Heat recovery system and method suitable for low-load wet operation of ultra-supercritical boilers

Abstract

This invention discloses an energy recovery system and method suitable for low-load wet operation of an ultra-supercritical boiler, comprising: a water storage tank, an atmospheric expansion tank, a heat accumulator, a thermal oil storage tank, a feedwater heater, a steam-water separator, a feedwater pump, a deaerator, and an ultra-supercritical boiler. The ultra-supercritical boiler and the water storage tank form a loop. The water storage tank is also connected to the atmospheric expansion tank and a condensate tank in sequence via pipelines. A branch pipeline between the water storage tank and the atmospheric expansion tank is connected to the heat accumulator. The heat accumulator, the thermal oil storage tank, and the feedwater heater form a loop on their heat source sides. The inlet of the feedwater heater on its feedwater side is connected to the deaerator via the feedwater pump, and the outlet of the feedwater heater on its feedwater side is connected to the ultra-supercritical boiler via a high-pressure regenerative heater group. This energy recovery system and method can effectively recover heat from saturated condensate, improve the operating efficiency of the ultra-supercritical boiler, and improve the denitrification efficiency of the denitrification equipment under low load.

Description

Technical Field

[0001] This invention belongs to the field of deep peak shaving technology for coal-fired boilers, specifically relating to an energy recovery system and method suitable for low-load wet operation of ultra-supercritical boilers. Background Technology

[0002] With my country's economic development and continuous improvement in its comprehensive national strength, people are paying increasing attention to environmental issues. In the power generation sector, new energy sources such as wind power and solar energy have developed rapidly. However, new energy sources are characterized by randomness, volatility, and intermittency, and their large-scale grid connection can negatively impact the power grid load. Deeply exploring the peak-shaving capacity of traditional coal-fired power units is the most convenient, fastest, and most effective means of solving the problem of new energy power consumption.

[0003] Currently, supercritical and ultra-supercritical coal-fired power generating units are the mainstay in my country. However, during peak-shaving periods, a significant portion of them must operate under low or even ultra-low load conditions. For ultra-supercritical once-through boilers, when the load drops below 30% of the rated load, the steam generated in the boiler's water-cooled walls is less than the water-cooled wall flow rate, requiring the boiler to switch from dry to wet operation. At this time, the saturated steam in the water-cooled wall outlet medium is separated by the steam-water separator in the start-up bypass system before entering the superheater. The remaining saturated water is sent to the storage tank and then pumped back to the economizer via a drainage path below it. Furthermore, to maintain safe boiler operation and hydrodynamic stability within the furnace, the water level in the storage tank needs to be maintained at a reasonable level and continuously adjusted using a level control valve. The discharged condensate is sent to the atmospheric expansion tank, a process that causes considerable loss of working fluid and capacity, affecting the economic efficiency of the thermal power unit. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an energy recovery system and method suitable for low-load wet operation of ultra-supercritical boilers, which can fully utilize the condensate discharged from the water storage tank, thereby improving the boiler's operating efficiency.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution: a heat recovery system suitable for low-load wet operation of an ultra-supercritical boiler, comprising: a water storage tank, an atmospheric expansion vessel, a heat accumulator, a thermal oil storage tank, a feedwater heater, a steam-water separator, a feedwater pump, a deaerator, and an ultra-supercritical boiler. The ultra-supercritical boiler and the water storage tank form a loop. The water storage tank is also connected to the atmospheric expansion vessel and a condensate tank in sequence via pipelines. A branch pipeline between the water storage tank and the atmospheric expansion vessel is connected to the heat accumulator. The heat accumulator, the thermal oil storage tank, and the feedwater heater form a loop on their heat source sides. The inlet of the feedwater heater on its feedwater side is connected to the deaerator via the feedwater pump. The outlet of the feedwater heater on its feedwater side is connected to the ultra-supercritical boiler via a high-pressure regenerative heater group.

[0006] Furthermore, a liquid level regulating valve and a shut-off valve are sequentially installed on the pipeline between the water storage tank and the atmospheric expansion container.

