[Gasification] Empirical data on dryer systems

[Mark Ludlow]

> To Mark L.: the big drawback of counter-current drying with hot air
> stream is a bigger fire hazard. Please explain your vision regarding
> possible fire hazards. 

Hi Erik,

Perhaps we are envisioning different scenarios. While I don't necessarily
agree with your assumption about the 'big drawback', I think the very fact
that one would have an air stream hot enough to ignite wood would call into
question the source of this energy. I hope it's wood and not petroleum
based!

My assumption is that having a high-efficiency fuel drying system should be
a primary design constraint for gasifier systems. With higher dryer
temperatures comes the increasing likelihood of higher dissipative losses
across the dryer system boundary and assumed rates of drying that exceed the
ability of the wood substrate to transport water from its interior to its
surface where it can be evaporated. This can contribute to high exhaust
temperatures with lower water partial pressures than desirable and therefore
lower efficiencies.

In many places in the US wood reaches an equilibrium moisture content of
12-15% after exposure to ambient air. Passing warmed air or, better yet,
waste heat across wood with lots of surface area per unit of mass seems more
elegant than simply adding more driving potential without consideration of
concomitant losses in system efficiency.

Cheers,
Mark