A steel plant ultra-high temperature subcritical coal gas power generation system and a method for operating the same

Abstract

The application discloses a kind of steel plant superhigh temperature subcritical coal gas power generation system and its operating method, system includes boiler, steam pocket and generator unit, boiler furnace wall is water-cooled wall structure, boiler includes furnace, horizontal flue and tail flue communicated in sequence, horizontal flue is successively provided with screen superheater, high-temperature reheater and high-temperature superheater along flue gas flow direction, tail flue is successively provided with low-temperature reheater, low-temperature superheater, coal economizer and air preheater along flue gas flow direction, the lower part of furnace is provided with two pairs of waist narrowing interval, screen superheater and high-temperature reheater are provided with turbulence section between, operating method successively includes coal gas combustion in furnace, steam heating in horizontal flue, power generation, waste heat absorption in tail flue and flue gas emission etc. The present application has the advantages of small flue gas temperature fluctuation, high-temperature reheater and high-temperature superheater are not prone to over-temperature problem, and efficient and stable operation.

Description

Technical Field

[0001] This invention belongs to the field of coal gas power generation technology, specifically relating to an ultra-high temperature subcritical coal gas power generation system for steel plants and its operation method. Background Technology

[0002] With the rapid development of the steel industry, a large number of by-products are generated during the smelting process, one of which is blast furnace gas. Blast furnace gas is a colorless, odorless, and tasteless mixture of gases, mainly composed of CO, CO2, H2, CH4, N2, etc. Among them, CO accounts for 25% as the main combustible component, while H2 accounts for 0.67% and CH4 accounts for 0.11%, which are very small and have little impact on the total calorific value. In addition, the heat-absorbing components N2 (55%) and CO2 (15%) account for a large proportion. They neither participate in combustion to generate heat nor support combustion. On the contrary, they absorb a large amount of heat generated during combustion. Blast furnace gas is characterized by high output, low calorific value, and unstable combustion.

[0003] Ultra-high temperature subcritical gas power generation technology is a technology used by steel enterprises to produce steam by burning low-calorific-value gas in boilers, which then drives a steam turbine to generate electricity. This technology boasts advantages such as low construction investment, low energy consumption costs, short payback period, and good environmental performance, making it a highly economically efficient technology. In steel enterprises, besides 60% of blast furnace gas being directly used as raw material, the remaining 30% is used for power generation. However, current ultra-high temperature subcritical gas power generation systems still face the following problems: First, the combustion atmosphere of blast furnace gas within the furnace is poor, resulting in low combustion efficiency, uneven flue gas temperature distribution, and large temperature differences between different parts. This leads to significant temperature fluctuations at the flue gas discharge, affecting steam generation and the normal operation of the boiler. Second, the large difference in flue gas velocity and temperature on both sides of the furnace outlet poses a risk of overheating in the superheater and reheater on the side with higher flue gas temperature and velocity. Prolonged overheating of the superheater and reheater affects both their service life and the safe and stable operation of the gas boiler. Therefore, it is objectively necessary to develop a high-efficiency and stable ultra-high temperature subcritical gas power generation system for steel plants with small flue gas temperature fluctuations, low risk of overheating, and its operation method. Summary of the Invention

[0004] In order to solve the problems existing in the background technology, the purpose of this invention is to provide a high-efficiency and stable ultra-high temperature subcritical gas power generation system for steel plants with small flue gas temperature fluctuations, less prone to overheating problems, and its operation method.

[0005] The ultra-high temperature subcritical gas power generation system for steel plants described in this invention includes a boiler, a steam drum, and a generator set. The boiler wall is a water-cooled wall structure. The boiler includes a furnace, a horizontal flue, and a tail flue connected in sequence. A screen-type superheater, a high-temperature reheater, and a high-temperature superheater are arranged sequentially along the flue gas flow direction in the horizontal flue. A low-temperature reheater, a low-temperature superheater, an economizer, and an air preheater are arranged sequentially along the flue gas flow direction in the tail flue. The lower part of the furnace has two pairs of narrow sections spaced vertically, each pair of narrow sections... The two pairs of constricted sections are symmetrically arranged on two opposite side walls of the furnace. The cross-sectional shape of the constricted sections is an arch shape that tapers inward into the furnace. The two pairs of constricted sections divide the interior of the furnace into the main combustion chamber, the auxiliary combustion chamber, and the burnout chamber from bottom to top. Burners are respectively installed on the side walls of the main combustion chamber and the auxiliary combustion chamber. A turbulence section is provided between the screen-type superheater and the high-temperature reheater. In the turbulence section, flow dividers and pairs of flow convergent plates are alternately arranged. The flow dividers are located in the middle of the turbulence section, and the flow convergent plates are symmetrically arranged on both sides of the turbulence section.

