The Richardson-Zaki model for the sedimentation velocity can be used to build a simple but self-consistent simulation model for the ideal thickener. 0000054267 00000 n which shows that the line intersects the (C) axis at = fF and since. 0000099677 00000 n If the area of the thickener is given and the conditions in the feed pulp are known then. Hydraulic Fracturing Chemicals and Fluids Technology, The viscosity of ionic polymers is dependent on the pH. Suspension throughputs are limited to about 4000 m3 h1. The measurement is usually very reliable and indicates the amount of solids in the water column above the sensor. Experiments done with various drilling fluids showed that the mixed metal hydroxides system, coupled with propylene glycol (Deem et al., 1991), caused the least skin damage of the drilling fluids tested. Since four times more ink is theoretically used in 720 dpi prints than in 360 dpi prints, the savings in ink from using cationic cotton can be quite significant. The magnetic thickener is often used for magnetite slurry dewatering after the separation procedure. R.P. Thus, The maximum possible feed rate of solids to the thickener is, When the thickener is fed at a rate less than the maximum, the maximum concentration of the underflow can be calculated from the intersection with the horizontal axis of the operating line that passes through the given feed flux on the vertical axis and which is tangential to the flux curve as shown in Figure 6.10. 0000005561 00000 n Metso Outotecs end-to-end solutions integrate accurate, live data from various sources and incorporate advanced analytics enriched with machine learning, artificial intelligence, and the scope and scale of cloud. Clear liquid overflows into a launder around the periphery of the tank. The diluted feed flows past the dewatering cones which act in a similar manner to the plates found in lamella separators (see Section 1.1.2.3). To accelerate flocculation and help the removal of excessive fines, recirculation of some sedimented solids to the incoming feed is sometimes used. As a consequence, change in the solids feed rate or the settling characteristics of the solids will change the sludge level much more rapidly, therefore, high-rate thickeners require some form of automatic control. The measurable parameters that can be used for thickener control include thickener feed flow rate, feed density, underflow density, overflow clarity, bed level, bed mass, rake torque, rake height, solids settling rate and underflow rehology. It requires only a tenth to half of the area required in a conventional thickener under similar conditions of settling slimes. 0000009467 00000 n Better strategies (figure 3) keep the thickener inventory constant through feedback from either bed level or pressure, and utilize flow control to ensure that pipeline disturbances are never seen by the thickener. Either the maximum underflow concentration or the feed concentration can be specified and the other is fixed by the line drawn tangent to the settling flux curve. Figure 6.10. They are not usually a preferred technique for thickening suspensions. 0000008447 00000 n /Parent 430 0 R 0000008729 00000 n The Zubair consists of about 415-427 m (1,360-1,400 ft) of alternating sandstone, siltstone and shale, subdivided into three shale units interbedded with three sand units. They are highly effective in coal refuse thickening, gold recovery, CCD circuits, copper leaching, molybdenum processing and other mining and chemical flowsheets. By continuing you agree to the use of cookies. 0000003678 00000 n Column-supported design drives are supported by a stationarycentre column of steel or concrete, and are practical for thickenersup to 135 m in diameter. Often this rate limiting step is defined by pumping capacity. (16)(18), and (41)], the best approach is to carry out extensive sedimentation test work to build up a flux envelope: a three-dimensional representation where the normal flux curve of s versus C has a third axis representing sediment height. w qD@ X"k5n`U\b:C&P3.]~0p,= A circular thickener comprises a relatively shallow, open-top cylindrical tank with either a flat bottom or a bottom shaped in the form of an inverted cone (see Figures 1.2 and 1.3). 0000008635 00000 n All liquid that is not removed with the underflow leaves the unit as overflow through the clarifying cylinders which polish the effluent by promoting flocculation. Whether you aim to restore equipment to its original condition or upgrade for increased preformance, explore your options. Rely on OEM experts because not all parts are created equal. The feed slurry is assumed to spread instantly across the cross-section of the thickener and to dilute to concentration CL. Circular basin thickener showing rakes, drive head and walkway. 