A commercial C&I FILTRATION By Wayne E. Bernahl, W. Bernahl Enterprises, Ltd. & industrial article Is Dealkalization by Exchange

lkalinity in water is present in four condensate return piping of the system

forms: Dissolved carbon dioxide (CO2), and cause products (crud) to bicarbonate (HCO ), carbonate (CO ) return to the boiler, which will cause Right for You? 3 3 A and hydroxyl (OH). The bulk of alka- fouling to occur. Amines can be fed to linity in most naturally occurring water most condensates, which will neutralize Figure 1. Alkalinity sources is bicarbonate alkalinity com- the carbonic acid or film out on the bined with some CO2. The form of alka- condensate piping, but amines increase linity that is found in naturally occurring operating costs. The more alkalinity in water is a function of the water’s pH. the feedwater, the more amine required – Figure 1 illustrates this relationship. to neutralize the CO2. = OH + Neutrality H Methyl Orange Endpoint Phenol-Phthalein Endpoint Homeowners rarely think about The other breakdown product (OH) alkalinity. However, the presence of also can be a problem. OH alkalinity in alkalinity in water combined with water the boiler water can cause caustic “P” 5000 500 50 “M” 5 50 500 5000 hardness might cause a scaling problem gouging or under-deposit corrosion. mg/L Acidity OH Alkalinity mg/L in water heaters for the homeowner The potential for the problems mg/L CaCO3 mg/L CaCO3 because calcium carbonate (CaCO3) is associated with alkalinity in a boiler CO escapes quickly 2 Free CO gas Hydroxyl Alkalinity inversely soluble as the water temper- increase with increasing operating into environment 2 ature increases. The use of a simple pressure. Standard setting bodies such water softener usually can eliminate as the American Society of Mechanical Free Mineral Bicarbonate Alkalinity Acidity (FMA) Carbonate Alkalinity most scaling problems for the home- Engineers (ASME) or American Boiler owner. However, to the industrial water Manufacturers Association (ABMA) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 user, alkalinity can be a critical con- have published guidelines for boiler pH taminant that must be removed and and feedwater chemistry. A copy of controlled to prevent scale and cor- these should be obtained by anybody rosion of critical industrial processes operating industrial boilers. and to minimize total operating costs. Figure 2. Salt Splitting Dealkalization All problems associated with alkalinity Industrial heat exchange equipment increase operating costs to a point Raw Water usually has higher heat transfer rates where it may become cost effective to than a home water heater, and it usually remove the alkalinity from the water operates at much higher temperatures. before its intended industrial use. Therefore, the scaling potential is Alkalinity can be removed from water Dealkalizer greater. Scaling in industrial applica- by either membrane or Type II (Strong tions is well understood and can be processes. This article will cover the Anion Exchanger, prevented by any good water treatment three ion exchange processes used for Chloride Cycle) program, but it may require the use of removing alkalinity. expensive chemical additives and a Salt reduction in the cycles of concentration Salt Splitting Dealkalization To Process for the system. In a boiler operation, This method of dealkalization (see there is potential for both scaling and Figure 2) probably is the most prevalent Softener corrosion to occur. In a boiler, alkalinity in commercial and light industrial (Strong Acid entering with the feedwater will break applications and where low-pressure Cation Exchanger, down with heat and time to CO2 and boiler systems are involved. It utilizes Sodium Cycle) OH. The CO2 will go off with the steam the use of a Type II anion resin bed because it is a gas. As the steam cools, regenerated with salt (NaCl) or more

the CO2 dissolves back into the conden- often salt with a small amount of caustic sate where it forms carbonic acid. This (NaOH) added. The anion bed follows Figure 3. Split Stream Dealkalization acidic condensate then will corrode the a softener since the anion resin would

Raw Water Aerating Tower Figure 4. WAC Dealkalization Raw Water

Acid Salt Storage To Process Tank Salt Strong Acid Strong Acid Acid Degassifier To Process Cation Exchange Cation Exchange Resin Hydrogen Resin Sodium Weak Acid Strong Acid Cycle Cycle Cation Exchanger, Cation Exchanger, Hydrogen Cycle Sodium Cycle

10 Water Quality Products www.wqpmag.com June 2004 About the Author Wayne Bernahl is president of W. Bernahl Enterprises, Ltd. He has worked in the industrial water treatment marketplace for 38 years. He spent most of this time in technical marketing and consulting positions dealing with ion exchange and reverse osmosis applications.

