A gas-steam combined cycle cogeneration unit condensate waste heat utilization system

Abstract

The present application discloses a condensate waste heat utilization system for a gas-steam combined cycle cogeneration unit, comprising a first-stage water-water heat exchanger, a hot water air heater, a waste heat boiler condensate preheater, a second-stage water-water heat exchanger and a condensate system connected by pipelines; wherein the hot water air heater is located around the gas turbine air intake chamber, and the condensate in the condensate system sequentially enters the first-stage water-water heat exchanger, the hot water air heater, the waste heat boiler condensate preheater and the second-stage water-water heat exchanger, and heats return water from a heating network in the first-stage water-water heat exchanger for temperature increase, heats cold air entering the gas turbine in the hot water heater for temperature increase, heats waste heat of flue gas discharged from the gas turbine in the waste heat boiler condensate preheater for temperature increase, and heats circulating water from the heating network in the second-stage water-water heat exchanger for temperature increase, and then flows back to the first-stage water-water heat exchanger to form a closed-loop circulation.

Description

Technical Field

[0001] The present application belongs to the technical field of high back pressure heating of gas-steam combined cycle cogeneration, and in particular to a condensate waste heat utilization system of a gas-steam combined cycle cogeneration unit. Background Art

[0002] As my country's urbanization speed accelerates, the country's environmental protection requirements are becoming more and more stringent. Correspondingly, the proportion of coal-fired power plants and heating boilers will gradually decrease or even be shut down, resulting in a gap in regional heating. In this case, gas-fired units with high efficiency and low pollutant emissions have come into being. Gas-steam combined cycle cogeneration units are clean energy heating units. At the same time, through technical transformation, the exhaust heat energy of gas turbine waste heat boilers is recovered, which fully meets the national energy conservation and emission reduction and green development and ecological development requirements.

[0003] At present, the steam turbine exhaust pressure of the gas-fired thermal power plants that have been put into operation, especially the high back-pressure heating units, is high. In addition, since the heat network drain (water temperature is about 80°C) is also discharged into the condensate system, the condensate temperature is generally high, usually up to about 75°C. Taking a gas-fired power plant in the north as an example, it is known through experiments that the increase in condensate temperature directly leads to an increase in the exhaust temperature of the waste heat boiler and a decrease in efficiency. The waste heat boiler of the gas-fired power plant is generally not equipped with a heater. When operating in winter, cold air directly enters the boiler, affecting the main steam and reheat temperature entering the steam turbine, increasing gas consumption, and worsening the operating economy.

[0004] There are two common methods for recovering flue gas waste heat: preheating the workpiece; and preheating air to assist combustion. Preheating the workpiece with flue gas requires a large volume for heat exchange, often limiting the workspace. Preheating air to assist combustion is a preferred method, typically deployed on heating furnaces. It also intensifies combustion, accelerates furnace temperature rise, and improves thermal performance. This not only meets process requirements but also ultimately achieves significant overall energy savings. For gas-fired units, the conventional approach is to utilize the first waste heat recovery method, which recovers both the sensible heat of the flue gas and the latent heat of water vapor. Examples include spray-type flue gas heat exchangers, thermal storage devices, heat pumps, and the addition of bypass ducts to recover flue gas waste heat and reduce exhaust temperature. While these technical measures have some effectiveness, they increase fan power consumption or water consumption, limiting their energy conservation efforts.

[0005] In summary, how to solve the problem of high exhaust gas temperature of waste heat boiler has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] To address the above issues, the present invention provides a system for utilizing waste heat from condensate in a gas-steam combined cycle cogeneration unit. This system achieves high-level conversion of low-level flue gas waste heat, significantly improving the economic efficiency of system operation. The technical solution is as follows:

[0007] The present application provides a condensate waste heat utilization system for a gas-steam combined cycle cogeneration unit, comprising a first-stage water-water heat exchanger, a hot water air heater, a waste heat boiler condensate preheater, a second-stage water-water heat exchanger and a condensate system connected by pipelines; wherein the hot water air heater is located around the air inlet chamber of the gas turbine, and the condensate in the condensate system enters the first-stage water-water heat exchanger, the hot water air heater, the waste heat boiler condensate preheater and the second-stage water-water heat exchanger in sequence, and heats the return water from the heating network to increase its temperature in the first-stage water-water heat exchanger, heats the cold air entering the gas turbine to increase its temperature in the hot water heater, heats the condensate preheater with the waste heat of the flue gas discharged from the gas turbine to increase its temperature, and heats the circulating water from the heating network to increase its temperature in the second-stage water-water heat exchanger, and then flows back to the first-stage water-water heat exchanger to form a closed-loop circulation.

