1. Flow Measurement

2. 2 Objective To determine chemical dosage, air supply into the aeration basins, sludge volume to return into the biological reactors, to provide daily flow records required by regulatory agencies, and to evaluate infiltration/inflow during wet weather Locations Within an interceptor or manhole At the head of the plant Downstream of bar screen, grit channel, or primary sedimentation In the force main of pumping station Before the outfall

3. 3 Flow Measurement - continued Basic types of measurement  Differential pressure producers  Direct discharge measurement  Positive volume displacement measurement  Flow velocity-area measurement Flow meters Venturi type meter, orifice meter, propeller type meter, magnetic flow meter, ultrasonic flow meter, vortex meter, rotameter (variable-area meter), flumes, and weirs Liquid chemical flow Measured by positive displacement pumps (or rotameters)

4. 4 Flow Measurement - continued Selection Criteria  Type of application: open channel/closed conduits  Proper sizing: range of flow  Fluid composition: compatibility, solids, passage  Accuracy (±%) and repeatability  Headloss or hydraulic head available  Installation requirements: straight length, accessibility, disconnection method  Operating environment: explosion proof, resistance to moisture and corrosive gases, temp. range  Ease of maintenance: provision for flushing/rodding  Cost  Type and accessibility of the conduit

5. Flow Metering Devices in Wastewater Treatment Facilities RawPrimarySecondaryPrimaryReturnThickenedMixedProcess Metering deviceWWeffluenteffluentsludgesludgesludgeliquorwater For open channels Head/area Flumexxxx Weirxxx Other Magnetic (insert type)x For closed conduits Head/pressure Flow tubex a x a xx a x a x a,b xx Orificex Pitot tubex Rotameterx Venturix a x a xx a x a x a x Moving fluid effects Magnetic (tube type)_xxxxxxx Ultrasonic (doppler)xxxx c Ultrasonic (transmission)xxx Vortex sheddingxxx Positive displacement Propellerx Turbinexx a Flushing or diaphragm sealed connections recommended b Use with in-line reciprocating pumps not recommended c Solids content < 4% 5

6. 6 Venturi Type Flow Meter  Measure differential pressure  Consists of a converging section, a throat, and a diverging recovery section  The difference in two heads is analyzed by electrical or electromechanical instruments  Accuracy: ±1%; range: 4:1  Take considerable space (L/D = 5~20)  Cannot be altered for measuring pressure beyond a maximum velocity

7. 7 Flow Nozzle Meter  Measure differential pressure  A Venturi meter without the diverging recovery section  Less expensive than Venturi meter but higher headloss  Accuracy: < ±1%; range: 4:1

8. 8 Orifice Meter  Measure differential pressure  Easy to install and fabricate  Advantages: least expensive of all differential pressure devices and good accuracy (±1%)  Disadvantages: least efficient, high headloss, easy clogging, and narrow range of flows (4:1)

9. 9 Electromagnetic Meter  Faraday’s law: a voltage produced by passing a conductor through a magnetic field is proportional to the velocity of the conductor (wastewater)  Advantages: good accuracy (±1~2%), capable of measuring large range of flows (10:1), no headloss, and unaffected by temperature, conductivity, viscosity, turbulance, and suspended solids  Disadvantages: high initial cost and need for trained personnel to handle routine O&M

10. 10

11. 11 Turbine Meter  Use a rotating element (turbine)  A wide range of fluid applications covering from water to oils, solvents to acids  Limited to pipes running full, under pressure, and liquids low in suspended solids  Excellent accuracy (±0.25%) and a good range of flows (10:1)

12. 12 Acoustic Meter  Use sound waves to measure the flow rates  Sonic meter or ultrasonic meter depending on whether the sound waves are in or above audible frequency range  Determine the liquid levels, area, and actual velocity  Advantages: low headloss, excellent accuracy (2~3%), usable in any pipe size, no fouling with solids, and wide flow ranges (10:1)  Disadvantages: High initial cost and need for trained personnel to handle routine O&M

