According to the experimental weight-loss curves, the rate of weight-loss change (*α*) can be determined when the reaction has proceeded to a certain time (t):

$$\begin{array}{r}\alpha =\frac{{\omega}_{0}-{\omega}_{t}}{{\omega}_{0}-{\omega}_{\mathrm{\infty}}}\end{array}$$(1)As the gas flow of CO^{2} was constant in the experiment, and the reaction was under atmospheric pressure, so the *P*CO_{2} is a constant. According to the rate equation of gasification reaction of char-CO^{2} (2) and the Arrhenius Equation (3), the general form of kinetic Equation (4) can be obtained.

$$\begin{array}{r}\frac{d\alpha}{dt}=k(1-\alpha {)}^{n}\end{array}$$(2)$$\begin{array}{r}k=A\cdot {e}^{-\frac{E}{RT}}\end{array}$$(3)$$\begin{array}{r}\frac{d\alpha}{dT}=\frac{A}{\beta}{e}^{-\frac{E}{RT}}(1-\alpha {)}^{n}=\frac{A}{\beta}{e}^{-\frac{E}{RT}}f(\alpha )\end{array}$$(4)The kinetic parameters calculated from the above equations are the apparent kinetic parameters of experience.

There are many computing method of kinetic parameters deduced from the general form of kinetic equations [13, 14, 15, 16]. This article used the integral method of Coats-Redfern, using the non-isothermal method of a single procedure of temperature control. That is to say the heating rate (*β*) is a constant. After solving the integral on both sides of the Equation (4) and set the initial state of the equation (*α* = 0, *T* = *T*_{0}), the Equation (5) was obtained as follow.

$$\begin{array}{r}{\int}_{0}^{\alpha}\frac{d\alpha}{f(\alpha )}=\frac{A}{\beta}{\int}_{{T}_{0}}^{T}{e}^{-\frac{E}{RT}}dT\end{array}$$(5)The reaction rate at the low temperature is negligible usually. So that the Equation (5) becomes:

$$\begin{array}{r}{\int}_{0}^{\alpha}\frac{d\alpha}{f(\alpha )}=\frac{A}{\beta}{\int}_{0}^{T}{e}^{-\frac{E}{RT}}dT\end{array}$$(6)Make the definition: $g(\alpha )={\int}_{0}^{\alpha}\frac{d\alpha}{f(\alpha )},$and the gasification reaction of C-CO_{2} can be described as a first-order reaction [17, 18]. So the reaction order n=1, and *f* (*α*) = 1 − *α*, the Equation (6) becomes:

$$\begin{array}{r}g(\alpha )=\frac{AR{T}^{2}}{\beta E}\left[1-\frac{2RT}{E}\right]{e}^{-\frac{E}{RT}}\end{array}$$(7)After solving the natural logarithm on both sides of the Equation (7):

$$\begin{array}{r}\mathrm{ln}\left[\frac{g(\alpha )}{{T}^{2}}\right]=\mathrm{ln}\left\{\frac{AR}{\beta E}\left[1-\frac{2RT}{E}\right]\right\}-\frac{E}{RT}\end{array}$$(8)During the experiments, the heating rate was determined (*β* = 288 K/min). Therefore, the reaction temperature, and most typically in terms of E, the value of ln$\left\{\frac{AR}{\beta E}\left[1-\frac{2RT}{E}\right]\right\}$is a constant. Set up $X=\frac{1}{T},Y=\mathrm{ln}\left[\frac{g(\alpha )}{{T}^{2}}\right]$the approximate line can be obtained by plotting to X-Y, and the activation energy(E) and the pre-exponential factor (A) can be calculated by Equation (7). Results of kinetics calculation are shown in .

Table 4 Kinetics calculation of carbon dissolving reaction

To study the relationship between the content of pulverized coal in the samples and changes of activation energy, the data of were plotted. Figure 3 shows that in the two temperature ranges of 1223 K~1373 K and 1373 K~1523 K, the activation energy of coke sample is the largest. After adding coal, the activation energy of the sample is significantly reduced. It shows that the reactivity of the sample becomes larger after adding coal.

At the same time, it can be seen that the activation energy in the temperature range of 1223 K~1373 K is generally greater than it in the temperature range of 1373 K~1523 K. This suggests that the carbon solution loss reaction in the temperature range of 1373 K~1523 K is more vigorous. In the temperature range of 1223 K~1373 K, the activation energy of samples reduced with the increase of the content of the pulverized coal, and the activation energy of samples added in 2#coal had the greater decrease. The results show that the different volatile contents of the coal have significant influence on the activation energy of the gasification reaction between pulverized coal and CO_{2}, and the higher volatile content, the smaller the activation energy. In the temperature range of 1373 K~1523 K, the activation

Figure 3 Relationship between reaction activation energy and the additive amount of coal

energy also reduced with the increase of the content of the pulverized coal, but the extent of decrease was not obvious, and the activation energy of samples added two coals was nearly. This is because when the reaction was carried out above 1373 K, the pulverized coal of reaction was gradually consumed, and more and more coke powders involved in the reaction. Especially to the samples added 2# coal, since the high volatile of the coal and the low content of fixed carbon, when the reaction proceeded to certain extent, the amount of coke participating in the reaction increased, and the reaction activation energy of the sample became larger slightly.

## Comments (0)

General note:By using the comment function on degruyter.com you agree to our Privacy Statement. A respectful treatment of one another is important to us. Therefore we would like to draw your attention to our House Rules.