Auto-cascade heat pump steam generation system and working method

Abstract

The invention belongs to the technical field of high-temperature heat pumps and waste heat recovery, and discloses an auto-cascade heat pump steam generation system and a working method.The auto-cascade heat pump steam generation system comprises a compressor, a condenser, an evaporator, a first heat exchanger, a second heat exchanger, a soft water pump and a gas-liquid separator, and the condenser comprises a third inlet, a third outlet, a fourth inlet and a fourth outlet; the first heat exchanger comprises a first inlet, a first outlet, a second outlet and a second inlet, the gas-liquid separator comprises a fifth inlet, a fifth outlet and a sixth outlet, and the second heat exchanger comprises a seventh inlet, a seventh outlet, an eighth outlet, an eighth inlet, a ninth inlet and a ninth outlet. The evaporator comprises a tenth inlet, a tenth outlet, an eleventh outlet and an eleventh inlet. By means of the method, industrial wastewater waste heat can be deeply recycled for steam supply, the utilization efficiency of industrial heat energy is remarkably improved, and steam supply energy consumption and cost are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature heat pumps and waste heat recovery, and in particular to a self-cascade heat pump steam generation system and a working method. Background Art

[0002] With the continuous development of the global economy, energy and environmental issues have become increasingly prominent; how to improve the energy efficiency of industrial production processes and reduce carbon dioxide emissions has become a common technical development direction for countries around the world. Steam, as an important heat carrier, is widely used in many industrial fields such as printing and dyeing, food, and medicine. Gas or electric boilers are currently the most important steam supply devices, but the energy efficiency of boilers is low, and the operating cost is limited by energy supply. Therefore, the industry urgently needs to develop new and efficient steam supply methods.

[0003] While the industrial production process consumes energy to supply steam, it also emits a large amount of waste heat resources. A large proportion of energy consumption in industrial production will be converted into waste heat resources of different forms and temperatures, and the efficiency of industrial waste heat recovery in my country is relatively low. Industrial wastewater is the most common form of waste heat emission. Wastewater with a certain temperature needs to be cooled or naturally dissipated to a suitable temperature before treatment, and this part of heat is wasted a lot.

[0004] The heat pump steam generation system is an emerging energy-saving technology. It uses a heat pump evaporator to recover the waste heat of industrial wastewater, and then heats water through a condenser to prepare steam. At present, many scholars have confirmed through theoretical research that it has significant energy-saving effects and good market application prospects. However, due to the limitations of heat pump working fluids and system energy efficiency, existing products mainly use high-temperature heat pump systems with high evaporation temperatures and high condensation temperatures. They mainly recover waste heat from industrial wastewater above 60°C, prepare low-temperature steam above 100-110°C, and then use steam compressors to compress the steam to a temperature above 130°C for use. The higher the required steam temperature, the higher the heat pump evaporation temperature needs to be. On the one hand, the wastewater flowing out of the evaporator still has a certain temperature, that is, the waste heat recovery of wastewater is not sufficient, and on the other hand, it is difficult to directly prepare higher temperature steam. In addition, the current steam generation method is generally hot water flash evaporation, and the flash steam obtained is saturated steam, which has strict requirements on pipeline insulation. Otherwise, the steam will condense due to heat dissipation, which will not only increase the technical requirements of subsequent compressors, but also lead to a certain amount of steam loss and heat energy waste.

[0005] Therefore, how to improve the waste heat recovery rate, reduce the wastewater discharge temperature, increase the steam supply temperature while ensuring higher system energy efficiency, and effectively control the superheat of steam to meet the transportation requirements are issues that urgently need to be addressed in the development and application of heat pump steam generation technology. Summary of the invention

[0006] In order to solve the problems of insufficient waste heat recovery and utilization of waste water in the above-mentioned prior art, and the fact that the steam generation method is generally hot water flash evaporation, the flash steam obtained is saturated steam, and strict requirements are placed on pipeline insulation, otherwise the steam will condense due to heat dissipation, which will not only increase the technical requirements of subsequent compressors, but also lead to a certain amount of steam loss and heat energy waste. The present invention proposes a self-cascade heat pump steam generation system and working method, which can reduce the waste water temperature to below 35°C, and adopts a vertical shell and tube heat exchanger to directly evaporate the water in the shell side to obtain steam, eliminating the water circulation subsystem of the traditional hot water flash evaporation, and reducing the system complexity and equipment cost.

