Improvements to Reduce Energy Costs at the Downers Grove Sanitary District FVOA 2010 Mini-Conference August 19, 2010 Nick Menninga General Manager
Dec 18, 2015
Improvements to Reduce Energy Costs
at the Downers Grove Sanitary District
FVOA 2010 Mini-ConferenceAugust 19, 2010
Nick MenningaGeneral Manager
– 11/22 MGD average/peak full treatment capacity
– Primary clarification
– Single-stage nitrification
– Tertiary sand filtration
– Anaerobic digestion
– Sludge dewatering and aging
– Excess flow primary and disinfection to 110 MGD total
Downers Grove Sanitary District, Illinois
Aeration Project
• 50-60% of an activated sludge plant electrical usage from aeration
• Traditional efficiency improvement: fine bubble diffused air
• Many other opportunities exist for improved efficiency in aeration system
Legacy Aeration System
• Various work-horse blowers
• Various aeration tank/diffuser arrangements
• Limited instrumentation and control
Improvements Identified
• New diffusers• New high-efficiency blower• Smarter use of tankage• I&C improvements• Potential electrical savings: 20%?
Blower Addition
ABS-HST Turbo-compressor– 2400 – 6000 cfm turn-
down, matches existing process demand
– low maintenance– fits in the room– reasonable sound levels– adiabatic efficiency
improved from 50% to 80%
– old blowers used as backup or for additional air if needed
New DiffusersSanitaire membrane plate
diffusers– Full-floor coverage – not
tapered– 9” circular plates– 10 drops per tank typical,
each with manual air-flow control
– Oxygen transfer efficiency (OTE) improved from 8% to >12%
Better Use of Tankage
• Convert deep aerobic digester tank to activated sludge service
• Remove shallow aeration tanks from service, reserve for use during excess flow or future process modifications
• Difficult channel interconnection required• Part of diffuser OTE improved efficiency
Instrumentation and Control
• LDO probes (Fluoroprobes) in each tank• Blower variable speed control• Air flow meters (2 total)• Manual butterfly valves on the drops• Dissolved oxygen feedback control in
plant SCADA (Allen Bradley PLCs/Ifix)
Project Costs
• Total project cost $1.4M
• Illinois Clean Energy Community Foundation grant of $250,000
Electricity Savings
• Average whole plant energy usage tracking:– before: 1,833 kWh/MG– after: 1,305 kWh/MG– reduction: 1/3 of plant total electricity use/volume treated
• Payback at $0.08 per kwh: < 7 years
Pumping
Flo-Matchers– Liquid rheostat– 1970’s technology– Lower flow = lower efficiency– Similar efficiency characteristics to
throttling discharge valve– 2 Lift stations
Recommended Improvements
• VFDs• Level control through
SCADA (Allen Bradley PLC/iFix)
• Expected Efficiency Improvements: 50%?
Project Costs
• Wroble Lift Station: 2 pumps, each at 150 hp, Project Cost $44,500
• Hobson Lift Station: 4 pumps, each at 250 hp, Project Cost $78,500 (no need to re-wind motors)
• Illinois Department of Commerce and Economic Opportunity (IDCEO) Grant: $36,127
Electricity Savings
• Wroble: 40% reduction• Hobson: 30% reduction• Payback at $0.08 per kwh: 3 years
Digester Gas
• Used first for digester heat• Previously had engine-driven blower
– No siloxane removal– Lost cost-effectiveness after 20 years of
operation
• Desiccant dehumidification in sand filter building
• Beginning to take restaurant grease trap waste to bolster production
Desiccant Dehumidifier
• Displacing 30 tons (50 hp) of electric-driven dehumidification
• Displacing gas-fired heat (8,500 therms/yr)
• Indirect fired• Solid-wheel desiccant media -
Munters
X 3
Project Costs
• Pilot project – equipment rental $15,000
• Equipment purchase - $120,000• Installation (duct work) - $33,000• Total $168,000
Energy Savings
• Natural gas use reduction measured: 868,000 cf
• Electricity reduction estimated from audit: 350,000 kwh/yr
• Payback at $1/therm and $0.08/kwh: 4 years
HVAC• As heat and AC package units are
replaced, upgrading to heat pumps that use effluent water as heat sink/supply– Grant from Illinois Clean Energy
Community Foundation for $38,400 approved this year
– Purchasing 3 units with total capacity of 30 tons, net cost around $36,000
– Expect $9,000 annual savings, 4 year payback
• Evaluating potential for digester gas fired unit heaters/absorption chillers
Funding Sources
• Illinois Clean Energy Community Foundation (ICECF) www.Illinoiscleanenergy.org
• Illinois Department of Commerce and Economic Opportunity (DCEO) www.commerce.state.il.us/dceo
• Illinois Environmental Protection Agency Revolving Loan Fund (IEPA SRF)
www. epa.state.il.us/water/financial-assistance/economic-stimulus/index.html
Conclusions
• Opportunities Exist for Any Budget• Grant Funding is Abundant and Will
Improve Cost-effectiveness of Projects
• Projects Stand on Economic Merit Alone: Green is Green
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