US2403017A - Steam generator - Google Patents

Description

K. F. NQRDLUND STEAM GENERATOR July 2, 946.

Filed March 22, 1941 5 Sheets-Sheet! 1 KARL FOLKE NORDLUND \NVENTOR M AHQ,

K. F. NORDLUND STEAM GENERATOR Filed March 22; 194i 5 Sheets-She t g \NVE NTOE,

KARL FOLKE NoraoLpNo July 2, 1945 K. F. NORDLUND 2,403,017

STEAM GENERATOR Filed March 22, 1941 5 Sheets-Sheet 3 Trr: E

INVE NTDR '-KAR.L FoLK; NDRDLVND July 2, 1946. K, F, RD UN 2,403,017

STEAM GENERATOR Filed March 22, 1941 5 Sheets-Sheet 4 KARL Fame NORLUND \NVENTO R Y 1946. K; F. Nokmuun f f 2,403,017

STEAM GENERATOR Filed March 22, 1941 5 Sheets-Sheet 5 Trlzilllu I A n u I u 2 INVENTOR KARL} FoLKE NORDLUN 0 Patented July 2, 1946 STEAM GENERATOR Karl Folke Nordlund, Ostertalje, Sweden Application March 22, 1941, Serial No. 384,711 In Sweden March 11, 1940 Claims.

My invention relates to the type of modern steam generators offering a high efiiciency, a small space and low costs by using repeatedly bent tube coils as steam generating tubes, the inside diameter of said tubes being generally very small, lying between and 40 mm. In contradistinction'to the steam generators of such kind as are now most used and in which the water is made to fiow through the tube coils by forced circulation, my invention is based on the use of simple known means for obtaining a natural circulation in the tube coils, special steps having been taken to rationally utilize the possibilities of reducing the space, specially the height, required by the steam generator and to generally adapt its construction to available spaces of any form and to simultaneously design the tube coils in such a way as to insure a safe operation in each special case. By this, all pump means to obtain forced circulation are dispensed with and the safe operation is independent of the function and attendance of said means. Choking means of various kinds, which in forced circulation are used to control the distribution of water to the tubes and which, as well as the screens which are used to protect said choking means, very often cause interruptions of the service due to said means being stopped up by impurities, are likewise dispensed with.

A condition of the invention is that the lengths of the tube coils can be dimensioned in such a way that the natural circulation is suflicient to cool the coils during operation which is possible as has been ascertained by researches made. But such steps require that the said length can be suitably varied, and these steps will be described in the following. The friction resistance in a tube coil, the various parts of which are subjected to a constant heat supply per unit of length, has proved to be proportional to the cube of the length if the ratio between the water quantity flowing into the coil and the steam quantity generated, the so-called circulation coefficient, also is assumed to be constant. Approximate comparisons between the lengths of the tube coils in natural circulation and in forced circulation can be made starting from the following statements. The pressure available to overcome the friction resistance may be assumed to be for example 1000 kg./m. in the former case, and it emanates, of course, from the difference inweight between the water in the descent tubes and the steam in the steam tubes. In the latter case it may be assumed to be 1 kg./cm. =10.000 ka/mE, thus 10 times as great, and it is gener- 2 ated in a pump. However, according to the abovementioned law the ratio between the tube lengths is only. Thus, whereas the lengths of the tube coils generally are 20 to 30 m. in forced circulation they may be 10 to 15 m. in natural circulation if heat transmission, inside diameter and circulation coefficient are the same at the comparison. .As a matter of fact, additional costs are incurred due to the increase of the number of beading points, but these costs are very small in comparison with the annual costs for the additional power consumption in the circulation pumps in forced circulation and other drawbacks connected therewith.

The tube coils intended for steam generation extend from one or more inlet headers which by means of separate, usually heat-insulated descent tubes are directly connected with the Water space of a higher situated steam separator so that the water flows on to the coils under self-pressure. The coils may end in one or more outlet headers which by means of separate, usually heat-insulated ascent tubes are connected with the steam separator, generally the steam space thereof. A few, often one or two descent tubes only are used for each inlet header, and the same applies to the number of ascent tubes for each outlet header. However, the coils may also end directly in the steam separator.