[0007] The present invention is realized by the following technical scheme: comprising a compressor, a condenser connected to the compressor outlet and an evaporator connected to the compressor inlet, and also comprising a first heat exchanger, a second heat exchanger, a soft water pump and a gas-liquid separator, wherein the condenser comprises a third inlet, a third outlet, a fourth inlet and a fourth outlet, the first heat exchanger comprises a first inlet, a first outlet, a second outlet and a second inlet, the gas-liquid separator comprises a fifth inlet, a fifth outlet and a sixth outlet, the second heat exchanger comprises a seventh inlet, a seventh outlet, an eighth outlet, an eighth inlet, a ninth inlet and a ninth outlet, and the evaporator comprises a tenth inlet, a tenth outlet, an eleventh outlet and an eleventh inlet; the third inlet is connected to the first outlet, the third outlet is connected to the second inlet, the fourth inlet is connected to the compressor outlet, the first inlet is connected to the soft water pump, the second outlet is connected to the fifth inlet, the fifth outlet is connected to the eighth inlet, the sixth outlet is connected to the seventh inlet, the seventh outlet is connected to the eleventh inlet, the eighth outlet is connected to the compressor inlet, the ninth outlet is connected to the tenth inlet, and the tenth outlet is connected to a one-way valve and a compressor inlet in sequence through a pipeline.

[0008] As a further preference, a second stop valve is provided at the soft water pump, a first stop valve is provided between the third outlet and the second inlet, a third stop valve is provided at the fourth outlet, and a fourth stop valve is provided at the ninth inlet.

[0009] As a further preference, an evaporation pressure regulating valve is provided between the eighth outlet and the compressor inlet, a first regulating valve is provided between the third inlet and the first outlet, and a second regulating valve is provided at the ninth inlet, so that the volume flow of the compressor is adjustable.

[0010] As a further preference, a first pressure controller is arranged between the fourth inlet and the compressor, and the first pressure controller is connected to the compressor through a signal line; a second pressure controller is arranged at the top of the condenser, and the second pressure controller is connected to the first regulating valve through a signal line; a third temperature controller is arranged at the eleventh outlet, and the third temperature controller is connected to the second regulating valve through a signal line.

[0011] As a further preference, a first expansion valve is provided between the fifth outlet and the eighth inlet, and a second expansion valve is provided between the seventh outlet and the eleventh inlet.

[0012] As a further preference, a first temperature controller is provided at the seventh outlet, and the first temperature controller is connected to the first expansion valve via a signal line; a second temperature controller is provided at the tenth outlet, and the second temperature controller is connected to the second expansion valve via a signal line.

[0013] As a further preference, the condenser is a vertical shell and tube condenser, the refrigerant circulates in the pipes inside the condenser, the refrigerant used in the condenser is a mixture of two pure refrigerants with different critical temperatures, the fourth inlet is arranged at the top of the condenser, the third outlet and the third inlet are arranged at the bottom of the condenser, the shell side of the condenser is provided with an upper liquid level limit, and the fourth outlet is arranged above the upper liquid level limit.

[0014] The present invention also provides a working method of the self-cascade heat pump steam generation system, comprising the following steps:

[0015] Step 1: System preheating and startup;

[0016] Step 11, open the second stop valve and the third stop valve, and start the soft water pump to replenish water to the condenser until the upper limit of the liquid level;

[0017] Step 12, close the second stop valve, the third stop valve and the soft water pump, turn on the compressor and start it at a low flow rate;

[0018] Step 13, open the fourth stop valve, and introduce waste heat waste water into the second heat exchanger. The refrigerant gas with low critical temperature in the gas-liquid separator is condensed by the second heat exchanger and throttled by the second expansion valve, and then enters the evaporator to absorb heat and evaporate into gas; the refrigerant liquid with high critical temperature in the gas-liquid separator is throttled by the first expansion valve and then enters the second heat exchanger to absorb waste heat of waste water and evaporate;

[0019] Step 14, the refrigerant gas with a high critical temperature flowing out of the second heat exchanger is mixed with the refrigerant gas with a low critical temperature flowing out of the evaporator and then enters the compressor for compression to increase the temperature and pressure;

[0020] Step 15: The compressed mixed refrigerant gas enters the condenser, and when the exhaust pressure of the compressor reaches a set value, the first stop valve is opened;

[0021] Step 16, repeating steps 11 to 15, gradually increasing the flow rate of the compressor to the set value, the water in the condenser is gradually heated and evaporated, and when the shell pressure of the condenser reaches the set value, the second stop valve and the third stop valve are opened, and the soft water pump is turned on at the same time, entering the heat pump steam supply stage;

[0022] Step 2: Heat pump steam supply:

[0023] Step 21, according to the pressure in the condenser, the second pressure controller controls the opening of the first regulating valve, and if the pressure increases, the second pressure controller sends a control signal to the first regulating valve to reduce the opening of the first regulating valve; otherwise, the opening of the first regulating valve is increased;

[0024] Step 22: The first pressure controller controls the flow rate of the compressor according to the exhaust pressure of the compressor. When the exhaust pressure increases, the first pressure controller sends a control signal to the compressor to reduce the flow rate of the compressor. When the exhaust pressure decreases, the first pressure controller sends a control signal to the compressor to increase the flow rate of the compressor.

