Efficiency Enhancement in Dry Roasting Processes Using Hybrid Gas-Electric Powered Thermal Sources: A Case Study in Nut Processing

Dry air nut roasting is a widely used process in the food industry that relies on a stream of hot air to dry and roast the main product (such as almonds, hazelnuts, walnuts, peanuts etc.). This process consists of two main phases: the drying phase, where most of the moisture content is significantly reduced, and the roasting phase, where the Maillard reaction develops the characteristic roasted flavor and crunchy texture of the final product. Traditionally, this energy-intensive process relies on conventional gas burners to achieve process temperatures up to 140-180℃. This case study investigates the benefits of implementing a hybrid thermal system that combines gas and electrical power by using an electric pre-heater supported by an on-site rooftop photovoltaic (PHV) ranging from 1 MW to 3 MW. At first an energetic model of the dry air roasting process is developed to correlate the required thermal power with the specific roaster’s productivity finding out that for specific process parameters assumptions the energy requirement is approximately 197 Wh/kg of net product. Subsequently gas savings relative to the range of installed electric pre-heater power (0–500 kW) are assessed: therefore, it has been possible to identify a peak annual gas savings up to 291 € per kW of pre-heater power installed and a reduction of CO2 emissions ranging up to 140 ton/year depending on actual heater configuration. Eventually, an economic assessment is finally conducted to investigate the most efficient use of the electricity produced from the photovoltaic referred to the market trading value of both electric energy and gas.