Development and validation of a novel process model for fluidized bed combustion: Application for efficient combustion of low‐grade coal

Abstract

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.

Flue gas analysis for biomass and coal co-firing in fluidized bed: process simulation and validation

“…In CFBR ash, char, and the bed material (inert sand) from the top of the riser is passed on to the cyclone, wherein the dense particles were separated from flue gases and were directed to the dense zone of the reactor for increased residence time and complete combustion. In this context, our work (on bubbling bed fluidized reactor) is not in complete correspondence with the earlier experiments of Saparov et al (2021). However, for biomass, the predominant fuel-S content is released during the devolatilization at low temperatures (Knudsen et al 2004).…”

“…In our previous work (Saparov et al 2021), properties of the Ekibastuz coal were measured according to ASTM requirements and modeled under combustion environment using basic kinetics. This type of bituminous coal is characterized as low-quality due to the high ash content of up to 40%.…”

“…Data from regression analysis was used in devolatilization units (DEVOLATC and DEVOLATB) using the RYield reactor to specify mass yields of devolatilization products. The designed process model was tested again with combustion of only Ekibastuz coal and the emissions of the four components were compared with those observed from the experiments of (Saparov et al 2021), wherein the reactor height was 7 m, diameter of 0.18 m and operating temperature of 1173 K (Table S7 in Supplementary Material), and as reported by us earlier. The results (Table 6) show a good agreement between the model prediction and the experiments.…”

“…In our previous work, we simulated combustion of lowgrade bituminous Ekibastuz coal utilizing the Aspen Plus using the fluid bed unit (Saparov et al 2021). The model was validated using the experiments on a pilot-scale circulating fluidized bed (CFB) coal combustion.…”

Special issue in honour of Professor Jamal Chaouki

“…We are pleased to report that 30 papers were initially submitted to the journal and after peer review, following the standard journal procedures, 28 papers were accepted. Due to the page limitation of each issue, we have decided to publish a full special issue with 16 papers as Part 1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and a special section in the coming issue (vol. 99, issue 12) with 12 papers as Part II.…”