Cooling water systems Additives

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. 

Petroleum greases and oils can be excellent corrosion inhibitors on a variety of alloys. The hydrophobic layer produced by oil or grease can prevent water from contacting surfaces and can, therefore, almost eliminate corrosion. Unfortunately, the addition of oil and grease cannot be recommended as a corrosion-reduction measure in cooling water systems for three basic reasons. 

Metal surfaces in a well-designed, well-operated cooling water system will establish an equilibrium with the environment by forming a coating of protective corrosion product. This covering effectively isolates the metal from the environment, thereby stifling additional corrosion. Any mechanical, chemical, or chemical and mechanical condition that affects the ability of the metal to form and maintain this protective coating can lead to metal deterioration. Erosion-corrosion is a classic example of a chemical and mechanical condition of this type. A typical sequence of events is ... 

Operation of this cooling water system was intermittent, resulting in long periods (30 days) of no-flow conditions. After IVi years, leaks were found at welded pipe junctions. Radiographic examinations revealed numerous additional deep corrosion sites at welds that had not yet begun to leak. 

Chemical additives are needed at some plants with recirculating cooling water systems in order to prevent corrosion and scaling. Chemical additives are also occasionally used at plants with once-through cooling water systems for corrosion controls. 

Chlorine and hypochlorite are used to control biofouling in both once-through and recirculating cooling water systems. The addition of chlorine to the water causes the formation of toxic compounds and chlorinated organics, which may be priority pollutants. 

Plant 1226 is a bituminous coal-, oil-, and gas-fired electricity plant [1]. The recirculator cooling water system influent was sampled from a stream taken from the river and the effluent from the cooling tower blowdown stream. The effluent stream is used again in the ash sluice stream. Table 7 presents the data. The following additives are combined with the cooling tower influent ... 

HE Half-life of cooling water chemical additives in the system (holding time index)... 

Where chlorine dioxide is used in large process cooling systems, it is not uncommon for significant levels of sulfides to be present in the cooling water system. A benefit of chlorine dioxide biocide is its additional ability to readily oxidize this sulfide however, good monitoring and control is necessary, as high initial sulfide levels can result in mineral acid formation and the potential for corrosion to occur ... 

The condensation of an aromatic nitro compound with a second reactant should have been performed in an aqueous solution with DMSO in the semi-batch mode. The nitro-compound is initially charged into the reactor with water and DMSO as solvent. Before the progressive addition of the second reactant had been started, the initial mixture was heated to the process temperatures of 60-70 °C. Then a failure of the cooling water system of the plant occurred. It was decided to interrupt the process at this stage and to maintain the mixture under stirring until the failure had been repaired. The feed of the second reactant was postponed and the jacket of the reactor had been emptied. 

Chloride ion concentration in a closed cooling water system may be concentrated as much as seven times and it can contribute to corrosion of stainless steel equipment. Brazos River water contains as much as 200 ppm during dry periods. Thus, it is doubtful that the increased chloride (7 ppm) would cause measurable additional corrosion in any case. 

One of the arguments against the use of ozone is the cost penalty and certainly there are indications that in comparison with chlorine, ozone is more expensive. Some cost data were published by Manzione [1991] in relation to a cooling water system with a comparison between chemical additive treatment (unspecified) and ozone. The figures are summarised in Table 14.15. 

Continuous ferrous sulphate addition has been used for many years to reduce water side corrosive attack of steam condenser tubes. It is usually applied to once through cooling water systems because of its low cost, to provide an iron-rich protective film on the tube surface. For recirculation systems other more expensive, corrosion inhibitors are generally employed. Two phases of the ferrous sulphate treatment programme may be recognised. The first phase involves the initial laying down of the protective film. The second phase involves the maintenance of the film, which would be otherwise destroyed by the shear effects of flow. 

The layout of the various sewer systems can begin with a careful indication of all the major equipment foundations, the locations of which are taken from the plot plan. Care should be exercised to indicate all pipe rack columns, lighting poles and all minor footings, which, if not shown, may result in interferences with the sewers. Underground cooling-water systems should be integrated into the sewer system layout as an additional system as it would be impossible to avoid interferences. The same can be said of any underground electrical utilities they must be also indicated on the sewer layout to avoid any interferences. 

In addition to weeds, acrolein is used to control fouling organisms in cooling water systems. Effective control was established in a once-through cooling system of a steel mill with continuous application of 200.0 p,g... 

Failure to remove excess reaction ECH from the system prior to condensate addition was due to the absence of cooling water flow to the ECH/water condenser. The cooling water system for the condenser had not been commissioned after the plant shutdown, and was isolated both at a manually operated valve and at a valve operated via the plant computer. The lack of condensing capacity resulted in high vapour flows to vent, with a consequent increased back-pressure on the reactor which caused a reduced evaporation rate. 

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