A steam turbine exhaust heat recovery system

Abstract

The utility model discloses a kind of exhaust steam heat recovery system of steam turbine, belong to thermal power generation and energy comprehensive utilization technical field.The system includes heat recovery condenser, the steam measuring space exhaust port of heat recovery condenser is communicated to ejector, cooling water drain port is communicated to heat pump unit, the cooling water drain port of heat pump unit is communicated to the cooling water inlet of heat recovery condenser, the condensate water drain port of heat recovery condenser and ejector is communicated to condensate tank;Exhaust steam enters heat recovery condenser and lower temperature cooling water pipe wall contact, exhaust steam releases latent heat of vaporization, condenses into condensate water, is pumped to condensate tank by condensate water.The temperature of cooling water after absorbing heat rises, exhaust heat recovery condenser, directly to production water place or into heat pump unit.The utility model changes "cooling" mode into "heating" mode by traditional, directly uses the low-temperature waste heat of steam turbine exhaust steam for heating, realizes the cascade utilization of energy.

Description

Technical Field

[0001] This utility model belongs to the field of thermal power generation and comprehensive energy utilization technology, specifically relating to a steam turbine exhaust heat recovery system. Background Technology

[0002] The main reason for the low efficiency of thermal power generating units is the large cold-end loss of the steam turbine. A large amount of low-grade heat carried by the exhaust steam after the steam turbine has done its work is carried away by the condenser circulating cooling water and diffused into the atmosphere, which is wasted. This results in a large amount of heat loss and evaporation loss of circulating cooling water.

[0003] Thermal power generation efficiency has always been a key indicator for measuring technological advancement and economic viability. However, even the most advanced ultra-supercritical coal-fired power plants struggle to break the 50% absolute power generation efficiency barrier; for most conventional coal-fired, gas-fired, and even nuclear power plants in operation, their cycle thermal efficiency generally hovers between 30% and 45%. This means that more than half, or even more, of the chemical energy of the fuel is not converted into electrical energy, but is lost in various forms.

[0004] Of these enormous heat losses, exhaust steam accounts for the vast majority. Although the work capacity of exhaust steam is very low, the heat it carries is still enormous, especially its latent heat of vaporization, which accounts for more than 70% of its total heat. In a traditional Rankine cycle, this portion of low-temperature heat energy must be released into the ambient air through the condenser and cooling system (such as circulating cooling water and cooling towers, or air-cooled islands) to achieve phase change condensation of the working fluid (from steam to water), thereby maintaining the high vacuum of the condenser and ensuring that the steam has sufficient expansion capacity to do work in the turbine. According to statistics, for a typical 1000MW condensing thermal power plant, the heat lost to the environment through cooling towers is as high as about 1500MW, which is almost equivalent to the total heat input of two units operating at full load. This huge energy waste not only represents an astonishing waste of energy, but also leads to a large amount of cooling water evaporation, the visual phenomenon of "white feathers" (cooling tower steam), and substantial thermal pollution, resulting in serious defects in both economic efficiency and environmental friendliness.

[0005] To address this challenge, the industry has explored and applied a variety of technical solutions, but each has significant limitations and has failed to fundamentally and ideally solve the problem.

[0006] 1. Conventional extraction combined heat and power (CHP) This is currently the most widely used form of combined heat and power.

[0007] Technical principle: During the operation of the steam turbine, a portion of steam that has not yet fully expanded and has a relatively high pressure and temperature (the extraction parameters are usually 0.8-2.5 MPa.a, 250℃-400°C) is extracted from the connecting pipe between the intermediate-pressure cylinder and the low-pressure cylinder (or other intermediate stages). This steam is then introduced into a dedicated heating network heater, where it heats the circulating water in the heating network through heat exchange, thereby providing heating or industrial heat to users.

[0008] limitation: (1) Serious “heat-electricity contradiction”: There is an inherent contradiction between steam extraction for heating and power generation. The more steam is extracted, the greater the heat supply, but the less steam enters the low-pressure cylinder to continue to do work and generate electricity, resulting in a decrease in power generation output.

