Absorption chillers are a cost-effective alternative to traditional cooling systems in certain applications. Although natural gas is often used to fuel absorption units, facilities should consider using waste heat has a no cost fuel source that can also help to improve overall energy efficiency. The principal advantages of Thermax Profetherm’s absorption chillers include the following:
- Lower fuel costs
- Minimize peak electric demand charges
- No CFC or HCFC refrigerants
- Possibility of using waste heat and dual fuel capability
- High reliability and low maintenance
Sizes and Types of Chiller Systems
Direct-fired absorption chillers can use natural gas and fuel oil as energy sources. Indirect-fired chillers can be powered with high or low-pressure steam and hot water. In many cases, waste steam or waste heated water from industrial processes is used to run absorbers. Tonnage for these units can range from 30 to 6,600 tons, but the most compelling feature is that these systems use water as a refrigerant, eliminating the issues associated with the handling and disposal of environmentally sensitive refrigerants. The absorption chiller operates at a partial vacuum (about 1/100th of normal atmospheric pressure), which allows the water to vaporize at a cold enough temperature (40°F) to chill water to around 44°F.
Absorption units are generally classified as single effect (stage), double effect, or triple effect. The classifications indicate the number of components in each system. Single effect units employ a single condenser and generator. The thermal efficiency of single effect systems is low, which hampers their cost competitiveness with electric systems. As a result, most systems sold commercially today are double effect. These systems use a high and low-temperature condenser and generator that more efficiently separates the refrigerant in the system. These systems have a higher initial cost, but are much more cost effective to operate. Still in development are triple effect chillers that offer substantial performance improvements over double effect systems.
Waste Heat Applications
Typical industrial applications for single-stage absorption chillers might be pulp mills, oil refineries, the food processing industry, or any application that has a high-volume, high-temperature waste heat output. Examples of good double-stage absorption chiller applications might be steam or gas turbine electric generation facilities, chemical plants, paper mills, or other facilities where medium-pressure steam is available. Some of the more common industrial applications where waste heat is used to fuel absorption chillers include the following:
- Petroleum refiners use process waste gases and fuels to fire the boilers which produce steam for both process needs and to supply absorption chillers that are producing process chilled water.
- In the pulp and paper industries, wood wastes are fired to provide both process steam and steam for absorption chillers. The chilled water can be used for process or comfort applications.
- Food canning and freezing industries recover waste heat from cooking and blanching operations to supply absorption chillers. Chilled water can then be used for product processing or comfort cooling.
- In the plastics, petrochemical, glass, and metallurgical industries, waste process heat can be used directly in the form of hot water or steam to supply absorption machines that produce process chilled water.
- In applications where combustion turbines are used for electric generation, exhaust heat can be captured in a waste heat boiler to supply steam to an absorber for comfort cooling or turbine inlet cooling for increased unit efficiency.