[Gasification] Flash torrefaction ?

[Ken Boak]

Philippe & List

Thankyou for reminding me about the torrefaction process.

To me, it appearsthat the process is a means of reducing moisture content,
reducing volatiles and acidic compounds and increasing energy density by
between 15% and 20%.   It also make the wood chips more friable and more
easily crushed and mechanically handled.

My interest lies in the use of torrefaction as an intermediate stage between
drying and pyrolisis of woodchips.  Following torrefaction, not only is
there less moisture in the woodchips, but they also enter the pyrolisis zone
pre-heated to around 250 C to 300 C, which requires less energy from the
combustion zone to provide the energy for pyrolisis.

Whilst I do not know whether flash torrefaction would be viable, as it seems
that time spent in the torrefaction zone and the torrefaction temperature
are key to the success of the process,  I believe that there would be
benefit  in torrefying the woodchips at the rate at which they were being
consumed by the gasifier, as a continuous process, with every chip spending
30 to 60 minutes in the torrefaction zone.

My interest in wood gas for dual fuelling a slow speed diesel engine,
suggests that the exhaust gases from the diesel engine (about 400 C) could
be used for torrefaction, drying and air preheating, which would appear to
be a sensible use of the waste products of combustion.

The exhaust gases, being mostly nitrogen and CO2 with some CO, O2 and
particulates, would appear to be reasonably inert and suitable to provide
heat for the torrefaction process.  Any excess air in the diesel exhaust
could be passed through an incandescent charcoal zone to further reduce the
charcoal and increase the gas temperature.

Once the hot exhaust gases had passed through a column of woodchips, and
lost much of their thermal energy, and picked up the volatile products of
torrefaction, might there be an argument suggesting that these gases should
be further passed through a charcoal reaction zone to further consume the
volatiles?

I found this link to a paper regarding torrefaction as a means of upgrading
biomass

http://www.techtp.com/tw%20papers/upgrading_biomass.htm

regards,


Ken