Particulate matter, removal

The detrimental effects of particulate matter on the atmosphere have been of some concern for several decades. In fact, the total output of particulate matter into the atmosphere has increased in Europe since medieval times (Brimblecombe, 1976), and, although the sources are various, there is special concern because of the issue of particulate matter from fossil fuel use (Cawse, 1982). Species such as mercury, selenium, and vanadium, which can be ejected into the atmosphere from fossil fuel combustion (Kothny, 1973 Lakin, 1973 Zoller et al., 1973), are particularly harmful to the flora and fauna mercury. Thus, there is the need to remove such materials from gas streams that are generated during fossil fuel processing. 

There are many types of particulate collection devices in use, and they involve a number of different principles for the removal of particles from gas streams (Licht, 1988). However, the selection of an appropriate particle removal device must be based upon equipment performance as antici-pated/predicted under the process conditions. To enter into a detailed description of the various 

Cyclones are low-cost particle collectors that have many potential applications in coal gasification systems however, they have low efficiency for collecting particles smaller than 10 pm but above this size collection efficiency can be at least 90%. Conventional applications for cyclones include use as precleaners, entrainment separators, and for controlling dust emissions from coal grinding and pulverizing (Chapter 6). 

The major requirements of the dust discharge are that upward gas flow into the cyclone body should be minimal while continuous discharge of the dust is maintained. This is often accomplished by the inclusion of baffles or straightening vanes at the discharge to suppress the vortex at this point, thus minimizing the up-flow. 

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Particulate matter removal, in industrial water treatment, 26 140-141 Particulate metal-matrix composites, 16 179... 

Fly ash Noncombustible particulate matter removed from stack gases Powdery, silt-Uke 160 Si, Al, Fe, Ca... 

HEPA filter performance for the removal of radioactive particulate matter in the ventilation system hot exhaust is ensured by means of administratively controlled TSR surveillance activities. HEPA filters are subject to periodic pressure drop testing to verity operability (i.e., to verify that the filters are not plugged). They are also subject to periodic efficiency testing to verify the required level of particulate matter removal efficiency. HEPA filters are to be replaced, In accordance with operating procedures, when they become plugged or when the required efficiency can no longer be achieved. 

The simplest means of particulate matter removal is sedimentation, a phenomenon that occurs continuously in nature. Gravitational settling chambers can be employed for the removal of particles from gas streams by simply settling under the influence of gravity. These chambers take up large amounts of space and have low collection efficiencies, particularly for small particles. 

The zinc oxide process was developed by Johnstone and Singh (1940) at the University of Illinois. Although development was utility sponsored, the process has not been used commercially. However, a considerable amount of pilot-plant work was conducted, and features of the process design were worked out in considerable detail. The process is illustrated in Figure 7-17. The flue gas is contacted with a solution of sodium sulfite and bisulfite and sulfur dioxide is absorbed, thus causing an increase in bisulfite content. The solution is next passed into a clarifier, in which particulate matter removed from the gas stream is separated, and finally into a mixer in which it is treated with zinc oxide. At this point, the original ratio of sulfite to bisulfite is restored, and zinc sulfite is precipitated in accordance with the following reactions ... 

In operation, a spark source is normally first flushed with argon to remove loose particulate matter from any previous analysis. The argon flow is then reduced, and the cathode is preheated or conditioned with a short bum time (about 20 sec). The argon flow is then reduced once more, and the source is ran for sufficient time to build a signal from the sample. The spark is then stopped, and the process is repeated as many times as necessary to obtain a consistent series of analyses. The arc source operates continuously, and sample signal can be taken over long periods of time. 

Extrusion. The filtered, preheated polymer solution is deHvered to the spinneret for extmsion at constant volume by accurate metering pumps. The spinnerets are of stainless steel or another suitable metal and may contain from thirteen to several hundred precision-made holes to provide a fiber of desired si2e and shape. AuxUiary filters are inserted in front of the fixture that holds the spinneret and in the spinneret itself to remove any residual particulate matter in the extmsion solution. 

Use of ultrafiltration (UF) membranes is becoming increasingly popular for clarification of apple juice. AH particulate matter and cloud is removed, but enzymes pass through the membrane as part of the clarified juice. Thus pasteurization before UF treatment to inactivate enzymes prevents haze formation from enzymatic activity. Retention of flavor volatiles is lower than that using a rack-and-frame press, but higher than that using rotary vacuum precoat-filtration (21). 

Removal of Particulate Matter. The amount of particulate entering a cooling system with the makeup water can be reduced by filtration and/or sedimentation processes. Particulate removal can also be accompHshed by filtration of recirculating cooling water. These methods do not remove all of the suspended matter from the cooling water. The level of fouling experienced is influenced by the effectiveness of the particular removal scheme employed, the water velocities in the process equipment, and the cycles of concentration maintained in the cooling tower. 

Filtration. Filtration is usually a misnomer for tertiary processes that remove particulate matter. Small particles are removed by adsorption rather than by physical straining. If secondary effluents contain a high concentration of soHds, filter beds clog and binding occurs at the bed surface. 

Ultra filtration. This process removes macromolecules, microorganisms, particulate matter, and pyrogens using a thin, selectively permeable membrane. Ultrafiltration caimot remove ions from water and is generally employed as a polishing process. 

J. G. Wilson and D. W. Miller, "Removal of Particulate Matter from Fluid-Bed Catalytic Cracking Unit Stack Gases," f AirPollut. Mssoc. 7, 682 (Oct. 1967). 

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