A system and method for adjustable cycling of flue gas usage and quantity

Abstract

The present application belongs to the field of metallurgy, and relates to a system and method for adjusting the use and amount of circulating flue gas, comprising a drying furnace, a coal mill, a bag powder collecting device and a pulverized coal fan connected in sequence, wherein a coal feeder and a raw coal bin are connected to the coal mill in sequence, the drying furnace is connected to a chimney and a hot blast furnace through a waste gas induced draft fan, and the pulverized coal fan is connected to the drying furnace through a circulating flue gas pipeline. When the hot blast furnace waste gas supply of the blast furnace is insufficient, the system can stabilize the temperature of the pulverizing system by adjusting the amount of circulating flue gas entering the drying furnace of the pulverizing system, so as to ensure the qualified moisture of the pulverized coal. Meanwhile, during the shutdown of the pulverizing system, a two-step strategy for the cooling process of the whole system is realized, that is, the pulverizing system is first cooled to a safe temperature range by continuously circulating inert circulating flue gas with low oxygen content and low temperature, and then the pulverizing system is rapidly cooled by a large amount of cold air. The shutdown safety of the pulverizing system is ensured, and the shutdown efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and relates to a system and method for adjusting the use and dosage of circulating flue gas. Background Technology

[0002] The pulverized coal preparation system primarily involves mixing high-temperature gases generated from the combustion of coal gas in the dryer with the exhaust gas from the blast furnace hot blast stove to dry the pulverized coal. Currently, most steel enterprises have flue gas recirculation functions in their pulverized coal preparation systems. However, the recirculated flue gas is only used to compensate for insufficient exhaust gas volume in the pulverizing system when the exhaust gas from the blast furnace hot blast stove is insufficient, making its purpose relatively limited. Furthermore, due to the low temperature of the recirculated flue gas and the lack of precise control and regulation of its volume, excessive recirculated gas entering the dryer of the pulverizing system often leads to temperature fluctuations and results in pulverized coal with unacceptable moisture content. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a system and method for adjusting the use and amount of circulating flue gas, which can adjust the amount of circulating flue gas entering the drying furnace of the pulverizing system according to production needs, so as to ensure the temperature stability of the pulverizing system and ensure that the moisture content of the pulverized coal is qualified.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a system for adjusting the use and quantity of circulating flue gas, comprising a drying furnace, a coal mill, a bag filter dust collector, and a pulverized coal fan connected in sequence. A coal feeder and a raw coal bunker are connected in sequence to the coal mill. The drying furnace is connected to a chimney and a hot air furnace through an exhaust gas induced draft fan. The pulverized coal fan is connected to the drying furnace through a circulating flue gas pipeline.

[0005] Optionally, an exhaust gas regulating valve is installed on the pipeline between the exhaust gas induced draft fan and the chimney; oxygen content monitoring points and air volume monitoring points are sequentially installed between the exhaust gas induced draft fan and the drying furnace; a combustion fan and a combustion fan regulating valve are installed on the drying furnace, and it is connected to the coal gas through a coal gas regulating valve; a hot air valve is installed on the pipeline connecting the drying furnace and the coal mill; a pressure gauge and a venting valve for emission are also installed on the drying furnace.

[0006] Optionally, a hot air valve and a temperature monitoring point are sequentially installed between the drying furnace and the coal mill. The hot air valve and the temperature monitoring point are connected to the first circulating flue gas regulating valve on the circulating pipeline through a second circulating flue gas regulating valve. A cold air shut-off valve for introducing air is also installed between the hot air valve and the temperature monitoring point.

[0007] Optionally, the coal feeder is connected to a raw coal bunker via a coal feeder inlet valve, and a coal mill inlet valve is installed between the coal feeder bunker and the coal mill; the coal mill is equipped with a coal mill outlet nitrogen filling valve connected to nitrogen, and a temperature monitoring point is installed on the pipeline connected to the bag filter dust collection device.

[0008] Optionally, the top of the bag filter dust collector is equipped with a pulse blowing device for introducing nitrogen gas, and the bottom is connected to the coal powder silo via a discharge motor and a coal powder vibrating screen. Temperature monitoring points and system air volume regulating valves are also installed on the pipeline connecting the bag filter dust collector and the coal powder blower.

[0009] Optionally, a circulating flue gas shut-off valve and a first circulating flue gas regulating valve are installed on the circulating flue gas pipeline.

