Roasting machine low-heating-value combustion system based on sectional heat supply

Abstract

The utility model discloses a roasting machine low-heat-value combustion system based on segmented heat supply. The roasting machine low-heat-value combustion system comprises roasting machine equipment, a combustion system, a high-temperature air pipe, a medium-high-temperature air pipe, a medium-temperature air pipe, an air inlet pipeline and an air exhaust pipeline. Hot air of a first cooling section, a second cooling section and a third cooling section is introduced into a preheating area and a burnt area; and finally, a temperature gradient is formed in the preheating section and the roasting section. And under the same condition, the low-calorific-value fuel with the calorific value of 7500kJ / m < 3 > can also meet the pellet quality requirement, the production cost is reduced, and the application of the low-calorific-value fuel is realized. The partition wall is used for preventing space on the two sides of the partition wall from air channeling, and the problem that air distribution is affected by pressure fluctuation in the prior art is avoided. And a self-circulation branch is further arranged, the oxygen content of the roasting rear section is reduced, therefore, emission of nitric oxide is reduced, and the phenomenon that the high-temperature pellets are extremely cold and burst is avoided.

Description

Technical Field

[0001] The utility model relates to the field of iron and steel metallurgy, in particular to a low calorific value combustion system of a roasting machine based on segmented heating. Background Art

[0002] With the implementation of green and low-carbon smelting technology in blast furnaces, it has become an inevitable trend to increase the proportion of pellets entering the furnace, develop high-quality pellets, especially flux pellets and magnesium-containing pellets, and improve the quality of ironmaking, which is in line with the strategic needs of my country's green development of steel. Belt roasting pellets, as a mainstream process, have absolute advantages in low carbon, energy conservation and emission reduction. The belt machine completes the drying, preheating, roasting and cooling processes on one device and is arranged in a closed plant. Due to the short process, less heat dissipation, good heat recovery, small footprint, high thermal efficiency and low overall energy consumption. The product is in a relatively static state from fabrication to finished product. The strength requirements for preheated balls are low, and there will be no problems such as ringing. There is less debris and dust generated. The refractory materials of the roasting machine are stationary throughout the process and do not contact the pellets. The process avoids rapid cooling and heating, and the refractory materials have a long life, less maintenance and high operating rate.

[0003] The existing belt roasting machine pellet production process is limited by fuel conditions and must use high calorific value gas fuels such as natural gas and coke oven gas as heat sources. Low calorific value fuels have low calorific value, insufficient heat supply, and the combustion temperature cannot meet the roasting temperature requirements. The belt roasting process cannot be used in factories that lack coke oven gas or natural gas. This major defect directly affects the promotion of the belt roasting pellet technology.

[0004] The prior art discloses a device for producing pellets using low calorific value fuel. Low calorific value coal gas is first burned to generate high temperature and low oxygen hot flue gas, which is then transported and introduced into the hood of the preheating section, roasting section and soaking section of the belt roaster through the hot flue gas pipeline, and mixed with the recycled tail gas in the drying and preheating sections and the cooling section of the belt roaster. According to the temperature requirements of different sections, it is used for drying and preheating of the pellets in the belt roaster process. In the high temperature roasting section, high temperature and low oxygen hot flue gas is coupled with a staged combustion process, and burned in a high temperature and low oxygen atmosphere to form a high temperature roasting environment with uniform temperature distribution, so as to increase the roasting temperature of the pellets and supply high temperature heat. The number and arrangement of high temperature and low oxygen burners are set according to the temperature and thermal control requirements to meet the roasting temperature requirements of the high temperature section. However, it has the following shortcomings: This method requires the addition of a set of external combustion furnaces, and the flue gas generated by the combustion furnace is used to heat the hot air from a cold section, so that its temperature is increased and then burned with the low calorific value gas. Since the air volume in the first cooling section is large, the required flue gas volume of the combustion furnace will also increase, which not only increases the process energy consumption, but also fails to utilize the heat carried by the flue gas itself, increasing heat loss.

[0005] The prior art discloses another belt roasting machine with graded cooling and stepwise utilization of hot air, including: cooling stage one, cooling stage two and cooling stage three, the hot air temperatures generated by cooling stage one, cooling stage two and cooling stage three are not less than 1100°C, 600-800°C and not more than 300°C respectively, and the generated hot air is respectively transported to the roasting stage, preheating stage and blast drying stage through pipelines, by grading the cooling stage and providing hot air of different temperatures to the roasting stage, preheating stage and blast drying stage respectively, the stepwise utilization of heat is realized, the energy utilization rate is improved, the energy consumption of the process is reduced, and low calorific value fuel can be used. However, it has the following shortcomings: this method simply separates the cooling stage and transports it to different process stages. The second and third cooling stages share a cooling fan. The preheating and roasting stages are connected, which causes pressure fluctuations and affects air volume distribution. The cold air in the first cooling stage directly contacts the high-temperature pellets, causing rapid cooling of the pellets and generating stress, which leads to cracks in the pellets. The roasting stage belongs to the high-temperature area, and a large amount of nitrogen oxides are generated during the combustion process. In actual production, similar factory measured values ​​are all around 450mg / Nm 3 above. Utility Model Content

[0006] In view of the above-mentioned defects in the prior art, a low calorific value combustion system for a roaster based on segmented heating is provided to improve the effect of roasting materials using low calorific value fuels, avoid cracks in pellets, and generate a large amount of nitrogen oxides.

