Solid feedstock of up to 200 m³, such as maize silage, is pre-stored and  conveyed in regular intervals into the digesters by a walking-floor discharger. The technology is exceptionally durable and needs low maintenance due to the acidproof plastic panels and the slow running hydraulic drawbars installed in the solid reinforced concrete container. The specific transport quantity can be adapted by changing the oil flow rate. Apart from that, the operation time of the floor discharger is set via the PLC-control by the operator of the biogas plant. If desired, the feeding system is also available in a scale-equipped steel version.

By means of robust spiral conveyors of 4 mm stainless steel the solids are forwarded to a mixing pump. The mixing pump is parallely fed with liquid manure or digestate, so that the solids are constantly mixed with liquids and immediately forwarded into the digesters. This technology guarantees a low-maintenance operation as well as a flexible feeding of all digesters. It is not possible in many other concepts with digester-connected screw conveyors. A further important feature of this technology is the low need of electricity. Due to the homogenisation before the fermenters, the mixers do not need much energy for mixing solids with liquids.

Below-grade installed feedstock pipelines are basically of high quality polyethylen. Other producers still use inferior material such as PVC or similar ones. Due to the ultraviolet irradiation by the sun and increased mechanic demands we use overground pipelines of stainless steel. Thus, pipe-leakages are almost impossible over many years.

All internal pump procedures of the plants from BioConstruct are in general realised by just one rotary piston pump. Thereby, we contrast with many producers still using several pumps in a biogas plant. The advantages of our technology are obvious: significant lower repair and maintenance costs as well as a better operation safety – because: the more components there are, the more troubles can occur. For the big biogas plants we recommend to store the important spare parts in order to keep the "heart" going. Due to the practical at-grade-position all maintenance works can be done at once.

The compact technological building is mostly installed between two fermenters. The roof of the sand-lime-brick-building serves as a podest for the optical control of filling levels, overpressure and underpressure valves or adjustments of the mixers. The central pump station and the heat distribution are installed inside. The control system and the switch boards are installed inside as well, but in a separate room. Furthermore, the whole feeding technology is positioned in the building, so that the maintenance can be done in a weather protected area. The clou is that the technological building is always free of frost - and free of charge. This is due to the warm walls of the heated digesters. By means of this relatively easy construction, considerable costs can be saved - just clever, compact, BioConstruct.

 On a biogas plant, tubes and pipes are led at numerous places through the walls of the fermenters. These places are potential leakages for biogas or feedstock. We use special gasket seals in order to avoid an uncontrolled leakage in any case. Additionally, we weld the pipes in the interior of the fermenter together with a stainless steel plate. This plate will be fixed solidly to the concrete. In order to gain triple safety, the opening is covered at the outside of the fermenter by a plate of stainless steel as well.  This is security to the max!

For biogas plants up to an installed capacity of 750 kW, BioConstruct usually constructs concrete fermenters with a height of 6,40m. For bigger biogas plants enameled steel fermenters are a proven alternative, since they can be built much higher offering more capacity with the same diameter. BioConstruct recommends the construction of at least two digesters, so that the operator is still able to maintain the gas production in case of malfunctions.  Even after a complete emptying of the fermenter, the biology can be "run up" by means of the feedstock from the second fermenter. This takes place in less than a day. With just one fermenter this process can possibly last several weeks and valuable profits can consequently get lost.

Final storage tanks from BioConstruct are built of monolithic reinforced concrete - either cast in place or pre-cast. With diameters up to 40 m and heights up to 6,40 m, volumes of up to 8.000 m³ can be reached.

If desired, the final storage tanks can be equipped with a gas accumulator roof. Therefore, the volume of storage can be increased in order to bridge interruptions of the CHP. Furthermore the regularly inserted digested output of the digesters can keep on producing gas in the anaerobic milieu. As per some operators, this additional gas leads up to 5% more turnover.

The walls of our concrete fermenters with a height of 6,40 m (quality C 30/37) are surfaced with a special synthetic cover. This protection film avoids that the aggressive acids in the biogas, such as hydrogen sulphide, can harm the concrete. The coating is applicated threefoldly by our mechanics, after the hardening of the concrete. Without such a coating the danger of the concrete washing out is significantly higher.

Biogas plants that are filled with significant amounts of solid matter need an effective mixing technology. Good mixing avoids the development of swimming and sinking layers and increases the bubbling-up of biogas out of the liquids. Thus and for the purpose of minimizing the maintenance costs we prefer an installation of a giant paddle mixer. This mixer is horizontally installed in the fermenter and moves the substrate in a considerable diameter of approx. 4 m. The gearbox and the engine of the mixer are situated at the outside of the fermenter so that it does not need to be opened for maintenance and repair works; valuable biogas does not get lost. The low power consumption due to the slow rotation of the mixer minimizes the electricity costs. A paddle is the perfect unity of effective mixing and low operation costs.

