A boiler-machine coupled system for improving efficiency under low load and reducing cold source loss
By constructing a low-temperature flue gas recirculation system, the latent heat of steam extracted from the turbine is used to heat the low-temperature flue gas, which is then sent into the furnace for energy recovery. This solves the problem of difficulty in reducing cold source losses in existing technologies and enables efficient operation of the unit under low and medium loads.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- NORTH CHINA POWER ENG
- Filing Date
- 2025-08-11
- Publication Date
- 2026-07-17
Smart Images
Figure CN224516750U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of coal-fired power generation technology, specifically relating to a furnace-machine coupling low-load efficiency improvement system that reduces cold source loss. Background Technology
[0002] Traditional coal-fired power plants primarily consider efficiency under rated operating conditions, while coal consumption increases significantly under medium and low load conditions. Improving the economic efficiency of units under medium and low loads and achieving high efficiency across all operating conditions is one of the key technologies for the next generation of coal-fired power plants.
[0003] The efficiency of a power unit primarily depends on the boiler efficiency and the turbine's absolute internal efficiency. As the load decreases, boiler efficiency generally doesn't decrease significantly, while the turbine's absolute internal efficiency shows a marked downward trend. The turbine's absolute internal efficiency 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 cold source losses, i.e., the heat released into the environment by the exhaust steam from the turbine's low-pressure cylinder through the condenser. The turbine's absolute efficiency is generally around 50%, with cold source losses accounting for approximately 50%.
[0004] Steam turbine extraction and regenerative heating systems fully utilize the latent heat of steam to heat condensate and feedwater, representing a typical application for reducing cold source losses. The boiler's input heat comes from air, raw coal, and feedwater. Existing technologies for returning the latent heat of extracted steam to the boiler, such as using extracted steam to heat the air system before the air preheater (e.g., primary and secondary cold air), complicate the issue by increasing exhaust gas temperature and reducing boiler thermal efficiency. Similarly, heating the air system after the air preheater (e.g., primary and secondary hot air) has been found in engineering practice to be difficult to achieve in practice, even under low-load conditions, with primary and secondary hot air temperatures generally exceeding 320℃, approaching the critical parameters for steam. Considering the high temperature of the heated medium, factors such as air temperature rise, heat exchange end differences, and appropriate extraction steam parameter matching, it can be argued that using extracted steam to heat the air is practically insufficient to reduce cold-end exhaust steam volume and minimize cold source losses. 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. Utility Model Content
[0005] The technical problem to be solved by this utility model is to provide a boiler-turbine coupling low-load efficiency improvement system to reduce cold source loss, solve the problem that the existing technology is difficult to reduce cold source loss, and realize the full utilization of the latent heat of steam extraction from the turbine, reduce cold source loss, and improve the thermal economy of the unit at low and medium loads by innovating the system structure and constructing a low-temperature carrier that can recover the latent heat of steam extraction from the unit.
[0006] According to the technical solution of this utility model, this utility model provides a boiler-turbine coupled low-load efficiency improvement system for reducing cold source loss, including a boiler and a steam turbine. The boiler is connected to a boiler flue gas duct and a boiler feedwater duct. A recirculated flue gas duct is led out from the boiler flue gas duct, and the output end of the recirculated flue gas duct is connected to the boiler furnace. Multiple flue gas heaters are connected in series on the recirculated flue gas duct, including a flue gas condensate heater and a flue gas steam heater, with the flue gas steam heater located downstream of the flue gas condensate heater. Multiple [other types of heaters] are connected in series on the boiler feedwater duct. There are one high-pressure heater and multiple low-pressure heaters; each flue gas condensate heater corresponds to at least one low-pressure heater, and the input and output sides of the flue gas condensate heaters are connected to the corresponding input and output sides of the low-pressure heaters through condensate pipes to form a loop, and a pump is installed on the condensate pipes; the intermediate-pressure cylinder and the low-pressure cylinder of the steam turbine are connected to regenerative steam extraction pipes, which include low-pressure regenerative steam extraction pipes and high-pressure regenerative steam extraction pipes; the low-pressure regenerative steam extraction pipes are connected to the low-pressure heaters; the high-pressure regenerative steam extraction pipes are connected to the flue gas steam heaters.
