Hydrothermal carbonation - a magical route to bioenergy

A great idea from the field of bioenergy with magical attraction. What if there were a process technology with which the renewable raw material biomass could be converted into any form comparatively easily and the geomorphological effect of many millennia replaced by just a few hours?

Biochar hydrothermal carbonization HTC pyrolysis biocoal

Despite the “shovel guitar player” in the photo, coal mining in a mine was certainly not a great pleasure. The extraction of coal now has a more attractive alternative. The director of the Max Planck Institute for Colloid and interface research (Potsdam), Markus Antonietti, has an article in the magazine MaxPlanckResearch (2/2006) received over 1000 questions from all over the world and was very surprised by this overwhelming feedback (see also article HTC in Berlin-Brandenburg).

The article was about a process called "hydrothermal carbonization" (HTC) that he and his team described. The process has been known for over half a decade. The process itself is much older ("carbonization"). A detailed investigation and considerations for a large-scale use are only now becoming increasingly interesting again. And the apparently so simple, with great effect, is actually very attractive.

What is so revolutionary about hydrothermal carbonization and what makes the idea so fascinating?

The process engineering looks in simplified form as follows. Biomass is placed in a pressure vessel and a catalyst is added to accelerate the reaction. The container is hermetically sealed and properly heated with thermal energy (180 ° C). The rest is done by time, which means that there is a wait of about 12 hours. This treatment of the decoction creates a kind of coal dust and water in the container. Pure coal dust is obtained after drying. In this article you will find further information on the production of biochar by HTC, pyrolysis or torrefaction

Gasification pyrolysis gasification torrefaction coal biochar

It is therefore not a way of generating energy, but rather a process to process organic matter. In a way, a refinement of biomass into a certain one molecular structure. It is particularly exciting that by slightly changing the general conditions (duration of cooking and temperature) different products can be generated. By varying the cooking time, either humus, peat, brown coal or a type of petroleum can be produced.

Perhaps the conversion of hydrothermal carbonization is not quite as fascinating as the possibility of turning water into wine or stone into gold, but the undermining or Outwitting time has something magical about it. The process is a kind of “Earth History in Time Lapse”.

According to Marcus Antonietti, the most effective use of the coal powder is not the subsequent combustion, but the conversion into electricity in one Carbon fuel cell. At Harvard University there is a pilot plant with an electrical efficiency of 60%. In addition, for the process of HTC only Waste materials and no high-quality biomass that could also be used as food.

Critical examination of the process

I do not want to stand up and make any speculations about process engineering based on remote diagnostics, but of course at this point a curious reader may ask some questions about the hydrothermal carbonization process.

  • The most obvious question in my opinion is the question of the energy balance? If the pressure vessel has to be heated to 12 ° C for 180 hours (including catalysts) without producing any energy or triggering an exothermic reaction, how can a good overall energy yield take place when the coal dust is subsequently used? Does the produced coal dust provide enough energy that the previous energy-intensive processing and drying is worthwhile? Perhaps the required amount of heat from the steadily increasing use of CHP systems could be used to run the process. In the near future, large amounts of heat will be generated (e.g. from CHPs), for which there are not always enough uses (especially in summer). Nevertheless, the amount of heat required would have to be taken into account in the energy balance.
  • What exactly or how big is the difference between hydrothermal carbonization and pyrolysis (biomass gasification)? Do the two differ mainly in their framework conditions (higher temperature and higher pressures during pyrolysis) or are there more fundamental differences? The products of the process appear to be similar (synthesis gas, coal). In particular, indirect pyrolysis with exclusion of oxygen and hydrothermal carbonization sound to me according to the same process under a different flag.

Despite my skeptical or at least critical attitude, I am pleased with the new one (Newly developed) process engineering very much and I keep my fingers crossed for the further development of hydrothermal carbonization.

