Characterisation and pneumatic conveying of cohesive lactose powders

A significant issue faced within the dairy industry is challenges of reduced or inadequate flow  of lactose due to a lacking understanding of powder flow properties. The reliable flow of lactose in industry is of vital importance due to the impacts on the final product quality and efficiency of the production process, with poor flow leading to wastage, maintenance costs and downtime. Additionally, for the accurate design and optimisation of a conveying system particle  acceleration length, conveying velocity, load ratio and powder flow profile are essential investigations. Consequently, these parameters coupled with in depth characterisation of lactose flow properties are mandatory for the accurate design of the conveying system to ensure  the successful operation of the production process.  

There are two key pillars to this research, the first focusing on characterising the physical, dynamic, bulk and shear properties of five lactose powders throughout a range of bench tests,  and investigating approaches to both quantitatively and qualitatively assess powder rheology. The flowability was evaluated with various characterisation and analytical techniques – most notably Freeman Technology FT4 Rheometer investigations, static angle of repose analysis, Carr’s Compressibility Index (CCI), Hausner Ratio (HR), and shear cell tests. Prominent  powder properties most influential during pneumatic conveying were prioritised, with powder  properties in the various stress state environments of a complete conveying system examined independently. The second key pillar of the research involved conveying the characterised lactose powders on a lab-scale pneumatic conveying test rig, monitoring, and analysing the behaviour of the powders, the flow dynamics, powder acceleration length, and volume fraction.  Additionally, the level of in-line adhesion to pipe walls, deposition pattern and quantity post  conveying was a key focus, with approaches investigated to optimise the conveying process,  and mitigate the level of deposition and fouling. 

The various characterisation bench tests were conclusive on the flowability of each of the five  lactose products and resulted in a comprehensive database of powder flow information. Flow  function of the products ranged from 2.75 to 6.15, the static angle of repose ranged from 46.4 to 53.3º, and there was a Hausner Ratio range of 1.34 to 1.74. The results enabled categorisation  of the five products to three distinct groups – easy flowing (Milei Lactose, Meggletose 70),  cohesive (Domo Lactopure, Arla Foods) and significantly cohesive (Meggletose 200). Additionally, the bench test information enabled links to be drawn between the flow profiles experienced in the experimental conveying test rig with the powder properties, novel research  in this area. Powder particle size and distribution, and powder permeability were determined two of the key powder properties influencing conveying performance. Optimisation of the test  rig was subsequently achieved through altering line geometry, adjusting conveying conditions,  and optimising the bend design. The most influential change to line geometry involved  increasing the length of straight pipe between bends, therefore enabling further reacceleration  prior to being conveyed around the bends. Optimisation of conveying conditions was achieved  through increasing the fluid velocity and decreasing solids feed rate. Optimisation of the bend  design involved the use of bend flow aids, also known as smart bends, to mitigate the impact  of the bends, thus maximising the conveying performance.