Plastics calorific values

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. 

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. 

Flashless mortar-type smokeless proplnt with calorific value 900—llOOcal/g is made from NC (12.2-13-4% N) 50-8, NG 12-44, cooling plasticizer 2—10, (0aNOC2H4)2N(NO2) 0—35%, small amt of stabilizer, small amt desensitizer and small amt inorganic salt to aid ignition. Thickness depends on burning time desired. Example of one compn used NC(13.25% N)... 

The calorific value of fhe plastics pyrolysis oils was befween 33.6 and 53.4 MJ kg depending on fhe composition of fhe original plastic polymer. The calorific value was high aparf from fhe oil derived from fhe polyesfer/sfyrene copolymer resin used in the manufacture of composite. This was attributable to the high oxygen content of the original... 

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. 

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. 

Table-1 and -2 indicate compositions of input refuse and produced pyrolysis gas components, respectively. Since no flue gas from combustion bed is mixed into the pyrolysis bed, calorific value of the pyrolysis gas shows extremely high. When using the group-m material, plastics-rich group classified by a pre-treatment subsystem, its calorific value is approx. 2.93 x 10 KJ/Nm3 (7000kcal/Nm3), In the steady state of the operation, the gas components showed almost constant. 

From an economic point of view, used plastic can be considered as both an important source of valuable chemicals, mainly hydrocarbons, and an energy source. The calorific value of most plastics is similar to that of fuel oils and higher than that of coals. Plastic wastes can therefore be viewed as potential fuels, when other alternatives of valorization are not possible.9... 

Various boilers can use plastic waste as fuel. However, the requirements on the regularity of the particle size and on the calorific value limit their applications. 

Moreover, energy recovery is probably the best solution for very contaminated and dispersed plastics (for example, the yoghurt pot which is a multi-layered material, with low mass and whose residual content after consumption can be significant). It is tme that the high calorific value of plastics helps regulate the incineration of honsehold waste, improve the quahty of effluents (fewer micropollutants and unbumed compounds in slag) and conserve oil used in the production of heat and electricity. Most European cities are equipped with urban heating networks, which could become possible due to the incineration of urban waste. 

Having a calorific value of ca. 30.2 MJ/kg, which is about equivalent to that of coal, PET is readily suited for the incineration process. However, like other plastics its combustion requires 3-5 times more oxygen than for conventional incineration, produces more soot, and develops excessive heat that thus calls for special incineration equipment to cope with these problems. 

Table 43 Calorific values of plastics compared with conventional fuels...

Recycling as energy because of their high calorific value, all types of plastics can readily be incinerated in efficient plants which can harness the thermal energy liberated the resulting ash is a safe and compact landfill. 

Fractions with high calorific values can be used in cupola or blast fiunaces in production or processing of iron. Cupola furnaces are used mainly to melt scrap metal with coke. In blast furnaces, metallic iron is melted in iron ore reduction. For this purpose, along with the coke highly sulfurous heavy oil or coal is injected and gasified with the hot blast. Plastic material can substitute the heavy oil to a certain extent [19]. Use of plastics in blast furnaces require prior comminution to a diameter of max. 5 mm, since this granulate is introduced into the lower section of the blast furnace out of a pressurized container at 0.4—0.5 MPa through a lance. 

Unfilled and unreinforced plastics have high calorific values, low moisture contents and therefore gasify, ignite quickly and incinerate at low temperatures [22]. The calorific value of reinforced plastics depends on their chemical composition and the portion of mineral filling and reinforcing materials. Table 8 provides an overview of the calorific values of different materials. 

---