US2875992A

US2875992A - Vapor washing apparatus

Info

Publication number: US2875992A
Application number: US541431A
Authority: US
Inventors: Edward A Pirsh; Jr Edwin J Wagner
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1955-10-19
Filing date: 1955-10-19
Publication date: 1959-03-03
Anticipated expiration: 1976-03-03

Description

Filed oct. 19, 1955 INVENToRs Edward A. Pirsh Edwin J. Wagner, Jr.

AT TRNEY.

flow path UnitedStates Patent O 2,875,992 l vAroR WASHING APPARATUS Application ctober 19, 1955, Serial No. 541,431 2 Claims. (Cl. 261-98) This invention relates to apparatus for purifying high pressure steam, and more particularly to washing apparatus for removing silica vapor from the high pressure steam produced in a vapor generator.

It is known that high pressure steam usually contains solid impurities that are either in the vapor state or mechanically entrained in the vapor as minute particles of solids. These impurities pass with the steam from the vapor generator and the impurities are usually subsequently released when the vapor is cooled during subsequent use in, for example, expansion engines. The impurities frequently cause diliculties from deposition in superheater tubes or in other tubular conduits leading to the expansion engine. When the expansion engine is of the turbine type the impurities are deposited on the surfaces of the turbine, resulting in a gradual loss of turbine efficiency and capacity.

' Heretofore mechanical means had been used with success in the removal of the mechanically entrained impurities in the steam. Such means have taken the form ofv cyclone separators, tortuous path separators, and the like. However, when the steam is generated at high pressures, as is common today, the mechanical removal of the entrained solids does not effectively remove the vaporized impurities, such as silica and siliceous compounds, which vare present in the steam delivered by the vapor generator. f

It is known that silica vapors can be removed from high pressure steam by washing the steam with a relatively pure wash water. Apparently the wash water contacting the steam absorbs the silica vapors and the absorbed silica can be removed from the steam with the wash water. The effectiveness of the wash water removal of the impurities is largely dependent upon the intimacy of contact between the steam vand the wash water, and the effective removal of the wash water from the steam after washing contact with the steam. In the present invention,wash water is atomized, i. e.,

" dispersed into droplets, by the action of owing streams of high velocity steam through the wash water. This is accomplished by providing spaced perforated trays in the ow path of the steam moving through a steam and water drum toward the steam outlet thereof. In such devices the eective contact between wash water and the steam can only be attained through a relatively narrow range of steam volumetric ilows throughv the washing device. In accordance with this invention We provide a mass of woven metallic mesh material which ispositioned between the vertically spaced perforated trays. In operation the upper tray is supplied with wash water and serves as a distributing means for the downward llow of wash water through the perforations of the tray. The water moving downwardly through the washing device contacts the mass of woven wire material with the water adhering to the surfaces of the mass so as to afford an extensive surface for contact between the downwardly moving wash water and the upwardly moving steam.

2,875,992 Patented Mar. 3, 1959 ICC The wash water draining from the mass of woven wire cloth deposits upon a lower perforated tray where it is again atomized and contacted by the ascending streams of steam. Theperforated lower tray not only adds to the overall eciency of steam and wash water contact, but also serves as a distributor for the steam entering the washer;

While the eiective operation of the perforated trays, insofar as silica removal is concerned, is limited between a definite dispersion point and a flood point where the upper and lower limits are determined by the steam velocity through the perforations and the amount of wash water used, the mass of wire mesh is not so limited and is capable of creating `silica absorptive conditions between the washwater and the steam through a greatly increased range of steam flow conditions.

`The various features of novelty which characterize our invention are pointed out with particularity in the claimsyanneXed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had `to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a sectional part elevation of a steam and water drum containing the steam washing apparatus of the present invention; and

Fig. 2 is an enlarged perspective view, of a portion of the steam washing apparatus shown in Fig. l.

As shown in the drawings, the steam and water drum 10 of a steam generator is provided with a plurality of riser tubes (not shown) which discharge a mixture of steam and water into the drum. Ordinarily the riser tubes are positioned to discharge into the lower segment of the drum. A steam outlet 11 consisting of a row of tubular connections vis positioned in the upper portion of the drum for the discharge of saturated steam to the customary superheater headers of the vapor generating and superheating unit. The drum 10 is provided with suitable downcomer connections (not shown) at the opposite ends thereof for the downward movement of water into the-circulatory system of the steam generator. In the embodiment of the invention shown the steam and water mixture entering the drum 10 through the riser tubes is passed through a plurality of steam and Water separators 12 with the water discharging from the separators into the water space 13 in the' lower portion of thedrum 10 and the steam passing upwardly from the separators 12 into the steam space in the upper portion of the drum.

The drum 10 is provided with structural members spaced from the inner surface of the drum to provide a chamber 15 which vcollects the steam andwater mixture discharged by the riser tubes for the distribution of the mixture into tangential inlet ducts 16 individually connected to ea^cl of the steam and water separators. The separators 12 disclosed in the drawings are of the cyclone type and are described and claimed, for example, in U. S. Patent 2,368,211. .As shown, the separators'are arranged in rows for parallel flow of steam from the chamber 15 and are each provided withy a corrugated plate scrubber 17 upwardly adjacentthe upper steam outlet 18 from the separator. With the construction dry steam is discharged from the upper outlet portion of the steam separators 12 and is passed in .an upward direction toward the steam outlet 11.