[0007] In some implementations, a desulfurization device is installed in the boiler flue gas duct, and the recirculated flue gas duct is located downstream of the desulfurization device.
[0008] In some implementations, an air preheater, a dust collector, an induced draft fan, a desulfurization device, and a chimney are sequentially arranged along the flue gas conveying direction on the boiler flue gas duct.
[0009] In some implementations, the recirculated flue gas duct is located between the desulfurization unit and the chimney.
[0010] In some embodiments, a hot flue gas-cold flue gas heat exchanger is provided between the downstream flue gas steam heater in the recirculated flue gas duct and the furnace of the boiler; a flue gas bypass duct is provided on the boiler flue gas duct in parallel with the air preheater, and the hot flue gas-cold flue gas heat exchanger is located on the flue gas bypass duct.
[0011] In some implementations, a hot flue gas-cold flue gas heat exchanger and a hot flue gas condensate heat exchanger are connected in series on the flue gas bypass duct, with the hot flue gas condensate heat exchanger located downstream of the hot flue gas-cold flue gas heat exchanger.
[0012] In some implementations, the output end of the recirculated flue gas duct forms two branch ducts, which are respectively connected to the uppermost burnout air duct of the furnace and the flue gas nozzle located below the lowermost burner of the furnace.
[0013] In some embodiments, a flue gas demister is provided on the upstream side of the recirculated flue gas duct; an adjustable damper is provided on the boiler flue gas duct between the recirculated flue gas duct and the chimney; or an adjustable fan is provided in the recirculated flue gas duct.
[0014] In some embodiments, the flue gas condensate heater includes three arranged in sequence, and the low-pressure heater includes four arranged in sequence, wherein the two middle adjacent low-pressure heaters correspond to the same flue gas condensate heater, and the other two low-pressure heaters correspond one-to-one with the other two flue gas condensate heaters.
[0015] In some implementations, a feedwater pump and a deaerator are connected in series on the boiler feedwater pipeline between the high-pressure heater and the low-pressure heater; the flue gas steam heater is connected to the condenser.
[0016] Compared with the prior art, the beneficial technical effects of this utility model are as follows: This invention constructs a low-temperature flue gas recirculation system, utilizing flue gas as a heat recovery carrier. By setting up multi-stage stepped flue gas heaters, it fully utilizes the latent heat of steam extracted from the turbine, reduces cold source losses, and improves the thermal economy of the unit at low and medium loads and even rated loads. It is an innovation and reconstruction of the boiler-turbine system, with strong technical and economic feasibility, and is worthy of development and promotion. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the system structure provided by this utility model.
[0018] Explanation of reference numerals in the attached figures: 1. Boiler; 11. Boiler feedwater pipeline; 111. High-pressure heater; 112. Low-pressure heater; 113. Feedwater pump; 114. Deaerator; 12. Boiler flue gas pipeline; 121. Air preheater; 122. Dust collector; 123. Induced draft fan; 124. Desulfurization unit; 125. Chimney; 126. Hot flue gas and cold flue gas heat exchanger; 127. Hot flue gas condensate heat exchanger; 21. High-pressure cylinder; 22. Medium-pressure cylinder; 23. Low-pressure cylinder; 24. Generator; 31. Low-pressure regenerative steam extraction pipeline; 32. High-pressure regenerative steam extraction pipeline; 4. Recirculating flue gas pipeline; 41. Flue gas condensate heater; 42. Flue gas steam heater; 43. Flue gas demister; 51. Primary air fan; 52. Secondary air fan. Detailed Implementation
[0019] This invention provides a boiler-turbine coupling low-load efficiency improvement system to reduce cold source losses, solving the problem of existing technologies' difficulty in reducing cold source losses. Based on improving the thermal economy of the unit at low and medium loads, it constructs a low-temperature flue gas recirculation system. The system utilizes the steam extraction system of the turbine's low-pressure cylinder reheating system to heat the low-temperature flue gas. The heated flue gas is then sent into the furnace for the next cycle. This system uses low-temperature flue gas as a carrier for heating with the latent heat of the extracted steam, and enters the furnace in a recirculating manner, realizing the full utilization of the latent heat of the extracted steam, reducing the exhaust volume of the low-pressure cylinder, and improving the thermal economy of the unit.
