With increasingly stringent environmental restrictions, the iron and steel industry is faced with multiple targets such as energy conservation, emission reduction, and cost control, hence, making industrial-environmental management a multi-objective optimization (MOO) problem. Existing studies adopt MOO models to address this issue, however, their methods result in high-dimension problems that increase computational cost and the difficulty to formulate optimal management schemes. This study builds a constrained MOO model in China's iron and steel industry, and introduces a dimensionality reduction technique to identify redundant objectives which can be omitted without altering the Pareto dominance structure of the original high-dimension problem. NSGA-II is then applied on the resulting lower-dimension problem to optimize the application of five types of Energy Conservation and Emission Reduction (ECER) measures, consisting of 23-process equipment and 55-ECER technologies. Results show that: (1) The high-dimension problem can be reduced to a four objective optimization problem. The four key-objectives are cost, energy, CO2, and PM intensity control. Hence, ECER policies should focus on these four key-objectives since optimizing them will synergistically minimize redundant objectives like NOx and SO2 emissions; (2) For the resulting lower-dimension problem, solution quality increases as reflected by algorithm verification metrics (spacing metric and hypervolume indicator), while computational cost is reduced by 73% and the decision making process is simplified significantly; (3) By-production reutilization and cleaner production technologies are the most attractive measures, contributing about 60% of ECER potential and only 30% of total cost. Equipment upgrading also has good ECER effects, but requires strong economic incentives, while end-of-pipe and renewable energy technologies have the lowest ECER potential. In sum, this study proposed a methodology to reduce the complexity of ECER optimization under multiple objectives, and provided suggestions to enhance industrial-environmental management under increasing environmental restrictions.
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