Abstract:
A vertical electrostatic coalescer comprises a first and second electrode surface and a horizontally disposed foraminous surface. The first electrode surface and horizontally disposed foraminous surface are at ground potential. The first and second electrode surfaces share the same planar orientation relative to the central longitudinal axis of the vessel. The unique arrangement of the vessel and opposing pairs of first and second electrode surfaces provides for a substantially uniform voltage field around a perimeter of the vessel and an effective voltage field for coalescence within a center of the vessel. A circular-shaped distributor pipe or a distributor housing serves to absorb momentum of the incoming emulsion stream and distribute the stream into an interior of the vessel.

Description:
REFERENCE TO PENDING APPLICATIONS 
       [0001]    This application is not based upon any pending domestic or international patent applications. 
       FIELD OF INVENTION 
       [0002]    This invention relates generally to electrostatic coalescers, and, more particularly, to an improved vertical coalescer to promote separation of glycerin from biodiesel. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional biodiesel production employs homogeneous alkaline catalysts to transform seed oils or animal fats into fatty acid alkyl esters and glycerin. The normal volume ratio of alkyl esters to glycerin is 10:1. Separating the glycerin from the ester layers by capitalizing on their different specific gravities—1.26 kg/L for glycerin and 0.86-0.90 kg/L for esters—is common but cost inefficient. 
         [0004]    Large quantities of water are required to remove glycerin and spent catalyst from the ester layer, which tends to reduce the market value of the glycerin byproduct. Static or centrifugal separators are difficult to manage and tedious to operate, lending considerable risk to the quality of the final alkyl ester product, which must meet ASTM specifications (D6751-07b) before any use in on-road vehicles as biodiesel. 
         [0005]    Newer continuous processes for biodiesel production using heterogeneous catalysts enable the transeterification reaction to proceed continuously. Such continuous processing requires the application of cost effective, time efficient, and complete separation of glycerin from the alkyl ester stream. Because no water is used in these newer solid catalytic processes, the quality of the glycerin is higher (about 98%) and its market value considerably greater than glycerin from homogeneous catalytic processes. The lower volume glycerin streams, which typically range from less than 400 barrels per day to as much as 1,000 barrels per day, require a continuous, rapid separation for their economy. 
         [0006]    Recent tests conducted by the inventors have shown that glycerin can be readily and rapidly coalesced by an electrostatic field and the separation rate is increased by the development of large glycerin droplets. Although electrostatic coalescence is a proven, effective method for crude oil dehydration, electrostatic coalescers are not well-suited for biodiesel production. These crude oil coalescers are typically large, horizontally oriented vessels. A need exists, therefore, for smaller, vertically oriented, electrostatic coalescers to promote the separation of glycerin from alkyl fatty acid esters in the continuous production of biodiesel. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An electrostatic coalescer for promoting glycerin coalescence in biodiesel e comprises an vertically disposed vessel having a fluid inlet located at a lower portion, a first fluid outlet located at a bottom, and a second fluid outlet located at a top of the vessel. In a preferred embodiment, two or more vertically disposed first and second electrode surfaces are located in an upper portion of the vessel. The electrodes radially extend outward from and about a central longitudinal axis of the vessel. The vessel is at ground potential and a portion of one or more of the first electrode surfaces is in communication with an interior surface of the vessel. A portion of one or more of the second electrodes is in communication with a power supply. Various types of power supply and electric circuitry may be employed to create effective electric fields for coalescence of the glycerin droplets contained in the emulsion. 
         [0008]    Each first electrode surface lies adjacent to a second electrode surface, and each adjacent first and second electrode surfaces have substantially equal angular spacing therebetween. The first electrode surface preferably has a substantially uniform cross sectional area. The second electrode surface preferably has a teardrop-shaped cross sectional area. The unique arrangement of the vessel and opposing pairs of first and second electrode surfaces provides for a substantially uniform AC voltage field around a perimeter of the vessel and an effective DC field for coalescence within a center of the vessel. A field in the range of 2 kV/inch to 8 kV/inch is preferable for coalescing the glycerin. 
         [0009]    The electrostatic coalescer further comprises a circular-shaped distributor pipe or a distributor housing that serves to absorb momentum of the incoming emulsion stream. An array of ports located about a periphery of the distributor pipe—or an array of ports located on an upper surface of the housing—substantially evenly distributes the stream into an interior of the vessel. As the glycerin-in-biodiesel stream enters the electric field established by the electrode surfaces, glycerin droplets coalesce. Once the droplets reach a size that overcomes gravity, the droplets fall to a glycerin phase located at a lower portion of the vessel. A level control monitors the glycerin phase and controls an outlet valve. 
