US2202768A - Fluid heat exchange apparatus - Google Patents

Description

, May 28, 1940.

E. G. BA ILEY FLUID HEAT EXCHANGE APPARATUS Original Filed July 10, 1934 INVENTIOR 3 Sheets-Sheet 1 Erwin G Bai/ey A kl azv May 28, 1940. E, B L Y 2,202,768

FLUID HEAT EXCHANGE APPARATUS Original Filed July 10, 1934 3 Sheets-Sheet 2 Fj Z INVENTOR Ervin Baz/ey May 28, 1940. E. G. BAILEY 2,202,768

v FLUID HEAT EXCHXNGE APPARATUS 1 Original Filed July 10, 1934 3 Sheets-Sheet I5 INVENTOR [twin 6. Bailey A B //6 /20 I A v RNEY Patented May 28, 1940 PATENT OFFICE FLUID HEAT EXCHANGE APPARATUS Ervin G. Bailey, E sto Pa, s g r Th Babcock & Wilc0' x Company, Newark, N. J., a corporation of New Jersey Application, July 10, 1934, Serial No. 734,455 Renewed August 28, 1937 18 Claims.

This invention is concerned with improvements in fluid heat exchange apparatus, and the invention is exemplified in steam generating systems wherein a radiantly heated superheater of the wall tube type is combined in a novel manner with a large boiler furnace having fluid cooled walls.

An object of the invention is to provide a steam generating system in which a radiant superheater is operated inconjunction with a modern high temperature boiler furnace in such a way that certain operative disadvantages of radiant super heaters are'minimized and their periods of out! age materially reduced.

The operation of wall tube superheaters, as previously arranged, indicates that their tubes often become damaged by overheating at sudden load changes and under starting conditions. One reason for this damageis the difficulty which i ts been experienced in properly. coordinating steam flow through the superheater and the absorption of. heat transmitted by radiation to it. It is a further object of the present invention to effect such coordination. A further difficulty arises when coal is burned in the furnace at temperatures that partially or wholly melt the ash. Under these conditions, deposits of slag collecting on the superheater tubes reduce the superheat and at times,' such-deposits break off or are melted off, with a consequent rise of superheat. It is a further object of this'invention to minimize fluctuations of superheat due to such causes.

It. has been proposed to locate the tubes of a radiant sup'erheater in proximity to water tubes to protect them from overheating, and it has also been proposedto shield the tubes with refractory coverings to limit their, metal temperatures. vIt is an object of the present invention to eliminate such expensive protective structures and to make it possible to safely and successfully use bare tubes in a radiant superheater without danger of overheating the metal and Without the fluctuations of superheat due to changing thicknesses of ash deposits when the tubes are in slagged condition. I

It has been the practice to install radiant superheaters in the parts of furnace walls directly sitioned is mainly radiant and derived from four sources; first, the solids suspended in the gases, such as ash or carbon in course of combustion; second, the refractory of the furnace Wa ls; third,

the solids of the fuel bed when beds are used; and fourth, the furnace gases themselves, principally the carbon dioxide and water vapor constituents. These four sources of radiant heat fall into two classes, solids and gases. The radiation from the solids is relatively the more intense, and the superheat hasdepended largely on such radiation.

In the present invention the arrangement is such as to minimize the radiation received by the superheater from the high temperature stage of the. furnace, and to make the superheat depend mainly on radiation of gases beyond the high temperature stage of the furnace, at the same time minimizing or eliminating slag and ash deposits on the superheater tubes.

These results are accomplished by providing a furnace slag screenbetween the zone of initial combustion the furnace and ,a gaseous space inadvance of the boiler tube bank, and by loeating the superheater tubes in one or more of the walls of this screened gas space.

.By this arrangement the radiation from the furnace below the screen to the superheater wall tubes is minimized while the hot gas inthe space beyond the screen may radiate directly to the superheater and be itself screened from furnace radiation so that the gas may decrease in temperature by its own radiation to the superheater.

Any slag crash not depositedon the screen tubes, and passing through the superheating zone will be cooler when it reaches the superheater tubes. eliminated, especially so when, as is normally the practice in such furnaces, their walls have water tubes to cool them.

