Combined Use of Simulation Modeling and Linear Programming for Logistic Design of the Slurry Distribution Systems

摘要

The continuous development of new plants for anaerobic digestion has led to the need to manage in a rational and environmental way the distribution of the digestate that comes out of the process. The EU, national and regional regulation establish timewindows when it is possible to carry the slurry and limits the amount of Nitrogen per hectare from livestock to be distributed in the field. Purpose of the study was to optimize the slurry distribution through the combined use of simulation and linear programming [LP], taking into account the regulation and the timeliness of the operation required by the crops. Based on the field trials was built a dynamic, discrete-event simulation model using Extendsim~R software (Imaginethat Inc, USA). The main results were the working chain field performance and the logistic costs, as a function of: field distance (1 to 10 km step 1 km), plot size (2, 4, and 6 ha) and rate of Nitrogen distributed per ha (170 and 340 Kg N.ha~(-1), as were the limit imposed by the European directive and Italian law on vulnerable and non-vulnerable soils). In particular, the simulation model showed how the cost of distribution per unit of fertilizer depends mainly on field distance from the slurry source and secondarily on the rateof application. The LP model, starting from the simulation results as input allowed to schedule the slurry distribution, the tillage and the crop planting. The following factors were considered: the spatial field distribution vs. the digestate source, the weeks of the year where slurry distribution is allowed by law, the timeliness factor to plant the crop and the weekly manpower available. LP model run for the whole year (52 weeks) and schedule, week by week, the area to be feed with slurry, the area to be tilled and the area to be planted. The tool will be further implemented to simulate many different distribution methods and options including umbilical systems. The long term goal is to provide an advanced support system for the logistic design andmanagement of the slurry distribution system.