Exhaust steam waste heat recovery system for boiler of power plant

Abstract

The invention discloses a power plant boiler exhaust steam waste heat recovery system, and aims to improve the energy utilization efficiency of a boiler system and solve the problems of insufficient heat energy recovery, incomplete gas separation and unstable system operation in the prior art. The system comprises a deaerator, a regular drainage flash tank, a first steam-water mixer, a second steam-water mixer, a degassing buffer tank, a degassing water storage tank, a first hot water pump, a second hot water pump and the like. Oxygen, carbon dioxide and other non-condensable gases in demineralized water are removed through the precise gas separation device, and meanwhile, the frequency converter is adopted to adjust the operation speed of the pump so as to improve energy efficiency and ensure stable operation of the system. Through optimization design and material selection, the heat exchange efficiency, the gas separation effect and the overall reliability of the system are improved, the recovery efficiency of boiler waste heat is remarkably improved, energy consumption and environmental pollution are reduced, and high application value and energy-saving effect are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste heat recovery and utilization, and particularly relates to a waste heat recovery system for boiler exhaust steam in a power plant. Background Art

[0002] With the continuous improvement of energy utilization efficiency, energy conservation and environmental protection of boiler systems have become important research directions in the energy field. As an important means to improve energy utilization efficiency, the waste heat recovery system for boiler exhaust steam has been increasingly emphasized.

[0003] Currently, the boiler exhaust steam system in a power plant usually generates a large amount of heat energy, which is directly discharged into the environment in the form of waste heat in traditional systems, resulting in energy waste and environmental pollution. In existing waste heat recovery systems for exhaust steam, although some devices have recovered the heat of boiler exhaust steam to heat water, thereby saving energy, there are still some technical problems, especially in aspects such as heating water quality, deaeration, and gas separation.

[0004] Although devices such as deaerators, steam-water mixers, and buffer tanks in the prior art can recover a certain amount of heat energy and heat water, the heat exchange efficiency during the mixing process of high-temperature steam and demineralized water is relatively low, making it difficult to fully utilize the heat of the steam. In addition, the treatment effect of deaeration equipment also has certain limitations, and it is easy to cause incomplete removal of oxygen, carbon dioxide, and other non-condensable gases in the demineralized water, thereby affecting the stability of the subsequent water quality and the operation efficiency of the boiler. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a waste heat recovery system for boiler exhaust steam in a power plant, which can achieve improved heat exchange efficiency, enhanced gas separation effect, and better recovery of waste heat from boiler exhaust steam.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: A waste heat recovery system for boiler exhaust steam in a power plant includes a deaerator and a regular blowdown flash tank connected to the boiler, and also includes a demineralized water inlet pipe, an outlet pipe, a first steam-water mixer, a degassing buffer tank, a second steam-water mixer, a degassing water storage tank, and a first hot water pump; The first steam-water mixer mixes the demineralized water conveyed by the demineralized water inlet pipe with the steam conveyed by the deaerator, and sends the heated demineralized water into the degassing buffer tank. The degassing buffer tank directly flows the hot demineralized water into the inner side of the degassing water storage tank by gravity; The second steam-water mixer mixes the demineralized water conveyed by the demineralized water inlet pipe with the steam conveyed by the regular blowdown flash tank, and sends the heated demineralized water into the degassing water storage tank; Both the degassing buffer tank and the degassing water storage tank separate water and gas through degassing equipment and discharge the separated gas to the outside. The degassing water storage tank discharges the demineralized water through the first hot water pump and the water outlet pipe and sends it back to the demineralized water inlet pipe.

[0007] Furthermore, a second hot water pump is also provided on the pipeline connecting the degassing water storage tank and the water outlet pipe. The second hot water pump is connected in parallel with the first hot water pump on the pipeline. The second hot water pump and the first hot water pump are used alternately, and both the second hot water pump and the first hot water pump are connected with frequency converters.

[0008] Furthermore, a first stop valve is connected to the liquid inlet ends of both the second hot water pump and the first hot water pump, and a check valve is connected to the liquid outlet ends of both the second hot water pump and the first hot water pump.

