[Date Prev][Date Next][Date Index]

Re: E-M:/ U.S. Supreme Court Again Support Clean Air

Enviro-Mich message from Rane Curl <ranecurl@engin.umich.edu>

On Tue, 6 Mar 2001, John Rebers wrote:

> Two questions/comments relative to CO2 emissions.
> 1) What about co-generation plants? There is a significant amount of heat
> left after the steam turbines are done; I had the general impression that
> other co-generation could better capture the total heat output, although
> I'm not familiar with the engineering details. How do Michigan and the U.S.
> in general compare to other countries in use of co-generation plants?

It is a question of what you want, work (as represented by electric
generation) or heat. A modern electric plant condenses the steam to
produce a vacuum, as that increases the efficiency of the turbines, but
then it has no heat to export. A steam heating plant for a building just
heats, and produces no work. A co-generation plant sacrifices some of the
electric generation possible in order to export heat in the form of steam.
Different applications need different proportions of heat and work. A key
fact in this, however, is that it is easy to convert 100% of work to heat
(electric light bulbs, other heating applications), but it is impossible
to convert 100% of heat to work (the Second Law of Thermodynamics). The
steam power cycle tops out *theoretically* at ca. 50% efficiency, and that
is not attainable in practice because of essentially ncessary
inefficiencies throughout the process (e.g., to transfer heat from flames
to water in tubes).

> 2) Although steam plants may generate electricity at close to the maximum
> efficiency, electricity use in the US is relatively inefficient after it
> leaves the generation plant. One way for utilities to limit CO2 emissions
> would be to encourage the use of more efficient appliances and otherwise
> limit consumption. Is energy efficiency being promoted by any Michigan
> utilities? Any chance that this could be a direction the EPA will promote?

That is absolutely true. Electricity is used for many heating application
for which direct fuel combustion would be much more efficient. Direct
house heating is an example, which is approaching 90% efficient with
combustion, but hardly 35% with electric heating (which can be improved a
little with a "heat pump"). Beyond such choices, we could burn less fossil
fuel to make electricity by just not using so much electricity. A lot of
outdoor lighting is unnecessary. There is more efficient indoor lighting
than incandescent bulbs (compact fluorescent - or LEDs). 

The idea that has to be adopted is that it is not just wasteful to use
power inefficiently or needlessly, but it is also a growing threat to the
world's societies.

--Rane L. Curl

ENVIRO-MICH:  Internet List and Forum for Michigan Environmental
and Conservation Issues and Michigan-based Citizen Action.   Archives at

Postings to:  enviro-mich@great-lakes.net      For info, send email to
majordomo@great-lakes.net  with a one-line message body of  "info enviro-mich"