Low grade waste heat recovery with a novel cascade absorption heat transformer

Absorption heat transformers have been widely applied to utilize waste heat from industrial plant. In this work, a novel cascade absorption heat transformer (NCAHT) is proposed to produce low-pressure steam by using low-grade waste heat. The proposed system is composed of two subsystems: LiBr/H2O AHT cycle and NH3/H2O AHT cycle. NCAHT utilizes the low-grade waste heat using a cascade approach. The effects of feed concentration, generator temperature, HPP pressure, LPP pressure, and concentration range are analyzed to provide guidance to NCAHT design. The designed NCAHT aims to achieve the maximal COP. The maximal COP is 0.227. When the NCAHT is applied in a 10 million tons capacity oil refinery to recovering low-grade waste heat, the total investment is estimated to be about 85 million CNY, the profit is expected to reach 66 million CNY per year, and the static payback period is about 1.3 year. The performances show that NCAHT has an outstanding adaptability, and its practical applications are also considered. This work provides a new approach to producing high quality energy using low-grade waste heat.