This article extends the discussion presented in “Introduction to Fluidization” (CEP, Nov. 2014) and explores some common pitfalls and challenges that may occur when designing and operating a fluidization process.
If not monitored closely, the particle fines level in a fluidized bed can lead to challenges in operation. Too high of a fines level could overload the separation equipment such as cyclones, filters, and electrostatic participators. Too low of a fines level could limit the full potential of the unit, especially for beds with Geldart Group A powders. Typically, a fines level of at least 5–15 wt% provides the best results. For fluidized bed reactors and similar type units, the addition and retention of fines must be considered in all aspects of design. This means that cyclone systems have to be designed and operated correctly, otherwise the fines required for good fluidization will quickly leave the bed.
Bed slugging is also a major pitfall associated with fluidized beds. This occurs when a bubble pushes up all or part of a bed into the freeboard region. This phenomenon can cause overloading of cyclones and other downstream equipment and reduced mass transfer (i.e., productivity), as well as significant mechanical stress.
Additional common pitfalls that the article explores include: high system pressure and bed expansion, inadequate pressure drop in the dipleg, gas bypassing, and particle attrition. The article also details the hurdles associated with operating cyclone separators within fluidized beds.