CN118728502A - A coal-fired unit coupled molten salt heat storage system that takes into account both economy and rapid load change requirements - Google Patents

Abstract

The present invention provides a coal-fired unit coupled with a high-temperature molten salt heat storage rapid load change system, which achieves the purpose of decoupling the boiler and the steam turbine by embedding a large-capacity high-temperature molten salt heat storage system between the boiler and the steam turbine of the coal-fired unit to store high-parameter steam heat. The output power of the steam turbine is reduced while the boiler evaporation capacity is maintained above 30% THA conditions. A trade-off between the unit's economy and the demand for rapid load change is achieved by controlling the return of heat storage exhaust steam to the unit. According to the balance between power supply and demand, the system has three types of operating modes, namely heat storage mode, heat release mode and isolation mode.

Description

A coal-fired unit coupled molten salt heat storage system that takes into account both economy and rapid load change requirements

Technical Field

The present invention relates to the field of peak regulation of thermal power generation technology, and in particular to a coal-fired unit coupled with a molten salt heat storage system.

Background Art

Facing the "dual carbon" goal, in the process of accelerating the construction of a new power system with renewable energy as the main body in my country, coal-fired units will gradually transform from the main power source to a regulating power source that provides supporting auxiliary services. Therefore, improving the deep peak regulation and flexible operation capabilities of coal-fired units is not only a practical requirement for the smooth transformation of coal-fired power units, but also an important guarantee for the construction of a new power system. However, in the actual operation process, when the unit is deeply adjusted to this load, the unit's operating parameters will deviate too much from the design parameters, which poses a great challenge to the safety and economy of the unit's operation. For this reason, it is necessary to adopt a coupled high-temperature molten salt heat storage and energy storage system to achieve decoupling of the machine and boiler to a certain extent.

Summary of the invention

The present invention intends to couple the high-temperature molten salt heat storage process during the original operation of the unit, and embed a large-capacity high-temperature molten salt heat storage system between the boiler and the steam turbine of the coal-fired unit to store high-parameter steam heat, thereby achieving the purpose of decoupling the boiler and the steam turbine. The steam turbine output power can be reduced while the boiler evaporation capacity is maintained above 30% THA working conditions.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

A molten salt heat storage system coupled with a coal-fired unit that takes into account both economy and rapid load change requirements, characterized in that it comprises a molten salt heat absorber, a boiler, a medium-pressure cylinder, a low-pressure cylinder, a generator, a hot tank, a cold tank, a molten salt heat emitter, a feedwater heater, a high-pressure heater, a feedwater pump, a deaerator, a low-pressure heater, a condensate pump and an air condenser that are connected in a coordinated manner; the molten salt heat absorber is connected to the hot tank, the cold tank, the low-pressure cylinder, the boiler and the feedwater heater, and a main steam extraction valve is provided at the steam inlet of the molten salt heat absorber; the molten salt heat emitter is connected to the hot tank, the cold tank and the feedwater heater; a feedwater bypass pipeline connected to the molten salt heat emitter is provided at the feedwater inlet of the high-pressure heater, and a valve and a bypass water pump are provided on the feedwater bypass pipeline; the low-pressure cylinder is connected to the generator, the medium-pressure cylinder, the air-to-air condenser and the low-pressure heater, and a condensate pump is provided at the liquid outlet of the air-to-air condenser; the deaerator is connected to the high-pressure heater, the low-pressure heater and the medium-pressure cylinder, and a feedwater pump is provided at its liquid outlet.

According to the balance between power supply and demand, the coal-fired unit coupled molten salt thermal storage system has three types of operation modes, namely heat storage mode, heat release mode and isolation mode.

When the system is in heat storage mode, the main steam extraction valve is opened, and part of the high-temperature and high-pressure main steam enters the molten salt heat absorber to heat the molten salt, thereby reducing the heat energy entering the steam turbine and reducing the output power of the unit. The main steam entering the molten salt heat exchanger has a lower temperature after heat exchange, but still has high energy, so it is divided into three parts and returned to the unit to achieve cascade utilization of energy. The first part is reduced in pressure and flows into the low-pressure cylinder to continue to work, and the second part is reduced in pressure and enters the cold reheat steam pipeline to supplement the boiler evaporation. The remaining part enters the feedwater heater to heat the boiler feed water, and then after pressure reduction and mixed cooling, it is mixed with part of the condensate and flows into the deaerator.

When the system is in heat release mode, open the valve on the feedwater bypass pipe at the feedwater inlet of the high-pressure heater to start the additional molten salt heat storage thermal cycle to respond to the load demand of the power grid. Part of the feedwater is extracted from the inlet of the high-pressure heater, and the flow is controlled by the regulating valve installed in the outlet pipeline. The bypass water pump increases the pressure and heats it when it flows through the molten salt heat releaser. The heated bypass feedwater merges with the feedwater flowing through the high-pressure heater and enters the boiler. In the heat release process of the coal-fired unit coupled with the molten salt heat storage system, the reduction in the feedwater flow through the high-pressure heater will reduce the steam extraction of the heat recovery system, so that more steam can enter the steam turbine to do work and generate higher output power.

