Thermal power plant flue gas low-temperature waste heat recovery system and method

Abstract

The invention relates to a thermal power plant flue gas low-temperature waste heat recovery system and method.The system comprises an acid gas removal system, a heat pump system, a high-pressure deaerator system and an expansion power generation system which are sequentially connected, the acid gas removal system conducts acid removal on acid-containing wet flue gas and discharges the acid-removed wet flue gas to the heat pump system, and the heat pump system is connected with the high-pressure deaerator system; the heat pump system compresses, heats and pressurizes the wet flue gas, separates the wet flue gas into a gas phase and a liquid phase and discharges the gas phase to the high-pressure deaerator system, the high-pressure deaerator system conducts heat exchange through the gas phase and discharges non-condensable gas to the expansion power generation system, and the expansion power generation system expands outwards to do work through the non-condensable gas. According to the invention, after the grade of vapor phase latent heat in the waste flue gas is improved, the heat of the vapor phase latent heat is recovered, so that the vapor consumption of the high-pressure deaerator is reduced, the tail end waste heat of the whole flue gas treatment process is recycled, the non-condensable gas pressure energy is recovered for power generation, and the waste energy is fully utilized.

Description

Technical Field

[0001] The invention relates to the technical field of energy conservation, and in particular to a technology for recovering low-temperature waste heat from flue gas in a thermal power plant. Background Art

[0002] Waste heat recovery from flue gas in power plants is a common waste heat recovery process. According to the different temperature grades of flue gas, different waste heat boilers or steam turbine generator systems are set up to recycle energy. Generally, the terminal flue gas contains acid and water and the pressure is not high, which is a difficult energy source to utilize. However, the gas phase latent heat of water vapor contains a large amount of thermal energy, which has great recovery potential and recovery value in the process. However, the industry is not fully recycling this part of the heat energy. Usually, low-pressure wet flue gas directly enters the tail gas treatment unit and is discharged after being treated to meet the standards, resulting in a large waste of energy, which is neither energy-saving nor environmentally friendly. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a system and method for recovering low-temperature waste heat from flue gas in a thermal power plant, which can realize the effective recycling of low-grade energy from flue gas in a thermal power plant.

[0004] According to one aspect of an embodiment of the present invention, a low-temperature waste heat recovery system for flue gas in a thermal power plant is provided, which includes an acid gas removal system, a heat pump system, a high-pressure deaerator system and an expansion power generation system connected in sequence, wherein: the acid gas removal system is used to deacidify acid-containing wet flue gas and discharge the deacidified wet flue gas to the heat pump system; the heat pump system is used to compress, increase the temperature and pressure of the wet flue gas, separate it into gas phase and liquid phase, and discharge the saturated gas phase to the high-pressure deaerator system; the high-pressure deaerator system is used to utilize the gas phase for heat exchange and discharge non-condensable gas to the expansion power generation system; the expansion power generation system utilizes the non-condensable gas to expand externally to perform work.

[0005] According to another aspect of an embodiment of the present invention, a method for recovering low-temperature waste heat from flue gas in a thermal power plant is provided, which is characterized in that it includes the following steps: (1) the acid-containing wet flue gas is passed through an acid gas removal system for deacidification, and then the deacidified wet flue gas is discharged to a heat pump system; (2) the heat pump system compresses the deacidified wet flue gas, increases the temperature and pressure, and then separates it into a gas phase and a liquid phase, and discharges the gas phase to a high-pressure deaerator system; (3) the high-pressure deaerator system uses the gas phase for heat exchange and generates non-condensable gas; (4) the non-condensable gas enters an expansion power generation system and expands externally to perform work.

[0006] The present invention has at least the following advantages and features:

[0007] The flue gas low-temperature waste heat recovery system and waste heat recovery method of the embodiment of the present invention eliminate the dehydration unit originally required in the prior art, and recover the gas phase latent heat of water vapor under the saturated gas phase partial pressure, thereby improving the quality of heat, and releasing the heat in the high-pressure deaerator, reducing the consumption of primary steam, while optimizing some processing units, and recovering low-grade heat on the basis of simplifying the process. The heat recovery method of the flue gas low-temperature waste heat recovery system of the present application is more energy-efficient in terms of process. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Schematic diagram of a system for recovering low-temperature waste heat from flue gas in a thermal power plant according to Example 1 of the present invention.