[0009] Furthermore, gas discharge ports are provided at the upper ends of both the degassing buffer tank and the degassing water storage tank.

[0010] Furthermore, filters are connected to the liquid inlet ends of both the first steam-water mixer and the second steam-water mixer, and second stop valves are connected to the liquid inlet ends of both filters.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: First of all, the first steam-water mixer and the second steam-water mixer utilize the heat of the boiler exhaust steam to heat the demineralized water through high-efficiency heat exchange technology. This design improves the heat exchange efficiency between steam and demineralized water and avoids the problem of insufficient heat energy recovery in the existing system. By selecting appropriate materials (such as stainless steel 316L and 304), the high-temperature resistance and corrosion resistance of the heat exchanger are improved, thus ensuring the long-term stable operation of the system in a high-temperature environment.

[0012] Secondly, the degassing buffer tank and the degassing water storage tank effectively remove oxygen, carbon dioxide and other non-condensable gases in the demineralized water through degassing equipment, solving the problem of unsatisfactory gas separation effect in the prior art. Through the precisely designed gas discharge ports and highly corrosion-resistant materials (such as copper alloy and stainless steel), the smooth discharge of gas is ensured, preventing the risk of gas leakage and unstable system operation. The water quality in the degassing water storage tank is maintained stable, avoiding the phenomenon that the dissolved gas in the water affects the operation of the boiler.

[0013] In addition, the first hot water pump and the second hot water pump are operated in parallel, and the operation speed of the pump is adjusted by combining with a frequency converter, making the control of the water flow more precise and effectively solving the problems of unstable operation and low energy efficiency of the water pump in the traditional system. The frequency converter can automatically adjust the pump speed according to the actual load of the system, improving the energy use efficiency and ensuring the smooth operation of the system, reducing the probability of failure.

[0014] Through the meticulous design and material selection of each component, the system of the present invention not only improves the thermal energy recovery efficiency, reduces energy waste, but also optimizes the gas separation and water quality control processes, greatly enhancing the operational reliability and energy-saving effect of the power plant boiler system. At the same time, the parallel pump design and intelligent control scheme of the system effectively extend the service life of the equipment and reduce the maintenance cost. Brief Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the overall structure of the waste heat recovery system of the present invention.

[0016] In the drawings, the list of components represented by each reference numeral is as follows: 1, demineralized water inlet pipe; 2, outlet pipe; 3, deaerator; 4, first steam-water mixer; 5, deaeration buffer tank; 6, second steam-water mixer; 7, regular blowdown flash tank; 8, deaeration water storage tank; 9, first hot water pump; 10, second hot water pump. Detailed Embodiments

[0017] In order to make the purpose and advantages of the present invention more clear, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific implementation manners of the present invention, and does not strictly limit the scope of protection specifically claimed by the present invention. Embodiment 1

[0018] As Figure 1 shown, a power plant boiler exhaust waste heat recovery system includes a deaerator 3 and a regular blowdown flash tank 7 connected to the boiler, and also includes a demineralized water inlet pipe 1, an outlet pipe 2, a first steam-water mixer 4, a deaeration buffer tank 5, a second steam-water mixer 6, a deaeration water storage tank 8 and a first hot water pump 9; The first steam-water mixer 4 mixes the demineralized water transported by the demineralized water inlet pipe 1 with the steam transported by the deaerator 3, and sends the heated demineralized water into the deaeration buffer tank 5; the first steam-water mixer 4 adopts advanced heat exchange technology, and through an efficient heat exchange surface design (for example, using a shell-and-tube heat exchanger made of stainless steel 316L, model HX-300), realizes the effective heat exchange between steam and demineralized water. The heat of the steam quickly heats the demineralized water through conduction, convection and other methods, improving the thermal energy utilization rate. The deaeration buffer tank 5 directly flows the hot demineralized water into the inner side of the deaeration water storage tank 8 by gravity; the deaeration buffer tank 5 is made of high-temperature resistant and corrosion-resistant carbon steel (model Q235B), which can withstand high temperature and relatively high pressure, and ensure long-term operation stability.

