Evaporation pressure reference controller for lithium bromide absorption refrigeration system

Abstract

The invention discloses an evaporation pressure reference controller for a lithium bromide absorption refrigeration system. The evaporation pressure reference controller comprises a pressure detection unit, a reference unit, a comparison unit and an execution unit. The pressure detection unit detects 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 volume of the lithium bromide solution so as to approach to the solution circulation volume under the full-load design working condition of the system, and the adjustment benchmark is the full-load design working condition of the system. The evaporation pressure serves as an absolute physical reference, the solution circulation amount is dynamically adjusted, the system is made to adapt to the heat source load, the concentration automatically avoids the crystallization line, and the functions of load monitoring, crystallization early warning, energy efficiency calculation and the like are provided. And the device is suitable for various low-grade heat source scenes such as hot water, steam and flue gas, can be used for new machine manufacturing and stock transformation, and reduces the equipment size and the manufacturing cost.

Description

Technical Field

[0001] This invention relates to the field of absorption refrigeration system control technology, specifically to a control device and method that uses evaporation pressure as a physical reference and achieves system self-adaptation by adjusting the solution circulation rate. It is applicable to the manufacturing of new single-effect, double-effect, and multi-effect lithium bromide absorption refrigeration systems and the retrofitting of existing systems. It is particularly suitable for scenarios with large fluctuations in heat source quality and low-grade waste heat recovery, such as industrial waste heat, solar thermal collection, geothermal utilization, low-pressure steam, low-temperature flue gas, and low-calorific-value fuel gas. Background Technology

[0002] Lithium bromide absorption refrigeration systems, driven by thermal energy, are widely used in central air conditioning, industrial waste heat recovery, and other fields. Unlike compression refrigeration systems, lithium bromide systems have a fundamental structural flaw: the compressor frequency of a compression system can be adjusted in real time according to the load, while the absorbent (lithium bromide) charge in a lithium bromide system is fixed at installation and cannot be changed during operation. Furthermore, the refrigerant—water—is also injected in a single charge at installation and cannot be changed during operation. This "double fixed" characteristic (fixed absorbent + fixed refrigerant) makes the system behave like a "fixed-frequency" device, unable to adapt to load changes by adjusting the refrigerant circulation volume as in a compression system, and can only passively bear the consequences of heat source fluctuations. This is the root cause of frequent crystallization failures and low efficiency.

[0003] Furthermore, lithium bromide systems must rely on vacuum pumps to maintain a high vacuum (typically around 6 mmHg absolute pressure) to ensure water evaporates at low temperatures. This external constraint, together with the internal "double-fixed" characteristic, constitutes the system's operating boundary.

[0004] Traditional lithium bromide systems must be designed based on the lowest possible heat source temperature, with a large heat exchange area reserved to address the risk of crystallization when the heat source temperature rises. This principle of "designing for the lowest possible grade and trading area for safety" results in large equipment size, high material costs, and still cannot completely prevent malfunctions caused by heat source fluctuations. Specifically: when the heat source temperature is below the design value, the solution concentration is low, the risk of crystallization is small, but the cooling capacity and COP drop sharply; when the heat source temperature is above the design value, the cooling capacity is sufficient, but the solution is over-concentrated and prone to crystallization. The evaporation pressure reference control of this invention enables the system to actively adapt to changes in the heat source for the first time, eliminating the need to reserve area for extreme operating conditions and achieving safe and efficient operation over a wide range of heat sources. Summary of the Invention

[0005] This invention provides an evaporation pressure reference controller for lithium bromide absorption refrigeration systems. Using evaporation pressure as the absolute physical reference, it dynamically adjusts the solution circulation rate to automatically adapt the system to changes in the heat source, reducing the risk of crystallization and potentially enabling equipment miniaturization and cost optimization. This invention overcomes the limitations of traditional "design with the lowest grade heat source," enabling lithium bromide absorption refrigeration systems to directly utilize low-grade heat sources (such as hot water below conventional design temperature, steam below conventional design pressure, and flue gas below conventional design temperature) and operate safely and efficiently over a wide heat source range.

