Steam chiller saves energy at DUBAL plant

Dubai Aluminium (DUBAL) recently claimed that it has leveraged a nominal volume of the steam produced by the captive cogeneration and combined cycle DUBAL power station to drive the UAE's first absorption chiller using waste heat.

Built on the rooftop of DUBAL's desalination plant control building, the new absorption chiller has assumed the functions formerly fulfilled by the electrically driven vapor compression air-conditioning chillers used for comfort cooling of the building. According to Tayeb Al Awadhi, Vice President, Power & Desalination, the absorption chiller uses high-vacuum conditions to lower the boiling point of water to 3.7 degrees Celsius (versus 100 degrees Celsius at atmospheric pressure) while leveraging the chemical affinity of Lithium Bromide (LiBr) to absorb water.

At this low temperature, highly concentrated LiBr absorbs the water vapor given off in the boiling process effectively. As the LiBr becomes dilute, its capacity to absorb water vapor reduces. A heat source is required to re-concentrate the LiBr – steam, flue gases or even hot water. In DUBAL, steam generated from waste energy was utilized.

Heating causes the solution to release the absorbed water vapor, which is then cooled in a separate chamber to become a liquid refrigerant (in the form of chilled water) through condensation. The process uses just 40 percent of the electricity consumed by the conventional electrically driven chillers and uses a nominal 0.6 tons of steam per hour to produce sufficient cooling for the same purpose.

Lithium Bromide and similar Ammonia absorption cooling cycles have been used worldwide in applications from small kerosene powered refrigerators to district heating and cooling applications common in Europe.

Al Awadhi said DUBAL's new absorption chiller has the capacity to reduce the corporation's energy consumption by approximately 626,800 kWh per year. Based on the standard conversion factor, this equates to a reduction in CO2 generation by about 350 tons per year, also equivalent to an estimated 180 cars off the road per year. "Installing this first absorption chiller was a pilot project, targeted at demonstrating the concept's ability to save energy and protect the environment. The concept can also be used for other applications where energy-efficient cooling is required - such as equipment cooling."

DUBAL's absorption chiller was officially inaugurated by Abdulla Kalban, President and CEO recently and was attended by selected guests from the Dubai Supreme Council of Energy, of which DUBAL is a member. Kalban said the absorption chiller is expected to reduce the auxiliary power consumption of the DUBAL plant, thus offering broader economic and environmental benefits to the business. “It will also add real value by using readily available steam from our Power and Desalination Plants without compromising the processes of either."