Steam injector

Abstract: A steam injector comprises a casing (2) having a water supply port (5) and a steam intake port (1), the casing being generally composed of two halves fastened integrally, a water nozzle (16) and a steam nozzle both disposed in the casing and communicated with the water supply port and the steam intake port, respectively, a steam-water mixing nozzle (6) disposed on the downstream side in the casing and a diffuser (7) disposed further downstream side in the casing. The steam injector further includes a guide member such as guide vane (20) or spacer ring for guiding the steam to the steam-water mixing nozzle. The steam injector may includes a needle valve disposed in a steam jetting nozzle, disposed axially in the central portion of the casing, which is provided with a hear transfer preventing structure such as hollow wall structure provided on the outer peripheral surface of the steam jetting nozzle. The water nozzle may be composed of a wear resisting material and the wear resisting material may be provided on the surfaces of the steam jetting nozzle and the diffuser.

Description: BACKGROUND OF THE INVENTION The present invention relates to a steam injector for jetting highly pressurized water adapted to a boiler water supply particularly utilized for a water supply system in an emergency core cooling system such as light water reactor. A steam injector is generally utilized for a water supply system in a steam locomotive or a boiler of one type in which a steam is flown in its central region or another type in which a water is flown in its central region. First, with reference to Fig. 9, one type of the steam injector in which the steam is flown in its central region will be described. Namely, a steam injector shown in Fig. 9 has a casing 302 provided with a steam intake port 301, and a steam jetting nozzle 304 provided with a needle valve 303. The front, righthand as viewed, end of the steam jetting nozzle 304 is positioned naer a water suction port 305. A steam-water mixing nozzle 306 and a pressure increasing diffuser 307 are arranged on a downstream side of the steam jetting nozzle 304, which are communicated with a discharge port 309 through a check valve 308. The steam-water mixing nozzle 306 is provided with a throat portion 310 to which an overflow discharge port 312 communicating with an overflow water duct 311 is opened, which is otherwise closed in accordance with an operation. In the steam injector of the structure described above, when the needle valve 303 is drawn out from the steam jetting nozzle 304 by the operation of a handle 313 connected to one end, lefthand end as viewed, of the needle valve 303 and the steam taken into from the steam intake port 301 is hence jetted from the steam jetting nozzle 304, the pressure at the water suction port 305 is made negative by the condensation of the steam to a value below an atmospheric pressure and the water is sucked from a tank or the like. The steam is flown, while being condensed by a low-temperature water (less than 70°C) sucked from the water suction port 305, into the steam-water mixing nozzle 306 and then constitutes a downstream water flow at the throat portion 310. Namely, because an enthalpy η g , of the steam is higher than an enthalpy n l of a saturated water by an amount corresponding to latent heat of evaporation, the latent heat evaporation is converted into a kinetic energy to thereby form a high velocity water flow. When this high velocity water flow passes the diffuser 307, the pressure is increased by an amount of ΔP shown in the following equation in accordance with a hydrodynamic theory. ΔP = (1/2) ρ w U t 2 (ρ w = water density; U t = flow velocity of high velocity water flow passing the throat portion) According to this equation, a discharge pressure higher than the steam supply pressure can be obtained by the steam injector. When the pressure on the outlet side of the diffuser 307 is sufficiently increased, the check valve 308 is automatically opened to thereby jet the pressurized water through the discharge port 309. However, in the steam injector of the structure described above, only the discharge pressure of about 7kg/cm 2 G could be obtained, and such discharge pressure is a value which can merely be utilized for a boiler of a steam locomotive. It is considered that the cause of such limited low pressure increase resides in the fact that the longitudinal, i.e. axial, sectional area of the steam jetting nozzle 304 is made small or narrow towards the front end thereof. Various attempts and studies have been carried out for increasing the discharge pressure utilized for the steam injector for an emergency core cooling system. Fig. 10 also shows a conventional example provided on the basis of these various attempts and studies. The steam injector shown in Fig. 10 has substantially the identical structure to that of Fig. 9, but it is not provided with a needle valve such as that 303 in Fig. 9. Namely, the steam injector has a structure as a diffuser having gradually increased inner diameter towards the downstrem side of the steam to thereby obtain a supersonic steam flow. A second nozzle is further located at the discharge side of the steam-water mixing nozzle 306 and the overflow discharge port 312 is formed on the upstream side of the throat portion 310. According to the steam injector of this structure, it is possible to obtain the discharge pressure of the amount about six or more times of the steam injector shown in Fig. 9. As described above, in the steam injector, the steam is mixed with the low-temperature water to