Flue gas recirculation combined low-order regenerative steam extraction energy closed efficiency raising system
By constructing a flue gas recirculation composite low-order regenerative steam extraction system in coal-fired power units, the low-temperature flue gas is heated by steam extraction from the turbine and then recirculated to the boiler, solving the problem of high coal consumption under medium and low load conditions, realizing full utilization of the latent heat of extraction steam and reducing cold source losses, thus improving the thermal economy of the unit.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- NORTH CHINA POWER ENG
- Filing Date
- 2025-05-19
- Publication Date
- 2026-05-12
AI Technical Summary
Existing coal-fired power units have high coal consumption under medium and low load conditions, making it difficult to effectively utilize the latent heat of steam extracted from the turbine, resulting in serious cold source losses and reducing the thermal economy of the units.
A closed-loop energy efficiency improvement system is constructed by constructing a flue gas recirculation combined with low-order regenerative steam extraction. This system involves setting up recirculating flue gas pipes and flue gas steam heaters in the boiler flue gas pipes, and using the steam extraction system of the low-pressure cylinder of the steam turbine to heat the low-temperature flue gas, which then enters the furnace to form a low-temperature flue gas recirculation system. This fully utilizes the latent heat of the extracted steam and reduces the loss of cold source.
It improves the thermal economy of the unit at low and medium loads and rated loads, reduces cold source losses, fully utilizes the latent heat of extracted steam, and reduces coal consumption. In particular, it significantly improves power generation efficiency under low and medium load conditions.
Smart Images
Figure CN224228736U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of coal-fired power generation technology, specifically relating to an energy-closed efficiency improvement system for flue gas recirculation combined with low-order regenerative steam extraction. Background Technology
[0002] Traditional coal-fired power plants mainly consider efficiency under rated operating conditions, but coal consumption increases significantly under medium and low load conditions.
[0003] Unit efficiency primarily depends on boiler efficiency and turbine absolute internal efficiency. As load decreases, boiler efficiency generally decreases only slightly, while turbine absolute internal efficiency shows a significant downward trend. Taking a 1,000 kW wet-cooled unit as an example, boiler efficiency drops from 95.4% of rated operating conditions to 94.63% of rated operating conditions at 30%; turbine absolute internal efficiency decreases from 51.4% of rated operating conditions to 46.6% of rated operating conditions at 30% and 44.5% of rated operating conditions at 20%. This demonstrates that improving unit efficiency at low and medium loads hinges on increasing turbine absolute internal efficiency at these loads.
[0004] The absolute internal efficiency of a steam turbine reflects the actual thermal efficiency of the turbine unit's thermodynamic cycle. The heat input from the boiler to the turbine, after deducting the portion used for power generation, is manifested as a cold source loss, i.e., the heat released into the environment by the exhaust steam from the low-pressure cylinder of the turbine through the condenser. The absolute efficiency of a steam turbine is generally around 50%, with cold source losses accounting for approximately 50%.
[0005] Steam generates electricity by performing work within a steam turbine, primarily utilizing the energy of its superheated portion. Latent heat constitutes the majority of steam's enthalpy, while the enthalpy of the superheated portion accounts for a smaller portion. Taking ultra-supercritical main steam with parameters of 28 MPa.a and 600℃ as an example, its enthalpy is 3465.7 kJ / kg, the enthalpy of the low-pressure cylinder exhaust is 2417.9 kJ / kg, and the effective enthalpy drop for work is 1047.8, accounting for 30% of the total enthalpy. Fully utilizing the latent heat of steam while minimizing exhaust to the low-pressure cylinder is an important direction for improving the efficiency of coal-fired power units. The steam turbine extraction and regenerative heating system, which fully utilizes the latent heat of steam to heat condensate and feedwater, is a typical application for reducing cold source losses.
