Agitators for biogas

The right agitator for each plant!

The right agitator for each plant! The submersible and the rod agitators originate from our well-proven manure technology, while the large wing agitators are not related to slurry technology. The stirring devices should always be designed about an inch larger than required.

So you have a buffer in case an agitator should fail. Moreover, the internal power consumption of large agitators with short stirring intervals is usually lower than of small agitators with a longer duration of agitation. In existing systems the internal current consumption can be lowered by repowering measures.

In this case, we recommend our Tristar product, for example. When selecting the agitator technology, there are several criteria each plant operator must evaluate for himself: What stirring tasks need to be done? For instance, blending in the mixing pit, extracting gas by stirring in fermenter/post-fermenter or homogenising and dissolving floating covers in the substrate storage room.

When choosing the proper agitating technology, there are various criteria to be valued by the plant operator.

• Equalisation of temperature and concentration in the substrate.
• Mixing of solids and liquid.
• Transfer of liquid on the heating pipes.
• Which liquids and solids are to be stirred or mixed?
• Is the fermenter charged with liquid media or via solids dispenser?
• Are there alternating filling levels?
• Where is stirring power required the most?
• What role does the energy consumption play? The internal current consumption range required for the stirring devices is between approx. 2.3 and 13% (savings potential).
• How significant is the purchase price?
• Should it be possible to disassemble the agitator when the stirring vessel is full?
• How many operating hours can be expected annually?
• Having regard to noise pollution to the vicinity: especially multi-stage gear units should not be underestimated.

For the various stirring tasks and the various customer requests arising from answering these questions, we offer different types of agitators. A combination of various agitators might be useful in many cases. Do not be impressed by short-term fashion trends: power savings up to 70% are possible with any agitator technology when comparing too small devices with a suitably sized equipment.

All information is subject to change.                               ** eminently suitable    * suitable    o partly suitable    - unsuitable
A professional consultation is suggested.

Submersible motor agitators (TBM and AT-MIX) from 1.5 to 19 kW

The revolution speed of the blades is approx. 330 RPM, the propeller diameter amounts up to 910 mm depending on the engine power rating. We offer installation accessories for open containers as well as gas-proof wall and ceiling ducts. The submersible agitators can be changed when used in a filled container and they are economically priced. Accessories are available in V2A and V4A versions. Our submersible agitators are generally fitted with face seals. They are suitable especially for varying liquid levels because no other agitator can change position so easily. Rod mixers (Rührmaster, Fermix, Bobumix and 1031) from 11 to 30 kW

Depending on the version, the rotational speed can vary between 110, 210 or 420 RPM. The propeller diameters are in the range of 580 and 1400 mm. The mixers can be supplied for ceiling installation or for diagonal wall installation at the bottom or at the top. When mounted on the ceiling or on the wall in a slanted position, the angles of inclination can be aligned by means of a rack jack. Therefore, the agitator is easily adjustable to varying filling levels and is as well removable when used in a filled tank.

Large wing mixers from 11 to 15 kW

The diameter of each of the 4 propellers is 2300 mm. The nominal speed is 25 RPM and the rotational speed is adjustable via a frequency converter. The stirring rod extends downwards through the wall, inclining to the bottom. The bearing is attached in an elevated position preventing wear and tear due to e.g. penetrating sand. Stirring rod and wings are made of stainless steel, the gearing support parts are hot-dip galvanized.

It might be advisable to utilize a combination of various agitators.

All agitators can be equipped with smooth start-up or frequency converter (rotation speed control). If the engines have to start more frequently it is recommended to use a soft start device.

After having selected the appropriate agitator, the issue arises with the material they are made of. For mixers which are immersed permanently, cast iron or hot galvanized steel would be sufficient. Those parts used for application with permanently alternating water levels or mounted in a gas compartment, the material consist of at least stainless steel V2A = 1.4301. If the sulfur content is higher, it is advisable to chose the 1.4571 standard. It is important to care for the equipotential bonding. This should be carried out by professional electricians.

Finally some general hints:

Stainless steel propellers often show a shorter durability than those made of hardened steel, because stainless steel is much softer and, due to abrasion, tends to wear out faster.

Mind the details: Are the carrying cables made of V4A and is the pulley’s diameter large enough? You also should consider the consequential charges like costs and availability of spare parts and replacement devices.

Every biogas plant includes an Ex-zone map.

If agitator systems should be installed within an Ex-zone, the installation must be performed according to the requirements for the protection area.

Simply proceeding in accordance with the ATEX guidelines is not sufficient!