Jim, take a look into how coconuts are processed into "activated char" for britta water filters.
They use a screw type tube, on a revolving pyrolizer to "lock" air out of the system. Regards, Greg Manning Canadian Gasifier Ltd. On Sun, Sep 11, 2011 at 2:40 AM, jim mason <[email protected]> wrote: > On Mon, Sep 17, 2007 at 5:34 AM, Mark Loftin <[email protected]> wrote: >> Jim, >> I assume when you say "star" valve you also mean "rotary" valve. > > > i was looking around for info on rotary valves and found our old > thread on the topic. seems i was asking myself the same question 4 > years ago, and still don't see a good answer. > > here's some updates and links (as well as continuing dissatisfaction > with the solutions) that might be of interest. any new or improved > ideas for how to make this problem of air tight chunk fed less > horrible would be much appreciated. reading through the old thread > below was also helpful. > > > ------------------------------------ > > feed air locks are long known a sensitive and expensive piece of > machinery. the usual go to solutions are either rotary star vavles > or double dump flap valves. > > double dump valves are typically considered more forgiving and less > fuel fussy, but they are very large, usually in the upwards direction, > and the actuating mechanism can get complicated. you also need to > control the fill into them or the top flap will get stuck, and control > the stack up below, or the bottom flap won't open. > > rotary valves promise more compact forms and drive, without the need > to control fuel in feed, but always have the problem of fuel pinching > at the entry between rotor and housing. the second main problem seems > the high maintenance needed to keep the tolerances adequate for seal. > some of the more interesting ones use a tapered rotor in housing so > gap tolerance is an "easy" linear movement of the shaft inwards or > out. > > the pinching problem is most "easily" dealt with by only passing small > size solids through it, and or raw power to cut the fuel. both of > these routes are not attractive for feeding wood chips in small scale > gasification apps. > > two lesser used routes i've recently found that seem interesting- > > 1. controlling the feed rate to the rotary valve so the the Vs only > partially fill. > usually this is done with an auger feeding the rotary valve, but other > other methods are possible. either way it usually gets rid of the > passive feed from the overhead hopper into the rotary valve. here's > one nice example of an auger fed rotary valve: > http://www.heizomat.at/index.php?page=produkte&ucat=hackgutkessel&id=zellenradschleuse > anyone know of more of these? and yes, know you are back to having > to control the feed as in a double dump valve. > > 2. using an side feed rotary valve with a controllable cut to > similarly prevent the full filling of the star V. > > i only recently learned of this category of side feed star valves that > try to fix the pinch through changing the fill level of the V by fill > path geometry change. you can see some of these units here: > http://www.carolinaconveying.com/html/side_entry_rotary_airlock.html > > the idea is to get the fill to the side of the rotor on the upswing. > once the rotor vanes get angled up enough the material falls into the > V, which is set up before the V gets to the formal housing, and thus > the pinch issue at the edge is moot. no metering solution is needed > at the inlet. the outlet can still have a metering/overfill problem. > > either the side fill rotary or top fill rotary can have an added cut > ledge that helps to control the amount of fill into the Vs of the > rotor. this cut plate is set quite far above the rotor circumference > so it itself does not become a binding point. angle of repose is > assumed between the cut plate and rotor. > > you can see an example of a side entry rotary valve with a cut plate > on page 7 in the drawings in this pdf. > http://allpowerlabs.pbworks.com/f/Side%20Entry%20Rotary%20Valve.pdf > > looking at these geometries, i don't see any reason we can't use a > regular top to bottom rotary valve, and mount it on it sideways to the > desired angle. this will achieve the same cut off and gravity fill of > the V cups. to this we can then add a cut plate to further increase > fuel flow happiness. > > mounting a standard rotary valve on its side will complicate the > hopper and reactor flanges, but potentially less so than the major > cost of the more exotic side entry rotary valves. if we can use a > regular star valve, there are lots of cheap sources for them, as they > are commodity material handling tech around the world. whether their > maintenance is tolerable is another issue. > > neither will likely make a rotary valve suddenly wonderful, though it > might move things towards tolerable. > > anyone else have any other ideas and/or examples of interesting air > tight feeding systems? > > > j > > > > On Mon, Sep 17, 2007 at 5:34 AM, Mark Loftin <[email protected]> wrote: >> Jim, >> I assume when you say "star" valve you also mean "rotary" valve. We >> worked for some time to get a rotary valve to work as the ash remover >> for our pressurized downdraft units. The rep said that this type valve >> is commonly used in coal-fired boilers to remove slag and residue >> (pretty close to the gasifier residue removal service). The valve was >> well made and easy to tear down and re-build. However, in gasification >> residue removal service, the basic problems we ran into were: >> >> 1. Unburned feedstock (chip) falling into the valve during start-up and >> jamming the rotor, >> 2. Overheating and seizing (galling) during start-up when hot embers >> were flowing through >> 3. Never a good positive seal due to need for relatively precise >> temperature control (thermal expansion and low machining tolerances are >> the "seal") >> >> We're still thinking of ways to use these type valves since their design >> and simplicity just seems too inviting for this service. Possibly some >> combination of rotary valve with a good-sealing flap valve might work in >> residue service. They probably are a better "fit" on the feedstock end >> since the temps are cooler. In this service, you could get a flexible >> rubber piece installed on the end of the blades to form a better seal. >> As I recall, the price was around $3,500, which to us was acceptable >> since this was for commercial equipment. We've since moved on to a >> "double flap" valve design for this service. >> >> M. Loftin >> >> jim mason wrote: >>> what is the collected wisdom here on sources for star valves? >>> >>> granular fuel handling and ash/char handling often requires star >>> valves to maintain air seal while moving solid material. i have not >>> been able to find common installations of these elsewhere for >>> repurposing in gasification. the ones i do find from general >>> industrial supply sources are terribly expensive. >>> >>> there must be lots of these used in ag and food processing that are >>> more resonable. >>> >>> anyone have leads or experience to offer? >>> >>> jim >>> >>> >>> -------------------------------------------------------------------------------- >>> jim mason >>> website: www.whatiamupto.com >>> current project: mechabolic (http://www.mechabolic.org) >>> announce list: http://lists.spaceship.com/listinfo.cgi/icp-spaceship.com >>> >>> _______________________________________________ >>> Gasification mailing list >>> [email protected] >>> http://listserv.repp.org/mailman/listinfo/gasification_listserv.repp.org >>> http://gasifiers.bioenergylists.org >>> http://info.bioenergylists.org >>> >>> >>> >> >> _______________________________________________ >> Gasification mailing list >> [email protected] >> http://listserv.repp.org/mailman/listinfo/gasification_listserv.repp.org >> http://gasifiers.bioenergylists.org >> http://info.bioenergylists.org >> > > > > -- > ------------------------------------------------------------------------------ > 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 > > _______________________________________________ > 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/ > -- Regards, Greg Manning, Brandon, Manitoba, Canada _______________________________________________ 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/
