Optimization of cooling towers

The load on a cooling tower depends on the flow and temperature of the water returning from the process. The controlled variable is the temperature of the cooling water that is sent back to the process and the manipulated variable is the air flow through the tower, which can be changed either by adjusting the speed of variable-speed fans or by starting and stopping a number of constant-speed fans.

View full article →

Power plant water issues: Effectively cleaning cooling tower fill

While once-through cooling was a common feature at many power plants in the last century, environmental regulations regarding intake and discharge issues have basically forced a transition to cooling towers, or in some cases air-cooled condensers, for new projects.  Essential to steady heat transfer in cooling towers, and also their physical stability, is proper chemistry control.  But even with diligent chemical feed and monitoring, cooling towers, and especially the tower fill, can accumulate scale and microbiological deposits that inhibit heat exchange, and, in worst case scenarios, may induce partial collapse of the tower.  This article examines methods to clean tower fill before fouling causes irreversible damage.

Background

Cooling tower performance is highly dependent on the efficiency of contact between the hot return water from heat exchangers and the cool air being pulled or blown through the tower.  Heat transfer is enhanced by the use of cooling tower fill, which, over the decades, has evolved into sophisticated designs to maximize air-water contact.  An illustration of high efficiency PVC film fill is shown below.

 

 

Figure 1. High efficiency cross-fluted fill (Photo courtesy of Brentwood Industries)

 

The transition from early splash fill designs to modern high efficiency types reduced cooling tower capital and operating costs.  However, the generally tortuous path that provides good contact between air and water also makes these fills highly prone to fouling.  Advanced fouling results in a ~10x weight gain, leading to fill collapse into the sump and expensive fill replacement. 

Proper Chemical Treatment

While this article focuses on methods to clean tower fill that has begun to accumulate deposits, it is paramount to understand that proper chemical treatment during normal operation is essential to prevent severe or sudden scaling and fouling problems.  With regard to scale (and corrosion) control in cooling systems, the four-decade long methodology of phosphate/phosphonate treatment is giving way to polymer-based, non-phosphorus chemistry for two primary reasons.  One is that phosphorus discharges to the environment are being increasingly regulated and restricted due to problems with toxic algae blooms that have afflicted numerous bodies of water.  Secondly, the new polymer programs are proving to be more effective for scale and corrosion control in cooling systems.  (Post, R., Kalakodimi, R., and B. Buecker, “An Evolution in Cooling Water Treatment”; PowerPlant Chemistry Journal).

The most serious issues in cooling systems are usually related to microbiological fouling.  Thus, virtually all systems have as primary treatment some form of oxidizing biocide, most commonly bleach but also possibly gaseous chlorine, bleach/sodium bromide, chlorine dioxide, monochloramine, and monobromamine.  A problem at many facilities, and this is particularly true in the power industry, is that the regulations developed for and by the United States Environmental Protection Agency (USEPA) allow no more than 0.2 ppm free available chlorine average residual for 2 hours per day as “Best Available Technology.”  For plants so constrained, treatment is only allowed for less than 9 percent of any day, thus giving microbes a chance to settle and begin forming protective slime layers.

 

Figure 2

 

Options for dealing with fouled fill

Many facilities have suffered from fouled cellular plastic fill.  Replacement of the fill in kind is a potential solution, but potentially sets up repeat situations.  Another option is a switch to low-fouling fill designs that generally feature a more vertical flow pattern, less surface texturing, and sometimes wider spacing between the plates, all at the expense of some cooling efficiency.  Since fill replacement can be expensive in terms of both materials and outage time, others have chosen to clean the fill chemically, or sometimes, mechanically.  The choice of replacement vs. cleaning, as well as the cleaning methodology, requires careful consideration.  The decision depends on the extent of the fouling, the physical and chemical nature of the foulant, the type of fill, and environmental considerations in dealing with cooling tower blowdown.  For example, in heavily fouled film packs, some passages may be completely blocked, preventing the cleaning solution from flowing through, and perhaps acting as a filter for solids removed in other parts of the pack.  The total mass of deposits, if released at once into the recirculating water flow will result in very high suspended solids, and blowdown may have to be diverted or treated prior to discharge.  The type of foulant also varies considerably depending on the nature of the circulating water and the treatment chemistry employed.  Over time, the fouling matrix behaves as a filter media, trapping additional suspended solids in the crevices of the fill pack and impeding air and water flow.  At this point, the efficiency criteria that constituted the driving force for selecting the fill has become null. 

Figure 3.  Fouled film fill that is no longer effective.

The loss in cooling tower capability as a function of weight gain for a fill of offset flute design is trended in Figure 4.

 

Figure 4.  Tower capability loss vs. fill weight gain for a standard offset flute cellular plastic fill pack. (Monjoie, Michel, Noble, Russell, and Mirsky, Gary R., Research of Fouling Film Fill.  Cooling Technology Institute, TP93-06, New Orleans, LA, 1993.)

 

Over time, the high efficiency fill becomes increasingly less efficient, may gain as much as 10x its initial weight, begins to extrude around the supporting beams, and ultimately collapses into the sump.  At the point where performance loss becomes obvious to operators or the fill begins to deform, it is too late to consider cleaning as an option; fill replacement is required.  However, if the fouling is detected in its early and moderate stages, several cleaning options are available, depending on the nature of the foulant.

Cleaning Options For Cellular Plastic Fill

The most appropriate method for cleaning tower fill depends on several factors, including safety concerns, system metallurgy, in-service vs. out-of-service cleaning, potential impact on plant operations, disposal options for the cleaning solution, impact on the environment, and the chemical and physical nature of the foulant.

Mineral Scales

Hard mineral deposits most commonly consist of silica/silicates or calcium carbonate (calcite).  Silica solubility is lowest at low temperature, and deposits often occur near the bottom of the counterflow fill pack where the temperature is lowest, the water is most concentrated, and uneven water/air distribution can lead to dry spots or locally concentrated areas.  Calcite deposits often occur throughout the fill pack, but are generally heaviest toward the bottom.  Higher temperature near the top of the fill pack has the lowest calcite solubility and promotes faster deposition kinetics.  However, as the water passes through the fill, the minerals are concentrated slightly by evaporation, and the pH will rise slightly as excess CO2 is stripped.

One technique that can be used effectively on either type of hard scale in its early stages is to apply certain types of surfactants that penetrate the hard deposit and induce it to spall from the slightly flexible plastic substrate. The surfactant is typically applied in addition to the normal scale inhibitor program for an extended period of 60-180 days. This program is never 100% effective, but will often result in removal of 70-80% of the fouling minerals.  Prior to implementing the cleaning process, it is imperative to identify and correct the scaling condition.

