Cyclone steam/water separator

Abstract: A conical cyclone separator (20) to separate steam from water in a steam/water mixture supplied to a steam drum of a boiler, comprises a conical portion (21) with upper (30) and lower (22) cylindrical portions. Unlike conventional separators which include a tangential inlet (26) extending for only the axial length of the conical portion (21) of the separator (20) a separator of the invention has an inlet (26) which extends by approximately 20% of its length over the lower cylindrical portion (22) of the housing and is thus vertically elongate compared with the inlet of a conventional separator.

Description: The invention relates to a cyclone separator to separate steam from water, in a steam/water mixture. Patent specification US-A-2 271 634 to Fletcher discloses a cylindrical cyclone separator having a circular whirl chamber, a tangential inlet, a central steam outlet located at the top of the circular whirl chamber, and a water outlet located at the bottom of the whirl chamber. To prevent water from being discharged through the steam outlet, means are provided for increasing the downward component of the incoming stream of steam and water mixture. This means is a segmented plate having downwardly and rearwardly inclined edges that cause the incoming steam and water mixture to be deflected downwardly towards the water outlet of the separator. Patent specification US-A-2 293 740 to Kooistra discloses a similarly designed cyclone separator that does not utilize the segmented plate but rather employs a bottom cup at the bottom of the whirl chamber which confines the steam to the upper portion of the whirl chamber and prevents it from passing down into the separated water as it discharges from the whirl chamber into the drum. Patent specification US-A-2 321 628 to Rowand, et al. discloses a cyclone separator which is closer in configuration to the present standard shown in Figure 1 of the present application. The circulator whirl chamber in this reference is the frustum of a cone at the upper portion and substantially cylindrical at the lower portion where the water is discharged. Again, a tangential inlet is employed to deliver the steam water mixture into the cyclone separator, and is of a vertical extent substantially equal to that of the tapered portion of the whirl chamber. The tapered configuration acts to direct the entering steam water mixture into a slightly downward direction to prevent upward spread of the deflected water and enhance separation of the steam therefrom. US Patent specification US-A-2 346 672 to Fletcher discloses a substantially cylindrical cyclone separator this time having, instead of a tangential inlet, a large steam/water inlet which extends over a large fraction of the perimeter of the cyclone separator. As indicated in the reference, the inlet can extend to approximately one third of the perimeter of the cyclone separator to provide adequate flow capacities. One object is to produce a separator or densifier which operates effectively with low pressure drop so that it can be advantageously used where only a small pressure head is available. Patent specification US-A-2 395 855 to Fletcher discloses a substantially cylindrical cyclone separator having a tangential inlet and where the steam outlet centre is located eccentric of the whirl chamber centre to effect enhanced separation of steam from the water. This design also employs the segmented plate seen in the previously described patents. Patent specification US-A-2 402 154 to Fletcher and the aforementioned US-A-2 395 855 are both divisionals of the same application. US-A-2 395 855 is drawn to the particular type of fluid separator itself; while US-A-2 402 154 is drawn to the combination of this device in a steam generator. Patent specification US-A-2 434 637 to Brister, Patent specification US-A-2 434 663 to Letvin and Patent specification US-A-2 434 677 to Stillman are all drawn to various aspects of the perforated cone used at the top of the cyclone separator to enhance separation of the steam from the water. Patent specification US-A-2 532 332 to Rowand is drawn to the particular construction of the separators which today are generally considered are secondary scrubbers. Patent specification US-A-2 732 028 to Coulter is also drawn to a cyclone separator device very similar to that employed at this time. The cyclone separator has the aforementioned frustoconical upper section and generally cylindrical lower section with a tangential steam water inlet located on the side of the frustoconical section. The overall emphasis of this reference is drawn to means of simplifying the construction for accessability and repair of the elements located in the steam drum. This is accomplished by dividing the steam space in the drum into separate compartments, one or more of which are open to the water space of the drum into the necessary drum safety valves while one or more of the other compartments are open to the steam and water separators of the drum the saturated steam outlets. Partitions are used to accomplish this division and they are effective in maintaining the separation of the drum components during normal operation but are easily broken when the safety valves are opened. Patent specification US-A-2 891 632 to Coulter is drawn to a cyclone steam separator quite similar to that disclosed in the earlier mentioned Fletcher specification US-A-2 346 672 with the exception that instead of the steam water inlet being located only approximately along one third of the circumference of the separator, this cyclone separator has the entire circumference provided with an array of vanes that "slice" the incoming steam water mixture into thin sheets to enhance separation of the steam from the water. Figure 1 of the accompanying drawings is a side view of a conventional cyclone separator which is in current use by the Applicants of this application. Such a conventional cyclone separator, generally designated 4, comprises a conical portion 8 to which a vertically elongate tangentially connected steam/water inlet 6 is connected. The inlet 6 corresponds in axial length to the axial length of the conical portion 8. The cyclone separator 4 includes an upper cylindrical steam outlet 10 which, in use, is surrounded by a cap with a perforated cover (not shown). A lower cylindrical water outlet 12 having a water outlet ring 14, is connected to the bottom of conical portion 8 to discharge water which has been separated from the steam/water mixture. According to the invention there is provided a cyclone separator to separate steam from water in a steam/water mixture, comprising: a separator housing having a conical portion with an axial length, an upper edge and a lower edge, an upper cylindrical steam outlet portion connected to the upper edge of the conical portion and having a central opening to discharge steam from the housing, a lower cylindrical water outlet portion having a bottom water outlet ring to discharge water from the housing and an axially elongate steam/water mixture inlet connected tangentially to the housing, the inlet having a width to height ratio of 1:6.5 and an axial length amounting to 60% of the axial length of the housing, and extending the full axial length of the conical portion; characterised in that 20% of the axial length of the inlet extends over the lower cylindrical portion of the housing. Thus the invention can provide a modified conical cyclone separator for applications that require a lower pressure drop than a standard conical cyclone would give, for an equivalent number of or an equivalent steam capacity of the separators. The new conical cyclone gives increased capacity for both steam and water, lower pressure drop and is unaffected by water level fluctuations. Such a low pressure drop conical cyclone separator is a modified version of a standard conical cyclone separator. The major difference in the two separators is that the new cyclone separator's tangential inlet has been lengthened by about 76.2mm (3 inches). This increase in length increases the cyclone inlet flow area by 28%. The lengthening of the tangential inlet, extends the inlet into the lower cylindrical portion of the cyclone separator. In the conventional cyclone separator of Figure 1, the axial length of the conical portion of the separator, and also the coextensive axial length of the inlet, amounts to approximately one half of the total height of the separator. In a separator of the invention, the axial length of the inlet may amount to approximately 60% of the total height of the separator with approximately 20% of this height extending into the cylindrical portion of the separator. This modification has been found substantially to decrease the pressure drop of the separator without adversely affecting the capacity of the separator. Figure 1 is a vertical sectional view of a conventional conical cyclone separator; Figure 2 is a view similar to Figure 1 of a cyclone separator according to the invention. Figure 3 is a horizontal sectional view of the separator of Figure 2; Figure 4 is a graph showing moisture carryover versus steam flow for both a conventional cyclone separator and a cyclone separator according to the invention; Figure 5 is a graph showing conical cyclone pressure drop versus steam flow for both a conventional cyclone separator and a cyclone separator according to the invention; and Figure 6 is a graph showing moisture carryover versus water level for both a standard cyclone separator and a cyclone separator according to the invention. Referring to the drawings and in particular, to Figures 2 and 3, a conical cyclone separator generally designated 20 is mounted within a steam drum (not shown). The purpose of the cyclone separator 20 is to improve the efficiency of separation between steam and water in a steam/water mixture, by swirling the mixture at high velocity around the interior of the separator. The greater mass of the water causes it to move to the outside of the swirling stream leaving a concentration of steam which is discharged through an upper cylindrical outlet 30. From the outlet 30, the steam is further separated and treated by conventional scrubbers and other equipment (not shown). The water which has been removed from the mixture is discharged through a lower cylindrical portion 22 and a ring shaped water outlet 24 at the bottom of the separator. The separator includes a main conical portion 21. An axially elongate tangentially connected steam/water inlet 26 is connected to the separator. As best shown in Fig. 3, the tangential opening between the inlet 26 and the interior of the separator 20, amounts to approximately one third of the circumference of the separator. As with the separator illustrated in Fig. 1, the separator of Figs. 2 and 3 has a maximum inside diameter of approximately 292mm (11.5 inches) with the inlet 26 having a width, in horizontal section, 52.4mm, (2.063 inches) between a tangential outer wall 28 and an inner edge 32 of an inner wall 34. The width to height ratio for the inlet 26 is thus approximately 1:6.5. In the conventional separator of Fig. 1, this ratio is approximately 1:5. Extensive tests have been conducted to compare the performance of the conical cyclone separator of Figs 2 and 3, with the performance of the conventional separator of Fig. 1. In Figs. 4, 5 and 6, the performance of a low pressure drop cyclone separator is compared with a standard cyclone separator. As shown in Fig. 4, the steam flow capacity for the separators is the same. In Fig. 5, depending upon flow and pressure conditions, the reduction in pressure drop can range between 25% and 40%. The water level sensitivity results of Fig. 6, show that the low pressure drop cyclone separator did not have a significant impact on water level sensitivity of the arrangement. Based upon the data shown in Figs. 4-6, performance of a low pressure conical cyclone separator as shown in Figures 2 and 3 has been formulated as follows: (1) steam capacity is the same as a standard 292mm (11.5 inch) ID conical cyclone separator, and (2) the pressure drop is 30% less than a standard 292mm (11.5 inch) ID conical cyclone separator. A relatively simple modification can thus yield substantially improved results in an unexpected manner.