[0006] The normal operation of a lithium bromide absorption refrigeration system depends on two fundamental constraints: first, a low-pressure environment maintained by a vacuum pump (typically around 6 mmHg absolute pressure) allows water to evaporate at low temperatures; second, a fixed refrigerant water charge ensures that the total amount of water vapor participating in the phase change within the evaporator is limited by the law of conservation of mass. Under these two constraints, when the evaporation pressure deviates from the target value... At the same time, by adjusting the solution circulation rate to change the generation / absorption rate, the amount of water vapor in the evaporator can be forced back to the same level. The corresponding equilibrium state. The external pressure reference maintained by the vacuum pump and the internal material conservation with a fixed water charge together constitute the physical basis for achieving closed-loop stability in evaporation pressure reference control.

[0007] It is particularly important to emphasize that the fundamental premise for the closed-loop stable operation of the evaporation pressure reference control of this invention is that the refrigerant water charge must be greater than or equal to the amount required for the system to operate at its highest heat source grade. This premise stems from the rigid constraint of material conservation— When the heat source grade increases, the generator's evaporation rate increases, and more refrigerant vapor enters the evaporator. If the liquid water reserve in the evaporator is insufficient to provide enough steam to match the generator's vapor production, the evaporation pressure will drop or even collapse, and the system will be unable to maintain stable operation. Conversely, only when the water charge is sufficient can the evaporator have enough liquid water for evaporation under any operating conditions, and the evaporation pressure can be reliably controlled near the reference value by adjusting the solution circulation rate.

[0008] This requirement of "sufficient water supply" is fundamentally different from the large margin in traditional designs used to passively withstand extreme conditions: the margin in traditional designs is to "toughen up" heat source fluctuations to prevent crystallization, while the sufficient water volume required by this patent is to "ensure that the control system has a usable controlled object"—the evaporation pressure itself. Without this premise, no control algorithm can function effectively.

[0009] The amount of water required by the system at the highest heat source grade can be determined based on thermodynamic calculations (evaporator heat load, latent heat of vaporization, allowable liquid level fluctuation range, etc.) and dynamic simulation, parameters that can be obtained by those skilled in the art through conventional experiments. Based on this premise, the controller of this invention adjusts the solution circulation rate to enable the system to achieve concentration self-adaptation and efficient operation over a wide heat source range.

[0010] The value of this invention lies in its "two-way adaptation"—automatic protection against crystallization under high-grade heat sources, and enabling the system to operate close to its thermodynamic limit efficiency under low-grade heat sources. For any given heat source grade, an absorption refrigeration system has a thermodynamically determined maximum possible conversion efficiency (determined by both Carnot efficiency and internal irreversible losses). Without control, the system operates far below this limit due to deviations in evaporation pressure; however, under EPRC control, by maintaining the evaporation pressure at 6 mmHg, the system operates close to the theoretical optimal condition at that heat source temperature, achieving the maximum possible efficiency at that heat source grade.

[0011] When the heat source quality improves, the generator temperature rises, and the evaporation rate increases. Without control, the generator outlet concentration will spike, easily leading to crystallization. However, under this control, the upward trend in evaporation pressure is detected, and the controller immediately increases the solution circulation rate, allowing more dilute solution to enter the generator, creating a dilution effect and suppressing excessive concentration increases. Ultimately, with the evaporation pressure locked at 6 mmHg, the generator concentration only rises slightly, always staying away from the crystallization line. This mechanism allows the system to safely utilize a high-quality heat source exceeding design values.

[0012] Technical solution: The controller includes a pressure detection unit, a reference unit, a comparison unit, and an execution unit.

[0013] The pressure detection unit is located at the evaporator and is used to monitor the absolute pressure inside the evaporator in real time. Ceramic capacitive or piezoresistive pressure sensors can be used.

[0014] The reference unit provides the target evaporation pressure. The corresponding reference signal can be provided by a spring to provide a mechanical reference, or by an electronic reference source to provide an electrical signal reference.

[0015] The comparator unit is connected to the pressure detection unit and the reference unit, receiving the pressure signal and the reference signal, and outputting the pressure deviation signal. It can be a mechanical comparator (such as a lever linked to a spring) or an electronic PID controller.

