Title of Invention

AN APPARATUS FOR PURIFYING AN EV APORATION PRODUCT TO PRODUCE PURE STEAM AND METHOD THEREOF

Abstract

An evaporation product discharged from a lower end a failing-film evaporator enters a downpipe (7), makes a 180° turn at a bottom of the downpipe, and moves upward through an annular rising channel (9) defined between the downpipe and an intermediate housing (10). As the evaporation product moves along a spiral path (12) defined by the spiral fins, centrifugal forces urges water droplets and impurities to a radial outward periphery where they pass through openings (13) in the intermediate shell as pure steam continues through the spiral path and out a pure steam outlet (21). A cooling jacket (15) chills a peripheral wall of an outer shell (14) adjacent the holes such that the discharged water droplets condense on the outer shell and flow down a reject water return path to a reject water reservoir at the bottom of the outer shell.

Full Text

AN APPARATUS METHOD FOR PURIFYING AN EVAPORATION PRODUCT TO PRODUCE PURE STEAM AND METHOD THEREOF Field of the invention The present invention relates to a method for purifying an evaporation product to produce pure steam. Particularly, the invention relates to the production of pure steam using a falling-film evaporator and rising channels for separating water droplets and impurities. Background of the invention Highly purified steam is required for various medical purposes, such as production of 10 pharmaceuticals, demanding sterilization applications and production of water for injec- tion. A method and device for production of such steam are disclosed in US patent 3,875,017. A falling film evaporator as disclosed therein comprises a vertical bundle of evaporation tubes enclosed into a heating jacket, which in turn is enclosed by an outer shell so that an annular space is formed between the heating jacket and the outer shell. Water fed 15 into the evaporating tubes at their upper end flows down the inner surface of the tubes, thereby evaporating and forming steam, which emerges at the lower ends of the tube bun dle. The flow of steam makes a 180° turn and flows upwards in the space between the heating jacket and the outer shell. Fins forming a spiral path are attached to the outer sur face of the heating jacket, leaving a narrow gap between their edges and the inner surface 20 of the shell. The steam flowing upwards is forced into a spiraling path, whereby water droplets in the evaporation product are driven towards the outer shell by centrifugal force. The droplets adhere to the outer shell wall and form a film of water flowing downwards and finally forming a pool of liquid at the bottom of the device. From there, a stream of water proportional to the amount of pure steam produced is withdrawn as a reject stream. 25 As the water phase in the evaporation product tends to be rich in impurities, these are en- riched into the reject stream. From above the spiral path, pure steam is led to the consumption points or to a condenser for producing highly pure water. A variation of the device is disclosed in US patent 5,983,842. The evaporation product emerging from the lower ends of the tube bundle is brought into a circular motion by baffle 30 fins at the bottom of the device, and the rising space narrows towards the top. The spiral path is arranged into the top of the rising space and it is closed, i.e. the fins reach the inner surface of the outer shell. No downwards-flowing reject phase is formed, but the droplets accelerate and are collected into an annular channel above the spiral path. A separate tube returns the resulting water phase to the bottom of the device. 2 Summary of the invention An improved method and device have been invented for enhancing the separation of water droplets and impurities in the rising channel of a falling film evaporator for production of highly pure steam. A further object of the invention is a system for the production and dis- 5 tribution of pure steam, the system comprising the improved device. The device according to the present invention is used together with a vertical tube bundle with a heating jacket, i.e. a conventional type of falling film evaporator. The evaporation product emerges from the lower end of the tube bundle. According to the invention, the device for separating water droplets and impurities from 10 the evaporation product comprises a length of downpipe through which the evaporation products initially flows before making a 180 ° turn and entering a rising channel between the outer surface of the downpipe and the inner surface of an intermediate shell. The downpipe may be initially tapered, forming a funnel. Spiral fins adapted in the upper part of the rising channel set the evaporation product in an 15 upwardly spiraling, circular motion. According to the present invention, the intermediate shell is provided with at least one opening or outlet slit, allowing droplets carried by cen trifugal force to the periphery of the spiral path to leave.. Outside the openings, a cooled surface in the outer shell ensures, that condensation of steam takes place. Steam condensing on the inner surface of the outer shell causes a radial outward stream 20 carrying steam, water droplets and impurities to the said inner surface. A water film is formed which flows down said surface in the space between the outer and intermediate shells. A pool of water is formed on the bottom of the unit, submerging the lower edge of the intermediate shell. A controlled stream of reject water is withdrawn from the pool. The pure, dry steam leaving the upper end of the spiral path exits the device. 