[Default] On Sat, 5 Oct 2013 06:41:23 +0530,Anand Karve <[email protected]> wrote:
>Dear Stovers, > fuel in the form of a combustible gas seems to be a pre-requisite for an >internal combustion engine. Even liquid fuels are atomised before >introducing them into the cylinder of an i.c.engine. Wood gasifies when >heated, but this gas is used in internal combustion engines only after >filtering out the tar. Why is it necessary to filter out the tar? This is more a question for the sister [gasification] list, it's complex. Cylinder walls and valves are cold relative to the offgas so tars condense on the surfaces, they then contaminate the oil. We are used to very high mileages/hours between oil changes with expensive oil, running on dirty gas reduces the service interval and increases costs. There was a large pyrolysis plant in Germany that distilled pyrolysis offgas of beech to produce acetic acid and the gases left over were used in a big reciprocating engine but it had to be stripped and cleaned regularly. On the other hand a reciprocating engine will run quite happily on biogas from a digestion plant, a friend has a 200hp MAN running on biogas which has clocked 27000 hours from new and is just approaching its first major service. In UK town gas (basically the offgas from pyrolysis of bitumous coal) was used to run reciprocating engines but the gas was thoroughly cleaned before being injected into the network. As the town gas plants became redundant and ripe for redevelopment there were problem from the soil being heavily contaminated with nasty organic compounds from the cleaning process. You would have less problem running the engine on char in a down draught gasifier. There is a class of ic engine that will run quite happily on pyrolysis offgas but it all becomes a trade off of capital cost verses operation and maintenance costs, on the large scale a steam turbine has a fifth of the O&M costs of a large diesel, so even though the diesel may be 25% better at converting the heat energy to motion if the fuel is relatively cheap the steam system wins. ( generally coal is far cheaper than liquid or gaseous fuels). AJH _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://stoves.bioenergylists.org/