         [0010]    In another preferred embodiment, the electrostatic coalescer comprises one or more horizontally disposed first electrode surfaces located in an upper portion of the vessel. The electrode surface may be a circular shaped bar grate. A portion of the electrode surface is in communication with an inner surface of the vessel, which is at ground potential. Two or more horizontally disposed second electrode surfaces are oriented substantially parallel to the first electrode surface and are located a substantially equal distance above and below the first electrode surface, respectively. A passageway through the first electrode surface allows for a connector to connect the two second electrode surfaces to one another without communicating with the first electrode surface. The second electrode surface may comprise two or more rods of varying length, each rod oriented parallel to the other with each end of the rods lying a substantially equal distance from an opposing inner surface of the vessel. A power supply external to the vessel is in communication with one of the second electrode surfaces. 
         [0011]    A better understanding of the invention will be obtained from the following description of the preferred embodiments and the claims, taken in conjunction with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross-sectional view of a vertical electrostatic coalescer having a circular conduit for distributing an inlet stream of biodiesel and glycerin and employing an electric field to coalesce the glycerin droplets in the biodiesel. The electric field comprises circumferentially arranged and vertically disposed electrode surfaces. 
           [0013]      FIG. 2  is a view of the electrostatic coalescer taken along section line  2 - 2  of  FIG. 1 . Electrode surfaces having a charge alternate with and are substantially equally spaced between electrode surfaces at ground potential. 
           [0014]      FIG. 3  is a view taken along section line  3 - 3  of  FIG. 1 . A circular conduit having an array of ports serves to absorb momentum of the inlet stream and substantially evenly distribute the stream into an interior of the coalescer. 
           [0015]      FIG. 4  is a view taken along section line  4 - 4  of  FIG. 1 . A set of concentric rings provides support and spacing for the circumferentially arranged fin-shaped electrode surfaces 
           [0016]      FIG. 5  is view of a typical operating environment for the electrostatic coalescer. 
           [0017]      FIG. 6  is a cross-sectional view of another embodiment of the vertical electrostatic coalescer having a distributor housing and employing an electric field. The electric field comprises horizontally disposed electrode surfaces, one surface having the same charge as a power supply, the other surface being at ground potential. 
           [0018]      FIG. 7  is a view of the electrostatic coalescer taken along section line  7 - 7  of  FIG. 6 . An open, circular-shaped baffle helps to control turbulence and a flow of biodiesel to an outlet. 
           [0019]      FIG. 8  is a view taken along section line  8 - 8  of  FIG. 6 . An electrode surface at charge comprises a plurality of different length rods, the rods being arranged in parallel with each rod end being a substantially equal distance from an opposing inner surface of the coalescer. 
           [0020]      FIG. 9  is a view taken along section line  9 - 9  of  FIG. 6 . An electrode surface at ground potential comprises a circular bar grate having circular passageways therethrough. 
           [0021]      FIG. 10  is a view taken along section line  10 - 10  of  FIG. 6 . 
           [0022]      FIG. 11  is a view taken along section line  11 - 11  of  FIG. 6 . A distributor housing having an array of ports serves to absorb momentum of the inlet stream and substantially evenly distribute the stream into an interior of the coalescer. 
           [0023]      FIG. 12  is a view taken along section line  12 - 12  of  FIG. 6 . An open, cylindrical-shaped baffle helps to control turbulence and a flow of coalesced glycerin to an outlet. 
           [0024]      FIG. 13  is a cross-sectional view of another embodiment of the vertical electrostatic coalescer having a distributor housing and employing an electric field. The electric field includes a cylindrical wire screen having the same charge as a power supply and a centrally disposed, vertical closed cylinder being at ground potential. 
