Jim,
We built one for our boiler feed. It has a few features that some others
lack.
It operates in sync with the conveyor above. It has a clutch drive. If
it jams a sensor stops it and the conveyor in less than a second. it
then goes through 8 reversals before triggering an alarm or until it
frees up and restarts.
The steel portion of the rotor has about 3/4"-1" clearance to the
housing. A slightly over full sized peice of 1/8" (300F) rubber is
sandwitched to the rotor and forms a flexible seal. I don't know the
pressure limits or the leakage rates. The bottom quadrant or 75 degrees
of the housing expands out to release any edge jams. I change the rubber
every two years, ~600 tonnes/year.
Except for the odd alarm (0-4/year) where we have to remove a long
piece, or the occasionally adjustment to the clutch slippage, it has
been trouble free. I can't say that for most devices around here.
Alex
On 9/11/2011 3:40 AM, jim mason 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
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