US3279441A

US3279441A - Apparatus for and a method of cooling superheated steam

Info

Publication number: US3279441A
Application number: US299362A
Authority: US
Inventors: Lippert Walter; Verheyen Georg
Original assignee: Babcock and Wilcox Ltd
Current assignee: Babcock International Ltd
Priority date: 1962-09-14
Filing date: 1963-08-01
Publication date: 1966-10-18
Anticipated expiration: 1983-10-18

Description

Oct. 18, 1966 w P T ET AL 3,279,441

APPARATUS FOR AND A METHOD OF COOLING SUPERHEATED STEAM Filed Aug. 1, 1963 INVENTQRS Walrer Llpperr BY Geor Verheyen ATTQBN United States Pate t 3,279,441 APPARATUS FOR AND A METHGD GI CGQLING SUPERHEATED STEAM Walter Lippert, Munich-Gladbach, and Georg Verheyen,

Gberhansen, Rhineiaud, Germany, assiguors to Babcoclr & Wiicox, Limited, London, England, a corporation of Great Britain Filed Aug. 1, 1963, Ser. No. 299,362 Claims priority, application Germany, Sept. 14, 1962, 1) 39,841 6 Claims. (Cl. 122-459) This invention relates in general to a system for removin superheat from superheated steam and more particularly to apparatus for and method of cooling superheated steam to its saturation temperature by passing the superheated steam into direct contact with the medium that removes the superheat.

The known steam attemperators or coolers in which superheated steam is transformed into saturated steam or steam of low superheat of identical pressure by the injection of water or by bubbling through a water bath have disadvantages which consist in that the water is withdrawn with the cooled steam in the 'form of a steam-water mixture. Therefore, only clean condensate or fully desalted water can be used in order to insure the cleanliness of the cooled steam. Furthermore, the Water has to be fed to the cooler at a pressure higher than the steam pressure. Also, special devices, which are often expensive or complicated, are necessary for control of the supply of injected water or of the level of the water bath. There is also a difference in the masses or weights, respectively, of the steam cooled and to be cooled due to the fact that in this type of steam cooling process the steam to be cooled is mixed directly with the cooling medium, this difference varying in the case of varying superheated steam temperatures.

The above-mentioned disadvantages do not occur, however, when the superheated steam is cooled to saturation temperature by means of a surface condenser or cooler in which the superheated steam comes into indirect contact with the cooling medium. In this case, however, the loss of part of the latent heat of the steam is hardly to be avoided due to condensation. Condensation could be prevented only if the temperature of the cooling medium flowing through the surface condenser were approximately equal to the saturation temperature of the superheated steam. In most cases, however, no cooling medium with the suitable temperature is available. In addition, the surface condenser would necessitate a relatively large heat exchange surface due to the small temperature difference between the cooling medium and saturation temperature of the superheated steam. An expensive control device would be necessary for cooling the superheated steam to saturation temperature without condensation in the event a surface condenser is used with raw Water as a cooling medium having a temperature substantially lower than the saturation temperature. In addition to the temperature impulse of the control device, steam quality would also have to be considered. Also, the sudden heating of the raw water in the surface condenser has to be avoided in order to prevent scale formation therein which otherwise would have to be taken into account.

These disadvantages of prior-art cooling systems can be avoided by means of the invention, according to which superheated steam is cooled to its saturation temperature in a cooler comprising a vessel containing a steam space and a water bath of clean condensate at a temperature corresponding to the saturation temperature of the superheated steam. The superheated steam is bubbled through the water bath so that it gives up its superheat to the condensate, thereby causing evaporation of a part of the "ice condensate. Then the latent heat of the condensate evaporated, having a heat value equal to the superheat of the superheated steam, is removed by a heat exchanger arranged in the saturated steam space of the superheated steam cooler. The exchanger is of the surface condenser type and cooled by any cooling medium, with the condensate derived from heat exchange with the surface condenser being recirculated into the Water bath of the super heated steam cooler.

In this system condensate only serves as an intermediate heat transfer medium Which, in changing its state, absorbs and transmits the superheat of the superheated steam to another cooling medium, which may be raw water or any other suitable fluid. The temperature of the raw water may be any temperature below the saturation temperature of the superheated steam. The intermediate heat transfer medium remains in the superheated steam cooler and thus does not have to be replenished or replaced. The surface type condenser serves not for the direct cooling of the superheated steam but for the removal of the superheat of the superheated steam by condensation of the condensate vapor after the superheat has been transformed into the latent heat of the condensate evaporated, with the condensate thus being returned to its original state and then recirculated to the water bath of the superheated steam cooler.

