Energy-Efficient Waste Water Treatment For American Electric Power May 17, 2017 Kelly Kissock, Ph.D., P.E. Director: University of Dayton Industrial Assessment Center 937-229-2835 kkissock@udayton.edu
Industrial Assessment Center Program Sponsored by U.S. Department of Energy (DOE) Began during 1970 s energy crisis 28 centers at universities throughout the U.S. 20 no cost assessments per year for mid sized manufacturers Goals Help industry be more resource efficient and costcompetitive Train new energy engineers Advance practice and science of energy efficiency
University of Dayton Industrial Assessment Center Conducted 970+ assessments since 1981 Savings opportunities: 12 Simple payback: 2 years Identified savings: 12% Implemented savings: 6%
All Waste Water Treatment Facilities Qualify for Free IAC Energy Assessment San Diego State IAC: 9 free WWT assessments 49 energy efficiency opportunities $3,278,437 per year in savings 1/3 implemented after 9 months. San Francisco State IAC 10 free WWT assessments 76 energy efficiency opportunities $3,746,308 per year in savings 2/3 implemented after 9 months. If interested contact Kelly Kissock, Ph.D., P.E. 937-229-2835 kkissock@udayton.edu
Waste Water Treatment Steps
Electrical Consumption Benchmark Data Energy consumption increases with level of treatment and decreases with plant influent level
Biggest Energy Users Pumping 15% Aeration 64% Activated Sludge Process
Electrical Power: W e W e = V P / [Eff pump x Eff drive x Eff motor x Eff vfd ] V = volume flow rate P = pressure gain to overcome inlet/outlet effects and friction Eff = efficiencies of pump/fan, drive, motor and VSD
Fluid Flow System Saving Opportunities Reduce pump P Employ energy-efficient flow control V Improve pump, motor or VFD efficiency
Reduce Pump P
Use Large Diameter Pipes W friction = V P friction P friction =k / D 5 W friction = V k / D 5 Work to overcome friction varies inversely with 5 th power of pipe diameter Doubling pipe diameter reduces pump power by: 1- (1/2) 5 = 97% 2 inch 18 ftwg 4 inch 0.6 ftwg
Use Smooth Pipes W friction = V P friction P friction ~ friction factor f f steel = 0.021 f plastic = 0.018 Plastic pipe reduces pump power by: (0.021 0.018) / 0.021 = 14% Material Roughness (m) Glass, plastic Smooth Copper, brass, lead 1.5 x 10 6 (tubing) Cast iron uncoated 2.4 x 10 4 Cast iron asphalt 1.2 x 10 4 coated Commercial steel or 4.6 x 10 5 welded steel Wrought iron 4.6 x 10 5 Riveted steel 1.8 x 10 3 Concrete 1.2 x 10 3
Use Gradual Elbows and Fittings W friction = V P friction P friction ~ loss coef k k std = 0.29 k long rad = 0.18 Long-radius elbows reduce pump power by: (0.29 0.18) / 0.29 = 38%
Minimize Elevation Gain: Increase Initial Reservoir Level W elev = V P elevation difference between inlet and outlet Reducing elevation difference reduces pump power by: (20 15) / 20 = 20%
Employ Energy Efficient Flow Control
Flow Control Systems designed for peak flow Systems operate at less than peak flow Use energy efficient method to control (reduce) flow
Energy Inefficient Flow Control By-pass Valve By-pass loop (No savings) Flow Control Valve (Small savings) Intermittent Flow (Proportional savings)
Energy-Efficient Flow Control Trim impellor for constant-volume systems VFD for variable-volume systems
Pump and System Curves P Pump Curve System Curve P 1 Operating Point W f = V P V 1 V
Bypass Flow: Zero Energy Savings P Pump Curve System Curve Wf at low flow requirement Wf at peak flow requirement V 2 = V 1 V When bypassing, V and P through pump are constant Bypass power = 100% of peak power Savings compared to peak = 0%
