[Gasification] heat required for drying

[Kevin Chisholm]

Dear Paul

This is a neat concept, but if you carry it further, my very simplistic 
analysis suggests it is effectively the same as a "two step downdraft 
gasifier. There are no fundaments "energy consideration changes", and as 
such, if a single stage downdraft gasifier has too much endothermic heat 
load to work, then the two stage system would not work either.

Have I missed something?

Kevin


----- Original Message ----- 
From: "Paul Francesco" <pfv at centurytel.net>
Cc: <gasification at listserv.repp.org>
Sent: Saturday, December 16, 2006 7:05 AM
Subject: Re: [Gasification] heat required for drying


>I thought I posted this to the list, but apparently I just hit "reply"
> and it went out as an off list post. Can anyone tell me why drying
> cannot be accomplished as follows:
>
> This is probably a little off the wall but:
>
>     If you had 2 downdraft gasifier main hoppers, - #1 filled with
> conditioned chips with the hearth lit- directing the raw gas up through
> #2 so as to act as a chip conditioner and partial gas conditioner "tar
> removal" then when #1 is spent. #1 gets filled with "wet" chips and the
> hearth in #2 is lit and the flow positions reversed, wouldn't that
> effectively and efficiently act to cool  the gas, remove tar and
> condition the upcoming fuel load?
>
>    Some setback would have to be observed between the 2 hoppers to
> avoid ignition is the second unit but the heaviest tars would be
> deposited nearest the hearth to be lit on the next load. and the char
> bed may already be prepared for the "new run".
>
>    Granted extra attention may have to be paid to later removal of
> moisture. Anyway just a thought from the woodwork.
> Paul
>
>
> Mark Ludlow wrote:
>
>>Hi Toby,
>>The most fruitful approach may be a condensing air-to-air heat exchanger 
>>on
>>the exhaust stream that recovers at least apportion of the evaporative
>>enthalpy and transfers it to the incoming air. I've seen some industrial
>>installations where a significant amount of warm air flow was exhausted 
>>and
>>replenished with unheated fresh make-up air that used large surface area
>>aircoils as well as honeycomb exchangers to advantage.
>>Mark
>>
>>-----Original Message-----
>>From: gasification-bounces at listserv.repp.org
>>[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Toby Seiler
>>Sent: Wednesday, December 13, 2006 5:33 AM
>>To: gasification at listserv.repp.org
>>Subject: [Gasification] heat required for drying
>>
>>Dear Erik,
>>
>>  I'm probably repeating something that you know.  It takes just over 1000
>>btu to turn one pound of water (liquid) into vapor (after reaching 212f) 
>>and
>>in the condensation gives back about 970 btu. Of course one pound of water
>>raised one degree is a btu., but ambient to 212f is relatively small when
>>considering phase change, but not inconsequential.  Then come issues like
>>the molecular bound water versus free water, when dealing with woody
>>material.  Generally, I believe drying must target a 10 to 16% moisture
>>content which is about the end of free water and beginning of bound water 
>>in
>>wood.  Calculating the incoming weight of the water content in the fuel 
>>less
>>the outgoing desired will give the weight desired to be removed (as 
>>vapor),
>>times the 1000 btu/lb (plus ambient to 212f), gives the energy required to
>>come out of the process, divided by efficiency, for input energy.
>>
>>  One would think that some practical use would exist for the energy given
>>up and not just discharge to the atmosphere as steam.  It takes a lot of
>>energy to dry, but the wise was of the energy from condensation seems
>>prudent.
>>
>>
>>  Regards,  Toby Seiler
>>
>>
>>
>>
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>>
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