16 responses to "hydrothermal carbonation - a magical path to bioenergy"

  1. Dominique Beurret

    We have a proven pyrolysis reactor process (closed CO2 cycle from vegetative biomass coal and through which oil and biogas are produced). We are looking for cooperation with local authorities, researchers, investors, coal burner manufacturers or similar. If your research and development department or the marketing department would contact us, we would be very happy.
    Best Regards
    D. Beurret

  2. For a critical examination of the process

    - Difference to pyrolysis: pyrolysis takes place at a much higher temperature, so it needs a lot more energy; The pressure is saturated in both. I don't think wet material can be used in pyrolysis, but I'm not sure. I'm just getting used to the topic

    - Hydrothermal carbonization is an exothermic reaction in which the oxygen content and hydrogen content are reduced. (Dehydration and decarboxylation) At the beginning you need initial energy, which can be recovered later. But the exact course of the reaction has not yet been clarified. The reaction equations are still under research.

  3. For me, both processes for the energetic use of biomass sound very similar. I find the idea that the methods of HTC and pyrolysis can best be distinguished from one another by quantitative limit values ​​for the parameters of pressure and temperature.

    If you are digging deeper into the topic and maybe find something, it would of course be nice to make a precise scientific distinction between pyrolysis and to experience hydrothermal carbonization (if there is one already). In any case, both processes are very attractive and I am curious to see what they will mean for the development of bioenergy.

    Good luck with your further research!

  4. Bernhard Geiser

    There are several articles on Wikipedia:

    About Europe's first commercial (and apparently energy neutral) application:

    ithaka-journal.net/europas-erst-biokohle-produktion- goes-in-betrieb

    about exactly how it works:
    ithaka-journal.net/pyrolysis reactor

  5. It is really important that the process 1. can use totally wet material and 2. is exothermic.

    The use of biomass has a big problem - the low energy density. Without compression, biomass can be transported a maximum of 30km without turning the energy balance into a negative. Thermal compression processes, such as pyrolysis, including “torrefaction”, have the disadvantage that the water content must first be removed (squeezed out and evaporated). Thats expensive.

    With hydrothermal carbonization, on the other hand, part of the energy contained in the biomass is used for the process and, after compression, only approx. 6% of the energy is required for evaporation of the residual water, which can then also be obtained from the waste heat of the plant using heat exchangers . The "waste water" contains all the nutrients of the plants and can be used again immediately as fertilizer and for irrigation.

    The whole thing pays off. We have a Model case for Kenya examined. Lake Victoria is suffocated by water hyacinths.
    But these have 95% water content and are hardly usable to use - we thought, until we came across this technology. There are harvesting machines for aquatic plants and plants near the beach can be used to produce biochar, which can then be pressed and sold in place of charcoal. 90% of households in Kenya use charcoal for cooking. As a result, the deforestation in the country is catastrophic and the prices for charcoal are rising extremely. Deforestation is therefore already spilling over into neighboring countries. Nairobi gets its charcoal from over 200km away. Not only do we have a financially viable project, but also many advantages for the environment (removal of overfertilization from the lake, avoidance of clear-cutting) and the people who get numerous jobs and inexpensive charcoal.

    The "Triple Bottom Line - People-Planet-Profit" is perfectly fulfilled here. Is anyone interested in helping to put together funding?

  6. Thank you for the concrete information on the energy balance of hydrothermal carbonization and the presentation of the project in Kenya.

    The HTC probably has to be calculated on a case-by-case basis and can then have very positive effects even under today's technological conditions. The project to improve water protection and energy supply in Kenya is a great example of this! An advantage of the project in East Africa is that it promises improvements for local citizens on many levels. Therefore, the question of energy efficiency in the production of biochar is not the top priority when it comes to securing the energy supply in general.

    What is meant by “putting together a financing”? Are you looking for more employees or investors? You have probably already asked GIZ.

    I wish the HTC project in Kenya good luck! Thanks to the website of the LVEMP II project the development can be followed live.

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