Hot air supply system and method for preparing white carbon black through rice hull gasification
By optimizing the hot air supply process of the rice husk gasification to precipitate black device, and utilizing multi-stage flue gas-to-flue gas heat exchange and mixed air treatment, the problems of complex device structure and high energy consumption were solved, thereby improving stability and safety and reducing energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU CTP POWER CO LTD
- Filing Date
- 2026-03-06
- Publication Date
- 2026-05-01
AI Technical Summary
Existing rice husk gasification equipment for producing precipitated silica suffers from problems such as complex structure, high energy consumption, and poor operational stability, especially low flue gas separation efficiency, large heat exchanger temperature difference, poor safety, and low ash production capacity.
The system employs a rice husk gasification device, a primary gas-to-gas heat exchanger, a bag filter dust collector, a secondary gas-to-gas heat exchanger, a waste heat boiler, a mixing air device, and an SCR denitrification device. Through multi-stage flue gas-to-flue gas heat exchange and mixing air treatment, the hot air supply process is optimized, the heat exchange end difference is reduced, and the dust removal efficiency and denitrification effect are improved.
It improved the operational stability and safety of the equipment, reduced energy consumption, simplified the process, increased the production capacity of rice husk ash, and achieved efficient hot air supply.
Smart Images
Figure CN121950337A_ABST
Abstract
Description
Hot air supply system and method for producing precipitated silica from rice husk gasification Technical Field
[0001] This invention relates to the field of silica preparation technology, and in particular to a hot air supply system and method for producing silica from rice husk gasification. Background Technology
[0002] Rice husk gasification is a process that uses high temperatures (typically 800-1200℃) and oxygen-deficient conditions to convert the organic components (such as cellulose, hemicellulose, and lignin) in rice husks into combustible gases (such as CO, H2, and CH4) through a thermochemical reaction, while retaining inorganic components (mainly silicon dioxide). This process effectively removes elements such as carbon and hydrogen, resulting in the enrichment of silicon dioxide. The ash produced after rice husk gasification contains 90%-95.5% silicon dioxide, which exists in an amorphous structure and exhibits high reactivity. This ash can be directly used as a raw material for silica, significantly improving the purity of the raw material.
[0003] In the process of preparing precipitated silica from ash residue, approximately 550°C hot air or clean hot flue gas is required. Referring to Figure 1, in the prior art, the waste heat generated during rice husk gasification is typically used to provide the aforementioned 550°C hot air for the precipitated silica preparation process. The structure of the rice husk gasification process device includes a rice husk gasification unit 1, a primary cyclone separator 2, a secondary cyclone separator 3, a combustion chamber 4, a multi-stage heat exchanger 10, a bag filter 8, an induced draft fan 9, and a chimney 7. The rice husks undergo a thermochemical reaction in the rice husk gasification unit 1, and the resulting flue gas is sequentially passed through the primary cyclone separator 2 and the secondary cyclone separator 3 for dust removal, and then enters the combustion chamber 4 for combustion. The combusted flue gas (approximately 850°C) enters the multi-stage heat exchanger 10 through a flue gas connecting pipe at the bottom of the combustion chamber 4, where it exchanges heat with the cold air (approximately 50-80°C) from the precipitated silica preparation process system in stages. After heat exchange, the cold air is heated to approximately 550°C and utilized by the silica preparation process system. After the flue gas cools (to approximately 180°C), it is purified by a bag filter 8, and then a portion is driven by an induced draft fan 8 to be discharged from the chimney 7, while the other portion is transported to the combustion chamber 4 via a recirculation fan 6. Combustion air for combustion in the combustion chamber 4 is provided by a combustion air fan 5. Specifically, a spiral ash cooler 11 is installed at the bottom of the secondary cyclone separator 3 to collect rice husk ash.