thereby condense the steam, the thus released latent heat of evaporation is converted into the kinetic energy and then into the pressure energy to obtain highly pressurized water. Accordingly, for the operation of the steam injector, it is necessary for the water to be supplied to have a temperature being sufficiently low to the extent capable of condensing the steam, and usually, the water has a temperature lower by about more than 70°C than the steam saturation temperature. For example, when the steam injector is operated in the atmospheric pressure, it is necessary to use the water having a temperature of less than 30°C because of the steam saturation temperature of 100°C. Figs. 11 and 12 further show other examples of the steam injectors of the prior art each in which the water is flown through the central region of the steam injector. Fig. 11 represents a horizontal type one and Fig. 12 represents a vertical type one, but both the steam injectors have basically similar structures to each other. That is, in the steam injector shown in Fig. 12, a water nozzle 316 is incorporated in a body 315 connected to the casing 302 and a needle valve 303 is inserted into the water nozzle 316, wherein the pressure of the steam is increased together with a steam from an adjacent steam suction port by a steam-water mixing nozle 306 disposed on the downstream side of the water nozzle 316. The steam injector shown in Fig. 12 has substantially the same structure as that of Fig. 11 but it is not provided with the needle valve. In a case where the conventional steam injectors are utilized as emergency water supply systems, the operation condition and the pressure are deemed as variable factors in balance to conditions on the water supply side, so that it is necessary for the injector side to reach a rated pressure as soon as possible and to keep a stable operation for a long time. Furthermore, it is desired to control the startup characteristic from the operation free from a complicated control system. Moreover, in the case of the steam injector being utilized as a fluid driving source, it is necessary for the steam injector to keep stable jetting condition. In the conventional structue of the steam injector, there is a case in which the jetting condition of the steam injector reaches the rated power in a certain time interval just after the operation of the steam injector and the jetting prressure lowers as the time passes thereafter. This is considered to be based on the deformation between the steam nozzle and the mixing nozzle due to temperature variation and pressure variation on the periods of the waiting condition and the operating condition. Accordingly, suppression of such deformation will result in the improvement of the operational characteristics. Although the adjustments of the flow rate and the pressure may be treated with the location of the needle valve, the performance of the steam injector is significantly affected by the positional relationship between the steam nozzle and the steam-water mixing nozzle and it is hence necessary to keep this positional relationship most suitable. However, in the conventional steam injectors, the operating temperatures are different from each other at the starting time at a normal temperature and at the operating time at a high temperature. This temperature difference results in the change of the positional relationship, which adversely affects on the originally expected performance. From FR-A-431.245 there is known a steam injector comprising a casing provided with a steam intake port and a water supply port, a steam nozzle disposed inside the casing and communicated with the steam intake port for introducing steam into the casing, the water nozzle disposed inside the casing and communicated with the water supply port for introducing water into the casing, wherein the steam nozzle and the water nozzle are formed by at least two different parts, one being mounted to each other, the steam injector further comprises a steam-water mixing nozzle disposed inside the casing and on a downstream side of the steam nozzle and the water nozzle, a diffuser disposed inside the casing and on a downstream side of the steam-water mixing nozzle, said diffuser being provided with a throat portion, and a discharge port formed on the casing on a downstream side of the diffuser. The different parts of this prior art steam injector are fastened by means of bayonet locking devices to each other. The positional relationship between the steam nozzle and the mixing nozzle has not been severely considered for between them there is positioned one of the bayonet locking devices. Furthermore, these parts can easily be cooled by an outer atmosphere which causes temperature differences resulting to different thermal expansion between the heated steam nozzle and the casing to which this nozzle and the mixing nozzle are fixed. A typical steam pressure used in the mentioned prior art steam injector is 0,7 MPa. Modern steam injectors, especially when they are used for the water supply device of emergency cooling systems of a power plant, are working with steam pressures as high as 7 MPa. It is an object of the present invention to provide a steam injector with an improved operating stability and safety. This object is achieved by a steam injector according to the appended main claim. Appended subclaims 2 to 8 are directed towards advantageous embodiments of the steam injector according to the main claim. The water nozzle and the steam-water mixing nozzle are unitarily assembled, so that the relative positional relationships among the steam