Coal-fired power generating unit dual-pressure dual-regenerative collaborative boiler flue gas waste heat regenerative system

Abstract

The utility model belongs to the technical field of boiler flue gas waste heat recovery, and particularly relates to a dual-pressure dual-regenerative collaborative boiler flue gas waste heat regenerative system of a coal-fired power generating unit. Comprising a low-temperature economizer, an air preheater and bypass flue subsystem, a high-pressure heat medium water subsystem, a low-pressure heat medium water subsystem, a primary / secondary air subsystem, an electric dust remover, an induced draft fan, a desulfurizing tower, a flue gas heater and a chimney. The air preheater and bypass flue subsystem comprises an air preheater and a bypass flue; the high-pressure heating medium water subsystem comprises a high-pressure heating medium water heat exchanger and a high-pressure heating medium water circulating pipeline; the low-pressure heating medium water subsystem comprises a low-pressure heating medium water heat exchanger, a flue gas heater and a low-pressure heating medium water circulating pipeline; the primary / secondary air subsystem heats primary / secondary air through the low-pressure heat medium water subsystem, the high-pressure heat medium water subsystem and the air preheater. And through double-pressure and double-regenerative cooperation, flue gas waste heat in front of the desulfurization tower can be effectively recovered, and the power generation coal consumption of the unit is further reduced by more than 1g / kWh.

Description

Technical Field

[0001] This utility model belongs to the field of boiler flue gas waste heat recovery technology, specifically a coal-fired power generation unit dual-pressure dual-regenerative synergistic boiler flue gas waste heat recovery system. Background Technology

[0002] High-efficiency recovery of waste heat from flue gas in coal-fired power plants is an important research direction for improving the power generation efficiency of coal-fired power generating units. In recent years, there has been extensive practical application in both new and retrofitted old units, leading to the development of various related technologies. The most direct way to recover waste heat from flue gas is by using a low-temperature economizer (see...). Figure 1 This method utilizes condensate to reduce the boiler flue gas temperature from approximately 125°C to 85°C or slightly higher. The reheated condensate is then returned to the low-pressure heating system, replacing part of the steam extraction in the turbine regenerative system. This increases the turbine's work output and improves the unit's cycle efficiency. While this system is simple, its waste heat recovery efficiency is relatively low, typically reducing power generation coal consumption by only about 1.5 g / kWh. To improve the effectiveness of flue gas waste heat recovery, domestic boiler flue gas waste heat recovery systems employing partial flue gas bypass have been introduced in recent years (see...). Figure 2 This system, when properly designed, can efficiently recover waste heat from flue gas, typically reducing coal consumption by 2–2.5 g / kWh. However, it often suffers from reduced boiler efficiency due to lower hot air temperature.

[0003] Furthermore, based on the aforementioned system, a deep utilization system for flue gas waste heat in seawater desulfurization coal-fired power generating units has been developed domestically, as the water balance of the seawater desulfurization system does not have requirements for the flue gas inlet temperature (conventional wet desulfurization systems require a flue gas inlet temperature of around 80°C). Before the electrostatic precipitator, the flue gas temperature is also reduced to 85°C, and after passing through the electrostatic precipitator and induced draft fan, the temperature rises to 95°C. Therefore, a heat transfer medium water heat exchanger is added to the flue between the induced draft fan and the desulfurization tower, reducing the flue gas temperature from 95°C to around 65°C, recovering approximately 30K of flue gas waste heat again. A drawback is that this portion of waste heat has a low grade and low utilization efficiency, potentially reducing coal consumption for power generation by approximately 1g / kWh. Moreover, this system also suffers from the problem of reduced boiler efficiency due to the lower hot air temperature at the air preheater outlet. Additionally, due to the complexity of the system's operating control logic, the actual operating performance often falls short of the design values.

[0004] Furthermore, to further improve the efficiency of flue gas waste heat utilization and simultaneously enhance the operational flexibility of the unit, the developer of this utility model patent has previously proposed a dual-regenerative theory for coal-fired power generating units and a method for constructing a dual-regenerative synergistic energy-saving and flexible operation system for coal-fired power generating units. A series of schemes for dual-regenerative synergistic flue gas waste heat utilization in coal-fired power generating units have been established. The patent application number is 202510465088.2, and the patent title is: "Coal-fired Power Boiler System Based on Low-Temperature Air Preheater for Recovering Flue Gas Waste Heat." This scheme can effectively improve the flue gas waste heat recovery effect while simultaneously increasing the unit's cycle efficiency, operational flexibility, and environmental performance. Although this scheme solves most of the problems existing in the aforementioned system, the following problems still exist:

[0005] (1) The inlet flue gas temperature of the electrostatic precipitator is 85°C. The low-temperature part of the heat medium water heat exchanger (or low-temperature economizer) arranged upstream often suffers from severe corrosion, which seriously affects the service life and operational reliability of the equipment. At the same time, the inlet flue gas temperature of 85°C is not in the comfortable operating temperature range of the electrostatic precipitator. The internal components of the electrostatic precipitator are at risk of corrosion, and the risk of ash accumulation is also high.

[0006] (2) The heat transfer medium water heat exchanger (or low temperature economizer) is usually arranged in the horizontal flue upstream of the electrostatic precipitator, which makes it very easy to cause serious ash accumulation in this area, especially when the load is low. Moreover, this arrangement is superimposed with the relatively low temperature flue gas environment, making the ash accumulation and corrosion more serious. This is a technical problem that is currently difficult to solve.

[0007] (3) After passing through the induced draft fan, the flue gas temperature rises from 85°C to 95°C. There is about 15K of flue gas waste heat that can be utilized before the flue gas enters the desulfurization tower. In the above schemes, except for the seawater desulfurization scenario where this waste heat is utilized, the other scenarios do not utilize this part of the flue gas waste heat. Although this part of the flue gas waste heat is recovered in the seawater desulfurization scenario, the dual heat recovery coordination was not well done when the system was designed. On the one hand, the waste heat utilization efficiency of the system is low, and on the other hand, the support for the low-load operation of the unit is not obvious, and the control logic is not clear enough.

[0008] (4) Due to environmental protection requirements or chimney corrosion prevention requirements, some units require the flue gas to be heated to a certain temperature after passing through the desulfurization tower, usually around 70°C. The heat exchanger upstream of the desulfurization tower and the flue gas heater in front of the chimney have serious corrosion problems.

