Whole tyre

Although tyres can be used as an alternate fuel, they are most often utilized as a supplemental fuel. Tyre fuel exists either in shredded form (known as TDF, or tyre-derived fuel) or as whole tyres. Tyre-derived fuel consists of tyre chips, usually no larger than 5 cm on a side (Blumenthal 1993). The size reduction procedure is itself an energy-intensive process, and costs increase as the particle size decreases (Atal Levendis 1995 Amari et aL 1999). The cost of cryogenic grinding of tyres can be as much as five times higher than that of pulverizing coal (Atal Levendis 1995). Whole tyres or TDF... 

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... 

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. 

The percentage sulphur (determined in the un-vulcanized reclaim) and the available rubber hydrocarbon are taken into consideration while evolving the compound formulation. It should be noted that reclaimed rubber is not all rubber. In arriving at the total rubber content in the rubber formulation containing reclaim, allowance must be made for its rubber content. For example in the following blend of smoked sheet and whole tyre reclaim, the total rubber content is to be considered as 100 parts instead of 125 parts as below and the proportion of other ingredients should be worked out accordingly on "parts per hundred rubber" (phr) basis. 

Whole tyre reclaim (rubber content-50%) - 50 parts Total -125 parts... 

Reactor Feed material o Temperatur C LWS PE 740 TWS-1 PE 780 TWS-1 used Syringes 720 TWS-1 tyre pieces 750 TWS-2 whole tyres 700... 

LWS laboratory scaled reactor, TWS-1 pilot plant, TWS-2 pilot plant for whole tyres, PE polyethylene, + trace detection... 

The whole tyres roll through a gastight lock into the reactor (Fig. 7). Observable events can be described as follows. The tyre, landing on the fluid bed gradually sinks into the sand. The material heats up and softens, its surface becoming covered with hot sand grains. 

Processes involving the use of solid acid catalysts have also been patented. According to Chen and Yan,40 plastic and/or rubber wastes are first subjected to a size reduction step, followed by separation of any metals present and washing to remove any non-plastic material such as paper, labels, etc. Subsequently, the polymer wastes are dissolved or dispersed in a petroleum oil, with a high content of polycyclic aromatic compounds at 300 °C, and catalytically transformed in an FCC reactor at temperatures of about 500 °C. Details are given for the conversion of different wastes used whole tyres, PE bags and PS foam. 

Irrespective of whether the source of waste rubber is whole tyres, tread buffings or GRG, the crumbing operation is sometimes carried out under cryogenic conditions (i.e., it is cooled to below around... 

Type of rubber crumb, e.g., crumb from truck tyre tread or whole tyre crumb... 

The type of ground rubber (e.g., whole tyre, tyre tread or other type, e.g., ethylene-propylene-diene monomer, EPDM). 

At the 4th Rubber Modified Asphalt Conference held in Akron, OH, USA in 2009, a wide-ranging paper was presented by Baumgartner [54] that addressed topics such as modified asphalt formulations, optimisation of the process temperature, and the ground tyre rubber loadings and particle size optimisation. The paper showed that rubber crumb produced from whole tyres contains around 30% reactive material for asphalt modification and that the asphalt source and chemistry directly influence the rubber loading and the final properties of the product. The processing time and temperature are also very important, as is the particle size of the crumb, which affects the efficiency of modification and the long-term performance. 

The syngas that is generated by the pyrolysis plant will be used to power it. The plant is capable of dealing with whole tyres, so does not need any pre-grinding step, and can be customised to meet local requirements. 

A large number of waste tyres are incinerated in cement kilns to produce Portland cement because they are particularly well suited to being a source of energy for this particular application. The reason for this is that the kilns operate at very high temperatures (e.g., 2,000 °C) and this converts the steel in the whole tyres to iron oxide as well as recovering the zinc oxide from the rubber and creating CO2 and sulfur dioxide. The sulfur dioxide does not escape from the kiln, as it reacts with the calcium oxide present to form calcium sulfate. These... 

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