CONTENTS Section Page SCOPE 2 REFERENCES...2 DESIGN PRACTICES ...2 GLOBAL PRACTICES...2
WATER AND WASTEWATER DESIGN GUIDE (emre Manual No. TMEE 080)...2
OTHER REFERENCES ...2
DEFINITIONS ...3
BACKGROUND...4
WASTEWATER TREATMENT ...5
COAGULATION / COAGULATION AID ...5
NUTRIENT ADDITION ...7
pH ADJUSTMENTS ...8
OXIDANTS ...10
FOAM CONTROL...11
COOLING WATER TREATMENT ...11
BIOLOGICAL CONTROL ...11
CORROSION CONTROL ...12
PH ADJUSTMENT ...13
BOILER FEED WATER TREATMENT...14
CONTROL AND MONITORING ...14
CHEMICAL PREPARATION AND HANDLING...14
Dry Feed Systems ...15
Dry Materials (in bags) ...16
TABLES Table 1 Summary of Typical Chemical Applications ...17
Table 2 Properties and Handling Considerations for Commonly Used Chemicals ...19
Table 3 Standard Water / Wastewater Analysis Sheet ...28
Table 4 Selection Chart for Bench Scale Polymer Testing Procedure... 29
FIGURES Figure 1 Controlled Volume Pump Feeder ...30
Figure 2 Typical Dry Chemical Feeder ...31
Figure 3 Anionic and Nonionic Polyelectrolyte Feed System...32
Figure 4 Cationic Polyelectrolyte Feed System ...33
Figure 5 Flow Through Solid Feeder for Hydantoin Chemical(6)...34
Figure 6 Typical Recirculated Cooling Water System...35
Revision Memo
12/02 Removed data from Properties of comercially available acids and bases tables. Added chemicals in Table 1.
SCOPE
This section presents guidelines for the use of chemicals in wastewater, cooling water, and boiler water treatments. The chemical applications, the injection points, and control and monitoring issues are discussed. Information on the applicability of the most commonly used water / wastewater chemicals is provided along with general guidelines for handling and feeding the chemicals.
REFERENCES DESIGN PRACTICES
Section XXVI-A Boiler Feedwater Treating Systems Section XXVII Cooling Water Systems
Section XIX-A Guidelines for Selecting Wastewater Treatment Systems Section XIX-A2 Flotation Units
Section XIX-A3 Media Filtration
Section XIX-A4 Coagulation / Flocculation / Clarification Equipment Section XIX-A5 Biological Treatment of Wastewater
Section XIX-A11 Chemical Oxidation
Section XX-A1 Dissolved Air Flotation Sludge Thickening Section XX-A3 Mechanical Sludge Dewatering
GLOBAL PRACTICES
GP 8-1-1 Cooling Towers
GP 9-4-2 Additional Requirements for Atmospheric Storage Tanks for Acids GP 19-6-1 Facilities for Corrosion Monitoring in Process Equipment
WATER AND WASTEWATER DESIGN GUIDE (EMRE Manual No. TMEE 080)
DG 11-2-1 Fixed Bed Ion Exchange Water Treating Units DG 11-2-2 Aqueous Membrane Systems
DG 11-3-1 Gas Chlorinators for Water Treating Service DG 11-4-1 Hot Process Water Treaters
DG 11-4-2 Cold Process Water Treaters
DG 11-6-1 Chemical Feeders for Boilers and Deaerators
DG 11-6-2 Chemical Feeders for Cooling Towers (Leased or Purchased) DG 11-6-3 Chemical Feeders for Wastewater Treating
DG 11-7-1 Wastewater Dissolved-Air Flotation System DG 11-7-2 Wastewater Induced Gas Flotation System DG 11-8-1 Gravity Belt-Filter Press System
OTHER REFERENCES
1. Betz Handbook of Industrial Water Conditioning, 7th Edition (1976).
2. Devine, T. A., Guidelines for Safety Evaluation of Chemical Injection Facilities, EE.92E.94 (December 1994). 3. Franco, R. J., Environmentally Acceptable Cooling Water Treatment, EE.34E.86 (March 1986).
4. Kemmer, F. N., ed., The Nalco Water Handbook, 2nd Edition, McGraw-Hill Book Company (1988). 5. Kilpert, R., et al, Cooling Tower Water Treatment Guidelines, EE.102E.78 (November 1978). 6. Robertaccio, F. L., Polyelectrolyte Guide, EE.20E.84 (February 1984).
7. Smith & Loveless, Inc., Engineering Data, Water & Wastewater Treatment Systems Chem-Tower Notes on Design (1989). 8. Water Environment Research Foundation, Project 91-ISP-5, Guidance Manual for Polymer Selection in Wastewater
Treatment Plant, (1993).
10. Metcalf & Eddy, Inc., Wastewater Engineering Treatment, Disposal, and Reuse, 3rd Edition (1991). 11. Refinery Construction Materials Manual, EMRE Manual No. EETD 028.
DEFINITIONS
Alkalinity - A measure of water's capacity to neutralize acids. Includes the total carbonate, bicarbonate, and hydroxide ion concentration in the water expressed in ppm (mg/l) as calcium carbonate (CaCO3) equivalent. Alkalinity is measured by double titration with acid and Phenolphthaline (P) and Methyl Orange (MO or M) indicators. The M-alkalinity includes carbonate, bicarbonate and hydroxyl ions and the P-alkalinity includes all hydroxyl and 1/2 of the carbonate ions.
Anions - Negatively charged ions in the water (e.g., sulfates, chlorides, nitrates, bicarbonates, etc.).
Baumé (Bé) - This unit is often followed by “Am. Std." which signifies “American Standard Baumé Scale." For liquids heavier than water, this scale is defined by the formula:
Degree Baumé = F 60 / 60 at Gravity Specific 145 145 o o − Eq. (1)
Brine - A solution of sodium chloride in water.
Bulking - A condition in the settling basin of a biological oxidation system where the sludge doesn't settle, or settles slowly, and may lead to floc carryover with the effluent.
Calcium Hardness - The concentration of calcium ion in the water, expressed in ppm (mg/l) generally as calcium carbonate (CaCO3) equivalent.
Cations - Positively charged ions in the water (e.g., calcium, magnesium, sodium, ammonium, etc.). Caustic or Caustic Soda - The chemical compound sodium hydroxide (NaOH).
Coagulants - Materials added to the water / wastewater or water / wastewater treatment sludge to allow agglomeration of small particles into larger particles to facilitate their separation from the water.
Coagulation Aids - Materials added to the water / wastewater or water / wastewater treatment sludge after a coagulant (primary coagulant) has been added to increase the speed of floc formulation and the floc size and strength. Polymers (also called polyelectrolytes) are the most commonly used coagulant aids.
Coagulation - The term coagulation is applied to the overall process of particle charge neutralization and physical combination (with the aid of chemicals) of small particles into masses sufficiently large to be settled or floated.
Colloid - A substance made up of very small, insoluble particles less than one micron in size. These particles are small enough so that they remain suspended in a liquid without settling to the bottom.
Conductivity - The ability of water to conduct electricity due to the presence of ionized material within the solution. Conductivity is expressed in micromhos/cm (or micro Siemens/cm), and is directly proportional to the amount of dissolved matter in the water / wastewater. As a rule of thumb, for wastewater streams at pH 7 the Total Dissolved Solids (TDS) of that stream in ppm (mg/l) can be approximated by multiplying the conductivity in units of micromhos/cm or microSiemens/cm by 0.7. Flash Mix Tank or Rapid Mix Tank - An agitated drum or tank in which chemicals are rapidly mixed with the water / wastewater in order to improve the effectiveness and speed of reaction.
Floc - Suspended particles formed by the agglomeration of smaller suspended particles.
Flocculation - The term flocculation is applied to the process of particle charge neutralization and physical combination (with the aid of chemicals) of small particles into masses sufficiently large enough to be settled or floated. The word flocculation is often interchangeably used with the word coagulation.