[0006] Furthermore, the generator set includes a connected steam turbine and a generator. The exhaust steam outlet of the low-pressure cylinder of the steam turbine is sequentially connected to a condenser, a condensate pump, and a deaerator. The outlet of the deaerator is connected to the inlet of the economizer, and the outlet of the economizer is connected to the steam drum. The steam outlet of the high-pressure cylinder of the steam turbine is connected to the low-temperature reheater, the steam outlet of the low-temperature reheater is connected to the high-temperature reheater, and the steam outlet of the high-temperature reheater is connected to the steam inlet of the steam turbine.

[0007] Furthermore, the burner installed on the side wall of the main combustion chamber is a double swirl burner, and the burner installed on the side wall of the auxiliary combustion chamber is a direct current burner, with the nozzle of the direct current burner arranged at an angle downwards.

[0008] Furthermore, the water-cooled wall consists of an upper part and a lower part, with the lower part being a spiral tube coil structure and the upper part being a vertical tube coil structure.

[0009] Furthermore, the cross-sectional area of ​​the horizontal flue is larger than that of the furnace.

[0010] Furthermore, the total length of each pair of constricted waists extending into the furnace is one-third to one-half of the furnace length.

[0011] The operation method of the ultra-high temperature subcritical gas power generation system in a steel plant according to the present invention includes the following steps:

[0012] ① Combustion of blast furnace gas in the furnace: Blast furnace gas and air are simultaneously delivered to each burner, and are injected into the main combustion chamber and auxiliary combustion chamber respectively by the burner and ignited. The high-temperature flue gas and some of the incompletely burned blast furnace gas continuously flow upward and are fully burned in the burnout chamber. The high-temperature flue gas flows into the horizontal flue, and the water in the steam drum flows into the water-cooled wall. The water absorbs the heat in the furnace and forms water vapor before flowing back into the steam drum.

[0013] ② Steam heating in the horizontal flue: The high temperature generated in step ① flows into the horizontal flue, while some water in the steam drum flows through the screen-type superheater, vaporizes and forms water vapor which flows back to the steam drum. The water vapor in the steam drum is first sent to the low-temperature superheater for preliminary heating, and then sent to the high-temperature superheater for heating to produce superheated steam. The temperature of the superheated steam is not lower than 570℃ and the pressure is not lower than 17.3MPa.

[0014] ③ Power generation: The superheated steam generated in step ② is transported to the generator set for power generation. At the same time, the high-temperature flue gas flows downward from the top of the tail flue, transporting the low-pressure steam output from the high-pressure cylinder of the generator set to the low-temperature reheater for preliminary heating. The heated steam is then sent to the high-temperature reheater for heating to generate reheated steam. The temperature of the reheated steam is not lower than 568℃ and the pressure is not lower than 3.8MPa. It is then sent to the generator set for power generation.

[0015] ④ Waste heat absorption in the tail flue: The condensate discharged from the generator set is sent to the economizer for preliminary heating. The heated water is then sent to the steam drum. At the same time, cold air is sent to the air preheater for preheating, so that the air temperature reaches 200℃~300℃. After preheating, the air is sent to the burner.

[0016] ⑤ Flue gas emission: After the residual heat is absorbed in step ④, the flue gas temperature drops to below 200℃ before being discharged.

[0017] Furthermore, in step ③, a steam buffer tank is installed on the pipeline between the steam outlet of the high-temperature superheater and the steam inlet of the generator turbine.

[0018] Furthermore, in step ④, a gas preheater is installed in the tail flue below the air preheater. The gas preheater's outlet is connected to the burner's inlet, so that the gas temperature rises to above 160°C after preheating, while the flue gas temperature drops to below 140°C.