flow-in portion, the water flow-in portion and the steam-water mixing portion can be accurately set in accordance with the desired design. Furthermore, the positional relationships can be substantially constantly maintained without being influenced with the operation change or temperature change. Particularly, with respect to the water nozzle, since one end thereof is formed as a free end, a free extension may be allowed, and in such a case, the separation of the water from the steam can be performed by the location of the seal ring. The guide means such as guide vane is formed so as to have a streamline shape, so that the pressure loss at this portion can be reduced. The mixing degree of the water and the steam can be facilitated by forming the guide vane in a reverse streamline shape. The further natures and features of the present invention will be more clarified by the following descriptions made with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 shows an elevational section of a first embodiment of a steam injector according to the present invention; Fig. 2 is an elevational section of an inner main portion, in an enlarged scale, of a casing of the steam injector of Fig. 1; Fig. 3 is a sectional view taken along the line III-III of Fig. 2; Fig. 4 is a sectional view taken along the line IV-IV of Fig. 2; Fig. 5 is an elevational section similar to that of Fig 2, but is related to a second embodiment according to the present invention; Fig. 6 is a perspective view of a spacer ring disposed in the steam injector of Fig. 5; Fig. 7 is a longitudinal section of a third embodiment of a steam injector according to the present invention; Fig. 8 is a longitudinal section of an inner main portion, in an enlarged scale, of a casing of the steam injector of Fig. 7; Figs. 9 to 12 are elevational and longitudinal sectional views of steam injectors according to the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first preferred embodiment of the present invention will be described hereunder with reference to Figs. 1 to 4, in which detailed explanations or descriptions of the elements or members corresponding to those shown in Figs. 25 to 28 are omitted herein. Further, in theses Figs. 1 to 4, solid arrows denote the steam flow directions and dotted arrows denote the water flow directions. The steam injector of the first embodiment relates to a type corresponding to the steam injector of Fig. 28, in which a water nozzle is arranged at substantially the central portion of the steam injector. Referring to Fig. 1, a steam intake port 1 is formed to a body 15 connected to a casing 2 and a water nozzle 16 is incorporated in the body 15 at substantially the central portion thereof. The body 15 is constructed as a portion of the casing 2 and connected thereto by means of bolt and nut assembly. A water suction port 5 or passage is formed to the inner central portion of the casing 2 so as to penetrate therethrough to thereby communicate with the water nozzle 16. In an illustrated vertical state, a diffuser 7 is welded to the lower surface portion of the body 15. A steam-water mixing nozzle 6 is formed to the diffuser 7 at an upstream side thereof and a discharge port 9 is also formed at a downstream side of the diffuser 7. As shown in Fig. 2 as an enlarged view, sealing performance of the water nozzle with respect to the body 15 is kept by a seal ring 17, which is fastened to the body 15 by means of bolts 19 through a press plate 18. A guide vane 20 is interposed along a circumferential direction between the front end, i.e. downstream end, of the water nozzle 16 and an inlet port of the steam-water mixing nozzle 6. In the first embodiment of the structure described above, the water nozzle 16 is connected to the steam-water mixing nozzle 6 and coupled thereto through a plurality of guide vanes 20 to thereby integrate the water nozzle 6, the guide vanes 20 and the steam-water mixing nozzle 16. It is desired to effect surface treatment to the surfaces of these structural elements to reduce the surface roughness. The seal ring 17 disposed at substantially the central portion of the body 15 attains a function for separating the water flown from the water nozzle 16 from the steam from the steam intake port 1. As shown in Fig. 2 or Fig. 4A, it is desired for the guide vane 20 to have a streamline shape to make smooth the flow or to have a reversed streamline shape as shown in Fig. 4B. On the contrary, the shape of the guide vane 20 may be formed to the shape reverse to the above for facilitating the mixing degree of the steam and water in the steam-water mixing area. According to this first embodiment, the relative position between the water nozzle 16, the steam intake port 1 and the steam-water mixing nozzle 6 is fixed irrespective of specified conditions to achieve the stable performance of the steam injector. Furthermore, the reduction of the pressure loss can result in the improvement of the performance of the steam injector, and the mixing efficiency can be also improved by intentionally causing the turbulent flow of the steam. A second embodiment of the steam injector according to the present invention will be described hereunder with reference to Figs. 5 and 6, in which like reference numerals are added to portions or elements corresponding to those in the first embodiment. One main difference of the second embodiment from the first embodiment resides in the location of a spacer ring 21 in place of the guide vanes 20. An outer appearance is shown in Fig. 6 as a perspective view. As shown in Fig. 6, the spacer ring 21 has a frustconical body having