Flocculation Tank - A process whereby suspended particles and colloidal particles, which cause turbidity and color in water, are combined by physical means (with the aid of chemicals) into masses sufficiently large to be settled or floated.
Hardness - The concentration of calcium and magnesium ions in water, expressed in ppm (mg/l) as calcium carbonate (CaCO3) equivalent.
Hardness Alkalinity - The concentration of calcium and magnesium bicarbonate and carbonate salts in water, expressed in ppm (mg/l) as calcium carbonate (CaCO3) equivalent.
Hydroxide Alkalinity - The free hydroxide ions in water, expressed in ppm (mg/l) as calcium carbonate (CaCO3) equivalent. Ion - Electrically charged particle formed when a molecule dissociates into positive and negative particles in water (e.g., salt into sodium + and chloride - ions).
Makeup or Makeup Water - The water required to replace circulating water which is lost by evaporation, drift, blowdown, and leakage. It is expressed in percent of water circulated.
Nutrients - Chemical elements such as nitrogen, potassium, phosphorous, etc., which are essential for bacterial growth in biological wastewater treatment systems.
Once-Through Cooling System - A system in which cooling water passes through heat exchange equipment once and is then discharged directly, with no recycle or circulation.
Polymer or Polyelectrolyte - A polymeric organic compound commonly added to water / wastewater to promote coagulation and flocculation of suspended material. It is also added to water / wastewater treatment sludges to enhance thickening and dewatering. The following are the three basic types and uses of polymers:
1. Anionic (negative charge) - generally serve as coagulant aids to inorganic or organic primary coagulants by increasing the rate of coagulation and the size and roughness of floc particles.
2. Cationic (positive charge) - serve as primary coagulant alone or in combination with inorganic coagulants or with anionic or nonionic polymers. Some cationic polymers with very high molecular weights may also be used as coagulant aids.
3. Nonionic (no net charge) - serve as coagulant aids in a manner similar that of both anionic and cationic polymers.
Recirculated Cooling System - A system in which water is circulated to coolers in a loop and the heat absorbed from this cooling operation is dissipated by a cooling tower or some other type of heat exchanger.
Recirculation - An undesirable condition in which part of the cooling tower discharge vapor stream is recirculated through the tower resulting in increased inlet air wet bulb temperature.
Sludge - The accumulated semi-liquid suspension of settled solids deposited in tanks or basins from raw or treated water / wastewaters. Dissolved-Air Flotation and Induced-Air Flotation floats and Granular-Media Filter backwash are also included in this definition for the purpose of this Design Practice.
Sludge Conditioning - The addition of inorganic or organic chemicals to increase the efficiency of sludge thickening and/or dewatering.
Sludge Dewatering - The removal of water from a sludge or slurry, usually by mechanical means, to greater than 10 wt% solids.
Sludge Thickening - Thickening is a process which aims to increase the solids content of a dilute slurry by removing some of the water content by gravitational or flotation means. Typically, gravity thickeners can produce sludges with 4-6% solids by weight. Flotation thickeners typically conditions sludges to between 4 and 8% solids by weight.
Softening - The process of removing calcium and magnesium ions from water.
Specific Gravity (SG) - The specific gravity of a liquid is the ratio of the weight of a given volume of the liquid to the weight of an equal volume of water. Thus the specific gravity of a solution of chemical at 60°/60°F refers to the weight of a given volume of chemical at 60°F as compared with the weight of an equal volume of water at 60°F.
Turbidity - A term referring to the lack of clearness in a water due to the presence of suspended or colloidal matter and expressed in Nephelometric Turbidity Units (NTU).
BACKGROUND
Chemical addition facilities are an integral part of many grassroots water / wastewater treatment process unit designs. They are necessary for the proper operation and performance of the facility. However, chemical addition may also be retrofitted on existing process units to improve the unit's functional performance, decrease its operating cost, or extend its capability to process larger than design flow rates of water / wastewater and/or water / wastewater treatment sludges.
The designer of the chemical feed systems should provide as much flexibility as possible in the design of the chemical injection system to allow optimum selection of the application point(s) and take advantage of different chemicals offered by vendors. This flexibility is particularly important for coagulant and coagulant aid addition points.
Reference 2, Guidelines for Safety Evaluation of Chemical Injection Facilities, should be used when designing or receiving a chemical feeding and handling system. The application guide is especially written to facilitate a safety evaluation of vendor provided chemical injection facilities. The guidelines cover the storage container, injection pump, and injection point.
Table 1 provides a summary of the chemicals which are most commonly used in water / wastewater treatment applications. Table 2 provides detailed information such as chemical formulas, available forms, storage considerations, and safety considerations for the commonly used chemicals in Table 1. Figures 1 to 6 illustrate the various types of chemical feeding systems used in water / wastewater treatment. A water / wastewater analysis (see Table 3) can be very useful in determining the required chemical application.
WASTEWATER TREATMENT COAGULATION / COAGULATION AID
General - Chemical coagulation is accomplished by one or a combination of the following two basic mechanisms:
1. Particle Charge Neutralization - Most suspended matter in wastewater has an apparent negative surface charge. This negative surface charge on the particles creates a net repulsive force between particles, thereby inhibiting agglomeration of the suspended matter. The addition of positively charged metal ions or cationic polymers can neutralize these surface charges and allow particle agglomeration either with or without a coagulant aid.
2. Particle Bridging - The addition of metal salts can form metal hydroxides under the proper set of pH and dosage conditions. These metal hydroxides form large sets of molecules that attach themselves to the suspended particles, thereby bridging the gap between particles and drawing them together into a strong floc lattice structure. Polymers can also be effective particle bridging chemicals.
Particle Charge Neutralization using polymer chemicals is the preferred mechanism for coagulation because it generally requires less chemical and produces less sludge than Particle Bridging.
Primary Coagulant - Cationic polymers are the preferred primary coagulant for coagulation. In the past, Bentonite, Diatomaceous Earth, and metal salts were commonly used as primary coagulants. Some manufactures provide blended products which contain both a metal salt and a polymer. However, due to improved polymer technology, polymers are now recommended for new applications. Cationic polymers have advantages over other primary coagulants as follows:
• Easier to store and handle.
• Used as neat polymers, eliminating mixed / diluted solution tank. • Produce less sludge (which ultimately must be disposed of).
• Resulting sludge contains less water, is less acidic, and can be more easily dewatered. • Performance is less pH dependent.
• Do not add to the total dissolved solids concentration.
Coagulant Aid - In cases when different types and large doses of primary coagulant fail to produce a satisfactory floc, a polymeric coagulant aid should be added after the primary coagulant. Very high molecular weight (> 1 x 106) polymers like the nonionic polymers and low molecular weight (< 20,000) polymers like the anionic polymers have proven successful and are recommended coagulant aids.
Applications - Chemical coagulation is applied for suspended solids and free oil removal during wastewater treatment to enhance separation of solids and oil from the wastewater, in clarification and thickening, in sludge dewatering, and in metals removal.
1. Flotation Processes (DP XIX-A2) - Chemical coagulation is almost always required to attain even moderate degree of free oil and suspended solids removal from flotation processes. By chemically agglomerating the small diameter particles, impingement and attachment of air bubbles on the larger floc particles is enhanced, thereby improving the efficiency of the flotation process. Normally, chemical coagulation will also help increase the concentration of oil and solids in the float from these processes.
Dissolved Air Flotation (DAF) process units are generally preceded by chemical flocculation equipment (i.e., a flash mix and a flocculation tanks). The primary coagulant is generally added in the flash mix tank. If a coagulant aid is required, it is added in the flocculation tank or injected in the influent line just prior to the flotation unit.
Induced Gas Flotation (IGF) process units do not normally have a flash mix or a flocculation tank. The primary coagulant is injected directly into the influent line far enough upstream of the flotation unit to allow complete mixing with the wastewater. If a coagulant aid is required, it is injected in the influent line just prior to the flotation unit. Static or in-line mixers are generally used for direct injection.