[0007] Furthermore, the shut-off valve is provided with branch pipes at both ends, and the branch pipes are connected to the heat storage side of the heat accumulator.

[0008] Furthermore, the inlet branch pipe on the heat storage side of the heat accumulator is provided with a heat accumulator inlet valve, and the outlet branch pipe on the heat storage side of the heat accumulator is provided with a heat accumulator outlet valve.

[0009] Furthermore, the heat storage medium in the heat accumulator is molten salt.

[0010] Furthermore, the outlet end of the heat release side of the heat accumulator is connected to the top of the heat transfer oil storage tank via a heat transfer oil circulation pump, the bottom of the heat transfer oil storage tank is connected to one end of the heat source side of the feed water heater, and the other end of the heat source side of the feed water heater is connected to the inlet end of the heat release side of the heat accumulator.

[0011] Furthermore, the water heater is a thermally conductive heat exchanger.

[0012] Furthermore, the ultra-supercritical boiler consists of an economizer, a water-cooled wall, and a steam-water separator connected in sequence. The outlet of the steam-water separator is connected to the inlet of the water storage tank, and one outlet of the water storage tank is connected to the inlet of the economizer via a circulating water pump. The economizer is also connected to a high-pressure regenerative heater group.

[0013] Furthermore, the present invention also provides a method for operating the heat recovery system applicable to low-load wet operation of an ultra-supercritical boiler, the specific process of which is as follows:

[0014] A. When the ultra-supercritical boiler is in the start-up state, open the liquid level regulating valve and the shut-off valve, close the heat accumulator inlet valve and the heat accumulator outlet valve, and the water enters the water storage tank through the steam-water separator and is discharged into the atmospheric expansion tank, and then sent back to the condenser or the unit circulating water system through the condensate tank.

[0015] B. When the load inside the ultra-supercritical boiler is greater than 30%, the ultra-supercritical boiler is in dry operation, and the liquid level regulating valve, shut-off valve, accumulator inlet valve and accumulator outlet valve are all closed, and the circulating water pump is closed.

[0016] C. When the load in the ultra-supercritical boiler is below 30%, the ultra-supercritical boiler is in wet operation. The circulating water pump is turned on, and part of the condensate in the water storage tank is sent back to the economizer through the circulating water pump. It then returns to the steam-water separator through the water-cooled wall. When adjusting the opening of the liquid level regulating valve to adjust the water level in the storage tank, the shut-off valve is closed, and the accumulator inlet valve and accumulator outlet valve are opened. The condensate discharged from the storage tank flows into the heat storage side of the accumulator, where the heat is stored in the molten salt in the accumulator. The condensate with reduced temperature is discharged into the atmospheric expansion tank and sent back to the condenser or the unit's circulating water system through the condensate tank.

[0017] Furthermore, under operating condition C, the heat transfer oil circulation pump sends the heat transfer oil in the heat transfer oil storage tank to the heat release side of the heat accumulator, and the heat in the heat accumulator is output to the heat source side of the heat transfer oil storage tank and the feed water heater, thereby raising the water temperature at the inlet of the high-pressure regenerative heater group.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention is applicable to the heat recovery system of ultra-supercritical boilers operating under low load and wet conditions. When the load in the ultra-supercritical boiler is less than 30%, the water level in the storage tank is adjusted by the liquid level regulating valve, eliminating the problem of unstable condensate flow and the resulting unstable heat loss. At the same time, this invention stores this part of the heat in the heat accumulator. When needed, the stored energy can be stably output through the heat accumulator, thereby converting the unstable heat source into a stable heat source.

[0020] 2. This invention applies to the heat recovery system of an ultra-supercritical boiler operating under low load and wet conditions. The heat stored in the accumulator is transferred to the feedwater at the inlet of the high-pressure regenerative heater group through heat transfer oil. On the one hand, the increase in water temperature can reduce the high-pressure steam extraction, which is beneficial to improving the cycle efficiency of the thermal power unit. On the other hand, if the high-pressure steam extraction remains unchanged or is only reduced appropriately, the water temperature at the economizer inlet will increase, which will reduce the heat absorption on the flue gas side and increase the outlet flue gas temperature, thereby improving the denitrification efficiency of the denitrification equipment operating under low load. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the energy recovery system of the present invention applicable to low-load wet operation of an ultra-supercritical boiler;

[0022] Figure 2This is a flowchart illustrating the energy recovery system of the present invention applicable to low-load wet operation of an ultra-supercritical boiler.

