Az Liht.docx

A-Z LITE® Overall Program Application: Corrosion Control: The A-Z LITE® program uses a combination of ortho-phosphate, zinc, and tolyltriazole to provide corrosion protection for mild steel and yellow metals (copper containing alloys). Additional corrosion protection is provided by a phosphonate (PBTC) which also inhibits calcium carbonate deposition. Application is at moderately alkaline pH in most cases, the exception being waters with low calcium (< 100 ppm), where the pH may be near 9. As in all robust programs, a combination of anodic and cathodic inhibitors are used in the program. Anodic corrosion inhibition is accomplished by ortho-phosphate from two possible sources: product feed and make-up water. At the anodic site, ortho-phosphate can be thought of as a plugging inhibitor by direct reaction with the soluble iron generated at the corrosion site. All metal loss occurs at the anodic site with formation of an iron phosphate plug. This film is self limiting because as less iron is generated from the corrosion process, less phosphate will precipitate. Because the pH is higher in this program, less corrosion potential exists and maintaining ortho phosphate levels above 5 ppm soluble will provide adequate corrosion protection. More detail is shown in the CPP. Local plant conditions may dictate that higher or lower residuals be maintained to obtain the desired results. Cathodic corrosion protection is controlled by several mechanisms. With the infusion of oxygen in water, an electrochemical reaction occurs at the cathode where hydroxyl ions are formed causing a localized high pH condition. When this occurs, a zinc hydroxide film forms at the cathode. In addition, a calcium organophosphate (PBTC) film will form under these alkaline conditions. A controlled zinc phosphate and calcium phosphate film is the third reaction which completes the cathodic corrosion inhibition. With the low levels of zinc (0.5 - 2 ppm) used in this program, protection of yellow metals cannot be assured when conductivity exceeds 2000 mS/cm. Under these circumstances, tolyl-triazole (TT) should be applied as part of the program. Even if there are no yellow metal heat exchangers, brass valves, bearings, or valve trim could allow copper to solubilize into the water and redeposit on mild steel. This would cause mild steel pitting by galvanic mechanisms. Phosphate and zinc residuals are expressed as soluble. This means that the phosphates and zinc are analyzed after filtration through a 0.45 m filter. In addition to maintaining proper soluble residuals, splits (the difference between filtered and unfiltered analyses) should be maintained at less than 1 ppm for optimum results.

Deposition / Fouling Control: When a cooling water program is operated under alkaline conditions in the presence of calcium, calcium carbonate can become a potential scalant. To prevent this from occurring, an effective calcium carbonate inhibitor such as PBTC must be employed. Polymer dispersants are used in cooling water systems to control two types of fouling. To insure adequate corrosion protection, adequate levels of zinc and phosphate must be present in the system. Thus, the solubility products of calcium phosphate, zinc phosphate, zinc hydroxide, and iron phosphate are exceeded. By preventing these components from precipitating in the bulk water, they are kept in the soluble form and available for controlled chemical / physical reactions at the highly active anodic and cathodic sites at the metal surfaces. Polymer dispersants keep the very small particles from agglomerating into larger particles and forming troublesome deposits. Dispersants also keep miscellaneous small suspended solids present in the system from agglomerating and forming deposits, especially in low flow areas. High stress conditions consist of high temperature, high calcium level, high iron level, long holding time index, and high aluminum level. Since the species responsible for corrosion protection (zinc hydroxide, zinc phosphate, and calcium phosphate) encountered in the AZ-Lite program exhibit reverse temperature solubility, high temperature increases the supersaturation level of these species. High temperature also increases the kinetic driving force for particle growth and deposition. High calcium level increase the supersaturation of calcium phosphate. High iron level, in addition to increasing the supersaturation of iron phosphate, tends to deactivate polymers by adsorbing on their surfaces. Polymers have a tendency to deactivate with time so a system with a long holding time index will tend to put a stress on a polymer. In addition to forming aluminum phosphate, which is a foulant, aluminum also tends to deactivate polymers in the same Manner as iron.