2. Filtration Processes (DP XIX-A3) - Use of chemical coagulation, optimized with respect to both chemical type(s), dosage(s), and point(s) of injection, can improve effluent quality, extend the run length of Granular-Media Filtration (GMF) units, and increase the concentration of oil and solids in the backwash. The primary coagulant is injected directly into the influent line far enough upstream of the filtration unit to allow complete mixing with the wastewater.
3. Clarification (DP XIX-A4 and XIX-A5) - Primary coagulants, and sometimes coagulant aids, are used to help settle out suspended material in the clarifier. They also help chemically treat dispersed growth of biological solids. Both the primary coagulant and coagulant aid are added upstream of the clarifier.
4. Sludge Thickening by Flotation (DP XX-A1) - In sludge thickening by flotation or gravity filtration, cationic polymers are the preferred primary coagulant. A coagulant aid is not generally required. The cationic polymer is injected directly into
the influent line far enough upstream of the thickener to provide complete mixing with the sludge. It may also be added in a feed mixing tank. However, care should be exercised in controlling the intensity of mixing in this tank to avoid excessive shearing of the sludge.
5. Sludge Dewatering (DP XX-A3) - For low shear sludge dewatering processes such as belt filter pressing, vacuum filtration, and centrifugation, the primary coagulant is usually injected in the influent pipe just prior to, or directly into a low intensity mixing tank which precedes the process unit. In some cases, it is also possible to eliminate the need for a gentle mixing tank by injecting the primary coagulant into the influent line upstream of an in-line mixer, or far enough upstream to allow complete mixing of the chemical with the sludge. If a coagulant aid is required, it is injected immediately before the dewatering process unit.
For high shear sludge dewatering processes, such as high-pressure filtration, the primary coagulant is added to the sludge in a batch mixing tank prior to the filter press. Diatomaceous Earth is sometimes useful as a precoat material on the pressure filter cloth. A precoat both enhances the concentrated sludge cake release from the cloth and prevents plugging of the cloth during the filtration process. Waste FCCU catalyst fines can also be used as a filter cloth precoat material. If a precoat is used on the filter cloth, it is generally applied directly to the filter cloth in slurry form prior to feeding the sludge to the filter.
6. Metals Removal - Depending on the metal, chemical coagulation followed by gravity separation, flotation, or filtration can remove undissolved and some dissolved heavy metals which may be chelated or coprecipitated by the chemicals, such as EDTA and Iron salts, respectively. Similarly, a small reduction in both the dissolved and undissolved heavy metals occurs by adsorption on biological solids and undissolved heavy metals are removed by incorporation into the biological solids floc.
The primary coagulant, which forces the precipitation of metals, is typically added in the flash mix tank. If required, a coagulant aid is usually added either in the flocculation tank or in the influent line just prior to the separation unit where the metal precipitate is removed from the wastewater.
Types and Dosages - The types and dosage rates of coagulant / coagulant aid required to provide the best performance for specific applications cannot be theoretically predicted and must be determined by bench laboratory tests and field trials. Table 4 summarizes the bench scale tests that will help determine the best combination of chemicals and the optimum dosages for a particular wastewater. If pilot plant facilities are used to optimize new process unit design parameters, concurrent tests on these units may also be utilized to determine the optimum chemical type(s) and dosage(s).
As a general guide for initial lab tests or as a design guide for grassroots facilities where there is no wastewater available, chemical dosage ranges are as follows:
TREATMENT TYPE POLYMER TYPE TYPICAL DOSAGE RANGE
PRIMARY COAGULANT Cationic 1 - 10 ppm (mg/l) as neat polymer
COAGULANT AID Anionic or Nonionic 0.1 - 3 ppm (mg/l) as neat polymer
Design guidelines / parameters for coagulation / coagulation aid / flocculation are as follows:
• The chemical feed system for cationic polymers (Figure 4) typically includes a bulk storage tank (temporary semi–bulk storage tanks may be provided by supplier) and a spared pumping configuration.
• The chemical feed system for anionic or nonionic polymers (Figure 3), typically includes a bulk storage tank (temporary semi–bulk storage tanks may be provided by supplier), a mixing tank, a mixture storage tank, and two spared pumping configurations (one set for the bulk tank and the second for the mixing tank).
• The coagulant / coagulant aid should be injected via dosing pumps. Normally, 2-100% capacity pumps are provided for each pump configuration. Positive displacement metering pumps are used for rates up to 100 gph (0.1 L/s). Centrifugal pumps with flow control are used for higher rates. As with any pumps or equipment, area classifications should be considered in selecting and specifying them.
• The bulk storage tank should provide a minimum inventory of 15 days at the design consumption rate.
• The mixing tank and the mixture storage tank for anionic and nonionic polymer feed systems should not exceed 48 hours of inventory.
• The bulk tanks should contain a slow speed, blade type agitator. The intensity of mixing energy supplied depends on the emulsion tendency, the nature of the solids in the stream, and shearing intensity if in sludge service.
• The bulk storage tank should be equipped with a level gage that is visible from the unloading connection. • Dilution water shall be clean condensate or equivalent water quality. Potable water must never be used.1
• A pressure relief valve should be provided downstream of each pump system even if built-in relief valves are provided with the pumps. The set pressure is to be 10% above the operating pressure at the pump discharge or 10% above the process equipment design pressure, whichever is greater.
• Sizing of the facilities may require consultation with the chemical(s) suppliers. Concentrations and activity of vendor supplied chemicals can vary and have an effect on storage volumes and pumping rates.
• Commonly used worldwide polymer suppliers are as follows. The company distribution area and internet web address are listed below.
Company Web Address Distribution Area
Ashland Specialty Chemical Company www.ashchem.com North America Vulcan Chemicals www.vul.com North America Baker Petrolite www.bakerhughes.com/bakerpetrolite International GEBetz Chemicals www.gebetz.com International ONDEO Nalco Chemical Co. www.ondeonalco.com International US Filter - Stranco www.stranco.com International
** This list is provided as a convenience to the user and is not intended as an endorsement. Other suppliers should also be contacted; they may provide unique products unavailable from the suppliers on this list.
NUTRIENT ADDITION
Microorganisms require nutrients in addition to the primary carbon food source. Macronutrients consist of nitrogen (N) and phosphorus (P). Micronutrients, or trace elements, are also required by microorganisms. The micronutrients (K, Fe, Mg, Ca, Zn, Cu, Co, etc.) are typically found in refinery and petrochemical wastewaters in sufficient concentrations. However, the macronutrients are often insufficient. Because nitrogen and phosphorus are essential for microorganism growth and reproduction, they are also essential for waste degradation.
Nitrogen - There are several forms of nitrogen found in wastewater: organic nitrogen, ammonia, nitrate, and nitrite. Ammonia nitrogen exists in aqueous solution as either the ammonium ion or ammonia, depending on the pH of the solution.
As a rule of thumb:
PPM (mg/L) of Nitrogen required for bio-growth = ppm (mg/l) of BOD5 in the wastewater/20
If supplemental nitrogen is required, there are several sources of nitrogen that can be used. The recommended nitrogen source is ammonium salts due to their easier handling and mild corrosivity. The advantages and disadvantages for the most common sources of nitrogen are as follows:
NITROGEN SOURCE ADVANTAGES DISADVANTAGES
Ammonia 2 (NH3)
• Requires small dosages due to high strength
• Gas toxic at concentrations over 100 ppm in air
• Gives off pungent, irritating odor
• Corrosive
• Safety equipment required
Ammonium Hydroxide 2
(NH4OH) • Available in bulk liquid • Gives off pungent, irritating odor • Corrosive
• Safety equipment required
Ammonium Salts2
e.g., (NH4)2SO4 • Relatively easy to handle • Only mildly corrosive
• Tends to cake
• Safety equipment required
Urea2
(NH2CONH2) • Relatively easy to handle •
Corrosive
➧ 1: Unless isolation and backflow concerns are addressed to meet local and/or minimum ExxonMobil Requirements.