0000152203 00000 n The model is based on the requirement that at the steady state all the solid must pass through every horizontal plane in the thickener. The printed samples were steamed for 10 minutes and then washed with the five-step washing procedure. Simple density control strategies using PID feedback loops (figure 2) do not allow for the dead time inherent in the system and may lead to cyclic loading and emptying with the consequent underflow variability. Terms of Service apply. Schematic of an E-Cat high-rate clarifier (sometimes referred to as a thickener clarifier) showing the internal circulation of liquors. Such a copolymer provides a stable aqueous colloidal dispersion at an acid pH lower than 5.0 but becomes an effective thickener for aqueous systems upon adjustment to a pH of 5.510.5 or higher (Robinson (1996,1999)). This indicates that the level of cationization was high enough to strongly bond all the ink molecules, preventing any color migration to the white background. Other variants include the vertical flow clarifier, the blanket clarifier and the circular clarifier; the latter is similar in form to a conventional circular thickener but of a much lighter construction. {$CJZzw(&DQIQ;w:vz>?vqsua.SzR\h/hzP1?W_}/>?tW_?r9/>?2~xt wO~O?}_tzO?7yr>u. The potential benefits of clarifiers that incorporate recirculation are offset by the short residence time of liquid and the strictly limited solids storage capacity. To establish this solids inventory it is necessary to operate with the solids feed rate in excess of the solids withdrawal rate for some period during startup, then at steady state operation, the solids feed rate should match the withdrawal rate. 0000009107 00000 n Thickeners, with tractor-driven raking arms. endobj WesTech drives with lifting capability and high torque capacity contribute to the machines superiorperformance. Thus the maximum underflow concentration and the underflow pumping rate is fixed by the abscissa intercept and by the slope of the line HDE in Figure 6.10. At rest these fluids exhibit a very high viscosity but are thinned to an almost water-like consistency when shear stress is applied. Although deep cone thickeners are relatively cheap to install and occupy a small floor area, their operating costs can be higher. 0000005000 00000 n 0000148386 00000 n Bed level is not always reliable as probes can foul or be obscured by entrained solids. By the correct use of high molecular weight, fast-acting flocculants, however, large flocs that sediment very quickly can be generated to allow thickeners with high solids handling capacities and relatively small floor areas to be produced. Typical particle size and feed concentration range: 150 m and <15% w/w. Our operations span the globe and we are close to 10,117 employees, present in more than 60 countries. ScienceDirect is a registered trademark of Elsevier B.V. ScienceDirect is a registered trademark of Elsevier B.V.
Sludge blanket-fed thickeners have the feed delivered into the sludge blanket instead of the top feed well. Errol G. Kelly, in Encyclopedia of Physical Science and Technology (Third Edition), 2003. The quantity qC + (C) is sometimes referred to as the demand flux because this flux must be transmitted through every horizontal level in the thickener otherwise the thickener could not operate at steady state. 0000100391 00000 n WesTechs technical staff can assist in testing process practicality, equipment sizing, and aid in solving other problems encountered in todays sophisticated and automated flowsheets. where C+ and C represent the concentrations of solids above and below the discontinuity respectively. This is achieved by having (naturally) equisettling particles, by a sufficiently high initial concentration, or by the formation of uniform flocs by the addition of a flocculant. Inthe bridge-supported design, suitable for thickeners up to 50 m indiameter, the drive is supported by the bridge, driving the rakes witha centre shaft. As the underflow solids concentration increases from high rate to paste thickener, the yield stress increases. 0000008495 00000 n Theoretically, the behavior (and thus the area) of a thickener can be analyzed by the Kynch flux analysis. 0000018933 00000 n Analyses of slurry compression have been described, but none has been shown to be universally reliable. Circular thickeners are frequently constructed to large scales and can be used to raise suspension concentration prior to another solid/liquid separation process. It has a flocculent mix chamber, inclined settling plates and automatic sludge level control system. FLSmidth A/SVigerslev All 772500 Valby, CopenhagenDenmark, +45 3618 1000 0000152566 00000 n The effective settling area Ae is thus given by. This requires the solution of a non-linear equation, for the intermediate concentration CM after which the maximum concentration of the pulp in the discharge is calculated from, The smallest volumetric discharge rate that is possible for steady-state operation is calculated from. 0000007245 00000 n
