Process contamination/leaks

The standard disinfectant for many of the world s potable drinking water supply systems (ozone and others are also widely used) and the product of choice for large cooling systems, usually available as a gas for lowest cost, but can be provided by liquids such as sodium hypochlorite (bleach) or solids such as calcium hypochlorite or isocyanurates. Any process contaminant leak tends to increase the chlorine demand, requiring additional chlorine to maintain disinfection rate. Poor penetrant of biomass and significantly reduced efficiencies over pH 8.0. 

There are many process contaminants that may be inadvertently carried back with the condensate following either the purposeful injection of live steam into, say, an industrial manufacturing process or that can infiltrate the system due to a leaking heating coil, an open surge tank, or similar access point. 

The installation is evacuated for drying to 1 mbar, minimum below 10 mbar. The almost horizontal plot at A is most likely related to some evaporation of water. For the documentation of the process the leak rate of the plant must be measured to prove that no outside perhaps contaminated, air can enter the plant during phase 3. This test (see Section 2.2.8) is best done at the end of phase 1. 

Condensate, however, may not always be usable as boiler feedwater, due to the presence of certain process contaminants (see Table 1). When steam is used for heating, to power equipment, and for varied process applications, condensate comes into contact with oil and other impurities. Contamination from fuel-oil heaters or leaking seals in steam-driven equipment, such as pumps, turbines or compressors, is common. Also, the raw water used as plant makeup, may contain significant levels of solvents, uel oils, gasolines and greases. In addition to these general contamination sources, each industry has its unique one. (Table II). If any of these contaminants become entrained in the returned condensate stream, numerous and sometimes unpredictable problems in the boiler and related systems cs.n occur. 

Recent developments and adaptations of high-speed seal technology have brought gas barrier seals into mixer applications. With a gas such as nitrogen as the barrier fluid, process contamination is virtnally eliminated, and a pressure monitor can be used to detect leaks. The problem is that gas is a poor lubricant for the seal surfaces. However, by machining swirls or pockets in the inside surface of the seal faces, gas pressure can be raised locally to lift the seal surfaces apart. 

A second, and more subtle, problem to do with utilities is their potential for process contamination. On one refinery, e.g., the highly toxic and corrosive chemical hydrogen fluoride (HF), which is discussed in Chapter 5, leaked into the instrument air system. This had the effect of spreading HF all around the refinery it was even being vented from instrument lines in the control rooms. 

Foulants enter a cooling system with makeup water, airborne contamination, process leaks, and corrosion. Most potential foulants enter with makeup water as particulate matter, such as clay, sdt, and iron oxides. Insoluble aluminum and iron hydroxides enter a system from makeup water pretreatment operations. Some well waters contain high levels of soluble ferrous iron that is later oxidized to ferric iron by dissolved oxygen in the recirculating cooling water. Because it is insoluble, the ferric iron precipitates. The steel corrosion process is also a source of ferrous iron and, consequendy, contributes to fouling. 

Both iron and aluminum are particulady troublesome because of their abiUty to act as coagulants. Also, their soluble and insoluble hydroxide forms can each cause precipitation of some water treatment chemicals, such as orthophosphate. Airborne contaminants usually consist of clay and dirt particles but can include gases such as hydrogen sulfide, which forms insoluble precipitates with many metal ions. Process leaks introduce a variety of contaminants that accelerate deposition and corrosion. 

The double opposed seal is used in applications where a zero process leakage is mandated. The seal consists of two seal faces, with the process side seal reversed. An inert gas is injected between the two seals at a positive differential over the process gas pressure. A small amount of the inert gas leaks into the process. The process must be able to accept the contamination of the buffer gas for this seal to be used. 

Plant or processes or systems of work which minimize generation of, or suppress or contain, the hazardous dust, fume, biological agent etc. and limit the area of contamination in the event of spills and leaks. 

Condensate contaminated by process leaks is unsuitable for reuse as... 

Process leaks from phenols, glycols, and various other organics badly contaminate the FW system and lay down sticky films in lower pressure boilers and varnish in higher pressure systems. 

Process leaks of sugars, fats, colloidal materials, pectins, emulsions, and proteins cause stable foams in the boiler, leading to carryover and a further contamination cycle. 

Process leaks from food and beverage production or wood leachates often produce sugars, colloidal materials, pectins, emulsions, and proteins that cause stable foams in the boiler. These lead to carryover and further steam-condensate line contamination. The temporary use of a demulsifier or defoamer as part of the water treatment program may be of particular benefit, but again the condensate is unsuitable for return to the boiler. Other process leaks include ... 

Sources of land pollution include direct dumping of domestic and industrial solid waste, excessive application of agrochemicals, and indirect contamination resulting from leaks or from leaching of hazardous components from liquid waste disposal sites or from atmospheric fallout. Land may also become contaminated by chemicals processed, stored or dumped at the site, perhaps in the distant past. Such contamination may pose a health risk to workers on the site, those subsequently involved in building, construction or engineering works, or the public (e.g. arising from trespass), and to animals. 

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