Abstract:
A device for processing water having high concentrations of scale forming compounds and high solids content in a high efficiency vapor compression distillation system wherein a plate-in-frame heat exchanger is submerged in a boiling solution contained in a boiler drum. An impeller in the drum continuously circulates the boiling solution through the heat exchanger at a velocity to prevent suspended solids from accumulating and to inhibit scale formation on the boiling surfaces of the heat exchanger.

Description:
BACKGROUND OF THE INVENTION 
     In Applicant&#39;s pending patent application Ser. Nos. 08/320,233 and 08/320,235 filed Oct. 11, 1994 now U.S. Pat. Nos. 5,587,053 and 5,587,054, respectively, the disclosures of which are incorporated herein by reference, there are disclosed a boiler and condenser device including a plate-in-frame heat exchanger employed in a vapor compression distillation system. When processing feed streams containing high concentrations of scale forming compounds, it has been found that scale accumulates on the surfaces of the boiling chambers because of the stagnate water in the boiling chambers and the dry spots which form on the partially submerged surfaces of the boiling chambers. Also, when processing feed streams containing high concentrations of suspended or dissolved solids, it has been found that the concentration of the feed stream causes suspended solids to settle out of suspension, and the dissolved solids to precipitate out of solution. These released solids accumulate in the boiling chambers and interfere with the efficient operation of the plate-in-frame heat exchanger if not continuously removed from the boiling chambers. 
     To allow the boiler and condenser device and associated vapor compression distillation system disclosed in the aforementioned pending applications to operate at a high level of energy efficiency while processing feed streams having high solids content and high concentrations of scale forming compounds, the device of the present invention has been devised. 
     SUMMARY OF THE INVENTION 
     The device of the present invention comprises essentially a boiler drum containing a plate-in-frame heat exchanger of the type disclosed in the above-noted pending patent application Ser. No. 08/320,233 filed Oct. 11, 1994 now U.S. Pat. No. 5,587,053, wherein a plurality of alternating boiling and condensing chambers are provided, whereby the interior surface of each condensing chamber forms a condensing surface, and the exterior surface of each condensing chamber forms a boiling surface. The boiler drum contains a volume of boiling solution, and the plate-in-frame heat exchanger is submerged in the boiling solution. The condensing chambers are sealed from the boiling solution in the drum, but the boiling chambers communicate with the solution in the drum and provide spaces between adjacent condensing chambers to form interpasses for the solution in the drum. An impeller is mounted in the lower portion of the drum for continuously circulating the boiling solution and concentrate up through the interpasses between adjacent condensing chambers. The impeller imparts sufficient velocity to the boiling solution to prevent suspended solids from accumulating on the boiling surfaces and also inhibits scale formation on the boiling surfaces. A portion of the boiling solution is vaporized and flows outwardly from the drum through a blower and into the condensing chambers. 
     The boiler drum and associated plate-in-frame heat exchanger are incorporated in a high efficiency vapor compression distillation system of the type disclosed in the above-noted pending patent application Ser. No. 08/320,235 filed Oct. 11, 1994 now U.S. Pat. No. 5,587,054, which also may include a source of scale inhibiter adapted to be metered into the incoming feed water. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram of a vapor compression distillation system employing the boiler drum device of the present invention; 
     FIG. 2 is a perspective view of the boiler drum employed in the system of FIG. 1; 
     FIG. 3 is a fragmentary, sectional, side elevational view of the boiler drum shown in FIG. 2; 
     FIG. 4 is a view taken along line 4--4 of FIG. 3; and 
     FIG. 5 is a view taken along line 5--5 of FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings and, more particularly to FIG. 1, the device 1 of the present invention comprises a boiler drum 1 containing a volume of a boiling solution 2. A plate-in-frame heat exchanger 3, of the type disclosed in U.S. Pat. No. 5,587,053 is mounted in the boiler drum 1 and is submerged in the boiling solution 2. An impeller 4 driven by a motor 5 is mounted in the lower portion of the boiler drum for circulating the boiling solution 2 through the boiling chambers in the heat exchanger 3. The boiling solution enters the bottom portion of the boiler drum 1 through an inlet 6. 
     The heat exchanger 3 includes a plurality of alternating boiling and condensing chambers, whereby the interior surface of each condensing chamber forms a condensing surface, and the exterior surface of each condensing chamber forms a boiling surface. The condensing chambers are sealed from the boiling solution 2 in the drum 1, but the boiling chambers are open to the boiling solution 2 and provide spaces between adjacent condensing chambers, to thereby provide interpasses for the boiling solution 2 in the drum. By this construction and arrangement, the boiling solution 2 flowing through the interpasses is heated by the boiling surfaces of the condensing chambers. A portion of the boiling solution 2 is vaporized, and the vapor flows through an outlet 7 on the top of the drum 1, through a blower 8 and into an inlet 9 to the condensing chambers of the heat exchanger 3. The condensate flows from the condensing chambers through an outlet 10 to a condensate hot well 11. The concentrate from the boiling chambers flows through an outlet 12 at the bottom of the boiler drum 1 to a concentrate pump 13. From the pump 13, the concentrate is fed to a heat exchanger 14 employed for preheating the inlet feed. Similarly, the condensate from the hot well 11 flows to a condensate pump 15 which pumps the condensate to another heat exchanger 16 which can also be employed for preheating the inlet feed. 
