International Sorption Heat Pump Conference 2008, 23-26 September, 2008, Seoul, KOREA RENEWABLE ENERGY BASED 40 TR - NH 3 -H 2 O GAX OPERATED ABSORPTION COOLING SYSTEM G. Rengasamy, 1 R.Saravanan 1* , S. Arivazhagan 2 , K.Sivakumar 3 and C. Narendran 3 1 Institute for Energy Studies, Anna University, Chennai - 600025, INDIA 2 St. Joseph’s College of Engineering, Chennai – 600119, INDIA 3 Guha Industries, Chennai – 600 058, INDIA Email : rsaravanan@annauniv.edu ABSTRACT The performance evaluation of an absorption cooling system with generator absorber heat exchange (GAX) using ammonia-water as working fluid is presented in this paper. The system designed for a cooling capacity of 40 TR uses biomass (fire-wood, GCV: 14.65 MJ/kg) as the heat source to operate a milk chilling plant handling 55,000 litres per day. The evaporator operates at -2 to 0°C to chill milk down to 4 - 6°C from an initial temperature of 34°C with sink temperature at 30 - 35°C. The real coefficient of performance is 0.52 considering auxiliary power consumption with source and sinks media temperatures of about 120 and 30 o C respectively. The emission reduction due to this installation is about 586 tons of CO 2 per year. INTRODUCTION Increased use of high grade energy, which is obtained from combustion of primary energy sources such as fossil fuels, contributes to climatic changes and global warming as a result of green house emission. Therefore, systems that work satisfactorily with less high-grade energy attract worldwide interest. The vapour absorption cooling systems have a large potential for decreasing consumption of electrical energy [1]. Ammonia absorption system, with a wide evaporating temperature of +5 to - 60°C, is the best choice for refrigeration with low cost steam, heat produced from biomass, coal and natural gas or renewable source like solar or geothermal. Steam fired ammonia absorption systems have been successfully employed in freeze-drying, cold storages, dairies, ice making plants, meat and fish processing, blast furnaces, solvent recovery, refineries and fertilizer plants [2–3]. The COP of the absorption system increases with reutilization of absorption heat generated during absorption of refrigerant vapor in unsaturated mixture [4]. This phenomenon is utilized by the GAX technology where heat generated during an absorption process is used for a desorption process in a generator. The theory of the GAX cycle was first proposed and patented by Altenkirch in 1914, although it did not receive much attention until the 1980s. When pressures and concentrations in the absorber and generator are maintained properly, there is a temperature overlap such that some of the heat of absorption can be rejected to the generator. Recuperating the energy in this fashion reduces the amount of energy required from natural gas to separate ammonia from water in the generator. Thus, for a given cooling or heating load, less energy is required to drive the cycle, and the COP increases. In recent years, the investigation and application of the GAX cycle attracted more and more attention in the field of the cascading use of high quality energy and the efficient use of solar energy, terrestrial heat and low quality heat. A GAX absorption system with natural gas- fired generator has been modeled for the heating and cooling modes, by Srinivas et al [5]. Analysis of a gas- fired ammonia-water GAX absorption cycle based on modular simulation by Engler et al [6] has shown a COP of 1.0. Studies on a 10.6 kW air cooled ammonia-water GAX absorption cycle with hybrid natural gas – solar energy source by Velazquez and Best [7] have reported a cooling COP of 0.86 with 16.9 kW of internal energy integration. Extensive studies on advanced ammonia- water GAX absorption cycles have also been reported by Kang et al [8 – 10]. In this paper, the performance of a 40 TR ammonia absorption GAX refrigeration system for milk chilling with bio-mass as heat source is discussed. WORKING PRINCIPLE GAX cycle retains the essential components of a single effect vapour absorption refrigeration cycle: generator, rectifier, absorber, condenser, pre-cooler, evaporator, throttle valves and solution pump. The difference between a traditional single effect cycle and GAX is the internal heat recovery; part of the absorption heat is recovered by the generator, which leads to a decrease of the thermal energy supply in this device, increasing the COP of the system. The Figures 1 shows the schematic of the GAX absorption cooling system. In this system, partial absorption of refrigerant vapour occurs first in solution cooled absorber where the heat of absorption is removed by strong solution from the water cooled absorber. CONDENSER SOLUTION COOLED ABSORBER WATER COOLED ABSORBER SOLUTION PUMP SOLUTION HEAT EXCHANGERS GAX REFLUX CONDENSER RECTIFIER G E N E R A T O R CHILLED WATER IN CHILLED WATER OUT HOT WATER IN HOT WATER OUT EVAPOARTOR COOLING WATER IN COOLING WATER OUT Figure 1 Schematic of GAX absorption system