US2876748A

US2876748A - Vapor generating and superheating unit with vapor temperature controls

Info

Publication number: US2876748A
Application number: US409086A
Authority: US
Inventors: Harvey H Nelken
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1954-02-09
Filing date: 1954-02-09
Publication date: 1959-03-10
Anticipated expiration: 1976-03-10

Description

March 10, 1959 H. H. NELKEN 2,376,748

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLS Filed Feb. 9, 1954 5 Sheets-Sheet l SUPERHEATER FURNACE I I I I I I I I I I l I I I x I I I I I I l -I I I l I 170 .506 /72' I66 I 64 lNV TOR March 1959 H H.- NELKEN 2,876, 48

VAPOR GENERATING AND SUPERHEATING'UNIT WITH 1 VAPOR TEMPERATURE CONTROLS T Filed Feb. 9, 1954 5 Sheets-Sheet 2 TMIIJA.

PRIM.S.H. STAGE 2 ATTORNEY March 1959 H. H. NELKEN 2,876,748

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLS Filed Feb. 9, 1954 5 Sheets-Sheet 3 H.Nelken I ATTORNEY March 10, 1959 H. H. NELKEN 7 VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLS Filed Feb. 9, 1954 5 Sheets-Sheet 4 TlEfE- I l PRIM SH 1 mi; A- i //2 i l i I X I /74f PRIM SH. STAGE 1 Numb ' ATTORNEY March 10, 1959 H. NELKEN I 2,376,748

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLS 1 Filed Feb. 9, 1954 5 Sheets-Sheet 5 PRIMARY REHEATER SUPE RHEATER T33 I elken ,tion in the cost of generated power.

VAPOR GENERATING AND SUPERHEATING UNIT WITH VAPOR TEMPERATURE CONTROLS Harvey H. Nelken, River Edge, N. J., assiguor to The Bab'cock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application February 9, 1954, Serial No. 409,086

13 (Ilaims. (Cl. 122-240) This invention relates to a vapor generating and superheating-unit. I t

The invention is more particularly concerned with a vapor generating and superheating unit of the radiant boiler type and having its components so constructed and arranged that it provides for the reliable operation of the unit with a high degree of availability. The vapor generating and superheating unit of the invention is capable of producing 1,700,000 pounds steam per hour at a temperature of the order of 1100 F. and at a pressure in excess of 2000 p. s. i. with minimum requirements as to space occupied by the unit and when combined with the other necessary components for the production of electric power. In addition, the unit is capable of producing power at a greatly reduced cost of vapor per unit of power.

More specifically, the invention involves a vapor generating and superheating unit of the radiant boiler type having a large volume furnace, with its rectangular cross section of the order of 60 x 30 feet, and with its height of the order of 150 feet. The furnace has a plurality of lateral outlets at its upper part leading in parallel from the longer side of furnace cross section. These outlets lead to parallel and separate gas pass constructions each having its own set of liquid cooled enclosing walls, and with the gas passes spaced from each other so as to facilitate accessibility and promote effectiveness of structural support. A convection vapor superheater or reheater is arranged in each gas pass and when, for example, the superheater has a convection section in each of the separate gas passes, these two sections are crossconnected in series as to vapor flow in order that the vapor temperature at the final outlet of the vapor heater is not affected by unbalanced gas flow in the two parallel gas passes.

The illustrative unit being of the capacity of the order of 1,700,000 pounds of vapor per hour, marks a milestone in the progress of the art of steam generation and steam superheating in units assoicated with steam turblues and electric generators for electrical power production. One of the outstanding accomplishments in this art is represented by the present invention which attains, with its associated power plant units, a marked reduc- To a considerable extent, this result is attained by the magnitude of the steam generating and superheating unit, but, in addition, the fabrication of such a large unit is something more than a mere enlargement of previously suggested units. For example, although there have been suggested in the prior art, units of the type of the illustrative unit, the suggested units having radiant boiler furnaces of the order of 30 feet square in horizontal cross section with a height of from 60 to 90 feet. When a unit was considered of a capacity almost double that of the suggested units, serious problemswere encountered. One such problemrelated to the limitation on the minor dimension of the cross section of such a gas pass, such limitation being imposed by the characteristics of the .retractible to the superheater.

2,876,748 Patented Mar. 10, 199

ice

soot blowing apparatus necessary for periodic use in the cleaning of the convection surfaces in the associated gas passes. Such cleaning devices, even when employed from opposite sides of a furnace or a gas pass, impose a restriction of the minor cross section dimension of that gas pass of the order of 20-25 feet. Also, because the soot blowers are retractible there is a minimum withdrawal space necessary externally of the unit, to keep the cost of the unit within a reasonable range. The illustrative unit meets these requirements while at the same time providing a unit of a capacity far beyond the for the superheaters, reheaters and other convection heating apparatus, and by arranging the parallel gas passes as" entirely separate enclosures with their adjacent walls spaced from each other sufliciently to provide for manual access therebetween for the purposes of maintenance, cleaning and repair. The illustrative unit also promotes the maximum capacity within a given space requirement by providing that the parallel passes lead from the same face or side of the furnace, or its rectangular cross section outlet.

