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Biotech Regulatory and Quality Support

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Design and Its Impact on Sizing

 

The goal for improving coalescer design is to maximize efficiency while preventing liquid reentrainment. Reentrainment occurs when liquid droplets accumulated on a coalescer element are carried off by the exiting gas. This occurs when velocity of the exiting gas, or annular velocity exceeds the gravitational forces of the draining droplet. 

We earlier discussed the importance of correct coalescer sizing. In designing and sizing a coalescer, the following parameters must be taken into account:

 

  • Gas velocity through the media,
  • Annular velocity of gas exiting the media,
  • Solid and liquid aerosol concentration in the inlet gas, and
  • Drainability of the coalescer

 

Each of these factors with the exception of the inlet aerosol concentration can be controlled. At a constant gas flow rate, media velocity can be controlled by either changing the coarseness of the medium’s pore structure or by increasing or decreasing the number of cartridges used. The coarser the medium, however, the less efficient the coalescer will be at removing liquid. 

At a constant gas flow rate, the exiting velocity of the gas can be controlled by increasing or decreasing the size of the vessel or the space between the cartridges. 

Drainage can be improved by either selecting low surface energy coalescer materials or by treating the coalescer medium with a chemical that lowers the surface energy of the medium to a value lower than the surface tension of the liquid to be coalesced.13 Having a low surface energy material prevents liquid from wetting the filter medium and accelerates drainage of liquids down along the medium’s fibers. The liquid coalesced on the fibrous material falls rapidly through the network of fibers without accumulating in the pores where it would otherwise be pushed through by the gas and be reentrained. Figure 6 shows the effect that a chemical treatment can have on a coalescer. It shows that the maximum flowrate of a chemically treated cartridge is more than twice that of a similar cartridge that is not treated. 

 

 

Design and Its Impact on Sizing

 

The goal for improving coalescer design is to maximize efficiency while preventing liquid reentrainment. Reentrainment occurs when liquid droplets accumulated on a coalescer element are carried off by the exiting gas. This occurs when velocity of the exiting gas, or annular velocity exceeds the gravitational forces of the draining droplet. 

We earlier discussed the importance of correct coalescer sizing. In designing and sizing a coalescer, the following parameters must be taken into account:

 

  • Gas velocity through the media,
  • Annular velocity of gas exiting the media,
  • Solid and liquid aerosol concentration in the inlet gas, and
  • Drainability of the coalescer

 

Each of these factors with the exception of the inlet aerosol concentration can be controlled. At a constant gas flow rate, media velocity can be controlled by either changing the coarseness of the medium’s pore structure or by increasing or decreasing the number of cartridges used. The coarser the medium, however, the less efficient the coalescer will be at removing liquid. 

At a constant gas flow rate, the exiting velocity of the gas can be controlled by increasing or decreasing the size of the vessel or the space between the cartridges. 

Drainage can be improved by either selecting low surface energy coalescer materials or by treating the coalescer medium with a chemical that lowers the surface energy of the medium to a value lower than the surface tension of the liquid to be coalesced.13 Having a low surface energy material prevents liquid from wetting the filter medium and accelerates drainage of liquids down along the medium’s fibers. The liquid coalesced on the fibrous material falls rapidly through the network of fibers without accumulating in the pores where it would otherwise be pushed through by the gas and be reentrained. Figure 6 shows the effect that a chemical treatment can have on a coalescer. It shows that the maximum flowrate of a chemically treated cartridge is more than twice that of a similar cartridge that is not treated.