HK1060991B - Method and device for the producition of pure steam - Google Patents

Description

Method and device for producing pure steam

Technical Field

The present invention relates to the production of high purity steam for specific purposes. More particularly, the invention relates to the production of pure steam using a falling film evaporator and an upcomer for separating water droplets and impurities.

Background

High purity steam is used for many medical purposes, such as the production of pharmaceuticals, the production of water for injection, and sterilization conditions. A method and apparatus for producing such steam is disclosed in U.S. patent 3,875,017. A falling film evaporator as disclosed therein comprises a vertical bundle of evaporating tubes contained in a heating jacket which is in turn enclosed by an outer shell, so that an annular space is formed between the heating jacket and the outer shell. Water is fed from the upper ends of the evaporating tubes and flows down the inner surfaces of the tubes, thereby evaporating and forming steam, which exits at the lower end of the tube bundle. The steam flow then turns through an angle of 180 ° and flows upwards through the space between the heating sleeve and the outer shell. Fins forming a helical path are attached to the outer surface of the heating sleeve leaving a narrow gap between its edge and the inner surface of the outer shell. The upwardly flowing steam is forced into a spiral path whereby water droplets in the evaporation product are driven towards the outer shell by centrifugal force. The water droplets adhere to the outer housing wall and form a film of water flowing downward and eventually a flow pool at the bottom of the device. Thereby, a water stream proportional to the amount of pure steam produced is discharged as a waste water stream. Since the aqueous phase in the evaporation product tends to be rich in impurities, these aqueous phases are concentrated in the waste water stream. Pure steam is directed from above the spiral path to a consumption point or a condenser to produce high purity water.

A variation of the device is disclosed in us patent 5,983,842. Wherein the evaporation product comes out of the lower end of the tube bundle and is brought into a circular motion by the blocking fins at the bottom of the device; the riser space narrows towards its top. The helical path is arranged at the top of the riser space and is closed, i.e. the fins reach the inner surface of the outer shell. No downwardly flowing waste water phase is formed, but the water droplets are accelerated and collected in an annular channel above the spiral path. A separate pipe returns the produced aqueous phase to the bottom of the device.

Disclosure of Invention

An improved method and apparatus has therefore been invented for enhancing the separation of water droplets and impurities in the rising path of a falling film evaporator to produce high purity steam. It is a further object of the present invention to provide a system for producing and dispensing pure steam comprising the aforementioned improved apparatus.

The apparatus according to the invention is used with a vertical tube bundle with heating jackets, so it is a falling film evaporator of conventional form. The evaporation product comes out of the bottom end of the tube bundle.

According to the invention, said means for separating the water droplets and impurities from the evaporation product comprise a downcomer through which the evaporation product starts to flow, then turns through an angle of 180 ° and enters an ascending channel between the outer surface of said downcomer and the inner surface of an intermediate casing. The down pipe may initially be tapered to form a funnel.

Helical fins in the upper portion of the riser channel set the evaporation product in an upward, helical, circular motion. According to the invention, the intermediate housing is provided with at least one opening or outlet slit allowing water droplets to be carried away by centrifugal force to the periphery of the spiral path. Outside the opening, a cooling surface in the outer casing ensures that condensation of steam takes place.

Steam condensing on the inner surface of the outer shell causes a radially outward flow to carry steam, water droplets and impurities to the inner surface. A water film is formed in the space between the outer and intermediate shells, downstream from the inner surface. A pool of water is formed on the bottom of the device and submerges the lower edge of the intermediate housing. Discharging a controlled flow of waste water from the basin. Pure, dry steam leaves the spiral path and exits the device.

The invention makes it possible to use removable internals in the steam generator, which is easy to manufacture and clean, since the entire plant does not have to employ a proven pressure vessel.

Brief Description of Drawings

The present invention will be described in detail with reference to the accompanying drawings; wherein:

fig. 1 shows a steam generator comprising a falling-film evaporator provided with a separating device according to the invention;

figure 2 shows a detail of a separating apparatus according to the invention;

FIG. 3 is a top view of the device of FIG. 2, an

Fig. 4 shows a system for producing pure steam, which system comprises the device of fig. 2.

Modes for carrying out the invention

Figure 1 shows a shell and tube heat exchanger arranged in a vertical position to form a falling film evaporator. The evaporator tube 1 is enclosed in a jacket 2, and the heating medium is conducted through the evaporator tube 1 via an inlet and outlet opening 4, 5. Make-up water enters the upper end of the evaporator tube through inlet 6. At the lower end of the evaporator, a separating device according to the invention is connected.

