A dual-axis steam heat pump system and method of controlling the same

Abstract

The application discloses a double-shaft steam heat pump system and a control method thereof, and belongs to the technical field of heat pumps. The system aims at overcoming the shortcomings of low economy and incapability of continuous high-load operation of the existing heat pump. The heat pump system comprises a cylinder body, a first shaft body and a second shaft body which are rotatably connected to the cylinder body. The cylinder body is provided with a first expansion stage, a second expansion stage, a first compression stage and a second compression stage. The second compression stage is communicated with the first expansion stage through a reflux channel. Refrigerant enters a buffer tank through a cylinder drain valve, and is pumped into a refrigerant steam drum through a booster pump. The first shaft body drives the first expansion stage and the second compression stage, and the second shaft body drives the second expansion stage and the first compression stage. The refrigerant of the second compression stage does not need to be completely liquefied, and part of the refrigerant is refluxed to the first expansion stage in a gaseous state from the reflux channel, only a small amount of energy is released, continuous high-load operation of the unit is realized, and the economy of the heat pump system is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat pumps and relates to a double-shaft steam heat pump system and a control method thereof. BACKGROUND

[0002] A heat pump is a system device for transferring heat from a low-temperature heat source to a high-temperature heat source, and can be divided into a compression heat pump and an absorption heat pump according to different principles. The compression heat pump adopts high-level electric energy to drive a compressor, and has wide adaptability to the temperature range of waste heat sources, but in the existing split heat pump, the refrigerant needs to be completely condensed after releasing heat and then flows back to the expansion stage, so the continuous high-load running capability is poor, resulting in low economy of the unit. SUMMARY

[0003] The application proposes a double-shaft steam heat pump system and a control method thereof to overcome the shortcomings of low economy and inability to continuously run at high load of the existing heat pump.

[0004] The application is implemented as follows:

[0005] A double-shaft steam heat pump system, characterized in that it comprises a cylinder body, a first shaft body rotatably connected to the cylinder body, and a second shaft body in transmission sleeve connection with the first shaft body, the cylinder body is provided with a first expansion stage, a second expansion stage, a first compression stage and a second compression stage, the second compression stage is communicated with the first expansion stage through a backflow channel, the second expansion stage, the first compression stage and the second compression stage are provided with a drain valve at the bottom, the refrigerant passes through the drain valve into a buffer tank and is sent into a refrigerant drum through a booster pump, the first shaft body drives the first expansion stage and the second compression stage, and the second shaft body drives the second expansion stage and the first compression stage.

[0006] The first expansion stage comprises first expansion moving vanes, first expansion stationary vanes, a first refrigerant nozzle and a first waste heat flue gas coil, and the second expansion stage comprises second expansion moving vanes, second expansion stationary vanes, a second refrigerant nozzle and a second waste heat flue gas coil.

[0007] The first compression stage comprises first compression stationary vanes, a first centrifugal impeller and a first desalted water coil, and the second compression stage comprises second compression stationary vanes, a second centrifugal impeller and a second desalted water coil.

[0008] The first refrigerant nozzle and the second refrigerant nozzle both comprise a plurality of nozzles, the first refrigerant nozzle is uniformly connected with a first refrigerant ring pipe, and the second refrigerant nozzle is uniformly connected with a second refrigerant ring pipe.

[0009] The refrigerant drum is provided with an electric heater.

[0010] A heat pump system control method, characterized in that a first compression stage pressure P C1 is preset, the pressure PC1 , control the first expansion stator flow D R , the first refrigerant nozzle flow D i , the second refrigerant nozzle flow D j .

