US2240100A - Water tube steam generator and parts thereof - Google Patents

Description

April 29, 1941.

M. SCHMIDT WATER TUBE STEAM GENERATOR AND PARTS THEREOF Original Filed July 17, 1935 as L i/fo e Patented Apr. 29, 1941 WATER- TUBE STEAM GENERATOR AND PARTS THEREOF Martin Schmidt, Kassel-Land, Germany Original application .July 17, 1935, Serial No. 31,895. Divided and this application April 23, Serial No; 203,885. In Germany August 6,

6 Claims.

This invention relates to improvements in water-tube steam boilers and parts thereof.

' This application is a division of my application Serial Number 31,896, filedJuly 1 7, 1935.

Water-tube boilers are known which have steam-generating tubes to which only so much water is fed as can be "evaporated by one passage through the tubes, the steam generated from this water being then withdrawn. Such boilers contain only a small quantity of water in those parts which are subjected to heat. Consequently, they can be heated upzin a short time and have the advantage that they cannot explode. Their efl'lcient operation, however, is dependent to a great extent on reliable and accurate adjustment of the feed water and constant regulation of the source of heat.

If the water feeding apparatus fails, the cooling of those parts of the heated tube surfaces which are normally'cooled by the steam-water mixture and steam flowingthrough the tubes immediately ceases, and there is danger that the tubes will be burned out. 1

Water-tube boilers are also known which, in addition to the quantity of water which is continuously fed into them and converted into steam during a single passage through the tubes, contain a further quantity of water, so that a steamwater mixture is delivered by the steam-generating tubes into the drum, where the separation of the steam from the excess water takes place. The water flows through downcomer tubes to a lower collector, from which the steam-generating tubes extend, and into which feed-water corresponding to the quantity evaporated is fed.

For the establishment of the natural circulation desirable in such a water-tube boiler, the inertia of the comparatively large mass of water on the downcomer side is disadvantageous;

In addition, considerable time is necessary for the generation of steam on heating up, because the water heated at each passage does not immediately return to the steam-generating tubes, but impinges in the first place against the water in the downcomers and loses its kinetic energy, while fresh feed-water follows from the lower water container. On starting up, therefore, a comparatively large quantity of water must be heated to the point of evaporation.

In order to avoid these disadvantages and to improve the natural circulation, according to the present invention, the water in the steam-generating tubes, after the removal of steam therefrom, continues its flow to downcomer tubes by which it is led to the steam-generating tubes, the

two types of tubes thus forming circulating units, through which the circulating water content of the steam-generator is divided into separate or individualcirculations independent of each other.

.An essential advantage of the invention consists in the fact that the velocity of the water flowing from the steam-generating tubes to the downcomer tubes is utilized for the circulation. As the water carried upwards in the steam-gencrating tubes continues to flow past the highest point, no water column can form in the upper part of the steam-generating tubes which would hinder the free outflow of steam. In consequence of the division of the water content of the new water-tube boiler into many small quantities which are present as circulating units, no mass of water of large inertia is present at any point of the boiler. The smaller the resistance to flow in the individual circulation units, the more easily movable arethe small quantities of water.

In consequence only slight pulsations with small reactions can occur, whichdo not disturb the steady circulation, so that an efiicient cooling of the heated steam-generating surfaces is ensured by the water flowing past them. I

;In consequence of the favorable conditions of circulation, the water content, in itself small, of a circulation unit can be altered within wide limits without danger.

With a large water content, the process of evaporation is similar to that in a water-tube boiler with natural circulation. The water content is, however, in relation to the heating surface or to the quantity of water evaporated,-only a, fraction of that in ordinary water-tube boilers. With average water content, which is present in normal working, the evaporating process takes place as in a flash boiler with an excess of feed. The more the water content is decreased, the

moresimilar is the process of evaporation to that circulation in the tubes. Sudden changes in di rection and alterations of cross-section are avoided in order not to dissipate the kinetic energy of the moving steam-water mixture.

In the new boiler, the water cannot take an arbitrary path as" in water-tube boilers with the. additional that a uniform cooling ofzall the tubes is assured.

