[Gasification] Re Chip drying without pyrolysing

James Joyce james at jamesjoyce.com.au
Mon Jan 27 00:58:26 CST 2014

I will weigh in with my 5 cents. I have seen and operated a lot of different dryers on a lot of different biomasses and have done a lot of "make do with whatever you can" drying for testing purposes. If I was asked for a generic or fool proof set of parameters I would say:

1. Drying air (or steam) at not more than 130 deg C (270 deg F). Anyone trying to dry using a drying medium at more than 140 deg C is asking for trouble and can only avoid it with active process controls and appropriate system design to manage the risks.

2. Maintain a superficial velocity of at least 0.025 metres per second (1 inch per second) around the particles ... by flowing gas through a static bed or tumbling the biomass through the gas.

The reason for 1 is that you cannot get ignition or torrefaction at 130 deg C (unless you dry it for weeks and get spontaneous combustion... and if you have to do that you obviously didn't have condition 2 right).

The reason for 2 is that heat alone will not move humid air or vapour out of a deep pile (deep being anything more than 10 times the mean particle diameter). If you do not have some velocity you will get recondensation in many cases.

Of the two items, relative gas flow is the most important. I have seen shipping containers of wood chip dried from 50% moisture to under 20% in a matter of days using ambient (30 deg C) air with 70% relative humidity at the inlet end. Admittedly the same job can be done in under 30 minutes in rotary drum dryer at 130 deg C ... but I guess the point is that provided you have gas flowing past the particles for long enough the humidity will depart until you reach the equilibrium moisture for those conditions (5 - 12 wt% for most biomass under moderate atmospheric conditions ... ie. 3 to 35 deg C).



Date: Sun, 26 Jan 2014 01:04:15 +0000
From: Thomas Koch <tk at tke.dk>
To: Discussion of biomass pyrolysis and gasification
	<gasification at lists.bioenergylists.org>
Cc: Discussion of biomass cooking stoves
	<stoves at lists.bioenergylists.org>
Subject: Re: [Gasification] Chip drying without pyrolysing; Biocoal
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If you blow some air up through the chips pile it becomes much easier

Thomas Koch

Fra: Gasification [mailto:gasification-bounces at lists.bioenergylists.org] P? vegne af darius_tamizi
Sendt: 26. januar 2014 01:57
Til: Discussion of biomass pyrolysis and gasification
Cc: Discussion of biomass cooking stoves
Emne: Re: [Gasification] Chip drying without pyrolysing; Biocoal manufacture.

Drying static rawwoodchip pile with heat is almost impossible.

With temp lower than 150C, water vapor condense before leaving the pile.

With temp higher than 150C, you will get fire from the drychip at the bottom

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