Fouling minimizing

R. Sondhi and R. Bhave, Role of Backpulsing in Fouling Minimization in Crossflow Filtration with Ceramic Membranes, 7. Membr. Sci. 186, 41 (2001). 

Ripple tray and vapor flute—High capacity with fouling minimization for quench oil and quench water towers... 

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. /... 

When fouling is present or possible, ultrafiltration is usually operated at high Hquid shear rates and low pressure to minimize the thickness of the gel polarization layer. 

When fouling is absent, the optimum concentration is 0.37 C. If the permeate soHds are of primary value, it is usually preferable to diafilter at the minimum retentate volume to minimize permeate dilution. 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

High Water Velocities. The abiUty of high water velocities to minimize fouling depends on the nature of the foulant. Clay and silt deposits are more effectively removed by high water velocities than aluminum and iron deposits, which are more tacky and form interlocking networks with other precipitates. Operation at high water velocities is not always a viable solution to clay and silt deposition because of design limitations, economic considerations, and the potential for erosion corrosion. 

These various reactions should be minimized to avoid plugging the catalyst and to prevent fouling of the downstream air preheaters, when these components condense from the gas at the lower temperatures. 

In the case of particulate fouling, one of the more common types, insuring a sufficient flow velocity and minimizing areas of lower velocities and stagnant flows to help keep particles in suspension is the most common means of deahng with the problem. For water, the recommended tubeside minimum velocity is about 0.9 to 1.0 m/s. This may not always be possible for moderate to high-viscosity fluids where the resulting pressure drop can be prohibitive. 

The above analysis indicates that the high concentrations of sulfur-containing deposits and corrosion products were caused by the influence of large organisms. Bacterial contributions to corrosion and associated fouling were minimal. 

Preferable to recirculating where acceptable vaporization rates can be maintained (less than 25-30%). This type is chosen when there is a need to minimize exposure of degradable and/or fouling substances to high temperatures. Used for large duties, dirty process, and frequent cleaning required. The process is usually in the shell side. This type is used in 95% of oil refinery thermosyphon applications. 

In the depropanizer tower the propane and lighter gases are taken overhead to become feed to the ethylene and propylene recovery facilities. Separation is accomplished at a relatively low overhead temperature of -25°F to minimize reboiler fouling by olefin polymerization. 

The A, Aq, T and Tq valves can be supplied either with a flat periphery for tightest shutoff against liquid weepage at turndown rates or with a three-dimpled periphery to minimize contact with the tray deck for fouling or corrosive conditions. 

The following are some of the steps that can be taken to minimize coking/fouling ... 

Reviewing the overhead water wash most overhead condensers are washed continually to minimize fouling. Since multiple bundles are common, solenoids and a PLX3 can be used to wash one bundle at a time, for approximately ten minutes each. This can lower the pressure drop and increase the available cooling with minimal impact. 

On-line solvent or water wash to minimize blade fouling on both the compressor and turbine. 

If slurry pumparound is the heat medium, consider HCO pumparound to minimize fouling. 

Hyperfiltration (Reverse Osmosis) is a form of membrane distillation or desalination (desalting) operating with membrane pore sizes of perhaps 1 to 10 Angstrom units. The various individual RO component technologies have improved tremendously over the last 20 to 25 years, and resistance to fouling and permeate output rates have benefited. Nevertheless, all RO plants remain susceptible to the risk of fouling, and adequate pretreatment and operation is essential to minimize this problem. 

Some chemical product manufacturers claim a need for higher dose rates (say, up to 10 ppm) to minimize scaling and fouling tendencies, but this is usually prohibitively expensive and may well prove to be an overdose. 

Zeolite softeners were limited in application because of their potential for rapid fouling by ferric hydroxide or calcium carbonate, and a narrow operating pH range of 5.8 to 8.3 was therefore preferred to minimize this problem. 

Caution Part A should be carried out in an efficient hood to minimize exposure to the foul-smelling thiophenol. See benzene warning, Org. Syn., 58, 168 (1979). 

This chip micro reactor was designed to have transparent reaction sections, to provide a large specific surface area of the flowing liquid, and to minimize fouling by crystallization of insoluble photoproducts [72-74]. 

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