Air-Conditioning Using Waste Heat Energy
Authors: Kumar Raja , Kumar A. , Rabbou Mahrous Abd , Qambar Najem 
Published: November 2015

All oil & gas building facilities such as control room, electrical room, substation and personal accommodation etc., require a comfortable indoor condition for its proper functioning. They have to be designed not only for prevailing outdoor conditions like high ambient temperature, humidity, also for hazardous conditions. Around 40 to 50% of electrical energy generated in the plant is utilized to maintain such indoor condition with an air-conditioning system. In many oil & gas processing plant, gas turbine units are used to generate electric energy to meet the plant demand. Wherein large amount of energy is wasted in flue gas of gas turbines. An attempt is made to capitalize these energy by way of tapping the unused heat energy from the flue gas and utilize it for plant heating & cooling needs.

By and large, conventional air-conditioning system is used which consist of main components such as compressors, condenser, evaporator, expansion device, refrigerant etc., Apart from condenser fans and evaporator fans, compressor performs the hard work such as compress the refrigerant and circulating it in the system. Hence it generally consumes major portion of energy spent in the range of 60 to 70%. This paper defines alternative air-conditioning system to achieve the same cooling effect using waste heat energy from flue gas of gas turbine. This will give the benefit of optimizing power consumption and consequently reduce the global warming.

Vapour Absorption System is proposed to provide the cooling effect instead of conventional Vapour Compressor System. Other main components such as condenser, evaporator & expansion valve exist in Vapour absorption system. This system requires heat source to perform the action of Compressor. Our objective is to utilize the waste heat energy of the flue gas from gas turbine to usable thermal energy for air-conditioning. This will reduce global warming by reducing enthalpy thrown out to atmosphere and CO2 emission. As the Vapour Absorption System does not have major moving component such as compressor and purely functions as heat exchanger between two mediums, it is a rugged & robust system lasting for a long duration.

The Vapour Absorption System uses dual medium, a refrigerant medium and an absorbing medium. It works based on the principle of chemical action between these two medium having strong affinity of absorbing each other and form a mixture of solution. When the mixture of solution is heated from any available heat source, the refrigerant in the mixture gets vaporized leaving behind the absorbent medium. The heat energy in the flue gas of Gas Turbine Generator (GTG) is utilized to vaporize the refrigerant present in the mixture of medium. The vaporized refrigerant then follows a cycle similar to conventional air-conditioning system and provide cooling in evaporate. Further due to the affinity of absorbing medium in the absorber, the refrigerant flows back to form a mixture of solution again and continues to operate in cyclic manner.

ZADCO carried out a study in an upcoming oil & gas field development project and proposed to utilize the flue gas heat energy from the gas turbine for the heating and cooling needs of the facility. The flue gas heat energy is transferred to thermic oil through a heat recovery unit to raise the temperature of thermic oil. The hot oil is circulated to various process heating needs and finally to Vapour Absorption unit and collected in reservoir after transferring the heat energy. The Vapour Absorption unit provides the cooling needs of the plant building facilities.