13. 13 Parshall Flume  Consists of a converging section, a throat, and a diverging section  Self-cleaning and small headloss  Converts depth readings to discharge using a calibration curve  Less accurate (±5~10%)  Range: 10:1 ~ 75:1

14. 14 Palmer-Bowlus Flume  Creates a change in the flow pattern by decreasing the width of the channel without changing its slope.  Installed in a sewer at a manhole which causes the back-up of the water in the channel. By measuring the upstream depth, the discharge is read from a calibration curve.  Lower headloss than the Parshall flume  Less accurate (±5~10%)

15. 15 Weirs (Rectangular, Cipolletti, Triangular, or V-Notch)  The head over the weir is measured by a float, hook gauge, or level sensor  Measure the flow in open channels Accuracy: ±5%; Range: 500:1  Advantages: relatively accurate, simple to install, and inexpensive  Disadvantages: large amounts of headloss and settling of solids upstream of the weir and more maintenance

16. 16 Ultrasonic Meter  Measured based on the time required for an ultrasonic pulse to diagonally traverse a pipe or channel against the liquid flow.  Clamp-on types measure flow through the pipe without any wetted parts, ensuring that corrosion and other effects from the fluid will not deteriorate the sensors.  Accuracy: ± 1% for a flow velocity ranging from 1 to 106 ft/sec. Should be free of particles and air bubbles. http://www.sensorsmag.com/ articles/1097/flow1097/main. shtml

17. 17 Vortex Meter  The frequency at which the vortices are generated is proportional to the velocity of the liquid flow.  Accuracy: ± 1% for a flow range of 12 to 1.  Headloss: two times the velocity head

18. 18 Rotameters  Consist of glass tube containing a freely moving float.  May be used for both gas and liquid flow measurement  Read or measured visually  May be applied for very low flow rates, 0.1~140 gph for water and 1~520 scfm for air.

19. 19 Selection Guide (1) Flow Meter Recommended Service Turndown Typical Pressure Loss Typical Accuracy Required upstream pipe, Ф Effects from changing viscosity? Turbine Clean, viscous liquids 20 to 1High +/- 0.25% of rate 5 to 10High Positive Displacement Clean, viscous liquids 10 to 1High +/- 0.5% of rate NoneHigh Electromagnetic (Mag-Meter) Clean, dirty, viscous, conductive liquids and slurries 40 to 1None +/- 0.5% of rate 5None Variable Area (VA, Rota-meter) Clean, dirty, viscous liquids 10 to 1Medium +/- 1 to 10% FS NoneMedium Thermal Mass Flow (TMF) Clean dirty viscous liquids some slurries 10 to 1Low+/- 1% FSNone Coriolis Mass Meter Clean, dirty. viscous liquids, some slurries 10 to 1Low +/- 0.5% of rate None Orifice Plate Clean, dirty, liquids some slurries 4 to 1Some +/- 2 to 4% FS 10 to 20High FS=full scale http://www.buygpi.com/selectionguide.aspx

20. 20 Selection Guide (2) Flow Meter Recommended Service Turndown Typical Pressure Loss Typical Accuracy Required Upstream pipe, Ф Effects from changing viscosity? Pitot tubeClean liquids3 to 1Very low +/- 3 to 5% FS 20 to 30Low Ultrasonic (Doppler) Dirty, viscous, liquids and slurries 10 to 1None+/- 5% FS5 to 30None Ultrasonic (Transit Time) Clean, viscous, liquids some dirty liquids (depending on brand) 40 to 1None +/- 1 to 3% FS 10None Venturi Some slurries but clean, dirty liquids with high viscosity 4 to 1A little+/- 1% FS5 to 18High VortexClean, dirty liquids10 to 1Medium +/- 1% of rate 10 to 20Medium

