Pump Handbook by Igor J. Karassik, Joseph P. Messina, Paul Cooper, Charles C. Heald

Подождите немного. Документ загружается.

9.16.1 HYDRAULIC TRANSPORT OF SOLIDS 9.343

EXAMPLE

5 Consider an inclined suction pipe located on a dredge ladder. Pipe length 

59 ft (18 m), D  25.6 in. (0.65 m), angle to the horizontal  30°. Determine the deposi-

tion velocity and the head losses at the proposed operating velocity of 21.3 ft/s (6.5 m/s).

Assume S

 2.65 and C

 0.20. For a horizontal pipe, it is calculated that V

 15.7

ft/s (4.8 m/s) and at the proposed operating velocity i

 0.0373, (i

 i

)  0.0239.

Solution From Figure 9, at 30°, D  0.33, equivalent to an increase in V

in USCS units, or

in SI units.

The resulting limit velocity in the inclined pipe is 15.7  5.0  20.7 ft/s, 4.8  1.5

 6.3 m/s, which is slightly less than the proposed operating velocity. At the operating

velocity Eq. 31 gives the excess gradient, i(30°), as

where 0.0239 represents the solids effect in the horizontal pipe. Thus i(30°) equals

0.0207  0.1650 or 0.1857. The clear water gradient i

was 0.0373, giving a total value

of 0.223, and on multiplying this by the suction-pipe length of 59 ft (18 m), the drop is

found to be 13.2 ft (4.0 m) of water.

SYSTEM DESIGN AND ANALYSIS_______________________________________

Operating and Economic Considerations

In order to compare the merits of differ-

ent transport systems, it is necessary to have a measure of the energy required to move

a given quantity of product over a given distance. In slurry transport, the solids are nor-

mally the “payload” while the conveying liquid is merely the “vehicle.” The specific energy

consumption is therefore to be related to the solids transported rather than to the mix-

ture. However, the power which the pump must supply is used to drive the slurry as a

whole, and is given by r

H where H is the head in height of water and Q

is the vol-

umetric flow rate of the mixture. The payload of solids is delivered over the line length,

L, at a volumetric rate that is the product of the delivered solids concentration C

and

the mixture flow rate. If the application is a hoisting system, with the line directed ver-

tically upwards, the rate at which energy is being added to the solids is r

L or

L, and the efficiency of the system can be obtained by dividing the power

input, giving S

L/H. In this case the specific energy consumption is the inverse of the

efficiency i.e.

(33)

where, as before, H is the head supplied by the pump in height of water.

In the more usual case of an essentially horizontal pipeline, potential energy will not

be added to the solids, and thus from the physicist’s viewpoint no work will be done. How-

ever, in industrial practice transporting solids along the line represents useful work in the

economic sense.We can no longer speak of efficiency in the physicist’s terminology, but the

appropriate economic measure of specific energy consumption is still given by Eq. 33. With

H/L now equal to the friction gradient, i

, the expression is written

(34)SEC 

SEC 

¢i130°2 0.0239 cos 30°  11.6510.202 sin 30°

0.333119.62211.65210.6524

1>2

 1.5 m>s

0.333164.42

1.65125.6>1224

1>2

 5.0 ft>s

9.344 CHAPTER NINE

To obtain a value in horsepower-hour/ton-mile, this ratio is multiplied by 5.33, and for

kWh/tonne-km the factor is 2.73. If the power supplied to the pump is required, the expres-

sion must be divided by pump efficiency, and the efficiency of the drive train or motor can

be taken into account in the same way.

The lower the SEC, the more energy-effective the pipeline is as a means of transport.

Since S

is fixed by the nature of the solids, the quotient i

is the basic variable to be

considered.

Homogeneous Slurries Figure 10 is from Chapter 12 (written by Clift) of Wilson et al.

(1997). The figure shows in simple generalized terms, the effect of changes in solids con-

centration on the resistance of a piping system to flow of a homogeneous, non-settling slurry.

At velocities sufficiently high for the slurry to be in turbulent flow, the head lost in flowing

through the system (measured as head of a fluid with the slurry density) can be estimated

by treating the slurry as a fluid with an effectively constant friction factor, as shown in con-

nection with Eq. 13. However, in laminar flow, to the left of the turbulent curve, the system

head varies strongly with concentration, as shown schematically in Figure 10 where C

< C

. The transition between laminar and turbulent flow is indicated roughly by the

intersection of the laminar system characteristic with the turbulent curve. Therefore, as

illustrated, the transition velocity increases somewhat with solids concentration.

