Internal energy and exergy recovery in high temperature application absorption heat transformers
Abstract In this paper, the design of a triple absorption heat transformer (TAHT) using the working fluids water and lithium bromide is dissected and reassembled using heat exchange network modelling in order to determine the optimum number and locations of internal heat exchange units within the system. It is found that the conventional design of the TAHT does not employ heat exchangers effectively, and that thus by rearranging these units system COP may be increased by 11.7% while exergy destruction within the system (its irreversibility) can be reduced by 21%. Strategically adding an extra one or two heat exchangers increases the COP by 16.4% and 18.8% while decreasing exergy destruction by 28% and 31.5% respectively compared to a conventional TAHT design.
Economic evaluation of an industrial high temperature lift heat transformer
Heat transformers are closed cycle thermodynamic systems which allow waste heat energy to be recycled by increasing its temperature. TAHTs (Triple stage heat transformers) are capable of increasing the temperature of supplied heat by up to ∼140 °C. This paper attempts to analyse the industrial attractiveness of such cycles by conducting a case study on the potential installation of a TAHT in a small Irish oil refinery, examining various different natural gas price scenarios. The choice of waste heat energy being recycled is shown to be pivotal to the success or failure of the installation. TAHTs are demonstrated to show most benefits when applied to waste heat streams with large quantities of latent heat. The usage of more efficient and cost effective equipment instead of conventional shell and tube heat exchangers within the system dramatically increases the potential economic return from the heat transformer. At the present gas price, the capital cost of (conventional) equipment is too high to make this investment financially attractive for the current industrial example, with excessive payback periods predicted. However a return to natural gas price levels observed in 2008 and 2009 would make the unit economically viable.
Performance simulation of the absorption chiller using water and ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate as the working pair
Abstract The thermodynamic performance of the absorption chiller using water and ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]) as the working pair was simulated. In addition, the effects of evaporation temperature on the performance coefficient, COP, generation temperature, concentration of strong solution and flow rate ratio were also analyzed. At the same condensing and absorbing temperature, the simulating results indicated that the performance coefficient for the water + [EMIM][DMP] was lower than that for aqueous solution of lithium bromide (H 2 O + LiBr) but still higher than 0.7, while the generation temperature was lower than that for H 2 O + LiBr, which indicated that the working pair, water + [EMIM][DMP], was capable of being used as a novel working pair for the absorption chiller driven by lower temperature level waste heat or hot water generated by common solar collector.