[Gasification] a proposed mobile gasifer concept

[Daniel Chisholm]

Comments on this idea appreciated.  It's from my "go after the low
hanging fruit" file...

There could be money to be made if you can save a lot of diesel fuel
used in the industry trucking by means of using producer gas.  I think
it is important to observe that there's no need to replace 100% of the
diesel fuel used in each and every truck.  Replacing a good fraction
(30%? 70%) of the fuel oil used by each truck is good enough to build a
business case on.

Trucking is a far more attractive application than passenger cars,
because each installation operates more hours per year, and each
installation uses more power.  So the per-unit dollar savings are
greater, which allows a relatively complex and costly producer gas
system to be more easily paid for.

Reducing the fuel consumption of my VW diesel Golf by 60% would save me
1440L of diesel fuel per year (60% time 40,000km times 6L/100km).  OK,
that's worth (round numbers) about $1500/year to me.  Even if the
gasifier's fuel, operating and maintenance costs are zero (talk about a
best case!), it will be a hard sell indeed to convince me that the
breakeven point of such a gasifier is north of $5000.

But what about saving 35%-50% of the fuel burned by a transport truck
that drives 100,000 km/year and burns 20L/100km.  That is an annual fuel
savings of 7000L-10,000L/year of diesel fuel.  At a buck a litre, this
will pay for a much more expensive gasifier than in the passenger car
scenario.

Consider this application:

        - Design a mobile gasifier that produces enough gas for about
        50hp of mechanical power output.
        
        - Optimize it for constant load - it's OK for it to have two
        modes only:
                - idle (flaring gas)
                - design load.  Steady, constant gas output (enough for
                30hp).
        
        - Mount this on a transport truck, which has (say) a 350hp
        engine but an average power requirement of 60hp.  When the
        gasifier is in "on" mode, a computer permits 0-100% of the gas
        to flow into the diesel's intake air stream.  The balance of the
        gas is flared, so the gas generator always sees a steady load.
        
        - The engine's first 50hp is provided by diesel-piloted producer
        gas.  Injector fuel flow stays at idle volumes, producer gas
        flow is controlled from 0-50hp worth.  The unused portion of the
        gas flow would be flared.
        
        - Up to (say) 100hp of power demand, keep feeding that 50hp of
        producer gas, but increase the fuel flow to the diesel
        injectors.
        
        - Above 100hp of power demand, start fading out the producer gas
        fraction, so that by (say) 200hp the fuel flow to the engine is
        100% diesel fuel.  This avoids high-load detonation problems,
        and does not require derating the engine.  Flare the unneeded
        portion of the producer gas.  As soon as max power demand goes
        away, can immediately switch back to pilot-fuelled producer gas.

I would suggest using pulverized charcoal as a fuel, rather than wood.
It has a higher energy density per unit of volume (which will be at a
premium), can be delivered in sealed containers, and pneumatically
conveyed and metered.  (Or instead of dry charcoal, could store it as a
pumpable water-based slurry)  The sealed containers would be loaded on
full of charcoal, and when empty of fuel they would be used to store the
ash that the gasifier produces.

I would suggest that the pulverized charcoal comes from a stationary
woodchip-fired boiler.  It's easy to burn the volatiles from biomass,
but it is difficult to completely burn the char.  Make a virtue of this
- just burn off the easy volatiles, and use your very carbon-rich
"ash" (nearly pure carbon) to produce pulverized charcoal motor fuel.

Pulverized charcoal (dry or slurry) would permit a high-density
grateless gasifier to be built.  Tar production and treatment would be
much simpler than with wood as a fuel.

That ought to be enough on this one for now...

-- 
- Daniel
Fredericton, NB  Canada