The influence of different conditions on the sulfur-capture efficiency during fluidized-bed desulfurization was studied using both experimental and modeling methods. The effects of the temperature (∼1120 or ∼1200 K) and gas atmosphere (90% N2 or 90% CO2) were studied using one limestone type. The CO2 atmosphere increased the degree of conversion compared to traditional air combustion conditions using both calcination–sulfation and direct sulfation methods. The scanning electron microscopy–energy-dispersive spectrometry analysis of spent sorbent particles revealed different sulfation patterns in different conditions. The N2 atmosphere produced a network sulfation or core–shell sulfation structure depending upon the temperature. Direct sulfation produced a core–shell structure with a thicker sulfate layer. A uniform pattern was observed for many particles in the CO2 atmosphere using indirect sulfation. The experimental results were analyzed using a time-dependent one-dimensional particle model that can accommodate simultaneous reactions. The model was used to interpret the test results and to determine the magnitude of reactions and diffusion rates as a function of the radius and time. The development of a Thiele number, conversion curve, and conversion profile during the reactions was used to explain the observed results.

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Carbon capture and storage is a concept to reduce greenhouse gas emissions of energy production from fossil fuels. In oxy-fuel combustion, the fuel is burned in a mixture of oxygen and recycled flue gas. This generates CO 2 -rich flue gas from which the CO 2 is easily separated and compressed. Foster Wheeler Power Group is developing the existing design tools and process models of air-fired circulating fluidized bed boilers to implement specific features of oxycombustion. The validation data is produced from bench-scale and pilot-scale experiments at the VTT, Technical Research Centre of Finland. A three-dimensional circulating fluidized bed (CFB) furnace model is developed and applied by Lappeenranta University of Technology for predicting the effects of oxycombustion in full scale units. This paper presents concept studies and initial 3D modeling results based on a 460 MW e supercritical CFB power plant at Lagisza, and pilot-scale studies with flue gas recirculation demonstrating real oxygen combustion conditions.

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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