Instruments measure the height of the interface between thickened slurry at the bottom of the thickener and the clarified liquor at the top. The deep cone thickener shown in Figure 1.5 is again broadly similar in form to a conventional thickener, but the sides of the inverted cone have a much steeper angle, in the region of 37. Bed mass is generally measured by a pressure transducers mounted at the bottom of the tank (figure 4). << In 2021, FLSmidth generated revenue of DKK 17.6 billion. Operating thickeners for extended periods at high torque levels can negatively impact on gearbox and bearing lifetimes. Rise rate parametrizes the area required to recover the design flow or solids loading, the design dry tonnage. High-capacity thickener operates on the principle of using the polyelectrolyte polymers more efficiently than in a conventional thickener. Calculate the maximum discharge concentration if the thickener is fed at 100kg/s. 0000161931 00000 n Spare and wear parts built to perform. This water is recycled in the process. This normally occurs in the hindered or compression zones. High-rate Thickeners are designed to provide roughly 12 times the throughput of conventional machines of similar size. Particle properties affect the degree of separation that can be achieved with sedimentation. 0000158964 00000 n Despite the simple structure of a thickener it is quite difficult to see or measure what is happening inside. 0000087268 00000 n 1 0 obj Copyright 2022 Elsevier B.V. or its licensors or contributors. Table16.4.
In mining applications, thickening through sedimentation is applied to both the product and tailings streams to recover water. WesTechs design provides for deaeration of the thickener feed prior to flow into the feedwell. The primary duty of a clarifier is to remove relatively small amounts of solid from more dilute suspension to yield a clarified liquid overflow and a generally unwanted solids sludge underflow. Rake torque is the most fundamental instrument and an accurate indicator of when things have already gone really wrong! 0000090466 00000 n where k is thickener surface use coefficient, usually k = 0.75; ov is overflow mass density, t/m3. These properties must be considered when selecting a rise rate, solids loading, and bed depth for a thickener. (1) Awl chute, (2) feed tank, (3) overflow chute, (4) magnetic system, (5) water supply pipe, (6) adjusting valve.
The free settling behavior of a slurry is governed by a Richardson-Zaki equation. 0000154181 00000 n This site is protected by reCAPTCHA and the Google Our wide offering covers complete solutions, quality equipment and parts, as well as expert services for multiple industries. Lower-yield stress muds, as produced in a high-rate thickener, require less torque to move rakes through the mud. Figure 1.3. This calculation is illustrated in Illustrative example 6.1. &l U&e\^ The analysis leading to equation 6.20 for the batch settler can be used to develop an expression for the rate at which a discontinuity will move in a continuous thickener. E-DUC and P-DUC feed-dilution systems maximise flocculation efficiency and settling rates. With stable feed types, turbidity and bed level are often used as indicators of insufficient flocculant addition. 0000008968 00000 n Tanks with a diameter smaller than 25 m are usually formed from steel and have flat bottoms with rake arms at an angle less than 10. Get the info you need to more effectively design, manage, and maintain your operations. 1385 0 obj <>/Filter/FlateDecode/ID[<5EF41B497A8E614997006AB7757F1474>]/Index[1363 52]/Info 1362 0 R/Length 101/Prev 402860/Root 1364 0 R/Size 1415/Type/XRef/W[1 3 1]>>stream The rate of sedimentation should be as high as reasonably possible to both increase throughput and reduce floor area. 1363 0 obj <> endobj In a similar manner to the lamella separator (see Section 1.1.2.3), the effective settling area is increased to allow sedimenting solids to slide down the plates and into the collecting well. Where it is not possible to change the surface chemistry coagulants and flocculants can be effective in improving settling rates. In batch settling q = 0 so that f(C) and (C) are identical. The centre column supports the drive, rake, cage and rake mechanisms, while the truss bridge, extending from, the centre pier to the tank periphery, supports the walkway and, available for accelerated delivery, and include either welded, or bolted elevated steel tank designs up to 40 m in diameter and. The feed mixture is gently and continuously introduced to the feedwell in which exists a pool of settling suspension along with any additional coagulant or flocculant. 0000163397 00000 n This allows system properties to be described in a general way for any size unit. Tailored service packages delivering performance outcomes - Your goals are our goals. This formation thickens from south to north, and the shale/sand ratio increases from a clean sand interval in the southwest to 45% sand/shale in the north and northeast.
