Absorption Power Cycle with Libr Solution Working Fluid – Design of the First Proof of Concept

orc2019 Tracking Number 61

The most common technology for utilizing low temperature and low power heat sources in a decentralized power system is the organic Rankine cycle (ORC). Nevertheless, there are appearing new alternative concepts providing theoretically higher efficiency, but they are far behind the technological maturity level of the ORC. One such concept is an absorption power cycle (APC) working with an aqueous solution of lithium bromide (LiBr) as a working fluid. According to our findings and theoretical studies, the perspective application of APC is in low power output of no more than a few dozens of kW, and for heat sources at temperatures below 150 °C. Other features of APC include a high temperature glide across heat exchangers resulting in high exergy efficiency, and large volumetric flow rate of the vapour allowing to build an efficient turbine for small power output. This cycle has, however, to the best knowledge of the authors, never been experimentally explored. To assess the possibilities of the actual application, a proof-of-concept APC unit is designed. This work is a methodological design analysis of an experimental unit based on a thermodynamic model presented. The design of the APC unit is adapted for the following heat source: heat input 20 kW from a topping ORC unit, in 90 °C water (intermediate cycle). Calculation and sizing model results in expected <0.5 kW turbine output with high and low pressures 13 kPa and 6 kPa respectively. Alongside with the calculation methodology, the final design of the APC unit is presented. The equipment consists of a custom shell & tube desorber (evaporator) and absorber (condenser) with a design described, an axial impulse turbine made by additive manufacturing from plastic and micro gear pumps. The construction of these components and of the whole apparatus is, at the time of writing this article, underway. Commissioning, experimental results, and a subsequent proof of application potential of the APC concept will be a subject of future work.