For optimum vapor or steam heating, the invention not only provides cross connected secondary superheater sections which 'are disposed in separate gas passes leading in parallel from the combustion zone, the invention also provides for superheat and reheat control. To this end the reheater surface is disposed in one of the parallel gas passes and at least the major part of the primary superheater surface is disposed in the other gas pass.

The total secondary superheater surface is divided be-- tween the two gas passes.

In connection with the vapor heating provisions referred to immediately above there is a recirculated gas system affecting each gas pass, taking partially cooled parts of the load range,'so as to overcome, for instance;

the natural tendencies of convection vapor heaters to fail to develop a predetermined high temperature 'over such lower portions of the load range.

The invention also involves attemperation as a part of the entire control setup, but this attemperation is limited Preferably attemperation takes place in the steam flow at a position between the primary superheater and the secondary superheater.

In addition to the 'above mentioned components invention involves the proportioning' of the total gas flow; between the two gas passes for the purpose of controlling vapor temperature, and particularly reheat temperature. The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specifica tion. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated.

ating and superheating unit, on the line 1-1 of Fig. 2;-

Fig. l-A is another vertical section of the same unit,

p on the line 1A-1A of Fig. 2;

Fi 2 s a Pl n ecti n t he ame n on h line 2-2 of Fig. 1;

Fig. 3 is an isometric diagrammatic view of the convection components of the Fig. 2 unit; and

Fig. 4 is a vertical section of another unit embodying some of the features of the Fig. 2 unit.

The vapor generating and superheating unit shown in Figs. 1-3 has a combustion component including two vertically

elongated furnaces

10 and 12 defined by upright vapor generating wall tubes including the tubes of the division wall 14, separating the furnaces. The furnace 10, further shown in Fig. 1, is fired by vertically spaced rows of

burners

16, 18 and 20 and the other furnace 1 2, shown in Fig. 1A is similarly fired by rows of

burners

22, 24 and 26.

The vapor generating tubes of the furnaces discharge generated vapor into the drum at a rate of the order of 1 9 Po s o ap P r ou at a pres o he rder of; 23 0 p unds. per squar nch he n ra apor item he r s uperh ed to a p t re ot the order of 10 50 F. in convection superheater sections selectively disposed in two convection gas passes leading from the furnace. One gas pass leads directly rearwardly from the furnace 12 and the other, parallel to the first, leads directly rearwardly from the other furnace 10, as shown in Figs. 1 and 2. Fig. 1A shows the gas pass leading from the furnace 12.

The Fig. 1 gas pass 32 includes a lateral sub-pass 34 at the upper part of the unit discharging gases into the gas turning space 36 from which the gases proceed through the downpass 38. In the lateral sub-pass 34 the high temperature gases first pass over the pendent superheater section 40, constituting stage 2 of the secondary superheater, from which vapor superheated to a temperature of the order of 1050 F. passes to a high pressure prime mover such as a turbine. From the second stage 40 of the secondary superheater the gases next pass over the bank of horizontally spaced upright tubes 42 constituting stage 1 of a primary superheater.

Beyond the primary superheater stage 1 the gases turn in the space 36 and pass downwardly over the successive banks 44-46 of horizontal tubes constituting the leading part of stage 1 of the primary superheater. These banks of tubes, as well as the bank of upright tubes 42 are formed by continuous, or serially connected tubes receiving vapor at their inlet ends from header components 48-50. connected, in turn, to the discharge ends ofsuperheater supply wall tubes, disposed along the walls of the downpass 38. The inlet ends of these rows of

wall tubes

52 and 54 are in communication with the vapor space of the drum 30. A similar arrangement of superheater supply wall tubes is associated with the other downpass 106. In this downpass 106 vapor passes from superheater supply wall tubes to the headers 1-16', 118 and 120 and thence through appropriate conduits to the inlet header components 48, 4-? and d at the bottom of downpass 38. The header components 116, 118 and 120 are disposed at the walls of downpass 106. The superheater

supply wall tubes

122 and 124, for headers 116, 118 and 120 are arranged along the gas pass walls and having their inlet ends in communi cation with the vapor space of the drum 3%), through connections such as the header 123 and the conduits 125.

Below the banks of tubes 44-46 of stage 1 of the primary superheater the heating gases next pass over the tubes of the economizer 56 and then through the ductwork 58 to the regenerative air heater 60. The ductwork 58 has mounted therein a row of gas flow regulators 62 for proportioning the flow of heating gases over the pertinent vapor heaters (i. e., primary and secondary superheater components) Below the air heater 60 ductwork 64 is provided for flow ofthe gases to a flueor stack. Secondary air passes to the other side of the air heater from a forced draft fan 66 and interposed ductwork 68; From the air outlet side of the air heater, heated air flows through

ductwork

70, 72, to the windbox 74 enclosing the

bumers

16, 18 and 20.

