Chlorine-water system

Chlorine Vehicle ndStabilizer. Sulfamic acid reacts with hypochlorous acid to produce /V-ch1orosu1famic acids, compounds in which the chlorine is stiU active but more stable than in hypochlorite form. The commercial interest in this area is for chlorinated water systems in paper mills, ie, for slimicides, cooling towers, and similar appHcations (54) (see INDUSTRIALANTIMICROBIALAGENTS). 

FIGURE 4.1.1. Potential-pH diagram for the chlorine-water system at 25°C [6]. (Wifli permission from NACE and CEBELCOR). 

FIGURE 56.7 Pourbaix diagram of the copper-chlorine-water system. 

Solubility data for the chlorine-water system have been published by Whitney and Vivian (1941). These authors point out that the two-phase system may be visualized as consisting of chlorine gas at such a partial pressure that it is in equilibrium with molecular chlorine in the solution—a relationship which can be assumed to follow Henry s law. In addition, the dissolved molecular chlorine will be in equilibrium with hypochlorous acid and hydrogen and chloride ions in the solution in accordance with the following reaction ... 

However, Carey et al. invoked a procedure attributed to Vivian and Whitney for allowing for this hydrolysis. Vivian and Whitney were concerned with the chlorine-water system, for which the line is concave upward at the lower end, becoming visually straight from about 400 mm Hg to about 1 atm. The concavity is conventionally taken to indicate that chlorine is more soluble in water than it would be if hydrolysis did not occur. It is conventionally believed that when a chemical reaction occurs, the solubility in water is high. It is also believed that when a chemical reaction occurs, Henry s law is not obeyed and when Henry s law is obeyed, it is concluded that no chemical reaction has occurred. Such generalizations have no scientific content. It will be noticed that the plot for CHCI2F is decidedly convex upward. To me the hydrolysis depicted by Carey et al. in their symbolic terms could not be reversible the chlorine-water system was assumed to be reversible. 

Polypropylene pipe and fittings were selected for a high-purity, highly chlorinated water system in a medical research facility. In the first four years of operation, the system sustained an excessive number of leaks. This paper is an account of the investigation of the causes of those leaks. 

Saline Water for Municipal Distribution. Only a very small amount of potable water is actually taken by people or animals internally, and it is quite uneconomical to desalinate all municipally piped water, although all distributed water must be clear and free of harmful bacteria. Most of the water piped to cities and industry is used for Htfle more than to carry off small amounts of waste materials or waste heat. In many locations, seawater can be used for most of this service. If chlorination is requited, it can be accompHshed by direct electrolysis of the dissolved salt (21). Arrayed against the obvious advantage of economy, there are several disadvantages use of seawater requites different detergents sewage treatment plants must be modified the usual metal pipes, pumps, condensers, coolers, meters, and other equipment corrode more readily chlorination could cause environmental poUution and dual water systems must be built and maintained. 

Antimicrobial efficacy is also affected by demand in the cooling water system, specifically demand exerted by ammonia. Chlorine reacts with ammonia to form chloramines, which are not as efficacious as hypochlorous acid or the hypochlorite ion in microbiological control. Bromine reacts with ammonia to form bromamines. Unlike chloramines, bromamines are unstable and reform hypobromous acid. 

Continuous chlorination of a cooling water system often seems most pmdent for microbial slime control. However, it is economically difficult to maintain a continuous free residual in some systems, especially those with process leaks. In some high demand systems it is often impossible to achieve a free residual, and a combined residual must be accepted. In addition, high chlorine feed rates, with or without high residuals, can increase system metal corrosion and tower wood decay. Supplementing with nonoxidizing antimicrobials is preferable to high chlorination rates. 

Sodium hypochlorite and calcium hypochlorite are chlorine derivatives formed by the reaction of chlorine with hydroxides. The appHcation of hypochlorite to water systems produces the hypochlorite ion and hypochlorous acid, just as the appHcation of chlorine gas does. 

Halogen donors are chemicals that release active chlorine or bromine when dissolved in water. After release, the halogen reaction is similar to that of chlorine or bromide from other sources. SoHd halogen donors commonly used in cooling water systems include l-bromo-3-chloro-5,5-dimethyIhydantoin, l,3-dichloro-5,5-dimethyIhydantoin, and sodium dichloroisocyanurate. 

THMs are a byproduct of the chlorination process that most public drinking water systems use for disinfection. Chloroform is the primary THM of concern. EPA does not allow public systems to have more than 100 parts per billion (ppb) of THMs in their treated water. Some municipal systems have had difficulty in meeting this standard. 

