Removal Of Glycerin From Biodiesel Using An Electrostatic Process
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.
This application is a divisional application of U.S. patent application Ser. No. 13/857,594, filed Apr. 5, 2013, which was a divisional application of U.S. patent application Ser. No. 12/261,208, filed Oct. 30, 2008, which issued as U.S. Pat. No. 8,414,756 on Apr. 9, 2013, the contents of which are hereby incorporated by reference in their entirety.
FIELD OF INVENTIONThis invention relates generally to electrostatic coalescers, and, more particularly, to an improved vertical coalescer to promote separation of glycerin from biodiesel.
BACKGROUND OF THE INVENTIONConventional 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.
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.
Newer continuous processes for biodiesel production using heterogeneous catalysts enable the transesterification 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.
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 alky fatty acid esters in the continuous production of biodiesel.
BRIEF SUMMARY OF THE INVENTIONAn 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.
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.
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.
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.
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.
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:
Referring to
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
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.
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.
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.
Returning to
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.
Referring now to
As illustrated in
Returning to
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.
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.
Claims
1. A method for promoting glycerin coalescence in a biodiesel stream comprising the steps of:
- passing the biodiesel stream into vertically elongated, closed vessel through a fluid inlet located at a lower portion of said vessel;
- establishing a voltage field around a perimeter portion of said vessel and in a center portion of said vessel, said voltage field established by a set of grounded first electrodes located in an upper portion of said vessel and arranged as a horizontal planar grid lying perpendicular to a central vertical axis of said vessel and having supports which connect the grid to the vessel; and a first and a second set of charged second electrodes located in the upper portion of said vessel, the first and second sets arranged as horizontally oriented parallel rods lying perpendicular to the central vertical axis of said vessel, the first set lying entirely above and the second set lying entirely below the horizontal planar grid of grounded first electrodes;
- coalescing glycerin in the biodiesel stream as the biodiesel stream flows upwardly through the voltage field, augmenting separation thereof from the biodiesel stream;
- collecting the coalesced glycerin in a glycerin phase at a bottom of said vessel;
- removing said glycerin phase from said vessel through a first fluid outlet located at a lower portion of said vessel; and
- removing a remaining portion of the biodiesel stream from said vessel though a second fluid outlet located at a top portion of said vessel.
2. A method according to claim 1 wherein a horizontally disposed foraminous surface is located in a lower portion of said vessel and is in communication with an interior surface of said vessel to ground the foraminous surface.
3. A method according to claim 1 wherein one or more connector passageways are located on an interior surface of said horizontal planar grid and allow for one or more connectors connectable to said first and second sets of second electrodes to pass therethrough.
4. A method according to claim 1 wherein a voltage between each opposing pair of first and second electrodes is in a range of 2 kV/inch to 8 kV/inch.
5. A method according to claim 1 wherein a distributor housing is connected to said fluid inlet and has an array of ports located at an upper portion of said distributor housing.
6. A method according to claim 1 further comprising the step of regulating the level of the glycerin phase in said vessel with a level control located in a lower portion of said vessel.
Type: Application
Filed: Mar 17, 2016
Publication Date: Jul 14, 2016
Inventors: Gary W. Sams (Spring, TX), William A. Summers (Des Moines, IA), Sarabjit S. Randhava (Evanston, IL), Harry G. Wallace (Tulsa, OK)
Application Number: 15/073,109