[0016] The execution unit is connected to the comparison unit and adjusts the circulation rate of the lithium bromide solution based on the pressure deviation signal. ,make Approaching The adjustment reference for the execution unit is the solution circulation rate under the system's full-load design conditions. The execution unit can take one of the following three forms: • Variable frequency solution pump: The solution circulation rate is changed by adjusting the pump speed; • Electric regulating valve: Installed on the solution pipeline, the solution circulation rate is changed by adjusting the valve opening; • Pressure difference driven slider: The left side of the slider is connected to the generator pressure and the right side is connected to the absorber pressure. Under the action of the pressure difference between the generator and the absorber, the slider overcomes the spring force to generate displacement, change the opening of the solution channel, and automatically adjust the solution circulation volume. Beneficial effects

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Physical reference control: based on evaporation pressure As an absolute physical reference, it does not depend on empirical parameters, enabling the absorption system to have direct physical reference control capability; 2. Variable frequency drive (VFD) modification: By dynamically adjusting the solution circulation rate, the lithium bromide system is transformed from "fixed frequency" control to "variable frequency" control, which can adapt to changes in heat source load; 3. Concentration self-adaptive: No direct concentration control is required; the concentration changes naturally with the heat source and always remains below the crystallization line. 4. Multiple implementation methods: Provides three solutions: variable frequency pump, regulating valve, and differential pressure slider, to adapt to different application scenarios; 5. Integration with design conditions: Based on the full-load design cycle, parameters are clearly defined and debugging is simple; 6. Miniaturization potential: Dynamically matching load eliminates the need for excessively large heat exchange areas for extreme operating conditions, potentially reducing equipment size; 7. Cost optimization potential: Reducing the heat exchange area is expected to lower material costs, while operating energy consumption is also expected to decrease; 8. Feasibility of retrofitting existing units: Retrofitting can be achieved simply by adding a controller without replacing the main unit, providing a technical solution for energy-saving upgrades of old units; 9. Multi-effect system compatibility: Unified control benchmark, flexible execution unit location, suitable for various absorption systems; 10. Online load monitoring: Combined with flow feedback, the system cooling load can be calculated in real time, providing real data support for energy efficiency management, green building certification, and carbon accounting, and realizing the integration of "control + data"; 11. Crystallization safety margin early warning: Real-time calculation of crystallization margin, and proactive alarm when it falls below the threshold, improving system safety; 12. High-efficiency utilization of low-grade heat sources: This invention breaks through the limitations of traditional "design with the lowest grade" approach, enabling lithium bromide absorption refrigeration systems to directly utilize low-grade heat sources (such as 60-90℃ hot water, 0.05MPa steam, and 180-260℃ flue gas) that are below conventional design standards. Without control, the system efficiency is far below the thermodynamic limit; EPRC control, by maintaining stable evaporation pressure, allows the system to approach the theoretical maximum conversion efficiency at a given heat source grade. The cooling capacity of 60℃ hot water can reach 27%-37% of the design value (i.e., the theoretical limit under this condition), enabling the efficient recovery of previously wasted industrial waste heat. 13. Adaptability to existing retrofit: The differential pressure slider solution does not require replacing the original fixed-frequency solution pump. It only requires adding a slider to the dilute solution pipeline and leading out a pressure signal pipe to achieve low-cost and high-reliability retrofit of existing units. It is particularly suitable for scenarios with extremely high requirements for electrical control reliability (such as military and ocean-going industries). 14. Adaptive to multiple heat sources: This invention is not only applicable to hot water units, but also to steam and flue gas lithium bromide absorption refrigeration systems, providing key technical support for industrial waste heat recovery, distributed gas energy supply and other fields. Attached Figure Description

[0018] Figure 1 A schematic diagram of the variable frequency solution pump solution of the present invention.

[0019] Figure 2 A flowchart of the control method of the present invention.

[0020] Figure 3 Reference chart of evaporation pressure in lithium bromide absorption system. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection. The effects mentioned in the embodiments are theoretical expectations, and specific values ​​need to be determined based on actual engineering applications.