[0025] Step 23, according to the temperature of the waste water discharged from the eleventh outlet of the evaporator, the third temperature controller controls the opening of the second regulating valve, and if the temperature of the waste water discharged from the eleventh outlet increases, the opening of the second regulating valve is reduced; otherwise, the opening of the second regulating valve is increased;

[0026] Step 24: If the temperature detected by the first temperature controller rises, a control signal is sent to the first expansion valve to increase the opening of the first expansion valve, otherwise the opening of the first expansion valve is reduced; if the temperature detected by the second temperature controller rises, a control signal is sent to the second expansion valve to increase the opening of the second expansion valve, otherwise the opening of the second expansion valve is reduced.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention utilizes the characteristics of the mixed working fluid of the self-cascade heat pump system to prepare steam from the condensation heat of the refrigerant with a high critical temperature, and then uses its evaporation endothermic characteristics after throttling to liquefy the refrigerant with a low critical temperature while recovering the high-temperature part of the waste heat of the industrial wastewater. Afterwards, the liquefied low critical temperature refrigerant continues to deeply recover and utilize the waste heat of the industrial wastewater in the evaporator, and the wastewater temperature can be reduced to below 35°C, thereby ensuring the temperature requirement for generating steam and greatly improving the efficiency of recovering and utilizing the waste heat of industrial wastewater, while increasing the steam supply and shortening the wastewater treatment cycle.

[0029] 2. The present invention adopts a vertical shell and tube condenser to directly evaporate the water in the shell side to obtain steam, eliminating the water circulation subsystem of the traditional hot water flash evaporation, reducing the complexity of the system and the equipment cost. At the same time, the refrigerant in the top tube of the heat exchanger heats the steam generated by evaporation to directly meet the steam supply requirement of a certain superheat degree.

[0030] 3. The present invention adopts a three-flow second heat exchanger, which effectively integrates the self-cascaded intermediate evaporative condenser and the heat exchanger for evaporating the high critical temperature refrigerant to recover the waste heat of industrial waste water. Combined with the setting of the vertical condenser, it can reduce the number of equipment in the system and the space requirements of the equipment.

[0031] 4. The present invention can greatly promote the industrial application of heat pump steam generation systems and make significant contributions to energy conservation, emission reduction and reduction of enterprise production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the system of the present invention.

[0033] Indicated in the figure:

[0034] 1. Compressor; 2. Condenser; 3. First heat exchanger; 4. Gas-liquid separator; 5. First expansion valve; 6. Second heat exchanger; 7. Evaporation pressure regulating valve; 8. Second expansion valve; 9. Evaporator; 10. Check valve; 11. Soft water pump; 12. First regulating valve; 13. Second regulating valve; 14. First pressure controller; 15. Second pressure controller; 16. First temperature controller; 17. Second temperature controller; 18. Third temperature controller; 19. Second stop valve; 20. First stop valve; 21. Third stop valve Valve; 22, the fourth stop valve; a1, the first inlet; a2, the first outlet; a3, the second outlet; a4, the second inlet; b1, the third inlet; b2, the third outlet; b3, the fourth inlet; b4, the fourth outlet; c1, the fifth inlet; c2, the fifth outlet; c3, the sixth outlet; d1, the seventh inlet; d2, the seventh outlet; d3, the eighth outlet; d4, the eighth inlet; d5, the ninth inlet; d6, the ninth outlet; e1, the tenth inlet; e2, the tenth outlet; e3, the eleventh outlet; e4, the eleventh inlet. DETAILED DESCRIPTION

[0035] Advantages and features of the present invention will be illustrated and explained by the following non-limiting description of preferred embodiments thereof, which are given by way of example only with reference to the accompanying drawings.

[0036] like Figure 1As shown, the present invention provides a self-cascade heat pump steam generation system, including a compressor 1, a condenser 2, a first heat exchanger 3, a gas-liquid separator 4, a second heat exchanger 6, a one-way valve 10 and a soft water pump 11. The outlet of the compressor 1 is connected to the fourth inlet b3 of the condenser 2, and the fourth inlet b3 is the refrigerant inlet of the condenser 2 and is arranged at the top of the condenser 2. The third outlet b2 of the condenser 2 is connected to the second inlet a4 of the first heat exchanger 3 through a pipeline, and the third outlet b2 is the refrigerant outlet of the condenser 2 and is arranged at the bottom of the condenser 2, and the second inlet a4 is the refrigerant inlet of the first heat exchanger 3. In order to facilitate and quickly establish the exhaust pressure of the compressor 1, a first stop valve 20 can be set on the pipeline between the third outlet b2 and the second inlet a4. The second outlet a3 of the first heat exchanger 3 is connected to the fifth inlet c1 of the gas-liquid separator 4 through a pipeline. The gas-liquid separator 4 further comprises a fifth outlet c2 and a sixth outlet c3, wherein the fifth outlet c2 is the liquid outlet of the gas-liquid separator 4, i.e., the outlet of the refrigerant with a high critical temperature in the mixed refrigerant used in the present invention; and the sixth outlet c3 is the gas outlet of the gas-liquid separator 4, i.e., the outlet of the refrigerant with a low critical temperature in the mixed refrigerant used in the present invention. The sixth outlet c3 is connected to the seventh inlet d1 of the second heat exchanger 6 through a pipeline, and the fifth outlet c2 is connected to the eighth inlet d4 of the second heat exchanger 6 through a pipeline, and a first expansion valve 5 may be arranged between the fifth outlet c2 and the eighth inlet d4. The eighth outlet d3 of the second heat exchanger 6 is connected to the evaporation pressure regulating valve 7 and the inlet of the compressor 1 in sequence through a pipeline. The seventh outlet d2 of the second heat exchanger 6 is connected to the second expansion valve 8 and the eleventh inlet e4 of the evaporator 9 in sequence through a pipeline. The tenth outlet e2 of the evaporator 9 is connected to the check valve 10 and the inlet of the compressor 1 in sequence through a pipeline. The seventh inlet d1 is the refrigerant inlet of the second heat exchanger 6 with a low critical temperature, and the seventh outlet d2 is the refrigerant outlet of the second heat exchanger 6 with a low critical temperature; the eighth inlet d4 is the refrigerant inlet of the second heat exchanger 6 with a high critical temperature, and the eighth outlet d3 is the refrigerant outlet of the second heat exchanger 6 with a high critical temperature. The eleventh inlet e4 is the refrigerant inlet of the evaporator 9, and the tenth outlet e2 is the refrigerant outlet of the evaporator 9.

