US2046349A - Superheating water tube boiler - Google Patents

Description

y 1936- c. s. TURNER 2,046,349

SUPERHEATING WATER TUBE BOILER Filed Sept. 7, 1934 I 2 sheets-Sheet 1 v INVENTOR. @kaflts 5 fz'zrrzer July 7, 1936. c. s. TURNER SUPERHEATING WATER TUBE BOILER ,2 Sheets-Sheet 2 Filed Sept. '7, 1954 @lzarles BU Patented Jul 7, 1936 A UNITED I STATES PATENT OFFICE SUPERHEATING WATER TUBE BOILER Charles S. Turner, Detroit, Mich. Application September 1, 1934, Serial No. 743,069

'1 Claims. (01. 122-473) This invention relates to superheater bollers, and is directed to the improvement of water tube boilers in general and of the superheater constructions disclosed in my copencling applications, Serial Nos. 496,868, filed November 20, 1930, superheater construction", 512,675, filed January 31, 1931,, superheater construction, 534,490, filed May 2, 1931, Fluid cooled superheater construction, 590,108, filed February 1, 1932, "superheater assembly, and 699,541, filed November 24, 1933, superheater construction in particular.

In marine boilers especially compactness in proportion to steam delivery is of course important, and they are ordinarily, therefore, not only arranged in a compact manner, but operated at a relatively high rating which involves very rapid heat transference. In providing such boilers with superheater equipment it has heretofore been considered impossible to subject that equipment to the direct radiant heat from the burners, and superheaters as applied to such boilers have accordingly been commonly placed in guarded positions remote from the furnace and operated by convection only. No matter what the type of such superheaters, however, the practice has been to provide special steam inlet headers to which an ofitake from the steam drum of the boiler has been connected by suitable piping. v

An important object of the present invention, therefore, is the provision of means whereby marine and other water tube boilers may be equipped with superheating apparatus not only of markedly greater efiiciency than any heretofore available, but which requires the use of no additional drums, inlet headers, connecting pipe, or other external accessories for the superheater other than a water inlet and a take off for superheated steam, and in which the functions of the eliminated elements are all' performed by and within the conventional steam drum of the boiler itself, and the construction thus rendered more compact than those now in use incorporating superheaters.

Still another object is the provision of improved means for controlling radiant superheater elements by partially shielding the same in a novel manner to limit the quantity of radiant heat to which they are subjected without destroying the substantially proportional accessibility of various portions of the elements to radiant heat.

Other objects and-advantages will be apparent from the following description, wherein reference is made to the accompanying drawings illustrating preferred embodiments of my invention and wherein similar reference numerals designate similar parts throughout the several views.

In the drawings:

Figure 1 is a vertical sectionalelevation of a marine boiler, shown somewhat diagrammatically and illustrating a typical application of my invention.

Figure 2 is an enlarged detailed section of one of the superheater elements taken substantially on the line 2-2 of Figure 1, and looking in the direction of the arrows.

Figure 3 is an enlarged and fragmentary vertical section of the lower portion of a similar boiler incorporating my invention in somewhat modified form.

Figure 4 is a horizontal section taken substantially on the line 44 of Figure 3, and

Figure 5 is an enlarged and fragmentary vertical section of the upper portion shown in Figure 4.

Referring now to the drawings, reference character l designates generally the angular banks of water tubes of an A-type marine boiler, which is shown somewhat diagrammatically in the conventionalparts thereof which are unaifected by addition of my invention, and which serves merely to exemplify a preferred application of my invention. The superheater comprises a plurality of elements arranged generally paral-. lel to the water tubes l0 and terminating at their upper ends in the same steam drum 2|. In the embodiment shown .in Figures 1 and 2 the superheater elements, generally designated 20, are shown arranged in front of the first row of water tubes and directly exposed to radiant heat.

