Comparing 3 Methods of Recycling Scrap Tyres

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PyrolysisReclaiming Rubber using MSD-10 Continuous Screw DevulcanizerTyre-Derived Fuel
Burning scrap tyres in a reactor, in a low or oxygen-free environment, with temperature of over 430°CThermo-mechanical devulcanizing process at atmospheric pressure and conducted at 220 – 250°CScrap tyres are burned as replacement fuel in cement plants and steel mills at 1450 – 2000°C
Equipment to process tyres:-
Tyre shredding
Steel separation
Pyrolysis reactor
Oil refining

Tyre shredding
Steel separation
Continuous Screw Devulcanizer
Refining mills


Tyre shredding
Products are:-
Heavy fuel oil  – 40%
Gas               – 10%
Carbon waste – 35%
Steel (PCT)    – 15%

Rubber        – 70%
Steel (TBR) – 30%

36 GJ/Ton of energy
Manufacturing Cost/Ton:-
Scrap tyres @ RMB2000
Production  @ RMB  700
Total           @ RMB2700

Scrap tyres @ RMB2000
Production  @ RMB1200
Total           @ RMB3200

Scrap tyres @ RMB2000
Production  @ RMB  100
Total           @ RMB2100

Revenue/Ton of Scrap Tyres:-
Fuel oil 0.4 Ton @ RMB5000
Gas     0.1 Ton @ RMB6000
Char   0.35 Ton @ RMB1000
Steel  0.15 Ton @ RMB1600
Total Revenue    = RMB3190

Profit = RMB490

Devulcanized rubber 0.7 Ton @ RMB5000
Steel                       0.3 Ton @ RMB1600


Total Revenue                      =  RMB3980

Profit = RMB780

Replacing 1 Ton coal @ RMB 800





Loss = RMB1300

Environmental / Health Concerns:-
Inherent risk of explosion and fire
Air pollution from emission of Sulphur Dioxide, Carbon Dioxide and Nitrous Oxide
Carbon waste has little commercial value,
could be used as landfill

Very little emission to air
No water is discharged
No residual waste.
Complete reutilization of raw materials

Air pollution from emission of Sulphur Dioxide, Carbon Dioxide and Nitrous Oxide
Water pollution from ash leachate
Solid waste products, e.g. ash
Inefficient energy conversion

*Costs are based on production capacity of 10 Ton/day for pyrolysis and reclaiming tyre and on the local prices in Shanghai for June 2014. Cost differences, especially for labour, can be expected due to regional variations.

MSD-10 Continuous Screw Devulcanizer

devulcanizer Management of Scrap Tyres

The management of scrap tyres depends very much on local economic and industrial conditions and could be classified into following categories:

  • Product recycling – for civil engineering applications like coastal protection.
  • Material recycling – tyres broken down and materials reprocessed into new products.
  • Energy recovery – incineration to extract the heat value from tyre.
  • Landfill – storage of tyres when better solutions not available.

Direct disposal of scrap tyres in landfill is the least desired option, and should be adopted only when no viable commercial or energy recovery alternative exists.

Material recycling applications like reclaim rubber and pyrolysis are the most widely adopted methods.  Energy recovery options divert scrap tyres for use as supplementary non-fossil fuel.

 

Energy Recovery

Recovery by energy generation yields about 36 GJ/Ton as tyre-derived fuel, about the same energy value of 30GJ for a ton of coal.  When scrap tyres has a commercial value, as in China where they are sold for RMB 2,000 (USD 320) per ton, higher than the fuel they replace (e.g. coal @ RMB800/Ton), then this method is no longer viable economically.

 

Pyrolysis

When scrap tyres are recycled by the pyrolysis method, end products are heavy-grade oil, carbon char, scrapped steel and gas. The oil has to be refined and could be used as industrial fuel or mixed with diesel. The char may be used as filler for producing asphalt or cement, but its market demand is uncertain. Gas produced during pyrolysis and not condensed as fuel could be used for burning but must be processed properly otherwise it would escape into the atmosphere and pollute the air with carbon monoxides, sulphur oxides and polycyclic aromatic hydrocarbons which may be harmful to human communities living nearby.

 

Reclaiming Rubber

In reclaiming rubber by the continuous screw devulcanizing method, there is no residual waste and the process is energy efficient.  Energy consumption is minimized because scrap tyre is recycled to the original components – rubber polymers/carbon black compound, steel and nylon/polyester which could be reused as raw materials. Energy consumed or lost is minimized, thereby making this method of recycling scrap tyres a very green and sustainable commercial activity.

 

Energy Balance

When recycling scrap tyres, the energy balance of the activity should be considered to ensure the conversion is energy efficient and carbon footprint is reduced.

The energy required to produce 1 ton of tyre is about 190 GJ/Ton; this energy equivalent is derived by adding the energy required to produce the component materials of polymers, steel, nylon/polyesters and other additives. The net calorific value of burning the tyre as fuel is only 36 GJ/Ton and about 1GJ is required to cut the tyre into pieces, making a net loss of 155 GJ for every ton burned.

Looking from another angle to put this energy efficiency into perspective:-

  • To make a ton of natural rubber requires the same amount of energy to drive a car from Brussels to Singapore (about 10,560 km).
  • To make a ton of synthetic rubber requires the energy equivalent of driving from Rome to Sydney (about 15,000 km).
  • To reclaim a ton of rubber only requires the energy to drive from Paris to Geneva (about 400 km).

Thus, when we select the ideal recycling method to process scrap tyres, we should consider the commercial viability first to ensure its sustainable development, and then also the energy security benefits derived from its contribution to reduction of carbon footprint and meeting climate change mitigation implementation targets.

Reclaim Rubber Sheets

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