Spray drying is one unit operation for which particle size is a critical parameter. Figure 3 shows an in-line laser diffraction analyzer measuring the output from a small lab-scale dryer.
The instrument measures the entire product stream, producing data with high statistical signifi cance. Its installation as close as possible to the exit minimizes time delays. A feedback control loop allows manipulation of either atomizer pressure or feed to maintain particle size at a given set point. Increasing feed rate produces coarser particles; increasing atomization pressure has the opposite effect. Figure 4 shows data from the in-line system
Justifying an investment in on-line analytical instrumentation relies on having confi dence in the technology and being able to make a reliable estimate of the potential gains. With on-line particle size analyzers based on laser diffraction, users routinely report payback times of between six months and a year. Economic advantage fl ows from many sources: reduced waste, manpower, energy, material, plant capacity; better product quality; automated control; and faster process development and optimization. The detailed case for justifi cation is unique to individual plants but the themes are well understood and common to all. The database of case studies demonstrating benefit, across all industry sectors, grows each year. Consultancy services offering mobile particle sizing technology make it easier to understand the potential for each and every plant.