Cooling Tower Water Conservation: Simple Strategies ...€¦ · Tampa Convention Center • Tampa,...

Tampa Convention Center • Tampa, Florida

Cooling Tower Water Conservation:Simple Strategies & Advanced Treatment

Track 2 – Core Energy Technologies Advanced Water Management

Eric ElamWater Savers LLC, RTS Water

August 15th, 2017

Energy Exchange: Connect • Collaborate • Conserve2

Cooling towers come in all sizes

Energy Exchange: Connect • Collaborate • Conserve

Cooling Tower Water Use

Overflow

Make-up

Fill Material

Fan and Motor

Drift Eliminators

Process Return

To Process

BlowDown

ConductivityController

Typical Cooling Tower Flow Diagram

Six Ways of Water Loss• Evaporation• Blowdown• Drift loss• Wind loss• Overflow• Leaks

Water Use Equations for Cooling Towers

MU = E + BD + D + LWhere

MU = MakeupE = EvaporationBD = BlowdownD= Drift and wind loss - accounts for less than 0.001% of water use

L = Leaks, overflows, and other losses- Should be controllable with proper fill valves and routine maintenance

E = 1% x CWFR x ∆T/10 x 60min/hr x Annual Runtime Hours

WhereE = EvaporationCWFR = Condenser Water Flowrate∆T= Temp Change Across Tower- Generally towers are designed at 10oF ∆T - Higher ∆T generally translates to higher evaporation, but towers experience shorter

runtimes in order to meet load requirements

Annual Runtime Hours = Actual operating hours- Can be estimated using ASHRAE Full Load Equivalent Hours

Full Load Equivalent Cooling Hours by RegionTampa Area = 3,068 FLE Cooling HoursRegion Specific FLE Cooling Hours:

• Pacific Northwest = 100-700• Northern CA = 200-800• Northeast = 300-900• Midwest = 700-1200• Mid-Atlantic = 1000-1500• Southern CA = 1200-2000• Southeast = 1500-2300• Texas & Florida = 1700-4000• Hawaii = 5000

Be Mindful of System Redundancy

Evaporation is a function of Cooling LOAD!

So, Water Conservation opportunities result primarily from a reduction in

blow-down losses by increasing cycles of concentration.

0 1 2 3 4 5 6 7 8 9

10 11 12

1 2 3 4 5 6 7 8 Cycles of Concentration

2.0 kWh/ton-hr.

1.5 kWh/ton-hr.

1.0 kWh/ton-hr.

0.5 kWh/ton-hr.

Process

Cooling Tower Water UseGallons per Ton-Hour

Water Quality Dictates Cycles of Concentration Limits

• pH• TDS (Total Dissolved Solids)• TSS (Total Suspended Solids)• Calcium Hardness• Total Silica• Organic Contamination

What Determines the Amount of Blowdown?• There are many factors that

limit cooling water concentration

• The blowdown required is the least needed to satisfy ALL of the constraints.

• The only control the operator has to meet these limits is blowdown.

Typical CWS Water Chemistry Limits

Parameter Limit Constraint

Conductivity < 4000 uS

Towerwarranty

Calcium > 75 ppm

Corrosion Control

LSI < 2.5 Calcium Scale Control

Silica < 180 ppm

Silica ScaleControl

MagnesiumSilicate <25,000

MgSiO2 ScaleControl

pH 8 – 9 Corrosion ControlDischargeLimits

Cycles of Concentration (CoC)A Measurement of Cooling Tower Water Efficiency

CoC = MU / BDBD = E / (CoC – 1)CoC = κ condenser / κmake-up

Whereκ = (kappa) Conductivity in µS/cm, or µmhos

- Condenser water conductivity is presumably at or near the blow-down setpoint- Make-up water conductivity will fluctuate seasonally and depends on water

sourcing

Cost Savings & Water Conservation Strategies

Sewer Exemption Sub-Metering

Evaporation Credits are available from most Water/Sewer Providers, especially in metropolitan areas.

Each Provider may have a different policy/procedure for obtaining the evaporation exemption, and may also impose significant fees/permitting requirements in effort to recover lost revenue.

Evaporation Credits are NOT a water conservation measure! But they can result in significant cost savings opportunities.