[0006] Common approaches to returning the latent heat of extracted steam to the boiler include heating the air, heating the economizer inlet feedwater, or heating the raw coal. However, these approaches are all insufficient to reduce the amount of steam discharged from the cold end and minimize the loss of cold source heat. Utility Model Content
[0007] The technical problem to be solved by this utility model is to provide an energy-closed efficiency improvement system for flue gas recirculation combined with low-order regenerative steam extraction, which solves the problem of high coal consumption of existing coal-fired power units under medium and low load conditions. Through system structure innovation and the construction of a low-temperature carrier that can recover the latent heat of the unit's extraction steam, the latent heat of the steam turbine extraction is fully utilized, the cold source loss is reduced, and the thermal economy of the unit under medium and low loads is improved.
[0008] According to the technical solution of this utility model, this utility model provides an energy-closed efficiency improvement system for flue gas recirculation combined with low-order regenerative steam extraction, including a boiler, the boiler being connected to a boiler feedwater pipe and a boiler flue gas pipe; a multi-stage low-pressure heater is installed in the boiler feedwater pipe; a low-pressure regenerative steam extraction pipe is connected to the intermediate-pressure cylinder and / or low-pressure cylinder of the steam turbine, and the low-pressure regenerative steam extraction pipe is correspondingly connected to the low-pressure heater; an air preheater, a dust collector, an induced draft fan, a desulfurization device, and a chimney are sequentially arranged in the boiler flue gas pipe along the flue gas conveying direction; a recirculated flue gas pipe is led out from the boiler flue gas pipe between the downstream of the dust collector and the upstream of the desulfurization device, and the output end of the recirculated flue gas pipe is connected to the furnace of the boiler, and one or more flue gas steam heaters connected in series are installed in the recirculated flue gas pipe; a flue gas heating steam extraction pipe is led out from the low-pressure regenerative steam extraction pipe, and the output end of the flue gas heating steam extraction pipe is connected to the flue gas steam heater.
[0009] In some implementations, the inlet of the recirculated flue gas duct is located between the induced draft fan and the desulfurization unit.
[0010] In some implementations, the inlet of the recirculated flue gas duct is located between the dust collector and the induced draft fan, and a variable frequency recirculation fan is installed in the recirculated flue gas duct.
[0011] In some embodiments, the outlet of the recirculated flue gas duct is located on the front and rear walls of the furnace below the lowest burner of the boiler and above the inflection point of the cold ash hopper; or, the outlet of the recirculated flue gas duct is located on the front and rear walls of the furnace above the highest burner of the boiler and near the burnout air.
[0012] In some implementations, an output electrically adjustable baffle is provided at the output end of the recirculated flue gas duct.
[0013] In some implementations, an input electric shut-off baffle is provided at the inlet end of the recirculated flue gas duct, and a valve is provided in the flue gas heating extraction duct.
[0014] In some embodiments, the number of flue gas steam heaters is N, where N is a positive integer. The low-pressure regenerative steam extraction pipeline is the Nth stage steam extraction pipeline at the end of the medium-pressure cylinder. The flue gas steam heaters correspond one-to-one with the low-pressure regenerative steam extraction pipelines. The N low-pressure regenerative steam extraction pipelines are sequentially connected to the N flue gas steam heaters arranged along the flue gas conveying direction in order of increasing extraction pressure.
[0015] In some embodiments, the boiler feedwater pipeline is sequentially equipped with a multi-stage low-pressure heater, a deaerator, a feedwater pump, and a multi-stage high-pressure heater along the water transport direction. The multi-stage low-pressure heater includes low-pressure heater No. 9, low-pressure heater No. 8, low-pressure heater No. 7, low-pressure heater No. 6, and low-pressure heater No. 5, arranged sequentially along the water transport direction. The multi-stage high-pressure heater includes high-pressure heater No. 3, high-pressure heater No. 2, and high-pressure heater No. 1, arranged sequentially along the water transport direction. There are three flue gas steam heaters. The low-pressure regenerative steam extraction pipeline consists of a five-section extraction pipeline and a six-section extraction pipe of the intermediate-pressure cylinder. The system includes seven extraction steam pipes; the fifth extraction steam pipe is connected to the No. 5 low-pressure heater, the sixth extraction steam pipe is connected to the No. 6 low-pressure heater, and the seventh extraction steam pipe is connected to the No. 7 low-pressure heater; the flue gas heating extraction steam pipe drawn from the fifth extraction steam pipe is connected to the downstream flue gas steam heater among the three flue gas steam heaters, the flue gas heating extraction steam pipe drawn from the sixth extraction steam pipe is connected to the middle flue gas steam heater among the three flue gas steam heaters, and the flue gas heating extraction steam pipe drawn from the seventh extraction steam pipe is connected to the upstream flue gas steam heater among the three flue gas steam heaters.
