Improving the efficiency of a cataphoresis oven with a cogenerative organic Rankine cycle unit

In process industries, large amount of medium and low grade heat is generated and wasted due to the absence of internal heat demand. However, in the last decades, several technologies have been proposed to convert waste heat into electricity. Among them, Organic Rankine cycles (ORCs) are, currently, the most technically mature and economically feasible process to convert the low-grade heat into electricity. Therefore, in this study, the ORC technology is proposed to generate electricity from the low-grade heat released by the oven of a paint and cataphoresis facility. To design the ORC unit and select the working medium, an “in-house” optimization tool has been developed. A single-objective optimisation approach is adopted to maximize the ORC electric power while the heat rejected by the ORC condenser is used to heat the pre-treatment vats line. The ORC purchasing costs are estimated by means of an economic analysis. The ORC design has been made using real data acquired during a 5-year monitoring project. A recuperative-ORC, operating with R245fa, guarantees to maximize the net electric power. The ORC nameplate power and efficiency are 31.2 kW and 11.2%, respectively while the payback time is approximate 4 years. Being ORC also able to heat the paint vat, the facility costs can be abated of 15-20 k$/years.