[0010] A method for adjusting the use and volume of recirculated flue gas, using a system for adjusting the use and volume of recirculated flue gas as described above, includes the following steps:

[0011] S1, coal powder is prepared and system temperature is adjusted by circulating flue gas;

[0012] S11. When the pulverized coal preparation system is running normally, if the oxygen content monitoring value at the back end of the exhaust gas induced draft fan exceeds 8%, it proves that the amount of exhaust gas generated by the blast furnace hot blast stove is insufficient. The pulverized coal fan will draw air back from the chimney into the pulverizing system.

[0013] S12, gradually reduce the opening of the exhaust gas regulating valve and temporarily reduce the coal feeder until the oxygen content of the exhaust gas from the hot blast stove drawn into the system is below 6% and remains stable.

[0014] S13, open the circulating flue gas shut-off valve and fully open the first circulating flue gas regulating valve;

[0015] S14, restore the coal feed rate of the coal feeder;

[0016] S15. Since the temperature of the circulating flue gas is not high, it needs to be compensated for heat after entering the drying furnace together with the exhaust gas from the hot blast stove. At this time, the amount of gas burned in the drying furnace needs to be increased to maintain the inlet temperature of the coal mill at about 280°C. When the amount of gas burned in the drying furnace reaches the maximum and the inlet temperature of the coal mill is still below 260°C, the opening of the first circulating flue gas regulating valve should be gradually reduced to reduce the amount of circulating flue gas entering the drying furnace until the inlet temperature of the coal mill reaches the specified range.

[0017] S16. During the process of adjusting the circulating flue gas volume, contact the blast furnace at any time and pay attention to the blast furnace hot blast stove burning situation. Adjust the opening of the exhaust gas regulating valve and the first circulating flue gas regulating valve in a timely manner to ensure sufficient gas volume and stable temperature of the entire pulverizing system.

[0018] S2, the pulverizing system is cooled by circulating flue gas and then shut down;

[0019] S21. Upon receiving a shutdown notification from the pulverizing system, immediately stop the gas supply to the drying furnace; open the circulating flue gas shut-off valve, and open the initial opening of the second circulating flue gas regulating valve to 30%-40%;

[0020] S22, gradually reduce the coal feed rate of the coal feeder, reduce the opening of the exhaust gas regulating valve, and increase the opening of the second circulating flue gas regulating valve to keep the coal mill outlet temperature below 75°C during the process of reducing the coal feed rate.

[0021] S23. When the coal feed rate drops below 10t / h and the coal mill outlet temperature stabilizes below 75℃, stop the coal feeder directly and closely monitor the changes in the coal mill outlet temperature. If it exceeds 95℃, open the coal mill outlet nitrogen charging valve to charge nitrogen gas for cooling.

[0022] S24. When it is confirmed that the residual coal powder in the coal mill has been completely extracted, turn off the exhaust fan, close the hot air valve, open the dryer furnace vent valve, and cut off the heat source of the entire front end of the coal mill.

[0023] S25, fully open the second circulating flue gas regulating valve, first pass through the circulating flue gas cooling system; during the circulation process, the circulating flue gas continuously loses heat and the temperature will gradually decrease. After the coal mill outlet temperature drops below 60℃ and the powder collection device outlet temperature drops below 50℃, the cold air shut-off valve is opened, and a large amount of cold air is drawn into the system to quickly cool the system.

[0024] S26. When the coal mill outlet temperature is below 40℃, stop the pulverized coal fan and the shutdown is complete.

[0025] Optionally, in steps S12 to S15, the system air volume regulating valve should be constantly monitored according to the pressure changes of the drying oven, and the drying oven pressure should be kept within the range of -200 to +50 Pa during the adjustment process.

[0026] Optionally, in steps S21 to S23, the system air volume regulating valve should be constantly monitored according to the pressure changes of the drying oven, and the drying oven pressure should be kept within the range of -200 to +50 Pa during the adjustment process.

[0027] The beneficial effects of this invention are as follows: This invention provides a system and method for adjusting the use and quantity of circulating flue gas. When the supply of exhaust gas from the blast furnace hot blast stove is insufficient, this system can stabilize the temperature of the pulverizing system and ensure that the moisture content of the pulverized coal meets the required standards by adjusting the amount of circulating flue gas entering the drying furnace of the pulverizing system. Simultaneously, during the shutdown of the pulverizing system, a two-step strategy for cooling the entire system is implemented: first, the pulverizing system is continuously cooled to a safe temperature range through the continuous circulation of inert circulating flue gas with low oxygen content and low temperature; then, a large amount of cold air is used to rapidly cool the pulverizing system. This ensures both the safety of the pulverizing system shutdown and improves shutdown efficiency.