[0019] The second steam-water mixer 6 mixes the demineralized water conveyed by the demineralized water inlet pipe 1 with the steam conveyed by the regular blowdown flash tank 7, and sends the heated demineralized water into the deaeration storage tank 8; the second steam-water mixer 6 also adopts an efficient heat exchange design to ensure that the heat exchange between the steam and the demineralized water can be carried out quickly and evenly, and is made of stainless steel 304 material (model HX-400) to increase corrosion resistance and improve service life.

[0020] Both the deaeration buffer tank 5 and the deaeration storage tank 8 separate water and gas through deaeration equipment and discharge the separated gas to the outside; gas discharge ports are provided at the upper ends of the deaeration buffer tank 5 and the deaeration storage tank 8; the gas discharge ports adopt a sealed design to prevent gas leakage and ensure the safe operation of the system. The gas discharge device uses copper alloy material (model CuZn40Pb2), which has excellent corrosion resistance and avoids oxidation problems during long-term use.

[0021] The deaeration storage tank 8 discharges the demineralized water through the first hot water pump 9 and the outlet pipe 2 and sends it back to the demineralized water inlet pipe 1; the first hot water pump 9 adopts an efficient electric pump (model LHB-75), which has a high flow rate and pressure output, can ensure the stable circulation of the demineralized water, and is suitable for water treatment systems under high temperature and high pressure environments.

[0022] As Figure 1 shown, a second hot water pump 10 is also provided on the pipeline connecting the deaeration storage tank 8 and the outlet pipe 2, and the second hot water pump 10 is connected in parallel with the first hot water pump 9 on the pipeline; the second hot water pump 10 and the first hot water pump 9 are used alternately, and both the second hot water pump 10 and the first hot water pump 9 are connected with frequency converters; the frequency converter (model ABB VFD-A) can automatically adjust the running speed of the pump according to the system load, so as to achieve energy saving and stable water flow control, reduce energy consumption and extend the equipment life.

[0023] As Figure 1 shown, the inlet ends of both the second hot water pump 10 and the first hot water pump 9 are connected with first stop valves, and the outlet ends of both the second hot water pump 10 and the first hot water pump 9 are connected with check valves; the first stop valve is made of stainless steel material (model Z15T), which can effectively control the flow rate when the pump starts and stops, ensuring the normal operation of the system; the check valve is made of copper alloy material (model BRZ-40), which has strong corrosion resistance, prevents backflow, and ensures the one-way flow of water.

[0024] As Figure 1As shown in the figure, filters are connected to the liquid inlet ends of the first steam-water mixer 4 and the second steam-water mixer 6, and second stop valves are connected to the liquid inlet ends of both filters; the filters are made of stainless steel (model SS304) and are equipped with precision filter meshes (pore diameter 0.05 mm), which can effectively remove impurities and particles in the demineralized water and prevent damage to subsequent equipment; the second stop valve (model Z20H) is used to control the flow rate to ensure the normal operation of the filter.

[0025] Example 2: Application of Heat Exchange Technology between the First Steam-Water Mixer and the Second Steam-Water Mixer This example mainly focuses on the heat exchange technology between the first steam-water mixer and the second steam-water mixer. By adopting an efficient heat exchange design in the first steam-water mixer 4 and the second steam-water mixer 6, the demineralized water is heated by the heat exchange between steam and demineralized water, thereby improving the heat exchange efficiency. In this example, the first steam-water mixer 4 is made of stainless steel 316L, which has excellent corrosion resistance and high temperature resistance and can withstand the impact of high-temperature steam. The design parameters of the first steam-water mixer 4 are: the maximum heat exchange power is 500 kW, and the surface area of the heat exchanger is 30 m².

[0026] The second steam-water mixer 6 is made of stainless steel 304, its maximum heat exchange power is 400 kW, and the surface area of the heat exchanger is 25 m². This design can ensure that the heat exchange efficiency between steam and demineralized water reaches more than 90%, significantly improving the thermal energy utilization rate.