[0007] The technical solution adopted by the utility model to solve the above technical problems is:

[0008] The low calorific value combustion system of a roaster based on segmented heating is characterized by:

[0009] The roasting machine equipment includes, from left to right, a blast drying section, an exhaust drying section, a preheating section, a roasting section, a soaking section, a first cooling section, a second cooling section, and a third cooling section. The material is input from the blast drying section and output from the third cooling section. Partition walls are provided between the blast drying section and the exhaust drying section, between the exhaust drying section and the preheating section, between the preheating section and the roasting section, between the roasting section and the soaking section, and between the second cooling section and the third cooling section.

[0010] Combustion system, the combustion system includes gas pipeline and burner. The gas pipeline is divided into several branches, which are distributed in the preheating section and roasting section. The burner is installed on the outer wall of the combustion chamber on both sides of the roasting machine.

[0011] High-temperature air duct, medium-high-temperature air duct, and medium-temperature air duct. The roasting section is divided into the roasting front section and the roasting rear section, and the secondary cooling section is divided into the secondary cooling front section and the secondary cooling rear section. The high-temperature air duct is connected between the roasting rear section and the top of the primary cooling section, the medium-high-temperature air duct is connected between the roasting front section and the top of the secondary cooling front section, and the medium-temperature air duct is connected between the preheating section and the top of the secondary cooling rear section.

[0012] The air inlet duct and the exhaust duct are connected with the bottom of the second cooling section and the third cooling section, the first cooling section and the third cooling section form a passage, and the exhaust duct is connected with the bottom of the preheating section and the roasting section.

[0013] According to the above technical scheme, it also includes a blast drying branch, which is composed of a fan and a pipeline. The blast drying branch is connected between the third cooling section and the bottom of the blast drying section, and the top of the blast drying section is connected to the entrance of the first cooling section by a pipeline, and a fan is provided at the entrance of the pipeline to the first cooling section.

[0014] According to the above technical scheme, the combustion system also includes a primary combustion-supporting branch and an oxygen-enriched interface; the burner is connected between the roasting section and the gas pipeline, and between the preheating section and the gas pipeline, the primary combustion-supporting branch is connected between the burner and the three cooling sections, and the primary combustion-supporting branch is composed of a fan and a pipeline; the oxygen-enriched interface is connected to the primary combustion-supporting branch, the end of the primary combustion-supporting branch connected to the burner is divided into multiple branches, the gas pipeline is divided into multiple branches, and the ends of the gas pipeline and the primary combustion-supporting branch are mixed one by one and connected to the corresponding burner.

[0015] According to the above technical solution, the air of the third cooling section transported by the primary combustion-supporting branch accounts for 10% to 15% of the air required for combustion; the oxygen enrichment rate of the primary combustion-supporting branch is controlled at 3%.

[0016] According to the above technical scheme, it also includes a self-circulation branch arranged between the equalizing section and a cold section. The self-circulation branch includes a connecting pipe connected between the equalizing section and the bottom of the cold section, a self-circulation fan arranged on the connecting pipe, and a high-temperature air duct branch section connected between the high-temperature air duct and the equalizing section. The top of the blast drying section is connected to the connecting pipe by a pipe.

[0017] According to the above technical solution, a cooling air outlet is also provided at the air inlet of the self-circulating fan.

[0018] According to the above technical scheme, it also includes an exhaust drying branch, which is composed of a pipeline and a fan. The exhaust drying branch is connected between the bottom of the rear roasting section and the top of the exhaust drying section, and the bottom of the exhaust drying section is connected to the exhaust duct.

[0019] According to the above technical solution, a branch pipe is provided on the exhaust drying branch, and the branch pipe is connected to the medium-temperature air duct at the front end of the top of the preheating section.

[0020] According to the above technical solution, the exhaust duct is connected to the exhaust drying section, the preheating section, and the bottom of the roasting section at the same time. A main exhaust fan is installed in the exhaust duct, and the exhaust duct is connected to the external purification equipment and chimney in turn.

[0021] The utility model has the following beneficial effects:

[0022] 1. Make full use of the heat of the flue gas by introducing the hot air from the first, second and third cooling sections into the preheating zone and the burning zone; finally, a temperature gradient is formed in the preheating section and the roasting section. The hot air at different temperatures is burned in stages to increase the combustion temperature of the high temperature section, thereby increasing the furnace temperature. Under the same conditions, the calorific value is 7500kJ / m 3 The low calorific value fuel can also meet the quality requirements of pellets, reduce production costs, and realize the application of low calorific value fuel. In addition, partition walls are provided between the preheating section and the roasting section, between the roasting section and the soaking section, and between the second cooling section and the third cooling section. The partition walls are used to prevent air from flowing through the space on both sides of the partition walls, avoiding the problem of pressure fluctuation in the prior art, thereby affecting the air volume distribution.