[0009] Based on the above issues, how to construct a flue gas waste heat recovery system to achieve coal saving and improve unit cycle efficiency is an urgent problem to be solved. Utility Model Content

[0010] To address the problems mentioned above, this utility model provides a dual-pressure dual-regenerative boiler flue gas waste heat recovery system for coal-fired power generating units. Through the technical solutions disclosed in the embodiments of this utility model, the waste heat of flue gas before the desulfurization tower can be effectively recovered and integrated into the dual-regenerative system, further reducing the coal consumption of the unit for power generation by more than 1g / kWh.

[0011] The purpose of this utility model is to provide a dual-pressure dual-regenerative boiler flue gas waste heat recovery system for coal-fired power generation units, including: a low-temperature economizer, an air preheater and bypass flue subsystem, a high-pressure heat medium water subsystem, a low-pressure heat medium water subsystem, a primary air subsystem, a secondary air subsystem, an electrostatic precipitator, an induced draft fan, a desulfurization tower, a flue gas heater and a chimney.

[0012] The air preheater and bypass flue subsystem includes: an air preheater and a bypass flue for discharging flue gas from the boiler, wherein the air preheater is located on the main flue for discharging flue gas from the boiler.

[0013] The high-pressure heat transfer water subsystem includes a high-pressure heat transfer water heat exchanger and a high-pressure heat transfer water circulation pipeline. Heat transfer water from the turbine low-pressure heater system flows through the high-pressure heat transfer water circulation pipeline and then through the high-pressure heat transfer water heat exchanger. Part of the heat transfer water flows back to the turbine low-pressure heater system through the high-pressure heat transfer water circulation pipeline, and the other part enters the primary air high-pressure heater circulation pipeline and the secondary air high-pressure heater circulation pipeline. The high-pressure heat transfer water heat exchanger is located on the main flue.

[0014] The low-pressure heat transfer water subsystem includes: a low-pressure heat transfer water heat exchanger, a flue gas heater, and a low-pressure heat transfer water circulation pipeline. The heat transfer water flows through the low-pressure heat transfer water circulation pipeline and then through the low-pressure heat transfer water heat exchanger. Part of the heat transfer water flows into the flue gas heater through the low-pressure heat transfer water circulation pipeline, and the other part enters the primary air low-pressure heater circulation pipeline and the secondary air low-pressure heater circulation pipeline. The low-pressure heat transfer water heat exchanger is installed on the main flue.

[0015] Both the primary air subsystem and the secondary air subsystem heat the primary air and the secondary air through the low-pressure heat transfer water subsystem, the high-pressure heat transfer water subsystem, and the air preheater;

[0016] The main flue also includes an electrostatic precipitator, an induced draft fan, a desulfurization tower, a flue gas heater, and a chimney. The flue gas discharged from the main flue passes sequentially through the air preheater, the high-pressure heat medium water exchanger, the electrostatic precipitator, the induced draft fan, the low-pressure heat medium water exchanger, the desulfurization tower, the flue gas heater, and the chimney.

[0017] Furthermore, the flue gas temperature at the inlet of the electrostatic precipitator is 95±5℃, the high-pressure heat medium water heat exchanger is arranged in the main flue upstream of the electrostatic precipitator, and the low-pressure heat medium water heat exchanger is arranged in the main flue downstream of the electrostatic precipitator.

[0018] The high-pressure heat medium water heat exchanger is arranged below the outlet flue of the air preheater and bypass flue subsystem, and is arranged vertically with the flue gas flowing from top to bottom.

[0019] The low-pressure heat transfer medium water heat exchanger is arranged in two stages. The first stage is arranged on the flue between the outlet of the electrostatic precipitator and the inlet of the induced draft fan, where the flue gas temperature drops from about 96±5°C to about 85°C. The second stage is arranged on the flue between the outlet of the induced draft fan and the inlet of the desulfurization tower, where the flue gas temperature drops from about 85°C to about 75°C.

[0020] Furthermore, the air preheater includes a primary air preheater and a secondary air preheater, which are located on the main flue and are used to heat the primary air and secondary air entering the boiler intake channel by using the waste heat of the flue gas discharged from the main flue.

[0021] The bypass flue is equipped with a bypass flue regulating valve, a bypass low-pressure heater, and a bypass high-pressure heater. The bypass flue regulating valve is used to distribute the flue gas flow rate discharged from the main flue and the flue gas flow rate discharged from the bypass flue. The bypass low-pressure heater is used to heat the feedwater from the turbine low-pressure heater system using the waste heat of the flue gas discharged from the bypass flue. The heated feedwater flows back to the turbine low-pressure heater system. The bypass high-pressure heater is used to heat the feedwater from the feedwater pump using the waste heat of the flue gas discharged from the bypass flue. The heated feedwater and the boiler main feedwater flow together into the low-temperature economizer.

[0022] The setting or removal of the bypass flue depends on whether there are space constraints during the retrofitting of in-service units.

[0023] Furthermore, the high-pressure heat medium water subsystem also includes: a high-pressure heat medium water inlet valve, a high-pressure heat medium water pump, a primary air high-pressure heater inlet valve, a secondary air high-pressure heater inlet valve, and a high-pressure heat medium water return valve.

[0024] The high-pressure heat transfer water circulation pipeline is sequentially equipped with a high-pressure heat transfer water inlet valve, a high-pressure heat transfer water pump, a high-pressure heat transfer water heat exchanger, and a high-pressure heat transfer water pump. Heat transfer water from the turbine low-pressure heater system flows through the heat transfer water circulation pipeline sequentially through the high-pressure heat transfer water inlet valve, the high-pressure heat transfer water pump, and the high-pressure heat transfer water heat exchanger. Part of the heat transfer water flows back to the turbine low-pressure heater system through the high-pressure heat transfer water circulation pipeline and the high-pressure heat transfer water return valve, while the other part enters the primary air high-pressure heater circulation pipeline and the secondary air high-pressure heater circulation pipeline.

[0025] The primary air high-pressure heater circulation pipeline is equipped with a primary air high-pressure heater inlet valve. The heat medium water entering the primary air high-pressure heater circulation pipeline flows into the primary air high-pressure heater after passing through the primary air high-pressure heater inlet valve.