[0022] Example 1: Variable Frequency Solution Pump Solution like Figure 1 As shown, the controller includes a pressure sensor 200, a PID controller 300, a frequency converter 400, and a variable frequency solution pump 500. The pressure sensor 200 is installed at the evaporator 100 to detect the evaporation pressure in real time. PID controller 300 receives Signal and preset reference The inverter 400 calculates the deviation and outputs a control signal. Based on the control signal, the inverter 400 adjusts the speed of the variable frequency solution pump 500, thereby changing the solution circulation volume. Solution circulation rate under full-load design conditions. This serves as the reference frequency for the frequency converter. This solution is not only applicable to single-effect systems, but also to double-effect or multi-effect systems. The controller can be installed on the dilute solution pipeline from the absorber outlet to the high-voltage generator. The control principle remains the same, making it suitable for various absorption refrigeration systems.

[0023] Example 2: Differential Pressure Driven Slider Solution This solution uses a differential pressure driven slider as the execution unit. For example... Figure 1 As shown, the slider is installed on the high-temperature concentrated solution pipeline between the generator outlet and the solution heat exchanger. The slider has left and right pressure chambers isolated from the main flow channel, which are connected to the generator chamber and absorber chamber respectively via pressure-conducting pipes, thus sensing the generator pressure. and absorber pressure It is unaffected by the outlet pressure of the solution pump and the solution temperature. One end of the slider is connected to a spring, and the other end of the spring is fixed to the end cover of the valve body. The preload of the spring corresponds to the pressure difference between the generator and the absorber under full-load design conditions.

[0024] During the system design phase, the pressure difference between the generator and the absorber is first calculated based on the thermodynamic parameters under full-load design conditions, and the spring preload is set accordingly to ensure that the slider is at the designed opening position under full load.

[0025] When changes in heat source load lead to changes in evaporation pressure Deviation from target value At that time, generator pressure and absorber pressure The corresponding changes cause the pressure difference between the generator and the absorber to change. The slider, under the influence of pressure difference, overcomes the spring force and displaces, thereby adjusting the opening of the solution channel and changing the solution circulation rate. This change in solution circulation rate, in turn, affects the generation process and evaporation pressure, forming a negative feedback loop. Automatic approach .

[0026] This solution requires no external power supply or electronic controller. The slider is driven by the system's own pressure difference between the generator and absorber, achieving purely mechanical adaptive control. This solution is particularly suitable for retrofitting existing lithium bromide units that use fixed-frequency solution pumps—no need to replace the original solution pump; only a slider needs to be installed on the high-temperature concentrated solution pipeline between the generator outlet and the solution heat exchanger, with a pressure signal pipe leading out. The solution pump still provides the main power for the dilute solution circulation, while the slider automatically adjusts the concentrated solution return flow rate according to the pressure difference, achieving the same evaporation pressure stability as the variable-frequency pump solution.

[0027] Example 3: Control Method

[0028] like Figure 2 As shown, the control method of the present invention includes the following steps: 1. During system installation and commissioning, determine the solution circulation rate under full-load design conditions. Set target evaporation pressure ; 2. Real-time monitoring of evaporation pressure ; 3. Calculate the pressure deviation. ; 4. Calculate the cyclic adjustment amount based on ∆P using the PI control law; 5. Adjust the execution unit to make; 6. Repeat steps (2)-(5) to make It stabilized near the benchmark value.

[0029] Example 4: Thermodynamic Analysis Based on Evaporation Pressure Figure 3 The evaporation pressure in the lithium bromide absorption system was demonstrated. With solution concentration Heat source temperature The thermodynamic relationship between them is shown in the figure. Several operating conditions with heat source quality above and below the design quality are illustrated, reflecting the theoretical laws governing the change of concentration with heat source quality in both uncontrolled and controlled (EPRC) environments: In an uncontrolled system, when the heat source quality is higher than the design value, the generator outlet concentration rises sharply and quickly slides towards the crystallization zone (red area in the figure), leading to crystallization failure. When the heat source quality is lower than the design value, the concentration is too low and the cooling efficiency decreases. However, under EPRC control, regardless of the heat source quality, the concentration always fluctuates adaptively with the heat source, but is stably controlled within a safe range below the crystallization line, and achieves optimal performance near the design value.

