Efficient and Flexible Tri-Generation With Two-Stage Absorption Chiller
Aiming for the European and North American tri-generation market, highly-efficient systems are being developed. At the moment, single-stage absorption chillers are typically coupled to co-generation engines through a single hot water loop at temperatures below 100°C (210°F). In this configuration, the heat from the exhaust gas at temperatures of about 400-500°C (750-930°F) is transferred to the water loop, which is accompanied by a significant loss of exergy. A substantial increase in system performance can be achieved by a stepwise utilisation of the exhaust gas enthalpy in a Double-Effect and a Single-Effect cycle. In this combination of one-and two-stage chillers the coefficient of performance (COP) increases from about 0.7 to almost 1.0 whereby the cooling capacity rises by about 25%. In order to facilitate optimum adaptation of the aggregates - i.e. motor engine and absorption chiller - and to give maximum flexibility an innovative system concept has been developed. The new coupling scheme is based on a standard direct-fired Double-Effect chiller and introduces only minor design changes, like adaptation of the thermal layout of the exhaust gas driven regenerator heat exchanger of the chiller. No additional low temperature regenerators are required. In case of simultaneous heating and cooling the system supports a continuous switchover between maximum cooling and maximum heating capacity. In this mode up to 80% of the driving heat for cold production can be recovered as useful heat at temperatures up to 100°C (210°F). A description of the coupling scheme together with a discussion of energetic and operational characteristics of the concept is presented. Full-scale demonstration projects are under preparation.