Recycle

By Eli Rabett

April 04, 2009

Read original

One of the things missing in the debate about coal is that the energy used is less than half of the energy produced. In the case of electrical generation, the electrical energy produced is only a third. Thomas Casten and Philip Schewe write in the American Scientist that up to three wedges may be available (ok, that is the outer limit) with current technology by paying attention to rejected heat. They write that

The power industry is peculiar. What other business throws away two-thirds of its input? In what other industrial field has energy efficiency been flat since the Eisenhower administration? Indeed, in terms of total energy usage, Thomas Edison‘s early power plants in the late 1800s converted more of the input energy to useful work than any of today’s electric-only power plants. How can that be? Surely modern electrical generators are better than those used a century ago. Yes, they are, but that isn’t the economic point.

Edison used the castoff heat from his generators to warm nearby homes and factories. Consolidated Edison, the descendant company of the one he founded, still delivers heat to thousands of Manhattan buildings via the largest commercial steam system in the world. But few modern fossil- fueled power plants bother to use their heat. They instead vent it into the air. Why throw this valuable thermal energy away? Why burn money? The reasons for this lie in the evolution of the power business, but basically it comes down to one logistical factor: As the years went by, larger plants required more real estate and were built farther from the customer. After all, who wants a sooty coal plant next door? Electricity easily travels many miles, so power plants could be built hundreds of miles away, where they could tap the energy of a river, or where local coal was especially cheap.

Today, emissions from modern coal burning plants are much lower, and can be made lower still. Indeed, instead of beating on China not to build coal burning plants, everyone should be beating on China to build modern coal burning plants and close down the old soot belching ones, eliminating a large portion of the black carbon problem. Using waste heat in South (e.g. India/Pakistan) and Southeast Asia for cooking could make another contribution. Even using the waste heat to process the dung used today for cooking would be a relative winner.

Casten and Schewe think there is a minimum of one wedge and the possibility of two or three to be gotten from using waste heat. The magnitude of what can be gotten is that waste heat use in Denmark accounts for about 50% of the energy used, in the US, 8%. The US uses a lot more energy.

Its not only large power plants that can use waste heat. There are small units that produce heat and electricity to power and warm a house. It’s not just coal, natural gas in pipelines runs at much higher pressures than used in homes. The expansion could be used to power turbines. Many industrial process produce heat which can be used to produce electricity or for heating, and increasingly they are purchasing heat from power plants. Dow Chemical was an early adopter of these strategies.

Optimizing energy recycling requires planning and a favorable regulatory environment. It is worth doing. (The paper is behind a paywall, but available to all Sigma Xi members, e.g. the smart bunnies=:>)

Comments?

Contact us to discuss how energy recycling can help your organization.