[0016] Compared with the prior art, the beneficial technical effects of this utility model are as follows:
[0017] This utility model's energy-closed efficiency improvement system, which combines flue gas recirculation with low-level regenerative steam extraction, aims to enhance the thermal economy of the unit at low and medium loads. It constructs a low-temperature flue gas recirculation system, utilizing the regenerative steam extraction system of the turbine's low-pressure cylinder to heat the low-temperature flue gas. The heated flue gas is then sent into the furnace for the next cycle. This system uses the low-temperature flue gas as a carrier for latent heat heating during steam extraction, i.e., a heat recovery carrier, entering the furnace in a recirculating manner. By setting up one or more stages of stepped steam-flue gas heaters, it fully utilizes the latent heat of the turbine's steam extraction, reduces the exhaust volume of the low-pressure cylinder, reduces cold source losses, and improves the thermal economy of the unit at low and medium loads, and even at rated loads. This represents an innovation and restructuring of the boiler-turbine system, with strong technical and economic feasibility, making it worthy of development and promotion. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the system structure of an embodiment provided by this utility model.
[0019] Figure 2 This is a schematic diagram of the system structure of another embodiment provided by this utility model.
[0020] Explanation of reference numerals in the attached figures:
[0021] 1. Boiler; 11. Boiler feedwater pipe; 12. Boiler flue gas pipe; 121. Air preheater; 122. Dust collector; 123. Induced draft fan; 124. Desulfurization unit; 125. Chimney; 21. High-pressure cylinder; 22. Medium-pressure cylinder; 23. Low-pressure cylinder; 24. Generator; 31. Low-pressure regenerative steam extraction pipe; 32. Flue gas heating steam extraction pipe; 4. Recirculated flue gas pipe; 41. Flue gas steam heater; 42. Output power 43. Variable frequency recirculation fan; 5. Deaerator; 6. Feed water pump; 7. No. 5 low-pressure heater; 82. No. 6 low-pressure heater; 83. No. 7 low-pressure heater; 84. No. 8 low-pressure heater; 85. No. 9 low-pressure heater; 91. No. 1 high-pressure heater; 92. No. 2 high-pressure heater; 93. No. 3 high-pressure heater; 101. Primary air fan; 102. Secondary air fan. Detailed Implementation
[0022] This utility model provides an energy-closed efficiency improvement system for flue gas recirculation combined with low-order regenerative steam extraction, which solves the problem of high coal consumption in existing coal-fired power units under medium and low load conditions. Through system structure innovation and the construction of a low-temperature carrier that can recover the latent heat of the unit's extraction steam, the system makes full use of the latent heat of the steam turbine extraction steam, reduces cold source losses, and improves the thermal economy of the unit under medium and low load conditions.
[0023] Please see Figure 1 This utility model discloses a closed-loop energy efficiency improvement system for flue gas recirculation combined with low-level regenerative steam extraction, comprising a boiler 1, which is connected to a boiler feedwater pipe 11 and a boiler flue gas pipe 12. The boiler feedwater pipe 11 is equipped with multi-stage low-pressure heaters. The turbine includes a high-pressure cylinder 21, an intermediate-pressure cylinder 22, a low-pressure cylinder 23, and a generator 24 connected in series. A low-pressure regenerative steam extraction pipe 31 is connected to the intermediate-pressure cylinder 22 and / or the low-pressure cylinder 23 of the turbine. The low-pressure regenerative steam extraction pipe 31 is correspondingly connected to the low-pressure heaters, using suitable steam to heat the boiler feedwater through the low-pressure heaters.