[0028] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0030] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0031] Attached reference numerals: 1. Hot blast stove; 2. Chimney; 3. Exhaust gas regulating valve; 4. Exhaust gas induced draft fan; 5. Oxygen content monitoring point; 6. Air volume monitoring point; 7. Drying furnace; 8. Combustion fan; 9. Combustion fan regulating valve; 10. Gas regulating valve; 11. Vent valve; 12. Hot air valve; 13. Cold air shut-off valve; 14. Temperature monitoring point; 15. Raw coal bunker; 16. Coal feeder inlet valve; 17. Coal feeder; 18. Coal mill inlet valve; 19. Coal mill outlet nitrogen charging valve; 20. Temperature monitoring point; 21. Bag filter dust collection device; 22. Pulse blowing device; 23. Unloading motor; 24. Coal powder vibrating screen; 25. Coal powder bunker; 26. System air volume regulating valve; 27. Coal powder fan; 28. Pressure gauge; 29. ​​Circulating flue gas shut-off valve; 30. First circulating flue gas regulating valve; 31. Second circulating flue gas regulating valve; 32. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0034] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0035] Please see Figure 1 This is a system for adjusting the use and quantity of circulating flue gas, comprising a dryer 7, a coal mill 19, a bag filter 22, and a pulverized coal fan 28 connected in sequence. A coal feeder 17 and a raw coal bunker 15 are connected in sequence to the coal mill 19. The dryer 7 is connected to a chimney 2 and a hot air furnace 1 via an exhaust gas fan 4. The pulverized coal fan 28 is connected to the dryer 7 via a circulating flue gas pipeline. An exhaust gas regulating valve 3 is installed on the pipeline between the exhaust gas fan 4 and the chimney 2. Oxygen content monitoring point 5 and air volume monitoring point 6 are sequentially arranged between furnaces 7; combustion fan 8 and combustion fan 8 regulating valve are installed on the drying furnace 7, and it is connected to the gas through gas regulating valve 10; hot air valve 12 is installed on the pipeline connecting the drying furnace 7 and the coal mill 19; pressure gauge 29 and vent valve 11 for discharge are also installed on the drying furnace 7; hot air valve 12 and temperature monitoring point 2114 are sequentially arranged between the drying furnace 7 and the coal mill 19. The second circulating flue gas regulating valve 32 connects to the first circulating flue gas regulating valve 31 on the circulating pipeline between 114 and 12; a cold air shut-off valve 13 for introducing air is also provided between the hot air valve 12 and the temperature monitoring point 2114; the raw coal bunker 15 is connected to the coal feeder 17 through the coal feeder 17 inlet valve 16; a coal mill 19 inlet valve 18 is provided between the coal feeder bunker and the coal mill 19; the coal mill 19 is equipped with a coal mill 19 outlet nitrogen filling valve connected to nitrogen, and is connected to the bag filter... Temperature monitoring point 2114 is installed on the pipeline connected to the powder collection device 22. A pulse powder blowing device 23 for introducing nitrogen is installed at the top of the bag powder collection device 22, and the bottom is connected to the coal powder silo 26 through the unloading motor 24 and the coal powder vibrating screen 25 respectively. Temperature monitoring point 2114 and system air volume regulating valve 27 are also installed on the pipeline connecting the bag powder collection device 22 and the coal powder blower 28. A circulating flue gas shut-off valve 30 and a first circulating flue gas regulating valve 31 are installed on the circulating flue gas pipeline.

[0036] A method for adjusting the use and volume of recirculated flue gas, using a system for adjusting the use and volume of recirculated flue gas as described above, includes the following steps:

[0037] 1. Pulverized coal preparation and system temperature adjustment via circulating flue gas.

[0038] (1) When the coal powder preparation system is running normally, if the oxygen content monitoring value at the back end of the exhaust gas induced draft fan 4 exceeds 8%, it proves that the amount of exhaust gas generated by the blast furnace hot blast stove 1 is insufficient, and the coal powder fan 28 draws air back from the chimney 2 into the pulverizing system.

[0039] (2) Gradually reduce the opening of the exhaust gas regulating valve 3 and temporarily reduce the coal feed rate of the coal feeder 17 until the oxygen content of the exhaust gas from the hot air furnace 1 is lower than 6% and remains stable.

[0040] (3) Open the circulating flue gas shut-off valve and fully open the circulating flue gas regulating valve 1.

[0041] (4) Restore the coal feed rate of coal feeder 17.