[0008] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the first-stage water-water heat exchanger is connected to the heat network circulating water return pipe and the heat network circulating pump inlet pipe, and the condensate in the condensate system enters the first-stage water-water heat exchanger to heat the heat network return water in the heat network circulating water return pipe and heat it up before being connected to the heat network circulating pump inlet pipe.

[0009] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the return water from the heat network in the first-stage water-water heat exchanger is heated from 35°C to 71°C by heat exchange, and the condensate in the first-stage water-water heat exchanger is cooled from 78°C to 60°C by heat exchange.

[0010] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the condensate flowing out of the first-stage water-water heat exchanger enters the hot water heater to heat the cold air entering the gas turbine from -5.5°C to 19°C, and the condensate in the hot water heater is cooled from 60°C to 40°C through heat exchange.

[0011] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the condensate flowing out of the hot water heater enters the waste heat boiler condensate preheater and exchanges heat with the waste heat of the flue gas exhausted by the gas turbine, and is heated from 40°C to 130°C; the exhaust gas temperature of the waste heat boiler condensate preheater is reduced to 70°C.

[0012] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the second-stage water-water heat exchanger is connected to the heat network circulation pump outlet pipe and the heat network circulation water supply pipe, and the condensate flowing out of the waste heat boiler condensate preheater enters the second-stage water-water heat exchanger to heat the heat network circulation water in the heat network circulation pump outlet pipe to increase the temperature and then connect to the heat network circulation water supply pipe.

[0013] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the temperature of the heat network circulating water in the second-stage water-water heat exchanger is raised from 68°C to 115°C through heat exchange, and the condensate in the second-stage water-water heat exchanger is cooled from 130°C to 78°C through heat exchange, and then flows back to the first-stage water-water heat exchanger.

[0014] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, a condensate recirculation pump is provided on the pipeline connecting the waste heat boiler condensate preheater and the second-stage water-water heat exchanger.

[0015] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the hot water heater includes several hot water heater heat exchange units, and the several hot water heater heat exchange units are arranged around the air intake chamber of the gas turbine. Layered shutters are provided on the heat dissipation surface of the hot water heater heat exchange unit to adjust the air volume entering the waste heat boiler condensate preheater.

[0016] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, the hot water heater heat exchange unit includes a plurality of heat exchange tubes, and aluminum fins are provided on the outer wall surfaces of the heat exchange tubes.

[0017] The beneficial effects brought about by the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit of the present application are as follows: the present application reduces the inlet water temperature of the waste heat boiler condensate preheater (waste heat boiler low-temperature economizer) 3 within a certain range by adding a two-stage water-water heat exchanger and a hot water air heater, and at the same time adds a hot water air heater system around the gas turbine air inlet chamber to realize the function of high-level conversion of low-level flue gas waste heat, which can greatly improve the economy of system operation. The present application heats the cold air with a low-temperature heat source by adding a hot water air heater, so that the low-grade heat is converted into high-grade new steam heat. Under the same gas volume, the purpose of improving the unit cycle thermal efficiency can be achieved, and the amount of cooling water in the heat network and the amount of high back pressure exhaust steam can be reduced. The present application can indirectly recover the waste heat of flue gas. Without affecting the electric power, the gas volume of the gas turbine remains unchanged, the exhaust temperature can be reduced by 30°C, and the heating capacity is significantly improved. The system of this application is simple. Compared with the current flue heat exchange and scaling, it increases the inlet air temperature of the waste heat boiler within a certain range, reduces the boiler exhaust temperature, indirectly utilizes the waste heat of condensate, increases the heating supply, and saves gas at the same time, which is beneficial to increasing the gas supply to residents and protecting people's livelihood. The entire system has a simple structure, uses conventional materials, is low in cost, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 This is a flow chart of the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit of the present application;

