Abstract
Purpose
Metal ore smelters have significant environmental footprints due to very high energy consumption and the resulting large quantities of waste heat. The industry recognizes, therefore, the need for implementation of changes to improve process economics by reducing primary energy consumption through recovery and repurposing of waste heat. However, when deciding the merit of a process modification, it should not only be based on economic gains (which have previously been highlighted), but also on environmental impacts. For the latter, life cycle assessment (LCA) is a well-established and useful tool. But across the mineral processing industry, LCA is not commonly incorporated into decision-making processes.
Methods
We have investigated the environmental gains from introducing low-grade heat recovery and repurposing within a smelters’ sulphuric acid plant. An LCA model was developed to first assess the environmental impact of existing sulphuric acid making processes across four standard potentials (global warming, acidification, eutrophication, and relative human toxicity). The model was then used to examine the potential of installing heat pumps to capture waste heat from water cooling towers associated with sulphuric acid production and repurposing it to replace existing on-site electric heaters.
Results and discussion
The study found that replacing electric heaters made significant improvements in a range of environmental impacts. The results of the model show a potential 13% reduction in electricity consumption, with a 53% reduction from the mist precipitators in global warming, acidification, eutrophication, and relative human toxicity potential.
Conclusion
The LCA comparison showed a potential 13% reduction in overall electricity consumption through the addition of low-grade heat capture using heat pumps, as well as a 5% reduction in heat load on the cooling towers. Together, this would lead to a 21% reduction in carbon dioxide equivalent emissions from the mist precipitators and cooling towers, as well as acidification, eutrophication, and relative human toxicity potential.
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Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
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This work was supported by the Mitacs Accelerate program and the National Science and Research Council (NSERC).
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Communicated by Andrea J Russell-Vaccari
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McLean, S.H., Chenier, J., Muinonen, S. et al. A case study comparison of a sulphuric acid plant with and without on-site low-grade heat recovery and repurposing. Int J Life Cycle Assess 27, 655–664 (2022). https://doi.org/10.1007/s11367-022-02052-x
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DOI: https://doi.org/10.1007/s11367-022-02052-x