Settling chamber

Since the pressure drop through a settling chamber is small, and because low gas velocities are used, the chamber is not subject to abrasion and may therefore be used as a precleaner to remove very coarse particles and thus minimize abrasion on subsequent equipment. 

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Other than the biofilter and culture chambers, recirculating systems typically also employ one or more settling chambers or mechanical filters to remove soHds such as unconsumed feed, feces, and mats of bacteria that slough from the bio filter into the water. Each recirculating system requires a mechanical means of moving water from component to component. That usually means mechanical pumping, though air-lifts can also be used. 

Dilute This is a fully expanded condition in which the solids particles are so widely separated that they exert essentially no influence upon each other. Specifically, the solids phase is so fuUy dispersed in the gas that the den sity of the suspension is essentially that of the gas phase alone (Fig. 12-29). Commonly, this situation exists when the gas velocity at all points in the system exceeds the terminal setthng velocity of the solids and the particles can be lifted and continuously conveyed by the gas however, this is not always true. Gravity settling chambers such as prilling towers and countercurrent-flow spray diy-ers are two exceptions in which gas velocity is insufficient to entrain the sohds completely. 

Vapors (from drying) are removed at the feed end of the dtyer to the atmosphere through a natural-draft stack and settling chamber or wet scrubber. When employed in simple drying operations with 3.5 X 10 to 10 X 10 Pa steam, draft is controlled by a damper to admit only sufficient outside air to sweep moisture from the cylinder, discharging the air at 340 to 365 K and 80 to 90 percent saturation. In this way, shell gas velocities and dusting are minimized. When used for solvent recovery or other processes requiring a sealed system, sweep gas is recirculated throu a scrubber-gas cooler and blower. 

U Length of gravity settling chamber in direction of gas flow m ft ... 

Open-hearth furnaces oxygen blow. Fumes, smoke, SO, particulates Proper hooding, settling chambers. 

Municipal, 227 metric tons per day, before settling chamber 0.032 0.35... 

Settling chambers, low-pressure-drop cyclones, and dynamic precipitators are among the most common and important devices applied in end-of-pipe control applications for dust and particulate matter. 

Flyash - Flyashes are finely divided matter generally entrained in flue gases that arise from combustion. Particles range from 1 /im in size on down. This is not within the operational range of gravity settling chambers. Wet... 

In specifying settling chamber dimensions, gas flow velocities must be maintained below the reentrainment velocity (pick-up velocity) of deposited particulate. As a general guideline, linear gas velocities are kept below 10 ft/sec (600 ft/min = 304.8 cm/sec). This is satisfactory for most materials however, some low-density particulates are reentrained at lower velocities. 

As noted, settling chambers are used to control PM, and primarily PM greater than 10 micrometers (/im) in aerodynamic diameter. Most designs only effectively collect PM greater than approximately 50 /im (Wark, 1981 Perry, 1984 EPA, 1998). 

Despite low collection efficiencies, settling chambers have been used extensively in the past. The metals refining industries have used settling chambers to collect large particles, such as arsenic trioxide from the smelting of copper ore. 

Power and heating plants have used settling chambers to collect large unbumed carbon particles for reinjection into the boiler. They are particularly useful for industries that also need to cool the gas stream prior to treatment in a fabric filter (Mycock, 1995). 

Temperature-. Inlet gas temperatures are only limited by the materials of construction of the settling chamber, and have been operated at temperatures as high as 540°C (1000°F) (Wark, 1981 Perry, 1984). 

Pollutant Loading-. Waste gas pollutant loadings can range from 20 to 4,500 grams per standard cubic meter (g/sm ) (9 to 1,970 grains per standard cubic foot (gr/sef)). Multiple-tray settling chambers can only handle inlet dust concentrations of less than approximately 2.3 g/sm (1.0 gr/sef) (Mycock, 1995 Parsons, 1999 Steinbach, 1999 Josephs, 1999). 

Other Considerations Leakage of cold air into a settling chamber can cause local gas quenching and condensation. Condensation can cause corrosion, dust buildup, and plugging of the hopper or dust removal system. The use of thermal insulation can reduce heat loss and prevent condensation by maintaining the internal device temperature of the above the dew point (EPA, 1982). No pretreatment is necessary for settling chambers. 

There are two primary types of settling chambers the expansion chamber and the multipletray chamber. In the expansion chamber, the velocity of the gas stream is significantly reduced as the gas expands in a large chamber. The reduction in velocity allows larger particles to settle out of the gas stream (EPA, 1982 Wark, 1981 Perry, 1984 Mycock, 1995 EPA, 1998). A multiple-tray settling chamber is an expansion chamber with a number of thin trays closely spaced within the chamber, which causes the gas to flow horizontally between them. While the gas... 

Advantages of settling chambers include (Wark, 1981 Corbitt, 1990 Perry, 1984 Mycock, 1995 and EPA, 1998) ... 

Trays in multiple-tray settling chamber may warp during high-temperature operations. 

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