Four Forms of Alkalinity water can control the amount of • The use of hazardous acid in the Increasing cycles of concentration in Water alkalinity in the final effluent. The regeneration process. reduce water usage and waste split stream dealkalization process has • The capital and operating cost of effluents. In boiler operations, the following advantages. a degassifier is required. the energy cost must be taken • Dissolved Carbon Dioxide (CO ) 2 • The feed of small amounts of into account. Increased cycles of • Bicarbonate (HCO3) • Alkalinity in the final blend can be caustic may be required to raise concentration, reduced blowdown, controlled to a desired level. the pH of the final effluent to increases in condensate return and • Carbonate (CO3) • TDS is removed to the extent that acceptable levels. heat recovery processes all save energy • Hydroxyl (OH) the alkalinity is removed. and have large paybacks to the overall • The operating capacity of the SAC If a water source is high in alkalinity, operation. The use of chemical foul if any hardness (calcium and resins are higher than those of the some form of dealkalization should be additives may be reduced and magnesium) found its way onto the Type II anion resin used in the salt- considered by most industrial and estimates for reduced maintenance resin. While alkalinity is removed, the splitting process requiring smaller commercial users of the water as a way costs need to be included. total dissolved solids (TDS) of the water resin volumes. to prevent operating problems and are not changed. Therefore, levels of reduce total operating costs. Do your You may find that a dealkalization

CO2 in a boiler’s condensate would The disadvantages include homework, educate yourself and make process is a cost-effective addition to decrease, resulting in lower amine sure all costs and available processes your water treatment process that has usage. However, there may be no • The use of hazardous acid in the are considered in your evaluation. a very short payback period. WQP ability to increase the boiler’s cycles of regeneration process is required. concentration because the TDS in the • The capital and operating cost of a feedwater has not changed. In fact, the degassifier is required. For more information conductivity of the feedwater actually • The feed of small amounts of caustic on this subject, LearnMore! may increase slightly. Salt splitting may be required to raise the pH of write in 1014 on the dealkalization has the following the final effluent to acceptable levels. For more information related to this article, reader service card. advantages. go to www.wqpmag.com/lm.cfm/wq060404 Weak Acid Cation • Salt is a non-hazardous material Dealkalization and, therefore, is used to When the influent water is both high in regenerate the resin. hardness and alkalinity and has hard- • Often, excess softener capacity can ness to alkalinity ratios of 1 or more, be converted to use as a dealkalizer. dealkalization using a weak acid cation (WAC) resin (Figure 4) becomes However, this process also has the extremely efficient and cost effective. following disadvantages. The process involves using an extremely efficient WAC resin to exchange hydro- • Relatively low dealkalizer operating gen for hardness that is associated with capacities (8–10 Kg/ft3) are achieved. alkalinity. The water is then put over a

Therefore, larger vessels using more degassifier to remove the resulting CO2, resin and regenerants are required. which removes TDS. A conventional • The process does not remove softener then removes any permanent any TDS. hardness remaining in the effluent of the • Anion resins are susceptible to degassifier. Again, a very small amount fouling from organics and hardness of caustic may have to be fed to raise getting through the softener. the final effluent pH to desired levels. • High-quality, evaporated grades of salt are required for regeneration. The advantages of the WAC dealkali- zation process include the following. Split Stream Dealkalization Split stream dealkalization (see Figure 3) • Very high operating capacities can utilizes two beds of strong acid cation be obtained. (SAC) resin operated in parallel. One • Automation can be achieved of the beds is operated in the sodium through the use of a simple online form as a softener and the other bed is pH meter. operated in the hydrogen form such as • TDS reduction allows for increased the cation vessel of a demineralizer. cycles of concentration in This bed is normally regenerated with downstream industrial processes.

sulfuric acid (H2SO4). The feedwater • Softener capacity is minimized flow is then split between the two vessels. because the WAC resin removes This yields one soft water source the bulk of the hardness in the containing 100 percent of the influent dealkalization process. alkalinity and one acidified water source • WAC resin operating efficiencies containing zero alkalinity. In fact, this minimize acidic regenerant waste. source has free mineral acidity (FMA). The two streams are then blended The disadvantages of the WAC dealka- together and put over a degassifier, lization process include the following.

which removes the CO2 that is created by the FMA of the acidified water • The WAC process is not efficient source and the alkalinity from the on all water chemistries, especially softened water source. Controlling the those with high levels of sodium percentage of each flow in the blended alkalinity.

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