The green-wave slogan ”Waste is displaced resources” is certainly true. However, recycling works best where resource recovery can be made into profitable industry. The key to profitable recycling lies in reliable and efficient classification and separation technology.
The value of recycled materials depends on the fraction purity. As an example, a 1000 bottle PET batch is useless if it contains 1 PVC bottle. In practice, there will be an economically motivated trade off between fraction purity, recovery, and capacity. In any case, the value in waste is relatively low so instrumentation cost must be kept down.
The sweet relation of the technology and economics have to analyse, without profit nobody can exist....
and the cost effective procedures and automation can make a difference .
ENVIRONMENTAL IMPACT OF WASTE TYRES
Tyres are designed to last and are therefore difficult to break down and separate into their constituent parts.
Adding to this problem, disposal releases potentially harmful compounds into the environment, e.g. polyaromatic hydrocarbons (PAHs), benzene and phenol which have suspected carcinogenic properties. Studies in Sweden estimate that 14 tonnes of PAHs are deposited onto Swedish roads each year through tyre wear (ENDS 1999). Landfill disposal and incineration also release these harmful substances.
Most countries have relied on landfilling to dispose of tyres but the limited space and the potential for reuse has led to many countries imposing a ban on this practice. Landfills are not leak-proof which means that hazardous substances generated during the decomposition of material can filter down through the site and into the surrounding area. In this way it has the potential to pollute water courses and affect living organisms. Tyres tend to rise to the surface of landfill sites and restrict the future use of the land (Pavlou 1997).
Burning tyres can have a serious environmental impact. Whilst tyre fires are uncommon, they produce vast quantities of harmful emissions that will pollute the atmosphere and water courses through run-off. The high energy content of tyres means they can burn for long periods. For example in Wales, a tyre fire started in 1989 in a covered tip containing 10 million tyres was still burning nine years later.
ranulation
Scrap tyres can be ground into a crumb and used in a variety of applications. These include:
- carpet underlay
- children's play areas
- cones and bollards
- landscape mulch
- rubber car mats
- sports surfaces.
Research is also underway into the use of crumb rubber in road surfaces to reduce noise pollution. The Highways Agency and the Road Traffic Research Laboratory have laid crumb rubber from 6,000 tyres on a 2.5km stretch of dual carriageway and are monitoring the results (Warmer Bulletin 1999b). If successful, widespread use is extremely likely which would strengthen the presently fragile crumbing industry.
Energy Recovery
The 48% rubber content of tyres makes them a high energy source and therefore a potential fuel. One application for this valuable energy source is to power high-temperature kilns used by the cement industry. In 1997 24,000 tyres were disposed of this way and the STWG predict that cement kilns could be used to dispose of a further 145,000 per year (Warmer Bulletin 1999b). TheSTWG is now being criticised for placing too much emphasis on this process and disregarding other potential solutions (Materials Recycling Week 1999b).
Energy requirements comprise 70% of the cost of the kiln, so a more cost-effective source of energy in the form of waste tyres is an attractive option. This form of incineration involves the complete combustion of the tyre leaving no residue that has to be disposed of afterwards. However, burning the tyres produces emissions that have to be carefully controlled to ensure they do not enter the environment. Gases are therefore filtered and cleaned (a process known as scrubbing) so that the final emissions are within limits set by the Environment Agency (EA).
For a waste recovery system to be widely adopted it must be economically viable to use waste rather than virgin energy sources. At present, use of tyre waste in cement kilns is economical but if emission limits are tightened, the cost of installing purification equipment may outweigh the cost saving of using tyre waste as a fuel (Warmer Bulletin 1999b).
Pyrolysis
There is one commercially operated pyrolysis plant in the UK. The operation is small enough to be transportable so it can be taken to where there is a large stockpile, as opposed to tyres being bulk transported to one site. It is able to process up to 90,000 tyres per year. Unlike incineration, the energy is recovered in a form that can be stored and used when needed. Table 1 lists the by-products that are produced.
everytime i sip a tea , i tried to take a ecyclable one... but mostly i am getting only plastic, i just asked my purchase guy, who told about the big difference in the price factor , that we cannot afford in the time of recession .....
i just asked " in the time of recession , recession is started before 1 month , this purchasing is started before 1 year" \
he just smiled.. a recyclable smile...
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