Introduction

0.1 General

In production and handling of fertilizers dust generation is of great concern by both producers and users of the fertilizer products. For health and environmental reasons, it is of great interest to control and reduce the amount of dust generation. In the fertilizer industries there are a wide variety of apparatus for dust determination, most being used as “in-house” methods in plants and laboratories.

The content of this document was developed by CEN/TC 260/WG 2 between 1991 and 2000 in order to develop a standard dust test. A spouting bed apparatus was designed for gravimetric determination of dust, and after two preliminary ringtests a conclusive ringtest involving six laboratories was carried out. Not being able to develop a statistical significant method for the determination of dust, TC 260 decided by resolution 105/1997 to change the deliverable of this work item into a CEN Technical Report. The change of deliverable has been approved by CEN/BT with its resolution BT C172/1999.

0.2 General background

When handling fertilizer grains, dust is at every moment generated on the surface. The fertilizer thus contains more or less free dust, and has a potential for generating more dust (abrasion dust) when subject to subsequent handling.

In all existing gravitational test methods dust will be generated during the testing time, and the two types of dust will be measured simultaneously. The scope of the method is expressed in Annex A and the aim is to:

“...specify a method for the determination of the dust potential of solid fertilizers and is applicable to granular and prilled fertilizers.

Dust particles, which cause reduced visibility in air are too small to be determined by this method.”

0.3 Background for choice of method

Fluidized particle powders are generally divided into four characterizing groups (A, B, C, D) [1]. Group C particles are small, cohesive and are difficult to fluidize. Aeratable powders belong to group A, and many fluidized bed catalysts characterize this group. Sand typifies group B, in which inter-particle forces are negligible, in contrast with group A powders. Large and/or dense particles in general belong to group D, and fertilizer particles (2 mm to 4 mm) in air are in this group. A flow diagram can be used to broadly identify flow regimes appropriate to combinations of gas velocity and particle properties. It can be shown that the fertilizer system is in the lower part of the spouted bed regime.

A criterion that can be used to distinguish between group B and D is the numerical inequality that classifies a powder as spoutable if:

(ρ_p – ρ_f) ⋅ d_p^1,24 > 0,23

For a typical fertilizer this value will be about 1,4 and about 0,5 for an urea prill.

From previous experiments with other methods based on a fluidized bed and the above calculations, it was decided to base the method upon the spouted bed principle.

PD CEN/TR 14061:2021

Fertilizers. Determination of dust content

Current

Published:

30 Sep 2022