Fouling, and Deposition

In a similar vein, technical discussions in textbooks and papers, up to only a few years ago, tended to cover problems such as corrosion, carbonate scaling, and microbiological control as individual topics that were somehow unrelated to each other. Such discussions were often quite theoretical and had little in common with field practicalities and realities. 

This is not to say that the most theoretical treatises were unwelcome or unenlightening, but they were most probably almost irrelevant for all practical purposes. Fortunately, the welcome and developing trend today is to provide textbooks and papers that balance detailed discussions on particular topics with case histories (complete with photographs) from real cooling systems and other areas of water treatment. 

NOTE In this chapter there is discussion concerning some individual aspects of corrosion, fouling, and deposition, but every attempt is made to link them together into a coherent whole. It is also incumbent upon the reader and water treatment practitioner to consider each specific problem or aspect of water management in the light of the complete, dynamic, cooling water system. 

In addition, modem chemical polymer treatments tend to have wider applications than before, so, for example, many deposit control agents are also antifoulants as well as antiscalents, which only serves to confuse the issue. 

However, a dictionary definition of fouling includes to obstruct (with foreign matter), to entangle, to impede, while a foulant is described as fetid, stinking, and putrid. Thus the definition of foulant should, of necessity, include matter of microbiological origin, plus its degradation products. 

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A first operation on the crude, desalting (washing by water and caustic), extracts salts (NaCl, KCl and the MgCb that is cdn eft4rdJt6 NaCl by the caustic), reduces acid corrosion as well as it minimizes fouling and deposits. /... 

In practice, both fouling and deposition actions are likely to occur simultaneously to some degree or other in a boiler system. Furthermore, corrosion processes and the entry of contaminants into the steam-water system usually results in some form of deposition occurring elsewhere in the system. 

Uniform rates of corrosion such as general etch corrosion seldom occur in steam-water circuits. Rather, pitting, tuberculation, and other complex types of corrosion tend to predominate. These forms of corrosion often result directly or indirectly from reactions occurring in particular areas of the system where fouling and deposition may be present. 

Other system problems Uncontrolled and excessive water losses Pump, valve, steam trap losses and no water meter leads to Oz pitting, Fe fouling and deposits of carbonate... 

Oil and hydrocarbon leaks. FW system fouling and deposit binding Non-wettable boiler surfaces. 

Oil and hydrocarbon leaks that return with the condensate coat heat-exchange surfaces and cause FW system fouling and deposit binding. These materials must be removed or they will reenter the boiler to produce nonwettable boiler surfaces, and create serious problems. Oil in condensate should be removed by the use of an inline pre-coat filter. The pre-coating should be either aluminum hydroxide ox ferric hydroxide becaue both these hydrous oxide gels have an affinity for oil. 

Condenser leaks permit dissolved solids, oxygen, organics, and suspended solids to enter the CR system and from there to enter the FW system. This is a very serious problem and leads to feed system fouling and deposition and the depassivation of metal surfaces, which in turn induces pitting corrosion to occur. 

The reaction products cause fouling and deposition in FW lines, the FW tanks of small boilers, and the economizers of large systems. 

Where present in boiler MU water, both iron and manganese may present fouling and deposition problems in the pre-boiler section. These problems may extend to the boiler section, and therefore these metals must be removed at source. Typically, this is achieved by oxidation followed by filtering off the flocculated iron. (Process examples are aeration towers, contact with chlorine, pressure filters with BIRM media, manganese greensand filters, etc.)... 

Fouling and deposition in boiler sections may occur unintentionally through the application or misapplication of chemical water treatment programs. Internal treatment-related boiler section problems may... 

To increase equipment reliability and plant efficiency, corrosion inhibitors are used in boiler and cooling water programs to control fouling and deposition on critical heat-transfer surfaces. In cooling systems, corrosion inhibition is commonly achieved through the use of passivators, which encourage the formation of a protective metal oxide film on the metal surface ( 1). ... 

Help prevent fouling and deposit formation on fuel injector nozzles... 

Under the high temperature conditions of the JFTOT procedure, olefinic compounds could undergo polymerization-type reactions to form high-molecular-weight materials. These heavier compounds can foul and deposit onto the rating tube or filter screen. Tube darkening and/or filter screen plugging can result. 

Corrosion, fouling, and deposition processes of some degree most probably will have been steadily taking place for some time prior to the evaluation being made. If an index or model is to be used, the makeup water source should always be the starting point and cycled-up cooling water composition calculated from this point (despite the problems of accurately assessing the cycled-up water pH). 

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