25 The invention enables the use of detachable inner parts in the steam generator, which pro- vides for easy maintenance and cleaning, as the whole of the apparatus need not be pressure vessel certified. Brief description of the/accompanying drawings 30 The invention is disclosed in detail below with reference to the accompanying drawings, wherein Figure 1 shows a steam generator comprising a falling film evaporator provided with a separator unit according to the present invention, Figure 2 shows details of a separator unit according to the present invention, 3 Figure 3 is a top view section of the unit of Fig. 2, and Figure 4 shows a system for the production of pure steam, which system includes the device of Figure 2. 5 Disclosure of the invention Figure 1 shows a shell-and-tube heat exchanger arranged in a vertical position to form a falling film evaporator. Evaporation tubes 1 are enclosed in a jacket 2, through which a heating medium is conducted via in- and outlets 4 and 5. Feed water enters the upper ends of the evaporation tubes through inlet 6. At the lower end of the evaporator, a separating 10 device according to the invention is connected. The construction of the separating device is shown in Figure 2. The evaporation product enters downpipe 7. In the embodiment shown, the upper end of the downpipe is shaped as a funnel in order to maintain the same outer diameter in the separator as in the evaporator. The evaporation product emerges from the lower end of the downpipe, encounters the wa 15 ter surface 8 on the bottom of the device, and turns 180 ° to enter the annular rising channel 9 between the downpipe and intermediate shell 10. Spiral fins 11 form a spiral path 12 for the evaporation product. The spiral movement of the evaporation product causes centrifugal force which force water droplets in the product to the periphery of path 12. Foreign matter present in the evapora- 20 tion product may act as nuclei for condensation, and this phenomenon thus enhances the transport of this matter to the periphery of the spiral path. Pure, dry steam leaves spiral path 12 and exits the device at connection 21. At least one opening 13 is provided the intermediate shell 10 to allow droplets to enter space 16 between the intermediate shell and outer shell 14. Outer shell 14 is provided with 25 a temperature control jacket 15. As this jacket is used to cool the inner surface of shell 14, steam in space 16 condense on said inner surface and form a descending water film. The condensation ensures, that no backflow occurs into spiral path 12 through openings 13. A suitable number of openings 13 of an appropriate shape may be provided. Droplets and impurities driven to the inner wall of shell 10 by centrifugal force pass through the open- 30 ings, and are carried to the cooled inner wall of outer shell 14 by the radial outward stream caused by condensation of steam. The openings may be designed as vertical slits in the outer periphery of the spiral path, i.e. in shell 10. One or more slits running in parallel to the spiral fins is also possible, as well 4 as circular, oval or other shapes of openings, possible arranged with edges enhancing the capture of droplets in circular motion along the spiral path. The surface of the pool of water formed from condensate and droplets is kept above lower edge 17 of intermediate shell 10; thus flow of evaporation product is possible only along 5 the route described. Spacer indents 18 may be provided to center the lower end of the in- termediate shell. A reject flow rich in impurities is withdrawn at 19. A sight glass 20 may be provided to monitor the water level. Figure 3 shows a top view of the unit of Figure 2, with the top cut off at the level of the temperature control jacket. The large arrows indicate the circular movement of the evapo 10 ration product in the spiral path. Openings 13 are shown with baffles 16 to enhance the capture of droplets and impurities carried to the periphery of the path, as shown by the small arrows Preferably, the temperature of outer shell 14 is be controlled to effect a suitable rate of condensation. To conserve energy, feed water can be used in jacket 15: By means of this 15 temperature control, the amount of reject water formed can be controlled according to load and purity requirements. Figure 4 shows a system for the production of pure steam. To a falling film evaporator 22, feed water is provided by means of pump 23. The evaporator comprises a separating unit 24 according to the present invention. Heating steam enters through valve 25, while con- 20 densate leaves by connection 26 (tubing not shown). Pure steam leaves the evaporator via line 27 and control valve 28, and enters the distribution network which includes pure steam line valves 29 and pure steam traps 30. Reject water enriched in impurities leaves separat ing unit 24 through line 31. Feed and return lines 32,33 for the temperature control jacket are provided. 25 In prior art devices, corrosion and the closed structure of the separator units caused prob- lems as the steam paths were not easily accessible The inner structure was integrated with the pressure vessel shell, and could not be altered without going through the tedious proce dure involved with pressure vessel construction. In the disclosed device according to the invention, only the outer shell part must fulfil pressure vessel requirements. Accordingly, 30 the inner parts and/or details thereof can be manufactured from any required, corrosion- proof material, and may be removed for cleaning and inspection. Such materials include fluorocarbon polymers, ceramic materials and special steels or other metals which need not be suited for being joined by welding to the pressure vessel shell. The inner parts may also be exchanged to suit different throughputs