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The 1 st generation oxyfuel CFB (Circulating Fluidised Bed) technology has been demonstrated up to 30MW th scale and the commercial concept for 300 MW e air/oxy flexible CFB power plant is available. Currently, the development of 2 nd generation oxyfuel CFB technology is ongoing aiming to reduce significantly -around 50% -the overall efficiency penalty of CO 2 capture in power plants compared to 1 st generation concepts. The 2 nd generation oxyfuel CFB plants are designed only to oxyfuel operation with CCS.The experimental results of the test campaigns with 0.1 MW th pilot scale CFB unit and laboratory scale BFB (Bubbling Fluidised Bed) unit under high oxygen concentrations of feed gas are presented. The pilot scale tests were carried out with Spanish anthracite and petroleum coke mixture and with Polish bituminous coal. Two Spanish limestone types were used for infurnace sulphur capture. Test matrix of pilot scale CFB unit contained 11 test balances with varying feed gas O 2 concentrations (between 21…42 vol-%) and O 2 staging to primary and secondary gas feeds (primary gas O 2 share 50…80 vol-%) at different bed temperature levels (820…920ºC). Combustion performance and emission formation was studied at air combustion and varying oxyfuel combustion conditions.The fuel impulse tests with laboratory scale BFB included 16 tests with Spanish anthracite and Polish bituminous coal in varying feed gas O 2 concentrations (5…50 vol-%) with two fuel size fractions (0.5-2.0 mm and 4.0-8.0 mm) at constant bed temperature level (850ºC). The main objective was study how high O 2 concentration effects on char reactivity and formation of nitrogen oxide emissions.Toni Pikkarainen et al. / Energy Procedia 63 ( 2014 ) 372 -385 373 A one dimensional model for laboratory scale BFB was used to further develop existing sub-models' descriptions and parameters in the one dimensional model (1D-model) for pilot scale CFB in order to improve modelling capabilities in oxygen combustion conditions. Firstly the sub-models' equations for different phenomenon -e.g. pyrolysis, char combustion and reactions of nitrogen species -were implemented and validated with bench scale experimental data. Secondly, the sub-model parameters found in bench scale modelling for char reactivity and NO x formation were implemented to the 1D-model of pilot scale CFB combustor. According to the results of the validation modelling against pilot scale experimental results, the combustion was successfully scaled up as the modelled temperature profiles and flue gas oxygen contents were well in line with measurements. Anyhow, further validation of the combustion model is needed by modelling of dynamic responses of pilot scale experiments. The pilot scale 1D-model was not able to predict NO x formation with the sub-model adapted from the bench scale model. Further model development and experimental work are needed with different particle size fractions at different operating conditions. The improved modelling capabilities under high oxygen concentrations can be utiliz...

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A shrinking particle model with apparent reaction rate parameters is frequently applied in the modeling of burning of coal particles in boilers. In oxy-fuel combustion, the nitrogen in the gas atmosphere is replaced by carbon dioxide and water vapor, enhancing the burning rate by gasification. A shrinking particle model, including the gasification taking place inside the particles, is presented. Boundary layer combustion of CO reduces the burning rate of char because of consumption of oxygen, allowing for less to reach the particle surface. This is accounted by an effective Sherwood number. Analytical and numerical solutions for combustion of char and char inventory in the bed are extended to include the effect of internal gasification and boundary layer combustion of CO. Measured char inventories in air and oxy-fuel conditions in pilot-scale circulating fluidized-bed combustion are compared to calculated char inventories. The modeling results are also applicable for pulverized fuel combustion.