Claims: A cyclone separator (20) to separate steam from water in a steam/water mixture, comprising: a separator housing having a conical portion (21) with an axial length, an upper edge and a lower edge, an upper cylindrical steam outlet portion (30) connected to the upper edge of the conical portion (21) and having a central opening to discharge steam from the housing, a lower cylindrical water outlet portion (22) having a bottom water outlet ring (24) to discharge water from the housing and an axially elongate steam/water mixture inlet (26) connected tangentially to the housing, the inlet (26) having a width to height ratio of 1:6.5 and an axial length amounting to 60% of the axial length of the housing, and extending the full axial length of the conical portion (21); characterised in that 20% of the axial length of the inlet extends over the lower cylindrical portion (22) of the housing. A cyclone separator according to claim 1, wherein the housing has a maximum inside diameter of 292mm (11.5 inches) and the inlet (26) extends by 76.2mm (3 inches) over the cylindrical portion (22) of the housing. A cyclone separator according to claim 2, wherein the inlet (26) includes an outer tangential wall (28) and an inner wall (34) having an inner edge (32), the inlet (26) having a width between the outer wall (28) and the inner edge (32) of 52.4mm (2.063 inches).

Inventors: ALBRECHT MELVIN JOHN, ALBRECHT, MELVIN JOHN
Applicants: BABCOCK & WILCOX CO, THE BABCOCK & WILCOX COMPANY
Application year: 1990
Main classification: F22B37
IPC codes: B04C5, B01D19, F22B37