European Bio-Energy Projects

NESSIE
Objectives
The project aims to develop a new robust
and reliable biomass-based CHP system for
small and medium ranges (< 10 MW rated
thermal capacity), which can be operated
with both bulk and baled biomass.
The new combustion system should lead
to an investment cost reduction of min.
33% compared to conventional grate-fired
boilers, due to the simple construction of
the boiler without refractory material and
mechanical moving parts within the firing
zone. A reduction in operation costs can
be expected from short start-up time
(reduced fuel stock), low stack loss and
more complete combustion, even in
the case of inhomogenities.
Improved demand-side management should
lead to a complete new district heating
system with fewer losses in the heating
grid and a smaller boiler for a maximum of
full-load operating hours.
New small-scale combustor
based on baled biomass
Challenges
In the small and medium capacity range the
most important technical challenge is the
conception, design, construction and testing of
a prototype of a new high turbulence combustor
for biomass bales of different fuel types, in
order to obtain evidence that the combustion of
bales can be reached without prior size reduction.
As regards the compactness of the combustion
chamber, the new system approaches that of
high-performance gas- and oil-fired burners.
Another problem addressed is the question of
appropriate fuel supply. The new concept
encourages a supply of baled biomass cultivated
in the nearest vicinity of the CHP plant, resulting
in lower procurement costs and emissions due
to transport.
A number of thermodynamic cycles have been
suggested for the small to medium power range,
with the conventional steam (Rankine) cycle
ranking first as regards a maximum yield in heat
and power, but with relatively low electric
efficiency, compared to fossil-fired steam cycles,
because of limitations in both the steam
temperature and the steam pressure. The
proposed new ‘modified’ Rankine cycle will be
tested in simulations (scale-up study).
The state of the art in district heating systems
is to design the combustion plant for the
expected heat demand of the supplied system,
where the peak demand is covered by an
additional, usually fossil-fuel-fired, system in the
central or in the distribution net, and the
dimensions of the distribution system pipes
have to be designed for peak demand.
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Larger dimensions bring about more investment
costs and greater losses in the system during
part- load operation, while the operation of the
combustion system off the rated parameters
causes higher emissions and operating costs.
A novel decentralised heat accumulation system
with added new functionality enables the use of
the maximum heat content of the house substations
(hot-water tanks) as integrated
decentralised buffering installations for district
heating systems to compensate for the time
between energy supply and consumption, with
loading and unloading controlled by the central.
Five major technological risks have been
identified as well as appropriate countermeasures:
melting point of the ashes, humidity
of the biomass, chlorine content of the biomass,
recycling of the ash, and improper functionality
of the demand-side management installations.
Project structure
The project is being carried out by companies and
research institutes from Austria, Germany, Poland
and Denmark. The project consortium groups
experts in energy-supply management, cultivation
and biomass quality, combustion technology,
manufacturing of boiler components, power-plant
construction and operation, and energy supply
control software technology. The broad European
dimension will contribute to shortening the time
to market and to the dissemination of the results.
The work comprises three parts, the most
important being the design, assembling, testing
and optimising of the pilot plant. In addition, a
variety of energy crops that can be supplied as