[0026] The secondary air high-pressure heater circulation pipeline is equipped with a secondary air high-pressure heater inlet valve. The heat transfer water entering the secondary air high-pressure heater circulation pipeline flows into the secondary air high-pressure heater after passing through the secondary air high-pressure heater inlet valve.

[0027] Furthermore, the low-pressure heat medium water subsystem also includes: a low-pressure heat medium water circulation pump, a flue gas heater inlet valve, a primary air low-pressure heater inlet valve, and a secondary air low-pressure heater inlet valve;

[0028] The low-pressure heat transfer water circulation pipeline is sequentially equipped with a low-pressure heat transfer water circulation pump, a low-pressure heat transfer water heat exchanger, a flue gas heater inlet valve, and a flue gas heater. After the heat transfer water flows through the low-pressure heat transfer water circulation pipeline, it flows through the low-pressure heat transfer water circulation pump and the low-pressure heat transfer water heat exchanger in sequence. A portion of the heat transfer water then flows through the heat transfer water circulation pipeline, passing through the flue gas heater inlet valve and the flue gas heater in sequence, while the other portion enters the primary air low-pressure heater circulation pipeline and the secondary air low-pressure heater circulation pipeline.

[0029] The primary air low-pressure heater circulation pipeline is equipped with a primary air low-pressure heater inlet valve. The heat medium water entering the primary air low-pressure heater circulation pipeline flows into the primary air low-pressure heater after passing through the primary air low-pressure heater inlet valve.

[0030] The circulation pipeline of the secondary air low-pressure heater is equipped with a secondary air low-pressure heater inlet valve. The heat medium water entering the circulation pipeline of the secondary air low-pressure heater flows into the secondary air low-pressure heater after passing through the secondary air low-pressure heater inlet valve.

[0031] Furthermore, the primary air subsystem includes: a primary air fan, a primary air low-pressure heater, and a primary air high-pressure heater sequentially arranged in the primary air intake channel, wherein the primary air low-pressure heater is located in the primary air low-pressure heater circulation pipeline, and the primary air high-pressure heater is located in the primary air high-pressure heater circulation pipeline;

[0032] The primary air delivered by the primary air fan is heated sequentially by the primary air low-pressure heater, the primary air high-pressure heater, and the primary air preheater.

[0033] Furthermore, the secondary air subsystem includes: a blower, a low-pressure secondary air heater, and a high-pressure secondary air heater sequentially arranged in the secondary air intake channel, wherein the low-pressure secondary air heater is located in the circulation pipeline of the low-pressure secondary air heater, and the high-pressure secondary air heater is located in the circulation pipeline of the high-pressure secondary air heater.

[0034] The secondary air delivered by the blower is heated sequentially by the secondary air low-pressure heater, the secondary air high-pressure heater, and the secondary air preheater.

[0035] In summary, the dual-pressure dual-regenerative synergistic boiler flue gas waste heat recovery system for coal-fired power generating units disclosed in this utility model can bring the following beneficial effects:

[0036] (1) Setting up a dual-pressure heat transfer water system with high and low pressure working together can improve the utilization efficiency of flue gas waste heat. The low-pressure heat transfer water system recovers the waste heat of flue gas in the low-temperature zone and uses it to heat the primary air, secondary air and / or the low-temperature flue gas at the desulfurization tower outlet; while the high-pressure heat transfer water system recovers the waste heat of flue gas in the higher-temperature zone. Part of the waste heat is used to further heat the primary air and secondary air, and part of the waste heat is used to heat the working fluid water from the turbine low-temperature heater system, resulting in better waste heat utilization.

[0037] (2) The dual-pressure heat transfer water system, together with the air preheater and bypass flue subsystem located upstream, constitutes a flexible and efficient dual-regenerative synergistic flue gas waste heat recovery system. This system can efficiently recover waste heat from low-temperature flue gas and improve the unit's cycle efficiency. At the same time, by increasing the inlet flue gas temperature of the air preheater, the combustion air temperature can be effectively increased. Especially during low-load operation, this not only helps to ensure stable combustion in the furnace and complete combustion of pulverized coal, improving operational stability and economy, but also facilitates staged combustion, reduces NOx generation, and has good environmental performance.

[0038] (3) After setting up a dual-pressure heat medium water system with high pressure and low pressure working together, the low-pressure heat medium water heat exchanger and flue gas heater of the low-pressure heat medium water subsystem are made of anti-corrosion materials, which can effectively prevent equipment corrosion. At the same time, since the high-pressure heat medium water subsystem works in a higher flue gas temperature range, the risk of low-temperature flue gas corrosion of the equipment in the high-pressure heat medium water subsystem is greatly reduced, so the safety and reliability of the whole system is greatly improved.

[0039] (4) Increase the inlet flue gas temperature of the electrostatic precipitator from 85°C to 95±5°C so that the electrostatic precipitator can work in the high-efficiency dust removal zone, and at the same time effectively reduce the risk of low-temperature corrosion and high-temperature damage to its internal components.

[0040] (5) The waste heat generated by the flue gas temperature rise of about 10K after passing through the electrostatic precipitator and induced draft fan is recovered, and an additional 20K of waste heat is recovered through the low-pressure heat transfer medium water heat exchanger. At the same time, the waste heat left by the flue gas temperature rising from 85°C to 95±5°C before the electrostatic precipitator is also recovered by the low-pressure heat transfer medium water heat exchanger. The low-pressure heat transfer medium water subsystem effectively recovers the waste heat of the flue gas before the desulfurization tower and effectively integrates it into the dual regenerative system, further reducing the coal consumption of the unit's power generation by more than 1g / kWh based on the existing patented technology (patent application number 202510465088.2, patent name: coal-fired power generation boiler system based on low-temperature air preheater for recovering waste heat of flue gas).

[0041] (6) After the outlet flue gas temperature of the high-pressure heat medium water heat exchanger (i.e. the inlet flue gas temperature of the electrostatic precipitator) is increased from 85°C to 95±5°C, the high-pressure heat medium water heat exchanger can be arranged below the outlet flue of the air preheater, arranged vertically, and the flue gas flows from top to bottom, which can avoid a large amount of ash accumulation, greatly improve the safety and reliability of the equipment, and can be integrated with the boiler design. The type of the heating surface used is close to that of the low-temperature economizer, only the materials need to be appropriately adjusted, and the construction cost will also be greatly reduced. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A system diagram of a current technology that uses a low-temperature economizer to recover waste heat from flue gas.

