There are very limited literature on kinetics modeling for biomass gasification sup­ported by kinetics parameters determined using experimental data. Sheth and Babu (2009) estimated kinetics parameters for biomass pyrolysis process using kinetics modeling approach. The kinetics constant of two reactions involved in the pyrolysis was calculated by minimization of least square error between the model results and the experimental data. The experimental data were chosen from the literature. The values of activation energy and pre-exponential factor of Arrhenius constants for both reac­tions were calculated by the minimization of the objective function as follows:

F (ЛЛЛЛ ) = £(,j — Wt, j )2

І=1

Wang and Kinoshita (1993) developed a reaction kinetics model for biomass O2- steam gasification. The wood was taken as biomass and the generalized equation was presented as follows:

CH14O0.59 + yO2 + zN2 + wH2O = XjC + x2H2
+x^CO + X4H2O + X5CO2 + x6CH4 + x7N

Furthermore, four main reactions were considered including char gasification, boudouard, methanation, and methane reforming reaction as follows:

Char Gasification

C + H2O ® CO + H2

Boudouard

C + CO2 ® 2CO

Methanation

C + 2H2 ® CH4

Steam Reforming

CH4 + H2O ® CO + 3H2

The rate constant of all these reactions was calculated by the minimization of the difference between the experimental data and calculated data. The equation used was as follows:

m 0 2

Minf (*ap К2 . К3 . К4 ) = МІП ZZ (j — Xexp, j)

The experimental data were taken from their previous work on O2-steam gasification using sawdust as biomass (Wang and Kinoshita 1992). Moreover, the modeling results were validated with the experimental work. In addition, residence time, temperature, pressure, equivalence ratio, and moisture have been investigated on the product gas composition.

Resende and Savage (2010) described the kinetics model for the supercritical steam gasification for hydrogen production. The model consists of 11 reactions. The rate equations of each reaction were taken as first order for each species. The final concentration was calculated using mole balance equations; for example, the con­centration of CO2 was calculated using the equitation as follows:

where k10 is for forward water gas shift reaction and k10r is for reversible water gas shift reaction. The equilibrium constant for the water gas shift reaction was calculated as follows:

C C

H2 CO2

C C

CO H2O

The kinetics parameters were calculated by the minimization of the objective function which is the sum squared difference between the model results and experi­mental values. The experimental data were taken from their previous work based on the supercritical steam gasification of lignin and cellulose (Resende and Savage

2009) . Furthermore, the model was validated with the experimental data and the results showed good agreement.

Salaices (2010) developed a reaction kinetics model for catalytic steam gasifica­tion of biomass surrogates using as model compounds. The kinetics model was based on the coherent reaction engineering approach. The reaction rates were based on the dominant reactions. The reactions like methanation and boudouard reactions were neglected. So the rate of each species was calculated as follows;

ri = Ifij = rWRG + rSR + rDRM

There are only dominant reactions, i. e., water gas shift, steam reforming, and dry methane reforming considered. For example, the rate of formation of hydrogen was calculated as follows:

Furthermore, the kinetics constants have been calculated using experimental data with best parameter estimations and minimizing the least squares objective function via optimization toolbox of MATLAB.

19.2 Conclusion

The literature review on the experimental work of biomass steam gasification showed that the pure steam is best gasification agent for hydrogen production. Steam gasification with CaO as sorbent improved the concentration of hydrogen in

the system and also acts as catalyst. Catalytic steam gasification showed higher yield of hydrogen. So, there is need to integrate steam, CaO, and catalyst together for high purity and higher yield. Furthermore, EFB has potential for hydrogen pro­duction, so there is also need to study the biomass steam gasification using EFB as biomass for hydrogen production. The literature review on the modeling and simu­lation of biomass gasification showed that there are several works published on kinetics modeling for conventional gasification but limited work on biomass steam gasification specifically for hydrogen production. So there is a need to develop reac­tion kinetics model including the carbonation reaction along with the main steam gasification reactions. As kinetics model provides important data regarding the con­version of biomass to hydrogen which is essential to improve the process. The pre­dictions from the kinetics model are more accurate compared to the thermodynamic equilibrium models, so the process can be simulated better with the experimental data. In addition, there is also need to work on the determination of the Arrhenius kinetic constant for all reactions involved in steam gasification with CaO for hydrogen production from biomass.