[0024] An air preheater 121, a dust collector 122, an induced draft fan 123, a desulfurization device 124, and a chimney 125 are sequentially arranged along the flue gas conveying direction in the boiler flue gas duct 12. A recirculating flue gas duct 4 is led out from the boiler flue gas duct 12 between the dust collector 122 and the desulfurization device 124. The output end of the recirculating flue gas duct 4 is connected to the furnace of the boiler 1. One or more flue gas steam heaters 41 connected in series are installed in the recirculating flue gas duct 4. A flue gas heating steam extraction duct 32 is led out from the low-pressure regenerative steam extraction duct 31. The output end of the flue gas heating steam extraction duct 32 is connected to the flue gas steam heater 41, so that a portion of the extraction steam is drawn from the low-pressure regenerative steam extraction duct 31 and enters the flue gas steam heater 41 to heat the flue gas circulating to the furnace of the boiler 1.
[0025] This scheme primarily establishes a low-temperature flue gas recirculation system by adding a recirculating flue gas pipeline 4, a flue gas steam heater 41, and a flue gas heating extraction steam pipeline 32. This system extracts flue gas between the downstream of the dust collector and the upstream of the desulfurization system. Simultaneously, based on the flue gas temperature, low-pressure steam is extracted from the turbine's low-pressure cylinder regenerative system. The first-stage extraction is constrained by meeting the heat exchanger terminal differential pressure; lower extraction pressures result in better economic efficiency and create conditions for the stepped heating of the flue gas steam heater. The number of stages is constrained by achieving the coal consumption reduction target (e.g., a 2g / kWh reduction in power generation coal consumption under 50% operating conditions, or even higher), while also considering investment costs. This utilizes the low-temperature flue gas as a carrier for recovering latent heat of steam and reducing cold source losses. Due to the low initial flue gas temperature, a first-stage extraction steam pressure above 0.1 MPa is sufficient to meet engineering requirements, and the unit has suitable extraction points. The flue gas recirculation suction point, i.e., the input end of the recirculated flue gas duct 4, is located after the dust collector 122. This not only results in low flue gas temperature but also low dust content, creating conditions for using a low-cost, highly durable recirculation fan. After implementing flue gas recirculation, this scheme increases the flue gas flow rate from the furnace inlet to the tail-end heating surface, generally enhancing heat exchange at the heating surface and increasing the working fluid outlet temperature, thus positively impacting boiler operation. Furthermore, this scheme will not affect existing boilers and auxiliary systems, including their existing capacity and operational adaptability.
[0026] Furthermore, such as Figure 1 In the illustrated embodiment, the input end of the recirculated flue gas duct 4 (in other words, the flue gas extraction point) is located between the induced draft fan 123 and the desulfurization unit 124, thus utilizing the induced draft fan 123 as the power source for flue gas circulation. This scheme must fully consider the sensitivity of flue gas recirculation volume adjustment with load fluctuations. Its advantage is that it eliminates the need for an additional recirculation fan within the recirculated flue gas duct 4, resulting in lower costs and reduced investment. Generally, under medium to low load conditions, the flue gas temperature at the inlet of the induced draft fan 123 is around 85°C, and the flue gas temperature at the outlet of the induced draft fan 123 is around 90°C. After absorbing the latent heat of steam, the flue gas temperature at the output end of the recirculated flue gas duct 4 can reach approximately 150°C.
[0027] Considering the sensitivity of the low-temperature flue gas recirculation system to load adjustments, it is preferable to install a recirculation fan at the inlet of the induced draft fan as the power source for flue gas circulation. Figure 2 In another embodiment shown, the input end of the recirculated flue gas duct 4 is located between the dust collector 122 and the induced draft fan 123, and a variable frequency recirculation fan 5 is installed in the recirculated flue gas duct 4 to track load adjustments by variable frequency speed regulation.
