US1996134A - Superheater element - Google Patents

Description

April 2,1935. A. WILLIAMS 1,996,134

' SUPERHEATER ELEMENT Original Filed Jan. 5, 1933 Y 2 Sheets-Sheet 1 lNV ENTOR ARTHUR MLL/ MS UIKW,

ATTORNEY April 1935' A. WILLIAMS I SUPERHEATER ELEMENT Original Filed Jan. 5, 1935 2 Sheets-Sheet 2 INVENTOR filer/(0k MLL/A Ms l mMW T ATTORNEY Patented A t-.2, 1935 1 UNITED STATES SUPERHEATER ELEMENT Arthur villiams, Hammond, Ind., assignor to The Superheater Company, New York, N. Y.

Continuation of application Serial No. 650,262, January 5, 1933. This application December 5, 1933, Serial No. 700,963

10 Claims. (01. 122-462).

The history of the use of superheated steam in locomotives shows that originally the engineers who designed superheaters for such locomotives had difllculty in persuading railroads to use steam with high superheat. One of the main reasons for this was the fact that there were practical difliculties to overcome, such, for' example, as problems of lubrication. This period, however, has long since passed and railroads, having overcome the difliculties referred to and having thoroughly recognized the benefits to be gained from superheat, have become insistent on higher and higher degrees of superheat. The situation has thereby become reversed and the engineers designing the locomotives, and the inventors providing new forms of superheaters,

have been pressed to furnish degrees of superheat higher than they have been furnishing. A

comotive boiler design are the result of years of experience and may be assumed to represent the best arrangement possible under prevailing conditions. This standard arrangement may be briefly stated to be as follows.

The gas passages through the 'body of the boiler are divided into two groups, one of which isTa set of unobstructed tubes and the other of which is a set of flues, usually of larger diameter than the tubes, and 0601 pied by the superheater elements.

- The superheater elements are of tubular form and take their supply of steam froma header in the smoke box, returning it to the header in superheated state. I r

The fiues and tubes deliver the gases that pass through them 'to the smoke box at the front end of the boiler whence these gases pass tothe at-' mosphere through the stack. The draft to cause the gas fiow from the fire box. through the fiues and tubes to the smoke box and atmosphere is created by exhaust steam from the engine passing through a suitable nozzle. A

distributedover the entire grate in the fire box,

Unless this is true the fuel on some portions of the grate will burn faster than that on other portions. This equal distribution of the draft. over the grate depends directly upon a proper propgrtioning of the flow of the gases through the flues and tubes, and anything that interferes with such flow distribution through the fiues and' tubes is inadmissible. I

The most usual form of superheater element is one made up of four straight tube length's'arranged in the flues, these lengths being connected by three return bends into a continuous structure through which the steam flows in series. The first length, which is connected to the header, carries steam from the smoke box end toward the fire box, the second length returns it toward the front end, thethird length again carries it from the smokebox toward the fire box and the fourth length conveys it forward and to the header.

There are many thousands of "locomotives with such superheater elements, and any new form of element that is proposed must preferably, if not necessarily, be of such configuration that it fits into the fines of such a standard arrangement and that such new elements can be directly substituted for the. old elements. For

this purpose it is further requisite that the ends of such new element fit directly to the header in the same manner that the ends of the old element did. v

There are several factors which influence the degree of superheat furnished by a superheater. Whatever factors are selected to increase the superheat in designing a new form of superheater element, the resulting element shouldnot materially alter the resistance to the fiow of the geses through the flues, nor raise the smoke box temperature, nor disturb the gas distribution over the fiue sheet, nor entail inadmissibly high metal temperatures at any part of the superheater element. These are essential requirements and no superheater element heretofore proposed and able to increasematerially the degree of superheat, has met them all. Either one or another of these requirements has been violated and the unit has for this reason been objectionable and has not gone into use beyond more or less experimental stages. An illustrative example of a superheater element delivering steam withincreased superheat is one in which the steam flows from the smoke box end toward the fire box end in the annular space between two concentrically arranged pipes and returns through a pipe located within the inner of the two pipes. The