[0009] Explanation of symbols: 1-acid gas removal system, 2-heat pump system, 3-high-pressure deaerator system, 4-expansion power generation system, 5-condensate reflux pump, 6-gas-liquid separator, 7-compressor, 8-acid gas removal device, 9-high-pressure deaerator heater, 10-high-pressure deaerator DETAILED DESCRIPTION

[0010] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0011] The low-temperature waste heat recovery system of flue gas in a thermal power plant in this embodiment includes an acid gas removal system 1, a heat pump system 2, a high-pressure deaerator system 3 and an expansion power generation system 4 connected in sequence, wherein the acid gas removal system 1 deacidifies the acid-containing wet flue gas and discharges the deacidified wet flue gas to the heat pump system 2, the heat pump system 2 compresses the deacidified wet flue gas, increases the temperature and pressure, separates it into a gas phase and a liquid phase, and discharges a saturated gas phase to the high-pressure deaerator system 3, the high-pressure deaerator system 3 uses the gas phase for heat exchange and discharges non-condensable gas to the expansion power generation system 4, and the expansion power generation system 4 uses the non-condensable gas to expand externally to perform work. The non-condensable gas in the high-pressure deaerator system 3 is connected to the expansion power generation system 4, and the external expansion work is performed to realize the conversion of pressure energy into electrical energy, thereby realizing the reuse of the low-temperature and low-pressure energy in the flue gas. The low-pressure dry flue gas at the outlet of the expansion power generation system 4 enters the post-treatment process.

[0012] The acid-containing wet flue gas contains, for example, nitrogen, carbon dioxide, water vapor, oxygen and acidic gases, etc. The acidic gases are, for example, sulfur dioxide, nitrogen dioxide and the like.

[0013] Preferably, the heat pump system 2 includes a compressor 7 and a gas-liquid separator 6, wherein the inlet of the compressor 7 is connected to the outlet of the acid gas removal system 1, and the outlet of the compressor 7 is connected to the first inlet of the gas-liquid separator 6. The compressor 7 compresses the wet flue gas after acid removal, increases the temperature and pressure, and forms a gas-liquid two-phase mixed gas. The gas-liquid separator 6 separates the gas-liquid two-phase mixed gas from the outlet of the compressor 7 into a gas phase and a liquid phase.

[0014] Preferably, the high-pressure deaerator system 3 includes a high-pressure deaerator heater 9 and a high-pressure deaerator 10, the inlet of the high-pressure deaerator heater 9 is connected to the gas phase exhaust port of the heat pump system 2 (gas-liquid separator 6), the high-pressure deaerator heater 9 utilizes the gas phase from the heat pump system 2 (gas-liquid separator 6) to heat the hot water in the high-pressure deaerator 10, and the high-pressure deaerator heater 9 discharges non-condensable gas to the expansion power generation system 4 through the top opening, and discharges condensed water at the bottom.

[0015] Furthermore, the high-pressure deaerator system 3 also includes a condensate reflux pump 5, whose inlet is connected to the bottom condensate discharge port of the high-pressure deaerator heater 9, and the outlet is connected to the second inlet of the gas-liquid separator 6 in the heat pump system 2. The condensate reflux pump 5 replenishes the condensate from the high-pressure deaerator heater 9 into the gas-liquid separator 6.

[0016] Preferably, the liquid phase outlet of the gas-liquid separator 6 is connected to the inlet of the compressor 7 in the heat pump system 2, and the condensed water in the gas-liquid separator 6 is replenished to the inlet of the compressor 7 in the heat pump system 2 (for example, in the form of pressure self-reflux). In this way, the superheat generated by the gas phase after pressurization can be eliminated.

