Greetings Ken, and list members. Ken, I'm going to point you to a video of the "underside" of a whole log (or split) "cordwood as we call it here" stove that is a downdraft gasifier.
I can speak at length privately, however only somewhat on list, as this is a proprietary design. Here's the link to the video: http://youtu.be/DNYCfgEdYpg Greg Manning On Thu, Dec 26, 2013 at 12:59 PM, Ken Boak <[email protected]> wrote: > > Happy Christmas to the gasification list. > > At this time of year, during the festive holiday season, I get a bit more > time to manage the running of our woodstove, as it rapidly warms the room > and produces a cheery effect. > > Our property is fairly conventionally heated by natural gas, but a few > years back, I took the decision to invest in a woodstove with back-boiler, > to provide an alternative or back-up to the gas fired system. > > The woodstove has a flat steel tank at the rear, the "back boilerr", in > place of a couple of the firebricks lining. This circulates heated water > entirely by the thermosyphon principle to a radiator located in the > bedroom/workroom directly above the stove. So in effect the stove heats the > living room/kitchen area directly, and the room upstairs by circulating > hot water. > > No electricity is required for circulation, and if worse-case we had an > extended power outage, this stove would provide heat and comfort in the two > main occupied areas of the house. Stoking it and attending it is often more > interesting than what is being shown on TV! > > With a few days off work, I have had time to monitor the stove and make > some assessments of its overall performance. Its a fairly traditional > stove, a rectangular box,, made from bolted together cast iron panels and > partly lined with firebrick. It's described as a multifuel stove - having > been supplied with a cast iron removable grate for burning coal - which is > not used when burning wood. It's approximately 24" wide, 12" deep and 18" > tall. > > In the UK, a common size for firewood logs, intended for the domestic > woodstove is about 10" (254mm) long, and equal to a 1/4 round taken from a > limb that may have been 5 or 6" in diameter. The reason for this is that > there is a lot of coppiced hardwood, which has become mis-managed in the > last 20 years, so there are a lot of trees with 6" diameter shoots. The > popularity of the "firewood processor" machine, means that a lot of this > wood is now coming on the market as domestic firewood, and sold to > suburbanites at vastly inflated prices (about $0.50 per kilo). > > I am burning a mixture of kiln dried Silver Birch, and air dried other > species which includes ash, oak and sweet chestnut. The silver birch splits > well and makes excellent kindling. One log is split into 8 or 10 kindling > sticks and these are built into a pyramid around 2 or 3 sheets of scrunched > up newspaper. Lighting is quick and easy - as the birch is kiln dried, and > within 5 minutes you will have a roaring fire and the larger logs can be > added. > > The logs have an average weight of approximately 1 kg. I have found that > a normal burn rate of these is two per hour. I burn two at a time, and > each hour, add a further two to the burning char bed from the previous > logs. With firewood having a calorific value of approximately 4kWh/kg - I > estimate the fuel input is in the order of 8 to 10kW. > > Of course, with a traditional stove, so much of the heat energy is lost up > the chimney, and goes to create the draft. The efficiency of the stove, > might be in the region of 50% - somewhat better than the open wood fire. > It occurred to me that by way of a 2 stage gasification process, it would > be possible to increase the overall system efficiency, resulting in less > wood consumption, or more heat output per log. > > This leads to a question - is it possible to design a gasifier aimed at > handling whole log gasification - where a log is 10" long and no more than > 6" across? Can you recreate the temperatures, turbulence and reactants, > found within the combustion zone of the woodstove, and use this to > thermally process a single firewood log, at the rate of one every 30 > minutes or so? > > I've had some ideas on how this can be done, effectively using a length of > 6" diameter stovepipe/fluepipe to make a compact gasifier. Logs would be > loaded in from the top, and the length of the pipe chosen to perhaps hold 4 > logs at any time - about 1m (40") tall. The bottom log would sit in the > combustion zone - so the end of this log is constantly under the action of > the air nozzles. The logs above are subjected to the elevated temperatures > and begin to pyrolise, char and split on their descent down the tube. > > Beneath the combustion zone would be a fairly conventional hearth, and > reduction zone, with the char supported by a grate below that. For an > overall idea of the system - think of HS Mukundas open top gasifier. > > Use of twin-wall stainless flue pipe would allow the air to be pre-heated > in the outer annulus - adding to the overall efficiency. The hot syn-gas > could be burned in whatever appropriate burner geometry deemed necessary > for either radiant space heating or water heating with a suitable heat > exchanger coil. > > I hope to try to build a prototype of this over the next 10 days (a > working gasification holiday?) and to see whether a log can be reduced in > this manner. If all that is needed is heat, then the restrictions to > produce a tar free gas need not apply. If one can use whole logs, without > having to resort to woodchip - then this will be a considerable saving in > mechanical handling and wood processing. > > At the end of the day - this gasifying stove needs to be as simple to > operate as the existing woodstove. Reloading with a couple of logs each > hour, and no sophisticated need for fan- forced draft or electricity to > operate. Draft would come from the chimney as per now - about 25 to 30 > feet, 6" diameter. > > If anyone has experience of something similar - please let me know. > > > Happy Holidays > > > > Ken > > > > > > _______________________________________________ > Gasification 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/gasification_lists.bioenergylists.org > > for more Gasifiers, News and Information see our web site: > http://gasifiers.bioenergylists.org/ > >
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