Abstract:
A novel design of filters for removing iron rust particulates and other polymeric sludge from refinery and chemical process streams that are paramagnetic in nature is provided. The performance of these filters is greatly enhanced by the presence of the magnetic field induced by magnets. Basically, the filter comprises a high-pressure vessel with means to support the plurality of magnets in the form of bars or plates that are encased in stainless steel tubes or columns. Filters with various configurations are disclosed for accommodating the removal of contaminants from the process streams of different industries, with high efficiency for contaminants removal, simple construction, low operational and maintenance costs, and low hazardous operation.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part application of application Ser. No. 12/112,623 that was filed on Apr. 30, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Process streams in refineries are often contaminated with components that are detrimental to down-stream process units and/or are corrosive to the process equipment, or they are contaminated with solid matter, such as iron rust, which tends to interfere with process lines, valves, and pumps. The contaminants must be removed before the streams enter certain parts of the process or process units in order to maintain the process or unit performance. A filtration screen, filter housing or cartridge containing adsorbents or filtration media is usually placed in front of the process unit to remove the bulk of the undesirable matters. For example, a RONNING-PETTER multiplex filter is used to remove solid matters from atmospheric distillation residual oil before it is fed to a hydrotreater at temperatures around 200° C. Tri-cluster elements are installed in the filter to increase the filtration area. A drawback of these filtration devices is that they can be overwhelmed by large quantities of solid matters and iron rust from corrosion in a short time. As a result, processes streams frequently bypass such filtration devices as contaminant build-up cause operational problems, such as increased pressures and/or reduced flow rates. In addition, rejuvenation of conventional filtration devices requires their disassembly replacement of the filter element, which is a costly, time-consuming, and environmentally hazardous task. 
         [0003]    Process streams in chemical plants are generally cleaner than those of refineries in terms of solid matters, but chemical streams usually contain polar components that polymerize to form solid sludge, or decompose to form more active species that cause corrosion or related problems. Activated carbon is frequently used as the adsorbent to remove the active species from the process stream. U.S. Pat. No. 4,861,900 to Johnson describes the use of activated carbon to remove small amounts of compounds that are catalyst poisons in the catalytic hydrogenation of sulfolenes to sulfolanes. 
         [0004]    Similarly, U.S. Pat. No. 3,470,087 to Broughton describes a technique for removing polar solvent from a hydrocarbon product stream through an adsorption cycle with activated carbon and thereafter, recovering the adsorbed solvent through a desorption cycle. It has been demonstrated that adsorption-desorption arrangements with activated carbon is impractical because these units become quickly saturated with solid sludge or fine rust particles that strongly adheres to adsorbent thereby making the units difficult to clean. Other adsorbents, such alumina, silica gel and zeolitic materials have also been employed to remove polar matters from process streams. For example, U.S. Pat. No. 3,953,324 to Deal describes a method of adsorbing polar solvent with silica gel from a product stream at low temperatures and then flashing a feed mixture at higher temperatures in order to recover the adsorbed solvent from silica gel. This method encounters that same problems attendant with adsorption-desorption methods using activated carbon. 
         [0005]    A method for removing both suspended particulate matter, such as iron rust, as well as dissolved ionic and polar impurities from a process stream is described in U.S. Pat. No. 5,053,137 to Lal. The technique entails passing a contaminated solvent, sulfolane, through a pair of columns that are arranged in series, with the first column containing cation exchanger resin and the second containing anion exchanger resin. Although this method is effective, it is not commercially feasible because only small amounts of solvent can be cleaned due to limited capacity of the ion-exchanger resins. Moreover, the procedure produces a large quantity of hazardous waste. Finally, a method that combines filtration, adsorption, and ion exchange for removing the contaminants from a liquid stream is disclosed U.S. Pat. No. 3,985,648 to Casolo. Unfortunately, the system is complex in both process design and implementation because process requires multiple ion-exchange columns, including both cation and anion exchangers, and adsorption columns. 
         [0006]    Therefore, there is a need in the refining and chemical industries for efficient, safe, and easily regenerable filters that are particularly suited for removing contaminants that include (i) solid materials, (ii) polymerized sludge that is generated by actives in the process streams, and/or (iii) iron rust that is generated by corrosive species that attack various materials used in refining and chemical process equipment. 
