Progress in reducing industrial energy demand and carbon dioxide (CO 2 ) emissions is evaluated with a focus is on the situation in the United Kingdom (UK), although the lessons learned are applicable across much of the industrialized world. The UK industrial sector is complex, because it may be viewed as consisting of some 350 separate combinations of subsectors, devices and technologies. Various energy analysis and carbon accounting techniques applicable to industry are described and assessed. The contributions of the energy-intensive (EI) and nonenergy-intensive (NEI) industrial subsectors over recent decades are evaluated with the aid of decomposition analysis. An observed drop in aggregate energy intensity over this timescale was driven by different effects: energy efficiency improvements; structural change; and fuel switching. Finally, detailed case studies drawn from the Cement subsector and that associated with Food and Drink are examined; representing the EI and NEI subsectors, respectively. Currently available technologies will lead to further, short-term energy and CO 2 emissions savings in manufacturing, but the prospects for the commercial exploitation of innovative technologies by mid-21st century are far more speculative. There are a number of nontechnological barriers to the take-up of such technologies going forward. Consequently, the transition pathways to a low carbon future in UK industry by 2050 will exhibit large uncertainties. The attainment of significant falls in carbon emissions over this period depends critically on the adoption of a limited number of key technologies [e.g., carbon capture and storage (CCS), energy efficiency techniques, and bioenergy], alongside a decarbonization of the electricity supply. © 2016 The Authors. WIREs Energy and Environment published by John Wiley & Sons, Ltd. How to cite this article:WIREs Energy Environ 2016Environ , 5:684-714. doi: 10.1002 INTRODUCTIONT he industrial sector accounted for almost one-third of world primary energy use and approximately 25% of world carbon dioxide (CO 2 ) emissions from energy use and industrial processes in 2005.1 High growth in production and energy use have been seen in the emerging economies, such as India and China, with China being responsible for 80% of worldwide growth in industrial production over the past 25 years.1 In contrast, the UK has seen a reduction in industrial energy use whilst continuing to increase output in economic terms.2 It accounts for some 21% of total delivered energy and 29% of CO 2 emissions. Industry is also very diverse in terms of manufacturing processes, ranging from highly energyintensive (EI) steel production and petrochemicals processing to low-energy electronics fabrication. 2 The former typically employs large quantities of (often high-temperature) process energy, whereas the latter tends to be dominated by energy uses associated with space heating. Around 350 separate combinations of subsectors, devices and technologies can be identified 2 ; each combination offers quite differe...

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Energy-related carbon emissions from UK manufacturing have fallen, between 1990 and 2007, by approximately 2% per annum. This reduction could be caused by a number of effects that can act to increase or decrease the level of emissions. Decomposition analysis has been used to separate the contributions of changes in output, industrial structure, energy intensity, fuel mix and electricity emission factor to the reduction in carbon emissions. The primary reason for the fall in emissions was found to be a reduction in energy intensity. The manufacturing sector was also split into two subsectors: the energy-intensive (EI) subsector, and the non-energy-intensive (NEI) subsector. The NEI subsector, somewhat surprisingly, was found to have made greater relative reductions in its energy-related carbon emissions over the study period. This was principally due to much greater relative improvements in energy intensity. There is evidence that the EI subsector had made greater relative improvements in energy intensity in the period preceding 1990, and so this may have limited improvements post 1990.

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A database of the heat demand, and surplus heat available, at United Kingdom industrial sites involved in the European Union Emissions Trading System, was used to estimate the technical potential of various heat recovery technologies. The options considered were recovery for use on-site, using heat exchangers; upgrading the heat to a higher temperature, using heat pumps; conversion of the heat energy to fulfill a chilling demand, using absorption chillers; conversion of the heat energy to electrical energy, using Rankine cycles; and transport of the heat to fulfill an off-site heat demand. A broad analysis of this type, which investigates a large number of sites, cannot accurately identify site level opportunities. However the analysis can provide an indicative assessment of the overall potential for different technologies. The greatest potential for reusing this surplus heat was found to be recovery at low temperatures, utilising heat exchangers; and in conversion to electricity, mostly using organic Rankine cycle technology. Both these technologies exist in commercial applications, but are not well established, support for their development and installation could increase their use. The overall surplus heat that was technically recoverable using a combination of these technologies was estimated at 52PJ/yr, saving 2.2MtCO 2e /yr in comparison to supplying the energy outputs in a conventional manner. It is thought that a network and market for trading in heat and the wider use of district heating systems could open considerable potential for exporting heat from industrial sites to other users.