[0017] The method for recovering low-temperature waste heat from flue gas in a thermal power plant of this embodiment includes the following steps: (1) passing the acid-containing wet flue gas through the acid gas removal system 1 for deacidification, and then discharging the deacidified wet flue gas to the heat pump system 2; (2) the heat pump system 2 compresses the deacidified wet flue gas, increases the temperature and pressure, and then separates it into a gas phase and a liquid phase, and discharges the gas phase to the high-pressure deaerator system 3; (3) the high-pressure deaerator system 3 uses the above-mentioned gas phase for heat exchange and produces non-condensable gas; (4) the non-condensable gas enters the expansion power generation system 4 and expands to the outside to do work. The non-condensable gas in the high-pressure deaerator system 3 is connected to the expansion power generation system 4, expands to the outside to do work, and realizes the conversion of pressure energy into electrical energy, thereby realizing the recycling of the low-temperature and low-pressure energy in the flue gas. The low-pressure dry flue gas at the outlet of the expansion power generation system 4 enters the post-treatment process.

[0018] Preferably, the heat pump system 2 includes a heat pump compressor 7 and a gas-liquid separator 6 connected to the outlet of the compressor 7. In step (2), the wet flue gas after deacidification is compressed, heated and pressurized by the compressor 7, and then the heated and pressurized gas enters the gas-liquid separator 6, is separated into a gas phase and a liquid phase, and the gas phase is discharged to the high-pressure deaerator system 3.

[0019] Preferably, the high-pressure deaerator system 3 includes a high-pressure deaerator heater 9 and a high-pressure deaerator 10. In step (3), the gas phase enters the high-pressure deaerator heater 9 for heat exchange, heats the hot water in the high-pressure deaerator 10, and produces non-condensable gas and condensed water, and discharges the non-condensable gas to the expansion power generation system 4.

[0020] Furthermore, the high-pressure deaerator system 3 also includes a condensate reflux pump 5 connected to the gas-liquid separator 6 . In step (3), condensate from the high-pressure deaerator heater 9 is supplied to the gas-liquid separator 6 through the condensate reflux pump 5 .

[0021] Preferably, in step (2), the liquid condensate produced in the gas-liquid separator 6 (for example, in the form of pressure self-reflux) is supplemented to the inlet of the compressor 7 in the heat pump system 2. This can eliminate the superheat produced by the gas phase after pressurization.

[0022] Furthermore, in step (2), softened water is also sprayed into the inlet of the compressor 7 through the softened water pipeline of the power plant. Since the non-condensable gas and water vapor will become superheated steam during the boosting operation of the compressor 7, spraying softened water into the inlet of the compressor 7 can eliminate overheating.

[0023] The flue gas low-temperature waste heat recovery system and waste heat recovery method of this embodiment eliminate the dehydration unit originally required in the prior art, and recover the gas phase latent heat of water vapor under the saturated gas phase partial pressure, thereby improving the quality of heat, and releasing the heat in the high-pressure deaerator, reducing the consumption of primary steam, while optimizing some processing units, and recovering low-grade heat on the basis of simplifying the process. The heat recovery method of the flue gas low-temperature waste heat recovery system of this application is more energy-efficient in terms of process.

[0024] This embodiment achieves the effective recycling of low-grade energy of flue gas in thermal power plants by upgrading the grade of low-grade heat sources in low-temperature and low-pressure flue gas at the end of flue gas in the power plant, recovering its heat, and converting excess pressure energy into electrical energy.

[0025] Example 1

[0026] like Figure 1 As shown, Example 1 of the present application provides a process system for recovering low-temperature waste heat from flue gas in a thermal power plant, including: an acid gas removal system 1, a heat pump system 2, a high-pressure deaerator system 3, and an expansion power generation system 4. Among them, the acid gas removal system 1 is connected to the heat pump system 2, and the wet flue gas after acid removal is compressed, heated and pressurized, and then heat is supplied to the high-pressure deaerator heater 9 of the high-pressure deaerator system 3. After the heat exchange, the gas phase water vapor in the wet flue gas releases heat and condenses, and the gas-liquid two-phase separation is realized in the high-pressure deaerator heater 9, and the condensed water is supplemented into the gas-liquid separator 6 in the heat pump system 2 through the condensate reflux pump 5. The condensed water in the gas-liquid separator 6 is supplemented to the inlet of the compressor 7 in the heat pump system 2 in the form of pressure self-reflux, so as to eliminate the superheat generated by the gas phase after pressurization. The non-condensable gas in the high-pressure deaerator heater 9 in the high-pressure deaerator system 3 is connected to the expansion power generation system 4. The expansion power generation system 4 includes an expander and a generator. After external expansion and work, the pressure energy is converted into electrical energy, thereby reusing the low-temperature and low-pressure energy in the flue gas.