[0023] 2. Set up a blast drying branch. The exhaust gas discharged from the blast drying section is very humid, with a moisture content of about 7%. The heat radiation capacity of saturated water vapor is greater than that of dry air. Therefore, the first cold section uses hot air with high humidity for cooling. The hot air with high humidity is blown into the bottom of the first cold section by a fan (located at the bottom of the first cold section) to cool the 1200℃ high-temperature pellets. After passing through the material layer, the hot air is heated to ~1100℃ and enters the high-temperature air duct. It is then sent to the rear section of the roasting to participate in the reaction, which is beneficial to the furnace temperature increase. Further optimization uses a calorific value of 7500kJ / m 3 process for burning low calorific value fuels.

[0024] 3. Extract part of the 250-300℃ hot air from the third cooling section as the primary combustion air, and transport it to the burner through the primary combustion branch to control the combustion flame; while ensuring the safety of combustion and eliminating the probability of explosion, the gas can be preheated. Set an oxygen enrichment interface on the primary combustion branch to enrich the primary combustion air with oxygen, reduce the amount of smoke, and increase the combustion temperature. Further optimize the use of calorific value 7500kJ / m 3 process for burning low calorific value fuels.

[0025] 4. A self-circulating branch is set between the equalizing section and the preheating section. The self-circulating branch reduces the oxygen content of the high-temperature air delivered to the rear section of the roasting, allowing the fuel to burn in a high-temperature, low-oxygen concentration atmosphere, thereby achieving the purpose of reducing nitrogen oxide emissions. In addition, the high-temperature gas from the self-circulating branch is mixed with the gas from the blast drying section to increase the temperature of the gas entering the first cooling section, avoiding excessive temperature differences between the hot air temperature and the material layer in the first cooling section; a reasonable cooling sequence is used to achieve uniform cooling of the pellets, avoiding temperature differences between the upper, middle, and lower material layers, which leads to thermal stress inside the material layer and the phenomenon of extremely cold bursting of high-temperature pellets.

[0026] 5. The air inlet of the self-circulating fan is also equipped with a cold air outlet, which can draw cold air from the atmosphere to cool down when the temperature is too high.

[0027] 6. In order to avoid the inlet temperature of the medium-temperature air duct at the front end of the preheating section being too high, a branch pipe is installed on the exhaust drying branch. The branch pipe is connected to the medium-temperature air duct at the front end of the top of the preheating section and merges with the hot air from the second cooling section, making the temperature slightly lower than the hot air in the subsequent medium-temperature air duct, further increasing the new temperature gradient.

[0028] The above description is only an overview of the technical solution of the utility model. In order to more clearly understand the technical means of the utility model and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiment of the utility model with the accompanying drawings. The specific implementation method of the utility model is given in detail by the following embodiments and their drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present application. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1 It is a principle diagram of an embodiment provided by the utility model;

[0031] In the figure, 1. blast drying section; 2. exhaust drying section; 3. preheating section; 4. roasting section; 5. equalizing section; 6. first cooling section; 7. second cooling section; 8. third cooling section; 9. materials; 10. partition wall; 11. gas pipeline; 12. high-temperature air duct; 13. medium-high temperature air duct; 14. medium-temperature air duct; 15. air inlet duct; 16. exhaust duct; 17. blast drying branch; 18. burner; 19. primary combustion-supporting branch; 20. oxygen-enriched interface; 21. self-circulation branch; 22. cold air outlet; 23. exhaust drying branch. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1 The principles and features of the present invention are described, and the examples given are only used to explain the present invention, and are not used to limit the scope of the present invention. The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become clearer according to the following description and claims. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0033] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a component centered. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a component centered. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a component centered. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0035] Reference Figure 1 As shown, the utility model provides a low calorific value combustion system for a roasting machine based on segmented heating.

[0036] Example 1

[0037] The roasting machine equipment includes, from left to right, a forced air drying section 1, an exhaust air drying section 2, a preheating section 3, a roasting section 4, a soaking section 5, a first cooling section 6, a second cooling section 7 and a third cooling section 8. Materials 9 are input from the forced air drying section and output from the third cooling section. A bellows is provided at the bottom of each of the above sections. Partition walls 10 are provided between the forced air drying section and the exhaust air drying section, between the exhaust air drying section and the preheating section, between the preheating section and the roasting section, between the roasting section and the soaking section, and between the second cooling section and the third cooling section.

[0038] The combustion system includes a gas pipeline 11 and a burner 18. The gas pipeline is divided into several branches, which are distributed in the preheating section and the roasting section. The burners are installed on the outer wall of the combustion chamber on both sides of the roasting machine. The gas is transported from the external pipe network to the roasting chamber after decompression treatment.