           [0025]      FIG. 14  is a view taken along section line  14 - 14  of  FIG. 13 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    An electrostatic coalescer as described below is not limited in its application to the details illustrated in the accompanying drawings. The coalescer is capable of other embodiments and of being practiced or carried out in a variety of ways. The phraseology and terminology employed herein, therefore, are for purposes of description and not limitation. Elements illustrated in the drawings are identified by the following numbers:
     10  Electrostatic coalescer     12  Vessel     14  Vessel top     16  Vessel bottom     18  Contact rod     20  Emulsion inlet     22  Glycerin outlet     24  Biodiesel outlet     26  Support leg     28  Baffle     30  Distributor conduit     32  Port     34  Distributor housing     36  Port     38  Pipe with tee outlet     40  Brace     42  Electrode     44  Fastener     46  Insulated connector     48  Support     50  Electrode     52  Rod     54  Fastener     56  Passageway     58  Brace     60  Insulated hanger     62  Insulated hanger     64  Ring     66  Ring     68  Spoke     70  Electrode     72  Electrode     74  Centralizer     76  Tab     78  Cap     80  Float assembly     88  Baffle     90  Power source     92  High voltage connection     94  Conductor     96  Foraminous plate     98  Electrode     100  Electrode     102  Hangar assembly   
 
         [0071]    Referring to  FIG. 1 , in a preferred embodiment an electrostatic coalescer  10  comprises a vertically oriented vessel  12  having an inlet  20 , a heavy component (glycerin) outlet  22 , and a lighter component (biodiesel) outlet  24 . Positioned within vessel  12  is a first electrode surface  70  and a second electrode surface  72 . Electrode  70  is in communication with vessel  12 , which is at ground potential, via a set of tabs  76 . Because glycerin is such a poor conductor, it is preferable to add a ground in the form of a foraminous plate  96 , which is attached to vessel  12  and located in a lower portion of vessel  12 . Plate  96  may also be a wire screen or bar grate. Electrode  72  is connected by a conductor  94  to a power source (not shown). Conductor  94  enters an interior of vessel  12  through a contract rod  80  located on an exterior surface of vessel  12 . The power source is of a type well known in electrostatic coalescence and the electrical circuitry employed may incorporate multiple frequency wave forms. For more detailed information on power sources and related circuitry used in electrostatic coalescence, review U.S. Pat. No. 6,860,979, entitled “Dual Frequency Electrostatic Coalescence” and issued to Gary W. Sams on Aug. 7, 2002, and application Ser. No. 11/057,900, entitled “Multiple Frequency Electrostatic Coalescence,” filed Feb. 15, 2005, by Gary W. Sams, both of which are hereby incorporated by reference. 
         [0072]    Electrodes  70 ,  72  form an electric field within an interior of vessel  12 . The electrodes  70 ,  72  are oriented so that the glycerin-in-biodiesel stream passes between and about adjacent pairs of electrodes  70 ,  72  and through the electric field. As illustrated in  FIGS. 2 and 4 , each electrode  72  preferably has a teardrop-shaped cross sectional area and is suspended vertically by a pair of rings  64 ,  66  that are oriented horizontally and arranged concentric to a central longitudinal axis of vessel  12 . Electrode  70  preferably has a substantially uniform cross sectional area. The rings  64 ,  66 , in turn, are suspended by three insulated hanger rods  62  which electrically insulate vessel  12  from a charge being applied to ring  64  at connection point  92 . Four substantially equally spaced spokes  68  connect rings  64  and  66  to one another. 
         [0073]    The electrodes  72  radially extend outward in relation to a central longitudinal axis of vessel  12  so that each electrode  72  relative to each adjacent electrode  70  preferably has substantially the same angular spacing therebetween. An inner lateral edge and an outer lateral surface of each electrode  72  lies a substantially equal distance from an opposing inner surface of vessel  12  and the central longitudinal axis of vessel  12 , respectively. Through the above arrangement, electrodes  72  carry a charge but remain insulated from vessel  12  and electrode  70 . 
         [0074]    Each electrode  70  radially extend outward from a hollow cylindrical-body centralizer  74 . The electrodes  70  are preferably arranged so that each electrode  70  relative to each adjacent electrode  72  has substantially the same angular spacing therebetween. Centralizer  74  is arranged concentric to the central longitudinal axis of vessel  12  and has a conical-shaped end cap  78  at each end. End cap  78  prevents emulsion from entering an interior of centralizer  74  and serves to reduce turbulence within vessel  12 . 
         [0075]    A portion of an outer lateral edge of electrode  70  connects to a tab  74  located on an inner surface of vessel  12 . Adjacent pairs of electrode  70  form a space within which an electrode  72  is contained. Each electrode  72  has substantially equal angular spacing from each electrode  70 . The relative spacing and shape of electrodes  70 ,  72  also work to control turbulence within vessel  12 . Additionally, because an exterior surface of centralizer  74  is in contact with an inner lateral edge of electrode  70 , centralizer  74  functions as an electrode. Similarly, an inner surface of vessel  12  functions as an electrode. The configuration and positioning of electrodes  70  and  72  relative to each other and to vessel  12  and centralizer  74  provides for a substantially uniform electric field preferably in a range of 2 to 8 kV per inch spacing between electrodes  70  and  72 . 
         [0076]    Returning to  FIG. 1 , and also referring to  FIG. 3 , the glycerin-in-biodiesel stream flowing into inlet  20  is routed to a distributor conduit  30 , preferably circular shaped. Conduit  30  has an array of substantially evenly spaced circular-shaped ports  32  located about its periphery  30   a.  Conduit  30  absorbs momentum of the incoming glycerin-in-biodiesel stream and reduces its velocity, thereby controlling turbulence within vessel  12  while distributing the stream substantially evenly within vessel  12 . As the stream disperses into the interior of vessel  12  it migrates upwardly toward the electric field created by electrodes  70  and  72 . As the emulsion travels through the electric field, a bulk of the dispersed glycerin coalesces. 