[0020] Figure 2 This is the layout diagram of the hot water heater in this application;

[0021] Figure 3 It is a top view of the heat exchange unit of the hot water heater of the present application;

[0022] Figure 4 This is a three-dimensional structural diagram of the heat exchange unit of the hot water heater of the present application;

[0023] Figure 5 It is a schematic diagram of the heat exchange tube structure of the heat exchange unit of the hot water heater of this application.

[0024] Figure numerals: 1-hot water heater, 2-first-stage water-water heat exchanger, 3-waste heat boiler condensate preheater, 4-second-stage water-water heat exchanger, 5-condensate recirculation pump, 6-condensate system, 7-heating network circulating water return pipe, 8-heating network circulating pump inlet pipe, 9-heating network circulating pump outlet pipe, 10-heating network circulating water supply pipe, 11-boiler low-pressure steam drum and deaerator, 12-hot water heater heat exchange unit, 13-heat exchange tube, 14-aluminum fin. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by persons of ordinary skill in the field to which this disclosure belongs. The words "first", "second" and similar terms used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0027] This application provides a condensate waste heat utilization system for a gas-steam combined cycle cogeneration unit, such as Figure 1As shown, a system flow chart of the present application is given, including a first-stage water-water heat exchanger 2, a hot water heater 1, a waste heat boiler condensate preheater 3, a second-stage water-water heat exchanger 4 and a condensate system 6 connected by pipelines; wherein the hot water heater 1 is located around the air inlet chamber of the gas turbine, and the condensate in the condensate system 6 enters the first-stage water-water heat exchanger 2, the hot water heater 1, the waste heat boiler condensate preheater 3 and the second-stage water-water heat exchanger 4 in sequence, and heats the return water from the heating network to increase its temperature in the first-stage water-water heat exchanger 2, heats the cold air entering the gas turbine to increase its temperature in the hot water heater 1, heats the condensate preheater 3 with the waste heat of the flue gas discharged from the gas turbine to increase its temperature, and heats the circulating water from the heating network to increase its temperature in the second-stage water-water heat exchanger 4, and then flows back to the first-stage water-water heat exchanger 2 to form a closed-loop circulation. According to the above embodiment, the present application reduces the inlet water temperature of the waste heat boiler condensate preheater (waste heat boiler low-temperature economizer) 3 within a certain range by adding a two-stage water-water heat exchanger and a hot water air heater, and at the same time adds a hot water air heater system around the gas turbine air inlet chamber to realize the function of high-level conversion of low-level flue gas waste heat, which can greatly improve the economy of system operation. The present application can indirectly recycle flue gas waste heat. Without affecting the electric power, the gas volume of the gas turbine remains unchanged, the exhaust temperature can be reduced by 30°C, and the heating capacity is significantly improved. The system of the present application is simple. Compared with the current flue heat exchange, scaling, etc., it increases the inlet air temperature of the waste heat boiler within a certain range, reduces the boiler exhaust temperature, indirectly utilizes the waste heat of condensate, increases the heating supply, and saves gas at the same time, which is conducive to increasing the gas supply to residents and protecting people's livelihood. The entire system has a simple structure and uses conventional materials. It is low in cost and has significant economic and social benefits.

[0028] This application adds a hot water heater to heat the cold air through a low-temperature heat source, so that the low-grade heat is converted into high-grade new steam heat. With the same amount of gas, the purpose of improving the cycle thermal efficiency of the unit can be achieved, and the amount of cooling water in the hot network and the amount of high back-pressure exhaust steam discharged can be reduced.

