Plastics energy content

Plastics have many advantages. Included are the facts that they have the lowest energy consumption in the recycling processes of about 2 MJ/kg (2 to 2.5 MJ/I) and when incinerated the highest recovery energy content exists of about 42 MJ/kg. Some comparisons with other materials are provided. (1) Processing waste paper requires 6.7 MJ/kg and as a general rule about twice as much paper is needed compared to plastics for... 

As for routes (2) and (3), the conclusion in this paper, as one can find back in many LCAs, is that the difference in environmental terms is not big. After all, both routes make use of the energy content (or carbon content) of the plastics, with a (close to) 100% efficiency. This is a striking point, since route (2) is labelled as incineration with energy recovery whereas route (3) is labelled as recovery , and hence in legal terms an option that scores... 

Some work was also done by Consaga et al. on cyclodextrin nitrates with a view to replacing NC [5]. The composites of this invention are mixtures of (i) a cyclodextrin nitrate or a mixture of cyclodextrin nitrates and (ii) an energetic organic nitrate plasticizer. These composites are useful as replacements for nitrocellulose (NC) because they are more thermally stable and less sensitive to impact and yet have comparable or greater energy content than NC. However, cyclodextrin nitrates are dry powders that are sensitive to electrostatic discharge (ESD). 

Because of their low density, plastics comprise approximately 20% by volume of landfilled solid waste, although they contribute only about 7% of the total weight. Public opposition limits the disposal of plastics via incineration, despite their comparatively high energy content. These factors have stimulated considerable interest in the development of biodegradable plastics as replacements for conventional plastics, particularly in packaging and disposable applications. 

Finally, there is the option of burning the plastic for fuel. Although much of the value of the plastic is wasted, at least the energy content is recovered. Again, a mixture of various polymers can be used, although there is some concern about burning poly(vinyl chloride) because of its chlorine content. 

It can be seen that a significant proportion of the energy content of the waste is recovered by the gasification of the char and that the ultimate residue is decreased in comparison with the quantity of bottom ash produced compared with direct incineration. Solid plastic waste represents a significant stream for conversion back to energy [89]. 

The quality of the product is of primary importance in developing a recycling technology converting plastics into fuels by pyrolysis. Today the characterization of a liquid fuel from any sources is obviously based on the qualification methods and standards of fuels from mineral oil. The properties of the pyrolysis-derived fuels from plastics are expected to be similar to conventional fuels (energy content, viscosity, density, octane and cetane number, flash-point, etc.). However, in addition to the familiar ranking values it is necessary to know more about the chemical composition of the plastic pyrolysis oil, because of the peculiarities as follows ... 

Operation with Emphasis on Material Recovery Figure 2 shows this type of operation. The input material consists primarily of substances with relatively high energy contents, such as used tyres, plastics, rugs, wood and special organic industrial wastes. 

Figure 6-5 shows the burning rate characteristics as a function of (N02). The burning rate increases linearly as pressure increases in In p versus In r plots and also increases as (N02) increases. The effect of the addition of the plasticizer, DEP, on the burning rate is evident, i.e., the burning rate decreases as the energy content... 

The energy content of plastics is comparable to that of ordinary combustibles such as diesel oil (Figure 3.12). It has been shown that the addition of between 7.5 and 15 wt% of plastics waste to municipal solid waste improves combustion in the gas phase as well as of the solid residues due to a more stable and intensive combustion zone [58]. It also reduces waste volume by two thirds [59]. The mineralised combustion residues need to be disposed of as hazardous waste. 

The biodegradabUity of a plastic is useful, except in medical applications, when it is beneficial to growing plants. It is not a feasible solution of the waste problem since it requires expensive dump volume. In the waste dump, the plastic continues to be converted into the greenhouse gas carbon dioxide by the bacteria, just as it would if incinerated, but without utilization of its energy content. 

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