When the system is in isolation mode, the heat storage device neither stores nor releases heat, and the valve on the feed water bypass pipeline and the main steam pipeline bypass valve are closed for isolation.

The present invention intends to couple the high-temperature molten salt heat storage process during the original operation of the unit. Under the deep peak-shaving operation conditions, the boiler evaporation capacity is maintained at 30% THA conditions. By storing heat, part of the boiler output heat is preserved, so that the unit output power can be further reduced to 20% THA conditions. In order to give full play to the role of coal-fired power units in "peak supply guarantee" during peak electricity demand, when the heat storage unit releases heat in this article, the boiler evaporation capacity is maintained at 75% THA conditions, and all the stored energy is released to the original thermal system. In addition to adding a molten salt heat storage unit, the present invention makes little change to the original system. It can be connected to the original system only by adding valves and pipelines, and the temperature of the heating medium is close to the temperature of the access point when the stored heat is released.

In addition, the present invention adopts main steam as the heat source, the pinch point temperature difference of the molten salt heat absorber is 5K, and HITEC salt is selected as the heat storage medium. In the whole cycle, the operating temperature range of the heat storage medium of the molten salt heat storage system is 453.15K-743.15K.

Compared with the prior art, the present invention has the following beneficial effects:

A large-capacity high-temperature molten salt heat storage system is embedded between the boiler and the steam turbine of the unit to store the heat of high-parameter steam, thereby achieving decoupling of the boiler and the steam turbine. The heat storage exhaust steam is divided into three parts and returned to the unit to achieve the cascade utilization of energy. The energy loss in the heat storage link is small, which improves the economy of the deep peak regulation process of the coal-fired unit. In addition, the present invention has a simple structure, convenient operation, strong innovation, low cost for the transformation of existing equipment, and a fast load change rate for the unit, which can improve the stability of the deep peak regulation of the coal-fired unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of the present invention.

List of reference numerals:

1-molten salt heat absorber, 2-boiler, 3-medium pressure cylinder, 4-low pressure cylinder, 5-generator, 6-hot tank, 7-cold tank, 8-molten salt heat releaser, 9-feed water heater, 10-high pressure heater, 11-feed water pump, 12-deaerator, 13-low pressure heater, 14-condensate pump, 15-air condenser, 16-bypass water pump, 17-mixing desuperheater, 18-main steam extraction valve.

DETAILED DESCRIPTION

The present invention is further described below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention provides a molten salt heat storage system coupled with a coal-fired unit that takes into account both economy and rapid load change requirements, including a molten salt heat absorber 1, a boiler 2, a medium-pressure cylinder 3, a low-pressure cylinder 4, a generator 5, a hot tank 6, a cold tank 7, a molten salt heat emitter 8, a feedwater heater 9, a high-pressure heater 10, a feedwater pump 11, a deaerator 12, a low-pressure heater 13, a condensate pump 14 and an air condenser 15 that are connected in a coordinated manner; the molten salt heat absorber is connected to the hot tank, the cold tank, the low-pressure cylinder, the boiler and the feedwater heater, and ... A main steam extraction valve 18 is provided at the steam inlet of the heat exchanger; the molten salt heat exchanger is connected to the hot tank, the cold tank and the feed water heater; a feed water bypass pipeline connected to the molten salt heat exchanger is provided at the feed water inlet of the high-pressure heater, and a valve and a bypass water pump 16 are provided on the feed water bypass pipeline; the low-pressure cylinder is connected to the generator, the medium-pressure cylinder, the air-to-condenser and the low-pressure heater, and a condensate pump is provided at the liquid outlet of the air-to-condenser; the deaerator is connected to the high-pressure heater, the low-pressure heater and the medium-pressure cylinder, and a feed water pump is provided at its liquid outlet.

According to the balance between power supply and demand, the coal-fired unit coupled molten salt thermal storage system has three types of operation modes, namely heat storage mode, heat release mode and isolation mode.

When the system is in heat storage mode, the main steam extraction valve is opened, and part of the high-temperature and high-pressure main steam enters the molten salt heat absorber to heat the molten salt, thereby reducing the heat energy entering the turbine and reducing the output power of the unit. The main steam entering the molten salt heat exchanger has a lower temperature after heat exchange, but still has high energy, so it is divided into three parts and returned to the unit to achieve cascade utilization of energy. The first part is decompressed and flows into the low-pressure cylinder to continue to work, and the second part enters the cold reheat steam pipeline after decompression to supplement the boiler evaporation. The remaining part enters the feedwater heater to heat the boiler feed water, and then after decompression and mixing desuperheater 17, it is mixed with part of the condensate and flows into the deaerator.

