Wind-light-coal-storage multi-energy complementary power station peak shaving system and operation method

Abstract

The invention discloses a wind-light-coal-storage multi-energy complementary power station peak shaving system and an operation method. The system comprises a coal-fired power generation unit, an electric heating pump, a heat storage tank, a cold storage tank, a heat exchanger, wind power and photovoltaic power generation equipment, a power controller and the like. Redundant electric quantity of a power grid is consumed through a heat pump and converted into heat energy and cold energy in two qualities to be stored respectively in a power off-peak period, meanwhile, a high-temperature heat storage tank is adopted to store part of exhaust steam of a pressure cylinder in a steam turbine, part of condensed water of the steam turbine is heated through heat storage in a cascade mode in a power peak period, and meanwhile, cold storage release is matched with a high-vacuum-degree condenser; and the unit output is improved. According to the invention, power storage is replaced by cascade cold storage and heat storage, flexible and efficient peak regulation of the power station is realized, and the new energy power consumption level can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical fields of wind-solar power generation, energy storage, power station peak shaving, and new energy power consumption, and particularly relates to a peak shaving system and operation method for a wind-solar-coal-energy storage multi-energy complementary power station. Background Art

[0002] New energy power generation such as solar energy and wind energy has strong time-varying and reverse peak shaving characteristics, posing great challenges to the safe peak shaving of the power grid. Coal-fired power stations are the main body of flexible power sources in China, and deep peak shaving operation of coal-fired units will become a normal state in the next few years. Improving the operation flexibility of coal-fired units to promote the consumption of new energy power is a key technology in the energy and power industry. Currently, there are the following technical problems in the peak shaving flexibility of conventional coal-fired units: (1) The energy comprehensive utilization level of peak shaving methods such as electric boilers and bypass main steam is low. In order to expand the unit operation range and improve the peak shaving capacity, the thermal economy of the unit will be further sacrificed.

[0003] (2) The existing coal-fired unit peak shaving technologies have problems such as inflexible parameter adjustment and inflexible selection of heat sources and cold sources. Conventional unit peak shaving technologies face practical problems such as low energy utilization efficiency and small peak shaving depth, and it is difficult to achieve coordinated improvement among key performances such as the thermal economy, flexible operation range, and load change rate of the unit.