and purity requirements. WE CLAIM: 1. An apparatus for purifying an evaporation product to produce purified steam, the apparatus comprising: a falling film evaporator, a downpipe for receiving the evaporation product from the falling-film evaporator; a pressure vessel defined by an outer shell, the outer shell surrounding the downpipe and defining a reject water reservoir in a lower portion thereof, an upper surface of the reject water reservoir being disposed below and spaced from a lower end of the downpipe; an intermediate shell mounted in the pressure vessel outer shell to define a condensate return path therebetween and surrounding the downpipe, a lower end of the intermediate shell being disposed below an upper surface of the reject water in the reject water reservoir; a rising channel including spiral fins mounted between the downpipe and the intermediate shell to define a spiral path for the evaporation product to rise upward therethrough; at least one aperture in the intermediate shell adjacent the spiral fins such that water droplets and contaminants in the evaporation product moving along the spiral path are propelled centrifugally through the aperture; a cooling jacket on the outer shell vertically aligned with the fins and displaced from the intermediate shell for actively cooling a surface of the outer shell to condense water droplets which passed through the at least one aperture. 5 2. The apparatus as claimed in claim 1, wherein at least one of the downpipe, the spiral fins, and the intermediate shell are removable from the pressure vessel. 3. The apparatus as claimed in claim 1, wherein the downpipe, the spiral fins, and the intermediate shell are fabricated of a different material from the pressure vessel. 4. The apparatus as claimed in claim 1, wherein the outer shell defines an inwardly projecting baffle adjacent the aperture to divert droplets and impurities moving along a peripheral edge of the spiral path through the at least one aperture. 5. The apparatus as claimed in claim 1, wherein the falling-film evaporator has an inlet for receiving feed water and an outlet which supplies evaporation product through the downpipe comprising: an interconnection between the cooling jacket and the feed water inlet such that the feed water cools the cooling jacket and is warmed by the condensate prior to entering the falling-film evaporator inlet. 6. The apparatus as claimed in claim 1, comprising a pressure vessel outlet disposed at a lower end thereof for selectively removing the reject water to maintain the upper surface of the reject water reservoir between the lower end of the downpipe and above the lower end of the intermediate shell. 7. A method for purifying an evaporation product to produce purified steam, the method comprising: evaporating water with a falling film evaporator to generate an evaporation product; 6 flowing the evaporation product from the falling film evaporator downward through a downpipe into a pressure vessel; collecting condensed reject water in a lower portion of the pressure vessel below a lower end of the downpipe; flowing the evaporation product from the pressure vessel upward through a rising channel which surrounds the downpipe; with fins in the rising channel, causing the evaporation product to follow a spiral path upward through the rising channel; propelling water droplets and contaminants in the evaporation product flowing along the spiral path centrifugally through at least one aperture defined in an inner shell surrounding the rising channel; actively cooling a surface of an outer shell which surrounds the inner shell at least adjacent the at least one aperture; condensing water droplets which have passed through the inner shell aperture on the cooled surface of the outer shell, the water droplets which have condensed on the cooled surface flowing downward along the cooled surface to the lower portion of the pressure vessel; discharging the evaporation product from the rising channel to produce the purified steam. 8. The method as claimed in claim 7, comprising: actively cooling the cooled surface with feed water; passing the feed water from the cooled surface to an inlet of the falling film evaporator; 7 evaporating the feed water in the falling film evaporator to form the evaporation product 9. The method as claimed in claim 7, comprising: intermittently removing the reject water from the lower portion of the pressure vessel. 8 An evaporation product discharged from a lower end a failing-film evaporator enters a downpipe (7), makes a 180° turn at a bottom of the downpipe, and moves upward through an annular rising channel (9) defined between the downpipe and an intermediate housing (10). As the evaporation product moves along a spiral path (12) defined by the spiral fins, centrifugal forces urges water droplets and impurities to a radial outward periphery where they pass through openings (13) in the intermediate shell as pure steam continues through the spiral path and out a pure steam outlet (21). A cooling jacket (15) chills a peripheral wall of an outer shell (14) adjacent the holes such that the discharged water droplets condense on the outer shell and flow down a reject water return path to a reject water reservoir at the bottom of the outer shell.

Documents:

00306-kolnp-2003-abstract.pdf

00306-kolnp-2003-claims.pdf

00306-kolnp-2003-correspondence.pdf

00306-kolnp-2003-description(complete).pdf

00306-kolnp-2003-drawings.pdf

00306-kolnp-2003-form-1.pdf

00306-kolnp-2003-form-18.pdf

00306-kolnp-2003-form-3.pdf

00306-kolnp-2003-form-5.pdf

00306-kolnp-2003-g.p.a.pdf

00306-kolnp-2003-letters patent.pdf

306-KOLNP-2003-CORRESPONDENCE.pdf

306-KOLNP-2003-FORM 27.pdf

306-KOLNP-2003-FORM-27.pdf