Improvement of energy efficiency in ethanol production supported with solar thermal energy – A case study

Abstract

The decrease of natural reserves of non-renewable energy sources increases the energy prices. That initiates the fossil fuel replacement with renewable energy sources. The sun is an unlimited source of heat, but that is not enough used for industrial processes. The main reason is the complexity of heat integration between solar heating systems, process streams, and heat storage. Streams in batch processes and the solar heat delivery are time dependent. The intensity and the duration of insolation affect the capacity of the heat that can be used or stored.This study attempts to offer and approve solutions for thermal integration between solar thermal system and process streams. For that purpose is used Pinch technology for batch processes and solution algorithm is proposed. The analysis is based on a plant for ethanol production in the city of Bitola. The heat recovery is solved with design of Heat Exchanger Network. The rest of heat demand is supplied from the solar heating systems.The purpose of this paper is the possibility for maximal replacement of the required thermal energy from fossil fuel by solar heat. Three approaches are offered. They include the heat integration of a solar heating system with and without heat storage. Two options for thermal storage are suggested. The heat storage used the pressurized water and thermal oil as separated cases. The proposed solutions are adapted to the process schedule. The size of the equipment for the solutions does not depend only on the manufacturing process and its schedule, but also depends on possibilities for collecting thermal radiation from the sun. The geolocation of the plant and the used meteorological parameters for the day of the year have a substantial impact on the final decision. The proposed 18 solutions are designed for the three characteristic days – equinox, winter and summer solstices; for systems with evacuated tubes and parabolic concentrators. The economic analysis selected the most attractive solution – heat integration with evacuated tubes and heat storage with pressurized water at the winter solstice. This solution replaced approximately 35–40% of calculated heat demand delivered by the use of fuel oil.