Overflow Pumps

Overflow Pumps These can be omitted if the thickeners are located at increasing elevations from first to last so that overflows are transferred by gravity or if the mixture of underflow and overflow is to be pumped. Overflow pumps are necessary, however, when maximum flexibility and control are sought. 

Overflow pump suction lines are designed for about a one foot/second velocity, unless a higher velocity is necessary to keep small solids or precipitates in suspension. Suction line sizes should be larger than discharge sizes. 

Thickener, single compartment, concrete with 3 m walls, overflow weir, launder excluding central rake, excavation, site preparation, piping feed launder, overflow pump. PM cost = 400000 for a surface area = 100 m with n = 0.38 for the range 80-2000. L-i-M = 3.1. L/M = 0.4. Alloy cost factors c/s X 0.7, concrete X 1.0 rubber lined for acid-leach mineral processing X 1.22. 

The softened seawater is fed with dry or slaked lime (dolime) to a reactor. After precipitation in the reactor, a flocculating agent is added and the slurry is pumped to a thickener where the precipitate settles. The spent seawater overflows the thickener and is returned to the sea. A portion of the thickener underflow is recirculated to the reactor to seed crystal growth and improve settling and filtering characteristics of the precipitate. The remainder of the thickener underflow is pumped to a countercurrent washing system. In this system the slurry is washed with freshwater to remove the soluble salts. The washed slurry is vacuum-filtered to produce a filter cake that contains about 50% Mg(OH)2. Typical dimensions for equipment used in the seawater process may be found in the Hterature (75). 

Industrial separations are conducted in gravity or bath separators for a coarse feed, and in centrifugal separators for a fine feed (2,6,10). In gravity-type separators the feed and medium are introduced to the surface of a large quiescent pool of the medium. The float material overflows or is scraped from the pool surface. The heavy particles sink to the bottom of the separator and are removed using a pump or compressed air. The dmm separator (Fig. 13), up to 4.6 m dia and 7 m long, processes approximately 800 t/h, and treats feed of size up to 30 cm dia, operates in the gravity or the... 

In order to handle accidental spills or overflows, a spill basin maybe provided, into which the flow is diverted if the concentration of a particular constituent exceeds a predetermined value. If equalization precedes biological treatment, in addition to the organic loading, high fluctuations in temperature, salinity, and toxic organics must also be considered. After the spill is contained, the wastewater flow is diverted back to the equalization basin. The contents of the spill basin are then pumped at a constant controlled rate to the equalization basin. 

Cleaners. Cleaner formulations can be classified with respect to the abiUty to emulsify oils, keep them in solution or to reject oils, spHt them out of solution. The latter type loosens the oil, and the separated oil does not dissolve but is rejected, and usually floats to the top of the cleaner solution. For the cleaner that rejects oil, the tank needs to be skimmed constantly. This is most easily accompHshed usiag the overflow weir, sump, and recirculating pump arrangement. OH-rejecting cleaners last longer. 

After the tank is filled, pumping is continued and overflow is permitted at the same flow rate. Find the concentration in the tank when it first becomes fuU, and find how long it takes for the effluent concentration to get within 95% of the steady state value. 

Overflows cause by pump failure or restrictions in discharge piping... 

Chimneys (risers) blocking flow to draw sump forcing liquid to overflow prematurely. Flooding of trayed section below pump around. Lack of response to pump around flow changes. Design error. 

On small installations an elevated tank above the furnace would be used (refer to Figure 37). The savings from eliminating the pumps, valving, and slurry lines are offset by the additional cost of a structure to support the tank and a rotary feed valve. The tank is fitted with a screened overflow. A dewatering screw conveyor is used for feeding the furnace. 

Principal Option for Containment/ Recovery Excavation Vacuum extraction Temporary cap/cover Hydraulic modification No action Groundwater pumping Subsurface drains Hydraulic barriers Low permeability barriers No action Overflow/underflow containment (i.e. oil booms) Run off/run on control Diversion/collection No action Capping/ nsulation Operations modifications Gas collection/removal No action... 

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