Weir design

Rising sludge can also be caused by internal solids overloading and hydraulic overloading to the secondary sedimentation. Poor sedimentation clarifier design and operation in terms of flow-through velocity, weir design, and so on are also possible causes. 

An alternate configuration (Fig. 3), the "bucket and weir" design, eliminates the need for a liquid interface controller. Both oil and water flow over weirs where level control is accomplished by a simple displacer float. Oil overflows the oil weir into an oil bucket where its level is controlled by a level controller operating the oil dump valve. Water flows under the oil bucket and then over a water weir. The level downstream of this weir is controlled by a level controller operating the water dump valve. 

The third method uses two weirs, eliminating need for an interface float. Interface level is controlled by height of the external water weir relative to the oil weir or oudet height This is similar to the bucket and weir design of horizontal separators. Advantage of this system is that it eliminates the interface level control. The disadvantage is that it requires additional external piping and space. 

The correction term Fw (2-5,9,13,31) corrects the equation for the distortion of the liquid flow pattern as it approaches the weir, and is shown in Fig. 6.23 (18). Some variations of Eq. (6.49) for unique weir designs are... 

FIGURE 5.7 Removal at the settling zone (a) inboard weir design at outlet zone (b). 

There are several variations of the swept-back weir design. The weir can be segmental (Fig. 6.76) or semicircular. The downcomer wall can follow the contour of a swept-back weir (Fig. 6.76) or it may be a straight vertical wall (Fig. 6.5d). The former type of wall is more expensive, but it provides more downcomer area and better utilization of tray space than the latter. 

Figure 6.7 Unique outlet weir designs, (a) Adjustable (b) swept back (c) rectangular notch (cl) Intermittent triangular notch (e) continuous triangular notch. (Parts a, and c toe from Henry Z. Kister, excerpted by special permission from Chemical Engineering, September 8,1980 copyright by McGraw-Hill, Inc., New York, NY 10020.)...

Anonymous (1952). Clarence E. Blee. Engineering News-Record 149(Jul.24) Frontispiece. P Anonymous (1959). Blee, Clarence E. Who s who in engineering 8 221. Lewis New York. Blee, C.E. (1929). Tests on model dam determine baffle weir design. ENR 103(23) 931-933. Blee, C.E. (1953). Development of Tennessee River Waterway. Trans. ASCE CT 1132-1146. Rich, G.R., Blee, C.E., Jessop, G.A. (1955). Discussion of Modernization of the Hales Bar Plant. Trans. ASCE 120 557-561. 

Figure 10-5. Downcomer and weir designs (A) circular pipe, (B) straight segmental, (C) sloped...

A slurry of liquid and suspended solids is fed along the centre line, to some fixed position within the bowl, and is accelerated outwards to join the pond of liquid held on the bowl wall by the centrifugal force. This same force then causes the suspended solids to settle, and accumulate at the bowl wall. The clarified liquid then flows along the bowl, to leave at one end of it, over some kind of weir design, which sets the level of the liquid surface in the bowl. 

A weir (described in Problem 5.25) is being designed for use in sea water (5% denser than fresh water). Perform a dimensional analysis for the rate of flow and explain how the calibration for the same weir designed for fresh water should be altered for use with sea water. 

A three-phase flooded weir separator is normally used where gas, water, and condensate flow rates are very high. In this design, NLL must be above the weir height. In the flooded-weir design, water and condensate holdups are high. This type of separator is very common where slug is a design consideration. 

All static studies at pressures beyond 25 GPa are done with diamond-anvil cells conceived independently by Jamieson [32] and by Weir etal [33]. In these variants of Bridgman s design, the anvils are single-crystal gem-quality diamonds, the hardest known material, truncated with small flat faces (culets) usually less than 0.5 nun in diameter. Diamond anvils with 50 pm diameter or smaller culets can generate pressures to about 500 GPa, the highest static laboratory pressures equivalent to the pressure at the centre of the Earth. 

Multiple IJquid-Path Plates. As the Hquid flow rate increases in large diameter crossflow plates (ca 4 m or larger), the crest heads on the overflow weirs and the hydrauHc gradient of the Hquid flowing across the plate become excessive. To obtain improved overall plate performance, multiple Hquid-flow-path plates maybe used, with multiple downcomers. These designs are illustrated and discussed in detail in the Hterature (49). 

The kettle reboiler is shown in Fig. ll-3.5ishell-side, this common design provides adequate dome space for separation of vapor and hquid above the tube bundle and surge capacity beyond the weir near the shell cover. 

Sedimentation Tanks These tanks are an integral part of any activated-sludge system. It is essential to separate the suspended solids from the treated liquid if a high-quality effluent is to be produced. Circular sedimentation tanks with various types of hydraulic sludge collectors have become the standard secondary sedimentation system. Square tanks have been used with common-wall construc tion for compact design with multiple tanks. Most secondary sedimentation tanks use center-feed inlets and peripheral-weir outlets. Recently, efforts have been made to employ peripheral inlets with submerged-orifice flow controllers and either center-weir outlets or peripheral-weir outlets adjacent to the peripheral-inlet channel. 

Depth tends to be determined from the retention time and the surface overflow rate. As surface overflow rates were reduced, the depth of sedimentation tanks was reduced to keep retention time from being excessive. It was recognized that depth was a valid design parameter and was more critical in some systems than retention time. As mixed-liquor suspended-solids (MESS) concentrations increase, the depth should also be increased. Minimum sedimentation-tank depths for variable operations should be 3.0 m (10 ft) with depths to 4.5 m (15 ft) if 3000 mg/L MESS concentrations are to be maintained under variable hydraulic conditions. With MESS concentrations above 4000 mg/L, the depth of the sedimentation tank should be increased to 6.0 m (20 ft). The key is to keep a definite freeboard over the settled-sludge blanket so that variable hydraulic flows do not lift the solids over the effluent weir. 

Inlet weir on tray blocking flow from tray above. Limited capaeity. High pressure drop as rates were increased. Design and inspection error. 

Trusses over weir restricting vapor disengagement from downcomer in high pressure system. Premature flooding. Design error. 

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