The use ofa' small number of descent tubes and ascent tubes is possible thereby that the circulating water quantity, and thus also the circulation coefficient, is held at a low value. It is, therefore, of great importance that the circulation coefiicients be as equal as possible in the various parallel connected steam generating tubes, since in each case the lowest occurring circulation coefficient must be sufiiciently great in order that the corresponding tube shall be cooled satisfactorily during operation. Consequently, the invention also includes means by which it is possible to use parallel connected tubes of approximately the same length and to supply approximately the same amount of heat to the tubes whereby in the simplest way the circulation coefficients are caused to assume the same or similar value. a risk that the flow in the tubes does not absolutely obtain a constant direction, or that the steam flows in one direction and the water In certain cases there isv 3 another direction. In both these cases there may be dangerous stagnations of steam which in serious cases might lead to the tubes being burnt. Therefore, also means for eliminating such risks are included in the invention which without said means would not give a complete safe operation.

Finally, the steam generator should be provided with known means for heating the feed water to full steam generation temperature .prior to said water being allowed to mix with the other circulation water, such as economizers or steam preheaters or other suitable means. Thus, the circulation water will practically always have the same temperature as the steam whereby a retardation of the steam generation in the steam generating tubes will be avoided, and consequently the driving pressure for the circulation, that can be called driving pressure only, will be as great as possible, dangerous pulsations of a certain character being simultaneously prevented in the steam generating tubes.

The invention is illustrated in affixed hereto.

In the drawings:

Figs. 1 and 2 are a vertical section, and a horizontal section respectively,'of a steam generator with horizontal tube coils in a horizontal flue.

Fig. 3 is a horizontal section and Fig. 4 a vertical section through a fireplace in which three of the fireplace walls have been lined with horizontal tube coils.

Fig. 5 is a vertical section through a fireplace, the ceiling of which has been provided with horizontal tube coils and which at the bottom hasbeen provided with a granulation grate, likewise consisting of tube coils spread in horizontal planes, the aspect of which will be clear from the horizontal section in Fig. 6. 7

Figs. '7 to 11 show a very practical solution of the problem of arranging tube coils for natural circulation in a horizontal fiue in case the height of the steam separator above the flue should be very insignificant.

Figs. 1-2 to 14 show an arrangement of tube coils lining walls in the fireplace as well as forming a convection surface in a horizontal flue behind the fireplace. I

The above specification contains arrangements in vertical flues as well as arrangements in horizontal fiues. By a suitable combination of vertical and horizontal fiues it is possible to utilize a space of almost any form for constructing a steam generator. Particularly the use of tube coils in horizontal fines is of great importance for the the drawings construction of a steam generator of compact volume and very specially of compact height, which steam generator may be used in locomotives, ships, motorcars, aeroplanes andso on in those cases in which the space available in the Figs. 1 and 2 show the simplest possible arrangement of tube coils in a horizontal flue, which, however, necessarily entails that the steamseparator is situated at a certain level above the roof of the fiue and not immediately on said roof. The

coils 22 are here situated in horizontal planes uni.-

connectedto one another by means 'of return bends.