Fig. 1A shows the gas pass leading from the fur nace 12, this gas pass structure being separated from the gas pass 32by access and maintenance space 82, as indicated in Fig. 2. This space advantageously enhances maintenance of the illustrative unit by facilitating the installation and use of elfective soot blowers from positions between the gas passes 32 and 80.

The gas pass 80 includes the lateral, or horizontal, sub-pass 84. Gases entering this sub-pass first contact the horizontally spaced upright tubes of the bank of tubes 86 constituting stage 1 of the secondary superheater. These tubes lead from the inlet header 88 to the outlet header 90.

Upon leaving stage 1 of the secondary superheater (bank of tubes 86) the gases next pass over and between the horizontally spaced upright tubes constituting the bank of tubes 92 of the second reheater stage, these tubes leading from the inlet header 94 to the

twin outlet headers

96 and 98.

After leaving reheater stage 2 the gases pass over and between the spaced upright tubes constituting the bank of tubes 100 of reheater stage 1, these serially connected return bend tubes being pendently supported, at least in part, from the inlet header 102 and outlet header 104.

The reheater stage 1 (bank of tubes 100) is disposed in a gas turning space above a downpass 106 in which the banks of tubes 108110 of stage 2 of the primary superheater are disposed. These serially connected return bend tubes lead from the lower inlet header 112 to the outlet header 114, disposed above the gas turning space in which stage 1 of the reheater is located.

The inlet header 112 receives vapor through connections 174 and 176 from primary superheater first stage outlet header 43.

At the lower end of the downpass 106 there is a series of gas flow regulators 126 for controlling gas flow over stage 1 of the secondary superheater (bank of tubes 86), reheater stage 1, reheater stage 2, and stage 2 of the primary superheater, all disposed in the gas pass 80.

It is within the purview of the invention that the gas flow regulators 126 together with their counterparts 62 in the other gas pass and a common control system, acting from reheat temperature and load, shall function as gas flow proportioning means to maintain a predetermined reheat temperature over a wide load range and this action shall obtain whether the gas flows are subject to a common recirculated gas connection, or not. Such a common connection may involve a unitary duct formed by the

ducts

156 and 166.

Where such a unitary duct is involved, the

windboxes

74 and 136 may also constitute an integral windbox and the gas passes 38 and 106 may be connected by a common duct below the economizers therein.

Beyond the gas flow regulators 126 the gases flow through a duct 128 to the regenerative air heater 130 from which heated secondary air flows through

ductwork components

132 and 134 to the windbox 136 disposed around the rows of

burners

22, 24 and 26. Air flows through duct 138 from the forced draft fan 140 to the air heater, and the heating gases flow from the air heater through ductwork 142 to a stack.

Fig. 2 shows a horizontal section of the furnace division wall 14, constructed of wall aligned vapor generating tubes having their upper parts oppositely bent out of their wall alignment to form the

platens

14a and 14b spaced as shown to provide inter-communication be tween the furnaces for pressure equalization and for gaseous movements in response to the. control of gas proportioning between the gas passes, 32. and 80 or in response to other furnace. gas flow control such as the variation in flow of recirculated gases to the. furnaces. to control reheat. The Fig. 1A gas pass (also indicated asp-awasin Fig. 2 as the gas pass 80) may be termed a reheater gas pass, since all of the reheater surface is disposed therein. Likewise, the furnace 12 of Fig. 1A might be termed the reheater furnace. It is provided with a hopper bottom 144 into and through the throat 146 of which are discharged partially cooled heating gases from an opening or passage 158 leading from the manifold 156. The system for effecting such recirculation includes a duct 150 connecting an opening 148 in duct 128 with the inlet of a recirculated gas fan 152. The outlet of the fan is connected by a duct 154 to the manifold 156 from which a plurality of outlet ducts 158 are in communication with the throat 146.

When operating conditions are changed in such a way as to have a tendency to cause reheat vapor temperature to drop below its optimum value of 1000 F. as when the load decreases, the flow of recirculated gas through the above described system and thence through the furnace 12 and its gas pass is increased to increase gas mass flow over the reheater stages and thereby have a corrective influence at least partially offsetting the tendency of reheat temperature to drop. This corrective influence may be combined with automatic control of the gas proportioning dampers, 126 and 62, to attain a predetermined reheat, or the latter control may be used alone to attain the same eifect.

