Chemical Feed Systems Best Practices

Chemical Feed Systems
Best Practices
NJAWWA Annual Conference
Atlantic City, NJ
March 18th, 2015
John Perry
Director of Public Works and Water and Sewer Utilities
Montville Township, NJ
What are Chemicals used for?
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Coagulants – they bridge particles together
pH/Corrosion Adjusters
Oxidants & Disinfectants
Polymers –
• Coagulant
• Expensive (compared to typical coagulants)
• Critical to dewatering equipment and high rate
clarification processes
• Can be very damaging to membranes
Different Phases
 Solid, liquid and gas phases
 Solids
 Less expensive on a per pound basis
 But more complex to feed
 Liquids
 Bulk (delivered) concentration
 Different feed concentrations
 Gas
 Done through eductor using water
 Systems are more reliable
 Safety concerns
Components
 Delivery – dry, liquid, gas
 Storage – tanks, bags and batch, cylinders
 Conveyance –
 Pumps, feeders and eductors
 Pipes – materials and diameter
 Suction
 Discharge
 Dilution Water
 Injectors
Delivery
• Delivery – dry, liquid, gas
• Secondary containment for delivery area.
(Regulated under DPCC if total storage is
above 20,000 gallons)
• Quick Connect with in-line check valve.
• Sampling valve
• Alarms at delivery area
• Safety showers at delivery area
Chemical Delivery
NJ DPCC/DCR (Discharge Prevention Containment and
Countermeasure)
 Requires plans for Hazardous Materials storage. Requires secondary
containment
 The most common water treatment chemicals regulated by DPCC are alum, hypo,
KMnO4, ferric chloride and fuel oil.
NJ TCPA N.J.A.C. 7:31
 The Toxic Catastrophe Prevention Act was established in 1985.
 Identifies and regulates Extremely Hazardous Substances. (EHS) Chlorine, Sulfur
Dioxide and Ozone are the most common water treatment chemicals regulated by
TCPA.
Other Risk Management Programs for EHS:
 OSHA Process Safety Management - 29 CFR 1910.119
 US EPA 40 CFR 68 - Federal Chemical Accident Prevention Provisions
Main Requirements of a Plan
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Site Overview
Process Safety Information
Process Hazard Analysis (Risk Assessment)
Standard Operating Procedures
Operator Training
Mechanical Integrity (Preventative Maintenance)
Management of Change
Safety Review
Main Plan Requirements Cont..
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Compliance Audits
Accident Investigation
Employee Participation
Hot Work Permits
Contractor/Subcontractor Safety
Emergency Response
Annual Reports
Chemical Storage Tanks
Bulk Chemical Hoppers
Positive Displacement Pumps
 Positive displacement pumps are commonly used for
pumping chemical solutions.
 They are not used for water distribution purposes due to
their pulsating type flow and their tendency to develop
excessive pressure build up when pumping against a
closed valve.
 Unlike centrifugal pumps, positive displacement pumps
must always have an unobstructed discharge.
 Extensive damage can occur to the pump and piping if
the positive displacement unit is operated against a
closed valve.
Positive Displacement Pumps
 Two broad classifications of positive
displacement pumps are reciprocating and
rotary.
 Of the reciprocating type pumps, the piston
and diaphragm type are the one most
commonly used
Positive Displacement Pumps: Reciprocating
 Piston/Plunger
 Diaphragm
Piston Pumps
 As the piston retracts, the
discharge check valve is
pulled closed, and the
suction check valve is
pulled open. Fluid is drawn
into the pump cavity.
 As the piston pushes
forward, the suction valve
is pulled closed and the
discharge valve is pushed
open. Fluid is expelled.
Diaphragm Pumps
 Diaphragm pumps use
the reciprocating
action of a diaphragm
to move the liquid.
 Similar to piston
pumps, check valves
are provided on the
inlet and outlet sides
to control the flow of
liquid in the pump
chamber.
Positive Displacement Pumps:
Rotary (Single Rotor)
 Flexible Tubing/
Peristaltic (Wave)
A vacuum is created by
the rollers compressing
the hose and moving
along
Liquid is drawn into
vacuum
Rollers capture liquid
between them and move
liquid towards discharge
Positive Displacement Pumps:
Rotary (Single Rotor)
 Screw
Progressive Cavity Pumps
 A progressive cavity pump is
another type of positive
displacement pump.
 Progressive cavity pumps are
equipped with a helical or
spiral rotor.
 The rotor consists of a shaft
with a helical surface, which
rotates in a rubber sleeve.
 As the shaft turns, it traps
fluid between the shaft and
sleeve, and forces toward the
upper end of the sleeve.
Positive Displacement Pumps:
Rotary (Multiple Rotors)
 Gear
Gear pumps
External gear pumps come in single
or double configurations.
Handle viscous and watery-type
liquids.
