Open access publications in the SLU publication database

Abstract

When straw is used as a fuel, the choice of logistics system from field to heating plant plays an important role for both costs and fuel quality. More than 80 % of the total fuel costs can often be assigned to different logistics operations, including harvest, loading, transport, unloading, storage, etc. The fuel quality, expressed in terms of moisture content, heating value, ash content, ash softening temperature, etc., is also, to a certain degree, dependent on the logistics, i.e. the choice of machinery, storage methods, etc. The objective of this study was to identify important factors that influence the choice of logistics system for fuel straw, and to further develop an existing simulation model for straw handling. This model was then applied to a system for delivery of fuel straw to a fictitious small-scale heating plant in the municipality of Sölvesborg in south Sweden. There are a number of factors that determine the outline of the logistics systems for fuel straw. Some examples are not controllable, such as the weather (e.g. amount of rain, temperature, relative humidity), geography (e.g. road network, size, shape and concentration of fields), soil properties (e.g. soil type and drainage characteristics), and crop-related characteristics (e.g. yield, harvest time and drying properties). By means of data from SMHI (Swedish Meteorological and Hydrological Institute), Lantmäteriet (the Swedish mapping, cadastral and land registration authority) and Jordbruksverket (Swedish Board of Agriculture), the impact of these factors can be modelled. Thereby the conditions for straw harvest in specific regions in Sweden can be investigated. Discrete event simulation is a very useful tool to model the whole machine system from field to heating plant (or storage). Different sets of machinery, storage strategies, types of organisation, etc. can be simulated and analysed by means of different quantitative and qualitative measures. The simulation programme used in this study (Arena) has a great flexibility and can also be used for simulation of handling of other biofuels with similar harvest and handling difficulties (short harvest periods, dependence on the weather, extensive transport work, etc.). The results from the application of the model to a small-scale plant showed that the costs varied from 140 SEK/MWh to 170 SEK/MWh. The operations with the largest potential to further reduce costs were considered to be transport and storage. Further studies are also required regarding machine capacities, storage losses, etc. in order to get more reliable data for the simulations and cost calculations. Costs for handling of chopped straw were considerably higher compared to baled straw. However, it was concluded that there is a potential to reduce costs by including chopped crops with other harvest times (e.g. energy grass, maize, hemp) in the handling system, and also by including other possible areas of use (production of briquettes, biogas, etc.).