A similar recirculated gas system is shown in Fig. 1 as applied to the superheater furnace 10. It includes a duct 160 connecting a recirculated gas inlet 162 in ductwork 58 with the inlet of a fan 164 the outlet of which is connected to the recirculated gas manifold 166 by a duct 168. The manifold is connected with the hopper bottom throat 170 by a plurality of outlet ducts 172 distributed throughout the length of the manifold.

The illustrative unit further promotes control of vapor temperature on the reheater and superheater sides by proportioning gas Weight or gas flows through the separate gas passes and their furnaces by means of the pro portioning dampers or gas flow regulators 126 (Fig. 1A) and 62 (Fig. 1). Preferably such proportioning of gas flows through the separate gas passes 32 and 80 is utilized, in the illustrative unit, to adjust reheat temperature in reference to superheat, or primarily for maintaining a predetermined reheat temperature, and control of recirculated gas flow is effected to maintain superheat temperature at a predetermined value. control and recirculated gas flow control are efiected Both proportioning automatically from combinations of influences in both of which load is a factor. In the propo-rtioning combination reheat temperature is also involved as an influence, and in the recirculated gas flow control combination superheat temperature is involved.

The pertinent system and arrangement of superheater-s and reheaters and their connections (shown in perspective or isometric form in Fig. 3) avoids any substantial unbalance of secondary superheater heating effects which might otherwise occur as a result of the arrangement of superheater and reheater furnaces and their separate furnaces and gas passes. As here shown, steam (from the drum enters the header at the lower end of the downpass 38 which receives gases from the superheater furnace 10. The header 50 receives the steam from

header components

48, 49, 116, 118 and 120 which, in turn, are directly connected to the vapor space of the drum by superheater supply wall tubes, such as 52, 54, 122 and 124, header 123 and tubes 125. The headers 116, 118 and 120 are directly connected to the header 50 by appropriate pipes or conduits (not shown). From this header 50 steam flows through the banks of

tubes

44, 45, 46 and 42 of stage 1 of the primary superheater to the outlet header 43 and thence through the parallel lines 174 and 176 to the inlet header 112 of stage 2 of the primary superheater in the gas pass leading from the reheater furnace 12. From this header the steam (or vapor) flows through the tubes of the banks of

tubes

10,8, 109 and to the outlet header 114.

Lines

178 and 180 lead through appropriate attemperators (not shown) and conduct the superheated steam from the primary superheater outlet header 114 to the inlet header 88 (secondary superheater stage 1) and thence the steam flows through the bank of tubes 86 of stage 1 of the secondary superheater to the outlet lines and 192 conduct exhaust steam from a turbine stage to the inlet header 102 of stage 1 of the reheater. Itthen passes through the bank of tubes 100 to the outlet header 104. Thence it is conducted to the inlet header 94 by the

plural lines

194 and 196. From header 94 steam passes through the tubes 92 to the

twin outlet headers

96 and 98. Thence the reheated steam returns to the turbine for further use.

The Fig. 4 vapor generating and superheating unit has vertically elongated furnaces 200 and 202 defined by vapor generating tubes and fired by burners 204209 in a manner similar to that of the previously described unit. However, the convection gas pass from the reheater furnace 202 leads laterally to the right from the upper part of that furnace, over the second stage 210 of the secondary superheater and then into a gas turning space 212. Thence the gases proceed downwardlythrough the downpass 214 and over the banks of

tubes

216, 217, 218, 220 of a reheater having an inlet header 222 and

twin outlet headers

224 and 226 from which

reheater outlet lines

228 and 230 lead to a turbine.

The entrance for the gas pass leading from the superheater furnace 200 is directly opposite the entrance of the gas pass leading from the furnace 202, the gases passing to the left from the upper part of the furnace 200 through a horizontal gas pass component and over the banks of tubes 232 and 234 of the first stage of the secondary superheater. Thence the gases pass into the gas turning chamber 236 and then downwardly through the primary superheater gas pass.238 in which are located the banks of horizontally disposed return bend tubes 240-244 constituting the primary superheater through which steam passes from the inlet header 25 to the outlet header 252.

Superheated steam from the primary superheater outlet header 252 flows upwardly through the conduits 254 and then through superheat attemperators 256 to the inlet header 258 for stage 1 of the secondary superheaten,

272 and 274 leading to the inlet header 276 of stage 2- of the secondary superheater. From this stage the superheated steam passes through the

twin headers

278 and 280 and through the connected superheater outlets 282 and 284 to a point of use.

Saturated steam from the steam and water drum 300 passes through

superheater supply tubes

302 and 304 leading in opposite directions from the drum and along the roof of the unit. Some of the conduits 302 lead.

to the superheater inlet header 306 from which'wall tube connections 308 lead to the rear superheater supply wall tubes 310 and along the rear wall 312 to the header 314 at the bottom of the reheater gas pass.