In this way, stickiness is reduced or Radiation from solids does not vary with rate of combustion in the same proportion as does steam flow through the superheater, especially after sudden load changes, but gas Weight'does vary almost in proportion to steam flow. Immediately after a reduction of load, a radiant superheater exposed to solid radiation will give an increase of superheat and hotter tubes, because for a time the solid radiation isv not reduced after the steam flow has lessened. On the other hand, gaseous radiation will be promptly reduced because the reduction of gas flow which accompanies reduction of steam flow and causes it, results in a lessened mass of gas radiating with consequent greater gas cooling and lessened radiation. Thus with the arrangement of the invention with its furnace slag screen in front of the superheater, minimizing furnace radiation there to, the superheat and the metal temperature will be more steady under all load changes than without it.

The present invention contemplates a steam boiler and furnace organization which renders an incorporated radiant superheater successful in operation, not only on account of the limiting of the superheater largely to gas radiation, but also on account of the tempering of the furnace gases and any suspended ash before they move into heat radiating position relative to the superheater.

The invention will be describedwith reference,-

to the accompanying drawings, in which:

Fig. 1 is a vertical section illustratii g one embodiment of the invention including a wall tube,

radiant superheater and a convection superheater associated with a furnace having covered furnace screen tubes. 1

Fig. 2 is a vertical section illustratinga mod- Fig. 3 is a vertical section illustrating another embodiment in which a convection superheater is disposed below the level of the bottom of'the wall tube superheater and above the furnace screen tubes.

Fig. 4 is a transverse sectiontakenon the line 4-4 of Fig. 1 and indicating the structure of the refractory covered furnace screen.

In Fig. 1 of the drawings Ill indicates a boiler furnace fired by stokers l2. As shown, the 'fur'-' nace has a gas outlet at its upper portion.- The furnace screen indicated in Fig. 1 includes refractory covered tubes I6 and I8, the inclination and grouping of the tubes governing the'heat radiation to the walls above the screen. These tubes connect headers 28 and 22 and extend across the furnace outlet. The headers may be connected into the boiler circulation system by suitable connections 2| and 23.

Above the level of the furnace screen and be low the level of the steam generating section "of water tubes 24 is a gas space. Onthe' wall of the chamber providing this space is a radiant superheater of the wall tubetype; Immediately above the level of the wall tube superheater is a convection superheater 28 extending across the gas pass beneath the steam generating section.

As shown in Fig. l of the 'drawings,"the tubes of the convection superheater extend through a baflie 30 the lower end of which supported by the bent water tubes 32 connected to the headers 34 and 36. The superheater inlet header 38 receives saturated steam through the connections.

4!] leading from the steam space of the drum 42.

From the outlet header 44 steam flows through the line 46 to the inlet header 48 of the first wall tube radiant superheater. This header is connected by wall tubes 58 to an outlet'header 52 from which steam flows through the T-fitting 54 and the superheated steam main 56 to a point of use. The inlet header 58 for a second radiant superheater receives steam through a line 62 leading from the outlet header 44 of the convection superheater. The outlet header 64 is directly connected to the steam main 56 as shown.r It will be seen that, in this modification, the radiant superheater and the convection superheater have a series connection, with the two sections or parts of the radiant superheater connected in parallel.

The stoker fired furnace shown in Fig. 1 water tubes in its walls. The wall tubes 65 for the right hand wall are connected to'headers 68' tubes. connected. to the steam space of the drum 42 by horizont'al" circulat'ors 88, and the downtake refractory I -walltube superheater (relative to gas flow).

consists of ;tube loops which are held in their ophas and 18, the latter having a conduit" preferably communicating with the drum 42 to maintain boiler circulation through that part of the furnacewall system. At the opposite furnace wall are headers 14, 16 and 18 connected by wall tubes and 82. The upper header is connected by tubes 84 to the drum 42.. u

As shown in Fig.1 as well as'inFigs. 2; and 3, there is a' bank of horizontally inclined boiler In each instance the uptake headers are headers 38 are connected to the water space of the drum bynipples 90.

In Figs'..1-and 3 there is a convection superheater.

In the Fig. 3 modification. the convec tion superheater!!!) is positioned forwardly of the It erative relationships by connectors lllll which preferably mutually support adjoining loops while permitting expansion. 1 Each superheater tube comprises a plurality of these loops, and each: tube is connected to an inlet'header I02 which receives steam through multiple connections I84" the spaced along the header'and leading from steam space of the drum 42. u I

The outlet header I06 for the convection superindicated at I08 and- H0.

point of use.