[0020] Please see Figure 1 This utility model discloses a boiler-turbine coupling low-load efficiency improvement system for reducing cold source losses, comprising a boiler 1 and a steam turbine. The boiler 1 is connected to a boiler flue gas duct 12 and a boiler feedwater duct 11. Multiple high-pressure heaters 111 and multiple low-pressure heaters 112 are connected in series on the boiler feedwater duct 11. Typically, a feedwater pump 113 and a deaerator 114 are also connected in series on the boiler feedwater duct 11 between the high-pressure heaters 111 and the low-pressure heaters 112. The steam turbine includes a high-pressure cylinder 21, an intermediate-pressure cylinder 22, a low-pressure cylinder 23, and a generator 24 connected in series.
[0021] A recirculated flue gas duct 4 is led out from the boiler flue gas duct 12. Preferably, a desulfurization device 124 is installed in the boiler flue gas duct 12, and the recirculated flue gas duct 4 is located downstream of the desulfurization device 124, leading out the desulfurized low-temperature flue gas. The output end of the recirculated flue gas duct 4 is connected to the furnace of the boiler 1. Multiple flue gas heaters are connected in series on the recirculated flue gas duct 4. The flue gas heaters include a flue gas condensate heater 41 and a flue gas steam heater 42. The flue gas steam heater 42 is located downstream of the flue gas condensate heater 41. The flue gas heaters are used to heat the led-out low-temperature flue gas in stages.
[0022] The intermediate-pressure cylinder 22 and low-pressure cylinder 23 of the steam turbine are connected to regenerative steam extraction pipes, which include a low-pressure regenerative steam extraction pipe 31 and a high-pressure regenerative steam extraction pipe 32. The low-pressure regenerative steam extraction pipe 31 is connected to a low-pressure heater 112; specifically, each low-pressure regenerative steam extraction pipe 31 is connected to a low-pressure heater 112, thereby heating the water in the boiler feedwater pipe 11. After heat exchange, the low-pressure extracted steam generally enters the condenser and then the condensate system.
[0023] Each flue gas condensate heater 41 corresponds to at least one low-pressure heater 112. The input and output sides of the flue gas condensate heater 41 are connected to the input and output sides of the corresponding low-pressure heater 112 through condensate pipes to form a loop, and a pump is installed on the condensate pipes. Specifically, the corresponding flue gas condensate heaters and low-pressure heaters are a group. Different flue gas condensate heaters correspond to different low-pressure heaters. In a group structure, the two sides of the low-pressure heater are connected to the two sides of the flue gas condensate heater through condensate pipes, and a pump is installed on the condensate pipes. The water flow direction is shown by the arrow in the figure. This allows a portion of the condensate heated by the extracted steam in the boiler feedwater pipe 11 to be extracted for preliminary heating of the low-temperature flue gas. The condensate after heat exchange then returns to the inlet of the corresponding low-pressure heater 112.
[0024] The high-pressure regenerative steam extraction pipe 32 is connected to the flue gas steam heater 42, thereby using high-pressure steam extraction to further heat the flue gas; more specifically, the flue gas steam heater 42 is connected to the condenser, and the high-pressure steam extraction enters the condenser and then the condensate system after heat exchange.
[0025] This invention constructs a reasonable low-temperature flue gas recirculation system (including recirculated flue gas pipeline 4, flue gas heater, etc.), using low-temperature flue gas as a carrier for recovering latent heat of steam and reducing cold source losses. Typically, the temperature of the recirculated flue gas increases after being heated by extracted steam, resulting in increased exhaust gas temperature and decreased boiler efficiency when it is sent into the boiler. To maximize the utilization of the latent heat of low-grade extracted steam and extract as much steam as possible from the unit, the reduction in boiler efficiency caused by flue gas recirculation is offset. The flue gas recirculation extraction point is preferably located downstream of the desulfurization system, where the temperature of the flue gas after desulfurization is generally around 45°C, which can further increase revenue.