Since in the new boiler, even under difierent conditions of load and operation, for example,

even with varying quantities of water in the cir-. culation units, the riser parts of the circulation units are well cooled, the heating surfaces can be worked at a high rating.

The new boiler combines the essential ad;

vantages of known flash boilers and water-tube water mixture at the upper end of the evaporating tube is dissipated.

Such a loss of kinetic energy is disadvantageous, for example, if the water, more or less freed from steam, continues to circulate by being led through downcomers back to the evaporating tubes, because on account of the check to the circulation, the massof water 'must be accelerated again.

In contrast to such arrangements, this part of the present invention is characterized by the fact that, over a sufficiently long stretch of the flow-path of the mixture, transfer ducts are proboilers without the disadvantages mentioned above as occurring in boilers of these types.

As contrasted with the flash boiler, the new is ensured and a further latitude in the water content is provided so as to prevent on the one hand undesirable loss of water and on the other hand an unpermissible overheating of the steam in the circulation units.

On account of the lower degree of sensitivcness 3.

of thenew boiler, the feed, a above mentioned, can be to a certain extent accelerated or delayed; in addition, if the feed pump fails, the steamgenerating tubes are not immediately endangered.

It will be seen that in a water-tube boiler according to the present invention, it is necessary to provide efiicient apparatus for separating the steam and Water and a further part of the present invention deals with apparatus which, while suitable for the specific use referred to, is also applicable generally for separating gas and/or vapor from a mixture of gas and/or vapor and liquid flowing through a tube, but for convenience this part of the invention will be described below with reference to a mixture of steam and water except where otherwise indicated.

Hitherto the separation of steam from a mixture of steam and water produced in evaporating tubes, has been commonly effected in a steamand-water drum into which the open ends of the evaporating tubes deliver.

If the discharge of these tubes lies below the surface of the water, the steam generated must then force its way through the superincumbent layer and in consequence must entrain a quantity of water, but even if the evaporating tubes discharge into the steam space of the drum, the steam must still contain a large proportion of water because, inthe mixture ejected, the steam and water are in. a state of relative turbulence and so prevent the desired sudden separation of the steam and water particles.

For such reasons, in order to obtain dry steam, steam separators ordriers have been-constructed which for the separationof the steam and water rely either on the impact principle, or on the action of centrifugal force, or on sudden changes of direction. I

In all these cases, however, the disadvantage is present that the kinetic energy in the steamvided leading to a pipe or container and con- .nected, to the mixture tube, so that over this stretch the gas orvapor can freely separate and pass into the connected pipe or container from the liquid, which continues to flow in the mixture tube.

In consequence of this arrangement, no separator container is interposed in the flow-path of the mixturaand in addition the tube traversed by the mixture doesnot pass through a container.

In contrast to the processes of separation carried out in steam-separating drums and in known steam driers, the separation of steam and water according to this part of the present invention is not brought about through stopping or interrupt- 111g" the flow of water, preferably assisted by the action of impact,- or by sudden changes of direction, but; by providing a sufficiently long stretch of the path of flow, and thereby a sufiicient length of time, so thatthe steam can escape freely from the water, which continues its course unchecked.

The separation of the steam from the moving mixture is effected by connecting a riser tube to a section of tube preferably running either horizontally or with a slight inclination. In this sectionfior example, a lead-off pipe is connected to the mixture tube into which pipe issue holes or openings are provided in the upper wall of the mixture tube. l

Further objects and advantages of the invention willappearmore fully from the following description, particularly when taken in conjunction with the accompanying. drawing which forms a pantthereof. A

In the drawing:

Figure 1 shows a diagrammatic view of a circulation unit according to the invention.

Figure 2 is a cross section, on a larger scale, of the upper part of theunit showing one form of apparatus for separating the steam generatedfrom the circulating water,'

Figure 3 shows diagrammatically one form of a group of circulation units connected in series to forms, coil with'a horizontal axis.

Figure 4 shows .a modification having a plurality of circulating unit's fed from a reservoir.