[0004] The device shown in Figure 1 and its hot air supply method can meet the current application requirements for hot air in the production of silica, but it has the following drawbacks: First, the separation efficiency of the flue gas after rice husk gasification through cyclone separation is low, and the dust content of the flue gas is still very high, which can easily lead to ash blockage in subsequent burners, affecting the stability and lifespan of the equipment. Second, due to the large temperature difference between the heat exchangers (approximately 850°C flue gas and 50°C cold air), multiple heat exchangers are required, as shown in Figure 1. At least six heat exchangers are required under this temperature difference, which not only increases costs but also reduces safety. Furthermore, to further purify the flue gas, an SCR denitrification device (not shown in the figure) is usually installed at a suitable location between the heat exchanger stages, which not only increases the complexity of heat exchanger design and installation but also negatively impacts the stability of the SCR catalyst. Third, the flue gas temperature after cooling is approximately 180°C, and direct discharge through the chimney is not energy-efficient. The installation of an induced draft fan and chimney also increases the complexity of the device structure. Finally, the vitrified ash obtained after the flue gas is filtered by a bag filter can only be discarded, resulting in very low ash production capacity.
[0005] In summary, the existing method of obtaining hot air by directly exchanging heat between cold air and flue gas from secondary combustion after gasification suffers from problems such as complex structure, high energy consumption, poor operational stability, and high cost. Most existing technologies for hot air supply in precipitated silica employ similar solutions and exhibit similar issues. Therefore, a new solution is urgently needed to improve the operational stability of the device while reducing energy consumption and costs. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a hot air supply system and method for producing precipitated silica from rice husk gasification, thereby solving the technical problems of complex device structure, high energy consumption, and poor operational stability in existing technologies.
[0007] The technical solution adopted in this invention is as follows: This invention provides a hot air supply system for producing precipitated silica from rice husk gasification, comprising a rice husk gasification device, a primary gas-to-gas heat exchanger, a bag filter dust collector, a secondary gas-to-gas heat exchanger, a waste heat boiler, a mixing device, and an SCR denitrification device connected in sequence; the rice husk gasification device is used to output dust-laden gas after rice husk gasification, which is initially cooled by the primary gas-to-gas heat exchanger and then cleaned by the bag filter dust collector; the clean gas is further cooled by the secondary gas-to-gas heat exchanger, combusted in the waste heat boiler to form high-temperature flue gas, and then cooled by the mixing device before passing through the SCR denitrification device to become clean flue gas; the clean flue gas, as the cold-side gas, is heated by heat exchange in the secondary gas-to-gas heat exchanger and the primary gas-to-gas heat exchanger to form target clean flue gas, which is used for precipitated silica production, and is directly discharged after waste heat utilization, without the need for a chimney and induced draft fan.
[0008] A preferred technical solution is that the outlet of the air mixing device is connected to the SCR denitrification device and the waste heat boiler respectively, so that part of the flue gas output by the air mixing device is subjected to SCR denitrification and the other part enters the waste heat boiler to regulate the combustion temperature.
[0009] The temperature of the dust-laden gas is 700-800℃, the temperature of the clean flue gas after denitrification is 400-480℃, and the temperature of the target clean flue gas after passing through a two-stage gas-to-gas heat exchanger and a one-stage gas-to-gas heat exchanger is 520-580℃.
[0010] The dust-laden gas reaches a temperature of 460-550℃ after passing through two stages of gas-to-gas heat exchange. The waste heat boiler is connected to a combustion blower to introduce ambient temperature air, causing the gas output from the secondary gas-to-gas heat exchanger to burn and generate high-temperature flue gas of 800-900℃.
[0011] After denitrification, the clean flue gas is heated by at least 30°C in the secondary gas-to-gas heat exchanger, and the dust-laden gas is cooled to 550-650°C in the primary gas-to-gas heat exchanger.
[0012] The air mixing device is connected to a mixing blower to introduce ambient temperature air, which is mixed with the high temperature flue gas output from the waste heat boiler to cool it down, thereby obtaining flue gas with a temperature of 410-490℃, suitable for SCR denitrification, so as to carry out efficient denitrification.
[0013] The temperature is 400-490℃, and the flue gas temperature suitable for SCR denitrification is 450℃; the temperature at which clean flue gas is formed after denitrification is 430℃.
[0014] The mixing blower also provides a portion of temperature-controlled air, which is used to mix with the target clean flue gas to form target clean flue gas at a preset temperature.
[0015] The ambient air temperature is 20°C.