[0009] (2) “High quality, low use” waste: The steam used is steam that has already done some work but still has a high grade (value). Using it to produce low-temperature hot water that only requires 70℃-130°C is a typical “over-devalued” energy utilization method. From the perspective of the second law of thermodynamics (value analysis), it is extremely uneconomical and causes a huge waste of high-quality energy.

[0010] (3) Failure to recover the core cold end loss: This scheme only recovers the heat of the intermediate stage steam extraction, while the huge latent heat of low temperature carried by the exhaust steam of the turbine (the main body of the cold end loss) is still completely discarded through the cooling system, and the recovery potential is limited.

[0011] 2. High back pressure circulating water heating Technical Principle: By completely eliminating the cooling function of the condenser, the operating back pressure of the steam turbine is significantly increased (for example, raising the vacuum state to an absolute pressure of 30kPa-50kPa or even higher), causing the exhaust steam temperature to rise accordingly to above 70℃-80℃. At this point, the turbine exhaust steam is no longer "exhaust steam" requiring condensation, but directly becomes the heat source for heating the circulating water in the heating network. The circulating water flows through the condenser (which now acts as the basic heater for the heating network) to absorb the latent heat of condensation from the exhaust steam before being delivered to heat users.

[0012] limitation: (1) Power generation efficiency deteriorates sharply: The significant increase in back pressure severely reduces the effective enthalpy drop of steam in the turbine, resulting in a sharp drop in power generation efficiency and a significant increase in coal consumption per unit of power generation. Its power supply economy is even far lower than that of pure condensing generator units.

[0013] (2) "Electricity determined by heat load" and rigid operation: The power generation of the unit is entirely determined by the heat load, and it has almost lost the ability to participate in the grid peak shaving. During the non-heating season or when the heat load is low, the unit cannot operate economically and may even have to be shut down.

[0014] (3) Endangering unit safety: High back pressure operation affects the working environment of the last few stages of the steam turbine, especially the last stage blades. Increased steam density and changes in flow velocity may cause serious problems such as flow instability, flutter, stress exceeding limits, and erosion, posing a severe challenge to the design and safety of the steam turbine itself. This technology is usually only applicable to the modification of small heating extraction steam units or specially designed cogeneration units, with a narrow range of applications.

[0015] 3. Absorption heat pump technology Technical principle: Utilizing a driving heat source (such as a small amount of high-grade extracted steam or combustion steam), an absorption heat pump system using lithium bromide-water as the working fluid is operated. The heat pump uses the circulating cooling water (or the exhaust steam itself) in the condenser as a low-temperature heat source, extracts heat from it, and "pumps" the heat to a higher temperature level, outputting hot water that can be used for heating.

[0016] limitation: (1) High initial investment: The absorption heat pump body and auxiliary system equipment are expensive, resulting in high initial construction costs.

[0017] (2) The economic viability of the system is questionable: The system requires a valuable driving heat source (steam extraction or fuel), and this energy cost must be included. At the same time, the system itself has heat exchange losses and pump power consumption, and its coefficient of performance (COP) is usually only around 1.6-1.8. The final calculated overall energy efficiency improvement and economic benefits are often not ideal, and the investment payback period is relatively long.

[0018] (3) Increased system complexity: Another complex chemical heat and mass transfer system has been introduced, which has high requirements for operation and maintenance and puts reliability to the test.

[0019] 4. Supplemental heating from electrode / gas boilers This is not a heat recovery technology, but a supplementary means to address insufficient heat load. Specifically, during peak heat demand periods, electric or steam boilers are started to directly produce hot water to supplement the heating supply.

[0020] Limitations: This not only fails to recover waste heat, but also consumes high-grade electricity or high-quality gas, which is a huge step backward from the perspective of energy utilization in the whole society. It is both economically and environmentally unfriendly, and should only be used as a last resort in extreme situations.