- outer of the two concentric pipes and the space between the inner of the twoconcentric pipes and the return pipe. It is true that a superheater with such elements furnishes higher superheat than one with the usual four-pipe elements. It is also true that the resistance to the flow of the gases can be held to substantially the same figure as that in the four-pipe superheater, so that the firing is not adversely affected. But the metal temperatures at the fire-box end of the elements become objectionably high and deterioration correspondingly rapid. In addition, the differential stresses from unequal heating are large and difficulty of maintenance is the result. This illustrates that such units may furnish higher superheat but that they fail to meet all of the essential requirements mentioned.

A superheater comprising elements according to the form invented by me on the other hand normally delivers steam of a temperatureapproximately 50 F. higher than the superheater having elements of the most usual form such as briefly described above and at the same time meets every one of the requirements stated. I

have not only established this in an experimental unit but have demonstrated it conclusively in a locomotive which has been equipped with a superheater having my improved element and which has been in daily fast freight service on a railroad in this country for some months. Careful tests on this locomotive have shown this beyond question.

The superheater in accordance with my invention will now be briefly described. Reference is made in connection with this description to the drawings in which Fig. l is a fragmentary longitudinal vertical section of a locomotive equipped with a superheater having tubular elements in accordance with the invention; Fig. 2 is a horizontal longitudinal section of one of the flues containing an improved element according to the invention; Fig. 3 is a vertical section of such a flue with an element according to the in-. vention in place; and Figs. 4, 5, 6 and 7 are re-' spectively sectional views on lines 4-4, 55, 6- and 1-1 of Fig. 3.

The invention is illustrated in connection with a locomotive of the ordinary type. The fire box I delivers gases to the enlarged flues 2-2 containing the superheater units and to the fire tubes 3, which are of smaller diameter and contain no superheater units, such gases being delivered from the front ends of the hues and tubes to the smoke box 4 whence they flow out through the stack 5. 6 is the barrel of the boiler and 1 is the dry pipe conveying steam from the boiler steam space to the superheater header 8. This superheater header delivers steam to the tubular superheater elements or units which return it in a superheated state to compartments inthe header 8 separated fromthose which first delivered the saturated steam to the superheater elements. The superheated steam is delivered by the header Bto two steam pipes (one of them appearing-at 9) leading to the two steam chests. The header 8 shown in the drawing is of the same form as that used in present practice for elements made up of four straight tube lengths connected in series. Theuse of elements according to my'invention call for no change in the construction of this header. .The size and number of the flues 2 also is the same as in the present ordinary practice. Elements according to my invention can therefore be directly substituted for the ordinary four-pipe elements. This is an extremely advantageous feature and in fact is practically essential.

The preferred form of the unit or element will now be described in more detail.

The element is made up of-two portions or sections. The first of them comprises two co-axiallye arranged spaced tubes, the outer one being shown at I0 and the inner one at I I. These two tubes are joined at their front and rear ends and the annular space closed as indicated at I2 and I3 respectively, the joint preferably being not at right angles to the axis of the tube but inclined to it. A pipe is connected at l5 to communicate with the annular space between the two tubes to supply steam to this space. This pipe I4 is provided with an enlarged end l6 of a shape like that of the ordinary superheater element in use at the present time. This enlarged end is secured to the superheater header 8 by the ordinary or any desired means.

To the rear end of this double or concentric tube section of the element a pipe I! is secured to receive the steam from the annular space between the two tubes.

This pipe. I! continues backward toward the fire box and forms the first leg of a four-pipe section of the element. It is connected to the second length l8 by means of the return bend ,I9 and the forward end of this length I8 is the interior of the inner pipe I l of the concentric pipe section and extends out at the front end into the smoke box, being bent upward toward the headerand provided with anenlarged end 24 for connection to the header.

