[Gasification] OT - ORC/scroll/induction - was: Re: solar collector

[Daniel Chisholm]

(I've labelled this "OT" because it's not _directly_ gasification.  If
it is inappropriate, or if it becomes so, I trust that someone will let
me know, at which point I'll stop....)


On Tue, 2007-06-02 at 20:19 -0500, GFWHELL at aol.com wrote:
>   
> Dan .
> I hadn't thought of running the scroll in reverse.
>  I anticipate running in the direction it was designed for.
> By filling the enclosure through the suction line with high pressure
> vapor. But I could try your system as well.?

Geoff, I may well be missing something here - please correct me if I'm
wrong, because that will make your project a *whole* lot simpler!!

When I imagine a motor driving a scroll compressor in the regular
direction of rotation, I see low pressure, low temperature gas going
into the suction line, entering in large chambers of the scroll
mechanism, and being compressed as the chambers reduce in volume, then
they discharge through the high pressure port ("head side" in
refrigeration lingo ;-) as this smaller chamber passes over the
discharge port.

If one was to admit high pressure gas into the suction side, and have a
lower pressure at the discharge side, my imagination breaks down and I
just can't see how/why the scroll will want to turn at all.... Help!?!!!


> My idea was to run the pump up to speed on the grid, and then speed
> the thing up to "over synchronous "speed  with some high pressure
> vapor, at which time it becomes an induction generator.

That's definitely the way to do it, I agree.  The only thing that we are
differing on is whether this will have to be done in the "regular"
direction of rotation or reverse, and whether the gas flow will be in
the "regular" direction or the reverse.  For both our sakes, I hope you
are right, and I've been missing out on seeing a really simple way that
the system just wants to work....!


BTW, after I wrote my email yesterday I thought of another relatively
small detail.  I assume that there will be a check valve in or near the
discharge port (this is so that when the compressor is stopped, you
don't get a reverse flow of hot gas into the low pressure side of the
system).  In a reciprocating piston compressor, such a check valve is an
intrinsically necessary part of the compressor.  Fortunately, with a
scroll compressor you can remove it and the scroll will work just fine
as a compressor (or, as we wish, an expander!)

Another thought, if you are not a refrigeration technician, or you
otherwise have difficulty in getting access to R22, you can use propane
as your working fluid instead of R22.  Check out a Mollier diagram of
each, they are _nearly_ plug-compatible.  Two differences:

* lubricating oil is much more miscible in propane than R22, which is a
real advantage (one of the difficulties in an R22 system in comparison
to R12 is making sure the oil returns to the pump)

* propane is flammable, so you want to take into consideration what will
happen when leaks occur at various places in your system.

> Every time, a propane container is filled from a storage tank without
> a pump, your system for filling boilers are prevalent!

That requires that the receiving container be at a lower temperature
than the source container.  This can certainly be done on a hobbyist
scale, but I haven't seen it done commercially (have you?).

My idea (see separate email "Rankine feed....") is that the pressure
between the two containers be equalized, and that the liquid simply flow
downhill.  This requires either large enough connecting pipes so that
liquid and vapour can glug past each other, or the addition of a vapour
vent between the headspace regions of both vessels.

> I am intrigued by the concept of generating power using  the natural
> thermal gradient which exists in large areas of the world, namely the
> air temperature and the ground temperature,  not forgetting old SOL.

Yes, it is pretty interesting.  In order for it to work (economically, I
mean), it will have to be done at a reasonable-enough capital cost.
Like other "free" sources of energy (hydro, solar, geothermal, tidal,
wind), the overall cost of your energy is your cost of fuel (zero), plus
operating and capital recovery - unfortunately this tends to be
somewhere between large and huge.

But this is where (IMO) small-scale experimentation can really make a
great contribution.  A backyard-made-with-junk-parts project operate in
a completely different regime of capital and construction costs.  And
more importantly, it is actually feasible to do this sort of project at
the guy-in-a-workshop level (much more so than, say, a steam or gas
turbine, or even, dare I say it, an engine-grade gasifier?!)

> Our great grandfathers forgot more about the conservation of energy
> than we will ever learn. A man would wrestle a piece of coal out of
> the ground by hand,  and it would be evaluated into how much work it
> would perform.

I hear that the old farmhouses around here would (~100 years ago) burn
20 cords of wood in a winter (cut with axe and hand saw, hauled by
horse).  Nowadays one might burn 3-5 cords, which is a helluva lot of
work to produce.  Using a chainsaw......

> I was most impressed with the guys who devised a system possessing no
> mechanical moving parts which harnessed a river which had a 35 ft
> gradient over 750 yards. The system provided 1,000 000 cubic ft of
> compressed air @ 100 psi per hour.That was back in 1906.

You really must tell us about that, or supply a pointer....


-- 
- Daniel
Fredericton, NB  Canada