[0021] In summary, existing waste heat recovery or cogeneration technologies all have significant shortcomings: they either cannot address the core of cold-end losses (such as steam extraction for heating), or although they can recover all waste heat, they severely sacrifice power generation efficiency and operational flexibility (such as high back pressure heating), or the systems are complex and economically unsound (such as heat pump technology). Summary of the Invention

[0022] In order to overcome the shortcomings of the prior art, the purpose of this utility model is to provide a turbine exhaust heat recovery system. This exhaust heat recovery system can recover all the latent heat of the exhaust steam by adding a heat recovery condenser, a heat pump unit, and introducing a new cold source as a heat exchange medium, thereby achieving the effects of energy saving and consumption reduction and avoiding the discharge of alkaline exhaust steam into the main steam system, which would cause environmental pollution.

[0023] To achieve the above objectives, the technical solution adopted by this utility model is as follows: A steam turbine exhaust heat recovery system includes a heat recovery condenser 1. The exhaust steam inlet of the heat recovery condenser 1 is connected to the exhaust steam outlet of the steam turbine 6 or an extraction port opened on the original condenser 1a connected to the exhaust steam outlet of the steam turbine 6 via a pipeline. The condensate drain outlet of the heat recovery condenser 1 is connected to the condensate tank 9 via a pipeline.

[0024] A condensate pump 5 is installed on the pipeline between the condensate drain outlet of the heat recovery condenser 1 and the condensate tank 9.

[0025] The condensate pump 5 is equipped with a condensate filter 7 in its front-end pipeline.

[0026] The steam vent of the heat recovery condenser 1 is connected to the steam inlet of the ejector 2 via a pipe, and the condensate drain of the ejector 2 is connected to the front end pipe of the condensate filter 7 via a pipe.

[0027] The cooling water drain outlet of the heat recovery condenser 1 is connected to the production water inlet and the cooling water inlet of the heat pump unit 3 via pipelines.

[0028] The condenser-side water inlet of heat pump unit 3 is connected to the low-temperature production water outlet through a pipe, and the condenser-side drain outlet of heat pump unit 3 is connected to the production water outlet through a pipe.

[0029] The evaporator-side water inlet of heat pump unit 3 is connected to the cooling water inlet of heat recovery condenser 1 via a pipeline.

[0030] The heat pump unit 3 is either an electric heat pump unit or a lithium bromide absorption heat pump unit.

[0031] A cooling water circulation pump 4 is installed on the pipeline between the evaporator-side water inlet of the heat pump unit 3 and the cooling water inlet of the heat recovery condenser 1.

[0032] A cooling water filter 8 is installed at the front end of the cooling water circulation pump 4 on the pipeline between the evaporator-side water inlet of the heat pump unit 3 and the cooling water inlet of the heat recovery condenser 1.

[0033] The pipe between the evaporator-side water inlet of the heat pump unit 3 and the cooling water inlet of the heat recovery condenser 1 is connected to the low-temperature raw water supply pipe at the front end of the filter.

[0034] The outlet pipes of the cooling water circulation pump 4 and the condensate pump 5 are both equipped with check valves.

[0035] Multiple cooling water circulation pumps 4 and condensate pumps 5 are provided and connected in parallel to the corresponding pipelines.

[0036] The drain outlet of the condensate tank 9 is connected to the steam generation system required by the steam turbine 6 after passing through a heating and deoxygenation device, forming a Rankine cycle.

[0037] The exhaust steam inlet of the heat recovery condenser 1 is connected via a pipeline to the exhaust steam outlet of multiple steam turbines 6 or to the extraction port opened on the original condenser 1a that is connected to the exhaust steam outlet of the steam turbine 6.

[0038] The heat recovery condenser 1 can be a single unit or multiple units connected in parallel.

[0039] Compared with the prior art, the beneficial effects of this utility model are as follows: 1. Based on the original condenser and related equipment remaining unchanged, the turbine 6 further connects the exhaust steam to the heat recovery condenser 1. The condensate drain outlet of the heat recovery condenser 1 is connected to the condensate tank 9 through a pipeline. After passing through the heating and deoxygenation device, the drain outlet of the tank is connected to the steam generation system required by the turbine 6, thus creating a closed loop and forming a Rankine cycle.

