tag:blogger.com,1999:blog-15306282.post116250815710687047..comments2023-11-03T02:18:41.733-07:00Comments on WattHead - Energy News and Commentary: E3's 'Integrated Biorefinery' to Start Production SoonJesse Jenkinshttp://www.blogger.com/profile/00297127385884430247noreply@blogger.comBlogger1125tag:blogger.com,1999:blog-15306282.post-1162903447879614012006-11-07T04:44:00.000-08:002006-11-07T04:44:00.000-08:00Hi Jesse,recently I've been thinking a lot about n...Hi Jesse,<BR/><BR/>recently I've been thinking a lot about net energy and efficiency again.<BR/><BR/>Net energy is a great concept when you've got a process that has something (say Diesel) as its sole input and output and we want to know whether there's any net output, and how large it is. <BR/><BR/>This breaks down when we are talking a conversion of one form of energy into another (say natural gas to space heat in a building). <BR/><BR/>Here efficiency comes in, and that works really well as a concept when we are comparing pure conversions such as:<BR/><BR/>natural gas boilers (sole input natural gas, sole output space heat)<BR/><BR/>coal fired power plants (sole input coal, sole output electricity).<BR/><BR/>It's when there are multiple different inputs and outputs when things get confused.<BR/><BR/>What do you compare a CHP unit to? How about an ethanol plant? Should that be compared to a natural gas to liquids facility? Or an oil refinery? And what do comparisons of that sort based on a single efficiency or net energy number actually tell us?<BR/><BR/>This has gotten me to think a bit more about a case where a simple efficiency metric does apply.<BR/><BR/>Let's assume for the sake of argument that we want to produce liquid fuels from biomass, and if only to power plug-ins or necessary air travel, and that we want to convert ligno-cellulosic biomass, because at present that's got high yields for low agronomic inputs.<BR/><BR/>We can always speculate about other biomass feedstocks (say algae directly produce kerosene from water and carbon dioxide), but sticking with lignocellulosic biomass,<BR/><BR/>a valid question is how can we best convert that into liquid fuels.<BR/><BR/>To get a pure efficiency question, assume a biorefinery with wood as its sole input, and liquid fuels as the sole output (with any electricity or process heat consumed internally), <BR/><BR/>what is the best technology we've got for that plant at the moment and what are the key hurdles?<BR/><BR/>As far as I can see, the key advantage of the biological route is the huge conversion efficiency of sugar to ethanol. Bacteria can be fed 100 kWh of sugar, and convert that to greater than 97 kWh of ethanol, and live on the less than 3 kWh they extract in the process. <BR/><BR/>The key disadvantages of the biological route are that the sugar is in the form of cellulose which needs enzymes for conversion to sugar, and/or a lot of process energy,<BR/><BR/>and that the product ethanol is in dilute solution, with separation of the ethanol by distillation requiring a lot of process energy.<BR/><BR/>But, how serious are these hurdles? How difficult are they to overcome? How much can research help?<BR/><BR/>If enzymatic hydrolysis and molar sieves live up to their promise, it seems to me, that well over 90% of the cellulose and hemi-cellulose energy should be convertible to ethanol (ie some process energy will still be required, either from burning part of the cellulose or from burning part of the lignin).<BR/><BR/>For gasification followed by Fischer-Tropsch, efficiency of 40% is claimed, maybe 50% if some of the output is not liquid fuels but rather electricity and process heat. But what are the hurdles there?<BR/><BR/>If that was really the limit, a biorefinery processing the cellulose and hemicellulose to ethanol, and the lignin to Fischer-Tropsch liquid and just enough electricity and process heat to power the refinery without external inputs might be the most efficienct solution.<BR/><BR/>You know in principle, a catalyst(s) that convert(s) lignocellulosic biomass at room temperature into kerosene at near 100% efficiency could be found. So why can't we get close in the case of Fischer-Tropsch or gasification? There'll be a host of practical difficulties, but can they be circumvented/overcome, and if so, how fundamental is the challenge?<BR/><BR/>The surprising bottom line for me is how little I know about where the real showstoppers are, and how difficult they are to overcome;<BR/><BR/>and nor do I think do the people deciding on what should get research funding.Heikohttps://www.blogger.com/profile/06839810379331430109noreply@blogger.com