Internal fouling

Heaters can be located in the space between the trms and the dryer housing, where they are not in direct contact with the product, and thermal efficiencies up to 3500 kj/kg (1500 Btu/lb) of water evaporated can be obtained by reheating the air within the dryer. Steam is the usual heating medium. The hi cost of heating electrically generally restricts its use to relatively small equipment. For materials which have a tendency to foul internal heating surfaces, an external heating system is employed. 

Internal pore fouling This is caused by the deposition of material inside the porous structure which often leads to significant flux decline and irreversible fouling. Internal pore fouling can be due to adsorption, precipitation, pore plugging or particle adhesion. 

Piping systems Heat exchanger fouls Internal coil leaks... 

The reactor design is tolerant of high fly ash loadings. Techniques were developed to clean fouled internals in situ. 

Montagne, X., D. Merrier and J.-C. Guibet (1987), "Fouling of automotive diesel injectors. Test procedure, influence of composition of diesel oil and additives". SAE paper No. 87-2118, International fuels and lubricants meeting, Toronto, Ontario. 

Commonly used heat-transfer surfaces are internal coils and external jackets. Coils are particularly suitable for low viscosity Hquids in combination with turbine impellers, but are unsuitable with process Hquids that foul. Jackets are more effective when using close-clearance impellers for high viscosity fluids. For jacketed vessels, wall baffles should be used with turbines if the fluid viscosity is less than 5 Pa-s (50 P). For vessels equipped with cods, wall baffles should be used if the clear space between turns is at least twice the outside diameter of the cod tubing and the fluid viscosity is less than 1 Pa-s (10... 

The condenser was plagued by rapid attack on waterside surfaces. The entire internal surface was fouled with silt and other deposits, beneath which a cuprous oxide layer was present (Fig. 4.23). Localized areas of metal loss were present beneath mounds of corrosion product. Some of these localized areas were deep enough to threaten tube integrity. 

Figure 5.18 Heavily fouled and corroded internal surface of a galvanized carbon steel pipe.

Design to allow for internal and external fouling resulting in reduction of heat transfer capacity... 

R. Baboian, International Congress of Marine Corrosion and Fouling, Juni 1976. 

Internal plugging of flow passages of eompressor (fouling). 

Bath level loss can be the result of too high a bath temperature. This is often caused by the temperature controller on the process stream. Fouling of the process coil, internal and/or external, means a hotter bath is needed to accomplish the same heat transfer. The coil should be removed and cleaned. 

It would appear obvious for startup, and in some cases full-time operation. that a suction strainer or filter is mandatory. The reason for ilic strainer is to keep Junk and pipe scale out of the compressor. Fines from pipe scale and rust will make short work of the internal bore of a cylinder and are not all that good for the balance of the components. In some severe ca.ses, cylinders have been badly damaged in a matter of a few weeks. The strainer should be removable in service for cleaning, particularly when it is intended for permanent installation. Under all circumstances, provision must be made to monitor the condition of the strainer. Much frustration has been expended because a compressor overheated or lost capacity and no one knew if the strainer had fouled or blinded. 

For compressors in general and for some types in particular, the cleanliness of the gas stream is the key factor in a reliable operation. Moisture or liquids in various forms may be the cause of an early failure or in some-cases a catastrophic failure. Corrosive gases require material considerations and yet even this may not entirely solve the loss of material issue that can certainly cause early shutdowns or failures and high maintenance cost. Fouling due to contaminants or reactions taking place internal to the ( i-pressor can cause capacity loss and the need for frequent shutdowns. 

Cake layer formation builds on the membrane surface and extends outward into the feed channel. The constituents of the foulant layer may be smaller than the pores of the membrane. A gel layer can result from denaturation of some proteins. Internal pore fouling occurs inside the membrane. The size of the pore is reduced and pore flow is constricted. Internal pore fouling is usually difficult to clean. 

The quality of the FCC feed also impacts coke buildup in the reactor internals and vapor line and fouling/coking of the main column circuit. The asphaltene or the resid content of the feed, if not converted in the riser, can contribute to this coking. 

The liquid distributor is the most important internal structure of a packed column. The distributor strongly influences packing efficiency. It must spread the liquid uniformly, resist plugging/fouling, provide free space for gas flow, and allow operating flexibility. 

Gilbert, P. T., Considerations arising from the use of dissimilar metals in seawater piping systems , 5th International Congress on Marine Corrosion and Fouling, Barcelona (1980)... 

Most waterside problems develop insidiously. Over time, scale and other types of deposit are gradually formed on internal heat transfer surfaces, which gradually raises the cost of providing heat energy. Some types of deposition can be very difficult and costly to remove. Corrosion wastes away the fabric of the plant (sometimes very quickly) and may produce an unexpected and untimely boiler plant shutdown, with a consequential loss of space heating, electricity, or process manufacturing capability. Likewise, fouling reduces the size of waterways and increases boiler operational problems. 

Higher rates of sludging also take place in the boiler vessel. In turn, this potential fouling problem requires additional maintenance time because more frequent internal surface cleaning, wash-down, and boiler vessel sludge removal usually is required. Carryover of contaminants into the steam also is more likely. 

Fouling and deposition in boiler sections may occur unintentionally through the application or misapplication of chemical water treatment programs. Internal treatment-related boiler section problems may... 

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