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CN-122015369-A - Heat pump system for concentration and evaporation and sectional control method of compressor of heat pump system

CN122015369ACN 122015369 ACN122015369 ACN 122015369ACN-122015369-A

Abstract

The application relates to the technical field of heat pump systems, and provides a compressor sectional control method of a heat pump system and a concentrated evaporation heat pump system. The method is applied to a heat pump system comprising a refrigerant loop and a concentrated evaporation loop, and the control process comprises the following steps of sequentially or switchably executing the starting steps of controlling a compressor to run at an initial frequency and gradually rise until the temperature of a condenser outlet or a heating medium reaches a first threshold value, adjusting the frequency of the compressor by taking a target evaporation amount as a set value in a closed loop to enable the real-time evaporation amount to approach the target in the early stage of evaporation, monitoring the evaporation amount and the pressure ratio in the middle stage of evaporation, reducing the frequency if the evaporation amount is lower than a first flow rate threshold value which is set in a descending manner and the pressure ratio exceeds the first threshold value, and starting a hot gas bypass valve to maintain running when the suction pressure is lower than the first pressure threshold value in the later stage of evaporation. The scheme can adapt to load change, prevent the too low suction pressure, the too large pressure ratio and the pressure fluctuation, and improve the stability and the energy efficiency of the system.

Inventors

  • ZHOU DEQIANG
  • WEN SUZHEN
  • LIU BINBIN
  • DAI CHENXUAN
  • CHEN JIANMEN
  • YANG HUIBIN
  • WANG XIANG
  • Yue Houmin
  • YUAN JIE
  • JIN XIANSONG
  • JIN SONGQING
  • JIN ALONG
  • JIANG AIHUA
  • MAO JUNHUI
  • XIE YUHAO

Assignees

  • 浙江青风环境股份有限公司

Dates

Publication Date
20260512
Application Date
20260413

Claims (12)