[0019] Furthermore, in step ②, the heat absorption ratio of the screen-type superheater is 8.1% to 8.8%, the heat absorption ratio of the low-temperature superheater is 10.5% to 11.8%, and the heat absorption ratio of the high-temperature superheater is 10.9% to 12.1%.

[0020] The beneficial effects of this invention are as follows:

[0021] I. This invention improves the furnace structure of the boiler by incorporating two pairs of constricted sections within the furnace. Each pair of constricted sections is symmetrically positioned on opposite side walls of the furnace, and the cross-sectional shape of the constricted sections is an arch shape that tapers inward into the furnace. These two pairs of constricted sections divide the internal space of the furnace into relatively independent main combustion chamber, secondary combustion chamber, and burnout chamber. The main combustion chamber ensures complete combustion of the blast furnace gas. The secondary combustion chamber serves two purposes: firstly, it appropriately increases the ignition point to promote the combustion of the blast furnace gas; secondly, it separates the main combustion chamber from the burnout chamber, ensuring the formation of a high-temperature zone within the main combustion chamber and guaranteeing that the low-calorific-value blast furnace gas can ignite and burn stably within the main combustion chamber. The burnout chamber ensures that the blast furnace gas that has not been fully combusted in the main and secondary combustion chambers is burned as completely as possible within the burnout chamber. The constricted sections in this invention can also form a radiating arch, allowing heat to be concentrated near the burner nozzle to heat the fuel just entering the main and auxiliary combustion chambers, ensuring smooth ignition of the blast furnace gas. Secondly, when the low-calorific-value blast furnace gas rises through the two pairs of constricted sections, it can also promote secondary mixing of the blast furnace gas. This not only ensures smooth ignition and stable combustion of the low-calorific-value gas inside the furnace, but also improves the uniformity of flue gas temperature distribution inside the furnace, reduces temperature fluctuations when the flue gas is discharged, ensures the normal and efficient operation of the boiler, and thus ensures the stable operation of the entire power generation system.

[0022] Second, this invention improves the internal structure of the horizontal flue by setting a turbulence section between the screen-type superheater and the high-temperature reheater. After the blast furnace gas is fully combusted inside the furnace, a large amount of high-temperature flue gas is generated. After entering the horizontal flue, the high-temperature flue gas passes through the screen-type superheater, the turbulence section, the high-temperature reheater, and the high-temperature superheater in sequence. The screen-type superheater absorbs the heat in the high-temperature flue gas in advance, which can reduce the temperature of the high-temperature flue gas and generate steam using this heat. Subsequently, the high-temperature flue gas enters the turbulence section and passes through the diverter plate and the converger plate in sequence. The high-temperature flue gas is continuously diverted, deflected, and collided, and is constantly mixed in this process to average the flue gas temperature. This solves the problem of large temperature difference between the two sides of the horizontal flue and prevents the high-temperature reheater and high-temperature superheater on the side with higher flue gas temperature from overheating, ensuring the long-term safe and stable operation of the boiler, and thus ensuring the stable operation of the entire power generation system.

[0023] In summary, this invention incorporates two pairs of constricted sections within the furnace to ensure a favorable combustion atmosphere for the blast furnace gas in the main combustion chamber, thereby improving combustion efficiency and uniformity of flue gas temperature distribution within the furnace. This reduces temperature differences between different parts, minimizes temperature fluctuations during flue gas discharge, and ensures stable steam generation, normal boiler operation, and the overall normal operation of the power generation system. Secondly, by incorporating turbulence sections within the horizontal flue, high-temperature flue gases can collide, converge, and mix, averaging temperatures across the flue and reducing temperature differences. This prevents the risk of overheating in the high-temperature reheater and superheater on one side of the horizontal flue, ensuring the long-term safe and stable operation of the entire power generation system. This invention offers advantages such as minimal flue gas temperature fluctuations, reduced risk of overheating in the high-temperature reheater and superheater, and highly efficient and stable operation. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0025] Figure 2 This is a top view of the horizontal flue 2 in this invention.

[0026] In the diagram: 1-furnace, 2-horizontal flue, 3-tail flue, 4-screen superheater, 5-high temperature reheater, 6-high temperature superheater, 7-low temperature reheater, 8-low temperature superheater, 9-economizer, 10-air preheater, 11-shrinkage, 12-main combustion chamber, 13-auxiliary combustion chamber, 14-burnout chamber, 15-burner, 16-diverter plate, 17-converging plate, 18-steam turbine, 19-generator, 20-condenser, 21-condensate pump, 22-deaerator, 23-steam buffer tank, 24-gas preheater, 25-steam drum. Implementation

[0027] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention are within the protection scope of the present invention.