[0029] By analyzing and calculating the winter heating operating data of a gas-steam combined cycle direct air-cooled high back pressure heating unit, it is known that the exhaust gas temperature of the gas unit's waste heat boiler is relatively low, belonging to low-grade heat, and requires low-temperature water for recovery. Using the gas-steam combined cycle cogeneration unit condensate waste heat utilization system of this application, it is calculated that the gas saving rate of the flue gas waste heat recovery system is 4.9% to 9.14% when the heating load is in the range of 575.5MW to 322.5MW; under the 75% load condition, the gas saving rate is about 6.6%, that is, the gas saving amount per hour is 6.22t / h. Since the actual calorific value of the gas of Jiajie Thermal Power Company is 48.45MJ / kg, which is higher than the design calorific value (47.47MJ / kg), the gas saving rate under the 75% load condition is 6.1t / h, which is equivalent to a volume flow rate of 8830m3 / h. If the flue gas waste heat recovery system is put into operation for 90 days, the amount of gas saved will be 19.0728 million cubic meters, and the energy-saving effect is very obvious.

[0030] According to the relationship characteristics between power generation and gas turbine output at different air temperatures in the gas turbine thermal calculation book provided by the manufacturer, it can be seen that under the same gas volume, the output of the gas turbine is basically not affected by the inlet air temperature. After the use of the hot water heater, the temperature of the cold air entering the combustion chamber increases, and the final result is that the gas turbine exhaust temperature increases. Under the condition of a certain low-temperature economizer inlet water temperature, the heat absorbed by the air can be basically converted into the heat of the new steam of the unit, realizing the high-grade conversion of low-grade energy.

[0031] For example, when the gas turbine is under full load, when the gas turbine inlet air temperature is 10℃, the designed rated temperatures of the boiler main steam and reheat steam are 540℃ and 568℃ respectively. When the inlet air temperature rises, the main and reheat steam temperatures are maintained unchanged by the attemperating water system. When the inlet air temperature is -5.5℃, the main steam and reheat steam temperatures are 7.9℃ and 7.5℃ lower than the design values. When the inlet air temperature is -22.7℃, the main steam and reheat steam temperatures are 28.4℃ and 33.9℃ lower than the design values. During the unit's heating period, under high back pressure operation with the exhaust pressure unchanged and full-load rated gas flow, when the inlet air temperature is heated from -22.7°C to -5.5°C, the new steam parameters change, increasing the turbine output by 11.16MW and the heat carried by the waste heat boiler air, increasing the unit output by 6.22MW, for a total of 17.39MW, with a waste heat thermal power conversion rate of 76%. When the inlet air temperature is heated from -5.5°C to 10°C, the new steam parameters change, increasing the turbine output by 3.76MW and the heat carried by the waste heat boiler air, increasing the unit output by 5.59MW, for a total of 9.45MW, with a waste heat thermal power conversion rate of 45%. After the inlet air temperature exceeds 10°C, the main and reheat steam parameters maintain rated operation. If the inlet air temperature rises by 15.5°C, the heat carried by the waste heat boiler air increases, increasing the unit output by 5.59MW, with a waste heat thermal power conversion rate of 27.1%.

[0032] From the calculation of variable operating conditions, it can be seen that within a certain temperature range, with the upper limit of the gas turbine exhaust temperature as the limit, the use of a heater to increase the inlet air temperature can achieve the purpose of significantly improving the steam turbine power generation output. Therefore, adding a gas turbine inlet air heater plays an important role in improving the thermal efficiency of the entire machine cycle.

[0033] Increasing the condensate recirculation flow rate at the economizer outlet and lowering the economizer inlet water temperature can increase the economizer's heat dissipation and indirectly reduce the exhaust gas temperature. Tests have shown that a 20°C decrease in economizer inlet water temperature can reduce the exhaust gas temperature by 16°C. When the unit operates at high backpressure, the condensate outlet temperature is 70°C. Considering the effects of shaft temperature rise and the high drain temperature after extraction steam heating, the condensate temperature will rise further. Furthermore, the addition of a water-to-water heat exchanger also introduces a certain end-to-end difference, resulting in a water temperature entering the economizer exceeding 75°C (78°C can be considered). To achieve the desired 70°C exhaust gas temperature reduction, the economizer inlet water temperature needs to be further reduced to 40°C, based on the increased capacity of the water-to-water heat exchanger in the heat network. Considering a total water flow of 1200 t / h entering the two economizers, this heat can raise the air temperature by 46.7°C. Due to this significant temperature rise, the economizer inlet water temperature needs to be lowered overall. For example, a reduction of the inlet water temperature to 60°C would increase the air temperature by 24.5°C. Using this method, the water demand is 600t / h, and the calculated heat absorption of the high back pressure exhaust steam is 21MW.

