[Gasification] Empirical data on dryer systems

Sat Dec 9 12:46:29 CST 2006

Erik,

There is considerable experience in fuel drying among list members. It's
just a topic that hasn't been discussed much. People on this list who are
developing or providing small scale gasifiers for commercial use will
probably show you a picture of their dryer but not discuss the details. 

I can design one for you. That's what I do for a living. We have designed,
installed and fixed all kinds of fuel drying and processing systems since
the 1970s. (See: www.trmiles.com  )We have built feeders and dryers for
gasifiers and pyrolyzers from 250 g/hr to 40 tph. Just this week I was in
Montana with the engineer for whom we built our first gasifier fuel system
in 1976. Others on the list have similar experience.

You will find there are a variety of small scale dryer solutions. At a
hunting and fishing resort called Snowshoe in Northern Ontario the owner
used to generate heat and power using an Imbert gasifier. He claimed that
split cordwood simply dried in the extremely cold winter if he left it out
long enough. 

For your application a batch bin dryer or a small continuous belt dryer
would both be suitable. Small scale chip systems usually use batch dryers.
Or they use continuous dryers based augers, woven belts, moving floors or
vibrating conveyors with perforated plates. They are often custom built. 

Rotary drum dryers like the Barr-Rosin have been the most reliable for
industrial systems. They are usually very expensive at the small scale. Drum
dryer design and operation has changed significantly over the years. A major
cost in drying these days is emission control so exhaust gas is increasingly
re-circulated and indirectly heated systems are used.

Indirect and direct steam systems where exhaust vapor is recovered are
thermally the most efficient systems. The most innovative dryers have been
developed in Europe in recent years. These are very expensive for North
America. You will find a few systems like the GEA/Niro Exergy dryers in
Denmark and Sweden.

Flash or suspension drying is most suited to finely divided materials that
are handled in suspension. They are used for fiber drying and for peat or
other finely divided feedstocks that will typically be used in suspension
pyrolysis or gasification, or in fluidized beds. The morphology of fine
materials permits rapid heating and short residence times which are the
defining characteristics of flash drying. Some semi-mechancal flash drying
systems are now being promoted. One of my clients has a system I think would
be very suited to easily milled fuels at a small scale.   

Reports are available for several small scale drying studies for biomass
fuels that have been funded by the EU and in the US by US DOE and US
Department of Agriculture. If you develop a bibliography of these we can put
it on the web. 

Fuel selection, preparation, handling, sizing, drying and feeding are all
essential topics for gasification. A FUEL topic is something that is on the
list of things to add to the Gasification website but the site is only being
developed as time permits.     

There is information about dryers on the message archives and on the
website.  

You will find some messages referring to fuel drying by using the (Google)
search on the http://gasifiers.bioenergylist.org .

The general site search utility has been temporarily disabled due to server
problems. We expect to put it back sometime next week.

Regards,

Tom Miles

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Rodenhuis, E.J.
(Erik Jan, Student TBK)
Sent: Saturday, December 09, 2006 2:25 AM
To: gasification at listserv.repp.org
Subject: Re: [Gasification] Empirical data on dryer systems

Hey all!

Is this topic not worth considering a thought? I hoped to get some get
some ideas and figures about dryers. Couldn't find much discussion on
this topic in the archives Or do you just not have a clue ;-)

Erik

-----Oorspronkelijk bericht-----
Van: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] Namens Rodenhuis, E.J.
(Erik Jan,Student TBK)
Verzonden: donderdag 7 december 2006 13:46
Aan: gasification at listserv.repp.org
Onderwerp: [Gasification] Empirical data on dryer systems

Dear list,

For downdraught gasification of biomass generally is assumed that the
moisture content of the biomass is below 15% (wb). As the moisture
content of green wood is mostly higher and I have seen sawmills use
water-cooled band saws, you need to dry the wood waste before it is
suitable to gasify. Main options seem to be drum drying of flash/ring
drying.

Drum Drying:

-        Co-current to reduce fire hazard

-        Tair,in = 230 - 1100 degr. Celsius

-        Tair, out = 70 - 110 degr. Celsius

-        Empirical data on energy consumption 5 - 12 GJ/ton of water
evaporated, see poster presentation Mani:
http://www.biocap.ca/images/pdfs/conferencePosters/Mani_S_P1.pdf

-        General statements made in diverse publications: "high"
investment cost, "low energy use"

 Flash Drying

-        short residence time < 30 sec

-        drying at lower temperatures Tair,in = 100 - 650 degr Celsius

-        "low investment, high energy use"

A few other systems available:
http://barr-rosin.com/english/pdf/airstream.pdf 

As we have will have with a downdraught gasifier with an ic-engine some
low quality waste energy streams are available, namely from gas cooling
(gas-gas shell-and-tube heat exchanger) and from the exhaust gases, I am
interested to know what the general ideas about which drying system
suits best. There might be some other criteria like the controllability
of the process and fire hazards.

Maybe there is somebody who can give some rule of thumb for investment
cost and energy consumption of a 1 ton/h drying system. When assuming
that we want to dry the wood waste (let's assume chips) from MCwet 30%
to a moisture content of 15% we need to evaporate 115 kg H2O/h.

Any hints or leads to good literature on the web on this topic??

Regards,

Erik Jan Rodenhuis 