Study of the high heating rate devolatilization of bituminous and subbituminous coals-Comparison of experimentally monitored devolatilization profiles with predictions issued from single rate, two-competing rate, distributed activation energy and chemical percolation devolatilization models

This paper deals with the measurement and modeling of devolatilization profiles obtained with 7 different coals. To do so, a specifically designed flat flame reactor (FFR) has been used to reproduce industrial heating rates (similar to 10(6) Ks(-1)) with peak particle temperatures (PTp) ranging from similar to 1000 K to similar to 1300K. The thermal history of the fuel particles has been characterized by coupling particle image velocimetry (PIV) and pyrometry measurements so as to be integrated in empirical and phenomenological models including single rate, two-competing rate, distributed activation energy (DAE) and chemical percolation devolatilization (CPD) ones. Final yields ranging from similar to 70% to similar to 89% with respect to the initial fuel volatiles content have been measured for PTp approximate to 1000K. As expected, a decrease of the devolatilized fractions with an increase of the fuel rank has been observed while releases of volatiles exceeding the proximate analysis predictions have been recorded for temperatures higher than similar to 1090 K. Besides, the experimental conditions investigated in this work and especially the high heating rate delivered by the FFR used allowed testing the ability of devolatilization models from the literature to simulate data obtained in conditions relevant to coal power plant applications which should be of particular interest for future CFD calculations. The main findings highlighted through the comparison work proposed herein can be summed up as follows: 1) The single kinetic rate model integrating the original parameters proposed by Badzioch and Hawksley globally reproduces measured weight losses for bituminous coals while needing adjustments for lower rank fuels; 2) Different kinetic constants tabulated in the literature for two-competing rate models have been tested and turned out to be unsuitable to simulate the devolatilization profiles we monitored. Insights regarding most adapted parameters and optimization procedures that might be operated are, nonetheless, discussed; 3) Adjusting the standard deviation of the activation energy introduced into the DAE model consistently with the thermal gradient experienced by the fuel particles may lead to improved agreements between measured and simulated data; 4) The CPD model slightly overstimates devolatilization rates at low temperatures while showing the best performances to predict the final devolatilization yields for all the studied coals (including the subbituminous one) due to the structural approach integrated in such a modeling tool. (C) 2016 Elsevier B.V. All rights reserved.

本文涉及对7种不同煤种获得的脱挥发分曲线的测量和建模。为此，使用了一种专门设计的平面火焰反应器（FFR）来重现工业升温速率（类似于10⁶ K/s），颗粒峰值温度（PTp）范围从约1000 K到约1300 K。通过结合粒子图像测速（PIV）和高温测量来表征燃料颗粒的热历史，以便将其整合到包括单速率、双竞争速率、分布活化能（DAE）和化学渗透脱挥发分（CPD）等经验和唯象模型中。对于PTp约为1000 K的情况，测量得到相对于初始燃料挥发分含量的最终产率从约70%到约89%。正如预期的那样，观察到随着煤阶的升高脱挥发分比例降低，同时对于高于约1090 K的温度，记录到挥发分释放量超过工业分析预测值。此外，本工作所研究的实验条件，特别是所使用的FFR提供的高升温速率，使得能够测试文献中的脱挥发分模型在模拟与燃煤电厂应用相关条件下获得的数据的能力，这对于未来的CFD计算应该具有特别的意义。通过本文提出的比较工作所强调的主要发现可总结如下：1）整合了Badzioch和Hawksley提出的原始参数的单动力学速率模型总体上能重现烟煤的测量失重情况，但对于低阶燃料需要调整；2）对文献中针对双竞争速率模型列出的不同动力学常数进行了测试，结果表明它们不适合模拟我们所监测的脱挥发分曲线。然而，讨论了关于可能采用的最合适参数和优化程序的见解；3）根据燃料颗粒所经历的热梯度一致地调整引入DAE模型的活化能标准偏差，可能会使测量数据和模拟数据之间的一致性得到改善；4）CPD模型在低温下略微高估了脱挥发分速率，但由于这种建模工具中整合的结构方法，它在预测所有研究煤种（包括次烟煤）的最终脱挥发分产率方面表现最佳。（C）2016 Elsevier B.V.保留所有权利。