Granule

The granule refers to a solid fertiliser form distinguished by spherical particles produced through agglomeration of concentrated liquid onto recycled nuclei within a rotating drum, fluidised bed, or pan granulator^[1]. At NPK facilities, the neutralisation liquor is sprayed into a granulation drum together with salts and recycle material; the water evaporated is carried away by co-current airflow, after which the granules undergo drying and sizing, with oversize material crushed and returned to the process^[2]. For calcium ammonium nitrate, the ammonium nitrate solution is sprayed into a granulator; the product is subsequently dried, screened, and the fines sent back for recycling^[3].

Most fertiliser granules measure between 2 and 4 mm; this consistency ensures satisfactory distribution during spreading^[4]. Their mechanical stability stems from the spherical shape, which reduces inter-particle contact points^[4]. To guard against moisture uptake and caking, granules may be treated with non-hygroscopic substances^[4]. The European regulation on fertilising products stipulates a test protocol whereby prills or granules, having first been treated with oil and drained, are rolled between sheets of filter paper following a defined cycle of circular movements^[5].