Figures 5 to 7 show difierent forms of construction of the separating apparatus, partly in elevation and partly in section.

Figure 8-is a cross section onthe line 8 8 of Figure'l. H v I In the circulation units shown in Figures 1 to 4;, theheated riser or steam generating tube is indicated at I, and the unheated or only slightly heated downcomer at 2. In the upper part of theunit, the riser isconnectedto the downcomer by a bend having a large radius of curvature and at. the bottom by a bond with asmaller radius of curvature, sudden changes' of direction being thus avoided throughout .so that a circulation unit is provided with a closed circulating path free from obstruction.

to the intermediate tube 4 which is provided with holes or slits 5 opening thereinto. In addition, a connecting pipe I is provided between the steamoutlet duct 6 and the downcomer 2, so that water condensed or entrained can escape into the downcomer.

By virtue of the bend of large radius, the steam-water mixture in the riser l is transferred without substantial resistance to flow into the more or less horizontal length 4, in which it can continue flowing at a high velocity. In this length of tube 4 a comparatively long path is provided in which steam can separate by passing through the openings 5 into the steam lead-oi! pipe 6.

The length within which the separation o steam from the continuously moving water is completed is indicated in Figure 2 by a.

In this modification, the individual circulatin units, each formed of riser and downcomer parts, are independent from one another so that the circulation of the individual small quantities of water likewise takes place with complete independence in each unit. This construction has the advantage that the circulation is not disturbed by steam-generating processes working under other conditions of circulating and .heating, so that no deflection of the flow of water occurs through suction due to other steamgenerating tubes.

In the form of the invention shown in Figure 3, three circulation units, each comprising a riser and a. downcomer, are connected into a group closed in itself. The first riser l is connected to the next downcomer 2, this downcomer to the second riser, this again to the next downcomer, this downcomer to the third riser and this to the third downcomer, which is connected back to the first riser.

The unit is fed through the pipe 3 into the downcomer 2 which delivers into the first riser I only. On the other hand, steam is withdrawn through a lead-01f pipe 6 provided at the upper part of each individual circulation unit formed of a riser and a downcomer.

The circulation in an individual unit is in this form no longer completely independent of the circulation in the other units, but the advantage is secured that the total circulation is divided into individual circulations and each circulation unit contains only a small mass of water, though variable between wide limits, and that at no point of the boiler can a large mass of water accumulate which by its inertia could check the circulation.

As a modified form, however, each downcomer of a group may be fed, as will be described below.

Figure 4 shows circulating units with a reservoir 8 arranged in the feed pipe, the water level in this reservoir being lower-than the points where the steam is led off and lower also than the uppermost heated sections of the risers l of the circulating units.

From the lower part of the reservoir, feed pipes 9 lead to the downcomers 2 of the circulation units, while steam lead-off pipes 6 deliver steam into the upper part of the reservoir. The feed water which flows into the reservoir after passing through a trickle preheater It, for example, is heated by the steam in the reservoir 8. The feed pipe is indicated at 12, and the steam pipe leading to the place of consumption at l3.

This reservoir is then connected with the circulating units by the water inlet tubes which deliver into the downcomers. The feed is delivered into this reservoir and from it each unit takes the feed water required. In consequence, the water content in the tubes even with irregular feed or load varies less rapidly.

The water content of the boiler is in this way increased without exercising a disturbing influence on the circulating system. Such a reservoir, to which a water-level indicator can be fitted, is advantageously applied to larger boilers with several circulating systems connected in parallel. The water level in the reservoircan, moreover, be subjected to larger variations of level, without endangering the cooling of the in-' dividual units.

It is, therefore, possible with a new boiler provided with this arrangement to withdraw suddenly, in a manner known in itself, larger quantities of steam, without the necessity of immediately adjusting the firing and feed, since even with smaller water content of the circulating units, the upper heated parts of the steamgenerating tubes are still well cooled. On the other hand, thepossibility exists of feeding boilers with reservoirs only from time to time.