[0011] According to the first expansion stage energy balance equation, the second expansion stage energy balance equation, the first compression stage after-stage pressure can be calculated by the ideal gas state equation first expansion stator flow D R , the first refrigerant nozzle flow D i , the second refrigerant nozzle flow D j ,

[0012] The first expansion stage energy balance equation is:

[0013]

[0014] H0 is the specific enthalpy of the refrigerant entering the first expansion stator, Q x1 is the flue gas waste heat load of the first expansion stage, dD i / dτ is the first refrigerant nozzle flow differential entering the first expansion stage, H L is the specific enthalpy of saturated liquid, and H1 is the specific enthalpy of the refrigerant at the outlet of the first expansion stage;

[0015] The second expansion stage energy balance equation is:

[0016]

[0017] Q x2 is the flue gas waste heat load of the second expansion stage, dD j / dτ is the second refrigerant nozzle flow differential entering the second expansion stage, and H2 is the specific enthalpy of the refrigerant at the outlet of the second expansion stage;

[0018] The first compression stage after-stage pressure can be calculated by the ideal gas state equation:

[0019]

[0020] V C1 is the volume from the outlet of the first compression stage to the inlet of the second compression stage, M is the molar mass of the refrigerant medium, t is the time of the refrigerant from the outlet of the first compression stage to the inlet of the second compression stage, R is the gas constant, and T1 is the average absolute temperature of the refrigerant from the outlet of the first compression stage to the inlet of the second compression stage.

[0021] Control the desalted water flow D Z of the second desalted water coil to make the second compression stage energy balance.

[0022] The energy balance equation of the second compression stage is:

[0023]

[0024] H3 is the specific enthalpy of the refrigerant at the inlet of the second compression stage, △H is the enthalpy difference of the desalted water, D d is the flow of the drain valve corresponding to the second compression stage.

[0025] When the refrigerant temperature of the first compression stator blade is too high, the flow of the first refrigerant nozzle is first increased, and the second refrigerant nozzle is put into use when the first refrigerant nozzle has been put into use completely. When the refrigerant temperature of the first compression stator blade is too low, the second refrigerant nozzle is first withdrawn, and the first refrigerant nozzle is withdrawn when the second refrigerant nozzle has been withdrawn completely.

[0026] The double-shaft steam heat pump system and the control method thereof provided by the application do not need to completely liquefy the refrigerant of the second compression stage, and part of the refrigerant is returned to the first expansion stage in a gaseous state from the return channel, only a small amount of energy is released, continuous high-load operation of the unit is realized, and the economy of the heat pump system is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 is a schematic view of a sectional structure of the heat pump system;

[0028] Fig. 2 is a schematic view of a sectional structure of the heat pump system at a second angle;

[0029] Fig. 3 is a schematic view of the refrigerant path between the drain valve and the first expansion stage and the second expansion stage.

[0030] BRIEF DESCRIPTION OF DRAWINGS: 100, cylinder body; 110, drain valve; 120, buffer tank; 130, refrigerant steam drum; 131, booster pump; 132, regulating valve; 200, first shaft body; 210, second shaft body; 220, gearbox; 300, first expansion stage; 310, first expansion moving blade; 320, first expansion stator blade; 330, first refrigerant nozzle; 331, control valve; 332, first refrigerant ring pipe; 340, first waste heat flue gas coil; 400, second expansion stage; 410, second expansion moving blade; 420, second expansion stator blade; 430, second refrigerant nozzle; 431, control valve; 432, second refrigerant ring pipe; 440, second waste heat flue gas coil; 500, first compression stage; 510, first desalted water coil; 520, first compression stator blade; 530, first centrifugal impeller; 600, second compression stage; 610, second desalted water coil; 620, second compression stator blade; 630, second centrifugal impeller; 700, return channel. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to make the technical solution of the present invention easier to understand and master. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] This embodiment provides a dual-axis steam heat pump system, such as Figs. 1-3 As shown, the system includes a cylinder body 100 and a first shaft 200 rotatably connected to the cylinder body 100, and a second shaft 210 drivenly connected to the first shaft 200. The cylinder body 100 is provided with a first expansion stage 300, a second expansion stage 400, a first compression stage 500, and a second compression stage 600. The second compression stage 600 is connected to the first expansion stage 300 through a return channel 700. The bottom of the second expansion stage 400, the first compression stage 500, and the second compression stage 600 are provided with drain valves 110. A booster pump 131 and a regulating valve 132 are provided between the buffer tank 120 and the refrigerant steam drum 130. The refrigerant enters the buffer tank 120 through the drain valve 110 and is sent to the refrigerant steam drum 130 by the booster pump 131. The first shaft 200 drives the first expansion stage 300 and the second compression stage 600, and the second shaft 210 drives the second expansion stage 400 and the first compression stage 500.