2
Design guidelines / parameters for ammonium sulfate feed systems are described below. The preferred method of feeding ammonium salts is to prepare a bulk solution and follow the recommended procedures for bulk liquid chemicals.
• The chemical feed system for ammonium salts (Figure 1) typically includes a bulk storage tank and a spared pumping configuration.
• The ammonium salt solution should be injected via dosing pumps. Normally, 2-100% capacity pumps are provided. Positive displacement metering pumps are used for rates up to 100 gph (0.1 L/s). Centrifugal pumps with flow control are used for higher rates.
• The bulk storage tank should provide a minimum inventory of 15 days at the design consumption rate. • The bulk storage tank should contain an agitator.
• The bulk storage tank should be equipped with a level gage that is visible from the unloading connection. • Dilution water shall be clean condensate or equivalent water quality. Potable water must never be used.1
• A pressure relief valve shall be provided downstream of each pump system even if built–in relief valves are provided with the pumps. The set pressure is to be 10% above the operating pressure at the pump discharge or 10% above the process equipment design pressure, whichever is greater.
• Protective facilities, e.g., safety shower and eye wash, should be within 50 ft of the injection facilities (GP 3-2-6). Phosphorus - The usual forms of phosphorous found in aqueous solutions include orthophosphate (PO4–3, HPO
4–2, H2PO4–1, H3PO4), polyphosphate (molecules with two or more phosphorus atoms), and organic phosphate.
As a rule of thumb:
PPM (mg/L) of Phosphorus required for bio-growth = ppm (mg/l) of BOD5 in the wastewater/100
If an appropriate amount of phosphorus for bio–growth is not found in the wastewater for biotreatment, phosphorus may be added. Several sources of phosphorus are available, however typically phosphoric acid (H3PO4) is used. The phosphoric acid is a low strength acid and is added in relatively low dosages, hence there is no significant effect on the wastewater pH. The advantages and disadvantages for the most common sources of phosphorus are as follows:
PHOSPHORUS SOURCE ADVANTAGES DISADVANTAGES
Phosphoric Acid (H3PO4) 2 • Available in bulk liquid
• Easy to pump and meter flow
• Corrosive
• Safety Equipment Required
Phosphate2
• Neutral Solution • Low strength solution due to solubility limitations
Design guidelines / parameters for phosphoric acid feed systems are as follows:
• The chemical feed system for phosphoric acid addition (Figure 1) typically includes a bulk storage tank and a spared pumping configuration.
• The phosphoric acid should be injected via dosing pumps. Normally, 2-100% capacity pumps are provided. Positive displacement metering pumps are used for rates up to 100 gph (0.1 L/s).
• The bulk storage tank should provide a minimum inventory of 15 days at the design consumption rate. • The bulk storage tank should be equipped with a level gage that is visible from the unloading connection.
• Dilution water, if required, shall be clean condensate or equivalent water quality. Potable water must never be used.1 • A pressure relief valve shall be provided downstream of each pump system even if built-in relief valves are provided with
the pumps. The set pressure is to be 10% above the operating pressure at the pump discharge or 10% above the process equipment design pressure, whichever is greater.
• Protective facilities, e.g., safety shower and eye wash, shall be within 50 ft of the injection facilities (GP 3-2-6).
pH ADJUSTMENTS
General - Refineries and petrochemical plant's wastewater often contain acidic or alkaline materials that may require pH adjustment prior to discharge to receiving waters, or prior to chemical or biological treatment.
➧ 1
: Unless isolation and backflow concerns are addressed to meet local and/or minimum ExxonMobil Requirements.
2
Acids - Any strong acid can be used effectively to neutralize alkaline wastes, but cost considerations usually limit the choice to sulfuric or hydrochloric acid. The reaction rates are practically instantaneous. Some advantages and disadvantages for these two recommended acids are:
ACID ADVANTAGES DISADVANTAGES
Sulfuric Normally Lower Cost Corrosive
Dangerous to handle
May form CaSO4 precipitation in the presence of calcium
Hydrochloric No Heated Dilution
Most effective
Corrosive
Dangerous to handle
Gives off pungent irritating odor Volatile
Properties of commercially available forms are as follows:
WT OF CHEMICAL PER VOLUME OF SOLUTION SOLUTION TYPE WT% OF CHEMICAL lb/gal g/l SG OF SOLUTION BAUMÉ 93 14.19 1700 1.8279 65.7 Sulfuric Acid (H2SO4) 98 15.02 1799 1.8361 66.0 32 3.096 371.0 1.1593 19.9 Hydrochloric Acid (HCl) 36 3.542 424.4 1.1789 22.0
Bases - Sodium Hydroxide, also called caustic soda, is the most commonly used base due to its availability as an aqueous solution. The advantages of liquid caustic (< 50 wt% strength) over other bases are:
• It is easier to unload (tank trucks) and handle. • Delivery cost is lower than any other dry bases.
The commercially available strengths for caustic are as follows:
WT OF CHEMICAL PER VOLUME OF SOLUTION SOLUTION TYPE WT% OF CHEMICAL* lb/gal g/l SG OF SOLUTION BAUMÉ 20-25 2.035 243.8 1.2191 26.1 Sodium Hydroxide (NaOH) 50 6.364 762.7 1.5253 49.9 Note:
*
For caustic with strength greater than 50%, special care must be provided. Consult EMRE's Water and Waste Section.Applications - Wastewater typically requires pH adjustment in the following wastewater treatment areas.
1. Prior to Secondary Oil and Suspended Solids Separation - The primary purpose of adjusting the pH at this point is to assure that the proper pH range is maintained for optimum performance of inorganic coagulants and coagulant aids. 2. Biological Treatment - Aerobic biological treatment systems operate effectively within a relatively narrow pH window.
The pH in the biological reactor should be controlled between 6.5 and 8.5 (optimum range is 7 to 8). Therefore, pH control is required to prevent upsets of the biological treatment system.
Aerobic treatment under non-nitrifying conditions uses H+ ions tending to increase pH. The increase in pH is only slightly because alkalinity is also produced.
Biological nitrification of ammonia consumes about 7 pounds of alkalinity for every pound of ammonia (expressed as CaCO3) which is oxidized to nitrate. If the influent wastewater to the biological treatment plant does not have sufficient
alkalinity, the pH can be significantly lowered and the biological process upset by alkalinity consumption through nitrification. It is recommended to control the pH of the basin, which is easier to control than the feed.
Anaerobic biological decomposition of organic matter may either produce or consume alkalinity depending on the organic composition of the feed. The alkalinity in the anaerobic biological treatment system should be maintained at a minimum of 1000 ppm (mg/l) as CaCO3 equivalent to avoid process upsets which can be caused by extreme pHs (optimum pH range is 6.5 to 7.5).
3. Prior to Final Discharge - Generally, if the final discharge of the wastewater is preceded by biological treatment, additional pH adjustment is not necessary. Otherwise, it may be necessary to adjust the pH of the final discharge to comply with local regulations.
Dosages - The dosage rates for acids / bases have been traditionally predicted by bench-scale tests. More recently, computer modeling via the Environmental Simulation Program (ESP) has been successfully used in ExxonMobil to predict dosage requirements for acids and bases. This model is available through EMRE's Water & Waste Section. Pilot plant facilities can also be used to determine the optimum chemical dosages in certain cases.
Design guidelines / parameters for pH adjustment chemical feeders are as follows:
• The chemical feed system for liquid acid / base (Figure 1) typically includes a bulk storage tank (temporary storage tanks may be provided by supplier) and a spared pumping configuration.
• The acid / base should be injected via dosing pumps. Normally, 2-100% capacity pumps are provided. Positive displacement metering pumps are used for rates up to 100 gph (0.1 L/s). Centrifugal pumps with flow control are used for higher rates.