[0028] Taking into account the ash and slag falling, pulverized coal ignition, and stable combustion performance of coal-fired boilers, and combined with the boiler combustion method, in this embodiment, the output end of the recirculated flue gas duct 4 is located below the lowest burner of boiler 1 and above the inflection point of the cold ash hopper on the front and rear walls of the furnace. In other words, the recirculated flue gas is injected into the furnace from below the lowest burner and above the inflection point of the cold ash hopper, with the air inlets arranged on the front and rear walls of the furnace; or, the output end of the recirculated flue gas duct 4 is located above the highest burner of boiler 1, near the burnout air on the front and rear walls of the furnace. The specific final solution generally needs to be confirmed with the boiler manufacturer. As a supplementary explanation, burners are installed on the furnace walls of boiler 1, and the burners are generally multiple and arranged in multiple layers at multiple height positions; the lower part of boiler 1 is the cold ash hopper, the side wall of the cold ash hopper is inclined, and the inflection point of the inclined surface and the vertical surface is formed between the side wall of the cold ash hopper and the furnace wall.
[0029] Preferably, an output electrically adjustable damper 42 is provided at the output end of the recirculated flue gas duct 4, thereby allowing flexible adjustment of the amount of flue gas entering the boiler 1, or blocking the recirculated flue gas duct 4. More preferably, an input electrically adjustable shut-off damper 43 is provided at the input end of the recirculated flue gas duct 4, and valves are provided in the flue gas heating extraction steam duct 32. After closing both the input electrically adjustable shut-off damper 43 and all valves in the flue gas heating extraction steam duct 32, the low-temperature flue gas recirculation system is blocked. In this way, partial load can be used as the design condition as needed, mainly aiming to improve the thermal economy of the unit at low loads, while the low-temperature flue gas recirculation system is not used under rated operating conditions and higher load conditions.
[0030] Furthermore, the number of flue gas steam heaters 41 is N, where N is a positive integer of 1 or higher, such as 1, 2, 3 or 4. The low-pressure regenerative extraction steam pipe 31 is the Nth stage extraction steam pipe at the end of the intermediate-pressure cylinder 22 (i.e., the N pipes with the lowest extraction steam pressure in the extraction pipes connected to the intermediate-pressure cylinder). The flue gas steam heaters 41 correspond one-to-one with the low-pressure regenerative extraction steam pipes 31. And (for cases where N is 2 or higher), the N low-pressure regenerative extraction steam pipes 31 are connected sequentially to the N flue gas steam heaters 41 arranged along the flue gas conveying direction in order of increasing extraction steam pressure, so that the flue gas is gradually heated in a stepped manner as it flows through the N flue gas steam heaters 41.
[0031] More specifically, such as Figure 1 In the illustrated embodiment, the boiler feedwater pipeline 11 is sequentially equipped with a multi-stage low-pressure heater, a deaerator 6, a feedwater pump 7, and a multi-stage high-pressure heater along the water transport direction. The multi-stage low-pressure heaters include, sequentially arranged along the water transport direction, a No. 9 low-pressure heater 85, a No. 8 low-pressure heater 84, a No. 7 low-pressure heater 83, a No. 6 low-pressure heater 82, and a No. 5 low-pressure heater 81. The multi-stage high-pressure heaters include, sequentially arranged along the water transport direction, a No. 3 high-pressure heater 93, a No. 2 high-pressure heater 92, and a No. 1 high-pressure heater 91.
[0032] There are three flue gas steam heaters 41. The low-pressure regenerative steam extraction pipe 31 is the last three-stage steam extraction pipe of the intermediate-pressure cylinder 22, specifically the fifth, sixth, and seventh stage steam extraction pipes of the intermediate-pressure cylinder 22. The fifth stage steam extraction pipe is connected to the fifth low-pressure heater 81, the sixth stage steam extraction pipe is connected to the sixth low-pressure heater 82, and the seventh stage steam extraction pipe is connected to the seventh low-pressure heater 83. The flue gas heating steam extraction pipe 32 leading from the fifth stage steam extraction pipe is connected to the downstream flue gas steam heater 41 among the three flue gas steam heaters 41; the flue gas heating steam extraction pipe 32 leading from the sixth stage steam extraction pipe is connected to the middle flue gas steam heater 41 among the three flue gas steam heaters 41; and the flue gas heating steam extraction pipe 32 leading from the seventh stage steam extraction pipe is connected to the upstream flue gas steam heater 41 among the three flue gas steam heaters 41.