[0044] Figure 2 This is a system diagram of a boiler flue gas waste heat recovery system that uses partial flue gas bypass in the existing technology;

[0045] Figure 3 This is a system example diagram illustrating a dual-pressure dual-regenerative co-generation boiler flue gas waste heat recovery system for a coal-fired power generating unit, according to an exemplary embodiment.

[0046] Figure 4 This is a system example diagram illustrating a dual-pressure dual-regenerative boiler flue gas waste heat recovery system for a coal-fired power generation unit according to another exemplary embodiment.

[0047] 1-Low-temperature economizer, 2-Air preheater, 21-Primary air preheater, 22-Secondary air preheater, 3-Bypass flue, 31-Bypass flue gas regulating valve, 32-Bypass low-pressure heater, 33-Bypass high-pressure heater, 4-High-pressure heat transfer medium water heat exchanger, 41-High-pressure heat transfer medium water inlet valve, 42-High-pressure heat transfer medium water pump, 43-Primary air high-pressure heater inlet valve, 44-Secondary air high-pressure heater inlet valve, 45-High-pressure heat transfer medium water return valve, 5-Electrostatic precipitator 6-Dust collector, 7-Exhaust fan, 8-Low-pressure heat medium water heat exchanger, 9-Low-pressure heat medium water circulating pump, 10-Flue gas heater inlet valve, 11-Primary air low-pressure heater inlet valve, 12-Secondary air low-pressure heater inlet valve, 13-Desulfurization tower, 14-Flue gas heater, 15-Chimney, 16-Primary air fan, 17-Exhaust fan, 18-Primary air low-pressure heater, 19-Secondary air low-pressure heater, 10-Secondary air high-pressure heater. Detailed Implementation

[0048] The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and 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.

[0049] The following is in conjunction with the appendix Figure 3 and Figure 4 The present invention will be described in detail with specific embodiments.

[0050] Coal-fired power generating units typically have two regenerative systems: a boiler flue gas-air regenerative system and a turbine extraction regenerative system. Both systems recover waste heat intended for release into the environment, improve its energy quality through a high-temperature heat source (furnace), and then reuse it for power generation; hence the term "regenerative." When constructing a deep regenerative system for boiler flue gas waste heat, both systems must be optimized holistically to maximize the unit's cycle efficiency. Flue gas waste heat is used to heat combustion air, which returns to the furnace with the combustion air; this is defined as air-carrying regenerative. Flue gas waste heat is used to heat working fluid water, which then returns to the turbine regenerative system with the working fluid water; this is defined as water-carrying recirculation. The utilization efficiency is higher when flue gas waste heat is carried by combustion air, and lower when carried by working fluid water; that is, air-carrying regenerative is always more efficient than water-carrying regenerative. The design requires a reasonable coordination of the two regenerative systems to maximize the regenerative effect of flue gas waste heat, improve the unit's cycle efficiency, and reduce coal consumption for power generation.

[0051] This utility model provides a dual-pressure dual-regenerative boiler flue gas waste heat recovery system for coal-fired power generation units, including: a low-temperature economizer 1, an air preheater 2 and a bypass flue subsystem, a high-pressure heat medium water subsystem, a low-pressure heat medium water subsystem, a primary air subsystem, a secondary air subsystem, an electrostatic precipitator 5, an induced draft fan 6, a desulfurization tower 8, a flue gas heater 9 and a chimney 10.

[0052] For example, the core of the dual-pressure dual-regenerative co-generation boiler flue gas waste heat recovery system in this invention is the establishment of a dual-pressure co-generation heat transfer water system, namely a high-pressure heat transfer water subsystem and a low-pressure heat transfer water subsystem. The low-pressure heat transfer water subsystem is used to recover waste heat from the flue gas in the low-temperature zone, while the high-pressure heat transfer water subsystem is used to recover waste heat from the flue gas in the higher-temperature zone. The high-pressure heat transfer water subsystem operates in the higher-temperature zone, significantly reducing the risk of low-temperature flue gas corrosion to the equipment.

[0053] The air preheater and bypass flue subsystem includes: air preheater 2 and bypass flue for discharging flue gas from the boiler. Air preheater 2 is located on the main flue for discharging flue gas from the boiler.

[0054] The high-pressure heat transfer water subsystem includes: a high-pressure heat transfer water heat exchanger 4 and a high-pressure heat transfer water circulation pipeline. The heat transfer water from the turbine low-pressure heater system flows through the high-pressure heat transfer water circulation pipeline and then through the high-pressure heat transfer water heat exchanger 4. Part of it flows back to the turbine low-pressure heater system through the high-pressure heat transfer water circulation pipeline, and the other part enters the primary air high-pressure heater circulation pipeline and the secondary air high-pressure heater circulation pipeline. The high-pressure heat transfer water heat exchanger is located on the main flue.

[0055] For example, the high-pressure heat transfer water subsystem and the air preheater and bypass flue subsystem located upstream of it, through optimizing parameters such as the primary and secondary air temperatures at the inlet of the air preheater 2, the flue gas outlet and inlet temperatures, and the bypass flue gas ratio, jointly constitute a dual-regenerative synergistic flue gas waste heat recovery system. Figure 3 and Figure 4 As shown, one arrangement of the high-pressure heat medium water heat exchanger 4 is to place it below the outlet flue of the air preheater 2, vertically, with the flue gas flowing from top to bottom.

[0056] The low-pressure heat transfer water subsystem includes: a low-pressure heat transfer water heat exchanger 7, a flue gas heater 9, and a low-pressure heat transfer water circulation pipeline. After the heat transfer water flows through the low-pressure heat transfer water heat exchanger via the low-pressure heat transfer water circulation pipeline, part of it flows into the flue gas heater 9 through the low-pressure heat transfer water circulation pipeline, and the other part enters the primary air low-pressure heater circulation pipeline and the secondary air low-pressure heater circulation pipeline. The low-pressure heat transfer water heat exchanger 7 is installed on the main flue.

