-temperature waste heat exchanger 201 to 500°C. The heat recovered by the high-temperature heat exchanger is used to heat the clean flue gas at the outlet of the exhaust fan 207. This clean flue gas is heated from 200°C to 300-400°C and finally sent to the inlet flue gas pipe of the kiln tail flue gas unified waste heat recovery and denitrification system 300. That is: the clean flue gas inlet of the high-temperature waste heat exchanger 201 is connected to the outlet of the exhaust fan 207 through a flue gas pipeline, and the clean flue gas outlet of the high-temperature waste heat exchanger 201 is connected to the outlet flue gas of the first-stage preheater 101 through a flue gas pipeline and then enters the flue gas inlet of the denitrification tower 301.

[0036] The quench chamber 203 rapidly and in large quantities mixes the bypass vent gas from the outlet of the high-temperature heat exchanger 201 with cold air, causing this portion of harmful gas to be suddenly cooled to 200°C. At this point, the harmful substances in the flue gas become solid and mix with the dust in the flue gas. The quench fan 202 pressurizes outdoor air and blows it into the quench chamber 203. In addition, the cold air in the quench chamber 203 is provided by the quench fan 202. The inlet of the quench fan 202 is connected to the outside via a pipe, and the outlet of the quench fan 202 is connected to the quench chamber 203 via a pipe.

[0037] The cyclone separator 204 performs primary dust removal on the flue gas exiting the quench chamber 203, collecting large dust particles first. The collected dust naturally falls into the kiln tail 5-stage preheater, returning to the kiln tail preheater system. The ash collected by the cyclone separator 204 in this invention falls back to the 5-stage preheater via the ash discharge pipe. The ash collected by the bag dust collector 205 is then transported to the ash silo or ash tank for storage via the ash conveyor zipper 206 and, optionally, a pneumatic ash conveyor or elevator.

[0038] The baghouse dust collector 205 performs secondary dust collection on the flue gas exiting the cyclone separator 204, further purifying the flue gas. The purpose of this secondary dust collection is twofold: first, to reduce the dust content in the flue gas entering the high-temperature waste heat exchanger and the subsequent kiln tail flue gas unified waste heat recovery and denitrification system 300; and second, and more importantly, because this portion of fine dust is rich in harmful substances such as potassium, sulfur, and chlorine, it needs to be removed to prevent it from re-entering the kiln tail preheater system. This dust is discharged via the ash conveyor zipper 206 and then transported by subsequent gas conveying or elevator equipment to an ash silo or ash tank for temporary storage.

[0039] The exhaust fan 207 pressurizes and transports the low-dust-content flue gas from the bag dust collector outlet to the high-temperature waste heat exchanger 201. The flue gas from the outlet of the high-temperature waste heat exchanger 201 is then transported to the flue gas inlet pipe of the kiln tail flue gas unified waste heat recovery and denitrification system 300.

[0040] The kiln tail flue gas unified waste heat recovery and denitrification system 300 consists of a denitrification tower 301, a kiln tail waste heat boiler 302, a kiln tail high-temperature fan 303, an ash conveying unit 304, and connecting pipes and ash conveying pipes between the various devices. The flue gas outlet of the first-stage preheater 101 is connected to the clean flue gas outlet of the high-temperature waste heat exchanger 201 and the flue gas is merged, entering the kiln tail flue gas unified waste heat recovery and denitrification system 300 together. At this time, the pipeline is divided into two paths: one enters the flue gas inlet of the denitrification tower 301, and the other enters the inlet of the kiln tail high-temperature fan 303. The pipeline entering the inlet of the kiln tail high-temperature fan 303 is referred to in the art as the large bypass pipeline.

[0041] The flue gas outlet of the denitrification tower 301 is connected back to the main bypass pipeline. After this connection point, air is drawn from the main bypass pipeline and connected to the inlet of the kiln tail waste heat boiler 302. Before the main bypass pipeline enters the kiln tail high-temperature fan 303, the flue gas outlet of the kiln tail waste heat boiler 302 is connected to the main bypass pipeline.