[0040] 2. In this invention, the steam outlet of the steam measurement space of the heat recovery condenser 1 is connected to the ejector 2 through a pipeline to maintain the vacuum and thermodynamic performance of the heat recovery condenser 1. The high vacuum greatly reduces the exhaust pressure of the turbine 6, allowing the steam to expand to a lower pressure inside the turbine 6, thereby maximizing the conversion of heat exchange energy into mechanical energy and significantly improving the work capacity of the turbine 6 and the thermal efficiency of the entire cycle.

[0041] 3. In this invention, the cooling water drain outlet of the heat recovery condenser 1 is connected to the production water inlet and the cooling water inlet of the heat pump unit 3 through pipes. The condenser side inlet of the heat pump unit 3 is connected to the low-temperature production water drain outlet through pipes, and the condenser side drain outlet of the heat pump unit 3 is connected to the production water outlet through pipes. This avoids the waste of exhaust steam thermal efficiency and further improves thermal efficiency.

[0042] 4. This utility model is equipped with a condensate filter 7 and a cooling water filter 8 in the pipeline, which can remove solid impurities in the medium, protect the normal operation of downstream equipment, and improve the stability of the system.

[0043] In summary, this utility model connects to the exhaust steam discharged from the steam turbine, recovers all latent heat, achieves energy saving and consumption reduction, and avoids the environmental pollution caused by the discharge of alkaline exhaust steam into the main steam system. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structural principle of this utility model.

[0045] In the diagram, 1 is the heat recovery condenser, 1a is the original condenser, 2 is the ejector, 3 is the heat pump unit, 4 is the cooling water circulation pump, 5 is the condensate pump, 6 is the steam turbine, 7 is the condensate filter, 8 is the cooling water filter, and 9 is the condensate tank. Detailed Implementation

[0046] The structural and working principles of this utility model will be described in detail below with reference to the accompanying drawings.

[0047] like Figure 1 As shown, a turbine exhaust steam heat recovery system includes a heat recovery condenser 1. The exhaust steam inlet of the heat recovery condenser 1 is connected to the exhaust steam outlet of the turbine 6 via a pipeline, and a flow regulating valve is installed on the pipeline. The exhaust steam outlet is located at an appropriate position on the exhaust pipe of the turbine 6. In another embodiment, the exhaust steam inlet of the heat recovery condenser 1 is connected to an extraction port opened on the original condenser 1a, which is connected to the exhaust steam outlet of the turbine 6. The condensate drain outlet of the heat recovery condenser 1 is connected to a condensate tank 9 via a pipeline. The exhaust steam enters the heat recovery condenser 1 and comes into contact with the cooler cooling water pipe wall, releasing its latent heat of vaporization and condensing into condensate. The condensate drips into a hot well and is sent to the condensate tank 9 by the condensate pump 5. The cooling water absorbs heat, its temperature rises, and it is discharged from the heat recovery condenser 1, going directly to the production water supply or into the heat pump unit.

[0048] In the other two embodiments, the exhaust steam inlet of the heat recovery condenser 1 is connected to the exhaust steam outlet of the three steam turbines 6 through pipelines according to the actual production environment, or connected to the extraction steam outlet opened on the original condenser 1a connected to the exhaust steam outlet of the steam turbine 6. In addition, the three heat recovery condensers 1 are set up in parallel to work together according to the total amount of heat that can be recovered.

[0049] A condensate pump 5 is installed on the pipeline between the condensate drain outlet of the heat recovery condenser 1 and the condensate tank 9. A condensate filter 7 and a condensate discharge valve are installed on the pipeline at the front end of the condensate pump 5. The condensate filter 7 is a Y-type filter, or a basket filter in another embodiment. The condensate discharge valve is a manual valve, or an electric shut-off valve in another embodiment.

