Abstract— Gasification is a thermo-chemical process to convert

carbon-based compounds such as biomass and coal into a gaseous

fuel. Among the various types of gasification methods, fluidized bed

gasification is one which is considered as more efficient method than

others as biomass is fluidized in a mixture of air/oxygen and steam.

In the present study, a comprehensive steady state process model has

been developed for biomass gasification in atmospheric fluidized

beds using Advanced System for Process Engineering (ASPEN

PLUS) simulator. Three ASPEN PLUS reactor models namely,

RYIELD for drying and decomposition of biomass into its elements,

RGIBBS for achieving both chemical and phase equilibrium of

volatile matter available in biomass and RCSTR for carrying out char

gasification have been used. The fluidized bed reactor has been

divided into finite small elements because there exists change in

number of moles, change in partial pressures of all the components

along the height of the reactor as the reactions take place inside the

reactor. To consider the change in superficial velocity which results

from change in number of moles along the height of the reactor, each

of these elements has been simulated by one RCSTR. Finally, the

effects of steam to biomass ratio, equivalence ratio and temperature

on the composition and lower heating value of product gas have been

studied. Using optimization tool available in Aspen Plus, the

optimum values of steam to biomass ratio and equivalence ratio have

been found out.

Keywords— Biomass, gasification, Aspen Plus, gas composition,

heating value, optimization, steam to biomass ratio and equivalence

ratio.

I. INTRODUCTION

IOMASS refers to plant based materials such as dead

trees, branches, wood chips and even municipal solid

waste. The process of conversion of biomass (or any other

carbonaceous material) to syngas is called as gasification.

Gasification occurs when oxygen and/or steam is reacted at

high temperatures with available carbon in biomass within a

gasifier. Air gasification produces a poor quality gas with

regard to the heating value, around 4-7 MJ m-3

, while O2 and

steam blown processes result in a syngas with a heating value

in the range of 10-18 MJ m-3

Lv et al.,. However, gasification

with pure O2 is not practical for biomass gasification due to

prohibitively high costs for O2 production using current

commercial technology (cryogenic air separation). The syngas

thus produced can be combusted in gas turbine or in an engine

to generate electricity and heat.

K. Anand Kishore1 is with the National Institute of Technology Warangal-

506004, Telangana, India (e-mail: kola@nitw.ac.in).

K. A. V. Ramanjaneyulu was with the National Institute of Technology

Warangal-506004, Telangana, India (e-mail:ramanji.kalva@gmail.com).

II. SIMULATION DETAILS

In a typical atmospheric fluidized bed gasifier, feed together

with bed material are fluidized by the gasifying agents, such as

air and/or steam, entering at the bottom of the bed. The

objective of this study is to develop simulation capable of

predicting the steady-state performance of an atmospheric

fluidized bed gasifier by considering the hydrodynamic and

reaction rate kinetics simultaneously. The products of

homogeneous reactions are determined in RYIELD reactor

and RGIBBS reactor, and reaction kinetics are used to

determine the products of char gasification. A drawback in

using ASPEN PLUS is the lack of a library model to simulate

fluidized bed unit operation. However, it is possible for users

to input their own models, using FORTRAN codes nested

within the ASPEN PLUS input file, to simulate operation of a

fluidized bed. The work presents the simulation of fluidized

beds for biomass gasification in Aspen Plus. Fig. 1 shows a

simple schematic diagram fluidized bed gasifier. A preheated

mixture of oxygen and steam is introduced at the bottom of the

gasifier and flows upward with biomass to react with.

Fig.1 Schematic illustrative diagram of fluidized bed gasifier.

III. RESULTS AND DISCUSSION

Effect of Temperature on Syngas composition:

The effect of gasifier temperature on produced syngas

composition is shown in Fig.3. The temperature considered

varies from 700 °C to 1000 °C. The composition of syngas

varying with a small range with increasing gasifier

temperature. It can be seen that H2 composition and CH4

composition are almost independent of temperature. According

to Le Chatelier’s principle, higher temperatures favour the

Simulation of Biomass Gasification in

Fluidized Bed Using Aspen Plus

K. Anand Kishore1 and K. A. V. Ramanjaneyulu

2

B

6th International Conference on Chemical, Biological and Environment Sciences (ICCEBS'2015) Sept. 13-14, 2015 Dubai (UAE)

28

reactants in exothermic reactions and favour the products in

endothermic reactions. Therefore the endothermic reaction that

is steam gasification was strengthened with increasing

temperature, which resulted in an increase of CO composition.

