25 Oktober 2018

A biofuel ‘automatically’ generating heat

Breakthrough in autothermal pyrolysis

Pyrolysis – a process of biomass decomposition – can be organized automatically. That is, it is sufficient to heat biomass to a certain temperature and then the process proceeds in the autothermal mode due to its own heat release. This technology was studied by the scientists from Tomsk Polytechnic University in the article published in Journal of Thermal Analysis and Calorimetry (IF 2.209; Q2). The development of research in this domain will make energy generation out of biofuel more resource efficient and feasible.

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Photo: Arkadievsky peat, the Tomsk Oblast, Russia.

The scientists presented the study results for such types of biomass as pine sawdust, chips from various types of wood, straw, two types of peat – from the Arkadievsky and Sukhovskoe deposits of the Tomsk Oblast. They are the most common types of biomass in the region and typical for Russia as a whole. In order to generate heat and energy valuable products, including tar, solid carbonaceous residue and combustible gas, TPU scientists subjected it to pyrolysis, the process of thermal decomposition of organic matter in an oxygen-free environment.

On the planet, there is a huge amount of organic matter which can be used as biofuel, i.e. products of the plant and animal worlds as well as the vital activity of human society. Such fuel is certainly much more environmental friendly compared to traditional fuels.

The co-author of the study, Roman Tabakaev, a research fellow at the Butakov Research Center says: “However, to replace or just compete with fossil organic raw materials, fuel production out of biomass should become more feasible.”

One of the ways to produce heat from biomass is pyrolytic processing. Pyrolysis is the basis for many modern technologies – the production of biofuels out of biomass, conversion of biofuels, etc. Despite the fact that pyrolysis is known for a long time, scientists have not come to a common opinion as to whether this technology is energy-consuming. Some believe this is an unprofitable wasteful technology as it requires energy expenses to decompose organic matter. The other prove that pyrolysis can run with heat release that can be used to maintain the process itself. The study carried out by TPU researchers vividly prove this assumption.

In autothermal processes, the reaction temperature is maintained due to own thermal release. Practically, it allows the reduction of the cost of the technological process, increasing the efficiency of processing and the reduction of the number of auxiliary equipment.

In the respect of pyrolysis, an autothermal regime is a process in which the magnitude of the thermal effect exceeds thermal costs. That is, at the decomposition of biomass more heat should be released than it takes to heat it. To identify the values of these indicators – the heat effect and heat costs – for specific biomass types, the authors of the article conducted thermogravimetric (TGA) and differential thermal analyzes, and also experimentally processed the above-mentioned biomass samples.

‘The experimental and analytical data obtained indicate that during the pyrolysis of straw, chips, sawdust and peat from the Sukhovskoy deposit the amount of heat released is more than it is required for their heating. In the case of peat from the Arkadievsky deposit, the thermal effect was less than the cost of heating,’
– notes Roman Tabakaev.

This effect for straw and wood is associated with the processes of decomposition of cellulose, lignin, and hemicellulose during pyrolysis. These processes generate additional heat. In the case of Sukhovskoy peat, this effect is due to the decomposition of cellulose, humic and fulvic acids.

Thus, the difference between the received and spent heat for dried straw samples was +654.5 kilojoules per kilogram (kJ / kg), for chips – +282.0 kJ / kg, for sawdust – +303.6 kJ / kg, for Sukhovskoy peat – +275.3 kJ / kg.

“In the article, the calculations show the possibility of organizing such an autothermal pyrolysis. This data is confirmed by the results of recent physical experiments with straw, which showed that when the temperature of the straw reaches 365 ° C, it continues to rise without additional heating, ‘independently’, to 430 ° C.

Our current task is to physically perform pyrolysis in an autothermal regime with the continuous supply of raw materials to the reactor, for which we are now creating an experimental installation,” says the scientist.

Source: Tomsk Polytechnic University, press release, 2018-09-18.

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