Reduced speeds with high-viscosity
liquids results in greater efficiency.
Two gears come into and out of
mesh to produce flow.
Uses two identical gears rotating
against each other.
Chemical Eductors
Volumetric Feeders
o The bulk material is discharged from a hopper with a
constant volume per unit of time by regulating the
speed of a feeding device.
o The actual volume of material fed is determined
through calibration. The feeding accuracy is
dependent on the uniformity of the material flow
characteristics and the bulk density.
o Volumetric feeding can, however become inaccurate if
the bulk density of the solid that is being handled
varies. The feeder cannot recognize a density change
because it simply discharges a certain volume per unit
of time.
o Examples of volumetric type feeders include screws,
belts, rotary valves and vibratory.
Gravimetric Feeders
o The bulk material is discharged from a
hopper by weighing the material
being fed.
o The weighing system with control
compensates for non-uniform
material flow characteristics and
variations in bulk density, and
therefore provides for a high degree
of feeding accuracy.
o A gravimetric feeder relies on
weighing the material to achieve a
required discharge rate or batch
weight.
Disinfection Options
Disinfection Agents
• Chlorine
• Compressed Chlorine Gas - Cl2
• Solution of Sodium Hypochlorite - NaOCl
• Dry Calcium Hypochlorite (HTH) - Ca(OCl)2
• Chloramine
• Chlorine + Ammonia = NH2Cl (monochloramine)
• Chlorine Dioxide
• Chlorine + Sodium Chlorite + Acid = ClO2
• Ozone - O3
• UV
• Sonic and Electromagnetic Pulse
• Membranes
Disinfection
 Primary Disinfection
 The destruction or inactivation or removal of pathogens
 Secondary Disinfection
 Maintain residual
 Control regrowth
 Prevent nitrification (NH2Cl)
Oxidizing Potential of Various Reagents
Oxidizing Reagent
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Ozone
Hydrogen Peroxide
Permanganate
Chlorine Dioxide
Hypochlorous Acid
Chlorine Gas
Hypobromous Acid
Oxygen
Bromine
Hypoiodous Acid
Hypochlorite
Chlorite
Iodine
Oxidizing Potential
2.07
1.77
1.67
1.57
1.49
1.36
1.33
1.23
1.09
0.99
0.94
0.76
0.54
Chlorine is the Most Commonly-Used
Disinfectant/Oxidant
 Effective at inactivating bacteria, viruses
 Less effective at inactivating protozoan cysts (Giardia,
Cryptosporidium)
 Provides a relatively long-lasting residual in distribution system
 Inexpensive compared to hypo, ozone, UV
 Reacts with organic material in water to form halogenated
disinfection by-products
(trihalomethanes, haloacetic acids)
Compressed Chlorine Gas
 Basic Chemistry
 Cl2 + H2O ---> HOCl + HCl
 HOCl <---> H+ + OCl-
Chlorine Species
 HOCl Hypochlorous acid
pH
 free chlorine residual
 Up to 100 times more effective than
hypochlorite ion
 OCl– - Hypochlorite ion
Compressed Chlorine Gas
 Advantages
 Least costly of approved disinfectants
 Relatively easy to use
 Provides residual
 Disadvantages
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Extremely hazardous chemical
Produces DBPs
Tastes and odors
Highly reactive-requires booster stations
Chlorine Properties
 Liquid is 1.5 times as heavy as water
 Gas is 2.5 times as heavy as air
 Liquid vaporizes readily at atmospheric pressure and
normal temp
Effect of pH
Concentration of species
Dissociation of Hypochlorous Acid
100%
80%
60%
[OCl-]
[HOCl]
40%
20%
0%
5
6
7
8
pH
9
10
What Does
this Mean
Chlorine Feed
 Three states
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Gas under pressure – cylinder to chlorinator
Gas under vacuum – chlorinator to ejector
Chlorine Solution – ejector to diffuser
Each state requires a different method of handling
Chlorine Handling Issues
 Storage: compressed gas – 85%
liquid, 15% gas
 Max Withdrawal Rate
 150 lb cylinder = 40 lb/day
 1 ton container = 400 lb/day
 Absorbs heat – freezing of
lines at high rates
 Higher rates require
evaporator
Common Problems with
Chlorine Gas
Operator Safety
Public Safety
TCPA/RMP
Storage
Emergency Response
Equipment - Training
 Toxic Gas Release
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Solution of Sodium Hypochlorite
 Advantages
 Non-hazardous
 Easy to use
 Provides residual
 Disadvantages
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Can be costly (location dependent)
Produces DBPs
Solution strength decays
Tastes and odors
Sodium Hypochlorite
 More expensive than chlorine gas
 Deteriorates rapidly in a warm/hot environment
 12.5 or 15% solution typically used
 Deterioration rate increases with higher solution strength
 Dilution by 50% will reduced decomposition rate by
a factor of 4
 Used because of safety concerns with chlorine gas
and EPA Risk Management Program, NJ TCPA
 Easier to handle than chlorine gas
Hypo Concerns
Common Problems with NaOCl
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Pump stoppage due to out-gassing (loss of prime)
Leaking pipe joints
Degradation of concentration
Unstable residual
Ambient corrosion
DPCC (containment)
Operator safety
Sodium Hypochlorite Degradation –
Average Manufacturer @ 70 Degrees F
 Time of Manufacture - 12.5 Trade Percent
 2 Days Later – 12.43 Trade Percent
 7 Days Later – 12.25 Trade Percent
 14 Days Later – 12.01 Trade Percent
 21 Days Later – 11.78 Trade Percent
 28 Days Later – 11.55 Trade Percent
 35 Days Later – 11.34 Trade Percent
Case Study
 Largest chlorine gas leak occurred at WTP using
hypo. Truck delivered FeCl3 (pH=4) into hypo
tank by mistake. Hypo pH dropped from 12 to 5
almost instantly, releasing 12,000 lbs of chlorine
gas
 Incompatible with acid – do not store near
hydrofluosilic acid or sulfuric acid.