Throttling: Small Energy Savings Throttled System Curve P Design System Curve Wf at low flow requirement Wf savings Wf at peak flow requirement V 2 = V 1 / 2 V 1 V With throttling, V decreases but P increases Throttling power = 67% of peak power Savings compared to peak = 33%
Intermittent : Proportional Energy Savings P Pump/Fan Curve System Curve Wf at peak flow requirement Wf average Wf savings V 2 = V 1 / 2 V 1 V Pump operating time is proportional to flow Intermittent power = 50% of peak power Savings compared to peak = 50%
VFD : Big Energy Savings P Pump/Fan Curve System Curve Wf at peak flow requirement Wf savings Wf at low flow requirement V 2 = V 1 / 2 V 1 V Pump power is proportional to cube of flow Impellor/VFD power = (V 2 /V 1 ) 3 = (1/2) 3 = 12% of peak power Savings compared to peak = 88%
Flow Control Savings Summary at 50% Flow Bypass: 0% Throttling: 34% Intermittent: 50% VFD: 88%
Should Make Intuitive Sense Bypass (all the lights on, all the time) Throttling (pedaling bike hard with brakes on) Intermittent pump/fan operation (tortoise and hare)
Eliminate Intermittent Pumping: Pump Slow, Pump Long More energy to pump at high flow rate for short period than low flow rate longer Pump slow, pump long Example: Current: Two pumps in parallel for 10 hours/day Recommended: One pump for 11 hours/day Fraction Savings: 14%
Optimize VFD Control Most variable flow systems use pressure as control variable for VFD Savings depend on location and setpoint of pressure sensor Savings maximized when pressure is dynamically reset based on valve position
Variable Flow Pumping Control: Pressure Sensor at Discharge
Variable Flow Pumping Control P at Intermediate End Use
Variable Flow Pumping Control P at Most Remote End Use
Variable Flow Pumping Control Maximum Open Valve Pressure Reset
Variable Flow Pumping Control Summary P A B C D A: Pset,discharge (Worst) B: Pset,midway C: Pset,remote D: Pset,max valve (Best) V 2 = V 1 / 2 V 1 V
WWT Plants: Use Advanced Digital Sensors for Control Analog sensors age over time and lose calibration New digital sensors remain calibrated and transmit continuous data to improve control
IAC Experience with VFDs at WWT plants
Resize Over-sized Pumps Pump operating at offdesign point M at Eff = 47% Replace with properly sized pump at Eff = 80% Savings: 1-(.47/.80) = 41%
Refurbish Inefficient Pumps Pump impellors degrade over time Pump efficiency and capacity decline Mechanical refurbishment: +5.4% Sandblasting and coating: +6.2% Impeller coating: +1.5%
Resize Over-sized Motors Motor efficiency declines at low loads. Motor power factor declines at low loads.
IAC Experience with Oversizing at WWT Plants
Energy Efficient Motors
Motors: Energy Cost >> Purchase Cost Purchase and Energy Costs (20 hp motor at 8,000 hours/year over 20 years) 150,000 120,000 ($) 90,000 60,000 30,000 0 Purchase Energy 20-hp, 93% efficient motor costing $1,161 Motor 75% loaded, 8,000 hrs/year, $0.06 /kwh Annual energy cost = 20 hp x 75% x.75 kw/hp / 93% x 8,000 hr/yr x $0.06 /kwh = $5,806 /yr Over 20-yr life, energy cost is 100x greater than purchase cost!
1% Improvement in Efficiency Equals Purchase Cost Consider 20 hp motor, 93% efficient, 80% loaded, 6,000 hr/yr, 10 years Cost of electricity If efficiency = 93%, then 10 year electricity cost = $77,500 If efficiency = 94%, then 10 year electricity cost = $76,600 Savings = $77,500 - $76,600 = $900 Cost of motor Purchase cost = $1,000 Thus, Purchase premium efficiency motors!