Larger tanks between 25 and 200 m diameter are normally made from a combination of concrete and steel and employ rakes designed to match the angle of the conical bottom. 0000143427 00000 n Metso Outotec in brief. Generally, operators directly manipulate the underflow pump speed to maintain a constant solids inventory; site process engineers determine the inventory set-point. 0000019505 00000 n Mixed hydroxides of bivalent and trivalent metals with a three-dimensional spaced-lattice structure of the garnet type (Ca3Al2[OH]12) have been described (Burba et al., 1992; Mueller et al., 1997). Higher torque is an indicator of higher underflow density (Yield stress dependent) and bed depth. In other words, the solid must not get held up anywhere in the thickener. Schematic representation of the ideal thickener operating at steady state. If the thickener is operating at steady state, the discontinuities must not move and (C+, C) must be zero across every discontinuity. %%EOF Turbidity sensor, either at a fixed height or attached to a motorized cable spool. Lower solids sg will reduce the settling velocity and the underflow density. Thickeners or thickener plants--optimizing the performance and cost of thickened tailings.
0000086056 00000 n The construction and form of the rake are important design parameters as is the rating of the motor in the central drive head which must be capable of moving the rake through the thickened solids both during normal operation and during start-up of the rake after a stoppage. Bed mass is utilized to control thickener inventory. 0000156895 00000 n 0000142242 00000 n Figure 1.2. Simple systems with constant feed can use flocculant pump speed control, more advanced control systems utilize a ratio controller to maintain a constant grams per ton dose rate. In practice, with a fixed inventory (bed pressure) the bed expands or contracts depending upon the flocculation effectiveness. Ideally, they are characterized by all particles settling at the same (hindered) rate. P.J. Pilot or laboratory size equipment is available for testing or purchase. The key features for high-capacity thickeners are the feedwell design and the feed slurry dilution method. In particular, pH responsive thickeners can be prepared by copolymerization of acrylic or methacrylic acid ethyl acrylate or other vinyl monomers and tristyrylpoly(ethyl-ene-oxy)x methyl acrylate. However, maldistribution and solids re-entrainment problems can sometimes limit their effectiveness, a problem which also occurs in an alternative design incorporating inclined tubes rather than plates. We offer, beam- or truss-type bridges, depending on thickener diameter. The right hand side of equation 6.35 is the negative of the slope of the chord connecting two points on the flux curve and these chords must be horizontal to satisfy the steady state requirement. Choose a service area or learn more about what we can offer. Learn about us, our purpose, vision, business and strategy. 0000137705 00000 n Although particle motion is slowed by hindered settling effects, each settles at its own rate, so that the process is one of sedimentation classification. The stability of the interface requires that the higher conjugate concentration can exist only at concentration CM at which the total settling flux has a local minimum so that condition 6.25 is satisfied with f(C) replacing (C). Fast-acting flocculant is dosed into the feedwell and into the rising dilution liquor as required. 0000144657 00000 n An instrument called a Clarometer (figure 4) is available which provides an on-line settling rate measurement.
