OxyFuel combustion is discussed as one of the key technologies for the efficient separation of CO2 from combustion of fossil fuels (especially coal). Since coal plays only a minor role as primary energy source in Austria, the broadening of the scope towards OxyFuel of other fuels like biomass or waste fuels is necessary to reduce greenhouse gas emissions from Austrian energy sector. The investigation of OxyFuel technology for alternative fuels besides the large coal-oriented projects is interesting also from the strategic point of view. The presented project aims at the generation of knowledge in order to design and operate capture ready co-firing and waste/sludge incineration plants.
OxyFuel does not use air with its fixed O2 content as the oxidation agent but a synthetic mixture of pure O2 and recycled exhaust gas where the O2 content may be varied. This means an additional degree of freedom and allows improved operation especially for low calorific fuels. During sewage sludge combustion the addition of heavy fuel oil can be omitted when using oxygen enriched air. If the quantity of air-nitrogen into the process is reduced, the exergetic efficiency of the process increases. If N2 is largely omitted the formation of thermal NOx can be avoided.
Fuels are selected with respect to the technical potential on the European market and with respect to basic physical properties. The selected fuels are investigated by using standardised analytic methods. It is expected that wood and waste wood, different municipal waste fractions as well as sewage sludge are among the fuels to be investigated.
An existing 100 kW fluidized bed laboratory installation for OxyFuel combustion will be retrofitted in order to allow the supply of the alternative fuels. Experiments with different fuels will be carried out on the 100 kW installation. Variation of operating parameters covers the operating temperature, the O2 content in the oxidation gas, the O2 content in the exhaust gas (air ratio), the solids circulation, and, along with load variations, also of the fluidisation regime.
On the basis of the experimental results, semi-empiric correlations can be formulated. These correlations can be used as model equations and allow a predictive simulation of the laboratory installation. The model of the OxyFuel fluidised bed reactor will be validated by experimental data and will be available as engineering tool for further activities.
A techno-economic assessment of retrofitting an existing industrial sewage sludge combustion facility together with the clarification of legal issues with the responsible authorities will be carried out. It provides the basis for the decision whether the actual retrofit will be undertaken following this project. Besides of that, the results will represent a case study for the economics of capture-ready combustion facilities in Austria.
Werner Höltl M.Sc
Vienna University of Technology
Institute of Chemical Engineering
tel.: +43 (1) 58801 159 82
fax: +43 (1) 58801 15999
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