NUMERICAL MODEL FOR THE DYNAMIC SIMULATION OF A LARGE SCALE COMPOSTING SYSTEM

摘要

A numerical model simulating airflow pattern, heat and mass transfer, and degradation in the two dimensional cross-section of a deep bed composting vessel was developed. The model accounts for compressibility of the material and predicts spatial and temporal changes in state variables. The model was validated at a commercial facility that composts a mix of biosolids, bark and sawdust. Simulations were performed to quantify the effects of (1) initial moisture level, (2) depth of bed, (3) ambient air temperature, (4) cooling air recirculation, (5) material degradability and (6) blockage of plenum, on cost of aeration and spatial homogeneity of degradation within the vessel. Results show that cost of aeration is lowest when the material is at an initial moisture level of 55% and the bed depth is 3.5 m. Energy required per unit of dry matter degraded decreases as the ambient temperature increases. The increased aeration requirement when cooling air was recirculated was quantified, and shows that overall energy requirements are reduced by recirculating air. Aeration energy requirements and system throughput were compared under different operating parameters.