Pneumafil offers two types of self-cleaning pulse filter systems for gas turbine inlets: up-draft ("Pneuma-Pulse") and cross flow.
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 self-cleaning baghouse systems, it is traditionally used for high dust level pollution control systems.
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
- Ability 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.
Cleaning Action
As contaminants build up on the surface of the filter media, the differential pressure in the plenum, relative to ambient, will increase. When the differential pressure reaches a preset limit, a pressure switch activates the timer/sequencer board. The timer/sequencer board signals a solenoid valve to open, releasing the pressure holding a pneumatic air valve closed. The opening of the air valve allows a blast of clean, dry, compressed air to leave the air header and proceed: 1) through the air valve, 2) into the distribution blow pipe, and 3) out through the accelerator / inducer nozzles. The blast of compressed air enters the cartridge, and, for a fraction of a second, effectively stops the airflow into the cartridges. The compressed air pressure wave continues down into the cartridges and radially outward, impacting the accumulated dust off the cartridge.
The low velocity of the entering airflow allows only surface loading of the filter media, thus enabling the compressed air pressure wave, from the cleaning pulse, to effectively remove any accumulated particulate. Some of the finer particles may become re-entrained on adjacent filter cartridges, however, the tendency is for the dust to collect and blow off in particles large enough to fall away from the adjacent cartridges.
Cartridges in the first row are pulsed first, then the timer/sequencer selects the next row and the pulse-cleaning procedure is repeated. The number of elements cleaned at any instant and the time interval between pulses are chosen so that no significant degradation of the airflow is evident. The timer/sequencer board continues to sequence the cleaning operation throughout the cartridges until the overall differential pressure reaches a preset lower limit. At that time the cleaning process ceases until called upon again by a high differential pressure reading.