[0037] The evaporation pressure regulating valve 7 can not only stabilize the evaporation pressure of the high critical temperature refrigerant in the second heat exchanger 6, but also throttle and reduce the pressure of the high critical temperature refrigerant after evaporation to ensure that its pressure is the same as the low critical temperature refrigerant gas evaporated in the evaporator 9, and then remixed and compressed by the compressor 1 for repeated circulation.

[0038] The first heat exchanger 3 further includes a first inlet a1 and a first outlet a2, which are the inlet and outlet of the first heat exchanger 3 for replenishing soft water, respectively. The first inlet a1 is connected to the soft water pump 11 and the second stop valve 19 in sequence through a pipeline. The first outlet a2 is connected to the third inlet b1 of the condenser 2 through a pipeline, and a first regulating valve 12 may be further provided between the first outlet a2 and the third inlet b1. The third inlet b1 is the inlet for replenishing soft water of the condenser 2, and is provided at the bottom of the condenser 2. The first regulating valve 12 is used to adjust the flow rate of replenishing soft water in the condenser 2. The condenser 2 further includes a fourth outlet b4, which is the steam outlet of the condenser 2, is connected to the third stop valve 21 through a pipeline, and supplies steam to the outside.

[0039] The present invention uses the first heat exchanger 3 as a subcooler, which can not only increase the subcooling degree of the high critical temperature refrigerant component after liquefaction, but also increase the temperature of the soft water supply entering the condenser 2, shorten the sensible heat exchange time before the soft water supply evaporates, and the soft water supply enters from the bottom of the condenser 2, which can disturb the soft water in the condenser 2, thereby enhancing the heat exchange effect.

[0040] The condenser 2 is a vertical shell and tube condenser. The refrigerant circulates in the pipes in the condenser 2, and the soft water is supplied in the rest of the pipes outside the condenser 2. The pipe passage in the condenser 2 is called the tube side, and the part outside the pipes in the condenser 2 is called the shell side. The shell side is provided with an upper limit of the liquid level, and the fourth outlet b4 is provided above the upper limit of the liquid level. The position of the upper limit of the liquid level can be designed according to the required superheat of the steam supply to generate the superheated steam required by the industry. The compressed mixed refrigerant enters the condenser 2, and first heats the steam above the liquid level. By controlling the liquid level height, the superheat of the steam can be regulated, and the pressure of the steam can also be adjusted.

[0041] The second heat exchanger 6 further includes a ninth inlet d5 and a ninth outlet d6, which are respectively the waste heat waste water inlet and outlet of the second heat exchanger 6. The ninth inlet d5 is connected to the second regulating valve 13 and the fourth stop valve 22 in sequence through a pipeline; the ninth outlet d6 is connected to the tenth inlet e1 of the evaporator 9 through a pipeline, and the tenth inlet e1 is the waste heat waste water inlet of the evaporator 9. The evaporator 9 further includes an eleventh outlet e3, which is the waste heat waste water outlet of the evaporator 9.

[0042] The second heat exchanger 6 is a three-stream heat exchanger. The present invention adopts the middle stream to circulate the refrigerant with a high critical temperature, and the two side streams to circulate the waste heat waste water and the gaseous refrigerant with a low critical temperature respectively. The evaporation heat absorption characteristics of the high critical temperature refrigerant are utilized to absorb the heat of the waste heat waste water and the condensation heat of the gaseous low critical temperature refrigerant respectively. In actual application, the refrigerant liquid with a high critical temperature can also be divided into two streams, which enter the waste heat waste water heat exchanger and the low critical temperature refrigerant gas condenser respectively.

