Lactose smearing in transport lines : a thesis presented in partial fulfilment of the requirements for the degree of Masters in Process Engineering at Massey University

Abstract

The smearing of lactose in pneumatic conveying lines, leads to cakes of lactose building up within the lines. This is an undesirable situation as it leads to reduced throughput, caused by the narrowing of the lines and the increase in downtime required to unblock and clean the pipes. This study was carried out to investigate the causes of smearing and identify solutions to this problem. Impact testing was carried out, to look at the breakage behaviour of lactose. This identified that energy of impact is the main consideration for the breakage of lactose in pneumatic conveying. This is not only the energy contained before impact, but also the way in which the energy is dissipated during contact. The use of rubber proved an effective technique in lowering the amount of breakage, due to its ability to adsorb and disperse the impact energy during contact. Testing was carried out looking at the ability of sliding contact to cause the adhesion of lactose to a surface. The results showed that combination of the frictional forces and the sliding velocity can provide enough energy to cause the lactose to adhere. The conclusion drawn was the same as that for impact testing, with energy being the main consideration in the breakage and adhesion of lactose to surfaces. A link between amorphous lactose formation and the smearing was found, with the build up in the conveying lines having a higher amorphous concentration than was found on the free flowing lactose powder. An attempt to show a change in the amorphous concentration of α-lactose crystals after impact proved unsuccessful, although the use of a polarised microscope showed the formation of amorphous lactose on the impact surface. Calculations looking at the amount of amorphous lactose that would have formed after impact, identified that the concentrations were below the levels measurable using the methods available. Following on from impact testing work, a rubber lined bend was placed in a section of the conveying line at Lactose New Zealand. Monitoring of this bend showed it to be successful in preventing the adhesion of lactose to walls of the conveying pipe. However, there was a small amount of wear observed at the entrance of the bend. This was concluded to be due to a design defect as the rubber was raised above the level of the main line. More testing needs to be done, with a change in design, to allow a conclusion on the applicability of rubber for preventing lactose buildup to be drawn.