• Whether fixed or portable, the bulk storage tank should provide a minimum inventory of 15 days at the design consumption rate.
• The fixed bulk storage tank should be equipped with a level gage that is visible from the unloading connection. • Dilution water, if required, shall be clean condensate or equivalent water quality. Potable water must never be used.1 • A pressure relief valve shall be provided downstream of each pump system even if built-in relief valves are provided with
the pumps. The set pressure is to be 10% above the operating pressure at the pump discharge or 10% above the process equipment design pressure, whichever is greater.
• Protective facilities, e.g., safety shower and eye wash, shall be provided within 50 ft of the injection facilities (GP 3-2-6). • A feedback / feedforward control loop is recommended to compensate for the inherent short retention time of in–pipe
injection.
• Use of feedback, feedforward, or both for pH control will depend on the application and control band. (Consult with EMRE's Environmental Section on specific applications)
• A pH analyzer with high and low alarm is generally provided to control the amount of acid / base feed.
OXIDANTS
Applications - Oxidants like hydrogen peroxide have been used to oxidize small quantities of sulfide, phenols, and other organics in wastewater, at their source such as tank bottoms, desalters, or in pre-treated wastewaters. Hydrogen peroxide is usually added in a flash mix tank or a junction of a flow splitter box with a high level of mixing, or a static mixer may need to be employed in a line.
Hydrogen peroxide has also been used to control severe cases of filamentous bacteria or bulking (poor settling) of biological solids in activated sludge clarifiers. The injection point is the biological sludge recycle line.
The use of hypochlorite or other halogenated compounds for oxidation is generally recommended only for sulfide control in fairly clean or low organic contamination wastewaters (such as stagnant pond or lagoon waters). The use on organic laden wastewaters, expecially those containing phenolic compounds, could potentially form halogenated organics, and therefore is not recommended. Use of hypochlorite for biological sludge bulking control should only be considered after use of peroxide has been tried. Hypochlorite use needs to be carefully controlled to avoid killing off desirable microbes in the activated sludge. Dosage - The dosage rate of hydrogen peroxide generally ranges between 50 to 200 ppm (mg/l) for controlling biosolids bulking. The dosage should be started at a low level (50 wppm) and increased gradually in steps, until the bulking is controlled. For oxidation of sulfide and phenols contamination, a guideline of 3 wppm of H2O2 (100% basis) per 1 wppm of sulfide, and 4 wppm of H2O2 per 1 wppm of phenols is typical, but temperature, pH and reaction time need to be considered, especially for organic contaminants such as phenol.
1
Design guidelines / parameters on the use of hydrogen peroxide are given below. Refer to DP-XIX-A11 on Chemical Oxidation for more details on use of hydrogen peroxide for treatment.
• The chemical feed system for hydrogen peroxide (Figure 1) typically includes a bulk storage tank (permanent or temporary) and a spared pumping configuration.
• The oxidant should be injected via dosing pumps. Normally, 2-100% capacity pumps are provided. Positive displacement metering pumps are used for rates up to 100 gph (0.1 L/s). Centrifugal pumps with flow control are used for higher rates. • For permanent facility, the bulk storage tank should provide a minimum inventory of 15 days at the design consumption
rate.
• The bulk storage tank should be equipped with a level gage that is visible from the unloading connection. • Dilution water, if required, shall be clean condensate or equivalent water quality.
• A pressure relief valve shall be provided downstream of each pump system even if built-in relief valves are provided with the pumps. The set pressure is to be 10% above the operating pressure at the pump discharge or 10% above the process equipment design pressure, whichever is greater.
• Protective facilities, e.g., safety shower and eye wash, shall be provided within 50 ft of the injection facilities. (GP 3-2-6). ➧ • Peroxides are strong oxidants and should not be added directly to very oily waters or in plant sewer systems that can dry
out. Consult plant safety personnel and supply vendors for safe application. Permanent systems will require a peroxide addition pump cut off , when there is no flow of wastewater in the lines being treated . Usuallly, commercial grades of 35% H2O2 are preferred to ensure there is enough dilution water, and a minimal temperature rise due to the exothermic reaction of the peroxide with the contamination.
• Due to oxidative nature of chemicals, materials of construction will require review.
FOAM CONTROL
The most typical application of defoamers in wastewater treatment is in biological treatment units. Usually, defoamers are only used on a sporadic basis to eliminate serious foaming problems. Defoamer type and dosage may be selected by placing influent water, or water from the biological treatment in a 2-L graduated cylinder which is moderately aerated with a sparger. The effectiveness of the chemical type and dosage in reducing the tendency of the water to foam is evaluated visually. Typically silicone based antifoams are used due to their low toxicity.
Design guidelines / parameters on the use of defoamers are given below.
• Defoamers are most commonly sprayed on the surface of the wastewater in the reactor basin rather than injected directly into the bulk wastewater. Spray application may be performed using a portable tank and spray system or a permanently installed spray system.
• For small volume, liquid defoamers, gravity feed directly from the drum using a needle valve.
• For large volume feed, more accurate dose control, and/or high viscosity defoamers, metering pumps are recommended. • Prepare the defoamer as 5% solutions for feeding convenience. The solution should be continuously agitated to maintain
a homogeneous solution.
• Because the products are non-corrosive, metal or plastic feed lines can be used. Avoid use of rubber gaskets or hoses which may dissolve in prolonged contact with defoamers.
• The best time to apply a defoamer is shortly before the foam becomes troublesome, such as when the foam layer is building in a biox basin/tank or clarifier, thus allowing for adequate mixing and reaction time. Although defoamers can collapse foam, they are more effective when applied before it develops.
COOLING WATER TREATMENT BIOLOGICAL CONTROL
The operating conditions in recirculated cooling water are ideal for the growth of biological matter. To control the biological activities, a biocide chemical is added to the water treatment program. Oxidizing biocides such as chlorine, sodium hypochlorite, chlorine dioxide, or bromine-associated compounds are most commonly used with good results.
For either once-through or recirculation system, facilities should be provided for feeding the biocide into the back of the cooling tower basin. If chlorine is used, it must be present in the cooling water as free residual to be effective.
Chlorine - For recirculating cooling systems, the design capacity of the chlorine feeder shall be based on achieving a 0.1-0.3 wppm (mg/l) free chlorine residual in the recirculating water flow or a minimum dosage of 7 wppm (mg/l) at maximum design cooling water flow rate (see DG 11-3-1).
For once-through cooling water systems, shock chlorination once a day is normally practical and the chlorinator design should be based on achieving a chlorine residual of 1 wppm (mg/l) in the effluent for 1 hour. The chlorine required by the organics and other reducing agents in the water must be satisfied before any residual chlorine will appear in the effluent. In the absence of water data, the chlorination system design capacity should be based on 10 wppm (mg/l) minimum instantaneous dosage for maximum cooling water flow.
Chlorine may be fed either as gaseous chlorine (100% Cl2) or the commercial liquid sodium hypochlorite (12.4 wt% Cl2). Liquid hypochlorite is becoming popular due to the higher costs associated with precautions, equipment, and procedures required to minimize the risks associated with handling gaseous chlorine. The hypochlorite solution is fed using a metering pump which should be sized to feed an equivalent of 15 ppm 100% Cl2 if field data is lacking (refer to DG 11-6-2). Spills or overflow from the sodium hypochlorite storage tank may be sent to the cooling tower basin.
The use of gaseous chlorination is being reduced but may still be appropriate in some locations subject to local approval. The gas from either commercial cylinders or an evaporator is dissolved in a water slip stream by means of an eductor. This results in a chlorine solution strength of approximately 0.1 wt%. This solution should be evenly distributed below the water surface by means of a lateral pipe arrangement at the rear of the cooling tower basin, opposite the cooling water pumps. Gaseous chlorine will tend to lower the system pH due to the HCl byproduct.
