Ikelic - Alliance Digital Repository

GENERAL
VERMONT BIOMASS GASIFIER WILL USE
BATTELLE DESIGN
A 200-ton per day biomass gasification plant is
under construction at the McNeil generating sta
tion in Burlington, Vermont. Potential feedstocks
for the gasifier include wood waste, crop
residues, yard wastes and energy crops. The
project will be carried out in two phases. In the
first phase, a 200-ton per day gasifier based on
Battelle technology will be constructed and
operated at the McNeil site. The product gas will
be used in the existing McNeil power boilers. In
the second phase, a gas combustion turbine will
be installed to accept the product gas from the
gasifier and form an integrated combined cycle
system.
The design and development of the Battelle
biomass gasifier was described by M. Paisley of
Battelle and R. Overend of the National Renew
able Energy Laboratory at the 13th EPRI Con
ference on Gasification Power Plants, held in San
Francisco, California in October.
The development of the indirectly-heated Battelle
High Throughput Gasification Process was in
itiated in 1977. Detailed process development
activities began in 1980 with the construction and
startup of a Process Research Unit (PRU) at
Battelle's West Jefferson, Ohio Laboratory.
Process Description
The Battelle biomass gasification process
produces a medium-BTU product gas without the
need for an oxygen plant. The process
schematic in Figure 1 shows the two reactors
and their integration into the overall gasification
process. This process uses two physically
separate reactors: 1) a gasification reactor in
which the biomass is converted into a medium-
BTU gas and residual char and 2) a combustion
reactor that burns the residual char to provide
heat for gasification. Heat transfer between reac
tors is accomplished by circulating sand between
the gasifier and the combustor.
1-12
The gasification process utilizes circulating
fluidized-bed reactors to take advantage of the
inherently high reactivity of biomass feedstocks.
The reactivity of biomass is such that through
puts in excess of 3,000 pounds per hour per
square foot can be achieved. In other gasifica
tion systems throughput is generally limited to
less than 200 pounds per hour per square foot.
As an added benefit, the high heatup rates pos
sible through indirect heating with a circulating
sand phase along with the short residence times
in the gasification reactor effectively reduce the
tendency to form condensable tar-like materials
which results in an environmentally simpler
process.
According to Paisley and Overend, the basic
uniqueness of the Battelle process compared to
other biomass gasification processes is that it
was designed to exploit the unique properties of
biomass while the other processes were either
developed for coal gasification or were heavily in
fluenced by coal gasification technology.
Several characteristics of the process and the
resulting benefits are:
- Constant
High Throughput-ln excess of
3,000 Ib/hr-ft2. A 200-dry-ton per day
facility
will have a "footprint,"
excluding
biomass storage, of approximately
20 feet by 30 feet and will utilize a gasifier
less than 3 feet in diameter.
Fuel Flexibility-The process has been
demonstrated with a wide range of
biomass fuels including sawdust, wood
chips, shredded bark, hog fuel, refusederived
fuel, and energy plantation crops
such as hybrid poplar and switch grass.
Gas Heating Value-By cir
culating
hot solids between the gasifier
and combustion reactors, it is possible to
produce a medium-BTU gas without re
quiring
oxygen in the gasifier. The cir-
THE SYNTHETIC FUELS REPORT, JANUARY 1995