Tyres combustion

See Ozone Combustible gases, or Ethylene Steel-braced tyres... 

This chapter will present a short overview of worn tyre management practices, with data for the USA, followed by a discussion of the effects of energy recovery through tyre combustion on both solid waste products and atmospheric emissions. In addition to reviewing... 

Conserve natural resources Reduce NO, emissions Complete tyre combustion Large market... 

Pulp and paper mills. The second largest consumers of tyre fuel ate pulp and paper mills (Table 1, Fig. 4). Because the production of pulp and paper is an energy-intensive process, these facilities typically have their own boilers and turbines to meet electrical needs. Pulp and paper mills use TDF instead of whole tyres to supplement wood waste as fuel. The wood waste, also referred to as hog fuel, consists of chipped bark and other unusable tree parts (Barlaz et al. 1993). The use of TDF helps maintain constant combustion conditions in the stoker grate boiler system, which are not easily achieved using wood waste alone (Ohio Air Quality Development Authority 1991). The fuel-feeding process of these types of boilers, however, requires that the TDF be almost entirely free of wires (Jones et al. 1990). This requirement increases the costs of fuel significantly. 

Electric utility and industrial boilers. The use of tyres in electric utility and industrial boilers comprises 26% of the market for tyre fuel (Fig. 4). Although whole tyres can be used in some industrial boilers, most facilities combust TDF mixed with coal in a variety of concentrations ranging from as little as 2 to as much as 40% TDF by weight (e.g., Tesla 1994 EPA 1997 Ohio Air Quality Development Authority 1991). There are many different types of boilers that can utilize TDF combustion to augment energy generation (see Amari et al. 1999), the most popular of which is the cyclone-fired boiler. This type of boiler typically requires TDF pieces to be smaller than 2.5 cm x 2.5 cm, and the tyre chips must be de-wired prior to combustion (Ohio Air Quality Development Authority... 

Solid waste products from tyre combustion... 

Data from Polasek Jervis (1994), for pure tyre ash. Major elemeni oxides add up to only 71 wt% no further details available. Data from Lemieux (1994), collected after co-firing natural gas and TDF crumbs. Major element oxides add up to 85 and 87 wt%, respectively. Ash represents fly ash from combustion of TDF crumbs, whose fuel characteristics are listed in Tables 4 and 5. Lemieux (1994) suspected that some elements (Al, Si, Zr) may have originated from the rotary kiln insulation. 

Fig. 6. Comparison of normalized concentrations of chemical components of fly ash from two boilers. Values represent concentrations in fly ash from combustion of coal / tyre blends normalized to the respective concentrations in fly ash from combustion of pure coal (data from Table 7).

Another key factor determining the emission levels is the bulk equivalence ratio ((l>) in the furnace, a parameter that describes the relative amounts of fuel and air. Levendis and co-workers (1996, 1998fo) have shown that for both coal and tyre (and for various blends thereof) the specific emissions, that is, the mass of a certain pollutant relative to the mass of fuel burned, vary systematically when the combustion environment changes from fuel-lean (low ) to fuel-rich (high results document that, at a given temperature,... 

A larger-scale tyre combustion experiment was performed by Lemieux Ryan (1993) in order to collect emission data from a simulated open waste tyre fire. In addition to identifying a large number of organic compounds, including... 

Uncontrolled open fires in tyre dumps may burn for several months (e.g., Rhinehard tyre fire in Winchester, Virginia), generating many hazardous products of incomplete combustion, which are released directly into the atmosphere (EPA 1997). Owing to safety concerns and other factors (e.g., meteorological conditions, fire-fighting activities), it is difficult to collect air samples from the smoke plumes of these fires. The available field data revealed potentially hazardous levels of several PAHs and CO, as well as relatively high concentrations of Pb and Zn in such plumes (Ohio Air Quality Development Authority 1991 EPA 1997). 

Besides these laboratory experiments there are several emission studies on controlled tyre co-combustion in large-scale industrial facilities, including cement and lime kilns, utility boilers, and pulp and paper mills (Ohio Air Quality Development Authority 1991 EPRI 1991 EPA... 

Fig. 7. Comparison of normalized metal emissions from two stoker boilers. Values represent emissions from combustion of coal/tyre blends normalized to the respective emissions from combustion of pure coal. Purdue University data set is for 5 wt% TDF. Symbols for University of Iowa data set A, 4 wt% TDF , 8 wt% TDF. Data without error bars have standard deviations that are smaller than the symbols. Data from Table 8.

The relatively large heating value of tyres makes the use of TDF or whole tyres for combustion in utilities, industry, and manufacturing the most promising method for waste tyre management. 

In addition to collection and transportation costs, there are major expenses associated with the preparation of the tyres for combustion or with modifications to the fuel feeding systems of power plants (e.g., Goddard 1992 Lamarre... 

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