Variable Speed Waste Water Pumping

Transcription

1 Variable Speed Waste Water Pumping Challenges & Opportunities Kristel Zaman Marketing & Business Development Manager Flygt Large Systems Xylem North America

2 Background VFDs have become common during the last years Pump industry is looking for ways to increase operational flexibility Budget constraints drive the need for energy savings and efficiency VFD prices have steadily gone down Reliability has gone up Intelligent pump controls are being introduced and are gaining ground

3 What s Special with Waste Water Pumping? Non-clog pumps are designed to function best at a certain speed Modern Trash - Tough stringy solids tend to cling to impeller leading edges High starting torque and operational torque needed Reduction in speed (flow) equals decrease in power, this is reduction of power that keeps a pump clog-free Pipe velocities must be above certain minimum value to avoid sedimentation of heavy solids

4 VFD + Wastewater Pump Aspects: Pump sump and system analysis Pump controls and variable speed drive Specific energy Pump mechanical & hydraulic Process control Pump sump level control

5 Pump and Pump System Aspects - Pump Sumps Floating debris Sedimentation Odor problems Clogging Start level Stop level Snoring level at cleaning

6 Pump and Pump System Aspects - High Energy Consumption or Risk of Sedimentation? When flushing the discharge line on regular basis, it is possible to reduce the minimum fluid velocity below 2.5 feet/s without having sedimentation problems.

7 Pump and Pump System Aspects Check Valves Swing Check Valves have lower friction losses at lower velocities than ball type check valves. Water Hammer VFD s can be used to soft start and soft stop pumps. Won t soft stop in power fail Minimum Speed Limitations Cooling Systems Shaft Resonance Recirculation Other factors

8 Pump Controls and VFD s External Control Programmable Control Programmed for pump alternation, level control, speed references Internal Control VFD controls each pump individually based on program inputs. Inputs are connected directly to the drive and the drive has program variables for control based on the inputs. No external controller

9 EMC and Motor Cabling Requirements Ensure a power supply free from excessive harmonics and follow good EMC (Electromagnetic compatibility) engineering practices: Built in Harmonic Filters Addition of Output Filters for long cable lengths Protect against voltage spikes due to switching frequency Use the shortest possible power cables Use shielded sensor cables and position the cable shield as close as possible to the connection terminals Separate signal and power cables by more than 1.5ft in parallel runs Use twisted sensor leads along the entire cable route Ground the cable screens at both ends

10 Specific Energy The most useful measure to compare energy efficiency in pump systems 10

11 Inflow Duration Diagram for Waste Water Pump Station

12 Process control aspects -Variable speed pump systems How can we minimize energy consumption? Reducing the total pumping head Maximizing pumping efficiency H stat 12

13 Process Control Aspects -Minimizing energy usage Specific Energy = Energy Volume H η 13

14 Energy optimization function SmartRun VFD Specific Energy value Pumping cycle 1 Pumping cycle 2 Pumping cycle Every pump cycle a new speed is being calculated based on the energy efficiency of the last cycle

15 Pump Hydraulic Aspects - Clogging is Common Long operational times tends to pack solids hard in impeller Lack of pump cycling eliminates beneficial back flushing Reduced speed reduces available energy at impeller to pass solids Soft stopping prevents clogs from dislodging naturally

16 Pump mechanical aspects - Reverse rotation 16

17 Maximizing Pump Efficiency in VFD Systems Select pumps that: Deliver sustained efficiency (self-cleaning pumps) Operates to the right of the best efficiency point at full speed in order to achieve maximum efficiency when the speed is reduced. Determining the optimal performance of a typical variable speed pump system requires the analysis of pump curve

18 Pump Sump Level Control at Variable Speed - Two Level Control Principles Traditional constant level control Optimized constant level control

19 Opportunities and Challenges + Better process control + Energy savings + Smoother operation + Reduced maintenance costs - No energy savings - Increased energy use - Increased clogging - Increased maintenance costs Conclusion: All pump system and pump station aspects need to be considered in order to achieve a well operating pump station.

20 Flood & Wastewater Pumping Complete Solution

21 PDF of the white paper

22 Questions? Thank you! Kristel Zaman Marketing & Business Development Manager Flygt Large Systems Xylem North America