According to the invention, no control device is necessary for the superheated steam cooler if the superheated steam is to be cooled to its saturation temperature. However, the invention can be applied to cases in which the superheated steam is cooled to a temperature above its saturation temperature. In this case the superheated steam inlet of the cooler is connected with the saturated steam outlet thereof by means of a bypass line controlled by a valve permitting mixing of saturated steam discharging from the cooler with a portion of the superheated steam and regulated in dependence of the temperature of the mixed steam.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed 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 drawing and descriptive matter in which We have illustrated and described a preferred embodiment of the invention.

The drawing represents the embodiment of the invention in a simplified form. The superheated steam cooler comprises a substantially cylindrical upright metallic vessel 10 closed at its upper and lower ends by substantially semielliptical walls or

heads

12 and 14, respectively, and contains a water bath 16 of clean condensate in its lower portion and a saturated steam space 18 in its upper portion, with a saturated steam outlet 20 formed in the head 12 and connected for flow to a conduit 22 and with a drain outlet 24 formed in the head 14. superheated steam is supplied to the cooler by means of a conduit 26 and an inlet pipe 28 extending through the circumferential wall of the vessel 10 in sealing relation therewith at a position above the level of the bath 16, with the pipe 28 being connected for discharge to a distribution pipe 30 having a horizontal portion immersed in bath 16 and formed with a multiplicity of circular outlets 32 along its length.

A surface type condenser 34 is disposed within the vessel 10 and comprises vertically extending multilooped tubular elements 36 provided With a cooling water inlet 38 and a cooling water outlet 40. An upright metallic jacket 42 surrounds and is spaced from the cooling element 36, to form a fluid flow space 43, has its upper end closed by a flange 44, opens at its lower end into the water bath 16 at a position below the horizontal portion of pipe 30 and extends through the head 12 in sealing relation therewith. A saturated steam pipe 46 is disposed within the vessel 10, has its upper discharge end connected to jacket 42 and it lower inlet end immersed in and opening to condensate bath 1'6 and beveled to provide an enlarged steam inlet opening in the event of operation with a relatively low water level, and ha its lower portion formed with vertically spaced rows of circular openings 48, some of which open to the saturated steam space 18 and the remainder of which open to water bath 16.

In operation, the superheated steam to be cooled flows through

conduit

26, 28 and distributor pipe 30 to and through outlet 32, and then bubbles through the water bath 16, the temperature of which is equal to the saturation temperature of the superheated steam. The superheated steam is cooled down to its saturation temperature while bubbling through the water bath, thereby transmitting its superheat to the water bath 16 and causing evaporation of a part of the contents of the water bath, and then passes through the steam space 18 to the outlet 20. The contents of the water bath as well as the steam inlet openings 48 situated above the water level are determined so that saturated steam flows through pipe 46 at a rate corresponding to the rate at which condensate is evaporated from the water bath, if the load is at a constant level. Thus the pressure prevailing in the saturated steam pipe 46 is lower than that in the vessel 10. The condensate evaporated flows through the pipe 46 to the surface condenser 34 and then passes in indirect heat exchange relation with the cooling medium passing through the tubular elements 36 to condense the vapor, with the condensate then returning to the water bath 16 by way of the outlet formed in the lower end of jacket 42. The cooling elements 36 of the surface condenser are proportioned and arranged to satisfy the highest load of the superheated steam cooler. When the load or the superheated steam inlet temperature increases a higher amount of heat is transmitted to the Water bath, the water level decreases due to the higher rate of evaporation of the water bath, the rate of flow of cooling medium through tubular elements 36 is increased by suitable means such as a valve 39, and simultaneously the cooling surfaces of the condenser 34 are loaded more due to the fact that more of the steam inlet Openings 48 of the pipe 46 are above the water level of the bath. Thus the amount of the recirculated condensate increases and a higher amount of heat is removed from the superheated steam cooler by the increased cooling medium flowing through the tubular elements 36 of the surface condenser. The condenser coolant flow is adjusted to remove as much heat as was absorbed by the condensate cooling the superheated steam. In the event the load of the superheated steam cooler increases, the amount of the recirculated condensate increases, the amount of the heat removed from the superheated steam cooler increases, and the rate of flow of cooling medium through tubular elements 36 is increased to balance the quantity of heat absorbed by the cooling fluid with the amount of heat given up in desuperheating the incoming steam. On the other hand, in case of a drop in load, the amount of the recirculated condensate decreases, and the cooling medium flow rate is decreased to reduce the amount of the heat removed and thereby eifect the same balance between heat input and heat removed. Thus the apparatus tends to control itself automatically. In the case of a constant load, the water level of the water bath remains unchanged since the amount of recirculated condensate also remains unchanged.

