Is reverse osmosis water treatment really worth the expense?

Transcription

1 Is reverse osmosis water treatment really worth the expense?

2 Introduction to UC Davis UC Davis Boiler Plant & Steam System Reverse Osmosis Technology Project Description Project Benefits

3 Opened in 1909 as University of CA Farm School Ranked 8 th greenest college in the US by Sierra Club 32,000 students, 33,000 employees 5,300 acres (largest of UC campuses) Over 950 buildings Building Age Under 25 yrs 25 to 50 yrs Over 50 yrs Percentage 40% 42% 18%

4 Over 23 mi of underground steam & condensate piping serving 90 buildings Served by 4 steam boilers at the Central Heating and Cooling Plant

5 Boiler No. Boiler Make & Type Year Installed Primary Fuel NOx Level (ppm) Capacity (lb/hr) 1 Babcock & Wilcox water-tube 1967 Nat Gas <30 100,000 2 Babcock & Wilcox water-tube 1967 Nat Gas <30 100,000 3 English water-tube 2000 Nat Gas <30 75,000 4 Rentech water-tube 2009 Nat Gas <5 150,000 TOTAL MAIN CAMPUS STEAM PRODUCTION CAPACITY (lb/hr) 400,000* *Maximum capacity determined by 400,000 lb/hr deaerator tank, boiler design operating pressure is 150 psig

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7 2009: Steam Plant Expansion project replaced an aging dealkalizer/ softener system with RO system Change prompted by new wastewater limits for EC (Electrical Conductivity) in discharge Installed two RO units, each sized for 90 GPM and 70% recovery

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9 Campus Wastewater Treatment Plant constructed in Tertiary treatment process meets strict limits for conventional pollutants, bacteria, and metals, but does not reduce salts. State Water Quality Control Board, concerned about potential impacts to agriculture and domestic water supplies, added new Electrical Conductivity (EC) limit. Campus didn t agree with the underlying science or basis for limit, but committed to actions that would reduce salt discharges to comply with EC limits. If this failed, campus would have been compelled to pursue other water supply options.

10 Amount of salt present in a liter of water: k 158k Electrical Conductivity of Sources Above (μs/cm) Our source water quality: Davis Well Water Typical Value Conductivity (μs/cm) 550 Silica Content (ppm) 30 Hardness (ppm) 100 Alkalinity (ppm) 220

11 Pre-RO System - One Month s Supply of Salt for the Plant (33,000 lbs):

12 Images courtesy of FILMTEC Membranes by Dow Water Solutions

13 RO is a type of filtration but there is a waste stream (concentrate) that carries away the contaminants Images courtesy of FILMTEC Membranes by Dow Water Solutions

14 Siemens M280 Series Highlights: GPM of high-purity water Membrane salt rejection 99% nominal Up to 98% of dissolved inorganics Over 95% of total dissolved organics All colloidal and suspended matter >0.05 micron Fully automatic

15 Unit Cost: $54,000 Installation Cost: $20,000 (including design, electrical, controls integration, and start-up) Total Initial Cost: ($54,000 + $20,000) * 2 units = $148,000

16 Pre-treatment Chemistry Chlorine Reduction Bisulfite (Sodium Metabisulfite) Dispersant/anti-scalant High-performance polymeric additives and sequestrates which inhibit silica scales, carbonate scales, and disperse colloidal particles at threshold levels Daily Sampling and Data Logging/Trending Membrane Maintenance/Replacement Approximately $3k/year for our system

17 EC Reduction in Plant Discharge Water Make-up Water Reduction Results in Significant Cost Savings: Water Cost Savings Treatment Cost Savings Fuel Cost Savings

18 Total EC reduction of 13% at WWTP influent after installing the RO system 1400 WWTP Influent Conductivity µs/cm

19 Higher Purity Water Means Higher Cycles (Less Blowdown) Less Blowdown = Less Makeup Water Makeup Water Savings Drive Other Savings

20 Condensate Makeup Feedwater Boiler Water Blowdown Steam Header DEAERATOR TANK BOILER Condensate System Losses Steam Distribution CONDENSATE TANK

21 Less Blowdown = Less Makeup Water Makeup Water Savings Outweigh Concentrate (Reject) Water Losses Comparison Blowdown % MU Water Savings (lb/hr) RO System Reject Rate (lb/hr) Before RO 20% Baseline Annual Water Cost Savings ($/year) With RO System 2% 17,137 3,672 $66,190 Annual avg boiler steam prod. rate of 75k lb/hr, 9% steam system losses, water rate of $1.00/CCF & sewer rate of $2.50/CCF

22 Less Blowdown = Less Makeup Water Reduced Alkalinity Requires Less Amines Less Blowdown = Less Chemicals Going Down Drain O2 Scavenger, Corrosion & Scale Inhibitors Costs Drop Comparison Blowdown % Makeup Water Savings (lb/hr) Annual Treatment Cost Savings Before RO 20% Baseline With RO System 2% 17,137 $102,126 Annual average boiler steam production rate of 75k lb/hr, water treatment rate reduced from approx $0.25/klb stm to $0.08/klb stm, annual savings include cost of RO membrane cleaning/replacement

23 Less Blowdown = Less Makeup Water Less Makeup Water = Less Heating Energy OR Less Blowdown = Less Energy Going Down the Drain RO System Pump Power Becomes Insignificant Comparison Blowdown % MU Water Savings (lb/hr) RO Pump Power Consumption ($/year) Before RO 20% Baseline Annual Fuel Cost Savings ($/year) With RO System 2% 17,137 $726 $396,692 Annual average boiler steam production rate of 75k lb/hr, gas rate of $0.70/therm, and elec rate of $0.10/kWh

24 Total Annual Potential Savings Summary Reject Water and Pump Power Losses insignificant at high cycles Comparison Blowdown % MU Water Savings (lb/hr) Total Annual Savings ($/year) Before RO 20% Baseline Annual GHG Savings (tons CO2/year) With RO System 2% 17,137 $564,283 2,834 Annual average boiler steam production rate of 75k lb/hr, GHG conversion of metric tons CO2/therm of natural gas

25 Cost savings dependent on current boiler cycles: Blowdown Level Reduction MU Water Savings (lb/hr) Estimated Total Savings ($/yr) Simple Payback (Years) 20% to 2% 17,000 $565, % to 2% 11,700 $375, % to 2% 6,800 $208, Assuming boiler annual average steam production rate of 75,000 lb/hr, steam system losses of 10%, costs of $0.10/kWh Elect, $0.70/therm NG, $1/CCF Water, $2.50/CCF Sewer

26 Condensing Economizer Boiler Flue Gas Heat Recovery Project