Investigation of anti-fouling processing aids in the primary evaporation of whey permeate

Abstract

The production of lactose via the concentration of whey permeate is an important process in the dairy industry. Hautapu dairy factory, owned by Fonterra Cooperative Group, process milk into a range of dairy-based products including; Cheese, Milk Protein Concentrate and Lactose. This project was focused around reducing fouling during the evaporation of whey permeate for the production of lactose powder. As whey permeate is heated in evaporators, mineral salts precipitate and accumulate onto the stainless steel heat exchange surfaces. This layer of mineral scale, known as fouling, greatly reduces the amount of heat transfer used for evaporating the whey permeate. Once the fouling gets to a point where it is no longer achievable to reach the concentrated solids target, the evaporator is shut down and cleaned with chemicals to remove the scale build up.

To decrease the amount of scale build up, a process aid is added to the whey permeate. This process aid A , or PAA, is a polyphosphate that when added to the feed stream gives longer run times. This project was aimed at establishing the chemistry behind the inhibiting abilities of PAA and its interaction with whey permeate. It is known that PAA acts as a complexing agent with calcium when it is added to the permeate stream which prevents it from forming calcium phosphate, the main source of fouling.

In the course of the research, it was fortuitously discovered that PAA works very inefficiently as an inhibitor in whey permeate because of its ability to form an insoluble salt with free calcium ions. The consequence of this was that high calcium levels in whey permeate lead to PAA precipitating out of solution rendering it an ineffective anti-fouling agent to prevent further scale build up. As a result of this, alternative inhibitors were considered and tested for their calcium tolerance and calcium phosphate inhibiting properties. From these considerations, carboxymethyl inulin was regarded as the most favourable replacement candidate for PAA. This resulted in plans being set down for a future industrial trial involving the carboxymethyl inulin.