[0030] The gray horizontal dashed line represents the control reference of EPRC. This value is uniquely determined by the water evaporation temperature of 4°C under air conditioning conditions and serves as the absolute physical reference for the system. It should be noted that the realization of this pressure reference depends on the low-pressure environment maintained by the vacuum pump; and the system's ability to operate stably near this reference further depends on the rigid constraint of the refrigerant water charge—it is this constraint that creates a definite negative feedback relationship between the amount of water vapor in the evaporator and the amount of solution circulating.

[0031] As shown in the figure, under EPRC control, the operating point is always within the safe zone, which reflects the core idea of ​​"using evaporation pressure as a reference and concentration adaptive heat source".

[0032] Example 5: Upgrading of Existing Systems

[0033] For existing lithium bromide units, the evaporation pressure reference controller of this invention can be installed. In practice, the existing fixed-frequency solution pump can be retained, an electric regulating valve can be installed on the solution pipeline, and the controller can be connected to the original control system. The reference opening of the regulating valve under full-load design conditions is determined through on-site commissioning. The controller adjusts the valve opening according to the evaporation pressure deviation, achieving the same control logic as the variable-frequency pump. Theoretically, this solution can reduce the crystallization risk of existing units, with significant expected energy-saving effects.

[0034] Example 6: Online Load Monitoring and Remote Surveillance Based on any of the EPRC controllers in Examples 1 to 6, online load monitoring can be further implemented. The controller obtains the real-time evaporation pressure through a pressure sensor. Simultaneously, the current solution circulation volume is obtained through the feedback signal from the execution unit. (Such as the speed signal of a variable frequency pump or the opening signal of a regulating valve). Based on thermodynamic relationships: in The concentration difference between the concentrated solution at the generator outlet and the dilute solution at the absorber outlet can be expressed as: and heat source temperature It was calculated using the built-in lithium bromide solution thermophysical property database; The latent heat of vaporization of water. The controller calculates the cooling load in real time. The data is then uploaded to a local display screen or cloud monitoring platform via a communication interface. This embodiment enables the EPRC to not only have control functions, but also to provide real-time load data for energy efficiency monitoring, green building certification, and carbon emission reduction accounting, achieving integrated "control + data".

[0035] Example 7: Online monitoring of crystallization safety margin (optional) As an extended function of the present invention, the controller can adjust the real-time evaporation pressure. and cooling water temperature The concentration of the concentrated solution at the generator outlet is calculated using the built-in crystallization line database. and its safety margin with the crystallization line This margin can be output via the communication interface for maintenance personnel to reference. It should be noted that since this invention fundamentally eliminates crystallization through water fill volume surplus and evaporation pressure benchmark control, this embodiment serves only as a safety redundancy monitoring measure and does not affect the normal operation of the system.

[0036] Example 8: Online Energy Efficiency Calculation

[0037] Based on Example 7, the controller adjusts according to the real-time load. and heat input from heat source (Calculated using heat source flow rate and temperature difference), the system's current energy efficiency can be calculated in real time: The calculated COP value can be output through the communication interface for use by the energy efficiency management platform.

[0038] Example 9: Data Support for Green Building Energy Efficiency Evaluation

[0039] The controller of this invention is installed in a lithium bromide absorption refrigeration system and operated continuously for a full refrigeration season. The controller continuously records load data, generates load curves, and calculates the system's actual operating energy efficiency (COP). During the green building certification process, this data can be used as actual operating data to support the energy efficiency requirements of the chiller and heat source units in GB / T 50378-2019 "Evaluation Standard for Green Buildings," and an energy efficiency compliance certificate can be issued.

[0040] Example 10: Data Support for Carbon Emission Reduction Accounting

[0041] In building energy-saving renovation projects, the controller of this invention is installed in the lithium bromide absorption refrigeration system before the renovation to continuously monitor load data and obtain a baseline load curve. After the renovation, monitoring is performed again, and the load data under the same operating conditions is compared to quantify the load changes and carbon emission reduction effects brought about by the energy-saving renovation, providing traceable data for carbon trading and carbon neutrality certification.