         [0077]    As the coalesced droplets grow in size, gravity overcomes the electric field that suspends the droplets between the electrodes  70 ,  72 , and the droplets fall to a glycerin phase collecting at a bottom  16  of vessel  12 . A float assembly  80  monitors the level of glycerin being collected. Once the level of glycerin reaches a predetermined level, a valve (not shown) opens and allows the glycerin to exit vessel  12  through outlet  22 . 
         [0078]      FIG. 5  illustrates a typical operating environment for the electrostatic coalescer  10 . The transesterification reaction occurs upstream from the coalescer, whether by the conventional process involving the admixture of triglycerides, methanol and the homogeneous alkaline catalyst, or by the newer process employing a heterogeneous, acid catalyst in which triglycerides and methanol are admixed and then stirred with the solid catalyst or passed over a fixed bed containing the solid catalyst. Once the reaction is complete, the feed to the electrostatic separator in either case, containing biodiesel and glycerin, will have been cooled and stripped of residual methanol and water, as appropriate. This feed to the electrostatic coalescer  10  will consist of biodiesel and glycerin in an approximate ratio by volume of 10:1. 
         [0079]    Referring now to  FIG. 6 , another preferred embodiment of electrostatic coalescer  10  is illustrated. In this embodiment, electrodes  42  and  50  form an electric field. Electrode  42  is in communication with vessel  12 , which is at ground potential, via a fastener  44  that attaches electrode  42  to an internal brace  58 . Foraminous plate  96  is also at ground potential. Electrode  50  is connected to a power source (not shown) by a conductor  94  and is suspended by insulated hangers  62  that connect to an electrode supporting structure  46 . The electrodes  42 ,  50  are each oriented in a horizontal plane, with a pair of electrodes  50   a  and  50   b  being positioned substantially parallel to and a substantially equal distance above and below electrode  42 , respectively. An insulated connector  46  connects electrodes  50   a  and  50   b.    
         [0080]    As illustrated in  FIGS. 8 and 10 , electrode  50  preferably comprises a series of varying length rods  52   a,    52   b,  each rod  52   a,    52   b  being held by a pair of fasteners  54  and arranged so that adjacent rods  52   a,    52   b  are parallel to one another and the end of each rod  52   a,    52   b  lies a substantially equal distance from an opposing inner surface of vessel  12 . As illustrated in  FIG. 9 , electrode  42  preferably comprises a circular-shaped bar grate being arranged concentric to vessel  12  and having two circular-shaped passageways  56  located on its interior surface. Insulated connector  50  passes through passageway  56 , thereby isolating electrodes  42  and  50  from one another. The relative spacing and shapes of electrodes  42 ,  52  also work to control turbulence within vessel  12 . 
         [0081]    Returning to  FIG. 6 , and also referring to  FIGS. 7 ,  11 , and  12 , the glycerin-in-biodiesel stream flowing into inlet  20  is routed to pipe  38  having a tee at one end and being located within a distributor housing  34 . One end of the tee of pipe  38  mates against a bottom surface of housing  34 , the other end faces an array of substantially evenly spaced circular-shaped ports  36  located on an upper surface of housing  34 . Housing  34  and pipe  38  absorb momentum of the incoming glycerin-in-biodiesel stream and reduce its velocity, thereby controlling turbulence within vessel  12  while distributing the stream substantially evenly within vessel  12 . 
         [0082]    As the stream disperses into the interior of vessel  12  it migrates upwardly toward the electric field created by electrodes  42  and  50 . As the stream travels through electric field F, a bulk of the dispersed glycerin coalesces. As the coalesced droplets grow in size, gravity overcomes the electric field F that suspends the droplets between the electrodes  42  and  50  and the droplets fall to a glycerin phase collecting at a bottom  16  of vessel  12 . A circular-shaped open-top baffle  48  serves to control a flow of glycerin to outlet  22 . Similarly, a circular-shaped open-bottom baffle serves to control the flow of biodiesel to outlet  24 . 
         [0083]      FIGS. 13 and 14  illustrate another embodiment of electrostatic coalescer  10 . In this embodiment, electrodes  98  and  100  form an electric field. Electrode  98  is a foraminous surface, preferably a cylindrical wire screen, connected to a power source (not shown) by conductor  94  and suspended by insulated hangers  62 . Electrode  100  is a solid surface, preferably a hollow, closed end, cylinder in communication with vessel  12 , which is at ground potential, via a hanger assembly  102 . The electrodes  98 ,  100  are each oriented in a vertical plane. Foraminous plate  96  is at ground potential. 
         [0084]    While electrostatic coalescer  10  has been described with a certain degree of particularity, many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. The invention, therefore, is limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled.