Wet digestion in the LARAN® loop digester

This technology is used primarily for the treatment of solid-rich suspensions of different origins, as well as relatively moist solid waste. Depending on the waste input and the location conditions, plants may be designed in either single- or two-stage configurations and can be operated in both mesophilic and thermophilic modes. Typical applications for this technology are:
  • Digestion of industrial waste products, e.g. organic suspensions from distilleries, potato processing or ethanol production
  • Digestion of sewage sludge
  • Digestion of very moist waste which contains little disturbants such as food and restaurant waste or expired food
  • Co-digestion of different feedstock (usually as a combination of a liquid/suspension with one or more solid fractions)
The characteristic element of the STRABAG wet digestion technology is the patented LARAN® loop digester. In this digester, the suspension is circulated and mixed by way of gas injection into a centrally arranged draft tube. This tube can also be designed as a double-jacket pipe for process heating. Depending on the feedstock, this type of mixing can be combined with a proprietary STRABAG system for sediment and/or swimming layer control and removal . A further benefit of the LARAN® loop digester can be seen in the possibility for inline desulphurisation of the biogas without the use of chemicals. This is achieved by way of a unique and patented H2S suppression function which feeds a metered air flow into the draft tube.

For the treatment of organic waste with a higher content of disturbants, such as kitchen waste or separately collected biowaste, the wet digestion technology is combined with a wet mechanical pre-treatment stage. STRABAG offers a variety of its own systems and components for this purpose, such as a special hammer mill, a pulper or a pulper/drum screen combination.

Process characteristics and benefits
  • High decomposition performance and biogas production rate thanks to optimised process parameters, in particular good mass transfer and reliable gas release as a result of the vertical mixing in the digester (frequent pressure changes)
  • Mixing is achieved without moving parts inside the digester
  • Digester volumes up to 12,000 m³ can be realised
  • Flexible and applicable to a wide range of feedstock
  • This patented STRABAG system offers reliable sediment and/or swimming layer control and removal at simple design of vessel, even when using a flat or only slightly sloped digester bottom
  • Double-jacket draft tube allows heat input without the risk of digester blockage



Published on website: 03.03.2015 – Last Update: 05.08.2024 14:16:55
Wet digestion in the LARAN® loop digester
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