     As an alternate, the concentrate from the pump 13 can be fed to a gas fired wiped film evaporator 17 wherein the vapor therefrom flows through a heat exchanger 18 for preheating the inlet feed. The condensate formed in the heat exchanger 18 can be selectively fed into the inlet feed or to the distilled water outlet. 
     A source of scale inhibitor 19 communicates with the feed inlet line 20 and is fed to the incoming feed line 20 through a metering pump 21. 
     The preheated liquid feed material to be purified enters a gas stripper 22 wherein noncondensable gases are extracted from the top of the stripper 22 by a vacuum pump 23. The degassed feed flows from the bottom of the stripper 22 to a pump 24. The pump 24 pumps the feed to a make up heater 25 from which the heated liquid feed material flows through the inlet 6 to the boiler drum 1. 
     The vacuum pump 23 not only communicates with the stripper 22 but also with the condensate hot well 11, to thereby provide the system with a vacuum, whereby the temperature of the boiling chambers is matched with the temperature of the incoming feed material. The details of the construction of the boiler drum 1 are shown in FIGS. 2 to 5, wherein it will be seen that the drum includes a cylindrical body portion la having a layer of insulation 1a on the outer surface thereof and a depending integral conical portion 1b and a semi eliptical top portion 1c having a circumferential flange 1d adapted to be fastened to a corresponding flange 1e on the top edge of the cylindrical body portion 1a. The plate-in-frame heat exchanger 3 is mounted in the cylindrical body portion 1a and spaced inwardly from the sidewall thereof. The heat exchanger 3 is provided with a tunnel 3a having a depending conical portion 3b terminating in a cylindrical portion 3c. 
     The impeller 4 is positioned in the tunnel 3a between the conical portion 3b and the cylindrical portion 3c. The drive shaft 4a for the impeller 4 extends downwardly through the conical end 1b of the drum 1 and is connected to the motor 5 supported on a platform 5a secured to the conical portion 1b of the drum by suitable hangers 5b. The feed inlet 6 extends through the wall of the conical portion 1b, and the end thereof is turned upwardly as at 6a to direct the incoming liquid feed material into the cylindrical portion 3c of the tunnel 3a. The concentrate outlet 12 and a clean-out fitting 12a are connected to the lower end of the conical portion 1b of the drum. 
     The steam inlet 9 and concentrate outlet 10, communicating with the condensing chambers of the heat exchanger 3, extend through the sidewall of the cylindrical body portion 1a of the drum. 
     The semi eliptical top portion 1c of the drum includes an upwardly-extending dome portion 1f to which the steam outlet 7 is connected. A mesh mist eliminator 1g is mounted in the dome portion 1f, and the semi eliptical portion 1c is also provided with a manway and view port 1h, a fitting 1i adapted to be connected to a liquid level indicator, and a vent fitting 1j. 
     The drum 1 is supported in a vertical standing position by a plurality of tubular or structural steel legs 26 having their upper end portions welded to the cylindrical portion 1a of the drum, the legs being stabilized by cross braces 26a. 
     To explain the operation of the boiler drum 1, it is to be understood by those skilled in the art that the plate-in-frame heat exchanger 3 includes a plurality of alternating boiling and condensing chambers shown diagrammatically in FIG. 3 as at 3d and 3e, whereby the interior surface of each condensing chamber 3e forms a condensing surface, and the exterior surface of each condensing chamber 3e forms a boiling surface for each boiling chamber 3d. The heat exchanger 3 is submerged in a volume of boiling solution 2 as shown in FIG. 1. The condensing chambers 3e are sealed from the boiling solution 2, but the boiling chambers 3d are in free communication with the boiling solution and provide spaces between adjacent condensing chambers 3e to thereby form interpasses for the boiling solution 2 in the drum 1. The impeller 4 circulates the boiling solution 2 through the heat exchanger 3 causing the boiling solution to flow through the interpasses to be heated by the boiling surface of the condensing chambers 3e. A portion of the boiling solution 2 is vaporized, and the vapor flows through the outlet 7 at the top of the drum 1 and into the inlet 9 to the condensing chambers 3e. The condensate from the condensing chambers 3e flows through the condensate outlet 10 while the concentrate from the boiling chambers 3d flow through the concentrate outlet 12. 
     The impeller 4 causes a continuous circulation of the boiling solution 2 upwardly through the tunnel 3a, through the boiling chambers 3a and then downwardly between the space between the heat exchanger 3 and the sidewall of the cylindrical portion 1a of the drum 1. The impeller 4 imparts sufficient velocity to the boiling solution 2 to prevent suspended solids from accumulating on the boiling surfaces and to inhibit scale formation on the boiling surfaces of the condensing chambers, whereby interference with the efficient operation of the heat exchanger is prevented. 
     The drum conical portion 1b, the tunnel 3a, and the impeller 4 are all designed such that the flow velocity along the conical drum walls near the bottom of the cone is very low, thus allowing the suspended solids to settle to the bottom and be removed through concentrate outlet 12. 
     It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, and that various changes in the shape, size, and arrangement of parts may be resorted to, without departing from, the spirit of the invention or scope of the subjoined claims.