[0004] Therefore, the present invention proposes a peak shaving system and operation method for a wind-solar-coal-energy storage multi-energy complementary power station. Through the integration of heat pumps, coal-fired power generation, and new energy power, the complementary and interchangeable of multiple energy forms such as heat, electricity, and cold are realized. Through the integration of a cascaded heat storage and cold storage system, the cross-time and space utilization of multiple energy flows is realized. Using heat storage and cold storage instead of electricity storage, the coordinated improvement of system economy and flexibility is achieved, thereby greatly improving the new energy power consumption level. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art, by using heat storage and cold storage instead of electricity storage to promote the coordinated improvement of peak shaving efficiency and flexibility, with the expectation of greatly improving the new energy power consumption level, the present invention provides a peak shaving system and operation method for a wind-solar-coal-energy storage multi-energy complementary power station. The system includes a coal-fired power generation unit, an electric heat pump, a heat storage tank, a cold storage tank, a heat exchanger, wind and photovoltaic power generation equipment, a power controller, etc. During the power valley period, the heat pump is used to consume the excess power in the power grid and convert it into two qualities of energy, heat and cold, which are respectively stored. At the same time, a high-temperature heat storage tank is used to store the extraction steam from the intermediate pressure cylinder of the steam turbine. During the power peak period, the heat storage is used for cascaded heating of part of the condensate water of the steam turbine, and at the same time, the cold storage is released to match the condenser with a high vacuum degree to improve the electric output of the unit. The present invention uses cascaded heat storage and cold storage instead of electricity storage to realize flexible and efficient peak shaving of the power station, and can greatly improve the new energy power consumption level.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A peak shaving system for a wind-solar-coal-energy storage multi-energy complementary power station, comprising a steam turbine intermediate pressure cylinder 101, a steam turbine low pressure cylinder 102, a shell side of a condenser 103, a condensate pump 104, a regulating valve A 201, a cold fluid side of an eighth-stage low-pressure heater 105, a cold fluid side of a seventh-stage low-pressure heater 106, a regulating valve B 202, a cold fluid side of a sixth-stage low-pressure heater 107, a cold fluid side of a fifth-stage low-pressure heater 108, and a deaerator inlet pipe, which are connected in sequence; the fifth, sixth, seventh, and eighth extraction steam pipes of the steam turbine are respectively connected to the steam inlet pipe of the fifth-stage low-pressure heater 108, the steam inlet pipe of the sixth-stage low-pressure heater 107, the steam inlet pipe of the seventh-stage low-pressure heater 106, and the steam inlet pipe of the eighth-stage low-pressure heater 105; the drain pipe of the fifth-stage low-pressure heater 108 is connected in sequence to the drain side of the sixth-stage low-pressure heater 107, the drain side of the seventh-stage low-pressure heater 106, the drain side of the eighth-stage low-pressure heater 105, and the shell side of the condenser 103; the outlet pipe of the condensate pump 104 is also connected in sequence to a regulating valve E 205, a cold fluid side of a heat exchanger C 121, a cold fluid side of a heat exchanger B 120, a regulating valve C 204, and the deaerator inlet pipe; the outlet pipe of the cold fluid side of the seventh-stage low-pressure heater 106 is also connected in sequence to a variable-frequency water pump 301, a regulating valve D 203, and the inlet of the cold fluid side of the heat exchanger B 120; the outlet of the high-temperature heat storage tank 116 is connected in sequence to a hot water pump A 302, a heat fluid side of the heat exchanger B 120, a regulating valve G 206, and the inlet of the normal-temperature storage tank 118; the outlet of the low-temperature heat storage tank 117 is connected in sequence to a hot water pump B 303, a heat fluid side of the heat exchanger C 121, a regulating valve F 207, and the inlet of the normal-temperature storage tank 118; the outlet of the cold storage tank 119 is connected in sequence to a cold water pump 305, a cold fluid side of a heat exchanger D 122, a regulating valve H 208, and the inlet of the normal-temperature storage tank 118; the outlet pipe of the normal-temperature storage tank 118 is connected in sequence to a normal-temperature water pump 304, a switching valve D 209, a cold fluid side of a heat exchanger A 115, and the inlet of the high-temperature heat storage tank 116; the outlet pipe of the normal-temperature storage tank 118 also communicates with the evaporator and the condenser inlets of an electrothermal pump 114 respectively through the pipe where the normal-temperature water pump 304 is located; the outlet pipe of the evaporator of the electrothermal pump 114 is connected to the inlet of the cold storage tank 119 through the pipeline where the switching valve C 211 is located; the outlet pipe of the condenser of the electrothermal pump 114 is connected to the inlet of the low-temperature heat storage tank 117 through the pipeline where the switching valve B 210 is located; the exhaust pipe of the steam turbine intermediate pressure cylinder 101 is also connected in sequence to a switching valve A 212, a heat fluid side of a heat exchanger A 115, and the shell side of the condenser 103; the outlet of the tube side of the condenser 103 is connected in sequence to a cooling tower 109, a heat fluid side of a heat exchanger D 122, and the inlet of the tube side of the condenser 103; the steam turbine intermediate pressure cylinder 101 and the steam turbine low pressure cylinder 102 are connected to a coal-fired power station generator 110 through a mechanical shaft; the coal-fired power station generator 110, a wind power generation device 112, and a photovoltaic power generation device 113 are respectively connected to the three inlets of a power controller 111 through circuits;The two outlets of the power controller 111, namely A and B, are respectively connected to the power grid and the heat pump 114 through circuits.

[0007] The described wind-solar-coal-energy storage multi-energy complementary power station peak shaving system operates in the following manner during the low electricity consumption period: Close the control valves D 203, control valve C 204, control valve E 205, control valve G 206, control valve F 207, and control valve H 208, so that the heat exchangers B 120, heat exchanger C 121, and heat exchanger D 122 do not work; Close the variable frequency water pump 301, hot water pump A 302, hot water pump B 303, and cold water pump 305; Open and adjust the switching valve A 212, switching valve D 209, and normal temperature water pump 304, so that the cold and hot fluid outlet temperatures of the heat exchanger A 115 both reach the set values; Adjust the power controller 111 according to the electricity load required by the power grid to preferentially absorb the power generation of the wind power generation equipment 112 and the photovoltaic power generation equipment 113, adjust the power of the heat pump 114 through the power controller 111, use the power generation that cannot be absorbed by the power grid to drive the heat pump 114, and at the same time open and adjust the switching valve B 210, switching valve C 211, and normal temperature water pump 304, so that the inlet temperatures of the low-temperature heat storage tank 117 and the cold storage tank 119 reach the set values.