[0042] Example 11: Low-grade hot water utilization scenario The controller of this invention is installed in a lithium bromide absorption refrigeration system utilizing industrial waste heat. This industrial waste heat fluctuates between 60°C and 90°C, representing a typical low-grade heat source (below the conventional design temperature of 95°C for single-effect units). At such low heat source temperatures, crystallization is no longer a problem (low solution concentration, far from the crystallization line), but the cooling capacity and energy efficiency drop drastically—when the hot water temperature drops from 95°C to 60°C, the cooling capacity of the uncontrolled system decreases by approximately 80%–90%, and the COP drops to below 10% of the design value, rendering the system almost useless.

[0043] At a given heat source temperature of 60℃, an absorption refrigeration system possesses a theoretically maximum efficiency determined by thermodynamics. Without control, the system operates far below this limit due to deviations in evaporation pressure. However, under EPRC control, by maintaining the evaporation pressure at 6 mmHg, the system approximates the theoretically optimal operating condition at this heat source temperature, achieving the highest possible conversion efficiency at this heat source grade. Simulation studies show that EPRC control enables the cooling capacity of 60℃ hot water to reach 27%–37% of the design value, which is essentially the system's achievable performance limit at this heat source temperature, allowing for the efficient recovery of previously unusable 60–90℃ hot water.

[0044] It should be noted that the safe and efficient utilization of the aforementioned low-grade heat sources is based on the premise that the refrigerant water charge meets the requirements of the highest heat source grade. The water charge has been determined according to this principle during system design to ensure that there is sufficient liquid water in the evaporator to participate in phase change under any operating condition, providing a reliable physical basis for evaporation pressure reference control.

[0045] Example 12: Utilization Scenario of Low-Grade Steam and Flue Gas

[0046] The controller of this invention is installed in a lithium bromide absorption refrigeration system utilizing industrial waste heat steam. The pressure of this waste heat steam fluctuates between 0.05 MPa and 0.3 MPa, covering a wide pressure range from low grade (0.1 MPa below the conventional design pressure) to medium-high grade (above 0.1 MPa). In the low-grade range (0.05–0.1 MPa), the system efficiency is extremely low without control; in the high-grade range (0.1–0.3 MPa), the risk of crystallization is high without control. The EPRC controller maintains stable evaporation pressure, approaching the theoretical limit efficiency in the low-pressure range, and automatically protects against crystallization in the high-pressure range, achieving safe and efficient operation across the entire pressure range.

[0047] At a vapor pressure of 0.05 MPa, absorption refrigeration systems possess a theoretically maximum efficiency determined by thermodynamics. Without control, the system is almost inoperable; however, EPRC control, by maintaining a stable evaporation pressure, allows the system to approach the theoretical limit at this heat source grade, achieving 30%–40% of the design cooling capacity—this is the highest achievable efficiency under this condition.

[0048] Similarly, in scenarios utilizing industrial flue gas, the flue gas temperature typically fluctuates between 180 and 260°C (lower than the conventional design temperature of 280°C for single-effect units). Within this temperature range, the solution concentration is far below the crystallization line, and crystallization is not a problem, but the system cannot operate stably without control. The EPRC controller can ensure stable system operation, achieving the theoretical limit of efficiency for this heat source grade (approximately 40%–50% of the design value).

[0049] Based on simplified theoretical model estimation, the performance comparison of different heat source types under EPRC control is shown in Table 1.

[0050] Table 1: Performance Comparison of Low-Grade Heat Sources under EPRC Control (Based on Simplified Model Estimation) Heat source type Heat source quality Crystallization risk Uncontrolled relative efficiency EPRC control relative efficiency hot water 60℃ extremely small 5%∼8% 27%~37% (approaching the theoretical limit) hot water 70℃ extremely small 10%∼15% 44%~55% (approaching the theoretical limit) hot water 80℃ extremely small 20%∼24% 66%~72% (approaching the theoretical limit) hot water 90℃ extremely small 35%∼43% 88%~91% (approaching the theoretical limit) hot water 95℃ medium 55%∼60% 100% (Design Points) steam 0.05 MPa extremely small 5%∼10% 30%~40% (approaching the theoretical limit) smoke 180∼260℃ extremely small Unable to run stably 40%~50% (approaching the theoretical limit) Note: The data in Table 1 are based on estimates using a simplified thermodynamic model; the actual values ​​should be determined by actual experiments. "Approaching the theoretical limit" means the highest possible thermodynamic efficiency achieved by the system under a given heat source grade. Design Basis Explanation