Dry Calcium Hypochlorite
 Advantages
 Calcium Hypochlorite Tablet
Feed Systems
 Gravity Feed
 Non-hazardous chemical, but is an oxidant
 Pressure Feed
 Does not degrade as long as kept dry
 First approved by NJDEP mid1990’s
 Disadvantages
 Feed rates up to 650 lb/day
chlorine
 More difficult to use
 Produces DBPs
Advantages of Tablet Systems
 Safety - Operator and Neighborhood friendly
 Easy to handle and operate
 Low Maintenance
 Compact Chemical Storage
 Dry, Stable Chlorine Source
 No Risk Management Plan Requirements
 No Secondary Containment
 Convenience
 Separate room not required
Chlorine Dioxide
 Advantages
 Strong disinfectant
 Effective at Inactivating Bacteria, Viruses, and Protozoa
Cysts
 Maintains a good residual in the distribution system
 Does not form DBPs
 Disadvantages
 Requires specialized mixing equipment
 Requires filtered water pH of 8
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Hazardous chemical
MCL on chlorine dioxide = 0.8 ppm
MCL on chlorite = 1.0 ppm
Tastes and odors with new household carpeting
Chloramines
Cl2
• Advantages
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Stops DBP formation
Little taste and odor when monochloramine
Provides persistent residual
Does not react with distribution materials
More effective in penetrating biofilms
• Disadvantages
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NH3
Weaker disinfectant
Requires more operational control
Reaction with free chlorine residual
Potential for nitrification
Ozone – What is it?
 Created by a high intensity reaction which splits O2
into separate O molecules, which attach to other O2
molecules and form O3.
 Extremely reactive. It is the most powerful
disinfectant in the world.
 Residual ozone dissipates quickly, with a half life of
about 30 minutes.
Ozone
 Advantages
 Very effective disinfectant and oxidant
 No DBPs of concern
 No tastes and odors
 Disadvantages
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Hazardous chemical
Costly -requires specialized equipment
No residual - need chlorine in some form
Forms bromate in presence of bromide (bromate
MCL = 10 ppb)
Ozone Oxidation and Disinfection
As a comparison based on 99.99% of bacterial concentration
being killed and time taken: Ozone is
 25 times of that of HOCl (Hypochlorous Acid)
 2,500 times of that of OCl (Hypochlorite)
 5,000 times of that of NH2Cl (Chloramine).
 Further more, ozone is at least 10 times stronger than
chlorine as a disinfectant.
COMPONENTS OF AN OZONATION
SYSTEM
INFLUENT
OZONE
OZONE GENERATOR
AIR/OXYGEN PREPARATION
AIR
CONTACT
CHAMBER
OZONE DESTRUCTOR
VENT
OTHER OXYGEN APPLICATIONS
EFFLUENT
Alternative paths for enriched oxygen recycle
Basic Ozone Application
Pre-ozonation
Raw Water
Screening
Clarification
Ozone
Disinfection
Filtration
Distribution
Residual
Disinfection
Ozone Generators –
Large Scale
Ozone Generators – Small Size
Ozone GeneratorsMedium Size
Inside the Unit
Oxidation: Why?
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Iron removal
Manganese removal
Taste and odor control
Algae
Hydrogen sulfide
Color removal
VOC removal (advanced oxidation)
Potassium Permanganate
(KMnO4)
• Strong Oxidizer
• Purple in color
• Form - Crystals
• Density - 90 to 100 lbs./ft3
KMnO4 Applications (Drinking Water)
• Taste and Odor
• Manganese removal
• THM reduction
• Fe, H2S, Ra and As Control
• Zebra mussel control
• Biofilm control
Standard Dosage Estimates
• 1 part of Fe requires 0.94 parts of
KMnO4 for treatment.
