Study On The Wall Deposition Of Milk Powder Produced By Spray Drying With Pneumatic Nozzle

One of the largest obstacle is wall deposition among a series of problems which was faced with in milk powder produced by spray drying, although the spray drying technology has been widely used in diary products industry. The paper aims to study the influence of spray drying parameters such as inlet air temperature, feed flow rate, solid concentration on the wall deposition of milk powder with YC-015 spray dryer, by combining the experiment with the numerical simulation.The single factor and the response surface test were conducted respectively for three variables by setting up the spray drying experiment platform. Then a small powder samples was taken to the environmental scanning electron microscopy (SEM) to observer the micro-structure of powder, the infrared vacuum drying oven was used to measure the water content. The analysis of experiment data shows that the optimum parameter condition with the lowest wall deposition was:air inlet temperature at 473K, solid concentration at 25%, pump speed at 55r/min. And the interaction between air inlet temperature and pump speed was significant, which should be taken into consideration when the parameters were chosen for spray drying of milk.The spray dryer model was meshed and refined near the atomizer nozzle with hexahedral using GAMBIT software. The gravity and drag-force of particles, couple interaction with continuous phase, and the spray model with wave were considered, to tracking the particles with unsteady method, consequently obtain the properties of continuous phase and discrete phase in spray dryer, including the distribution of temperature, velocity, humanity and particle residence time.To understand the wall deposition comprehensively, the particle mean diameter and the cyclone separator performance were also studied at the end of the paper. Result proves that the particle mean diameter was positively affect by air inlet temperature and feed flow rate, and negatively influenced by relative velocity between gas and liquid. The separate performance of separator used in experiment was better when the particle size distribution from 1μm to 20μm, and the probability of deposition will increase when exceeding this scale.