The structure of the separation device is shown in fig. 2. The evaporation product enters the downpipe 7. In the embodiment shown in the figures, the upper end of the downpipe is shaped as a funnel in order to keep the outer diameter of the separating device and the outer diameter of the evaporator the same. The evaporation product comes out of the lower end of the downpipe, meets the water surface 8 on the bottom of the device and is turned 180 ° backwards to enter the annular rising channel 9 between the downpipe and the intermediate housing 10. The helical fins 11 form a helical path 12 for the evaporation product.

The spiral motion of the evaporation product generates a centrifugal force that causes the water droplets in the evaporation product to reach the periphery of the path 12. Impurities in the evaporation product may act as nuclei for condensation and this phenomenon may enhance the transport of such substances to the periphery of the spiral path. Pure dry steam leaves the spiral path 12 and leaves the device at the junction 21.

At least one opening 13 is provided in the intermediate housing 10 to allow water droplets to enter the space 16 between the intermediate and outer housings 14. The outer housing 14 is provided with a temperature control sleeve 15. Since this sleeve serves to cool the inner surface of the outer shell 14, the steam in the space 16 condenses on the inner surface and forms a falling film of water. This condensation ensures that there is no backflow through the openings 13 in the spiral path 12. An appropriate shape and number of openings 13 may be provided. Water droplets and impurities driven by centrifugal force to the inner wall of the intermediate shell 10 pass through the openings and the radially outward flow/stream generated by steam condensation is carried to the cooled inner wall of the outer shell 14.

The opening may be designed as a vertical slit on the outer periphery of the spiral path, i.e. the middle housing 10. One or more slits parallel to the helical fins, circular, oval or other shaped openings, and may also be provided with edges to enhance the ability to catch water droplets moving circumferentially along the helical path.

The pool surface formed by condensation and water droplets is held above the lower edge 17 of the intermediate housing 10; the flow of the evaporation product can then only take place along the planned route. Spacing indentations 18 may be provided to center the lower end of the middle housing. A reject stream rich in impurities is discharged at 19. A sight glass 20 may be provided to monitor the water level.

Fig. 3 shows a top view of the device of fig. 2, wherein the device is cut away at the top at the location of the temperature control sleeve. The large arrows represent the circular movement of the evaporation product in the spiral path. The openings 13 are shown with barriers 16 to enhance the trapping of water droplets and impurities carried to the periphery of the path, as indicated by the small arrows.

Preferably, the temperature of the outer shell 14 is controlled to achieve a suitable condensation rate. To conserve energy, make-up water may be used in the sleeve 15. By means of such temperature control, the amount of waste water formed can be controlled according to load and purification requirements.

Figure 4 shows a system for producing pure steam. Make-up water is supplied to a falling-film evaporator 22 by means of a pump 23. The evaporator comprises a separating device 24 according to the invention. Heated steam enters through valve 25 while condensate exits through fitting 26 (tubes not shown). Pure steam leaves the evaporator through line 27 and control valve 28 and enters the distribution network, which includes pure steam line valve 29 and pure steam valve 30. The reject water enriched in impurities leaves the separation unit 24 through line 31. Supply and return lines 32, 33 for the temperature control sleeve are provided.

In the prior art devices, this is problematic due to corrosion and the enclosed structure of the separation device, since the steam path is not easily accessible. The internal structure is integral with the pressure vessel housing and cannot be changed without going through the lengthy procedure involving the construction of the pressure vessel. In the device according to the disclosure, only the outer housing part has to meet the requirements of the pressure vessel. Accordingly, the components and/or details thereof may be made of any desired corrosion resistant material and may be removed for cleaning and inspection. Such materials include fluorocarbon polymers, ceramic materials and specialty steels or other materials that are not necessarily suitable for joining by welding to the pressure vessel shell. The inner components may also be replaced to meet different input and decontamination requirements.

Claims (7)

1. A method for cleaning an evaporation product for the production of pure steam, wherein the evaporation product is subjected to a rotational movement in a spiral path, water droplets are separated by centrifugal force, characterized in that water droplets and impurities carried to the periphery of the spiral path are transported through at least one opening provided on the outer surface of the spiral path, and the water droplets and impurities are collected on an actively cooled surface outside the opening.

2. The method according to claim 1, wherein the evaporation product is produced in a falling film evaporator.

3. Method according to claim 1, characterized in that the temperature of the cooling surface is controlled by means of water used as make-up water.

4. Device for purifying an evaporation product for the production of pure steam, with a pressure vessel shell, an uptake space for the evaporation product and fins in the uptake space for forming a spiral path, characterized in that at least one opening is provided on the outer surface of the spiral path and a temperature-regulating surface is provided outside the opening.

5. The device of claim 4, wherein the opening is a vertical slit.

6. The apparatus of claim 4, wherein at least one of the parts in the pressure vessel shell is removable.

7. The apparatus of claim 4, wherein at least one of the parts in the pressure vessel shell is made of a different corrosion resistant material than the pressure vessel shell.