Others of the conduits 302 conduct saturated steam from the drum 300 to superheater supply side wall headers 316 from which superheater supply wall tubes 318 lead downwardly to connection with the superheater supply header component 318' at the bottom of the reheater pass. The header components 318' and 314 are connected with a cross conduit 321 leading to similarly disposed

header components

250 and 320 at the left hand side of the unit and at the bottom of the primary superheater gas pass.

At the opposite side of the unit the superheater supply conduits 304 lead to the header 322 from which the tubes 324 lead to superheater supply wall tubes 326 along the left hand wall 328 of the primary superheater gas pass. They lead downwardly along that wall to connection with the header 250. Other tubes 330 lead downwardly from the header 322 and then through roof portions 332 and then through wall tubes also disposed along the wall 328. Others of the superheater supply conduits 304 conduct saturated steam along the roof of the unit and then downwardly to side wall headers 334 from which side wall tubes 336 lead to both of the side wall header components 320. Thus some of the saturated steam passes from the drum 300, is superheated in the walls of the reheater gas pass and then passes to the primary

superheater inlet headers

250 and 320 from which it flows through the primary superheater including the banks of tubes 240244.

At the lower part of the primary superheater gas pass there is an economizer section 340. After passing over the tubes of this economizer section the gases pass downwardly, subject to the proportioning flow regulation of the dampers 342. Then they pass into breeching 344 which is provided with a lateral outlet 346 from which part of the gases pass through ductwork 348 to the inlet of a recirculating fan 350, the outlet of which is connected by the ductwork 352 to a manifold 354 from which spaced gas outlets 356 distributed along the length of the manifold lead into the throat 358 of the hopper bottom of the superheater furnace 200. The flow of recirculating gases through the system including the recirculated gas fan 350 is controlled in such a manner as to increase (toward an optimum) superheated and reheat steam temperatures by controlling the speed of the fan 350 and/or regulating appropriate dampers associated with the ductwork 348. Such control may be efiectivc from appropriate variable influences such as representations of load, and superheat temperature.

At the opposite side of the unit, and at the lower end of the reheater gas pass including the banks of

reheater tubes

216, 217, 218, 220, there are banks of tubes 360 and 362 of another economizer section. Gases pass from these economizer sections through and between the proportioning dampers 364 to breeching 366 in, one wall of which there is a recirculated gas outlet 368 connected by ductwork 370 to the inlet of a recirculated gas fan 372. The outlet of this fan is connected by ductwork 374 to a manifold 376 from which regularly spaced recirculated gas outlets 378 distributed along the length of the manifold lead into the throat 380 of the hopper bottom of the reheater furnace 202. This recireulated gas system may be controlled in the manner indlcated in the description of the recirculated gas system at the opposite side of the unit.

The Fig. 4 unit is subject to gas proportioning between the two furnace sections and the pertinent gas passes leading therefrom, for adjustment of reheat, with respect to superheat, over a wide load range. Such proportioning may be effected by the dampers 364 at the outlet end of the reheater gas pass and/or by the appropriate control of the dampers 342 at the outlet end of the primary superheater gas pass.

The wall tubes of the furnaces 200 and 202 are connected into the circulation of the unit by means of apptopriate large, diameter downcomers 400 leading down-.

watdly from the water space of the. drum 30.0,, and through the intermediacy of appropriate headers and conduits including the hopper bottom headers 402-407 which are connected to furnace wall tubes.

The furnace sections 200 and 202 are separated by a division wall 420 formed by closely spaced steam generating tubes leading upwardly from the

hopper bottom headers

402 and 403. At the lower parts of the furnaces these division wall tubes may be tangent so as to constitute a fairly gas-tight wall, but at the upper part of the furnace sections adjacent division wall tube sections,

such as 422 and 424, are separated so as to form pressure equalization passages between the sections of the furnace. In both of the illustrative units there are two gas passes leading in parallel from separately fired furnaces.

In both units one of the gas passes has disposed therein all of the reheater surface while the other gas pass has a predominant proportion of the total primary superheater surface. Also, in both units, the total secondary superheater surface is divided between the two gas passes with the steam or vapor flowing through one of the secondary superheater stages and then through the other. Each unit discloses a recirculated gas system for each gas pass and its associated furnace, and each unit, similarly, includes attemperators for superheat control.

In the operation of the illustrative units the flow of recirculated gas is increased when there would otherwise be a drop in temperature of the vapor at the secondary superheat outlet. This permits a predetermined superheat to be attained over a wide load range, and particularly at low loads.

Generally, the flow of recirculated gas is so controlled as to effect a desired vapor temperature of superheated vapor, and this is particularly true at the lower part of the load range. Such control, of course, in this part of the load range, means that the flow of recirculated gas over both the superheater and the reheater stages will be increased.

Proportioning of gas flow between the two gas passes leading from the separate furnace sections is also used for steam temperature control. Here, again, this proportioning is controlled primarily to maintain reheat at the desired value and if this action has a tendency to result in the increase of superheat above the predetermined value, then the attemperators are operative to maintain the superheat at the desired value. The gas flow proportioning between the two gas passes is preferably effected by automatic control of one or both sets of the dampers, such as 342 and 364 in the Fig. 4 modification, and 126 and 62 in the other modification.

