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GAS INJECTION
Function
An effective mixing of the substrate is very important for a
flawless operation. A good mixing supports an equal distribution
of the raw sludge in the digester. Thereby unfavourable and
concentration fluctuations and harmful temperature differences are
prevented.
A steady mixing of the sludge avoids the formation of
sedimentation layers. Theses layers mainly consist of sand and
other heavy ballast materials. By their sedimentation they cause a
massive reduction of the usable digester volume. Furthermore the
mixing prevents the formation of a persistent floating sludge
layer and the scum can be removed by sludge removal.
Another positive effect of the mixing is the enhanced separation
of the digester gas from the sludge.
Design
Two components are necessary for the gas injection:
• gas injection lance
• gas compressor
The injection lances are installed in the digester from top to
bottom so that the gas will stream out just above the ground. The
injected gas bubbles upwards through the sludge and generates a
turbulence that provides the mixing effect. To achieve a good
distribution of the gas, several lances are installed. Over a ring
pipe system on the head of the digester the gas is equally induced
to the lances. Due to this installation the lances can be easily
removed for inspection without emptying the digester.
A gas compressor provides the necessary pressure to get over the
pressure caused by the filling level of the digester. This height
varies between 10 and 30 m. For this reason there are different
gas compressors available to deliver the necessary flow rate and
pressure. These are low maintenance rotary compressors that
guarantee a low-wear continuous operation.
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EQUIPMENT
