Selection Criteria

The following influencing variables play significant roles in establishing the most important criteria for selection and design of filter facilities:

• The spectrum of particle-size distribution (which can vary appreciably)
• Composition of the pollutant particles
• Dust concentration
• Temperature
• Relative humidity.

The most commonly encountered particle concentrations lie within the range of 0.01 … 0.5 mg/m³, with particle sizes typically < 0,1 … 5 µm. In arid climates and in heavy-industry areas, however, greater concentrations and larger particles are often found (e.g., up to > 100 mg/m³ and > 100 µm).

For optimal selection of a filter system, it is essential for the planning engineer to obtain as exact knowledge of local circumstances as possible:  e.g., particle concentration, height of air-intake openings, wind directions, any possible emitters of pollutants in the vicinity, and the like. Also required for effective system design is information on requirements for air purity (depending on the type of turbine), intake volume flow, as well as the maximum permissible pressure difference for the air-intake system. This information is essential for proper coordination of the various filter stages, and for assurance of long filter service life.

The following criteria are critical for the design of filter systems under such circumstances:

• The type, concentration, and size distribution of the air pollutants encountered
• Local climate conditions:  e.g., temperature, relative humidity, annual precipitation figures, wind, etc.
• Other local conditions.

Other system-specific parameters, such as the following, are also important:

• Mode of operation of the plant, as well as length of operational cycles
• Air consumption by the systems
• Maximum pressure loss and minimum degree of filtration
• Constraints and possibilities for installing the systems
• Investment and operational costs.