[0033] The first expansion stage 300, the second expansion stage 400, the first compression stage 500, and the second compression stage 600 are integrated on the cylinder block 100, improving the compactness of the heat pump system, reducing heat loss, and increasing efficiency. The refrigerant in the second compression stage 600 does not need to be completely liquefied; a portion of the refrigerant returns to the first expansion stage 300 in gaseous form through the return channel 700. This reduces energy release by only a small amount, significantly improving the efficiency of the second compression stage 600, enabling continuous high-load operation of the unit, greatly improving the economy of the heat pump system. Furthermore, the dual-shaft, two-stage compression improves the steam parameters for heat pump heating, and the two-stage expansion improves the utilization efficiency of flue gas waste heat.

[0034] The first expansion stage 300 includes first expansion moving blades 310, first expansion stationary blades 320, first refrigerant injection pipes 330 and first waste heat flue gas coils 340, and the second expansion stage 400 includes second expansion moving blades 410, second expansion stationary blades 420, second refrigerant injection pipes 430 and second waste heat flue gas coils 440. Both the first expansion stationary blades 320 and the second expansion stationary blades 420 have stationary blade holding rings, and the heat pump system has a controller for controlling the opening of the stationary blade holding rings to control the refrigerant flow of the first expansion stationary blades 320 and the second expansion stationary blades 420, and the controller is also used to control the number of injection pipes of the first refrigerant injection pipes 330 and the second refrigerant injection pipes 430 to work, so as to achieve the purpose of adjusting the injection refrigerant flow, and each injection pipe is controlled to be opened or closed through a control valve 331, 431. The first shaft body 200 drives the first expansion moving blades 310 to move, and the second shaft body 210 drives the second expansion moving blades 410 to move, to provide power for the refrigerant flow. The first shaft body 200 has a rotating speed of 3000r / min, and the rotating speed ratio is between 3:1 and 6:5. The first expansion stationary blades 320 have an adjustment range of 25-50°, the first expansion moving blades 310 have a pressure ratio of 2-3.5, the second expansion stationary blades 420 have an adjustment range of 30-40°, and the second expansion moving blades 410 have a pressure ratio of 1.5-2. Both the first refrigerant injection pipes 330 and the second refrigerant injection pipes 430 include 16-24 injection pipes arranged in a ring shape around the axis of the first shaft body 200. The expansion moving blades and the expansion stationary blades are beneficial to the pressure stability of the expansion stage.

[0035] The first compression stage 500 includes first compression stationary blades 520, first centrifugal impellers 530, first desalted water coils 510, and the second compression stage 600 includes second compression stationary blades 620, second centrifugal impellers 630 and second desalted water coils 610. Both the first compression stationary blades 520 and the second compression stationary blades 620 have stationary blade holding rings to control the refrigerant flow, and the stationary blade holding rings are controlled by a controller. The heat pump system is provided with a water system to supply water to the first desalted water coils 510 and the second desalted water coils 610, and the heat pump system supplies heat to the water in the water system, so as to realize the transfer of flue gas waste heat to the water system, form hot water and high-temperature steam, and complete the utilization of flue gas waste heat. The heat pump system is provided with a waste heat flue gas system to provide flue gas with waste heat to the first waste heat flue gas coils 340 and the second waste heat flue gas coils 440. The first compression stationary blades 520 have an adjustment range of 25-50°, the first centrifugal impellers 530 have a pressure ratio of 2-3, the second compression stationary blades 620 have an adjustment range of 15-45°, and the second centrifugal impellers 630 have a pressure ratio of 2.5-3.5.

[0036] The first refrigerant nozzle 330 and the second refrigerant nozzle 430 each include a plurality of nozzles, and the first refrigerant nozzle 330 is uniformly connected with the first refrigerant ring pipe 332, and the second refrigerant nozzle 430 is uniformly connected with the second refrigerant ring pipe 432. The refrigerant in the refrigerant drum is evenly distributed into the nozzles through the refrigerant ring pipe.

