Gas concentration in the interstitial atmosphere of a wheat silo-bag. Part I: Model development and validation

The silo-bag is a hermetic storage system of about 200 tonnes of capacity widely adopted in Argentina for storing dry grains.A heat and mass transfer model which predicts grain storage temperature and moisture content (MC) as function of weather conditions was applied in combination with a lumped-capacity differential equation for gas transfer to simulate the gas exchange in silo-bags. CO2 production rate based on variable grain storage temperature, MC and storage time was taken into account and evaluated using the correlation developed by White et al. (1982) for wheat. The model was run for the climatic conditions of the South East of Buenos Aires province, Argentina, for a storage period of 6 months, from summer (January) to winter (July). The gas concentration predicted by the model in silo-bags within a range of 12–15% w.b MC was compared with data available from a series of field experiments. For CO2, SE increased from 1.2 points % in the dry MC range (12–13.5% w.b) to 2.7 points % in the wet MC range (14-15% w.b). For O2, SE was 2.5 points % for dry and 1.9 points % for wet MC range, respectively. Overall, the general trends of measured gas evolutions were compatible with the simulated ones.

► A lumped-capacity model for gas transfer was developed to simulate O2 and CO2 exchange in a silo-bag. ► The model was validated by comparing predicted and measured concentrations from wheat silo-bags. ► The main factor affecting gas concentration in silo-bag was grain moisture content.