Mixed plastics waste incineration

ENERGY RECOVERY THROUGH COMBINED INCINERATION OF MIXED PLASTICS WASTE AND SOLID MUNICIPAL WASTE... 

From mixed plastics, the formation of ethene, methane and hydrogen increase with temperature but the formation of propene and higher hydrocarbons decreases. Whether the isolation of olefins can compete economically with the oil cracking process remains to be seen, but the total hydrocarbon pyrolysate is similar to naphtha, the feedstock for petrochemicals production. It should be noted that because pyrolysis is primarily a non-oxidative process carried out under carefully controlled conditions, the possibility of dioxin formation is much reduced. In 1995 about 100 kT of mixed plastics wastes were converted into chemical feedstocks in Europe by pyrolysis, and this is expected to increase at the expense of incineration over the next ten years. 

LCA have been successfully utilised in the field of plastics waste management, for example, to assess differences in environmental performance between different waste incineration strategies [24] or related activities such as the flue gas cleaning process of plastic waste incinerators [25], to compare the environmental performance of different scenarios for the management of mixed plastics waste as well as that of specific plastic waste fractions [25-32]. 

The most suitable disposal systems for polymers in collected mixed plastics waste are pyrolysis with recovery of useful chemicals or incineration with heat energy. Degradable plastics will not interfere with these processes. 

Municipal solid waste incinerators (MSWIs) are a robust treatment method for very different mixed waste types of different origin. The typical MSWI handles waste of a calorific value between 9 and 13 MJ/kg. They are the key technology for the treatment of integral household waste in countries such as Denmark, Sweden, the Netherlands and Germany. Some 7% of this integral household waste consists of plastics. Treatment of... 

Finally, other relevant treatment options for plastics waste include landfill and mechanical recycling. Since these options (unlike Vinyloop and cement kiln incineration) are not even similar to feedstock recycling we discuss them here only very briefly. Mechanical recycling of plastics (be it PVC or other plastics), needs dedicated collection of the plastic waste in question. This is only possible for selected plastic flows (high volumes, recognisable products, products consisting mainly of one plastic). Landfill can accept plastic waste in any waste context (pure plastic type, MPW, mixed materials). I will only address the costs of these alternative technologies. 

As feedstock recycling and pyrolysis is not incineration there are no toxic or environmentally harmful emissions. Pyrolysis recycling of mixed plastics thus has great potential for heterogenous plastic waste that cannot be economically separated. 

The pyrolysis process for waste recycling is frequently done at larger scale than analytical pyrolysis. However, analytical pyrolysis studies are performed independently for the understanding and the optimization of such processes [10,16-19]. Also, model mixtures can be used in parallel with real samples. For example, the comparison of thermal degradation products from real municipal waste plastic and model mixed plastics can help understand the compounds generated in waste incinerators. In one such study [20], analytical pyrolysis of real municipal plastic waste obtained from Sapporo, Japan and model mixed plastics was carried out at 430 °C in atmospheric pressure by batch operation. The chlorinated hydrocarbons found in degradation liquid products of poly(ethylene)/poly(propylene)/ poly(styrene)/poly(vinyl chloride) and other polymeric mixtures were monitored. It was determined that the presence of poly(ethylene terephthalate), in addition to chlorinated plastics in the waste, facilitates... 

As well as direct incineration of plastics waste, imder clean and efficient conditions, there has been some research into conversion into fuel oil, by chemical methods. The Veba Combi-Cracking (VCC) process produces synthetic crude oil under liquid phase hydration. In trials, 100 tonnes of mixed and contaminated plastics waste from normal domestic sources was hydrated to high quality oil, similar to that used as a source for diesel fuel. With metal-free granular material, costs were estimated at about DM 500/tonne. The process has also been used with polyurethane waste, producing oil that can be mixed with new oil (but costing over twice). 

Dehydrochlorination of PVC is a facile reaction and is expected to take place on incineration of the plastic waste [52, 53]. The corrosive fumes can potentially affect the incinerator structure itself and if allowed to escape into the atmosphere will contribute to the acidification of the environment. Analysis of flue gases from mixed MSW incinerators typically show very small amounts of HCl (<2000 mg/m of gas) [54]. Either the amounts generated are quite low or tlie HCl formed in the incinerator undergoes reaction with other waste components or incineration products. 

Municipal Solid Waste and Hazardous Waste Waste incineration is the most effective method of waste reduction. All other recycling routes involve more waste in the total recycling chain (Fig. 13.29). The special case of mechanical recycling substituting wood or concrete, apparently saving more waste than they replace, is due to the assumptions made. In the case of concrete substitution, the portion in excess of 1 kg/kg of recycled plastic results from the low density of mixed plastics compared with the far heavier concrete product. The wooden product generates more MSW on final disposal than the mixed plastic solely because of the assumed life expectancy ratio of 4. 

---