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    Design and Control of Spray Dryer

    2018-4-8 14:25:11

    The challenges facing both designers and users are to increase production,  improve powder quality and reduce costs. This requires an understanding of the  process and a robust control implementation.
     Spray drying consists of the following phases:

    1. Feed  preparation: This can be a homogenous, pumpable and free from impurities  solution, suspension or paste.
    2. Atomization  (transforming the feed into droplets): Most critical step in the process. The  degree of atomization controls the drying rate and therefore the dryer size.  The most commonly used atomization techniques are:

    1.  Pressure nozzle atomization: Spray created by forcing the fluid through an  orifice. This is an energy efficient method which also offers the narrowest  particle size distribution.
     2.  Two-fluid nozzle atomization: Spray created by mixing the feed with a  compressed gas. Least energy efficient method. Useful for making extremely fine  particles.
     3.  Centrifugal atomization: Spray created by passing the feed through or across a  rotating disk. Most resistant to wear and can generally be run for longer  periods of time.

    1. Drying:  A constant rate phase ensures moisture evaporates rapidly from the surface of  the particle. This is followed by a falling rate period where the drying is  controlled by diffusion of water to the surface of the particle.
    2. Separation  of powder from moist gas: To be carried out in an economical (e.g. recycling  the drying medium) and pollutant-free manner. Fine particles are generally  removed with cyclones, bag filters, precipitators or scrubbers.
    3. Cooling  and packaging.

    A control system must therefore provide flexibility in the way in which  accurate and repeatable control of the spray drying is achieved and will  include the following features:

    1. Precise  loop control with setpoint profile programming
    2. Recipe  Management System for easy parameterisation
    3. Sequential  control for complex control strategies
    4. Secure  collection of on-line data from the system for analysis and evidence

    Local operator display with clear graphics and  controlled access to parameters


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