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Published in Heinz P. Bloch, Kenneth E. Bannister, Practical Lubrication for Industrial Facilities, 2020
Heinz P. Bloch, Kenneth E. Bannister
Centrifuges have been used for decades. They operate on the principle that substances of different specific gravities (or densities) such as oil and water can be separated by centrifugal force. Centrifuges achieve a form of accelerated gravity settling, or physical separation. At a given setting, centrifuges are suitable for a narrow range of specific gravities and viscosities. If they are not used within a defined range, they may require frequent, difficult readjustment. They will not remove entrained gases such as hydrogen sulfide, ethane, propane, ethylene, etc., or air. Although centrifuges provide a quick means to separate high percentages of free water, they are maintenance intensive because they are high-speed machines operating at up to 30,000 RPM. More importantly, they can only remove free water to 20 wppm above the saturation point in the very best case, and none of the dissolved or emulsified water. In fact, centrifuges often have a tendency to emulsify some of the water they are intended to remove.
Drinking Water Treatment
Published in Louis Theodore, R. Ryan Dupont, Water Resource Management Issues, 2019
Louis Theodore, R. Ryan Dupont
Following flocculation, agglomerated particles enter a clarification unit where they are removed by sedimentation by gravity. In the sedimentation processes, the majority of the solids are removed by gravitational settling; particles that do not settle and are still suspended are removed during the filtration process. Sedimentation is generally accomplished in rectangular or circular basins and is often enhanced by the addition of inclined plates or tubes (plate or tube settlers), which increase the effectiveness of the process by effectively increasing the surface area of the sedimentation basin (Figure 11.2). Two parameters frequently used to describe the clarification process are the surface overflow rate (SOR) and the hydraulic retention time (HRT). The SOR is a hydraulic loading rate expressed in gpd/ft2. SORs for conventional sedimentation generally range from 500 to 1500 gpd/ft2. Typical HRTs range from 1 to 2 hours, although many states require up to 4 hours for full-scale surface water treatment plants (U.S. EPA 2019a).
Cutting Fluids
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
Common separation methods include settling tanks, centrifuges, cyclones, and magnetic separators [4,37]. A settling tank is a large tank with two or more baffles (Figure 14.2); as the fluid moves under and over successive baffles, tramp oils and lighter impurities rise to the surface, where they can be skimmed off, and chips and other heavy debris settle on the bottom, where they can be similarly removed. The effectiveness of the tank depends on the settling time or the volume of the tank divided by the inlet flow rate; if the settling time is too short, not all impurities will settle out, there will be an increased tendency to foam since coolant bubbles will not have time to burst, and coolant temperature will be more difficult to control [21,33,38]. Settling times should be 5 min for small systems [4], 7–10 min for general purpose systems [39], and 10–15 min for large systems [4,37]. Centrifuges and cyclones separate debris from the coolant through centrifugal action [4,37].
Excess pore pressure generation during slurry deposition of gold tailings
Published in International Journal of Mining, Reclamation and Environment, 2021
G. Lebitsa, G. Heymann, E. Rust
In settling columns, deposited slurry undergoes both sedimentation and consolidation during the settling process. Sedimentation is taken as the settling of solid particles or groups of particles in a fluid under the influence of gravity where particle segregation forms part of the sedimentation process with particle size segregation reported to be the most prevalent mode of segregation [42]. Consolidation on the other hand emphasises the expulsion of pore water from a tailings material together with the dissipation of excess PWPs as well as the resulting settlement that takes place due to the loss of water. Figure 4 illustrates sedimentation and consolidation processes that take place in hindered settling of sandy materials with little or no clay in settling columns [43,44]. It is noted that under this scenario sedimentation is inclusive of consolidation.
Head Loss Investigations Inside 90° Pipe Bend for Conveying Of Fine Coal–Water Slurry Suspension
Published in International Journal of Coal Preparation and Utilization, 2020
Jatinder Pal Singh, Satish Kumar, S.K. Mohapatra
Settling is the phenomena by which the solid particles settle down from the liquid phase. The term settling velocity indicates the velocity at which the solid particles from slurry suspensions settle down and results in choking of pipeline. It is very important to study the effect of solid concentration on settling velocity during the design of slurry transportation system. The slurry should be transported at a flow velocity higher than settling velocity so that the choking of pipeline does not take place. Settling velocity becomes more crucial during transportation of fine slurry because fine particles settle more readily than coarser particles. The settling velocity of coal–water slurry at different solid concentrations was calculated using empirical correlation discussed by Streeter, Wylie, and Bedford (1998). In slurry flow systems, there are two main forces which are responsible for the settling of particles. The primary force is gravity, and the other major force is drag force (i.e., enacting due to the flow of solid particles in the carrier liquid) as shown in Figure 8. The gravity force is not affected by average slurry velocity, but drag force is dependent on flow velocity. As solid particles accelerate in slurry flow, the drag force starts acting in the opposite direction. Settling velocity of slurry at different solid concentrations is calculated by the formula given below (Streeter, Wylie, and Bedford 1998):
Characterization and migration of oil and solids in oily sludge during centrifugation
Published in Environmental Technology, 2018
Jun Wang, Xu Han, Qunxing Huang, Zengyi Ma, Yong Chi, Jianhua Yan
This paper studied the migration behaviors of oil and solids in oily sludge during centrifugation. Solid particles size distribution results demonstrate that their settling behavior depends on particle size, density difference and liquid viscosity. The migration of oil phase was characterized by GPC. The results show that the molecular weight of oil in upper layer is 32.6% lighter than that of oil in bottom layer when heptane is added. S/O ratio has a correlation with the quality of recovered oil. When S/O ratio increased from 1:2 to 5:1, average oil molecular weight in upper layer decreased from 1044 to 846. This study proposed a quantitative model to predict the oil residues’ fraction in solids after sedimentation. The model indicates that capillary residues increase when particle sizes decrease. Oil film is extremely hard to remove when particles are smaller than 0.23 μm. Oil recovery ratio can be improved by increasing the centrifugal rotation speed, but it gains less when the rotation speed is high enough. The model-predicted oil residue ratios are in good agreement with experimental results.