[0008] The described wind-solar-coal-energy storage multi-energy complementary power station peak shaving system operates in the following manner during the high electricity consumption period: Close the switching valve A 212, switching valve D 209, and normal temperature water pump 304, so that the heat exchanger A 115 does not work; Cut off the circuit of the heat pump 114 through the power controller 111, and close the switching valve B 210 and switching valve C 211, so that the heat pump 114 does not work; Open and adjust the control valves D 203, control valve C 204, and control valve E 205, open and adjust the flow rate and flow direction of the variable frequency water pump 301, and adjust the opening degrees of the control valve A 201 and control valve B 202, so that the proportions of the heated condensate water in the heat exchangers B 120 and heat exchanger C 121 respectively reach the set values; Open and adjust the opening degrees of the control valves G 206 and control valve F 207, open and adjust the flow rates of the hot water pump A 302 and hot water pump B 303, so that the cold and hot fluid outlet temperatures of the heat exchangers B 120 and heat exchanger C 121 both reach the set values; Open and adjust the opening degree of the control valve H 208 and the flow rate of the cold water pump 305, so that the cold and hot fluid outlet temperatures of the heat exchanger D 122 both reach the set values.

[0009] Compared with the prior art, the present invention has the following advantages: (1) During the low electricity period, extract the exhaust steam from the intermediate pressure cylinder of the steam turbine to reduce the electricity output of the thermal power unit. At the same time, use the heat pump to consume the excess electricity of the power grid, realizing the low irreversible conversion and storage of electricity-thermal-cold. While ensuring energy efficiency, it greatly improves the load reduction capacity of the unit.

[0010] (2) By adopting cascade thermal energy storage and cold energy storage to achieve cross-time and cross-space energy storage and utilization, the energy efficiency level of the system is improved.

[0011] (3) During the peak power period, the cascade release of stored heat is used to cascade heat the condensate water, and the release of stored cold energy matches the improvement of the condenser vacuum degree. Multiple measures are taken simultaneously to improve the load-lifting capacity of the unit.

