Slurry Pumping Topics Covered Piping Basics Cavitation Field

Slurry Pumping

Topics Covered • • • Piping Basics Cavitation Field Maintenance Slurry Basics Pump Selection Testing Slurry Effect of Slurry on Pump Performance Field Work Pump Spacing 2

Piping Basics 3

• Bernoulli’s Equation Where (Darcy-Weisbach equation) 4

TDH Friction Losses (Hf) Hydraulic Gradient—Absolute pressure changes in the system 5

Consideration for Slurry pipeline Design • Design requirements: – – Solids transport rate Concentration, fixed or varied (affects cost) Pipeline diameter Slurry Type, settling or non-settling • Slurry specifics: – Size – Type – Concentration 6

Cavitation • Typical conditions required for cavitation – Boiling liquid (usually caused by a local pressure drop) – Moving flow – Pressure increase downstream (leads to vapor bubble collapse) 7

Cavitation 8

Mitigation of Cavitation • NPSHA—Net Positive Suction Head (Available). When NPSHA at any point reaches zero, the liquid vaporizes. • NPSHR—Net Positive Suction Head (Required). Local pressure at pump vanes may be less then NPSHA, as a result NPSHR is needed. • Slurry concentration increases with increased suction (vacuum). NPSHR of the pump limits the concentration of the slurry (3: 25, 3 -b) 9

Water Hammer 10

Modeling Sample Parameters • • Phosphate Matrix Approximately 4. 5 miles of pipe Velocity of 15, 000 GPM (~17 ft/s) Design flow of 16, 000 GPM (~18 ft/s) 40% slurry concentration 2, 000 TPH production rate 19” pipe diameter (Typical) 11

Friction Factor per slurry concentration 0. 048 friction factor at design velocity of 18 ft/s, Slurry Hydraulic Gradient J ( ft slurry / ft ) Solid lines: const. CW (%) 0. 06 0. 05 5% 0. 04 10% 15% 0. 03 20% 0. 02 30% 40% 0. 01 0 0 5 10 15 20 Mixture Velocity V (ft/sec) 12

Flow rate vs. Pipeline Head Increase in pipe head of approximately 100 ft Solid lines: const. CW (%) 1400 Pipeline Head ( ft slurry ) 1200 5% 1000 10% 800 15% 20% 600 30% 400 40% 200 0 0 5000 10000 15000 20000 Flowrate ( gpm ) 13

Pit water required vs. Production/Cost increases significantly with decreased concentration for the same targeted production rate Solid lines: const. C W (%) Dashed lines: const. gun water (gpm) 6 Specific Energy Consumption (hp-hr/ton-mi) 5% 10% 5 15% 20% 4 30% 40% 3 8000 10000 2 12000 14000 1 16000 17000 0 0 500 1000 1500 2000 2500 3000 Production (tons/hr) 14

Field considerations • Pipe wear can be monitored with an ultrasonic thickness measuring device • Pipe should be rotated to increase service life • Vertical pipes experience much less wear than horizontal pipes • Long radius elbows wear much better than short radius elbows • Booster pump location is critical to properation • Pump start up should be sequential and not all at once in order to reduce system pressures and possible water hammer 15

Slurry Basics • Slurry is a mix of something solid and liquid. • Water is the primary liquid used in hydraulic transport of solids. • In theory, there is no limitation on the size of particles that can be transported hydraulically. • In practice, maximum solid size is about 12 inches in diameter. 16

Slurry Basics Cont’d • What you need to know when designing a slurry pumping system – – Particle size of solids in slurry Type of slurry being pumped Concentration rate of slurry Desired flow rate • Pencil Test – Get a sample of the slurry you want to pump. – Poke a pencil in to the sample about ½”. – If the pencil stands on its own, it may not be a slurry concentration that can be pumped. 17

Slurry Types • Settling (also known as heterogeneous) – Matrix material – Head vs. flow rate is U shaped • Non-settling (also known as homogeneous) – Fine clays (solids less than 80 microns) – Head vs. flow rate shows a laminar and turbulent flow region – In theory, pipeline velocity can be low, but larger particles may settle if velocity is too low 18

Slurry Concentration • Slurry concentration is usually defined in one of three ways: 1. 2. 3. • • Cv – Concentration by volume Cw – Concentration by weight Sm – Mean specific gravity of the slurry Pump selection by engineers is usually done using Sm, while mine personnel use Cw. Formulas available to convert from one concentration definition to another. 19

Pump Selection • To select the correct pump for a system, items that need to be known are: – – – Sump static head Entrance loss Suction pipe friction loss Discharge pipe friction loss Static discharge head Exit loss • Pump curves and a system curve are also useful to have. 20

Pump Selection Cont’d Pump Curve System Curve 21

Pump Selection Cont’d • System curve is overlaid on to the pump curve. Where the curves cross will be the operating point.

Pump Selection Cont’d • Also need to know the classification of the slurry being pumped: – Class 1: Mildly Abrasive (Dirty Water) – Class 2/3: Slightly Abrasive (Medium Size Particles) – Class 4: Highly Abrasive (Large Particles) - Knowing the abrasiveness of the slurry allows for proper planning of wear on pump parts.