[0016] The present invention also provides a method for a hot air supply system for producing precipitated silica from rice husk gasification, comprising: cooling the dust-laden gaseous fuel after rice husk gasification using a primary gas-to-gas heat exchanger; collecting rice husk ash through a filter bag to obtain clean gas; cooling the clean gas again using a secondary gas-to-gas heat exchanger; and then burning the clean gas in a waste heat boiler to obtain high-temperature flue gas. After the high-temperature flue gas is cooled by a mixing device, at least a portion of it undergoes denitrification through an SCR denitrification device, and then sequentially passes through a secondary gas-to-gas heat exchanger and a primary gas-to-gas heat exchanger for heat exchange, finally obtaining clean flue gas at the temperature required for precipitated silica production. The remaining heat is utilized and then directly discharged into the atmosphere, eliminating the need for a chimney and induced draft fan.
[0017] The technical solution of this invention can achieve at least some of the following beneficial effects: This invention cools, removes dust from, and combusts rice husk gasification gas to obtain high-temperature flue gas. After cooling and denitrifying the high-temperature flue gas, it forms low-temperature clean flue gas. The high-temperature flue gas is then exchanged with the low-temperature clean flue gas to obtain the target clean flue gas. The waste heat of this target clean flue gas is directly used for the preparation of silica. After the waste heat is utilized, the clean flue gas can be directly discharged. This invention directly utilizes the heat exchange between high-temperature flue gas and low-temperature clean flue gas to obtain the target clean flue gas, breaking through the traditional method of directly exchanging heat between clean air and rice husk gasification combustion flue gas to obtain hot air. This optimizes the hot air supply process, thereby improving operational stability and safety and reducing energy consumption. Specifically, this is reflected in the following aspects: This invention uses a two-stage gas-to-gas heat exchanger to achieve heat exchange between the high-temperature flue gas after combustion and the low-temperature clean flue gas after denitrification, that is, using a flue gas-to-flue gas heat exchange method to obtain the target clean flue gas. Firstly, the temperature of the high-temperature flue gas after combustion in the waste heat boiler is reduced by using a mixing device, thereby reducing the heat exchange difference (dust-laden gas at 700-800℃ and clean flue gas at around 430℃). Based on this reduced heat exchange difference, only two-stage gas-to-gas heat exchangers are needed to ensure that the flue gas entering the waste heat boiler meets certain temperature requirements. Compared with the traditional six-stage heat exchangers used for large heat exchange differences (flue gas after combustion at approximately 850℃ and cold air at 50-80℃), this greatly improves safety and reduces costs.
[0018] The mixing device of this invention serves two purposes: firstly, it reduces the heat exchange terminal temperature difference and provides a suitable temperature range for SCR denitrification, facilitating efficient denitrification of flue gas and obtaining clean flue gas, thus enabling direct discharge of the target clean flue gas after waste heat utilization. Secondly, the flue gas cooled by the mixing device can be used to adjust the combustion temperature in the waste heat boiler, promoting complete combustion and ensuring the complete decomposition of toxic and harmful substances in the fuel gas.
[0019] The purpose of this invention, which incorporates a baghouse dust collector between two stages of gas-to-gas heat exchangers, is to achieve efficient dust removal at a suitable temperature, obtaining clean fuel gas and rice husk ash. Compared to traditional cyclone separators, this significantly reduces the temperature requirements for the flue gas being separated, improves dust removal efficiency, prevents ash vitrification, and greatly enhances rice husk ash production capacity.
[0020] This invention makes full use of the heat generated by the flue gas inside the system, and the resulting flue gas can be directly discharged; and compared with the traditional steam boiler solution, it does not generate steam, which not only simplifies the process, but also reduces the system energy consumption.
[0021] Other features and advantages of the invention will be set forth in the following description or may be learned by practicing the invention. Attached Figure Description
[0022] Figure 1 is a schematic diagram of a system structure in the prior art that uses the waste heat generated during the gasification of rice husks to provide hot air for the preparation of silica.
[0023] Figure 2 is a schematic diagram of the system structure according to an embodiment of the present invention.
