Optimisation of logistics for different supply and distribution systems at large biogas plants
The proposed project aims at increasing the added value of biogas production made of agricultural raw materials by logistic measures both on the input and the output side of a biogas plant. The results will support/improve the economic efficiency with regard to biogas production from energy crops and therefore the sustainable development.
The present project records and assesses all the pre-processing activities (consisting of acquisition and storage of raw material) as well as the post-processing activities (consisting of fermentation residue processing and application) and identifies potential methods to optimize the process. The aim of the project was to add value to biogas production from agrarian crops by adjusting the logistical methods used at the pre- and post-operation sides of the plant and to identify possible ways to optimize the system along the logistics chain. The data used for the project is derived from detailed surveys, measurements, and recordings of 16 Austrian biogas plants. The results of our analyses regarding procurement of substrate, separation and biogas slurry application were incorporated into a GAMS modelling and optimization program. The resulting optimization model compares and considers different types of plant parameters to show ways to simultaneously optimize crop cultivation, harvesting methods, harvesting logistics, and biogas slurry application. It is intended to present new approaches to all transportation processes within the periphery of biogas production plants with a view to optimizing these processes. The goal is to reduce transportation needs so that people living in the vicinity will be less exposed to traffic and the population as a whole will more readily accept biogas plants.
Data derived from procurement logistics studies indicate that optimal coordination of engine power and working width of the harvester is a prerequisite for optimal efficiency of the harvester. For crops that are mowed before chopping, the size of the windrow also has an effect on the efficiency of the harvester. Factors that significantly affect the mass flow rate in this transportation chain include haul distance, loading volume, loading density, achievable transportation speed and the number of transport vehicles used.
Separation of the fermentation residue helps to get the residue into a shape that is easily transportable, storable, and manageable so that can it be used for nutrient export at a competitive price. Two different separator types were assessed and it was shown that the screw extractor separator was definitely better suited for biogas slurry than the rotation screen separator. The screw extractor separator excelled with a high throughput and good separation efficiency. In addition, the working time requirement during operation is mini-mal and it is a low-maintenance machine. To achieve the same results with a rotation screen separator, the plastics press cylinder and the rotating screen have to be adapted to the substrate-specific conditions existing in modern biogas plants, especially to the temperatures and the DM-content.
When assessing fermentation residue application with slurry tanks, it was found that the most significant factor influencing capacity and energy consumption is the volume of the tank, in addition to the haul distance. The longer the haul distance, the more significant is the influence of the tank volume. The application rate per hectare based on 10 m3 fermentation residue used, on the other hand, is minimal as long as the application rate is varied by varying the transportation speed. Empty running at the field site causes the working time requirement per 10 m3 fermentation residue output to increase, starting at about 3 ha. The volume flow rate of bandspreaders with a trip hose system and broadcast spreaders was comparable to the use of slurry tanks. Bandspreaders with a trip hose system are preferable to broadcast spreaders because of lower emissions. An umbilical cord fermentation residue spreading system can be installed at fermentation residue storage places or at mobile buffers at the field. However, umbilical cord slurry spreading only becomes financially interesting at a continuous plot size of 3 ha because of the preparation times involved.
Economic cost estimates show that silo maize is a superior substrate concerning substrate procurement costs (relative to methane yield), harvest and application of the slurry. If several crops are used, there will be several different harvest times so that there is less storage requirement. The use of cattle and/or pig slurry and the installation of a cover for the slurry storage areas are advantageous. Depending on the individual crop or crop combination used in the biogas plant, the costs for substrate procurement and slurry application will differ considerably. The substrate procurement costs includes all the costs used for planting and cultivating the crop, the cost for harvesting the crop and hauling it to the silo and any opportunity costs for the cultivated land. The costs for the harvest were based on timed harvests of raw materials and then calculated subject to the yield and haul distance for different forage harvester performances and transportation capacities of transportation units or the necessary rolling weight of the vehicles used. The slurry application costs is calculated for the slurry tank method, the umbilical cord fermentation residue spreading method, and two-phase methods. Based on the results from the optimization models, a list was produced ranking the crops (or crop combinations) from most cost efficient to least cost efficient. The most efficient crops are silo maize, sorghum, and corn, and the least efficient crops are feeding rye, sun flowers or a combination of the two. Apart from the cereal plants, the crops should be harvested with large forage harvesters no matter what the haul distance.
Ao.Univ.Prof. Dipl.-Ing. Dr. Thomas Amon
BOKU Wien, Department für Nachhaltige Agrarsysteme, Institut für Landtechnik
- HBLuFA Francisco Josephinum
- Institut für Agrar- und Forstökonomie (BOKU Wien)
- ARGE Kompost und Biogas