[0043] The compressor 1 is a compressor with adjustable volume flow, preferably variable frequency regulation, which is used for energy regulation of the heat pump system necessary for suitable waste heat wastewater working conditions or changes in steam supply requirements; when the suction and exhaust gas pressure of the compressor 1 is too high, in order to ensure system stability and operating energy efficiency, the compressor 1 can be a two-stage compression or multi-stage compression compressor; the lubricating oil system of the compressor 1 is not reflected in the present invention, and the heat of the oil cooling can also be used to preheat the soft water supply.

[0044] The refrigerant used in the present invention is a mixed refrigerant formed by mixing two pure refrigerants with different critical temperatures in a certain proportion. The selection of refrigerant components needs to be based on the waste heat wastewater outlet temperature and the steam supply temperature, and the proportion of each component needs to be optimized according to the actual operating conditions. The refrigerant with a low critical temperature is used to meet the requirements of the waste heat wastewater outlet temperature, and the evaporation temperature should not be higher than 30°C, and can be R22, R134a, etc.; the refrigerant with a high critical temperature is used to heat and supply soft water to evaporate and generate steam. In order to meet the positive pressure requirement of the steam temperature not lower than 100°C, the temperature of the refrigerant with a high critical temperature needs to be not lower than 120°C, and can be R245fa, R1234ze, etc.

[0045] A first pressure controller 14 is provided between the fourth inlet b3 and the compressor 1. The first pressure controller 14 is connected to the compressor 1 through a signal line. The flow of the compressor 1 is controlled by frequency conversion and other methods according to the exhaust pressure of the compressor 1. When the exhaust pressure increases, the flow of the compressor 1 is reduced, and when the exhaust pressure decreases, the flow of the compressor 1 is increased. The first pressure controller 14 can also be set with a high-pressure fuse pressure value. When the pressure exceeds the high-pressure fuse pressure value, that is, when the pressure control fails, an alarm or emergency shutdown is performed. A second pressure controller 15 is provided at the top of the shell side of the condenser 2. The second pressure controller 15 is connected to the first regulating valve 12 through a signal line to adjust the flow of the soft water supply entering the condenser 2. When the pressure increases, the opening of the first regulating valve 12 is reduced, the flow of the soft water supply is reduced, and the steam space above is increased. When the system of the present invention is in operation, the steam pressure is controlled first, and the steam superheat is secondly guaranteed to be within a certain range.

[0046] The seventh outlet d2 is provided with a first temperature controller 16, which is connected to the first expansion valve 5 through a signal line and controls its opening, and is used to adjust the flow rate of the liquid high critical temperature refrigerant entering the second heat exchanger 6. When the temperature rises detected by the first temperature controller 16, a control signal is sent to the first expansion valve 5 to increase the opening of the first expansion valve 5, thereby ensuring that the refrigerant component with a low critical temperature can be completely liquefied in the second heat exchanger 6. The tenth outlet e2 is provided with a second temperature controller 17, which is connected to the second expansion valve 8 through a signal line and controls its opening, and is used to adjust the flow rate of the low critical temperature refrigerant entering the evaporator 9. When the temperature rises detected by the second temperature controller 17, a control signal is sent to the second expansion valve 8 to increase the opening of the second expansion valve 8. A third temperature controller 18 is provided at the eleventh outlet e3, and the third temperature controller 18 is connected to the second regulating valve 13 via a signal line, and is used to adjust the flow rate of the waste heat waste water; when the temperature of the waste water discharged from the eleventh outlet e3 increases, the opening of the second regulating valve 13 is reduced, and the flow rate of the waste heat waste water entering the ninth inlet d5 is reduced. By controlling the temperature of the waste water discharged from the eleventh outlet e3, it can be ensured that the waste heat of the industrial waste heat waste water can be fully recovered and utilized.

[0047] The present invention provides a self-cascade heat pump steam generation system comprising three cycles, namely a mixed refrigerant cycle, a soft water supply cycle and a waste heat waste water cycle.

[0048] The replenishment soft water circulates from the second stop valve 19, passes through the soft water pump 11, the first inlet a1, the first heat exchanger 3, the first outlet a2, the first regulating valve 12, the third inlet b1, the condenser 2 and the fourth outlet b4 in sequence, and finally discharges steam to the outside through the third stop valve 21. The replenishment soft water exchanges heat with the mixed refrigerant in the first heat exchanger 3, absorbs heat, evaporates and increases pressure in the condenser 2, and finally is discharged from the fourth outlet b4 of the condenser 2.

[0049] The waste heat waste water circulates from the fourth stop valve 22, passes through the second regulating valve 13, the ninth inlet d5, the second heat exchanger 6, the ninth outlet d6, the tenth inlet e1 and the evaporator 9 in sequence, and is finally discharged from the eleventh outlet e3. The waste heat waste water is used for the refrigerant with a high critical temperature to absorb heat and evaporate in the second heat exchanger 6, and for the refrigerant with a low critical temperature to absorb heat and evaporate in the evaporator 9, and is finally discharged from the eleventh outlet e3.