[0023] Among them, 1-water storage tank, 2-liquid level regulating valve, 3-stop valve, 4-atmospheric expansion container, 5-accumulator inlet valve, 6-accumulator outlet valve, 7-accumulator, 8-thermal oil circulating pump, 9-thermal oil storage tank, 10-feed water heater, 11-steam-water separator, 12-economizer, 13-water-cooled wall, 14-circulating water pump, 15-high-pressure regenerative heater group, 16-condensate tank, 17-feed water pump, 18-deaerator. Detailed Implementation

[0024] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings.

[0025] like Figure 1 This invention provides an energy recovery system suitable for low-load wet operation of an ultra-supercritical boiler, comprising: a water storage tank 1, an atmospheric expansion vessel 4, a heat accumulator 7, a thermal oil storage tank 9, a feedwater heater 10, a steam-water separator 11, a feedwater pump 17, a deaerator 18, and an ultra-supercritical boiler. The ultra-supercritical boiler and the water storage tank 1 form a loop. The water storage tank 1 is also connected to the atmospheric expansion vessel 4 and a condensate tank 16 in sequence via pipelines. The atmospheric expansion vessel 4 expands the capacity and reduces the pressure, causing partial evaporation of the discharged condensate. This steam is directly discharged into the atmosphere, resulting in heat loss. A branch pipeline between the water storage tank 1 and the atmospheric expansion vessel 4 is connected to the heat accumulator 7 for heat storage. The heat source side of the heat source unit 7, the heat transfer oil storage tank 9, and the feedwater heater 10 forms a loop. By building a heat transfer path between the water storage tank 1 and the atmospheric expansion container 4, stable heat transfer is achieved, preventing condensate from directly entering the atmospheric expansion container from the water storage tank 1, thus avoiding heat loss. The feedwater inlet of the feedwater heater 10 is connected to the deaerator 18 through the feedwater pump 17, and the feedwater outlet of the feedwater heater 10 is connected to the ultra-supercritical boiler through the high-pressure regenerative heater group 15, which raises the water temperature at the inlet of the high-pressure regenerative heater group 15, thereby reducing the turbine extraction steam required by the high-pressure regenerative heater group 15 and improving the circulation efficiency of the boiler unit.

[0026] In this invention, a liquid level regulating valve 2 and a shut-off valve 3 are sequentially installed on the pipeline between the water storage tank 1 and the atmospheric expansion vessel 4. The liquid level regulating valve 2 is used to adjust the water level in the water storage tank 1 to ensure that the water level in the water storage tank 1 is stable when the load in the ultra-supercritical boiler is less than 30%. The shut-off valve 3 has branch pipelines at both ends, which are connected to the heat storage side of the heat accumulator 7. The shut-off valve 3 ensures that all the condensate from the liquid level regulating valve 2 enters the heat storage circuit. Specifically, a heat storage inlet valve 5 is installed on the inlet branch pipeline of the heat storage side of the heat accumulator 7, and a heat storage outlet valve 6 is installed on the outlet branch pipeline of the heat storage side of the heat accumulator 7. The heat storage side of the heat accumulator 7 can operate according to the opening and closing state of the liquid level regulating valve 2 to store intermittent heat. In this invention, the heat storage medium in the heat accumulator 7 is molten salt.

[0027] In this invention, the outlet end of the heat-dissipating side of the heat accumulator 7 is connected to the top of the heat transfer oil storage tank 9 via a heat transfer oil circulation pump 8. The bottom of the heat transfer oil storage tank 9 is connected to one end of the heat source side of the feedwater heater 10, and the other end of the heat source side of the feedwater heater 10 is connected to the inlet end of the heat-dissipating side of the heat accumulator 7. The heat transfer oil circulation pump 8 sends the heat transfer oil from the heat transfer oil storage tank 9 to the heat-dissipating side of the heat accumulator 7. After absorbing heat from the heat accumulator 7, the heat transfer oil transfers the heat to the feedwater. In this invention, the feedwater heater 10 is a thermally conductive heat exchanger.