• 0.5 part of Mn requires 1.00 part of
KMnO4 for treatment.
Coagulation
 Since colloidal and microbial
particulates tend to be
negative in overall charge,
introduction of a positively
(cationic) charged metal
based coagulant is necessary
for charge neutralization.
 Once charge neutralization
occurs, particulates collide
and adsorb to one another to
form larger floc particles.
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Adsorption of
positively charge
species on to
negatively charged
particle
Raw Water
Negatively charged
particles
Precipitation of
metal hydroxide
which absorbs
suspended particles
Coagulated
particles
•- •- •- •Coagulant addition
Flash Mix or Rapid
Mix
Flocculation
 Flocculation simply defined is the agglomeration of neutrally charged
(coagulated) particles to form amorphic settable floc.
 Flocculation allows particles to “bridge” with one another forming larger
and more dense floc.
 Coagulation is a very quick chemical reaction, accomplished between 1
and 3 seconds.
 High mixing rates and proper dispersion of coagulant are essential. Lack
of proper mixing or improper chemical dispersion will lead to coagulant
overdosing and poor floc formation.
Chemicals used for Coagulation
Iron
Inorganic Metal Species
Aluminum
 Aluminum Sulfate [Al2(SO4)3]
 Sodium Aluminate [ NaAlo2]
 Ferric Chloride [FeCl3]
 Ferrous Chloride [FeCl4]
 Ferrous Sulfate
[Fe2(SO4)3]
 Ammonia Alum
[Al2(SO4)3·(NH4)2SO4·24 H2O]
 Poly Aluminum Chloride (PAC)
 Organic Polymers
 Cationic
 Anionic
 Nonionic
Sometimes in-line or static mixers are used for rapid-mixing.
This type of mixer is illustrated here:
Mechanical Flocculator
L
H
Cross flow Flocculator (sectional view)
W
Plan (top view)
Hydraulic Flocculation
L
• Horizontally baffled tank
The water flows horizontally.
The baffle walls help to create
turbulence and thus facilitate mixing
W
Plan view (horizontal flow)
• Vertically baffled tank
The water flows vertically. The baffle
walls help to create turbulence and thus
facilitate mixing
H
L
Isometric View (vertical flow)
Hydraulic Flocculation: Pipe
Determining Proper Floc Size
 There are many ways to determine if you are
coagulating/flocculating properly.
 Jar Testing
 Zeta Potential
 Streaming Current Monitors
 Pilot Studies
Jar Tests
 The jar test – a laboratory procedure to determine the optimum pH
and the optimum coagulant dose
 A jar test simulates the coagulation and flocculation processes
Determination of optimum pH
 Fill the jars with raw water sample
(1000 or 2000 mL) – usually 6 jars
 Adjust pH of the jars while mixing
using H2SO4 or NaOH/lime
(pH: 5.0; 5.5; 6.0; 6.5; 7.0; 7.5)
 Add same dose of the selected
coagulant (alum or iron) to each jar
(Coagulant dose: 5 or 10 mg/L)
water treatment
Jar Test
67
3/6/2015
pH/Corrosion Adjusters
To drop pH for coagulation – Sulfuric acid
To raise pH for corrosion or for faster
oxidation of manganese
Sodium Hydroxide (caustic soda) –
liquid concentration
Lime – dry – quick or hydrated?
Soda Ash - dry
Figure Courtesy of Environment Canada (www.ns.ec.gc.ca)
pH Scale
Caustic Soda
Choice 25% or 50%.
25%
More expensive
Crystallization Temp 0 Deg F
50%
Less expensive
Crystallizes at 55 Deg F – Heat trace recommended
Higher pH – More calcification
Lime
Choice quicklime (CaO) or Hydrated Lime (Ca(OH)2)
 Lime Feed Handbook and ZMI/Portec
Quicklime
Less expensive
Need to slake - exothermic
Hydrated lime
More expensive
Slaker not required
Instrumentation - Instruments are commonly used to
measure and/or control the following parameters in water
treatment plants
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Location
Raw water influent
Pump well
Pump header
Electrical equipment
valves
Parameter/Function
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Flow, pH, pressure
Tank Level
Pressure, flow
Run time meters
Limit switches
Control
 Control systems can be manual, semi-automatic or automatic.
 Turning a hand wheel to open or close a valve is an example of
manual control.
 Semi-automatic control requires manual initiation of an
automatic function. A typical example would be pressing a
control button at a panel, which in turn causes an electric valve
to open or close.
 The automatic control method uses instruments to
automatically control the process or equipment.A typical
example would be a variable speed pump which automatically
speeds up or slows down to maintain a set pressure.
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