Hi Ken, Not to flog this horse(power) to death, but are you saying that the combustion chemistry (and composition of the exhaust gas) is substantially different at idle than when an engine is running higher up its horsepower curve? I fully realize that the heat flux would be greater. But intuitively, it seems as if when a load were placed on a normally aspirated, running engine, disproportionately more fuel would be required and thus there would be more products of combustion--including water--by design. Carbureted engines used to run pretty rich at idle, but ECMs have addressed that issue for the most part on fuel injected powerplants. I realize that this may have little to do with fueling with biogas!
Modern industrial tunnel dryers are often counter-flow; the driest product comes in contact with the driest (lowest RH) air and this air, in turn, 'preheats' the new product coming into the dryer, principally through surface condensation, i.e. latent heat transfer. Efficiency is at its highest when the exhaust is saturated. This is the principle behind 93%+ eff. Furnaces and water heaters. This is a quite different scenario from a packed-bed arrangement where the feedstock closest to the engine dries much sooner than higher layers. Once dry, it serves no useful function in the feed bed and is responsible for much of the pressure drop through the dryer. A live-bottom hopper/dryer would address this, I suppose. If anyone has any dewpoint measurements of IC exhaust gases under various load conditions in a woodgas-fueled engine, I would be very interested in having these data. I am too lazy to crank the numbers on this one! Very best regards, Mark -----Original Message----- From: Ken Calvert [mailto:[email protected]] Sent: Saturday, December 18, 2010 11:29 PM To: [email protected]; Discussion of biomass pyrolysis and gasification Subject: Re: [Gasification] Drying fuel with IC exhause and otherpleasures... Mark, sure you can watch the condensation from an engine ticking over, and which you have probably just started, but I challenge you to bore a hole in the floor of your car and point a IR beam thermometer down on the exhaust pipe when you are doing >80mph. You wouldn't be worrying about relative humidity then. Its apples with apples, not iceblocks out of the frig! Ken C. ----- Original Message ----- From: "Mark Ludlow" <[email protected]> To: "'Guag Meister'" <[email protected]>; "'Discussion of biomass pyrolysis and gasification'" <[email protected]> Sent: Sunday, December 19, 2010 3:26 PM Subject: Re: [Gasification] Drying fuel with IC exhause and otherpleasures... > You are right in a way, Peter. But the water has to leave the wood, yes? > Where will it go if the surrounding atmosphere is saturated with water? > > Let me illustrate with an extreme example: Try drying wood at, say, 110C > in > a pressure cooker, with the wood covered with water. > > If the exhaust gas has room for the vapor phase of water, the water will > be > carried away; if it does not (if it is already near its dewpoint), the gas > will become supersaturated and nucleate condensation will occur. There > will > be rain in the forecast. > > I held my hand to the exhaust pipe of my 3.6-l automobile while it was > idling. It was not scorchingly hot but it was palpably humid. Not exactly > Science, I admit. > > Best, Mark > > -----Original Message----- > From: Guag Meister [mailto:[email protected]] > Sent: Saturday, December 18, 2010 4:48 PM > To: 'doug.williams'; 'Discussion of biomass pyrolysis and gasification'; > [email protected] > Subject: Re: [Gasification] Drying fuel with IC exhause and other > pleasures... > > Hi Mark ; > > This is true, but 100C is a special case because the water can exist as > both > a liquid and gas. If we discuss a slightly higher temperature, it may be > clearer. If you heat wet wood to 105C by any means, all the water present > in the wood will be a gas. Yes it will be in equilibrium, but since water > as a gas occupies 100x more volume than water as a liquid, you will have > succeeded in driving off 99% of the water. You could even do the heating > with saturated steam and it would still work. > > Please correct me if there are any errors in the logic. > > Best Regards, > Peter G. (armchair gasifierist) > Thailand > www.gac-seeds.com > > > --- On Sat, 12/18/10, Mark Ludlow <[email protected]> wrote: >> If the IC exhaust is saturated at >> 100C, the best the wood can do is reach an >> equilibrium moisture content with respect to this >> environment. > > > > > > > > > _______________________________________________ > The Gasification list has moved to > [email protected] - please update your email contacts to > reflect the change. > Please visit http://info.bioenergylists.org for more news on the list > move. > Thank you, > Gasification Administrator _______________________________________________ The Gasification list has moved to [email protected] - please update your email contacts to reflect the change. Please visit http://info.bioenergylists.org for more news on the list move. Thank you, Gasification Administrator
