Electrostatic filters

Small solid particles, present in dust and grit emissions, have very low settling velocities (Table 4.4) The collection efficiencies of simple cyclones are tlierefore, as shown in Figure 17.3, relatively low. Fabric filters, electrostatic precipitators or wet scrubbers may be required to remove particles <5 pm in size with an acceptable efficiency. Therefore the cost of pollution control inevitably increases when dealing with particle size distributions skewed towards the lower end. 

The air quality in preparation and aseptic areas can be one of the greatest sources of product contamination. However, this problem can be minimized by use of the equipment currently available to provide clean air essentially free from microorganisms and dirt particles. Depth-type filters, electrostatic filters, and dehumidification systems are used to remove the major... 

Particulate removal requirements vary depending on the use of the product gas. For example, particulate levels must be reduced to below 50 mg/Nm3 for gas engines and below about 15 mg/Nm3 (>5 im) for turbines, and to perhaps 0.02 mg/Nm3 for synthesis gas systems. The primary types of systems include cyclonic filters, barrier filters, electrostatic filters, and wet scrubbers. 

As cyclones are less effective as the particle size decreases, secondary collection units are frequently required, i.e., filters, electrostatic precipitators, and scrubbers. When dry collection is not required, elimination of cyclones is possible if allowance is made for heavy solids loads in the scrubber (see Gas-Solids Separations see also Sec. 14). 

In addition, some processes create considerable amounts of particulate matter and other emissions from catalyst regeneration or decoking processes. Volatile chemicals and hydrocarbons are also released from equipment leaks, storage tanks, and wastewaters. Other cleaning units, such as the installation of filters, electrostatic precipitators, and cyclones, can mitigate part of the problem. 

A review of Table 8 and Fig. 3-2 indicates that large-diameter particles can be removed with low-energy devices such as settling chambers, cyclones, and spray chambers. Submicron particles must be removed with high-energy units such as bag filters, electrostatic precipitators, and venturi scrubbers. Intermediate particles can be removed with impingement separators or low-energy wet collectors. Obviously, other equipment performance characteristics as noted in Table 8 will also have their influence on the final equipment... 

SO2 is also obtained commercially from metal sulfide ores by roasting in fluidized bed furnaces (equation 11). The reaction is carried out at 650 1100 °C, with the resultant SO2 being filtered electrostatically to remove ash and then freed of AS2O3 impurities before being used in the preparation of SO3. 

Existing pollution control devices can remove as much as 99% of the trace elements (except mercury and selenium) from the combustion gases. Substantial amounts of mercury and, to a lesser extent, selenium are emitted with the combustion gases. There are a number of ways to reduce trace-element emissions due to coal combustion. These pollution control options include switching to coals with a lower trace-element content, selectively mining those parts of coal beds with lower trace-element contents, cleaning the mined coal, and using pollution control devices such as fabric filters, electrostatic precipitators, and combustion gas scrubbers. 

Bio-oils were produced m 1995-1998 from various wood species on fast pyrolysis pilot plants, which differed by their construction features NREL (ablative pyrolysis with hot gas filter, poplar wood, 1996), Aston FB (fluidized bed, poplar wood, 1995), IWC, TP 29 (fluidized bed, bamboo, beginning of 1998) BTG (rotating cone, pine wood, 1995), VTT (circulating fluidized bed, pine wood, 1997), IWC, E-filter (electrostatic precipitator, beech wood, end of 1998) and IWC Kl-FIO from different coolers (beech wood, end of 1998). 

Simprosys 3.0 contains 20 unit operation modules and 2 utilities as displayed in Figure 60.2. The 20 unit operation modules include solid dryer, liquid dryer, burner, cyclone, air filter, bag filter, electrostatic precipitator, wet scrubber, scrubber condenser, fan/blower, compressor, steam jet ejector, pump, valve, heater, cooler, heat exchanger that can also be used as an evaporator, liquid-vapor separator. 

A number of different techniques are available for the removal of particulates from gas emissions, including baghouses (also known as fabric filters), electrostatic... 

Roaster gases are cleaned by a combination of cyclones, bag filters, electrostatic precipitators, venture scrubber, etc. 

Planetary coolers and those grate coolers which have to operate in conjunction with highly efficient dust collection equipment (granular bed filters, electrostatic precipitators, fabric filters with air-to-air coolers) will require a relatively large... 

Abundance sensitivity becomes critical when measuring extreme isotope ratios (>100 000) or when neighbouring elements are present in the sample at high concentrations. In ICP-MS this occurs for isotope ratio measurements of elements such as U and Th (extreme ratios) or boron isotope ratio measurements in the presence of high carbon contents (tailing of onto "B). Specially designed filters (electrostatic filter, quadrupole lenses) can increase the abundance sensitivity up to 2 x 10 (see Chapter 2, section 2.2.1 for further details). In the case of boron, a simple matrix separation can help. In the majority of isotope ratio measurements however abundance sensitivity effects are negligible. 

Fabric filters can cope with most industrial gas cleaning problems economically and efficiently. Filtering of hot gases before heat exchanging, catalytic oxidation in combination with bag filters, electrostatic precipitators in fabric filters with conductive filter media, dry scrubbing to bind the gaseous components, anti-static performance of filter materials, adhesive dust repellent finishes, and chemical protection of fibres are just some of the uses. 

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