[0050] The steam vent of the heat recovery condenser 1 is connected to the steam inlet of the ejector 2 via a pipeline to maintain the vacuum and thermodynamic performance of the heat recovery condenser 1. The high vacuum significantly reduces the exhaust pressure of the turbine 6, allowing the steam to expand to a lower pressure within the turbine 6, thereby maximizing the conversion of heat exchange energy into mechanical energy and significantly improving the work capacity of the turbine 6 and the thermal efficiency of the entire cycle. The condensate drain of the ejector 2 is connected to the front end of the condensate filter 7 via a pipeline. The ejector 2 directs non-condensable gas and air leaking into the heat recovery condenser 1 to the steam vent of the heat recovery condenser 1, where it is extracted and discharged into the main steam system.

[0051] The cooling water drain outlet of the heat recovery condenser 1 is connected to the production water inlet and the cooling water inlet of the heat pump unit 3 via pipelines, and a cooling water drain valve is installed on the pipeline. This valve is a manual valve, or an electric shut-off valve in another embodiment. The heat pump unit 3 used in this system is an electric heat pump unit, and in other embodiments, a lithium bromide absorption heat pump unit or similar type may also be used.

[0052] The condenser-side inlet of heat pump unit 3 is connected to the low-temperature production water outlet via a pipeline, and the condenser-side outlet of heat pump unit 3 is connected to the production water source via a pipeline. The production water source includes preheated demineralized water, domestic hot water for the plant area, and heating.

[0053] The evaporator-side water inlet of the heat pump unit 3 is connected to the cooling water inlet of the heat recovery condenser 1 via a pipeline, and a cooling water drain valve is installed on the pipeline. This valve is a manual valve, or an electric shut-off valve in another embodiment.

[0054] The heat pump unit 3, driven by a high-temperature heat source (steam, hot water, gas, oil, superheated flue gas), extracts the heat energy from the heated cooling water and outputs medium-temperature or high-temperature hot water. The heat pump unit 3 employs a compression heat pump, and in another embodiment, an absorption heat pump.

[0055] A cooling water circulation pump 4 is installed on the pipeline between the evaporator-side water inlet of the heat pump unit 3 and the cooling water inlet of the heat recovery condenser 1.

[0056] The heat pump unit 3 can be selected as an electric heat pump unit or a lithium bromide absorption heat pump unit depending on the type of driving energy. In one embodiment, an electric heat pump unit is used, and in another embodiment, a lithium bromide absorption heat pump unit is used.

[0057] The cooling water comes from raw water (natural water sources such as groundwater and reservoir water in winter) or cooling water after cooling by heat pump unit 3. Driven by cooling water circulation pump 4, it provides cooling water to heat recovery condenser 1 to realize continuous recovery and effective utilization of waste heat from exhaust steam.

[0058] A cooling water filter 8 is installed on the pipeline between the evaporator-side water inlet of the heat pump unit 3 and the cooling water inlet of the heat recovery condenser 1, at the front end of the cooling water circulation pump 4. The cooling water filter 8 is a Y-type filter, or in another embodiment, a basket filter.

[0059] The pipeline between the evaporator-side water inlet of the heat pump unit 3 and the cooling water inlet of the heat recovery condenser 1 is connected to a low-temperature raw water inlet pipeline at the front end of the filter, and a raw water shut-off valve is installed on the pipeline. In this embodiment, a manual valve is used, while in another embodiment, an electric shut-off valve is used.

[0060] The outlet pipes of the cooling water circulation pump 4 and the condensate pump 5 are both equipped with check valves.

[0061] Two cooling water circulation pumps 4 and two condensate pumps 5 are provided and connected in parallel to the corresponding pipelines.

[0062] The drain outlet of the condensate tank 9 is connected to the steam generation system required by the steam turbine 6 after passing through the heating and deoxygenation device. It is then returned to the boiler and reheated into steam to form a Rankine cycle.

[0063] This system has three operating modes: "low-temperature raw water direct heat exchange operation mode", "heat pump unit indirect heat exchange operation mode" and "mixed heat exchange mode". It will not increase the back pressure of turbine 6. When the raw water shut-off valve is opened and the cooling water drain valve is closed, it is the low-temperature raw water direct heat exchange operation mode. When the cooling water drain valve is opened and the raw water shut-off valve is closed, it is the heat pump unit indirect heat exchange operation mode. When both the cooling water drain valve and the raw water shut-off valve are opened, it is the mixed heat exchange mode.

