Economic Issues of Biomass Energy Conversion - Biomass Gasification, Pyrolysis and Torrefaction - page 39

2.3.5 Pyrolyzer Cost
Based on a large number of data, Bridgwater et al. (2002) developed the fol-
lowing two empirical correlations for fast pyrolysis reactor, feeding system,
and liquids recovery.

0 : 6194 in euro

TPC 40 : 8 ð 1000Q Þ ð reference year 2000 Þ

5

where Q is in kilogram oven dry ton of prepared wood per hour.
Electricity may be generated of using pyrolysis oil in a multifuel diesel
engine-generator set. Capital cost for this is correlated (Bridgwater et al., 2002)
as below:

0 : 954 in euro

: ð

P e ; gross Þ

ð Þ

TPC 5 903 1 reference year 2000 (2.4)

where P e,gross is gross generator output in MW e .

2.3.6 Comparison of Capital Costs
Electricity generation from biomass has three options: gasification based com-
bined cycle, combustion based steam cycle, and gasification based gas engine.
In an IGCC option, biomass is gasified into combustible gases, which are
cleaned and burnt in the combustion chamber of a gas turbine cycle, which
operates a gas turbine. The exhaust gases from the gas turbine carry substantial
amount of sensible heat that is enough to generate high-pressure steam when
cooled downstream. The high-pressure steam drives a steam turbine. Both tur-
bines (gas turbine and steam turbine) drive generators to produce electricity.
Such plants are generally used for capacities in excess of 100 MWe. These are
expensive in absolute terms but have high energy conversion efficiency.
The next option is direct combustion of biomass in a boiler and to run a
steam turbine with this steam to generate electricity based on Rankine cycle.
Such steam plants are used for intermediate-sized plants.
The third option involves gasification of biomass in small gasifiers. The gas
is then cleaned and used in a compression ignition engine. Such gas engine
plants are generally used in small capacities especially in remote locations.
Table 2.4 gives the specific capital cost (cost per kW installed) of above
three options for electricity generations from biomass. Gas engines that are
used for smaller than 5 MW capacity has low absolute capital cost but excep-
tionally high specific capital cost. In general, a sharp decline in the capital
cost is noted between 5 and 20 MWe capacities. The specific capital cost
reduced at a much gentler pace between 20 and 100 MWe capacities. For
that reason, the electricity generation cost reduced from 20 to 5 cents/kWh
(1994 dollar and biomass cost $50/ton (dry ash free) while the IGCC plant
capacity increased from 5 to 100 MWe (Bridgwater, 1995).