Fouling processes

Figure 1 The microbial fouling process on surfaces of certain macroalgae in aquatic environments is controlled by the selective oxidation of bromide with hydrogen peroxide and bromoperoxidase. Although chloride is many orders of magnitude more abundant in the sea, bromide is oxidized to hypobromous acid in situ.

Disinfection by-products (e.g., adsorbable organic halides such as trihalomethanes) are more than 50% decreased compared to equivalent chlorine treatments in standardized AOX test with STABREX3. In practice, disinfection by-products are decreased even further in STABREX applications because less oxidant is required to control the microbial fouling process compared to bromine or chlorine applications. 

To avoid, or diminish the fouling process, a blend of PVA with cellulose (CELL) has been obtained by spin coated of the PVA (M=50 000 99% hydrolysis degree) / glutaraldehyde (GA) solution (corresponding to 0.005 or 0.01 moles of GA/ mole of PVA... 

In the light of this somewhat uncertain future for AF technologies based on metals and synthetic, environmentally-persistent, biocides, researchers have returned to the study of the biological basis of the fouling process in the search for environmentally-benign substitutes (Yebra et al., 2004). The first and more evident idea is to look into AF compounds naturally present in the marine... 

The fouling process may be characterized as a rate dependent kinetic process describable by the material balance relation... 

Removal of naphtha and distillate fractions from the crude oil under atmospheric pressure distillation requires charge temperatures to be maintained below the cracking temperature of the crude oil components. This temperature will vary but can typically range from 750°F to 800°F (398.9°C to 426.7°C). Occasionally, even lower temperatures may be required. Above these temperatures, crude oil components can begin to thermally crack and foul processing equipment. 

A variety of liquids have been treated with reverse osmosis and ultrafiltration membranes ranging from seawater, to wastewater, to milk and yeast suspensions. Each liquid varies in composition and in the type and fraction of the solute(s) to be retained by the membrane. Complicating factors include the presence of substances such as oil in seawater and wastewater [12-15]. The presence of the oil normally necessitates an additional pretreatment step further complicating the fouling process. The presence of humic acids in surface water and wastewater also needs special attention [16,17]. The fouling phenomena, the preventive means (i.e., pretreatment), and the frequency and type of membrane cleaning cycle are all dependent on the type of liquid being treated. 

A dual mode fouling process, similar to that observed for humic acids [35], was found for protein (i.e., bovine serum albumin [BSA]) fouling of microfiltration (ME) membranes. Protein aggregates hrst formed on the membrane surface followed by native (i.e., non-aggregated) protein. The native protein attached to an existing protein via the formation of intermolecular disulhde linkages. 

Forced-circulation reboilers are especially suitable for handling viscous and heavily fouling process fluids see Chantry and Church (1958). The circulation rate is predictable, and high velocities can be used. They are also suitable for low vacuum operations and for low rates of vaporization. The major disadvantage of this type is... 

As the fouling process is dynamic, the thickness of the deposit will change with time, as indicated in the earlier discussion. As a result, the temperature distribution will change, and if heat passes from the heat transfer surface to the bulk fluid, the surface/deposit... 

In common with all fouling mechanisms, two process variables can have a profound influence on the extent and the rate of the fouling process temperature and fluid velocity across the heat transfer surface. 

To check the behavior of SCR elements they have to be tested at regular intervals. For this purpose a test programme was developed which includes catalyst activity and selectivity tests in a bench-scale system with surface analysis and characterization of catalysts using highly sensitive surface techniques. By combining these experimental techniques valuable information on ageing and fouling processes on the catalysts is obtained. 

Fouling processes on surfaces are common to all equipment involving hydrocarbon feeds at temperatures over 300°C. They are therefore widespread inside pyrolysis coils because they both operate at high temperatures and are fed by hydrocarbon fractions, which are responsible for the deposit formation. Fouling in pyrolysis coils has always had a negative impact on the behaviour of... 

After the pioneering work done by Dente and Ranzi (1983), the different mechanisms and features of fouling processes were more fully understood and clearly singled out (see for instance Albright, 2002 Albright and Marek, 1988 Blaikley and Jorgensen, 1990 Cai et al., 2002 Chan et al., 1998 Dente et al., 1983 Froment, 1990 Kopinke et al., 1988 Wauters and Marin, 2002 Zou et al., 1987). 

---