Waste Heat Refrigeration

There are hundreds of applications where available waste energy could be used to generate refrigeration. A few of these applications would be in the food processing industry where exhaust heat from a power generating turbine could be used to drive an ammonia-water absorption refrigeration cycle to produce low temperature refrigeration. Bio-gas could also be produced from animal and vegetable waste with digestion.
Another application would be to replace mechanical refrigeration in natural gas plants with an absorption cycle. Other applications include:

1. Chicken processing
2. Petro-chemical such as ethylene plants
3. Pre-cooling air to gas turbines
4. Ethanol plants
5. Overhead condensers to distillation columns
6. Fish processing

Historically the price of energy has not justified expensive capital equipment. In today’s world a waste heat refrigeration system can easily justify itself with a 2-3 year pay-back.

The ammonia absorption refrigeration process involves a conventional absorption/distillation cycle. In more detail the process is as follows. A heat load from an external source evaporates pure ammonia liquid in a flooded evaporator. The resultant ammonia vapor is absorbed in a conventional shell and tube absorber by a liquid heavy in water, “lean” in ammonia. The heat of absorption is transferred to cooling water in the absorber. From the absorber the ammonia “rich” solution is pumped to a distillation column which is driven by waste heat energy supplied to the bottoms reboiler. The “rich” ammonia-water solution is split into high pressure overhead pure ammonia and a “lean” ammonia-water bottoms solution which is used to absorb the vapors in the absorber. The overhead vapor condenses at about 200-250 psig at 95 to 120 degrees Fahrenheit. The bottom reboiler operates at about 270 F° to 350 F°. The evaporator and absorber represent the “low pressure” side which corresponds to the desired refrigeration temperature of the external heat load. The only mechanical energy required by the system is the re-circulating pump.

The features that we introduce into this design include Sep-Pro Systems enhanced tubes in the heat exchangers, a gas driven pump, and intermediate formate for non-ideality. Additionally, we have developed the most accurate process simulation available with a combination of multiple equations of state and empirical data. Sep-Pro Systems also internally builds all the necessary heat exchangers, vessels, and towers.