21. 21 Flow Sensors SensorRangeAccuracyAdvantagesDisadvantages Orifice3.5:12-4% of full span Low cost Extensive industrial practice High pressure loss Plugging with slurries Venturi3.5:11% of full span Lower pressure loss than orifice Slurries do not plug High cost Line under 15 cm Flow nozzle3.5:12% full span Good for slurry service Intermediate pressure loss Higher cost than orifice plate Limited pipe sizes Elbow meter3:1 5-10% of full span Low pressure lossVery poor accuracy Annubar (Pitot tube) 3:1 0.5-1.5% of full span Low pressure loss Large pipe diameters Poor performance with dirty or sticky fluids Turbine20:1 0.25% of measurement Wide rangeability Good accuracy High cost Strainer needed, especially for slurries Vortex shedding 10:1 1% of measurement Wide rangeability Insensitive to variations in density, temperature, pressure, and viscosity Expensive Positive displacement 10:1 or greater 0.5% of measurement High reangeability Good accuracy High pressure drop Damaged by flow surge or solids

22. 22 Checklist for Design of Flow-Measuring Device  Characteristics of the liquid (SS, density, temp., pressure, etc.)  Expected flow range (max. and min.)  Accuracy desired  Any constraints imposed by regulatory agencies  Location of flow measurement device and piping system (force main, sewer, manhole, channel, or treatment unit)  Atmosphere of installation (indoors, outdoors, corrosive, hot, cold, wet, dry, etc.)  Headloss constraints  Type of secondary elements (level sensors, pressure sensors, transmitters, and recorders)  Space limitations and size of device  Compatibility with other flow measurement devices if already in operation at the existing portion of the treatment facility  Equipment manufacturers and equipment selection guide

23. 23 Design Example Conditions  92-cm (36-inch) force main  Max. flow: 1.321; min. flow: 0.152 m 3 /sec  Measurement error: < 0.75% at all flows  Headloss: < 15% of the meter readings at all flows  Capable of measuring flows of solids bearing liquid  Reasonable cost Select a Venturi meter Design equation Use Bernoulli energy equation for two sections of pipe with the assumption that the headloss is negligible and the elevations of the pipe centerline are the same.

24. 24 Governing Equations Bernoulli’s equation [Pressure head]+[Elevation head]+[Velocity head] whereP = pressure, m; ρ = density, kg/m 3 ; z = elevation, m; v = velocity (m/sec), and g = 9.8 m/sec 2. Continuity equation Q = v 1 A 1 = v 2 A 2 where A = Cross-sectional area. 0 0

25. 25 Design Example - continued whereQ = pipe flow, m 3 /sec; C 1 = velocity, friction, or discharge coefficient h = piezometric head difference, m; A 1 = force main cross-sectional area, m 2 ; A 2 = throat cross-sectional area, m 2 ; and D 1 and D 2 = diameter of the pipe and the throat, m. Standard Venturi meter Tube beta ratio (throat  /force main  ): 1/3~1/2 K = 1.0062 (1/3 beta ratio), 1.0328 (1/2 beta ratio) C 1 = 0.97~0.99; normally provided by the manufacturer

26. 26 Design Example - continued Develop calibration equation: Assume C 1 = 0.985 = 0.7489  h m 3 /sec h = (Q/0.7489) 2 At Q max, h = 3.111 m; at Q min, h = 0.041 m Headloss calculations K = 0.14 for angles of divergence of 5° h L /h = 0.147 < 0.15; thus acceptable

27. Level Measurement

28. 28 Level Measurement  Essential item in plant operations  Levels of all chemical storage tanks and silos, and the pressure of water or compressed air lines - that is, the water level in the distribution mains and the utility lines.  Liquid levels: a float, pressure elements, bubbler systems, or ultrasonic systems  Dry, powdery materials: ultrasonic systems, photocell systems, rotary paddle switches, diaphragm units, wire strain gauge systems, and load cells (measure the total weight).

