Double-Rankine-cycle waste heat utilization regulation and control method and system with steam turbine as security support

Abstract

The invention discloses a double-Rankine-cycle waste heat utilization regulation and control method and system with a steam turbine as a security support. Waste heat of a coal-fired unit provides driving heat energy for a waste heat power generation organic Rankine cycle system; when the coal-fired unit operates at a full load, the waste heat power generation organic Rankine cycle system operates based on the waste heat of the coal-fired unit at the full load; when the coal-fired unit is in sliding pressure operation under load reduction, and the minimum temperature difference between the heat source temperature and the environment temperature of the waste heat power generation organic Rankine cycle system is smaller than delta T or the total heat of waste heat is too small, a path of condensed water is led out from the front of a water feeding valve of a deaerator in the coal-fired unit to a waste heat collecting device; the lowest condition of safe operation of the waste heat power generation organic Rankine cycle system is met; the safe operation of the waste heat power generation organic Rankine cycle system is realized by changing the working condition of the steam turbine and adjusting the waste heat resource; it is ensured that the waste heat power generation organic Rankine cycle system can operate safely and stably under all working conditions, and the safety of all systems of a whole power plant is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power station boilers and steam turbine systems, and specifically relates to a double Rankine cycle waste heat utilization control method and system using a steam turbine as a safety backup. Background Art

[0002] Adhere to the energy development strategy of prioritizing energy conservation, vigorously promote energy-saving and carbon-reduction transformation of coal-fired power plants, and further tap the energy-saving potential of coal-fired power units. This is not only a response to energy conservation and emission reduction policies, but also improves the survivability of thermal power units in new power systems and alleviates the operating and survival difficulties of coal-fired power units.

[0003] Exploiting low-grade waste heat from power plants, including flue gas waste heat, circulating water waste heat, continuous deaerator exhaust, and ash hopper heating steam drainage, is an effective way to improve energy conservation and efficiency in coal-fired power plants. Currently, the main technologies for utilizing low- and medium-temperature waste heat include low-temperature economizers, heat pumps, and organic Rankine cycle (ORC). Low-temperature economizers and heat pumps have achieved significant results in power plant energy conservation, but both are forms of thermal utilization. Similar to the traditional steam Rankine cycle, the ORC uses low-boiling-point organic matter instead of water as the circulating working fluid. This allows for low-temperature vaporization, generating high-pressure steam that drives an expander to produce work. This cycle offers superior performance compared to the steam Rankine cycle in low- and medium-temperature thermal energy utilization. Its simple structure, low maintenance costs, and wide range of working fluid options have made it widely used in various low- and medium-temperature thermal energy applications. ORC power generation technology has matured in recent years and is widely used by domestic and international companies in industrial waste heat recovery, geothermal energy, and biomass incineration. It is currently the most promising approach for converting low- and medium-temperature waste heat into power. Fluctuations in the load of coal-fired power plants result in fluctuations in the quality of waste heat. Chinese patent publication number CN118582267A provides a method and system for recovering waste heat and energy from a coal-fired power plant based on an organic Rankine cycle. The method includes: The coal-fired power plant generates waste heat and energy from the ... How to use the main steam turbine as a safety net for the waste heat recovery system while ensuring the safe operation of ORC, coordinately optimize the cycle parameters of the waste heat recovery system and the main steam turbine thermal system, and develop a waste heat collection method suitable for the dual Rankine cycle system of organic Rankine + inorganic Rankine. This is of great significance for improving the collection and efficient utilization technology of waste heat energy from coal-fired power units. Summary of the Invention

