Life cycle assessment and techno-economic analysis of mining industries: prospect of solar industrial process heating system integration

In Australia, the leading industrial sector mining and mineral processes consume a significant portion of fossil-fuel driven energy for generating industrial process heat, which can be replaced by alternating energy generation resources like solar energy. Australia has one of the highest levels of solar radiation on earth which is adequate to generate process heat to supply industrial demand. The necessity of solar process heat integration into the mining industries has always been overlooked due to the knowledge gap about the environmental impacts of fossil-fuel generated mining processes and also due to the lack of comprehensive research about operating industries that are already utilising solar resources for process heat generation. Mining processes which require fossil fuel replacement needs feasibility analysis to understand the adaptability level of solar process heat integration in these mining processes. This PhD thesis by publications aimed to identify environmental impacts that were generated from the key mining industries and fill the knowledge gaps in regards to solar thermal process heat integration in mining industries through the life cycle assessment. The leading mining industries were investigated in this thesis by considering their energy-intensive processes and the feasibility analysis using appropriate solar thermal system design. The environmental impact was assessed through modelling of life cycle assessment system, based on the comprehensive inventory dataset which was developed in the purpose of this thesis, analysed using LCA tool and solar thermal analysis software. In this study, ten mining processes were investigated, which are aluminium , ilmenite, rutile, gold, silver, lead, zinc, copper, manganese, and uranium. The processes considered for the impact analysis are mining, extraction, beneficiation, and refining processes. Life cycle environmental impact analysis of those selected mining industries was conducted to quantify which mining processes are harmful to environmental sustainability. These results were the key indicator to rectify the mining processes from where to start renewable energy integration. According to the results found from the analysis, the energy-intensive mining industries which were harmful to sustainability are aluminium (refining), gold (beneficiation and refining), rutile (extraction), and uranium (extraction). Bauxite to alumina production processes was extensively analysed, which showed that alumina smelting and refining consumes a huge amount of fossil fuel-generated energy and emits harmful particles towards the environment, while the climate change impact is 10.91 kg CO2 eq. Similarly, in the ilmenite-rutile mining process, as the mining ore goes deep down to the earth, the more energy and equipment were required for extraction. Three different types of uranium extraction process were evaluated, which shows that in-situ leaching mining impacts over open-pit mining and underground mining (climate change is 6.3 kg CO2 eq for open-pit mining, 26.67 kg CO2 eq for underground mining, and 75.895 kg CO2 eq for in-situ leaching of 1 kg of uranium). Gold-silver-lead-zinc-copper beneficiation and refining processes were assessed separately, which showed gold beneficiation and refining were the most energy-intensive and harmful emissive process, due to the energy consumption during the mining and use of heavy machinery (climate change impact is 0.97 kg CO2 eq from copper, 3640.55 kg CO2 eq from gold, 0.268 kg CO2 eq from lead, 62.12 kg CO2 eq from silver, and 0.41 kg CO2 eq from zinc which is 1 kg in mass). In the next phase, the feasibility of the solar process heat integration, including techno-economic analysis, was conducted based on many solar collector designs. Different types of solar collectors were arbitrarily integrated and simulated in those chosen mining processes to identify the most suitable and least impactful solar collector type. It has been found that evacuated tube collector has better performance rather than for flat plate solar collector in terms of sustainability. At the last stage, a techno-economic analysis was conducted to study the feasibility of the chosen solar collector for two different locations in New South Wales, Australia. The location was chosen arbitrarily as there were several operating mines nearby those locations. The study compares three designs of solar industrial process heating systems: buffer tank system with or without flow heater, and external heat exchanger. The study found that the buffer tank system with continuous flow heater for process heating made of evacuated tube collector would be the most beneficial in terms of solar fraction and annual fuel savings. Using the evacuated tube collector, the solar fraction would vary from 70.2% to 81.5% while using the flat plate collector the solar fraction would vary between 34.2% to 44.2%.