[0034] By adopting a two-stage water-to-water heater heat exchange system and a high-level waste heat conversion system for hot water air heaters, the flue gas waste heat, which is between 70°C and 50°C, is recovered through the air-to-water heat exchanger and sent to the high-back-pressure inlet, dissipating 25.6MW of high-back-pressure exhaust heat. The two systems dissipate a total of 46.6MW of high-back-pressure exhaust heat. This application maintains the same gas flow rate without affecting electrical power, reduces exhaust temperature by 30°C, and significantly improves heating capacity.

[0035] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1 As shown, the first-stage water-water heat exchanger 2 is connected to the heat network circulating water return pipe 7 and the heat network circulating pump inlet pipe 8. The condensed water in the condensed water system 6 enters the first-stage water-water heat exchanger 2, heats the heat network return water in the heat network circulating water return pipe 7, and then is connected to the heat network circulating pump inlet pipe 8.

[0036] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1 As shown, the return water from the heat network in the first-stage water-water heat exchanger 2 is heated from 35°C to 71°C by heat exchange, and the condensed water in the first-stage water-water heat exchanger 2 is cooled from 78°C to 60°C by heat exchange.

[0037] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1 As shown, the condensate flowing out of the first-stage water-water heat exchanger 2 enters the hot water heater 1 and heats the cold air entering the combustion engine from -5.5°C to 19°C. The condensate in the hot water heater 1 is cooled from 60°C to 40°C through heat exchange.

[0038] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1 As shown, the condensate flowing out of the hot water heater 1 enters the waste heat boiler condensate preheater 3 and exchanges heat with the waste heat of the flue gas discharged by the combustion engine, and is heated from 40°C to 130°C; the exhaust gas temperature of the waste heat boiler condensate preheater 3 is reduced to 70°C.

[0039] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1As shown, the second-stage water-water heat exchanger 4 is connected to the heat network circulation pump outlet pipe 9 and the heat network circulating water supply pipe 10. The condensate flowing out of the waste heat boiler condensate preheater 3 enters the second-stage water-water heat exchanger 4 to heat the high back pressure outlet heat network circulating water in the heat network circulation pump outlet pipe 9 and then connects to the heat network circulating water supply pipe 10 after heat exchange and temperature increase.

[0040] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1 As shown, the heat network circulating water in the second-stage water-water heat exchanger 4 is heated from 68°C to 115°C by heat exchange, and the condensed water in the second-stage water-water heat exchanger 4 is cooled from 130°C to 78°C by heat exchange, and then flows back to the first-stage water-water heat exchanger 2.

[0041] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 1 As shown, a condensate recirculation pump 5 is provided in the pipeline connecting the waste heat boiler condensate preheater 3 and the second-stage water-water heat exchanger 4. Condensate flowing out of the waste heat boiler condensate preheater 3 is partially transported to the second-stage water-water heat exchanger 4 via the condensate recirculation pump 5, and the remaining portion is transported to the boiler's low-pressure steam drum-cum-deaerator 11.

