Example of a biogas installation

The fermenter constructed from stainless steel

The heart of a biogas unit is the digester in which biological processes take place. We are giving special attention to this feature. During the formation of gasses, their very aggressive composition will attack quite a number of materials. Thus, in the domain of biogas, the hardware suppliers only employ resistant materials for their units. Here, the material of choice for container construction and installations is high-grade steel - stainless. This way, due to varying operational demands, the container walls are constructed of two different materials:

• in the area of substrate/feedstock storage, V2-A is employed;
• in the area of the gas storage, V4-A is employed.

 

The Roof

The floating dome is ultraviolet resistant and is pretensioned with a bubble inflation air blower (capacity: approx. 50 - 70 W) on approx. 3 mbar. An internal membrane buffers the variable volume for the development of gas so that additional gas storage will not be required as a rule. At the centrally arranged intermediate support, end-lengthened clamping devices will be applied which prevent sinking of the inner membrane. Restressing of the belts will not be necessary.

Heat Balance

The biogas process essentially has to rely upon constant temperature control. We can reach a stable heat balance by means of a well-dimensioned pipe heating in the lower third of the fermenter and an outward insulation by means of polystyrene die plates (k-value: approx. 0.35 W/m²K). The advance temperature is regulated via a mixer valve in order to avoid incrustations at the pipes due to excess temperatures and to prevent damages of the biology. As a rule, the heating technology also allows us to carry out digestion in the thermophilic temperature range of 55°C. The exterior weather protection is consisting of aluminium trapeze plates in RAL standard colours.

Mixing Technology

For consistent homogeneous mixing, one long wave agitator units (dimensioned according to the volume of the fermenter) with an impeller blade (diameter approx. 2.4 m) on a stainless steel shaft are employed. The agitator unit will be installed in an inclined position with a gas-tight entry point and possesses a revolution speed of up to approx. 40 rotations/min (as standard infinitely variable via frequency converter). The bearing support of the agitator unit is positioned outside the fermenter where also the drive motor is situated. No power will be transmitted onto the container wall.
The essential advantages of this agitator unit:

• temperature resistant, also within the thermophilic range of up to 55°C,
• forming crusts and sedimentation layers inside the fermenter will be reliable treated by the submersible motor stirring units. By means of this agitator combination a thin crust can be maintained which can significantly improve the gas quality
• the energy input of agitator capacity is lower than in the case of submersible motor stirring units,
• due to low rotation values no shear forces which would be harmful for the bacterial mass will be generated,
• an evenly distributed gas yield will be provided

Photo 1: Occurring floating or sinking layers will be reliably treated by the submersible motor stirring unit. By means of this agitator combination light floating layers can be allowed which considerably add towards an improvement of the gas quality

 

 

Pumping Technology

The manure is separately stored in the concrete pre-production storage. The amount of manure pumped into the fermenter per day is about 8-9 m3 per day. The size of the pre-production storage depends on the way the manure is brought to the fermenter. For example, if the manure is brought to the fermenter every week, the pre production storage should be able to hold 8 m3 * 7 days = 56 m3. The submersible motor stirring units allow for intensive intermixing and provide a consistently homogeneous feedstock mix.
Essential advantages of the pre-storage tank technology are:

• the energy input is lower than in the case of an input of solid matter
• the solid materials have already been homogenized before entry into the fermenter
• as a rule, the costs for the unit will be lower
• a further reduction in particle size can be achieved via the use of our macerator technology
• Foreign materials which can arrive on the site with the feedstock are sedimented in the pre-storage tanks and do not enter the fermenter,
• increased operational security due to a monitored mixing pit

Photo 2: Pump-units

 

By means of an auger pump, the liquid substrates are automatically pumped from the prepits into the fermenter. Manual control is also possible. The composition amounts are recorded and documented. Solids like rapeseed press cake are brought into the fermenter with a specialized dosification unit.

Control unit

All biogas units of the hardware supplier are equipped with a control which is without precedent in this class of units.
The control will in particular offer the following advantages:

• All important input parameters like kinds of substrates and daily input amounts as well as entry times can be preselected. This way, a gapless documentation, e.g., according to the criteria of the regulations on biological waste or of the regulations of the special disposal companies will become possible.
• Filling levels in the individual unit sections will be automatically monitored and documented.
• Pumps and agitators will be automatically switched. This way, supervision efforts can be considerably reduced and costs can be saved. By a documentation of the operating times, the economic efficiency of the unit on the one hand and the process on the other hand can be observed.
• Process parameters such as temperature, pH-value process, gas analysis values, etc., will be automatically recorded and documented. This is enabling reliable optimization of the operation of the unit and - if applicable - allows a provision of evidence.
• All recorded process data can be descriptively visualised on a monitor and can be printed out if required. This makes it easier to supervise the process and allows for an early recognition of problems. Corrective measures can be introduced early enough.
• Failures can be avoided and higher operational security is given.
• Supervision of the gas quality
• Long distance data transmission, automatic message of error report, e.g., on mobile phone
• Recording, securing and visualization of the data of the co-generation unit.

Combined Heat and Power

The co-generation unit to be employed will be delivered completely preassembled in a sound insulated container for an installation outside. The heat which is generated by engine combustion is transferred to the heating system via cooling water and - optionally - via an exhaust gas heat-exchanger. Excess heat is led off to the container roof via an emergency cooler.
The approved industrial engine with generator is mounted above in a vibration absorbing tub construction. The tub construction simultaneously takes up the extended oil supply so that large oil changing intervals can be reached. Power generation is realized via synchronous generator. The installed alternator is able to generate power without a need for a drid connection. (Optionally, the unit can be delivered as emergency generator.)


Design:

• in case of a container construction type, the control can be installed inside a detached room with separate entrance,
• emergency cooling
• biogas dryer for dehydration of the biogas
• waste gas sound absorber and waste gas pipe
• gas mains with flashback
• storage - programmable - control (SPS) with display and operating terminal
• large oil pan with oil circulation lubrication
• heating distributor: 4 exits; the exits for the fermenter are issued with circulating pump
• biogas meter

Conducted assembly and taking into operation on site.
The control and regulation unit is accommodated inside an external switching cabinet and monitors all processes of the co-generation unit system with regard to the optimization of capacity or related to biogas.
Current capacity and temperature values, possible error reports, etc. are displayed on a monitor by pressing of function keys. The store-programmable control and the operating terminal are offering clear handling for the switching unit developed according to VDE guidelines for trouble-free continuous operation without supervision.