To keep such an element in its place in the flue,

supports 25, 26 and. 21 are used. The first of these embraces the two tubes in the fore part of the flue, the second, i. e. 26, is secured to the outer of the two concentric pipes and thethird, 21, embraces the four pipes of the four-pipe section. While only one support of each of these three kinds is shown, it will be obvious that more than one can be used if required.

Thesingle pipe 23 is further supported inside of the inner ports 28.

Enlarged inlet end l6 of the pipe I4 is in communication with a chamber of the header 8 which supplies saturated steam to it while the enlarged end 24 of pipe 23 communicates with .a chamber to which the superheated steam is delivered by the superheater element and from which it flows to the steam pipes 9. The particular element shown in Figs. 2 and 3 and just described in one of the top row of elements. It will be understood that there are several horizontal rows below this top row, the ordinary arrangement including a' total of four horizontal rows. The only difierence between the successive rows is the variation in the connecting pipes extending from the header 8 toward the flues. Outside of this obvious and necessary variation the elements are strictly iden-- tical.

As stated above, the above-mentioned careful tests in a locomotive equipped with a superheater such as described have shown that in normal operation the degree of superheat averages 52 F. higher than is obtained with the standard usual elements having four straight pipe lengths extending through the entire flue. The temperaof the two cc-axial tubes by supwhile I am not certain that I can fully explain the reasons for them, the following factors apparently enter into these results.

In the first place I take advantage of the well known benefit of having the steam flow in a direction counter to that of the gases, doing this through that portion of the flue in which a real advantage results from doing so. This portion is the one where the gas temperature has been materiallyreduced. With very high gas tempera' tures, while the counterflow principle still results in some advantaga this advantage becomes relatively small. In a superheater elementarranged according to my invention the counterflow principle is used throughout the forward-portion ofthe flue where the gas temperature has fallen sufficiently so that this principle results in a material advantage: From a certain point backward toward the fire box it would be inadvisable for a number of reasons to utilize the counterfiow principle, particularly to utilize it by means of the concentric tube type of element. From this point on I therefore abolish'the counterflow principle and use a double-loop or four-pipe section which results in a rapid steam flow and consequentefficient. cooling of the metal walls. This fourpipe section necessitates three return bends and it is the presence of these three return bends and particularly the forward one of the three which apparently materially aids good heat abstraction from the gases by thoroughly stirring them up. After the heating of the steam in this four-pipe section, I take advantage of the known arrangement whereby the steam is returned to the front end through a pipe located'within the inner gas core of the concentric portion of the element. The advantage of this is that not only is the hot steam prevented from losing a portion of its superheat as it passes through the forward portion of the flue, but it actually picks up additional heat because the gas in the interior of the concentric unit is shielded against radiation to water cooled surfaces and therefore remains hotter than would be the case wereit not so shielded.

The net result is that the unit rially higher superheat heater elements and 'does so without sacrificing any of the desirable features pointed out fully above.

.My experimental work has shown that the'-,temperatures obtained are almost identically the same as those obtained with asuperheater of the type referred toabove in which. the units are made up of two, concentric tubes extending back all the way into the flue without any four-tube section and with a return tube inside of the inner tube. In other words my units give as high superheat as the units which are theoretically probably the most nearly correct for heat transfer, and do so without approaching the metal temperatures present in such concentric tube units.

One other striking result appears from my ingives a matethan the ordinary supervestigations of the improved unit which is that if the relative lengths of the two sections of the-element are varied, the resistance to gas flow through the flue will vary, the resistance increasing not only as the length of the four-pipe section is increased beyond a certain amount but increasing'also as this length is decreased below a certain amount. The explanation for this is probably as follows.