In Tampa area, the cost savings can equate to nearly $16 per Ton annually. (Lower Rate, Higher Cooling Load)In DC area, the cost savings can equate to nearly $18 per Ton annually. (Higher Rate, Lower Cooling Load)

Traditional Chemical Treatment

Traditional chemical treatments typically involve 3 main components:

Anti-scalant – to combat against scale forming compounds such as calcium, magnesium

Biocide – to combat against algae, bacteria, and other biofouling contaminants

Corrosion Inhibitor – to prevent degradation of mechanical components and piping.

Depends on Regional Make-up Water Quality

Traditional Chemical Treatment

Contact your Chemical Treatment Provider about opportunities for High Cycle water treatment programs,

and real-time monitoring capabilities.

Major treatment providers get very comfortable operating in the 3 cycle range.

THIS MEANS 50% of Evaporative load is lost as Blow-down Waste

What if there was ANOTHER OPTION?

Treat water from the source!

Advanced Water Treatment SolutionsPartial Softening

Softeners are designed to remove calcium hardness• They do so by exchanging with sodium, which

results in higher conductivity of make-up water, but lowered calcium hardness

• Allows for an increase of blow-down set-point• Why not make up with fully softened water?

Corrosivity is increased, which can shorten life of capital equipment.

Partial Demineralization

Demineralization = Reverse Osmosis• Softeners will not reduce conductivity or remove

silica, so demineralization approach may be an effective solution

• Partial De-min utilizes pre-filtration and softening, and ultimately generates ideal condenser water make-up quality by blending RO permeate with filtered water

• Can achieve 15+ cycles of concentration, while effectively maintaining corrosion rates

MMF MMF SOFT SOFT

From Ground Water

System

WMBrineTank

ChemTank

Sensors

To Softeners

SensorsFrom softener, filter backwash, and nanofilter discharge

CityWater

(2 inch copper or steel)

Nanofilter Unit BreakTank

Advanced Water Treatment SolutionsSide-stream Filtration

Side-Stream Filtration DOES NOT Save Water• Allows for better high cycle cooling tower

operation by filtering out debris, organics, and some bacterial contaminants

• Reduces bio-film on heat transfer surfaces• May result in heat transfer efficiency gains

of 5-15% depending on current tower conditions

• But, will actually result in increased water consumption due to filter backwashing

Advanced Water Treatment Solutions

Real-time Monitoring & BAS Integration with Advanced Controllers

BAS Integration Capable utilizing BACNet or MODBUS• Allows for real-time monitoring of system conditions• Creates alarm case conditions for targeted maintenance• Provides for accurate measurement and verification of

system performance, with over 30 critical data points

• MCRD Parris Island (Parris Island, SC)– Eleven locations with small packaged Partial Softening and Side-

stream Filters (100-300 ton chiller systems)– One location with Centralized Partial Softeners and localized Side-

Stream Filters (4x200 ton chiller system)

MCRD Parris Island

• NMSHA (Beaver, WV)– Centralized Partial Softening and SSF (750 ton chiller system)

• Corpus Christi Army Depot (Corpus Christi, TX)– Phase 1 – (4 space cooling systems ~2,730 ton total cooling capacity)

• Central Demineralization Plant with Distributed Make-up• Localized Side Stream Filtration, • BAS Integration

– Phase 2 – (10 process cooling towers ~500 ton equiv. each)• Partial Softening• Side-stream Filtration

CCAD – Phase 1

CCAD – Phase 2

• Department of Interior HQ (Washington, DC)– Groundwater Collection– Partial Demineralization– Side-stream Filtration– BAS Integration

DOI HQ

• Several underground sumps pits to capture ground water• 2-large sump pumps discharging water to storm sewer system

Its what you cant see that matters the most

DOI HQ

• Water flow were measured at 30 gallons per minute• 43,200 Gallons per day or 15,768,000 Gallons per year potential• Cooling tower annual make-up is 6,500,000 gallons per year

Measurement and Verification

DOI HQ

Ground Water Collection and Re-Use

DOI HQ

Water Reclamation System Overview

DOI HQ

Ground Water Filtration System

DOI HQ

Eric ElamVice President – Design & EngineeringWater Savers LLC, RTS Watereelam@watersaversllc.com

THANK YOU

Cooling Tower Water Conservation: Simple Strategies ...€¦ · Tampa Convention Center • Tampa,...

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