For large cooling systems, where the predominant scale deposit is calcite, the fill can be cleaned by reducing the operating pH and/or cycles of concentration until the water is undersaturated with respect to calcite at the fill conditions.  Calcite often serves as the binder for the deposit matrix, so dissolving the calcium carbonate in the deposit matrix can be disproportionately effective.  In principle, any degree of undersaturation will be effective over time.  Sulfuric acid is an obvious choice for many plants that already use it for pH control, but very careful planning involving plant personnel, the chemical supplier, and any outside contractors is required before using such a hazardous chemical. Other plants may prefer to use safer, less corrosive acids such as organic acids or inhibited sulfamic acid. [4]  Some organic acids are more effective than mineral acids at intermediate pH, and are synergistic with sulfuric acid.  At pH 5, application of the appropriate organic acid will accelerate the rate of calcite dissolution by 10-20x as compared to sulfuric acid alone.

For predominantly light calcium carbonate scaling, off-line foam acid cleaning has been used very successfully, at least on smaller towers. Strong acid foam is applied by skilled specialists from the top of the fill pack. The nature of the foam allows the acid to contact the scale as it slowly passes downward through the fill.  The relatively low volume of spent and mostly neutralized foam cleaning solution is either collected in the sump and disposed of, or is allowed to mix with other circulating water from neighboring tower cells that may be in service, depending on plant safety and environmental requirements.

Mineral scales can also be mechanically cleaned with some success in situ or ex situ.  Due to its brittle nature relative to the flexible PVC, the scale can be dislodged with some success by mechanically cleaning the fill pack in-situ from below.

Microbiological/Organic Deposit Matrices

Deposits where microbiological growth or organics serve as the binder for the deposit matrix are characterized by a soft, sometimes putty-like consistency.  Unlike mineral scales, deposits of microbiological origin tend to accumulate primarily in the middle of the fill pack.  Water velocities directly under the spray nozzles are generally high enough to discourage microbiological adhesion.  For this reason, microbiologically initiated fouling sometimes goes undetected because it is not visible on inspections from the top looking down beneath the spray headers.  As the water velocity slows down several inches into the fill, microorganisms begin to colonize the surface, acting as a filter for suspended solids passing through the fill.  Fouling tends to be more intense in the middle of the fill than at the bottom because suspended solids are filtered out prior to reaching the bottom layer, and because the last few inches of fill do not physically support a thick, soft deposit mass.  The inability to clearly view microbiological fouling from either top or bottom, combined with the difficulty of inspecting the middle layers of fill, often allows this type of fouling to progress undetected until it has reached an advanced stage.  Plant personnel have attempted to monitor fill fouling during tower operation using sections of fill suspended from load cells, or by cutting an access window into the end of the tower casing to allow a middle section to be removed periodically for inspection using a man lift, or by suspending a section of fill beneath the main fill pack to allow it to be easily inspected and weighed.  All of these methods can work, but none have proven to be totally satisfactory.

Several effective methods exist to remove biological-silt matrix deposits from cooling tower fill.  Hyperhalogenation is a widely attempted method, but its effectiveness is usually disappointing.  Potential corrosion of system components and the need to dechlorinate prior to discharge are important considerations.

Microbiological matrices often have high water content and will shrink and detach from surfaces when thoroughly dried.  However, effectively drying out cooling tower fill can prove problematic even with the help of fans, even if the tower is located in a low humidity climate.  Chlorine dioxide has also been used as a cleaner for cooling tower biofilms with some success.  However, the most widely practiced and effective cleaning method for deposits with microbiological or organic binders is hydrogen peroxide (H2O2) due to its oxidizing strength and the physical action of the oxygen micro-bubbles produced as the chemical reacts with organic deposits.  The positive environmental profile of hydrogen peroxide involving rapid breakdown to water and oxygen, and its ease of application are additional factors favoring peroxide as a tower fill cleaner.  Typical dosages are in the range of 500-3,000 ppm active H2O2.  As with most cleaning operations, the addition of low levels of surfactants will help loosen deposits.  Polymeric dispersants are generally added to assist in keeping the removed solids in suspension until they can be blown down.

Much of the biomass consists of extracellular and intracellular water and organics that will dissolve with peroxide cleaning.  A substantial portion of the deposit typically contains much mud and silt that will be released into the water.  Figures 5 and 6 illustrate the appearance of a slime-clay matrix on moderately fouled high efficiency cooling tower fill before and after cleaning. 

 

 

In cases where the deposit contains a high percentage of inorganics, the circulating water can be expected to become highly turbid.  The potential for high suspended solids in the cooling tower blowdown should be anticipated when cleaning a severely fouled system and taken into account in the job planning scope.

Summary

  • Every effort should be made to prevent deposition from occurring in the first place.  A fill type should be specified that is compatible with reasonable expectations for the system, considering influent water quality, microbiological control, presence or absence of pre-treatment equipment, and the possibility for external foulants that might enter the tower through airborne contamination or process fluid leaks. 
  • The microbiological and deposit control program should be diligently monitored to ensure that it is within expectations and delivering the required results. 
  • The performance of any pretreatment and sidestream solids removal equipment should be reviewed to ensure such equipment is delivering and maintaining suspended solids within specifications.
  • Plant personnel should be proactive with inspection and monitoring.  There are more options, and less expensive ones, if the fouling is detected at an early stage.
  • Periodic, light, preventative maintenance tower fill cleanings should be considered.  Most high efficiency fills tend to gain weight slowly over time. Annual preventative maintenance cleanings can stabilize or reverse that trend.
  • If cleaning is indicated, safety and environmental considerations must be adequately addressed.  Cleanings require careful planning and coordination between plant personnel and the chemical supplier/consultant.  Personnel safety is critical.  Also, cleanings can release many suspended solids that if not carefully controlled can foul equipment or present disposal problems without proactive planning.
  • If fouling occurs, all remediation options should be considered, but, generally, the least costly and least aggressive methods applicable to the nature and quantity of the deposit should be the starting point.  Identifying and correcting the fouling conditions at an early stage is least expensive, and preferable to aggressive cleaning or ultimate fill replacement if the fouling conditions are allowed to persist.
  • All systems are different, and careful consultation with the cleaning vendor and water treatment experts should be a priority.

 You can find the original article @ https://www.power-eng.com/2019/08/21/power-plant-water-issues-effectively-cleaning-cooling-tower-fill/#gref

August 08, 2018

0 comments

chemicals ›   controllers ›   cooling ›  


Bringing color to water treatment

Lakewood NexSys brings industrial grade control technology to the industrial water treatment industry. It not only provides colorful screens but a fully functional touch screen that shows menus designed for humans. It can also connect to your network without any special interface of software. View full article →

How can a cooling tower spread Legionnaires' Disease?

It really should be one of the happiest, most carefree destinations on the planet; however perennial family favourite, Disneyland, found itself at the epicentre of an outbreak of Legionnaire’s disease just before Christmas, as you might have read elsewhere. As well as being an obvious PR disaster for the globally-renown resort behemoth, any possible risk presented by the presence of the potentially deadly respiratory infection could spell more far-reaching bad news for those directly affected by an episode.  View full article →
November 21, 2017

0 comments

chemicals ›   cooling ›  


Choose the right biocide for your cooling tower

Control of the three major microbiological classes, bacteria, algae and fungi, and macroorganisms including zebra mussels, is essential for healthy cooling tower operation. For many years, chlorine was the treatment chemical of choice. However, chlorine use is declining due to environmental, safety and performance-related issues. This article examines the positive and negative aspects of chlorine and of replacement oxidizing biocides.

