Re: manure->methane -> power

puppet_sock@xxxxxxxxxxx wrote: 
Elmo wrote:
[snip]

Gas cogeneration
systems can run 70-80% energy efficiency converting to electricity leaving
(do the subtraction) as the waste heat.



For suitable values of the word "efficiency." A heat engine
cannot violate the laws of physics. To get 70 % efficiency
out of a heat engine operating with a "cold" side round
about room temperature, you'd need the "hot" side to be
at about 900 C. That's high even for a dedicated power plant.

It's likely that your reports are including in the efficiency
calculations some estimate of the part of the heat used for
whatever the "co" part is. Like, 30 percent goes to electricity,
40 percent goes to heating the building, total 70 percent used,
so 70 percent efficient. Getting 30 percent out as electricity
would only require a "hot side" of about 200 C.
Socks

Looked slightly further -- http://www.gas.or.jp/gasfacts_e/p_09/
found the breakdown was in an industrial situation:
   Electrical Energy produced 25-40%  (similar to your 30%)
   Used waste heat[1] (hot water, heating, production processes) 40-50%
   Unused waste heat 20-30%
Since these don't add up, it's likely that the amount which is used is
variable depending on demand for whatever it can be used for.

I read about a medium sized (300 cow) dairy in Cowlifornia that had
installed a methane digester and a 75KW generator.  Net metering
allowed them to get credit for putting electrons back onto the grid,
excess heat from the generator used to heat water that is used for
cleaning and to keep the digester at an efficient production temperature.
And they still got some fertilizer value out of the digester's liquid
by-product.  They figured the savings would pay the investment back in
3-4 years.



[1]Used waste -- see also:military intelligence, jumbo shrimp, oxymoron

--
"It is inaccurate to say that I hate everything.
I am strongly in favor of common sense, common honesty, and common decency.
This makes me forever ineligible for public office." - H. L. Mencken
.

Relevant Pages

  • Re: Slow Stealth
    ... almost all of its heat energy into electricity. ... Efficiency: 75% ... Helium Coolant Reservoir + Intercooler at 3000-1123K ...
    (rec.arts.sf.science)
  • Nanowires convert heat to electricity
    ... Phonon effects boost thermoelectric efficiency ... low-cost devices that convert waste heat to electricity. ... who have shown that arrays of tiny silicon wires have extremely ...
    (sci.physics)
  • Re: Efficiency of utilities
    ... heating is "less efficient" than gas heating. ... Or is it that a) electricity is more expensive per kWh, ... don't think they've ever achieved much more than about 50% efficiency - the ... If they heat up, we're using the heat, if they ...
    (uk.tech.digital-tv)
  • [OT] Re: Gore brainwashing world to ban the light bulb!
    ... tungsten, carbon arc, CFL, I get 1 kilowatt of heat in the room. ... Efficiency 100%. ... I think that somewhere between 5 and 15% of the electricity going ... because all the energy goes into heating the room rather than ...
    (comp.os.vms)
  • Re: Johnny
    ... Global Warming and waste heat ... energy in whatever mass absorbs it, is pretty much the last stopping ... As much fossil fuels and electricity ...
    (uk.local.cumbria)
Loading