As a rule, choose an initial impeller displacement value so that D is close to Vt to increase the accuracy of the selection. Locate the appropriate impeller diameter from the impeller displacement table D (see Table 10.2) so that TOR is within the recommended range. Since the tank is deeper than 6 feet, flat (turbine) impellers cannot be used therefore, canted impellers are chosen. Determine the volume for one compartment (Vt). In this case, three compartments 10 x 10 feet square (~3 x 3 m). Convert the compartment to symmetrical shapes. If the maximum mud weight is not known, use 20 lb/gal fluid density (2.4 SG).Īll compartments will be solids-removal sections. Maximum mud weight is anticipated to be 16 lb/gal (1.92 SG). ExampleĪ compartment is 30 feet long, 10 feet wide, and 10 feet high (Figure 10.12). In all cases, if H <5 feet (~1.5 m), a radial flow impeller should be specified. This leaves adequate free space above the maximum fluid operating level. The working volume for round tanks with flat bottoms is: For gallons:įor round tanks with dish or cone bottoms, calculations for working fluid volume are based on straight wall height (i.e., this height is measured from the tank top to where the tank joins the cone or dish at the bottom). Working volume for square or rectangular tanks is calculated by knowing dimensional values for length (L), width (W), and height (H in feet for gallons, in meters for liters): For gallons: This will allow for a little extra capacity in emergencies, slightly out of level installations, and/or fluid movement on floating rigs. Maximum fluid working volumes in compartments should not be higher than 1 foot (about 3/o m) from the top of the tank. Rectangular tanks should be converted to nearly square compartments if possible. When defining the area in which to mix, it is best to work with symmetrical shapes like squares or circles (as viewed in a plan drawing or overhead view of the tank layout). Agitators should be placed where the shaft is centered in the tank or compartment. In symmetrical compartments, the fluid has a nearly equal distance to travel from the center of the impeller shaft or from the impeller blade tip before it contacts the vessel wall. Greater than 85 seconds, proper suspension may be jeopardized and solids will begin to settle.įor contour impeller applications, values must be significantly faster (i.e., smaller numbers) to achieve the same results, but because of the impeller design, air entrainment is less probable. Table 10.2 60-Hz Impeller Displacement D Values Impeller Type Removal Addition Suction Reserve PillĬanted/flat 50-75 50-75 65-85 50-80 40-65 Table 10.1 Typical Turnover Rate Values, in seconds As the TOR approaches 40 seconds, the chance for vortex formation and possible air entrainment increases. D = impeller displacement, in gpm or lpm (as displayed in Table 10.2).įor flat and canted impeller applications, TOR should range between 40 and 85 seconds.This is the time, in seconds, required to completely move the fluid in a compartment (Table 10.1) and can be calculated by knowing the tank volume and impeller displacement: where Impeller sizes are determined by calculating the TOR (sometimes called time of rollover) for each compartment.
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