[0028] In this invention, the ultra-supercritical boiler consists of an economizer 12, a water-cooled wall 13, and a steam-water separator 11 connected in sequence. The outlet of the steam-water separator 11 is connected to the inlet of the water storage tank 1, and one outlet of the water storage tank 1 is connected to the inlet of the economizer 12 through a circulating water pump 14. The economizer 12 is also connected to a high-pressure regenerative heater group 15.

[0029] like Figure 2 The present invention also provides a working method for a heat recovery system suitable for low-load wet operation of an ultra-supercritical boiler, the specific process of which is as follows:

[0030] A. When the ultra-supercritical boiler is in the start-up state, open the liquid level regulating valve 2 and the shut-off valve 3, close the accumulator inlet valve 5 and the accumulator outlet valve 6, and the water enters the water storage tank 1 through the steam-water separator 11 and is discharged into the atmospheric expansion tank 4, and then sent back to the condenser or the unit's circulating water system via the condensate tank 16.

[0031] B. When the load inside the ultra-supercritical boiler is greater than 30%, the ultra-supercritical boiler is in dry operation, and the liquid level regulating valve 2, the shut-off valve 3, the accumulator inlet valve 5 and the accumulator outlet valve 6 are all in the closed state, and the circulating water pump 14 is in the closed state.

[0032] C. When the load in the ultra-supercritical boiler is below 30%, the ultra-supercritical boiler is in wet operation. The circulating water pump 14 is turned on, and part of the condensate in the water storage tank 1 is sent back to the economizer 12 through the circulating water pump 14, and then back to the steam-water separator 11 through the water-cooled wall 13. The opening of the liquid level regulating valve 2 is adjusted to adjust the water level in the water storage tank 1, so that part of the condensate is discharged to control the water level in the water storage tank 1. The shut-off valve 3 is closed, and the accumulator inlet valve 5 and accumulator outlet valve 6 are opened. The condensate discharged from the water storage tank 1 flows into the heat storage side of the accumulator 7, where the heat is stored in the molten salt in the accumulator 7. The condensate with reduced temperature is discharged into the atmospheric expansion tank 4 and sent back to the condenser or the unit circulating water system through the condensate tank 16.

[0033] Under operating condition C, regardless of whether the liquid level regulating valve 2 is open, the heat transfer oil circulation pump 8 sends the heat transfer oil from the heat transfer oil storage tank 9 to the heat release side of the heat accumulator 7. The heat in the heat accumulator 7 is output to the heat source side of the heat transfer oil storage tank 9 and the feedwater heater 10, achieving stable heat output and raising the water temperature at the inlet of the high-pressure regenerative heater group 15. On the one hand, the increased water temperature can reduce the high-pressure steam extraction, which is beneficial to improving the circulation efficiency of the thermal power unit. On the other hand, if the high-pressure steam extraction remains unchanged or is only reduced appropriately, the increased water temperature at the economizer inlet will reduce the heat absorption on its flue gas side and increase the outlet flue gas temperature, thereby improving the denitrification efficiency of the denitrification equipment under low load.

[0034] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A heat recovery system suitable for use in a ultra supercritical boiler during low load wet operation, characterized in that, include: The system includes a water storage tank (1), an atmospheric expansion vessel (4), a heat accumulator (7), a thermal oil storage tank (9), a feedwater heater (10), a feedwater pump (17), a deaerator (18), and an ultra-supercritical boiler. The ultra-supercritical boiler forms a loop with the water storage tank (1). The water storage tank (1) is also connected to the atmospheric expansion vessel (4) and the condensate tank (16) in sequence through pipelines. The branch pipeline between the water storage tank (1) and the atmospheric expansion vessel (4) is connected to the heat accumulator (7). The heat source side of the heat accumulator (7), the thermal oil storage tank (9), and the feedwater heater (10) forms a loop. The water inlet on the feedwater side of the feedwater heater (10) is connected to the deaerator (18) through the feedwater pump (17). The water outlet on the feedwater side of the feedwater heater (10) is connected to the ultra-supercritical boiler through the high-pressure regenerative heater group (15). A liquid level regulating valve (2) and a shut-off valve (3) are sequentially installed on the pipeline between the water storage tank (1) and the atmospheric expansion container (4). The shut-off valve (3) has branch pipelines at both ends, and the branch pipelines are connected to the heat storage side of the heat accumulator (7).