[0037] The refrigerant drum 130 is provided with an electric heater, so as to facilitate heating of the liquid refrigerant to a saturated state in the starting stage of the heat pump system. The liquid refrigerant can flow into the buffer tank 120 from the trap 110, and then flow into the refrigerant drum 130 through the booster pump 131 and the regulating valve 132 to supply saturated refrigerant to the refrigerant nozzle.

[0038] In use, the refrigerant drum 130 supplies refrigerant to the first refrigerant nozzle 330 and the second refrigerant nozzle 430, the first refrigerant nozzle 330 sprays refrigerant into the first expansion stage 300, the waste heat flue gas system supplies flue gas with waste heat to the first waste heat flue gas coil 340 and the second waste heat flue gas coil 440, the refrigerant absorbs the waste heat of the flue gas, rapidly expands and vaporizes, and then flows into the second expansion stage 400, mixes with the refrigerant sprayed by the second refrigerant nozzle 430, and the entropy value is reduced, thereby having the ability to absorb more waste heat of the flue gas and improving the efficiency of waste heat absorption. Subsequently, the refrigerant flows into the first compression stage 500, and the compression process increases its temperature and pressure to become superheated refrigerant steam, exchanges heat with water in the water system through the first desalted water coil 510, becomes saturated refrigerant steam, and then enters the second compression stage 600 to become superheated refrigerant steam again. At this time, the refrigerant has a high pressure and temperature, so that the hot water in the second desalted water coil 610 is converted into superheated steam, and the refrigerant is converted into saturated liquid refrigerant and enters the buffer tank 120 through the trap 110. Part of the refrigerant remains in a gaseous state and passes through the backflow channel 700, the first expansion moving blade 310 and the first expansion stationary blade 320 to enter the first expansion stage 300. The refrigerant in the buffer tank 120 is sent into the refrigerant drum 130 by the booster pump 131.

[0039] The heat pump system control method presets a first compression stage 500 post-stage pressure PC1, and controls a first expansion stationary blade 320 flow DR, a first refrigerant nozzle 330 flow Di and a second refrigerant nozzle 430 flow Dj according to the PC1.

[0040] The first expansion stationary blade 320 flow DR, the first refrigerant nozzle 330 flow Di and the second refrigerant nozzle 430 flow Dj can be calculated according to a first expansion stage 300 energy balance equation, a second expansion stage 400 energy balance equation and a first compression stage 500 post-stage pressure ideal gas state equation.

[0041] The first expansion stage 300 energy balance equation is:

[0042]

[0043] H0 is the specific enthalpy of the refrigerant entering from the first expansion vane, Q x1 The waste heat load of the flue gas in the first expansion stage, dD i / dτ is the differential of the first refrigerant nozzle flow rate entering the first expansion stage, H L H1 is the enthalpy of saturated liquid refrigerant and H2 is the enthalpy of refrigerant at the outlet of the first expansion stage.

[0044] Second expansion stage energy balance equation:

[0045]

[0046] Q x2 For the waste heat load of the flue gas in the second expansion stage, dD j / dτ is the differential of the flow rate of the second refrigerant nozzle entering the second expansion stage, and H2 is the specific enthalpy of the refrigerant at the outlet of the second expansion stage.

[0047] The pressure after the first compression stage can be expressed using the ideal gas law:

[0048]

[0049] V C1 Let M be the volume from the outlet of the first compression stage to the inlet of the second compression stage, M be the molar mass of the refrigerant, t be the time it takes for the refrigerant to travel from the outlet of the first compression stage to the inlet of the second compression stage, R be the gas constant, and T1 be the average absolute temperature of the refrigerant from the outlet of the first compression stage to the inlet of the second compression stage.

[0050] Control the demineralized water flow rate D of the second demineralized water coil Z This is to balance the energy of the second compression stage.

[0051] Energy balance equation for the second compression stage:

[0052]

[0053] H3 is the specific enthalpy of the refrigerant at the second compression stage inlet, ΔH is the enthalpy difference of the demineralized water, and D... d This is the flow rate of the steam trap corresponding to the second compression stage.

[0054] When the refrigerant temperature of the first compressor stationary blade is too high, the flow rate of the first refrigerant nozzle is increased first. Once the first refrigerant nozzle is fully engaged, the second refrigerant nozzle is then engaged. When the refrigerant temperature of the first compressor stationary blade is too low, the second refrigerant nozzle is withdrawn first. Once the second refrigerant nozzle is fully withdrawn, the first refrigerant nozzle is then withdrawn.