[0039] The high-temperature air duct 12, the medium-high-temperature air duct 13, and the medium-temperature air duct 14, the roasting section is divided into the roasting front section and the roasting rear section, and the secondary cooling section is divided into the secondary cooling front section and the secondary cooling rear section; the high-temperature air duct is connected between the roasting rear section and the top of the primary cooling section, the medium-high-temperature air duct is connected between the roasting front section and the top of the secondary cooling front section, and the medium-temperature air duct is connected between the preheating section and the top of the secondary cooling rear section;

[0040] The air inlet duct 15 and the air exhaust duct 16 are connected to the bottom of the second cooling section and the third cooling section, the first cooling section and the third cooling section form a passage, and the air exhaust duct is connected to the bottom of the preheating section and the roasting section.

[0041] In this embodiment, the hot air in the preheating section is composed of medium-temperature air of 500-700°C from the rear end of the second cooling section; the hot air in the roasting section is divided into two sections, the hot air at the front end of the roasting section comes from the high-temperature air of 900-1000°C at the front end of the second cooling section, and the hot air at the rear end of the roasting section comes from the high-temperature hot air of 1100°C in the first cooling section, and finally a temperature gradient is formed in the preheating section and the roasting section. The hot air staged combustion technology is adopted to increase the temperature of the combustion-supporting air and make full use of the heat of the flue gas. The secondary hot air of different temperatures is staged in the preheating section and the roasting section to increase the combustion temperature of the high-temperature section and increase the theoretical combustion temperature of the high-temperature section. Under the same conditions, the calorific value of 7500kJ / m 3 The low calorific value fuel can also meet the pellet quality requirements, thereby reducing production costs and realizing the application of low calorific value fuel. In addition, partition walls are provided between the preheating section and the roasting section, between the roasting section and the soaking section, and between the second cooling section and the third cooling section. The partition walls are used to prevent air from flowing through the space on both sides of the partition walls, thereby avoiding the problem of pressure fluctuation in the prior art, thereby affecting the air volume distribution.

[0042] Example 2

[0043] The structure and principle of Example 2 are similar to those of Example 1, except that in order to further increase the temperature of the secondary air input from the first cold section to the rear section of roasting, a blast drying branch 17 is also included. The blast drying branch is composed of a fan and a pipeline. The blast drying branch is connected between the third cold section and the bottom of the blast drying section, and the top of the blast drying section is connected to the entrance of the first cold section by a pipeline, and a fan is provided at the entrance of the pipeline to the first cold section.

[0044] In this embodiment, the three cooling sections cool the material layer, and the three cooling fans provide suction force, sucking cold air from the environment, entering the three cooling sections from the upper furnace cover, and finally cooling the pellets to below 120°C and then transporting them to the screening area. The temperature of the cold air after heat exchange is 300°C; the fan of the blast drying branch sends it to the bellows at the bottom of the blast drying section to dry the raw ball material layer, and the dried waste gas is circulated to the bottom entrance of the first cooling section through the pipeline. In this process, the exhaust gas discharged from the blast drying section has a high humidity, with a moisture content of about 7%, and the heat radiation capacity of saturated water vapor is greater than that of dry air. Therefore, the first cooling section adopts hot air with high humidity for cooling. The hot air with high humidity is blown into the bottom of the first cooling section by the fan (located at the bottom of the first cooling section) to cool the high-temperature pellets of 1200°C. After passing through the material layer, the hot air is heated to 1100°C and enters the high-temperature air duct. It is sent to the rear section of the roasting from the high-temperature air duct to participate in the reaction, which is conducive to the heating of the furnace.

[0045] Example 3

[0046] The structure and principle of Example 3 are similar to those of Examples 1 and 2, except that: in order to ensure the safety of combustion and eliminate the probability of explosion, the gas is preheated; the combustion system includes a primary combustion-supporting branch 19 and an oxygen-enriched interface 20; the burner is connected between the roasting section and the gas pipeline, and between the preheating section and the gas pipeline, the primary combustion-supporting branch is connected between the burner and the three cooling sections, and the primary combustion-supporting branch is composed of a fan and a pipeline; the oxygen-enriched interface is connected to the primary combustion-supporting branch, the end of the primary combustion-supporting branch connected to the burner is divided into multiple branches, the gas pipeline is divided into multiple branches, and the ends of the gas pipeline and the primary combustion-supporting branch are mixed one by one and connected to the corresponding burner.

[0047] In the embodiment shown in the figure, the primary combustion branch is connected to the blast drying branch, and the two are connected to the air outlet pipe leading out from the bottom of a cold section. The fan of the primary combustion branch is a heat-resistant fan that can withstand 300°C hot air.