an upper, as viewed, portion having a diameter smaller than that of the lower portion and has an inclined or tapered side surface to which a plurality of flow passages 24 are formed. Reference numeral 25 denotes an inner surface of the body of the spacer ring 21 formed as an abutting surface against the water nozzle 16 and reference numeral 26 denotes an outer surface of the body formed as an abutting surface against the steam-water mixing nozzle 6. The spacer ring 21 of the structure described is fitted, at its water nozzle side, into a side groove 22 formed to an outer periphery of the front portion of the water nozzle 16 and fitted, at its steam-water mixing nozzle side, into a side groove 23 formed to an upper surface of the steam-water mixing nozzle 6, and then fixed to these groove portions by welding means, for example. According to the second embodiment, the water nozzle or the steam jetting nozzle 4 and the steam-water mixing nozzle 6 can be separately manufactured and these structures can be thereafter connected through the spacer ring 21 to constantly maintain the flow passage, and furthermore, the manufacturing of such spacer ring 21 can be optionally made in accordance with the design conditions or requirement. A third embodiment of the steam injector according to the present invention will be described hereunder with reference to Figs. 7 and 8, in which the steam injector is incorporated with a needle valve 3 for adjusting the flow rate and other structure is similar to that of the first embodiment. In this third embodiment, the steam jetting nozzle 4 is fastened to the body 15 by means of bolts 19 through a press plate 18 and the seal ring 17 is interposed between the press plate 18 and the seal ring 17. The steam pressure can be adjusted by displacing the needle valve 3 in the steam jetting nozzle 4 to change its flow diameter. The needle valve 3 is moved by the operation of a handle 13 in the steam jetting nozzle 4 along a guide member 27 attached to the inside of the casing 2 by means of bolts 28. According to this third embodiment, stable performance of the steam injector can be attained and the reduction of the pressure loss results in the improvement of the performance of the steam injector. Furthermore, the mixing efficiency can be also improved by intentionally causing the turbulent flow of the steam. It is to be noted that the present invention is not delimited to the described preferred embodiments and many other changes or modifications may be made without departing from the scope of the present invention.

Claims: A steam injector comprising: a casing (2) provided with a steam intake port (1) and a water supply port (5), a steam nozzle disposed inside the casing and communicated with the steam intake port for introducing steam into the casing, a water nozzle (16) disposed inside the casing and communicated with the water supply port for introducing water into the casing, wherein the steam nozzle and the water nozzle are formed by at least two different parts, one being mounted to the other; a steam-water mixing nozzle (6) disposed inside the casing and on a downstream side of the steam nozzle and the water nozzle; a diffuser (7) disposed inside the casing and on a downstream side of the steam-water mixing nozzle, said diffuser being provided with a throat portion; and a discharge port formed to the casing on a downstream side of the diffuser, characterized in that a plurality of guide vanes (20) disposed in the casing along a circumferential direction of the steam-water nozzle (6) are provided as a guide means for unitarily combining the steam nozzle, the water nozzle (16) and the steam-water mixing nozzle (6) to keep constant relative positional relationships among these nozzles. A steam injector according to claim 1, characterized in that each of said guide vanes (20) has a streamline structure with respect to a flow direction of a steam-water mixture. A steam injector according to claim 1, characterized in that each of said guide vanes (20) has a counter-streamline structure with respect to a flow direction of a steam-water mixture. A steam injector according to claim 1, characterized in that said guide means comprises a spacer ring (21) disposed along circumferential directions of the water nozzle (16) and the steam-water mixing nozzle (6) and provided with a plurality of flow passages (24). A steam injector according to claim 4, characterized in that said water nozzle (16) and said steam-water mixing nozzle (6) are provided with side grooves (22, 23) formed to outer peripheral portions thereof and said spacer ring (21) is fitted into the side grooves. A steam injector according to claim 4, characterized in that said spacer ring (21) has a frustconical structure having an upstream side end having a diameter smaller than that of a downstream side end. A steam injector according to claim 1, further comprising a seal ring means (17) disposed between the water nozzle (16) and the casing (2). A steam injector according to claim 1, characterized in that a steam jetting nozzle (4) is disposed inside the casing so as to axially extend therein and have a front end facing the steam-water mixing nozzle (6) and a needle valve (3) disposed in said steam jetting nozzle to be axially movable therein.

Inventors: MIYANO HIROSHI, NARABAYASHI TADASHI, TAKAHASHI HIDEAKI, TANAKA NOBUHIKO, YAMADA KATSUMI, YASUDA MAKOTO, MIYANO, HIROSHI, NARABAYASHI, TADASHI, TAKAHASHI, HIDEAKI, TANAKA, NOBUHIKO, YAMADA, KATSUMI, YASUDA, MAKOTO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1992
Main classification: F04F5
IPC codes: F04F5