Claims

1. A dual axis steam heat pump system, characterized by, The application relates to a refrigerant compressor, which comprises a cylinder body, a first shaft body rotatably connected to the cylinder body, a second shaft body in transmission connection with the first shaft body, a first expansion stage, a second expansion stage, a first compression stage and a second compression stage arranged on the cylinder body, a drain valve arranged at the bottom of the second compression stage, a buffer tank, a booster pump, a refrigerant steam drum, a first expansion moving vane, a first expansion stationary vane, a first refrigerant nozzle and a first waste heat flue pipe, a second expansion moving vane, a second expansion stationary vane, a second refrigerant nozzle and a second waste heat flue pipe.

2. A binary axial steam heat pump system according to claim 1, wherein, The first expansion stage comprises a first expansion moving vane, a first expansion stationary vane, a first refrigerant nozzle and a first waste heat flue pipe, and the second expansion stage comprises a second expansion moving vane, a second expansion stationary vane, a second refrigerant nozzle and a second waste heat flue pipe.

3. A binary axial steam heat pump system according to claim 1, wherein, The first compression stage comprises a first compression stationary vane, a first centrifugal impeller and a first desalted water coil, and the second compression stage comprises a second compression stationary vane, a second centrifugal impeller and a second desalted water coil.

4. A binary axial steam heat pump system according to claim 2, wherein, The first refrigerant nozzle and the second refrigerant nozzle each comprise a plurality of nozzles, the first refrigerant nozzle is uniformly connected with a first refrigerant ring pipe, and the second refrigerant nozzle is uniformly connected with a second refrigerant ring pipe.

5. A binary axial steam heat pump system according to claim 1, wherein, An electric heater is arranged in the refrigerant steam drum.

6. A control method of a dual-axis steam heat pump system as claimed in claim 1, characterized by, Preset first compression stage post pressure P C1 , according to P C1 , control the first expansion static blade flow D R , the first refrigerant nozzle flow D i , the second refrigerant nozzle flow D j ; According to the first expansion stage energy balance equation, the second expansion stage energy balance equation, the first compression stage post-stage pressure can be calculated by the ideal gas state equation, the first expansion static vane flow D R , the first refrigerant nozzle flow D i , the second refrigerant nozzle flow D j , The energy balance equation of the first expansion stage is: H0 is the specific enthalpy of the coolant entering from the first expansion stator, Q x1 dD is the flue gas waste heat load of the first expansion stage, dD i / dt is the first coolant nozzle flow rate differential entering the first expansion stage, H L is the specific enthalpy of the cold coal saturated liquid, H1 is the specific enthalpy of the coolant exiting the first expansion stage; The energy balance equation of the second expansion stage is: Q x2 dD j dτ is the second refrigerant nozzle flow differential into the second expansion stage, and H2 is the specific enthalpy of the refrigerant at the exit of the second expansion stage. The post-stage pressure of the first compression stage can be obtained by using the ideal gas state equation: V C1 M is the molar mass of the refrigerant medium, t is the time of the refrigerant from the first compression stage outlet to the second compression stage inlet, R is the gas constant, and T1 is the average absolute temperature of the refrigerant from the first compression stage outlet to the second compression stage inlet. controlling the desalinated water flow D of the second desalinated water coil Z to enable energy balance of the second compression stage; The energy balance equation of the second compression stage is: H3 is the second compression stage inlet refrigerant specific enthalpy, AH is the enthalpy difference of desalted water, D d is the second compression stage corresponding to the flow of the drain valve.

7. The control method of a heat pump system according to claim 6, characterized by, When the refrigerant temperature of the first compression stationary vane is too high, the flow of the first refrigerant nozzle is first increased, the second refrigerant nozzle is then put into use when the first refrigerant nozzle has been put into use, and the second refrigerant nozzle is withdrawn first when the refrigerant temperature of the first compression stationary vane is too low, and the first refrigerant nozzle is then withdrawn when the second refrigerant nozzle has been withdrawn.

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