Each element 20 consists of a unitary assembly of tubes welded together as at l8 to provide heat bridges therebetween. In the form shown crosssectionally in Figure 2 the water tubes l are directly welded in circumferentially spaced relation to the surface of the larger central tube l2 for steam to be superheated. The purpose and proportioning of these parts will be discussed in greater detail later. The upper extremity of each of the units 20 thus formed is projected into the upper steam drum 2i of the boiler, in which all are of course sealed. A suitable water levelis exemplified at 25. The central, superheating tube I! may project to a point near the top of the drum and well above the water level, while the cooling tubes I5 preferably terminate at a lower point but also above the water level. Both the tubes l2 and I5 are open at their ends within the drum, but such open ends constitute the outlets of the water tubes l5 and the inlets of the steam tubes l2, Hats, as 2621, may be arranged over each, to guard against the undesired splashing of water thereinto. At their lower extremities the superheater assemblies 20 are carried through the sides of the furnace walls 29 and project therebeyond, a water inlet header, as 30, being provided into which the lower ends of water tubes I6 are connected, while the superheater tubes l2 terminate in an outlet header 33.

Water is supplied to the water inlet header 30 and so to tubes l5 by means of a conduit 3! connecting the header with one of the mud drums, as 40, of the boiler. A throttle valve 36 is arranged in the water inlet line 35 for a purpose presently to be described. and is automatically controllable in response to the outlet temperature of the superheated steam, as by the thermostatic means diagrammatically represented at 38. A manually operable by-pass valve, as 42, is also provided to enable flooding the water tubes when desired independently of the thermostatic control. For purposes of discussion it may be assumed that during normal operation the effect of the throttling valve is to maintain the water in the assembly at a reduced level, although actually, while substantially only water may be present at the bottom ends of the water tubes, and this condition may exist for only a short distance up the tubes, there is always some entrained water, even in the zone above what may-be termed the eflective water level, where the steam bubbles have become so large as to constitute practically the entire content. That is to say, the constantly increasing steam bubble size makes the water level indefinite, although his none the less real from a practical standpoint, while the presence of entrained water above such theoretical level affords the upper part of the assembly a desirable protection by reason of the'heat absorbing power which although greatly reduced, still remains therein to some extent.

As shown in Figure 2, the cooling tubes l5 may be arranged only upon the exposed side of each superheater tube l2, since only those areas subjected to radiant heat need the protection thereof, although this is of course a matter of choice. The water tubes l5 and the connecting welds i8 are so proportioned and positioned that in the area below the theoretical level, where mainly water is present in the cooling tubes, less than the desired amount of heat can reach the steam within the central tube II, the balance being carried away by the water, while when or where the cooling tubes contain virtually no water or nothing but bubbles, as explained above, the presence of saturated steam and the small amount of entrained water therein cannot prevent the proper absorption of heat by the superheating tube l2, and in fact the wallsof the cooling tubes and the welds then may assist in conducting heat to the steam tubes.

In operation, steam; is generated in water tubes ID in the normal manner and delivered to the steam drum 2|. Instead of the usual take-off and connecting means at the top of the drum. however, the steam leaves the drum directly through the superheater tubes 12, entering their open tops and flowing downwardly therethrough. During normal operation the steam is superheated while flowing downwardly through the tubes l2, and is then delivered to the outlet steam header 33, whence it may be conducted to the engines (unshown) or any desired destination. The degree of superheat is regulated byvarying the amount of water in the cooling tubes by throttling its admission to vary the theoretical level and so the effective length of the superheater unit. This regulation is ordinarily eflected automatically by the throttle valve 36, which is thermostatically controlled, as above stated, in reapom to outlet steam temperature and arranged to decrease the flow and so depress the effective level when such temperature falls below a desired point, and to open the valve to allow the flow to increase and such level to rise when the temperature exceeds that point. The water tubes ID, by reason of their outermost positioning will be seen to act as a screen to limit the quantity of radiant heat which can reach the steam tube.