[0028] like Figures 1-2As shown, the ultra-high temperature subcritical gas power generation system for steel plants described in this invention includes a boiler, a steam drum 25, and a generator set. Both the steam drum 25 and the generator set are existing technologies. The steam drum 25 is used for water storage and for gas-liquid separation of the mixture of steam and water. The boiler wall is a water-cooled wall structure. The boiler includes a furnace 1, a horizontal flue 2, and a tail flue 3 connected in sequence. A screen-type superheater 4, a high-temperature reheater 5, and a high-temperature superheater 6 are sequentially arranged along the flue gas flow direction in the horizontal flue 2. Generally, the screen-type superheater 4 is located directly above the furnace 1. A low-temperature reheater 7, a low-temperature superheater 8, an economizer 9, and an air preheater are sequentially arranged along the flue gas flow direction in the tail flue 3. 10. Two pairs of constricted waists 11 are arranged at intervals at the bottom of the furnace 1. Each pair of constricted waists 11 is symmetrically arranged on two opposite side walls of the furnace 1. The cross-sectional shape of the constricted waists 11 is an arch shape that shrinks inward into the furnace 1. The two pairs of constricted waists 11 divide the interior of the furnace 1 from bottom to top into a main combustion chamber 12, an auxiliary combustion chamber 13 and a burnout chamber 14. Burners 15 are respectively arranged on the side walls of the main combustion chamber 12 and the auxiliary combustion chamber 13. A turbulence section is arranged between the screen-type superheater 4 and the high-temperature reheater 5. In the turbulence section, a flow divider 16 and a pair of flow convergent plates 17 are alternately arranged. The flow divider 16 is located in the middle of the turbulence section, and the flow convergent plates 17 are symmetrically arranged on both sides of the turbulence section.

[0029] This invention improves the structure of the boiler furnace 1 by incorporating two pairs of constricted sections 11 within the furnace 1. Each pair of constricted sections 11 is symmetrically positioned on opposite side walls of the furnace 1. The cross-sectional shape of the constricted sections 11 is an arch shape that tapers inwards into the furnace 1. These two pairs of constricted sections 11 divide the internal space of the furnace 1 into relatively independent main combustion chamber 12, auxiliary combustion chamber 13, and burnout chamber 14. The main combustion chamber 12 ensures complete combustion of the blast furnace gas. The auxiliary combustion chamber 13 serves two purposes: firstly, it appropriately increases the combustion point of the blast furnace gas, promoting its combustion; secondly, it separates the main combustion chamber 12 from the burnout chamber 14, ensuring the formation of a high-temperature zone within the main combustion chamber 12 and guaranteeing that the low-calorific-value blast furnace gas can ignite and burn stably within the main combustion chamber 12. The burnout chamber 14 ensures that the blast furnace gas that has not been fully combusted in the main combustion chamber 12 and auxiliary combustion chamber 13 is burned as completely as possible within the burnout chamber 14. The constriction 11 in this invention can also form a radiating arch, allowing heat to be concentrated near the nozzle of the burner 15, heating the fuel that has just entered the main combustion chamber 12 and the auxiliary combustion chamber 13, ensuring that the blast furnace gas can ignite smoothly. Secondly, when the low-calorific-value blast furnace gas in the furnace 1 rises through the two pairs of constrictions 11, it can also promote secondary mixing of these blast furnace gases, which can not only ensure the smooth ignition and stable combustion of the low-calorific-value gas in the furnace 1, but also improve the uniformity of the flue gas temperature distribution in the furnace, reduce the temperature fluctuation when the flue gas is discharged, ensure the normal and efficient operation of the boiler, and thus ensure the stable operation of the entire power generation system.