Submersible mixers are particularly installed in the final storage tanks for the purpose of a short-term mixing before emptying the tanks by trucks. As the submersible mixers are very effective they consume a lot of electric power. Also the difficult accessibility for maintenance and repair, makes us using them as "emergency-mixers" only. Such case of "emergency" can be a breakdown of the the giant paddle mixer or the appearance of a pertinacious solid swimming layer. For those short-term utilisations the submersible mixer is proved and thus recommended by BioConstruct as a supplement to the long axis mixer.

The more sensors, monitoring stations, engines and power units are installed in a biogas plant, the higher is the grade of automation and control. However, the sources of errors increase at the same time. BioConstruct always optimizes this "tightrope walk" between maximum control and minimal liability to errors. By means of a regular contact of our electrical engineering department to our customers we can continously adjust the control system. Basically we apply process-control-systems by Siemens. This widespread technology can be operated by the local electrician, so that failures can be resolved very quickly. We regularly integrate the local electricians into the construction of the plant - in order to provide local serive a its best. Additionally, all defects and errors are sent to the mobile phone of the operator.

Our concrete fermenters are basically equipped with a flexible gas accumulator roof. This construction saves costs, as the necessary covering of the fermenter is combined with a accumulation of gas. In general, the accumulators of 500 kW biogas plants have a capacity volume of 1.300 m³. Provided that the biogas plant is operated in a clever way, it guarantees that no valuable gas must be burned in the flare, even in case of a CHP has to be switched of for several hours. The interior membrane of the gas accumulator is covered with a weather protection film. By this means it  is protected against UV light and strong wind. The weather protection film is put in shape by steadily blowing air between the inner gas membrane and the weather protection film. The indication of the filling level is effected by rope length indicators that can be controlled optically and electronically.

Below-grade passed gas-tubes are made of high-quality polyethylene (high pressure). Due to the UV light of the sun, we use stainless steel for overground applications.

In biogas plants with a power range of up to 1 MW the desulphurization is realised with a controled air admixture into the gas room of the last gasfilled digester or storage tank. This technology is sufficient for biogas plants loaded with low-protein energy crops like maize silage and small amounts of liquid manure. Additionally, it is almost maintenance-free and reasonably priced. 

BioConstruct recommends the application of a "wash-dryer" for gas in order to clean the biogas. In such a module the vapour in the gas is completely condensed. Furthermore the biogas is separated from suspended sediments and silicates (salts). The drying procedure in the wash-dryer takes place by spraying cold water of 2°C into the gas. By this means the biogas is cooled down to less than 10°C. Instead of this many of our competitors use dry coolers, cooling down the gas without washing only. Experiences of operators show that biogas cleaned by this module contributes to a longer lifespan of especially the spark plugs and the whole engine in general.

BioConstruct prefers gas engines from Jenbacher and MAN. These experienced partners guarantee a long lifespan of the most expensive component of the whole plant. The CHP are often installed in big concrete buildings of pre-cast elements. In contrast to steel containers, the concrete containers have a higher durability and are less in emissions. Furthermore, engines in concrete buildings are easier to handle possibility due to the spacious dimensions. For biogas plants with an installed capacity of up to 1 MW, we prefer using gas-CHP only. Therefore, the maintenance costs are noticeable lower in comparison to biogas plants with more than one CHP; bigger CHP normally have a higher efficiency factor as well. Generally speaking, we are convinced of the gas engine technology. We do not recommend dual fuel engines needing a supportive firing with heating oil - they are often not up-to-date any more.

We prefer a building of concrete for the CHP. In contrast to common steel containers, concrete buildings offer vital advantages: it is effectively insulated, has a longer lifetime and offers more space inside for regular maintenance works.

The floor discharger is situated in a reception tank of concrete. As rubbing and acids are natural enemies for the concrete, the reception tanks on BioConstruct plants are built with high-quality PE-plates inside. By means of this construction we achieve a long service life via a lower wear-and-tear.

The heating system in biogas plants from BioConstruct excells due to its quality in materials and execution. The distributor is located in a maintenance-friendly position in the main technical building. From this point the heat is forwarded to the different substations and to external consumers. The subordinate heat distributors for each digester are in comparison to those of the competitors made of stainless steel equipped with ball valves. The interior heating of the digesters is either realised via stainless or normal steel-tubes, which are mounted to the digester's walls. Such heat transfer is up to three times more effective in comparison to systems using heat pipes inside the walls of the digesters. Into the bargain we think the transfer of almost boiling hot water through the walls is a significant danger for the stability of the concrete tanks.