[0024] Explanation of reference numerals in the attached diagram: 1. Rice husk gasification device; 2. Primary cyclone separator; 3. Secondary cyclone separator; 4. Combustion chamber; 5. Combustion fan; 6. Recirculation fan; 7. Chimney; 8. Bag filter; 9. Exhaust fan; 10. Multi-stage heat exchanger; 11. Spiral ash cooler; 12. Primary gas-to-gas heat exchanger; 13. Bag filter; 14. Secondary gas-to-gas heat exchanger; 15. Waste heat boiler; 16. Mixing air device; 17. Mixing air blower; 18. Combustion blower; 19. Ash cooler; 20. SCR denitrification device. Detailed Implementation
[0025] The specific embodiments of the present invention are described below with reference to the accompanying drawings.
[0026] As shown in Figure 2, the hot air supply system for producing silica from rice husk gasification according to the present invention includes a rice husk gasification device 1, a primary gas-to-gas heat exchanger 12, a bag filter dust collector 13, a secondary gas-to-gas heat exchanger 14, a waste heat boiler 15, a mixing device 16, and an SCR denitrification device 20 connected in sequence. The rice husk gasification device 1 is used to output dust-laden gas after rice husk gasification. The gas is initially cooled by the primary gas-to-gas heat exchanger 12 and then cleaned by the bag filter dust collector 13. The clean gas is cooled a second time by the secondary gas-to-gas heat exchanger 14 and then burned in the waste heat boiler 15 to form high-temperature flue gas. After being cooled by the mixing device 16, it becomes clean flue gas after passing through the SCR denitrification device 20. The clean flue gas, as the cold-side gas, is heated by heat exchange in the secondary gas-to-gas heat exchanger 14 and the primary gas-to-gas heat exchanger 12 in sequence to form the target clean flue gas. The target clean flue gas is used for silica production. After the waste heat is utilized, it is directly discharged without the need for a chimney and an induced draft fan.
[0027] As a preferred embodiment, the temperature of the dust-laden gas is 700-800℃, preferably 750℃, the temperature of the clean flue gas after denitrification is 400-480℃, preferably 430℃, and the temperature of the target clean flue gas obtained after passing through a two-stage gas-to-gas heat exchanger and a one-stage gas-to-gas heat exchanger is 520-580℃.
[0028] As a preferred embodiment, the temperature of the dust-laden gas with a temperature of 700-800℃ is 550-650℃ after heat exchange in the primary gas-to-gas heat exchanger 12, preferably 590℃; after heat exchange in the secondary gas-to-gas heat exchanger 14, the temperature is 460-550℃, preferably 510℃; the waste heat boiler 15 is connected to a combustion blower 18 to introduce ambient temperature air, so that the gas output from the secondary gas-to-gas heat exchanger 14 is combusted to generate high-temperature flue gas of 800-900℃.
[0029] As a preferred method, part of the flue gas output from the mixing device 16 enters the SCR denitrification device 20 for denitrification, and the other part is input into the waste heat boiler 15 to adjust the temperature of the high-temperature flue gas after combustion, so that the temperature of the high-temperature flue gas is preferably 850°C.
[0030] As a preferred embodiment, the air mixing device 16 is connected to the air mixing blower 17 to introduce ambient temperature air, which is mixed with the high-temperature flue gas output from the waste heat boiler 15 for cooling, resulting in flue gas with a temperature of 410-490℃, suitable for SCR denitrification, for efficient denitrification. The inlet flue gas temperature of the SCR denitrification device 20 is preferably 440℃. Preferably, after denitrification, the clean flue gas is heated by at least 40℃ in the secondary gas-to-gas heat exchanger 14, meaning the heated flue gas at least 470℃ exchanges heat with dust-laden fuel gas at 700-800℃ in the primary gas-to-gas heat exchanger 12, ultimately obtaining the target clean flue gas at 520-580℃.
[0031] As a preferred embodiment, the mixing blower 17 also provides a portion of temperature-controlled air, which is used to mix with the target clean flue gas to form target clean flue gas at a set temperature, preferably set at 550°C.
[0032] The ambient temperature air is preferably 20°C.
[0033] Specifically, the filter bag dust collector 13 preferably adopts a ceramic filter bag dust collection device, and its bottom is equipped with a cold ash collector 19 to collect rice husk ash.
[0034] Specifically, both stages of the gas-to-gas heat exchanger adopt shell-and-tube heat exchangers, which are preferably made of 316L stainless steel to achieve high temperature and corrosion resistance.
