Numerous models have been developed in Aspen Plus for the combustion of different coal types in fluidized bed reactors. However, these models are case‐specific, particularly with respect to coal type and bed reactor type, implying limitations to general application of these models. Moreover, these processes were generally developed step‐wisely by employing a series of model blocks to simulate fluidized bed reactors in Aspen Plus. In this study, a novel hybrid approach for modelling coal combustion has been implemented to comprehensively design a model for conversion of low‐grade coal under various operating conditions. The proposed model combines sequential modelling of drying/pyrolysis (devolatilization) and combustion of coal by means of conventionally used units (RYIELD and RGIBBS), and a newly used unit (FLUIDBED) in Aspen Plus. The model validation was performed by experiments on the combustion of low‐grade coal in a pilot‐scale circulating fluidized bed reactor (CFBR). Experimental data were used to further calibrate the Aspen Plus model and decrease model uncertainties. The results obtained from the developed simulation model were found to be in good agreement with the experimental data. Discrepancies of less than 15% were observed, in most of the predictions of molar fractions for the resultant flue gas composition, including NOx and SOx, emissions which were at ppm levels. As a result, the model can easily be used for design, scale‐up, and simulation of coal combustion as well as for other feedstock like biomass in fluidized bed with process optimization based on sensitivity analysis.
Tropospheric NO 2 concentrations obtained from the measurements of the Ozone Monitoring Instrument on board the NASA Aura satellite from 2005 to 2016 were studied to identify major NO 2 emission hot spots, trends, and seasonal variations over Kazakhstan. Emission hot spots are observed over the locations of thermal power plants (Ekibastuz) and major urban and industrial regions (Almaty and Shymkent), as well as the capital city (Astana). Some decreasing trends have been observed for NO 2 over Ekibastuz, whereas the regions of Almaty and Shymkent showed increasing trends due to industrial growth. The seasonal pattern of the NO 2 concentration shows a difference between three industrial cities of Almaty, Shymkent, and Ekibastuz versus the rest of Kazakhstan. In these three cities, a NO 2 maximum is found during wintertime, which we attribute to seasonality of emissions associated with electricity production and the longer chemical lifetime of NO 2 in winter. In contrast, in Astana and the rest of Kazakhstan, the NO 2 concentration reaches a maximum in the summer.
Coal-conversion technologies, although used ubiquitously, are often discredited due to high pollutant emissions, thereby emphasizing a dire need to optimize the combustion process. The co-firing of coal/biomass in a fluidized bed reactor has been an efficient way to optimize the pollutants emission. Herein, a new model has been designed in Aspen Plus® to simultaneously include detailed reaction kinetics, volatile compositions, tar combustion, and hydrodynamics of the reactor. Validation of the process model was done with variations in the fuel including high-sulfur Spanish lignite, high-ash Ekibastuz coal, wood pellets, and locally collected municipal solid waste (MSW) and the temperature ranging from 1073 to 1223 K. The composition of the exhaust gases, namely, CO/CO2/NO/SO2 were determined from the model to be within 2% of the experimental observations. Co-combustion of local MSW with Ekibastuz coal had flue gas composition ranging from 1000 to 5000 ppm of CO, 16.2%–17.2% of CO2, 200–550 ppm of NO, and 130–210 ppm of SO2. A sensitivity analysis on co-firing of local biomass and Ekibastuz coal demonstrated the optimal operating temperature for fluidized bed reactor at 1148 K with the recommended biomass-to-coal ratio is 1/4, leading to minimum emissions of CO, NO, and SO2.
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