In Japan there is such a demand among the citizens to
increase the buying price of biomass derived power at price
higher than 20 J-Yen in order to control the amounts of CO
2
emission to the environment. However, it is technically
indispensable to connect the electric output to the commercial
power grid line via inverter system thus the cost down of
inverters should be further examined.
5.2 Energy Balance for the Feasibility Study
The energy balance for the feasibility study was
considered. Based on the feasibility study, the feed stock is
charged at rate of 100kg/h on dry basis. Energy utilization in
the form of energy electricity output and hot water supply is
shown in Figure 1
2
. Out of a total of 249kW syngas produced
from the gasification plant, 107kW is circulated for operation
of the plant system and approximately 70kW is supplied for
combustion for use in the high temperature steam intensifier.
The saturated steam at 130
o
C is heated up to superheated
steam at 1000
o
C at a rate of 80kg/h. Cold gas efficiency is
calculated to be 54%. If the heat of hot water from the gasifier
is included in the results the cold gas efficiency will increase
to 70%. If both power generation and heat of hot water from
engine is included, the total energy conversion rate is 58%. In
case of combined heat and power (CHP) plant using natural
gas or petroleum this value seems rather conservative.
However, when employing unused energy resources that are
renewable for CHP, it is an acceptable value of efficiency for
this type of system that requires energy for both pre-drying of
feed stock before charging to the gasification system and for
making up the temperature loss that occurs due to
endothermic reactions during the gasification
6.
Conclusions
(1) The thermogravimetric (TG) data obtained from the
char made from crushed tree branches showed that the
use of steam environment increased the reaction rate by
7 times with increase in reaction temperature from 800
o
C
to 1000
o
C. This clearly shows that high temperature
steam helps promote reaction rates at higher
temperatures.
(2) Decrease in moisture content from 50% to 35%
increased the lower heating value (LHV) of the syngas
produced by approximately 1.4 times using crushed tree
branches of less than 30mm sizes.
(3) Stable operation of the gasification system has been
demonstrated using a continuously charged feed stock at
a rate of 46kg/h (moisture at 35%) to provide syngas of
9.2MJ/Nm
3
LHV and cold gas efficiency of 52.6%.
Stable operation of absorption chiller type air
conditioner at 50kW is also demonstrated using the
syngas produced.
(4) 50kW of electric power generation was demonstrated
with use of the syngas under the condition of 60kg/h of
feed stock charging rate.
(5) An investment cost of 55 million J-Yen for the
system can be depreciated in 7 years based on this our
feasibility study.
(6) The energy balance study showed cold gas efficiency
of 54% at a fed rate of 100kg/h (dry basis) to the gasifier.
The total energy conversion efficiency was 58% when
heat energy required in the hot water is utilized from the
gasification system and the engine is used for power
generation system.
525
465
60
142
107
78
262
43
21
107
105
Boiler
Gasifier
Hot Water
Electricity
Recirculating Syngas
Syngas
Hot Water
Feeder
32.9
26
Syngas
249
184
37
Hot Water
Drinking
Water
50
177
245
50
50
70
High
Temperature
Steam
Exhaust Gas
Heat Losses
16
Dust Filter
30
625
Endothermic Reaction
SyngasCooler
Generator with
Diesel Engine
Fuel for SI
Fuel for GasifierHeater
Hot Air for
Dryer
Preheating
Feedstock
with Hot Char
Ground Hopper
Q
SGT
Q
FS
Q
INPUT
Q
E
Q
HW1
Q
HW2
Q
SGO
Steam
Intensifier
LHVof Syngas
0.62
0.58
Gross Thermal Efficiency (Electricity
＋
H. Water)
te
= (Q
E
+ Q
HW2
)
/ Q
INPUT
0.54
0.70
Cold Gas Efficiency
c
= Q
SGT
/ Q
FS
Syngas + H. Water
SGW
= (Q
SGO
+ Q
HW1
)
/ Q
FS
Gross Thermal Efficiency (Syngas
＋
H. Water)
tg
= (Q
SGO
+Q
HW1
) / Q
INPUT
Figure1
2
. Energy Balance of the Gasification System for Deployment Feasibility
Unit of numbers in this figure:
kW
2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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