Microbiocides generally belong to one of two groups: oxidizers and non-oxidizers. The former attack cells by oxidizing (an electron transfer reaction) microorganism cell components. Non-oxidizers react with cell components via different chemical processes. Oxidizing biocides are still the most common biological control agents, and even though chlorine use is declining, it continues to be an important player in the cooling water treatment industry.

Chlorine

When chlorine is injected into a cooling water stream, it disproportionates into hypochlorous and hydrochloric acid as follows:

Cl2 + H2O Æ HOCl + HCl

HOCl is the oxidant that attacks cell structures. An increase in pH increases the dissociation of HOCl into the hypochlorite ion (OCl-):

HOCl H+ + OCl-

Although both HOCl and OCl- are oxidants, OCl- is a much weaker disinfectant, possibly because the charged OCl- ion has a more difficult time penetrating the cell wall. Chlorine`s biocidal efficiency greatly decreases as the pH rises above neutral. (See sidebar.)

For years, the most popular cooling water treatment program at many facilities was low-level sulfuric acid feed to control calcium carbonate formation, with supplemental feed of chromate and zinc for corrosion inhibition. This suited chlorine as a microbiocide because the mildly acidic pH maintained the chlorine residual predominantly as HOCl. However, chromate discharges to the environment have been banned due to the potential release of toxic hexavalent chromium. Modern cooling tower treatment programs operate in the less corrosive alkaline range of pH 8.0 to 9.0, in which advanced calcium carbonate scale inhibitors have replaced sulfuric acid. Such programs do not favor chlorine as a microbiocide. This problem has been exacerbated by the development of more efficient cooling tower fill (Figure 1), whose close spacing makes the material susceptible to pluggage.

Safety issues are another factor in chlorine`s reduced popularity. Chlorine gas is quite hazardous, and regulations governing its storage and leak detection are becoming increasingly stringent. Rather than deal with the safety requirements for gaseous chlorine, many plant managers are opting for alternatives.

The potential for formation of chlorinated organics has also become an important issue. Many halogenated organics are known or suspected carcinogens, and tighter restrictions are being placed on the amount of allowable halogenated organics. In 1979 the Environmental Protection Agency (EPA) set an interim maximum contaminant level (MCL) of 0.100 ppm for total trihalomethanes (TTHM`s). The agency has proposed to reduce the MCL to 0.080 ppm, and may lower the standards even further in the future.

In 1982, the power industry was required to meet optimized technology-based standards for chlorine use. The requirements limited the maximum chlorine discharge from cooling towers to 0.5 ppm, with an average discharge of 0.2 ppm for no more than two hours per day. In 1985 the EPA announced more stringent ambient water quality criteria, which applied to all industries. These guidelines limited fresh-water chlorine concentrations at the boundary of a calculated effluent mixing zone to 0.011 ppm over a four-day average, or 0.019 ppm average for one hour. Restrictions for salt water are even more stringent at 0.0075 ppm and 0.013 ppm, respectively.

The regulations have made it particularly difficult to use chlorine to control cooling water biological fouling. The situation has been further complicated by the spread of macrofouling species, the most notable of which are zebra mussels and Asiatic clams. Continuous or semi-continuous chlorination is necessary to control the growth of macrofoulers, especially adults, but continuous chlorination is expensive, particularly when bleach is the biocide. Continuous chlorination can also harm non-target organisms in once-through cooling systems. Many facilities must dechlorinate their cooling water prior to discharge in order to comply with water quality standards. This process typically requires the feed of a reducing agent, such as sodium bisulfite, into the effluent.

Bromine

A popular substitute for chlorine is bromine (Br2). Like chlorine, bromine reacts with water to produce a hypohalous acid, in this case HOBr. Bromine has nearly the same oxidizing power as chlorine, but it offers several advantages over chlorine in certain conditions. First, the dissociation of HOBr occurs at a higher pH than HOCl (Figure 2), which makes it more effective in alkaline environments. Second, bromine does not react irreversibly with ammonia as does chlorine. Chloramines are much less effective disinfectants than free chlorine, which makes chlorination of ammoniated waters problematic. Third, bromine is less corrosive than chlorine to copper alloys.

Bromine may be introduced into a cooling water system by several different methods. Most common is to react liquid sodium bromide (NaBr) with chlorine or sodium hypochlorite in a sidestream loop of the cooling water makeup. Chlorine activates the bromide salt to hypobromous acid as follows:

NaBr + HOCl Æ HOBr + NaCl

Sodium bromide, being the bromine analog of common table salt (NaCl), is stable and may be stored in a simple bulk tank. NaBr is usually supplied as an aqueous solution of approximately 40 percent concentration. The sodium bromide and chlorine or sodium hypochlorite should be fed separately into the slipstream to obtain at least a 100:1 dilution. This prevents the formation of undesirable bromate byproducts.

Like chlorine, bromine is toxic to non-target organisms and it can form halogenated organics. For these reasons plant cooling water discharges containing bromine are regulated similarly to chlorine, although some states or EPA regions have established more restrictive standards for bromine residuals.

Even though the cost of sodium bromide adds to the total delivered cost of the oxidants, users often find it possible to reduce the overall quantity of oxidant required to achieve the equivalent performance. Frequently, the reduction in chlorine consumption more than offsets the cost of the sodium bromide, especially where liquid sodium hypochorite is the chlorine source.

Solid Choices

For smaller cooling water systems, solid bromine donors may be a cost-effective alternative to the arrangement mentioned above. One of the most common solid biocides is bromo- chloro-dimethyl-hydantoin, or BCDMH, which releases bromine as it dissolves in water. Several of the major water treatment vendors supply solid bromine or chlorine donors in granules, pellets, or tablets along with a feed system. As water passes through the dissolving vessel, the BCDMH dissolves at a controlled rate to release HOBr and HOCl:

C5H6O2N2BrCl + 2H2O Æ C5H8O2N2 + HOBr + HOCl

Solid donor systems are also available for strictly chlorine-releasing products. Some of the most common chlorine-based solid donors include dichloro-dimethyl-hydantoin, calcium hypochlorite [Ca(OCl2)] and chlorinated isocyanurates. The latter two compounds are widely used as swimming pool chemicals, but will also work well in some cooling water applications. Specific feed systems are available for each halogen donor. All of these products are strong oxidizers and must be handled and stored properly; it can be hazardous to use one compound in a feeder designed for another.

Prominent advantages of the solid halogen donors are:

Handling--no potential for liquid spills;

Stability--stable compared to bleach;

Effectiveness--strong oxidizers that work well at alkaline pH and in the presence of ammonia;

Water Chemistry--less corrosive to system materials; do not significantly alter cooling water pH; and

Environmental and Safety Factors--no chance of toxic gas or liquid release.