Design guidelines / parameters on the use of gas chlorinators are given below. It is also recommended that the safety guidelines published by the Manufacturing Chemists Association and the Chlorine Institute be followed.
• Dilution water for the chlorinator must not be less than 50°F (10°C), or ice formation may cause plugging problems. • Continuous rates of chlorine gas withdrawal should not exceed 400 pounds (180 kg) per 24 hours from each one ton
cylinder, at room temperature (70°F or 21°C). This rate may be exceeded (up to 50%) for periods not exceeding 2 hours. Rule of thumb is not to design for more than 4 cylinders operating in parallel. When the feed rate exceeds 3000 pounds (1360 kg) per day the liquid chlorine should be fed to an evaporator upstream of the chlorinator (see DP XXVII).
• If the ambient temperature can be expected to be below 50°F (10°C) for extended periods, a building should be provided for the chlorinator and cylinders.
• Weighing scales should be provided to determine when shipping containers should be replaced and to verify chlorine feed rates.
• Analyzers to measure the free chlorine residual in the circulated cooling water should be provided. • Chlorine leak detectors and a catch basin for major spills shall be provided.
Dichloroisocyanuric Acid Salts, Mixture (Sodium Bromide) - This chemical shall only be fed with a Calgon “Towerbromâ" feeder or equivalent. Calgon Towerbrom feeder is a flow through feeder where the chemical is dosed into the water. Mix only with water and use clean dry utensils. Do not add this product to any dispensing device containing remnants of any other product (like hydantoin-based bromine products (BCDMH) or other organic material). Such misuse may cause a violent reaction leading to fire or explosion.
Bromo chloro dimethylhydantoin - Solid flow through feeder as shown in Figure 5 should be used. Fresh makeup water, e.g., well or river, which cannot be contaminated with hydrocarbon should be used as dilution water. Recycled cooling tower slipstream should not be used. Bromo chloro treaters can exhibit high temperatures due to oxidation of hydrocarbons (or any other oxidizable substance) when there is no flow through the vessel. Therefore, use of fresh water is the preferred choice regardless of design or chemical. Appropriate training should be provided for all personnel using bromicide.
CORROSION CONTROL
To reduce corrosion to an acceptable level, chemical corrosion inhibitors which form protective films on heat transfer surfaces are the most effective protection. Inhibiting corrosion is accomplished by phosphates, zinc, nitrites, and molybdate salts. The use of chromate, which is a reliable corrosion inhibitor, is prohibited by environmental constraints. Nitrite is not practical for use in an open system due to atmospheric oxygen converting the nitrite to nitrate.
The corrosion inhibitors most frequently used in ExxonMobil recirculating cooling water systems are shown in descending order of preference, provided their use meets all environmental requirements:
1. Stabilized Phosphate (Ortho / Polyphosphate) or Alkaline Phosphate. 2. Alkaline or Zinc Alkaline Phosphate.
3. All Polymers (Organic (Polymer) Salts).
Design guidelines / parameters for corrosion inhibitors design are given below. The following guides in sizing equipment will allow the use of any vendor proprietary products when final selection by the owner is made. See Report No. EE.102E.78,
Cooling Tower Water Treatment Guidelines, and Report EE.34E.86, Environmentally - Acceptable Cooling Water Treatments,
for detailed discussion of acceptable commercial chemicals. • Generally, two chemical feeders are provided.
• If the water treatment program to be used is known, design for the chemical rates specified by the vendor or discipline specialist. Otherwise, design for 100 wppm (mg/l) of each commercial liquid product in the recirculated cooling water. The design feed rate should be based on the design total blowdown flow (both uncontrolled and controlled) since this is where the product is lost. For 100 wppm (mg/l) concentration, the chemical rates will be as follows:
– Gallons/Hour Chemical = 0.006 x Blowdown (gpm) – Liters/Hour Chemical = 0.36 x Blowdown (L/s)
• The design capacity of the metering pump should be two times this calculated number. Normally 2-100% design capacity pumps are provided. Positive displacement pumps are used for rates up to 100 gph (0.1 L/s).
• Specifications for chemical feeders may be found in DG 11-6-2 and Tables 1 and 2.
• A final check should be made with the owner and the discipline specialists as to the treatment program selected, and if there is a need for an additional chemical feeder.
pH ADJUSTMENT
The cooling water treatment program selected and the site water quality will determine the need for pH adjustment. Computer modeling using the Environmental Simulation Program (ESP) can assist in predicting acid requirements. This model is available from EMRE's Water and Waste Section. Routine monitoring of pH of the water in an existing cooling unit will establish the guidelines for periodic adjustment of the chemical dosage to the unit.
Design guidelines / parameters to pH adjustment design for cooling towers are given below. In addition, follow the guidelines under pH Adjustment for Wastewater Treatment.
• In cases where a controlled pH control program is being used, the pH of the recirculated cooling water should be controlled in accordance with the program requirements. Normally, acid addition is required to accomplish this. This is due to free carbon dioxide being stripped across the cooling tower to approximately 5 ppm (mg/l). For example, if the alkalinity must be controlled to between 25 and 50 ppm (mg/l) for a pH of 7.0 to 7.5, the volume of 98% sulfuric acid (66°Bé) required to treat the makeup water is calculated using the following equation:
Note: 93% sulfuric acid should be used if ambient temperatures will be less than 35°F (2°C).
Gal/h of 100% (66°Bé) H2SO4 = 3.26 x 10–5 x (Alkalinity in Makeup Water (Customary) as wppm CaCO3) x (Makeup Rate in gpm)
or
Kg/h of 100% (66° Bé) H2SO4 = 7.93 x 10–3 x (Alkalinity in Makeup Water (Metric) as wppm CaCO3) x (Makeup Rate in L/s)
• Hydrochloric acid may also be used for pH control. The gallons per hour of 20° Bé hydrochloric acid required are 3.6 times the amount of 66° Bé sulfuric acid. In metric units, the weight of 32% (20° Bé) hydrochloric acid required is 2.27 times the weight of 100% (66° Bé) sulfuric acid.
• The metering pump should be designed for a maximum feed rate of two times the design feed rate. A proper mesh-screen strainer is required on the pump suction piping to minimize plugging. Normally, 2-100% capacity pumps are provided. Positive displacement metering pumps are used for rates up to 100 gph (0.1 L/s). Centrifugal pumps with flow control are used for higher rates.
• Specifications for chemical feeders for the cooling towers may be found in DG 11-6-2.
• A pH analyzer with high and low alarm is provided to control the amount of acid feed. The acid should be added to the cooling tower makeup water (Figure 6).
BOILER FEED WATER TREATMENT
Chemical treatment of the boiler water protects the steam generating system from the impurities remaining in the Boiler Feedwater (BFW). The BFW which is pumped from the deaerator is free of oxygen and carbon dioxide which may have been present in the make-up water or condensate streams. Types and amounts of other impurities remaining in the BFW will depend on the method of make-up water treatment (which is usually a function of steam quality requirements) and the source(s) of return condensate streams.
Reliable and separate feed systems are required for: 1. Oxygen Scavenging
2. Condensate Dosing
3. Internal Boiler Water Quality Control
Design guidelines / parameters for boiler water treatment chemical feed system are given below.
• Each system typically includes a storage tank and a spared pumping configuration.
• Chemicals storage should provide a minimum inventory of 24 hours at the design consumption rate.
• Provide two metering pumps (normal plus spare) each for the oxygen scavenger and the condensate dosing facilities. This is based on a single deaerator system. For multiple deaerators, additional dedicated systems should be provided.
• Boiler water chemicals injection shall be via dedicated metering pumps for each boiler. A common spare pump, capable of serving any boiler shall also be provided.
• Sizing of the facilities may require consultation with the chemical(s) supplier(s). Concentration and activity of vendor supplied chemicals can vary and have an effect on storage volumes and pumping rates.
