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PNEUMA-PULSE UP-DRAFT DESIGN

The up-draft design is the original self-cleaning concept and has stood the test of time in many hundreds of gas turbine installations throughout the world. Derived from the self-cleaning baghouse systems, it is traditionally used for high dust level pollution control systems in industry.

In the Pneuma-Pulse design, cylindrical filter cartridges are attached to the underside of a horizontal aperture plate ("grid plate" or "tube sheet") using a "twist lock" mount system. There are no loose fasteners, cranks, or threaded rods required to hold the elements in place.

Unfiltered air enters the gas turbine inlet system and passes upward and radially inward through the filter medium. The filtered air then exits the cartridge vertically upward into a clean air plenum located immediately above the grid plate. Multiple filter modules are grouped together to feed a common clean air plenum.

The dust that is collected on the cartridges is periodically removed by compressed air pulsing. Pneuma-Pulse systems use accelerator/inducer nozzles in place of venturis, yielding lower initial pressure drop and more efficient cleaning. The operating airflow resistance is comparable to that of conventional three stage filter systems.

Pneuma-Pulse design strengths:

• Resistance to snow
• Resistance to liquid precipitation
• Able to handle very heavy dust concentrations

CROSS FLOW DESIGN

The cross flow self-cleaning pulse filter was developed to provide a smaller footprint at sites where space is limited; for example, in power plants that are to be installed in urban areas.

In this inlet design, two cartridges - one cylindrical and one conical - are installed one behind the other over a support cradle. These cartridge pairs are clamped in horizontal rows onto a vertical aperture plate (grid plate). Unfiltered air enters the inlet filter system through weather hoods located immediately upstream of the filter cartridges and then passes horizontally and radially inward through the filter medium. The filtered air exits the cartridge horizontally through the grid plate into a clean air plenum located immediately downstream.

The filters surface load, and cleaning action is similar to the Pneuma-Pulse design. The pulsing sequence starts at the top row of the gas turbine inlet and progresses downward. This helps minimize the tendency for dust from upper rows to become captured on lower rows of elements. Also, since more air is needed to dislodge the dust cake, the valves, compressed air header, and blowpipes are slightly different from the Pneuma-Pulse design.

Cross flow designs strengths:

• Small footprint
  
• Conducive to cooling systems (initial or retrofitted)
  
• Slightly lower pressure drop

The horizontal configuration of the cross flow filter cartridges requires some form of weather protection (rain hoods). Also, because of the available frontal area of the cross flow design, the air entrance velocity into the dedicated gas turbine inlet weatherhoods is much too high to prevent the ingress of fine free moisture (i.e. fog and mist). This free moisture forms a mud-like cake on the surface of the filter cartridges that simply cannot be released by the pulsing action. Since cross flow cartridges are oriented horizontally, free moisture can drain from the outside to the inside of the cartridges and thus be ingested into the clean air plenum. Here, the solution would be to place a separate bank of coalescers upstream of the pulse cartridges. This bank would remove and drain collected fine mist and fog.