The steam purifying unit 20 of the inventionis disposed within the steam drum downwardly adjacent the steam outlet 11, and is positioned in the steam space 14 of the drum 10. The unit includes depending plates 21 attached at their upper ends .to the drum and forming a closed structure open at its lower end .in communication with thesteam space14 and enclosing the loweri end of lthe outlet 11;

The steam purifier unit is provided with a vpair of l Y horizontally disposed vertically spaced upper and lower perforated

trays

23 and 24, respectively. In `a preferred arrangement of the unit, the trays '23 and 24 are vertically spaced approximately 6" apart for effective use of the device with each of the trays formed of a metallic platewhich is punched or otherwise perforated with a plurality of circular openings which have'an aggregate area of approximately 33 percent of the total area of each tray. The perforations are of the order of 3/16 in diameter and are arranged in a triangular spacing of approximately fyg, center to center ofthe perforations.

In accordance with the present invention a mass 25 of woven wirecloth is inserted inthe space between the upper and lower trays. The wovenfwire cloth is formed from light gage stainless steel wire, of for example .0111 inch diameter, which Vis loosely woven together to vform a mesh-which may be compacted into a mass having a density of approximately l2 pounds per cubic foot. As shown in a preferred embodiment in Figs. l and 2, the mass of wire mesh is approximately 3" in depth and is installed in the intertray space so that the upper edge surface 26 of the mass 25 is approximately l below the upper tray 23 and having its lower surface 27 approxi- Vmately `2 above the upper surface of the lower tray 24.

Means are provided for the delivery of relatively pure wash waterto the upper tray 23. The wash water may originate inthe feed water for the boiler, or may originate 'in a separate supply of distilled water of high purity. The Vwash water .is delivered at a controlled rate through a supply ypipe 28 which is provided with a plurality of branch pipes 30 which terminate upwardly adjacent the upper tray.23` and substantially in vertical alignment with the centerline of thetray. Each of the branchpipes 30 isj-provided with aspray nozzle head 31 which is constructed and arranged to project the wash water downwardly in a multiplicity. ofstreams distributedl across the cross sectional area of the steam purifying unit20. As

.shown in Fig. l, the pipe 28 is extended through a drum inlet nozzle 32,-so as to avoid thermal shock to the wall of the drum 10.

In assembling the washing unit 20 the plates 21 are supported from the drum, and

thetrays

23 and 24 are attached to the plates by 'through bolts 33. The mass of wire mesh material is positioned by ka plurality of stainless ysteel strips 34%" -x 1" in section extending across the unit and attached to angle` members on the plates 21. The stripsare disposed on edge and occupy less than 10% ofthe cross sectional area of the Vunit20. A corrugated plate scrubber 35 is spaced above the tray 23, in the path of steam ow, immediately below the perforated distributor or` dry pan 36 adjacent the steam outlets 11. The corrugated plate scrubber and the dry pipe are utilized to lremove droplets of moisture entrained in the steam ,passing toward the steam outlet 11. The scrubber 35 is directly mounted between vand supported from the plates 21.

In the operation of the steam'purifying unit 20 the the flood point yof the unitsv operation.

wash water'is ysupplied-to the upper tray 23 in/a quantity substantially equivalent to,` for example, l() percent of the total boiler feed water. -T he wash water will gravitate downwardly through the perforations of the tray 23 and will fall upon the mass 25 of woven wire immediately below the tray and will be substantially completely distributed across the entire cross sectional area of the mass 25. The water flowing down through the mass of wire mesh willbe deposited upon the lower tray 24, from which the water passes through the perforations thereof to discharge downwardly under the influence of gravity onto the bale 22 positioned below the steam purifying unit 20. The wash water thereafter joins the water in the water space 13 of the drum and, mingling therewith is conducted through downcomers into the circulatory system of the steam generator.

With the washrwater owing through the steam purifyingunit in a downward directionunder the influence of gravity, the Vsteam passing into the opening between the depending plates 21 and the baille 22 wilLmove up-v wardly toward the-steam outlet 11. The relationshipbetween the total volume of steam passing upwardly through the steam purifying unit and the'total area of the perforations in the tray determines the degree ofmixing between the steam and the wash water. As the volumeof steam increases VVin the rate of its flow through the apparatus the steam velocity through the perforations Vincreases until the velocity of the ascending steam leads to an atomization of the Wash water on lthe trays. This relationship between the velocity of the steam and its effect upon the wash water is known as the dispersion point.

When the dispersion point is reached the wash water is atomized'into a mist of water 'droplets which is in -intimate contact with the ascending streamsV ofsteam. This intimate contact leadsV to an effective exchange between thefwash water and, for example, silica vapor included .in the steam. At the dispersion point the mist of wash water, created by the velocity of the steam passing through the'perforations, will rise within the space .between the tray 24 and the lower surface of the mass 25 Vof woven wire mesh, with the mist separating from the steam, and returning to the tray for reatomizationby the steam.