A recent advance in polymer technology, the new High Stress Polymer molecule, allows operation at higher stress levels than was previously possible. With High Stress Polymer it is now possible to operate systems at the following stress conditions: Condition Prism limit High Stress Polymer limit Temperature ( oF) 135 180 Calcium (ppm as CaCO3 ) 750 1200 Iron (ppm) 2 8

Holding time index (hr) 72 225 Aluminum (ppm) 0.5 2 In some cases, it would be possible to operate above the Prism limits while still using the Prism dispersant. The High Stress Polymer will give better results at these conditions. While the High Stress Polymer is superior to regular Prism for control of calcium, zinc, and iron phosphate based scale, the goal of this program is not to minimize polymer dosage but to ensure program success. Therefore we do not suggest a reduction of polymer feed when switching from on polymer to the other but to maintain the active polymer feed rate consistently. Determining Program Dosage: Calcium The AZ-Lite program is operable over a wide range of calcium levels, from 15 to 1200 ppm (as CaCO3). Guidelines are shown in the accompanying charts. In general, 4 ppm of polymer active is necessary for satisfactory operation, no matter how low the calcium is. As calcium and/or alkalinity increase, the amount of polymer needs to be increased to adequately control the tendency of calcium and zinc phosphate to precipitate. As calcium levels increase above 750 ppm, Super Prism should be substituted for Prism. In some cases, it would be possible to operate above the Prism limits while still using the Prism dispersant. The High Stress Polymer will give better results at these conditions. Phosphate Soluble phosphate levels as a function of calcium and alkalinity are given in the program guidelines. The goal in the AZ-Lite program is to maintain soluble phosphate residuals in the range that gives optimal corrosion protection without contributing to deposit formation. The phosphates should be analyzed on filtered samples using a 0.45 m filter when possible. Splits (difference between filtered and unfiltered results) should be maintained at <1 ppm. If splits are greater than this and the soluble phosphate is in the right range, dispersant feed should be increased. Zinc Since very low levels of zinc are being used, it is important to maintain a minimum of 0.5 ppm of soluble zinc. If the zinc splits (unfiltered minus filtered) are > 1 ppm, indicating precipitation, the dispersant dose must by increased. Other possible reasons for low soluble zinc are excessive phosphate, high pH, sulfide leaks, or other high stress conditions. Iron

As in any program containing inorganic phosphate, high iron levels from the make up water or mild steel corrosion will increase the chance of iron phosphate precipitation. Iron levels up to 2 ppm call for increased polymer dosages (1 ppm active polymer per ppm iron). Above 2 ppm iron, High Stress Polymer should be substituted for Prism and an additional 1 ppm active polymer per ppm iron should be added to the program.. If the iron is from the make up water, iron removal prior to introduction into the cooling system is the best option to allow optimum program results. If the high iron levels are from corrosion, higher zinc levels are needed to reduce mild steel corrosion. Higher than normal blowdown should also be initiated until iron levels return to normal. Silica Silica should be maintained below 180 ppm. The use of Nalco 7304 (silica stabilizer) is recommended if higher levels are expected in the tower water. Magnesium silicate may also be a problem in alkaline programs. The CPP will give the maximum pH that can be maintained without magnesium silicate precipitation as a function of temperature, magnesium, and silica concentration. Holding time index Long holding time index increases the consumption of polymer and causes some degradation of inhibitor species. If ortho-phosphate levels are too high (and orthophosphate is not being fed), additional polymer will have to be fed to control calcium phosphate deposition. A general guideline is to feed an additional 5% dispersant for each ppm of phosphate above the maximum recommended level in the CPP. In addition, since the High Stress Polymer dispersant is more stable than the Prism dispersant, High Stress Polymer should be fed if the holding time index is greater than 72 hours. It should be possible to treat systems with holding time indexes up to 225 hours. Temperature Temperature is a significant stress factor for any program. While maximum heat exchanger water exit temperatures of 180 oF (82.2 C) have been tested in the field, these should be approached with caution and careful monitoring or system performance. The dispersant doses in the CPP are adequate for temperatures up to 120 oF (48.9 C). Above 120 oF (48.9 C), the dispersant dose should be increased by 1.67% for each 1 oF (0.56 C) rise in temperature. High Stress Polymer should be substituted for Prism at temperatures greater than 135 oF (57.2 C). In some cases, it would be possible to operate above the Prism limits while still using the

