From raw slurry with sand to clean sand and sandfree slurry


Raw slurry is scraped to the raw slurry pit (I). A powerful mixer is thoroughly mixing sand and slurry before it is pumped to the sandwasher (6) with the raw slurry pump (1).

In the pipe leading to the sandwasher, a macerator (5) is installed to ensure to chop coarse dry matter particles such as pieces of wood, cow teeths, etc., whereas stones and other solid objects are kept back in the macerators stone trap. This way the cyclone of the sandwasher will be kept free from clogging.


The flush water tank contains thin liquid partly coming from the cyclone owerflow, partly from the rotating screen (7). It can also consist of surface water or water collected from the silage storage space.

A mixer (4) mixes the liquid before it is pumped into the raw slurry pipe with the flush water pump (3).


The thick liquid from the rotary screen (7) consists of the sandfree slurry still containing the fibrous organic material. The slurry can then be stored or treated further, e.g. in a biogas plant.

1. Slurry pump for raw slurry
2. Mixer
3. Flushwater pump
4. Mixer
5. Macerator
6. Sandwasher
7. Rotary Screen

A: Flowmeter
B: Dry matter measurer
C: Clean water

Proces description

The mixer (2) in the raw slurry pit starts mixing a few minutes before the start of the raw slurry pump (1), the flush water pump (3) and the macerator (5).

Raw slurry is pumped through the macerator (5) and dry matter measurer (B) and is mixed with flush water being pumped into the pipe by the flush water pump (3).

The mixture is pumped through the dry matter measurer (B) and recirculated to the raw slurry pit (I). The dry matter measurer regulates the flow of the pumps until the required dry matter percentage is obtained. Once this is achieved recirculation stops and pumping of the mixture to the sandwasher (6) starts. Liquid flow to the sandwasher (6) is controlled by a flowmeter (A). Automatic control of dry matter and flow allows to achieve the highest possible retention of sand.

Slurry and sand are now separated in the sandwasher’s cyclone, the sand sediments in the sandwasher where it is flushed with clean water (C) and transferred out of it by the auger for reuse. See also the separate operational description of the sandwasher.

Sandfree slurry is running from the sandwasher (6) to the rotating screen (7) where the slurry is separated into a thin and a thick fraction containing the fibrous organic material. The thin fraction runs back to the flush water tank II, while the thick fraction runs to tank III for sandfree slurry.

When the raw slurry pit is empty, the process stops automatically.

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Ulrik Folkmann

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