R/0 unit Reverse Osmosis Unit for water purification in small aquariums and miniature yard-ponds, utilizes a membrane under pressure to filter dissolved solids and pollutants from the water. Two different filter membranes can be used the CTA (cellulose triacetate) membrane is less expensive, but only works with chlorinated water and removes 50-70% of nitrates, and the TFC membrane, which is more expensive, removes 95% of nitrates, but is ruined by chlorine. R/0 wastes water and a system that cleans 100 gallons a day will cost ft-om 400 to 600 with membrane replacement adding to the cost. A unit that handles 140 gallons a day will cost above 700,00. 

Hliiull. In v.tive B 5th ijifcni-.O pr< SM re ViilvL-. fail [jpai C)peration Excessive chlorine How to Tower Water Basin - high chlorine level to cooling water -potential for excessive corrosion in cooling water system Rotameter Relief valve an pressure check valve outlet in Nnilk-... 

It is worthwhile drawing attention to health hazards associated with film infected water systems which also cause corrosion. Two of the most common are Legionnaires disease and so called humidifier fever . Because of strong adhesion of biofilms and diffusion rates through the film treatment based on cleaners and chemical sterilisers such as chlorine often fail similar considerations apply to other systems in industry, e.g. food, paint, oil and gas are examples where biofilm activities have given massive problems. 

When coolers or condensers are shut-down but remain full of water, the amount of current required to maintain satisfactory cathodic protection is considerably reduced. If the current is not reduced over-protection occurs and excessive amounts of chlorine can be generated which would tend to accumulate in the upper section of the water boxes causing considerable corrosion, not only to the water boxes, but also possibly to the tubes. To ensure against this a stand-by condition should be included on the control panel which effectively reduces the current required under shut-down conditions. This control is effected by a limit switch fitted to the outlet valve of the condenser or cooler concerned. It is impossible to determine exact requirements for the protection of circulating water systems in advance and it is normal to adjust the current to provide protection during commissioning. 

Biofilms which may develop in water systems are known to provide ideal habitats for the survival and growth of Legionella(5). Chlorine does not readily penetrate such biofilms and destroy Legionella(6). 

The use of chlorine dioxide in water systems results in its reduction to chlorite and chloride. In the UK the Drinking Water Inspectorate (DWI) restricts the use of chlorine dioxide in potable water supplies to a maximum of 0.5ppm total oxidants expressed as chlorine dioxide. This ensures that chlorite (and any chlorate) concentrations do not reach levels of potential harm to humans. 

The ACTIV-OX system has been developed to meet the needs for a safe and controllable chlorine dioxide system for application in small water using systems. The system instantaneously delivers over 90% of the available chlorine dioxide at a pH of 4 compared to other systems which require lower pH and or longer reaction times (Fig 1 and 2). 

The ACTIV-OX chlorine dioxide system evaluated in this trial overcomes many of the problems associated with chlorine dioxide for the small water user. A chlorine dioxide precursor solution and a dilute acid solution are mixed in a 1 1 ratio immediately prior to injection into the water to be treated. The dose rate of chlorine dioxide is controlled by water meter signal to two proportioning pumps. The mixing of the two chemicals immediately produces a chlorine dioxide solution which is diluted to the required strength by injection into the water to be treated (Fig 3). 

The newly developed ACTIV-OX chlorine dioxide system has effectively delivered continuous low levels of chlorine dioxide which were effective in controlling Legionella in a hot and cold water system without the need for prior disinfection. 

STABREX Stabilized Liquid Bromine9 is far more stable than liquid chlorine bleach. For example, several tons of the new product were shipped to India and stored for one year above 90 °F. The product remained within specification (less than 10% degraded) for the entire year, after which it was successfully used to control fouling in an industrial water system. Chlorine would have completely degraded in this time under these conditions. Chemical wastage was eliminated. Accident risk in transporting oxidant was reduced because less volume was necessary. Table 2 shows the stability of the new product compared to industrial strength chlorine bleach in well-controlled laboratory tests. 

The benefits of replacing chlorine with STABREX are in reducing environmental toxicity (because it is less toxic to aquatic wildlife), in reducing accident risk (because it is less hazardous and easier to handle), and in reducing chemical waste (because it works better, is more stable in transport/storage, is less volatile and less reactive). Environmental toxicity and accident risk have been substantially reduced in more than 2,500 industrial water systems worldwide. 

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