When the boiler is first started and no superheated steam is flowing, the valve 36 would normally be closed, and the burners would accordingly elevate the superheater units to a dangerous temperature if provision were not made for flooding the water tubes. Flooding is accomplished to safeguard the tubes by means of a manually operable by-pass around the thermostatic valve, such as is shown in Figure 1 at 42; By opening the by-pass.valve the water tubes may of course be flooded and maintained so until steam commences -to flow, after which the bypass may be closed and steam generation within the tubes I! will quickly reduce the effective level therein to the proper point where it will be held under the automatic regulation of the thermostatic valve.

The screening function of tubes I5 is highly desirable where boilers are operated at high ratings involving the extremely rapid heat transfers employed in marine work, although in boilers operated at lower rates of heat transfer the screening effect might not be desired, in which event the steam tubes might be arranged outermost, and the water tubes in an inner position in which neither they nor the saturated steam therein could interfere with the impingement of radiant heat against the steam tubes.

The superheater units 20 are ordinarily of such length that in normal operation the effective water level in tubes I! may be held at a relatively low point. From a practical standpoint the area above such level constitutes the eflective superheating surface. Virtually no superheating can take place below the water level, for the parts are so proportioned that substantial equilibrium is maintained in this area under normal heat delivery to the exteriors of the units. This proportioning and relationship will presently be discussed in greater detail. In order to prevent undesired desuperheating of the steam while passing through the water-containing portions of the superheater elements outside the zone of heat absorption, where such equilibrium could not be maintained if the bridging welds were present,,the welds l8 preferably extend only as far as the boundary of the zone of heat-absorption at the lower end. The absence of the bridging welds in the area beyond the inner surface of walls 29 so tremendously decreases the possible heat flow between the tubes l2|5 as to virtually insulate one from the other, so that no desuperheating can take place.

In Figures 3, 4, and 5 'is shown another embodiment in which each of the superheater elements, shown cross sectionally in Figure 4, comprises a central water tube ii, the external surface of which carries radially projecting helically disposed ribs l8, between which its surface is concaved to received the externally arranged steam tubes I2', which are fitted thereinto and welded to the tips only of the rib portions of the water tube, as at l8. This places the steam tubes in a more exposed position which under some conditions may render external screening desirable, as will presently be explained, but achieves important benefits in restricting direct heat conduction between the steam and water tubesand so preventing desuperheating, as will also further appear. Each of the superheater units, designated 20', may project at its upper extremity into the steam drum 2| in similar fashion to the embodiment first described. The steam tubes 12' extend to a point near the top of the drum, where their open inlet ends are guarded by a hat 26, while the central water tube I5 stops at a lower point, though also abovethe water level, where it is also guarded by a hat as 21'. The latter hat not only guards the cooling tube, but prevents it from so discharging saturated steam and water that it could enter the steam tubes.

A suitable manner of sealing the units 20 in the lower wall of the steam dmm 2| is also detailed in Figure 5. The sleeve 22 is tightly expanded into the drum or otherwise sealed in place, and is internally dimensioned to receive the unit 20, which after being fitted thereinto is welded thereto as at 24 to completely seal the union.

The steam tubes l2 are shown connected at their lower extremities to a manifold 44, after passing through which the steam is discharged into outlet header 33', while the water tubes l5 project entirely through the manifold andare connected to water inlet header This header is in turn connected to the mud drum 40, whence the cooling water supply is derived as through take-oil pipe 35'. A thermostatically controlled throttle valve designated 36' is shown arranged to control the water supply to enable regulation of level within the central water channel in response to output steam temperature as in the embodiment previously described, while the manually operable by-pass, as 42', may be similarly provided.

