Variable Frequency Drives for Water/Wastewater. Discussion on Pump Optimization Principles and Need to Know Drive Technology

Transcription

1 Variable Frequency Drives for Water/Wastewater Discussion on Pump Optimization Principles and Need to Know Drive Technology

2 Pumps in Water Wastewater 2

3 WWW Challenges: Drivers/Trends Demand for WWW Age of infrastructure Legislative compliance Reduced financial resources Energy efficiency awareness Energy use Typical wastewater process 0.3% 0.1% 1.4% 0.5% energy usage breakdown Aeration 3.2% 3.9% 8.1% Collection Anaerobic Digestion Lighting and Buildings 14.2% 14.3% 54.1% Belt Press Clarifiers Grit RAS Chlorination Process = 91.9% Gravity Thickening 3

4 Water energy use 71% of consumed electricity is used to turn motors 65% of this energy is used for fluid applications Wastewater energy use

5 Finnish Technical Research Center Report: Expert Systems for Diagnosis of the Condition and Performance of Centrifugal Pumps Evaluation of 1690 pumps at 20 process plants: Average pumping efficiency is below 40% Over 10% of pumps run below 10% efficiency Major factors affecting pump efficiency Throttled valves Pump over-sizing Seal leakage causes highest downtime and cost 5

6 System Curve Uncertainty Results in Uncertain Pump Operation - and higher costs 6

7 Pump Curves 7

8 Pumps System Overview and Fundamentals 8

9 Overview The pumping system: Components Pumps Motors, engines Piping Valves and fittings Controls and instruments Heat exchangers Tanks Others End-use Water treatment Wastewater treatment Water distribution Power generation Irrigation 9

10 Overview, continued Electric utility feeder Transformer Motor breaker/ starter Adjustable speed drive (electrical) System Approach Component optimization involves segregating components and analyzing in isolation System optimization involves studying how the group functions as one as well as how changing one component can help the efficiency of another Motor Coupling Pump Fluid System Served Process(es) 10

11 Pump Fundamentals There are two basic types of pumps: 1. Centrifugal 2. Positive Displacement (PD) Use a rotating impeller to increase velocity of a liquid and its stationary components direct discharge flow to convert velocity to increased pressure Types include axial, mixed flow, and radial Move a set volume of liquid and pressure is obtained as the liquid is forced through the pump discharge into the system Types include piston, screw, sliding vane, and rotary lobe 11

12 Pump Fundamentals, continued Centrifical Pumps Impart energy to the liquid by increasing its speed in the impeller and then converting the speed to pressure through diffusion in the volute. 12

13 Pump Fundamentals, continued PD Pumps Impart energy by applying mechanical force directly to the liquid through a collapsing volume 13

14 Energy Efficiency in Pumps Load Characteristics Water Wastewater Load Characteristics Variable Torque Constant Torque Constant Power Typical Applications Centrifugal Pumps and Blowers Positive Displacement Pumps, Blowers, Mixers, and Chemical Feed Pumps No applications Energy Savings Potential Substantial Potential Largest of all VFD applications Lowest Potential No Potential The Main Target ( first priority) The Next Step ( second priority) 14

15 Pump Fundamentals, continued Centrifical pumps are constant head devices, where head loss causes a pressure drop. Frictional head loss increases with the square of velocity change of the liquid in the pipe. Static head is the energy needed to overcome an elevation or pressure difference between the suction and discharge vessels. In most cases: 15

16 Pump Fundamentals, continued System Head Curve Produced by US DOE PSAT Software Friction Head Static Head 16

17 Pump Fundamentals, continued Friction May occur in pump systems due to irrecoverable hydraulic losses in: Piping Valving Fittings (e.g., elbows, tees) Equipment (e.g., heat exchangers) Used to control flow or pressure by: Automated flow and pressure control valves Orifices Manual throttling valves 17

18 VFD Benefits with Pumps 18

19 Energy Efficiency in Pumps Motor Costs 19

20 Energy Efficiency in Pumps Energy Wastes How your money is wasted! Car example : try to regulate the speed of your car keeping one foot on the accelerator the other on the brake. Pump example : try to adjust the pump output running the motor at full speed control the flow with a throttle valve Still one of the most common control methods in industry.. with a considerable waste of energy 20

21 VFD Benefits with Pumps Physical Laws for Centrifugal Loads Its Pure Physics: Due to the laws that govern centrifugal pumps, the flow of water decreases directly with pump speed Affinity laws of centrifugal loads : Flow = f (motor speed) Pressure = f (motor speed) 2 Power = f (motor speed) 3 21

22 VFD Benefits with Pumps Physical Laws for Centrifugal Loads A motor running at 80% of full speed requires 51% of the electricity of a motor running at full speed. 22

23 VFD Benefits with Pumps Physical Laws for Centrifugal Loads A motor running at 50% of full speed requires 12.5% of the electricity of a motor running at full speed. 23

24 VFD Benefits with Pumps Physical Laws for Centrifugal Loads A small reduction in speed produces a significant reduction in power Relevant applications : Pumps The resisting torque of centrifugal pumps varies with the square of the speed : T = kn² Power is a cubed function P = kn³ EX 50HP 10Hrs/day, 250 With 15% average speed reduction ATL = $7,460 VFD = $4,188 Savings = $3,272 Today, less than 10% of these motors are controlled with Variable Speed Drives 24