The above described control system can be further augmented by differential firing of the furnaces.

It is within the purview of the invention that the control of the, gas flow regulators for gas proportioning, the control of the attemperators, and the control of the separate recirculated gas flow systems, would be automatically controlled from a set of appropriate variables, such as those mentioned above.

Referring again to Fig. 1 of the drawings, it is to be noted that throat is a passage formed by tube supported

walls

500 and 502, the lower parts of which are inclined so as to direct the incoming recirculated gases somewhat in the direction indicated by the arrow 504. The gases thus proceed toward the right hand furnace wall 506 and when the burners, such as 16, 18 and 20, are short flame turbulent burners, the continuance of the recirculated gases as a stratum along the wall 506 is promoted.

Under some velocity conditions of the gases entering the lower part of the furnace 10, the recirculated gases, or a part of them, may also act to fill up the lower part of the furnace, with the higher density and lower temperature gases, thus rendering the lower part of the furnace relatively inefiective as to the absorption of radiantly transmitted heat for vapor generation in the wall tubes of that part of the furnace... The interposition of a thick stratum of recirculated gases immediately adjacent the gamma.

wall 506 also results in the reduction of heat absorption by the steam or vapor generating tubes along that part of the wall covered by the stratum. Such reduction in the furnace heat absorption preferably takes place with an increase of the amount ofrecirculated gases entering the furnace, and it correspondingly decreases the rate of vapor generation.

concomitantly, with the reduction of furnace heat absorption at decreasing load, the increase in the amount of recirculated gases affords an increase in the gas mass flow over the convection banks of vapor heating tubes disposed in the gas pass beyond the furnace and thus compensates for an inherent tendency of such convection heaters to result in undesirably low temperatures at the outlets of the vapor heaters.

It is to be understood that the upwardly inclined throat 170, directing recirculated furnace gases toward the rear furnace wall 506, has its wall 502 formed by vapor generating tubes leading upwardly from a lower header 508 to the wall 506 and thence upwardly along that wall, around the arch 510 and then, as screen tubes 512, in front of the secondary superheater section 40. Some of these tubes continue as roof sections 514 over the roof of the furnace, and then to connections with the drum 30. Others extend through the roof at 516 and connect at superposed positions to the drum 30, as indicated at 518.

At the opposite side of the throat 170 the wall 500 is supported or defined by vapor generating tubes leading upwardly from the front wall header 520 along the upper throat wall 500 and then along the inclined hopper bottom wall 522. These tubes then continue upwardly along the left hand furnace wall 524, past the burners and then to connections with the drum 30. The side walls of the furnace are formed by closely arranged vapor generating tubes having their upper ends connected to such headers as the side wall header 526 and their lower ends connected to corresponding headers at the bottom of the furnace. These upper and lower headers are appropriately connected into the fluid circulation of the unit by appropriate circulators between the drum 30 and the upper headers, and by appropriate downcomers leading downwardly from the liquid space of the drum 30. The lower ends of such downcomers are connected to the side wall headers at the lower part of the furnace. The structure described immediately above also applies to the furnace 12 which is shown in Fig. 1A and it is considered that the pertinent description need not be substantially duplicated with reference to the furnace 12.

What is claimed is:

1. In a high capacity vapor generating and superheating unit, a vertically elongated furnace having its walls defined by vapor generating tubes, an upright division wall including closely arranged upright vapor generating tubes separating the furnace into two sections, exterior wall means forming a first gas pass leadinglaterally from one furnace section, exterior wall means forming a second gas pass parallel to the first gas pass and leading from the other furnace section, said gas passes and their adjacent walls being substantially spaced with a free access and maintenance space between the adjacent walls, fuel burning means for separately and independently firing the fur-.

naccs, stage 1 of a pendent vapor superheater including a bank of upright tubes disposed in one of the gas passes, stage 2 of the same vapor superheater including another bank of pendent upright tubes disposed in the other of the gas passes, and vapor conducting tubes connecting the vapor outlet of stage 1 to the vapor inlet of stage 2, and means for conducting the superheated vapor from the outlet of stage 2 to a point of use.

2. In a high capacity vapor generating and superheating unit, a furnace defined by vapor generating tubes, a division wall including upright vapor generating tubes separating the furnace into two sections, the division wall being constructed to provide furnace gas pressure equalization openings therein, a first gas pass leading laterally from one furnace section, a second gas pass leading later,-

ally from the other furnace section, independent fuel burning means for separately and independently firing the furnaces and thereby changing the rates of gas flow through the furnace sections and the gas passes, other means for changing gas flows through the gas passes when changes in vapor generating rate occur, a reheater in one of the gas passes, a first stage of a vapor superheater disposed in one of thegas passes, a second stage of the same vapor superheater disposed in the other of the gas passes, and vapor conducting tubes connecting the outlet of the first stage to the inlet of the second stage and means for conducting the superheated vapor from the outlet of the second stage to a point of use.

