US1961138A - Steam or vapor generator - Google Patents

Description

June 5, 1934. H. c. EGLOFF STEAM OR VAPOR GENERATOR Filed March 24. 1932 2 Sheets-Sheet 1 r w 8 0 w k o a w y i I r R I 0 w. 2L 6, 101. 0 0 o 0 Z w. m

W IIE/ENTB June 5, 1934. A H. c. EGLOFF 1,961,138

STEAM 0R VAPOR GENERATOR Filed March 24. 1932 2 Sheets-Sheet 2 6 .g HFKBQE 0 W 6 I 1 w A Patented June 5, 1934 UNITED STATES PATENT OFFICE Application March 24, 1932, Serial No. 600,924 In Germany April 27, 1931 2 Claims.

This invention relates to steam or vapor generators of the high pressure type without liquid circulation.

Steam generators of this type have hitherto fl been proposed in which the working medium, fed

to the system at a pressure above the critical pressure, was converted at the supercritical pressure into steam and expanded in the superheating zone by a rapid fall of pressure to the desired delivery or working pressure. With such generators however a large amount of power is necessarily consumed by the feed apparatus and in addition the sudden fall of pressure taking place in the system results in such a high speed of flow of the medium that the tube walls are liable to be subjected to rapid mechanical wear.

When, on the other hand, the working medium is fed to the system at a pressure below the critical value, the system is usually so short that the resulting speed of flow is too low and a fine mixture of the steam and water is not produced, the steam bubbles tending-to adhere to the inner walls of the tube and thereby causing the latter to be subjected to excessive local heating.

With a view to overcoming the above difficulties the working medium is fed, in accordance with the present invention, at a pressure below the critical pressure into a tube the heating surface of which is at least twenty-four thousand times the internal cross-sectional area of the tube, whereby the pressure of the medium falls gradually to the working pressure at the delivery end of the tube. In this way the power consumed for feeding the medium and maintaining a rate of flow thereof which exceeds the natural rate of ascension of the steam bubbles is reduced, 2, fine uniform mixture of steam and liquid medium being produced.

Though the feed pressure is thus raised and the length of the tube increased as compared with known constructions, the rate of flow of the medium and also the fall of pressure within the tube are maintained at values which will not tend to result in rapid wear of the internal wall of the tube.

In order to obtain the desired results in accordance with the present invention it is desirable to reduce to a minimum any conditions, such for example as enlargements or restrictions of the tube cross-section, which will tend to cause irregularities in the flow of the medium through the tube. Thus, for example, if a sudden enlargement were introduced into the tube the flow of medium at the enlarged portion would be reduced so that steam bubbles would adhere to the inner surface of the tube at this portion resulting in a risk of local superheating and also disassociation and corrosion phenomena. On the other hand if a throttling point were introduced into the tube the medium would tend to be dammed immediately prior to the throttling point whereupon,

in passing through this throttling point the medium would be rapidly accelerated. As a result not only would local superheating be liable to occur at that part of the tube immediately prior to the throttling point but the high speed of flow of the medium while passing there through coupled with effects of a chemical nature would tend to cause rapid mechanical wear of the tube walls.

In order to overcome these difficulties therefore the tube according to the invention is preferably free from any increase or reduction, such as would be caused by enlargements or throttling points, at any part of the length of the tube between the inlet where the medium is introduced and the outlet at which superheated steam is delivered, disturbance of the flow of the medium within the tube being thus avoided.

The speed of flow of the working medium through the tube of a generator according to the invention is increased so that there will be a consequential increase of the quantity of working medium flowing through the tube, this increase of working medium necessitating a corresponding increase in the supply of heat. This additional supply of heat may be obtained by supplying heating medium at an increased pressure, the resulting increase in the speed of flow of the hot gases tending to produce uniform heating of the working medium.

In a steam generator of medium capacity embodying the present invention with a tube the mean internal diameter of which is, say, 30 mm., the length of the tube will be several hundred meters, this length being 1,000 meters or more in the case of large installations. Even in the case of generators of small capacity the heating surface will be not less than twenty-four thousand times the mean internal cross-sectional area of the tube.

In the accompanying drawings, Fig. l is a diagram illustrating the principle, and

Fig. 2 is a perspective of one embodiment of the invention.

The accompanying drawings show three curves drawn with tube lengths L in meters as abscissse .105 and pressures D in atmospheres as ordinates. The curve 1 illustrates the course of pressure in the tube according to the invention, whilst curves 2 and 3 respectively indicate by way of comparison with the curve 1 the courses of pressure pro- 1-10 duced in generators of known type. It is assumed that all three generators corresponding to the curves 1, 2 and 3 respectively are of substantially the same capacity and that the working or delivery pressure at the ends of the tubes is 100 115 atmospheres.