The greatest portion of the resistance to the gas flow offered by the concentric pipe section is due to resistance at the point where the gases .enter this section. The higher the temperature of the gases and the greater therefore their volume, the greater will be this factor. If therefore the four pipe portion is shortened, so locating the entrance to the concentric portion in a zone of higher gas temperature, this factor rapidly rises and the total resistance increases. If the length of the four pipe portion is increased and the unit approaches the construction of the usual four pipe unit, the resistance offered by the four pipe portion approximates that offered by the full four pipe form, and on this is superimposed the resistance of a shortened concentric tube portion with its high entry resistance. For

a given set of conditions, I give the concentric tube portion of my improved unit-substantially the same cross-sectional dimensions as a properly designed full-length concentric-tube section would have and similarly e the same size tubing and cross-sectional disposition for the four -tube portion as would be used in a fulllength four-tube section. I then find that the minimum resistance to gas flow is offered by'the unit when the length of the four-tube portion is between and per cent of the total over-all length of the unit. It must be remembered in this connection that this relative length of the two portions for an absolute minimum resistance to gas flow, dependent as it is upon the law'of gas temperature change in the flue or upon the gas and steam flow conditions, varies somewhat with the load. The above named limits will include centric-tube unit of the same cross-sectionas the concentric tube portion of the compound element, and also substantially the same as that of a fulllength four-tube unit 'of the same cross-section as the four-tube portion of the compound unit.

This application forms a continuation of my application Serial Number 650,262, filed January 5, 1933.

What I claim is:

1. A superheater element-for use in a locomotive fiue and having a counterfiow front portion' comprising two concentrically arranged tubes and a rear portion comprising four parallel pipes connected to provide for serial steam flow through them, the relative lengths of the two portions being such that for a given set of steam and gas conditions the resistance to gas flow is substantially the same as that in a concentric tube counterflow unit of the same overall length.

2. A superheater element for use in. a locomotive flue and having a counterfiow front portion comprising two concentrically arranged tubes and a rear portion comprising four parallel pipes connected to provide for serial steam flow through flow through the flue is substantially the minimum obtainable with a unit composed of two such portions of given cross-sectional dimensions in a given flue.

3. A superheater element for use in a locomotive flue and having a counterflow front porheater elements each comprising four parallel tube lengths located in a flue and extending substantially throughout the flue length and connected to the header and in series to each other, a set of superheater elements which can be placed into the flues and connected to the header without change in flues or headers, each element having a front portion comprising two concentrically arranged tubes and a rear portion comprising four parallel pipes connected to .provide for serial steam flow through them, the construction of the elements being such that they-offer substantially the same resistance to gas flow through the flues as would be presented by elements comprising four parallel tube lengths extending sub-' stantially throughoutthe flue length. I

5. A superheater element for use in a locomotive flue and having a front portion with which the gases come in contact last made up of two concentrically placed pipes and a rear portion with which the gases come in contact first comprising four pipes connected for serial steam flow I through them, and a return tube 'for the steam located within the inner of the concentric pipes, the steam flow being through the portions in .the

' order named.

comprising two concentrically arranged tubesseparated by an annular space and a rear portion comprising four parallel pipes connected to provide for serial steam flow through them, means to deliver steam to the annular space, means to conduct steam from the annular space to the first of said four pipes, and means to conductsteam away from the last of said four pipes.

7. A superheater element for use in a locomoand a pipe extending through the inner of said concentric pipes to conduct steam away last of said four pipes.

8. A superheater element for use in a locomotive flue and, having a counterflow front portion comprisingtwo concentrically arranged tubes and a rear portion comprising four parallel pipes from the connected to provide for serial steam flow through them, the length of the rearv portion being at least twenty per element.

9. .A superheater element for use in a locomocent of the total length of the tive flue and havinga counterflow front portion I comprising two concentrically arranged tubes and a rear portion comprising four parallel pipes connected to provide'for serial steam flow through them, the length of the rear portion being not more than forty- 'flve per cent of the total length of the'element. i a

10. A superheater element for use in a locomotive flue and having a counterflow front portion comprising two concentrically arranged tubes and a rear portion comprising four parallel pipes connected to provide for serial steam flow through them, the length of the rear portion being approximately thirty-se'ven per cent of the length of the front portion, whereby for a given set of steam and gas conditions-the resistance to gas flow is substantially the'same as that in a .concentric tube counterflow unit of the same overall length- ARTHUR WILLIAMS

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