A packed bed consists of a packing, which may be a catalyst, sand or some other solid packing, which has been distributed into a vessel to form a surface.

The packed bed provides a long and often tortuous route for a gas or liquid to pass through. Liquids may be pumped through the bed as a means of filtrations as is the case in the water industry.

Gases may be passed counter current through the packed beds as a means of ensuring intimate contact and effective reaction in either “passive” or ”catalyst” packing.

In all cases the purpose of the packing is to encourage intimate contact and a residence time.

By the very nature of a packed bed, it is almost impossible to see what is happening inside the bed, yet the priority is to ensure intimate contact of the two fluids within the bed. A second requirement is to monitor for blockages or “channelling” which change the flow of the fluids and reduce the effectiveness. 

This reduces performance, decreases yield and increases costs.

Applications:

  • Packed Beds/Bubble Columns
  • Research/Process Monitoring
  • Separation Process
  • Research/Process Monitoring and Development
  • Monitor distillation, adsorption and catalysis

Photo: Packed bed with multiple measurement planes

Process tomography can measure flow through packed beds. Process tomography sensors can subtract out the packing in columns and then determine how gas or liquids is distributed in a plane.

The concentration variations through the bed can be determined.  Solutions can be developed and evaluated by changing the:

  • packing
  • flow conditions
  • distributor design

Tomography data can be presented as:

  • statistical measures
  • bulk concentration
  • images to compare against process models

Depending on the nature of the continuous phase, either a p2+ or m3000 can be used.  The p2+ is applied for aqueous systems, such as bubble columns, the m3000 is used for “dry” columns or those filled with organic materials. 

In each case circular sensor arrays are designed into the column.  Where it is necessary to minimise wall effects it is possible to have the sensors milled down to provide a smooth internal surface.

The m3000 can also be used in combined ECT (Electrical Capacitance Tomography) and ERT (Electrical Resistance Tomography) modes to provide information on multiple phases, although it should be noted that this requires specialist support from ITS.

Key benefits include:

  • shorten cycle times by measuring reaction conditions through bed
  • increase yield by measuring phase concentration and boundaries
  • measure flow velocities to identify areas of good and poor contact
  • development of new distributor arrangements

Register to access our "Radial flow packed bed reactor CFD validation" case study available from the Download section on the right.

Register to access our "Radial flow packed bed reactor CFD validation" case study available from the Download section on the right.

Publications:

Using electrical capacitance tomography to monitor gas voids in a packed bed of solids, Robert B White,2002 Measurement Science and Technology, 13, 1842-1847

Bolton, Hooper, Mann and Stitt (2004) Flow distribution and velocity measurement in a radial flow fixed bed reactor using electrical resistance Tomography, Chemical Engineering Science, Vol. 59, No. 10, pp 1989-1997

For more information about this paper, please contact ITS.

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