[0030] This invention improves the internal structure of the horizontal flue 2 by setting a turbulence section between the screen-type superheater 4 and the high-temperature reheater 5. After the blast furnace gas is fully combusted inside the furnace 1, a large amount of high-temperature flue gas is generated. After entering the horizontal flue 2, the high-temperature flue gas passes through the screen-type superheater 4, the turbulence section, the high-temperature reheater 5, and the high-temperature superheater 6 in sequence. The screen-type superheater 4 absorbs the heat in the high-temperature flue gas in advance, which can reduce the temperature of the high-temperature flue gas and generate steam. Then the high-temperature flue gas enters the turbulence section and passes through the diverter plate 16 and the converging plate 17 in sequence. The structure is simple, and the high-temperature flue gas is continuously diverted, deflected, and collided, and is continuously mixed in this process to average the flue gas temperature. This solves the problem of large temperature difference between the two sides of the horizontal flue 2 and prevents the high-temperature reheater 5 and high-temperature superheater 6 on the side with higher flue gas temperature from overheating, ensuring the long-term safe and stable operation of the boiler, and thus ensuring the stable operation of the entire power generation system.

[0031] The generator set includes a connected steam turbine 18 and a generator 19, both of which are existing equipment. Steam drives the rotor of the steam turbine 18 to rotate, and the rotor drives the generator 19 to generate electricity. The exhaust steam outlet of the low-pressure cylinder of the steam turbine 18 is sequentially connected to a condenser 20, a condensate pump 21, and a deaerator 22. The condenser 20 liquefies the exhaust steam discharged from the steam turbine 18 into water at approximately 40°C, improving water resource utilization efficiency and reducing water waste. The deaerator 22 removes oxygen from the condensate, and the outlet of the deaerator 22 is connected to the inlet of the economizer 9. The outlet of the economizer 9 is connected to the steam drum 25. The economizer 9 uses the waste heat of the flue gas to preheat the condensate, thereby increasing the condensate temperature and improving the vaporization efficiency of the condensate. The steam outlet of the high-pressure cylinder of the steam turbine 18 is connected to the low-temperature reheater 7. The steam outlet of the low-temperature reheater 7 is connected to the high-temperature reheater 5. The steam outlet of the high-temperature reheater 5 is connected to the steam inlet of the steam turbine 18. The low-temperature reheater 7 heats the low-temperature and low-pressure steam discharged from the high-pressure cylinder of the steam turbine 18. Subsequently, the high-temperature reheater 5 heats the steam again, thereby improving the steam power generation efficiency.

[0032] The burner 15 installed on the side wall of the main combustion chamber 12 is a double swirl burner. Blast furnace gas and air can form a rotating jet in the double swirl burner. The rotating jet can form a high-temperature flue gas recirculation zone that is conducive to ignition and make the airflow strongly mixed, which is beneficial to improving the combustion efficiency of blast furnace gas. The burner 15 installed on the side wall of the auxiliary combustion chamber 13 is a direct current burner. The nozzle of the direct current burner is arranged at an angle downward. The airflow ejected by the direct current burner is a direct current jet. When the direct current burner is arranged at an angle downward, it can shoot the hot airflow generated by the combustion of blast furnace gas into the main combustion chamber 12, thereby increasing the temperature in the main combustion chamber 12, ensuring the high temperature zone in the main combustion chamber 12, and ultimately ensuring that the low-calorific-value blast furnace gas can be fully burned in the main combustion chamber 12.

[0033] Preferably, the water-cooled wall includes a connected upper and lower part, with the lower part being a spiral coil structure and the upper part being a vertical coil structure. The blast furnace gas burns in the main combustion chamber 12 and the auxiliary combustion chamber 13, resulting in a higher temperature in the lower part of the water-cooled wall. The spiral coil structure of the water-cooled wall surrounds the main combustion chamber 12 and the auxiliary combustion chamber 13. Each tube in the spiral coil structure can pass through the perimeter of the furnace 1 and the burner 15, ensuring the uniformity and continuity of heat absorption by the entire water-cooled wall tube. Therefore, a spiral coil structure is used in the lower part of the water-cooled wall, while the upper part of the furnace is the combustion chamber, where the temperature is relatively low. A vertical coil structure water-cooled wall is used in this area to meet the usage requirements and is easier to install.