In the Fig. 2 embodiment of the invention,;

there is no convection superheater, the saturated steam passing directly from the drum 42 through the line H6 'andother suitable lines to the headers ll4 and- 58."

The furnace shown ineach of the Figs. 2 and 3 embodimentsis a slag tap furnace provided with a refractory floor I I8 and aslag tap opening I20. The furnace walls are provided with headers and tubes arranged after .themanner in which the corresponding elements in the Fig. 1 embodiment are arrangedfexcept that bottom headers I22 are shown as provided for bottom supported walls while in Fig. 1 they are shown as for top sup-- ported walls. v

Each furnace ofthe Figs. 2v and .3 embodiments is providedwith a fuel burner 124 for burning pulverized fuel insuspension. Gas or oil might also be burned in these furnaces.

The furnace of Fig.1 has a stoker, and in all of the illustrated embodiments of the invention the combustionis substantially completed in the furnace below the level of the; screen tubes and,

the solid radiation takesplace below the screen level.;

-.-In the described apparatus the gas radiation varies with the quantityofgaspassing the screen tubes-l6 and I8, Thiscondition facilitates the maintenance of superheat at a. desired value, because of the relatively steady-relation between.

gaseous radiation and steam flow. In the event that load conditions demand it,.the gaseous radi--, ation may be supplemented by, solid radiation (here considered as furnace radiation) effected by changes in combustion conditions to cause the flame to pass the screen in part. Such sup plemental radiation-may be from soli ds insusf pension or from the furnace walls. It may also be considered generally as radiation from the furnace. In either event the screen tubes are preferably arranged so as to direct furnace radiation toward the wall tubes which will reduce reradiation to the generating tubes. The screen tubes also act to reduce the absorption of furnace radiation by the gas body above the screen, and permit the gas temperature to fall. A flat superheat curve is obtained by the regulation or control over solid radiation effected through combustion changes, and the action of the screen tubes.

When the furnace is of the water wall type as shown, the temperature of the gases passing the furnace screen may be controlled with reference to the ash fusion temperature of the coal by the proportioning of the cooled wall area and the rate of combustion, and the gases radiating to the wall superheater above the screen are thus controlled in radiating intensity. Also the tendency for ash or slag to stick to the tubes is controlled.

In one modification of the invention illustrated the screen tubes (such as It and I8) are provided with refractory coverings 86 (see Fig. 4). Under normal operating conditions the outside surfaces of these coverings will be hotter than the tubes and will remain sticky with molten slag upon their surfaces. This will cause the screen to catch and retain ash particles, preventing them from rising into the gas space above the screen thereby limiting the heat radiation from sus pended solids in the gas zones in front of the wall tube superheater.

In all embodiments of the invention the wall tube superheater while fully exposed to radiation of all the gases leaving the furnace has its tubes protected from furnace radiation by reason of the interposition of a screen of water tubes across the furnace outlet and in advance of the gas radiation space. Furthermore, the separate superheater tubes are in upright posi tions, where they may be advantageously pendently supported from their upper headers. Both of these circumstances reduce outages and prolong superheater life, thus overcoming difficulties which have been experienced in the operation of such devices.

While the invention has been described with reference to certain particular embodiments of the invention it is to be understood that it is not limited thereto but is of a scope commensurate'with the scope of the subjoined claims.

What is claimed is:

1. In a steam boiler, a water wall furnace, means for burning fuel in the furnace with combustion particles in suspension, a superheater composed of upright tubes adjacent a wall of the boiler, water tubes extending across the path of furnace gases passing to the superheater form a screen, a bank of steam generating tubes beyond the superheater with reference to gas flow, and a convection superheated positioned between the first superheated and the generating tubes.

2. In a boiler, a water wall furnace, a steam generating section above the furnace, a radiant superheater interposed relative to the furnace and the steam generating section and consisting of tubes located adjacent the wall, Water tubes acting as a screen and extending across thepath of furnace gases moving from the furnace to positions wherein they cause the superheater to be heated by gaseous radiation, and a convection superheater having tubes extending across the path of the furnace gases moving from the water tubes to positions in front of the wall tube superheater. 1

3. In a steam generating installation, a boiler furnace having an outlet for furnace gases, a

superheater consisting of upright tubes extend-- ing along the walls of the outlet, refractory covered water tubes extending across the outlet in front of the superheater'in relation to gas flow, a steam generating section having tubes positioned beyond the superheater relative to gas flow, and a Stoker so coordinated with the furnace and the water tubes that. combustion may be completed before the furnace gases pass the screen formed by the water tubes.

