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.