Cement production is an environmentally relevant process responsible for 5% of total anthropogenic carbon dioxide emissions and 7% of industrial fuel use. In this study, life cycle assessment is used to evaluate improvement potentials in the cement production process in Europe and the USA. With a current fuel substitution rate of 18% in Europe and 11% in the USA, both regions have a substantial potential to reduce greenhouse gas emissions and save virgin resources by further increasing the coprocessing of waste fuels. Upgrading production technology would be particularly effective in the USA where many kiln systems with very low energy efficiency are still in operation. Using best available technology and a thermal substitution rate of 50% for fuels, greenhouse gas emissions could be reduced by 9% for Europe and 18% for the USA per tonne of cement. Since clinker production is the dominant pollution producing step in cement production, the substitution of clinker with mineral components such as ground granulated blast furnace slag or fly ash is an efficient measure to reduce the environmental impact. Blended cements exhibit substantially lower environmental footprints than Portland cement, even if the substitutes feature lower grindability and require additional drying and large transport distances. The highest savings in CO(2) emissions and resource consumption are achieved with a combination of measures in clinker production and cement blending.

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A model for input- and technology-dependent cradle-to-gate life cycle assessments (LCA)was constructed to quantify emissions and resource consumption of various clinker production options. The model was compiled using data of more than 100 clinker production lines and complemented with literature data and best judgment from experts. It can be applied by the cement industry for the selection of alternative fuels and raw materials (AFR) and by authorities for decision-support regarding the permission of waste co-processing in cement kilns. In the field of sustainable construction, the model can be used to compare clinker production options. Two case studies are presented. First, co-processing of four different types of waste is analyzed at a modern precalciner kiln system. Second, clinker production is compared between five kiln systems. Results show that the use of waste (tires, prepared industrial waste, dried sewage sludge, blast furnace slag) led to reduced greenhouse gas emissions, decreased resource consumption, and mostly to reduced aggregated environmental impacts. Regarding the different kiln systems, the environmental impact generally increased with decreasing energy efficiency.

The iron and steel industry represents an important case for industrial ecology due to its ability to accept waste-derived inputs and due to the generation of useful by-products. With the objective of supporting environmentally conscious decisions regarding resource use and waste management, a life cycle assessment (LCA) tool for ironmaking was developed. The tool combines mass flow-based process models with an LCA database to assess the use of alternative resources in ironmaking, considering various process configurations. The article contains a description of the tool and a case study illustrating two areas of application. In the first part of the case study, an inventory analysis focused on the effects of feedstock recycling of waste plastics in ironmaking on heavy metal distribution is presented. It is demonstrated how uncertainties in input heavy metal concentrations and mass transfer can be incorporated into the model to predict the heavy metal loads in the process outputs. In the second part, the substitution of coke with a range of alternative reducing agents are assessed with regard to impact on climate change and fossil resource depletion. It was found that the use of sustainably sourced charcoal and waste-derived reducing agents is beneficial both with respect to the impact on climate change and fossil resource depletion at the respective calculated coke replacement ratio, whereas the results for heavy oil, coke oven gas, and raw tar indicate that trade-offs between impact categories occur. The results also highlight the importance of considering the avoided impacts of alternative treatments for waste-derived resources. Keywords:blast furnace industrial ecology life cycle assessment (LCA) mass flow model sustainable resource use waste management Supporting information is available on the JIE Web site

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