[0004] The present invention aims to provide a dual-Rankine cycle waste heat utilization control method with a steam turbine as a safety net, and a method for collecting and utilizing waste heat from coal-fired power generation units with ORC operation as the boundary. This waste heat collection and utilization method, based on the waste heat energy quality characteristics and the energy consumption patterns of coal-fired power generation units, uses the main steam turbine as the safety net for the waste heat recovery system, ensuring that the waste heat energy quality meets the ORC operation boundary conditions. The cycle parameters of the waste heat recovery system and the main steam turbine thermal system are collaboratively optimized to develop an optimal waste heat collection and utilization method for coal-fired power generation units with ORC operation as the boundary. This method can improve the operating economy of the entire ORC power generation coupled with coal-fired power generation system, reduce fossil energy consumption, reduce carbon emissions, conserve energy and protect the environment, and bring direct economic benefits to the power plant. It also improves the safety of the ORC system operation, improves the safety of the overall power plant operation, and reduces the system's accident rate and the corresponding maintenance work.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a dual Rankine cycle waste heat utilization and control method with a steam turbine as a safety backup, wherein the waste heat of a coal-fired unit provides driving heat energy to a waste heat power generation organic Rankine cycle system; When the coal-fired unit is running at full load, the waste heat power generation organic Rankine cycle system is running at full load based on the waste heat of the coal-fired generator unit; When the coal-fired unit is operating at a reduced load and in sliding pressure, the temperature, pressure, and flow of the waste heat of the coal-fired generator set decrease, and the minimum temperature difference between the heat source temperature and the ambient temperature of the waste heat power generation organic Rankine cycle system is less than ΔT or the total amount of waste heat is too small. Condensate is then diverted from the water supply valve of the deaerator in the coal-fired generator set to the waste heat collection device to increase the minimum temperature difference between the heat source temperature and the ambient temperature of the waste heat power generation organic Rankine cycle system or the total amount of waste heat, thereby meeting the minimum conditions for safe operation of the waste heat power generation organic Rankine cycle system. By changing the operating conditions of the coal-fired power generation unit's steam turbine, the waste heat resources are adjusted to ensure the safe operation of the organic Rankine cycle system for waste heat power generation. Through the coordinated regulation of the dual Rankine cycles, the waste heat is fully utilized for power generation when the main unit is at full load; in the unit's sliding pressure drop load stage, the waste heat carrier parameters (temperature and heat flow) are adjusted by dynamically introducing condensate water, which solves the problem of organic Rankine cycle operation interruption caused by insufficient waste heat quality under low operating conditions and expands the effective working range of the waste heat power generation system; the active adjustment of the steam turbine operating conditions is used as a benchmark guarantee for waste heat supply to ensure the stability of waste heat resource parameters and avoid the mismatch of the heat source of the waste heat power generation system caused by sudden changes in the main cycle parameters, thereby triggering a protective shutdown. The overall system is strengthened from the perspective of thermal coupling. Robustness: By utilizing the condensate from the deaerator water supply system as a regulating medium, the waste heat collection device is supplemented with heat in real time in the form of a working fluid bypass. When the waste heat is insufficient at low load, the minimum temperature difference (ΔT threshold) between the heat source end and the ambient end can be quickly compensated, ensuring that the organic Rankine cycle working fluid completes an efficient phase change expansion process within the designed temperature range. A closed-loop control logic is formed between the operating status of the main generator set and the heat source demand of the waste heat power generation system, achieving an optimal balance between energy-saving power generation and waste heat recovery within a wide load range of the main unit, reducing the risk of frequent start-stop or inefficient operation of traditional waste heat power generation systems due to heat source fluctuations.

[0006] Furthermore, the load of the coal-fired unit is reduced so that the coal-fired unit is in 30% THA condition.

[0007] Furthermore, the waste heat carrier includes at least one of the following: continuous exhaust steam of the deaerator, drain of the electrostatic precipitator ash hopper, steam drain of the air preheater soot blowing and warming pipe, steam drain of the low-temperature economizer soot blowing and warming pipe, and steam drain of the denitrification soot blowing and warming pipe.

[0008] Furthermore, ΔT is determined according to the working fluid of the organic Rankine cycle system.

[0009] In the second aspect, the present invention also provides a dual Rankine cycle waste heat utilization system with a steam turbine as a safety backup, including a coal-fired unit, a waste heat collection device and a waste heat power generation organic Rankine cycle system. The waste heat carrier inlet of the waste heat collection device is connected to the waste heat carrier outlet of the coal-fired unit, and the outlet of the waste heat collection device is connected in sequence to the pipeline booster pump, the hot side inlet of the organic Rankine cycle system evaporator, the hot side inlet of the waste heat cascade utilization heat exchanger and the condenser of the coal-fired unit. The cold side of the waste heat cascade utilization heat exchanger is connected to the outlet of the condensate pump group in the coal-fired unit and the inlet of the low-pressure heater.

