vol 8, issue 7

Carbon 2050 targets - 'dirty' industries to spoil the party

15 July 2013
By Sean Davies
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A steel plant lit up at night

Even cutting-edge technologies can offer only a limited benefit to cutting steel-plant emissions

Could the consumption of five energy-hungry materials sectors derail the global carbon reduction policy?

Despite their best endeavours to become more energy-efficient the global manufacturing sector will not meet its targets for limiting climate change, scuppering any hopes of the UK meeting its 2050 carbon reduction targets.

Combined research from the United States and Europe has analysed the potential for energy reduction in manufacturing by looking at the five materials whose production consumes the most energy.

These materials – steel, cement, paper, plastics and aluminium – represent roughly half of energy used and more than half of carbon dioxide emitted in the manufacturing sector. The research was carried out by Professor Timothy Gutowski from the department of mechanical engineering at MIT along with colleague Sahil Sahni from the department of materials science and engineering. In Europe, Cambridge University was represented by Julian Allwood from the department of engineering and the Netherlands by Michael Ashby from the department of environmental and innovation studies at Utrecht University.

The research, led by Gutowski, studied how materials manufacturing might meet the energy-reduction targets proscribed by the Intergovernmental Panel on Climate Change, which has suggested a 50 per cent reduction in CO2 emissions by 2050 as a means of avoiding further climate change. Meanwhile, economists have estimated that global demand for materials will simultaneously double.

Even under the most optimistic scenarios, these energy-intensive processes were predicted to miss targets massively and researchers concluded that the manufacturing sector as a whole would only be able to reduce energy use by 50 per cent, far short of its 75 per cent goal.

It recognised that their attempts to curb energy use are likely to be restrained by the thermodynamic limits of the processes, the result, the team observed, is that energy efficiency for many important processes in manufacturing is approaching a plateau.

"The energy intensity of the materials is defined as the energy required to produce a material from its raw form, per unit mass of material produced," Gutowski explains. "The energy is usually measured as the lower heating value of the primary fuels used plus any other primary energy contributions.

"These energy requirements are dominated by two main steps – harvesting and refining. For metals from minerals, this would involve the mining, crushing, washing and separation of the ore from the surrounding material [called gangue], and the chemical-reduction process that produces the refined material from its ore [called smelting in metal processing].

"The energy requirements for materials represent about 20 per cent of all energy used on the planet," Gutowski says. "A similar portion would apply to the CO2 emissions, so it is an important sector that needs attention and needs improvements if we intend to meet IPCC goals to reduce CO2."

The five selected industries are energy-intensive and have been working hard to reduce their energy consumption, if for no other reason than to reduce their escalating energy bills. They have succeeded to the tune of about 1 to 1.5 per cent improvement a year. "We need to be careful when we talk about how they use energy, if we define energy intensity, in terms of the energy required per kilogram of material produced, actually these materials – in particular steel and cement – are not that energy intensive as compared to other materials," Gutowski adds. "These materials are important from an energy point of view because we use them in such large quantities. The 75 per cent energy reduction comes from the IPCC goals to limit global warming in the face of growing demand, if the only options for that improvement were energy intensity improvement and recycling."

The report looked at the entire process from harvesting through to refining. The conclusion was that the energy use for these five materials was dominated by refining requirements.

Technological enhancements

The researchers studied the benefits that could be achieved through both best available technologies as well as cutting-edge technologies along with improved recycling.

There is a very long list of the technologies that could be employed to move to best available technologies. Briefly, for steel there are such things as: bi-product gas recovery; thin slab casting; direct carbon injection; and other methods of coke substitution including pulverised coal, natural gas and oil. These are limited, however. For aluminium, the industry is looking at better ways of presenting materials such as point feeders and possibly inert anodes in the not too distant future.

For paper, there are such technologies as: continuous digesters; new drying technology; black liquor gasification; and combined heat and power.

For cement, the sector is looking to move from wet to dry grinding, and there are various clincker substitutes including fly ash, which can reduce the energy required for cement.

For plastics, improved cracking, using high-temperature furnaces and the use of advanced distillation columns are all options. "There are a number of other things we can do mostly by managing the heat, for example, gas turbine integration," Gutowski says. "All of these would include attempts to use combined heat and power and the application of very efficient electric motors.

"The cutting-edge technologies argument is a theoretical argument based on halving the distance to the theoretical boundary," Gutowski adds. "We state pretty clearly that in some cases those technologies do not yet exist. This is a very aggressive scenario and we show that you cannot meet our goals.

"Energy intensity for recycling is always less, in some cases, much less. Generally speaking, metals and paper are already recycled at fairly high rates. With recycling we make the same type of assumptions, which is improvement within the current technology envelope, then we propose an aggressive assumption that the energy required to recycle materials could be halved, we are careful to make sure that this does not violate any thermodynamic limits. Again, this is an aggressive assumption and in some cases the technologies to do this may not yet exist."

Gutowski concedes that if the 50-56 per cent reduction can be met it would indeed be impressive, but argues that it is not realistic because of the aggressive strategies they have employed in the scenario. He feels that a more realistic number would be less than this, probably in the vicinity of 30 per cent. "Our strategy in this paper was to state the goals we needed to meet in order to hit IPCC climate change targets and then show that, even with very aggressive assumptions, the sector cannot hit it," he adds.

He points to the efforts being made in other sectors - such as the transportation and buildings sectors – as impressive but they are not as inhibited as the material sector. "Perhaps we did not point that out clearly enough in the paper, but the behaviour in the different sectors, building, transportation and manufacturing is vastly different," Gutowski explains. "I believe we drew attention to the thermodynamic limits in the paper. Practical limits would certainly apply to the collection of end-of-life materials. Also, we have not addressed the economic limits to any of these actions. Many of the things we are proposing would be extremely costly, and we cannot expect industry to do this without the proper incentives."

Other options

The research looked at another method of reducing energy use, namely material substitution. "The idea would be to substitute a material with a lower energy intensity for a material with a higher energy intensity," Gutowski says. "An example of this would be substituting concrete, bricks or wood for steel in buildings and infrastructure, or steel for aluminium or plastics in vehicles. If these materials could be substituted kilogram for kilogram, then they would reduce the energy to make these products. Furthermore, owing to the strong correlation between material price and energy intensity, this substitution could also save money.

"The main problem is that the material properties of the two substitutes may differ significantly, leading to very different designs. Hence, any analysis to determine the potential energy savings would require a full lifecycle assessment."

The report concludes that ultimately we face fundamental thermodynamic as well as practical constraints on our ability to improve the energy intensity of material production. The only solution, it determines, is a strategy to reduce demand by providing material services with less material. "We could greatly reduce material energy requirements if we could reduce demand," Gutowski adds. "This would require new thinking about how we use materials. Could the developed world work towards a goal of reducing their basic material requirements by half, while allowing the developing world to catch up to this new level?"

The result would have to lead to a reduction in material demand. "The essence of material efficiency is to be more efficient in how materials are used in the design of new products, to make products last longer and to optimise the operational intensity of the material goods." These are not new ideas, but to date they have not formed part of a strategy to reduce global energy use and carbon emissions. "New thinking in this area to address not only engineering challenges but also policy challenges is sorely needed. Whilst we see this approach as technically possible, we believe that many of the barriers will be behavioural, requiring significant inputs from the social sciences."

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