A surface activation function method to determine the intrinsic reactivity of coal char oxyfuel conversion
A surface activation function method to determine the intrinsic reactivity of coal char oxyfuel conversion
复制标题
确定煤焦富氧燃料转化本征反应性的表面活化函数方法
DOI：
10.1016/j.fuel.2018.11.100
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发表时间：
2019-03-01
期刊：
影响因子：
7.4
通讯作者：
Bie, Kang
中科院分区：
文献类型：
--
作者：
Liu, Yang;Fu, Pei-Fang;Bie, Kang
用等温和非等温热重分析煤/炭含氧燃料的燃烧动力学仍然存在争议。对两种煤焦（NCP无烟煤、DT烟煤）在不同的O-2/CO2和O-2/N-2气氛下动力学控制状态下的燃烧动力学进行了比较。我们建立了表征炭转化反应比表面积的表面活化函数（SAF， F(X)），然后用R(X) = kP(O2)(m) F(X)表示其固有反应速率，发现F(X) = X-a(1 - X)(c)的自催化模型（ACM）在等温和非等温条件下均适用，但ACM中的指数a和c以及活化能(E)在这两种条件下不同。这些有争议的结果可能是由指数函数exp（-E/RT）引起的，该函数在非等温条件下随转化率的变化而变化，从而影响了SAF的非线性建模结果。根据等温研究，温度对状态i中SAF的形式没有影响，因此用等温实验得到的本征SAF (F（X)(iso)）来拟合非等温数据是合理的。模拟结果表明，不同O-2/CO2和O-2/N-2气氛下的E-NCP = 207 ~ 220 kJ/mol，大于等温条件下的（178 ~ 179 kJ/mol）。当E-DT = 159 ~ 165 kJ/mol时，这与等温结果（163 ~ 167 kJ/mol）吻合较好。另外，虽然增加P-O2或用N-2代替O-2/CO2混合物中的CO2可以提高本征反应速率，但O-2分压（P-O2）对E没有影响。
The kinetics of coal/char oxyfuel combustion by isothermal and non-isothermal thermogravimetric analysis is still controversial. The two methods were compared according to the kinetics of two coal chars (NCP anthracite, DT bituminous) combustion in kinetics-controlled regime I under different O-2/CO2 and O-2/N-2 atmospheres. We have developed a surface activation function (SAF, F(X)) to describe the reactive specific surface area of char conversion, and then the intrinsic reaction rate can be expressed by R(X) = kP(O2)(m) F(X), the autocatalysis model (ACM) of F(X) = X-a(1 - X)(c) was found to be suitable under both isothermal and non-isothermal conditions, however, the exponents a and c in ACM as well as the activation energies (E) differ under these two conditions. These controversial results may be caused by the exponential function exp(-E/RT), which changes with the conversion ratio under non-isothermal conditions, which in turn affects the nonlinear modeling results of SAF. According to the isothermal study, temperature has no effect on the form of SAF in Regime I. Thus it is reasonable to use the intrinsic SAF obtained from isothermal experiments (F(X)(iso)) to fit the non-isothermal data. The modeled results show that E-NCP = 207-220 kJ/mol under different O-2/CO2 and O-2/N-2 atmospheres, greater than those under isothermal conditions (178-179 kJ/mol). While E-DT = 159-165 kJ/mol, this agrees well with the isothermal result (163-167 kJ/mol). Furthermore, it indicates that the O-2 partial pressure (P-O2) has no influence on E, even though increasing P-O2 or replacing CO2 in the O-2/CO2 mixture with N-2 increases the intrinsic reaction rate.