[0026] In a specific embodiment, 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 on the boiler flue gas duct 12. The recirculated flue gas duct 4 is located between the desulfurization device 124 and the chimney 125.
[0027] Electric regulating dampers or fans are installed between the desulfurization unit 124 and the chimney 125 or on the recirculated flue gas duct 4 to regulate the amount of flue gas drawn out. For example, with partial load as the design condition, the flue gas circulation volume is constrained to achieve the reheat steam temperature at the rated value (30% THA), aiming to improve the thermal economy of the unit at low and medium loads without affecting the existing boiler and auxiliary systems, including the existing capacity and operational adaptability.
[0028] For example, in the illustrated embodiment, an adjustable damper is provided on the boiler flue gas duct 12 between the recirculated flue gas duct 4 and the chimney 125, thereby allowing a portion of the flue gas required to enter the recirculated flue gas duct 4 by changing the duct pressure, eliminating the need for a fan in the recirculated flue gas duct 4. In other embodiments, an adjustable fan is provided in the recirculated flue gas duct 4 to provide power and extract the required amount of flue gas. Furthermore, considering the corrosion problem of installing a fan at the inlet of the recirculated flue gas duct 4, it is preferable to place the fan on the high-temperature side, for example, between the downstream flue gas steam heater 42 and the hot flue gas-cold flue gas heat exchanger 126.
[0029] Furthermore, a flue gas bypass pipe is installed on the boiler flue gas duct 12 in parallel with the air preheater 121. A hot flue gas-cold flue gas heat exchanger 126 is installed between the flue gas steam heater 42 at the downstream end of the recirculated flue gas duct 4 and the furnace of the boiler 1. The hot flue gas-cold flue gas heat exchanger 126 is located on the flue gas bypass pipe. Specifically, the inlet end of the flue gas bypass pipe is connected to the inlet pipe of the air preheater 121, and the outlet end of the flue gas bypass pipe is connected to the outlet pipe of the air preheater 121, so that the flue gas in the boiler flue gas duct 12 is divided into two paths, which undergo different heat exchange processes and then converge. The cold flue gas refers to the recirculated flue gas after being heated by steam extraction, and the hot flue gas refers to the flue gas at the air preheater inlet (high-temperature flue gas output from the furnace).
[0030] A hot flue gas-cold flue gas heat exchanger 126 and a hot flue gas condensate heat exchanger 127 are connected in series on the flue gas bypass pipe. The hot flue gas condensate heat exchanger 127 is located downstream of the hot flue gas-cold flue gas heat exchanger 126 and is connected to the condensate system, thereby further recovering energy from the flue gas output from the furnace by heating the condensate.
[0031] This design includes an air preheater flue gas bypass, ensuring that the flue gas exhaust temperature within the air preheater returns to its pre-recirculation level. The recirculated flue gas passes through the final stage flue gas steam heater and then enters the hot flue gas-cold flue gas heat exchanger 126 before finally entering the furnace. The bypass flue gas passes through the hot flue gas-cold flue gas heat exchanger 126 and then through the hot flue gas condensate heat exchanger 127, where its temperature decreases to the same level as the main flue gas at the air preheater outlet. It then merges with the air preheater outlet flue gas and enters the main flue gas system (entering the main flue gas pipeline 12 of the boiler).
[0032] Preferably, the output end of the recirculated flue gas duct 4 forms two branch ducts, which are respectively connected to the uppermost burnout air duct of the furnace and the flue gas nozzle located below the lowermost burner in the furnace. As a supplementary explanation, the furnace of the boiler 1 is equipped with ducts and burners in layers, including, for example, a primary air duct and a primary air fan 51 connected to the air preheater, a secondary air duct and a secondary air fan 52 connected to the air preheater, etc. In this scheme, considering the temperature level of the recirculated flue gas, the recirculated flue gas is fed into the furnace in two parts. More specifically, a small portion of the recirculated flue gas is fed into the furnace through an additional layer of flue gas nozzles below the lowermost burner, while the majority is fed into the furnace through the uppermost burnout air.