3. In a high pressure and high capacity vapor generating and superheating unit, a vertically elongated furnace with its boundaries defined by closely arranged upright vapor generating tubes, other vapor generating tubes defining a division wall separating the furnace into two sections, a vapor and liquid drum disposed at the top of the unit and having the outlets of the vapor generating tubes communicating therewith, a gas pass leading laterally from the upper part of the first section of the unit and including a downpass, a reheater disposed in said downpass, walls of said downpass having upright superheater supply tubes therealong, means conducting saturated steam from said drum to said superheater supply wall tubes, header .components disposed along the downpass walls at the bottom of said gas pass and having the outlet ends of the superheater supply tubes connected there to, a second gas pass leading laterally from the other section of the furnace and including a downfiow gas pass section having therein a plurality of banks of tubes of a convection primary superheater first stage, header components disposed along the walls at the lower end of the downfiow section of the second gas pass, conduits and superheater supply gas pass wall tubes conducting steam from the drum to the header components of the second gas pass, conduit means conducting the steam from the header components at the bottom of the first gas pass to the header components at the lower end of the second gas pass, and means conducting steam from the header components at the lower end of the downfiow section of the second gas pass to the convection primary superheater therein.

4. In a high pressure and high capacity vapor generating and superheating unit, a verticallylelongated furnace with its boundaries defined by closely arranged upright vapor generating tubes, other closely arranged upright vapor generating tubes defining a division wall separating the furnace into two sections, a vapor and liquid drum disposed at the top of the unit and having the outlets of the vapor generating tubes communicating therewith, a first gas pass leading laterally from the upper part of the first section of the unit and including a downpass, a convection reheater including a bank of tubes disposed in said downpass, walls of said downpass having superheater supply tubes leading downwardly therealong, means conducting saturated vapor from the drum to the upper ends of said superheater supply wall tubes, header components disposed along the downpass walls at the bottom of said gas pass and having said superheater supply tubes discharging thereinto, a second gas pass parallel to the first) of the second gas pass, conduits and superheater supply I gas pass wall tubes conducting vapor from the drum to the header components of the second gas pass, conduit means conducting vapor from the header components at the bottom of the first gas pass to the header components at the lower end of the second gas pass and means con ducting vapor from the header components at the lower end of the downflow section of the second gas pass to the convection primary superheater.

5. In a high pressure and high capacity vapor generating and superheating unit, a vertically elongated furnace with its boundaries defined by rows of upright vapor generating tubes, other vapor generating tubes defining division wall means separating the furnace into sections means independently firing the furnace sections, a vapor and liquid drum disposed at the upper part of the unit and having the outlets of the vapor generating tubes communicating therewith, a gas pass leading from the first section of the unit and including a downpass, vapor heating means constituting the second stage of a primary superheater disposed in said downpass, walls of said downpass having vapor supply tubes leading downwardly therealong, means conducting saturated vapor from the drum to the inlets of said vapor supply wall tubes, header means at the bottom of said gas pass having the outlets of the vapor supply wall tubes communicating therewith, a second gas pass leading from the other section of the furnace and ineluding a downflow gas pass section having vapor heating tubes of a first stage of a primary vapor superheater therein, header means disposed at the lower end of the second gas pass, conduits and vapor supply wall tubes conducting vapor from the drum to the header means of the second gas pass, conduit means conducting the vapor from the header means at the bottom of the first gas pass to the header means at the lower end of the second gas pass, and means conducting superheater vapor from the first stage of the primary superheater to the vapor inlet of the second stage of the primary superheater.

6. In a high pressure and high capacity vapor generating and superheating unit, a vertically elongated furnace with its boundaries defined by rows of upright vapor generating tubes, other vapor generating tubes defining a division wall separating the furnace into sections, a vapor and liquid drum disposed at the upper part of the unit and having the outlets of the vapor generating tubes cornmunicating therewith, a gas pass leading from the first section of the unit and including a downpass, vapor heating means disposed in said downpass, walls of said downpass having vapor supply tubes leading downwardly therealong, means conducting saturated vapor from the drum to said vapor supply wall tubes, header components at the bottom of said gas pass having the outlets of the vapor supply wall tubes in communication therewith, a second gas pass leading from the other section of the furnace and including a downflow gas pass section having therein a plurality of banks of vapor heating tubes constituting the first stage of a primary superheater, header components disposed along the walls at the lower end of the second gas pass, conduits and superheater supply wall tubes conducting, saturated vapor from the drum to the header components of the second gas pass, conduit means conducting vapor from the header components at the bottom of the first gas pass to the header components at the lower end of the second gas pass, means conducting vapor from the header components at the second gas pass to the vapor inlet of the first stage of the primary superheater.

