FLUID BED TECHNOLOGY

Fluidized beds are used for physical processes like mixing, classifying, drying, coating, granulation, agglomeration, adsorption, pneumatic transport and heating and cooling of bulk solids. The plants for combustion, pyrolysis, gasification, gas cleaning, water purification, catalytic or gas-solid reactions belong to chemical fluid bed processes. During the last years fluid beds have been applied more commonly for the processes of environmental technology, for example adsorptive or absorptive gas cleaning or for the fluidization of immobilized micro-organisms in the liquid phase for the production of active substances in the cleaning of sewages.

Fluid bed granulation

Fluid bed granulation in particular is very common as it has important advantages over other types of granulators including good heat and mass transfer, temperature homogeneity, mechanical simplicity and one-pot processing capabilities. In this process atomizable liquids (e.g., suspensions, solutions, emulsions or melts) can be converted into free-flowing granular solids by integration of a number of processes like wetting, drying, size enlargement by agglomeration, shaping and homogenization or separation into a single step of the process chain by using high heat and mass transfer. The most common basic principle is to atomise a liquid into a bed of fluidised particles. The liquid spray typically consists of a solute which acts as a coating medium, and a solvent in which the solute is dissolved or dispersed. By contacting the core particles the liquid droplets spread and partly penetrate into the core pores. The warm fluidisation air evaporates the solvent, leaving a coating layer of solute on the particle surfaces. Particle growth can occur by either inter-particle agglomeration or by surface coating. Agglomeration occurs when liquid bridges of coating solution form between colliding particles. If the liquid bridge is strong enough to prevent subsequent particle separation, the liquid bridge solidifies resulting in a permanent agglomerate. This tailor-made particle design is used in a wide range of industries, including pharmaceutics, foodstuffs, fertilizers, detergents, mineral processing and specialty chemicals.

Fluid bed coating

Another common fluid bed application is particle coating in fluid beds. It is a flexible and versatile process commonly used in the manufacture of many pharmaceutical and biotechnological products. In coating processes, agglomeration is generally unwanted and a number of other potential problems associated with the process include: spray drying loss of atomised coating droplets, attrition and breakage of the core particles and coating layer, deactivation of the active ingredient due to high temperature/humidity exposure and more. By constituting the boundaries these potential problems in all define the fluid bed coating process optimisation problem, and the engineering challenge is to navigate in between these often narrow borderlines. Seydlitz United Consultants offer consultancy in all aspects of fluid bed technology including drying, granulation and coating focussing on both product properties and process conditions.