(106c) Modeling Plasma Gasification of Biomass with Thermodynamic and Kinetic Approach in Series

Modeling Plasma
gasification of biomass with thermodynamic and kinetic approach in series

 

Babita K. Verma, Rajesh Elangovan, T. Renganathan, S.
Pushpavanam^*

Department
of Chemical Engineering, Indian Institute of Technology Madras,

Chennai
600036, India

*Corresponding author:spush@iitm.ac.in, Tel: +91-44-22574161

Plasma
gasification is a promising green technology in which carbon based feed-stocks
are converted to synthesis gas. In this process, a plasma arc is used to supply
heat to the reactor to sustain the endothermic gasification reactions. Plasma
gasification operates at temperatures above 2500 K. Here the reaction rates are
very high and this leads to lower residence time as compared to conventional gasification
[1]. This
drastically reduces the size of gasifiers operating at atmospheric pressure.
These advantages motivate the development of accurate mathematical models for
plasma gasifiers which can help to analyze the effect of various parameters on
the performance.

There
are two ways of modeling: Equilibrium and kinetic approach. The purely equilibrium
approach does not need information on all reactions which occur at the high temperatures
in the reactor here when using the non-stoichiometric approach. The purely
kinetic approach requires the consideration of heterogeneous reactions,
resistances associated with gas-solid interaction and the formation of radicals.
In the present work, the gasifier is modeled as consisting of a high
temperature zone followed by a quenching zone where the reactor contents lose
heat to the ambient. In the former the reactions are very fast and hence it can
be assumed to be at thermodynamic equilibrium. In the quenching zone the
reactant mixture cools down and the composition of the gases vary along the
reactor length at a finite rate determined by the reaction kinetics. This
motivates the reactor to be modeled as being made of two regions namely a
plasma gasifier zone (PGZ) which is simulated using a thermodynamic
non-stoichiometric approach and a quenching zone (QZ) which is simulated based
on a kinetic approach. The schematic representation of the plasma gasifier
model [2] is shown
in Figure
1

Figure
1.
Schematic representation of the plasma gasifier model

The
effect of various parameters – gasifier temperature, steam flow rate, air flow
rate and feed moisture content – on the performance of the gasifier is studied.
Figure 2 shows a typical result i.e. the effect of the gasifier
zone temperature on the heat duty and the cold gas efficiency existing in PGZ
and QZ region.

Figure 2: Effect of temperature on heat duty and CGE exiting PGZ
and QZ region (Air=13.25kg/hr, Steam=3.90 kg/hr, Moisture=10%)

References:

[1]      S. J. Yoon and J. G.
Lee, “Syngas Production from Coal through Microwave Plasma Gasification :
Influence of Oxygen , Steam , and Coal Particle Size,” Energy & Fuels,
vol. 26, pp. 524–529, 2012.

[2]      M. Gorokhovski, E. I.
Karpenko, F. C. Lockwood, V. E. Messerle, B. G. Trusov, and  a. B. Ustimenko,
“Plasma technologies for solid fuels: experiment and theory,” J. Energy
Inst., vol. 78, no. 4, pp. 157–171, Dec. 2005.