Electricity and water cogeneration utilizing aluminium furnaces waste heat integrating thermal storage organic rankine cycle

Abstract

High energy-intensive industries, including steel, chemicals, cement, and aluminium, contribute to about 75% of the industrial emissions of carbon dioxide globally and expelling large amounts of unrecovered waste heat into the atmosphere. Yet, there has been a challenge of studies that are conducted on recovering waste heat in the aluminium industry, especially in cast-house facilities, due to technical difficulties such as energy fluctuations in mass flow rate and temperature. In this study, the waste heat to power system is designed to generate power and freshwater in a cast-house facility with 18 furnaces by evaluating three methods in which the temporal waste heat from holding furnaces can be damped and exploited. These methods are: (1) implementing a temporal air injection, (2) optimising furnaces operation time shift, and (3) integrating sensible thermal heat storage. Organic Rankine Cycle is used for the waste heat to power conversion. The appropriate thermal energy storage design and a thermodynamic model of an Organic Rankine Cycle are investigated using temporal flue gas data that are collected on site from three furnaces. Reverse Osmosis technology is applied to produce water using the generated electricity. Results show that sensible heat thermal energy storage is the most suitable technology for damping the fluctuations of waste heat. By utilising waste heat from 18 remelting furnaces, a net power output of 323 kW can be produced to operate a Reverse Osmosis plant supplying 2419 m3 of fresh water daily, saving up to 2000 metric tons of carbon dioxide emissions annually. This study gives a comprehensive approach to deal with temporal waste heat in aluminium furnaces for smooth cogeneration.