Exergy analysis of carryover leakage irreversibilities of a power plant regenerative air heater

Abstract

Energy recovery devices can have substantial impact on process efficiency and their relevance to the problem of conservation of energy resources is generally recognized to be beyond dispute. One type of such a device, which is commonly used in fossil-fired and air conditioning systems, is the rotary regenerator, in which a stream of hot waste gas exchanges heat with fresh atmospheric air through the intermediate agency of a rotating matrix. As there are gas streams involved in the heat transfer and mixing processes, then there are irreversibilities, or exergy destruction, due to mixing, pressure losses I^ΔP and due to temperature gradients I^ΔP. These principle components of total process irreversibility are not independent and there is a trade-off between them. Therefore the purpose of this case study is to demonstrate the importance of the use of exergy analysis in the minimization of carryover leakage irreversibilities of a symmetric balanced rotary regenerator. The chemical exergy Ė_o and physical exergy Ė_ph are calculated and the ratio of chemical and physical irreversibilities has been evaluated for a rotary regenerator used for air preheating in a coal-fired power plant. A numerical finite difference technique has been used to calculate the fluid and matrix temperature distributions effect on the regenerator performance. The effects of variation of the principal design parameters on the irreversibilities and on the regenerator effectiveness are examined and recommendations are made for the selection of the most appropriate parameters.