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/
