Mechanical Technology March 2016

⎪ Sustainable energy and energy management ⎪

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. 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

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. q

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

SRF Characteristic

Units MJ/kg

SRF 1 SRF 2 SRF 3 Average

Net Calorific Value (NCV)

31

24

23

26

Moisture Content Ash Content Volatile Matter Fuel Reactivity Chlorine Content Sulphur Content Nitrogen Content Mercury Content Carbon

(wt/wt) % 1 (wt/wt) % 12 (wt/wt) % 88 (wt/wt) % 62 (%/min/K) 3

2 9

2

2

20 81 53

13 82 54

78 48

4

5

4

(wt/wt) % <0.2 <0.2 <0.2 <0.2

(wt/wt) % 0.9 (wt/wt) % 0.2

1.4 0.6

0.2 0.4

1

0.4

mg/MJ

<0.02 <0.02 <0.06 <0.06 <0.2 <0.2 <0.2 <0.2

Cadmium + Thallium content mg/MJ

Sum of heavy metals

mg/MJ

<30

<30

<30

<30

Interwaste (Solid Recovered Fuels) SRF analysis results. Refuse derived fuels from these waste materials are clean burning with have high calorific value.

Mechanical Technology — March 2016

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