The solid halogen donors are best for systems with a low or moderate chlorine demand, and where simple operation is desirable. Solid donors are generally more expensive than chlorine and even bleach, and can be slow to dissolve at water temperatures below 60 F.

Sodium Hypochlorite

Sodium hypochlorite (NaOCl) may be a suitable non-gaseous alternative. It comes in bulk solution, at a concentration ranging from 10 percent to 12.5 percent as NaOCl. The hypochlorite can be metered directly into the cooling system. An important point to remember about NaOCl is its effect on cooling water pH. Gaseous chlorine lowers the pH due to the production of both HOCl and HCl. Sodium hypochlorite tends to raise the pH.

Sodium hypochlorite will degrade over time to form sodium chloride, oxygen, and sodium chlorate (NaClO3). Temperature and impurities greatly affect decomposition. (See sidebar for specifications and storage guidelines for sodium hypochlorite.)

The improved safety and convenience of sodium hypochlorite versus gaseous chlorine has a tradeoff in cost. Chlorine gas in ton cylinders costs $0.15 to $0.20 per pound delivered. By contrast, 12.5 percent sodium hypochlorite costs around $0.60 per gallon ($0.059 per pound) delivered in bulk. This corresponds to $0.50 per pound on an equivalent Cl2 basis, or approximately three times the cost of gaseous chlorine.

Chlorine Dioxide

Chlorine dioxide (ClO2) is a powerful oxidizer with excellent biocidal properties. It offers several potential advantages compared to chlorine. Chlorine dioxide:

does not form halogenated organics,

is less corrosive to copper alloys than chlorine,

does not react with ammonia and primary amines,

efficiently destroys phenols and sulfides,

is not affected by pH like chlorine and works well in alkaline waters, and

is more effective against mollusks.

These advantages come at a price, however. Chlorine dioxide is a very reactive compound that is hazardous to transport at practical concentrations. It must be generated on-site from other reactive chemicals that also present some handling risks. Chlorine dioxide does not react with water or ionize in solution, thus it remains as a dissolved gas that is easily stripped across a cooling tower. The principal reaction product, chlorite, affects some forms of aquatic life at low levels. Chlorite can be difficult to neutralize with reducing agents.

Chemical costs for sodium chlorite are typically in the $0.50 to $1.00 per pound range for a 25 percent aqueous solution. This corresponds to $2.00 to $4.00 per pound of active ClO2. The costs of bleach or acid for reaction, along with the 80 percent to 95 percent efficiency of the ClO2 generation reactions, can push the price above $3.50 per pound, or over seven times the cost of chlorine. Still, there are some situations where the effectiveness of chlorine dioxide may offset the added cost.

Ozone

Ozone (O3) is a powerful, short-lived oxidant that is generated by passing air through an electric discharge. The air stream is then bubbled into the cooling water through a diffuser.

Ozone is too reactive to transport or store on-site, so it must be generated at the point of use. This requirement has so far limited ozone`s application to relatively small cooling systems. Ozone is the most powerful oxidant of all, but its oxidizing strength can be a mixed blessing. Ozone rapidly destroys biofilms and produces sparkling clear water, but it also breaks down most scale and corrosion inhibitors, and it slowly degrades plastic, rubber and gasket materials. Similar to chlorine dioxide, ozone does not ionize in water but remains a dissolved gas, which can be stripped during passage through the cooling tower. Ozone offers environmental advantages in that its residuals are short-lived, it does not produce halogenated reaction products, and it breaks down into oxygen, which can be beneficial. However, ozone can produce secondary oxidants if bromide is present, and it can also produce aldehydes and ketones via reaction with organics.

One of the major advantages of ozone is that no hazardous chemicals are transported, stored or handled on-site. For small cooling systems in sensitive locations, ozone can be an attractive alternative to chlorine. Researchers continue to investigate methods of ozone treatment for larger systems. p

Click here to enlarge image

Figure 1. Cooling tower film fill.

Click here to enlarge image

 

Click here to enlarge image

BCDMH

Click here to enlarge image

Dichloro-Dimethyl-Hydantoin

Click here to enlarge image

Trichloro Isocyanurate

pH Effect

At a pH of 6.5 tests have shown that a 1.0 ppm chlorine solution will kill 99 percent of all microorganisms within 30 seconds. At this pH, a large percentage of the dissolved chlorine exists as HOCl. The percentage rapidly decreases as pH rises.

Thus, in an alkaline cooling water treatment program with a pH between 8 and 9, the available hypochlorous acid is well below 50 percent (Figure 2).

Sodium Hypochlorite

Sodium hypochlorite will decompose into oxygen, sodium chloride, and sodium chlorate. The decomposition rate is affected by temperature and by the catalytic action of some metals, most notably iron and copper. A specification for bulk quantities of sodium hypochlorite should contain the following:

Iron concentration less than 0.5 ppm;

Copper concentration less than 1.0 ppm; and

pH range from 11.0 to 11.2.

Temperature can have a dramatic impact on hypochlorite solutions. For example, the half-life of a hypochlorite solution is reported to be 800 days at a temperature of 59 F. At 77 F the half-life drops to 220 days, and at 140 F, the half-life is only 3 days. Bulk storage tanks of sodium hypochlorite should be kept as cool as possible by sun-shading, painting them white, or both.

Fiberglass-reinforced-plastic is the recommended construction material for bulk storage tanks. Poly ethylene was once the material of choice, but cracking problems have been reported after exposure to hypochlorite.

Read More: http://www.power-eng.com/articles/print/volume-102/issue-7/features/choose-the-right-cooling-tower-chemicals.html

The Role of Organophosphates in Cooling Water Treatment

Cooling Water is used in large industries to remove unwanted process heat with the help of heat exchangers, condensers. Due to the continuous contact of water with the metallic surface corrosion, scale, deposition & fouling of the heat transfer surfaces occur. These cause equipment damage and operating losses and sometimes result in costly shutdown of the plant. Addition of chemical inhibitors in controlling these problems.

Chromate based inhibitors along with polyphosphates, have been in use for long and they have been reasonably effective against both corrosion and scaling. But they have their own limitation. Polyphosphates are hydrolyzed to orthophosphate at higher operating temperature of the cooling water circuit, which lead to orthophosphate scale. Orthophosphate formed is also a nutrient for bacterial growth chromates are toxic to aquatic life and ecological concern has been the primary reason for the search for new substances.

Among the various substance stadius organophosphates have been found to be the best. Organophosphate based formulations give comparable protection with respect to corrosion, scaling and fouling and they are hydrolytically stable. This stability of organophosphates permits greater flexibility, during operation, as they are stable over a greater range of pH and at higher temperature, thereby retaining their activity for longer periods of time. The control on various parameters is more relaxed and they are non – toxic. Phosphonate are compatible with most other chemicals used in cooling systems like chlorine, non-oxidizing biocides, silt control chemicals etc. slowly organophosphates are finding more acceptance the world over, primarily because of its freedom from environment problem.