[0027] In the following, in conjunction with the accompanying drawings, the process system and method of Example 1 are further described in detail with the flue gas of the thermal power plant without post-treatment as the starting stream. The flue gas first enters the acid gas removal system 1 (acid gas removal device 8) to remove acid gases such as sulfur dioxide and nitrogen dioxide in the flue gas. At this time, the main components of the wet flue gas after acid removal are nitrogen, carbon dioxide, and water vapor. This stream is connected to the heat pump system 2 as the gas source for the compressor 7, and the compressor 7 performs a boosting operation. Since the non-condensable gas and water vapor will become superheated steam during the boosting operation, softened water is sprayed at the inlet of the compressor 7 to eliminate overheating. Part of the softened water in this stream is transported by the softened water (deionized water) pipeline of the power plant, and part of it is the steam condensate after heat exchange in the heating unit (high-pressure deaerator heater 9) in the high-pressure deaerator system 3. Excess softened water is sprayed at the inlet of the compressor 7, and enters the gas-liquid separator 6 in the heat pump system 2 in a gas-liquid two-phase (saturated) state at the outlet of the compressor 7 to achieve gas-liquid two-phase separation. The saturated gas phase enters the high-pressure deaerator heater 9 of the high-pressure deaerator system 3, heats the hot water in the high-pressure deaerator 10, and after heat exchange, the water vapor is liquefied in the high-pressure deaerator heater 9, and gas-liquid separation is achieved in the high-pressure deaerator heater 9. The top of the high-pressure deaerator heater 9 is opened to discharge non-condensable gas, and the condensed water vapor condensate is sent to the gas-liquid separator 6 in the heat pump system 2 by the condensate reflux pump 5 at the bottom. The non-condensable gas discharged from the top of the high-pressure deaerator heater 9 in the high-pressure deaerator system 3 enters the expansion power generation system 4, expands externally to do work, realizes the conversion of pressure energy into electrical energy, and thus realizes the recovery of waste heat and waste pressure.

[0028] The embodiment of the present invention creatively optimizes and combines the heat pump system and the expansion power generation system. Through the combination of the two, the gas phase latent heat of water vapor in the waste flue gas is increased and its heat is recovered, thereby reducing the steam consumption of the high-pressure deaerator, thereby completing the recovery and utilization of the terminal waste heat of the entire flue gas treatment process, and recovering the non-condensable gas pressure energy for power generation, thereby making full use of waste energy.

[0029] Application examples:

[0030] Below, the flue gas treatment capacity per hour is 20000Nm 3 / h design, the process system parameters and treatment effects of Example 1 are listed in the following Table 1.

[0031] Table 1 Treatment effect of the low-temperature waste heat recovery system of flue gas in the thermal power plant in Example 1 of the present application

[0032]

[0033]

[0034]

[0035] It can be seen from the above Example 1 and application examples that the low-temperature waste heat recovery system for flue gas in a thermal power plant of the present invention creatively optimizes and combines the heat pump system and the expansion power generation system, and through the combination of the two, the gas phase latent heat of water vapor in the waste flue gas is increased and its heat is recovered, thereby reducing the steam consumption of the high-pressure deaerator, and further completing the recovery and utilization of the terminal waste heat of the entire flue gas treatment process, and recovering the non-condensable gas pressure energy for power generation, making full use of waste energy, simplifying the process and saving more energy.

[0036] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A low-temperature waste heat recovery system for flue gas in a thermal power plant, characterized in that: It includes an acid gas removal system, a heat pump system, a high-pressure deaerator system and an expansion power generation system which are connected in sequence, wherein: The acid gas removal system is used to remove acid from the acid-containing wet flue gas and discharge the deacidified wet flue gas to the heat pump system; The heat pump system is used to compress, increase the temperature and pressure of the deacidified wet flue gas, separate it into a gas phase and a liquid phase, and discharge the saturated gas phase to the high-pressure deaerator system; The high-pressure deaerator system is used to utilize the gas phase for heat exchange and discharge non-condensable gas to the expansion power generation system; The expansion power generation system is used to utilize non-condensable gas to expand externally and perform work.

