7.4.9 Inter-industry options
Some options for reducing GHG emissions involve more than one industry, and may increase energy use in one industry to achieve a greater reduction in energy use in another industry or for the end-use consumer. For example, the use of granulated slag in Portland cement may increase energy use in the steel industry, but can reduce both energy consumption and CO2 emissions during cement production by about 40%. Depending on the concrete application, slag content can be as high as 60% of the cement, replacing an equivalent amount of clinker (Cornish and Kerkhoff, 2004). Lightweight materials (high-tensile steel, aluminium, magnesium, plastics and composites) often require more energy to produce than the heavier materials they replace, but their use in vehicles will reduce transport sector energy use, leading to an overall reduction in global energy consumption. Life-cycle calculations (IAI, 2000) indicate that the CO2 emission reductions in vehicles resulting from the weight reduction achieved by using aluminium more than offsets the GHG emissions from producing the aluminium.
Co-siting of industries can achieve GHG mitigation by allowing the use of byproducts as useful input and by integrating energy systems. In Kalundborg (Denmark) various industries (e.g., cement and pharmaceuticals production and a CHP plant) form an eco-industrial park that serves as an example of the integration of energy and material flows (Heeres et al., 2004). Heat-cascading systems, where waste heat from one industry is used by another, are a promising cross-industry option for saving energy. Based on the Second Law of Thermodynamics, Grothcurth et al. (1989) estimated up to 60% theoretical energy saving potential from heat cascading systems. However, Matsuhashi et al. (2000) found the practical potential of these systems was limited to approximately 5% energy saving. Actual potential will depend on site-specific conditions.