Properties of Organophosphonates: Structurally, organophosphates have the carbon atom directly linked to the phosphorus atom. The two most widely used Organophosphonates in cooling systems are:

“Six phosphate based cooling system corrosion inhibitors were studied for their relative corrosion inhibiting capabilities by an accelerated static test. The static test was standardized by controlling pH and temperature and using an oxidizing accelerator, potassium persulphate. Results indicate that orthophosphate aminotrimethylene phosphonate and hexametaphosphate are the prospective corrosion inhibitors.

Six phosphate based inhibitors selected are Sodium Hexametaphosphate (SHMP), Sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), Sodium Orthophosphate (O-PO4), Aminotrimethylene Phosphonate (ATMP) and Hydroxyethylidene diphosphonate (HEDP), these are frequently used in non-chromate based cooling water treatment.

The key properties of Organophosphonates are:

1. Threshold effect and crystal distortion.

2. Hydrolytic Stability.

3. Sequestration characteristics.

4. deflocculation.

5. Chlorine stability

Corrosion Control: Corrosion Control of metallic surface can be obtained by inhibiting the cathodic, the anodic or both these reaction. A combination of Organophosphonates and zinc works synergistically to give very good corrosion protection by interfering with the cathodic reaction. Polyphosphates, when used as corrosion inhibitor, give rise to excessive orthophosphate sludges whereas Organophosphonates with Zinc give good corrosion protection without leading to any sludge formation.

Due to the sequestering ability of Phosphonate, the zinc ions are present in a complexed form limiting the rate of reaction of zinc with hydroxyl ions. Therefore, useful concentration of zinc hydroxide allows the formation of a thin hydroxide film at the surface giving the desired corrosion resistance.

Scale and Fouling Control: Organophosphonates are one of the best deposit control agents presently available. The threshold and crystal distortion property of these compounds interferes with the nucleation of the hardness crystals causing much higher levels of hardness to stay in solution. When scales are formed they are so distorted that they are non-adherent and form very soft sludges. Phosphonate also provide excellent

Control of hydrated ferric oxide deposits which are formed as a result of corrosion. They adsorb on the particle surfaces and reduce the attractive forces between individual iron particles. The sequestering ability of phosphonate enables it to control heavy matter (Fe, Cu & Zn) deposits and this control is far superior to other traditional chelants. Phosphonate also help to disperse suspended particles.

Choice of Phosphonate: From the two most commonly used phosphonate for cooling water treatment HEDP is preferred to ATMP for the following reasons:

  1. ATMP is more corrosive to Cu cooling systems involving Cu or Cu alloys, are therefore very sensitive to ATMP. With ATMP one would then have to use Cu corrosion inhibitors like Thiazoles and Trizoles making the treatment more expensive. The corrosivity towards Cu is due to the fact that a very strong complex with Cu is formed, the dissociation constant of the chelate being about 10 –13.

  2. HEDP has better stability to chlorine than the Nitrogen containing ATMP. Nitrogen containing compound have a tendency to form chloramines. Though, when complexed with Zinc. ATMP exhibits stability towards chlorine it should be used with caution in chlorinated cooling water systems especially when continuous chlorination is used.

    The addition of Zinc to ATMP to a certain extent inhibits the dissolution of copper. In the presence of ATMP, however, the powerful oxidizing potential of chlorine promotes the dissolution of copper, when chlorine is used as a biocide.

    The other phosphonate used to a much lesser extent are, ethylene diamine tetramethylene phosphoric acid, hexamethylene diamine tetramethylene phosphoric acid and diethylene triamine pentamethylene phosphoric acid.

Check out the complete article at http://www.altret.com/templates/images/editor/role-of-organo-phosphate-in-cwt.pdf

Orthophosphates versus Polyphosphates

The selection of a phosphate water treatment chemical additive can be one of the most difficult chemical treatment decisions that many public water systems will make. This is particularly true because the chemistry of orthophosphate and polyphosphate chemical additives is complex, and phosphate water treatment chemical additives are commercially available in an overwhelming number of chemical blends.

Orthophosphates and polyphosphates are salts derived from two different forms of phosphoric acid. Orthophosphates are small molecules, formed from the smallest and most basic form of phosphoric acid. Polyphosphates are larger molecules, formed from a longer chain version of phosphoric acid.

Even though the words orthophosphate and polyphosphate contain the word "phosphate," these two chemical compounds serve radically different water treatment purposes. A public utility system's failure to understand the significant differences between these two treatment compounds could result in serious water-quality problems and possible MCL violations. An incorrect selection of phosphate chemical blends by a public utility system could even create serious public health problems.

In public water systems, orthophosphates are used for lead and copper corrosion-control purposes. Orthophosphates chemically react with lead and copper atoms that have leached off of piping and have entered into the surrounding water. This chemical reaction of orthophosphates with lead and copper atoms forms lead and copper phosphate. The lead and copper phosphate is then electrochemically drawn back down onto the piping surface, where it forms a tough, water-resistant coating on the piping. This tough, water-resistant coating helps prevent further leaching off of lead and copper atoms into the surrounding water. Most public utility systems have experienced far greater success with orthophosphate lead corrosion control than they have experienced with orthophosphate copper corrosion control.

Polyphosphates are sequestering agents that are virtually ineffective against lead and copper corrosion. When a jury in a criminal trial is sequestered, that jury is "held in seclusion." A chemical sequestering agent is a chemical agent that surrounds another molecule or atom and holds that other molecule or atom "in seclusion." By surrounding the other molecule or atom and holding it in seclusion, the chemical sequestering agent hides the molecule or atom from sight and prevents it from entering into various chemical reactions. As a sequestering agent, polyphosphates will only sequester soluble "invisible-in-water" metals that have not been oxidized into their insoluble forms. Polyphosphate applied to water before the water is chlorinated will prevent invisible iron and manganese from becoming visible after the water is chlorinated.

As a sequestering agent, water treatment polyphosphate is used to sequester soluble iron atoms that remain in settled water before it is chlorinated or that leach off of iron piping in water distribution systems. By surrounding and sequestering these soluble iron atoms, they are prevented from displaying the typical reddish colors associated with iron oxides and iron hydroxides. Water treatment polyphosphates also interfere with the crystallization of and formation of calcium and magnesium carbonate scales, but not with the cystallization of and formation of magnesium hydroxide scales. If any soluble manganese atoms are still present in water after the floc has settled out, polyphosphates will also serve to sequester these soluble manganese atoms, preventing them from displaying the typical dark manganese dioxide color.

