Pyrolysis of wood is one of the first chemical processes adopted by humans. From the 12th century onwards, it was widely used in Russia to produce pine resin (used for tarring wooden ships and impregnating ropes), a process called tar-distillation.

It is believed that Sweden pioneered the use of pyrolysis technology on an industrial scale in the 16th century. The Swedes used the technology of impregnating shipboard wood with tanning pine resin from a simple pyrolysis process. The copper vat was filled with softwood logs and sealed so that no air could enter the vat. The vat was heated over an open flame to a temperature of 400°C-500°C, with oily resins accumulating at the bottom and draining through a hole in the bottom. With the development of metallurgy, there was another industry based on the technology of pyrolysis of wood – coal burning. When wood was burnt without air access, charcoal was produced.

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    Russian chemists Julia Lermontova and Alexander Letnyi were the first in the history of chemistry to point out that hard coal yields lighting gas (a mixture of hydrogen, methane, carbon monoxide and other combustible gases produced through the pyrolysis of coal or oil), which is worse in quality than gas of petroleum origin. In 1877 the effect of pyrolysis of hydrocarbons was patented by Alexander Letnyi.

As early as 1875, he discovered that at temperatures above 300° C, heavy oil residues partially decompose into lighter products — gasoline, kerosene, and gases. It was in 1877 that he first separated aromatic hydrocarbons from oil (benzene, toluene, xylene, anthracene, etc.); he established important regularities in the process of pyrolysis of oil. Almost at the same time the first plants were built in Kiev and Kazan. To produce gas for lighting, kerosine was subjected to pyrolysis. The industrial application of pyrolysis technology was greatly boosted by the First World War, when there was a great need for toluene, a raw material for the production of TNT. In the 20th century, a significant contribution to the development of new areas of wood pyrolysis was made by Professor D.V. Tishchenko.

In our country, solid fuel pyrolysis has been very important in the energy sector for a long time (before natural gas was used). At many enterprises, powerful gas-generating equipment was installed, and cars were equipped with engines running on gas generated in the pyrolysis process.

In the 1930s, industrialisation in the USSR was very rapid. This pace required a huge fleet of vehicles, which in turn required enormous quantities of hydrocarbon fuel - petrol and diesel. A constant shortage of petroleum products was felt.

In order to solve this problem, mobile gas generators, invented during the First World War, were widely used. The scheme of the gas generator set is simple. The fuel loaded into the gas generator is ignited through an air valve by a flare. The air required for gasification is sucked into the chamber through tuyere holes due to the vacuum created by the suction action of the engine. And its amount must be insufficient for complete combustion of the fuel. In this process, the carbon of the fuel combines with the oxygen in the air to form carbon dioxide (CO2) and carbon monoxide (CO). These then enter the reduction zone, where they pass through a layer of glowing coal on the grate.

This converts non-flammable CO2 into flammable CO. The hydrogen in the fuel partly combines with oxygen to form water, which is attached to the moisture in the fuel, and the rest is emitted in its pure form. Due to the high temperatures in the gasification chamber, some of the moisture combines with the carbon to form carbon monoxide and hydrogen. The carbon monoxide, together with the carbon dioxide previously formed and obtained from the reduction of carbon dioxide, goes into the generator gas. The hydrogen resulting from the decomposition of water combines with free hydrogen, with some of this hydrogen transferred to the generator gas and the other part reacting chemically with the carbon of the fuel to form methane.

Theoretically, all the oxygen in the air should be consumed during gasification, but in reality, some of it is retained and transferred to the generator gas. Water, not decomposed during gasification, passes into the generator gas in the form of steam. In the fuel layer immediately above the combustion zone, the pyrolysis (or dry distillation) of the fuel takes place, i.e. heating without air access. The products of the dry distillation are charcoal or coke and the volatile substances, resins and moisture that emerge in gaseous and vapour form. All the products of dry distillation in the described type of generator pass entirely through the combustion and reduction zone, where they undergo gasification processes, somewhat more complicated than described, but yielding the same basic products. Above the dry distillation zone is the drying zone, where the fuel is dried. At the outlet of the generator the gas has a high temperature and is clogged with ash and coal particles. In this form it cannot be used in the engine and must be cleaned and cooled before it enters the cylinders.

Worldwide, pyrolysis gas is being increasingly used as an alternative energy source, above all for heat. In many European countries pyrolysis gas has been a common fuel used to generate electricity, steam and hot water for decades. The thermal pyrolysis of hydrocarbons is now the main method for producing ethylene and propylene.

   Pyrolysis of solid fuel has the same essence as that of liquid fuel, which Letny wrote about. When splitting solid fuel molecules, a carbon-rich solid phase (coke, coal) and a gas phase containing hydrocarbon vapors (pyrolysis gas) are formed. Pyrolysis gas is obtained in the process of thermochemical transformations of solid fuel as in conditions without air access when heated to 500°C-1000°C with a heat of combustion of 3000-4000 kcal/Nm3, and in the combustion process with a lack of air by reaction With+O2=CO2+Q, then CO2+C=2CO-Q , C+H2O=CO+H2-Q with a heat of combustion of 900-1600 kcal/Nm3 Gorenje.

   The pyrolysis (gas-generating) boiler is based on the principle of pyrolysis combustion of fuel, the meaning of which is that under the influence of high temperature and in the absence of air, wood splits into a volatile part - pyrolysis gas and solid residue (ash). After burning solid fuel in the boiler furnace, which flows in the form of its smoldering, the released pyrolysis gas enters the gas afterburning chamber, after which it burns with a very clean flame. The combustion energy of pyrolysis gas from the afterburning chamber is taken through a heat exchanger and used to heat the coolant involved in the combustion process.Gorenje Thus, pyrolysis boilers with solid fuel have a higher efficiency and allow you to adjust the power.

In the conditions of rising prices of such energy carriers as gas and liquid fuel, the issue of gasification of solid fuels, in particular, wood and coal, becomes more urgent. Russia is one of the most forest-rich countries. We had the best scientists in the world working on pyrolysis, including wood pyrolysis. Pyrolysis boilers are profitable, efficient, and very economical heat equipment for any room!