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CN-122015329-A - Evaporation pressure reference controller for lithium bromide absorption refrigeration system

CN122015329ACN 122015329 ACN122015329 ACN 122015329ACN-122015329-A

Abstract

The invention discloses an evaporation pressure reference controller for a lithium bromide absorption refrigeration system, which comprises a pressure detection unit, a reference unit, a comparison unit and an execution unit. The pressure detection unit detects the absolute pressure in the evaporator in real time The reference unit provides a reference signal of the target evaporation pressure The comparison unit outputs a pressure deviation signal, and the execution unit adjusts the circulation amount of the lithium bromide solution according to the pressure deviation signal , Make Approach to The regulating standard is the solution circulation quantity under the full load design working condition of the system . The invention takes the evaporation pressure as an absolute physical reference, dynamically adjusts the circulation quantity of the solution, enables the system to adapt to the load of a heat source, automatically avoids the crystallization line in concentration, and provides the functions of load monitoring, crystallization early warning, energy efficiency calculation and the like. The method is suitable for various low-grade heat source scenes such as hot water, steam, flue gas and the like, can be used for manufacturing and stock reconstruction of new machines, reduces the equipment size and reduces the manufacturing cost.

Inventors

  • ZHANG HUI

Assignees

  • 张晖

Dates

Publication Date
20260512
Application Date
20260314

Claims (8)

  1. 1. An evaporation pressure reference controller for a lithium bromide absorption refrigeration system, characterized by taking evaporation pressure as an absolute physical reference, comprising: (a) The pressure detection unit is arranged at the evaporator and used for detecting the absolute pressure in the evaporator in real time ; (B) A reference unit for providing a target evaporation pressure A corresponding reference signal, wherein the target evaporation pressure is an absolute physical reference determined by physical properties of water and is independent of external parameters of the system; (c) The comparison unit is connected with the pressure detection unit and the reference unit, receives the pressure signal and the reference signal and outputs a pressure deviation signal; (d) An execution unit connected with the comparison unit for adjusting the circulation amount of the lithium bromide solution according to the pressure deviation signal Make the following Approach to ; Wherein the regulating standard of the execution unit is the circulation quantity of the solution under the full-load design working condition of the system 。
  2. 2. The vapor pressure reference controller of claim 1, wherein the execution unit is any one of: The variable frequency solution pump changes the circulation volume of the solution by adjusting the rotation speed of the pump; the electric regulating valve is arranged on the solution pipeline, and the circulation quantity of the solution is changed by regulating the opening of the valve; The pressure difference drives the sliding block, the sliding block is provided with two pressure cavities which are respectively communicated with the pressure of the generator and the pressure of the absorber, and the sliding block overcomes the spring force to generate displacement under the action of the pressure difference at two sides, so that the opening of the solution channel is changed, and the circulation quantity of the solution is automatically regulated.
  3. 3. The evaporative pressure reference controller of claim 1, wherein the controller automatically varies the lithium bromide solution concentration with the heat source load by adjusting the solution circulation amount to be always below the crystallization line.
  4. 4. A method of monitoring operation of an evaporative pressure reference controller according to any one of claims 1 to 3, comprising the steps of: a) Detecting the absolute pressure of the evaporator in real time, and obtaining the current circulation quantity of the solution through the feedback signal of the execution unit ; B) According to And The current refrigeration load is calculated according to the following formula by combining a built-in lithium bromide solution thermophysical database : Wherein the method comprises the steps of For the concentration difference between the generator outlet and the absorber outlet, Is the latent heat of vaporization of water; c) And outputting the calculated load value through a communication interface.
  5. 5. The method of claim 4, further comprising energy efficiency online computing based on real-time load And the heat source inputs heat, calculates the current energy efficiency (COP) of the system, and outputs the heat through the communication interface.
  6. 6. A lithium bromide absorption refrigeration system comprising an evaporation pressure reference controller according to any one of claims 1-3, wherein the system is a single-effect, double-effect or multi-effect absorption refrigeration system, the controller is arranged on a dilute solution pipeline from an absorber outlet to a high-pressure generator, and the circulation amount of the solution is regulated according to the evaporation pressure deviation, so that the system is always at the evaporation pressure reference Running nearby, the solution concentration is self-adaptive to the heat source load.
  7. 7. The lithium bromide absorption refrigeration system according to claim 6 wherein the system is retrofitted to an inventory of lithium bromide units with the controller.
  8. 8. The lithium bromide absorption refrigeration system according to claim 6 wherein the controller enables the system to accommodate low grade heat sources below conventional design temperatures or pressures specified in GB50736-2012 or DL/T5508-2015, the system operating at temperatures below 95 ℃ when the heat source is hot water, at pressures below 0.1MPa when the heat source is steam, and at temperatures below 280 ℃ when the heat source is flue gas.