To examine the operability of such a system with centrifugal pumps, we now superim-

pose the pump head-discharge characteristic on to the system characteristic. For fine slur-

ries the head delivered by the pump, evaluated in terms of the slurry density, is virtually

unaffected by the solids. Therefore the characteristic of a fixed speed pump appears as a

single curve in the coordinates of Figure 10, independent of slurry concentration.

FIGURE 10 Schematic system and pump characteristics for flow of a homogeneous slurry at three concentrations

(from Wilson et al., 1997)

9.16.1 HYDRAULIC TRANSPORT OF SOLIDS 9.345

Consider first a system which has been designed to operate in the laminar range, cor-

responding to point A in Figure 10 with slurry concentration C

. The curve labeled “Pump

1” represents the characteristic of a pump selected for this operating point.

Figure 10 shows the effect of varying solids concentrationl. If it decreases to C

then the

system operating shifts to point B, the new intersection of the system and pump charac-

teristics. Similarly, a concentration increase to C

shifts operation to point D. It was shown

on Figure 3 that relatively small variations in concentration can have strong effects on the

laminar flow curves. Thus the shifts from point A may result from quite small changes in

slurry consistency. Nevertheless, as shown by Figure 10, the associated changes in mean

velocity (and hence solids throughput) are amplified by the way the system and pump

characteristics intersect. Thus steady operation in laminar flow with a fixed-speed cen-

trifugal pump and with no flow control valve is possible only if the slurry consistency is

tightly controlled.

For variable solids concentration, two alternatives are available. One is to operate in

turbulent flow, at a point like E in Figure 10. “Pump 2” shows the head-discharge charac-

teristics of a centrifugal pump selected for this duty. By operating on the turbulent system

characteristic, variations in slurry consistency can be accommodated without significant

changes in mixture velocity. This is probably the main reason why many designers prefer

to use turbulent flow even for homogeneous slurries. The design point is then selected to

be in the turbulent range for the highest solids concentration expected. However, it should

be noted that this will not correspond to the lowest specific energy consumption. This is an

example of the general point that design for variable operation is usually incompatible

with design for minimum energy consumption.

The other option is to use a variable-speed pump. This is illustrated by points F and G

in Figure 10. If the solids concentration increases from C

to C

, then the pump speed is

increased to keep a constant flow rate. The corresponding increase in pump speed raises

the pump head-discharge characteristic to the broken curve shown passing through F.

Similarly, if the concentration falls from C

to C

, the pump is slowed down to give the

characteristic passing through point G. Again, it must be noted that there is an economic

penalty for designing for variable concentration, this time represented by the cost of the

variable-speed drive and the energy losses in the drive train.

Settling Slurries We now turn to problems of system operability for settling slurries.

(For a more detailed treatment see Wilson et al., 1997.) Figure 11 shows typical “system

characteristics” for a settling slurry at three delivered concentrations, in terms of head of

slurry, j

. Only the frictional contribution for horizontal transport is considered here. The

form of the system characteristics is typical of heterogeneous flow of a settling slurry. The

three slurry characteristics are scaled for three notional delivered relative densities, i.e.

three values of S

. The slurry curves all show the minimia typical of a heterogeneous

slurry flow. As is typical for heterogeneous slurries, the minimum friction gradient occurs

at velocities above the deposition point and the position of the minimum moves to some-

what higher velocities as the solids concentration increases.

Figure 11 also shows the point where j

equals i

. At this crossing point (but not else-

where) the heterogeneous slurry behaves like an “equivalent fluid,” with a value of 1.0 for

the coefficient A¿ in the homogeneous-flow equation (Eq. 5).

It is now appropriate to consider the behavior of this system with one or more variable-

speed centrifugal pumps, with characteristics shown in Figure 11 as “Pump (water” and

“Pump (mixture).”The latter decreases with increasing concentration, due to the effects of

solids on pump performance discussed earlier in this section. Therefore, to maintain a con-

stant head and flow rate at point A in Figure 11, the pump rotational speed must be

adjusted for the actual solids concentration.

