Environmental Engineering Reference
In-Depth Information
taBle 17.6
Potential energy from Biogas
Palm oil Production
(million t)
Pome
(million m
3
)
Biogas
(million m
3
)
electricity
(million kWh)
year
2002
13.35
45.63
1,278
2,300
2006
15.9
53.55
1,499
2,698
2008
17.73
59.23
1,658
2,984
It is estimated that 1 m
3
of biogas is equivalent to 0.65 L of diesel in terms of electricity
generation. Hence, the total potential biogas energy could substitute for 1077 million L of diesel per
year (based on 2008). This amounted to MYR1.83 billion. Again, the amount of biogas generated
by an individual palm oil mill is not significant for commercial exploitation. However, it may be
economically viable and indeed profitable if palm oil mills could collectively use their fiber, shell,
EFB, and biogas for steam and electricity generation beyond their own needs.
17.11 Producer Gas (synGas)
EFB, which are produced in abundance at palm oil mills, can be a good feedstock for gasification
to yield gaseous biofuel. EFB was fed into a biomass gasification system at temperatures ranging
from 700 to 1000°C to yield bioproducer gases (i.e., CO, hydrogen, and CH
4
). The producer gases
can be compressed for household cooking, power generation, and as intermediate material for the
production of Fischer-Tropsch liquid, methanol, and ammonia. MPOB has set up a semi-pilot-scale
downdraft biomass gasification system with a capacity of 50 kg/h at its Palm Oil Milling Technology
Centre (POMTEC) (Zulkifli et al. 2006; Zulkifli and Halim 2008). This system consists of a gasifier
and a gas purification system. The concentration of the component gases was as follows: CO, 18.5%;
hydrogen, 10.9%; and CH
4
, 3.4% at a maximum gasification efficiency of 76% at 99 m
3
/h gas flow.
17.12 B I o - o I l
Bio-oil can be derived from oil palm biomass, particularly by pyrolyzing powdered EFB via a
quartz fluidized fixed-bed reactor at temperatures in the range of 300 to 700ºC (Chow and Li 2003;
Mohamad et al. 2009). The char, bio-oils, and gases were collected via the pyrolysis of EFB. The
highest bio-oil yield (42%) was obtained at an optimal temperature of 500°C with a particle size of
91-106 μm and a heating rate of 100°C/min. The optimum char production was 42% at 300°C and
gas production reached an optimum at 46% at 700°C. The calorific values of bio-oil ranged from
16 to 23 MJ/kg. The moisture content of bio-oil varied between 18 and 22%. The ash content in the
bio-oil varied from 0.2 to 0.65%. The pH values of the bio-oil varied between 2.6 and 3.9. A great
range of chemical functional groups of phenol, alcohols, ketones, aldehydes, and carboxylic acids
were indicated in a Fourier transform infrared (FTIR) spectrum.
17.13 Palm oIl as a dIesel suBstItute
Many researchers have investigated the possibility of using vegetable oils (straight or blended) as
a diesel substitute. A good account of their attempts was reported in the 1983 JAOCS Symposium
on Vegetable Oils as Diesel Fuels (Klopfenstein and Walker 1983; Pryde 1983; Strayer et al. 1983).
The symposium revealed that vegetable oils have good potential as alternative fuels if the following
problems could be overcome satisfactorily. These include high viscosity, low volatility, and the
reactivity (polymerization) of the unsaturated hydrocarbon chains present in highly unsaturated oil.
