Wastewater recovery at Suomen Kerta Factory

Abstract

The candle factory of Suomen Kerta, located in Riihimäki, Finland, produces an enormous amount of wastewater due to the cooling of candles. The two machines handled in this master's thesis have respectively an annual water waste of 6 000 m³ and 11 000 m³. Currently, the company simply discharges its wastewater into a nearby river. The aim of this master's thesis is to reduce water consumption during the production of the candles in Suomen Kerta and to do this as energy efficiently as possible. In the first scenario, we investigated whether STES (Seasonal Thermal Energy Storage) systems are able to reduce the wastewater from the production process by storing the hot water seasonally. A technical comparison of different STES systems is made. Also it is researched whether it is possible to use the heat from the wastewater to produce electricity and then store this in batteries (ORC systems). This is investigated on the basis of the amount of energy that can be extracted from the temperature of the wastewater. In the second scenario, a closed hydraulic pump circuit will be designed to use the wastewater from machine A (30 °C) as cooling water in machine B (12 °C). Based on the results of this master’s thesis, STES will not offer a realistic solution but Suomen Kerta can invest in the construction of a closed hydraulic circuit for the reuse of their wastewater from machine A in several other machines. This results in water savings, money savings and a more environmentally friendly process.