[0064] The system's energy efficiency COP is greater than 200 under the "low-temperature raw water direct heat exchange operation mode" and greater than 6 under the "heat pump unit indirect heat exchange operation mode". Although this invention also uses a heat pump unit as part of the system, this is to ensure that the system can recover heat from the exhaust steam of turbine 6 even when the existing cold source is insufficient. Simultaneously, the heat pump unit can convert and upgrade the low-temperature heat source exhausted by turbine 6 into a high-quality heat source suitable for production, increasing the operational flexibility of the system and ensuring that heat recovery can still be achieved even when the existing cold source is insufficient, thus guaranteeing uninterrupted operation throughout the year.

[0065] Recovering waste steam heat is of great significance for significantly improving the overall energy efficiency of power plants, reducing coal consumption for power supply, reducing carbon emissions, and increasing heating revenue.

Claims

1. A steam turbine exhaust heat recovery system, characterized in that, It includes a heat recovery condenser (1), the exhaust steam inlet of the heat recovery condenser (1) is connected to the exhaust steam outlet of the turbine (6) or the extraction port opened on the original condenser (1a) connected to the exhaust steam outlet of the turbine (6), and the condensate drain outlet of the heat recovery condenser (1) is connected to the condensate tank (9) through a pipeline.

2. The system according to claim 1, characterized in that, A condensate pump (5) is installed on the pipeline between the condensate drain outlet of the heat recovery condenser (1) and the condensate tank (9). The exhaust steam inlet of the heat recovery condenser (1) is connected by a pipeline to the exhaust steam outlet of multiple steam turbines (6) or to the extraction port opened on the original condenser (1a) connected to the exhaust steam outlet of the steam turbine (6). The heat recovery condenser (1) can be one unit or multiple units connected in parallel.

3. The system according to claim 2, characterized in that, The condensate pump (5) is equipped with a condensate filter (7) in the front end pipe.

4. The system according to claim 3, characterized in that, The steam exhaust port of the heat recovery condenser (1) is connected to the steam inlet of the ejector (2) through a pipe, and the condensate drain port of the ejector (2) is connected to the front end pipe of the condensate filter (7) through a pipe.

5. The system according to claim 3, characterized in that, The cooling water drain outlet of the heat recovery condenser (1) is connected to the production water inlet and the cooling water inlet of the heat pump unit (3) respectively through pipelines. The condenser side inlet of the heat pump unit (3) is connected to the low-temperature production water outlet through a pipe, and the condenser side outlet of the heat pump unit (3) is connected to the production water outlet through a pipe. The evaporator-side water inlet of the heat pump unit (3) is connected to the cooling water inlet of the heat recovery condenser (1) via a pipeline; The heat pump unit (3) is selected as an electric heat pump unit or a lithium bromide absorption heat pump unit.

6. The system according to claim 5, characterized in that, A cooling water circulation pump (4) is installed on the pipeline between the evaporator side inlet of the heat pump unit (3) and the cooling water inlet of the heat recovery condenser (1).

7. The system according to claim 6, characterized in that, A cooling water filter (8) is installed at the front end of the cooling water circulation pump (4) on the pipeline between the evaporator side inlet of the heat pump unit (3) and the cooling water inlet of the heat recovery condenser (1).

8. The system according to claim 7, characterized in that, The pipe between the evaporator-side water inlet of the heat pump unit (3) and the cooling water inlet of the heat recovery condenser (1) is connected to the low-temperature raw water pipe at the front end of the cooling water filter (8).

9. The system according to claim 6, characterized in that, The outlet pipes of the cooling water circulation pump (4) and the condensate pump (5) are both equipped with check valves; Multiple cooling water circulation pumps (4) and condensate pumps (5) are provided and connected in parallel to the corresponding pipelines.

10. The system according to claim 1, characterized in that, The drain outlet of the condensate tank (9) is connected to the steam generation system required by the steam turbine (6) after passing through a heating and deoxygenation device, forming a Rankine cycle.

Images