Draft Tube Mixer:
Hermann Traxler (German origin) is manufacturer of Draft tube mixer. This technology is one of the best technology for mixing in anaerobic digesters. Necessity of this technology bold for anaerobic digester with higher volume.
Some of the features of this technology:
- Include motor, impeller and connection pipes (draft tube, ascending pipes).
- The Mixers is designed for digesters with capacity from 1,500 up to 15,000 cubic meter.
- The main principle of the best design and selection is based on mixing whole contents of the digester at least 8 times per day, in order to obtain maximum mixing and digestion efficiency.
- Due to vertically installation of the Draft Tube inside the digester with high length (constructed by pipe pieces, each piece is 6 meter), so connection of these tubes/pipes to each other should have different thickness compering with central section to resist against the weight of the upper tubes and vibration stress caused by the sludge movement and stroke of debris around the mixer pipes. So to have different thickness (6 to 15 mm) of this pipes Hermann Träxler recommended strongly Ductile Iron which is more reliable material instead of Stainless steel according the company experience.
- Increased the mixing efficiency by placing another Bell Mouth in top part of draft tube at impeller position.
Comparison with other technology for mixing:
The Draft Tube mixers is the best solution for sludge mixing and homogenization according to following reasons:
- More biogas production due to temperature uniformity in whole area of digesters
- Ease of elimination of scum layers at top of sludge by using splash disk
- Faster elimination of the foam at top of the digester by changing the rotation direction of mixer (from top to bottom).
- Prevention of particle sedimentation at the bottom of digester.
How to install mixers
The Draft Tube mixers can be installed in two methods on the upper part of the digester:
- Installation on concrete (Concrete type): This method is cheaper but require more civil works, construction time and more accuracy on construction also more expertise on digester construction.
- Installation on pre-fabricated steel structures that called Gas hood. Due to expertise and experience Hermann Traxler Company, could design a special model of Gas hood which could reduce bio gas leakage also achieving long life and lower operating costs of the mixer.