A gross misconception about polyphosphate is the belief that the use of polyphosphate sequestrants to hide iron and manganese is a casual, routine treatment technique for the removal of excess iron and manganese that was not removed during a water treatment plant's sedimentation and filtration processes. In reality, the use of polyphosphate to sequester iron and manganese that a plant failed to remove during the sedimentation and filtration processes is a desperation maneuver. Undesirable quantites of iron and manganese in raw water should be properly oxidized by aeration, permanganate, or ozone and should be deposited in sedimentation basins as part of the floc. Polyphosphates, which sequester iron and manganese for only a limited period of time, are not the ideal or the preferred solution for any water treatment plant's iron and manganese problems. Polyphosphates should only be used to catch the few particles of iron and manganese that were missed during the initial aeration and oxidation process.

Most phosphate treatment compounds used by public water treatment systems are actually blends of polyphosphates and orthophosphates. Polyphosphates are usually added in their sodium or potassium polyphosphate form. Orthophosphates are added in the sodium or potassium orthophosphate form or in an orthophosphate form that is mixed with zinc chloride or zinc sulfate. The zinc in the mixture plays no role in forming the coatings that prevent lead and copper corrosion. Instead, the zinc plays a significant role in protecting galvinized surfaces (galvanized means "zinc-coated") and in preventing asbestos fibers from eroding off of asbestos-cement piping. It should however be noted, some phosphate blends may also contain zinc polyphosphates, but zinc orthophosphate formulations are much more commonly used in public water treatment operations.

Phosphate water treatment mixtures are available in dozens of different blends. There is no perfect blend that is universally usable in all situations. If a water treatment system uses a blend with more polyphosphate than their system needs, the coatings laid down by the orthophosphate can be stripped away. If a water treatment system uses a phosphate blend with more orthophosphate than their system needs, iron can be stripped away from iron piping. Water treatment plants need to regularly assess the lead, copper, iron, manganese, and asbestos levels in their water and consult with a professional phosphate specialist whenever a change in phosphate blends seems to be warranted.

COMMON POLYPHOSPHATE SALTS: Sodium acid pyrophosphate, Tetrasodium pyrophosphate, Tetrapotassium pyrophosphate, Sodium tripolyphosphate, Potassium tripolyphosphate, Sodium trimetaphosphate, Sodium hexametaphosphate (glassy)

COMMON ORTHOPHOSPHATE SALTS: Monosodium orthophosphate, Monopotassium orthophosphate, Disodium orthophosphate, Dipotassium orthophosphate, Trisodium orthophosphate, Tripotassium orthophosphate, Zinc orthophosphate

Original post by

Cooling Product Testing and Control

With the extremely high cost of molybdenum in recent years, its use as a corrosion inhibitor or tracing agent in cooling water products, where product consumption is significant, has become essentially cost prohibitive. Other corrosion inhibitors such as phosphates, zinc, silicates, and organo- phosphorous compounds are now used largely in the absence of molybdates. Also, the use of molybdenum has been restricted in some areas because of environmental concerns, mostly centered around concentration limitations in municipally generated sludges.

Phosphates

Where orthophosphate or polyphosphates are in use, testing for the phosphate is a good and accurate test. There are a number of phosphate procedures, but all tests determine orthophosphate. Other forms of phosphate such as polyphosphate or organo-phosphates must first be converted to orthophosphate to determine their concentrations with a phosphate test procedure.

Control can become more complicated when there is phosphate in the makeup water. The form of the phosphate (orthophosphate, polyphosphate, or both) and the concentration range needs to be known so that it is accounted for in the cycled cooling water.

Example

Makeup water contains 0.5 ppm of orthophosphate and 0.4 ppm of polyphosphate as PO4. The cooling tower is operated at five cycles of concentration and a cooling water product that contains 4 % of orthophosphate is being applied. The desired inhibitor product dosage is 100 ppm.

At five cycles, there will be 2.5 ppm of orthophosphate from the makeup water orthophosphate, and 2.0 ppm of polyphosphate applied from the makeup water, but some of it will have reverted to orthophosphate. You should test for polyphosphate in the tower water initially and then periodically to determine the reversion rate for your system. Typically, we assume about a 50% reversion rate. The actual reversion rate will depend upon pH and retention time, and the specific type of polyphosphate.

If when tested the polyphosphate showed to be 1 ppm in the cycled tower water, then the total orthophosphate from the makeup would be 3.5 ppm. 100 ppm of the inhibitor product would add 4 ppm orthophosphate, so a tested residual of 7.5 ppm or orthophosphate would indicate that 100 ppm of the product was in the system.

Table 1: Phosphate Summary

Phosphate Concentrations

Orthophosphate (ppm)

Polyphosphate (ppm)

Makeup Water

0.5

0.4 as PO4

Tower Water,
5 Cycles Before Reversion

2.5

2.0

Tower Water, 5 Cycles After Reversion

3.5

1.0

Orthophosphate From Product

4.0

Total in Cycled Tower Water

7.5

1.0

 

Phosphonates

Most all cooling tower products contain one or more phosphonates that are used for scale inhibition, corrosion inhibition, or both. Phosphonate testing is not as accurate as phosphate testing, but they can be used for controlling product feed. Phosphonates are subject to oxidation to orthophosphate by chlorine or bromine and are lost to precipitation with cations such as calcium. If the system is chlorinated or brominated, assume a 20 – 30% degradation to phosphate. The actual amount can be determined by testing for residual phosphonates and phosphate.

There are several phosphonates tests that can be used:

Hach UV digestion, then phosphate test.
Boiling with acid and persulfate, followed by phosphate test. Palintest drop test.
Taylor drop test.

UV Digestion

The test procedure is the most accurate and has a reproducibility of about ± 10%. A persulfate reagent is used along with a UV light to decompose the organo-phosphate (phosphonate) to orthophosphate. An orthophosphate test procedure then determines the amount of phosphate contributed by the phosphonates. Any orthophosphate already present before the digestion is subtracted from the total orthophosphate after digestion. This can be done by adding reagent to the tower water that has not had the digestion and use this as the blank, or actually determine orthophosphate in the tower water and subtract it from the total orthophosphate determined after the persulfate digestion.

The amount of phosphorus in each specific phosphonate molecule varies, so there is a specific conversion factor from orthophosphate to phosphonate. Each ppm of orthophosphate created by HEDP digestion = 1.085 ppm HEDP. The phosphorus content of PBTC is much lower. Each ppm of orthophosphate created from the digestion of PBTC = 2.84 ppm of the PBTC molecule.

Phosphonate Test Example:

The cycled tower water has 6 ppm orthophosphate and a cooling water product that contains 2.5% PBTC and 1.8% HEDP is being applied at a desired dosage of 120 ppm.

Assuming all of the phosphonates remain as phosphonates and have not been oxidized in the cooling tower by bromine or chlorine and assuming it has not been lost to precipitation, you should get 3.05 ppm of orthophosphate from the phosphonates after a persulfate / UV digestion.