The length of the ribs [6 and the proportions and positioning of the tubes and of the bridging welds i8 are so calculated (by means well known and not necessary to be here detailed) that when and in those areas in which principally water is present within the central tube I5, the heat travels from the external surface of the assembly to the cooling water more readily than to the steam within tubes l2. This tendency of the water within central tube l5 to take the heat from the surface of the assembly when both water and steam to be superheated are present is so calculated that under such conditions, when heat is being delivered to the assembly at normal boiler rating, substantial equilibrium is maintained within the units below the water level so that the water can extract very little if any heat from the steam tubes, which action is prevented also by the insulating effect of the nonwelded association of those interfitting areas of the tubes between the welds. As to these areas, designated it should be noted that some gap is always involved even in what is commonly termed metal-to-metal" contact, and at the temperatures and rates of heat transfer here involved, this constitutes actual insulation. The steam tubes accordingly remain at approximately the same temperature as the steam within them, and no desuperheating takes place, whereas the xcess radiant heat which but for the presence of the water would continue to superheat the steam to a still higher temperature is absorbed by the water, and further superheating is thus prevented. It will thus be understood that the efrective superheating area of each unit is that above the eflective water level in the central tube l5 thereof, and that such length is subject to variation with the level by the above mentioned throttling of the water supply, conformably to the relation between the actual and desired output temperatures of superheated steam and the rate of steam generation in water tube lli'f Not only may the steam temperature be thereby held substantially constant at a desired level, but a further virtue of this arrangement is that maintenance of constant output steam temperature may be eflected throughout the entire range of boiler operation, from zero to maximum delivery.

It will be understood that the operation of the throttle valve is similar to that of an expansion valve, since below it the pressure is greater than above by reason of the head of water in the boiler, the pressure in the steam tubes of the superheating elements above the valve being less by reason of the reduced quantity of liquid, and the free vaporization of such liquid whichthere takes place. By reason of such free boiling of the throttled quantity of water, only gravity tends to hold the water in the bottoms of the steam channels. A sharply defined water level is thus avoided, and the presence of some entrained water throughout the steam tubes .as-

sured.

The tubes l2 are shown as helically coiled only within the zone of heat-absorption. Their indication in Figure 5 as straight at their upper ends within the drum is primarily to clarify that view, although this arrangement might advantageously be used in practise, since the effect of the intercoiling of the tubes is desired only within the zone of heating, where it assures substantially equal heat absorption by all steam tubes, thereby not only working all at the same rating but, which is more important, eliminating the undesirable raising of some steam tubes to a temperature higher than others, which would otherwise force undue heating of some in order that the average temperature of the steam delivered by all might be at a desired point. When coiled in this manner there is no necessity of either desuperheating as to any steam tubes, or heating some to a temperature higher than others in order to maintain. the desired average temperature.

As indicated at l8, the welding bridge per-- .bottoms of the units, at the boundary of the zone of heating, in order that in passing through the water-containing areas outside the zone of heat absorption the steam may not be desuperheated.

If, as is advantageous in some boilers, it is desired to reduce the quantity of radiant heat able to-reach the superheater thescreening effect of one of the rows of water tubes may be availed of. An improved manner of providing such screening is indicated in Figures 3 and 4. As there shown, the water tubes of the front row designated I0, are projected through and positioned in front of the superheater units, and are so staggered as to result in concentric grouping thereof about each unit in a manner imparting a wavular cross-sectional disposition to the tubes and enabling greater access of radiant heat to the superheater units than ability of such heat, which is of course propagated only in straight lines, to enter in wide angles and so impinge virtually the entire surface, as diagrammatically indicated by the arrows designated 89.

While it will be apparent that the illustrated embodiments of my invention herein disclosed are well calculated to adequately fulfill the objects and advantages primarily stated, it is to be understood that the invention is susceptible to variation, modification and change within the spirit and scope of the subjoined claims.

What I claim is:

1. In combination with a boiler having watercontaining steam generating portions arranged in a zone of heat absorption, and a collecting receptacle for saturated steam arranged thereabove and having a. water level therein, a water regulated superheater assembly arranged in the zone of heat absorption and incorporating a water control conduit and a superheater conduit integrated therewith to form a unitary assembly, the superheater conduit having an inlet end portion projecting into said receptacle and above the water level to receive therefrom steam to be superheated, and the watercontrol conduit having an outlet therein also above the water level.

