Innovative thermal processes and plants for food industry

The food industry is an integral component of the worldwide economy, transforming raw products into tradable food. The food industry is also one of the largest manufacturing sectors, resulting in significant final energy consumption that accounted for approximately 6% of the industry sector in 2014. The world demand for food is expected to increase as world population should increase from 7.1 billion in 2013 to 9.6 billion by 2050. Moreover, life standards are also expected to improve in developing countries, thus leading to a possible larger per capita consumption of food. Food industries are complex systems that can simultaneously require thermal, cooling and electric energy. Indeed, raw materials are usually cleaned, processed at different temperatures as a function of the food processing and combined to obtain finished products. The food industry sector is receiving increasing attention because of the opportunity to exploit innovative processing plants, the potential of increase in the energy efficiency and in the quality of final food products that lies in the plants, if correctly designed and managed. Research suggests that the adoption of smart energy monitoring systems is also important to understand how the plants operate and how they can be optimised. Given this picture, this thesis provides original, both theoretical and applied, contributions to the design of two different types of food processing plants: 1. A plant for steam batch thermal processes in unsteady state conditions. Many food processes require high amounts of steam. Design and operation of steam plants are particularly complex when steam is required for short and intermittent periods and with a varying time schedules. The discontinuous needs of steam can be fulfilled by using a thermal energy storage. The dynamic model of plant is here proposed. 2. A plant for food freezing at very low temperature. Freezing is a valuable method to increase food shelf life and to ensure high quality standards during long-term storage. Additional benefits to frozen food quality can be achieved by freezing at very low temperatures (« -50 °C): small ice crystals formation during fast freezing reduces food cell wall rupture, preventing water and texture loss during thawing. An innovative food freezing plant, based on a reversed Brayton cycle, is here presented. A numerical model of the reversed Brayton cycle was also developed. The thesis also provides a contribution in the data analysis of energy monitored data of domestic cold appliances and of a plant in a chocolate industry. The potential applications of the outcomes of this work are of considerable interest since the importance of food quality and food demand are expected to grow in the next future. Moreover, results of the design tools here presented indicate measures that can be adopted to properly operate the analysed food processing plants.