HIGHER GAS OUTPUT IN BIOGAS PLANTS. R+W COUPLINGS IN SUBSTRATE TREATEMENT
In the search for renewable energy sources, the production of biogas is a proven procedure for self-sufficiency in energy supply especially in rural areas. There agriculture provides sufficient raw materials for a biogas plant, so-called substrates, from liquid manure from animal husbandry and the cultivation of energy crops. Methane is produced during fermentation. Following fermentation this is fed to a reciprocating gas engine which generates the desired mechanical and thermal energy. The so-called cogeneration plant then produces electricity in addition to heat.
The energy yield is directly related to the quantity of gas available. However, in general the substrates consist of components of different biological structure and solubility in liquids. Substances with more solid structures therefore need a longer dwell time in the bioreactor until the bacterial hydrolysis generating the gas occurs.
The hoelschertechnic gorator® GmbH & Co. KG company, based in Gescher, Germany has developed a unique mechanical fragmentation process with the Gorator®, which
- reduces the dwell time in the fermenter to a minimum
- and accelerates the rate of hydrolysis and thus
- increases the gas yield.
The Gorator® consists of a cylindrical housing. An inclined disc rotates in its interior. The resulting wobble accelerates the centrally supplied substrate both axially and radially. The flow in the working space leads to high shearing forces, which leads to intensive mixing, fragmentation and digestion of the particles. The particles (e.g. vegetable fibre) are accelerated by the centrifugal forces in the direction of the stator consisting of a closed bushing and an open gap segment. The material is caught in transverse grooves located in the segments and it is then picked up by the inclined disc and mechanically shredded. The material remains in the working space and is further fragmented between the toothed disc and the stator until the particle size is sufficient to pass through the gaps. Thus, the infed material is prepared perfectly for the fermentation process.
The Gorator® is delivered with a drive power of 22-30 kW, depending on customer requirements. At a speed of about 1450 rpm and a nominal torque of more than 200 Nm. All infed substrates can be sufficiently fragmented with this power.
Mechanical safety coupling to increase operational safety
But what happens if, in addition to liquid manure and plants, other substances can be fed to the Gorator®? Not infrequently screws, small tools or stones find their way into the fragmentation process. In order to achieve high operational availability and investment security, a safety coupling of the ES2/450 type from R+W is integrated between the motor and the rotating Gorator®. The coupling has primarily the task of connecting the input and output shafts with each other and of transferring the torque without backlash. The coupling compensates for any misalignment occurring between the shafts by an elastomer insert made from high quality TPU. In this application, an elastomer insert with good damping properties (Shore hardness 98 Sh A) to achieve a balanced relationship between power transmission and simultaneous damping of application-induced vibrations could be developed. Moreover, the ES2 safety coupling with a 64 Sh D elastomer insert is available. This has higher torsional stiffness compared to the 98 Sh A elastomer insert.
The second task of the safety coupling tested by the TUV-Sud (Technical Inspection Association) is the mechanical limitation of the torque. If, as described above, an unusually hard object get into the material flow, then the Gorator® disk is blocked and the torque rises exponentially. At a pre-defined and set torque, the safety coupling separates within a few milliseconds the flow of power between the motor and the Gorator® rotor. This protects the most important implement of the Gorators® before damage due to high torque peaks. This protection is achieved by the spring-tensioned ball-detent principle. Due to the special detent principle in the body of the coupling, this process is absolutely backlash-free, even after several detents. The desired disengagement torque set in the factory can be changed or adjusted within an adjustment range. The possible adjustment range as well as the preset disengagement torque is stated on a so-called adjustment nut. Thus infinitely variable adjustment of the disengagement torque is possible by turning the adjustment nut due to the different pre-tensioning of the disc springs.
Depending on the requirements, the series is available in different variants. In the single-position/multi-position design of the ES2 safety coupling, the disc spring is pushed through so far in the disengaged position until it falls back to a very low value. However, the low residual force is sufficient to re-engage the coupling automatically. As soon as the overload is removed, the coupling in the single-position version engages after exactly 360° and is ready for operation again. The multi-position coupling in its standard version tries to re-engage every 60°. Other engagement angles are also possible optionally
The load locking version is used to secure the load in presses or lifts, for example. Here the input and output sides turn only a few degrees, to enable the switch plate, which can be sensed as in all other applications, to move sufficiently.
In the full disengagement version, the disc spring springs over completely and enforces separation of the input and output. The coupling then runs freely and re-engages again manually. The spring force of the disc spring falls to a very low value after disengagement. The process guarantees low wear and a very low residual friction of only 2 to 5 percent. This version allows particularly high speeds.
Using a full disengagement version, an operator of the above mentioned system can now safely remove any extraneous materials after a crash and can easily let the coupling re-engage. This reduces the downtimes to a minimum, and provides for greater yield in gas output. A method for even more economy in the operation of a biogas plant.
Wide range of variants for a wide range of applications
The practical requirements for the use of safety couplings can differ significantly from application to application. Indeed, requirements such as fast and reliable disengagement of input and output are the same, but individual and application-induced requirements, such as high torsional stiffness, mass moment of inertia, limited space or high speeds must be taken into account. The R+W Antriebselemente company reflects this need for a variety of variants and models and has a particularly compact and high-performance series in its range (SL), in addition to its classical safety coupling series (SK and ES).
In addition, the precision coupling specialist possesses long-standing know-how in the field of metal bellows and elastomer couplings and is also a competent contact partner and supplier in the field of high torque industrial couplings.
Sources Hoelschertechnic, Dipl.-Ing. Arno van de Sandt VDI R+W Christopher Monka