The tubes lie zigzag, and consequently every second coil is alternately situated as shown in Fig. 2. Due to the coil planes being situated at a level above one another equal to the tube diameter no special supporting means will be required for them, but they rest directly on one another in the bends. As the coils lie entirely in horizontal planes the circulation is obtained exclusively by the pressure difierence between the water column in the descent tube 20 and the steam and water column in ascent tube 2!. This arrangement is very advantageous from the standpoint of circulation. Due to the fact that the coils, which are of equal length mutually, are situated in planes parallel with the direction of flow of the flue gas the heat. supply, and thus also the quantity of generated steam, will be practically equal for all of the coils. However, the driving pressure available for overcoming the friction resistances becomes lower for the uppermost coils than for the lowermost coils. Thus, the circulation coefficient becomes somewhat lower in the uppermost coils than in the lowermost coilswhich difference becomes smaller the higher the level difference between the steam separator 3 and the uppermost tube coil is in relation to the height of the tube set. Consequently, by providing the steam separator at a sufficient height above the tube set it may be obtained that this difference becomes insignificant for a safe operation. However, if the fiue and thus also the planes of the coils are not horizontal but incline upwardly in the direction from inlet header to outlet header a driving pressure is obtained also in the steam generating tubes themselves, and therefore, if theinclination is sufficiently great, the steam separator may be located immediately above the uppermost point of the tube set.

Such a subdivision of the tube set that the length of the coils is limited in the desired way with respect to the circulation will here be necessary. However, thanks to the position of the coils it is here very easy to limit the coils just to the length proved to be necessary in the calculation.

The subdivision in the figure is made between the outlet header 26 and the inlet header 24 and between the outlet header 2'! and the inlet header 25.

As will be seen from the figure, the coil length may be larger, the more the flue gas has been cooled, and the less heat itconsequently gives off to the coils.

The descent tubes are connected to the inlet headers 23 to 25 at a point below the beading points in the headers. By this a water seal is formed which effectively prevents the steam from going backward through the'descent tubes to the steam separator and which in lieu thereof forces it to move toward the outlet headers and then to flow from there through the ascent tubes into the steam separator.

Figs. 3 and 4 show an arrangement for lining the walls in a fireplace with tube coils, said arrangement being very suitable in those cases where the steam separator is situated at a considerable height above the upper edge of the fireplace wall. Fig. 3 shows a horizontal section through the fireplace with the heating front to the left, and Fig. 4 shows a vertical cross section through the fireplace on the section line indicated in Fig. 3, whereby the coil system on the rear wall and on the side walls becomes visible. As willbe seen from Figs. 3 'and' l, s'ai'dfwalls are lined with tube coils. which lie in horizontal. planes. and. consis'tof thre horizontal portions, each of said portion being located on its individual fireplace Wall and which portions are connected to one another by means of bends which are bent at about right angles in the two corners of the rear wall. The horizontal portions passing through the brickwork and connecting the tube coil with the headers are also connected with the tube coil by bends. The front wall is in this case quite uncooled. The driving pressure for the circulation is completely determined by the difference in weight between the water column in the descent tube 60, the steam column in the outlet header 59 and the ascent tube 8|. The direction of flow of the circulation is insured by means of the water seal for the descent tube 60 completely in accordance with the arrangement according to Figs. 1 to 2.

Also in the tube coils according to Figs. 5 and 6 the driving pressure for the circulation is completely determined by the difference in weight between the water in the descent tubes 66 and the steam water mixture in the ascent tubes 10, the water seals 68 for the descent tubes insuring the direction of circulation from descent tube to ascent tube as described above.

Figs. 7 to represent one and the same flue in various projections and so on. Fig. '7 is a horizontal section through a horizontal flue just below its ceiling. The hot flue gas enters at the arrow l2 and leaves in a cooled condition at the arrow I3. This figure shows the portions of the coils 6 located in horizontal planes, said coils extending from the vertical inlet header 3 and being collected in the outlet header I!) located above the plane of the paper. Two vertical sections are designated in the figure, viz. 88 and 99. The section 8-8 is shown in Fig. 8. The water is taken from the steam separator l and. from there it is led through the descent tube 2 to the vertical inlet header 3 from where the coils extend. As will be seen, the steam separator is located only at an insignificantly higher level than the upper edge of the flue. The coils are by means of vertical coil portions 9 connected to the horizontal outlet header ID from where the steam water mixture is led to the steam separator I by means of the ascent tube II. The whole coil bundle, and thus also the whole tube set, rests on the flue gas screens 1 which, as wil1 be seen, traverse the flue to screen said gas off from underlying ash pockets, if any, and thus prevent the flue gas from taking short cuts past the convection surface, as well as extend along the direction of flow of the flue gas, whereby a suflicient support is obtained in the most suitable way.

