Fouling measurement techniques

Heat Transfer/Cooling Towers. . . Fouling Measurement Techniques Heat Transfer Research Inc. Ritter, R. B. Fischer, P. Suitor, J. W. 

The importance of fouling measurement techniques using monitors is likely to increase as the competitive nature of the process and power industries intensifies. In cooling water applications more effective use of additives can be achieved through their use wdth reduced costs and less environmental impact, as a result of accurate assessment of the fouling problem. 

Anemotherm - The Anemotherm, a hot wire anemometer, has been extensively applied to flare gas measurement and has been successfully used after modifications to reduce probe fouling. A technique used to reduce fouling is the installation of a steam coil around the tip of the probe, to prevent gases from condensing on the probe. 

Acoustic chemometrics has its greatest benefits in cases where haditional sensors and measurement techniques, such as flow, temperature and pressure transmitters cannot be used. In many processes it is preferable to use noninvasive sensors because invasive sensors may cause disturbances, for example fouling and clogging inside the process equipment such as pipelines, reactors cyclones, etc. In this chapter we concentrate mainly on new industrial applications for acoustic chemomehics, and only discuss the necessary elements of the more technical aspects of the enabling technology below - details can be found in the extensive background literature [3-5],... 

Almost any physical or chemical measurement technique, provided it is appropriate, may be used to estimate the extent of fouling in laboratory apparatus. Melo and Pinheiro [1984] discussed some of the more common methods. 

This experimental technique also allows the deposit growth to be characterized versus time by applying the method presented above for successive images and thus the cake growth kinetics to be obtained. The image acquisition rate is chosen by the operator (down to a few images per second) so that this measurement technique could be used for various membrane fouling kinetics. 

Sources of Error. pH electrodes are subject to fewer iaterfereaces and other types of error than most potentiometric ionic-activity sensors, ie, ion-selective electrodes (see Electro analytical techniques). However, pH electrodes must be used with an awareness of their particular response characteristics, as weU as the potential sources of error that may affect other components of the measurement system, especially the reference electrode. Several common causes of measurement problems are electrode iaterferences and/or fouling of the pH sensor, sample matrix effects, reference electrode iastabiHty, and improper caHbration of the measurement system (12). 

Zanker has presented a graphical technique for determining the fouling resistance (factor) for process or water fluid systems based on selected or plant data measurements, as shown in Figures 10-43A, 10-43B, and 10-43C. The design determination procedure presented by ZankeD is quoted here and used by permission from Hydrocarbon Processing... 

Hannaker and Buchanan [82] used a method based on wet oxidation with potassium persulfate [83] for the determination of dissolved organic content in concentrated brines following the removal of inorganic carbonates with phosphoric acid. The method involves wet oxidation with potassium persulfate at 130 °C followed by a hot copper oxidation and gravimetric measurement of the carbon dioxide produced. The technique overcomes difficulties of calibration curvature, catalytic clogging, and instrument fouling often encountered with instrumental methods. 

Combining these techniques, they carried out cultivations for 250-350 h, and were able to repeatedly use the same cartridge (four times at least) without measurable deterioration in filtration efficiency. However, when perfusion rate and cell concentration in the bioreactor increased, fouling eventually occurred. Van Reis et al. [92] provided backpressure on the filtrate line to control filtrate rates and so to avoid too high initial filtration rates, which can cause rapid fouling. De la Broise et al. [99] compared the filter performance using membranes of different pore sizes (2 and 10 pm). In both cases partial retention of the produced IgM was observed and membranes had to be changed every 5 days, the... 

Several configurations for the sensor are possible. An especially viable alternative would seem to be the competitive displacement of fluorescent label. Since this is an equilibrium, fouling or contamination of the surface should not alter the absolute result. Krull et al (75) have reported the reproducible immobilisation of a stable phospholipid membrane containing fluorophore in this context. Concurrent fluorescence polarisation measurements can offer the possibility of multidimensional analysis (76) and are in any case experiencing a rejuvenation of interest as a highly selective technique, when the effective molecular weight of the antibody is increased relative to the antigen, by immobilisation on a latex or metal particle (77)... 

Gowman and Ethier [49,50] developed an automated laser-based refractometric technique to measure the solute concentration gradient during dead-end filtration of a biopolymer solution. This paper attempts to reconcile theory with experimental data. The refractometric technique may be useful to other researchers working on quantification of membrane fouling. 

Prevention and Reduction of Liquid-Side Fouling. Among the most frequently used techniques for reduction of liquid-side fouling is the online utilization of chemical inhibitors/ additives. The list of additives includes (1) dispersants to maintain particles in suspension, (2) various compounds to prevent polymerization and chemical reactions, (3) corrosion inhibitors or passivators to minimize corrosion, (4) chlorine and other biocide/germicides to prevent biofouling, and (5) softeners, acids, and poliphosphates to prevent crystallization. Finally, an efficient mechanical removal of particles can be performed by filtration. An extensive review of fouling control measures is provided in Ret 150. 

Mass accumulation probes as the name suggests, are used to obtain a deposit that can be weighed, i.e. a direct measurement of the fouling per unit area of probe for given conditions. The technique has also been used to assess corrosion under the conditions within a combustion space. 

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