[0033] As a supplementary explanation, the specific connection and arrangement methods of each high-pressure heater, low-pressure heater, and deaerator 6 can be selected from existing technologies or other feasible methods to form a regenerative system. Generally, the extracted steam enters the high-pressure heater, low-pressure heater, deaerator 6, and flue gas steam heater 41 for heat exchange and becomes condensate, which is then output to the condenser and condensate pipe through pipelines. Common methods include staged gravity flow, but are not limited to this. In addition, the air preheater 121 is connected to a primary air duct and a secondary air duct. The primary air duct and the secondary air duct are respectively equipped with a primary air fan 101 and a secondary air fan 102. The air preheater 121 is used to heat the primary air and the secondary air. The primary air duct and the secondary air duct are connected to the boiler furnace. The more specific arrangement methods can be selected from existing technologies or other feasible methods. These specific arrangements are not improvements of this utility model, so they will not be described in detail and are not shown in the figures or are only simple illustrative examples.
[0034] Based on the system of this utility model, this utility model provides an energy-closing efficiency improvement method for flue gas recirculation combined with low-order regenerative steam extraction, which mainly includes the following contents.
[0035] This system forms a low-temperature flue gas recirculation system through a recirculated flue gas duct 4, a flue gas steam heater 41, a flue gas heating extraction steam duct 32 (and other related necessary components). During operation, the low-temperature flue gas recirculation system is only activated when the coal-fired power generation unit is operating below 50% THA. That is, the recirculated flue gas duct 4 and the flue gas heating extraction steam duct 32 are in a conductive state, extracting flue gas and steam in a predetermined manner. The flue gas is then heated by the heat of the steam in the flue gas steam heater 41 and sent into the furnace of the boiler 1. When the coal-fired power generation unit is operating under other conditions (i.e., above 50% THA), the recirculated flue gas duct 4 and the flue gas heating extraction steam duct 32 are in a blocked state, the flue gas steam heater 41 is not working, and the above-mentioned flue gas recirculation process is not performed. In a more specific embodiment, when the low-temperature flue gas recirculation system is running, the amount of recirculated flue gas in the recirculated flue gas duct 4 is 15% of the total amount of flue gas under 40% THA conditions.
[0036] It should be noted that, taking a 1,000 MW ultra-supercritical wet-cooled unit with double reheat as an example, the coal consumption for power generation under rated conditions is 264 g / kWh, and under 30% of rated conditions it is 303 g / kWh, an increase of 39 g / kWh compared to the rated conditions; under 20% of rated conditions, the coal consumption reaches 319 g / kWh, an increase of 55 g / kWh compared to the rated conditions. Another example is a 660 MW supercritical air-cooled unit with single reheat; the coal consumption for power generation under rated conditions is 295 g / kWh, and under 30% of rated conditions it reaches 335 g / kWh, an increase of 40 g / kWh compared to the rated conditions. Existing conventional coal-fired power generating units all exhibit significantly increased coal consumption under medium and low load conditions, making it difficult to meet the goals and needs of the new generation of coal-fired power plants operating at medium and low loads for extended periods. Therefore, improving the thermal economy of units under medium and low loads is particularly important.
[0037] The general considerations and problems regarding returning the latent heat of extracted steam to the boiler are as follows. The boiler's input heat comes from air, raw coal, and feedwater. Using extracted steam to heat the air system before the air preheater, such as primary and secondary cold air, will cause an increase in flue gas temperature, reducing boiler thermal efficiency and complicating the problem. Heating the air system after the air preheater, such as primary and secondary hot air, has been found in engineering practice to be difficult to achieve in engineering practice, even under low-load conditions, with primary and secondary hot air temperatures generally above 320℃, approaching the critical parameters of steam. Due to the high temperature of the heated medium, considering factors such as the air temperature rise, heat exchange end difference, and appropriate extraction steam parameter matching, it can be considered that it is difficult to achieve the goal of reducing cold-end exhaust steam volume and reducing cold source losses by heating the air through extracted steam. Even under low-load conditions, the economizer inlet feedwater temperature is generally above 240℃. Considering the high temperature of the heating medium, factors such as the feedwater temperature rise, heat exchange end difference, and appropriate extraction steam parameters, it can be concluded that it is difficult to reduce cold-end exhaust steam and minimize cold source losses by heating the economizer inlet feedwater using extraction steam. Due to the gas-solid two-phase characteristics and flammability of raw coal (pulverized coal gas flow), there is currently no mature engineering solution for using steam to heat raw coal to reduce cold source losses.
