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  Method for flow improvement and reduction of fouling in process equipmentUSPTO Application #: 20070017811Title: Method for flow improvement and reduction of fouling in process equipment Abstract: This invention relates to a method and apparatus for improvement of flow rates and reduction of fouling in process equipment such as for instance heat exchangers (2) where fluids are flowing in single or multiphase. This is obtained by imposing a DC-potential at the walls of the process equipment that exactly opposes the naturally ocurring potential due to interaction between the walls of the process equipment and the fluid flowing inside. An improved flow rate will cause that the heat exchanger (2) becomes more efficient, i.e. a lower deposition rate and a higher removal rate of inorganic agents. The fluid may be a pure fluid, colloidal fluid or contain inclusions in the form of particles. (end of abstract) Agent: Christian D. Abel - Norway, NO Inventor: Magne Waskaas USPTO Applicaton #: 20070017811 - Class: 204555000 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Non-distilling Bottoms Treatment, Electrical (including Simultaneous Electrical And Magnetic) Separation Or Purification Of Liquid Or Magnetic Treatment Of Liquid (other Than Separation), With Control Responsive To Sensed Condition The Patent Description & Claims data below is from USPTO Patent Application 20070017811. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This invention relates to a method and apparatus for improvement of flow rates and reduction of fouling in process equipment such as for instance heat exchangers where fluids are flowing in single or multiphase. An improved flow rate will cause that the heat exchanger becomes more efficient, i.e. a lower deposition rate and a higher removal rate of inorganic agents. The fluid may be a pure fluid, colloidal fluid or contain inclusions in the form of particles. BACKGROUND [0002] The formation of deposits (foulants) on heat transfer surfaces is a major cost factor in the installation and operation of heat exchangers. The accumulation of deposits on the heat transfer surfaces often results in reduced heat transfer rates and may cause other problems of operation. Heat exchangers are used in almost all kinds of industries including process industry and oil industry. Consequently, the fouling problem is present in almost all kinds of industries. The total fouling related costs for the industrialized world are estimated to be in the order of 40,000 million dollar U.S. per year [1]. [0003] Despite the enormous costs associated with fouling; only very limited research has been done on this subject. Reliable knowledge of fouling economics is important when evaluating the cost efficiency of various mitigation strategies. Despite the great practical experience with fouling preventing methods, and the results from ongoing research, the fouling in heat exchangers is still a great problem. Therefore, there is a great need for development of new and more effective methods to reduce or prevent the rate of fouling in heat exchangers [1]. PRIOR ART [0004] There are known several chemical and physical/mechanical methods for reducing/removing the scaling and/or fouling problem in systems where water and/or other process liquids are flowing. However, their efficiencies vary a lot from method to method, and they also suffer some disadvantages. [0005] One widely known and long used approach to handle the problem with scaling and/or fouling in heat exchangers is the so-called chemical methods where one or several agents is(are) added to the liquid(s) in the system in order to increase the solubility of the compounds that forms the scaling and/or fouling. These methods are known to be effective in both preventing formation of scaling/fouling and to dissolve already formed scaling/fouling. In the case of heat exchangers, it is common to either add the agent(s) to the process fluid, which often reduce the quality of the produced products, or to the cooling/ heating medium which may represent a pollution problem. These problems can be solved by performing periodic cleansing procedures where the heat exchanger is disconnected from the process line and flushed with a cleansing liquid. But in this case, the normal operation of the process must obviously be stopped with attendant increased operating costs. As a result, chemical treatments are often found to expensive and labour demanding to be an acceptable solution to the problem with scaling/fouling. [0006] It has therefore been an increased focus on preventing, and in some cases even reversing scale formation by applying an electric and/or magnetic field to the flowing water and/or process liquid. It is generally assumed that the cause of this effect is that exposing the water/liquid flow to electromagnetic fields may generate nuclear clusters in the bulk liquid that act as seed crystals, such that the scale- and/or fouling forming compounds are precipitated as solid suspended particles in the bulk liquid and then carried along with the bulk stream. An example of such technology is disclosed in EP 0720588, where water is subject to radiofrequency signals in order to prevent scale formation. It has also been reported that magnetic fields may be useful for preventing lime scaling in much the same manner as electric fields. An example of such technology is disclosed in U.S. Pat. No. 4,278,549. In WO 94/02422 it is described a device and method where the water flow is exposed to microwave radiation which frequency is tuned to be absorbed by one or several of the following ions/compounds of the water: Ca.sup.2+, Co.sub.3.sup.2-, HCO.sub.3.sup.