Prism dispersant. The High Stress Polymer will give better results at these conditions. For low flow, shell side exchangers, a combination of mechanical methods and increased polymer dosages should be used. Mechanical cleanings like air rumbling or reverse exchanger flow along with increased polymer levels will increase the life of the exchanger but will not keep it clean forever. Velocity The guidelines for this program have been specified for typical heat exchanger velocities of 3 ft/sec (0.914 m/s). Lower velocity exchangers can effectively be treated but an increase in polymer dosage is required. Typically exchangers operating at 3 ft/sec (0.914 m/s) have a tube wall (skin) temperature of 15-20 oF (8.33 - 11.11 C) above the exit water temperature. At 1 ft/sec (0.305 m/s), this differential may increase to as much as 40 oF (22.2 C). In addition, the diffusion of corrosion inhibitor to the metal surface is not as fast at the lower velocities. This increases the driving force for corrosion and fouling to occur. Increasing the polymer level will help offset this problem. At 2 ft/sec (0.61 m/s), the dispersant feed should be increased by 20 %; at 1 ft/sec (0.305 m/s), the dispersant feed should be increased by 40 %. At low flow rates additional mechanical aids such as air rumbling will aid in keeping the system clean. For low flow, shell side exchangers, a combination of mechanical methods and increased polymer dosages should be used. Mechanical cleanings like air rumbling or reverse exchanger flow along with increased polymer levels will increase the life of the exchanger but will not keep it clean forever. Conductivity Increased conductivity will increase the corrosivity of the water. High chloride levels are worse than high sulfate levels. A combination of both chloride and sulfate are the most corrosive. Generally, chloride levels about 500 - 750 ppm and sulfate about 750 - 1000 ppm can be tolerated. Above this range, an increase in the zinc level should be considered to prevent higher corrosion. Conductivity levels up to 10,000 mS/cm have been encountered with good control. Above 5,000 mS/cm, High Stress Polymer should be substituted for Prism dispersant. In some cases, it would be possible to operate above the Prism limits while still using the Prism dispersant. The High Stress Polymer will give better results at these conditions. Zinc levels should be increased by 10-30 %, with a corresponding increase in dispersant level. Suspended Solids Suspended solids will cause dispersant consumption by adsorbing on the polymer and deactivating it. Typical suspended solids level of 20-40 ppm do not typically

cause a major impact on polymer consumption. Suspended solids level of 50 -75 ppm will increase polymer demand by approximately 10%. Above this level, polymer dosages should be increased by 1 ppm active for every 10-20 ppm increase in suspended solids. It is important to differentiate the measurement of suspended solids by weight or by turbidity (light scattering). Small particles will have a high turbidity per unit weight because of their high surface area which scatters light. Large particles will not scatter as much light. Polymer consumption is strongly a function of surface area; thus turbidity is generally a better means of determining the potential effect of suspended solids. Aluminum Aluminum is a difficult problem for any cooling water treatment program which contains phosphate. The most common source is a poorly operated water treatment plant. While the lower levels of phosphate in this program make this less of a problem, aluminum phosphate will still form which will cause polymer deactivation and can be difficult to disperse. If the level of aluminum is above 0.5 ppm, High Stress Polymer should be substituted for Prism, since it is much more resistant to deactivation by aluminum. Dispersant dose should also be increased by 2 ppm active polymer per ppm of aluminum. An absolute limit of 2 ppm aluminum should be observed. Microbiological Control All cooling water programs require good microbiological control to achieve satisfactory results. AZ-Lite is no different. It can tolerate free halogen (Cl2 or Br2) levels of 0.5 to 1.0 ppm, although 0.2 - 0.5 ppm will generally give satisfactory microbiological control. The program components are tolerant of typical free halogen levels. The use of chlorine gas, bleach, ActiBrom, or STABREX are all compatible with this program. This information is provided by BioManage training. The polymer is also halogen resistant. Halogen should be fed to a supply header at the back of the basin to allow the biocide to sweep the basin limiting microbio growth in basin deposits. Make up water should be used as the drive water. If Tower water is used to drive the halogenation process, severe degradation of all program actives will occur. This is true for any program even the "Dianodic Plus" programs from Hercules BetzDearborn.