Renewable Resource Assessment and Use for Heat Supply in Alumina Production

Abstract

The aluminum industry is energy intensive and responsible for about 4% of global industrial emissions. Owing to the significance of aluminum in our daily lives and its demand growth rate, measures are necessary for emissions reduction in aluminum facilities worldwide. The United Arab Emirates (UAE) is the World’s sixth and fifth largest producer of alumina and primary aluminum respectively, with two aluminum smelter plants and an alumina refinery that are currently fossil energy powered. The overall objective of this research is the development of a thermodynamic model of key energy- and emission-intensive Bayer process steps in primary aluminum production, and the technical and economic evaluation of possible approaches for emissions reduction in these processes, focusing on UAE conditions. A sub-objective is to undertake a renewable energy assessment focusing on solar and wind energy in the UAE, and to evaluate their use for alumina production. An overview of the aluminum industry, key aluminum production processes, and their decarbonization options is presented, with the use of renewable electricity, electric and hydrogen boilers selected for application and evaluation towards the decarbonization of Bayer processes. A steady-state thermodynamic model of a natural-gas fueled Bayer process using high-temperature digestion of boehmitic bauxite for alumina production is developed. The modeled thermal energy demand, levelized cost of production and emissions are found consistent with values reported in the literature. The conventional process energy inputs are modified to evaluate the use of renewable electricity to power hydrogen or electric boilers to contribute reducing Bayer process emissions. To this end, a solar photovoltaic (PV) and wind resource assessment is performed in the UAE, using hourly surface solar irradiation and 100 m elevation wind speed data from the latest ERA5 database for a 20-year period (2003-22). The results indicate high solar PV potential and moderate wind power generation potential in the Western and South-western parts of the UAE. Multiple criteria are employed to identify potential renewable power plant sites to power aluminum facilities in the UAE. The energy output and levelized cost of solar PV and onshore wind electricity are evaluated at selected locations. Considering two promising locations, Ghiyathi and Al Dhafrah, the results indicate higher energy output and lower levelized cost of energy at the former than the latter due to higher available renewable resource.

The techno-economic characteristics and emissions reductions obtained via electrification of Bayer processes are compared for several scenarios, including partial and full renewable energy integration, versus grid electricity. Replacing natural gas fired steam production in the Bayer process by an electric boiler driven by renewable electricity produced at Ghiyathi could slightly reduce the total Bayer process SEC from 14.25 to 13.45 GJ/tAl, eliminate the Bayer process total emissions (0.88 tCO2eq/tAl), increase the current (2023) LCOP of alumina hydrate from 186 to 218 USD/tAl. and reduce the current (2023) equivalent LCOP of aluminum from 2832 USD/tAl to 2464 USD/tAl.

Date of Award	7 May 2024
Original language	American English
Supervisor	VALERIE Eveloy (Supervisor)