In this study, the compatibility of exergy destruction minimization as the main objective is checked by plotting coefficient of performance (COP), exergy coefficient of performance (ECOP) and overall exergy destruction rate by simultaneously varying input operating temperatures for a 28 TR cooling load absorption system. The component wise variation in exergy destruction is also considered and it is found that the maxima of COP and ECOP, and the minima of overall exergy destruction lies on a common point, and when the variation of operating temperatures is further extended, the exergy destruction in one of the component becomes negative, which marks the upper bound of the present analysis. At highest valid generator temperature (155 °C), the minimum possible overall exergy destruction rate is 53.50 kW and maximum COP is 0.523. Through inverse optimization using dragonfly algorithm, the same overall exergy destruction rate is achieved for a wide range of generator temperatures much below than 155 °C, and as low as 127.34 °C. The above variation is explained in terms of flow ratio, mass flow rate of steam and mass flow rate of cooling water.
The prediction of the working parameters is of importance for the optimum performance of the biomass gasification process. The gasification temperature, the initial moisture content of the biomass and the equivalence ratio are some of the main input parameters which decide the syngas composition and hence the gasification efficiency. Here, a modified equilibrium model based on a single global gasification reaction with equilibrium constants directly obtained from the available empirical relations is used to predict the syngas composition and the equivalence ratio at different values of moisture content and gasification temperature for two different biomasses (rubber wood and saw dust). The present model is relatively simpler than the available ones and is validated against both experimental and numerical data available for rubber wood and saw dust. Thereafter, the present modified model is used to study the variation in syngas composition, equivalence ratio, lower heating value of syngas and coldgas efficiency for different input values of gasification temperature and moisture content. Subsequently, an optimization problem is formulated by taking the ratio of equivalence ratio to the lower heating value of syngas as the objective function. The dragonfly algorithm is used for the optimization of the gasification problem. The maximum possible efficiency is calculated by varying the moisture content in the range of 5% to 25%, for different gasification temperatures varying in the range 800 o C to 1000 o C. The optimization results show that the maximum possible efficiency for rubber wood is 79.85% for 0.374 equivalence ratio and the same for saw dust is 85.00% for 0.302 equivalence ratio corresponding to the lowest gasification temperature and moisture content.
In this paper, two different methods of combining ammonia-water based power and cooling cycle are discussed in terms of turbine work output, cooling output, overall exergy destruction and exergy efficiency of the cycle. The two cycles are connected either in parallel or series configuration, in which the cooling sub-cycle is fed on the waste heat recovered from the liquid condensate of power sub-cycle. In both configurations, the cooling sub-cycle is feed on the high solution concentration, whereas, the low solution concentration is either feed directly (in parallel configuration) or converted into intermediate solution concentration (in series configuration), before feeding to the power sub-cycle. The concentration difference in the entire cycle is maintained by assuring partial vaporization during both generation and recuperation of ammonia vapors. The cooling output produced in parallel circuit is marginally higher than the corresponding series circuit due to lower absorber pressure under similar operating conditions. However, the turbine work output of the series circuit is comparably higher as compared to parallel circuit due to higher solution concentration and mass flow rate. But, this higher solution concentration increases the exergy input, pump work and hence overall exergy destruction in series circuit as compared to parallel circuit. Nevertheless, due to higher product output, exergy efficiency of series circuit is higher. For unit mass flow rate, the turbine work output improves from 9.11 kW (in parallel circuit) to 23.77 kW (in series circuit), cooling output marginally reduces from 63.29 kW (in parallel circuit) to 63.27 kW (in series circuit), overall exergy destruction increases from 140.30 kW (in parallel circuit) to 182.05 kW (in series circuit) and exergy efficiency improves from 7.16% (in parallel circuit) to 11.94% (in series circuit), when operated for 185 o C heat source temperature, 0.15 split fraction (only in series circuit) and 0.30 3 kmolof NH / kmolof sol basic solution concentration.
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