2. In combination with a boiler having water tubes for generating saturated steam arranged within a zone of heat absorption and having a collecting drum to which the upper ends of said tubes are connected and within which a water level is normally maintained, a water regulated superheater assembly arranged within the zone of heat absorption and incorporating a superheating tube and a water-control tube integrated therewith to form a unitary assembly, the water-control tube being adapted to generate saturated steam, controllable means for feeding water to the lower end of said watercontrol tube, said assembly being projected and sealed into the drum at its upper end and the superheating' tube having an open inlet end near the top thereof and above the water level, and the water-control tube having an open outlet end also within' the drum and above the water level, whereby a reduced water level may be held in the cooling conduit.

3. In combination with a boiler having water tubes for generating saturated steamv arranged within a zone of heating, a collecting drum to which the upper ends of said tubes are connected and within which a water level is normally maintained, and a flooded drum to which the lower ends of said generating tubes are connected, a water cooled superheater assembly arranged within the zone of heating and incorporating at least one superheating tube and at least one cooling tube, the latter adapted to generate saturated steam, said tubes being integrated to form a unitary assembly and arranged generally parallel to the generating tubes and connected to the collecting drum, the superheating tube having an inlet at its upper extremity projecting to a point near the top of the drum and above the water level, the cooling tube having an outlet portion at its upper extremity also projecting within the drum to a position above the water level, and said tubes having an outlet and an inlet respectively at their lower ends, including controllable means for feeding water to the cooling tube from said flooded drum. 7

4. In combination with a boiler having water tubes arranged within a zone of heating and bounding a zone of radiant heat, a collecting l drum to which the upper ends of said tubes are connected and within which a water level is normally maintained, and. a flooded drum to which the lower ends of saidgenerating tubes are connected, a water regulated superheater as- I0 sembly arranged in the path of radiant heat and incorporating regulating and superheating tubes integrated throughout their effective lengths within the zone of heat absorption and connected to and extending through a lower 15 wall of said collecting drum, the superheating tube having a continuation forming an inlet and opening within said drum near the top thereof and above the water level, and the regulating tube having an outlet continuation also opening 0 within said drum above the water level, controllable means for feeding water to the lower end of the regulating tube, whereby a reduced level may be held therein, and means for taking off superheated steam from the lower end 25 of the superheating tube.

5. In a steam boiler construction, in combination with a furnace, a boiler including a steam drum, a plurality of water tubes arranged in 1 exposed position with respect to radiant heat 30 from the furnace, a plurality of water-regulated superheater elements arranged at an angle to the horizontal and generally parallel to the wa-' ter tubes, a plurality of said water tubes being grouped about each of said elements in 35 spaced generally circumferential arrangement.

6. In a steam boiler construction, in combination with a furnace, a boiler including a steam drum, a plurality of water tubes connected to and extending downwardly from the bottom of the drum, and a plurality of water regulated superheater elements extending into said same drum and each comprising separate but integrated conduits for steam to be superheated and for regulating water, each of said conduits having an opening at its end within the drum and above the normal water level therein, a shield over each of said openings to guard against splashing thereinto, and means for regulatably admitting cooling water to the bottoms of the regulating conduits in each of said elements.

7. In a steam boiler construction, in combination with a furnace, a boiler including a steam drum, a. plurality of water tubes connected to and extending, downwardly from the bottom of the drum at spaced points therealong, anda plurality of water regulated superheater elements extending upwardly through the bottom of the drum also at spaced points therealong and each including separate conduits for steam to 60 be superheated and for regulating water, said conduits extending upwardly within said drum and each having an opening therein above the water level, the opening in the tube for regulating water constituting an outlet and that in the 65 superheater tube constituting an inlet, the inlet being located above the outlet means for regulatably admitting regulating water to the bottoms of the cooling conduits, and means for guarding said outlets against splashing of water into the 70 regulating water conduits.

CHARLES S. TURNER.

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