[Gasification] Bit more on solar kilns

David Coote dccoote at mira.net
Mon Feb 3 15:26:27 CST 2014

> ------------------------------
> Message: 3
> Date: Mon, 3 Feb 2014 12:22:29 +1300
> From: Doug<Doug.Williams at orcon.net.nz>
> To: gasification at lists.bioenergylists.org
> Subject: Re: [Gasification] Size of blower and tumbler required to dry
> 	chip in a solar kiln
> Message-ID:<20140203122229.168a9a7d312267a8475b86a5 at orcon.net.nz>
> Content-Type: text/plain; charset=US-ASCII
> Hi David,
>> My question is aimed at using a solar kiln to dry chip for use in a
>> biochar system or gasifier/combustion bioenergy system, Doug. This would
>> use material from waste woody biomass streams in regional Australia.
>> Likely to be a mix of eucalypt, conifers, acacias and exotics.
> > From a application perspective, anything is possible, but you need to sort your chip if you want the best result, and size does matter for most application of the final charcoal. Drying the chip before making charcoal would speed up the char making, but to include this activity internally to the timber kiln would not be beneficial if the main kiln timber being dried is hardwoods. You can boil water out of pine, but you need steady humidity and temperature for the hardwoods.
Solar kiln drying timber is well established with drying schedules for 
hardwoods and softwoods. They tend to use different drying schedules 
compared to a conventional kiln. But an interesting aspect to this work 
would be how these drying schedules would apply to chip from different 
species as against timber.

>> And I suspect a  blower would also be necessary but again I don't have a feel for what
>> size of fan would be suitable for this scale. Hence my query.
> Again if you have battery power, using truck radiator fans is an option for the plenum

I guess that would raise questions about how suitable a truck radiator 
fan would be for this application, how long they would last and so on. 
Tinkering is fun but I think COTS (commercial off the shelf) fans are 
cheap. If I can size a unit designed for this task and volume I'm likely 
to have less fuss in operation. I know some guys who do commercial HVAC 
systems so they may have some guidance.

> Given that I don't recall anyone pre-drying chips for charcoal production, it would seem a unnecessary step, unless the charcoal making system has this requirement.
Obviously useful for small scale conmbustion systems and gasifiers. If 
you can dry cheaply before char making this means that considerably less 
thermal energy from combustion is being used to drive off water in the 
charcoal manufacturing step. I would have thought this would be useful 
with respect to charcoal manufacture time and yields. The financial 
analysis is straightforwards as to whether the extra cost of the kiln 
and tumbler is justified. If a kiln is already in use for timber drying 
but not full-time ie time available for other uses the cost to the char 
drying of the kiln is proportionate. Solar kilns can be commercial 
systems or vernacular. A number of US universities and several NGOs have 
solar kiln designs.

>   Have you identified a system to make the char?

Initial system would be vernacular :) AKA 44 gallon drum based

Bye for now


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