[0042] A flue gas valve is installed on the main bypass pipeline between the inlet pipe outlet and the return point of the denitrification tower 301, and a flue gas valve is also installed on the main bypass pipeline between the inlet pipe outlet and the return point of the kiln tail waste heat boiler 302. During normal operation of the denitrification tower 301 and the kiln tail waste heat boiler 302, both of the aforementioned flue gas valves are in the closed state.

[0043] The above description is only a preferred embodiment of the utility model patent, but the utility model patent is not limited to the specific embodiments described above. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the utility model patent.

Claims

1. A comprehensive system for waste heat recovery and denitrification treatment of waste gas from cement kiln tail, characterized in that: The integrated system includes a kiln tail preheater system (100) and a unified waste heat recovery and denitrification system for kiln tail flue gas (300); a bypass venting pretreatment system (200) is provided between the kiln tail preheater system (100) and the unified waste heat recovery and denitrification system for kiln tail flue gas (300); wherein: The bypass exhaust pretreatment system (200) includes a high-temperature waste heat exchanger (201), a flue gas cooling unit, a first dust removal unit, a second dust removal unit, and an exhaust fan; the cooling unit consists of a quench fan (202) and a quench chamber; the second dust removal unit consists of a bag dust collector and an ash conveying mechanism. The high-temperature waste heat exchanger (201) converts the flue gas output from the kiln tail preheater system (100) at 900℃~1100℃ into flue gas at 450~550℃ and delivers it to the flue gas cooling unit. The flue gas cooling unit cools the 500°C flue gas to 180°C~210°C flue gas through the quench fan (202) and quench chamber (203) and then delivers it to the cyclone separator (204). The first dust removal unit removes large particles of cooling flue gas through a cyclone separator (204) to obtain the first dust removal flue gas; the kiln tail preheater system recovers large dust particles from the first dust removal flue gas. The second dust removal unit removes harmful substances from the first dust removal flue gas through a bag dust collector (205) to obtain the second dust removal flue gas; the ash conveying mechanism recovers the harmful substances from the second dust removal flue gas; The exhaust fan (207) pressurizes the second dust removal flue gas and delivers it to the high-temperature waste heat exchanger (201). The high-temperature waste heat exchanger heats the second dust removal flue gas to 300~400℃ and sends it to the kiln tail flue gas unified waste heat recovery and denitrification system (300).

2. The integrated system for waste heat recovery and denitrification treatment of waste gas from cement kiln tail as described in claim 1, characterized in that: The kiln tail preheater system (100) includes a staged preheater group (101) consisting of a first-stage preheater, a second-stage preheater, a third-stage preheater, a fourth-stage preheater, and a fifth-stage preheater, a decomposition furnace (102), a flue (103), and a cement production equipment unit; wherein: The kiln tail preheater system (100) provides two flue gas resources; one route delivers high-temperature flue gas to the kiln tail flue gas unified waste heat recovery and denitrification system (300) through the first stage preheater of the staged preheater group (101), and the other route delivers bypass exhaust flue gas to the bypass exhaust pretreatment system (200) through the smoke chamber (103).

3. The integrated system for waste heat recovery and denitrification treatment of waste gas from cement kiln tail as described in claim 1, characterized in that: The unified waste heat recovery and denitrification system (300) for kiln tail flue gas includes a denitrification tower (301), a kiln tail waste heat boiler (302), a kiln tail high-temperature fan (303), an ash conveying unit (304), and connecting pipes and ash conveying pipes between the various devices; wherein: The kiln tail flue gas unified waste heat recovery and denitrification system connects the flue gas outlet of the first stage preheater of the stage preheater group 101 with the second dust removal flue gas outlet of the high temperature waste heat exchanger (201) and performs flue gas merging. At this time, the pipeline is divided into two paths, one path enters the flue gas inlet of the denitrification tower (301), and the other path enters the inlet of the kiln tail high temperature fan (303). The waste heat boiler (302) at the kiln tail recovers the waste heat of the flue gas at the outlet of the denitrification tower and turns it into low-temperature flue gas at 180~200℃. Then, it is pressurized by the high-temperature blower (303) at the kiln tail and discharged into the subsequent process system at the kiln tail. The kiln tail flue gas unified waste heat recovery and denitrification system generates low-pressure steam of 0.8~1.2MPa from the waste heat of the flue gas and inputs it into the power generation equipment.

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