Industrial problems cooling water

Industrial Problems Cooling Water and Cooling-Water Treatment... 

Many sources contain scattered information concerning cooling water system corrosion and defects, and many literature studies describe corrosion processes and mechanisms from a predominantly theoretical viewpoint. Until now, however, no source discusses cooling water system corrosion with emphasis on identification and elimination of specific problems. Much of the information in this book is unique every significant form of attack is thoroughly detailed. Color photos illustrate each failure mechanism, and case histories further describe industrial problems. 

These filters are useful for retrofitting to existing cooling water systems that may be required to operate with a deteriorating water quality, and they usually present minimal installation problems. For most applications, however, they are installed in-line, and this can present installation problems in larger industrial process cooling systems that cannot be shut down. 

Around the world, the most widely used biocide for industrial cooling systems is gaseous chlorine. Typically, it is a low-cost maintenance item and generally very effective, but may present specific cooling water chemistry limitations, plus possible handling, safety, and environmental problems. (The relatively high capital costs associated with a gaseous chlorine system may also be a problem.)... 

For some industrial cooling water applications, where process contamination is often an inherent problem, a high chlorine/low bromine ratio product may be preferable. This type of problem can happen, for example, where repeated hot/cold cycles are part of the process and some valve leakage and interchange of water between circuits may occur. Thus, the (lower cost) chlorine component is employed in satisfying the contaminant halogen demand and the bromine component (perhaps with some degree of Br recycle) subsequently acts as a biocide. 

To prevent the problems caused by slime formation, various microbicides (slime-controlling agents) can be used. Of these, 5-chloro-2-methyl-4-isothiazo-line-3-one (Cl-MIT 1) is the most widely used as a slime-controlling agent, a bactericide, an algicide or a fungicide, for various industrial water systems such as those in cooling-water units or papermills, as it has an excellent microbicidal activity. [2]... 

The work of Mosko [116] is important in that he is one of the few workers who have given serious consideration to the determination of nitrite in water. His paper is concerned with the determination of chloride, sulphate, nitrate, nitrite, orthophosphate, fluoride and bromide in industrial effluents, waste water and cooling water. Two types of analytical columns were evaluated (standard anion and fast run series). Chromatographic conditions, sample pretreatment and the results of interference, sensitivity, linearity, precision, comparative and recovery studies are described. The standard column provided separation capabilities which permitted the determination of all seven anions. The fast run column could not be used for samples containing nitrite or bromide owing to resolution problems. 

Although heat is not often recognized as a pollutant, individuals in the electric power industry are well aware of the problems involved in the disposal of waste heat. Furthermore, waters released by many industrial processes are much hotter than the receiving waters. While in some cases an increase in water temperature can be beneficial (e.g., the production of clams and oysters can increase), in other cases it can have negative impacts. For example, many important commercial and game fish (e.g., salmon and trout) live only in cool waters. Higher water temperatures also increase the rate of dioxygen... 

Counterflow-induced draft towers, Figure 9.17(d), are the most commonly used in the process industries. Mechanical draft towers are capable of greater control than natural draft and in some cases can cool water to below a 5°F approach. The flow of air is quite uniform at a high velocity and the discharge is positive so that there is a minimum of backflow of humid air into the tower. The elevated fan location creates some noise and structural problems. It has been reported that mechanical draft towers at low water rates (19,800 gpm) perform better than natural draft towers. 

In general the discussion will concern aqueous systems, largely because it is within these systems that much work has been carried out to develop suitable additives, principally for cooling water application. Because aqueous systems are common to many industries, and the potential need for suitable fouling mitigation is widespread, the financial incentive has been present to develop suitable and effective additives. The principles may be applied to other systems but it is unlikely that if the process stream is unique, a suitable additive will have been developed and tested. The development of a chemical that will restrict or prevent, a particular fouling problem may be expensive and the development cost unjustified. Under these circumstances either the deposition problem has to be tolerated or a different technique applied (see Chapters 15 and 16). 

Fig. 16.3 gives the flow sheet of a cooling water system commonly used in power generation that is also used in the process industries. Chemicals such as acids, biocides, scale and corrosion inhibitors and dispersants are added to control problems of fouling in the recirculating system (described elsewhere in this book). The technique is generally applicable where the make-up water is generally of low hardness and silica and low concentration factors are employed. 

The importance of fouling measurement techniques using monitors is likely to increase as the competitive nature of the process and power industries intensifies. In cooling water applications more effective use of additives can be achieved through their use wdth reduced costs and less environmental impact, as a result of accurate assessment of the fouling problem. 

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