Steam and water separators well known in the art may be provided inside vessel in order to prevent the superheated steam coolor from priming at its saturated steam exit 20. These separators may be of the cyclone or similar type if arranged immediately upstream of outlet 20, or of the screen type if arranged above the water bath 16.

The water level of the water bath 16 may be indicated by means of a water gauge 49. Water bath to can be filled or drained by means of the drain pipe 24'.

The heat removed by the cooling water flowing through the tubular elements 36 of the surface condenser may be utilized in ways Well known in the art. In addition, the inlet 38 and outlet 4% of the tubular elements 36 of the surface condenser may be connected into the feed-water supply system of the steam generator which supplied the superheated steam to the superheated steam cooler.

Further, in accordance with the invention, if operating conditions require steam of low superheat instead of saturated steam, this can be achieved by mixing a part of the superheated steam passing to the superheated steam cooler with the saturated steam discharging from the cooler. Thus

conduits

22 and 26 are interconnected by a bypass conduit 50. A control valve 52, located in conduit 50 at its junction with conduit 22 and regulated in dependence on the prescribed steam temperature, controls the amount of superheated steam bypassing the superheated steam cooler and flowing to conduit 22. Thus valve 52 is provided with a control element 53 which continuously measures the value of the mixed steam temperature in the conduit 22 and translates any deviation from some preset value of superheated steam temperature into an impulse force change, which is transmitted to valve 52 to modify the flow of superheated steam passing through conduit 56 to conduit 22.

It is self-evident that the invention is not restricted to the embodiment described in the drawing. For example, the superheated steam cooler of the invention would also work if the jacket 42 as well as the saturated steam pipe 45 were omitted and a part of the cooling elements 36 were immersed in the water bath 16 In this case automatic control is achieved by changes in the height of the level of the water bath inundating the major or minor part of the cooling surfaces of the tubular elements 36 of the condenser.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form and mode of operation of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. Apparatus for cooling superheated steam to its saturation temperature comprising means forming a vessel containing a. steam space and a water bath of condensate below said steam space at a temperature substantially corresponding to the saturation temperature of the superheated steam to be cooled; a steam outlet from said steam space; means for flowing superheated steam through and in direct contact with said water bath so that the steam gives up its superheat to the condensate and flows in a saturated condition through said steam space to said outlet, thereby causing evaporation of a part of the condensate; a surface condenser in said steam space; means for passing saturated steam from said bath in indirect heat transfer relation with said condenser and at a rate corresponding to the rate at which condensate is evaporated in said bath so that the saturated steam gives up its latent heat to said surface condenser; said last named means including a conduit having its lower end immersed in and opening to said water bath, its lower portion formed with perforations extending above and below the level of said water bath, and its discharge end arranged to discharge saturated steam in heat transfer relation with said condenser; and means for recirculating the condensate resulting from heat exchange between the saturated steam and condenser to said water bath.

2. Apparatus for cooling superheated steam to its saturation temperature comprising means forming a vessel containing a steam space and a Water bath of condensate below said steam space at a temperature substantially corresponding to the saturation temperature of the superheated steam to be cooled; a steam outlet from said steam space; means including a perforated pipe immersed in said bath for flowing superheated steam through said Water bath so that the steam gives up its superheat to the condensate and flows in a saturated condition through said steam space to said outlet, thereby causing evaporation of a part of the condensate; a surface condenser in said steam space; means for passing saturated steam from said bath in indirect heat transfer relation with said condenser and at a rate corresponding to the rate of which condensate is evaporated in said bath so that the saturated steam gives up its latent heat to said surface condenser, said last named means including a conduit having its lower end immersed in and opening to said water bath, its lower portion formed with perforations, and its discharge end arranged to discharge saturated steam in heat transfer relation with said condenser; and means for recirculating the condensate resulting from heat exchange between the saturated steam and condenser to said water bath, said last named means including a jacket surrounding and spaced from said condenser and forming a fluid flow space arranged to receive the discharge from said conduit and opening at its lower end into said bath.

