Page 327 - Synthetic Fuels Handbook

FUELS FROM WOOD 313

production as compared to only fermenting the glucose from the second stage. Other pos-
sible products from the first stage carbohydrates are single-cell protein, furfural, and feed
molasses.
Methanol was once produced from wood as a by-product of charcoal manufacture, but
overall yields were low. To produce methanol from wood with a significantly higher yield
would require production of synthesis gas in a process similar to that used for production
of methanol from coal. Such processes for gasifying wood are less fully developed than the
two-stage hydrolysis process for production of ethanol. Another consideration in produc-
ing liquid fuels from wood is the amount of wood available to manufacture the fuels. For
converting wood to liquid fuel, the most optimistic assumption normally used is that wood
could be converted to liquid fuel in the ratio of Btu in liquid fuel/Btu in wood = 0.5. At
least in the short run it would be difficult to find more than 100 million dry tons of wood
per year (1.7 Quads equivalent) for this purpose. This would calculate to be a maximum
of 13 billion gallons per year if the output was methanol and the energy content of a ton
of dry wood is assumed to be 17 million Btu. On the order of 11.5 billion gallons per year
would be needed if methanol were added to gasoline at the rate of 10 percent methanol to
90 percent gasoline.
Projections of wood use for energy to 2010 are modest. Currently, 2.7 Quads of energy
are produced from wood. Projections of the total for 2010 are about 4.0 Quads. This does
not provide for a total growth of even 1.7 Quads. However, if we really want to get serious
about doing something to deter atmospheric CO accumulation the availability of wood for
2
energy, including solid as well as liquid fuel, could be increased; up to 10 Quads per year
might be very realistic. This runs counter to decreased usage of wood for all purposes, par-
ticularly from the national forests, to provide more wilderness, habitat for threatened and
endangered species, clean water, and other environment considerations. However it must
be remembered that, in some cases, more harvesting and cleanup of residues is needed to
increase the vigor of forest growth, to protect the forest against wildfire, and to prepare
the soil for new growth. In many cases open broadcast burning of logging slash is being
outlawed, and harvest of this material for fuel instead of open burning is a viable option for
better forest management as well as for profit.

10.4.3 Solid Fuels
Burning wood as a fuel is the largest current use of biomass derived energy. Wood can be
used in many forms as a solid fuel for cooking or heating, occasionally for steam engines,
and steam turbines that generate electricity. The particular form of wood fuel used depends
upon (among other things) its source, quantity, and quality. Available forms include logs,
bolts, blocks, firewood, stove-wood (often from split blocks), charcoal, chips, sheets, pel-
lets, and sawdust. Sawmill waste and construction industry by-products also include vari-
ous forms of lumber tailings.
The use of wood as a fuel source for home heat is as old as civilization itself. Historically,
it was limited in use only by the distribution of technology required to make a spark. Wood
heat is still common throughout much of the world, although it has been mainly replaced
with coal, oil, or natural gas heating. Wood heating has been singled out as a serious health
hazard in many regions of the world.
Early examples include the use of wood heat in tents. Fires were constructed on the
ground, and a smoke hole in the top of the tent allowed the smoke to escape by convection.
In permanent structures, hearths were constructed—surfaces of stone or another noncom-
bustible material upon which a fire could be built. Smoke escaped through a smoke hole
in the roof. The development of the chimney and the fireplace allowed for more effective
exhaustion of the smoke. Masonry heaters or stoves went a step further by capturing much