-, CO.sub.2, CaHCO.sub.3.sup.+, H.sub.2CO.sub.3, and H.sub.2O. It is believed that the electromagnetic radiation causes the precipitates to be form on a micro-scale in the bulk flow to be carried away instead of on the surfaces of the process equipment. [0007] In the case of scaling, or build up of precipitated CaCO.sub.3, the effect of such electro-magnetic treatment methods is thoroughly discussed by American Petroleum Institute [2] and scientists [3-10]. The results obtained from various experiments and tests are controversial. Some results show that the magnetic and/or electric fields reduce precipitation of calcium carbonate, others do not. However, the way the magnetic/electric fields are introduced, and the magnitude of the fields vary from experiment to experiment. Consequently, the parameters that describe the exposure system also vary from experiment to experiment. In addition, no quantitative relationship between the parameters that describe the magnetic/electric fields and the effect on the fluid flow system has been reported. Therefore, by this lack of scientific knowledge, it is almost impossible to fully control of the effect of those methods on deposition of calcium carbonate. [0008] However, theoretical and experimental investigations have been performed to understand the mechanisms of fouling and to reduce the rate of fouling in heat exchangers. The mechanisms include crystallization fouling, particulate fouling, biological fouling, chemical reaction fouling, corrosion fouling, and freezing fouling. However, it is unlikely that fouling is exclusively due to a single mechanism, but in many situations, one mechanism will be dominant. Results from the investigations on the various mechanisms involved in the fouling process have revealed that the following three parameters are of greater significance than others concerning control of the fouling process: the temperature gradient across the heat exchanger surface, the concentration of the foulant, and the flow velocity at the heat exchanger surface [11,12]. The latter effect is exploited in this invention. OBJECTIVE OF THE INVENTION [0009] The main objective of this invention is to provide a method and apparatus for improving/enhancing the flow velocity in process equipment where a process liquid is flowing in order to reduce/eliminate the problem with fouling. [0010] Another objective of this invention is to provide a method and apparatus for improving/enhancing the flow velocities at the heat transfer surfaces in heat exchangers in order to increase the efficiency of the heat exchangers and at the same time reduce/eliminate the problem of fouling. SUMMARY OF THE INVENTION [0011] The objectives of this invention are obtained by the method and apparatus as defined in the appended claims and/or the following description of the invention. [0012] The present invention is partly based on an effect that was discovered by the present inventor, and which formed basis for another invention that is protected by for example U.S. Pat. No. 6,334,957 or the corresponding EP 1 021 376. This patent family gives a thorough description of the effect, and is therefore included by reference in this application. Here, it will only be given a short summary of the effect: [0013] When a fluid flows through a pipe, there will be torn loose electric charges at the wall of the pipe due to shear forces in the boundary layer. This will give rise to an electric potential (the electric friction potential) at the pipe wall that will attract and retain charged particles, ions and dipoles in the fluid, and thus induce a friction force that reduces the flow velocity of the liquid in the pipe. This contribution the flow friction is often referred to as the electric contribution to the friction factor. [0014] The invention disclosed in U.S. Pat. No. 6,334,957 is based on that this build-up of electric charges at the fluid-solid boundary can be counteracted by imposing a DC electric potential on the pipe/duct wall that exactly balances the build-up of electrical charges on the wall. Then the electromagnetic force that attracted the ions and polar molecules will diminish, and the ions and polar molecules may freely follow the flowing fluid. In other words, the electrical contribution to the friction factor becomes zero, and the average flow velocity of the fluid will consequently increase, especially at the liquid-solid boundary (at the wall). U.S. Pat. No. 6,334,957 discloses a regulation method that ensures that the imposed DC potential exactly opposes the electric friction potential at all times and an apparatus for performing the method. [0015] The present invention is based on the discovery that the elimination of the electric friction factor for liquids flowing in pipes, heat exchangers, reactors and all other forms of industrial process equipment, is also a convenient and effective mean for preventing and in some cases