GAS-L: maximum pressure and the wooden "battery"

[Peter Singfield <snkm@btl.net>]

Dear All --

At 10:59 AM 2/1/2002 -0600, Hauserman wrote:
>Dear Bram, et al. -
>
>    Re. Maximum pressure for biomass gasification:  There are no
>"fundamental" barriers to gasifying biomass at 50 bar, or any other
>pressure.  In fact, it's been done, quite a few times - under rather
>expensive R&D projects. Certainly there are possible chemical advantages.
>And high pressures would permit much smaller reactor volumes for the same
>production rates, which would contribute to reduced capital costs.

More on pressure gasification --

http://www.rebresearch.com/MRessay.html

Fine example of replacing the theoretically perfect electric resistance
heating with a catalytic burner.

That burner being fueled by the waste gasses of this steam reforming/ H2
purifying (CO and a little H2 that slips thought the works)

All in all -- a tight little system.

In this case -- the fuel being reformed is methanol -- but this interesting
little device care not where the "product" gas comes from -- more on
alternative sources near the end of this com.

At the very least -- reading this "paper" through will result in some clear
answers regarding pressurized gasification -- with clear formula and examples.

The "Blurb" from this Url :

MEMBRANE REACTORS, FUNDAMENTAL AND COMMERCIAL ADVANTAGES, E.G. FOR METHANOL
REFORMING
Robert Buxbaum,
REB Research & Consulting
25451 Gardner
Oak Park, MI 48237
   Membrane reactors achieve efficiencies by combining in one unit a
reactor that generates a product with a semipermeable membrane that
extracts it. The result is a more compact design plus greater conversion.
Removal of a product increases the residence time for a given volume of
reactor and drives equilibrium-limited reactions towards completion. This
latter advantage is reviewed excellently by Armor1,2 while the former has
been, largely, ignored. In my opinion, a yet-larger advantage of membrane
reactors is that they expand the allowed range of temperatures and
pressures for a reaction. Membrane reactors fundamentally change the
pressure dependence of conversion in gas phase decomposition reactions so
that the reactions are preferentially performed at high pressures rather
than low. Higher pressures allow much smaller reactors and more efficient
purification. Membrane reactors can be advantageous also for sequential
endothermic and exothermic reactions, by using the product extraction to
promote heat transfer. Enhanced heat transfer permits plug flow where CSTR
designs would have been necessary otherwise. The net result is smaller
reactors, lower capital costs, and often fewer side-reactions. These
general benefits will be illustrated for methanol reforming to hydrogen. 

**********************

Everything is sitting on those shelves -- it is a simple matter of taking
them down and hooking them together.

>The etermal problem of  feeding light
>fluffy, bridging, non-free-flowing stuff thru lock hoppers into a gas-tight
>vessel becomes far more formidable as pressure increases.

The problem with pressurized gasification of biomass, coal and so forth --
is everyone is locked into a continuous flow model. Which has nightmare
proportions sealing problems.

Batch mode solves all of that. Biomass of proper humidity is heated (using
waste gas products and a catalytic heater) reforming temps and pressures.
The humidity of the biomass supplying the right amount of steam required.

So now we are talking a steel cylinder filled with biomass -- like a wooden
battery!

The product is bled off under any pressure to be further refined in the
device this man proposes.

Pressurizing is simply pressure regulating the release of product from this
batch reaction chamber -- or wood battery. In there, the biomass is
pyrolized and steam reformed -- tars and chars -- everything! But slowly --
over a long period.

The final result out the end of the membrane H@ purifier is two parts.

1: A waste gas that can still fuel a catalytic heater.

2: Pure H2 to feed the right kind of fuel cell.

I believed I described this all in detail on this list a few years back.
And it can be found in the archives.

Fine tuned balancing can be achieved by using a tin metal bath and this
reaction -- which is energy "neutral":

 H2O  +  Sn     ------> SnO2 + H2
 SnO2 + 2CO  ----->  Sn + CO2

As in balancing for max H2 -- and just the right amount of CO for "heat".
Extra CO being converted to H2 -- buy reducing SnO2 back to Sn.

