[Gasification] rotary valve sources/experience?

Bob Stuart bobstuart at sasktel.net
Sun Sep 11 03:08:35 CDT 2011

Perhaps a useful variation would be an air-tight feed hopper, so that  
combustion might get upset just once a day, with a human to deal with  
any problems.  The interruption could be kept quite brief if things  
were made for a rapid reloading process.

Bob Stuart

On 11-Sep-11, at 1:40 AM, jim mason wrote:

> On Mon, Sep 17, 2007 at 5:34 AM, Mark Loftin <moloftin at comcast.net>  
> 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 <moloftin at comcast.net>  
> 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
>>> -------------------------------------------------------------------- 
>>> ------------
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> ---------------------------------------------------------------------- 
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