  1. 1. A method for controlling the compressor of a heat pump system in sections, characterized in that the heat pump system comprises a refrigerant circuit formed by a compressor (1), a condenser (2), an expansion valve (3) and an evaporator (4) which are communicated through pipelines, and a concentrated evaporation circuit which exchanges heat with the evaporator (4) and the condenser (2), the method comprises the following control stages which are carried out sequentially or according to working condition switching: The starting stage comprises the steps of controlling the compressor (1) to run at an initial frequency, and gradually increasing the running frequency according to a preset period until the outlet temperature of the condenser (2) or the temperature of a heating medium of the concentration evaporation loop reaches a first temperature threshold; In the early stage of evaporation, a preset target evaporation capacity is taken as a set value, and the running frequency of the compressor (1) is regulated in a closed-loop control mode, so that the real-time evaporation capacity approaches to the target evaporation capacity; monitoring the real-time evaporation capacity of the concentration evaporation loop and the operation pressure ratio of the compressor (1); When the real-time evaporation amount is lower than a first flow rate threshold value which is set based on the target evaporation amount in a descending way, if the operation pressure ratio is higher than a corresponding first pressure ratio threshold value, the operation frequency of the compressor (1) is reduced; and in the later stage of evaporation, when the suction pressure of the compressor (1) is detected to be lower than a first pressure threshold value, a hot gas bypass valve connected between the condenser (2) and the evaporator (4) is opened, and part of high-temperature refrigerant is bypassed to the inlet of the evaporator (4) so as to maintain the operation of the system.
  2. 2. The method according to claim 1, wherein in the middle evaporation period, the target evaporation amount is defined as Q, the real-time evaporation amount is defined as F, and the operation pressure ratio is defined as R; Setting a series of flow thresholds fn=q× (1-n×k), where n is a positive integer increasing from 1, and k is a preset decreasing percentage coefficient; Setting a series of pressure ratio thresholds Rn=R0+n×m corresponding to the flow threshold Fn, wherein R0 is a preset reference pressure ratio, and m is a preset pressure ratio increment coefficient; and executing control logic, namely controlling the operation frequency of the compressor (1) to be reduced by a preset adjustment step length when the real-time evaporation quantity F is smaller than the flow threshold Fn which is currently judged and the operation pressure ratio R is larger than the corresponding pressure ratio threshold Rn.
  3. 3. The method according to claim 2, characterized in that the decreasing percentage coefficient k is 1%, the ratio increment coefficient m is 0.04, the reference ratio R0 is 1.50, and the adjustment step is 1.5% of the current operating frequency.
  4. 4. A method of controlling the compressor of a heat pump system according to claim 1, characterized in that during the start-up phase the initial frequency is 30% of the nominal frequency of the compressor (1), the preset period is 30 seconds, and the rise amplitude of the operating frequency is 5% of the nominal frequency per period.
  5. 5. The method of claim 1, further comprising a inverter heat dissipation control stage: Monitoring the temperature of a frequency converter supplying power to the compressor (1); When the temperature of the frequency converter exceeds a second temperature threshold value, a refrigerant pump (9) is started, liquid refrigerant is pumped from the outlet of the condenser (2), and the liquid refrigerant flows through a heat dissipation flow passage arranged for the frequency converter to cool the liquid refrigerant.
  6. 6. A method of controlling a compressor of a heat pump system according to claim 1, characterized in that in the start-up phase, if during the boost frequency it is detected that the suction pressure of the compressor (1) is below a second pressure threshold, the hot gas bypass valve is opened until the suction pressure is restored above the second pressure threshold.
  7. 7. The sectional control method of a compressor of a heat pump system according to any one of claims 1 to 6, further comprising: Monitoring the real-time evaporation amount; when the real-time evaporation capacity is larger than the set value of the target evaporation capacity, the split evaporation branch is controlled to be opened, so that part of gas phase working medium is split to the split evaporator (11) for auxiliary heat exchange, and liquid condensed by the split evaporator (11) enters the distillation tank (15).
  8. 8. A heat pump system for concentrating and evaporating for implementing the method according to any one of claims 1 to 7, characterized by comprising: a refrigerant circuit which is connected in sequence to the compressor (1), the condenser (2), the expansion valve (3) and the evaporator (4) and forms a closed cycle; a concentrating and evaporating circuit comprising a concentrating tank (5), wherein the concentrating tank (5) is thermally coupled with the evaporator (4) to absorb heat of gas-phase working medium generated by evaporation of liquid in the concentrating tank (5) through the evaporator (4), and the concentrating tank (5) is also thermally coupled with the condenser (2) to heat the liquid in the concentrating tank (5) through condensation heat released by the condenser (2) so as to realize continuous evaporation thereof; A hot gas bypass line connected to a refrigerant circuit between the condenser (2) and the evaporator (4) for bypassing the high-temperature refrigerant from the condenser (2) to the inlet side of the evaporator (4), the hot gas bypass line being provided with a hot gas bypass valve; And a control system in signal connection with the compressor (1), the hot gas bypass valve and configured to perform the staged control method.
  9. 9. Heat pump system for concentrated evaporation according to claim 8, wherein the compressor (1) is a magnetic levitation centrifugal compressor.
  10. 10. Heat pump system for condensation evaporation according to claim 9, further comprising a refrigerant cooling circuit comprising a refrigerant pump (9) and a heat dissipation runner, the inlet of the refrigerant pump (9) being connected to the liquid refrigerant outlet of the condenser (2), the outlet being connected to the heat dissipation runner, the heat dissipation runner being provided at the frequency converter of the compressor (1) for heat dissipation thereof.
  11. 11. The heat pump system for concentrating and evaporating according to claim 8, wherein the concentrating and evaporating circuit further comprises a split-flow evaporating branch comprising a split-flow evaporator (11) and a connecting line, one end of the connecting line is connected to the vapor phase working medium output line of the concentrating tank (5), the other end is connected to a distillation tank (15) via the split-flow evaporator (11), the split-flow evaporator (11) is thermally coupled with the refrigerant circuit to condense the split-flow vapor phase working medium, and a control valve (12) is provided on the split-flow evaporating branch, the control system is further in signal connection with the control valve (12) and configured to control opening of the control valve (12) when the real-time evaporation amount is larger than a set value of the target evaporation amount.
  12. 12. The heat pump system for concentrating and evaporating according to claim 8, wherein the concentrating and evaporating circuit further comprises: A stock solution supply unit (13) for supplying a liquid to be treated to the concentration tank (5); A distillation tank (15) for collecting the distillate condensed by the evaporator (4) and the split evaporator (11); A concentrated solution discharge unit (16) for discharging the concentrated solution when the concentration of the liquid in the concentration tank (5) reaches a set value or the evaporation amount is lower than the set value.