[0048] In this embodiment, part of the hot air at 250-300°C from the three cooling sections is extracted as the primary combustion air, and is transported to the burner through the primary combustion branch to control the combustion flame. An oxygen enrichment interface is set on the primary combustion branch to enrich the primary combustion air with oxygen, reduce the amount of flue gas, and increase the combustion temperature. The remaining secondary air required for combustion is provided by the high-temperature air of 1100°C in the first cooling section at the rear stage of roasting, the hot air of 900-1000°C in the second cooling section at the front stage of roasting, and the medium-temperature air of 500-700°C in the second cooling section at the preheating stage. The hot air in the medium-high temperature air duct is provided at the front stage of roasting, and the medium-temperature air in the medium-temperature air duct is provided at the preheating stage. Under the same conditions, the calorific value of 7500kJ / m 3 The low calorific value fuel can also meet the pellet quality requirements, reduce production costs, and realize the application of low calorific value fuel.

[0049] In Example 3, it is preferred that the air transported by the primary combustion-supporting branch to the third cooling section accounts for 10% to 15% of the air required for combustion, and the embodiment in the figure adopts 10%; the oxygen enrichment rate of the primary combustion-supporting branch is controlled at 3%.

[0050] Example 4

[0051] The structure and principle of Example 4 are similar to those of Example 3, except that: in order to reduce the amount of nitrogen oxides generated, prevent the thermal stress caused by cold air cooling, and prevent the high-temperature pellets from bursting due to rapid cooling; it also includes a self-circulation branch 21 arranged between the equalizing section and a cold section, the self-circulation branch includes a connecting pipe connected between the equalizing section and the bottom of the cold section, a self-circulation fan arranged on the connecting pipe, and a high-temperature air duct branch section connected between the high-temperature air duct and the equalizing section, and the top of the blast drying section is connected to the connecting pipe by a pipe.

[0052] In the embodiment shown in the figure, the blast drying section and the self-circulation branch share a fan at the bottom entrance of a cold section, and the cooling air entering the bottom of a cold section mainly comes from the mixed air of the blast drying section and the self-circulation branch. In this embodiment, a part of the flue gas enters the top of the equalizing section through the high-temperature air duct from a cold section. After the heat exchange between the equalizing section and the material layer is completed, the temperature is reduced to ~600℃; then, under the suction of the self-circulation fan, this part of the flue gas and the hot air with high humidity input from the blast drying branch are mixed in the air inlet duct of a cold section to form a new mixed gas, and the temperature is reduced to 300℃; during the process of the new mixed gas being transported through the high-temperature air duct, a part of it enters the top of the equalizing section through the high-temperature air duct from a cold section, and the above cycle is repeated.

[0053] First, in this cycle, under the suction of the self-circulating fan, part of the hot air transported from the first cold section to the high-temperature air duct flows back to the equalizing section. After the 1100℃ hot air completes heat exchange with the material layer in the equalizing section, the temperature drops to about 600℃, and then mixes with the exhaust gas discharged from the blast drying section again, cools to 300℃, and is blown back into the first cold section by the fan at the bottom of the first cold section. By increasing the temperature of the hot air entering the first cold section, it is avoided that the temperature difference between the hot air temperature in the first cold section and the material layer is too large, resulting in thermal stress inside the material layer, and the phenomenon of extremely cold bursting of high-temperature pellets.

[0054] Secondly, in this cycle, the air burned in the preheating section and roasting section is divided into primary flame retardant air and secondary combustion-supporting air.

[0055] Among them, the primary combustion air comes from the third cooling section, the air oxygen content is 21%, and the oxygen enrichment rate is considered to be 3%. An oxygen enrichment interface is set on the primary combustion air pipeline to enrich the primary combustion air with oxygen, reduce the amount of smoke, and increase the combustion temperature.

[0056] The secondary combustion air in the preheating section comes from the rear end of the secondary cooling section, with an oxygen content of 21%, but a temperature of only 500-700°C.

[0057] The secondary combustion air in the rear section of roasting comes from the 1100℃ high-temperature air after heat exchange in the first cold section. The cooling air in the first cold section comes from the exhaust gas from the equalizing section and the exhaust gas from the blast drying section in the self-circulating branch. The oxygen content is about 18%, which belongs to high-temperature and low-oxygen combustion. In this high-temperature and low-oxygen atmosphere, the fuel first undergoes a reorganization process such as cracking, resulting in completely different thermodynamic conditions from the traditional combustion process. Heat energy is released under delayed combustion with oxygen-deficient gas, and there is no longer a local high-temperature and high-oxygen zone that occurs in the traditional combustion process. This combustion is a dynamic reaction without a static flame, which can reduce NO in the high-temperature zone. X Amount generated.

[0058] The secondary combustion air in the front section of the roasting section comes from the front end of the secondary cooling section, with an oxygen content of 21% and an air temperature of 900-1000°C, which belongs to conventional combustion.

[0059] In Example 4, the air inlet of the preferred self-circulating fan is also provided with a cooling air outlet 22, which can draw cold air from the atmosphere to cool down when the temperature is too high.