[0010] Furthermore, the cold side outlet of the organic Rankine cycle evaporator is connected in sequence to the organic Rankine cycle turbine, the hot side of the organic Rankine cycle heat exchanger, the organic Rankine cycle condenser, and the organic Rankine cycle booster pump; the outlet of the organic Rankine cycle booster pump is connected to the cold side inlet of the organic Rankine cycle heat exchanger; and the cold side outlet of the organic Rankine cycle heat exchanger is connected to the cold side inlet of the organic Rankine cycle evaporator.

[0011] Furthermore, temperature and pressure monitoring devices are provided at the inlet and outlet of the waste heat collection device.

[0012] Furthermore, the condenser of the organic Rankine cycle system is connected to a circulating cooling water system.

[0013] Furthermore, a bypass pipeline is provided at the outlet of the pipeline booster pump to connect to the condenser of the coal-fired unit.

[0014] Furthermore, the temperature difference between the heat source temperature and the ambient temperature of the waste heat power generation organic Rankine cycle system is calculated to obtain an instruction for controlling the opening of the waste heat power generation system's water supply regulating valve. When the temperature difference is less than ΔT, it indicates that the temperature of the waste heat system's heat source is too low. In this case, the opening of the waste heat power generation system's water supply regulating valve needs to be increased to increase waste heat replenishment and ensure the safe operation of the organic Rankine cycle system. When the temperature difference is greater than ΔT, it indicates that the temperature of the waste heat system's heat source meets the requirements for the operation of the organic Rankine cycle system. In this case, the opening of the waste heat power generation system's water supply regulating valve needs to be reduced to reduce waste heat replenishment, ensuring the safe and economical operation of both the inorganic Rankine cycle power generation system and the waste heat utilization organic Rankine cycle power generation system of the large unit.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention ensures that the organic Rankine cycle system for waste heat power generation can operate safely and stably under all operating conditions through the close coordinated operation of the three systems of the coal-fired power generation inorganic Rankine cycle system, the waste heat high-efficiency recovery system and the waste heat power generation organic Rankine cycle system, with the coal-fired power generation inorganic Rankine cycle system as a backup, thereby improving the safety of all systems in the entire power plant; through the continuous and efficient power generation of the waste heat power generation inorganic Rankine cycle system, it can bring direct and stable waste heat power generation benefits to the power plant, increase the saleable electricity amount of the power plant, increase the profit of the power plant, and improve the economic efficiency of the power plant operation; by recovering the waste heat to generate electricity, the carbon emissions of the power plant are also reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of a double Rankine cycle waste heat utilization and control method using a steam turbine as a safety backup according to the present invention; In the figure, 1. boiler, 2. high-pressure cylinder of steam turbine, 3. intermediate-pressure cylinder of steam turbine, 4. low-pressure cylinder of steam turbine, 5. generator, 6. condenser, 7. high-pressure heater No. 1, 8. high-pressure heater No. 2, 9. high-pressure heater No. 3, 10. deaerator, 11. feedwater pump group, 12. low-pressure heater No. 5, 13. low-pressure heater No. 6, 14. low-pressure heater No. 7, 15. low-pressure heater No. 8, 16. condensate pump group, 17. water supply regulating valve of waste heat power generation system, 18. waste heat collection device, 19. pipeline booster pump, 20. organic Rankine cycle system evaporator, 21. waste heat cascade utilization heat exchanger, 22. organic Rankine cycle system turbine, 23. organic Rankine cycle system generator, 24. organic Rankine cycle system heat exchanger, 25. organic Rankine cycle system condenser, 26. organic Rankine cycle system booster pump. DETAILED DESCRIPTION

[0017] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0018] Example 1 A 350MW supercritical coal-fired unit has long been neglecting the generation of medium- and low-temperature waste heat during daily operation. The current waste heat and energy emissions are typically discharged directly from the deaerator's continuous exhaust and electrostatic precipitator ash hopper drains. Steam from furnace heating surface sootblower pipes, air preheater sootblower pipes, low-temperature economizer sootblower pipes, and denitrification sootblower pipes is recycled back to the drain expansion tank, resulting in heat loss. Heat return water is also recycled back to the condenser, resulting in significant heat loss. To recover the plant's waste heat and improve operational safety and economics, a patented dual-Rankine cycle waste heat utilization and control method with a steam turbine as a safety backup was implemented. Based on water quality requirements and long-term field statistical data, four waste heat types were initially selected for recovery. The waste heat parameters for the coal-fired unit during THA operation are shown in Table 1. When the coal-fired unit is operating at 30% THA, the waste heat parameters are shown in Table 2. The ambient temperature is 25°C, and the critical temperature for evaporation of the organic working fluid is 95°C.