According to curve 2 the medium is fed to the tube at a pressure above the critical pressure of 225 atmospheres whereupon external heat is supplied to the medium during the first relatively 120 fiat portion of the curve, the temperature of the medium being thus brought to the critical temperature. When the critical temperature is exceeded the liquid medium is converted directly into the gaseous state. The gaseous medium is next expanded, as indicated by the substantially vertical part of curve 2, until a pressure having a value between the critical pressure and the delivery or working pressure is attained, after which a rapid fall in pressure takes place in the evaporator until the delivery or working pressure is reached. In the case of a generator of large evaporation capacity the speed of the medium in the superheating portion may possibly rise to such a value that the pressure drop takes place along the line 2a, a sudden fall of pressure shown by the substantially vertical portion of the curve 2 being avoided.

According to the curve 3 the medium is fed to the tube at a pressure which is only slightly above the delivery or working pressure, whereupon the medium passes through a relatively short tube with a small pressure drop and low speed of flow.

In a steam generator according to the present invention the course of pressure variation is as indicated by the curve 1 from which it will be seen that the working medium is fed to the tube at a pressure below the critical pressure whereupon the pressure falls gradually to the working or delivery pressure at the outlet end of the tube. This gradual fall of pressure takes place in such a manner that the working medium flows through the tube at a speed which exceeds that at which steam bubbles naturally ascend whereby the steam generated forms such a fine mixture with the liquid portion that large steam bubbles cannot be produced at all.

It will be understood that instead of water any other suitable working medium may be employed. The length of tube can consist of several tubes connected together so as to iornnone continuous tube.

A further improvement of the invention consists in that, as shown in Fig. 2 of the drawings, any interruption of the tube through throttling members or drums is avoided, in order to prevent troubles occurring through disturbances of the flow.

The continuous tube, beginning at the inlet 10 and ending at the outlet 11, is subdivided into groups of tubes 12, l3, 14, 15 connected with each other through the tubes 16, 1'7, and 18. The groups of tubes 12, 13, 14, 15 are shaped in such a manner and built into the brickwork (for the sake of clearness not shown in the drawing) in such a way as to suit the shape of the spaces. The subdivision of the continuous tube into separate groups allows the continuous tube to be suited to any space conditions, even if the whole brickwork is shaped like a tower.

The working medium is led to the continuous tube at the inlet 10 as feed liquid, passes to the outlet 11 in the direction of the arrows and from here is led as service steam to the points of consumption (not shown in the drawings). In the construction shown in Fig. 2, the continuous tube shows neither sudden increases in cross-section caused by drum or sudden contractions in crosssection caused by throttling members, whereby the advantage is attained that the flow of working medium is not disturbed by being either suddenly retarded or suddenly accelerated.

Further, since the quantity of working medium flowing through the tube is relatively large owing to the increased speed of flow, there is the possibility of the rate of transmission of heat through the tube wall to the working medium being insufficient to raise the temperature of the working medium to the required superheating temperature. Though the rate of transmission of heat to the working medium could be increased by increasing the temperature difference, this course would be liable to result in the temperature outside the tube walls tending to rise to such a value that there would be a risk of excessive temperature stresses in those parts of the tube with which the hot gases come in contact. With a view to overcoming this diiiiculty the transmission of heat from the hot gases to the heating surfaces of the tube may be facilitated by increasing the pressure of the heating medium and therefore the speed of flow 01" the hot gases.

a heating surface not less than twenty-four thou- '1 sand times the internal cross-sectional area of said flow path, gradually lowering the pressure of the working-medium at a substantially uniform rate from the beginning of the continuous flow path to the desired pressure at the end of the flow path, producing combustion of fuel and passing the gases of combustion in a heat exchange relation to said flow path, so coordinating the quantity of fuel consumed and velocity of combustion gases in contact with said flow path with respect to the velocity of said workingmedium as to cause the Working-medium entering said flow path to be evaporated without local accumulation of gas at any place in the flow path, and to issue from the end of said how path as superheated gas.

2. A method of generating superheated gases, which comprises supplying liquid working-medium at a pressure of at least 120 atmospheres and at least 20 atmospheres higher than that obtaining subsequently, said pressure being below the critical pressure of the working-medium, utilizing said pressure for forcing said working-medium through a continuous flow path uninterrupted by sudden pressure drops and having a heating surface not less than twenty-four thousand times the internal cross-sectional area or" said flow path, gradually lowering the pressure of the workingmedium at a substantially uniform rate from the beginning of the continuous flow path to a pressure of at least atmospheres at the end of the flow path, producing combustion of fuel and passing the gases of combustion in heat exchange relation to said flow path, so coordinating the quantity of fuel consumed and velocity 01" combustion gases in contact with said flow path with respect to the velocity oi": said working medium as to cause the workingunedium entering said flow path to be evaporated without local accumulation of gas at any place in the flow path, and to issue from the end of said flow path as superheated steam.

HANS C. EGLOFF.

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