[0038] This utility model's energy-closed efficiency improvement system, which combines flue gas recirculation with low-level regenerative steam extraction, aims to enhance the thermal economy of the unit at low and medium loads. It constructs a low-temperature flue gas recirculation system, utilizing the regenerative steam extraction system of the turbine's low-pressure cylinder to heat the low-temperature flue gas. The heated flue gas is then sent into the furnace for the next cycle. This system uses the low-temperature flue gas as a carrier for latent heat heating during steam extraction, i.e., a heat recovery carrier, entering the furnace in a recirculating manner. By setting up one or more stages of stepped steam-flue gas heaters, it fully utilizes the latent heat of the turbine's steam extraction, reduces the exhaust volume of the low-pressure cylinder, reduces cold source losses, and improves the thermal economy of the unit at low and medium loads, and even at rated loads. This represents an innovation and restructuring of the boiler-turbine system, with strong technical and economic feasibility, making it worthy of development and promotion.
[0039] Taking a 1,000 kW double reheat unit as an example, the system setup and benefits are explained: The low-temperature flue gas recirculation system is only put into operation below 50% THA condition. With 40% THA condition as the design point, the recirculated flue gas volume is 15% of the flue gas volume under 40% THA condition, and the flue gas outlet is after the induced draft fan; a three-stage flue gas steam heater is set up, using the three-stage extraction steam (stages 8, 7, and 6) at the end of the intermediate pressure cylinder of the unit as the heating steam source, with extraction steam pressures of 0.169 MPa.a, 0.314 MPa.a, and 0.478 MPa.a, respectively. The flue gas temperature is heated from 90℃ to 140℃, and the coal consumption for power generation is reduced by about 3 g / kWh, which is very economical.
[0040] As a supplementary explanation, this system is applicable not only to low-load units but also to efficiency improvements under rated operating conditions. However, it will increase the capacity of equipment such as the denitrification SCR reactor, air preheater, and dust collector, resulting in a significant increase in investment. In engineering applications, it should be applied flexibly according to specific efficiency improvement requirements. Furthermore, in specific projects, this system should be rationally determined based on the set energy-saving targets by optimizing factors such as flue gas recirculation rate, number of stages in the cascade steam heater, boiler adaptability, and cost.
[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it; obviously, the described embodiments are some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model; for ease of description, only the parts related to the utility model are shown in the accompanying drawings. In the absence of conflict, the embodiments and features in the embodiments of this utility model can be combined with each other; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.
Claims
1. A closed-loop energy efficiency improvement system for flue gas recirculation combined with low-order regenerative steam extraction, characterized in that, Includes a boiler (1), which is connected to a boiler feedwater pipe (11) and a boiler flue gas pipe (12). A multi-stage low-pressure heater is installed in the boiler feedwater pipe (11); a low-pressure regenerative extraction pipe (31) is connected to the intermediate-pressure cylinder (22) and / or low-pressure cylinder (23) of the steam turbine, and the low-pressure regenerative extraction pipe (31) is connected to the low-pressure heater accordingly; An air preheater (121), a dust collector (122), an induced draft fan (123), a desulfurization device (124), and a chimney (125) are arranged sequentially along the flue gas conveying direction in the boiler flue gas duct (12). A recirculating flue gas duct (4) is led out from the boiler flue gas duct (12) between the downstream of the dust collector (122) and the upstream of the desulfurization device (124). The output end of the recirculating flue gas duct (4) is connected to the furnace of the boiler (1). One or more flue gas steam heaters (41) connected in series are arranged in the recirculating flue gas duct (4). A flue gas heating steam extraction duct (32) is led out from the low-pressure regenerative steam extraction duct (31). The output end of the flue gas heating steam extraction duct (32) is connected to the flue gas steam heater (41).