[0042] According to the above embodiment, when the high-back-pressure condenser is put into operation, the high back-pressure operation of the unit results in a high condensate temperature. This condensate temperature can be effectively reduced by the hot water heater system. After heat exchange in the first-stage water-to-water heat exchanger 2, the return water from the heating network returns to the heating network circulating pump inlet 8, reducing the condensate temperature from 78°C to 60°C while simultaneously increasing the return water from 35°C to 71°C. The required heating network water flow rate is 300 t / h per side. Hot water heaters 1 are arranged around the inlet of the gas turbine air intake chamber. These hot water heaters 1 are used to heat the cold air entering the gas turbine compressor, with the condensate serving as the heat source. After the condensate enters the heater 1 and releases heat, its temperature drops from 60℃ to 40℃, and the cold air increases from -5.5℃ to 19℃; after cooling, the 40℃ condensate enters the waste heat boiler condensate preheater 4, exchanges heat with the flue gas waste heat, the condensate temperature increases from 40℃ to 130℃, and the exhaust gas temperature drops to 70℃; the 130℃ condensate is pumped to the second-stage water-water-heat exchanger 4 through the condensate recirculation pump 5 for heat exchange with the high back pressure outlet hot network circulating water. The second-stage water-water heat exchanger 4 is placed on the condensate recirculation pipeline. After the high back pressure outlet hot network circulating water and the recycled condensate are heat exchanged through the second-stage water-water heat exchanger 4, they are connected to the hot network circulating water supply pipeline 10. The condensate is recirculated to the inlet of the first-stage water-water heat exchanger 2. The high back pressure outlet hot network water temperature increases from 68℃ to 115℃, and the condensate recirculation temperature drops from 130℃ to 78℃.

[0043] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 2 As shown, the hot water heater 1 includes several hot water heater heat exchange units 12, which are arranged around the gas turbine air intake chamber. Layered shutters are provided on the heat dissipation surfaces of the hot water heater heat exchange units 12 to regulate the air volume entering the waste heat boiler condensate preheater 3. According to the above embodiment, unlike traditional boiler heaters, the hot water heater heat exchange units 12 in this application are arranged on the three air inlet surfaces of the gas turbine inlet. By adding shutters on the heat dissipation side, the air volume is adjusted. At the same time, during high temperature periods, the heater can be deactivated and the shutters can be opened to reduce wind resistance. During actual operation, the gas turbine compressor operates under pressure regulation, and the wind resistance will not affect the efficiency of the gas turbine. The shutters on the heat dissipation surface of the hot water heater are controlled in layers, and the traditional overall control of the shutters is transformed into separate control of the upper and lower layers. The control method is remote electric control. By adjusting the opening of the upper and lower shutters, the inlet air volume of the waste heat boiler condensate preheater 3 can be flexibly adjusted, thereby controlling the condensate outlet temperature within a reasonable range to achieve the purpose of anti-freezing.

[0044] For example, in the condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit provided in one embodiment, Figure 3-5 As shown, the hot water heater heat exchange unit 12 includes several heat exchange tubes 13, and aluminum fins 14 are provided on the outer wall of the heat exchange tubes 13. The heat exchange tubes are stainless steel tubes and adopt a two-row heat exchange tube structure. Figure 3 、 Figure 4 As shown, the specifications are It also adopts a low wind resistance design, controlling the wind resistance within 150Pa to reduce its impact on the wind and smoke system.

[0045] To facilitate accurate and intuitive monitoring of the wall temperature of the hot water heater's heat exchange tubes, operators can install an online temperature monitoring device on the tube walls to monitor the heater's temperature field, guide winter antifreeze operations, and optimize operations. There should be no fewer than 300 monitoring points, arranged in four layers from top to bottom: two layers for air temperature and two layers for wall temperature. The monitoring points should be insulated. This monitoring system is equipped with a separate signal control cabinet, monitoring software, and host computer. The monitoring computer is placed on the main control console for easy access by operators.

[0046] Based on the flue gas temperature and enthalpy table, a formula can be fitted to relate the temperature and enthalpy of each flue gas component. Multiplying this by the volume of each component yields the sensible heat of the flue gas, which can then be calculated for different exhaust temperatures. Assuming a boiler exhaust temperature of approximately 100°C, the sensible heat recovery for a flue gas exhaust temperature of 70°C is calculated, with the heater inlet water at 60°C.

[0047] Through system analysis, heat balance calculations, and experimental verification, this application can achieve the following results: Based on a flue gas flow rate of 4200t / h and a temperature drop of 30°C, 38MW of heat can be recovered. After using a hot water heater, the unit load can be increased by 12.7MW by operating the unit at full load using pure high back pressure. Based on a flue gas flow rate of 4200t / h, pure high back pressure operation can increase the output by 10.9MW. Considering the actual steam extraction rate, the recovery power is calculated at 75%, and the recoverable power is 8.2MW. After deducting the power generation, the heating capacity can be increased by 29.8MW. Considering a certain coefficient of 96%, the waste heat heating capacity can reach 28MW. Based on the annual operation of this application system for 3 months per year, the economic benefits are significant. If the heat supply is constant, it can save gas, which has significant social benefits for ensuring the gas supply for people's livelihood in some gas-deficient areas.

