Skimming systems

Table 5.18 presents the removability of pollutants by two types of skimming systems ... 

The PetroTrap , a passive skimming system, is a long and narrow cylindrical device that uses an active buoy/filter system to remove free-floating hydrocarbon product from a well and store it in a collection cannister. The unit uses no electricity and can be installed quickly. According to the vendor, the PetroTrap is applicable for the recovery of most refined fuels. 

In Fig. 1 oil is skimmed only by the top pipe of a parallel double pipe skim system. In this design both the interceptor bay and oil sump are covered by floating slabs of epoxy-coaled polyurethane foam to reduce oil evaporation and hydrocarbon odors. 

Fig. 19.15 Skimming system of top fermentation showing one method of using a parachute that can be adjusted for height.

The fluorescence excifafion spectra in Figures 9.47(a) and 9.47(b) show the Ojj bands of the A B2 X Ai system of aniline (see Figure 5.19) and the aniline Ar complex in a skimmed supersonic jet of aniline seeded into the argon carrier gas. 

Silica. The main uses of siUca are in the treads of off-the-road tines for improved chunking and tear resistance and as a component of the bonding system for brass and 2inc-plated steel cord. These are commonly used in radial passenger and tmck tire belt skim stock. In addition the body pHes of steel radial tmck tires, hoses and belts, and footwear use significant volumes of siUca as a reinforcing filler. 

For wet ESPs, consideration must be given to handling wastewaters. For simple systems with innocuous dusts, water with particles collected by the ESP may be discharged from the ESP system to a solids-removing clarifier (either dedicated to the ESP or part of the plant wastewater treatment system) and then to final disposal. More complicated systems may require skimming and sludge removal, clarification in dedicated equipment, pH adjustment, and/or treatment to remove dissolved solids. Spray water from an ESP preconditioner may be treated separately from the water used to wash the ESP collecting pipes so that the cleaner of the two treated water streams may be returned to the ESP. Recirculation of treated water to the ESP may approach 100 percent (AWMA, 1992). 

Air flotation is simply the production of microscopic air bubbles, which enhance the natural tendency of some materials to float by carrying wastewater contaminants to the surface of the tank for removal by mechanical skimming. Many commercially available units are packaged rectangular steel tank flotation systems shipped completely assembled and ready for simple piping and wiring on site. 

In recapping, DAF is the process of removing suspended solids, oils and other contaminants via the use of bubble flotation. Air is dissolved into the water, then mixed with the wastestream and released from solution while in intimate contact with the contaminants. Air bubbles form, saturated with air, mix with the wastewater influent and are injected into the DAF separation chamber. The dissolved air then comes out of solution, producing literally millions of microscopic bubbles. These bubbles attach themselves to the particulate matter and float then to the surface where they are mechanically skimmed and removed from the tank. Most systems are versatile enough to remove not only finely divided suspended solids, but fats, oils and grease (FOG). Typical wastes handled include various suspended... 

The most common application of carbon adsorption in municipal water treatment is in the removal of taste and odor compounds. Figure 12 provides an example of a process flow diagram for a municipal water treatment plant. In this example water is pumped from the river into a flotation unit, which is used for the removal of suspended solids such as algae and particulate matter. Dissolved air is the injected under pressure into the basin. This action creates microbubbles which become attached to the suspended solids, causing them to float. This results in a layer of suspended solids on the surface of the water, which is removed using a mechanical skimming technique. Go back to Chapter 8 if you need to refresh your memory on air flotation systems. 

Four skimming connections with trycocks are normally provided at the outlet end of the drum, at the normal liquid level, and at 150 mm, 450 mm, and 500 mm below the normal level. Liquid hydrocarbon skimmed from these connections can be pumped to a suitable slop system. A coimection to the suction of a blowdown drum pumpout pump, if available, is adequate for this purpose. 

Option 1 system incorporates the emulsion breaking process followed by surface skimming (gravity separation is adequate if only free oils are present). 

System component A small mixing tank, two chemical feed tanks, a mixer, and a large tank equipped with an oil skimmer and a sludge pump. The mixing tank has a retention time of 15 min and the oil skimming tank has a retention time of 2.5 h. 

The trench method is applicable only when the water table is relatively shallow, less than 10 to 15 ft below the ground surface. For a deeper water table, the cost of the trench method becomes more expensive than other methods such as pump systems. Another limitation of the trench method is the soil structure. The soil above the water table has to be firm and well aggregated to allow for the trench to be self-supporting. Otherwise, embankment enforcement or screening would be needed. A third limitation is that continuous pumping and skimming is required to maintain a flow gradient towards the trench. Otherwise, the free product will move back and reenter the soil. 

The term passive interception is used to describe recovery systems that rely upon natural groundwater flow to deliver free-phase NAPLs to the collection facility without the addition of external energy (such as pumping). These systems often include linear interception-type systems such as trenches (or French drains), subsurface dams ( funnel-and-gate structures), combined hydraulic underflow with skimming, and density skimming units. 

During the design phase, all of the data derived from the hydraulic characterization are evaluated for use in the selection of recovery pumping equipment and for the determination of the most appropriate subsurface fixtures (whether wells, trenches, or drains, etc.). A variety of generic scenarios may be appropriate to optimize product recovery. If the product thickness is sufficient, the viscosity low, and the formation permeable, a simple pure-product skimming unit may be the best choice. Other combinations of permeability, geology, and product quality will require more active systems, such as one-pump total fluid, or two-pump recovery wells. 

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