2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 111 -
where:
H
g
is the heating value of a stoichiometric mixture of
producer gas and air in kJ/m
3
.
V
CO
is volume fraction of carbon monoxide in the gas
(before mixing with air).
V
H2
is volume fraction of hydrogen in the gas (before
mixing with air).
V
CH4
is volume fraction of methane in the gas (before
4 mixing with air).
Heating values of producer gas and air mixtures are
around 2500 kJ/m
3
. When this value is compared with the
heating value of a stoichiometric mixture of petrol and air
(about 3800 kJ/m
3
), the difference in power output
between a given engine fuelled by petrol and by producer
gas becomes apparent. A power loss of about 35% can be
expected as a result of the lower heating value of a
producer gas/air mixture.
An important factor determining the actual technical
operation, as well as the economic feasibility of using a
gasifier system, is the gasification efficiency. A useful
definition of the gasification efficiency if the gas is used
for engine applications is:
100%
g
g
gasifier
s
s
H Q
H M
K
u
u
u
(2)
In which:
gasifier
K
is the gasification efficiency (%)
H
g
is the heating value of the gas (kJ/m
3
)
Q
g
is the volume flow of gas (m
3
/s)
H
s
is the lower heating value of gasifier fuel
(kJ/kg)
M
s
is the gasifier solid fuel consumption (kg/s)
Although many researchers had experimentally studied
hydrogen production by biomass gasification, the
reforming of product gas the heating value of product gas
and the gasifier efficiency is still too low.
II. M
ATERIAL AND
M
ETHOD
The suction downdraft biomass gasifier system that
was constructed in this work is shown in Fig. 1. The
major component of a biomass gas engine system
consists of a 10 kWe electrical steam generator (Fig. 5), a
fixed bed downdraft gasifier (Fig. 8) with a screw press
feeder of 50 kg/hr (Fig. 4), a first cyclone (Fig. 6), an ash
keeper box (Fig. 7), a shell and tube heat exchanger (Fig.
9), a wet scrubber (Fig. 9), a packed bed filter (Fig. 10)
using charcoal as the media, a final cyclone (Fig. 11), a
draft forcing fan (Fig. 12), a flare test section (Fig. 13), a
gas engine of 1,455 cc connected to a 10 kWp generator
(Fig. 14). The fuel characteristics of mixed rice husk-
glycerol briquettes were analyzed by means of ASTM
D3172 standard for proximate analysis, ultimate analysis
based on ASTM D3176 standard and an analysis of
heating value based on the ASTM D2105 standard.
Results are shown in Table 1-2 corresponding to the
chemical formula of mixed rice husk-glycerol briquettes
of CH
1.67
O
0.61
. The heating value of rice husk-glycerol
briquette was about 15,038 kJ/kg. The rice husk and
glycerol were mixed with ratio of 3 kg : 500 ml, after
crushing, were separated into three different size ranges:
5x3 cm, 5x5 cm, and 5x7 cm as shown in Fig. 2. The
density was 1,143.37 kg/m
3
and the compressive strength
was 6.35 MPa based on the Thai Industrial Standards
Institute TIS-1505-2541 standard as given in Table 3. The
volume flow rate of air was varied up to 74.2 m
3
/hr with
the gasification time of 1 hr. It is applied in equivalent
ratio (ER) determination of 0.25. Air and steam were
used as gasifying agents. The operating temperature was
measured using the thermocouple wires connected to a
data logger. The steam feed rate is 11.7 kg/h and the air
feed rate is 197 kg/h. The gas composition was detected
using a flue gas analyzer model Testo 350 XL connected
to a notebook as shown in Fig. 3.
TABLE
I
P
ROXIMATE ANALYSIS OF MIXED RICE HUSK
-
GLYCEROL BRIQUETTES
Rice Husk-
Glycerol
Briquettes
MC (%) FC (%) VM (%) AC (%)
4.4
13.0
64.5
18.1
TABLE
II
U
LTIMATE ANALYSIS OF MIXED RICE HUSK
-
GLYCEROL BRIQUETTES
Rice Husk-
Glycerol
Briquettes
C
(%)
H
(%)
O
(%)
N
(%)
S (%)
41.8
5.8
33.9
0.36
0.0004
TABLE
III
P
HYSICAL CHARACTERISTICS OF MIXED RICE HUSK
-
GLYCEROL
BRIQUETTES
Size of Biomass
Fuel (cm)
Bulk Density
(kg/m
3
)
Compressive
Strength (MPa)
5x3
1,143.37
6.36
5x5
5x7
Fig. 1. Schematic diagram of biomass gasifier system at Thaksin
University.
