On Sun, Dec 26, 2010 at 9:08 AM, GF <[email protected]> wrote: > > > Hi Doug. > Your reference to "the inconvenience" of reclaiming ICE exhaust heat is > surely a design failure. > There has been a lot said about moisture content of raw fuel on recent > contributions,would you not agree that the temperature of the reaction zone > becomes lowered by wet fuel ,due to the endothermic effect of "to much water" > being present, leading to gas of deficient quality and tar?. > If so, additional heat needs to be applied to this area in order to convert > the "water trapped within the fuel" in to super heated steam, just before > being drawn through the "reaction zone". > Perhaps we should consider the ICE as the primary provider of heat for > pyrolization, and build the gasifier around it. > > GFWHELL >
gf, lots of progress is possible by claiming and recylcing these "waste heats" as we all know. the rub is in the mechanical difficulty in doing it. i've found gasifier design to be an interesting 3-d puzzle where you're trying to simultaneously solve thermal, chemical and mechanical problems. unfortunately, the optimized and most simple solutions for each bear little resemblance to the others. getting to a materials and cost minimized solution is not easy. and until you do, the effort to realign all these flows can easy outweigh the benefits. the main problem in heat recycling is that not all heat is created equal. you can't just create one big "heat pool" and return it en mass to the gasifier. you need to return different temp heats to temp appropriate points in the fuel making process. you need to segment the waste heats by temp, and return them to different temp spots in the gasifier. if you don't, you get problems like the tarbaby one described by ken, where drying was wanted, but pyrolysis was gotten instead. i've found the gasifier output gas, after tempering with air preheating, to be a more temp appropriate waste heat flow to use for fuel drying. though it has to be done through a heat exchanger, not direct contact flow. segmenting and properly associating the various wastes heats to the various points of heat need is a fun puzzle. many answers are possible. here's the one i currently like. this is the formalization of the 4 stages of heat exchange we use on the gek totti. http://wiki.gekgasifier.com/w/file/34212370/TOTTIThermalRelationships-700.jpg and in principle, yes, we can consider the engine to be the combustor for the gasifier. or really, the engine as an auxillary component to the gasifier, with a byproduct of mechanical energy. the waste heat int he ic exhaust is our biggest heat flow and highest temp available (save the gas right at the end of reduction). but sadly, ic exhaust isn't hot enough to do all the tar cracking work one needs to do. the engine can't be the only combustor in the system. you need something else to get to the 1000c or so to crack tars. given all the other losses in an engine, you can't really even get the gas out in the exhaust hot enough to heat char and gasses for reduction. back in the day i tried to figure out how to make the exhaust manifold on an engine into the actual gasifier. even for a charcoal gasifier. problem is the ic exhaust isn't really hot enough to run reduction, and the co2-h2o is extra nitrogen diluted given its source. the nitrogen dilution gets worse the more you recycle the engine gas flow. but yes, the ic exhaust gas is plenty hot and plenty heat flow to run pyrolysis. that's where i ended up with the pyrocoil scenario. you can get enough out of the ic exhaust to finish pyrolysis without any parasitic loads on the combustion and cracking zone. you will still have some raw heating fo the char to temps to pass through the combustion zone. how much this is depends on how hot your ic exhaust is. but the basic heat of pyrolysis, and a good amount of the heating of the char to combustion temps, can be taken out of the equation. doing all this gets you some more headroom to run wetter fuels, or do less combustion internally so you get a little less nitrogen diluted gas, and thus a higher energy density. it doesn't make all possible, but it helps. we regularly run 20-30% moisture fuel without problem. at the last workshop we ran some 44% and overwhelmed the system. lots of water passed through and plugged the filter. the philippines trip showed we could run air dried tropical wood in the 25-30% range. tom's gas analyzer showed 6mj/m3 energy density. a bit better than usual, but certainly not pure co-h2. there are many benefits one can get from extensive heat recycling. it doesn't, however, solve all problems. it can significantly widen the range over which reasonable running is possible, but there are still many ditches to fall in. lots of shoveling left to do . . . j -- ------------------------------------------------------------------------------ Jim Mason Website: http://www.whatiamupto.com Current Projects: - Gasifier Experimenters Kit (the GEK): http://www.gekgasifier.com - Escape from Berkeley alt fuels vehicle race: www.escapefromberkeley.com - ALL Power Labs on Twitter: http://twitter.com/allpowerlabs - Shipyard Announce list: http://lists.spaceship.com/listinfo.cgi/icp-spaceship.com _______________________________________________ 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