[0050] The mixed refrigerant cycle is divided into two paths: a high critical temperature refrigerant cycle and a low critical temperature refrigerant cycle. The high critical temperature refrigerant cycle starts from the condenser 2, passes through the third outlet b2, the first stop valve 20, the second inlet a4, the first heat exchanger 3, the second outlet a3, the fifth inlet c1, the gas-liquid separator 4, the fifth outlet c2, the first expansion valve 5, the eighth inlet d4, the second heat exchanger 6, the eighth outlet d3, the evaporation pressure regulating valve 7 and the compressor 1, and finally returns to the condenser 2 from the fourth inlet b3. The low critical temperature refrigerant cycle starts from the condenser 2, passes through the third outlet b2, the first stop valve 20, the second inlet a4, the first heat exchanger 3, the second outlet a3, the fifth inlet c1, the gas-liquid separator 4, the sixth outlet c3, the seventh inlet d1, the second heat exchanger 6, the seventh outlet d2, the second expansion valve 8, the eleventh inlet e4, the evaporator 9, the tenth outlet e2, the one-way valve 10 and the compressor 1, and finally returns to the condenser 2 from the fourth inlet b3. The high critical temperature refrigerant releases heat to the make-up soft water in the first heat exchanger 3 to maintain a certain degree of supercooling, is separated from the gaseous low critical temperature refrigerant in the gas-liquid separator 4, absorbs the waste heat of the waste heat waste water and the condensation heat of the gaseous low critical temperature refrigerant in the second heat exchanger 6 to evaporate into a gaseous state, is mixed with the gaseous low critical temperature refrigerant flowing out of the evaporator 9 at the inlet of the compressor 1, is heated and pressurized in the compressor 1, and finally enters the condenser 2. The low critical temperature refrigerant is separated from the liquid high critical temperature refrigerant in the gas-liquid separator 4, is condensed in the second heat exchanger 6, absorbs the waste heat of the waste heat waste water in the evaporator 9 to evaporate into a gaseous state, is mixed with the gaseous high critical temperature refrigerant flowing out of the second heat exchanger 6 at the inlet of the compressor 1, is heated and pressurized in the compressor 1, and finally enters the condenser 2.

[0051] The present invention also provides a working method of a self-cascade heat pump steam generation system, including a system preheating method and a heat pump steam supply control method, the specific contents of which are as follows:

[0052] Phase 1: System preheating and startup.

[0053] Step 11, open the second stop valve 19 and the third stop valve 21, and start the soft water pump 11 to replenish water to the condenser 2 until the upper limit of the liquid level is reached.

[0054] Step 12: Then close the second stop valve 19, the third stop valve 21 and the soft water pump 11, turn on the compressor 1 and start it at a low flow rate.

[0055] Step 13, open the fourth stop valve 22 at the same time, and introduce waste heat waste water into the second heat exchanger 6. The refrigerant gas with low critical temperature in the gas-liquid separator 4 is successively condensed by the second heat exchanger 6 and throttled by the second expansion valve 8 to enter the evaporator 9 to absorb heat and evaporate into gas; the refrigerant liquid with high critical temperature in the gas-liquid separator 4 is throttled by the first expansion valve 5 and enters the second heat exchanger 6 to absorb waste heat of waste water and evaporate.

[0056] Step 14: The refrigerant gas with a high critical temperature flowing out of the second heat exchanger 6 is mixed with the refrigerant gas with a low critical temperature flowing out of the evaporator 9 and then enters the compressor 1 for compression to increase the temperature and pressure.

[0057] Step 15, the compressed mixed refrigerant gas enters the condenser 2. After the exhaust pressure of the compressor 1 reaches the set value, the first stop valve 20 is opened to allow the high critical temperature refrigerant liquid condensed in the condenser and the uncondensed low critical temperature refrigerant gas to enter the gas-liquid separator 4 for separation.

[0058] Step 16, repeating steps 11 to 15, while gradually increasing the flow rate of the compressor 1 to the set value, the water in the condenser 2 is gradually heated and evaporated, and when the shell pressure of the condenser 2 reaches the set value, the second stop valve 19 and the third stop valve 21 are opened, and the soft water pump 11 is turned on at the same time, at this time, the third stop valve 21 exhausts steam to the outside, and after a period of time, it can supply usable high-temperature steam to the outside, entering the heat pump steam supply stage;

[0059] Stage 2, heat pump steam supply:

[0060] The refrigerant, make-up soft water and waste heat waste water of the heat pump system repeat the process of the waste heat stage. According to the changes in the user's steam demand, in order to maintain the stable and efficient operation of the heat pump system, the core parameters during the system operation process adopt the following control method:

[0061] Step 21, steam pressure control method:

[0062] According to the pressure in the shell side of the condenser 2, the second pressure controller 15 controls the opening of the first regulating valve 12 to adjust the flow of the soft water supply entering the condenser 2. When the pressure rises, the second pressure controller 15 sends a control signal to the first regulating valve 12 to reduce the opening of the first regulating valve 12 and reduce the soft water supply flow; otherwise, the opening of the first regulating valve 12 is increased. When the system is actually running, the steam pressure is controlled first, and the steam superheat is secondly guaranteed to be within a certain range.