[0019] Table 1 Four types of waste heat parameters of coal-fired units under THA operating conditions

[0020] Table 2 Parameters of four waste heat at 30% THA operating condition for coal-fired units

[0021] Comparing the waste heat parameters in Tables 1 and 2 shows that when the coal-fired unit load decreases, the waste heat resource parameters emitted by the unit also decrease due to the unit's sliding pressure operation. When the coal-fired unit is in THA mode, the waste heat carrier in Table 1 is discharged into the waste heat collection device and then transported to the waste heat power generation organic Rankine cycle system via pipeline booster pump 19. The waste heat heats the organic working fluid, and the organic working fluid evaporates, driving the turbine to generate electricity. At this time, the three systems of coal-fired power generation inorganic Rankine cycle system, waste heat high-efficiency collection system, and waste heat power generation organic Rankine cycle system are operating normally and stably.

[0022] When the coal-fired unit is operating at 30% THA, the waste heat carriers in Table 2 are discharged into the waste heat collection device and transported to the waste heat power generation organic Rankine cycle system via pipeline booster pump 19. At this point, because the waste heat resource temperature is below the critical temperature of 95°C for evaporation of the organic working fluid, and the waste heat flow rate is reduced, the organic working fluid cannot evaporate. As a result, the waste heat power generation organic Rankine cycle system shuts down or malfunctions, preventing normal power generation. At this point, the waste heat power generation system's water supply regulating valve 17 is opened to adjust the waste heat resource temperature and flow rate, ensuring that the waste heat temperature is greater than or equal to 95°C and that the evaporation rate of the organic working fluid meets the minimum flow rate for normal operation of the organic Rankine cycle system's turbine. Through the close coordinated operation of the three major systems of the coal-fired power generation inorganic Rankine cycle system, the waste heat high-efficiency recovery system and the waste heat power generation organic Rankine cycle system, with the coal-fired power generation inorganic Rankine cycle system as a backup, it is ensured that the waste heat power generation organic Rankine cycle system can operate safely and stably under all operating conditions, thereby improving the safety of all systems in the entire power plant; through the continuous and efficient power generation of the waste heat power generation inorganic Rankine cycle system, it can bring direct and stable waste heat power generation benefits to the power plant, increase the saleable electricity volume of the power plant, increase the power plant's revenue, and improve the economic efficiency of the power plant operation; by recovering waste heat to generate electricity, it is beneficial to reduce the carbon emissions of the power plant.

[0023] like Figure 1As shown, the present invention provides a system capable of implementing the above method, including a boiler 1, a high-pressure cylinder 2 of a steam turbine, an intermediate-pressure cylinder 3 of a steam turbine, a low-pressure cylinder 4 of a steam turbine, a generator 5, a condenser 6, a No. 1 high-pressure heater 7, a No. 2 high-pressure heater 8, a No. 3 high-pressure heater 9, a deaerator 10, a feedwater pump group 11, a No. 5 low-pressure heater 12, a No. 6 low-pressure heater 13, a No. 7 low-pressure heater 14, a No. 8 low-pressure heater 15, a condensate pump group 16, a waste heat power generation system water supply regulating valve 17, a waste heat collection device 18, a pipeline booster pump 19, an organic Rankine cycle system evaporator 20, a waste heat cascade utilization heat exchanger 21, an organic Rankine cycle system turbine 22, an organic Rankine cycle system generator 23, an organic Rankine cycle system heat exchanger 24, an organic Rankine cycle system condenser 25, and an organic Rankine cycle system booster pump 26. Among them, the boiler 1, the high-pressure cylinder 2 of the steam turbine, the intermediate-pressure cylinder 3 of the steam turbine, the low-pressure cylinder 4 of the steam turbine, the generator 5, the condenser 6, the No. 1 high-pressure heater 7, the No. 2 high-pressure heater 8, the No. 3 high-pressure heater 9, the deaerator 10, the feed water pump group 11, the No. 5 low-pressure heater 12, the No. 6 low-pressure heater 13, the No. 7 low-pressure heater 14, the No. 8 low-pressure heater 15, and the condensate pump group 16 are connected according to the structural layout of the existing coal-fired units. A pipeline is provided on the pipeline from the No. 5 low-pressure heater 12 to the deaerator 10 to connect the waste heat collection device 18, and a waste heat power generation system water supply regulating valve 17 is provided on the pipeline from the No. 5 low-pressure heater 12 to the waste heat collection device 18; the outlet of the waste heat collection device 18 is connected in sequence to the pipeline booster pump 19, the hot side inlet of the organic Rankine cycle system evaporator 20, the hot side inlet of the waste heat cascade utilization heat exchanger 21 and the condenser 6, and the cold side of the waste heat cascade utilization heat exchanger 21 is connected to the outlet of the condensate pump group 16 and the No. 7 The inlet of the low-pressure heater 14; the cold side outlet of the organic Rankine cycle evaporator 20 is connected in sequence to the organic Rankine cycle turbine 22, the hot side of the organic Rankine cycle heat exchanger 24, the organic Rankine cycle condenser 25, and the organic Rankine cycle booster pump 26, the outlet of the organic Rankine cycle booster pump 26 is connected to the cold side inlet of the organic Rankine cycle heat exchanger 24, and the cold side outlet of the organic Rankine cycle heat exchanger 24 is connected to the cold side inlet of the organic Rankine cycle evaporator 20.