[0060] Example 5

[0061] The structure and principle of Example 5 are similar to those of Examples 1-4, except that: it also includes an exhaust drying branch 23, which is composed of a pipeline and a fan, and the exhaust drying branch is connected between the bottom of the rear roasting section and the top of the exhaust drying section, and the bottom of the exhaust drying section is connected to the exhaust duct. In this embodiment, the hot air in the exhaust section comes from the hot exhaust gas in the rear roasting section, which is sent into the furnace cover by the heat recovery fan to fully dry the green ball material layer, and the dried exhaust gas is discharged from the exhaust duct.

[0062] In Example 5, in order to avoid the inlet temperature of the medium-temperature air duct at the front end of the preheating section being too high, a branch pipe is provided on the exhaust drying branch, and the branch pipe is connected to the medium-temperature air duct at the front end of the top of the preheating section. After the heat exchange between the waste gas in the roasting section and the material layer occurs, the temperature will reach 350℃~450℃. The waste gas is extracted by the fan on the exhaust drying branch, and a part of it is transported to the exhaust drying section to fully dry the material layer, and the other part enters the medium-temperature air duct at the front end of the preheating section through the branch pipe, and merges with the hot air from the second cooling section, so that the temperature is slightly lower than the hot air in the subsequent medium-temperature air duct, further increasing the new temperature gradient.

[0063] In Example 5, the exhaust duct is connected to the bottom of the exhaust drying section, the preheating section, and the roasting section at the same time, a main exhaust fan is arranged in the exhaust duct, and the exhaust duct is connected to the external purification equipment and the chimney in turn. The hot flue gas from the exhaust drying section, the preheating section, and the front section of roasting is extracted by the main exhaust fan after completing the drying, preheating, and roasting, and finally discharged to the atmosphere through the chimney after the flue gas is purified.

[0064] The method of using the utility model is as follows.

[0065] The outside air entering the combustion system is divided into three streams, namely A, B, and C; A enters the system from the air inlet duct at the top of the third cooling section, B enters the system from the self-circulating fan of the self-circulating branch, and C enters the system from the bellows at the bottom of the second cooling section.

[0066] A enters from the third cooling section and is divided into A1 and A2. A1 passes through the blast drying section and carries the water vapor in the material layer into the first cooling section. A2 is transported to the combustion system for gas preheating and combustion support. A1 is divided into A11 and A12 after being output from the first cooling section. A11 enters the roasting back section for combustion support, and A12 enters the equalizing section and is transported back to the first cooling section. A11 and A2 are further divided into E and F after combustion support. E is discharged into the atmosphere after treatment, and F is divided into two parts again, which enter the preheating section and the exhaust drying section and are discharged into the atmosphere after treatment.

[0067] B, A1, A12, and the gas transported back to the first cooling section are transported to the first cooling section together to adjust the temperature of the mixed gas entering the first cooling section;

[0068] C, enters from the second cooling section and is divided into two parts, entering the preheating section and the front section of roasting for combustion respectively. The combustion exhaust gas enters the atmosphere after being treated.

[0069] Working process and principle of this utility model:

[0070] In the first step, the fan of the blast drying branch sends the hot air from the third cooling section into the bellows at the bottom of the blast drying section to dry the raw ball material layer. The dried exhaust gas is connected to the inlet of the self-circulating fan of the self-circulating branch through a pipeline;

[0071] The exhaust gas discharged from the blast drying section is very humid, with a water content of about 7%. The thermal radiation capacity of saturated water vapor is greater than that of dry air, so it is beneficial to the heating of the furnace.

[0072] In the second step, the hot air in the exhaust drying section comes from the hot exhaust gas in the post-roasting section, and is sent into the furnace cover by the fan on the exhaust drying branch line to fully dry the green ball material layer;

[0073] In the third step, the hot air in the preheating section is composed of the hot air in the exhaust drying section and the 500-700℃ medium-temperature air in the medium-temperature air duct;

[0074] In the fourth step, the hot air in the roasting section is divided into two sections: the hot air in the front section of roasting comes from the 900-1000℃ high temperature air in the medium and high temperature air duct. The hot air in the rear section of roasting comes from the 1100℃ high temperature hot air in the high temperature air duct;

[0075] The hot flue gas from the exhaust drying section, preheating section and the front section of roasting is extracted by the fan of the exhaust duct after completing the drying, preheating and roasting effects. After the flue gas is purified, it is finally discharged into the atmosphere through the chimney.

[0076] The fifth step is to set a self-circulating branch between the first cold section and the equalizing section to reduce the thermal stress generated by cold air cooling and prevent the high-temperature pellets from being rapidly cooled and burst. First, the self-circulating fan extracts about 100°C of the exhaust gas discharged from the blast drying section as cooling air, which is pressurized and blown into a cold section bellows (connected to the self-circulating fan of the self-circulating branch in the figure) to cool the 1200°C high-temperature pellets. After passing through the material layer, the hot air is heated to about 1100°C and enters the high-temperature air duct. Under the suction force of the self-circulating fan, part of the hot air flows back to the equalizing section. After the 1100°C hot air completes the heat exchange between the equalizing section and the material layer, the temperature drops to about 600°C and then mixes with the exhaust gas discharged from the blast drying section again, cools down to 300°C, and is blown back into the first cold section by the self-circulating fan to complete a cycle;

[0077] The remaining hot air at about 1100℃ enters the high-temperature air duct and is sent to the rear section of the roasting. It is evenly distributed through the branch pipes of the high-temperature air duct and enters the furnace of the roasting section to participate in the oxidation and combustion reactions. The fan of the exhaust drying section then extracts the bellows flue gas from the rear section of the roasting at a temperature of 350-450℃ and transports it to the exhaust drying section and the front end of the preheating section.

