Exhaust Absorption Chiller

2.1 Working Principle

The exhaust Libr absorption chiller or we can call it as flue gas absorption chiller or heater, is a system, which uses the thermal energy of HT flue gas (300-600°C) to generate cooling or heating. The cycling working medium is the lithium bromide solution (LiBr). LiBr works as an absorbent and water works as refrigerant.

The system comprises primarily the HTG, LTG, condenser, evaporator, absorber, HT heat exchanger, LT heat exchanger, automatic air purging system, vacuum pump and canned pump, and so on.

Heating Principle: The refrigerant water in evaporator evaporates away from the surface of heat conducting tube. As heat in chilled water is taken away from the tube, the water temperature drops and quantities of cooling are generated. The refrigerant steam evaporated from the evaporator is absorbed by the mixed solution in absorber and therefore dilutes the solution. Then the diluted solution in absorber is delivered by solution pump to the LT heat exchanger, where the solution flow branches into two routes: one part of them is delivered to the HTG via the HT heat exchanger, where it is heated by HT exhaust to produce refrigerant steam, then the solution becomes an HT concentrated solution. The other part of the solution is delivered to the LTG, where it is heated by the refrigerant steam from the HTG. After refrigerant steam is produced, the solution becomes a LT concentrated solution. The HT concentrated solution in the HT heat exchanger releases heat before converging with the concentrated solution to form a mixed solution. After the mixed solution releases heat in the LT heat exchanger and enters absorber, it absorbs the refrigerant steam from the evaporator, becomes diluted solution and enters the next cycle, The refrigerant steam/water generated by the HTG is cooled in the condenser to form refrigerant water, which is further depressurized by a throtte valve. The depressurized refrigerant water is then delivered into the evaporator, where it is evaporated and used for refrigeration purposes, then the next cycle begins.

Heating Principle: The circulated cooling water flow is therefore stopped. The diluted solution in absorber is then delivered by solution pump to the HTG via the LT heat exchanger and HT heat exchanger, where it is heated by HT exhaust to produce refrigerant steam,. The refrigerant steam is directly delivered to the evaporator and absorber, where it is used to heat water in the evaporator (the water works as a heating medium) into hot water. After the heating process is completed, the refrigerant steam will condense into refrigerant water. The diluted solution in the HTG, which releases refrigerant steam, is condensed into concentrated solution, enters absorber and mixes with the refrigerant water to produce diluted solution. Then the diluted solution is delivered by solution pump to next cycle.

The aforesaid cycle occurs repeatedly to form a continuous heating process.

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.