New industries: a dramatic use of energy
29 Apr, 2009 10:00 am
In a study published in Environmental Science &Technology, researchers from the MIT and the University of Kentucky used a thermodynamic framework to characterize the material and energy resources used in manufacturing processes. The results show that the intensity of materials and energy used per unit of mass of material processed has increased by at least 6 orders of magnitude over the past several decades. Dusan Sekulic, one of the co-authors of the study, answers Scitizen's questions.
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Before I answer, let me clarify something fundamental. In everyday conversation we use the word ?energy? in a loose and casual way. But a scientist must carefully distinguish between ?energy? and "energy resources." ?Energy resources? can be transformed into various forms of energy (as a property of a given system) in various engineering settings (combustion chambers in power plants, reactor cores in nuclear plants, etc), and subsequently used in other forms in energy, manufacturing and many other processes. Moreover, the important point for us is not only how much available energy is ultimately used but how efficiently the energy made available from the resource is used -- that is, what percentage of its availability is (literally) lost.
I should also clarify: we are considering orders of magnitude differences in utilization of energy resources per unit of produced outcome (say, a piece of new material).
So from this point of view we must be careful to mark the difference between total energy resource use and the specific energy resource needed to get the desired outcome per unit of a product/service.
This specific energy use may be dramatically larger for modern advanced manufacturing processes than for traditional processes. But this is only part of the story. Such a comparison of the specific energy resource needed for, say, diffusion based processes vs. old-fashioned manufacturing processes such as machining does not necessarily tell us what is important.
In general, to understand the advantages/drawbacks and weigh the tradeoffs for a particular product, we need to look at the whole life cycle of the product in the context of sustainable development. A particular product may seem ?cheaper? in terms of energy resources used in its manufacture, if we look only at that stage. Expanding our focus a bit, we can include the quality of the product, the dematerialization benefits of its capacity to make us happy, which are important but not exclusive criteria for assessment of the sustainability issues. But what?s really critical is a careful consideration of resources use (energy and materials) along the life cycle of the product (whether produced by new or traditional technologies
So, at last, I can begin to answer your question: No, we are not surprised by the differences. These differences are simply the consequences of demand for a certain product given the state of current knowledge and the state of the art for making such things. In other words, we sometimes manufacture ?beyond our means? in the same way that some people use credit cards; i.e. we can be so driven to make a particular something now, despite current inefficiencies that indicate we can?t really ?afford? it (in the context of acceptable efficiency) , that we go ahead anyway, and are heavily ?taxed? by the laws of nature which do not let us accomplish our task without paying heavily for it in terms of energy resource use.
What is surprising is that in general people are still focused primarily on product utility, not on the price that we all must pay through, say, very large specific resources use now which is depleting resources that might be needed to further advance human desires. That is, we use our resources now as if we are confident that there will not be better and/or more efficient uses for them in the future.
Do these results put into question the quest for energy efficiency in the 21st century?
This is a difficult question. For some necessary manufacturing processes, we have no better alternative at present so they must remain surprisingly inefficient. Secondly, when we talk about increasing the efficiency of a given technology - especially a mature one - we have to accept the fact that such improvements tend to be stepwise and gradual, not dramatic. Innovative, radical leaps in technology are essential too. But one must be careful not to overestimate the role of "to be discovered? new technologies. There are limits imposed by the laws of nature on any kind of energy and/or material resource use. We do hope to help solve global sustainable development problems using new technological advances. At the end of the day, however, what matters is the aggregate (that is, global) resources use and/or impact. So, the big numbers do depend on small steps at the local level and that is why we must strive to improve our processes/technologies wherever possible.
As a result of your study, what do you advocate to reduce production costs in terms of energy/material use?
You can find overly-optimistic comments made by people who feel that the discovery of radical new technologies alone will solve all problems related to achieving sustainability. It is true that inventing better technologies will be important for achieving our goals but new technologies will never be sufficient in themselves as a solution so these comments can be seriously misleading.
We feel it would be useful to rigorously establish the limits imposed by physical laws on achieving energy efficient processes and products. Identifying the real limits to future improvements with not-yet-invented technologies is one way science can help us focus our work on the most realistic opportunities where new technologies can make a difference.
This theoretical vision has two important implications. The first emphasizes the wasteful energy/material use by present day technologies and human behavior. Although human progress cannot and should not be constrained by regulations imposed, informed awareness of the impact of and consequences of such unconstrained development is crucial. The second implication is that it is an illusion that we can produce new capital to serve as substitute for depleted natural capital. There is no such easy solution. So we have no choice but to come to grips with the difficult trade-offs and sacrifices necessary in a situation where our inevitable drive toward progress involves dissipation of resources and other negative impacts on society and the environment.
Source: Thermodynamic Analysis of Resources Used in Manufacturing Processes, Environ. Sci. Technol., 2009, 43 (5), pp 1584?1590 DOI: 10.1021/es8016655 Publication Date (Web): January 29, 2009
Dusan P. Sekulic is Professor at the Department of Mechanical Engineering, University of Kentucky; Director of brazing and heat exchangers programs at the UK Center for Manufacturing
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