There are many applications and configurations for which fluidized bed reactors have been successfully deployed in industry. The core element of a fluidized bed is the upward flow of a fluid (usually gas) through a bed of solids at a high enough flow rate to suspend or fluidize the particles in the fluid but not so high that they are transported out of the reactor. This leads to increased interaction between solids and fluid and decreased interaction of solids with each other and the wall. It also makes it easier to recover and/or recycle the bulk solids from the reactor. These characteristics give fluidized bed reactor systems advantages over other types of reactors for some applications, despite the increase in complexity compared to fixed bed reactors.
When to consider using a Fluidized Bed Reactor
If your process could be performed more optimally by moving solids, a fluidized bed reactor might be a good choice. Some applications where this may be true include drying, coating, absorption, granulation, catalytic reactions with fast deactivation rates, and reactions where one reactant is a solid, such as pyrolysis or combustion. If your process is a highly energetic gas-solid (or gas-gas solid catalyzed) reaction, fluidization can give better reaction temperature control (Cocco, Karri, & Knowlton, 2014), which may have advantages in selectivity and catalyst life compared to a fixed bed arrangement.
In practice, fluidization does limit the size and type of solid particle that can be processed. Although there are other factors such as particle density, typically fluidization is facilitated by particles which are rounded / smooth and 50-500 micron with no more than 10-25 ratio of largest to smallest particle size (Suppes, 2002). Limitations of fluidized bed reactors include bulk solids type and size limitations, more complex design and operation, potential for erosion of internals and attrition of solids, backmixing of gas (not an ideal plug flow reactor), difficulty in modeling and scaling up, and larger reactor volume and gas flow rates (especially at high pressure) (Cocco, Karri, & Knowlton, 2014). It is recommended that experimental validation of fluidization behavior be investigated prior to making a large investment.
Options for Solids Processing
Parr Lab-scale (or small pilot-scale) Fluidized Bed Reactor Systems can be used for catalytic reactions where the catalyst is loaded cold prior to startup and remains in the reactor for an extended length of time. For applications where solids addition and removal from the hot reactor are desired, multiple options exist. Particle recovery lines designed to enable the transport of solids help avoid plugging and solids holdup in the lines.
Options for solids addition include the batch addition of solids via solids charging port on the head, and continuous addition of solids via high pressure solids feeder. Parr’s high pressure solids feeder is a fairly new offering designed for continuous addition of free flowing solids during operation at temperature and pressure. Continuous recycle of bulk solids is not currently offered in Parr Fluidized Bed Reactor Systems.
Parr has developed innovative techniques for periodically removing and recovering bulk solids from our lab-scale fluidized bed reactors without needing to cool down the reactor or increase the gas velocity above operational levels. Optionally fines swept out with the gas flow at high flow rates may be captured separately from other larger particles (helpful if your product is a solid material).
Parr has the capability to customize our reactors to your specific process, even if it involves extreme conditions. For example Parr recently supplied multiple interchangeable high temperature fluidized bed reactors with 2-inch inside diameter made from three different materials of construction, two of which were rated for use up to 700 °C, with inlet gas preheated to 500 °C. Whether it is corrosion resistant materials of construction, high temperatures, high pressures, processing a mixture of solids, performing multiple steps in the same reactor (such as reaction and adsorption), or combining multiple unit operations, if you have a customization you would like built in to your Fluidized Bed Reactor System, contact Parr today and let us build one for you!
Cocco, R., Karri, S. B., & Knowlton, T. (2014, November). Introduction to Fluidization. Chemical Engineering Progress, pp. 21-29. Retrieved from https://www.aiche.org/sites/default/files/cep/20141121.pdf
Suppes, G. J. (2002). Heuristics in Chemical Engineering. Retrieved from Faculdade de Engenharia da Universidade do Porto: https://web.fe.up.pt/~sereno/heuristics.pdf