Steam contamination

Supercritial boilers use all-volatile treatments, generally consisting of ammonia and hydrazine. Because of the extreme potential for deposit formation and steam contamination, no soHds can be tolerated in supercritical once-through boiler water, including treatment soHds. 

Steam can be contaminated with soHds even when carryover is not occurring. Contaminated spray attemperating water, used to control superheated steam temperature at the turbine inlet, can introduce soHds into steam. A heat exchanger coil may be placed in the boiler mud dmm to provide attemperation of the superheated steam. Because the mud dmm is at a higher pressure than superheated steam, contamination will occur if leaks develop in the cod. 

Where small quantities of high-purity steam is required for electronic chip, pharmaceutical, sterilization, food preparation, and similar process applications, a small risk of steam contamination may exist. This may be caused directly by the use of amine treatments or indirectly through process contaminants or the transport of iron oxides. Consequently, alternative arrangements for steam generation are made. 

Carryover refers to the entrainment of BW (and the contaminating solids contained in the water) into the steam. Contamination of steam from entrained water may lead to deposits in superheaters, on turbine valves, and in steam traps, valves, and flash vessels. 

Almost all larger FT and HP boiler plants employ some form of external capital equipment for MU water and FW treatment. The rationale for installing capital equipment is to eliminate (or at least minimize) the level of mineral impurities, process contaminants, and noncondensable gases entering the boiler via the FW system to reduce the potential for the development of waterside deposition, corrosion, steam contamination, and other waterside problems. 

Contaminant-clearance validation studies are of special signibcance in biopharmaceutical manufacture. As discussed in Section 7.6.4, downstream processing must be capable of removing contaminants such as viruses, DNA and endotoxin from the product steam. Contaminant-clearance validation studies normally entail spiking the raw material (from which the product is to be purihed) with a known level of the chosen contaminant and subjecting the contaminated material to the complete downstream processing protocol. This allows determination of the level of clearance of the contaminant achieved after each purihcation step, and the contaminant reduction factor for the overall process. 

ESR spectra as well as additional experiments with very pure alumina (steaming, treatment with diluted acids, interaction with hydrogen sulfide) indicate that at least two factors can influence hydrogenation activity of USY zeolites obtained via steaming contamination of parent material with Fe ions and/ or formation of new active phase of altimina inside supercages. The catalytic sites are probably coordinatively unsaturated surface species, which are poisoned by carbonaceous deposits formed as the result of prolonged interaction with olefins. 

No risk factors for illness have been identihed other than estimated ingested dose [162], The investigation in North Carolina examined age, gender, the presence of chronic illness, medication use, and alcohol consumption during the implicated meal and fonnd no association with illness. As with other marine neurotoxins, brevetoxin is heat stable and thus, cooking contaminated seafood will not alter the risk of intoxication. Furthermore, the toxin is lipid rather than water-soluble [174] and thus, boiling or steaming contaminated food is similarly unlikely to alter the risk of intoxication. 

There is no mention in the standard of the positioning of socket outlets near kitchen sinks sockets are quite frequently installed directly above sinks with an obvious risk of water/steam contamination of the socket or the risk of apparatus powered from the socket falling into the sink. The NICEIC offers guidance to its members that sockets should be located at least 300 mm... 

In direct cycle plants, an additional source of secondary system contamination that needs to be considered is leakage from equipment for concentrating radioactive waste that involves steam heating. One such source of contamination is through tube leaks that allow contaminated waste to enter the condensed heating steam. Contaminated condensed water from such steam may then be introduced into the secondary system. 

Nitrobenzene. Nitrobenzene, of analytical reagent quality, is satisfactory for most purposes. The technical product may contain dinitrobenzene and other impurities, whilst the recovered solvent may be contaminated with aniline. Most of the impurities may be removed by steam distillation after the addition of dilute sulphuric acid the nitrobenzene in the distillate is separated, dried with calcium chloride and distilled. The pure substance has b.p. 210°/760 mm. and m.p. 5 -7°. 

Steps. Thermal-swing cycles have at least two steps, adsorption and heating. A cooling step is also normally used after the heating step. A portion of the feed or product stream can be utilized for heating, or an independent fluid can be used. Easily condensable contaminants may be regenerated with noncondensable gases and recovered by condensation. Water-iminiscible solvents are stripped with steam, which may be condensed and separated from the solvent by decantation. Fuel and/or air may be used when the impurities are to be burned or incinerated. 

Water as an impurity accelerates the oxidation rate. Figure 4 compares growth curves for Si02 under dry and steam conditions. Halogens can also be introduced to the oxidation process, thereby reducing sodium ion contamination. This improves dielectric breakdown strength, and reduces interface trap density (15). 

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

Before any remedial or preventive actions are implemented, an evaluation should be conducted as to appHcabiUty to the specific plant. The evaluation should continue while the actions are in progress. The main action should be to take measures to reduce the ingress of contaminants into the steam generator by using more rehable materials, such as in the condenser tubes, to reduce leakage. Contaminant control equipment, such as full-flow condensate deminerali2ers, should also be employed. 

Most fast reactors that use Na or NaK as coolant utilize an intermediate heat exchanger (IHX) that transfers heat from the radioactive core coolant to a nonradio active Hquid-metal coolant loop, which has the reactor s steam generator. This helps minimize the spread of contamination in the event of a leak or fire. 

Carbon produced by these latter reactions is formed in the catalyst pores, making it much more difficult to remove, and potentially causing physical breakage. Operating steam to carbon ratios are chosen above the minimum required in order to make carbon formation by these reactions thermodynamically impossible (3). Steam is another potential source of contaminants. Chemicals from the boiler feedwater or the cooling system are poisons to the reformer catalyst, so steam quality must be carefully monitored. 

Process condensate from reforming operations is commonly treated by steam stripping. The stripper is operated at a sufficiently high pressure to allow the overhead stripping steam to be used as part of the reformer steam requirement (71). Contaminants removed from the process condensate are reformed to extinction, so disposal to the environment is thereby avoided. This system not only reduces atmospheric emissions, but contributes to the overall efficiency of the process by recovering condensate suitable for boiler feedwater make-up because the process is a net water consumer. 

As the water evaporates into steam and passes on to the superheater, soHd matter can concentrate in a boHer s steam dmm, particularly on the water s surface, and cause foaming and unwanted moisture carryover from the steam dmm. It is therefore necessary either continuously or intermittently to blow down the steam dmm. Blowdown refers to the controHed removal of surface water and entrained contaminants through an internal skimmer line in the steam dmm. FHtration and coagulation of raw makeup feedwater may also be used to remove coarse suspended soHds, particularly organic matter. 

Activated carbon adsorption generally uneconomical for removal of >1000 ppm contaminant from large stream unless bed regenerated steaming often easiest regeneration method but creates new wastewater problem usually 3—5 kg steam requited per kg of carbon for regeneration. 

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