2. The heat recovery system according to claim 1, wherein, The heat storage side of the heat storage device (7) is provided with a heat storage inlet valve (5) and the heat storage side of the heat storage device (7) is provided with a heat storage outlet valve (6).

3. The heat recovery system according to claim 2, characterized in that, The heat storage medium in the heat accumulator (7) is molten salt.

4. The heat recovery system according to claim 3, characterized in that, The outlet end of the heat release side of the heat accumulator (7) is connected to the top of the heat transfer oil storage tank (9) via the heat transfer oil circulation pump (8). The bottom of the heat transfer oil storage tank (9) is connected to one end of the heat source side of the water supply heater (10). The other end of the heat source side of the water supply heater (10) is connected to the inlet end of the heat release side of the heat accumulator (7).

5. A heat recovery system suitable for low-load wet operation of an ultra-supercritical boiler according to claim 4, characterized in that, The water heater (10) is a thermally conductive heat exchanger.

6. A heat recovery system suitable for low-load wet operation of an ultra-supercritical boiler according to claim 1, characterized in that, The ultra-supercritical boiler consists of an economizer (12), a water-cooled wall (13), and a steam-water separator (11) connected in sequence. The outlet of the steam-water separator (11) is connected to the inlet of the water storage tank (1), and one outlet of the water storage tank (1) is connected to the inlet of the economizer (12) through a circulating water pump (14). The economizer (12) is also connected to a high-pressure regenerative heater group (15).

7. A method for operating the heat recovery system of claim 6, applicable to low-load wet operation of an ultra-supercritical boiler, characterized in that, The specific process is as follows: A. When the ultra-supercritical boiler is in the start-up state, open the liquid level regulating valve (2) and the shut-off valve (3), close the heat accumulator inlet valve (5) and the heat accumulator outlet valve (6), and drain the water from the steam-water separator (11) into the water storage tank (1) and discharge it into the atmospheric expansion tank (4), and send it back to the condenser or the unit circulating water system via the condensate tank (16). B. When the load in the ultra-supercritical boiler is greater than 30%, the ultra-supercritical boiler is in dry operation. The liquid level regulating valve (2), the shut-off valve (3), the accumulator inlet valve (5) and the accumulator outlet valve (6) are all closed, and the circulating water pump (14) is closed. C. When the load in the ultra-supercritical boiler is less than 30%, the ultra-supercritical boiler is in wet operation. The circulating water pump (14) is turned on, and part of the condensate in the water storage tank (1) is sent back to the economizer (12) through the circulating water pump (14). It then returns to the steam-water separator (11) through the water-cooled wall (13). When adjusting the opening of the liquid level regulating valve (2) and adjusting the water level in the water storage tank (1), the shut-off valve (3) is closed, and the accumulator inlet valve (5) and accumulator outlet valve (6) are opened. The condensate discharged from the water storage tank (1) flows into the heat storage side of the accumulator (7), where the heat is stored in the molten salt in the accumulator (7). The condensate with reduced temperature is discharged into the atmospheric expansion container (4) and sent back to the condenser or the unit circulating water system through the condensate tank (16).

8. The operating method of the heat recovery system for low-load wet operation of an ultra-supercritical boiler according to claim 7, characterized in that, In step C, the heat transfer oil circulation pump (8) sends the heat transfer oil in the heat transfer oil storage tank (9) to the heat release side of the heat accumulator (7), and the heat in the heat accumulator (7) is output to the heat source side of the heat transfer oil storage tank (9) and the water heater (10), so that the water temperature at the inlet of the high pressure regenerative heater group (15) rises.

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