[0033] Preferably, a flue gas demister 43 is provided on the upstream side of the recirculated flue gas duct 4 to separate liquid droplets in the flue gas to a certain extent, which helps to avoid or slow down corrosion of subsequent ducts and heaters.
[0034] like Figure 1 In the embodiment shown, the flue gas condensate heater 41 includes three arranged in sequence, and the low-pressure heater 112 includes four arranged in sequence, wherein the two adjacent low-pressure heaters in the middle correspond to the same flue gas condensate heater, and the other two low-pressure heaters correspond one-to-one with the other two flue gas condensate heaters. More specifically, the high-pressure heater 111 includes high-pressure heaters No. 0, No. 1, No. 2, No. 3, and No. 4 arranged sequentially, and the low-pressure heater 112 includes low-pressure heaters No. 6, No. 7, No. 8, and No. 9 arranged sequentially. The intermediate-pressure cylinder 22 and the low-pressure cylinder 23 are provided with three high-pressure regenerative steam extraction pipes 32 (e.g., including 3-stage unit steam extraction and 4-stage unit steam extraction) and four low-pressure regenerative steam extraction pipes 31 in order of gradually decreasing pressure. The three high-pressure regenerative steam extraction pipes 32 are respectively connected to three flue gas steam heaters 42. The four low-pressure heaters correspond to the flue gas condensate heaters 41 in the aforementioned manner, with low-pressure heaters No. 7 and No. 8 corresponding to the middle flue gas condensate heater 41. Overall, the temperature of the heating medium in the six flue gas heaters increases sequentially along the flue gas flow direction to heat the flue gas in stages.
[0035] In this invention, considering the very low extraction pressure of the low-pressure cylinder steam under low load (0.1–0.027 MPa at 40% operating conditions), and taking into account system resistance, the low-pressure extraction steam faces difficulties in entering the flue gas steam heater and suffers from poor drainage. Therefore, this invention proposes using low-temperature condensate to heat the flue gas within the low-pressure cylinder extraction range (indirectly using low-pressure extraction). After the condensate-flue gas heat exchanger, high-pressure extraction is used for heating in stages. The recirculated flue gas passes through the condensate-flue gas heat exchanger, the flue gas steam heater, and the bypass hot-flue gas-cold-flue gas heat exchanger before being sent into the furnace. With flue gas recirculation, the flue gas flow rate from the furnace inlet to the tail end heating surface increases, generally enhancing heat exchange at the heating surface and increasing the working fluid outlet temperature, thus having a beneficial effect on boiler operation. Taking a 1,000 MW unit as an example, with a 40% THA (Total Heat Amount) operating condition as the design point, considering boiler efficiency reduction under both 40% THA and 30% THA conditions, this system brings two coal-saving benefits: the contribution of extraction steam reheat and the contribution of recirculation parameter improvement. The coal consumption for power generation is reduced by 3.5 / 3.8 g / kWh, demonstrating significant efficiency improvement and strong feasibility. In specific projects, this system is rationally determined based on the set energy-saving targets by optimizing factors such as flue gas recirculation volume, the number of stages of the cascade steam heaters, boiler adaptability, and cost. This system is not only suitable for low-load units but also for improving efficiency 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 flexibly applied according to specific efficiency improvement requirements.
