Abstract:
A two-stage sealed magnetic filter continuously removes magnetic and non-magnetic contaminants from liquid process streams. Elongated non-magnetic holder sleeves encasing magnet bars attract magnetic contaminants while a screen cylinder captures non-magnetic contaminants. The magnet bars are accessible without having to open the interior of the housing to the environment. Thus, during maintenance, removing the magnet bars from the holder sleeves releases the magnetic contaminants that have adhered to the holder sleeves into the screen cylinder which partially encloses the holder sleeves. Contaminants are flushed out of the magnetic filter without exposing workers to potentially hazardous substances. Polymeric sludge occluded with iron compounds can be effectively removed from streams in refineries and chemical plants. The iron compounds are formed from carbon steel which is prevalent in plant machinery and that corrodes in the presence of acidic contaminants.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to techniques for removing contaminants from liquid process streams in refinery and chemical plants with a magnetic filter and particularly to employing and servicing a sealed magnetic filter that is designed so that, during clean-up service, contaminant particles are readily flushed therefrom without exposing the interior of the magnetic filter housing to the environment. 
     BACKGROUND OF THE INVENTION 
     Magnets have been used to remove ferromagnetic materials such as iron-containing particles fem fluid streams. The magnets are typically enclosed in filter devices that are incorporated online with the process streams. For large scale commercial applications, by employing alternate magnetic filters in parallel, with one operating while the other unit is being serviced, continuous operations with minimum downtime can be attained. Current magnetic filter designs usually require that the housing be dismantled using heavy machinery in order to access and remove the magnetic bars and thereafter clean off the contaminants. Aside from the inconvenience, this routine subjects operators to potential hazardous and/or flammable substances that may be present in the process fluids and contaminants. It also unnecessarily exposes air-sensitive process fluids to the environment. 
     SUMMARY OF THE INVENTION 
     The invention provides a magnetic filter that is particularly suited for removing degradation sludge, iron containing particles or flakes, as well as non-magnetic polymeric materials from the process streams in refinery and chemical plants. 
     In one aspect, the invention is directed to a magnetic filter for separating magnetic and non-magnetic contaminants from a contaminated liquid process stream in a refinery or a chemical plant that includes: 
     a housing having (i) an upper opening that is sealed with a detachable cover plate (ii) a process stream inlet (iii) a process stream outlet (iv) an interior region between the inlet and outlet and (v) a lower end, wherein the cover plate supports a plurality of vertically oriented, elongated non-magnetic holder sleeves with each holder sleeve being configured to accommodate one or more magnets that are disposed therein; and 
     a screen cylinder that is positioned in the interior region wherein the screen cylinder has (i) a rim defining an opening through which the plurality of holder sleeves are disposed and (ii) a filter screen that encloses lower portions of the plurality of holder sleeves wherein the filter screen is configured to capture contaminants thereon wherein the rim and cover plate define a flow channel that directs the contaminated liquid process stream from the inlet through the opening of the rim, pass the holder sleeves so that magnetic contaminants adhere to the exterior of the holder sleeves and through the filter screen where non-magnetic contaminants of the desired size are removed to form a treated process stream that leaves via the outlet and wherein the one or more magnets that are disposed in each holder sleeve can be removed from the holder sleeve without having, to open the cover plate and exposing the interior region to the environment. 
     The simple design of the magnetic filter affords easy clean-up service whereby workers can manually remove the magnetic bars from the holder sleeves to thereby release magnetic contaminants without the risk of being exposed to hazardous chemicals inside the magnetic filter. No mechanical or power lifting tool is required. The contaminants which include polymeric sludge are then removed by flushing the interior of the magnetic filter. Clean-up service of the magnetic filter can be implemented through an automatic sequencing device. 