It sometimes happens in industrial practice that the pipeline characteristics for dif-

ferent concentrations cross over at a single point at the water curve and at a suitable oper-

ating velocity, as shown schematically in Figure 11. This behavior is expected for

closely-graded materials with volumetric concentrations less than 20%, but may not apply

for broad gradings or higher concentrations. The results with the broadly-graded sand in

Table 3 show that j

was approximately constant (equal to 0.055 over a concentration

range 20% to 40%) for the selected velocity  15 ft/s (4.5 m/s). However, the operating point

9.346 CHAPTER NINE

FIGURE 11 Schmematic system and pump characteristics for heterogeneous (settling) slurry flow at various

delivered concentrations (after Wilson et al., 1997)

TABLE 3 Comparison of slurry friction losses and water friction losses for a broadly

graded sand with d

 7.1. Data from Sundqvist et al. (1996a)

Product Sand

Max. particle size, in. (mm) 0.4 (10)

Average, d

, in. (mm) 0.025 (0.65)

Portion of fine particles, X

Pipeline

—

Diameter, in. (m) 12 (0.3)

Velocity, ft/s (m/s) 15 (4.5)

Water friction losses, i

0.041

Conc. by volume, C

0.20 0.30 0.40

Slurry friction losses, j

0.055 0.055 0.055

was not located on the water curve (i

 0.041). It follows from Table 3 that the slurry fric-

tion losses, j

, exceeded the corresponding water losses, i

, by 35%.

The operating data for the sand in Table 3 are of great practical interest since they

demonstrate the energy-efficiency of transporting this product at very high solids concen-

trations. Experiments by Sellgren & Addie (1993) with this sand indicated that the pump

solids effect was not influenced greatly by increased solids concentrations. For the highest

concentration studied here, the maximum values of R

and R

were estimated to be 13 and

15%, respectively. An example including pipeline friction and the effect of solids on the

water efficiency of the pump is given in Table 4.

It follows that the energy required to overcome friction losses decreased from 0.039 to

0.024 HPh/ton (0.032 to 0.020 kWh/tonne) when C

was increased from 20 to 40%. The

decrease corresponds to about 37%. The capacity of the pipeline is in this case doubled by

the increase in concentration. Because the pump solids effect for this product and pump

9.16.1 HYDRAULIC TRANSPORT OF SOLIDS 9.347

TABLE 4 Data for the sand slurry of Table 3 in a 12 in. (0.3 m) diameter pipe using a

14 in. (0.35 m) by 12 in. (0.3 m) conventional heavy-duty pump with an impeller diam-

eter of 36 in. (0.91 m). Pipeline length  852 ft (260 m), flow rate  5200 US gpm (328

l/s) and velocity  15 ft/s (4.5 m/s). Volumetric concentrations 20, 30 and 40% (from

Sellgren and Addie, 1996)

Concentrations by volume (%)

20 30 40

Capacity, ton/h (tonne/h) 690 (627) 1035 (941) 1380 (1255)

Energy to overcome pipeline friction, 0.039 (0.032) 0.029 (0.024) 0.024 (0.020)

HPh/ton (kWh/tonne)

Pump head reduction, R

(%) 8 11 13

Required rotary speed (rpm) 333 338 342

Pump water efficiency (%) 79.5 79.4 79.3

Pump efficiency reduction, R

(%) 6 11 15

Pump efficiency (%) 74.8 70.7 67.4

Total energy, HPh/ton (kWh/tonne) 0.052 (0.043) 0.041 (0.034) 0.037 (0.030)

remained fairly moderate also for the highest concentration, the total energy requirement

per tonne decreased from 0.052 to 0.037 (0.043 to 0.030) with an increased C

value from

20 to 40%. The lowering then corresponds to about 30%.

The attrition of coarse and angular particles during circulation in a test-loop may have

a strong influence on friction losses and pump performance. However, the results in

Tables 3 and 4 with high solids concentrations and coarse particles embedded in a sand

slurry are not expected to have been significantly influenced by circulation effects. In

large-scale loop testing special loading and quick measurement procedures are now used

to evaluate the interaction of particle attrition, pipeline friction and pump performance.

In general, designing a system to transport a slurry combining broad grading and high

concentration requires pilot plant testing using the same material that will be pumped in

the prototype line.

The solids concentration used throughout this section (denoted C

or C

) refers to

delivered concentration, and this is incorporated in the design-oriented equations. Large

particles tend to have a lower velocity than small ones, and thus a larger resident (in situ)

concentration in the pipeline, and this feature should also be considered in designing once-

through pipelines on the basis of recirculating test-loop data.