[0034] The cross-sectional area of ​​the horizontal flue 2 is larger than that of the furnace 1. The high-temperature flue gas generated by the combustion of blast furnace gas in the furnace 1 flows upward into the horizontal flue 2. Since the cross-sectional area of ​​the horizontal flue 2 is larger than that of the furnace 1, the flow velocity of the high-temperature flue gas can be reduced, preventing the high-temperature reheater 5 and the high-temperature superheater 6 from overheating. At the same time, the flow of high-temperature flue gas from the furnace 1 with a smaller cross-section into the horizontal flue 2 with a larger cross-section is also conducive to the mixing of high-temperature flue gas, thereby reducing the temperature difference in various parts of the horizontal flue 2.

[0035] Preferably, the total length of each pair of constricted waists 11 extending into the furnace 1 accounts for one-third to one-half of the length of the furnace 1. If the total length of the constricted waists 11 extending into the furnace 1 is too short, it will not achieve the purpose of mixing gas, averaging flue gas temperature, and radiant heat. Conversely, if the total length of the constricted waists 11 extending into the furnace 1 is too long, it may lead to an excessively small cross-section inside the furnace 1, increasing the resistance to airflow inside the furnace 1 and affecting the combustion of blast furnace gas inside the furnace 1. The total length of each pair of constricted waists 11 extending into the furnace 1 can be determined according to the actual situation.

[0036] The operation method of the ultra-high temperature subcritical gas power generation system in a steel plant according to the present invention is characterized by including the following steps:

[0037] ① Combustion of blast furnace gas in furnace 1: Blast furnace gas and air are simultaneously delivered to each burner 15. The burners 15 inject the gas into the main combustion chamber 12 and the auxiliary combustion chamber 13 respectively and ignite it. The high-temperature flue gas and some of the incompletely burned blast furnace gas continuously flow upward and are fully burned in the burnout chamber 14. The high-temperature flue gas flows into the horizontal flue 2. The water in the steam drum 25 flows into the water-cooled wall. The water absorbs the heat in the furnace 1 to form steam and then flows back to the steam drum 25.

[0038] ② Steam heating in horizontal flue 2: The high-temperature flue gas generated in step ① flows into horizontal flue 2. At the same time, some water in steam drum 25 flows through screen-type superheater 4, vaporizes and forms water vapor, which flows back to steam drum 25. The water vapor in steam drum 25 is first sent to low-temperature superheater 8 for preliminary heating, and then sent to high-temperature superheater 6 for heating to generate superheated steam. The temperature of the superheated steam is not lower than 570℃ and the pressure is not lower than 17.3MPa. The superheated steam is ultra-high temperature and in a subcritical state. The heat absorption ratio of screen-type superheater 4 is 8.1% to 8.8%, the heat absorption ratio of low-temperature superheater 8 is 10.5% to 11.8%, and the heat absorption ratio of high-temperature superheater 6 is 10.9% to 12.1%. The heat absorption ratio mainly refers to the proportion of the total heat absorption of a corresponding component in the boiler. For example, the heat absorption ratio of a screen-type superheater 4 is 8.1% to 8.8%. There are many factors that affect the heat absorption ratio, mainly based on the heating surface of the corresponding component, and of course, it is also related to the position of the corresponding component in the boiler.

[0039] ③ Power Generation: The superheated steam generated in step ② is transported to the generator set for power generation. Simultaneously, high-temperature flue gas flows downward from the top of the tail flue 3, transporting the steam output from the high-pressure cylinder of the generator set to the low-temperature reheater 7 for preliminary heating. The heated steam is then sent to the high-temperature reheater 5 for further heating to generate reheated steam. The temperature of the reheated steam is not lower than 568℃ and the pressure is not lower than 3.8MPa. This reheated steam is then sent to the generator set for power generation. A steam buffer tank 23 is installed on the pipeline between the steam outlet of the high-temperature superheater 6 and the steam inlet of the turbine 18 of the generator set. In actual implementation, it was found that the superheated steam discharged from the high-temperature reheater 5 still has some fluctuations, and there are still some differences in the steam quantity and steam temperature. To solve this problem, the steam buffer tank 23 is installed. The superheated steam discharged from the high-temperature reheater 5 enters the steam buffer tank 23, which can play a buffering role and can output superheated steam at a constant pressure and quantity. At the same time, the superheated steam is transported to the steam buffer tank 23, which can also play a mixing role, further averaging the temperature of the superheated steam, ensuring the stable operation of the subsequent generator set, and improving the power generation efficiency.