[0027] Comparison Case: Compared with the common low-efficiency heat exchange systems in the existing technology, heat exchangers made of aluminum alloy or carbon steel are usually used in traditional systems, with low heat exchange efficiency and often unable to effectively recover the heat of boiler exhaust steam, resulting in energy waste. The high-efficiency stainless steel material and optimized design in this example have greatly improved the heat exchange efficiency, and the energy utilization rate has increased by about 15%.

[0028] Example 3: Gas Separation Device for Degassing Buffer Tank and Degassing Water Storage Tank This example focuses on solving the problem of incomplete gas separation in the existing technology. Both the degassing buffer tank 5 and the degassing water storage tank 8 are equipped with advanced degassing equipment. By optimizing the gas discharge device, oxygen, carbon dioxide and other non-condensable gases in the demineralized water can be effectively removed. In this example, the degassing buffer tank 5 is made of Q235B carbon steel, with good high-temperature resistance and can withstand water flow with a temperature range of 150°C to 200°C to ensure long-term stable operation.

[0029] The gas discharge port in the gas separation device is made of copper alloy (model CuZn40Pb2), which can resist corrosion and ensure the smooth discharge of gas, avoiding the risk of gas leakage. In actual tests, the gas separation efficiency of the degassing buffer tank and the degassing water storage tank reaches 98%, significantly reducing the dissolved gas content in water and improving the water quality stability.

[0030] Comparative case: Compared with the inefficient gas separation devices used in traditional systems, the existing technologies mostly adopt simple exhaust pipe designs with low gas separation efficiency, and can only remove 60% to 70% of the non-condensable gas, which leads to unstable water quality and decreased boiler operation efficiency. The gas separation efficiency of this embodiment is significantly improved, avoiding the influence of dissolved gas on the boiler and improving the operation stability of the system.

[0031] Example 4: Parallel operation and frequency conversion regulation of the first hot water pump and the second hot water pump This embodiment mainly involves the parallel operation design of the first hot water pump 9 and the second hot water pump 10. By adjusting the running speed of the pumps through a frequency converter, the smooth operation of the system is ensured and the energy efficiency is improved. The first hot water pump 9 adopts an LHB-75 type high-efficiency electric pump with a maximum flow rate of 120 m³ / h and a working pressure of 0.8 MPa, which can provide sufficient water flow to ensure the stability of the system.

[0032] The second hot water pump 10 operates in parallel with the first hot water pump 9, uses the same type of pump as the first hot water pump, and is equipped with an ABB VFD-A frequency converter. By adjusting the speed of the pump through frequency conversion, precise regulation can be achieved when the system load changes. The frequency converter automatically adjusts the pump speed according to the system load, ensuring that the system can operate efficiently under different loads and reducing energy waste at the same time.

[0033] Comparative case: Compared with the traditional constant-speed pump design, the traditional pump system cannot flexibly adjust the water flow according to the load change, resulting in low energy efficiency and serious energy waste when the load is low. By adjusting the pump speed through frequency conversion in this embodiment, it can be automatically adjusted according to the actual load demand, greatly improving the energy efficiency and reducing the energy consumption by more than 30%.

[0034] Example 5: Precision design and maintenance effect of the filter This embodiment solves the problem of poor filter effect in the existing technology and improves the long-term stability of the system. The liquid inlet ends of the first steam-water mixer 4 and the second steam-water mixer 6 are both connected with precision filters made of stainless steel (model SS304) and equipped with precision filter meshes with a pore size of 0.05 mm, effectively removing impurities and particles in the demineralized water, preventing these impurities from entering the subsequent equipment, and reducing equipment wear and failures.

[0035] The design of the filter ensures that the filtration effect reaches over 99%, and the filter element can be cleaned or replaced regularly according to the operation cycle, thus extending the service life of the system and reducing the maintenance cost.

[0036] Comparative case: In the prior art, many filters adopt a mesh structure with a larger pore size, which easily allows larger particulate impurities to pass through, affecting the stability of subsequent equipment. The design of the precision filter in this embodiment effectively removes impurities, ensuring the long-term and efficient operation of the system, and improving the filtration effect by approximately 25% compared with the traditional design.