3. Apparatus for cooling superheated steam comprising means forming a vessel containing a steam space and a Water bath of condensate below said steam space at a temperature substantially corresponding to the saturation temperature of the superheated steam to be cooled; a steam outlet conduit leading from said steam space; means including a superheated steam inlet conduit and perforated pipe immersed in said bath for flowing superheated steam through said water bath so that the steam gives up its superheat to the condensate and flows in a saturated condition through said steam space to said outlet, thereby causing evaporation of a part of the condensate; a surface condenser in said steam space; means for passing saturated steam from said bath in indirect heat transfer relation with said condenser and at a rate corresponding to the rate at which condensate is evaporated in said bath so that the saturated steam gives up its latent heat to said surface condenser, said last named means including a conduit having its lower end immersed in and opening to said Water bath, its lower portion formed with perforations, and its discharge end arranged to discharge saturated steam in heat transfer relation with said condenser; means for recirculating the condensate resulting from heat exchange between the saturated steam and condenser to said water bath, said last named means including a jacket surrounding and spaced from said condenser and forming a fluid flow space arranged to receive the discharge from said conduit and opening at its lower end into said bath; and means for mixing superheated steam with the saturated steam passing through said steam outlet conduit, said last named means including a bypass conduit interconnecting said steam outlet conduit and said superheated steam inlet conduit, and a control valve in said bypass conduit.

4. The method of cooling superheated steam to its saturation temperature which comprises passing a stream of superheated steam through and in direct contact with a water bath of condensate at a temperature corresponding to the saturation temperature of the superheated steam so that the steam gives up its superheat to the condensate, thereby causing evaporation of a part of the condensate, recondensing the condensate so evaporating by passing it in indirect heat transfer relation with a cooling medium, and recirculating the condensate resulting from such transfer to said water bath.

5. The method of cooling superheated steam to its saturation temperature which comprises passing a stream of superheated steam through and in direct contact with a water bath of condensate at a temperature substantially corresponding to the saturation temperature of the superheated steam so that the steam gives up its superheat to the condensate, thereby causing evaporation of a part of the condensate, passing saturated steam from said bath in indirect heat transfer relation with a cooling medium and at a rate corresponding to the rate at which condensate is evaporated in said bath so that the saturated steam gives up its latent heat to said cooling medium, and recirculating the condensate resulting from such transfer to said water bath.

6. The method of cooling superheated steam to its saturation temperature which comprises passing a stream of superheated steam through and in direct contact with a water bath of condensate at a temperature substantially corresponding to the saturation temperature of the superheated steam so that the steam gives up its superheat to the condensate, thereby causing evaporation of a part of the condensate, passing saturated steam from said bath in indirect heat transfer relation with a cooling medium and at a rate corresponding to the rate at which condensate is evaporated in said bath so that the saturated steam gives up its latent heat to said cooling medium, recirculating the condensate resulting from such transfer to said water bath, and increasing the flow rate of the cooling medium as the rate at which condensate is evaporated increases to thereby balance the amount of heat absorbed by the condensate with the amount of heat given up in desuperheating the incoming stream of superheated steam.

References Cited by the Examiner UNITED STATES PATENTS 2,062,397 12/1936 Chandler. 2,428,768 10/1947 Bertram 122459

Claims

4. THE METHOD OF COOLING SUPERHEATED STEAM TO ITS SATURATION TEMPERATURE WHICH COMPRISES PASSING A STREAM OF SUPERHEATED STEAM THROUGH AND IN DIRECT CONTACT WITH A WATER BATH OF CONDENSATE AT A TEMPERATURE CORRESPONDING TO THE SATURATION TEMPERATURE OF THE SUPERHEATED STEAM SO THAT THE STEAM GIVES UP ITS SUPERHEAT TO THE CONDENSATE, THEREBY CAUSING EVAPORTION OF A PART OF THE CONDENSATE, RECONDENSING THE CONDENSATE SO EVAPORATING BY PASSING IT IN INDIRECT HEAT TRANSFER RELATION WITH A COOLING MEDIUM, AND RECIRCULATING THE CONDENSATE RESULTING FROM SUCH TRANSFER TO SAID WATER BATH.