Basic Cooling Water Treatment principles John Cowpar Area Manager GE Water and Process Technologies.

Basic Cooling Water Basic Cooling Water Treatment principlesTreatment principles

John CowparArea Manager

GE Water and Process Technologies

USING WATERUSING WATER

POTENTIAL PROBLEMSPOTENTIAL PROBLEMS

CORROSION

DEPOSITION - Fouling Biofouling Scaling

Scale Formation Scale Formation

Results in loss of heat transfer efficiency Increased running costs Danger of under deposit corrosion Increased maintenance costs

Danger of bacteria Health implications

CorrosionCorrosion

Destruction of plant increased maintenance costs

Fouling loss of efficiency due to increased

pumping costs loss of heat transfer efficiency

Increased Biological Nutrients fouling and health implications

FoulingFouling Loss of heat transfer efficiency

increase in running costs Under deposit corrosion

increase in maintenance requirements Increased biological nutrients

health implications Blockages in system

increased operating costs and downtime

Objectives of Water Objectives of Water TreatmentTreatment MINIMISE SCALE MINIMISE CORROSION MINIMISE FOULING MINIMISE BIOFOULING MAXIMUM SAFETY MAXIMUM EFFICIENCY NON-POLLUTING

WHAT CAUSES OUR PROBLEMS?

DISSOLVED SOLIDSDISSOLVED SOLIDS

e.g. CALCIUM MAGNESIUM SODIUM CHLORIDE BICARBONATE SULPHATE SILICA IRON

DISSOLVED GASESDISSOLVED GASES

e.g. OXYGEN CARBON DIOXIDE NITROGEN SULPHUR DIOXIDE

SUSPENDED MATTERSUSPENDED MATTER

DUST/DIRT CONTAMINANTS e.g. OIL BIOLOGICAL e.g. ALGAE,

FUNGI, BACTERIA

TYPICAL WATER ANALYSIS CHARTTYPICAL WATER ANALYSIS CHART

Water Analysis ResultpH 7.7Colour 3.00 HAZENTurbidity 9.00 F.T.U.Solids - Suspended 5 mg/lChloride as Cl 44 mg/lAlkalinity as CaC03 144 mg/lAmmoniacal Nitrogen as N 0.140 ug/lIron (Total) as Fe 311 ug/lManganese (Total) as Mn 65 ug/lNitrate as N 4.0 mg/lTotal Hardness as CaC03 207 mg/lSulphate as S04 62.3 mg/lSilica - Reactive as Si02 6.9 mg/lSulphide as S 0.015 mg.lCarbon Dioxide - Free 2.50 mg.lSolids - Total Diss. at 180C 347 mg/lD.O. Concentration (Field Det.) 10.7 mg/lColiforms <10 /100mlE. Coli <10 /100mlFaecal Streptococci <1 /100mlSulphite Red. Clostridia 300 /20ml

HardnessHardness

Hardness is due to calcium and magnesium salts dissolved in water All hardness salts are less soluble in hot

water than in cold water (they show inverse solubility)

Different hardness salts have different levels of solubility

Hardness is normally reported as calcium carbonate

EVAPORATION

WINDAGE

BLEED

MAKE UP

M = E + W + B

Useful EquationsUseful Equations

E=R/100 x Temp Drop(degF)/10

W=R x 0.2/100 ( Forced Draught)W=R x 0.6/100 (Natural Draught)

B=E/(C-1) -W

M=E + B + W

SCALE FORMATIONSCALE FORMATION

SCALE CAN BE CONTROLLED BY:

PRE-TREATMENT

CHEMICALS

CONCENTRATION FACTOR

CORROSIONCORROSION

Iron ore is found in nature and requires a large input of energy to convert it into steel.

Steel corrodes in order to get back to its natural (lower energy) state

Corrosion is an electrochemical process

CORROSION CAN BE CORROSION CAN BE CONTROLLED BY:CONTROLLED BY:

REMOVAL OF OXYGEN ?

ADDITION OF CHEMICALS

CONTROL OF pH

BiofoulingBiofouling

What is Biofouling caused by?

• FUNGI

• ALGAE

• BACTERIA

FOULING/BIOFOULINGFOULING/BIOFOULING

Can be controlled by

Filtration Control of Concentration Factor (bleed) Dispersants Biocides

Customer Training WT200C Page 23

Open CoolingOpen Cooling

When evaporation occurs, the heat of evaporation is used to drive off the vapour

The loss of this energy results in a cooling effect in the water

Pure water is evaporated (gases may also be lost)

Dissolved solids remain in the water


Cooling WaterCooling Water

WATER DROPLET COOLS BY:

EVAPORATION

RADIATION

CONVECTION


Control of ConcentrationControl of Concentration

The number of times the solids build in the system water is termed the concentration factor (CF).