29. 29 Miscellaneous Flow Measurement Devices Depth Measurement Need to measure the flow depth and sewer slope and use Manning equation for flow estimation. Frequently used for interceptor flow estimation Open Flow Nozzle Crude devices used to measure flow at the end of freely discharging pipes. Must have a section of pipe that has a length of at least six times the diameter with a flat slope preceding the discharge. Examples: Kennison nozzle and the California pipe

30. 30 Level Measurement Devices Magnetostrictive RF Transmitter Radar Ultrasonic Magnetic Level Gauge Magnetic Switch Float Switch RF Switch Vibrating Fork Thermal Dispersion Seal Pot http://www.sensorsmag.com/sensors/article/articleDetail.jsp?id=360729

31. 31 Float System  The float-operated transmitter - simple and reasonably accurate system  The installation is very time consuming and expensive due to the need for a stilling well and a collection of wires, wheels, and tackles.  Requires a periodic maintenance to assure friction-free motion of the float and cable assembly.

32. 32 Pressure Elements  Very commonly used in water treatment plants  A pressure transducer connected to the pressure elements measures the water pressure at the base of the tank and directly reads the liquid level.  Pressure element type level measurers: the bourdon tube (has helical and spiral units; suited for high pressure measurement), bellow element (for intermediate pressures), diaphragm element (for small range in the low-pressure zone), and manometer (limited to pilot studies or temporary use).

33. 33 Bubble Tube System  Has a tube placed inside a tank which runs from the top and opens 3 in. from the bottom. During the operation, compressed air is supplied to the tube via a regulator or a purge rotameter.  Measure the back pressure of the hydrostatic head.  Widely used for open tanks  Advantages: simple design, easy accessibility and little concern over the corrosion of the pressure sensing device, and the ability to be installed at the bottom of the tank

34. 34 Ultrasonic Level Detector  Used to monitor either the water level in a tank or dry material stored in a storage bin open to the atmosphere.  Measured by means of an acoustic pulse; the ultrasonic transmitter and receiver units are located above the maximum level of the object. The time elapsed between pulse generation and the detection of the reflected pulse energy is a function of the speed of sound in air. Needs a temperature correction factor.

35. Valves

36. 36 Valve Selection  Purpose: Regulate the flow of water from reservoirs, tanks, or channels.  Primary functions: shut-off, throttle, prevention of backflow, or a combination of these functions  Considerations: type of fluid or gas to be regulated, temperature, flow range, pressure of the system, valve function, valve location, type of valve operator, and reliability and cost of the valve.

37. 37 Type of Fluid or Gas  Type 18-8 stainless steel: for corrosive liquid or gas  Type 316 stainless steel and Teflon seats: for ozone gas lines  No internal recess in the valve: for a chemical slurry  If abrasive matter is present in the liquid, the fluid passage must be composed of materials that are resistant to this type of erosion.

38. 38 Temperature  Important when valves are used in conjunction with auxiliary equipment such as heating boilers and certain types of chemical feed system - that handle exothermic chemicals such as caustic soda and sulfuric acid.  Ordinary valves used in the water treatment process should not be used at operating temperatures above 150°F due to thermal distortion, unless special metal parts are specified.

39. 39 Flow Range  Important when selecting throttling valves.  Most throttling valves have a limited range.  Not important for simple shut-off.  If the water velocity exceeds 35 ft/sec based on the valve port area, most valves are unsuitable for such service and the engineer must therefore specify special instructions for valve construction.

40. 40 Pressure Should know the max. differential pressure across the valve, and normal and extreme line pressure. Valve Function Isolation of a line, drainage or a tank, prevention of backflow, reduction in pressure, or flow modulation. Valve Location In a valve vault, a pipe gallery, in the wall at the entrance of a tank, at the exit of a pipeline,buried in the ground, or submerged in the water.

41. 41 Valve Operator Manual or power For manual valve, the type of operator (i.e., a wheel or a square nut with key) and the orientation of both the operator and system support must be specified. Power operators are energized by means of electricity, compressed air, water or oil. Reliability and Cost Compare the relative costs of the various sizes and types of valve for each application. List valve cost, projected maintenance costs and the cost of replacing equipment when necessary.

42. 42 Types of Valve (1)  Slide valve: a sliding disk travelling perpendicular to the flow direction - e.g., gate valve

43. 43 Gate Valve Best Suited Control: Quick Opening Recommended Uses: 1. Fully open/closed, non-throttling 2. Infrequent operation 3. Minimal fluid trapping in line Applications: Oil, gas, air, slurries, heavy liquids, steam, noncondensing gases, and corrosive liquids Advantages: Disadvantages: 1. High capacity 1. Poor control 2. Tight shutoff 2. Cavitate at low pressure drops 3. Low cost 3. Cannot be used for throttling 4. Little resistance to flow

44. 44 Types of Valve (2)  Rotary valve: a plug or disk moving in a rotary fashion - e.g., butterfly, ball, plug, and cone valves

45. 45 Butterfly Valve Best Suited Control: Linear, Equal percentage Recommended Uses: 1. Fully open/closed or throttling services 2. Frequent operation 3. Minimal fluid trapping in line Applications: Liquids, gases, slurries, liquids with suspended solids Advantages: Disadvantages: 1. Low cost and maint. 1. High torque required for 2. High capacity control 3. Good flow control 2. Prone to cavitation at lower 4. Low pressure drop flows

46. 46 Ball Valve Best Suited Control: Quick opening, linear Recommended Uses: 1. Fully open/closed, limited-throttling 2. Higher temperature fluids Applications: Most liquids, high temperatures, slurries Advantages: Disadvantages: 1. Low cost 1. Poor throttling characteristics 2. High capacity 2. Prone to cavitation 3. Low leakage and maintenance 4. Tight sealing with low torque

47. 47 Types of Valve (3)  Swing valve: a swing check valve preventing reverse flow - a combination of rotary and glove valves  Globe valve: a plug or disk moving parallel to the flow direction - e.g., home plumbing fixtures.

48. 48 Glove Valve Best Suited Control: Linear and equal percentage Recommended Uses: 1. Throttling service/flow regulation 2. Frequent operation Applications: Liquids, vapors, gases, corrosive substances, slurries Advantages: Disadvantages: 1. Efficient throttling 1. High pressure drop 2. Accurate flow control 2. More expensive than 3. Available in multiple other valves ports

49. 49 Types of Valve (4)  Multijet (sleeve) valve: inner and outer pipes covered with a multitude of small orifices - used exclusively to reduce high pressure and to control flow rate without causing cavitation.

50. 50 Valve Selection Select the proper type of valve, followed by sizing Evaluate the pressure drop characteristics and the working range of the valves Selection Criteria  Rangeability: the ratio between the max. and min. controllable flow rates.  Turn-down: a ratio of the normal max. flow rate vs. the min. controllable flow rate.  For water pressure control, the ball and butterfly valves should be selected for ordinary cases where there is a normal pressure drop of at least 15% but less than 30%.

51. 51 Valve Selection - continued  If a higher pressure drop such as 50% is expected, a valve with linear characteristics (plug or multijet valve) should be specified.  For the control of liquid level, a valve with linear characteristics such as a plug valve, is most appropriate.  Equal percentage valves are most appropriate for a fast acting process, in situations requiring high rangeability, if the dynamics of the system are not well known, and in the case of heat exchangers.

52. 52 Valve Sizing (1) STEP #1: Define the system The system is pumping water from one tank to another through a piping system with a total pressure drop of 150 psi. The fluid is water at 70ºF. Design (maximum) flowrate of 150 gpm, operating flowrate of 110 gpm, and a minimum flowrate of 25 gpm. The pipe diameter is 3 inches. At 70ºF, water has a specific gravity of 1.0. Key Variables: Total pressure drop, design flow, operating flow, minimum flow, pipe diameter, and specific gravity http://www.cheresources.com/valvezz.shtml

53. 53 Valve Sizing (2) STEP #2: Define a maximum allowable pressure drop for the valve Note the trade off: larger pressure drops increase the pumping cost (operating) and smaller pressure drops increase the valve cost because a larger valve is required (capital cost). The usual rule of thumb is that a valve should be designed to use 10~15% of the total pressure drop or 10 psi, whichever is greater. For the system, 10% of the total pressure drop is 15 psi which is used as our allowable pressure drop when the valve is wide open.