[0012] (4) Through the reasonable matching of the operation method and the system configuration, the present invention improves the accommodation level of new energy power such as wind energy and solar energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of a peak shaving system and an operation method for a wind-solar-coal-storage multi-energy complementary power station according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0015] In order to achieve the efficient and flexible coupling of energy storage technology, heat pump technology, wind and solar power generation technology and coal-fired power station peak shaving technology, a peak shaving system for a wind-solar-coal-storage multi-energy complementary power station according to the present invention is as Figure 1As shown in the figure, the system includes a steam turbine intermediate pressure cylinder 101, a steam turbine low pressure cylinder 102, the shell side of a condenser 103, a condensate pump 104, a regulating valve A 201, the cold fluid side of an eighth-stage low-pressure heater 105, the cold fluid side of a seventh-stage low-pressure heater 106, a regulating valve B 202, the cold fluid side of a sixth-stage low-pressure heater 107, the cold fluid side of a fifth-stage low-pressure heater 108, and a deaerator inlet pipe, which are connected in sequence. The extraction pipes of the fifth, sixth, seventh, and eighth stages of the steam turbine are respectively connected to the steam inlet pipes of the fifth-stage low-pressure heater 108, the sixth-stage low-pressure heater 107, the seventh-stage low-pressure heater 106, and the eighth-stage low-pressure heater 105. The drain pipe of the fifth-stage low-pressure heater 108 is connected in sequence to the drain side of the sixth-stage low-pressure heater 107, the drain side of the seventh-stage low-pressure heater 106, the drain side of the eighth-stage low-pressure heater 105, and the shell side of the condenser 103. The outlet pipe of the condensate pump 104 is also connected in sequence to a regulating valve E 205, the cold fluid side of a heat exchanger C 121, the cold fluid side of a heat exchanger B 120, a regulating valve C 204, and the deaerator inlet pipe. The outlet pipe of the cold fluid side of the seventh-stage low-pressure heater 106 is also connected in sequence to a variable-frequency water pump 301, a regulating valve D 203, and the inlet of the cold fluid side of the heat exchanger B 120. The outlet of the high-temperature heat storage tank 116 is connected in sequence to a hot water pump A 302, the hot fluid side of the heat exchanger B 120, a regulating valve G 206, and the inlet of the normal-temperature storage tank 118. The outlet of the low-temperature heat storage tank 117 is connected in sequence to a hot water pump B 303, the hot fluid side of the heat exchanger C 121, a regulating valve F 207, and the inlet of the normal-temperature storage tank 118. The outlet of the cold storage tank 119 is connected in sequence to a cold water pump 305, the cold fluid side of a heat exchanger D 122, a regulating valve H 208, and the inlet of the normal-temperature storage tank 118. The outlet pipe of the normal-temperature storage tank 118 is connected in sequence to a normal-temperature water pump 304, a switching valve D 209, the cold fluid side of a heat exchanger A 115, and the inlet of the high-temperature heat storage tank 116. The outlet pipe of the normal-temperature storage tank 118 also communicates with the evaporator and the condenser inlets of an electrothermal pump 114 through the pipe where the normal-temperature water pump 304 is located. The outlet pipe of the evaporator of the electrothermal pump 114 is connected to the inlet of the cold storage tank 119 through the pipeline where a switching valve C 211 is located. The outlet pipe of the condenser of the electrothermal pump 114 is connected to the inlet of the low-temperature heat storage tank 117 through the pipeline where a switching valve B 210 is located. The exhaust pipe of the steam turbine intermediate pressure cylinder 101 is also connected in sequence to a switching valve A 212, the hot fluid side of the heat exchanger A 115, and the shell side of the condenser 103. The outlet of the tube side of the condenser 103 is connected in sequence to a cooling tower 109, the hot fluid side of the heat exchanger D 122, and the inlet of the tube side of the condenser 103. The steam turbine intermediate pressure cylinder 101 and the steam turbine low pressure cylinder 102 are connected to a coal-fired power station generator 110 through a mechanical shaft. The coal-fired power station generator 110, a wind power generation device 112, and a photovoltaic power generation device 113 are respectively connected to the three inlets of a power controller 111 through circuits. The two outlets of the power controller 111 are respectively connected to the power grid and the electrothermal pump 114 through circuits.Through the above system design, the low-irreversibility conversion and cascade storage of surplus electricity throughout the year can be achieved. At the same time, rapid load increase and operation in a wide load range during the peak power period can be realized, thus greatly improving the system flexibility and the comprehensive energy utilization efficiency, and promoting the consumption of new energy power.

[0016] In order to develop the peak shaving system of the wind-solar-coal-energy storage multi-energy complementary power station more scientifically and effectively, it operates in the following manner during the low electricity consumption period: close the control valves Ding 203, Bing 204, Wu 205, Geng 206, Ji 207, and Xin 208, so that the heat exchangers Yi 120, Bing 121, and Ding 122 do not work; close the variable frequency water pump 301, hot water pump Jia 302, hot water pump Yi 303, and cold water pump 305, so that the outlet pipelines of the high-temperature heat storage tank, low-temperature heat storage tank, and cold storage tank are not in circulation; open and adjust the conversion valves Jia 212, Ding 209, and normal temperature water pump 304, so that the outlet temperatures of the cold and hot fluids of the heat exchanger Jia 115 both reach the set values; adjust the power controller 111 according to the electricity load required by the power grid to preferentially consume the power generated by the wind power generation equipment 112 and the photovoltaic power generation equipment 113, adjust the power of the electrothermal pump 114 through the power controller 111, use the power generated that cannot be consumed by the power grid to drive the electrothermal pump 114, and at the same time open and adjust the conversion valves Yi 210, Bing 211, and normal temperature water pump 304, so that the inlet temperatures of the low-temperature heat storage tank 117 and the cold storage tank 119 reach the set values. At this time, the system is in the energy storage stage. Through the above operation method, low-irreversibility electro-thermal-cold conversion of the system during the low electricity valley period can be achieved, and heat storage and cold storage in a cascade manner are used to replace electricity storage, so as to achieve the purpose of promoting the consumption of new energy power with heat storage and cold storage.

