Metal fouling

The rate of heat-transfer q through the jacket or cod heat-transfer areaM is estimated from log mean temperature difference AT by = UAAT The overall heat-transfer coefficient U depends on thermal conductivity of metal, fouling factors, and heat-transfer coefficients on service and process sides. The process side heat-transfer coefficient depends on the mixing system design (17) and can be calculated from the correlations for turbines in Figure 35a. 

Further improvements in bullets were made betw 1900 and WWI. They consisted in sharpening the nose(pointed-nose bullets), bevelling the base(boat-tailing, tapering) and replacement of steel and cupro-nickel in the jacket by gilding metal and allied alloys in order to eliminate excessive bore erosion and metal-fouling... 

Coppering is metal fouling accumulated in the bore of a weapon due to repeated firing. The metal (mostly Cu or its alloys) is deposited from the rotating bands or jackets of the projectiles... 

A variety of animals and plants, as well as colonies of microorganisms, may deposit from natural sea water onto the metal surface. The life processes and decomposition products may contribute directly to attack on the metal. Fouling may obstruct flow in heat exchangers and pipes, leading to such corrosive effects as are caused by overheating or impingement at local high-water velocities. 

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With the deposits of catalyst poisons as coke and heavy metals, fouling and pore mouth plugging phenomena can be observed [18, 19]. 

Those deactivation models accounting for both coke and metal sulfides are rather simple. Coke and metals foul residue hydrodesulfurization catalysts simultaneously via different processes, and decrease both intrinsic reaction rate and effective diffusivity. They never uniformly distribute in the commercial reactors. We have examined the activity and diffusivity of the aged and regenerated catalysts which were used at the different conditions as well as during the different periods. This paper describes the effects of vacuum residue conversion, reactor position, and time on-stream on the catalyst deactivation. Two mechanisms of the catalyst deactivation, depending on residue conversion level and reactor position, are also proposed. 

The material of construction of the tubular reactor can also influence fouling and plugging. Tubes made from polymeric materials, especially fluoropolymers, have been more successful than those made of glass and metals. Fouling and plugging can also be minimized by only carrying out the early part of the reactions in the tube, such as done with tube-CSTR systems [20-22]. 

Calorimetric Investigation of Incrustation of Foreign Matter on Superheated Metal (Fouling)... 

Metal oxides found in RO feed streams typically originate from corroded pipes found in the RO process. These metal oxides can deposit on the membrane surface and decrease the membrane flux. This type of fouling can be prevented by using the proper materials of constmction in the piping system to prevent corrosion. 

Cooling System Corrosion Corrosion can be defined as the destmction of a metal by chemical or electrochemical reaction with its environment. In cooling systems, corrosion causes two basic problems. The first and most obvious is the failure of equipment with the resultant cost of replacement and plant downtime. The second is decreased plant efficiency to loss of heat transfer, the result of heat exchanger fouling caused by the accumulation of corrosion products. 

The formation of anodic and cathodic sites, necessary to produce corrosion, can occur for any of a number of reasons impurities in the metal, localized stresses, metal grain size or composition differences, discontinuities on the surface, and differences in the local environment (eg, temperature, oxygen, or salt concentration). When these local differences are not large and the anodic and cathodic sites can shift from place to place on the metal surface, corrosion is uniform. With uniform corrosion, fouling is usually a more serious problem than equipment failure. 

Biofilms can promote corrosion of fouled metal surfaces in a variety of ways. This is referred to as microbiaHy influenced corrosion. Microbes act as biological catalysts promoting conventional corrosion mechanisms the simple, passive presence of the biological deposit prevents corrosion inhibitors from reaching and passivating the fouled surface microbial reactions can accelerate ongoing corrosion reactions and microbial by-products can be directly aggressive to the metal. 

They represent an improvement over earlier platinum on alumina catalysts in their abiHty to resist coke fouling when operated at low pressures. Dehydrogenation and hydrogenation occur on the active metal sites isomerization takes place on the acidic alumina surface. 

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