25 Efficiency of Pumping Systems 25

26 Efficiency of Pumping Systems Equations for efficiency Pump Energy Usage Pump Efficiency Measurement ( Q* H ) kw 16,667 kw kw = = * MGD (5308* η * η * η ) Q Motor Pump Drive Q = Flow( gpm) H = Head( ft) η = efficiency For Water Wastewater PSI conversion to ft = PSI * 2.31 η η Motor * η Wire to water Pump * η Drive ( Q * H ) = (5308* kw ) ( Q * H ) = (5308* kw ) 26

27 Sample Pump Calculations Actual Pump Data Single Pump Running Measurement Measured VFD Speed 54.1 Hertz Measured Power 32.3 kw Measured flow 716 GPM Measured head 74.5 PSI The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Two Pumps Running Measurement Measured VFD Speed 48 Hertz Measured Power 82.5 kw Measured flow 1452 GPM Measured head 75 PSI Three Pumps Running Measurement Measured VFD Speed?? Hertz Measured Power kw Measured flow 5125 GPM Measured head 79.4 PSI 27

28 Sample Pump Calculations FREQ KW PSIG TDH GPM GPM X TDH KW X 5308 EFFICIENCY? The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. PUMP QTY three pumps two pumps one pump FREQ KW GPM KW X EFFICIENCY kw/mgd PUMP QTY? three pumps two pumps one pump 28

29 VFD Benefits with Pumps Other Benefits In addition to Energy Saving, using a VFD has many other advantages: Less mechanical stress on motor and system Less mechanical devices - Less Maintenance Process regulation with PID regulators, load management functions Reduce noise, resonance avoidance Performance and flexibility, range settings, above base operations Easier installation and settings, drive mechanics Can be controlled with Automation, Communication networks 29

30 Steps to Obtain Pump Optimization 30

31 Pump Optimization Complete a detailed Pump Assessment Pumps are usually consuming more energy than necessary: The pump is oversized and has to be throttled to deliver the right amount of flow. Energy is lost in the valve. Pumps that are not running close to their best efficiency points (BEP) operate at lower efficiency. Throttled pumps usually fall into this category. Pumps are running with by-pass, or recirculation, lines open. Pumps are running although they could be turned off. The pump is worn and the efficiency has deteriorated. The pump/system was installed or designed incorrectly (piping, base plate etc.) 31

32 Pump Optimization Complete a detailed Pump Assessment To determine whether these reasons apply, some basic information is needed: Actual system demand (flow and pressure) Operational flow rate as a function of time (the duration curve) Flow controls The pump curve Where the pump operates on the curve 32

33 Process Energy Optimization Automation is the Key Develop consistent and appropriate milestone and deliverable expecta4ons Standardize program schedule tracking requirements Establish key energy management performance metrics Produce meaningful reports that allow for clear and concise decision- making Install addi4onal monitoring equipment as needed 33

34 Considerations for Variable Frequency Drives for Water and Wastewater 34

35 VFD Topics Type(s) Enclosure / Environment / Packaging Harmonics/ Harmonic Mitigation IEEE 519 Accessability Sustainability 35

36 VFD Considerations The industry has standardized on PWM 6 pulse drives. Where 6 Pulse refers to the Front end of the Drive and a bridge of 6 diodes converting incoming AC to DC power. A DC Bus (capacitor) Insulated Gate Bipolar Transistors (IGBT) as the output components. The output of which generates a simulated RMS waveform with a constant V/Hz ratio. 36

37 One of These 37

38 Packaging Open Enclosed MCC 38

39 Harmonics Reduction This continues to be a big topic for us in Water and Wastewater The Motor loads on VFD s are a large percentage of the total load. Many Consultants have standardized on designs by HP requiring Line reactors or Multipulse Drives (typically 18 pulse). There are multiple sloutions One size does not fit all. Schneider Electric offers as standard 18 pulse VFD, Matrix Filter VFD and Active Harmonic Mitigation. 39

40 18 Pulse Drive Using the same 6 Pulse Inverter STD 6 Pulse Inverter Line Reactor 18 pulse Diode Bridge Phase Shifting XFMR 40

41 Matrix Filter Drive using the same 6 pulse Inverter STD 6 Pulse Drive Matrix Filter 41

42 Matrix Filter Drive Matrix Filter Drive Harmonic Mitigation as good or better than 18 pulse. Better Mitigation given Voltage Imbalance Footprint of Drive is Typically smaller than 18 Pulse. Efficiency of Drive is better than 18 Pulse Losses of 18 Pulse bridge + Transformer + Line Reactor > Matrix Filter. Cost is Typically Lower than 18 Pulse Output to the Motor is Identical. What s Not To Like? 42

43 Data on side by side comparisons of 18 Pulse and Matrix Filter. 43

44 Accusine used with one or many 6 pulse drives 44

45 The Variable Frequency Drive for W/ WW The Altivar 61 is our Standard 6 pulse inverter for variable speed applications used in centrifugal pump and fan / blower applications offering the highest level of features, functions, and flexibility. This same inverter is the heart of our configured enclosed applications, 18 Pulse Drives, Motor Control Centers and our new Matrix Filter Drive.. All the Inverter parts, programming, troubleshooting, wiring, interfacing, etc is common. 45

46 Other Drive/System Application Considerations Enclosed Drive or Packaged Drive Short Circuit Current Rating. SE = 100k amps as standard Power Loss Ride Through especially for pump stations. SE meets Semi F47 standards Communication Capabilities SE offers Modbus Serial and 11 additional Protocols as options. Built in Web Server and diagnostic web displays with Ethernet. 46

47 Appendix 47

48 Standard Six Pulse Inverter in 6 pulse Drive Drive in MCC 18 Pulse Matrix Filter Drive 48