BioCoComb, Zeltweg, Austria
In the BioCoComb demonstration project, supported by the EC Thermie programme, a CFB gasifier for bark, wood chips, sawdust etc. was installed at the 137 MWe pulverised coal fired power plant of Verbund Austrian Hydropower AG in Zeltweg, Austria. The project team was formed by Verbund/Draukraft (Austria), ENEL (Italy), ESB (Ireland), EVS (Germany), Electrabel (Belgium) and Austrian Energy and Environment as the supplier of the gasifier. Scientific advise was given by the Technical University of Graz (Austria).
The process concept is based on the gasification of biomass (bark, wood chips, sawdust with a water content of 40-50%) in a fluidised bed. In this case, the air is fed to the system to exactly such an extent that part of the fuel burns and, while doing so, the heat is produced that is required for the gasification of the rest of the biomass, for the combustion of which not enough oxygen is available.
Because it is neither a matter of total combustion nor a matter of total gasification it is called partial gasification. The gas is led uncooled from the gasifier to the boiler, where it serves as auxiliary fuel and replaces part of the coal. Apart from the CO2-reduction, the NOx-reduction through „reburning“ is also of interest.
For integration into the power plant the fluidised bed gasifier is installed near the coal-fired boiler. In the gasifier the biomass is converted to gas that is then directly conveyed to the boiler via a hot-gasline as a second fuel. The partial gasification taking place in the reactor is sufficient respectively desired. Due to this process, pre-drying of the biomass and cleaning of the emerging gas is not necessary. Furthermore, this process can be used to reduce NOx-emissions, due to the fact that, with the aid of the gas, a second combustion takes place in the coal-fired boiler.
Investment Costs Co-firing Unit
The total costs for the BioCoComb project (engineering, biomass storage, conveying system, gasifier, connection to the coal boiler, commissioning and monitoring) were about 5.1 Mio. Euro. Assuming that the same project (10 MWth) will be replicated the total (investment) costs will be in the order of 3.7 Mio Euro. These costs include the preparation of the technical specifications, the tenders, the erection of the whole installation and the commissioning. For a commercial version of the project (100 MWth) the total (investment) costs will be in the range of 10 to 14.5 Mio Euro.
Status of the Installation
After the demonstration period the project can be referred to as very successful. The plant achieved stable operation with various fuels (bark, wood shavings, wood chips and also supplementary fuels) and showed an elastic behaviour regarding load changes, and with respect to the change of fuel quality, which is unavoidable in the case of biomass. Not only the ignition and gasification behaviour of the biomass in the gasifier fulfilled all expectations, also the combustion behaviour of the gas in the boiler. The process-engineering critical change-over from combustion to gasification mode and vice versa takes place gently, with only a slight temperature increase, which is within tolerable limits though. The quality of the gas is well-suited for co-combustion in the boiler.
In April 2001 the coal power station was conserved and it is, at the moment, not in operation, due to economic reasons. A restarting of the power station is possible, but depends on the future development of the electricity price.
Technical and Non-technical Barriers
As with most biomass/waste-fired units, operation of the Zeltweg CFB gasifier has proved troublefree. Inspection after the first demonstration period showed that the gasifier was in excellent condition, with no detectable damage. Also, as with most biomass/waste-fired units, problems arised in the preparation and feeding equipment. These were solved during the first demonstration period.
In Austria there was no subsidy for electricity produced by co-firing biomass in coal power stations until the end of 2002. This was the main reason that no co-firing installation was built in the last few years.