Double stage hot water absorption chiller

2.1 Working Principle

The dilute solution in absorber is pumped by the solution pump, heated in the heat exchanger, and then enters the generator. Within the generator, the dilute solution is heated to boiling by the working hot water, producing refrigerant steam while the solution is concentrated into a concentrated solution.

The refrigerant steam generated in the generator is cooled by cooling water, condensing into refrigerant water through U-type pipes into the evaporator water plate.

Due to the low pressure in the evaporator, refrigerant water is pumped by refrigerant pump and sprayed onto the evaporator tube. It absorbs heat from the cooling water, evaporating and thereby lowering the temperature of the cooling water in the tube to achieve refrigeration.

The concentrated solution from generator flows through a heat exchanger into the absorber, where it drips onto the absorber tube. Cooled by the circulating cooling water within the tubes, to absorb refrigerant steam from the evaporator and become a dilute solution. Thus, the concentrated solution continuously absorbs refrigerant steam generated by the evaporator, sustaining the evaporation process within the evaporator. The diluted solution, having absorbed the refrigerant steam, is pumped back to the generator for reconcentration. This completes one refrigeration cycle. Through continuous repetition of this process, the evaporator continuously outputs low-temperature chilled water for air conditioning or industrial cooling applications.

The double-stage hot water unit comprises two generators, two condensers, two evaporators, and two absorbers. The solution flows in series through the upper generator, lower generator, upper absorber, and lower absorber. Hot water flows countercurrently with chilled water and cooling water, creating countercurrent heat exchange.

By rationally distributing refrigeration capacity throughout the cycle, optimizing temperature differentials, and selecting appropriate temperature, pressure, and concentration parameters, the generation, condensation, evaporation, and absorption processes achieve ideal conditions. This enables the hot water heat source to be cooled to a lower temperature.

The aforesaid cycle occurs repeatedly to form a continuous heating process (Fig. 1-1). 

2.2 Process Flow Diagram

2.3 Main Components and Functions

1.Generator

Generation Function: The generator is the power source of the chiller. The heat source enters the generator and heats the diluted LiBr solution. Water in the diluted solution evaporates in the form of refrigerant steam and enters the condenser. Meanwhile, the diluted solution concentrates into a concentrated solution.

Featuring a shell-and-tube structure, the generator comprises the heat transfer tube, tube sheet, support plate, shell, steam box, water chamber and baffle plate. As the highest-pressure vessel inside the heat pump system, the generator has an internal vacuum approximate to zero (a micro negative-pressure).

2. Condenser

Condenser Function: The condenser is a heat generation unit. refrigerant steam from the generator enters the condenser and heats the DHW to a higher temperature. Then the heating effect is achieved. After refrigerant steam heats the DHW, it condenses in the form of refrigerant steam and enters the evaporator.

Featuring a shell-and-tube structure, the condenser comprises the heat transfer tube, tube sheet, support plate, shell, water storage tank and water chamber. Normally, the condenser and the generator are interconnected directly by pipes, so they have basically the same pressure.

3. Evaporator

Evaporator Function: The evaporator is a waste heat recovery unit. Refrigerant water from the condenser evaporates from the surface of the heat transfer tube, taking away the heat of and cools down the CHW inside the tube. Thus waste heat is recovered. refrigerant steam evaporating from the surface of the heat transfer tube enters the absorber.

Featuring a shell-and-tube structure, the evaporator comprises the heat transfer tube, tube sheet, support plate, shell, baffle plate, drip tray, sprinkler and water chamber. The working pressure of the evaporator is around 1/10 of the generator pressure.

4. Absorber

Absorber Function: The absorber is a heat generation unit. Refrigerant steam from the evaporator enters the absorber, where it is absorbed by the concentrated solution. The concentrated solution turns into a diluted solution, which is pump delivered into the next cycle. While the refrigerant steam is being absorbed by the concentrated solution, huge quantities of heat absorbed are produced and heat the DHW to a higher temperature. Thus the heating effect is achieved.  

Featuring a shell-and-tube structure, the absorber comprises the heat transfer tube, tube sheet, support plate, shell, purging pipe, sprayer and water chamber. The absorber is the lowest-pressure vessel inside the heat pump system and is under the greatest impact from non-condensable air.

5. Heat Exchanger

Heat Exchanger Function: The heat exchanger is a waste heat recovery unit used to recover the heat in the LiBr solution. Heat in the concentrated solution is transferred by the heat exchanger to the diluted solution for thermal efficiency improvement.

Featuring a plate structure, the heat exchanger has a high thermal efficiency and a notable energy saving effect.

6. Automatic Air Purge System

System Function: The air purge system is ready to pump out the non-condensable air in the heat pump and maintain a high vacuum condition. During operation, the diluted solution flows at a high rate to produce a local low pressure zone around the ejector nozzle. Thus the non-condensable air is pumped out of the heat pump. The system operates simultaneously with the heat pump. While the heat pump is working, the automatic system helps maintain a high vacuum inside and ensure system performance and a maximized service life.

The air purge system is a system composed of the ejector, cooler, oil trap, air cylinder and valve.

7. Solution Pump

The solution pump is used to deliver the LiBr solution and secure the normal flow of liquid working mediums inside the heat pump.

The solution pump is a wholly-enclosed, canned centrifugal pump featuring zero liquid leakage, low noise, high explosion-proof performance, minimal maintenance and a long service life.

8. Refrigerant Pump

The refrigerant pump is used to deliver refrigerant water and ensure the normal spray of refrigerant water on the evaporator.

The refrigerant pump is a wholly-enclosed, canned centrifugal pump featuring zero liquid leakage, low noise, high explosion-proof performance, minimal maintenance and a long service life.

9. Vacuum Pump

The vacuum pump is used for vacuum purging at the start-up stage and air purging at the operation stage.

The vacuum pump features a rotary vane wheel. The button to its performance is vacuum oil management. The prevention of oil emulsification has an obviously positive impact on air purging performance and helps lengthen the service life.

10. Electric Cabinet

As the control center of the LiBr heat pump, the electrical cabinet houses the main controls and electrical components.