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.
EXAMINING THE ECONOMIC VIABILITY OF AN ABSORPTION HEAT TRANSFORMER IN ENERGY INTENSIVE INDUSTRIES
Absorption heat transformers are closed cycle thermodynamic systems which are capable of upgrading the temperature of waste heat energy and, allowing it to be recycled within a plant. An industrial case study is conducted which examines the economic viability of installing a triple absorption heat transformer in a small oil refinery. Particular attention is paid to determining the suitability of different waste heat streams which have been made available. In the refinery examined, two waste streams of interest have been identified; a viscous residue oil line and a condensing Naphtha stream. A relatively large increase in temperature is required by the company in order that the recycled waste heat energy may be incorporated into its existing heat exchange network (HEN), and thus a triple stage heat transformer is being designed. Results obtained during this study indicate that the physical properties of the residue oil stream make it unsuitable for use in such heat recovery technology, while the Naphtha condensation may be utilised with more favourable outcomes. Based upon the current gas price being quoted by the refinery, it is demonstrated that this Naphtha stream on its own does not contain sufficient quantities of recyclable energy to ensure that the system is capable of generating an acceptable return upon investment. The suitability of such heat recovery to larger, more energy intensive sites is highlighted however, and it is demonstrated that if the quantity of suitable energy available were to increase by a factor of two or four then the economic indicators begin to show substantially more favourable results. Thus it may be concluded that at the current low gas price, the use of a triple stage absorption heat transformer is mainly suited to larger plants with sufficient waste energy available for recycling.
ABSORPTION REFRIGERATION CYCLE UTILIZING A NEW WORKING PAIR OF IONIC LIQUID TYPE
[mmim]DMP/CH_3OH solution used as a new working pair in absorption refrigeration has wide application potential.Empirical equations of saturated vapor pressure,heat capacity, excess enthalpy about this working pair were obtained based on experimental and literature data, p - t - x,h—ωcharts were drawn.Base on these,new working pair used in the single-effect absorption refrigeration cycle were studied,and compared with traditional working pairs.The results revealed that[mmim]DMP/CH_3OH as working pair is better than NH_3/H_2O system and is on a par with LiBr/H_2O system in circulation ratio,COP and other characteristic parameters in the certain operating conditions.