[Gasification] heat required for drying

[Mark Ludlow]

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
   
   

 
---------------------------------
Access over 1 million songs - Yahoo! Music Unlimited.
_______________________________________________
Gasification mailing list
Gasification at listserv.repp.org
http://listserv.repp.org/mailman/listinfo/gasification_listserv.repp.org
http://gasifiers.bioenergylists.org