The H2 that slips through the membrane purifier can simply be re-introduced
-- 80% more being extracted each pass.

All in all -- high over all efficiencies -- biomass to electrical energy --
and can be done easily in small sizes -- say 1 kwh to 10 kwh

As for the "batch"

Well, say 1.75 kwh btu per pound for biomass (wood)

Say 45% over all efficiencies (Yes -- and even more)

Say 1 kw for 24 hrs -- 24 kwh.

24 kwh times 1.55 = 37.2 kwh Fuel per gross batch for 24 hours operation.

37.2/1.75 = 21.25 lbs of biomass per batch.

This would be in a cylinder -- replaced every 24 hours.

Hardly reason enough to discourage batch processing??

Yes -- we are talking slow -- pressurized -- steam reformation (ultimately)
gasification. A wooden battery if you will??

It discharges -- and then is opened and re-charged.

You could have four or five "batteries" charges -- hooked on line -- just
switch from one to the other -- as required.

So -- say 10 kwh power plant -- 212.5 pound of wood. 

Wood the cost of a cylinder to hold 212.5 pound of wood be so prohibitive
as to make this unfeasible??

There is no reason to chip or pelletize -- the wood can be charged as solid
pieces or as dust.

It need not be dried -- can go in to "wet". The extra humidity -- as steam
-- passes straight through this device -- 
 
Why is this concept so hard to comprehend? Why bother with continuous
process??


Peter Singfield -- Belize

At 10:59 AM 2/1/2002 -0600, Hauserman wrote:
>Dear Bram, et al. -
>
>    Re. Maximum pressure for biomass gasification:  There are no
>"fundamental" barriers to gasifying biomass at 50 bar, or any other
>pressure.  In fact, it's been done, quite a few times - under rather
>expensive R&D projects. Certainly there are possible chemical advantages.
>And high pressures would permit much smaller reactor volumes for the same
>production rates, which would contribute to reduced capital costs.  However,
>this appears to be rather decisively off-set by a whole array of practical
>mechanical and economic constraints.  The etermal problem of  feeding light
>fluffy, bridging, non-free-flowing stuff thru lock hoppers into a gas-tight
>vessel becomes far more formidable as pressure increases. The same goes for
>ash removal. Then, although the reaction vessels, gas conditioning steps and
>piping may be a lot smaller, they are also  a lot more costly, per capacity.
>Though gases take up less space at high pressures, solids (feed and ash) do
>not. So these components are just as big but must be designed for higher
>pressures. Estimating these higher costs is even prohibitive, since few or
>none of these components are standard equipment, and will generally have to
>be designed/specified from scratch for any conceivable project. (I know  a
>few of you out there have done good work in this area: Tom Miles?  Michael
>Antal? Can you add anything more positive to this?)  My own hands-on in
>pressurized gasification  has only been with more-or-less-free-flowing
>coal, which is enough of a PinA to handle at high pressures, even 10 bar,
>and appears to be  potentially economic - if at all - only on huge scales.
>So -- until atmospheric biomass gasification becomes generally accepted
>commercially, probably in some future generation, I would not recommend
>worrying about pressurized processes --  appealing tho they may be to
>design.  But on the other hand -- Yeah, we need a backlog of good ideas
>whose times haven't come.
>
>              Bill Hauserman


-
Gasification List Archives:
http://www.crest.org/discussion/gasification/current/

Gasification List Moderator:
Tom Reed, Biomass Energy Foundation,  Reedtb2@cs.com
www.webpan.com/BEF
List-Post: <mailto:gasification@crest.org>
List-Help: <mailto:gasification-help@crest.org>
List-Unsubscribe: <mailto:gasification-unsubscribe@crest.org>
List-Subscribe: <mailto:gasification-subscribe@crest.org>

Sponsor the Gasification List: http://www.crest.org/discuss3.html
-
Other Gasification Events and Information:
http://www.bioenergy2002.org
http://solstice.crest.org/renewables/biomass-info/gasref.shtml
http://solstice.crest.org/renewables/biomass-info/