[0035] The present invention involves cooling, dust removal, and combustion of rice husk gasification gas to obtain high-temperature flue gas. This high-temperature flue gas is then cooled and denitrified to form low-temperature clean flue gas. Heat exchange between the high-temperature flue gas and the low-temperature clean flue gas yields the target clean flue gas. The waste heat of this target clean flue gas is directly utilized for the production of silica. After the waste heat is utilized, the clean flue gas can be directly discharged. This invention directly utilizes heat exchange between high-temperature and low-temperature clean flue gas to obtain the target clean flue gas, breaking through the traditional method of directly exchanging heat between clean air and rice husk gasification combustion flue gas to obtain hot air. This optimizes the hot air supply process, thereby improving operational stability and safety, and reducing energy consumption.
[0036] This invention utilizes a two-stage gas-to-gas heat exchanger to achieve heat exchange between the high-temperature flue gas after combustion and the low-temperature clean flue gas after denitrification, i.e., using a flue gas-to-flue gas heat exchange method to obtain the target clean flue gas. First, a mixing device is used to reduce the temperature of the high-temperature flue gas after combustion in the waste heat boiler, thereby reducing the heat exchange difference (dust-laden gas at 700-800℃ and clean flue gas at around 430℃). Based on this reduced heat exchange difference, only two stages of gas-to-gas heat exchangers are needed, ensuring that the flue gas finally entering the waste heat boiler meets certain temperature requirements. Compared with the traditional six-stage heat exchanger scheme that is used for large heat exchange differences (flue gas after combustion at approximately 850℃ and cold air at 50-80℃), this invention greatly improves safety and reduces costs.
[0037] The air mixing device serves two purposes: firstly, it reduces the heat exchange temperature difference and provides a suitable temperature range for SCR denitrification, facilitating efficient denitrification of the flue gas and obtaining clean flue gas. This allows for direct discharge of the clean flue gas after waste heat utilization. Secondly, the flue gas cooled by the air mixing device can be used to adjust the combustion temperature in the waste heat boiler, promoting complete combustion and ensuring the complete decomposition of toxic and harmful substances in the fuel gas.
[0038] The purpose of this invention, which incorporates a baghouse dust collector between two stages of gas-to-gas heat exchangers, is to achieve efficient dust removal at a suitable temperature, obtaining clean fuel gas and rice husk ash. Compared to traditional cyclone separators, this significantly reduces the temperature requirements for the flue gas being separated, improves dust removal efficiency, prevents ash vitrification, and greatly enhances rice husk ash production capacity.
[0039] Example 2: A hot air supply method for a hot air supply system for producing precipitated silica from rice husk gasification according to Example 1, comprising: cooling the dust-laden gaseous material after rice husk gasification using a primary gas-to-gas heat exchanger 12; collecting rice husk ash through a filter bag to obtain clean gas; cooling the clean gas again using a secondary gas-to-gas heat exchanger 14; then burning the clean gas in a waste heat boiler 15 to obtain high-temperature flue gas; cooling the high-temperature flue gas through a mixing device 16, at least a portion of which is denitrified by an SCR denitrification device 20; then passing through a secondary gas-to-gas heat exchanger 14 and a primary gas-to-gas heat exchanger 12 in sequence for heat exchange, finally obtaining clean flue gas at the temperature required for precipitated silica production; and directly venting the waste heat after it is utilized, without the need for a chimney or induced draft fan.
[0040] The method in this embodiment breaks through the traditional hot air process. After two gas-to-gas heat exchanges, flue gas-to-flue gas heat exchange is carried out to obtain hot flue gas at the temperature required for the preparation of precipitated silica. The waste heat of the hot flue gas can be directly discharged after being utilized.
[0041] In summary, this invention makes full use of the heat generated in the flue gas inside the system, and the resulting flue gas can be directly discharged, which not only simplifies the process but also reduces the system's energy consumption.