[0048] Although the embodiments of the present application have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the application as disclosed in the accompanying claims.

Claims

1. A gas-steam combined cycle cogeneration unit condensate waste heat utilization system, characterized in that: It includes a first-stage water-water heat exchanger, a hot water heater, a waste heat boiler condensate preheater, a second-stage water-water heat exchanger and a condensate system connected by pipelines; wherein, the hot water heater is located around the air inlet chamber of the gas turbine, and the condensate in the condensate system enters the first-stage water-water heat exchanger, the hot water heater, the waste heat boiler condensate preheater and the second-stage water-water heat exchanger in sequence, and heats the return water from the heating network to increase its temperature in the first-stage water-water heat exchanger, heats the cold air entering the gas turbine to increase its temperature in the hot water heater, heats the condensate preheater with the waste heat of the flue gas discharged by the gas turbine to increase its temperature, and heats the circulating water from the heating network to increase its temperature in the second-stage water-water heat exchanger, and then flows back to the first-stage water-water heat exchanger to form a closed system. The heat exchanger is connected to the heat network circulating water return pipe and the heat network circulating pump inlet pipe. The condensate in the condensate system enters the first-stage water-water heat exchanger, heats the heat network return water in the heat network circulating water return pipe by heat exchange and heats it up, and then connects it to the heat network circulating pump inlet pipe. In the first-stage water-water heat exchanger, the heat network return water is heated from 35°C to 71°C by heat exchange, and the condensate in the first-stage water-water heat exchanger is cooled from 78°C to 60°C by heat exchange. The condensate flowing out of the first-stage water-water heat exchanger enters the hot water heater, heating the cold air entering the gas turbine from -5.5°C to 19°C, and the condensate in the hot water heater is cooled from 60°C to 40°C by heat exchange.

2. The condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit according to claim 1 is characterized in that: The condensate flowing out of the hot water heater enters the waste heat boiler condensate preheater and exchanges heat with the waste heat of the flue gas discharged by the combustion engine, and is heated from 40°C to 130°C; the exhaust gas temperature of the waste heat boiler condensate preheater is reduced to 70°C.

3. The condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit according to claim 2 is characterized in that: The second stage water-water heat exchanger is connected to the outlet pipe of the heat network circulation pump and the heat network circulation water supply pipe. The condensate flowing out of the waste heat boiler condensate preheater enters the second stage water-water heat exchanger to heat the heat network circulation pump. The heat network circulating water in the outlet pipe is heated through heat exchange and then connected to the heat network circulating water supply pipe.

4. The condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit according to claim 3 is characterized in that: In the second-stage water-water heat exchanger, the heat network circulating water is heated from 68°C to 115°C by heat exchange, and the condensed water in the second-stage water-water heat exchanger is cooled from 130°C to 78°C by heat exchange, and then flows back to the first-stage water-water heat exchanger.

5. The condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit according to claim 1, characterized in that: A condensate recirculation pump is provided on the pipeline connecting the waste heat boiler condensate preheater and the second-stage water-water heat exchanger.

6. The condensate waste heat utilization system of a gas-steam combined cycle cogeneration unit according to claim 1, characterized in that: The hot water heater includes several hot water heater heat exchange units, which are arranged around the engine air intake chamber. Layered shutters are provided on the heat dissipation surface of the hot water heater heat exchange units to adjust the air volume entering the waste heat boiler condensate preheater.

7. The condensate waste heat utilization system of the gas-steam combined cycle cogeneration unit according to claim 6, characterized in that: The hot water heater heat exchange unit comprises a plurality of heat exchange tubes, and aluminum fins are arranged on the outer wall surfaces of the heat exchange tubes.

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