4. In a boiler, a furnace, a radiant superheater adjacent a furnace Wall and having upright wall tubes as its heating elements, refractory covered water tubes forming a screen and extending across the path of furnace gases moving to positions in front of the wall tubes, and means for burnin fuel in the furnace capable of regulating the flame travel of the furnace gases beyond the screen formed by the water tubes.

5. In combination, a bank of water tubes forming a steam generating section, a water wall furnace, means for burning pulverized coal in the furnace with combustion particles in suspension, a wall tube radiant superheater located forwardly of the steam generating section relative to gas flow, a row of tubes connected into boiler circulation and forming a screen extending across the outlet of the furnace, a convection superheater having tubes extending across the path of the gases as they move from the screen to positions in front of the Wall tube superheater, and means for conducting steam from the generating section to the convection superheater.

6. Fluid heat exchange apparatus comprising, in combination, a boiler tube bank of steam generating tubes, a furnace from which hot gases pass across said tubes, means for burning such a fuel in the furnace that the furnace gases carry combustion solids in suspension, a convection superheater having its heat absorbing tubes forming a screen extending across the furnace below said bank and dividing the furnace gas space below the generating tubes into first and second sections and limiting the passage of solids carried in suspension by the furnace gases from the first section to the second section and to said bank, and acting as a secondary screen to limit furnace radiation that can reach the gas body above the screen, a radiant superheater having upright tubes adjacent a wall of the second section of the furnace and positioned between the boiler tube bank and the screen, and means for connecting the screen tubes to a source of steam, the screen limiting radiation of heat from the first section to the second section.

'7. Fluid heat exchange apparatus comprising, in combination, a main boiler tube bank of steam generating tubes, a furnace from which hot gases pass across said tubes, means for burning such a fuel in the furnace that the furnace gases carry combustion solids in suspension, water tubes and a convection superheated forming a screen extending across the furnace below said bank dito the second section and to said bank, a radiant superheater having upright tubes adjacent a wall of said second section and positioned between the boiler tube bank and the water tube screen, means for connecting said superheaters to a source of steam, and means for connecting the screen tubes into fluid circulation, the screen limiting radiation of heat from the first section to the second section.

8. Fluid heat exchange apparatus comprising, in combination, a boiler tube bank of steam generating tubes, a furnace from which hot gases pass across said tubes, a means for burning such a fuel in the furnace that the furnace gases carry combustion particles in suspension, screen tubes dividing the furnace gas space below the generating tubes into first and second sections and so constructed as, to substantially prevent radiation from the first section to said second section and to limit the passage of combustion particles carried in suspension by the furnace gases from the first section to the second section and to said bank, said second section having a radiant superheater comprising a single row of wall tubes positioned between the boiler tube bank and the water tube screen, and means for connecting the screen tubes for fluid movement therethrough, the screen limiting radiation of heat from the first section to the second section.

9. A method of effecting fluid heat exchange which comprises, burning a slag forming fuel in a furnace in such a manner that the furnace gases carry combustion solids in suspension, cooling the solids in an outlet zone by subjecting the furnace gases to contact with a fluid cooled screen, superheating steam by absorbing heat mainly radiantly transmitted from the furnace gases after suspension carried solids have been emoved by the cooling operation, and varying combustion so that the flame limit is controlled with reference to the screen whereby a superheat represented by a fiat curve is obtained over a wide rating range. I

10. In combination, a furnace, a radiant superheater of the wall tube type, and a convection superheater having its tubes extending across the path of the furnace gases and positioned forwardly of the radiant superheater relative to gas flow.

11. In fluid heat exchange apparatus, a furnace, means for burning a slag forming fuel in the furnace, means forming a chamber into which the gases pass from the furnace, slag screen means extending across the path of furnace gases at a position between the furnace and the chamber to cause a deposition of solids carried in suspension by the gases, and a superheater comprising a single row of wall tubes disposed in an upright plane at one side of andparallel to the gas flow through said chamber, the construction of the screen being such that the radiant rays transmitting the major portion of the heat from the gases to the superheater emanate from the gases in said chamber and are in planes normal to said plane, said rays being of such length that radiantly transmitted heat of maximum intensity is absorbed by the superheater.-

12. In fluid heat exchange apparatus a furnace, means for burning a slag forming fuel in the furnace, a slag screen for limiting the passage of solids carried by the furnace gases and whereby radiant transmission of heat from solids carried in suspension in the chamber is substantially eliminated, and -a superheater comprising a single row of upright wall tubes disposed in a plane at one side of the gas flow in said chamher, the construction of the screen being such that the radiant rays by which the major portion of the heat is transmitted to said walltubes emanate from the gases in thechamber and are in planes normal to said plane, said wall tubes' being exposed unobstructively to gas radiation from the main body of gas beyond said slag screen.