Fig.3 Effect of temperature on Syngas composition

Effect of Steam to biomass Ratio on syngas composition:

Over the S/B range from 0 to 4, carbon conversion efficiency

exhibited decreasing trend, which can be explained by that

excessive quantity of low temperature steam lowered reaction

temperature and then caused gas quality to degrade. As shown

in Fig.4, in the S/B range from 0 to 4, the composition of H2

increases, this can be explained by more steam gasification

reaction is taking place because of increased steam quantity.

The change in CH4 composition is very small with increasing

steam-fuel ratio.

Fig.4 Effect of Steam to Biomass Ration on Syngas

Composition

Effect of Air to Biomass Ratio on syngas composition:

The effect of Air to Biomass ratio on the Syngas

composition is shown in Fig. 5. The effect of this ratio range

from o.5 to 1.8 was observed. In this range the mole fraction

of H2 decreases because increasing of Air to Biomass ratio

indirectly means that it will reduce the reaction temperature so

that the endothermic reaction that is steam gasification reaction

is weakened. In Fig.5 increasing the Air to Biomass ratio

increases the mole fraction of CO2 because of increasing the

flow rate of oxygen favours the oxidation reaction to occur.

Fig.5 Effect of Air to Biomass Ratio on Gas Composition.

IV. CONCLUSION

A model was developed for the gasification of biomass in an

atmospheric fluidized bed gasifier using the ASPEN PLUS

simulator. To provide the model, several ASPEN PLUS unit

operation blocks were combined with number of separator

blocks and a mixer block. The simulation analysis for the

product gas composition versus temperature, air to biomass

ratio and steam to biomass ratio was done.

Higher temperature improves the quality of syngas by

increasing the production of carbon monoxide and decreasing

the mole fraction of carbon dioxide. Increasing steam to

biomass ratio increases the production of hydrogen and carbon

dioxide and decreases the carbon monoxide. Increasing air to

biomass ratio decreases the production of hydrogen and

increases the carbon dioxide production.

REFERENCES

[1] Doherty W., Reynolds A., Kennedy D., The Effect of Air Preheating in a

Biomass CFB Gasifier using ASPEN Plus Simulation. Article, School of

Mechanical and Transport Engineering: 2009.

[2] Franco C., Pinto F., Gulyurtlu I. and Cabrita I., The study of reactions

influencing the biomass steam gasification process, Fuel, 82, 2003.

[3] Inayat A., Ahmad M.M., Mutalib A. and Yusup S., Effect of process

parameters on hydrogen production and efficiency in biomass

gasification using modeling approach Journal of Applied Sciences, 10,

2010.

[4] Lee, J.M.; Kim, Y.J.; Lee, W.J.; Kim, S.D. Coal-gasification kinetics

derived from Pyrolysis in a fluidized-bed reactor. Energy 1998.

[5] Lewis WK, Gilliland ER, Lang PM. Entrainment from fluidized beds.

Chemical Engineering Progress Symposium Series 1962.

[6] Li X.T., Grace J.R., Lim C.J., Watkinson A.P., Chen H.P., Kim J.R.

Biomass gasification in A circulating fluidized bed. Biomass and

Bioenergy 2004.

[7] Lv PM, Xiong ZH, Chang J, Wu CZ, Chen Y, Zhu JX, An experimental

study on biomass air–steam gasification in a fluidized bed. Bioresource

Technology, 2004.

[8] Matsui I, Kunii D, Furusawa T. Study of fluidized bed steam

gasification of char by thermogravimetrically obtained kinetics. J Chem

Eng Japan 1985.

[9] Nikoo, M.B.; Mahinpey, N. Simulation of biomass gasification in

fluidized bed reactor using ASPEN PLUS. Biomass Bioenergy 2008.

[10] Rajan RR, Wen CY. A comprehensive model for fluidized bed coal

combustors. AIChE Journal 1980.

6th International Conference on Chemical, Biological and Environment Sciences (ICCEBS'2015) Sept. 13-14, 2015 Dubai (UAE)

29

[11] Rapagna S., Jand N., Kiennemann A. and Foscolo P. U., Steam

gasification of biomass in a fluidized bed of olivine particles, Biomass

and Bioenergy, 19, 2000.

[12] Sadaka S, Ghaly AE, Sabbah MA. Two phase biomass air– steam

gasification model for fluidized bed reactors: Part I -model

development. Biomass and Bioenergy 2002.

[13] Sharmina Begum, Mohammad G. Rasul, Delwar Akbar and David

Cork. An Experimental and Numerical Investigation of Fluidized Bed

Gasification of Solid Waste,2014.

6th International Conference on Chemical, Biological and Environment Sciences (ICCEBS'2015) Sept. 13-14, 2015 Dubai (UAE)

30