Pyrolysis is a promising way of wooden sleepers recycling

Pyrolysis is a promising way of wooden sleepers recycling

Over the past 25 years environmental requirements in European countries have intensified and are aimed at limiting the use of wooden sleepers saturated with creosote. And in the Netherlands, creosote-saturated wooden sleepers are already banned for environmental reasons. This forces the railways to look for new, environmentally friendly solutions, such as pyrolysis.

The Ukrainian railway ranks sixth in Europe and twelfth in the world in terms of the total length of tracks – the operational length of the main sections is 22,3 thousand km. Today, about 75% of the railway track consists of wooden sleepers saturated with creosote to prevent rotting. Such widespread use of wooden sleepers is due to a number of their advantages. Wooden sleepers with a weight of about 80 kg are much lighter than reinforced concrete sleepers, the weight of which is 270 kg. This allows for laying and repair work by a team of workers without the involvement of special lifting mechanisms and tools.

Wooden sleepers have the necessary rigidity and elasticity to distribute the loads from the wheelsets of the rolling stock on the rails evenly. In addition, you can easily increase the track gauge in curves of a small radius (this procedure is necessary in some cases to prevent a possible derailment of wagons).

Sleepers made of wood are a good dielectric, in contrast to reinforced concrete sleepers, which conduct electric current well due to the metal reinforcement.

However, the standard service life of wooden sleepers sautrated with antiseptics is 14-25 years, but depending on environmental conditions and due to the intensification of traffic flows and an increase in loads and speeds, the service life can be reduced to 8-10 years and require regular replacement of worn sleepers … For example, on the railways of North America, 14 million of 700 million wooden sleepers have to be replaced annually.

Sleepers that have served their life should be disposed of or buried in special landfills for industrial waste. However, every year the space on landfills becomes less and less, and nowadays, due to overcrowding of landfills or their absence, used wooden sleepers are often stored in places not intended for this. This has a negative impact on the environment, so the problem of disposal of sleepers is of great importance.

One of the most common ways to dispose of wooden sleepers is incineration. A huge disadvantage of this method is a large amount of toxic substances (phenols, phenanthrene, acetone, butanol). These substances adversely affect not only the environment, but also human health, contributing to the emergence and development of various diseases, including cancer.

As a result of the release of toxic substances, it is also absolutely unacceptable to use old wooden sleepers for the construction of various barracks, utility rooms, flooring, bridges, and the like. In addition, such devices are fire hazardous – the fire spreads quickly, the premises burns out in 15-20 minutes.

A promising way of recycling sleepers can be pyrolysis – thermal decomposition without air access of waste wooden sleepers from the distillation of this coal oil. It is hoped that the use of pyrolysis for the disposal of sleepers will not only prevent environmental pollution, since the process is carried out in a sealed environment, but also obtain economic benefits. With the correct organization of the technological process, this utilization method will allow not only to cover the energy needs of the pyrolysis process, but also to use the excess heat generated for technical or household needs.

Utilization of used wooden sleepers as fuel based on gasification technology allows us to solve all pressing problems, providing:

• efficient use of sleepers as fuel for heat production;
• required environmental indicators;
• replacement of a significant amount of natural gas and coal fuel with a renewable fuel – spent railway sleepers.

The obtained thermal energy can be used for heating systems of both residential and industrial facilities. All this will make it possible to logically close the life cycle of used wooden railway sleepers, giving them the opportunity to re-efficiently work at the final stage of their existence.

One of the promising solutions for replacing wooden sleepers is the use of plastic sleepers. Compared to wooden, plastic sleepers have a number of advantages – they do not rot, do not split, and have a much longer service life (up to 50 years). Wooden sleepers can be gradually replaced with plastic ones and for this, the same equipment is used as when installing wooden sleepers. But the most important advantage of using plastic sleepers is their recyclability and reuse.

Railway magazine “Railway Supply”

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