[0017] In order to develop the peak shaving system of the wind-solar-coal-energy storage multi-energy complementary power station more scientifically and effectively, it operates in the following manner during peak and valley periods: close the switching valve A 212, switching valve D 209, and normal temperature water pump 304 to make the heat exchanger A 115 inoperative; cut off the circuit of the electrothermal pump 114 through the power controller 111, and close the switching valve B 210 and switching valve C 211 to make the electrothermal pump 114 inoperative. At this time, all the energy storage pipelines of the system are closed; open and adjust the control valve D 203, control valve C 204, and control valve E 205, open and adjust the flow rate and flow direction of the variable frequency water pump 301, and adjust the opening degrees of the control valve A 201 and control valve B 202 so that the proportions of the heated condensate in the heat exchanger B 120 and heat exchanger C 121 reach the set values respectively, thereby ensuring the temperature consistency when the working fluids in each pipeline are mixed; open and adjust the opening degrees of the control valve G 206 and control valve F 207, and open and adjust the flow rates of the hot water pump A 302 and hot water pump B 303 so that the outlet temperatures of the cold and hot fluids of the heat exchanger B 120 and heat exchanger C 121 reach the set values; open and adjust the opening degree of the control valve H 208 and the flow rate of the cold water pump 305 so that the outlet temperatures of the cold and hot fluids of the heat exchanger D 122 reach the set values. At this time, the system is in the energy release stage. Through the above operation method, the system can quickly increase the load during the electricity peak period, and broaden the upper limit of the system operation range in the way of cascaded heat storage and cold storage release, realizing the flexible and efficient coordinated operation of the system, so as to achieve the purpose of promoting the consumption of new energy power with heat storage and cold storage.