For long-distance freight pipelines it is worthwhile to devote considerable effort to

preparing and controlling slurry properties. For such lines solids concentrations range

from 0.25 (25%) for ores with S

of, say, 5.0, to 0.40 (40%) for coal with S

 1.4. Velocities

are usually maintained below 6.6 ft/s (2.0 m/s). For a typical 10 in. (0.25 m) pipe, annual

throughput of solids range from about 2.8 M tons (2.8 M tonnes) for ore to 1.4 M tons (1.3

M tonnes) for coal. The corresponding specific energy consumption, including a total pump

and drive-train efficiency of 75%, are respectively, 0.13 and 0.17 HPh/ton-mile (0.065 and

0.085 kWh/ton-km). For such cases the energy cost for pumping amounts to roughly half

the annual operating cost. This cost is, say, 20% to 30% of the total annual cost, which is

seen to be dominated by repayment of capital expenditure.

REFERENCES _______________________________________________________

Blatch, N. S. (1906). Discussion of “Works for the purification of the water supply of Wash-

ington D.C.” (Hazen, A. and Hardy, E. D.) Trans Amer. Soc. Civil Engrs. Vol. 57, pp. 400

—

409.

Brown, N. & Heywood, N. (1992). Slurry Handling Design of Solid-Liquid Systems. Else-

vier Science Publishers, United Kingdom.

9.348 CHAPTER NINE

Carstens, M. R. & Addie, G. R. (1981). A sand-water slurry experiment. Jour. Hydr. Div.

ASCE, Vol. 107, No. HY4, pp. 501

—

507.

Clift, R. Wilson, K. C., Addie, G. R. and Carstens, M. R. (1982). A mechanisitically-based

method for scaling pipeline tests for settling slurries.

Durand, R. (1951a). Transport hydraulique des matériaux solides en conduite, études

expérimentales pour les cendres de la central Arrighi. Houille Blanche, Vol. 6, No. 3, pp.

384

—

393.

Durand, R. (1951b). Transport hydraulique des graviers et galets en conduite. Houille

Blanche, Vol. 6, No. B, pp. 609

—

619.

Gillies, R. G., Shook, C. A. and Wilson, K. C. (1991). An improved two layer model for hori-

zontal slurry pipeline flow. Canad. J. Chem. Engng., 69, 173

—

178.

Hedström, B. O. A. (1952). Flow of plastics materials in pipes. Ind. and Eng. Chem., Vol. 44,

No. 3, pp. 651

—

656.

Kostuik, S. P. (1966). Hydraulic hoisting and pilot-plant investigation of the pipeline

transport of crushed magnetite. The Canadian Mining and Metallurgical Bulletin, Janu-

ary, 25

—

38.

Lumley, J. L. (1973). Drag reduction in turbulent flow by polymer additives, J. Poly Sci.,

Macromol, Rev. 7, A. Peterlin (Ed.), Interscience, New York, pp. 263

—

290 (1973).

Lumley, J. L. (1978). Two-phase flow and non-Newtonian flow. In Turbulence, P. Bradshaw

(Ed.), Tiopics in Applied Physics, Vol. 12, Springer-Verlag, Berlin (1978), Chapter 7.

Maciejewski, W., Oxenford, J. and Shook, C. (1993). Transport of Coarse Rock with Sand

and Clay Slurries, Hydrotransport, 12, Brügge, Belgium, pp. 705

—

724.

Mooney, M. (1931). Explicit formulas for slip and fluidity. J. Rheol. Vol. 2, p. 210 ff.

Newitt, D. M., Richardson, J. F., Abbot, M., & Turtle, R. B. (1955). Hydraulic conveying of

solids in horizontal pipes. Trans. Inst. of Chem. Engrs., Vol. 33, London, U.K.

Nnadi, F. N. & Wilson, K. C. (1992). Motion of contact load at high shear stress. J. Hydr.

Engrg., ASCE 118 (12), pp. 1670

—

1684.

Pugh, F. J. (1995). Bed-load Velocity and Concentration Profiles in High Shear Stress

Flows. Ph.D. Thesis, Queen’s University, Canada.

Rabinowitsch, B. (1929). Über die Viscosität von Solen. Zeitschrift physik. Chem., A 145,

p. 1 ff.

Sellgren, A. & Addie, G. (1996). Pump and pipleine solids effects of transporting sands with

different size distributions and concentrations. Proc. 13th Int. Conference on the Hydraulic

Transport of Solids in Pipes, Johannesburg, South Africa, pp. 227

—

236.

Sellgren, A. & Addie, G. (1998). Effective integrated mine waste handling with slurry

pumping. Proceedings Fifth International Conference on Tailings and Mine Waste. January

—

28, Ft. Collins, USA, pp. 103

—

107.

Shook, C. A. and Roco, M. C. (1991). Slurry Flow Principles and Practice. Butterworth-

Heinemann.