Pump Selection Cont’d • Slurry pump designs include horizontal, vertical, and submersible pumps. • The most common type of pump used in the phosphate industry is a horizontal, centrifugal pump. • These pumps are usually made of cast white irons. • White irons offer much better wear resistance than steel. • Pumps may also have rubber or urethane liners to combat wear and corrosion.

Pump Selection Cont’d • Do not add a safety factor to the system head. • Do not add a safety factor to the pump speed. • If needed, add safety factor to hp/motor sizing. • Consider variable speed motors when a range of flows is required.

Pump Selection Cont’d • In heavy duty service, pump must be sized correctly for solids in the pipeline. • Velocity too high can lead to premature wear of system components from internal impacts. • Velocity too low can lead to material build up in impeller housing leading to uneven wear and unstable operation.

Centrifugal Pump Parts 27

Shells and Impellers • Various shell and impeller types: 28

Shells and Impellers Note: QBEP is the best efficiency point for flow. 29

Pump Head • Head is used to measure the kinetic energy which a pump creates. Head is a measurement of the height of the liquid column the pump creates from the kinetic energy the pump gives to the liquid. • The units are in feet or meters. • Head is used because a pump’s pressure will change based on the specific gravity of the fluid being pumped, but the head will not.

Pump Head Cont’d • Various types of head: 31

Pump Head Cont’d • Pumping system diagram showing various heads: 32

Variation of Performance with Change in Speed • Flow rate (Q) increases linearly with speed (N) change. • Head (H) increases to the square of the speed change. • Power (P) increases to the cube of the speed change. • The relationships also hold true for change in impeller diameter. 33

Water Pumps vs. Slurry Pumps • Slurry pumps are typically much more robust than water pumps. • Slurry pumps are designed with replaceable parts due to wear on the pump. • Slurry pumps run at slower speeds than water pumps to help reduce wear. • Slurry pumps are more expensive to operate (~ 4 times more than H 2 O pumps) 34

Testing Slurry • Phosphate industry slurries are usually one of four types: – Matrix (raw unprocessed material) – Clay or Clay/Tailings Mix – Tailings (waste product) • Testing is done to determine: – – – Operating velocity Pipeline diameter Concentration Aid in pump selection Allow for energy and cost savings while increasing component life

Testing Slurry Cont’d • A slurry sample is taken and particle size analysis is done using sieves and shakers. • Laser diffraction can also be used to find particle size. • Dmax and D 50 are found through testing. • As a general rule of thumb, the largest particle should be no larger than one third of the pipeline diameter. • Viscometers can also be used to find the viscosity of the slurry.

Testing Slurry Cont’d • Small scale closed loop pumping systems can also be created to see how the system will perform.

Effect of Slurry on Pump Performance • The solids effect: – System requires more power input – Less efficient overall – Less system head • Increasing slurry density leads to more power needed, but same head, and same efficiency. • Higher viscosity in a slurry leads to more power needed, less head, less efficiency. • The solids effect decreases approximately in proportion to the increase in impeller diameter. 38

Effect of Slurry on Pump Performance • Various forms of erosion occur inside the pump housing which can lead to shortened component life 39

Field Work Pros: Cons: • Full scale data collection • Able to obtain transient system data • Observation of system in operation • Impact on plant production • Instrumentation set up is limited • Limited operational flexibility 40

Field Work • Field testing provides: – Ability to see full system in operation – Better understanding of pump operation and opportunities for improvement – Better understanding of pipeline operation and most efficient pipeline set up – Data collection from the system in real time under true load conditions – Support for the pump and pipeline models for future applications 41

Pump Spacing • Phosphate Matrix Pumping • Parameters: – – – – – Type B Matrix 2, 000 ton/hour 40% Solids by Weight 15, 000 GPM 17 FPS pipeline velocity 19 inch I. D. Piping 24, 200 feet of system Static Head of 100 feet 20 x 25 LSA 62 Pit Pump 18 x 20 WBC 54 Booster Pumps 42

Pump Spacing Cont’d • Using the FIPR spreadsheet, enter given parameters. 43

Pump Spacing Cont’d • Find the slurry hydraulic gradient (~. 044) 44

Pump Spacing Cont’d • Find the pipeline head (~1160 feet) 45

Pump Spacing Cont’d • Determining amount of pumps required: • TDH = 1160 -140 (from the pit pump) 1020 • Using pump performance curve for the WBC 54, 225 feet of head is produced by each booster. • 1020/225 => 5 boosters needed 46

Pump Spacing Cont’d • Determining pump spacing: • • Start with static head Suction pressure upstream TDH produced by each pump Net TDH available for friction • • Next booster would be at: TDH produced by pump • • Final Booster would be at: TDH produced by pump Less 40 psi for downstream pump Plus 20 psi from pit pump - 100 ft + 69 ft +225 ft 195 ft /. 044 = 4432 feet 225 ft /. 044 = 5113 feet 225 ft - 69 ft + 35 ft 191 ft /. 044 = 4340 feet 47