Dry fermentation, or plug flow reactor, as a challenger to the traditional wet fermentation process
Biogas has traditionally been produced by cylindrical so-called wet fermentation reactors (CSTR, continuous stirred-tank reactor). It is a highly established technology and often an optimal production process for wet feedstock materials that are handled at the point of origin. The most common of these are liquid manure and sewage sludge. For better biogas reactor functionality, its content must be very uniform and more than 90 % of it must be water.
However, because of the smaller required reactor volume and higher loading rate, slurries are now often dried prior to the process, whereby they are more advantageous for transporting and can be handled using the so-called plug flow (PFR, plug flow reactor) technology. Dry fermentation process allows handling even challenging feedstocks in the biogas process as it is less susceptible to contamination than the wet fermentation process, where difficult feedstocks can cause floating and sedimentation challenges. Dry fermentation process can handle feedstocks with total solids up to 35 %, such as dry hay and a wide range of biowaste streams, without adding extra water. The gas yield of dry fermentation process per cubic meter of reactor volume is significantly higher than in the wet fermentation process.
Advantages of dry digestion and wet digestion in a combination plant
Our partner builds a lot of top-of-the-line dry and wet digestion technology plants combining the key benefits of both technologies. High loading rate of the dry fermentation process ensures high usability and gas production per cubic meter of reactor volume. The long retention time of the wet fermentation process, in turn, allows a larger portion of the organic feedstock material to biodegrade.
Among other things, the combination plant has the following advantages:
- Plug flow reactor handles reliable, difficult feedstocks.
- Post-digester reactor ensures long retention time, thus, the optimal decomposition of organic material and the best possible biogas yield.
- Modular plant structure; treatment capacity can be easily increased by parallel reactors.
- Very low total energy consumption.
- Possibility to recycle liquid digestate within the process, reducing the need for adding extra water and often even removing it completely.