2. The thermal power plant flue gas low-temperature waste heat recovery system according to claim 1, characterized in that: The heat pump system includes a compressor and a gas-liquid separator; The inlet of the compressor is connected to the outlet of the acid gas removal system, and the outlet of the compressor is connected to the first inlet of the gas-liquid separator. The compressor is used to compress the wet flue gas after acid removal, increase the temperature and pressure, and form a gas-liquid two-phase mixed gas; The gas-liquid separator is used to separate the gas-liquid two-phase mixed gas from the compressor outlet into a gas phase and a liquid phase.

3. The thermal power plant flue gas low-temperature waste heat recovery system according to claim 2, characterized in that: The high-pressure deaerator system includes a high-pressure deaerator heater and a high-pressure deaerator; The inlet of the high-pressure deaerator heater is connected to the gas phase discharge port of the gas-liquid separator of the heat pump system, and the high-pressure deaerator heater is used to heat the hot water in the high-pressure deaerator by using the gas phase from the gas-liquid separator; The high pressure deaerator heater discharges non-condensable gas to the expansion power generation system through the top opening and discharges condensed water at the bottom.

4. The thermal power plant flue gas low-temperature waste heat recovery system according to claim 3, characterized in that: The high-pressure deaerator system also includes a condensate return pump, the inlet of the condensate return pump is connected to the bottom condensate discharge port of the high-pressure deaerator heater, and the outlet of the condensate return pump is connected to the second inlet of the gas-liquid separator in the heat pump system, so as to replenish the condensate from the high-pressure deaerator heater into the gas-liquid separator.

5. The thermal power plant flue gas low-temperature waste heat recovery system according to claim 4, characterized in that: The liquid phase discharge port of the gas-liquid separator is connected to the inlet of the compressor in the heat pump system, so as to replenish condensed water to the inlet of the compressor in the heat pump system.

6. A method for recovering low-temperature waste heat from flue gas in a thermal power plant, characterized in that: The following steps are involved: (1) passing the acid-containing wet flue gas through an acid gas removal system for deacidification, and then discharging the deacidified wet flue gas to a heat pump system; (2) The heat pump system compresses the deacidified wet flue gas to increase the temperature and pressure, and then separates it into a gas phase and a liquid phase, and discharges the gas phase to the high-pressure deaerator system; (3) The high-pressure deaerator system utilizes the gas phase for heat exchange and produces non-condensable gas; (4) The non-condensable gas enters the expansion power generation system and expands externally to perform work.

7. The method for recovering low-temperature waste heat from flue gas in a thermal power plant according to claim 6, characterized in that: The heat pump system includes a compressor and a gas-liquid separator connected to an outlet of the compressor; In step (2), the compressor is used to compress the deacidified wet flue gas to increase the temperature and pressure, and then the gas after the temperature and pressure increase enters the gas-liquid separator to be separated into gas phase and liquid phase, and the gas phase is discharged to the high-pressure deaerator system.

8. The method for recovering low-temperature waste heat from flue gas in a thermal power plant according to claim 7, characterized in that: The high-pressure deaerator system includes a high-pressure deaerator heater and a high-pressure deaerator; In step (3), the gas phase enters the high-pressure deaerator heater for heat exchange, heats the hot water in the high-pressure deaerator, and produces non-condensable gas and condensed water, and discharges the non-condensable gas to the expansion power generation system.

9. The method for recovering low-temperature waste heat from flue gas in a thermal power plant according to claim 8, characterized in that: The high-pressure deaerator system also includes a condensate reflux pump connected to the gas-liquid separator; In step (3), condensate from the high-pressure deaerator heater is fed into the gas-liquid separator via the condensate reflux pump.

10. The method for recovering low-temperature waste heat from flue gas in a thermal power plant according to claim 9, characterized in that: In step (2), the liquid phase produced in the gas-liquid separator is supplemented to the inlet of the compressor.

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