If the pitch between the horizontal coil planes in the vertical direction is made substantially qual to the outer diameter of the tubes, the coils will be able to support one another in the simplest way. Due to the fact that the horizontal coil portions lie zigzag relatively to one another they will rest on one another by means of the return bends located in th end of the horizontal coil portions. The lowermost of the horizontal coil portions rests on the earlier mentioned flue gas screens 1, and the coil portions located above said lowermost portion rest successively on one another, thus ultimately also on the lowermost coil portion and consequently also on the flue gas screens. Moreover, only small distance pieces or the like are necessary to maintain the order between the separate coils and the coil portions. This arrangement is clear in its entirety from Fig. 11 which shows the aspect of the section lll l in Fig. 8.

Apart from the projection Figures '7 to 9 the embodiment of each special tube coil will also be seen from the perspective sketch according to Fig. 10. From the vertical inlet header the tube coil extends in the horizontal direction and remains first entirely in the horizontal plane parallel with the flow direction of the flue gas, which plane may be laid through the beading points in the inlet header. In the beginning the coil consists of a number of straight horizontal portions M, which extend perpendicularly to the direction of flow of the flue gas and areconnected with one another by means of return bends. Then the coil assumes a vertical direction by means of a vertical portion 8, which leads the coil up to a higher situated horizontal plane where it consists again of a number of horizontal portions connected to one another by means of bends and disposed exactly in the same way as the lower horizontal portions. Finally, the coil is connected to the horizontal outlet header ID by means of the vertical portion 9.

The vertical as well as the horizontal straight tube portions of the tube coils dashed in the figure may, as will be seen from the figure, be so displaced that they will come right in front of the intervals between the corresponding tube portions appertaining to the coils drawn in full lines. Thus, a tube set, which is placed zig-zag throughout, is obtained as is desirable in view of the good heat transmission resulting from such an arrangement.

By such an arrangement the following advantages may be obtained in addition to those mentioned above: The main part of the tube coil is situated in planes which are parallel to the direc tion of flow of the flue gas. Moreover, the coils are of approximately the same length, and consequently they receive substantially the same amount of heat from the flue gas.

The driving pressure for the circulation substantially emanates from the vertical straight portions of the coils, and not from the ascent tube from the outlet header. If these straight portions were of the same length the driving pressure would be equal for all coils and thus also the circulation coeflicient. Yet, this is not the case. However, considering the figures one will find that the difierence in level between the end points of the uppermost coil is greater than half of the corresponding difierence in level for the lowermost coil, which. together with other circumstances, makes that the highest circulation coefiicient does not exceed the lowest coeflicient with more'than about 50%, this being a result which must be considered as very acceptable in comparison with water tube boilers for natural circulation of'a more normal type.

Figs. 12 to 14 show a steam generator which, for example, is provided with a chain grate in which the fire chamber is shaped like a parallelopiped and in which the flue gases leave the fireplace through an opening located in the upper portion of the rear wall. The gases then go in the horizontal direction through a horizontal flue where they are cooled in a convection surface. Then they extend through a vertical downward flue which also may contain heat transmitting surfaces of the same or of another kind whereby the flue gas is further cooled.