[0040] ④ Waste heat absorption in the tail flue 3: The condensate discharged from the generator set is sent to the economizer 9 for preliminary heating. The heated water is then sent to the steam drum 25, while cold air is sent to the air preheater 10 for preheating, raising the air temperature to 200℃~300℃. After preheating, the air is sent to the burner 15. A gas preheater 24 is installed in the tail flue 3 below the air preheater 10. The gas preheater 24 can use an existing tubular heat exchanger. The outlet of the gas preheater 24 is connected to the inlet of the burner 15, so that the temperature of the preheated gas rises to above 160℃, while the flue gas temperature drops to below 140℃.

[0041] ⑤ Flue gas emission: After the residual heat is absorbed in step ④, the flue gas temperature drops to below 200℃ before being discharged.

[0042] Verification has shown that the steel plant ultra-high temperature subcritical gas power generation system and its operation method described in this invention, through the setting of two pairs of narrow waists 11, ensures that the blast furnace gas has a better combustion atmosphere in the main combustion chamber 12, improves the combustion efficiency of the blast furnace gas, and improves the uniformity of flue gas temperature distribution in the furnace 1, reduces the temperature difference between different parts, reduces the temperature fluctuation when the flue gas is discharged, and ensures stable steam generation, normal boiler operation, and normal operation of the entire power generation system. Secondly, by setting a turbulence section in the horizontal flue 2, the high-temperature flue gas can collide, converge, and mix with each other in the turbulence section, which can level the temperature of different parts in the flue 2, reduce the temperature difference between different parts, and prevent the current situation where the temperature on one side of the horizontal flue 2 is too high, which may cause the high-temperature reheater 5 and high-temperature superheater 6 on that side to overheat, thus ensuring that the entire power generation system can operate safely and stably for a long time. This invention has the advantages of small flue gas temperature fluctuations, less tendency for overheating problems in high-temperature reheaters and high-temperature superheaters, and efficient and stable operation. The power generation efficiency is not less than 41.5%, which is nearly 6% higher than existing high-temperature and high-pressure power generation technologies, and has a good energy-saving and consumption-reducing effect.

Claims

1. A steel plant ultra-high temperature subcritical gas power generation system, comprising a boiler, a steam drum (25), and a generator set, wherein the boiler wall is a water-cooled wall structure, and the boiler comprises a furnace (1), a horizontal flue (2), and a tail flue (3) connected in sequence, wherein a screen-type superheater (4), a high-temperature reheater (5), and a high-temperature superheater (6) are arranged in sequence along the flue gas flow direction in the horizontal flue (2), and a low-temperature reheater (7), a low-temperature superheater (8), an economizer (9), and an air preheater (10) are arranged in sequence along the flue gas flow direction in the tail flue (3), characterized in that... The lower part of the furnace (1) is provided with two pairs of waists (11) spaced apart vertically. Each pair of waists (11) is symmetrically arranged on two opposite side walls of the furnace (1). The cross-sectional shape of the waists (11) is an arch shape that shrinks into the furnace (1). The two pairs of waists (11) divide the interior of the furnace (1) from bottom to top into a main combustion chamber (12), an auxiliary combustion chamber (13) and a burnout chamber (14). Burners (15) are respectively arranged on the side walls of the main combustion chamber (12) and the auxiliary combustion chamber (13). A turbulence section is provided between the screen-type superheater (4) and the high-temperature reheater (5). A flow divider (16) and a pair of flow convergent plates (17) are alternately arranged in the turbulence section. The flow divider (16) is located in the middle of the turbulence section, and the flow convergent plates (17) are symmetrically arranged on both sides of the turbulence section.

2. The ultra-high temperature subcritical gas power generation system for steel plants according to claim 1, characterized in that... The generator set includes a turbine (18) and a generator (19) connected together. The exhaust steam outlet of the low-pressure cylinder of the turbine (18) is connected in sequence to a condenser (20), a condensate pump (21) and a deaerator (22). The outlet of the deaerator (22) is connected to the inlet of the economizer (9). The outlet of the economizer (9) is connected to the steam drum (25). The steam outlet of the high-pressure cylinder of the turbine (18) is connected to the low-temperature reheater (7). The steam outlet of the low-temperature reheater (7) is connected to the high-temperature reheater (5). The steam outlet of the high-temperature reheater (5) is connected to the steam inlet of the turbine (18).