     In another aspect, the invention is directed to a method of removing magnetic and non-magnetic particles from a contaminated liquid process stream in a refinery or chemical plant that includes the steps of: 
     (a) providing, a magnetic filter device that comprises:
         a housing having (i) an upper opening that is sealed with a detachable cover plate (ii) a process stream inlet (iii) a process stream outlet (iv) an interior region between the inlet and outlet and (v) a lower end, wherein the cover plate supports a plurality of vertically oriented, elongated non-magnetic holder sleeves with each holder sleeve being configured to accommodate one or more magnets that are disposed therein; and   a screen cylinder that is positioned in the interior region wherein the screen cylinder has (i) a rim defining an opening through which the plurality of holder sleeves are placed and (ii) a filter screen that encloses lower portions of the plurality of holder sleeves wherein, the filter screen is configured to capture contaminants thereon wherein the rim and cover plate define a flow channel that directs the contaminated liquid process stream from the inlet through the opening of the screen cylinder, pass the holder sleeves and through the filter screen;       

     (b) connecting the contaminated liquid process stream to the inlet of the magnetic filter, such that as the contaminated liquid process stream initially flows pass the holder sleeves, magnetic contaminants adhere to the exterior of the holder sleeves and subsequently as the contaminated liquid process stream continues pass the filter screen non-magnetic contaminants of the desired size are removed by the filter screen to thereby form a treated process stream that exits through the outlet; 
     (c) terminating the flow of the contaminated liquid process stream into the inlet; 
     (d) withdrawing magnets from one or more of the holder sleeves, without having to open the cover plate and expose the interior region to the environment, to thereby release magnetic contaminants that have adhered to the exterior surface of the holder sleeves; 
     (e) flushing out magnetic and non-magnetic contaminants from the screen cylinder; and 
     (f) placing magnets back into one or more of the holder sleeves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of an embodiment of the magnetic filter; 
         FIG. 2A  is a cross sectional of the magnet bar assembly; 
         FIG. 2B  is a top view of the magnetic bar and holder sleeve assembly; 
         FIGS. 2C and 2D  are side and top views, respectively, of the holder sleeve assembly; 
         FIGS. 3A and 3B  are side and top views, respectively, of the screen cylinder; 
         FIG. 4A  depicts an operating cycle for the magnetic filter; and 
         FIG. 4B  depicts a maintenance cycle for the magnetic filter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , the magnetic filter comprises a housing  1  having an inlet, pipe section  38  that can be coupled to a contaminated process stream  2  and an outlet pipe section  40  from which treated process stream  3  exits. The housing  1  defines an interior region  30  which accommodates a screen cylinder  14  that has an upper rim  16 , a middle, vertical filtering section  25  that is preferably constructed of multiple metal screens having different mesh sizes, and a lower cone-shaped non-filtering section  34  that has an open tube or pipe  29  at the end. Threads  31  on its exterior allows tube  29  to be screwed onto a female threaded drain pipe  7 , which is welded onto support platform  36 . Valve  68 , which is normally closed during filtration, is opened during cleanup service to allow flush fluid to be discharged from the interior of screen cylinder  14 . Rim  16 , which preferably has a diameter that is larger than that of screen section  25 , is placed freely on a supporting ring  50  that is affixed to an inner wall of housing  1 . In positioning, cylinder screen  14 , tube  29  is screwed into drain pipe  7  until the top rim  16  fully engages supporting ring  50  to form a tight seal. 
     After the screen cylinder is secured, cover plate  5 , which is equipped with a plurality of vertically oriented elongated holder sleeves  13 , is fastened to an annular flange  6  that is welded to the outer perimeter along the opening in housing  1 . A polymer gasket  4  is positioned between cover plate  5  and flange  6  so as to form a tight seal as nuts  48  are threaded into bolts  46 . Holder sleeves  13  are preferably welded to top cover plate  5  to form integral units therewith. Each elongated holder sleeve  13  is constructed of a non-magnetic metal such as stainless steel and accommodates one or more magnet bars that are encased in a magnet bar assembly. The middle and lower portions of holder sleeves  13  are partially enclosed by screen cylinder  14 . 
     As shown in  FIGS. 2A and 2B , each magnet bar assembly  39  includes a non-magnetic tubular enclosure  10  that encases a magnet bar which consists of a plurality of short magnet blocks or cylinders  9  that are arranged in tandem with like poles positioned adjacent to each other. The blocks  9  are loaded into the sealed enclosure  10  which is then enclosed with guard plate  54  that has a pulling ring  11  attached to facilitate manual lifting. Holder sleeve  13 , magnet block  9  and tubular enclosure  10  preferably have circular cross sections. As further shown in  FIGS. 2C and 2D , when the magnet bar assemblies are inserted, into the holder sleeves  13 , the length of each magnet bar  8  extends from cover plate  5  to the lower end of holder sleeve  13 . Contaminants containing magnetic material are attracted by the magnetic field produced by the magnet bars  8 ; the contaminants adhere onto the entire exterior surface of elongated holder sleeve  13 , which is completely sealed from interior  30  so there is no leakage of process fluid into holder sleeves  13 . 
       FIGS. 3A and 3B  illustrate that screen cylinder  14  is preferably constructed of two concentric vertically arranged layers of non-magnetic metal screens  17  and  18 . The inner, finer screen  17  typically has a mesh size of 1 to 200 and preferably 10-100 wires per inch. The outer, coarser screen  18  typically has a mesh size of 10-100 and preferably 10-50 wires per inch. The top end of each screen  17 ,  18  is attached to rim  16 , which is equipped with a pair of handles  15 , and the lower side of each screen is attached to the upper perimeter  23  of the non-filtering section  34 , which is preferably configured as a cone with tube  29  at the apex. During the filtration cycle, should contaminants become separated from holder sleeves  13  or screens  17 ,  18 , the debris falls into and is collected in the funnel-shaped cone. The size of opening  56  in tube  29  must be large enough to accommodate the large particles that accumulate in the filtration process so that contaminates can be readily flushed out during cleaning. 
