Fouling analysis

M. G. Khedr, A case study of RO plant failure due to membrane fouling, analysis and diagnosis. Desalination. 120, 107-113 (1998). 

Kaiya Y., Itoh Y., Takizawa S., Fujita K. (1996), Fouling analysis and control in merribrane treatment process for potable purpose. World Filtration Congress, Budapest, Hungar)% May 96, 526-530. 

Arthanareeswaran, G. and Thanikaivelan, P. 2010. Fabrication of cellulose acetate-zirconia hybrid membranes for ultrafiltration applications Performance, structure and fouling analysis. Separation and Purification Technology lA 230-235. 

FIGURE 7.6. A complete methodology for fouling analysis and mitigation. 

To understand the namre of fouling, fouling analysis was conducted as the fourth task. Samples were taken from the deposits in some of the exchangers. The lab tests... 

Improved sensitivities can be attained by the use of longer collection times, more efficient mass transport or pulsed wavefomis to eliminate charging currents from the small faradic currents. Major problems with these methods are the toxicity of mercury, which makes the analysis less attractive from an eiivironmental point of view, and surface fouling, which coimnonly occurs during the analysis of a complex solution matrix. Several methods have been reported for the improvement of the pre-concentration step [17,18]. The latter is, in fact. 

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. 

In some cases periodic analysis of the seal fluid should he done to check for the accumulation of fouling materials, such as gels, which may he due to reaction of the seal fluid with process gases and materials. 

Analysis and prevention of fouling in tubes attached to micro mixers... 

The transfer of an automated analysis from the laboratory to the plant will often require special precautions for instance, while turbidities in a process stream can cause a loss of selective absorptivity in a spectrophotometric measurement, in potentiometric methods fouling of the electrodes, potential leakage in metal containers or tubing and loss of signal in remote control may occur (see later). 

Many of the conservation measures require detailed process analysis plus optimization. For example, the efficient firing of fuel (category 1) is extremely important in all applications. For any rate of fuel combustion, a theoretical quantity of air (for complete combustion to carbon dioxide and water vapor) exists under which the most efficient combustion occurs. Reduction of the amount of air available leads to incomplete combustion and a rapid decrease in efficiency. In addition, carbon particles may be formed that can lead to accelerated fouling of heater tube surfaces. To allow for small variations in fuel composition and flow rate and in the air flow rates that inevitably occur in industrial practice, it is usually desirable to aim for operation with a small amount of excess air, say 5 to 10 percent, above the theoretical amount for complete combustion. Too much excess air, however, leads to increased sensible heat losses through the stack gas. 

Figure 3.4. Energy-dispersive X-ray analysis spectra of an alumina membrane layer (a) before fouling and (b) after fouling.

New advances in the l.c. of carbohydrates are likely to come from three general areas. The first is in the development of more-durable and stable, stationary phases. At present, a major limitation on the use of commercial columns, especially those of the aminopropyl-bonded silica-gel variety, is their short life-time and ease of fouling. More-durable, resin-based columns that operate with the same solvent system and selectivity as aminopropyl silica-gel columns are currently available, and will see further use and development. The development of improved phases for supercritical, fluid-type l.c. will allow this method to be of use for analysis of various carbohydrates. ... 

In Figures 8 and 9 are shown the data for the dependence of the characteristic film buildup time t on Apg and U. In accord with the model, t is found to be independent of U, with only a very weak dependence on Apg indicated. This latter result could in part be a function of experimental inaccuracy. The data reduction for t introduces no assumptions beyond that needed to draw the exponential flux decline curves such as those shown in Figures 2 and 3. However, an error analysis shows that the maximum errors relative to the exponential curve fits occur at the earlier times of the experiment. This is seen in the typical error curve plotted in Figure 10. The error analysis indicates that during the early fouling stage the relatively crude experimental procedure used is not sufficiently accurate or possibly that the assumed flux decline behavior is not exponential at the early times. In any case, it follows that the accuracy of the determination of 6f is greater than that for t. 

A further level of sophistication is illustrated by a submersible UV/vis spectrometer, currently being developed for batch process analysis but potentially also applicable to continuous processes. This instrument also overcomes the sensor-fouling problem by using an auto cleaning system based on pressurised air [76]. 

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