CONTROL AND MONITORING
Control strategies for maintaining proper chemical dosages from the feeding systems generally fall into the following two categories:
• Feedback control. • Feedforward control.
Feedback control adjusts the dosage based on a process control measurement downstream of the chemical addition point. Feedforward control adjusts the dosage based on a process control measurement upstream of the addition point.
If the water / wastewater or sludge flowrate is very constant, the chemical pumping rate may be manually set after each test to provide the proper dosage. If the water / wastewater or sludge flowrate varies significantly, the dosing pump can be controlled by either a feedback or a feedforward control system to provide a chemical flowrate which is proportional to the flowrate, thereby maintaining the dosage established by the manual test.
The installation of automatic controls should be considered for all water / wastewater treating systems, because the annual cost of chemicals can be very high. Automatic controllers are available which continuously monitor the condition of the water / wastewater and automatically supplement necessary chemicals to keep the water / wastewater within set limits. The use of test exchangers and corrosion coupons are also useful in monitoring the effectiveness of the water treatment program. Complete systems may be available through cooling water treatment program vendor as a lease or purchase.
Manual control systems may be used in locations that have adequate technical personnel to perform routine water / wastewater analyses and to modify chemical treatment necessitated by sudden variations in water / wastewater composition, process contamination, etc.
CHEMICAL PREPARATION AND HANDLING
Specific requirements for chemical preparation and handling can be found in DGs 11-6-1, 11-6-2, and 11-6-3. Also see Report EE.92E.94 for additional design practices for chemical injection systems. General considerations for chemical preparation and handling, methods of chemical receipt, and a summary of information on the safety considerations for handling specific chemicals are provided in Table 2. Selection of chemical storage and delivery systems should consider the following:
• Shelf life of chemical.
• Hygroscopic tendency of chemical. • Quantity of chemical used. • Safety.
• Economics.
Bulk Liquid - This is the preferred method of receipt, because the chemical can be distributed as is with no preparation required.
In some areas, semi-bulk liquid chemicals will be available in returnable liquid containers. Where this is the case, the following should be provided:
1. Storage area for a reserve supply of full containers and for holdup of empty containers prior to return. The amount of holdup will be dependent on the location of the supplier, delivery frequency, and regularity of deliveries. Sufficient holdup should be provided to reduce the chance of running out of chemical to essentially zero. The storage area may have to be sheltered and heated depending on the location and the chemical properties.
2. Provide equipment to off load and handle the full and empty containers if this equipment is not available in the plant. 3. Provide an access road for truck deliveries.
4. Protective facilities, e.g., safety shower and eye wash, shall be provided within 50 ft of the injection facilities. (GP 3-2-6). In other cases, bulk liquids may be available as truck delivered parcels. In this case the following should be provided: 1. 15-day storage (outside). Heating may be required, depending on the properties of the chemical.
2. A compressed air supply at 30 psig (210 kPa) for unloading trucks. 3. An access road for tank truck deliveries.
4. Hose connections to storage tanks.
5. A gauge glass or local indicator for tank level plus remote level indication. 6. An overflow line on tanks, with a connection to the chemical sewer, if available.
7. A dessicator in the vent line or vent routed to a scrubber if using sulfuric / hydrochloric acid tank.
8. Protective facilities, e.g., safety shower and eye wash, shall be provided within 50 ft of the injection facilities. (GP 3-2-6). Liquid Chlorine Gas - Refer to Report EE.102E.78, Cooling Tower Water Treatment Guidelines, for information on chlorine handling and chlorinator operation. A copy of the safety guidelines published by the Manufacturing Chemists Association and Chlorine Institute should be available for each plant using a gas chlorinator.
DRY FEED SYSTEMS
Dry chemical feeders are selected over wet feeders for handling large volume requirements of chemicals available in dry form and in bulk. Bulk dry is the preferred method of receiving dry chemicals. Generally about 30 days of storage is provided. For design of a dry feeder system, there are several variables to consider to make sure that performance is consistent and reliable:
1. The characteristics of the chemical, including: a. Method of storage and transfer from inventory.
b. Tendency to cake or bridge, requiring protection from moisture, and vibrators or similar accessory devices to promote material flow.
c. Angle of repose, for proper design of hopper and chutes.
d. Particle size distribution, so that dusty materials can be confined, meet safety and work exposure guidelines, and kept from damaging electric devices.
2. The design of the silo, chutes, and hoppers to prevent size segregation and variability in density of the material entering the feed device.
3. The operation environment of the feeder, such as ranges of temperature and humidity, and dust loading in the air. 4. Materials of construction.
5. Safety.
6. Air emission control.
When usage is less than about 500 lb/day (225 kg/day), non-bulk receipt may be more economical. For non-bulk dry chemicals, consideration must be given to whether storage should be inside or outside depending on the quantity of chemical, hygroscopic nature of the chemical, chemical stability, and the prevailing weather conditions at the facility location. In addition, a safe and efficient method for transferring the dry material from non-bulk storage to bulk storage or a day tank must be provided.
If the dry chemical is highly soluble in water, the preferred method of chemical feeding is to prepare bulk or day quantities of solution and use the same feeding system which is recommended above for liquid chemicals (Figure 1). Where the dry chemical is not very soluble, use a dry volumetric chemical feeder system (Figure 2) or solid feeders (Figure 5).
The dry chemical in the volumetric feeders is stored in a hopper which is then fed by gravity into the feeder mechanism. The device for displacing the chemical at a controlled rate for the feed bin to the reservoir, or solution tank, may be:
1. A traveling belt, with some type of gate to control the depth and width of the band of chemical leaving the spout. 2. A screw or auger, turning on its axis in a tube.
3. A rotating table, or disk, directly below the hopper spout, with an adjustable doctor blade to deflect a controlled volume of chemical from the table into a receiver.
4. A rotating “paddle wheel" lock valve, similar in some respects to the liquid gear pump, delivering the measured volume contained in each compartment onto a conveyor belt as the lock valve slowly revolves.
Each of these devices can deliver chemical at a rate proportional to the flow of water / wastewater to be treated by using a flow meter signal either directly - to control belt speed, for example - or indirectly, through a timer.
Drums or Bags - Chemical handling facilities should be designed for operation by a single person. A fork lift should be available for moving chemical containers.
1. Outside Storage requires the following:
• Some protection for chemicals and operators.
• Cold treated soft water (less than 100°F or 38°C) for dilution of chemicals. Treated soft water should be piped into the area where chemicals are mixed. For cooling tower services, except salt water cooling systems, use the cooling water makeup for dilution.
2. Inside Storage - When the ambient temperature is below 55°F (13°C) for more than 48 consecutive hours, a heated and lighted building is required. The building should contain the following:
• Monorail or hoist to move chemicals.
• Eductor or feed screw for dry chemicals which are packaged in fiber drums.
DRY MATERIALS (IN BAGS)
1. For quantities of less than 1000 lb/day (450 kg/day), use an eductor or feed screw.
2. For quantities greater than 1000 lb/day (450 kg/day), provide a variable speed conveyor, automatic bag breaker and automatic pneumatic loading into silos. Each silo must be provided with high and low-level indicators, isolation valves, and chutes for transferring chemical by gravity to the dry chemical feeder located under the silo. Electric rappers and compressed air should be provided to keep the dry chemical flowing freely through the chutes.
