[Bioconversion] Veg Lister - torrified woodcips

Tue Nov 7 04:54:23 CST 2006

Dear Ken, I am a babe in the woods in this area, being a re-newable energy system designer but no
credentials with producer gas, but I would ask you, - is there any benefit in driving out the
water and volatiles at the lower temperature you suggest, - "by heating the biomass to around 250
to 300 C" and then re-introducing them to the char bed as you would have done anyway?
I understand that a great deal of efficiency can be achieved through pre-heating, - particularly
with exhaust gases, but do you really need to separate those heat released water and volatiles
and re-introduce them later, or is that for a particular purpose or have I mis-understood?
Cheers,
Geoff.

> Ken,
> I presume that you will torrify the wood chips indirectly with the exhaust
> gases if it is intended to recirculate the voltalies into the hearth of the
> gasifier?
>
> Have you any thoughts on the heat exchanger design? And what sort of volumes
> would you be processing at a time.
>
> The rest I agree is very exciting, particulerly the Diesel dual fuelling
> which seems to help solve the gas variabilty control problem.
>
> Must get on and complete my Fluidyne gasifier.
> Ken
>
>
>
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> -----Original Message-----
> From: bioconversion-bounces at listserv.repp.org
> [mailto:bioconversion-bounces at listserv.repp.org] On Behalf Of Ken Boak
> Sent: 07 November 2006 09:09
> To: Discussion of biological conversion to fuels and chemicals
> Subject: Re: [Bioconversion] Veg Lister - torrified woodcips
>
>
> Rex & List,
>
> A simple experiment can be done using a propane torch, and introducing
> propane into the air intake of the diesel engine.
>
> Provided that the engine governor is working and maintaining a fixed speed,
> it will be noticed that the governor acts to close the rack on the injection
> pump, thereby reducing the fuel (veg oil) injected.
>
> Details on the Ankur Scientific gasifier site, suggest that the quantity of
> pilot fuel can be reduced to about 20%, when wood gas is introduced in this
> manner.  As the calorific value of the gas is likely to be variable in
> nature, the governor will adjust the position of the injector pump rack to
> compensate.
>
> Wood gas should be mixed with air in approximately 50% ratio, using some
> sort of a mixing valve.  It should be remembered that the gasifier is
> relying on the suction from the engine to draw air through and gas out.  The
> mixing valve should ensure that the correct air ratios can be maintained for
> efficient gasification.
>
> On the 6hp Lister, the IP rack has sufficient travel to completely cut off
> the fuel supply, so closing down to 20% injection should not be a problem.
>
> The whole question of running a gasifier with a diesel engine in dual fuel
> mode is a very exciting one, particularly when it forms part of a combined
> heat and power system, that has to cope with varying electrical and thermal
> loads.   In Northern climates where the heat required might approach 10
> times the electricity requirement, this presents an interesting concept,
> where the gasifier can be used to provide additional thermal output when
> needed.
>
> It should be remembered that the diesel engine rejects approximately 1/3rd
> of its heat energy via its exhaust. Efficient utilisation of this heat is
> key to maintaining overall system efficiency.
>
> As the exhaust gases are emitted at approximately 300 to 400 C, they are of
> the right temperature range to initiate the drying and torrefaction of the
> woodchips, prior to them being pyrolised.
>
> Torrefaction is generally done by heating the biomass to around 250 to 300 C
> and maintaining it at these temperature for between 30 and 60 minutes.
> Torrefaction serves to drive off the volatiles, and reduce the internal
> water content of the fuel, resulting in approximately 30% mass loss, but
> only 10% energy loss, thus the energy density of the fuel is increased from
> around 19MJ/kg  to 22MJ/kg.  The 10% of energy loss driven off with the
> volatiles can be recouperated by circulating the torrefaction gases back
> through the incandescent charcoal bed. These volatiles will be further
> cracked and this will reduce the overall tar content in the final pyrolisis
> gases - which is a good thing if you are wanting to run an IC engine.
>
> Torrefaction alters the mechanical nature of the wood, making it more
> friable and brittle. This means that it is easier to process, and using a
> mechanical grater system such as proposed in the Kalle gasifier of 1943,
> torrefied wood could be ground within the gasifier to porduce smaller
> particle sizes - and thus more efficient gasification.
>
> Torrified wood is a stable substance and can be stored without re-absorption
> of water and the risk of the mosisture content rising, such that would occur
> with wood or charcoal.  Torrefied wood is a more homogenous fuel, and if
> produced from chips of the right particle size could provide an alternative
> fuel for woodstoves and possibly pellet stoves
>
> As only 10% of the energy content is lost in the torrefaction process, it is
> a far better fuel for barbeques compared with charcoal, and is easier
> toignite and burns with less initial smoke because the volatiles have
> already been partly driven off.
>
> So the hot exhaust of the Lister could be used to produce batches of
> torrified woodchips, which could either be used immediately within the
> gasifier,  or allowed to cool, stored and used much later for barbeque or
> heating fuel.
>
> There is approximately 2.5 to 3kW of thermal energy available in the exhaust
> of the Lister whilst running at full output.  Whilst mostly consisting of
> hot nitrogen, there is CO2, CO, H2O and some excess air O2. There will be
> some carbon particulates (soot) and possibly some unburnt fuel. All of these
> could be returned into the incandescent reduction zone of the gasifier for
> further utilisation.
>
> Any thoughts,
>
>
> Ken
>
>
>
>
> ----- Original Message -----
> From: "Zietsman, Rex" <Rex at Process.co.za>
> To: <bioconversion at listserv.repp.org>
> Sent: Tuesday, November 07, 2006 4:33 AM
> Subject: [Bioconversion] Veg Lister
>
>
>> Ken,
>>
>>
>>
>> Sorry for the slow brain... If I understand you correctly, the
>> governor will cut back the veg oil feed to the engine based on engine
>> speed. I am assuming that the fuel injection pump rack can cut back
>> that far when gas is being introduced. If so, it is a great win. The
>> trick then is to get a link between the governor and the gas feed such
>> that the veg oil contribution is about 20%. As you say, if there is no
>> gas available at the time, the fuel injection pump rack will
>> automatically be controlled by the governor to provide all the energy.
>> This is a particularly clever way of running a Lister.
>>
>>
>>
>> Rex
>>
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>
>
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