Environmental Engineering Reference
In-Depth Information
17.10 BIoGas From Pome
In addition to the solid residues, palm oil mills also generate large quantities of liquid waste in the
form of POME, which, because of its high biochemical oxygen demand (BOD), is required by law
to be treated to acceptable levels before it can be discharged into watercourses or onto land. In a
conventional palm oil mill, approximately 0.675 m
3
of POME is generated for every ton of FFB
processed. Hence, in 2008, approximately 59.23 million m
3
of POME was generated in Malaysia.
Anaerobic processes have been adopted by palm oil mills to treat their POME. The biogas produced
during the decomposition is a valuable energy source. It contains approximately 60-70% methane,
30-40% CO
2
, and a trace amount of hydrogen sulfide. Its fuel properties are shown in Table 17.5
together with other gaseous fuels.
Approximately 28 m
3
of biogas are generated for every cubic meter of POME treated. However,
most of the biogas is not recovered. So far, only a few palm oil mills use biogas for heat and
electricity generation (Quah et al. 1982; Gillies and Quah 1985; Chua 1991; Ma et al. 2009). In a
gas engine, it has been reported that approximately 1.8 kWh of electricity could be generated from
1 m
3
of biogas (Quah et al. 1982). The potential energy from biogas generated by POME is shown
in Table 17.6. Because palm oil mills already meet their energy needs by combusting fiber and
shell, there is no outlet for this surplus energy. Considering the costs of storing and transporting
the biogas, perhaps the most viable proposition is to encourage industries to locate in the vicinity of
the palm oil mills where the biogas energy can be directly utilized. This could result in substantial
savings in energy costs (Chua 1991).
taBle 17.4
Properties of Palm Briquettes
Product
calorific value (kJ/kg)
moisture content (%)
ash content (%)
Pulverized EFB
17,823
7.39
2.85
Pulverized
EFB + sawdust (50:50)
18,273
7.22
2.22
Pulverized
EFB + sawdust (40:60)
18,775
7.32
2.99
Sawdust
18,936
6.81
1.63
DIN 51731
17,500 (min)
0.7 (min)
<10.0 (min)
DIN 51731:
Test of Solid Fuels—Compressed Untreated Wood Requirements and Testing.
taBle 17.5
some Properties of Gaseous Fuels
Biogas
natural Gas
lPG
Gross calorific value (kJ/Nm
3
)
19,908-25,830
3797
100,500
Specific gravity
0.847-1.002
0.584
1.5
Ignition temperature (°C)
650-750
650-750
450-500
Inflammable limits (%)
7.5-21
5-15
2-10
Combustion air required (m
3
/m
3
)
9.6
9.6
13.8
Source:
Quah, S.K. and Gillies, D.,
Proceedings of National Workshop on Oil Palm By-Product Utilization
. Palm Oil
Research Institute of Malaysia, Kuala Lumpur, pp. 119-125, 1981.
All gases evaluated at 15.5°C, atmosphere pressure and saturated with water vapor. LPG, liquefied petroleum gas.
