Ammonia Absorption Refrigeration

Ammonia absorption refrigeration is old technology that has come of age. Waste heat recovery can be combined with absorption chilling to eliminate the electric power bill of mechanical refrigeration. For instance if a company has a power generating gas turbine, the high temperature exhaust heat can be converted to refrigeration with ammonia absorption (AARP) refrigeration. Typically if you need 0°F refrigeration you can produce 0.4 BTU’s of refrigeration for 1 BTU of waste heat from turbine exhaust.
            Industrial refrigeration is dominated by mechanical compression refrigeration. Ammonia absorption can economically replace a large fraction if there is a source of low value waste heat available such as flare gas, landfill gas, gas engine or gas turbine exhaust, reject low pressure steam, bio-waste and hot process streams.
            A typical scenario could be if you have 500 tons of refrigeration at 0°F. This would require close to 1200 Bhp (900kw).  At $.08/kwh, this unit would consume $605,000 of electrical power per year. The installed price of the ammonia absorption unit would be about $1,250,000. The installed price of a conventional mechanical compression ammonia refrigeration unit would be about $700,000. The net difference in equipment is  $550,000. The power savings would pay off the net difference in less than one (1) year.
            Refrigeration using waste heat recovery is going to make a significant impact in the industrial refrigeration market. Typical applications will be:

• Replacing mechanical refrigeration in natural gas liquids recovery plants.
• PetroChemical such as ethylene plants.
• Pre-cooling air to gas turbines.
• Chicken and beef processing.
• Overhead condensers to distillation columns
• Fish processing.

The ammonia absorption refrigeration process involves a conventional absorption/distillation cycle. In the 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 bottom 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.
Ammonia-water absorption or ammonia absorption refrigeration represents the same system.
            Sep-Pro, since it builds its own vessels, heat exchangers, control systems, can supply these systems at a competitive price. Our process simulation allows for quick evaluation of your waste heat utilization. Sep-Pro has a unique configuration of heat exchangers and distillation that keeps our price competitive.