Description

Evaporation pressure reference controller for lithium bromide absorption refrigeration system Technical Field The invention relates to the technical field of absorption refrigeration system control, in particular to a control device and a control method for realizing system self-adaption by taking evaporation pressure as a physical reference and adjusting solution circulation quantity, which are suitable for new machine manufacturing and stock reconstruction of single-effect, double-effect and multiple-effect lithium bromide absorption refrigeration systems. The method is particularly suitable for the scenes of large heat source grade fluctuation, low-grade waste heat recovery and the like, such as industrial waste heat, solar heat collection, geothermal utilization, low-pressure steam, low-temperature flue gas, low-heat-value fuel gas and the like. Background The lithium bromide absorption refrigerating system is driven by heat energy and is widely applied to the fields of central air conditioning, industrial waste heat recovery and the like. Unlike compression refrigeration systems, lithium bromide systems have a fundamental structural disadvantage in that the compressor frequency of the compression system can be adjusted in real time according to the load, while the absorbent (lithium bromide) charge of the lithium bromide system is fixed during installation and cannot be changed during operation. Furthermore, the refrigerant, namely water, of the lithium bromide system is injected once during installation, and the filling amount of the refrigerant cannot be changed in operation. This "double-fixing" feature (absorbent fixing + refrigerant fixing) makes the system, like the same "fixed frequency" device, unable to adapt to load changes by adjusting the refrigerant circulation as in a compression system, and able to passively withstand the effects of heat source fluctuations. This is the root cause of frequent and inefficient crystallization failures. In addition, lithium bromide systems must rely on vacuum pumps to maintain a high vacuum (typically around 6mmHg absolute) to ensure that the water evaporates at low temperatures. This external constraint, together with the internal "double-fixing" feature, constitutes the operating boundary of the system. In the conventional lithium bromide system design, the type must be selected according to the lowest possible heat source temperature, and a huge heat exchange area must be reserved to cope with the crystallization risk when the heat source is raised. The principle of 'using the lowest grade design and the area to change the safety' leads to large equipment volume and high material cost, and the failure of the heat source during fluctuation can not be completely avoided. Specifically, when the heat source temperature is lower than the design value, the concentration of the solution is low, the crystallization risk is low, but the refrigerating capacity and COP are rapidly reduced, and when the heat source temperature is higher than the design value, the refrigerating capacity is sufficient, but the solution is excessively concentrated, and the crystallization is very easy. The evaporation pressure reference control of the invention enables the system to actively adapt to the change of the heat source for the first time, does not need to reserve area for extreme working conditions, and realizes safe and efficient operation within a wide heat source range. Disclosure of Invention The invention provides an evaporation pressure reference controller for a lithium bromide absorption refrigeration system, which takes evaporation pressure as an absolute physical reference, and enables the system to automatically adapt to heat source change by dynamically adjusting solution circulation quantity, thereby reducing crystallization risk and simultaneously being expected to realize equipment miniaturization and cost optimization. The invention breaks through the limitation of the traditional design of the lowest grade heat source, so that the lithium bromide absorption refrigeration system can directly utilize the low grade heat source (such as hot water with temperature lower than the conventional design temperature, steam with pressure lower than the conventional design pressure and flue gas with temperature lower than the conventional design temperature) and can safely and efficiently operate within a wide heat source range. The normal operation of lithium bromide absorption refrigeration systems depends on two basic constraints, namely, a low-pressure environment (usually about 6mmHg absolute pressure) maintained by a vacuum pump, so that water can evaporate at a low temperature, and a fixed filling amount of refrigerant water, so that the total amount of water vapor of the internal parameters of the evaporator and the phase change is limited by conservation of materials. Under these two constraints, when the evaporation pressure deviates from the target valueThe wa