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Mechanical Technology — March 2016
21
⎪
Sustainable energy and energy management
⎪
SRF Characteristic
Units
SRF 1 SRF 2 SRF 3 Average
Net Calorific Value (NCV)
MJ/kg
31
24
23
26
Moisture Content
(wt/wt) % 1
2
2
2
Ash Content
(wt/wt) % 12
9
20
13
Volatile Matter
(wt/wt) % 88
78
81
82
Carbon
(wt/wt) % 62
48
53
54
Fuel Reactivity
(%/min/K) 3
4
5
4
Chlorine Content
(wt/wt) % <0.2 <0.2 <0.2 <0.2
Sulphur Content
(wt/wt) % 0.9
1.4
0.2
1
Nitrogen Content
(wt/wt) % 0.2
0.6
0.4
0.4
Mercury Content
mg/MJ
<0.02 <0.02 <0.06 <0.06
Cadmium + Thallium content mg/MJ
<0.2 <0.2 <0.2 <0.2
Sum of heavy metals
mg/MJ
<30
<30
<30
<30
Above:
A fluff bail at the end of the RDF
plant line.
Left:
Many waste materials, such as
wood, cardboard and non-recyclable
plastic materials can be dried, com-
pressed and pelletized, sometimes
with the aid of a binder such as wax,
to make solid RDF pellets.
Interwaste (Solid Recovered Fuels) SRF analysis results. Refuse derived fuels from these waste materials
are clean burning with have high calorific value.
furniture manufacturers and genera-
tors of non-recyclable plastic waste.
Possible uses for the fuel include power
stations, the cement industry, gasifica-
tion/pyrolysis plants and dedicated RDF
combustion facilities. “RDF is particularly
well suited to the cement industry, since
particulate emissions from the fuel tends
to be encapsulated in the end product
during the calcining process,” says
Nicholls. Calcining is the decomposition
of calcium carbonate (limestone) in a
rotating kiln to form calcium oxide (lime)
during the cement making process.
Properties of the RDF fuel produced
by Interwaste include: very high tempera-
ture flame (2 000 °C); low residence time
(below 5.0 seconds); inherent gas clean-
ing, particularly in the case of cement
kilns; and almost no ash production.
Two forms of RDF fuel can be pro-
duced. From wood-based waste, ex-
truded logs and pellets are produced for
use as solid fuel. From plastic waste,
however, a fuel called ‘fluff’ is produced
by shredding and baling the pre-sorted
plastic waste.
Nicholls says that Interwaste can
now offer a solid waste RDF with high
calorific value, diverting industrial waste
to save landfill space. “We are now able
to recover the energy value in waste that
would otherwise be wasted, for use as a
substitute fuel for valuable fossil-based
resources and reducing net greenhouse
gas emissions,” he says.
The energy generated from RDF is
considered to be green energy and could
therefore be eligible for carbon credits
and exempted from the Carbon Tax. “Its
use is in line with the Department of
Environmental Affairs’ waste recovery
objectives and qualifies as a contribu-
tor to the green economy.
“Available as a dense solid fuel
or as ‘fluff’ for direct injection into
burners, RDF offers a high degree
of flexibility with respect to calorific
value; the potential for zero waste
to landfill; a significantly lower ash
content than conventional fuels such
as coal; along with reduced particulate
emissions,” he concludes.
Interwaste is a leading environmen-
tal solutions management company in
South Africa and the SADC region, of-
fering holistic environmental solutions
ranging from legal compliance, technical
services, on-site management services,
resource recovery, solid and liquid waste
treatment, waste commodity trading,
waste logistics, waste disposal and
facilities management.
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