     In operation, as shown in  FIG. 1 , contaminated process stream  2  entering inlet  38  initially flows into plenum or chamber  42  where the process fluid expands and flows towards baffle  52 . The configurations and positions of holder sleeves  13  and baffles evenly distribute the flow of contaminated fluid initially downward into screen cylinder  14 . In this regard, the distance or gap between cover plate  5  and rim  16  should be optimized to allow the contaminated fluid to come into contact with as much of the holder sleeves as possible to maximize collection of magnetic contaminants. The strong magnetic fields developed by the plurality of the magnet bars in the holder sleeves  13  cause magnetic contaminants to deposit onto the outer surface of the holder sleeves  13 . Subsequently, as the process fluid passes through inner and outer screens  17 ,  18  ( FIG. 3B ) large particles, including both magnetic and non-magnetic contaminants, are removed from the liquid the screens. Treated process fluid which is substantially free of the contaminants is channeled towards plenum or chamber  44  and exits the magnetic filter through outlet  40 . The magnetic filter is structured as a two-stage filtration wherein the strength and numbers of magnet bars are sufficient to initially attract a desired amount of magnetic contaminants from the contaminated liquid process stream and then filter screen captures magnetic and non-magnetic contaminants of the desired size from the contaminated liquid, process stream. 
     Flow thorough inlet  38  and outlet  40  slows dramatically as the outer surfaces of holder sleeves  13  become layered with magnetic contaminants and screen cylinder  14  gets clogged with non-magnetic contaminants. Servicing the magnetic filter entails terminating the flow of contaminated process stream into the magnetic filter and then withdrawing magnet bars  8  from holder sleeves  13 . This releases major portions of the magnetic contaminants that have been deposited on the outer surface of holder sleeves  13  which fall into the cone of the non-filtering section  34  of screen cylinder  14 . A flush fluid, which is can be the cleaned process fluid, is introduced in a reverse direction through outlet  40 . The flush fluid passes through inner and outer screens  17 ,  18  and dislodges non-magnetic contaminants therefrom and washes off residual magnetic contaminants from the outer surface of holder sleeves  13 . The flush fluid, with entrained magnetic and non-magnetic contaminants, is discharged through the drain  7 . Once magnetic bars  8  are slidably reinserted into holder sleeves  13  and drain valve  68  is shut, the cleaned magnetic filter ready to be reconnected online. 
     A schematic diagram illustrating the filtering and cleaning operations with a magnetic filter is depicted in  FIG. 4A . During the filtration process, contaminated process fluid  92  flows through valve  72  and into magnetic filter housing  61  where contaminants are removed to yield a treated process fluid  93  that exits through valve  73 . To service the filter housing  61  that is loaded with contaminants, after closing valve  72  and opening valves  69  and  78 , a flush fluid is delivered through the outlet of filtering housing  61  through valve  73 . The flush fluid laden with contaminants including sludge is discharged through valve  78 . 
       FIG. 4B  illustrates an arrangement in which a settling tank  22  is employed to supply recycled treated flush fluid to a magnetic filter. When filter housing,  61  becomes loaded with contaminants as evidenced by higher levels of contaminants present in the exiting treated process liquid and/or by an increased in the pressure drop across filter housing  61 , valve  62  is shut to block the flow of contaminated process fluid  82 . Valve  63  that regulates the flow of treated process liquid  83  from the magnetic filter is also shut while a filter by-pass valve  69  is opened to maintain continuous process operations. After magnetic bars are removed from the holder sleeves as described above, flush fluid is introduced in a reverse direction into the housing outlet via valve  70  through line  20 . The flush fluid removes the magnetic and non-magnetic contaminants from the screen cylinder, in the manner which is described previously, and the flush fluid along with the contaminants are discharged through the bottom of filter housing  61  through valve  68 . The mixture of flush fluid and sludge is transferred to a settling tank  22  via line  21 . Decanted flush fluid is recycled from the top of settling tank  22  to filter housing  61  for repeated flush services; sludge is removed from the bottom of settling tank  22 . After the filter is cleaned, the magnetic bars are then replaced into the filter housing and operating cycle is started again. The cleaning sequence illustrated in  FIG. 4B  can be readily implemented with process controls that automatically initiate cleaning when high contaminant concentrations in the treated process liquid are detected and/or the pressure drop exceeds a predetermined level. 
     The inventive magnetic filter is particular suited for treating process streams containing large amounts of magnetic particles as well as polymeric sludge occluded with such particles. The magnetic particles can include both ferromagnetic and paramagnetic materials and substances. Carbon steel, a common material for plant construction, tends to corrode in the presence of acidic contaminants in process streams especially in refineries and chemical plants. The corrosion forms ferrous ions in the stream, which react with sulfur, oxygen and water to form FeS, FeO, Fe(OH) 2 , Fe(CN) 6 , and other paramagnetic compounds that take the form of fine particles and visible flakes. These paramagnetic materials tend to attract degradation sludge, thereby transforming a major portion of the contaminants paramagnetic. By employing a magnetic filter, a substantially large portion of the contaminants, including polymeric sludge that has magnetic particles incorporated therein, can be effectively removed from the process stream. Only a small portion of the contaminants remain non-magnetic (or weak-magnetic) and do not respond to the magnetic field generated by the magnet. However, given that the quantity of non-magnetic contaminants is relatively small, most of the non-magnetic contaminants are subsequently captured by the screen(s) of the screen cylinder.