       SUMMARY OF THE INVENTION 
       [0007]    This invention is directed novel filters that employ magnets for removing iron rust particulates and polymeric sludge, which are paramagnetic in nature, from refinery and chemical process streams. The performance of these filters is attributable to the presence of the magnetic fields that are induced by the magnets. The invention is based in part on the recognition that carbon steel, a common material in plant construction, is readily corroded by acidic components prevalent in process streams. The corrosion causes the formation of ferrous ions, which in turn react with sulfur, oxygen and water to form paramagnetic FeS, FeO, Fe(OH) 2 , Fe(CN) 6 , etc. that manifest as fine particles or visible flakes. These paramagnetic materials will attract other degradation sludge, making the whole mass of contaminants paramagnetic. Consequently, the entire mass of the contaminants can be readily removed from the process stream with the magnet filter device of the present invention. 
         [0008]    In one aspect, the invention is directed to a filtration apparatus for continuous online removal of contaminants from a process stream that comprises: (i) a pressure vessel that has a compartment, (ii) at least one magnet that is positioned within the compartment; and means for channeling the flow of the process stream containing contaminants pass the at least one magnet. Each magnet is preferably encased in housing that is made of stainless steel or other suitable corrosive resistant material. The housing can be integral with the vessel. The housing exterior, which is in contact with the process stream, serves as an adsorptive surface to which contaminants adhere. The inventive filtration apparatus can be readily scaled and configured to accommodate different operating conditions in order to minimize downtime and hazardous operations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIGS. 1A and 1B  illustrate cross sectional side and top views, respectively, of a filtration device with housing in the form of removable adsorptive tubes for low solid matters removal; 
           [0010]      FIGS. 2A and 2B  illustrate cross sectional side and top views, respectively, of a filtration device with housing in the form of non-removable adsorptive tubes for low solid matters removal; 
           [0011]      FIGS. 3A and 3B  illustrate cross sectional side and top views, respectively, of a filtration device with housing in the form of removable adsorptive tubes for high solid matters removal; 
           [0012]      FIGS. 4A and 4B  illustrate cross sectional side and top views, respectively, of a filtration device with housing in the form of non-removable adsorptive tubes for high solid matters removal; 
           [0013]      FIGS. 5A ,  5 B and  5 C illustrate cross sectional side, top, and front views, respectively, of a filtration device with housing in the form removable adsorptive slates for high solid matters removal; and 
           [0014]      FIGS. 6A ,  6 B and  6 C illustrate cross sectional side, top and front views, respectively, of a filtration device with housing in the form of non-removable adsorptive slates for high solid matters removal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    Filtration devices of the present invention are particularly effective in removing contaminants from process streams. One source of the contaminants is the corrosion of process equipment and another source is the presence of active species in the process streams that ultimately lead to the formation of polar polymeric sludge. It has been demonstrated that these contaminants are paramagnetic in nature and therefore are attracted to magnets. The contaminants generally comprise a mixture of different materials are acidic, low in pH, black and viscous, and tend to deposit throughout the process lines, including filters, heat exchangers, catalyst beds, thereby reducing process capacity and efficiency. Since most process equipment in the refining and chemical industries is made from carbon steel that is susceptible to corrosion by the acidic substances in the process streams, the contaminants are generated by oxidation due to air leakage in the system as well as by the chlorinated additives especially at elevated temperature and pressure operating conditions. It is believed that when carbon steel is corroded by acidic substances, the ferrous ions released react with sulfur, oxygen and water to create paramagnetic FeS, FeO, Fe(OH) 2 , Fe(CN) 6 , etc. in the form of fine particles or visible flakes. These paramagnetic materials may attract other degradation sludge, making the whole mass of the contaminants paramagnetic. Consequently, the entire mass of the contaminants can be continuously removed from a process stream with a filtration apparatus that is equipped with magnets. 
         [0016]    Magnetic intensity is temperature dependent. High temperatures can lead to a reduction in the magnetic field strength so it is preferable to avoid excessive operating temperatures which would rendering the filtration apparatus less efficient. Conversely, low temperatures operations are to be avoid especially during the cleaning stage otherwise, the paramagnetic matters will adhere to the stainless steel adsorptive housing surface too strongly so that contaminants do not readily fall off after the magnetic field is removed. 
         [0017]    The operating temperatures for the filtration devices typically range from 10 to 200° C., and preferably from 20 to 150° C. The superficial velocity of the process stream passing through the filtration devices typically ranges from 10 to 10,000 v/v/Hr, and preferably from 50 to 5,000 v/v/Hr. The pressure drop across the filtration device is an indicator of its remaining capacity. As the pressure drop reaches between 1 to 10 Kg/Cm 2 , and preferably between 1 to 5 Kg/Cm 2 , the filtration device should be removed from the service and cleaned. 