[0078] At the same time, a cooling air outlet is set at the air inlet of the self-circulating fan, which can draw cold air from the atmosphere to cool down when the temperature is too high;

[0079] In the sixth step, the second cooling section is divided into two sections, the front section and the back section. The fan on the air inlet duct connected to the second cooling section draws air from the atmosphere and pressurizes it into the bellows at the bottom of the second cooling section to cool down the high-temperature pellet material layer from the first cooling section. After the cold air completes the heat exchange with the hot material layer, it is heated to 900-1000℃ and sent to the front section of roasting through the medium and high temperature air duct to participate in the reaction;

[0080] With the cooling effect of the air in the second cooling section, the temperature of the material layer gradually decreases. The cooling air at the rear end of the second cooling section is heated to 500-700°C after passing through the material layer, and is sent to the preheating section through the medium-temperature air duct. The branch pipe at the front end of the medium-temperature air duct is mixed with part of the hot flue gas from the exhaust drying section to form a reasonable temperature gradient in the furnace of the preheating section to preheat the pellet material layer.

[0081] In the seventh step, the third cooling section is exhaust cooling. The upper part of the furnace hood is connected to the atmosphere through the air inlet duct, and cold air is sucked from the environment to cool the material layer. Since the temperature distribution of the material on the cross section of the roaster is from top to bottom, high at the top and low at the bottom, exhaust cooling can better reduce the temperature of the upper material. The cold air enters the third cooling section, passes through the material layer under the suction force of the blower drying section fan, completes the cooling of the material layer, and after uniform cooling, the pellets are discharged from the roaster to become qualified products. The cold air after heat exchange is also heated to 250-300℃, and is sent to the blower drying section through the blower drying branch. After being pressurized by the blower of the blower drying branch, it is blown into the blower drying section bellows to dry the raw pellet material layer and complete the entire air cycle.

[0082] In the above seven steps, the burners are installed on the outer wall of the combustion chamber on both sides of the roaster. The gas is transported to the roasting chamber from the external pipe network after decompression. In order to ensure the safety of combustion and eliminate the possibility of explosion, it is not easy to preheat the gas;

[0083] Adopt hot air staged combustion technology to achieve high temperature combustion by increasing the temperature of combustion-supporting air and increase the theoretical combustion temperature of the high temperature stage;

[0084] Extract part of the hot air at 250-300℃ from the outlet of the third cooling section as the primary combustion air, and transport it to the burner through the fan on the primary combustion branch. The primary combustion air volume accounts for 10% of the total air consumption for combustion, and is used to control the combustion flame.

[0085] The primary combustion-supporting fan is a heat-resistant fan that can withstand 300°C hot air; the remaining 90% of secondary air required for combustion: the high-temperature air in the high-temperature air duct is provided in the rear section of roasting, the hot air in the medium-high temperature air duct is provided in the front section of roasting, and the medium-temperature air in the medium-temperature air duct is provided in the preheating section. Under the same conditions, the calorific value is 7500kJ / m 3 The low calorific value fuel can also meet the pellet quality requirements, reduce production costs, and realize the application of low calorific value fuel.

[0086] In the above seven steps, controlling the combustion temperature or reducing the oxygen content can reduce the amount of nitrogen oxides produced.

[0087] The primary combustion air comes from the third cooling section, the air oxygen content is 21%, and the oxygen enrichment rate is considered to be 3%. An oxygen enrichment interface is set on the primary combustion air pipeline to enrich the primary combustion air with oxygen, reduce the amount of smoke, and increase the combustion temperature;

[0088] The secondary combustion air in the preheating section comes from the medium-temperature air duct, with an oxygen content of 21%, but a temperature of only 500-700°C.

[0089] The secondary combustion-supporting air in the front stage of roasting comes from the medium and high temperature air duct, with an oxygen content of 21% and an air temperature of 900-1000℃, which belongs to conventional combustion.

[0090] The secondary combustion-supporting air in the rear section of roasting comes from the high-temperature air duct. The cooling air in the first cold section is a mixture of the exhaust gas from the equalizing section and the exhaust gas from the blast drying section. The oxygen content is about 18%, which belongs to high-temperature and low-oxygen combustion. In this high-temperature and low-oxygen atmosphere, the fuel first undergoes a reorganization process such as cracking, resulting in completely different thermodynamic conditions from the traditional combustion process. Heat energy is released under delayed combustion with oxygen-deficient gas, and there is no longer a local high-temperature and high-oxygen zone that occurs in the traditional combustion process. This combustion is a dynamic reaction without a static flame, which can reduce NO in the high-temperature zone. X Amount generated.

