Seyed Mohammad Seyed Mahmoudi

Use of low grade heat sources in combined ejector–double effect absorption refrigeration systems

At a particular temperature range, heat sources are not hot enough to drive lithium bromide double-effect absorption refrigeration systems efficiently and are too hot to be used for the single effect systems because of the risk of crystallization. To make effective use of heat sources at this temperature range for refrigeration purposes, a combined ejector–double effect absorption cycles are proposed. A computational model is developed to study and compare the effect of operating parameters on the performance of combined and conventional single- and double-effect cycles from the viewpoints of first and second laws of thermodynamics. In addition, because of the importance of crystallization risk in these systems, the effect of varying working conditions on the possibility of crystallization is investigated too. The results show the advantageous performance of the combined cycle compared to that of the single- and double-effect systems at particular ranges of heat source temperature. These temperature ranges are extended at lower evaporator and higher condenser or absorber temperatures.

A comparative exergoeconomic evaluation of biomass post-firing and co-firing combined power plants

ABSTRACT This paper reports the results of energy, exergy and exergoeconomic analyses of biomass gasification-based power plants. Three configurations are considered: externally fired biomass combined cycle, biomass integrated co-firing combined cycle and biomass integrated post-firing combined cycle. The latter configuration is found to be more economically effective (on a large scale). The energy efficiency for the biomass integrated post-firing combined cycle plant is about 3% and 6% higher than the biomass integrated co-firing combined cycle and externally fired combined cycle plants, respectively. The parametric studies demonstrate that the energy and exergy efficiencies can be increased (for the three configurations) by raising the compressor pressure ratio; however, higher pressure ratios lead to lower values of the total product cost only for the biomass integrated post-firing plant. Increasing the gas turbine inlet temperature leads to a slight decrease in the unit product cost for the externally fired biomass combined cycle and the biomass integrated co-firing combined cycle.