3. The ultra-high temperature subcritical gas power generation system for steel plants according to claim 1, characterized in that... The burner (15) installed on the side wall of the main combustion chamber (12) is a double swirl burner, and the burner (15) installed on the side wall of the auxiliary combustion chamber (13) is a direct current burner, and the nozzle of the direct current burner is arranged inclined downward.

4. The ultra-high temperature subcritical gas power generation system for steel plants according to claim 1, characterized in that... The water-cooled wall includes a connected upper and lower part, the lower part being a spiral tube coil structure and the upper part being a vertical tube coil structure.

5. A steel plant ultra-high temperature subcritical gas power generation system according to claim 1, characterized in that... The cross-sectional area of ​​the horizontal flue (2) is greater than that of the furnace (1).

6. A steel plant ultra-high temperature subcritical gas power generation system according to claim 1, characterized in that... The total length of each pair of waists (11) extending into the furnace chamber (1) accounts for one-third to one-half of the length of the furnace chamber (1).

7. The operation method of an ultra-high temperature subcritical gas power generation system in a steel plant according to claim 2, characterized in that: Includes the following steps: ① Combustion of gas in the furnace (1): Blast furnace gas and air are simultaneously delivered to each burner (15), and the burners (15) inject them into the main combustion chamber (12) and the auxiliary combustion chamber (13) respectively and ignite them. The high-temperature flue gas and some of the blast furnace gas that is not fully burned continuously flow upward and are fully burned in the burnout chamber (14). The high-temperature flue gas flows into the horizontal flue (2), and the water in the steam drum (25) flows into the water-cooled wall. The water absorbs the heat in the furnace (1) to form water vapor and then flows back to the steam drum (25). ② Steam heating in the horizontal flue (2): The high-temperature flue gas generated in step ① flows into the horizontal flue (2), and at the same time, part of the water in the steam drum (25) flows through the screen-type superheater (4), vaporizes and forms water vapor which flows back to the steam drum (25). The water vapor in the steam drum (25) is first sent to the low-temperature superheater (8) for preliminary heating, and then sent to the high-temperature superheater (6) for heating to generate superheated steam. The temperature of the superheated steam is not lower than 570℃ and the pressure is not lower than 17.3MPa. ③ Power generation: The superheated steam generated in step ② is transported to the generator set for power generation. At the same time, the high-temperature flue gas flows downward from the top of the tail flue (3) and the steam output from the high-pressure cylinder of the generator set is transported to the low-temperature reheater (7) for preliminary heating. The heated steam is then sent to the high-temperature reheater (5) for heating to generate reheated steam. The temperature of the reheated steam is not lower than 568°C and the pressure is not lower than 3.8 MPa. It is then sent to the generator set for power generation. ④ Waste heat absorption in the tail flue (3): The condensate discharged from the generator set is sent to the economizer (9) for preliminary heating. The heated water is sent to the steam drum (25). At the same time, cold air is sent to the air preheater (10) for preheating, so that the air temperature reaches 200℃~300℃. After preheating, it is sent to the burner (15). ⑤ Flue gas emission: After the residual heat is absorbed in step ④, the flue gas temperature drops to below 200℃ before being discharged.

8. The operation method of a steel plant ultra-high temperature subcritical gas power generation system according to claim 7, characterized in that: In step ③, a steam buffer tank (23) is installed on the pipeline between the steam outlet of the high-temperature superheater (6) and the steam inlet of the generator turbine (18).

9. The operation method of a steel plant ultra-high temperature subcritical gas power generation system according to claim 7, characterized in that: In step ④, a gas preheater (24) is installed in the tail flue (3) below the air preheater (10). The gas outlet of the gas preheater (24) is connected to the gas inlet of the burner (15), so that the temperature of the gas after preheating rises to above 160°C, while the flue gas temperature drops to below 140°C.

10. The operation method of an ultra-high temperature subcritical gas power generation system in a steel plant according to claim 7, characterized in that: In step ②, the heat absorption ratio of the screen-type superheater (4) is 8.1% to 8.8%, the heat absorption ratio of the low-temperature superheater (8) is 10.5% to 11.8%, and the heat absorption ratio of the high-temperature superheater (6) is 10.9% to 12.1%.

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