According to this model, no matter what the conditions, i.e. Different materials have different catalytic action and may promote or reduce fouling for different processes. Pulsating flow in heat exchangers is a strategy to increase the level of turbulence [52-58]. Depending on the materials involved, this fouling can occur on both the primary and service surfaces of the exchanger, and sometimes both at once. However, for many materials, including those with the highest fouling factors such as sludges, it is best to analyse the substance in order to achieve an accurate result. CaCO3), the deposition rate is controlled by the slow reaction rate and the constant of reaction rate KRthat obeys the Arrhenius equation: Kern and Seaton [43] recommend for the removal rate the equation: Where τƒ is the shear stress exerted by the liquid flow on the fouling film. Higher heat transfer reduces fouling by reducing the interface temperature which is beneficial for certain fouling mechanism such as crystallization fouling of inverse solubility salts. Space and provision for removal and cleaning of tube bundles are required to be available. Muller-Steinhagen [37] informed that particulate fouling will be enhanced if particulate or fibrous material already exists in the solution. [13] found asymptotic behavior for calcium phosphate fouling (with some particulate fouling from suspended solids). They stated that water-based fluids can transport and deposit a wide variety of minerals, and corrosion products form due to the reaction of the aqueous fluids with the metals of construction. They have given guidelines for selecting between chemical and mechanical cleaning, and among the various types of chemical cleaning processes. Instead, Emerson Process Management suggested manufacturers use online capabilities to constantly monitor the state of exchangers’ performance. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2. They all result into an excess heat transfer surface area. Often this is a combination for several reasons. An alternative solvent family consists of aqueous solutions of chelating agents and organic acids with pH values of about 2 to 12. The delay period decreases with increasing temperature in chemical reaction fouling due to the acceleration of induction reactions. Shear forces at the interface between the fluid and deposited fouling are responsible for removal. Corrosion inhibitors (chromates and polyphosphates) can be used to reduce corrosion fouling [47]. In diffusion controlled processes, increasing the fluid velocity causes more fouling [24]. Chemical reaction fouling could be suppressed by reducing the number of these particles. Oversized pumps and fans are selected to compensate design over-surfacing the enhanced pressure loss from reduction in the flow area. Bott [45] said that they prevent the formation of nuclei thus preventing the crystallisation and mitigate fouling. There are also different terms used globally for the different types of fouling and this can lead to confusion about what is actually happening in a particular situation. Modelling is usually done taking into consideration only (a) flow velocity, (b) concentration, (c) wall and bulk temperature, and (d) time. We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. Corrosion is very important on the steam side of process equipment. The deposit layer also reduces the flow area, which increases the pressure drop. Addition of certain chemicals can slow down or terminate chemical reactions. HeadquartersIntechOpen Limited5 Princes Gate Court,London, SW7 2QJ,UNITED KINGDOM. All together, cost of cleaning, cleaning equipment, chemicals all are imposing extra to the capital cost of the plant. Fouling is a complex phenomenon due to involvement of a large number of variables. Glasstone, Sesonske. In processing tight crude oil, fouling is commonly due to asphaltene precipitation buildup. The present study focused on fouling phenomena, fouling models, environment of fouling, consideration of heat exchanger fouling in design and mitigation of fouling. Film boiling 5. pH value of the solution is one of the controlling parameter. The fouling materials can consist of either living organisms or a non-living substance (minerals or organic compounds). The inside diameter of the tube decreases and roughness of the tube increases due to fouling which, causes an increase in pressure drop. D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2. EDTA is a versatile chemical that forms metal ion complexes with higher equilibrium constants than citric acid. Thus bulk temperature has effects on chemical reaction rate and polymerisation rate. The U-factor is defined by an expression analogous to Newton’s law of cooling: The overall heat transfer coefficient, U, is related to the total thermal resistance and depends on the geometry of the problem. Non-uniform thermal expansion leads to lower deposit strength and hence less deposition. These are often found in heat exchangers of process industries, boilers, evaporators etc. Fouling rate is a dominating factor in designing a particular heat exchanger. Calcium sulphate seeds are generally used to avoid calcium sulphate scaling [48-49]. are examples of particulate fouling. The processes occur simultaneously and depend on the operating conditions. From a fundamental point of view the fouling mechanism follows certain stages in developing on a surface [17]. Unexpected fouling is an especially harmful problem that is becoming more common among facilities refining light tight crude oil. This can sometimes enhance other fouling mechanisms too, as microbial deposits may trap suspended particles. The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. Disadvantages of off-line chemical cleaning include corrosion damage potential, handling of hazardous chemicals, use of a complex procedure. For removing iron oxide from steel surfaces, citric acid and a mixture of formic and citric acid could be used [66]. Some of the common salts causes fouling are CaSO4, CaCO3 and Mg(OH)2, and SiO2. According to a report from the Department of Chemical Engineering at the Imperial College London, crude oil fouling in pre-heat trains is one of the main causes of energy inefficiency in heat exchangers. Transport is accomplished by a number of phenomena including diffusion, sedimentation and thermophoresis [20, 21]. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4. Wireless temperature and differential pressure measuring devices are one way to constantly monitor the performance and efficiency of a heat exchanger. I’m talking about heat exchanger fouling. A decrease in the performance of a heat exchanger beyond acceptable level requires cleaning. Region B: a steady deposit growth on the surface. Water-side deposits usually contain minerals, such as iron oxides (corrosion products), hardness (Ca and Mg carbonates) and silica, in individual cases other minerals can also be found. Of such factors Of such factors some may be related to the feed properties such as its chemical nature, density, viscosity, They mentioned that the general categories of solvents for process side scales include aqueous detergent solutions, true organic solvents and emulsions. Plus, the fouling causes excess energy consumption and decreased throughput by the crude unit fired heater. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317, W.S.C. Common causes for fouling in a heat exchanger- 1. Mechanical vibration of the heat transfer surfaces, Increased shear stress at the fluid/deposit interface, and. ISBN: 9780071077866. The removal rate increases with time for weak deposits and can eventually become equal to the deposition rate. Many of the heat transfer processes encountered in industry involve composite systems and even involve a combination of both conduction and convection. In some occasions standby heat exchangers are kept in process design in order to ensure uninterrupted operation while a fouled heat exchanger is taken under cleaning maintenance. Fouling Heat Exchangers, operating over dew point for acid vapor and above freezing for fluids containing waxes prevent corrosion and freezing fouling. These methods can be classified as: (1) chemical methods, (2) mechanical methods and (3) changing the phase of the solution. DOE Fundamentals Handbook, Volume 1 and 2. The heat transfer area of a heat exchanger is kept exaggerated to compensate retardation imposed by fouling. As a result chemical cleaning solvents with pH values from 4.5 to about 9.2 have been formulated that can remove Fe and Cu, as well as Ca, Ni and Cr.

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