W. CHEN ET AL. 235
gasification media. Kumabe et al. [5] carried out the co-
gasification experiments using Japanese cedar and Mu-
lias coal in a downdraft gasifier by using air and steam as
gasification media. It was found that with an increase in
the biomass ratio in the mixture, the H2 % decreased and
the CO2% increased while the CO % was independent of
the biomass ratio. A low biomass ratio led to the produc-
tion of a gas favorable for methanol and hydrocarbon
fuel synthesis, and a high biomass ratio led to the pro-
duction of a gas favorable for Dimethyl Ether (DME)
synthesis. The cold gas efficiency of the co-gasification
ranged from 65% to 85%.
Pan et al. [6] mixed the pine chips with black coal and
Sabero coal, in the ratio range of 0/100 - 100/0, respec-
tively. Experimental tests were carried out using air and
steam as gasification agent at gasification temperatures
of 840˚C - 910˚C and superficial fluidized gas velocities
of 0.7 - 1 .4 m/s using fludized bed gasifier. It was found
that the dry product gas heating value increases with in-
creasing blend ratio from 3700 to 4560 kJ/Nm3 for pine
chips/black coal, and from 40 00 to 4750 kJ/Nm3 for pine
chips/Sabero. Dry product gas yield raised with the in-
crease of the blend ratio from 1.80 to 3.20 Nm3/kg (pine
chips/black coal), and from 0.75 to1.75 Nm3/kg (pine
chips/Sabero coal), respectively. About 50% co-gasifi-
cation processes overall thermal efficiency can be achieved
for the two types of blend.
Lu et al. [7] studied the effect of the equivalence ratio
on the co-gasification of pine sawdust and bituminous
coal in a bubbling fluidized bed. It was found that when
blending fuel ratio is 50% - 50%, with ER increasing
from 0.2 to 0.28 the volume concentration of H2 rose
from 14.1% to 26.9%, and CO% decreased from 28.9%
to 21.8%. The CO2% showed an increasing tendency in
the range of ER, while those of CH4 and CnHm kept de-
creasing. The maximum of the lower heating value
(LHV), is about 7180 kJ/m3 when ER is 0.25. The gasi-
fication efficiency ranged from 44% - 53% and the car-
bon con- version rate was between74% to 76%.
Chen et al. [8] used the mesquite wood chips as feed-
stock for a fixed bed gasification experiment. It was
found that the HHV of the gas produced from the mes-
quite fuel decreased when equivalence ratio (ER) in-
creased from 2.7 to 4.2 and the HHV was in a range of
2400 kJ/Nm3 to 3500 kJ/Nm3.
Gerado et al. [9] used a mixture of dairy biomass (DB)
and Wyoming sub-bituminous coal (WYC) with a ratio
of 90:10 for co-gasification study in a 10 kW updraft
gasifier using air-steam as gasification media. Due to the
presence of higher amount of fixed carbon in the WYC,
the peak gasification temperature and the % of CO in the
end produced gas increased and the HHV of the producer
gas increased correspondingly. The HHV of the gases
varied from 3649 to 4793 kJ/ Nm3.
In these studies, the variation of HHV of the gases
produced and the gasification efficiency with ER and
mesquite: coal r atios were investig ated. It was also found
that the HHV of the product gas increased as coal % was
increased in the blends. In the current study, the Texas
based mesquite was blended with PRB coal for air gasifi-
cation in order to produce higher quality gas (i.e. in-
creased HV gas) and convert more volatile matter into
combustible gases (e.g. reduce the tar content in the
product gas due to higher Tpeak). The effect of the ER and
coal% in mesquite: coal blend (MCB) on the gasification
temperature, gas compositions, and HHV were investi-
gated. The main objective of this study was to use the
Texas based Mesquite and PRB coal blended fuel to pro-
duce higher quality gas (i.e. increased HV gas) and con-
vert more volatile matter into combustible gases (e.g.
reduce the tar content in the product gas due to higher
Tpeak) in an air gasification process. The effect of the ER
and coal percentage in mesquite: coal blend (MCB) on
the gasification temperature, gas compositions, and HHV
were investigated.
3. Sustainabilityof Mesquite
The sustainability of any energy source must satisfy the
following requirements: Abundance of energy sources,
maintaining integrity of environment including air, land
(soil) and water, renewability and affordability (i.e. low
cost)[10]. Most biomass fuels satisfy the requirement
including mesquite. The Mesquite (Prosopis glandulosa)
is a deciduous wood which can reach a height of 6 to 9 m
(20 to 30 ft), grows rapidly and furnish shade and wild-
life habitat where other trees will not grow [11]. It is an
extremely hardy, drought-tolerant plant growing on semi-
arid non-cultivated land s because it can draw water from
the water table through its long taproot and thus it can be
harvested nearly year round [11,12]. Depending upon
availability, mesquite can also use water in the upper part
of the ground. Mesquite trees have very strong regrowth
after top-kill damage [12]. Like many members of the
Legume Family, it fixes nitrogen in the soil where it
grows and therefore satisfies most of its nutrient needs
[13]. It is estimated that of the 21 M total h a of mesquite
in Texas alone [14,15] , about 20%, or 4.2 M ha, could
be harvested for bioenergy needs. At an average of 18
dry Mg/ha [12], this could amount to over 75 teragrams
(Tg) of total mass available. There is no planting, culti-
vation, irrigation and fertilization costs for this naturally
occurring, nitrogen-fixing species [12]. This species can
be used as feedstock to produce syngas and bio-oil in
small scale gasification units [4]. Since coal has higher
amount of char compared to mesquite, then the heat
value of gas produced could be enhanced by blending
small amount of coal with mesquite; such a process in-
creases the usage of gas produced from gasification of
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