[0042] (5) Since the temperature of the circulating flue gas is not high, it needs to be compensated for heat after entering the drying furnace 7 along with the exhaust gas from the hot blast stove 1. At this time, the amount of gas burned in the drying furnace 7 should be increased to maintain the inlet temperature of the coal mill 19 at about 280°C. When the amount of gas burned in the drying furnace 7 reaches the maximum and the inlet temperature of the coal mill 19 is still below 260°C, the opening of the circulating flue gas regulating valve 1 should be gradually reduced to decrease the amount of circulating flue gas entering the drying furnace 7 until the inlet temperature of the coal mill 19 reaches the specified range.

[0043] In steps (2)-(5) above, pay attention to the control of the system air volume regulating valve 27 at all times according to the pressure change of the drying oven 7, and keep the pressure of the drying oven 7 within the range of -200 to +50Pa during the adjustment process.

[0044] (6) During the process of adjusting the circulating flue gas volume, contact the blast furnace at any time and pay attention to the burning status of the hot blast stove 1 of the blast furnace. Adjust the opening of the waste gas regulating valve 3 and the circulating flue gas regulating valve 1 in a timely manner to ensure that the gas volume of the entire pulverizing system is sufficient and the temperature is stable.

[0045] 2. Cool the pulverizing system with circulating flue gas and then shut down the machine.

[0046] (1) Upon receiving the shutdown notification of the pulverizing system, immediately stop the gas supply to the drying furnace 7. Open the circulating flue gas shut-off valve 30, and open the initial opening of the circulating flue gas regulating valve 2 to 30%-40% (at this time, the coal feeder 17 has not yet stopped feeding coal, the system still needs some heat, and the circulating flue gas volume cannot be too large, which is used to regulate the system temperature).

[0047] (2) Gradually reduce the coal feed rate of coal feeder 17, reduce the opening of exhaust gas regulating valve 3, and increase the opening of circulating flue gas regulating valve 2. During the process of reducing the coal feed rate, keep the outlet temperature of coal mill 19 below 75℃. (When the coal feed rate is reduced, the heat required by the system is reduced, the load is reduced, and the pumping force is also reduced).

[0048] (3) When the coal feed rate drops below 10t / h and the outlet temperature of the coal mill 19 stabilizes below 75℃, the coal feeder 17 is stopped directly. Closely monitor the change in the outlet temperature of the coal mill 19. If it exceeds 95℃, open the nitrogen charging valve at the outlet of the coal mill 19 to charge nitrogen and cool it down.

[0049] In steps (1)-(3) above, pay attention to the control of the system air volume regulating valve 27 at all times according to the pressure change of the drying oven 7, and keep the pressure of the drying oven 7 within the range of -200 to +50Pa during the adjustment process.

[0050] (4) When it is confirmed that the residual coal powder in the coal mill 19 has been completely extracted (judged according to the no-load current of the coal mill 19), turn off the exhaust fan 4, close the hot air valve 12, open the vent valve 11 of the drying furnace 7, and cut off the heat source of the entire front end of the coal mill 19.

[0051] (5) Fully open the circulating flue gas regulating valve 2, and first pass through the circulating flue gas cooling system. During the circulation process, the circulating flue gas loses heat continuously, and the temperature will gradually decrease. After the outlet temperature of the coal mill 19 drops below 60°C and the outlet temperature of the powder collection device drops below 50°C, open the cold air shut-off valve 13. A large amount of cold air is drawn into the system, which quickly cools the system.

