Fouling deposits, impact

The manual operation of water jets for on-line cleaning has been used for the removal of fouling deposits for many years, although modern soot blowing equipment is often preferred. Similarly shot cleaning, which involves the release of metal shot so that as it falls under the influence of gravity, it impacts the heat-transfer surface and removes any accumulated deposits. The technique is not widespread on account of the potential damage that could occur. 

GC/MS analyses give evidence that some heavy ends material entering the vacuum tower rises through entrainment and impacts fouling on the upper trays. X-ray and combustion analyses reveal the deposit to be primarily organic the LOI value is 96 % S and N contents are low at 3.1 % and 1.8 %, respectively V and Ni values are only 0.9 % and 0.5 % and the Fe content is negligible. These data are typical for deposits caused by asphaltene precipitation. 

Example In certain types of heat exchangers, a gas flows normal to a bank of tubes carrying fluid at a different temperature, and heat transfer occurs at the interface. Fouling of the outside surface of the tubes by particles depositing from the flow reduces the heat transfer rate. If the tubes are I in. (outside diameter) and the gas velocity is 10 ft/sec, estimate the diameter of the largest particle [pp — 2 g/cm ) that can be permitted in the gas stream without deposition by impaction on the... 

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... 

The adsorption of organic compounds is an important process however, adsorption would only be responsible for a relatively thin deposit layer. The objective of this study is to understand the role of concentration polarisation (influenced by hydrodynamic conditions) and solution chemistry on the morphology of the fouling layers. The interactions of calcium and NOM are studied over a wide of pH and concentration range, contributing to an understanding of the interactions and the impact on NF. 

Wherever particles are involved, the problem of fouling, or deposition on surfaces arises. In the case of heat exchangers for combustion gases, thermal transfer efficiency may be drastically reduced by the deposition of the relatively highly insulating soot and flyash particles. In other contexts sulfuric acid and other corrosive vapor droplets diffuse or impact upon conduit surfaces thereby shortening their useful lifetime [1.22,25]. In all of these cases, numerous questions of kinetic theory arise including all the phoretic forces. In addition, particle interaction forces are ultimately responsible for delivery to the surface in question. 

The two-tube heat exchanger can be used to compare treatment, metallurgy, and the impact of heat flux on deposition by varying the flow in one of the tubes. At the end of the monitoring test period, which is at least 30 days, the heat trsmsfer tubes should be evaluated for scale deposition, fouling, and corrosion. Analysis usually includes ... 

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