54. 54 Valve Sizing (3) STEP #3: Calculate the valve characteristic For the system, Don’t go to the valve charts or characteristic curves and select a valve yet. Proceed to Step #4! where Q = design flowrate (gpm); G = specific gravity; and ΔP = allowable pressure drop across wide open valve.

55. 55 Valve Sizing (4) STEP #4: Preliminary valve selection Don't make the mistake of trying to match a valve with your calculated C v value. The C v value should be used as a guide in the valve selection, not a hard and fast rule. Some other considerations are:  Never use a valve that is less than half the pipe size  Avoid using the lower 10% and upper 20% of the valve stroke. The valve is much easier to control in the 10- 80% stroke range. Before a valve can be selected, decide what type of valve will be used. For the case, an equal percentage, globe valve will be used.

56. 56 Valve Sizing (5) STEP #4: Preliminary valve selection - continued The valve chart supplied by the manufacturer.

57. 57 Valve Sizing (6) STEP #4: Preliminary valve selection – continued The 2 inch valve appears to work well for the C v value at about 80~85% of the stroke range. If 1½ inch valve is used, two consequences would be experienced: the pressure drop would be a little higher than 15 psi at the design (max) flow and the valve would be difficult to control at maximum flow. Also, there would be no room for error with this valve, but the valve chosen will allow for flow surges beyond the 150 gpm range with severe headaches!

58. 58 Valve Sizing (7) STEP #5: Check the C v and stroke percentage at the minimum flow Judgments plays role in many cases. Select the valve for the range that the valve is operated most often. A C v of 6.5 that corresponds to a stroke percentage of around 35-40% is certainly acceptable. Although the pressure drop across the valve will be lower at smaller flowrates, using the maximum value gives us a "worst case" scenario. If the C v at the minimum flow would have been around 1.5, there would not really be a problem because the valve has a C v of 1.66 at 10% stroke and since the maximum pressure drop is used, the estimate is conservative. Essentially, at lower pressure drops, C v would only increase which in this case would be advantageous.

59. 59 Valve Sizing (8) STEP #6: Check the gain across applicable flowrates Gain is defined as: The difference between these values should be less than 50% of the higher value. 0.5 (3.3) = 1.65 > 3.3-2.2 = 1.1 No problem in controlling the valve. The gain should never be less than 0.50. Flow (gpm)CvCv Stroke (%)Δflow (gpm)ΔStroke (%)Gain 256.535 110-25 = 85 150-110 = 40 73-35 = 38 85-73 = 12 2.2 3.3 1102873 1503985 Gain = Δflow Δstroke or travel

60. 60 Valve Control Equal Percentage Equal increments of valve travel produce an equal percentage in flow change Linear Valve travel is directly proportional to the valve stoke Quick Opening Large increase in flow with a small change in valve stroke

61. 61 Equal Percentage a. Used in processes where large changes in pressure drop are expected b.Used in processes where a small percentage of the total pressure drop is permitted by the valve c. Used in temperature and pressure control loops Linear a. Used in liquid level or flow loops b. Used in systems where the pressure drop across the valve is expected to remain fairly constant (i.e., steady state systems) Quick Opening a. Used for frequent on-off service b. Used for processes where "instantly" large flow is needed (i.e., safety systems or cooling water systems)

62. 62 Control Valve Flow Characteristics

63. 63 Control Valve Flow Characteristics

64. 64 Inherent Flow Characteristics Linear - flow capacity increases linearly with valve travel. Equal percentage - flow capacity increases exponentially with valve trim travel. Equal increments of valve travel produce equal percentage changes in the existing C v. A modified parabolic characteristic is approximately midway between linear and equal- percentage characteristics. It provides fine throttling at low flow capacity and approximately linear characteristics at higher flow capacity. Quick opening provides large changes in flow for very small changes in lift. It usually has too high a valve gain for use in modulating control. So it is limited to on-off service, such as sequential operation in either batch or semi-continuous processes.

65. 65 Other Valves Check Valves  Restrict the flow to one direction. Relief Valves  Regulate the operating pressure of incompressible flow Safety Valves  Release excess pressure in gases or compressible fluids