Waste calorific value

The rotary kiln design allows for accepting a mix of high-chlorinated wastes (solvents, chlorinated tars, plastics). Such kilns are usually designed in relation to a specific optimal calorific value in the input. The input mix should be set in such a way that this optimal composition is approached (e.g., PVC waste and other waste streams with a lower calorific value). It is likely that a 100% input of PVC would lead to all kind of problems of temperature control due to its relatively high calorific value. Chlorine contents of over 50% can easily be accepted. A final demand is that the particle size should be 10 x 10 x 10 cm at maximum. This implies that sometimes waste has to be shredded before it can be put into the kiln. Other acceptance criteria have not been published in literature. 

The process needs input of lime and water next to the PVC waste. No energy input is needed since the organic condensate provides for the energy needed in the process. Energy needed for pretreatment can be up to 25-35 kWh/tonne. Downstream separation of the coke products needs another 30-40 kWh/toime. The process does not emit dioxins, metals or plasticisers. Due to internal recycling there are no aqueous waste streams. The reaction of lime with HCl forms some CO2. The coke product provides a calorific value. 

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... 

Eor (1), MSWIs, the maximum bonus is limited by the calorific value of the plastics waste (about 40 MJ/kg). Eurthermore, the energy recovery is relatively low due to technical limitations in comparison to normal power plants. Normally, at best some 20% electrical energy is recovered (or some 50%-70% calculated as primary energy). 

Incineration with energy recovery is examined as a means for the disposal of plastics waste, and data are presented for the calorific values of a number of materials. Chemical recycling techniques are also briefly reviewed. 

Material recycling is the objective for every material, but at some point reuse or collection, separation and further recycling will no longer yield a useful product. The so-called plastic waste still contains a high calorific value which can be recovered to produce heat or electricity. Even better it may be possible to recover the chemical feedstock originally manufactured from oil. These two possibilities are reviewed. 

Mastral, A.M., Callen, M.S., Murillo, R., and Garcia, T., Combustion of high calorific value waste material Organic atmospheric pollution, Environment. Sci. TechnoL, 33, 4155, 1999. 

The waste products from any process (gases, liquids and solids) which contain significant quantities of combustible material can be used as low-grade fuels for raising steam or direct process heating. Their use will only be economic if the intrinsic value of the fuel justifies the cost of special burners and other equipment needed to bum the waste. If the combustible content of the waste is too low to support combustion, the waste will have to be supplemented with higher calorific value primary fuels. 

Other factors which, together with the calorific value, will determine the economic value of an off-gas as a fuel are the quantity available and the continuity of supply. Waste gases are best used for steam raising, rather than for direct process heating, as this decouples the source from the use and gives greater flexibility. 

Quality of RDF can be roughly evaluated by calorific value, ash content, water content, and chlorine and sulfur content. Table 5 presents the quality of RDF depending on several kinds of waste. The table shows that RDF from industrial waste has lower water content and higher heating value than from household or commercial waste. This is because of the low percentage of organic fraction. 

Municipal solid wastes (MSW) gasification unit which is under development in the project consists of two fluid bed reactors (Figure 2). The first reactor is a gasifier, the second reactor is a combustion chamber for charcoal. To obtain producer gas of middle calorific value water steam is applied as a blowing. Fluid bed is organized by supplying water steam to gasifier (inert material is sand) and air to combustion chamber. The installation is equipped with all necessary devices to measure rate, temperature, and pressure. 

Let us consider that a mixed waste contains different components, each being characterized by its water content W, volatile matter VM and ash content A (the last two being on a dry basis). Assuming that each component behaves independently and using the hypothesis of additivity, it is possible to estimate the product yields after carbonization. Moreover, this model takes into account the different carbonization yields for each component (according their physical and chemical properties). From the C, H, O analysis of each component (easier than that for the rough mixture), it is possible to estimate the net calorific value of the char and the gases from the waste pyrolysis. 

An oil of low flash point in the range 14-18°C, and of 41-43 MJ Kg gross calorific value has been obtained in batch pyrolysis [36] of automobile tyre waste. In a pilot plant with semi-continuous feeding [37] the liquid yield of tyre waste decreased seriously with increasing temperature, and it was always lower in an atmosphere containing oxygen that in nitrogen. 

Table 19.1 lists the calorific values of some common polymers and compares them with some conventional fuels. As illustrated in the table, the calorific values of these plastics are very similar to those of liquid fuels. Thus, there is a potential for recycling of these waste plastics as liquid fuels. 

C. Diez et al.. Pyrolysis of tyres. Influence of the final temperature of the process on emissions and the calorific value of the products recovered. Waste Management, 24, 463-469 (2004). 

Pyrolysis can be performed for many different reactors. The prodnct distribntion varies markedly between the different reactor types and the reaction conditions, snch as temper-atnre, bed materials or catalyst. The aim of the pyrolysis is the redaction of wastes for landfilling and the prodnction of fnels. Especially fuel oil with a high calorific value is an interesting product. Char can be used as a fuel, but is also seen as a precursor for other carboneous materials such as activated carbon. The best way to obtain these products is decarboxylation of the polymer. In this way carbon oxide-rich gas is produced. 

In this work, special attention was paid to minimising the potential residues from PET recycling. Some works have been published on active carbons from granulated non-used PET [4], but none concerning the use of plastic wastes. The advantage of the pyrolysis of post-consumer PET is that all the products obtained present interesting applications (i.e., chemical products, gases with calorific value and a solid that can be used as an active carbon), as a result of which residual wastes can be minimised considerably. The aim of this work was to obtain valuable active carbons from the solid residue from PET pyrolysis. 

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