Table 2: Phosphate Summary

From PBTC: 120 ppm x 2.5% = 3 ppm
3 ppm PBTC
÷ 2.84 ppm PBTC per ppm PO4 =

1.06 ppm orthophosphate

From HEDP: 120 ppm x 1.8% = 2.16 ppm

2.16 HEDP ÷ 1.085 ppm HEDP per ppm PO4 =

1.99 ppm orthophosphate

From orthophosphate in the tower water:

6 ppm

Total orthophosphate in sample after digestion:

9.05 ppm

Orthophosphate from phosphonate digestion:

3.05 ppm

 

Boiling With Acid and Persulfate

A digestion can also be accomplished by adding acid and persulfate, then boiling for about 30 minutes. If just acid were used, only polyphosphate would be hydrolyzed or reverted to orthophosphate. It persulfate is also added, the organo-phosphates and polyphosphates will be digested to orthophosphate. This test would be more applicable for samples that do not have polyphosphates, since the test will not distinguish between orthophosphate developed from phosphonates or polyphosphates.

Phosphonate Drop Counts

We recommend the Palintest procedure. This procedure is less accurate and subject to interferences. It is best to determine the number of drops on a known product concentration and relate the number of drops to that concentration. It is advisable to also compare these results initially and periodically to the digestion method.

Where PBTC is in use, the Palintest method is preferred. The procedure buffers the pH to around 3.0 and is more effective at detecting the PBTC along with the HEDP and AMP.

On the Palintest method, each 0.7 ppm of HEDP or AMP in the water should require one drop of titrant, and each 2.0 ppm of PBTC should require one drop.

Polyphosphate and some organics will interfere with the test and show up as phosphonates. To account for this, a blank is run on the makeup water. If it takes two drops for the color change on the blank, then those two drops are subtracted from the test results of the treated water. Note that the blank results are not cycled up by the tower cycles. Polyphosphates revert to orthophosphate which does not interfere and experience has shown that cycling the blank should not be done. If the product contains polyphosphate and a residual in the cycled water, it will increase the number of drops required.

If fluorides are in the cycled tested water at > 1.0 ppm, this causes a substantial interference that may disqualify the drop test procedure from being usable. It is advisable to check with the city supplier to see if they add fluorides and at what level. If high fluorides are present, an idea that may work is to first run the drop test procedure on the tower water to get a baseline number. Then take a sample of the cycled tower water and add 100 ppm of product and see how many drops are required. Subtract the number of drops used for the baseline from the drops required for the 100 ppm sample to determine how many drops represent 100 ppm of product as a basis for setting control limits.

The Palintest end point is the drop when the color change from green/gray to blue/purple first occurs.

Palintest Phosphonate Drop Count Example:

The cooling water is treated with 140 ppm of a product that contains 2.5% PBTC and 1.8% HEDP. The product has a specific gravity of 1.16. There is no fluoride in the water.

First, determine the interferences in the makeup water by running the test procedure on an untreated sample. On this example assume it took two drops.

Next, make a 100 ppm solution. To do this add 1 gram or 0.86 mL (1mL/1.16 gram/mL) of the chemical product to 99 grams (99 mL) of makeup water. Mix this up well, then add 1 gram (1 mL) of this 1% solution to 99 grams (99 mLs) of makeup water. This is now a 0.01% solution or 100 ppm of the product. This would place 1.8 ppm of HEDP and 2.5 ppm of PBTC in the solution. Run the phosphonates test on this solution, and for this example it required the theoretical number of drops of about 6.

Table 3: Theoretical Phosphonate Titrant Usage

From HEDP: 1.8 ppm ÷ 0.7 ppm HEDP / Drop

2.5 Drops

From PBTC: 2.5 ppm ÷ 2.0 ppm PBTC / Drop

1.25 Drops

From Blank:

2 Drops

Total Drops:

5.75 drops, which will require 6 drops to see the color change.

140 ppm of product would be about (140 ÷ 100) x 4 drops = 5.6 drops or 5-6 drops + 2 drops for the blank = 8 drops. This can be confirmed by making a 140 ppm solution and testing it.

Azole, Zinc, or Silica Tests

The Hach test procedures for azole, zinc, or silica can be used to check product dosage if the specific ingredient is in the applied product. Remember, as with phosphonates, the applied concentrations and actual residuals can be different. Azole residuals decrease as they film with copper. Zinc is lost as it precipitates at the cathode or in the bulk water. Silica is lost as it films metal surfaces. In establishing control ranges and dosages, take into account some of this loss. For example, we may apply azole at 2 ppm, but have a desired residual in the water of only 1 ppm.

Mass Balance

Chemical dosages should be confirmed by mass balances and compared to chemical testing. Mechanisms should be set up on each system to conveniently determine water makeup, cycles, water loss, and chemical consumption. The concentration in the recirculating water should be calculated from the actual product usage and blowdown or water loss.

Mass Balance Example:

The cooling tower is operating at five cycles of concentration. The makeup meter shows 120,000 gpd makeup. At five cycles, this is a water loss of 24,000 gpd. The product being fed contains 1.8% HEDP, 2.5% PBTC, 1.5% BZT, and 1% zinc; and the desired dosage is 100 ppm.

Daily product use determined by drum level and confirmed with drawdown cylinder testing is 28 lbs per day. This is a calculated applied dosage of 140 ppm of product in the cycled cooling tower water (140/120 x 24,000/1000 = 28 lbs).

Chemical testing showed 4 drops of phosphonates (6 drops from the test – 2 drops for the blank), which was previously determined to represent 100 ppm product. Testing also revealed 1.5 ppm BZT and 0.8 ppm of zinc residuals in the water. All of the chemical tests show that some portion of the active component has been consumed or residuals would have been higher at 140 ppm of applied product.

Product Component

Expected Residuals with No Loss When Applied at 140 ppm

Calculated Dosage Based on Actual Residual

Product Loss to System Reactions

Phosphonate

8 drops

6 drops

= 100 ppm Product

40 ppm Product

BZT

2.1 ppm

1.5 ppm BZT

= 100 ppm Product

40 ppm product

Zinc

1.4 ppm

0.8 ppm Zinc

= 80 ppm Product

60 ppm Product

 

Conclusion

Mass balance is the most accurate way to determine applied dosage. If the product dosage was projected to be effective at 100 ppm, it is likely that this product is being overfed by 40%. Chemical testing suggests that there is more than sufficient residual of active components even after some loss to the system, so product dosage can be lowered and results monitored to confirm that desired results are maintained. There is expected to be some loss of active components as they react with the materials in the system and the impurities in the water.

Where molybdate is used or has been used as a monitoring method for product control and consumption, generally its loss to the system is minimal. That means that if the product shown above contained 1% molybdate as Mo,

it is likely that the test results would have been very close to 1.4 ppm Mo and the product dosage would have been decreased to 100 ppm to lower Mo to 1.0 ppm. Molybdate used as a tracer, then, would commonly yield a lower product usage rate because the other active components would not ordinarily be used to control the dosage.

Reduccion del uso de agua en torres de enfriamiento con automatización

Con la iniciativa del Estado para reducir el consumo de agua en un 20 por ciento para el año 2020, muchas plantas en California están tratando de ser más respetuosos con el medio ambiente. Una de esas instalaciones incluye un hospital líder en California, que trató de reducir los costos de tratamiento de agua para su sistema de climatización. El hospital cuenta con tres sistemas de torres de enfriamiento individuales que dan servicio a tres enfriadores centrífugos, con un total combinado de 2.800 toneladas de capacidad.

