2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 106 -
Abstract
--The production of low heating value gas by
thermal decomposition (pyrolysis, gasification) of biomass
(agricultural, agroindustrial and forestry residues) provides
a renewable source of heat and electric power generation via
diesel engines, gas turbines or fuel cells and for methanol
production. Energy production from biomass is
environmental friendly since the resulting combustion gases
do not add to the greenhouse effect. In the present study,
air gasification of village rice husk and sawdust was carried
out in a 100 mm ID and 1650 mm high fluidized bed gasifier
unit developed for this purpose. The unit comprised of
fluidized bed reactor, an air supply unit, biomass-feeding
unit, a high efficiency cyclone and an after burner. The
performance of the gasifier under different operating
conditions of fluidization velocities (0.53, 0.59, 0.68 and 0.73
m/s) and equivalence ratios (0.20, 0.25, 0.30, 0.35 and 0.40)
was evaluated in terms of gasifier thermal efficiency. The
thermal efficiency of the gasifier was found to be 36.39 to
57.04% for village rice husk and 51.43 to 72.30% for
sawdust gasification. The thermal efficiency was found to
decrease with in increase in the fluidization velocity.
Index Terms
-- Fluidized Bed Gasifier, Village Rice Husk,
Saw Dust, Thermal Efficiency, Equivalence Ratios,
Fluidization Velocity
I.
I
NTRODUCTION
The exploitation of the new and renewable energy
sources for meeting the ever-increasing energy
requirements has become more demanding for those
developing countries, which are importing significant
amounts of crude petroleum and its products. Among the
several alternative renewable energy sources, biomass
occupies a unique place. Biomass materials like
agricultural, agro-processing and forestry residues are
available in abundance in India [1]. Some of them are
available at such sites where need for generating power
also exists, for e.g. rice husk in rice mills, sawdust in saw
mills and bagasse in sugar mills. These residue type
biomass materials often pose disposal problems due to
their low fodder/fertilizer values. Thermal gasification of
such waste biomass for energy utilization is an attractive
proposition. The well-developed moving bed gasifiers
have not been found suitable for such low bulk density
and high ash content biomass [2]. A fluidized bed gasifier
accepts such biomass of fine granulometry as feedstock
[3]. In India large amount of biomass residues are
available which may be converted to fuel gases by
gasification.
The present experimental study was undertaken to
understand the gasification characteristics of village rice
husk (VRH) and saw dust (SD) in a fluidized bed. A
gasifier unit of 100 mm ID reactor diameter and 1650
mm total height was developed for the study. The
performance of the gasifier under different operating
conditions of fluidization velocity and equivalence ratio
was studied in terms of temperature profile in the reactor,
gas composition, gas heating value, gas yield, carbon
conversion efficiency, tar and particulate content of the
gas and the thermal efficiency of the gasifier for the two
feed stock. The two-biomass materials were obtained
locally (Roorkee, Uttaranchal, India) and were sun dried.
The rice husk was obtained from a rural rice huller and is
locally known as ‘
kamu
’. The sawdust was obtained from
a saw mill where normally hard wood was sawn. The
present paper reports the experimental operation of the
fluidized bed gasifier and its thermal efficiency.
II. E
XPERIMENTAL
A. The Gasifier Unit
A complete fluidized bed thermal gasifier unit was
designed, fabricated and installed in the laboratory. The
unit incorporated (i) a fluidized bed reactor with a
perforated type distributor plate, (ii) an air supply unit,
(iii) a biomass feeding unit, (iv) a cyclone, and (v) a
product gas after-burner. A schematic diagram of the
gasifier unit is shown in Fig.1. The fluidizing column, the
main part of the gasifier, was made from a stainless steel
pipe AISI 310 of 100 mm inner diameter, 1000 mm
length and a wall thickness of 5 mm. A sand loading port
of 25 mm diameter was provided at a height of 400 mm
above the distributor plate with a leg pipe of 300 mm
length and a lid, at an angle of 45
0
upwards. A similar leg
pipe of the same dimensions was provided at a height of
300 mm from the distributor plate inclined downwards at
an angle of 45º with the vertical. This was meant for the
withdrawal of the sand, the bed charge and the excess ash
as and when required. A multi-orifice type distributor
made of 3 mm thick stainless steel plate was fixed to the
bottom of the fluidizing column, sandwiched between the
Fluidized Bed Gasification of Village Rice Husk
and Sawdust: Gasifier Operation and Thermal
Efficiency
P.B. Gangavati
*
and B. Prasad
**
*
Department of Mechanical Engineering, Basaveshwar Engineering College,
(India)
**
Department of Chemical Engineering, Indian Institute of Technology
, (
India
)