even revert already formed fouling and scaling. That is, by enhancing the flow velocities at the surfaces of heat exchangers and other process equipment where fluids are flowing, one will reduce the deposition rate of precipitates thus reduce/prevent formation of scales, fouling, and any other types of solid deposits on the walls of the heat exchanger/process equipment. This is believed to be due to that the enhanced flow velocity at the solid-liquid boundary (the heat exchanger wall) will carry away a larger portion of the solid precipitates in the bulk stream. [0016] It is surprising that the effect of the modest increases of the flow velocities that are being obtained by removing the electric contribution to the flow friction factor is able to give an effective reduction of the deposition rate of precipitates such that the invention becomes an efficient tool for handling the problem of scaling/fouling in heat exchangers and other process equipment. Not to say that these modest velocity increases, usually in the order of 1-10%, are also able to increases the shearing action at the deposit-fluid interface sufficiently to remove already formed deposits. [0017] This surprising finding gives a substantial benefit over prior art methods which exploits electromagnetic fields/potentials to prevent fouling/scaling, since the prior methods are focused on that the electromagnetic fields/potentials must be sufficiently strong and act on the bulk liquid in order to enhance the nuclear clustering and precipitation of the scale and/or foulant forming compounds in the process liquid such that the precipitates will be carried away with the bulk flow. But in this case, one will inevitably alter the chemical conditions in the process fluid and may ionise one or more of the liquid compounds or electrically induce one or more electrochemical reactions in the process fluids. Thus, the prior art should be used with care in process industry in order not to induce detrimental side effects in the process. Another unwanted side-effect of these prior art methods is that the employed electromagnetic fields/potentials are almost certain to be of a different magnitude than the electric friction potential, such that the imposed potential will almost certain create a new electric friction potential that may very well be larger than the natural occurring friction potential. This will then slow the flow velocity, which enhances the deposition rate of precipitates. This may be one explanation of why many prior art methods are encumbered with instability. [0018] In the present invention, the imposed electric potential shall exactly counter-balance the natural occurring electric friction potential of the flow. Thus these potentials will cancel each other such that no electric fields will be felt by the process liquid. Consequently, there will be no risk of inducing any electrochemically alterations of the processes in the flowing process fluid, including alterations of chemical equilibriums, ionising compounds, creating radicals, induce unwanted chemical reactions etc. The naturally occurring electric friction potentials are usually small, in the order plus/minus a few Volts or less, such that one can manage with much less powerful and thus energy efficient fields than in prior art methods. The method according to the invention will therefore be absolutely risk free, both in terms of electrochemistry and handling safety, such that it becomes suited for all thinkable processes, no matter which process liquid that flows through the process equipment. [0019] Another benefit over prior art is that the invention is based on scientific knowledge, such that the method according to the invention will be fully controllable and give consistent results. A further advantage is that the invention represents no pollution problem since no matter is added or removed when implementing the invention and no chemical reactions are induced in the process fluids that may cause unwanted detrimental effects on the process and/or the environment. [0020] In the case of process liquids containing chemically active components, there will normally be another naturally occurring potential that must be taken into account. When a metal (e.g. heat transfer surface) is immersed in a solution (fluid), an electrical potential between the surface of the metal and the solution is established, i.e. the surface is electrified. Most of the metals will normally be negatively charged, and the electrical potential can be measured in relation to a reference cell (e.g. a standard calomel reference cell, SCE). The potential is named the corrosion potential. If the surface is electrified, an additional adhesion appears which is caused by the attractive forces between electrical charges on the surface and the counter-ions or/and dipole molecules in the fluid [13]. This phenomenon represents an additional contribution to the electric friction factor for the fluid flow at the heat transfer surface, which also should be countered by the imposed DC-field. Thus, in this application, the term electric contribution factor means the combined effect of the corrosion potential and the fluid flow friction potential on the total friction factor for the fluid flow. Continue reading... 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