2. The energy-closed-loop efficiency-enhancing system for flue gas recirculation combined with low-order regenerative steam extraction according to claim 1, characterized in that, The inlet of the recirculated flue gas duct (4) is located between the induced draft fan (123) and the desulfurization unit (124).
3. The energy-closed-loop efficiency-enhancing system for flue gas recirculation combined with low-order regenerative steam extraction according to claim 1, characterized in that, The inlet of the recirculated flue gas duct (4) is located between the dust collector (122) and the induced draft fan (123), and a variable frequency recirculation fan (5) is installed in the recirculated flue gas duct (4).
4. The energy-closed-loop efficiency-enhancing system for flue gas recirculation combined with low-order regenerative steam extraction according to claim 1, characterized in that, The output end of the recirculated flue gas duct (4) is located on the front and rear walls of the furnace below the lowest burner of the boiler (1) and above the inflection point of the cold ash hopper; or, the output end of the recirculated flue gas duct (4) is located on the front and rear walls of the furnace above the highest burner of the boiler (1) and near the burnout air.
5. The energy-closed-loop efficiency-enhancing system for flue gas recirculation combined with low-order regenerative steam extraction according to claim 1, characterized in that, An output electric regulating baffle (42) is provided at the output end of the recirculated flue gas duct (4).
6. The energy-closed-loop efficiency-enhancing system for flue gas recirculation combined with low-order regenerative steam extraction according to claim 1, characterized in that, An input electric shut-off baffle (43) is provided at the input end of the recirculated flue gas duct (4), and a valve is provided in the flue gas heating and extraction steam duct (32).
7. The closed-loop energy efficiency improvement system for flue gas recirculation combined with low-order regenerative steam extraction according to any one of claims 1-6, characterized in that, The number of flue gas steam heaters (41) is N, where N is a positive integer. The low-pressure regenerative extraction steam pipe (31) is the Nth stage extraction steam pipe at the end of the medium-pressure cylinder (22). The flue gas steam heaters (41) correspond one-to-one with the low-pressure regenerative extraction steam pipes (31). The N low-pressure regenerative extraction steam pipes (31) are connected to the N flue gas steam heaters (41) arranged along the flue gas conveying direction in order of extraction steam pressure from low to high.
8. The energy-closed-loop efficiency-enhancing system for flue gas recirculation combined with low-order regenerative steam extraction according to claim 7, characterized in that, The boiler feedwater pipeline (11) is equipped with a multi-stage low-pressure heater, a deaerator (6), a feedwater pump (7) and a multi-stage high-pressure heater in sequence along the water transport direction; The multi-stage low-pressure heaters include low-pressure heater No. 9 (85), low-pressure heater No. 8 (84), low-pressure heater No. 7 (83), low-pressure heater No. 6 (82), and low-pressure heater No. 5 (81) arranged sequentially along the water conveyance direction; the multi-stage high-pressure heaters include high-pressure heater No. 3 (93), high-pressure heater No. 2 (92), and high-pressure heater No. 1 (91) arranged sequentially along the water conveyance direction. The number of flue gas steam heaters (41) is three; the low-pressure regenerative extraction steam pipe (31) is the five-section extraction steam pipe, the six-section extraction steam pipe and the seven-section extraction steam pipe of the medium-pressure cylinder (22); The fifth-section extraction steam pipe is connected to the fifth low-pressure heater (81), the sixth-section extraction steam pipe is connected to the sixth low-pressure heater (82), and the seventh-section extraction steam pipe is connected to the seventh low-pressure heater (83). The flue gas heating extraction steam pipe (32) led out from the fifth-section extraction steam pipe is connected to the downstream flue gas steam heater (41) among the three flue gas steam heaters (41). The flue gas heating extraction steam pipe (32) led out from the sixth-section extraction steam pipe is connected to the middle flue gas steam heater (41) among the three flue gas steam heaters (41). The flue gas heating extraction steam pipe (32) led out from the seventh-section extraction steam pipe is connected to the upstream flue gas steam heater (41) among the three flue gas steam heaters (41).