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Combined cycle power plants with additional coal firing and catalytic combustion of unburnt fuel

The exhaust gases from gas turbines are at high temperature and contain significant levels of oxygen. These gases can therefore be used subsequently for coal combustion. This project carried out laboratory scale experiments and modelling assessments to demonstrate that, even with the low oxygen levels of modern gas turbines, the combustion of coal is possible. In addition, unburnts can be reduced by catalytic combustion and high levels of efficiency can be achieved.

The feasibility of using turbine exhaust gas as vitiated air for coal combustion was investigated and studies were made into coal combustion with vitiated air at laboratory scale. Further laboratory scale investigations were carried out to develop catalyst materials for the combustion of the remaining unburnt components in the flue gas. A computer model could then be designed that simulated the action of a pulverized coal burner using vitiated air. Finally a feasibility study was carried out that identified opportunities for optimizing the efficiency of the combined cycle power plants operating with pulverised coal and catalytic oxidation. This study also assessed the potential amount of carbon dioxide reduction. In the extensive coal combustion experiments that were carried out, pyrolysis occurred in 3 independent steps, where each step could be described by a complex n-th rate equation. Variations in the oxygen content and the heating rate had a significant influence on the combustion and burn-out of the coal. From these results, a combustion model could be derived with parameters that were applicable to high heating rates. Catalysts were successfully identified that could oxidize carbon monoxide and propane in unburnt flue gases completely, but no catalyst could oxidize methane or solid carbon. The results were applied in computer modelling of the combined cycle with vitiated air to identify optimum operational cycles.

Reported by

Technische Universität Braunschweig
35 Franz-Liszt-Strasse
38106 Braunschweig
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