El programa de tratamiento de agua actualmente en uso en la instalación estaba operando a 2,8 ciclos de concentración, resultando en 35,7 por ciento de la composición agua de la torre se sangró a la alcantarilla por el proveedor de tratamiento actual. Teniendo en cuenta la calidad del agua en la zona, estos eran los ciclos máximos de concentración que podrían lograrse sin emplear el uso de reblandecimiento ácido o agua. El ahorro que el hospital solicitó se realizaron mediante la revisión de varias formas de optimizar el programa de tratamiento de agua. Trabajando en estrecha colaboración con el Departamento de Agua y Energía (LADWP) Los Ángeles, se reveló que mediante la introducción de un programa de conservación de agua para reducir el uso del agua a través de mayores ciclos de concentración, la instalación realidad ahorraría más dinero que se gastaría para alterar el programa , por lo que el proyecto propuesto sostenible.

A través de pruebas y análisis de laboratorio, el equipo fue capaz de concluir que seis ciclos de concentración podrían alcanzarse, resultando en sólo el 16,7 por ciento del agua de maquillaje torre siendo desangrado en el sistema de tratamiento de alcantarillado. Esto se podría lograr mediante la introducción de un sistema de alimentación de ácido seguro que minimizaría escala, la corrosión y el ensuciamiento microbiológico para permitir el aumento de ciclos de concentración al mismo tiempo proteger personal de la instalación entre en contacto con los productos químicos.

La evaporación de la torre de refrigeración sigue siendo el mismo, pero el agua de Estados Unidos fue capaz de reducir la purga, cortando el consumo de agua en un estimado de 3.6 millones de galones por año y la disminución de los costos de agua y alcantarillado. La planta fue capaz de ahorrar más de $ 76.000 (ver Fig. 1).

química en cualquier momento en la torre de refrigeración está estresado por la adición de más ciclos, se requiere un control estricto de la química para evitar la formación de incrustaciones. Esto llevó a la introducción de controles de automatización avanzada de agua de Estados Unidos. El programa de automatización avanzada incluye notificaciones de vigilancia y alarmas inalámbricas para gestionar el rendimiento general del programa, y ​​el equipo de conductividad, pH, los niveles de inhibidor de incrustaciones, el uso de la torre de maquillaje, y la utilización de la torre de purga monitoreado.

En un momento dado, el personal del hospital y los representantes designados de agua de Estados Unidos, utilizando varios niveles de seguridad de la contraseña-protegida indicado por la instalación, se puede acceder de forma segura los datos para la revisión y ajuste en línea. Si los parámetros designados cayeron encima o por debajo del intervalo especificado, un representante de aguas US fue alertado para una respuesta rápida (véase Fig. 3).

Segundo para riego, torres de enfriamiento ofrecen el mayor potencial de ahorro de agua en California. Como un incentivo adicional, el estado de California ha puesto en marcha programas para rebajar la instalaciones para el coste de la automatización de sus sistemas. LADWP y el Distrito Metropolitano de Agua (MWD), por ejemplo, ofrecen tres programas que financian la automatización de las torres de enfriamiento debido a su capacidad para aumentar ciclos de concentración, lo que reduce el consumo de agua.

 

Esta permitido la financiación de agua de Estados Unidos para implementar el programa de automatización avanzada $ 34.000 a monitorear y controlar el programa de tratamiento de agua para este hospital sin costo alguno para el hospital.

Los resultados hasta la fecha para la instalación incluyen la reducción significativa en el consumo de agua, el agua baja y las facturas de aguas residuales y un control más eficiente debido a la automatización de software instalado para proteger los bienes de equipo.

You will find this article here: http://www.waterworld.com/articles/iww/print/volume-14/issue-5/columns/case-study/hospital-reduces-water-usage-in-cooling-towers-with-automation.html

HOSPITAL REDUCES WATER USAGE IN COOLING TOWERS WITH AUTOMATION

With the state's initiative to reduce water usage by 20 percent by the year 2020, many plants in California are striving to become more environmentally friendly. One such facility includes a leading California hospital that sought to reduce water treatment costs for its HVAC system. The hospital has three individual cooling tower systems that service three centrifugal chillers, with a combined total of 2,800 tons of capacity.

The water treatment program currently in use at the facility was operating at 2.8 cycles of concentration, resulting in 35.7 percent of the tower water makeup being bled to the sewer by the current treatment provider. Given the water quality in the area, this was the maximum cycles of concentration that could be achieved without employing the use of acid or water softening.

The savings that the hospital sought were realized by reconsidering various ways to optimize the water treatment program. Working closely with the Los Angeles Department of Water and Power (LADWP), it was revealed that by introducing a water conservation program to reduce water use through increased cycles of concentration, the facility would actually save more money than it would spend to alter the program, making the proposed project sustainable.

Through testing and lab analysis, the team was able to conclude that six cycles of concentration could be attained, resulting in only 16.7 percent of the tower makeup water being bled into the sewer treatment system. This could be achieved through the introduction of a safe acid feed system that would minimize scale, corrosion and microbiological fouling to enable the increase in cycles of concentration while also protecting facility staff from coming into contact with the chemicals.

The evaporation of the cooling tower remained the same, but U.S. Water was able to reduce blowdown, cutting water usage by an estimated 3.6 million gallons per year and decreasing water and sewage costs. The plant was able to save over $76,000 (see Fig. 1).

Anytime chemistry in the cooling tower is stressed by adding more cycles, tight control of the chemistry is required to prevent scale formation. This led to the introduction of U.S. Water's advanced automation controls. The advanced automation program included wireless monitoring and alarm notifications to manage the overall program performance, and the equipment monitored conductivity, pH, scale inhibitor levels, tower makeup usage, and tower bleed usage.

At any given time, designated hospital personnel and U.S. Water representatives, using various levels of password-protected security outlined by the facility, can securely access the data for review and online adjustment. If designated parameters fell above or below the specified range, a U.S. Water representative was alerted for quick response (see Fig. 3).

Second to irrigation, cooling towers offer the largest potential for water savings in California. As an added incentive, the state of California has put programs in place to rebate facilities for the cost of automating their systems. LADWP and the Metropolitan Water District (MWD), for example, offer three programs that finance automation for cooling towers due to their ability to increase cycles of concentration, which reduces water use.

This financing allowed U.S. Water to implement the $34,000 advanced automation program to monitor and control the water treatment program for this hospital at no cost to the hospital.

Results to date for the facility include significant reduction in water usage, lower water and sewage bills and more efficient monitoring due to the installed automation software to protect the equipment assets.

You will find the article at: http://www.waterworld.com/articles/iww/print/volume-14/issue-5/columns/case-study/hospital-reduces-water-usage-in-cooling-towers-with-automation.html