[0024] Temperature and pressure monitoring devices are provided at the inlet and outlet of the waste heat collection device 18 for real-time monitoring of the working condition of the waste heat collection device 18 .

[0025] The organic Rankine cycle system condenser 25 is connected to the circulating cooling water system and condenses the working medium through the circulating cooling water.

[0026] Example 2. The system described in this application includes an inorganic Rankine cycle system for coal-fired power generation, a waste heat high-efficiency recovery system, and an organic Rankine cycle system for waste heat power generation. Among them, the inorganic Rankine cycle system is a conventional coal-fired power unit. The coal-fired power unit will directly discharge a lot of waste heat and waste materials during daily operation, such as: continuous exhaust of the deaerator, draining of the electrostatic precipitator ash hopper, steam draining of the air preheater soot blowing and heating pipe, steam draining of the low-temperature economizer soot blowing and heating pipe, and steam draining of the desulfurization soot blowing and heating pipe; the waste heat recovery system is used to recover these discharged waste heat and waste materials. Generally, the lowest pressure of all the waste materials is selected and a certain pressure loss is considered as the rated pressure of the waste heat recovery system. All waste heat and waste materials are collected in the waste heat recovery device. If the waste material is steam, it can be connected from the bottom of the recovery device and cooled by the waste material in the recovery device. If the steam content in the waste material is very high, the medium in the recovery device can be divided into steam and water for recycling. If the waste material is water , then it can be depressurized by a throttle valve and then collected into a recovery device. The flash steam generated during the throttling and depressurization process can be recycled in a certain way according to the amount of flash steam. If there is little flash steam, water can be recovered from the top of the recovery device by spraying. If there is a lot of flash steam, the medium in the recovery device can be divided into steam and water for recycling. When the mass proportion of steam is less than 1%, the influence of steam bubbles on heat exchange can be ignored considering the investment comprehensively. The organic Rankine cycle system utilizes the low boiling point of the organic working fluid to absorb the low-temperature waste heat in the recovery device and evaporate, thereby driving the expander to generate power, directly bringing electricity benefits to the power plant. The heat discharged from the evaporator can be used to heat the condensate through the deep cascade utilization of the heat exchanger, further improving the thermal efficiency of the cycle, and finally recovering the residual gas to the condenser. The waste heat and residual gas are both utilized and recycled to the extreme, reducing the consumption of fossil energy, saving energy and protecting the environment, and improving efficiency.

[0027] In summary, the present invention ensures that the organic Rankine cycle system for waste heat power generation can operate safely and stably under all operating conditions through the close coordinated operation of the three major systems: the inorganic Rankine cycle system for coal-fired power generation, the high-efficiency waste heat recovery system, and the organic Rankine cycle system for waste heat power generation, with the inorganic Rankine cycle system for coal-fired power generation as a backup, thereby improving the safety of all systems in the entire power plant; through the continuous and efficient power generation of the inorganic Rankine cycle system for waste heat power generation, it can bring direct and stable waste heat power generation benefits to the power plant, increase the saleable electricity volume of the power plant, increase the revenue of the power plant, and improve the economic efficiency of the power plant operation; by recovering the waste heat for power generation, the carbon emissions of the power plant are also reduced.