Obviously it is not necessary that all the steam pipes of the circulation units should be led to the reservoir. All that is necessary is that a balance of pressure should be established between the reservoir and the circulation units, and for this purpose a connection of any sort between the steam lead-off sections of the circulation unit and the upper part of the reservoir is sufficient.

While one form of separator suitable for use with water-tube boilers in accordance with the present inventionhas been described with reference to Figure 2, many other constructional forms embodying the same principle of maintaining the velocity of flow of the water are possible.

Thus, in the form shown in Figure 5, the length of tube 69 in which the separation of the steam is completed from the moving mixture, is arranged horizontally.

In order to facilitate the separation of the steam, the cross-section of the tube 69 is enlarged as compared with the cross-section of the tubes H1 and H.

The mixture, for example, any heated liquid which contains volatile particles, flows through the tube 10, while the liquid freed from such particles flows through the tube 12 to any point, for further use or treatment.

The volatile constituents separated along the length a in the tube 69 pass through openings 13 in the upper tube wall to a lead-01f pipe M.

The individual openings through which the steam separated from the moving water passes from the mixture tube into the lead-ofi pipe could be replaced by any other suitable arrangement which would provide open space in the tube wall at points spaced along the length of the tube.

In Figure 6, the separation of the steam from the mixture is completed along the length a of a section of tube ll of gradually increasing crosssection connected to the inlet tube 16.

At the end of the length in which separation its direction of flow, passes into the tube 18, and the separated volatile constituents are led off through the pipe 59.

Figures? and 8 show a constructional form in which steam is separated from the water flowing through a tube and passed into a connected container, two mixture tubes connected to a common container 83 being shown in the example illustrated.

As the regions of separation are similarly arranged, it will be sufficient to describe one of them.

The riser tube 84 passes at its upperend into a straight length of tube 85, which is connected through a bend 86 to a downcomer 81. The upper wall of the length of tube 85 enters a slot provided in the wall of the container 83, the connection being made water-tight by a welded seam 88.

In the upper wall of the length of tube 85,

holes or slits 89 are provided which open into the container 83.

The steam separated from the flowing mixture along the length a can pass freely through the slits 89 into the container 83, while the water outside the container continues its course through the tube 85 and the bend 86 to the downcomer 81.

While I have described herein certain forms of my invention, I wish it to be understood that I do not intend to limit myself thereby except within the scope of the appended claims.

I claim:

1. In a water tube steam generator having a circulating system including a plurality of separate steam generating tubes, steam and water separating means included in the top of each tube, and means to introduce feed water into said system below said separating means; said feed water means comprising a steam and 'Water chamber, and water conducting means extending from the lower portion of said chamber to the lower portion of said tubes; said separating means comprising a substantially horizontally disposed section of each of said tubes which forms at least a portion of the top of each tube, and a second. tube engaging the exterior only of said section to provide communication with said section over a sufficiently long distance to permit separation of steam from water, and extending into the upper steam portion of said chamber.

2. In a water tube steam generator, at least one tube looped to form a vaporizer unit, a steam and water separator joined to the unit, and means for feeding water to said unit below said separator; said separator comprising a substantially horizontally extending tubular top portion forming an elongated steam separating surface of a length sufiicient to permit steam to rise and separate from an unidirectional flow of a steam and water mixture in said unit, and a second tube directly communicating with said top portion of said unit outwardly of the flow of the steam and water mixture therein, said second tube having an elongated steam collecting portion contiguous and coextensive with said separating surface and extending from said top portion substantially in the direction of the flow of the steam and water mixture in said top portion, for removing separated steam.

3. In a generator as in claim 2, said top portion of said unit being enlarged over said portion forming said steam separating surface.

4. In a generator as in claim 2, said top portion of said unit being enlarged over said portion forming said steam separating surface, and said second tube being substantially tangentially joined to said top portion.

5. In a generator as in claim 2, said top portion being perforated over said length, and said second tube communicating with said first tube through said perforations.

6. In a generator as in claim 2, said top portion having a plurality of perforations over said length, and said second tube being substantially tangentially joined to said first tube and communicating therewith through said perforations.

MARTIN SCHMIDT.

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