Fig. 12 shows a longitudinal section through the steam generator in the direction of motion of the chain grate. It will here be seen how the fireplace wallvisiblein the figure is lined with steam gen- .eratingtubes lying very close to one another in .the form of tube coils. vSaio'lcoils aresub-divided aaoaoi'r into two. systems of coils coupled in parallel to one another. One system extends from the inlet header 3 to whichthe water-is led from the steam separator I through the heat-insulated descent tube 2.. The coils give offamixture of steam and water to the outlet header 4 from which said mixture is led to the steam separator through the heat-insulated ascent tube 5. The other system is provided with water through the descent tube 5, and its coils 8 extend from the inlet header 1 connected therewith. In their latter portion said coils also extend in the horizontal flue 9 in which they form the convection surface 10. As will be seen from the figure, the portion of said coils located in the fireplace consists of a vertical portion ll connected with the inlet header, said portion being at the topby means of a small bend connected with a horizontal portion 12 which extends to one edge of the opening l3 of the horizontal flue. The further extension of the coils within the convection surface will be best seen from Fig. 13, which shows the aspect of the section 'l3l3 taken throughthe steam generator Figure 1d. As will be seen from this figure, they consist of a series of horizontal but straight tube portions M which are located in horizontal planes, thus in planes parallel with the direction of flow of the flue gas, and connected with one another by means of small return bends. As will be seen, said horizontal portions only extend to the middle 45 of the flue, its other half l6 being, quite symmetric herewith, filled up by a convection surface consisting of tube coils extending from the opposite side wall in the fireplace ll.

Thus, in this way tube coils from both of the side walls in the fireplace will be connected with coil parts each in its special portion of the horizontal flue. It will be seen from Fig. 13 and also from Fig. 12 that the coils are so arranged that if one follows the bundle of coils in the vertical direction one will find that the horizontal portions of every second coil are displaced half a pitch in relation to the other coil portion, whereby the tube set obtains a zig-zag character which is advantageous for the heat transmission.

At the back of the tube set the coils are connected with upward extending vertical portions l8 and I9, Fig. 12, which are directly connected to the steam separator I. How these coils are arranged in other respects will be seen from Fig. 14 which represents the aspect of the section I l-l4 in Fig. 12. From this it will be seen that the vertical portions, which are connected with the horizontal portions by means of small bends, arelocated in such a way that the pitch between them is substantially the same as between the horizontal portions. Further, every second portion appertaining to the tube coils represented in the dashed lines in the figure is also here displaced half a pitch along as well as perpendicularly to the plane of the paper, the zigzag character of the tube set being. maintained also in this range. Consequently, the smoke speed and thus also the heat transmission will be completely the same in the range in which the tubes extend vertically as in the range in which they extend horizontally.

The advantage of the arrangement shown in Figs. 12 to 14 consists therein that the driving pressure for the circulation, which arises in the vertical coil portions, 8*:in the fireplace due to the great difference in level, becomes so great that it will also be of use tothe coil portions in the horizontal 'flue for overcoming the friction resistance therein. Consequentlythe coils may be .8 considerably longer than would have been otherwise-possible. H I

I-IaVingnow described my invention, whatI ci'aim. as" new and desire to secure by Letters Patentis:

1. A steam generator, where steamis generated in tube coils of preferably small internal tube diameter, each tube coil having a horizontal portionincluding at least three separate straight coil parts and two tube bends connecting said straight parts, said horizontal portion being disposed entirely in an approximately horizontal plane, all these tube coils being in combination with simple means for obtaining a natural circulation in said coils, these simple means comprising at least one inlet header, which by means of at least one descent pipe is directly connected with the water space of a higher situated steam separator, so that the water flows onto the header and further onto the coils under self pressure and the steam-water-mixture is continuously brought back to the steam separator through the pipe system, only because the steam volume in the riser portions is lighter than. an equal water volume in the descent portions of the pipe system, an approximately horizontal flue in which the horizontal portions of the tube coils are arranged so as to form convection heating surfaces which fill. up most of the flue, so that the horizontal portions of the tube coils will be parallel to the how direction of the flue gases and as a consequence the various horizontal tube coil portions are supplied with about equal amounts of heat from the flue gases, each tube coil containing at least two different horizontal portions at different levels, connected with a vertically extended coil portion.