[0063] Step 22: Compressor flow rate adjustment method:

[0064] According to the exhaust pressure of the compressor 1, the first pressure controller 14 controls the flow of the compressor 1 through the flow regulation methods such as frequency conversion. When the exhaust pressure increases, the first pressure controller 14 sends a control signal to the compressor 1 to reduce the flow of the compressor 1. When the exhaust pressure decreases, the first pressure controller 14 sends a control signal to the compressor 1 to increase the flow of the compressor 1. The first pressure controller 14 can also set a high-pressure fuse pressure value. When the pressure exceeds the high-pressure fuse pressure value, that is, when the pressure control fails, an alarm or emergency shutdown is issued.

[0065] Step 23, waste heat wastewater flow control method:

[0066] According to the temperature of the waste water discharged from the eleventh outlet e3 of the evaporator 9, the third temperature controller 18 controls the opening of the second regulating valve 13 to adjust the flow rate of the waste heat waste water. If the temperature of the waste water discharged from the eleventh outlet e3 increases, the opening of the second regulating valve 13 is reduced to reduce the flow rate of the waste heat waste water entering the ninth inlet d5; otherwise, the opening of the second regulating valve is increased. By controlling the temperature of the waste water discharged from the eleventh outlet e3, it is ensured that the waste heat of the industrial waste heat waste water can be fully recovered and utilized.

[0067] Step 24: Expansion valve control method:

[0068] When the temperature detected by the first temperature controller 16 increases, a control signal is sent to the first expansion valve 5 to increase the opening of the first expansion valve 5, otherwise the opening of the first expansion valve 5 is reduced, thereby ensuring that the refrigerant component with a low critical temperature can be completely liquefied in the second heat exchanger 6. When the temperature detected by the second temperature controller 17 increases, a control signal is sent to the second expansion valve 8 to increase the opening of the second expansion valve 8, otherwise the opening of the second expansion valve 8 is reduced.

[0069] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A self-cascade heat pump steam generation system, comprising a compressor (1), a condenser (2) connected to an outlet of the compressor (1), and an evaporator (9) connected to an inlet of the compressor (1), characterized in that: The invention also comprises a first heat exchanger (3), a second heat exchanger (6), a soft water pump (11) and a gas-liquid separator (4); the condenser (2) comprises a third inlet (b1), a third outlet (b2), a fourth inlet (b3) and a fourth outlet (b4); the first heat exchanger (3) comprises a first inlet (a1), a first outlet (a2), a second outlet (a3) ​​and a second inlet (a4); the gas-liquid separator (4) comprises a fifth inlet (c1), a fifth outlet (c2) and a sixth outlet (c3); the second heat exchanger (6) comprises a seventh inlet (d1), a seventh outlet (d2), an eighth outlet (d3), an eighth inlet (d4), a ninth inlet (d5) and a ninth outlet (d6); the evaporator (9) comprises a tenth inlet (e1), a tenth outlet (e2), an eleventh outlet (e3) and a ninth outlet (d6); The invention relates to a compressor (1) comprising an outlet (e3) and an eleventh inlet (e4); the third inlet (b1) is connected to the first outlet (a2), the third outlet (b2) is connected to the second inlet (a4), the fourth inlet (b3) is connected to the outlet of the compressor (1), the first inlet (a1) is connected to the soft water pump (11), the second outlet (a3) ​​is connected to the fifth inlet (c1), the fifth outlet (c2) is connected to the eighth inlet (d4), the sixth outlet (c3) is connected to the seventh inlet (d1), the seventh outlet (d2) is connected to the eleventh inlet (e4), the eighth outlet (d3) is connected to the inlet of the compressor (1), the ninth outlet (d6) is connected to the tenth inlet (e1), and the tenth outlet (e2) is connected to the one-way valve (10) and the inlet of the compressor (1) in sequence through pipelines.

2. The self-cascade heat pump steam generation system according to claim 1, characterized in that: A second stop valve (19) is provided at the soft water pump (11), a first stop valve (20) is provided between the third outlet (b2) and the second inlet (a4), a third stop valve (21) is provided at the fourth outlet (b4), and a fourth stop valve (22) is provided at the ninth inlet (d5).

3. The self-cascade heat pump steam generation system according to claim (2), characterized in that: An evaporation pressure regulating valve (7) is provided between the eighth outlet (d3) and the inlet of the compressor (1), a first regulating valve (12) is provided between the third inlet (b1) and the first outlet (a2), and a second regulating valve (13) is provided at the ninth inlet (d5), so that the volume flow of the compressor (1) is adjustable.

