A comparative analysis of rankine and absorption power cycles from exergoeconomic viewpoint

Abstract

In this paper LiBr–H2O and NH3–H2O absorption power cycles and Rankine cycle which produce 1MW electrical power in same conditions of heat sources are compared from exergoeconomic point of view. Exergoeconomic analysis is performed using the specific exergy costing (SPECO) method. The results show that among these cycles, although the LiBr–H2O cycle has the highest first law efficiency, but unit cost of electricity produced by turbine for LiBr–H2O cycle is more than that for Rankine cycle. This value is lowest for the NH3–H2O cycle. Moreover, the NH3–H2O cycle has the highest and the LiBr–H2O cycle has the lowest exergy destruction cost rate. The generator, the absorber and the boiler in all considered cycles have the maximum value of sum of cost rate associated with capital investment, operating and maintenance, exergy destruction and exergy losses. Therefore, these components should be taken into consideration from exergoeconomic viewpoint. In parametric study, it is observed that in the constant generator temperature, as the generator pressure increases, unit cost of power produced by turbine for LiBr–H2O and Rankine cycles decreases. This value for Rankine cycle is lower than for LiBr–H2O cycle whereas Rankine cycle efficiency is less than the efficiency of LiBr–H2O cycle. Also, in LiBr–H2O cycle, at constant temperature of the generator, the value of exergy destruction cost rate is minimized and exergoeconomic factor is maximized at particular values of generator pressure and the more absorber pressure results the minimum value of total exergy destruction cost rate.