Experimental results from a 70 kW steam-generating butane heat pump using off-the-shelf components

In a large share of industrial process, heat demand is required as steam. One possibility for steam generation is to evaporate water against condensing refrigerant in a heat pump and compress it with a separate compressor to the desired final pressure. This work aims to demonstrate this process with a 70-kW butane (R600) heat pump and a small- scale centrifugal compressor for steam recompression. The high-temperature heat pump was built with a 6-cylinder reciprocating compressor, flat plate heat exchangers as the evaporator and condenser, and a tube-in-tube internal heat exchanger. The study shows transient data for the transition from water heating to steam generation. Furthermore, data from a parametric study on the steam generation rate was collected from 42 to 80 kg/ h. The compressor frequency had to increase linearly, while the COP was between 1.75 and 2 throughout the parametric study. Focus is on the flat-plate condenser where refrigerant is de-superheated, condensed, and subcooled on one side. In contrast, on the other side, subcooled water is heated to saturation temperature, evaporates, and is superheated. The heat transfer rate at 80 kg/h was approx. 67 kW with a difference of the refrigerant condensing and water evaporation temperature of 17 K and a pressure drop of 0.12 bar for the given condenser. https://docs.lib.purdue.edu/iracc/2580