Basic Cooling Water Treatment principles

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					Basic Cooling Water Treatment
principles
          John Cowpar
          Area Manager
       GE Water and Process
          Technologies
USING WATER
POTENTIAL PROBLEMS
CORROSION




DEPOSITION -   Fouling
                Biofouling
                Scaling
   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
   Corrosion
 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
   Fouling
 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 Treatment
 MINIMISE SCALE
 MINIMISE CORROSION
 MINIMISE FOULING
 MINIMISE BIOFOULING
 MAXIMUM SAFETY
 MAXIMUM EFFICIENCY
 NON-POLLUTING
WHAT CAUSES OUR PROBLEMS?
 DISSOLVED SOLIDS
 e.g.CALCIUM
 MAGNESIUM
 SODIUM
 CHLORIDE
 BICARBONATE
 SULPHATE
 SILICA
 IRON
 DISSOLVED GASES
     OXYGEN
 e.g.
 CARBON DIOXIDE
 NITROGEN
 SULPHUR DIOXIDE
 SUSPENDED MATTER


DUST/DIRT
CONTAMINANTS     e.g. OIL
BIOLOGICAL e.g. ALGAE,
 FUNGI, BACTERIA
TYPICAL WATER ANALYSIS CHART
    Water Analysis                         Result
pH                                   7.7
Colour                             3.00    HAZEN
Turbidity                          9.00    F.T.U.
Solids - Suspended                     5   mg/l
Chloride as Cl                       44    mg/l
Alkalinity as CaC03                 144    mg/l
Ammoniacal Nitrogen as N          0.140    ug/l
Iron (Total) as Fe                  311    ug/l
Manganese (Total) as Mn              65    ug/l
Nitrate as N                         4.0   mg/l
Total Hardness as CaC03             207    mg/l
Sulphate as S04                    62.3    mg/l
Silica - Reactive as Si02           6.9    mg/l
Sulphide as S                     0.015    mg.l
Carbon Dioxide - Free              2.50    mg.l
Solids - Total Diss. at 180C        347    mg/l
D.O. Concentration (Field Det.)    10.7    mg/l
Coliforms                           <10    /100ml
E. Coli                             <10    /100ml
Faecal Streptococci                  <1    /100ml
Sulphite Red. Clostridia            300     /20ml
          Hardness
         is due to calcium and
 Hardness
 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



MAKE UP



M=E+W+B       BLEED
Useful 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 FORMATION
SCALE CAN BE CONTROLLED BY:

 PRE-TREATMENT


 CHEMICALS


 CONCENTRATION   FACTOR
    CORROSION
 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
   CONTROLLED BY:

 REMOVAL    OF OXYGEN ?

 ADDITION   OF CHEMICALS

 CONTROL    OF pH
Biofouling
What is Biofouling caused by?


• FUNGI

• ALGAE

• BACTERIA
FOULING/BIOFOULING

 Can   be controlled by

   Filtration
   Control of Concentration Factor (bleed)
   Dispersants
   Biocides
               Open 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


Customer Training WT200C                         Page 23
               Cooling Water
                           WATER DROPLET
                               COOLS BY:

                            EVAPORATION


                              RADIATION

                             CONVECTION



Customer Training WT200C                   Page 24
               Control 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




Customer Training WT200C                           Page 25
               Bleed Control
       Effect             of too much or too little bleed:
             Too          much bleed :-
                   lowconcentration 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




Customer Training WT200C                                      Page 26
                x
                               While increasing concentration factor
                               reduces water use, it also increases
                               nutrients in the system water,
                               encouraging growth of bacteria and
 Water                         slimes. Therefore, we normally run
 Use                       x   most cooling systems between 2 and 5

                                    x
                                             x
                                                     x         x

               1           2        3        4       5         6
                                                  Concentration Factor
Customer Training WT200C                                               Page 27
               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


Customer Training WT200C                                         Page 28
               Non-biological Foulants
       Silt
       Rust
       Process            contamination
             all    removed by dispersant/bleed
       Oil
       Grease
            a  different chemical is required but the
               principle is the same

Customer Training WT200C                                 Page 29
          MICROBIOLOGY




Customer Training WT200C   Page 30
                          Microbiology
                                in
                   Industrial Cooling Systems

            •   Problematic Microorganisms
            •   The Biofouling Process
            •   Water Treatment Biocides
            •   Biocide Programming
            •   Monitoring and Control



Customer Training WT200C                        Page 31
                             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

Customer Training WT200C                                     Page 32
                              ALGAE

            • Classified as plants as they grow by
                  photosynthesis
            • Range in size from unicellular microscopic
              organisms to plants that can be up tp 50m in
              length




         Single cells                      Multi cellular

Customer Training WT200C                                     Page 33
                             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

Customer Training WT200C                                       Page 34
                           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



Customer Training WT200C                                  Page 35
                FACTORS CONTRIBUTING TO
                   MICROBIAL GROWTH
            •   Rate of incoming contamination
            •   Amount of nutrient present
            •   pH
            •   Temperature
            •   Sunlight
            •   Availability of oxygen/carbon dioxide
            •   Water velocities


Customer Training WT200C                                Page 36
                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




Customer Training WT200C                                                  Page 37
                   EFFECTS OF BIOFOULING


            • Fouling of: tower, distribution pipework, heat
              exchangers
            • Reduction in heat transfer efficiency
            • Lost production
            • Under deposit corrosion
            • Inactivation/interference with inhibitors


Customer Training WT200C                                       Page 38
            WATER TREATMENT BIOCIDES

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


            • Non-Oxidising Biocides
                  Prevent normal cell metabolism in any of the following
                    ways :
                  – Alter permeability of cell wall
                  – Destroy protein groups
                  – Precipitate protein
                  – Block metabolic enzyme reactions
Customer Training WT200C                                                     Page 39
                           OXIDISING BIOCIDES


            •   Sodium Hypochlorite
            •   Hypobromous Acid
            •   Chlorine dioxide
            •   Ozone
            •   Hydrogen Peroxide



Customer Training WT200C                        Page 40
                           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
Customer Training WT200C                                      Page 41
                  Non 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

Customer Training WT200C                                        Page 42
                           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

Customer Training WT200C                                    Page 43
                              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.


Customer Training WT200C                                       Page 44
               Control 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




Customer Training WT200C                           Page 45
Customer Training WT200C   Page 46
Customer Training WT200C   Page 47