[0057] Both the primary and secondary air subsystems heat the primary and secondary air through a low-pressure heat transfer water subsystem, a high-pressure heat transfer water subsystem, and an air preheater. The main flue also includes: an electrostatic precipitator 5, an induced draft fan 6, a desulfurization tower 8, a flue gas heater 9, and a chimney 10. The flue gas discharged from the main flue passes sequentially through the air preheater 2, the high-pressure heat transfer water heat exchanger 4, the electrostatic precipitator 5, the induced draft fan 6, the low-pressure heat transfer water heat exchanger 7, the desulfurization tower 8, the flue gas heater 9, and the chimney 10.

[0058] For example, the high-pressure heat transfer water subsystem is an open system with good operational flexibility. When the heat supplied to the primary and secondary air by the low-pressure heat transfer water subsystem changes, the high-pressure heat transfer water subsystem regulates the return flow of the heat transfer water through the high-pressure heat transfer water return valve to maintain a constant temperature of the primary and secondary air entering the air preheater. The high-pressure heat transfer water subsystem and the low-pressure heat transfer water subsystem constitute a dual-pressure heat transfer water system operating in synergy. The low-pressure heat transfer water subsystem absorbs the waste heat of low-temperature flue gas and preheats the primary / secondary air and / or heats the low-temperature flue gas through a flue gas heater. The high-pressure heat transfer water system absorbs the waste heat of relatively high-temperature flue gas and heats the primary / secondary air to the required temperature. The dual-pressure heat transfer water system, together with the air preheater and bypass flue subsystem located upstream, constitutes a dual-recovery synergistic flue gas waste heat recovery system.

[0059] The flue gas temperature at the inlet of electrostatic precipitator 5 is 95±5℃.

[0060] For example, the dual-pressure heat transfer water subsystem of this invention, which combines high-pressure and low-pressure operation, has a high-pressure subsystem for recovering waste heat from the flue gas above 95±5°C (i.e., waste heat from the higher temperature zone) before the electrostatic precipitator, and a low-pressure subsystem for recovering waste heat from the flue gas between 105±5°C and the flue gas temperature at the desulfurization tower inlet (around 75°C) (i.e., waste heat from the low-temperature zone). Increasing the flue gas temperature at the inlet of the electrostatic precipitator 5 (i.e., the outlet temperature of the high-pressure heat transfer water heat exchanger 4) from 85°C to 95±5°C will allow the electrostatic precipitator 5 to operate in a highly efficient dust removal zone, while effectively reducing the risk of low-temperature corrosion and high-temperature damage to its internal components. Simultaneously, because the flue gas temperature at the outlet of the high-pressure heat transfer water heat exchanger 4 is increased from 85°C to 95±5°C, the tendency for low-temperature flue gas corrosion in the high-pressure heat transfer water heat exchanger 4 will be significantly reduced.

[0061] After passing through the electrostatic precipitator 5 and induced draft fan 6, the flue gas temperature increases from 95±5°C to 105±5°C. The waste heat from the increased flue gas temperature at the outlet of the high-pressure heat transfer fluid heat exchanger 4, along with the waste heat from the temperature rise after passing through the electrostatic precipitator 5 and induced draft fan 6, is recovered together by the low-pressure heat transfer fluid heat exchanger 7. The synergy of the dual-pressure heat transfer fluid subsystem is also reflected in low-load operation. The waste heat recovered by the low-pressure heat transfer fluid subsystem is used to heat the air (primary and secondary air), which can raise the outlet flue gas temperature of the high-pressure heat transfer fluid heat exchanger 4, keeping the inlet flue gas temperature of the electrostatic precipitator 5 consistently at 95±5°C. This ensures the safe and reliable operation of equipment such as the high-pressure heat transfer fluid heat exchanger 4 and the electrostatic precipitator 5, while also helping to improve the unit's low-load operating performance.

[0062] It is understood that the air preheater 2 includes a primary air preheater 21 and a secondary air preheater 22. The primary air preheater 21 and the secondary air preheater 22 are located on the main flue and are used to heat the primary air and secondary air entering the boiler intake channel by using the waste heat of the flue gas discharged from the main flue. The bypass flue is equipped with a bypass flue regulating valve 31, a bypass low-pressure heater 32 and a bypass high-pressure heater 33. The bypass flue regulating valve 31 is used to distribute the flue gas flow rate discharged from the main flue and the flue gas flow rate discharged from the bypass flue. The bypass low-pressure heater 32 is used to heat the feedwater from the turbine low-pressure heater system by using the waste heat of the flue gas discharged from the bypass flue. The heated feedwater flows back to the turbine low-pressure heater system. The bypass high-pressure heater 33 is used to heat the feedwater from the feedwater pump by using the waste heat of the flue gas discharged from the bypass flue. The heated feedwater and the boiler main feedwater flow together into the low-temperature economizer 1.

[0063] The high-pressure heat transfer medium water subsystem also includes: a high-pressure heat transfer medium water inlet valve 41, a high-pressure heat transfer medium water pump 42, a primary air high-pressure heater inlet valve 43, a secondary air high-pressure heater inlet valve 44, and a high-pressure heat transfer medium water return valve 45; the high-pressure heat transfer medium water circulation pipeline is sequentially equipped with a high-pressure heat transfer medium water inlet valve 41, a high-pressure heat transfer medium water pump 42, a high-pressure heat transfer medium water heat exchanger 4, and a high-pressure heat transfer medium water pump 42. The heat transfer water from the turbine low-pressure heater system flows sequentially through the heat transfer water circulation pipeline, passing through the high-pressure heat transfer water inlet valve 41, the high-pressure heat transfer water pump 42, and the high-pressure heat transfer water heat exchanger 4. Part of it flows back to the turbine low-pressure heater system through the high-pressure heat transfer water circulation pipeline and the high-pressure heat transfer water return valve, while the other part enters the primary air high-pressure heater circulation pipeline and the secondary air high-pressure heater circulation pipeline. The primary air high-pressure heater circulation pipeline is equipped with a primary air high-pressure heater inlet valve 43. After passing through the primary air high-pressure heater inlet valve 43, the heat transfer water entering the primary air high-pressure heater circulation pipeline flows into the primary air high-pressure heater 15. The secondary air high-pressure heater circulation pipeline is equipped with a secondary air high-pressure heater inlet valve 44. After passing through the secondary air high-pressure heater inlet valve 44, the heat transfer water entering the secondary air high-pressure heater circulation pipeline flows into the secondary air high-pressure heater 16.