After the steam has reached a velocitycondition which results in the atomization of the wash water any increase in the steam velocity will increase the agitation of the wash water above the tray until the mass. of finely divided wash water and steam risesto the lower surface of the mass of woven wire mesh. When this condition occurs water will tend to be carried over by the steam into the mass 25 of woven wire. This condition'leads to a loss of eiciency in the separation of the entrained solids and silica vapor from the steam, and is known as The ood point can also'be reached by an increase in the rate of wash water delivery lto the tray 23.

After the -steam vhas Vbeen intimatelymixed with -the wash water, as described, the steam ascends through the mass 25 of woven wire mesh where it is in intimate contact with -the descending wash water. Thereafter the steam ascends through the upper tray 23 where the atomization of the wash-water described on .the lower tray 24 is repeated. Thus, in the lapparatus described the steam is subjected to two stages of intimate contactwith ,wash water by reason of the atomization of the wash water, with an intermediatestage where the steam is in contact with small wash water particles in the mass 25 of wire mesh. It is believed that the' water passed down through the wire mesh tends to follow a path generally along the point of contact between adjacent wires where such wires cross at an angle to each other. 4Due-to the small -size-of the wire used in themass 25 the water particles, or droplets, moving'downwardly through the mass 'islinelydividedand provides yan intimate contact between -substantially the same as in steam in the area immediately above the perforated tray is substantially reduced when the steam ow through the perforations is below the dispersion point, the wire mesh mass 25 maintains the eective contact between wash water and steam through a much wider range of steam ow through the steam purifying unit.

In an actual installation utilizing high pressure steam and boiler feed water, the described steam washing unit was found to be capable of removing significant quantities of silica from the steam over a relatively wide range of steam flow rates. For example, at a steam flow rate of 12,000 to 13,000 pounds of steam per hour per square foot of Washing unit area, and a wash water flow rate of approximately 7.5% of the steam ow rate, the silica removal approximated 82%. At a 6,000 pound per hour per square foot steam ow rate, i. e., at approximately 1/2 steam ow, and av water ow rate of approximately 16% of the steam flow, the silica removal from the steam was approximately 74%. With the mass 25 4of wire mesh material removed from the steam washing unit, and a third perforated tray substituted therefore, the silica removal from the steam approximatedv 72% -at full steam ow rating (with substantially the same steam and wash water flow rates as given in the example), while at l/z steam ow (water ow rates the example) the silica removal approximated 50%. Under both arrangements,

i. e., with and without the insertion of the mass 2.5, thev flood point or upper steam ow rate approximated 14,000 pounds of steam per hour per square foot of unit Z cross-sectional area with a wash water ow rate of 400 pounds per hour.

While the use of a greater thickness of wire mesh material in a unit 20 of the same or similar overall height increased the silica absorption eiiiciency of the steam washer, the ood point or steam washing capacity of the unit was drastically reduced.

While in accordance with the provisions of the patent statutes the applicants have illustrated and described the most eicient embodiment of their invention now known, it will be understood that changes in the relative spacing of the component parts of their steam washing apparatus may be used and some parts may be used alone or in combination without departing from the concept of the invention.

What is claimed is:

1. The combination with a steam and water drum having a steam outlet in theA upper portion thereof and means for introducing a steam and water mixture to said drum, of a steam washer positioned in the upper portion of said drum and interposed in the steam flow path to said outlet comprising horizontally disposed vertically spaced upper and lower perforated trays, a mass of woven wire mesh positioned between said perforated trays and having the upper and lower portions of said mass of woven wire mesh spaced from the adjacent surfaces of said trays, said lower tray being vertically spaced from the lower surface of said mass of woven wire mesh, and means for delivering wash water to the uppermost of said trays for downward ow of wash water through said steam washer countercurrent to the ascending stream of steam.

2. The combination with a steam and water drum having a steam outlet in the upper portion thereof and means for introducing a steam and water mixture to said drum,

y'of a steam washer positioned in the' upper portion of said drum and interposed in the steam ow path to said outlet comprising horizontally disposed vertically spaced upper and lower perforated trays, a mass of woven wire mesh positioned between said perforated trays andhaving the upper and lower portions of said mass of woven wire mesh spaced from the adjacent surfaces of said trays, said lower tray being spaced from the lower surface of said woven wire mesh an amount less than the thickness of the mass of woven wire mesh, and means for delivering wash water to the uppermost of said trays for downward ow of wash water through said steam washer countercurrent to the ascending stream of steam.

References Cited in the tile of this patent UNITED STATES PATENTS 655,727 Murphy Aug. 4, 1900 665,995 Colles Ian. l5, 1901 1,780,255 Wagner Nov. 4, 1930 1,988,262 Burckhalter et al. Ian. 15, 1935 2,490,080 Melvill Dec. 6, 1949 l2,661,075 Brister Dec. 1, 1953 2,712,929 Wilson July 12, 1955 FOREIGN PATENTS 148,811 Great Britain Oct. 10, 1921