         [0018]    In one aspect, the present invention provides a continuous filtration device designed specifically for chemical process streams that contain relatively small amounts of solid matters and active substances that are responsible for generating polymerized sludge or corrosion byproducts. In a preferred embodiment, a novel filtration device is applied to rejuvenate the extraction solvent in the circulation loop of an aromatic extraction process. This continuous filtration device can rejuvenate the contaminated extraction solvent by removing degradation and corrosion products from the solvent stream continuously without interruption thereby achieving high capacity and operation efficiency for the aromatic extraction process. Furthermore, with this filtration device, the workload of the existing, high-cost solvent regenerator is substantially reduced and the level of messy, hazardous solid sludge is substantially reduced as well. A preferred example of the extraction solvent is sulfolane. 
         [0019]    One version of the filtration device  100  which is shown in  FIGS. 1A and 1B  comprises a high-pressure vessel  102  defining a compartment  116  that is sealed from the environment with a removable top cover  104 . A supporting tray  108  is positioned within compartment  116  to accommodate a plurality of magnet housings  114 . Supporting tray  108  is preferably configured as a rack with a round circumference that matches the contour of compartment  116 . Each magnet housing  114  encases a magnetic bar  110  that has been removably inserted therein. Each magnet housing, which serves to isolate magnet bar  110  from direct contact with the contaminated process stream, is configured as a vertically elongated stainless steel tube with a square cross section and the plurality of tubes form a circular arrangement that is held by supporting tray  108 . The number of housings  114  and associated magnetic bars  110  employed in filtration device  100  typically ranges from 1 to 30 or more. A spring  106  is positioned between top cover  104  and inner cover  118 , which is on the plurality of housing  114 , to maintain the position of plurality of housing  114  within compartment  116 . A fine mesh screen cylinder  112 , which is configured as a basket made from metallic mesh material, is installed in the lower part of compartment  116  and encloses the plurality of magnet housing  114 . The plurality of magnet housing  114  fits within the inner perimeter of screen cylinder  112 . 
         [0020]    In operation contaminated a process stream containing sulfolane solvent, for example, enters filtration device  100  through inlet  130  and the flow of the solvent is channeled initially toward the lower end of compartment  116  so that the contaminated solvent flows through screen cylinder  112  pass the plurality of magnet housing  114  before the treated solvent exits through outlet  132 . The degradation and corrosion products are attracted and adhere to the stainless steel tubes of housing  114  with the aid of powerful magnetic bars  110 . The removal of the degradation and corrosion products by the magnetic bar is enhanced by the presence of inner screen cylinder  112  that distributes the flow of solvent more evenly over the plurality of magnet housing  114 . This enhancement becomes crucial when the level of residual degradation and corrosion products are to be kept to a minimum. The rejuvenated clean extraction solvent can be recycled back to the extraction column. 
         [0021]    After being on-stream for a certain period of time, the filtration device becomes loaded with the degradation and corrosion products and the pressure drop across the device increases. The stream is then switched to an auxiliary filtration device that has been installed in a parallel position with the on-stream device. Supporting tray  108  is lifted from compartment  116  along with the plurality of housing  114  that encases magnetic bars  110 . Supporting tray  108  is first placed in a container and upon removal of magnetic bars  110  from housing  114 , the attracted contaminants simply fall off the surface of housing  114  with the loss of the attractive force. This configuration of the filtration device is characterized by high efficiency for contaminants removal, simple construction and low maintenance costs. 
         [0022]      FIGS. 2A and 2B  show a modified version of the filtration device that includes magnet housing that is integral with the unit and is not removable therein. Specifically, filtration device  200  comprises a high-pressure vessel  202  that includes a process stream inlet  230  and a process stream outlet  232 . Except for the inlet and outlet, compartment  216  of filtration device  200  is enclosed from the environment. A plurality stationary magnet housing  214  configured as vertically elongated stainless steel tubes arranged in a circular fashion within compartment  216 . Each magnet housing  214  has an aperture on the sealed surface  204  of filtration device  200  so that housing  214  is as an integral part of the high-pressure vessel. Magnetic bars  210  are placed into magnet housing  214  from the outside. 
         [0023]    In operation, after contaminated extraction solvent enters filtration device  200  through inlet  230 , the degradation and corrosion products are attracted and adhere to the surfaces of the vertical stainless steel tubes of housing  214  with the aid of powerful magnetic bars  210  and are removed from the solvent. The rejuvenated clean extraction solvent leaves the device through outlet  232  and is recycled back to the extraction column. 