[0064] For example, the high-pressure heat transfer fluid subsystem includes a high-pressure heat transfer fluid heat exchanger 4, a high-pressure heat transfer fluid inlet valve 41, a high-pressure heat transfer fluid pump 42, a primary air high-pressure heater inlet valve 43, a secondary air high-pressure heater inlet valve 44, and a high-pressure heat transfer fluid return valve 45. The working fluid water of the high-pressure heat transfer fluid subsystem is supplied by the low-pressure heating system of the steam turbine, and after passing through the high-pressure heat transfer fluid inlet valve 41, it is sent to the high-pressure heat transfer fluid heat exchanger 4 by the high-pressure heat transfer fluid pump 42. After absorbing waste heat from the flue gas in the high-pressure heat transfer water heat exchanger 4, part of the working fluid water returns directly to the low-pressure heating system of the steam turbine through the high-pressure heat transfer water return valve 45, displacing some of the low-pressure extraction steam and thus increasing the power output of the steam turbine. The other part is supplied to the primary air high-pressure heater 15 and the secondary air high-pressure heater 16 through the primary air high-pressure heater inlet valve 43 and the secondary air high-pressure heater inlet valve 44, respectively, to heat the primary and secondary air. After releasing heat, the working fluid water returns to the inlet of the high-pressure heat transfer water pump 42, mixes with the working fluid water introduced from the low-pressure heating system of the steam turbine, and then enters the high-pressure heat transfer water pump 42 to form a heat transfer water circulation.

[0065] Furthermore, the arrangement of the high-pressure heat medium water heat exchanger 4 can be divided into two types: one is the conventional method, that is, arranged in the horizontal flue upstream of the electrostatic precipitator 5; the other is arranged vertically below the outlet flue of the air preheater 2, with the flue gas flowing from top to bottom (e.g., Figure 3 and Figure 4 The arrangement shown can avoid ash accumulation, greatly improve operational reliability, and can be integrated with the boiler design. The heating surface type used is similar to that of a low-temperature economizer, requiring only appropriate material adjustments, thus significantly reducing construction costs. The preferred embodiment of this utility model is... Figure 3 and Figure 4 The arrangement of the components is not limited, and the type of the heating surface of the high-pressure heat medium water heat exchanger is not restricted.

[0066] The low-pressure heat transfer fluid subsystem also includes: a low-pressure heat transfer fluid circulation pump 71, a flue gas heater inlet valve 72, a primary air low-pressure heater inlet valve 73, and a secondary air low-pressure heater inlet valve 74; the low-pressure heat transfer fluid circulation pipeline is sequentially equipped with the low-pressure heat transfer fluid circulation pump 71, the low-pressure heat transfer fluid heat exchanger 7, the flue gas heater inlet valve 72, and the flue gas heater 9. The heat transfer fluid flows through the low-pressure heat transfer fluid circulation pipeline, passing sequentially through the low-pressure heat transfer fluid circulation pump 71 and the low-pressure heat transfer fluid heat exchanger 7, and a portion of it flows sequentially through the flue gas heater inlet valve 72 and the flue gas heater 9. Another portion enters the primary air low-pressure heater circulation pipeline and the secondary air low-pressure heater circulation pipeline; the primary air low-pressure heater circulation pipeline is equipped with a primary air low-pressure heater inlet valve 73, and the heat medium water entering the primary air low-pressure heater circulation pipeline flows into the primary air low-pressure heater 13 after passing through the primary air low-pressure heater inlet valve 73; the secondary air low-pressure heater circulation pipeline is equipped with a secondary air low-pressure heater inlet valve 74, and the heat medium water entering the secondary air low-pressure heater circulation pipeline flows into the secondary air low-pressure heater 14 after passing through the secondary air low-pressure heater inlet valve 74.

[0067] For example, the low-pressure heat transfer fluid subsystem includes a low-pressure heat transfer fluid heat exchanger 7, a flue gas heater 9, a low-pressure heat transfer fluid circulation pump 71, a flue gas heater inlet valve 72, a primary air low-pressure heater inlet valve 73, and a secondary air low-pressure heater inlet valve 74. After passing through the electrostatic precipitator 5 and the induced draft fan 6, the flue gas temperature increases from 95±5°C to 105±5°C. The low-pressure heat transfer fluid heat exchanger 7 absorbs the waste heat from the flue gas, reducing the flue gas temperature to approximately 75°C, before the flue gas enters the desulfurization tower 8. The low-pressure heat transfer fluid subsystem distributes the recovered waste heat from the flue gas to the flue gas heater 9, the primary air low-pressure heater 13, and the secondary air low-pressure heater 14 as needed via heat transfer fluid. After releasing heat in these three heat exchangers, the heat transfer fluid returns to the inlet of the low-pressure heat transfer fluid circulation pump 71, achieving heat transfer fluid circulation. The low-pressure heat transfer fluid subsystem is a closed system and typically requires a pressure balancing system. After passing through the desulfurization tower 8, the flue gas temperature drops to around 50°C. For chimneys with anti-corrosion designs, flue gas at this temperature can be directly discharged, eliminating the need for a flue gas heater 9. The waste heat recovered by the low-pressure heat transfer medium water heat exchanger 7 is used entirely to heat the primary and secondary air. However, for some older units, the chimney design did not adequately consider preventing low-temperature flue gas corrosion, commonly known as a "dry chimney." In these cases, the flue gas temperature must be heated to around 70°C before being discharged through the chimney. Another scenario involves a "wet chimney" design, which prevents low-temperature flue gas corrosion, but local environmental regulations require the emitted flue gas to reach around 70°C. In both cases, the flue gas heater 9 is needed to heat the flue gas to around 70°C before it enters the chimney 10.

[0068] Furthermore, both the low-pressure heat exchanger 7 and the flue gas heater 9 are located in a region of high corrosion caused by low-temperature flue gas. The low-pressure heat exchanger 7, in particular, must be constructed using corrosion-resistant materials. These materials include metallic and organic materials. Metallic materials offer better mechanical properties, while organic materials provide better corrosion resistance, but their pressure resistance is insufficient. From an economic and reliability perspective, organic materials are more commonly used. Therefore, the low-pressure system is adopted for the heat exchanger water system in the low-temperature region.