[0028] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A double Rankine cycle waste heat utilization and control method using a steam turbine as a safety backup, characterized in that: The waste heat from the coal-fired units provides driving heat energy to the waste heat power generation organic Rankine cycle system; When the coal-fired unit is running at full load, the waste heat power generation organic Rankine cycle system is running at full load based on the waste heat of the coal-fired generator unit; When the coal-fired unit reduces its load, the temperature, pressure and flow of the waste heat of the coal-fired generator set decrease, and the temperature difference between the heat source temperature and the ambient temperature of the waste heat power generation organic Rankine cycle system is less than ΔT or the total heat of the waste heat is too small, a high-temperature condensate is drawn from the water supply valve of the deaerator (10) in the coal-fired generator set to the waste heat collection device (18), and a waste heat power generation system water supply regulating valve (17) is set on the pipeline from the high-temperature condensate to the waste heat collection device (18), so as to meet the minimum conditions for the safe operation of the waste heat power generation organic Rankine cycle system; By changing the operating conditions of the steam turbine of the coal-fired generator set, the waste heat resources are adjusted to ensure the safe operation of the waste heat power generation organic Rankine cycle system.

2. The double Rankine cycle waste heat utilization control method with steam turbine as a safety backup according to claim 1 is characterized in that: The load reduction of the coal-fired unit means that the coal-fired unit is in 30% THA condition.

3. The double Rankine cycle waste heat utilization control method with steam turbine as a safety backup according to claim 1 is characterized in that: The waste heat carrier includes at least one of continuous exhaust steam from the deaerator, drain water from the electrostatic precipitator ash hopper, steam drain water from the air preheater soot blowing and heating pipes, steam drain water from the low-temperature economizer soot blowing and heating pipes, and steam drain water from the desulfurization soot blowing and heating pipes.

4. The double Rankine cycle waste heat utilization and control method with steam turbine as a safety backup according to claim 1 is characterized in that: ΔT is determined according to the working fluid of the organic Rankine cycle system.

5. A double Rankine cycle waste heat utilization system with steam turbine as a safety backup, characterized in that: The invention comprises a coal-fired unit, a waste heat collection device (18) and a waste heat power generation organic Rankine cycle system, wherein the waste heat carrier inlet of the waste heat collection device (18) is connected to the waste heat carrier outlet of the coal-fired unit, the outlet of the waste heat collection device (18) is connected in sequence to a pipeline booster pump (19), the hot side inlet of an organic Rankine cycle system evaporator (20), the hot side inlet of a waste heat cascade utilization heat exchanger (21) and the condenser (6) of the coal-fired unit, and the cold side of the waste heat cascade utilization heat exchanger (21) is connected to the outlet of a condensate pump group (16) in the coal-fired unit and the inlet of a No. 7 low-pressure heater (14).

6. The double Rankine cycle waste heat utilization system with steam turbine as a safety backup according to claim 5 is characterized in that: The cold side outlet of the organic Rankine cycle evaporator (20) is connected in sequence to the organic Rankine cycle turbine (22), the hot side of the organic Rankine cycle heat exchanger (24), the organic Rankine cycle condenser (25), and the organic Rankine cycle booster pump (26); the outlet of the organic Rankine cycle booster pump (26) is connected to the cold side inlet of the organic Rankine cycle heat exchanger (24); and the cold side outlet of the organic Rankine cycle heat exchanger (24) is connected to the cold side inlet of the organic Rankine cycle evaporator (20).

7. The double Rankine cycle waste heat utilization system with steam turbine as a safety backup according to claim 5 is characterized in that: Temperature and pressure monitoring devices are provided at the inlet and outlet of the waste heat collection device (18).

8. The double Rankine cycle waste heat utilization system with steam turbine as a safety backup according to claim 5 is characterized in that: The organic Rankine cycle system condenser (25) is connected to the circulating cooling water system.

9. The double Rankine cycle waste heat utilization system with steam turbine as a safety backup according to claim 5, characterized in that: A bypass pipeline is provided at the outlet of the pipeline booster pump (19) to connect to the condenser (6) of the coal-fired unit.

10. The double Rankine cycle waste heat utilization system with steam turbine as a safety backup according to claim 5, characterized in that: The temperature difference between the heat source temperature and the ambient temperature of the waste heat power generation organic Rankine cycle system is calculated to obtain an instruction for controlling the opening of the water supply regulating valve (17) of the waste heat power generation system.

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