Claims

1. A wind-solar-coal-storage multi-energy complementary power station peak-shaving system, characterized by: The invention comprises a steam turbine intermediate pressure cylinder (101), a steam turbine low pressure cylinder (102), a condenser (103) shell side, a condensate pump (104), a control valve A (201), an eighth stage low pressure heater (105) cold fluid side, a seventh stage low pressure heater (106) cold fluid side, a control valve B (202), a sixth stage low pressure heater (107) cold fluid side, a fifth stage low pressure heater (108) cold fluid side, and a deaerator inlet pipe, which are connected in sequence; and the fifth, sixth, seventh and eighth stage steam extraction pipes of the steam turbine are respectively connected to the steam inlet pipe of the fifth stage low pressure heater (108), the steam inlet pipe of the sixth stage low pressure heater (107), the steam inlet pipe of the seventh stage low pressure heater (106) and the steam inlet pipe of the eighth stage low pressure heater ( The steam inlet pipe of the fifth-stage low-pressure heater (108) is connected in sequence to the drain side of the sixth-stage low-pressure heater (107), the drain side of the seventh-stage low-pressure heater (106), the drain side of the eighth-stage low-pressure heater (105) and the shell side of the condenser (103); the outlet pipe of the condensate pump (104) is also connected in sequence to the control valve E (205), the cold fluid side of the heat exchanger C (121), the cold fluid side of the heat exchanger B (120), the control valve C (204) and the deaerator inlet pipe; the outlet pipe of the cold fluid side of the seventh-stage low-pressure heater (106) is also connected in sequence to the variable frequency water pump (301), the control valve D (203), and the cold fluid side inlet of the heat exchanger B (120); the outlet pipe of the high-temperature heat storage tank (116) is also connected in sequence to the variable frequency water pump (301), the control valve D (203), and the cold fluid side inlet of the heat exchanger B (120); The inlet of the low-temperature heat storage tank (117) is connected in sequence to the hot water pump A (302), the hot fluid side of the heat exchanger B (120), the regulating valve G (206), and the inlet of the normal temperature storage tank (118); the outlet of the low-temperature heat storage tank (117) is connected in sequence to the hot water pump B (303), the hot fluid side of the heat exchanger C (121), the regulating valve F (207), and the inlet of the normal temperature storage tank (118); the outlet of the cold storage tank (119) is connected in sequence to the cold water pump (305), the cold fluid side of the heat exchanger D (122), the regulating valve S (208), and the inlet of the normal temperature storage tank (118); the outlet pipeline of the normal temperature storage tank (118) is connected in sequence to the normal temperature water pump (304), the conversion valve D (209), the cold fluid side of the heat exchanger A (115), and the inlet of the high temperature heat storage tank (116); the normal temperature storage tank (11 8) The outlet pipeline is also connected to the evaporator and condenser inlets of the electric heat pump (114) through the pipeline where the normal temperature water pump (304) is located; the evaporator outlet pipeline of the electric heat pump (114) is connected to the cold storage tank (119) inlet through the pipeline where the conversion valve C (211) is located; the condenser outlet pipeline of the electric heat pump (114) is connected to the low-temperature heat storage tank (117) inlet through the pipeline where the conversion valve B (210) is located; the steam exhaust pipeline of the steam turbine intermediate pressure cylinder (101) is also connected to the conversion valve A (212), the heat fluid side of the heat exchanger A (115) and the shell side of the condenser (103) in sequence; the tube side outlet of the condenser (103) is connected to the cooling tower (109), the heat fluid side of the heat exchanger D (122) and the tube side inlet of the condenser (103) in sequence;The steam turbine intermediate pressure cylinder (101) and the steam turbine low pressure cylinder (102) are connected to the coal-fired power station generator (110) through a mechanical shaft; the coal-fired power station generator (110), the wind power generation equipment (112), and the photovoltaic power generation equipment (113) are respectively connected to the three inlets A, B, and C of the power controller (111) through circuits; and the two outlets A and B of the power controller (111) are respectively connected to the power grid and the electric heat pump (114) through circuits. ; 2. The method for operating the peak-shaving system of a wind-solar-coal-storage multi-energy complementary power station during the low electricity consumption period as described in claim 1, characterized in that: Close the regulating valve D (203), regulating valve C (204), regulating valve E (205), regulating valve G (206), regulating valve F (207), and regulating valve Sin (208), so that heat exchanger B (120), heat exchanger C (121), and heat exchanger D (122) do not work; close the variable frequency water pump (301), hot water pump A (302), hot water pump B (303), and cold water pump (305); open and adjust the conversion valve A (212), conversion valve D (209), and normal temperature water pump (304), so that heat exchanger A (11 5) The outlet temperatures of the cold and hot fluids both reach predetermined values; the power controller (111) is adjusted according to the power load required by the power grid to preferentially absorb the power generated by the wind power generation equipment (112) and the photovoltaic power generation equipment (113); the power of the electric heat pump (114) is adjusted through the power controller (111); the power generated that cannot be absorbed by the power grid is used to drive the electric heat pump (114); and at the same time, the conversion valve B (210), the conversion valve C (211), and the normal temperature water pump (304) are opened and adjusted so that the inlet temperatures of the low-temperature heat storage tank (117) and the cold storage tank (119) reach predetermined values.

3. The method for operating the peak-shaving system of a wind-solar-coal-storage multi-energy complementary power station during peak electricity consumption as described in claim 1, characterized in that: The conversion valve A (212), the conversion valve D (209), and the normal temperature water pump (304) are closed, so that the heat exchanger A (115) does not work; the circuit of the electric heat pump (114) is cut off through the power controller (111), and the conversion valve B (210) and the conversion valve C (211) are closed, so that the electric heat pump (114) does not work; the control valve D (203), the control valve C (204), and the control valve E (205) are opened and adjusted, the flow rate and flow direction of the variable frequency water pump (301) are opened and adjusted, and the control valve A (201) and the control valve B (202) are adjusted. The opening degree of the regulating valve G (206) and the regulating valve F (207) is opened and adjusted, and the flow rates of the hot water pump A (302) and the hot water pump B (303) are opened and adjusted, so that the outlet temperatures of the cold and hot fluids of the heat exchanger B (120) and the heat exchanger C (121) both reach predetermined values; the opening degree of the regulating valve S (208) and the flow rate of the cold water pump (305) are opened and adjusted, so that the outlet temperatures of the cold and hot fluids of the heat exchanger D (122) both reach predetermined values.

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