[0069] By adjusting the inlet valve 72 of the flue gas heater, the inlet valve 73 of the primary air low-pressure heater, and the inlet valve 74 of the secondary air low-pressure heater, the low-pressure heat transfer fluid subsystem can switch between flue gas heating mode and flue gas non-heating mode. Simultaneously, through heat distribution, it can adapt to flexible operation under various temperature conditions in different seasons. The high-pressure heat transfer fluid subsystem is an open system with good operational flexibility. When the heat supplied by the low-pressure heat transfer fluid subsystem to the primary and secondary air changes, the high-pressure heat transfer fluid subsystem can compensate for the changes, maintaining a constant temperature for the primary and secondary air entering the air preheater.

[0070] Furthermore, the low-pressure heat transfer medium water heat exchanger 7 can be arranged in two stages. The first stage is located in the flue between the outlet of the electrostatic precipitator 5 and the inlet of the induced draft fan 6, reducing the flue gas temperature from approximately 96±5°C to around 85°C before the flue gas enters the induced draft fan 6. The second stage is located in the flue between the outlet of the induced draft fan 6 and the inlet of the desulfurization tower 8, reducing the flue gas temperature from 85°C to around 75°C before the flue gas enters the desulfurization tower 8. This arrangement does not significantly change the waste heat utilization effect of the flue gas, but it can reduce the power consumption of the induced draft fan 6, and the first stage can use relatively inexpensive corrosion-resistant materials.

[0071] Furthermore, the primary air subsystem includes: a primary air fan 11, a primary air low-pressure heater 13, and a primary air high-pressure heater 15, sequentially arranged in the primary air intake channel. The primary air low-pressure heater 13 is located in the primary air low-pressure heater circulation pipeline, and the primary air high-pressure heater 15 is located in the primary air high-pressure heater circulation pipeline. The primary air delivered by the primary air fan 11 is heated sequentially through the primary air low-pressure heater 13, the primary air high-pressure heater 15, and the primary air preheater 21. The secondary air subsystem includes: a blower 12, a secondary air low-pressure heater 14, and a secondary air high-pressure heater 16, sequentially arranged in the secondary air intake channel. The secondary air low-pressure heater 14 is located in the secondary air low-pressure heater circulation pipeline, and the secondary air high-pressure heater 16 is located in the secondary air high-pressure heater circulation pipeline. The secondary air delivered by the blower 12 is heated sequentially through the secondary air low-pressure heater 14, the secondary air high-pressure heater 16, and the secondary air preheater 22.

[0072] Furthermore, due to space constraints, the bypass flue 3 can be omitted during the retrofitting of in-service units.

[0073] For example, during the retrofitting of in-service units, if there is insufficient space to accommodate the bypass flue 3, then the bypass flue 3 will not be installed. In most cases, it is difficult to find sufficient space to accommodate the bypass flue 3 during the retrofitting of in-service units, and even if space is available, the bypass flue solution will be abandoned due to excessive retrofitting costs. Therefore, in Figure 4 The proposed retrofit plan for in-service units does not include bypass flues.

[0074] Understandable, Figure 3 and Figure 4 In the table, T0-T7 represent the changes in flue gas temperature, t0, t11, t21, t12, t21, ..., t14, t24 represent the changes in primary and secondary air temperatures, and s41, s42, s43, etc., marked with t represent the changes in water temperature.

[0075] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the substance and scope of the present invention. Various modifications made by those skilled in the art to the above embodiments after reading this specification are all within the scope of protection of the present invention.

Claims

1. A dual-pressure dual-regenerative boiler flue gas waste heat recovery system for a coal-fired power generating unit, characterized in that, The system includes: a low-temperature economizer, an air preheater and bypass flue subsystem, a high-pressure heat medium water subsystem, a low-pressure heat medium water subsystem, a primary air subsystem, a secondary air subsystem, an electrostatic precipitator, an induced draft fan, a desulfurization tower, a flue gas heater, and a chimney. The air preheater and bypass flue subsystem includes: an air preheater and a bypass flue for discharging flue gas from the boiler, wherein the air preheater is located on the main flue for discharging flue gas from the boiler. The high-pressure heat transfer water subsystem includes a high-pressure heat transfer water heat exchanger and a high-pressure heat transfer water circulation pipeline. Heat transfer water from the turbine low-pressure heater system flows through the high-pressure heat transfer water circulation pipeline and then through the high-pressure heat transfer water heat exchanger. Part of the heat transfer water flows back to the turbine low-pressure heater system through the high-pressure heat transfer water circulation pipeline, and the other part enters the primary air high-pressure heater circulation pipeline and the secondary air high-pressure heater circulation pipeline. The high-pressure heat transfer water heat exchanger is located on the main flue. The low-pressure heat transfer water subsystem includes: a low-pressure heat transfer water heat exchanger, a flue gas heater, and a low-pressure heat transfer water circulation pipeline. The heat transfer water flows through the low-pressure heat transfer water circulation pipeline and then through the low-pressure heat transfer water heat exchanger. Part of the heat transfer water flows into the flue gas heater through the low-pressure heat transfer water circulation pipeline, and the other part enters the primary air low-pressure heater circulation pipeline and the secondary air low-pressure heater circulation pipeline. The low-pressure heat transfer water heat exchanger is installed on the main flue. Both the primary air subsystem and the secondary air subsystem heat the primary air and the secondary air through the low-pressure heat transfer water subsystem, the high-pressure heat transfer water subsystem, and the air preheater; The main flue also includes an electrostatic precipitator, an induced draft fan, a desulfurization tower, a flue gas heater, and a chimney. The flue gas discharged from the main flue passes sequentially through the air preheater, the high-pressure heat medium water exchanger, the electrostatic precipitator, the induced draft fan, the low-pressure heat medium water exchanger, the desulfurization tower, the flue gas heater, and the chimney.

