Junmeng Cai

Determination of Drying Kinetics for Biomass by Thermogravimetric Analysis under Nonisothermal Condition

The nonisothermal drying kinetics of wheat straw and corn stalk has been studied by thermogravimetry. The experimental data have been obtained in order to fit to semitheoretical models widely used to describe drying behavior of agricultural products. Nonisothermal drying models—Newton, Henderson and Pabis, logarithmic, and Page—were evaluated based on the coefficient of determination (R 2), reduced chi-square (χ 2), and root means square error (RMSE). Pages model has been found to be the best for describing the nonisothermal drying characteristics of wheat straw and corn stalk. The activation energy values of wheat straw and corn stalk are determined to be 14.144 and 6.113 kJ mol−1, respectively.

A new iterative linear integral isoconversional method for the determination of the activation energy varying with the conversion degree

The conventional linear integral isoconversional methods may lead to important errors in the determination of the activation energy when the significant variation of the activation energy with the conversion degree occurs. Vyazovkin proposed an advanced nonlinear isoconversional method, which allows the activation energy to be accurately determined [Vyazovkin, J Comput Chem 2001, 22, 178]. However, the use of the Vyazovkin method raises the problem of the time‐consuming minimization without derivatives. A new iterative linear integral isoconversional method for the determination of the activation energy as a function of the conversion degree has been proposed, which is capable of providing valid values of the activation energy even if the latter strongly varies with the conversion degree. Also, the new method leads to the correct values of the activation energy in much less time than the Vyazovkin method. The application of the new method is illustrated by processing of theoretically simulated data of a strongly varying activation energy process.

Sensitivity analysis of three-parallel-DAEM-reaction model for describing rice straw pyrolysis.

The three-parallel-DAEM-reaction model was used to study the slow pyrolysis kinetics of rice straw based on thermogravimetric analysis (TGA) data. The kinetic parameters of the model were calculated using the pattern search method. A comparison between the predicted DTG data and experimental values showed good agreement. The influences of the kinetic parameters on the model for describing the experimental data of rice straw were analyzed by means of local parametric sensitivity analysis. The results indicated that the frequency factor and the mean value of the activation distribution for cellulose decomposition affect the model more strongly than other parameters, followed by the corresponding parameters for hemicellulose and lignin. The sensitivity of the model to the standard deviations of the activation energy distributions for all pseudocomponents is very slight.

Applicability of Fraser-Suzuki function in kinetic analysis of DAEM processes and lignocellulosic biomass pyrolysis processes

In this work, a new method for fitting the conversion rate curves of the distributed activation energy model (DAEM) and lignocellulosic biomass pyrolysis process was introduced. The method was based on the curve fitting technique using the Fraser–Suzuki function. Various simulated DAEM processes were analyzed. The results showed that the conversion rate curve of one DAEM process could be described well by a Fraser–Suzuki function. According to the obtained parameters of the fitted Fraser–Suzuki functions, the influences of the DAEM parameters on the conversion rate curves of the corresponding DAEM processes can be quantitatively obtained. The experimental data of the pyrolysis of cotton stalk, oilseed rape straw, and rice straw were fitted by the Fraser–Suzuki mixture model which involves three individual Fraser–Suzuki functions. It has been found that the Fraser–Suzuki mixture model can reproduce accurately the conversion rate curves of the pyrolysis of three lignocellulosic biomass samples. The Fraser–Suzuki mixture model provides an approach to separate lignocellulosic biomass pyrolysis into three parallel reactions which link to the decomposition of hemicellulose, cellulose, and lignin, respectively.

Logistic distributed activation energy model--part 2: application to cellulose pyrolysis.

The pyrolysis behavior of cellulose has been investigated by using thermogravimetric analysis (TGA). The non-isothermal TGA data obtained at different heating rates have been analyzed simultaneously. Pattern Search Method has been proposed for the estimation of the model parameter values. Predicted values from the logistic distributed activation energy model have been compared with the experimental data and the results have indicated that the model describes the kinetic behavior of cellulose pyrolysis very well. The mean value and standard deviation of the logistic activation energy distribution for cellulose pyrolysis are found to be 258.5718 kJ mol(-1) and 2.6601 kJ mol(-1), the reaction order is 1.1101 and the k(0) is 1.6218×10(17) s(-1).

A critical study of the Miura–Maki integral method for the estimation of the kinetic parameters of the distributed activation energy model

Using some theoretically simulated data constructed from known sets of the activation energy distribution f(E) (assumed to follow the Gaussian distribution [Formula in text] where E is the activation energy, E(0) is the mean value of the activation energy distribution, and σ is the standard deviation of the activation energy distribution) and the frequency factor k(0), a critical study of the use of the Miura-Maki integral method for the estimation of the kinetic parameters of the distributed activation energy model has been performed from three cases. For all cases, the use of the Miura-Maki integral method leads to important errors in the estimation of k(0). There are some differences between the assumed and calculated activation energy distributions and the differences decrease with increasing the assumed k(0) values (for Case 1), with increasing the assumed σ values (for Case 2), and with decreasing the b values (for Case 3).

Iterative linear integral isoconversional method: Theory and application

In this work, the theory of the iterative linear integral isoconversional method was illustrated in detail. This method allows the dependence of the activation energy (Eα) on the conversion degree to be accurately determined in a short time. Moreover, the method can yield the term [Aαf(α)] (Aα: the frequency factor at conversion α, f(α): the reaction model). The obtained Eα and [Aαf(α)] values can be used to reconstruct the kinetic conversion data at experimental and extrapolated conditions. The suggested method was applied to the experimental data of combustion of biomass fast pyrolysis char, and the corresponding kinetic parameters were obtained.

Logistic distributed activation energy model – Part 1: Derivation and numerical parametric study

A new distributed activation energy model is presented using the logistic distribution to mathematically represent the pyrolysis kinetics of complex solid fuels. A numerical parametric study of the logistic distributed activation energy model is conducted to evaluate the influences of the model parameters on the numerical results of the model. The parameters studied include the heating rate, reaction order, frequency factor, mean of the logistic activation energy distribution, standard deviation of the logistic activation energy distribution. The parametric study addresses the dependence on the forms of the calculated α-T and dα/dT-T curves (α: reaction conversion, T: temperature). The study results would be very helpful to the application of the logistic distributed activation energy model, which is the main subject of the next part of this series.

State of art of biomass fast pyrolysis for bio-oil in China: a review

AbstractThis paper presents a review of biomass fast pyrolysis for the production of bio-oil in Mainland China. The main contents are as follows. The feedstock for fast pyrolysis and main pyrolysis reactor developed in Mainland China are introduced. The process of fast pyrolysis for each pyrolysis reactor mentioned in this paper is described. The effects of key parameters of fast pyrolysis on fluidised bed reactor are illustrated. Finally, the properties, upgrading and application of bio-oil are discussed.

Amount, availability and potential uses for energy of agricultural residues in Mainland China

AbstractBased on the agricultural production statistics in 2006, an assessment of the amount and availability of agricultural residues in Mainland China has been carried out. The total quantities produced of agricultural residues (including crop residues and agroindustrial residues) in Mainland China are up to 800 million tons per annum. And more than 500 million tons of agricultural residues per annum are available for energy use in Mainland China. An attempt to describe the potential uses for energy of agricultural residues has also been made.