High capacity thickeners work on a broadly similar principle to conventional thickeners. The wash baths were also quite clear for these fabrics. The point E is directly below B in Figure 6.10. It can also reject some of the light and fine nonmagnetic minerals. The driving force for the separation is gravitational, where the differences in phase densities drive the separation of the solids and liquid. By controlling flocculation and solids inventory, the thickening process is stabilized and consistent, optimum; underflow density can be achieved through manual optimization. This target settling rate cannot be calculated explicitly but is manually optimized based on the performance history. Feedwells and flocculant dosing control have a significant influence on thickener performance. In that flux curves must themselves be experimentally evaluated [although in theory they can be derived from a combination of Eqs. These conjugate concentrations are further limited but the requirement that all concentration discontinuities must be stable as well as stationary. 0000090572 00000 n The positively charged mixed metal hydroxide particles attach themselves to the surface of negatively charged bentonite platelets. << If the slurry is behaving as an ideal Kynch slurry, well-defined sharp interfaces will develop in the thickener and the analysis below shows how these concentrations can be calculated. Proper level of the flocculation can be carefully controlled. 0000008682 00000 n 0000104111 00000 n %PDF-1.4 To achieve this balanced operation it is either necessary to measure both flows with a high level of accuracy or -- more practically -- to measure the solids inventory in the thickener tank. 0000157222 00000 n The corresponding volume may be 415 times smaller than with conventional thickeners in the same application. Increased inventory causes the rakes to interact with mud even at their tips which results in higher torques. In principle, this method allows the minimum area to be calculated, and also allows assessment of a thickener's ability to tolerate overload (i.e., act as a surge tank). 0000103382 00000 n 0 };|_]EJ. The recirculation may be either internal or external to the clarifier and often results in higher throughputs, albeit at the expense of greater mechanical complexity. In practice, the method assumes an ideal slurry: one in which the settling rate is a function of local concentration only. Our patented E-Volute feedwell offers Computational Fluid Dynamics (CFD)- optimised energy dissipation and solids distribution. Magnetic thickener. Gravity thickeners and clarifiers represent a class of solid-walled separator, where gravitational forces are used to raise the concentration of a suspension through sedimentation to produce a thickened sludge with a clear liquid as overflow. Under the assumption that the settled pulp is incompressible, the maximum discharge pulp concentration is CC and when the thickener discharges at this concentration, only one feed flux and one volumetric flux q is possible for the thickener as shown in Figure 6.10. 0000085949 00000 n Commercial designs exist for three basic flow arrangements, namely, crosscurrent, co-current and the most popular countercurrent, where the feed and clarified liquid flows can be most simply arranged. 0000008824 00000 n The maximum possible feed flux is fixed by the slope of the flux curve at the point of inflexion I. Privacy Policy and hb```e``- B@1V poC'72Y400d)PkpWs{M}9.v]{;``(h`(L`&C5X7,"@, t!C 0000098154 00000 n Choose your topic of interest or explore all discover stories. 0000151321 00000 n Sedimentation is the removal of suspended solid particles from a liquid by gravitational settling. /Length 19381 %|/4*1p5y1. Thickener polymers include poly(urethane)s, poly(ester)s, and poly(acrylamide)s, further, natural polymers, and modified natural polymers (Doolan and Cody, 1995). The formation contains the main oil reservoirs at Raudhatain occurring in the well-developed sand horizons, but many of the thin sand zones within the predominantly shale section also contain hydrocarbon. Flocculation, pulp level, underflow density, overflow quality, torque, and rake lift position can all be easily managed. 0000102365 00000 n This can be obtained from the batch settling curve as described in Section 6.2.1 or from a model of the settling velocity. where A=area of each plate; =efficiency factor, >1.0; N=number of plates; = inclination of plates to horizontal. The thickened product is discharged continuously through orifices or by means of periodical action valves. Care should be taken to ensure that flocculant dilution is maintained with changes in flocculant dosing rate.
trailer <]/Prev 366598>> startxref 0 %%EOF 265 0 obj <>stream In such an apparatus, an initial pulp is fed via the vertical pipe into the thickener. Standard bridge-supported high-rate thickener designs areavailable for accelerated delivery, and include either weldedor bolted elevated steel tank designs up to 40 m in diameter andare ideal for many applications. Cooling Tower Makeup Water and Sidestream Treatment, Industrial Sedimentation and Filtration Equipment(PDF), TOP Advanced Thickening Technology(PDF), Browse our complete library of brochures, case studies, and videos, Broadly adaptable to process fluctuations. When the more useful and widely applicable extended Wilhelm-Naide model is used for the sedimentation velocity, the analytical method used above does not produce nice closed-form solutions, and numerical methods are required to solve the equations iteratively. 0000008542 00000 n Increased levels of coarse material can create islands that give uneven high torque levels (with peaks at 2 or 4 times the rake rotation frequency) and rotating masses or doughnuts also cause rake torque to increase (with cycles equal to the rake rotation frequency).Measurement can be by hydraulic pressure, load cells or torque arms mostly supplied by the OEM and are essential to prevent rake drive damage.