➧ TABLE 1
SUMMARY OF TYPICAL CHEMICAL APPLICATIONS
CHEMICAL Sil ic a C ont rol Bi o c id e C o agulat io n C o agulat io n Ai d C ont rol of Bi ol o g ical Sol ids Sulf ide Rem o val Corrosi on C ont rol Foam Cont rol Me ta ls Rem o val Nu tri e n t A ddit io n Oxygen S cavengi ng pH Ad ju stm e n t S cal e/ Hardness C ont rol Slu dge C ondit ioni ng Organic C ondit ioni ng /R e m ov a l Aluminum Sulfate X X X Ammonia X X Ammonium Hydroxide X Ammonium Sulfate X Biocides (non-oxidizing) X
Boiler Polymer Treatment X
Brine X
Bromo Chloro Dimethylhydantoin X
Calcium Hydroxide X X X X X X Calcium Oxide X X X X X X Chlorine X Clay/Bentonite X X Cyclohexylamine X Defoamer X
Deformer (organic/silica based) X
Diatomaceous Earth X X
Dichloroisocyanuric Acid Salts X
Dispersants X Ethylenediamine Tetraacetic Acid X X X Ferric Chloride X X X Ferric Sulfate X X X Ferrous Chloride X X X X Ferrous Sulfate X X X X Hydrazine X Hydrochloric Acid X X Hydrogen Peroxide X X X X Hydroxylamines X X Magnesium Oxide X X Morpholine X Nitrilotriacetic Acid X X X Octadecylamine X Phosphoric Acid X X X X Polyaluminum Chloride X Polyelectrolytes X X X X1 X
Powder Activated Carbon X X X X
Sodium Aluminate X X X
CHEMICAL Sil ic a C ont rol Bi o c id e C o agulat io n C o agulat io n Ai d C ont rol of Bi ol o g ical Sol ids Sulf ide Rem o val Corrosi on C ont rol Foam Cont rol Me ta ls Rem o val Nu tri e n t A ddit io n Oxygen S cavengi ng pH Ad ju stm e n t S cal e/ Hardness C ont rol Slu dge C ondit ioni ng Organic C ondit ioni ng /R e m ov a l Sodium Carbonate X X X X Sodium Hydroxide X X Sodium Hypochlorite X Sodium Metaphosphate X X X Sodium Phosphate X X Sodium Sulfite X Sulfuric Acid X X Urea X
Volatile Oxygen Scavenger X
1
➧ Table 2
Properties and Handling Considerations for Commonly Used Chemicals(1)
CHEMICALS NAME [TRADE NAME] FORMULA CAS #(2) SOLUTION STRENGTH FED WEIGHT % COMMERCIAL FORMS & STRENGTHS WEIGHT % SHIPPING CONTAINER STORAGE CONSIDERATIONS CHARACTERISTICS, HANDLING, & SAFETY CONSIDERATIONS FEED SYSTEM FIG # Aluminum Sulfate (hydrate) [Alum] Al2(SO4)3•14 H2O (dry) Al2(SO4)3•49.6 H2O (liquid) 10043-01-3
20% Al2(SO4)3 Dry: off white powder, cake 15 to 17% Al2O3 Liquid
17% Al2O3
Bags, barrels, drums, bulk (rail car or truckload) Bulk (rail car or truckload)
• Bulk liquid is preferred: 20 wt% as Al2(SO4)3.
• Dry: if adequate liquid storage is not possible or practical. Maximum storage tanks should have dust collectors and minimum hopper slope of 60°.
• Keep in dry storage.
Dry: Hygroscopic, cakes in high humidity, soluble acidic, mildly corrosive if wet.
Liquid: Astringent, irritates eyes, nose, mucous membrane, and skin. Use protective clothing/gloves and eye protection. Avoid inhalation of aluminum sulfate dust or vapors.
1 for liquids 2 for dry Ammonia (anhydrous) NH3 7664-41-7 99 to 100% NH3 Liquefied gas: 99 to 100% NH3 Cylinders, tank cars, truck •
Bulk liquid. Light green or light brown liquid, freezing point approximately 5°F. Gives off pungent, irritating odor. Use protective clothing/gloves and eye protection. 1 Ammonium Hydroxide [Ammonia Water] NH4OH 1336-21-6 20% NH4OH Liquid: 29.4% NH3 Carboy, drums, tank trucks, rail cars
•
Bulk liquid. Store in a cool, dry, ventilated area.. Protect from direct sunlight.
Strongly alkaline clear solution. Causes burns to skin, irritant to eyes, nose, lung. Corrosive.
1 Ammonium Sulfate (NH4)2SO4 7783-20-2 25% NH3
Crystal Bags, drums,
bulk • Keep in cool, dry storage. White to brown acidic,soluble, hydroscopic crystals, tends to cake. Mildly corrosive. Irritant to eyes, skin, and respiratory tract. 1 Bromo chloro Dimethyl-hydantoin C5H6Br ClN2O2 126-06-7 As required Tablet or granular
Bags, Pails • Store dry in the original container. Keep container tightly closed when not in use. Store in cool, dry, well-ventilated area away from heat and open flames. Keep container off wet floors.
Severe eye irritant, can burn skin. Use protective clothing/gloves and eye protection. Highly exothermic. 5 Calcium Hydroxide9 [Hydrated Lime] Ca(OH)2 1305-62-0
5% Slurry Pre–mixed slurry or powder 93% Ca(OH)2
Bags, barrels, bulk (rail car or truckload)
• Bulk liquid is preferred: store as an on-site prepared slurry containing 5 wt% Ca(OH)2.
• Dry: if adequate liquid storage is not possible or practical, store in bags or drums or in bulk tank with hopper agitation.
Irritant of eyes, mucous membrane, and skin. Use protective clothing/ gloves and eye protection. Avoid inhalation of calcium hydroxide dust or vapors.
1 for liquids 2 for dry
TABLE 2 (Cont.)
PROPERTIES AND HANDLING CONSIDERATIONS FOR COMMONLY USED CHEMICALS(1)
CHEMICALS NAME [TRADE NAME] FORMULA CAS #(2) SOLUTION STRENGTH FED WEIGHT % COMMERCIAL FORMS & STRENGTHS WEIGHT % SHIPPING CONTAINER STORAGE CONSIDERATIONS CHARACTERISTICS, HANDLING, & SAFETY CONSIDERATIONS FEED SYSTEM FIG # Calcium Oxide [Quick lime] CaO 1305-78-8
5% slurry Granules, pebbles 90 to 96% as CaO
Bags, barrels, bulk (rail car or truckload)
• Bulk liquid is preferred: store as an on-site prepared slurry containing 5 wt% as CaO.
• Dry: if adequate liquid storage is not possible or practical, store in bags on pallets, in barrels, or in bulk tank, 60 days max. Provide dust collectors, hopper agitator, and hopper slope of 60°.
Forms calcium hydroxide with water (exothermic reaction), low solubility; hydroscopic; mildly corrosive if wet. Irritates eyes, mucous membrane, and skin. Keep dry and cool. 1 for liquids 2 for dry Chlorine Cl2 7782-50-5
100% Liquefied Gas One-Ton
Cylinder • Minimize cylinders onsite.
Yellow, pungent gas, extremely reactive in wet conditions; forms dense white vapor with ammonia. Toxic gas irritates skin, eyes, nose.
6 Clay [Bentonite] H2O• (Al2O3• Fe2O3•3MgO) 4SiO2•nH2O 1318-74-7 (Clay) 1302-78-9 (Ben.)
5% Slurry Powder, granules Bags, bulk (rail car or truckload) •
Bulk liquid is preferred: store as an on-site prepared slurry containing a maximum of 5 wt% Bentonite.
• Dry: if adequate liquid storage is not possible or practical, store in bags or in bulk tank with hopper agitation.
Inert, absorbs water quickly; higher concen-trations produce viscous slurries; proper mixing required. No significant hazard. Avoid inhaling Bentonite dust. 2 Corrosion Inhibitors a) Phosphate/ Phosphonate Based Inhibitor b) All Organic Inhibitor c) Zinc or Molybdenum Base Inhibitor Systems As recommended by vendor
Varied Varied • As recommended by vendor. • As recommended by vendor. 1 or 7 Cyclohexylamine [Neutralizing Amine] C6H11NH2 108-91-8 40% C6H11NH2 Liquid, blended with other neutralizing amines
Tanks, drums • Keep container closed when not in use. Keep from freezing.
Ignitable. Liquid and vapor irritate skin and mucous membranes. Strong alkaline. Use protective clothing/ gloves and eye protection.