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Pre-drying of moist fuels for power production

The overall motivation to undertake this research project was to contribute to the reduction of the greenhouse gases emission primarily carbon dioxide from power plants firing solid fossil fuels, in particular, low rank, high moisture fuels such as peat, brown coal and lignite. These fuels are one of the backbones of primary energy supply in various countries of the European Union as well as of Central and Eastern Europe which is mirrored by the fact that one fifth of the world's production is mined in those regions. In the industrial conversion of these fuels process improvements are expected to substantially alleviate any hazardous impact on the regional and global environment.

Therefore, a consortium comprising of nine partners from industry and universities including three partners from the Newly Associated States (NAS) concentrated on increasing the efficiency of power generation, maintaining boiler availability and reducing emissions from high-moisture fuels by investigating and applying cost effective pre-drying technologies during the project.

The experimental and theoretical investigations focused on different drying techniques and advanced pulverised fuel combustion methods. Fuels of six different countries were extensively analysed and characterised by standard and advanced methods prior to pre-drying by different drying techniques such as a directly and indirectly heated atmospheric fluidised bed dryer (10 kg/h), a pressurised steam dryer (22 bar / 5t/h), an ultra sonic dryer and a newly developed crusher dryer (500 kg/h). As an important result technological and fuel dependent improvements for the industrial implementation were proposed.

Combustion investigations with raw and pre-dried fuels towards ignition, burnout and emission behaviour as well as operational problems such as slagging and fouling and the utilisation of the ash in e.g. cement production were performed in facilities ranging from laboratory scale at 20 kW via 500 kW up to full scale boilers 300 MW. One important result was that NOx emissions as low as 200 mg/m{3} were achieved with pre-dried fuels, thus, omitting any additional flue gas treatment for complying with emission standards.

Furthermore, the process calculation of several concepts showed that the integration of the pre-drying technology into low rank fuel conversion offers a high potential to increase plant efficiencies and thus to substantially reduce the CO(2) emission by such a fuel treatment.

Several fuel and process dependent design and operation parameters were developed. Concluding it can be stated that based on the results the design of a full-scale demonstration plant is feasible prior to industrial application of such a pre-treatment for low rank solid fuels.

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Universität Stuttgart
Pfaffenwaldring 23
70569 Stuttgart
Germany
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