2000 Compost spreader

Due to the increasingly strict legal regulations in the handling and utilization of biowaste as spreading material on agricultural land, greater attention will be paid in the future to compliance with maximum area-related application rates.

Currently, compost is spread using universal spreading vehicles. These spreaders are primarily designed to spread various solid manures and sewage sludges. However, these differ considerably in physical properties from composts as delivered as fresh or finished compost from the composting plants. This leads to the fact that with the universal spreaders an exact quantity dosage as well as an even distribution is only possible under optimal conditions. The spreading problem is further aggravated by the great susceptibility of the distribution to crosswind influences, which occurs more frequently with the low density of finished compost.

The aim of a project funded by the Deutsche Bundesstiftung Umwelt and carried out in cooperation with the company Bergmann in Goldenstedt was the development of an exact distribution device for the application of biocompost. This spreading device is to be integrated into a conventional universal spreading vehicle. The following development goals were set:
- better quantity metering, tolerance < 15 wt.%,
- more uniform quantity distribution, longitudinally and transversely to the direction of travel with a VK < 15 %,
- possibility of spreading into standing crops,
- working width corresponding to a tramline spacing of 12 m,
- low susceptibility to crosswinds,
- low odor emission,
- prototype close to series production, capable of series production,
- adaptation of the spreading system to a series production vehicle.

Since the low mass of the spreading material means that targeted and wide trajectories are not possible, the development goals cannot be achieved by further development and optimization of the conventional spreading technology alone. For this reason, a new design of the overall spreading system was developed by means of preliminary tests and design methodological tools. Both mechanical and pneumatic systems were considered in the system evaluation. The evaluation decided in favor of a mechanical system. The reasons for this are the bulky as well as dusty spreading material components and the strong cohesive properties at increased material moisture.

The spreading material properties also make it necessary to perform the sub-tasks of metering, distribution and transport to the distribution units by separate sub-systems. Due to the low bulk density of approx. 300-500 kg/m³, the achievement of the given development goals is only possible by using several decentralized distribution devices. Under the aspects of functional safety, effort and costs, the system of a hopper discharge screw was considered to be the most suitable for metering. The advantage of this subsystem lies in its functional reliability even in the case of unfavorable spreading material properties, such as increased moisture and, in some cases, bulky material components. These considerations also led to the use of augers as the transport system to the spreading equipment, with the auger troughs taking over the function of the booms. Turntables equipped with a blading system turned out to be the most suitable distribution device. This functional principle could be adopted from conventional agricultural spreading vehicles. In order to achieve a symmetrical spread pattern from the overlapping of the individual spread patterns, four individual turntables were distributed across the width of the vehicle, with the outer turntables located at the ends of the retractable augers. Baffle plates are mounted at a short distance from the turntables, on the one hand to produce a more controlled spread pattern with fewer segregation phenomena, and on the other hand to achieve lower crosswind sensitivity by increasing the kinetic energy of the substrate parts just before they hit the target surface. To reduce construction and financing costs, the metering screws were designed in such a way that they also provide transport to the inner turntables. Here you can see a sketch of system : 1-dosing augers / unloading and dosage augers, 2-transport augers / conveyor augers, 3-turntables / rotating discs.

In order to be able to maintain the required distribution accuracy with different spreading material properties, the rotating discs are pivotably suspended. This allows the feed area of the material on the rotating disc as well as its inclination to be changed. To further influence the spreading pattern, a stepless speed control of the turntables is available. The mass flow is controlled by regulating the speed of the metering screws. To realize the stepless speed change, as well as to provide the necessary drive power, the drives are integrated into a separate hydraulic system. This system consists of a PTO-driven hydraulic pump, a control valve block, the tank, and the drive motors. The link between the material mass flow and the volumetric flow of the metering screws is established by means of a calibration test. For this purpose, the vehicle is equipped with a weight measuring system. The adaptation of the mass flow to changing driving speeds is realized by a speed measuring system. In the final phase of the project, a computer-aided control system on board the vehicle is planned for setting the controlled variables.

The research project ended in 1999.

Publications :

• Stieg, D.; Wagner, G. and Krause, R. : Exact spreader for biowaste compost - Development of an exact metering and distribution system in Landtechnik 1, 53rd Jg., Fachzeitschrift für Agrartechnik und ländliches Bauen, 10-11, 1998, Darmstadt, ISSN 0023-808
• Stieg, D. and Krause, R. : Spreading compost with precision. Eilbote -  The magazine for agricultural machinery. No.20, 46th Jg., 26-27, 1998, Winsen/Luhe.
• Stieg, D.; Wagner, G. and Krause, R. : Spreading compost with high precision. VDI Report No. 1356, 97-100, 1997, Braunschweig, ISBN 3-18-091356-8.
• Stieg, D. : Distribution systems of compost spreaders: With tines, chains and flails, profi-magazin für agrartechnik. No. 9, 1998, Münster ISSN 0937-1583
• Wilmer. H. : Big all-rounders ?! A comparison of three 18 t high-capacity spreaders. - profi-magazin für agrartechnik. No. 6, 1999, 20 - 25 , Münster, ISSN 0937-1583

Project work : Wille, Volker : Possibilities of an improved transverse and longitudinal distribution of compost, FG Agrartechnik, 1994

With the friendly support of :

Company Fehr, Kassel  - Company Bergmann, Goldenstedt - Deula, Witzenhausen