Innovative non-condensables purge system for closed cycle absorption heat pumps

Researcher:
Prof. Gershon Grossman | Mechanical Engineering

Categories:

Sustainability and Energy

The Technology

Non-condensable gases (NCG) are known to cause a significant deterioration in the condensation and absorption heat and mass transfer processes in absorption systems used for thermal cooling and heating. Most absorption systems on the market are chillers, which operate with different types of working fluids, mostly water/ammonia or aqueous lithium-bromide (LiBr/H20). In the latter, since water is the refrigerant, such chillers generally operate at relatively low pressure in the absorber, typically about 0.8 kPa, while the evaporator is operating at 4°C. This pressure is far below atmospheric pressure, which is about 100 kPa at sea level. In such a closed system, the presence of NCGs reduces the thermal power and efficiency of the machine. One source of NCGs is the leakage of air into the machine, which operates at sub-atmospheric pressure. When the ambient atmospheric pressure is higher than that of the absorption system, NCG may enter through connections of pipes, flanges and other components that comprise the unit assembly. In addition, small amounts of hydrogen gas are generated through chemical reaction of the working fluid with the steel surfaces inside the machine. The hydrogen may be present in sufficient volume to interfere with proper machine operation, and must be continuously removed. Corrosion inhibitors such as lithium molybdate reduce the hydrogen generation; nevertheless, proper operation of the system throughout its life requires periodic purging of the NCGs for satisfactory performance. The novel technology is a high-efficiency, motorless purge system for closed-cycle absorption heat pumps, adapted for both absorption heat transformers and absorption chillers, using a series of valves to control the entry and exit of absorbent solution into a low-pressure, secondary absorption vessel. A small percentage of the total circulating solution is forced under pressure into the secondary absorption vessel via a spray nozzle, causing adiabatic absorption of absorbate vapor by the solution. Non-condensable gases accumulate in the secondary absorber until a certain vapor pressure is reached, upon which, gas, and possibly liquid, are transferred to an exhaust vessel having an exit vent for non-condensable gases. In an absorption chiller system, the secondary absorber has an internal heat exchanger to lower the temperature of the solution within, to facilitate the absorption process.

Advantages

  • High-efficiency, motorless purge system

Applications and Opportunities

  • Closed cycle absorption heat pumps
arrow Business Development Contacts
Ilia Baskin
Director of Business Development, Engineering