CF is controlled by bleed to increase CF - decrease bleed to decrease CF - increase bleed


Bleed ControlBleed Control Effect of too much or too little

bleed: Too much bleed :-

low concentration factor waste of water waste of treatment

Too little bleed:- high concentration factor danger of scale and fouling increased nutrient in system danger of biofouling


1 2 3 4 5 6

xxx

x

x

Concentration Factor

WaterUse

x While increasing concentration factor reduces water use, it also increases nutrients in the system water, encouraging growth of bacteria and slimes. Therefore, we normally run most cooling systems between 2 and 5


Non-biological Fouling Non-biological Fouling

Treated by addition of dispersants dispersants (antifoulants) coat the

particles and so keep them apart The dispersed particles are then

removed from the system water either with the bleed or via a side

stream filter


Non-biological FoulantsNon-biological Foulants

Silt Rust Process contamination

all removed by dispersant/bleed Oil Grease

a different chemical is required but the principle is the same


MICROBIOLOGYMICROBIOLOGY


Microbiology in

Industrial Cooling Systems

• Problematic Microorganisms

• The Biofouling Process

• Water Treatment Biocides

• Biocide Programming

• Monitoring and Control


FUNGI

• Although yeast and some aquatic fungi are normally unicellular, most fungi are filamentous organisms

• Fungi form solid structures which can reach a considerable size

• Some wood destroying fungi exist, associated with deterioration of tower timber

• Fungi require presence of organic energy source

• Exist at between 5 to 38 C and pH 2 to 9 with an optimum of 5 to 6


ALGAE

• Classified as plants as they grow byphotosynthesis

• Range in size from unicellular microscopic organisms to plants that can be up tp 50m in length

Single cells Multi cellular


ALGAE• Algae cannot survive in the absence of air,

water or sunlight

• Basic difference is that algae utilise CO2 and water using sunlight as the energy source to assimilate food• Large quantities of polysaccharides (slime) can be produced during algal metabolism

• Plug screens, restrict flow and accelerate corrosion

• Provide excellent food source

• Exist between 5 to 65 C and pH 4 to 9


BACTERIA

• Universally distributed in nature

• Great variety of micro organisms

• Multiply by cell division

• Slime formation

• Pseudomonas (utilise hydrocarbon contaminants)

• Sulphur bacteria - anaerobic sulphate reducing bacteria

• Nitrogen cycle bacteria


FACTORS CONTRIBUTING TOMICROBIAL GROWTH

• Rate of incoming contamination

• Amount of nutrient present

• pH

• Temperature

• Sunlight

• Availability of oxygen/carbon dioxide

• Water velocities


THE BIOFOULING PROCESS

• Bacteria prefer to colonise surfaces– enables production of biofilm which acts to protect

and entrap food sources

• Planktonic bacteria– free swimming in bulk water

• Sessile bacteria– attached to surfaces


EFFECTS OF BIOFOULING

• Fouling of: tower, distribution pipework, heat exchangers

• Reduction in heat transfer efficiency

• Lost production

• Under deposit corrosion

• Inactivation/interference with inhibitors


WATER TREATMENT BIOCIDES

• Oxidising Biocides– Have the ability to oxidise organic matter eg. protein

groups

• Non-Oxidising BiocidesPrevent normal cell metabolism in any of the following

ways :

– Alter permeability of cell wall

– Destroy protein groups

– Precipitate protein

– Block metabolic enzyme reactions


OXIDISING BIOCIDES

• Sodium Hypochlorite

• Hypobromous Acid

• Chlorine dioxide

• Ozone

• Hydrogen Peroxide


Oxidising Biocides

• Rapid kill

• Cost effective

• Tolerant of contamination

e.g. Bromine, Chlorine Dioxide

• Minimal environmental impact

e.g. Bromine, Ozone, Peroxide, Chlorine Dioxide

• Ineffective against SRB’s

• Low residual toxicity

• Counts approaching potable water standards possible


Non Oxidising BiocidesNon Oxidising Biocides

• Screen water

• Select alternating biocide to prevent resistant strains from developing

• Effective against SRB’s

• Can protect system long after dosing.

• Contain biodispersant

• Higher dosage for kill possible

• Environmentally some have rapid breakdown e.g. DBNPA


BIODISPERSANTS

• Improves penetration of biocide within bacterial slime

• Disperse released bacteria and biofilm into bulk water for removal by blowdown

• Reduces ability for bacteria to attach to system surface

• Improves performance of both non oxidising and particularly oxidising biocides


Physical Methods

Ultra Violet and Ultra Filtration

• Only Effective At Point Of Use

• Cannot Kill Sessile Organisms

• Offer No Protection To Isolated Parts Of

System (Static Areas)

• Environmentally Acceptable.


Control of ConcentrationControl of Concentration

The number of times the solids build in the system water is termed the concentration factor (CF).

CF is controlled by bleed to increase CF - decrease bleed to decrease CF - increase bleed



Basic Cooling Water Treatment principles John Cowpar Area Manager GE Water and Process Technologies.

Documents

scale u

u dispersants u biocides

u steel

foulingbiofouling u

apart u

vapour u

system water u

control of concentration