[0051] The heat source temperature and pressure ranges mentioned in the above embodiments are derived based on theoretical simulations and thermal property models of lithium bromide solutions. Compared with traditional design standards, this invention significantly expands the heat source adaptability range to a region lower than the conventional design values. The specific values ​​can be optimized and determined according to actual operating conditions. The core of this invention lies in achieving heat source self-adaptation through evaporation pressure benchmark control, rather than limiting absolute values.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An evaporation pressure reference controller for a lithium bromide absorption refrigeration system, characterized in that, Using evaporation pressure as the absolute physical reference, including: (a) A pressure detection unit, installed at the evaporator, is used to detect the absolute pressure inside the evaporator in real time. ; (b) Reference unit, providing the target evaporation pressure The corresponding reference signal, the target evaporation pressure, is an absolute physical reference determined by the physical properties of water and does not depend on external system parameters; (c) A comparison unit, connected to 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 to the comparison unit, adjusts the circulation rate of the lithium bromide solution according to the pressure deviation signal. ,make Approaching ; The adjustment benchmark of the execution unit is the solution circulation rate under the full-load design conditions of the system. .

2. The evaporation pressure reference controller according to claim 1, characterized in that, The execution unit is any one of the following: • Variable frequency solution pump, which changes the solution circulation rate by adjusting the pump speed; • An electric regulating valve, installed on the solution pipeline, changes the solution circulation rate by adjusting the valve opening; • A differential pressure driven slider has two pressure chambers that are respectively connected to the generator pressure and the absorber pressure. Under the action of the pressure difference on both sides, the slider overcomes the spring force and generates displacement, thereby changing the opening of the solution channel and automatically adjusting the solution circulation volume.

3. The evaporation pressure reference controller according to claim 1, characterized in that, The controller adjusts the solution circulation rate to ensure that the lithium bromide solution concentration automatically changes with the heat source load, always remaining below the crystallization line.

4. A method for monitoring the operation of an evaporation pressure reference controller based on any one of claims 1-3, characterized in that, Includes the following steps: a) Real-time monitoring of the evaporator absolute pressure, and acquisition of the current solution circulation rate via feedback signal from the actuator unit. ; b) According to and Based on the built-in lithium bromide solution thermophysical property database, the current cooling load is calculated using the following formula. : in The concentration difference between the generator outlet and the absorber outlet. The latent heat of vaporization of water; c) Output the calculated load value through the communication interface.

5. The method according to claim 4, characterized in that, It also includes online energy efficiency calculation: based on real-time load. It takes heat input from the heat source, calculates the current energy efficiency (COP) of the system, and outputs it through the communication interface.

6. A lithium bromide absorption refrigeration system comprising the evaporation pressure reference controller according to any one of claims 1-3, characterized in that, The system is a single-effect, double-effect, or multi-effect absorption refrigeration system. The controller is installed on the dilute solution pipeline from the absorber outlet to the high-pressure generator, and adjusts the solution circulation rate according to the evaporation pressure deviation to ensure that the system is always at the evaporation pressure reference. It operates nearby, and the solution concentration adapts to the heat source load.

7. The lithium bromide absorption refrigeration system according to claim 6, characterized in that, The system is a modified version of an existing lithium bromide generator unit by adding the controller.

8. The lithium bromide absorption refrigeration system according to claim 6, characterized in that, The controller enables the system to adapt to low-grade heat sources with temperatures or pressures below the conventional design temperatures or pressures specified in GB50736-2012 or DL / T 5508-2015; when the heat source is hot water, the system operates at temperatures below 95°C; when the heat source is steam, the system operates at pressures below 0.1 MPa; and when the heat source is flue gas, the system operates at temperatures below 280°C.

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