Profile of pyrolysis (wood gasification)

The term pyrolysis has been gaining popularity again in the bioenergy circles for some years. Since I also had some questions and comments on the topic, but still wrote relatively little on this topic, I would like to briefly introduce it today.

Why is it "regaining" attention? Because pyrolysis already takes place during second worldwar was used and at that time was mainly seen as an attempt by fossil fuels become independent on a petroleum basis and be able to extract oil on a larger scale in your own country (Fischer-Tropsch synthesis, Bergius-Pier process). Germany has its own oil wells (Schleswig Holstein, Lower Saxony), but these quantities were too little for the war that followed. However, this dark chapter should not be the subject of the article, but the process itself and the current status.

3 ways to bioenergy

In general there is three ways to unlock biomass and release the stored bioenergy. Even if all processes are of course subject to the different levels of natural law and cannot be strictly separated, I would assign the processes to chemistry, biology and physics according to their triggering mechanisms.

  1. combustion: chemical conversion of the organic components through aerobic oxidation, whereby the stored energy is released in the form of heat (CHEMICAL)
  2. Fermentation: the process in biogas plants, in which a "digestion product" is created in the absence of oxygen but with the help of microorganisms (BIOLOGICAL). This is methane, which as part of the biogas is very rich in energy and can be burned. Another possibility is alcoholic fermentation (with oxygen), which produces ethanol (bioethanol).
  3. pyrolysis: a special relationship between pressure and high temperature (PHYSICAL) triggers a kind of structural breakdown in the biomass with subsequent sublimation. This suddenly transforms the organic substance into gas and solid residues. Long chain hydrocarbons are broken down into short chain ones.

All three forms are used in a wide variety of variations and indicate the known width Input materials, Substance quantities and varying process conditions. As far as I know, pyrolysis has not yet been clearly defined and is still subject to research in many areas. Many physico-chemical and procedural framework can easily be changed and a range of products is created (coke, gas, tar oil, charcoal -> hydrocarbons in various aggregate states).

The process of pyrolysis

Despite the difficulties in squeezing the process into a narrow framework, the temperature parameter can be used Low temperature pyrolysis (500 - 700 ° C) and high temperature pyrolysis (over 700 ° C) can be distinguished from each other. And depending on the structure of the process, a distinction is made between them Rotary tube pyrolysis from the Fluid bed pyrolysis.

The aim of the process is to break up the long hydrocarbons of the biomass into shorter ones by means of a high temperature. So the idea is similar to that of cracking in Oil refineriesbut less complex in structure. The biomass is sealed airtight in a corresponding reactor and then from the outside Supplied heat, By the anaerobic situation the burning (chemical change) of the organic constituents is prevented and the connections remain broken. There are also special procedures in which the high energy of a combustion (with oxygen) is used, but the permitted amount of oxygen is too small to allow a complete combustion to take place. The Partial combustion is used as a heat source. The above-mentioned products of the hydrocarbons are produced by the processes described.

The resulting hot exhaust gases are then used to generate energy (e.g. with the help of steam generation) and the solid residues can be used as high-quality carbon sources (activated carbon -> Soil improvement) used or too Dying be refined. In my opinion, the principle of the process is also in a technically slightly modified form (particularly high pressures) under the name of Hydrothermal carbonization in circulation, but I don't want to be specific - maybe the differences are bigger than I thought.

For which users is pyrolysis interesting?

The processes taking place and the procedural side of pyrolysis or wood gasification are of interest to many curious people. After all, it is about a digestion or conversion process for the fastest regenerating substances on this planet - biomass (organic matter).

As far as I know, it is interesting for the more practically savvy private user, above all for the following reasons.

  1. Cleaning process: Ovens can be cleaned with the help of the high temperatures that occur during the pyrolysis process. The residues of food in the oven are sublimed and thereby converted into a gas and a powder residue. Both are easier to remove than the original encrusted cheese remains. This saves time and nerves, but it is energy-intensive and should therefore be used consciously and not necessarily as a routine after every pizza.
  2. Bioenergetic plants with excess heat: I could imagine that a combination of two bioenergetic methods could be very effective. For example, some biomasses (e.g. very watery ones) can be fed directly into a biogas plant (1st process) for fermentation. The resulting biogas is converted into electricity in a block-type thermal power station (BHKW). This also creates a large proportion (around half) of thermal energy that cannot always be used because there are often no possible applications in decentralized regions and heat cannot be transported as loss-free as electricity. A pyrolysis stage (2nd process) could start here and the excess heat could be used as a kind of basic heat load for the gasification of relatively dry biomass. The overall efficiency of both systems can be increased by this special type of Combined power plant increase. Such an upgrade might pay off for very decentralized farmers or communities with existing biogas plants. In the following overview I have graphically illustrated this idea.

Biogas pyrolysis combination

With the help of one Sankey diagram it could be specially designed and calculated for each individual compilation.

Epilogue

During the Second World War, the process was not used in an energy-efficient manner and a lot of energy had to be invested in order to access the valuable resource oil for fuel. Today, after the Second World War and the oil crises, the process is experiencing another spring, but with the demand for large-scale production, a better one Energy balance to show. So the interest in the composition of the resulting products (coke, gas, tar oil, charcoal) has changed and that Efficiency requirements have increased. The full potential of the process has yet to be tapped and it will probably be a few more years until it is integrated into economic processes research thats it!

5 comments on “Profile of pyrolysis (wood gasification)”

  1. I have been observing the market for micro-CHPs for some time. I am fascinated by the technology of wood pellet combustion and power generation using a Stirling engine. This combination is offered in Germany as a Sunmachine. Her only problem is that in summer I don't know what to do with my excess hot water. If I press pellets again over hot water or U. (brown) coal could produce, that would be the highlight of the CHP market in terms of innovation and economy.

  2. So the market for CHPs and especially micro-CHPs is really very exciting, because with this technology, very fundamental changes in energy supply are conceivable. I also sometimes wonder in what form the excess heat generated in summer could be used. If you succeed here in a good development or a new concept, then I agree that it is not only good for the environment (increased efficiency), but also very interesting economically.

    So you have the overheated steam and can continue to use it in the warm seasons. The heat pipes must of course be laid, but then the energy of the steam can be used thermally or energetically. The idea of ​​using the steam to operate a pump or press seems very meaningful to me. One would have to calculate whether the contained energy content of the steam is still sufficient to press pellets or at least provides a good basis. Another possibility would be that the temperature of the steam can be used in any case to dry the biomass. And then carry out the pressing.

    For the thermal support of many pyrolysis processes (approx. 200 ° C), the energy content of the superheated steam should actually be slightly sufficient.

    The “Sunmachine” concept sounds good and the small size of micro-CHP units impresses me again and again. Unfortunately, I did not find any information on the performance spectrum of the systems on the site, because I would have been quite interested in them.

  3. THANK YOU! I have been trying for 2 days to find out what pyrolysis should be used for! NOW I KNOW IT: D

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