[0042] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A hot air supply system for producing precipitated silica from rice husk gasification, characterized in that, The system includes a rice husk gasification device (1), a primary gas-to-gas heat exchanger (12), a bag filter dust collector (13), a secondary gas-to-gas heat exchanger (14), a waste heat boiler (15), a mixing device (16), and an SCR denitrification device (20), connected in sequence. The rice husk gasification device (1) is used to output dust-laden gas after rice husk gasification. The gas is initially cooled by the primary gas-to-gas heat exchanger (12) and then cleaned by the bag filter dust collector (13). The clean gas is then passed through the secondary gas-to-gas heat exchanger (14) to obtain clean gas. 14) Secondary cooling: High-temperature flue gas is formed by combustion in the waste heat boiler (15), and then cooled by the air mixing device (16). After passing through the SCR denitrification device (20), it becomes clean flue gas. The clean flue gas is used as cold side gas. After passing through the secondary gas-to-gas heat exchanger (14) and the primary gas-to-gas heat exchanger (12) in sequence, it is heated to form target clean flue gas. The target clean flue gas is used for the preparation of white carbon black. After the waste heat is used up, it is directly discharged without the need for a chimney and induced draft fan.
2. The hot air supply system for producing silica from rice husk gasification according to claim 1, characterized in that, The outlet of the air mixing device (16) is connected to the SCR denitrification device (20) and the waste heat boiler (15) respectively, so that part of the flue gas output by the air mixing device (16) is denitrified by SCR and the other part enters the waste heat boiler (15) to regulate the combustion temperature.
3. The hot air supply system for producing silica from rice husk gasification according to claim 1, characterized in that, The temperature of the dust-containing gas is 700-800℃, the temperature of the clean flue gas after denitrification is 400-480℃, and the temperature of the target clean flue gas after passing through the secondary gas-to-gas heat exchanger (14) and the primary gas-to-gas heat exchanger (12) is 520-580℃.
4. The hot air supply system for producing silica from rice husk gasification according to claim 3, characterized in that, The dust-laden gas has a temperature of 460-550℃ after passing through two-stage gas-to-gas heat exchange. The waste heat boiler (15) is connected to a combustion blower (18) to introduce ambient temperature air, so that the gas output from the secondary gas-to-gas heat exchanger (14) is burned to generate high-temperature flue gas of 800-900℃.
5. The hot air supply system for producing precipitated silica from rice husk gasification according to claim 4, characterized in that, After denitrification, the clean flue gas is heated by the secondary gas-to-gas heat exchanger (14) and its temperature rises by at least 30°C. The dust-laden gas is heated by the primary gas-to-gas heat exchanger (12) and its temperature drops to 550-650°C.
6. The hot air supply system for producing silica from rice husk gasification according to claim 1, characterized in that, The mixing device (16) is connected to the mixing blower (17) to introduce ambient temperature air, which is mixed with the high temperature flue gas output from the waste heat boiler (15) to cool it down, so as to obtain flue gas with a temperature of 410-490℃, which is suitable for SCR denitrification, so as to carry out efficient denitrification.
7. The hot air supply system for producing silica from rice husk gasification according to claim 6, characterized in that, The temperature is 400-490℃, and the flue gas temperature suitable for SCR denitrification is 450℃; the temperature at which clean flue gas is formed after denitrification is 430℃.
8. The hot air supply system for producing silica from rice husk gasification according to claim 6, characterized in that, The mixing blower (17) also provides a portion of temperature-controlled air, which is used to mix with the target clean flue gas to form target clean flue gas at a preset temperature.
9. The hot air supply system for producing silica from rice husk gasification according to claim 6, characterized in that, The ambient air temperature is 20°C.
10. A method for a hot air supply system for producing silica from rice husk gasification according to any one of claims 1 to 9, characterized in that, include: The dust-laden gas after rice husk gasification is cooled once by a primary gas-to-gas heat exchanger (12). The rice husk ash is collected by a filter bag and clean gas is obtained. The clean gas is cooled again by a secondary gas-to-gas heat exchanger (14) and then burned in a waste heat boiler (15) to obtain high-temperature flue gas. The high-temperature flue gas is cooled by a mixing device (16) and at least part of it is denitrified by an SCR denitrification device (20). Then it passes through a secondary gas-to-gas heat exchanger (14) and a primary gas-to-gas heat exchanger (12) in sequence to exchange heat, and finally obtains clean flue gas at the temperature required for the preparation of precipitated silica. The residual heat is utilized and then directly discharged into the air without the need for a chimney and induced draft fan.