[0036] 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; for ease of description, this article only explains the key improvements of this utility model, and the other required or optional specific technical contents are not described in detail, and existing technology or any feasible method can be adopted; based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this utility model; 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 recorded 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 machine-boiler coupling low load efficiency improving system for reducing cold source loss, characterized in that, It includes a boiler (1) and a steam turbine. The boiler (1) is connected to a boiler flue gas pipe (12) and a boiler feed water pipe (11). A recirculating flue gas pipe (4) is led out from the boiler flue gas pipe (12). The output end of the recirculating flue gas pipe (4) is connected to the furnace of the boiler (1). Multiple flue gas heaters are connected in series on the recirculating flue gas pipe (4). The flue gas heaters include a flue gas condensate heater (41) and a flue gas steam heater (42). The flue gas steam heater (42) is located downstream of the flue gas condensate heater (41). Multiple high-pressure heaters (111) and multiple low-pressure heaters (112) are connected in series on the boiler feedwater pipe (11); each flue gas condensate heater (41) corresponds to at least one low-pressure heater (112), and the input and output sides of the flue gas condensate heater (41) are connected to the input and output sides of the corresponding low-pressure heater (112) through the condensate pipe to form a loop, and a pump is installed on the condensate pipe; The intermediate pressure cylinder (22) and low pressure cylinder (23) of the steam turbine are connected to regenerative extraction steam pipes, which include low pressure regenerative extraction steam pipe (31) and high pressure regenerative extraction steam pipe (32); the low pressure regenerative extraction steam pipe (31) is connected to the low pressure heater (112); the high pressure regenerative extraction steam pipe (32) is connected to the flue gas steam heater (42).
2. The system of claim 1, wherein the system further comprises a heat exchanger. A desulfurization device (124) is installed in the boiler flue gas duct (12), and the recirculated flue gas duct (4) is located downstream of the desulfurization device (124).
3. The system of claim 1, wherein the system further comprises a heat exchanger. An air preheater (121), a dust collector (122), an induced draft fan (123), a desulfurization device (124), and a chimney (125) are sequentially installed on the boiler flue gas duct (12) along the flue gas conveying direction.
4. The system of claim 3, wherein the system further comprises a heat exchanger. The recirculated flue gas duct (4) is located between the desulfurization unit (124) and the chimney (125).
5. The system of claim 3, wherein the system further comprises a heat exchanger. A hot flue gas-cold flue gas heat exchanger (126) is installed between the flue gas steam heater (42) on the downstream side of the recirculated flue gas duct (4) and the furnace of the boiler (1). A flue gas bypass pipe is installed on the boiler flue gas pipe (12) in parallel with the air preheater (121), and the hot flue gas and cold flue gas heat exchanger (126) is located on the flue gas bypass pipe.
6. The system of claim 5, wherein the system further comprises a heat exchanger. A hot flue gas-cold flue gas heat exchanger (126) and a hot flue gas condensate heat exchanger (127) are connected in series on the flue gas bypass pipe. The hot flue gas condensate heat exchanger (127) is located downstream of the hot flue gas-cold flue gas heat exchanger (126).
7. The boiler-machine coupling low-load efficiency improvement system for reducing cold source loss according to any one of claims 1-6, characterized in that, The output end of the recirculated flue gas duct (4) forms two branch ducts, which are respectively connected to the burnout air duct at the top of the furnace and the flue gas nozzle located below the burner at the bottom of the furnace.
8. The system of any one of claims 1-6, wherein the system is a boiler- furnace coupling low load efficiency improvement system with reduced cold source loss. A flue gas demister (43) is installed on the upstream side of the recirculated flue gas duct (4); an adjustable damper is installed on the boiler flue gas duct (12) between the recirculated flue gas duct (4) and the chimney (125), or an adjustable fan is installed in the recirculated flue gas duct (4).
9. The system of any one of claims 1-6, wherein the system is a boiler- furnace coupled low load efficiency enhancement system with reduced cold source loss, characterized in that, The flue gas condensate heater (41) includes three arranged in sequence, and the low-pressure heater (112) includes four arranged in sequence, wherein the two adjacent low-pressure heaters in the middle correspond to the same flue gas condensate heater, and the other two low-pressure heaters correspond one-to-one with the other two flue gas condensate heaters.
10. The system of any one of claims 1-6, wherein the system is a boiler- furnace coupled low load efficiency enhancement system with reduced cold source loss, and wherein the system further comprises a heat exchanger. A feedwater pump (113) and a deaerator (114) are connected in series between the high-pressure heater (111) and the low-pressure heater (112) on the boiler feedwater pipeline (11); the flue gas steam heater (42) is connected to the condenser.