[0052] (6) When the outlet temperature of the coal mill 19 is below 40°C, stop the coal powder fan 28 and the shutdown is complete.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for adjusting the use and dosage of recirculated flue gas, characterized in that, This method is based on a system that can adjust the use and amount of circulating flue gas. The system includes a dryer, a coal mill, a bag filter dust collector, and a pulverized coal fan connected in sequence. A coal feeder and a raw coal bunker are connected in sequence to the coal mill. The dryer is connected to the chimney and the hot air furnace through an exhaust gas fan. The pulverized coal fan is connected to the dryer through a circulating flue gas pipeline. An exhaust gas regulating valve is installed on the pipeline between the exhaust gas induced draft fan and the chimney; a hot air valve is installed on the pipeline connecting the dryer and the coal mill. A hot air valve and a temperature monitoring point are sequentially installed between the drying furnace and the coal mill. The hot air valve and the temperature monitoring point are connected to the first circulating flue gas regulating valve on the circulating pipeline through the second circulating flue gas regulating valve. A cold air shut-off valve for introducing air is also installed between the hot air valve and the temperature monitoring point. The coal mill is equipped with a nitrogen purging valve at the coal mill outlet, which is connected to nitrogen gas. The circulating flue gas pipeline is equipped with a circulating flue gas shut-off valve and a first circulating flue gas regulating valve. The method includes the following steps: S1, coal powder is prepared and system temperature is adjusted by circulating flue gas; S11. During normal operation of the pulverized coal preparation system, if the oxygen content monitoring value at the back end of the exhaust gas induced draft fan exceeds 8%, the amount of exhaust gas generated by the blast furnace hot blast stove is insufficient, and the pulverized coal fan will draw air back from the chimney into the pulverizing system. S12, gradually reduce the opening of the exhaust gas regulating valve and temporarily reduce the coal feeder until the oxygen content of the exhaust gas from the hot blast stove drawn into the system is below 6% and remains stable. S13, open the circulating flue gas shut-off valve and fully open the first circulating flue gas regulating valve; S14, restore the coal feed rate of the coal feeder; S15. Since the temperature of the circulating flue gas is not high, it needs to be compensated for heat after entering the drying furnace together with the exhaust gas from the hot blast stove. At this time, the amount of gas burned in the drying furnace needs to be increased to maintain the inlet temperature of the coal mill at 280℃. When the amount of gas burned in the drying furnace reaches the maximum and the inlet temperature of the coal mill is still lower than 260℃, the opening of the first circulating flue gas regulating valve is gradually reduced to reduce the amount of circulating flue gas entering the drying furnace until the inlet temperature of the coal mill reaches the specified range. S16. During the process of adjusting the circulating flue gas volume, pay close attention to the burning status of the hot blast stove and adjust the opening of the exhaust gas regulating valve and the first circulating flue gas regulating valve in a timely manner to ensure sufficient gas volume and stable temperature of the entire pulverizing system. S2, the pulverizing system is cooled by circulating flue gas and then shut down; S21. Upon receiving a shutdown notification from the pulverizing system, immediately stop the gas supply to the drying furnace. Open the circulating flue gas shut-off valve, and initially open the second circulating flue gas regulating valve to 30%–40%; S22, gradually reduce the coal feed rate of the coal feeder, reduce the opening of the exhaust gas regulating valve, and increase the opening of the second circulating flue gas regulating valve to keep the coal mill outlet temperature below 75°C during the process of reducing the coal feed rate. S23. When the coal feed rate drops below 10t / h and the coal mill outlet temperature stabilizes below 75℃, stop the coal feeder directly and closely monitor the changes in the coal mill outlet temperature. If it exceeds 95℃, open the coal mill outlet nitrogen charging valve to charge nitrogen gas for cooling. S24. When it is confirmed that the residual coal powder in the coal mill has been completely extracted, turn off the exhaust fan, close the hot air valve, open the dryer furnace vent valve, and cut off the heat source of the entire front end of the coal mill. S25, fully open the second circulating flue gas regulating valve, first pass through the circulating flue gas cooling system; during the circulation process, the circulating flue gas continuously loses heat and the temperature will gradually decrease. After the coal mill outlet temperature drops below 60℃ and the powder collection device outlet temperature drops below 50℃, the cold air shut-off valve is opened, and a large amount of cold air is drawn into the system to quickly cool the system. S26. When the coal mill outlet temperature is below 40℃, stop the pulverized coal blower.

2. The method according to claim 1, characterized in that: Oxygen content monitoring points and air volume monitoring points are sequentially installed between the exhaust fan and the drying furnace; the drying furnace is equipped with a combustion fan and a combustion fan regulating valve, and is connected to the gas through a gas regulating valve; the drying furnace is also equipped with a pressure gauge and a venting valve for discharge.

3. The method according to claim 2, characterized in that: The coal feeder is connected to the raw coal bunker via the coal feeder inlet valve, and a coal mill inlet valve is installed between the coal feeder and the coal mill; a temperature monitoring point is installed on the pipeline connecting the coal mill to the bag filter dust collection device.

4. The method according to claim 3, characterized in that: The top of the bag filter dust collector is equipped with a pulse blowing device for introducing nitrogen gas, and the bottom is connected to the coal powder silo via a discharge motor and a coal powder vibrating screen. Temperature monitoring points and system air volume regulating valves are also installed on the pipeline connecting the bag filter dust collector and the coal powder blower.

5. The method according to claim 4, characterized in that: During steps S12 to S15, pay close attention to the control of the system air volume regulating valve according to the pressure changes of the drying oven, and maintain the drying oven pressure within the range of -200 to +50 Pa during the adjustment process.

6. The method according to claim 4, characterized in that: In steps S21 to S23, pay close attention to the control of the system air volume regulating valve according to the pressure changes of the drying oven, and keep the pressure of the drying oven within the range of -200 to +50 Pa during the adjustment process.

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