         [0024]    When cleaning is required, the contaminated stream is switched to a bypass line that is installed in parallel to filter  200 . Magnetic bars  210  are removed from housing  214 ; upon removal of the magnetic bars, the attracted contaminants fall from outside of the vertical tubes due to the loss of the attractive force. The collected contaminant sludge is flushed from the filtration device with a diluent fluid, such as water or other low value stream. Once the magnetic bars are reinserted into the housing, the cleaned filtration device is for service. This simple design is especially attractive when the contaminants or the process stream is hazardous as it is not necessary to open and disassemble the filtration device or any other process equipment in order to remove the adsorbed contaminants from the device. 
         [0025]    As is apparent, the filtration devices depicted in  FIGS. 1 and 2  can be designed specifically for any chemical process stream, similar to the sulfolane solvent stream, which contains relatively smaller among of solid matters and active contaminants responsible for generating polymerized sludge or corrosion products. 
         [0026]    In another aspect, the present invention provides continuous filtration devices designed specifically for the refinery process streams that contain relatively larger amounts of solid matters, active substances which are responsible for generating polymerized sludge or corrosion products, and/or contaminants which are undesirable to the down-stream process unit. For example, the solid matter in the front-end process streams of refineries usually contains a significant amount of iron rust particulates and other degradation and corrosion products, which tend to accumulate in process lines, valves, and pumps. For these applications, filtration devices with greater filtration capacity, that is, equipped with more and/or larger magnetic bars, are required. 
         [0027]    In particular, for filtering dirtier refinery streams that have relatively larger flow rates and higher contaminant levels, magnetic filtration devices with different configurations to handle larger capacity may be required. In a preferred embodiment, the filtration device as shown in  FIGS. 3A and 3B  is, for example, applied to remove contaminants from straight-run gas oil before it is fed into a hydrodesulfurization (HDS) unit in the refinery. This filtration device can effectively replace the inefficient conventional filter and better protect the sophisticated panel heat exchanger, e.g., PACKINOX heat exchanger, and the catalyst bed of the HDS unit. Both the PACKINOX heat exchanger and the catalyst bed are vulnerable to plugging by iron rust and other paramagnetic particulates. Filtration device  300  cleans the gas oil by continuously removing iron rust particulates and other corrosion products from the stream. Thus a high capacity and operation efficiency of the PACKINOX heat exchanger and the HDS unit are maintained. As illustrated, filtration device  300  comprises a high-pressure vessel  302  with a removable cover  304  that is equipped with handle  306 , and a square or rectangular rack-shaped supporting tray  308  with magnet housing  314  in the form of vertically elongated stainless steel square tubes fitted within compartment  316  of high pressure vessel  302 . The stainless steel square tubes are preferably arranged in rows in a square or a rectangular matrix to increase the total contact area of the tubes for maximum solid loading. A magnetic bar  310  is placed in each stainless steel tube. To enhance the flow pattern of a process stream over the tubes, vertical partition plates  320  are placed between each row of the tubes to create a tortuous flow pattern pass the tubes. The number of housings  314  and associated magnetic bars  310  employed in filtration device  300  typically ranges from 1 to 100 or more. 
         [0028]    As the contaminated gas oil enters inlet  330  which is located in the lower part of one side of filtration device  300 , iron rust particulates and corrosion products are attracted and adhere to the outer surfaces of the vertical square stainless steel tubes aided by the powerful magnetic bars. The treated cleaned gas oil stream exits through outlet  332  that is located at the upper part on the side opposite inlet  330 . The removal of the iron rust particulates and corrosion products by the magnetic bars is optimized by packing the maximum number of square tubes in the matrix and positioning of the vertical partition plates. This arrangement keeps the level of residual iron rust particulates and corrosion products to a minimum. The filtration device yields substantially cleaned gas oil that is fed to the PACKINOX heat exchanger and the HDS unit. 
         [0029]    Once the process stream is diverted to an auxiliary filtration device as described above, remove the square or rectangular tray along with the stainless steel tubes and the magnetic bars. The tray supporting the plurality of housing and magnetic bars is removed; the attracted contaminants fall from the vertical tubes upon removal of the magnets therefrom. 