Sundqvist, A., Sellgren, A. and Addie, G. R. (1996a). Pipeline friction losses of coarse and

slurries: comparison with a design model, in Powder Technology, 89, pp. 9

—

18.

Sundqvist, A., Sellgren, A. and Addie, G. R. (1996b). Slurry pipeline friction losses for

coarse and high-density industrial products, in Powder Technology, 89, pp. 19

—

28.

Thomas, A. D. (1979). The role of laminar/turbulent transition in determining the critical

deposit velocity and the operating pressure gradient for long distance slurry pipelines,

Proc. Hydrotransport 6, BHRA Fluid Engineering, Cranfield, UK, pp. 13

—

26.

Thomas, D. G. (1963). Non-Newtonian suspensions. Part 1, physical properties and lami-

nar transport characteristics. Ind. and Eng. Chem. Vol. 55, No. 11, pp. 18

—

29.

Thomas, A. D. & Wilson, K. C. (1987). New analysis of non-Newtonian turbulent flow

—

yield-power-law fluids. Canad. J. Chem. Engrg., Vol. 65, pp. 335

—

338.

9.16.1 HYDRAULIC TRANSPORT OF SOLIDS 9.349

Wilson, K. C. (1979). Deposition-limit nomograms for particles of various densities in

pipeline flow, Proc. Hydrotransport 6, BHRA Fluid Engineering, Cranfield, UK, pp. 1

—

12.

Wilson, K. C. (1986). Modelling the effects of non-Newtonian and time-dependent slurry

behavior. Proc. Hydrotransport 10, BHRA Fluid Engineering, Cranfield, UK, pp. 283

—

289.

Wilson, K. C. (1988). Evaluation of interfacial friction for pipeline transport models. Proc.

Hydrotransport 11, BHRA Fluid Engineering, Cranfield, UK, pp. 107

—

116.

Wilson, K. C. (1989). Two mechanisms for drag reduction. Drag Reduction in Fluid Flows,

Techniques for Friction Control, Ed. H. R. J. Sellina nd R. T. Moses, pp. 1

—

8. Ellis Horwood

Ltd., Chichester, UK.

Wilson, K. C. & Addie, G. R. (1995). Coarse-particle pipeline transport: effect of particle

degradation on friction. Proc. 8th International Freight Pipeline Society Symposium,

pp. 151

—

156.

Wilson, K. C., & Judge, D. G. (1978). Analytically-based nomographic charts for sand-water

flow, Proc. Hydrotransport 5, Solids in Pipes, BHRA Fluid Engineering, Cranfield, UK,

pp. A1-1

—

11.

Wilson, K. C., & Nnadi, F. N. (1990). Behavior of mobile beds at high shear stress. Proc.

22nd Int’l Conference on Coastal Engineering, Delft, Netherlands, Vol. 3, pp. 2536

—

2541.

Wilson, K. C., & Thomas, A. D. (1985). A new analysis of the turbulent flow of non-

Newtonian fluids. Canad. J. Chem. Engrg., Vol. 63, pp. 539

—

546.

Wilson, K. C., & Tse, J. K. P. (1984). Deposition limit for coarse-particle transport in inclined

pipes. Proc. Hydrotransport 9, BHRA Fluid Engineering, Cranfield, UK, pp. 149

—

169.

Wilson, K. C. & Watt, W. E. (1974). Influence of particle diameter on the turbulent support

of solids in pipeline flow. Prod. Hydrotransport 3, BHRA Fluid Engineering, Cranfield, UK,

pp. E1-1

—

E1-13.

Wilson, K. C., Addie, G. R., Sellgren, A. and Clift, R. (1997). Slurry Transport Using Cen-

trifugal Pumps, 2nd Ed. Blackie (Chapman & Hall).

Wood, F. M. (1935). Standard nomographic forms for equations in three variables, Cana-

dian Journal of Research, Vol. 12.

9.16.2

APPLICATION AND

CONSTRUCTION OF

CENTRIFUGAL SOLIDS

HANDLING PUMPS

GRAEME ADDIE

ANDERS SELLGREN

9.351

This section discusses the application of centrifugal pumps to the transport of slurries as

introduced in Subsection 9.16.1.

Where the distance is large and the size of the solids less than about 100 microns,

positive displacement pumps are usually applied. If the solids to be transported are

smaller than about 60 mm in size, water is readily available or already part of the

process, and the distance is less than 12 miles (20 km), a pipeline driven by centrifugal

slurry pumps is usually more cost-effective than belt conveyors, trucks, or railway

transportation.

