Particle removal efficiency

Gas Filtration Vendors are the primary source for sizing baghouses, however the process engineer should at the very least make an estimate of the pressure drop requirements for an intended system. The pressure drop will, of course, provide information needed on the approximate size of the fan needed, and the energy requirements needed to operate a system. In fact, pressure drop is the primary parameter in establishing particle removal efficiency for a fabric filtration unit, and hence, is usually the starting place for discussions with the equipment supplier. 

A minimum particle removal efficiency of 99.97% for 0.3 micron particles. 

Particle removal efficiency increases with use Large fans is noisier and consumes more energy ... 

Double-sided brush scrubbing followed by a spin-rinse-dry step dominates the industry. An example of a double-sided brush scrubber is shown schematically in Fig. 16. The rollers keep the wafer positioned and rotating while the brushes dean debris from both the front and back sides of the wafer. The cleaning solution is delivered through the bristles themselves. Typically, the bristles are porous so that fresh solution can be delivered directly to the wafer and minimal amounts of debris accumulate on the brush. Increasing the down force increases the particle removal efficiency up... 

Fig. 14. Evolution of alumina particle removal efficiency from PECVD TEOS oxide as a function of pH. As expected, better results are obtained in areas A and B.

Both silicon oxide and alumina slurries can be efficiently removed on PECVD TEOS oxide or silicon nitride substrates in a conventional SCI or in a SCI without any water peroxide in the case of outcropping tungsten (see Fig. 5). When water peroxide is not present to continuously regrow a protective oxide layer, OH species can etch the silicon. In the latter case, the backside of the wafer must therefore be protected with a nitride or oxide layer to avoid a severe silicon roughening effect. Nevertheless to achieve the same particle removal efficiency obtained with a scrubber, power mega-sonics also have to be used (see Fig. 18). 

HF-based chemistry is particularly interesting due to its compatibility with all back-end metals and barriers. Unfortunately as the absolute values of tbe zeta potential in the A area of Fig. 13 are lower than in alkaline media, the removal mechanism is even more difficult. Indeed as seen in Fig. 19, the particle removal efficiency in the HF-HCl mixture is almost zero for actual alumina slurries. Very-high-power megasonics performed in a specific HF-compatible bath are absolutely necessary to obtain the same good residual particle level as with the scrubber. 

Figure 10 reports the filtration efficiency of the particles naturally contained in air at ambient temperature under the NMGBF prototype operating conditions mentioned in Table 4. Figure 10 shows that the gas-particle separation efficiency for submicronic particle is comprised between 54 to 96 %. Submicronic particles removal efficiency is the major limitation of the NMGBF as for granular bed filters. With particle diameters ranging from I to 10 pm, the efficiency reaches nearly 96%. 

A throwaway extended-pleated-medium dry-type filter with (1) a rigid casing enclosing the Ml depth of the pleats, (2) a minimum particle removal efficiency of 99.97% for thermally generated monodispersed DOP smoke particles with a diameter of 0.3 microns, and (3) a maximum pressure drop of 1 inch water gage when clean and operated at its rated airflow capacity. ... 

These figures prompt the suggestion [Williams and Edyvean, 1995] that the p ratio concept is of use only in absolute filter applications. At lower efficiencies, the simple particle removal efficiency = HfJ) is preferred. 

It is possible to remove small particles using dispersed or dissolved gas flotation devices. These units are primarily used for removing suspended hydrocarbons from water. Gas is normally dispersed into the water or released from a solution in the water, forming bubbles approximately 30-120 pm in diameter. The bubbles form on the surfaces of the suspended particles, creating particles whose average density is less than that of water. These rise to the surface and are mechanically skimmed. In the feed stream, chemicals called "float aids" are normally added to the flotation unit to aid in coagulation of solids and attachment of gas bubbles to the solids. The optimum concentration and chemical formulation of float aids are normally determined from batch tests in small-scale plastic flotation models on-site. Because of the difficulty of predicting particle removal efficiency with this method, it is not normally used to remove solids from water in production facilities. 

A maximum capacity of 40 ACFM per tube and a minimum of 10 ACFM are recommended. The maximum is recommended to prevent excessive wear of the tubes and the minimum is maintained to provide sufficient centrifugal force to accomplish satisfactory particle removal efficiency. The maximum can be exceeded and greater efficiency is obtained. This practice is recommended in specific applications only. 

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