Investigation of nitrogen loss during laboratory scale fixed-bed drying of digestate.

In addition to the drying kinetics of digestate, a comprehensive knowledge is necessary on nitrogen loss and ammonia emissions in order to appropriately develop and design a dryer. Otherwise, these phenomena would result in environmental concerns and reduce the nutrient value of digestate. Expectedly, drying parameters considerably affect drying time. In this study, drying experiments were conducted at a laboratory scale fixed-bed dryer. The drying experiments were performed on dewatered digestate that mainly consisted of grass and maize silage (initial moisture content 76.4% w.b., 0.026 kg N kg-1 DM). The drying air temperatures were adjusted to 60, 70 and 80 °C, the airflow rate varied between 150 and 250 m3 h-1, respectively. As the results have shown, the total nitrogen was reduced by 29 to 42% during drying. Almost all ammonium nitrogen was lost (92%). No relationship between nitrogen loss and drying air temperature or airflow rate could be proved. These results will be used as a basis for further investigation of continuous digestate drying at a semi-technical scale.

Measuring Device for Air Speed in Macroporous Media and Its Application Inside Apple Storage Bins.

In cold storage facilities of fruit and vegetables, airflow is necessary for heat removal. The design of storage facilities influences the air speed in the surrounding of the product. Therefore, knowledge about airflow next to the product is important to plan the layout of cold stores adapted to the requirements of the products. A new sensing device (ASL, Air speed logger) is developed for omnidirectional measurement of air speed between fruit or vegetables inside storage bins or in bulk. It consists of four interconnected plastic spheres with 80 mm diameter each, adapted to the size of apple fruit. In the free space between the spheres, silicon diodes are fixed for the airflow measurement based on a calorimetric principle. Battery and data logger are mounted inside the spheres. The device is calibrated in a wind tunnel in a measuring range of 0-1.3 m/s. Air speed measurements in fruit bulks on laboratory scale and in an industrial fruit store show air speeds in gaps between fruit with high stability at different airflow levels. Several devices can be placed between stored products for determination of the air speed distribution inside bulks or bin stacks in a storage room.