Description

Heat pump system for concentration and evaporation and sectional control method of compressor of heat pump system Technical Field The application relates to the technical field of heat pump systems, in particular to a heat pump system for concentration and evaporation and a sectional control method of a compressor of the heat pump system. Background The heat pump evaporation technology is used as a high-efficiency energy-saving concentration and separation means, and is widely applied to industries such as chemical industry, pharmacy, food, environmental protection and the like, in particular to the reduction treatment of high-salinity and high-concentration industrial wastewater. The basic principle is that a heat pump system (generally comprising a compressor, a condenser, an expansion valve and an evaporator) is utilized to recover the latent heat of steam generated in the evaporation process so as to heat raw material liquid, thereby greatly reducing the consumption of the system to external fresh steam and achieving the purpose of energy conservation. In the concentration and evaporation process of the waste liquid, as the water is continuously evaporated, the concentration of the stock solution in the concentration tank is continuously increased, so that the boiling point of the stock solution is increased, the fluidity of the stock solution is deteriorated, the heat transfer coefficient of the stock solution is reduced, and the evaporation rate (load) of the whole system is not constant, but is a dynamic change process from starting, climbing and stable operation to gradual attenuation. The running state of the compressor serving as a system core power and heat lifting component directly influences the energy efficiency, stability and processing capacity of the whole system. At present, the field of automatic control research and practice is focused on automation of process flows, such as automatic feeding, temperature and pressure monitoring, concentration standard discharge, safety chain protection and the like. Although the scheme improves the convenience and safety of system operation, the control core of the system often carries out logic or PID control around process parameters (such as liquid level, temperature and pressure), and does not carry out refined control on energy efficiency optimization of the core energy consumption equipment of the compressor under the full-working-condition variable-load operation. In the prior art, for the control of a heat pump compressor, a common way is simple start-stop control or PID regulation based on a fixed target (e.g. evaporation temperature). Under the working condition that the load continuously changes like concentration and evaporation, the control mode has obvious defects that the compressor is easy to trigger protection and stop due to the too low suction pressure in the starting and low load stages, the exhaust pressure (condensing pressure) is increased and the pressure ratio is increased when the compressor still maintains high-frequency operation along with the increase of the concentration of stock solution in the evaporation stage, the compressor works in an inefficient area, the energy consumption is obviously increased, the evaporation capacity is small in the later evaporation stage, the operation of the compressor can not be maintained due to the too low suction pressure, the evaporation process is interrupted in advance, and the final concentration effect is influenced. In addition, although the magnetic suspension centrifugal compressor has great potential in such applications due to the advantages of oil-free, efficient and wideband regulation, the problems of heat dissipation of the frequency converter, continuous operation of the system under low evaporation load and the like are also put higher demands on the control strategy. In summary, the control strategy of the existing concentrated evaporation heat pump system cannot realize the self-adaptive matching between the operation frequency of the compressor and the evaporation process load which dynamically changes, so that the comprehensive energy efficiency of the system is not high in the whole operation period, and the stability and the reliability are challenged under the working condition that the load is severely changed. Therefore, an intelligent control method and system capable of adapting to the load change of the whole concentrating and evaporating process and realizing efficient, stable and self-adaptive operation of the compressor are urgently needed. Disclosure of Invention The application aims to provide a heat pump system for concentration and evaporation and a sectional control method of a compressor of the heat pump system, which can be used for self-adapting to dynamic load change of the heat pump system in the concentration and evaporation process, effectively preventing energy efficiency reduction caused by over-low suction pressure and over-high medium-press