2. The coal-fired power generation unit dual-pressure dual-regenerative boiler flue gas waste heat recovery system according to claim 1, characterized in that, The flue gas temperature at the inlet of the electrostatic precipitator is 95±5℃. The high-pressure heat transfer medium water heat exchanger is arranged in the main flue upstream of the electrostatic precipitator, and the low-pressure heat transfer medium water heat exchanger is arranged in the main flue downstream of the electrostatic precipitator. The high-pressure heat medium water heat exchanger is arranged below the outlet flue of the air preheater and bypass flue subsystem, and is arranged vertically with the flue gas flowing from top to bottom. The low-pressure heat transfer medium water heat exchanger is arranged in two stages. The first stage is arranged on the flue between the outlet of the electrostatic precipitator and the inlet of the induced draft fan, and the second stage is arranged on the flue between the outlet of the induced draft fan and the inlet of the desulfurization tower.

3. The coal-fired power generation unit dual-pressure dual-regenerative boiler flue gas waste heat recovery system according to claim 1, characterized in that, The air preheater includes a primary air preheater and a secondary air preheater, which are located on the main flue and are used to heat the primary air and secondary air entering the boiler intake channel by using the waste heat of the flue gas discharged from the main flue. The bypass flue is equipped with a bypass flue regulating valve, a bypass low-pressure heater and a bypass high-pressure heater. The bypass flue regulating valve is used to distribute the flue gas flow rate discharged from the main flue and the flue gas flow rate discharged from the bypass flue. The bypass low-pressure heater is used to heat the feedwater from the turbine low-pressure heater system using the waste heat of the flue gas discharged from the bypass flue. The heated feedwater is then returned to the turbine low-pressure heater system. The bypass high-pressure heater is used to heat the feedwater from the feedwater pump using the waste heat of the flue gas discharged from the bypass flue. The heated feedwater and the boiler main feedwater flow together into the low-temperature economizer. The setting or removal of the bypass flue depends on whether there are space constraints during the retrofitting of in-service units.

4. The coal-fired power generation unit dual-pressure dual-regenerative boiler flue gas waste heat recovery system according to claim 1 or 2, characterized in that, The high-pressure heat medium water subsystem also includes: a high-pressure heat medium water inlet valve, a high-pressure heat medium water pump, a primary air high-pressure heater inlet valve, a secondary air high-pressure heater inlet valve, and a high-pressure heat medium water return valve. The high-pressure heat transfer water circulation pipeline is sequentially equipped with a high-pressure heat transfer water inlet valve, a high-pressure heat transfer water pump, a high-pressure heat transfer water heat exchanger, and a high-pressure heat transfer water pump. Heat transfer water from the turbine low-pressure heater system flows through the heat transfer water circulation pipeline sequentially through the high-pressure heat transfer water inlet valve, the high-pressure heat transfer water pump, and the high-pressure heat transfer water heat exchanger. Part of the heat transfer water flows back to the turbine low-pressure heater system through the high-pressure heat transfer water circulation pipeline and the high-pressure heat transfer water return valve, while the other part enters the primary air high-pressure heater circulation pipeline and the secondary air high-pressure heater circulation pipeline. The primary air high-pressure heater circulation pipeline is equipped with a primary air high-pressure heater inlet valve. The heat medium water entering the primary air high-pressure heater circulation pipeline flows into the primary air high-pressure heater after passing through the primary air high-pressure heater inlet valve. The secondary air high-pressure heater circulation pipeline is equipped with a secondary air high-pressure heater inlet valve. The heat transfer water entering the secondary air high-pressure heater circulation pipeline flows into the secondary air high-pressure heater after passing through the secondary air high-pressure heater inlet valve.

5. The coal-fired power generation unit dual-pressure dual-regenerative boiler flue gas waste heat recovery system according to claim 1 or 2, characterized in that, The low-pressure heat medium water subsystem also includes: a low-pressure heat medium water circulation pump, a flue gas heater inlet valve, a primary air low-pressure heater inlet valve, and a secondary air low-pressure heater inlet valve. The low-pressure heat transfer water circulation pipeline is sequentially equipped with a low-pressure heat transfer water circulation pump, a low-pressure heat transfer water heat exchanger, a flue gas heater inlet valve, and a flue gas heater. After the heat transfer water flows through the low-pressure heat transfer water circulation pipeline, it flows through the low-pressure heat transfer water circulation pump and the low-pressure heat transfer water heat exchanger in sequence. A portion of the heat transfer water then flows through the heat transfer water circulation pipeline, passing through the flue gas heater inlet valve and the flue gas heater in sequence, while the other portion enters the primary air low-pressure heater circulation pipeline and the secondary air low-pressure heater circulation pipeline. The primary air low-pressure heater circulation pipeline is equipped with a primary air low-pressure heater inlet valve. The heat medium water entering the primary air low-pressure heater circulation pipeline flows into the primary air low-pressure heater after passing through the primary air low-pressure heater inlet valve. The circulation pipeline of the secondary air low-pressure heater is equipped with a secondary air low-pressure heater inlet valve. The heat medium water entering the circulation pipeline of the secondary air low-pressure heater flows into the secondary air low-pressure heater after passing through the secondary air low-pressure heater inlet valve.

6. The dual-pressure dual-regenerative boiler flue gas waste heat recovery system for coal-fired power generating units according to any one of claims 1 to 3, characterized in that, The primary air subsystem includes: a primary air fan, a primary air low-pressure heater, and a primary air high-pressure heater, which are sequentially arranged in the primary air intake channel. The primary air low-pressure heater is located in the primary air low-pressure heater circulation pipeline, and the primary air high-pressure heater is located in the primary air high-pressure heater circulation pipeline. The primary air delivered by the primary air fan is heated sequentially by the primary air low-pressure heater, the primary air high-pressure heater, and the primary air preheater.

7. The coal-fired power generation unit dual-pressure dual-regenerative boiler flue gas waste heat recovery system according to any one of claims 1 to 3, characterized in that, The secondary air subsystem includes: a blower, a low-pressure secondary air heater, and a high-pressure secondary air heater, which are sequentially arranged in the secondary air intake channel. The low-pressure secondary air heater is located in the circulation pipeline of the low-pressure secondary air heater, and the high-pressure secondary air heater is located in the circulation pipeline of the high-pressure secondary air heater. The secondary air delivered by the blower is heated sequentially by the secondary air low-pressure heater, the secondary air high-pressure heater, and the secondary air preheater.

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