Types of solids transported vary from sag mill feed in a copper mine, iron ore, phos-

phate matrix, coal, rock salt, tar sands, red mud, various types of waste tailings, and

crushed rock and silt.An 18 in (0.45 m) diameter pipeline, for example, is capable of trans-

porting as many as 2200 tons/hr (2000 tonnes/hr) of sand. This equates to about one hun-

dred truckloads per hour over the distance involved.

The application that involves the largest quantities is in the dredging industry, con-

tinually maintaining navigation in harbors and rivers, altering coastlines, and mining

material for landfill and construction purposes. Because a single dredge may be required

to maintain a throughput of 7000 tons/hr of slurry or more, very large centrifugal pumps

are used. Figures 1 and 2 show, respectively, an exterior view of a dredge pump on test, and

a view of a large slurry pump impeller (Addie and Helmly, 1989).

Because the aim is to transport solids and not water, the higher the concentration of

solids, the better for energy consumption and capital cost. This does, however, mean that

wear due to the abrasive solids will be significant, requiring a special type of centrifugal

pump design and the use of special materials. Slurry pumps may be selected for low-

concentration dirty-water service. Most of what follows, however, is about pumps designed

and built to give cost-effective operation for heavy-duty slurry service, probably involving

significant wear.

9.352 CHAPTER NINE

FIGURE 1 Testing a dredge pump at the GIW hydraulic laboratory

SLURRY PUMP TYPES ________________________________________________

The majority of centrifugal slurry pumps that fit the above definition are constructed as the

single-stage horizontal radially split type.A sectional arrangement drawing of a single-wall

metal type is shown in Figure 3. Where elastomers are used, they must be supported with

an outer casing or sideplate. This type is commonly referred to as a double-wall type. An

example of a double-wall rubber-lined pump is shown as Figure 4.

Vertical cantilever and vertical submersible centrifugal pumps are also built in signif-

icant quantities and serve mostly in general cleanup and other service. These pumps on

occasion are called upon to operate as transporting devices and, depending on the design

and service, include the special features described later.

CENTRIFUGAL SLURRY PUMP HYDRAULIC DESIGN ______________________

In order to reduce wear, the hydraulic design of a slurry pump should be such that the

rotating wetted component and fluid velocities must be kept as low as practical while hard

metal or elastomer wetted-section thicknesses are increased. Impeller meridional sections

are also usually kept close to rectangular and with front sealing on a vertical face to min-

imize the axial rotating surfaces. Collectors (casings) are usually semi-volute (or even

9.16.2 APPLICATION AND CONSTRUCTION OF CENTRIFUGAL SOLIDS HANDLING PUMPS 9.353

FIGURE 2 Dredge pump impeller, 105 in (2.67 m) diameter

annular) to give better wear over a wider range of best-efficiency-point quantity (flow rate)

(BEPQ).

Where larger solids are to be pumped, the inside shroud impeller widths are usually

oversized, the number of vanes is reduced to two or three, and the vane overlap may be

reduced. All of these distortions modify or reduce the hydraulic performance. Given the

variety of types (and severity) of services, the design solution that provides the best com-

promise between wear life and efficiency and provides the end user with the overall low-

est total cost of ownership is not simple to achieve.Although specific to a particular slurry

type, Kasztejna et al. (1986) and Cooper et al. (1987) provide a good insight into some of the

design tradeoffs and special problems involved in the design of a centrifugal slurry pump.

In general, slurry pumps are of low specific speed (as defined in Section 2.1), in the

range of 750 to 2000 for N

, (14.5 to 39 for n

and 0.27 to 0.73 for 

). They employ three to

five vanes, have impeller inside shroud widths that are 75

—

200% wider than those a nor-

mal water pump, and use impeller vane and shroud thicknesses two to three times that of

a water pump. The results of these distortions flatten the constant-speed head-flow curves

and reduce efficiency by five or so percent. Typical head coefficients (as defined in Section

2.1) and efficiencies are shown in Figures 5 and 6.

In order to minimize wear over different ranges of percent of BEPQ, operation slurry

pump casings vary from the true volute water pump T type (shown schematically on Fig-

ure 7) through the semi-volute C type to the essentially annular A type. There are also a

few examples of what is called the OB type with recessed tongue and special extended

Pump Handbook by Igor J. Karassik, Joseph P. Messina, Paul Cooper, Charles C. Heald - 3rd edition

Подождите немного. Документ загружается.