[0091] The above description is only a preferred embodiment of the utility model and does not impose any form of limitation on the utility model. Any ordinary technician in the industry can smoothly implement the utility model as shown in the drawings of the specification and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the utility model using the technical content disclosed above are all equivalent embodiments of the utility model. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the utility model are still within the protection scope of the technical solution of the utility model.

Claims

1. The low calorific value combustion system of the roaster based on segmented heating is characterized by: include The roasting machine equipment includes, from left to right, a blast drying section, an exhaust drying section, a preheating section, a roasting section, a soaking section, a first cooling section, a second cooling section, and a third cooling section. The material is input from the blast drying section and output from the third cooling section. Partition walls are provided between the blast drying section and the exhaust drying section, between the exhaust drying section and the preheating section, between the preheating section and the roasting section, between the roasting section and the soaking section, and between the second cooling section and the third cooling section. Combustion system, the combustion system includes gas pipeline and burner. The gas pipeline is divided into several branches, which are distributed in the preheating section and roasting section. The burner is installed on the outer wall of the combustion chamber on both sides of the roasting machine. High-temperature air duct, medium-high-temperature air duct, and medium-temperature air duct. The roasting section is divided into the roasting front section and the roasting rear section, and the secondary cooling section is divided into the secondary cooling front section and the secondary cooling rear section. The high-temperature air duct is connected between the roasting rear section and the top of the primary cooling section, the medium-high-temperature air duct is connected between the roasting front section and the top of the secondary cooling front section, and the medium-temperature air duct is connected between the preheating section and the top of the secondary cooling rear section. The air inlet duct and the exhaust duct are connected with the bottom of the second cooling section and the third cooling section, the first cooling section and the third cooling section form a passage, and the exhaust duct is connected with the bottom of the preheating section and the roasting section.

2. The low calorific value combustion system for a roaster based on segmented heating according to claim 1 is characterized in that: It also includes a blast drying branch, which consists of a fan and a pipeline. The blast drying branch is connected between the third cooling section and the bottom of the blast drying section, and the top of the blast drying section is connected to the entrance of the first cooling section by a pipeline, and a fan is provided at the entrance of the pipeline to the first cooling section.

3. The low calorific value combustion system for a roaster based on segmented heating according to claim 1 or 2, characterized in that: The combustion system also includes a primary combustion-supporting branch and an oxygen-enriched interface; the burner is connected between the roasting section and the gas pipeline, and between the preheating section and the gas pipeline, the primary combustion-supporting branch is connected between the burner and the three cooling sections, and the primary combustion-supporting branch is composed of a fan and a pipeline; the oxygen-enriched interface is connected to the primary combustion-supporting branch, the end of the primary combustion-supporting branch connected to the burner is divided into multiple branches, the gas pipeline is divided into multiple branches, and the ends of the gas pipeline and the primary combustion-supporting branch are mixed one by one and connected to the corresponding burner.

4. The low calorific value combustion system for a roaster based on segmented heating according to claim 3 is characterized in that: The air of the third cooling section transported by the primary combustion-supporting branch accounts for 10% to 15% of the air required for combustion; the oxygen enrichment rate of the primary combustion-supporting branch is controlled at 3%.

5. The low calorific value combustion system for a roaster based on segmented heating according to claim 3 is characterized in that: It also includes a self-circulation branch arranged between the equalizing section and a cold section, the self-circulation branch includes a connecting pipe connected between the equalizing section and the bottom of the cold section, a self-circulation fan arranged on the connecting pipe, and a high-temperature air duct branch section connected between the high-temperature air duct and the equalizing section, and the top of the blast drying section is connected to the connecting pipe by a pipe.

6. The low calorific value combustion system for a roaster based on segmented heating according to claim 5 is characterized in that: The air inlet of the self-circulating fan is also equipped with a cooling air outlet.

7. The low calorific value combustion system for a roaster based on segmented heating according to claim 1 is characterized in that: It also includes an exhaust drying branch, which is composed of a pipeline and a fan. The exhaust drying branch is connected between the bottom of the rear roasting section and the top of the exhaust drying section, and the bottom of the exhaust drying section is connected to the exhaust duct.

8. The low calorific value combustion system for a roaster based on segmented heating according to claim 7 is characterized in that: A branch pipe is provided on the exhaust drying branch, and the branch pipe is connected to the medium-temperature air duct at the front end of the top of the preheating section.

9. The low calorific value combustion system for a roaster based on segmented heating according to claim 7, characterized in that: The exhaust duct is connected to the exhaust drying section, the preheating section, and the bottom of the roasting section. A main exhaust fan is arranged in the exhaust duct, and the exhaust duct is connected to the external purification equipment and the chimney in turn.

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