Agroscope Reckenholz-Tänikon Research Station ART, CH-8356 Ettenhausen

Tent-roof ventilation reduces emissions effect in slurry containers

Ammonia emissions mean a loss of nitrogen fertilisers for agriculture. They also pollute the environment. Part of the losses occur during slurry storage. In order to reduce these losses, artificial covers are required for new slurry containers. Tent roofs and floating foils in particular have caught on as artificial covers. The less permeable the cover, the more effectively it reduces emissions. Apart from this, no explosive gas-air mixture must be allowed to evolve under the cover, as happens when the methane concentration lies between 4.4 and 16.5 volume per cent (vol. %). A minimum air exchange must therefore prevent this concentration from being reached. Just how high the minimum ventilation rate must be depends on the maximum methane emission rate. The latter is influenced by several factors such as the qualities and temperature of the slurry, the temperature under the tent roof, and the thickness of any natural floating layers. How these factors affect the release of gas under practical conditions is to date unknown. For this reason, emission measurements were performed at a slurry silo with a tent roof at the ART for different external conditions and ventilation rates. Both the methane concentration as well as the ammonia and carbon dioxide concentration in the outgoing air flow were measured. The measurement results allowed us to deduce the minimum ventilation rate. From this, the necessary cross-section of the ventilation openings for any slurry containers with a tent roof can be calculated with a view to safe operation.

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