         [0030]      FIGS. 4A and 4B  depict a modified version of the filtration device that includes magnet housing that is integral with the unit and is not removable therein. Specifically, filtration device  400  comprises a high-pressure vessel  402  with a plurality of magnet housing  414  in the form of stationary vertically elongated square stainless steel tubes arranged in rows of a square or rectangle matrix. The tubes are an integral part of the high-pressure vessel. A magnetic bar  410  is placed inside each square stainless steel tube through an orifice on upper sealed surface of pressure-vessel  402 . Vertical partition plates  420  are placed between each row of the tubes to optimize flow pattern through compartment  416 . 
         [0031]    Operation of this filtration device is the same as that for the filtration device shown in  FIGS. 3A and 3B  however once filtration device  400  is taken off-line, the magnetic bars are simply lifted out of their stainless steel tube housing whereupon the contaminants fall off into compartment  416 . The adsorbed contaminant sludge is flushed away. 
         [0032]      FIGS. 5A ,  5 B, and  5 C illustrate another filtration device that is particularly suited for removing contaminants from refinery streams, such as the straight-run gas oil before it enters a HDS unit, and thereby maintain the high capacity and operation efficiency of the down-stream PACKINOX heat exchanger and the HDS unit. 
         [0033]    As shown, filtration device  500  comprises a high-pressure vessel  502  sealed with a removable cover  504  that is equipped with handle  506 , and a square or rectangular-shaped rack supporting tray  508  to which a plurality of magnet housing  514  in the form of vertically elongated stainless steel column or slates are attached and fitted in compartment  516  of high pressure vessel  502 . The stainless steel slates are arranged in parallel rows to increase the total contact surface area of the device for maximum solid loading. The space between adjacent parallel rows of slates defines a channel through which the contaminated gas oil flow. A magnetic plate  510  is placed inside of each stainless steel slate. The number of housings  514  and associated magnetic bars  510  employed in filtration device  500  typically ranges from 1 to 100 or more. 
         [0034]    As shown in  FIG. 5C , contaminated gas oil enters filtration device  502  through inlets  530  located at the lower part on the front side of the device. The iron rust particulates and corrosion products are attracted and adhere to the outside surface of the vertical stainless steel slates with the aid of the powerful magnetic plates. The cleaned gas oil stream exits through an outlet  532  located in the upper part of backside of the device. In this fashion, inlets  530  and outlets  532  define flow patterns that are parallel to the channels between adjacent slates. Moreover, the employment of multiple inlets better distributes the process stream flow so as to maximize the contact time between the process stream and slates. 
         [0035]    Once filtration device  500  is taken off-line, supporting tray  508  is lifted from compartment  516  and once the magnetic plates are removed from their corresponding stainless steel slates, the contaminants will fall off. 
         [0036]    Finally,  FIGS. 6A ,  6 B and  6 C depict a modified version of the filtration device that includes magnet housing that is integral with the unit and is not removable therein. Specifically, filtration device  600  comprises a high-pressure vessel  602  that defines compartment  616  into which are positioned a plurality of magnet housing  614  in the form of stationary vertically elongated stainless steel column or slates that are arranged in parallel across compartment  616 . The slates are an integral part of the high-pressure vessel. Except for the process stream inlets  630  and outlet  632 , compartment  616  is sealed from the environment. A vertical magnetic plate  610  is placed into each of magnet housing  614  through an aperture on sealed top  622  of pressure-vessel  602 . 
         [0037]    Operation of filtration device  600  is similar to that shown in  FIGS. 5A ,  5 B and  5 C however once filtration device  600  is taken off-line, the magnetic plates are simply lifted out of their stainless steel slate housings whereupon the contaminants fall off into compartment  616 . The adsorbed contaminant sludge is flushed away. 
         [0038]    It is expected that the filtration devices illustrated in  FIGS. 3 ,  4 ,  5 , and  6  will perform at such high levels that the filtered gas oil will be sufficiently free of particulates that the expensive PACKINOX heat exchanger can be replaced by a conventional, low cost tube and shell heat exchanger. 
         [0039]    Filtration devices of the present invention can be adapted for implementation to any refining process stream, similar to the straight-run gas oil stream, which contains relatively large among of iron rust particulates, corrosive products, and/or contaminants, which are undesirable to the down-stream process unit. In preferred embodiments, the filtration devices of this invention can be advantageously applied to following refinery streams: (1) feed to the C 5  and C 6  isomerization unit, (2) feed to the naphtha HDS unit, (3) feed to the reformer HDS unit, (4) feed to the kerosene HDS unit, (5) feed to the coke naphtha HDS unit, (6) feed to residual oil HDS unit, and (7) feed to coal tar naphtha HDS unit. 
         [0040]    The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in these embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.