* 13. In a water tube steam boiler having tubes forming a water circulating and steam generating system, a furnace, means forming a gas pass or gas radiation chamber leading from the furnace, a high temperature radiant superheater including a single row of Wall tubes along one. of two opposite upright sides of said gas pass and constituting a part of said means, a plurality of water tubes constituting a furnace screen extending across the path of the furnace gases to intercept radiation from the furnace to a sub-. stantial degree without imposing the convection: cooling effect of a deep bank of tubes, said screenseparating said chamber from the furnace, and

means for connecting the screen tubes into the: circulation system of the boiler, the gas space. of the gas radiation chamber in front of the superheater tubes being unobstructed in order. to provide a radiating gas body of effective Width.

14. In a water tube steam boiler, a furnace, a

radiant heat absorption chamber into which the heating gases pass from the furnace, fluid'coo'lefd: screen tubes extending across the path of furnace gases at a position between the furnace and said chamber, fuel burning means capable of regulating the flame travel of'the furnace gases.

beyond the screen tubes, and a superheater or reheater including upright wall tubes heated main-' ly by radiation and arranged along at least one side of said chamber.

15. In a water tube steam boiler, a furnace, a convection section including water heating tubes extending across the path of the gases beyond said chamber, a radiant heat absorption chamber into which the heating gases pass from the furnace, a gas outlet through which the furnace gases pass from said chamber to the convection-section, fluid cooled screen tubes extending across the path of furnace gases at a position between the furnace and said chamber, fuel burning means, and a radiant steam heater including upright wall tubes along at least one side of said chamber, the path of travel of the furnace gases past the heater being at least as great as the width of said gas outlet. i

l6. Ina water tube steam boiler, a furnace, Water heating tubes extending across the path of the furnace gases and constituting part of a convection stage, a furnace screen including tubes dividing the furnace into primary and secondary stages, means for burning fuel in suspension in the primary stage, a radiant steam heater exposed to heat radiated from all of the gases leaving the furnace and shielded by said screen from' radiation of solids in the furnace, and means for connecting the screen tubes into a fluid circuit. 1

17. In a water tube steam boiler, a' furnace, means for burning fuel in suspension in the furnace, a radiant superheater including tubes exposed to heat radiantly transmitted from the furnace gases, a convection superheater including spaced tubes extending across the path of the furnace-gases, connections'providing for the supply of steam the superheat of which is the result of the combined action of the radiant superheater and the convection superheater, and a fluid cooled screen extending across the path of the furnace gases ahead of the radiant super:

heater and co-operating with the furnace to increase the otherwise applicable ratio of gaseous radiation to the radiant superheater to the total radiation thereto, whereby a flat curve superheat may be maintained over a wide range of boiler loads.

18. In a water tube steam boiler; a multiple stage furnace including a high temperature combustion chamber in the primary furnace stage; spaced fluid heating tubes extending across the path of the furnace gases leaving the furnace and constituting part of a convection heat absorption stage; a gas radiating chamber constituting a secondary furnace stage; means including fluid cooled screen tubes separating the primary and secondary furnace stages with the secondary stage between the convection. heat absorption stage and the primary furnace stage, relative to gas flow; means forming a furnace gas inlet to the convection stage, and a steam heater of the furnace wall tube type presenting a heater face past which the furnace gases move in the secondary stage, the tubes of the heater extending in substantially the same direction-as gas flow.

ERVIN G. BAILEY.

CERTIFICATE OF CORRECTION. Patent No. 2,202,768. May 28, 19m.

ERVIN G BAILEY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 60, claim 1, after the word "super-heater" insert --to--; lines 65 and 611., same claim, and. second column, line 67, claim 7, for "superheated" read -superheater; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed. this 25rd day of July,'A. D. 191m.

, Henry Van Arsdale, (Seal) 7 Acting Commissioner of Patents.

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