4. The self-cascade heat pump steam generation system according to claim 3, characterized in that: A first pressure controller (14) is provided between the fourth inlet (b3) and the compressor (1), and the first pressure controller (14) is connected to the compressor (1) via a signal line; a second pressure controller (15) is provided at the top of the condenser (2), and the second pressure controller (15) is connected to the first regulating valve (12) via a signal line; a third temperature controller (18) is provided at the eleventh outlet (e3), and the third temperature controller (18) is connected to the second regulating valve (13) via a signal line.

5. The self-cascade heat pump steam generation system according to claim 4, characterized in that: A first expansion valve (5) is provided between the fifth outlet (c2) and the eighth inlet (d4), and a second expansion valve (8) is provided between the seventh outlet (d2) and the eleventh inlet (e4).

6. The self-cascade heat pump steam generation system according to claim 5, characterized in that: A first temperature controller (16) is provided at the seventh outlet (d2), and the first temperature controller (16) is connected to the first expansion valve (5) via a signal line; a second temperature controller (17) is provided at the tenth outlet (e2), and the second temperature controller (17) is connected to the second expansion valve (8) via a signal line.

7. The self-cascade heat pump steam generation system according to claim 6, characterized in that: The condenser (2) is a vertical shell and tube condenser. A refrigerant circulates in a pipe in the condenser (2). The refrigerant used in the condenser (2) is a mixture of two pure refrigerants with different critical temperatures. The fourth inlet (b3) is arranged at the top of the condenser (2), and the third outlet (b2) and the third inlet (b1) are arranged at the bottom of the condenser (2). The shell side of the condenser (2) is provided with an upper limit of the liquid level, and the fourth outlet (b4) is arranged above the upper limit of the liquid level.

8. A method for operating the self-cascade heat pump steam generation system according to claim 7, characterized in that: The following steps are included: Phase 1: System preheating and startup; Step 11, open the second stop valve (19) and the third stop valve (21), and start the soft water pump (11) to replenish water to the condenser (2) until the upper limit of the liquid level is reached; Step 12, close the second stop valve (19), the third stop valve (21) and the soft water pump (11), turn on the compressor (1) and start it at a low flow rate; Step 13, open the fourth stop valve (22), and introduce waste heat waste water into the second heat exchanger (6); the refrigerant gas with a low critical temperature in the gas-liquid separator (4) is condensed by the second heat exchanger (6) and throttled by the second expansion valve (8), and then enters the evaporator (9) to absorb heat and evaporate into a gaseous state; the refrigerant liquid with a high critical temperature in the gas-liquid separator (4) is throttled by the first expansion valve (5), and then enters the second heat exchanger (6) to absorb the waste heat of the waste water and evaporate; Step 14, the refrigerant gas with a high critical temperature flowing out of the second heat exchanger (6) is mixed with the refrigerant gas with a low critical temperature flowing out of the evaporator (9) and then enters the compressor (1) for compression to increase the temperature and pressure; Step 15, the compressed mixed refrigerant gas enters the condenser (2), and after the exhaust pressure of the compressor (1) reaches a set value, the first stop valve (20) is opened; Step 16, repeating steps 11 to 15, gradually increasing the flow rate of the compressor (1) to a set value, the water in the condenser (2) is gradually heated and evaporated, and when the shell side pressure of the condenser (2) reaches the set value, opening the second stop valve (19) and the third stop valve (21), and simultaneously starting the soft water pump (11), entering the heat pump steam supply stage; Stage 2, heat pump steam supply: Step 21, according to the pressure in the condenser (2), the second pressure controller (15) controls the opening of the first regulating valve (12), and when the pressure increases, the second pressure controller (15) sends a control signal to the first regulating valve (12) to reduce the opening of the first regulating valve (12); otherwise, the opening of the first regulating valve (12) is increased; Step 22: The flow rate of the compressor (1) is controlled by the first pressure controller (14) according to the exhaust pressure of the compressor (1); when the exhaust pressure increases, the first pressure controller (14) sends a control signal to the compressor (1) to reduce the flow rate of the compressor (1); when the exhaust pressure decreases, the first pressure controller (14) sends a control signal to the compressor (1) to increase the flow rate of the compressor (1); Step 23, according to the temperature of the waste water discharged from the eleventh outlet (e3) of the evaporator (9), the third temperature controller (18) controls the opening of the second regulating valve (13), and if the temperature of the waste water discharged from the eleventh outlet (e3) increases, the opening of the second regulating valve (13) is reduced; otherwise, the opening of the second regulating valve is increased; Step 24: If the temperature detected by the first temperature controller (16) rises, a control signal is sent to the first expansion valve (5) to increase the opening of the first expansion valve (5); otherwise, the opening of the first expansion valve (5) is reduced; if the temperature detected by the second temperature controller (17) rises, a control signal is sent to the second expansion valve (8) to increase the opening of the second expansion valve (8); otherwise, the opening of the second expansion valve (8) is reduced.

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