When the system is in heat release mode, open the valve on the feedwater bypass pipe at the feedwater inlet of the high-pressure heater to start the additional molten salt heat storage thermal cycle to respond to the load demand of the power grid. Part of the feedwater is extracted from the inlet of the high-pressure heater system, and the flow is controlled by the regulating valve installed in the outlet pipeline. The bypass water pump increases the pressure and heats it when it flows through the heat storage system. The heated bypass feedwater merges with the feedwater flowing through the high-pressure heater system and enters the boiler. In the heat release process of the coal-fired unit coupled with the molten salt heat storage system, the reduction in the feedwater flow through the high-pressure heater will reduce the steam extraction of the heat recovery system, so that more steam can enter the steam turbine to do work and generate higher output power.

When the system is in isolation mode, the heat storage device neither stores nor releases heat, and the valve on the feed water bypass pipeline and the main steam pipeline bypass valve are closed for isolation.

Claims (6)

1. The coal-fired unit coupling molten salt heat storage system taking economical efficiency and rapid load change requirements into consideration is characterized by comprising a molten salt heat absorber, a boiler, a medium-pressure cylinder, a low-pressure cylinder, a generator, a hot tank, a cold tank, a molten salt heat radiator, a feed water heater, a high-pressure heater, a feed water pump, a deaerator, a low-pressure heater, a condensate pump and an air condenser which are connected in a matched manner; the fused salt heat absorber is connected with the hot tank, the cold tank, the low-pressure cylinder, the boiler and the feed water heater, and a main steam extraction valve is arranged at a steam inlet of the fused salt heat absorber; the molten salt radiator is connected with the hot tank, the cold tank and the feed water heater; a water supply bypass pipeline connected with the molten salt radiator is arranged at a water supply inlet of the high-pressure heater, and a valve and a bypass water pump are arranged on the water supply bypass pipeline; the low-pressure cylinder is connected with the generator, the medium-pressure cylinder, the air-cooling condenser and the low-pressure heater, and a liquid outlet of the air-cooling condenser is provided with a condensate pump; the deaerator is connected with the high-pressure heater, the low-pressure heater and the medium-pressure cylinder, and a water supply pump is arranged at the liquid outlet of the deaerator; the heat storage system is provided with a heat storage mode, a heat release mode and an isolation mode.

2. The coal-fired unit coupling molten salt heat storage system taking both economy and rapid load change requirements into consideration according to claim 1, wherein in the heat storage mode, a main steam extraction valve is opened, and part of high-temperature and high-pressure main steam enters a molten salt heat absorber to heat molten salt, so that heat energy entering a steam turbine is reduced, and output power of the unit is reduced; the temperature of the main steam entering the molten salt heat exchanger is reduced after heat exchange, the main steam is divided into three parts and flows back to a unit to realize the cascade utilization of energy, the first part is depressurized and then flows into a low-pressure cylinder to continuously do work, and the second part is depressurized and then enters a cold reheat steam pipeline to supplement the evaporation capacity of a boiler; the rest third part enters a feed water heater to heat the feed water of the boiler, and then is mixed with part of condensed water to be led into a deaerator after being decompressed and mixed with a desuperheater.

3. The coal-fired unit coupling molten salt heat storage system with both economy and rapid load change requirements according to claim 1, wherein in the heat release mode, a valve on a water supply bypass pipeline at a water supply inlet of a high-pressure heater is opened, an additional molten salt heat storage thermodynamic cycle is started, and the power grid load requirements are responded; part of the feed water is pumped out from an inlet of the high-pressure heater, the flow is controlled by a regulating valve arranged on an outlet pipeline, the pressure is increased by a bypass water pump, the feed water is heated when flowing through a molten salt radiator, and the heated bypass feed water and the feed water flowing through the high-pressure system are converged and enter a boiler; in the heat release process of the coal-fired unit coupling molten salt heat storage system, the reduction of the water supply flow rate flowing through the high-pressure heater can reduce the steam extraction amount of the regenerative system, so that more steam enters the steam turbine to do work, and higher output power is generated.

4. The coal-fired unit coupling molten salt heat storage system with economical efficiency and rapid load change requirements according to claim 1, wherein in the isolation mode, the heat storage system does not store heat and release heat, and a valve on a water supply bypass pipeline and a main steam pipeline bypass valve are closed for isolation.

5. The coal-fired unit coupling molten salt heat storage system with both economy and rapid load change requirements according to claim 1 is characterized in that a high-temperature molten salt heat storage process is coupled in the system operation process, under the deep peak shaving operation condition, the evaporation capacity of a boiler maintains 30% of THA working conditions, and the heat output by a boiler part is stored through heat storage, so that the unit output electric power can be further reduced to 20% of THA working conditions; in the heat storage mode, the evaporation capacity of the boiler keeps 75% of THA working condition, and the stored energy is totally released to an original thermodynamic system.

6. The coal-fired unit coupling molten salt heat storage system with economical efficiency and rapid load change requirements according to claim 1, wherein the temperature difference between the clamping points of the molten salt heat absorber is 5K, HITEC salt is selected as a heat storage medium, and the operation temperature range of the heat storage medium is 453.15K-743.15K in the whole cycle.