Etude de la combustion de gaz de synthèse issus d'un processus de ...

Chapter 2
product syngas to match those optimal for the desired end-use, although, at added
complexity and cost. Specific applications are discussed in more detail below.
2.2.1 Power production
Electricity generation is carried out by ICE, Stirling engines or turbines. Fuel cells have
been proposed, but considerable development work is needed before these can be
seriously considered. Data are available for gas turbines and engines operating on
fossil fuels, but few robust data have been found on biomass-derived fuel gas
machines, owing to the unknown costs of modification and maintenance and machine
life.
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Essentially all biomass power plants today operate on a steam-Rankine cycle.
Biomass-steam turbine systems are less efficient than modern electricity coal-fired
systems in large part due to more modest steam conditions. The modest steam
conditions in biomass plants arise primarily because of the strong scale-dependence of
the unit capital cost of steam turbine systems-the main reason coal and nuclear steamelectric
plants are built at a large scale. Biomass plants are usually of modest scale
(less than 100 MW), because of the dispersed nature of biomass supplies, which must
be gathered from the countryside and transported to the power plant. If bio-electric
plants were as large as coal or nuclear power stations (500-1000 MW), the cost of
delivering the fuel to the plant would often be prohibitive. To help minimize the
dependence of unit cost on scale, vendors use lower grade steels in the boiler tubes of
small-scale steam-electric plants and make other modifications which reduce capital
cost, but also require more modest steam temperatures and pressures, thereby leading
to reduced efficiency. The best biomass steam-electric plants have efficiencies of 20-
25% (Bridgwater, 1995). In order to make higher cost biomass resources economically
interesting for power generation, it is necessary to have technologies which offer higher
efficiency and lower unit capital cost at modest scale. One technological initiative
aimed at improving the economics and efficiency of utility-scale steam cycle systems
would use whole trees as fuel rather than more costly forms of biomass (e.g.
woodchips).
Gasification with turbines
Gas turbines are noted for their efficiency; low emissions; low specific capital cost;
short lead times by virtue of modular construction; high reliability and simple operation
(Brander and Chase, 1992). Gas turbine integration with biomass gasification is not
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