[0037] The working principle of the present invention is as follows: The deaerator 3 sends the whole to the first steam-water mixer 4. At the same time, the demineralized water inlet pipe 1 sends demineralized water to the first steam-water mixer 4. The first steam-water mixer 4 mixes the steam and demineralized water and uses the heat of the steam to heat the demineralized water. The first steam-water mixer 4 sends the heated demineralized water to the deaeration buffer tank 5. The deaeration buffer tank 5 uses deaeration equipment to separate oxygen, carbon dioxide, and other non-condensable gases in the demineralized water and discharges them through the discharge port. The deaeration buffer tank 5 allows the hot demineralized water to flow into the deaeration storage tank 8 by gravity; At the same time, the regular blowdown flash tank 7 sends steam to the second steam-water mixer 6, and the demineralized water inlet pipe 1 also sends demineralized water to the second steam-water mixer 6 at the same time. The second steam-water mixer 6 mixes the steam and demineralized water and uses the heat of the steam to heat the demineralized water. The second steam-water mixer 6 sends the heated demineralized water into the deaeration storage tank 8. The deaeration storage tank 8 uses deaeration equipment to separate oxygen, carbon dioxide, and other non-condensable gases in the demineralized water and discharges them through the discharge port. Finally, the deaeration storage tank 8 uses the first hot water pump 9 or the second hot water pump 10 to discharge the demineralized water through the outlet pipe 2.

[0038] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. The structures, devices, and operation methods not specifically described and explained in the present invention are implemented according to the conventional means in the art without special instructions and limitations.

Claims

1. A waste heat recovery system for the exhaust steam of a power plant boiler, comprising a deaerator (3) and a regular blowdown flash tank (7) connected to the boiler, characterized in that: It also includes a demineralized water inlet pipe (1), an outlet pipe (2), a first steam-water mixer (4), a deaeration buffer tank (5), a second steam-water mixer (6), a deaeration water storage tank (8), and a first hot water pump (9); The first steam-water mixer (4) mixes the demineralized water conveyed by the demineralized water inlet pipe (1) with the steam conveyed by the deaerator (3), and sends the heated demineralized water into the deaeration buffer tank (5). The deaeration buffer tank (5) directly flows the hot demineralized water into the inner side of the deaeration water storage tank (8) by gravity; The second steam-water mixer (6) mixes the demineralized water conveyed by the demineralized water inlet pipe (1) with the steam conveyed by the regular blowdown flash tank (7), and sends the heated demineralized water into the deaeration water storage tank (8); Both the deaeration buffer tank (5) and the deaeration water storage tank (8) separate water and gas through deaeration equipment, and discharge the separated gas to the outside; The deaeration water storage tank (8) discharges the demineralized water through the first hot water pump (9) and the outlet pipe (2), and sends it back to the demineralized water inlet pipe (1) again; 2. The waste heat recovery system for the exhaust steam of a power plant boiler according to claim 1, wherein: A second hot water pump (10) is also provided on the pipeline connecting the deaeration water storage tank (8) and the outlet pipe (2). The second hot water pump (10) and the first hot water pump (9) are connected in parallel on the pipeline; The second hot water pump (10) and the first hot water pump (9) are used alternately, and both the second hot water pump (10) and the first hot water pump (9) are connected with frequency converters; 3. The waste heat recovery system for the exhaust steam of a power plant boiler according to claim 2, wherein: The liquid inlet ends of the second hot water pump (10) and the first hot water pump (9) are both connected with first stop valves, and the liquid outlet ends of the second hot water pump (10) and the first hot water pump (9) are both connected with check valves; 4. A waste heat recovery system for the exhaust steam of a power plant boiler according to claim 1, characterized in that: Gas discharge ports are provided at the upper ends of both the deaeration buffer tank (5) and the deaeration water storage tank (8); 5. A waste heat recovery system for the exhaust steam of a power plant boiler according to claim 1, characterized in that: The liquid inlet ends of the first steam-water mixer (4) and the second steam-water mixer (6) are both connected with filters, and the liquid inlet ends of the two filters are both connected with second stop valves.

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