Replace or Repair? Size Efficiency Cost Efficiency Cost Rew-Rep Rep-Rew S. P. (hp) Rewound Rewound ($) Engy Eff Engy Eff ($) ($/yr) ($) (yr) 1 73 220 84.6 275 68 55 0.8 5 82 330 89.8 432 191 102 0.5 10 84.7 500 91.7 686 324 186 0.6 15 85.5 550 92.6 911 484 361 0.7 20 87.3 600 93 1,071 505 471 0.9 30 88.2 760 93.8 1,553 731 793 1.1 50 90.6 980 94.4 2,482 800 1,502 1.9 60 90.8 1,116 94.8 3,280 1,004 2,164 2.2 75 91 1,320 95.3 4,476 1,339 3,156 2.4 100 91.2 1,650 95.4 5,645 1,738 3,995 2.3 150 91.8 2,400 95.5 8,624 2,279 6,224 2.7 200 92.3 2,650 95.7 10,680 2,771 8,030 2.9 250 92.9 2,860 95.8 13,043 2,933 10,183 3.5 300 93.1 3,080 96.1 14,084 3,621 11,004 3.0 500 92.8 4,400 96.6 25,725 7,630 21,325 2.8 Assuming 80% loaded, 6,000 hr/yr, $0.10 /kwh
Payback for Replacing Rather than Rewinding Motors Operating Hours: 4,000 hrs/year Simple Payback (Years) 10 9 8 7 6 5 4 3 2 1 0 $0.05 /kwh $0.08 /kwh $0.11 /kwh 0 50 100 150 200 250 Motor HP Source: US DOE Motor Master+ 4.0
Payback for Replacing Rather than Rewinding Motors Operating Hours: 8,000 hrs/year Simple Payback (Years) 10 9 8 7 6 5 4 3 2 1 0 $0.05 /kwh $0.08 /kwh $0.11 /kwh 0 50 100 150 200 250 Motor HP Source: US DOE Motor Master+ 4.0
WWT Plant Pumping Summary Treatment plants use multiple pumps to move water through treatment stages Minimize friction and lift Control flow with VFDs with advanced controls Right-size pumps and motors Repair degraded pumps Replace rather than repair motors
Aeration Systems Aerators maintain oxygen levels for aerobic digestion Aeration is typically most energy intensive processes: thus prime target for energy savings Three main types of aeration systems Activated Sludge Process
Mechanical Surface Aeration
Oxidation Ditch Aeration
Blowers push air through course, medium or fine pore aerators Diffused Air Aeration
Fine-pore Most Energy-Efficient Way to Add Oxygen to Water
Aeration Savings Opportunities Course to fine pore reduced blower energy by 30% with 24 month payback Replace 50% efficient positive-displacement rotary lobe blower with 70% efficient centrifugal blower Control aeration VFDs using Biochemical Oxygen Demand (BOD) Automatic DO control systems save 20-40% of aeration energy and usually prove cost-effective for activated sludge installations. Take aeration tanks out of service during periods of low flow, low organic loading, and/or high temperature.
Pre-treatment Savings Opportunities Sequence Influent Screen Blowers Based on Influent Flow
Disinfection Savings Opportunities Install a Low-Pressure High-Intensity Ultraviolet (UV) Radiation Disinfection System Match UV Lights to Flow
Solid Stream Treatment About 2/3 of plants use anaerobic digestion to break down solid sludge sediment Biogas produced as byproduct of solids stabilization is about 65% methane, and 35% CO 2 and can be burned. About 1/3 of plants use nitrification instead of anaerobic digestion to break down solid sludge sediment Waste treated by nitrification is great fertilizer
Solid Stream Saving Opportunities Pre-treat solid sludge with focused electric pulse to improve biogas output 3x to 6x ratio of energy produced as heat and biogas to electricity treatment with 4 year simple payback Use biogas to generate electricity or provide heat to maintain digester temperatures Sell waste treated by nitrification as fertilizer or burn for process heat
CO 2 Emission Abatement Potential Xylem
CO 2 Emission Abatement Potential Xylem Key findings: Significant emissions abatement does not require new technologies or carbon tax policy. All that is required is accelerated adoption and reinvestment in high efficiency technologies Primary barriers are awareness of opportunity and willingness to adopt solutions with higher capital investment but lower operating costs.
References and Photo Credits Recent Advancements in Wastewater and Water Treatment Technologies, C. Deppe and D. Kasten, IAC Directors Meeting, 2016 Energy Savings Opportunities in a Waste Water Treatment Facility, West Virginia IAC, 2016 Energy Efficiency Experience in Hawaii, A. Ganji, San Francisco State University IAC, IAC Directors Meeting, 2013 Energy Efficiency in Wastewater Treatment in North America_ A Compendium of Best Practices and Case Studies of Novel Approaches-WERF, 2011 Powering the Wastewater Renaissance: Energy Efficiency And Emissions Reduction In Wastewater Management, Xylem Inc., 2015 Following the Flow: An Inside Look at Wastewater Treatment, Water Environment Federation, 2009
Thank you! If interested in free energy assessment please contact: Kelly Kissock 937-229-2835 kkissock@udayton.edu