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Scientists from St. Petersburg Offer Railroaders an Environmentally Friendly Way to Recycle Sleepers

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Representatives of St. Petersburg Mining University and Oktyabrskaya Railway discussed the prospects of cooperation in the sphere of recycling of unfit for further use wooden sleepers. It is planned to use them as a raw material for the production of electricity or such marketable goods as methanol, ammonia, and hydrogen. However, this will only become a reality if the parties are convinced of the economic efficiency of the technology.

Even though reinforced concrete structures are used in the construction or reconstruction of the vast majority of modern tracks, they can be laid not everywhere. For example, they deteriorate quickly and become unusable in the polar climate. This means that the extremely urgent task of speeding up the process of recycling good old wooden sleepers will remain so for many years to come.

The thing is that it is extremely undesirable to burn them as ordinary firewood - it is dangerous for the environment and for the health of those who get into the area where the products of combustion spread. After all, various oils, antiseptics, or creosote, with which sleepers are impregnated, getting into the fire, release many toxic substances. Taking into account that in different years from 2 to 7 million cross ties with the length of 270 centimetres were out of use on Russian railroads, it is certainly unacceptable to allow such a development.

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What happens to the outdated rail supports in this case? There are two most common options: burial in specially designated landfills or storage in open areas, where used wood waits for the introduction of methods that can provide its relatively inexpensive and harmless to nature recycling.

If someone thinks that we are talking about some kind of "space" technology, it is not true. Sleepers, for example, after being crushed, can be burned in an incinerator - a powerful furnace equipped with burners that raise the temperature in the main chamber up to 800-1200 degrees and turn the furnace contents into ashes. The gases released during this process enter the second compartment, the afterburning chamber, where they are processed and lose harmful impurities. This, of course, significantly reduces the scale of pollutant emissions into the environment. Then you have a choice: either to take the waste remaining after cremation (and it is about 10 times less than the original volume of recyclable materials) to special sites or to make lightweight concrete for making paving slabs and other landscaping elements

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“Another effective way of utilization is gasification, i.e. thermal decomposition without oxygen access, in the process of which synthesis gas is produced. It can be used to produce electricity in combined-cycle plants (for example, in combination with methane - ed.) or as an intermediate for making various chemicals: methanol, ammonia, or synthetic fuels. Considering that Russian Railways is implementing a hydrogen fuel cell train project, hydrogen production may become more relevant. There are enough options, and now we are working to understand which of them will be the most cost-effective in this particular case. The fact is that any carbon-containing raw material can be used for gasification. Most often coal is used, but it can also be petroleum coke, peat, biomass, wood. Depending on the resource and technology used, the ratio of components in the synthesis gas varies greatly. That is why the effectiveness of gasification of sleepers needs to be studied further,” explained Ilya Beloglazov, associate professor of the department of technological processes and productions at St. Petersburg Mining University.

The technology is not new, of course. It was invented a hundred years ago by German scientists Franz Fischer and Hans Tropsch. It was their scientific work that allowed oil-poor Germany to obtain liquid fuel from coal, set up its production on an industrial scale, and thus lay the groundwork for the attack by Hitler’s army on Europe and then on the Soviet Union.

Several similar plants are operating in China today. One of them belongs to the Jincheng Anthracite Coal Mining Corporation and is located in Shanxi Province. Its capacity is 2,600 barrels per day. The Finns have considerably transformed the Fischer-Tropsch process and built a peat gasification unit in Oulu (this enterprise produces 300 tons of ammonia daily). Nevertheless, the essence of the method remains the same - synthesis gas is produced from carbon-containing raw materials, and from it, the product demanded by the market, in this case - NH3. By-products of the process are no less important. For example, the slag from the gas generator can be used as a construction material and the fly ash as a feedstock for the cement industry.

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“Scientists of St. Petersburg Mining University are engaged in research in the field of coal gasification together with their colleagues from Freiberg Mining Academy (FRG), where an appropriate pilot plant has been built. In the course of scientific experiments, we calculated the approximate cost price of a number of products obtained from both high-ash and low-ash Russian coal. To date, methanol production is the most economically efficient. If we talk about the prospects of cooperation with Oktyabrskaya Railway, they will depend on the results of our further research. Now at the department of automation of technological processes and production together with the center of ‘Digital Technologies,’ we are engaged in computer modeling of the technological cycle to calculate its profitability, as well as the search for a polygon, where semi-industrial tests will be carried out. It is clear that our task is primarily to minimize environmental damage, but business is also interested in zeroing economic losses, and ideally - making a profit from environmental activities,” said Ilya Beloglazov.

In addition, he noted that during the preliminary negotiations with the railway authorities they had discussed the possibility of building mobile pyrolysis units. Such units could be delivered directly to the places where the railroad tracks are reconstructed or the old sleepers are stocked, which would save a lot on logistics. Theoretically, the creation of such mini-factories is quite a realistic task, but the implementation of this idea in practice also requires serious preliminary analysis.