[Gasification] Wood Chip classificaton

[Luke Gardner]

Greg,
I like it, there is certainly more than one way to skin a cat.
I was leaning toward auguring up and out of a receiving hopper to a very 
slow moving and long declined trommel that has sections of screen to drop 
the fines out early on, and have airflow (salvaged heat) blown through the 
trommel opposite the flow of the wood to carry the moisture away.
I would agree that the passive approach takes about a full day of good 
solar...  10 hours if the layer is thin enough.
I found by scattering them on a tarp (for easy collection) that the top 
surface nearly "flashes"  off dry very quickly.  and then some hours later 
in  good summer sun,  if you pick a chip up it is dry on top and there will 
be condensation hanging out below it on the tarp, and its back will still be 
wet.  It's like they beg to be flipped over and placed somewhere else.  I 
believe that with minimal agitation (slow tumbling) in a thin migrating 
stream they could be dried rather quickly.
anyone?
Luke



-----Original Message----- 
From: Greg Manning
Sent: Saturday, April 14, 2012 5:23 AM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] Wood Chip classificaton

Good Morning All.

This is getting interesting.


I spoke with Pete a while back about this, and need to correct a
statement I made to him.

"correction the fines (under 3/16" bits) do need to be sifted out"
this was about a statement I made to him on the phone, about this
thread.

As far as drying wood chips, 3 things I have found are:

1) Sifting the fines before storage (even green) does promote faster
drying (this is relative as they still take a long time to dry).

2) The "top" about the first 2-3 inch layer of chips in a screened bin
dry quite quickly (days) where as the stuff at the bottom NO drying
action has taken place.

3) Removal of that "top layer" of dry chips to another area does
indeed cause the next 3-4" layer to dry quickly as well, and so on if
removed, as they dry.

I've studied this problem in depth, and have a somewhat simple
(ya-right) method of drying.

Sun, I'm in the process of designing a "sun lift", where as chips are
augured to an inclined day lift, the lift consists of  a wide belt (48
inches) that is inclined on just slightly less than the angle of
repose for the chips (about 30 degrees from horizontal), AND/OR, has
ledges that a small thin layer of chips rest on. This lift is some 12
feet tall, and once the chips reach the top they are captured in a
covered trough that connects to a chute that sends them to a second
storage area.

Here's the thing, the lift is rain protected, and has a sheet of clear
glass or plexiglass covering the area exposed to the sun.

The process ONLY runs during warm sunny days, and at that, the chips
entering the bottom take the entire day (10 hours) to reach the top.

using a light meter sensor that only triggers the units operation once
the sun gets to "X" brightness (cloudy days would not trigger the
unit).

Preliminary findings are that sample configurations of chips sitting
as a thin layer on a sheet of plywood (with the 30 degree inclination)
take about 6-7 hours to be "bone dry" in the sun with a small flow of
air from the base upwards (chimney effect) I simply used a couple of
2x6's on the sides to support a plexiglass cover and a bathroom
exhaust fan to provide the airflow.

This was a test "mock-up" to simulate the slow moving "belt" system I
am thinking of.

the chips that where placed on the board in the morning where 45+%
moisture green, a the end of the 7 hours, they where very "crisp" to
the touch, and snapped with a loud "crack" (indication of being very
dry) when pinched sideways, tested end of cycle moisture was under
13-15%. the layer was rough, but for the most part, I would say 2-1/2
inches thick.
extrapolation of the cost to do this is based on the following:

1/4 HP electric motor running for 10 hours a day at 10 cents a
kilowatt (I pay less than that, but know that some areas pay more) MY
sample motor under load uses 2.5 amps to work, therefore 2.5amps times
115 volts equals 288 watts/hour (VA's close enough) so say 4 hours
costs 10 cents or 25 cents a day, times 31 equals $ 7.75 a month (
I've rounded up on the costs, as to cover the cost of the bathroom
vent fan also).

Because the system runs so slowly the 1/4 hp motor (through two 60:1
reduction units one feeding the other) should develop enough torque to
run the belt and in-feed auger both. the output is gravity and I make
the assumption that someone would check on the unit at least once
every 2 days.

Greg Manning

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