A steam generator, where steam. is generated in tube coils. of preferably small internal tube diameter and considerable length, each tube coil having a serpentine portion being disposed entirely in an approximatel horizontal plane, all these tube coils being in, combination with simple means for obtaining a natural circulation in said. coils, these simple means comprising at least one inlet header, which by means of at least one descent pipe is directly connected with the water space of a higher situated steam separator, so that the water flows on to, the header and further on to the coils under self-pressure, and the steamwater-mixture is continuously brought back to the steam separator through the pipe system, only because, the steam volume in the riser portions of the pipe system is lighter than an equal water volume in the descent portions of the pipe system, an approximately horizontal flue in which the said horizontal serpentine portions of the tube coils are arranged so as to form convection heating surfaces which fill up most of the flue, so that the horizontal planes of the serpentine tube portions will be parallel to the flow direction of the flue gases and as a consequence the variou serpentine tube portions are supplied with about equal amounts of heat from the flue, gases.

3. A steam generator, where steam is generated in tube coils, of preferably small internal tube diameter and considerable length, each tube coil having a serpentine portion being disposed entirely in an approximately horizontal plane in combination with a, vertically extended tube .portion, all these tube coils being in combination with simple means for obtaining a natural circulation in said coils, these simple means comprising at least one inlet header, which by means of at least one-descent pipe-is directly connected with the water space of a higher situated steam separator, so that the water flows on to the header and further on to the coils under self -pressure and the steam-water-mixture is continuously brought back to the steam separator through the pipe system, only because the steam volume in the riser portions of the pipe system, particularly the above-mentioned vertically extended tube portions, is lighter than an equal water volume in the descent portions of the pipe system, said horizontal serpentine portions of the tube coils being arranged in an approximately horizontal flue so as to form convection heating surfaces which fill up most of the flue, so that the horizontal planes of the serpentine tube portions will be parallel to the flow direction of the flue gases and as a consequence the various serpentine tube portions are supplied with about equal amounts of heat from the flue gases.

4. A steam generator, where steam is generated in tube coils of preferably small internal tube diameter and considerable length, each tube coil having a serpentine portion being disposed entirely in an approximately horizontal plane in combination with a vertically extended tube portion, all these tube coils being in combination with simple means for obtaining a natural circulation in said coils, these simple means comprising at least one inlet header, which by means of at least one descent pipe is directly connected with the water space of a higher situated steam separator, so that the Water flows on to the header and further on to the coils under self-pressure and the steam-water-mixture is continuously brought back to the steam separator through the pipe system, only because the steam volume in the riser portions of the pipe system, particularly the above-mentioned vertically extended tube portions, is lighter than an equal water volume in the descent portions of the pipe system, said horizontal serpentine portions of the tube coils being arranged in an approximately horizontal flue so as to form convection heating surfaces which fill up most of the flue, so that the horizontal planes of the serpentine tube portions gases and as a consequence the various serpentinetube portions are supplied with about equal amounts of heat from the flue gases, the inlet header to the coils being situated at a level substantially below the horizontal fine and joined with the vertically extended tube portions, which cover the walls of the fireplace of the steam generator, the circulation thus being effective enough to cool even the long and narrow serpentine tube portions in the convection heating surface in the upper part of the steam generator.

5. A steam generator, Where the flue gas is leaving the fireplace through a convection heating surface, situated in a substantially horizontal flue, immediately below the roof of the fireplace, the said convection heating surface consisting of a number of rather long serpentine tube portions of small inner tube diameter, each such portion situated in a horizontal plane, one end of it being connected to a higher situated steam separator, the other end being connected to a vertical tube portion in the fireplace to form a connected steam generating tube coil, said vertical tube portion extending far below the said convection heating surface and at its lower end being connected to an inlet header, said inlet header being directly connected to the water space of the steam separator by means of at least one descent pipe, the water thus flowing under selfpressure to the said inlet header and further on to the steam generating tubes, and a natural circulation in the steam generating system being obtained substantially because of the considerable pressure difference between the Water column in the descent pipe and the rather high steamwater-column in the said vertical tube portions, this circulation thus being effective enough to cool even the long and narrow serpentine tube portions in the convection heating surface in the upper part of the steam generator and thus the necessary building height of the whole steam generator being maintained extremely low.

KARL FOLKE NORDLUND.

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