7. In a high capacity and high pressure vapor generating and superheating unit, two separately fired furnace sections each having its boundaries defined by upright vapor generating tubes, the furnaces being separated by a division wall of vapor generating tubes with some of the division wall tubes arranged to present gas communicating passages freely communicating with the gas spaces of the furnaces, a first gas pass leading from one furnace, one stage of a secondary superheater disposed in said gas pass, a reheater disposed in said gas pass beyond the secondary superheater stage, a second gas pass leading from the other furnace, a second stage of a secondary superheater disposed within the second gas pass, a primary convection. superheater disposed within the second. gas pass at a position beyond the second secondary super-- heater stage, gas flow regulators for proportioning the flow of gases between the respective gas passes for the purpose of regulating temperature of heated vapor, vapor flow connections establishing vapor flow from the primary superheater to the first stage of the secondary superheater and then to the second stage of the secondary superheater, a recirculated gas flow system for each of the furnaces and its associated gas pass, and means for separately controlling each recirculated gas flow system for maintaining predetermined heated vapor reheat temperatures over a wide load range.

8. In a high capacity and high pressure vapor generating and superheating unit, two separately fired furnace sections each having its boundaries defined by upright vapor generating tubes, the furnaces being separated by a division wall of vapor generating tubes with some of the division wall tubes arranged to present gas communicating passages freely communicating with the gas spaces of the furnaces, a first gas pass leading from one furnace,

a first stage of a secondary superheater disposed in saidgas pass, a reheater wholly disposed in one of said gas passes beyond the first stage of the secondary superheater stage, a second gas pass leading from the other furnace, a second stage of a secondary superheater disposed within the second gas pass, a primary convection superheater disposed within the second gas pass at a position beyond the second secondary superheater stage relative to gas flow, means conducting generated vapor to the inlet of the primary superheater, means connecting the vapor outlet of the primary superheater to the inlet of the first stage of the secondary superheater, means conducting superheated vapor from the outlet of the first stage of the secondary superheater to the inlet of the second stage of the secondary superheater, gas flow regulators for proportioning the flow of gases between the respective gas passes for the purpose of regulating temperature of heated vapor, a recirculated gas flow system for each of the furnaces and its associated gas pass for withdrawing heating gases from a position beyond vapor heating means and introducing the withdrawn gases into the furnace sections, and means for separately controlling each recirculated gas flow system for maintaining predetermined heated vapor temperatures over a wide load range.

9. In a high capacity and high pressure vapor generating and superheating unit, two separately fired furnace sections each having its boundaries defined by upright vapor generating tubes, the furnaces being separated by a division wall of vapor generating tubes with some of the division wall tubes arranged to present gas communicating passages freely communicating with the gas spaces of the furnaces, a first gas pass leading from one furnace, one stage of a secondary superheater disposed in said gas pass, a vapor reheater wholly disposed in said gas pass beyond the secondary superheater stage, a second gas pass leading from the other furnace, a second stage of a secondary superheater disposed within the second gas pass, a primary convection superheater disposed within the second gas pass at a position beyond the second secondary superheater stage relative to gas flow, means conducting generated vapor to the inlet of the primary superheater, means connecting the vapor outlet of the primary superheater to the inlet of the first stage of the secondary superheater, means conducting superheated vapor from the outlet of the first stage of the secondary superheater to the inlet of the second stage of the secondary superheater, gas flow control means proportioning the flow of gases between the respective gas passes for the purpose of regulating temperature of heated vapor, a recirculated gas flow system for each of the furnaces and its associated gas pass for withdrawing partially cooled furnace gases from the gas pass at a position beyond the vapor superheater or reheater and introducing the withdrawn gases into the associated furnace, and means for controlling each reheated vapor over a wide load range.

gamma 10. In a high pressure and high capacity vapor generating and superheating unit; a vertically elongated furnace with its boundaries including upright vapor gen erating wall tubes; other vapor generating tubes presenting an upright division wall separating the furnace into first and second furnace sections; means for independently firing the furnace sections; a single elevated vapor and liquid drum having the upper ends of the vapor generating tubes connected thereto; means forming separate first and second gas passes leading from the first and second furnace sections respectively; a convection vapor reheater wholly disposed in the first gas pass; a convection section constituting a stage of a primary vapor superheater disposed in the first gas pass down stream of the reheater in a gas flow sense; other convection tubes constituting another stage of the primary superheater in the second gas pass; superheater supply wall tubes in each gas pass conducting vapor passing from the drum to positions adjacent the inlets of the primary superheater stages; means conducting initially superheated vapor from the outlets of the superheater supply wall tubes of the first gas pass to the vapor inlets of the primary superheater stage in the first gas pass, means conducting vapor from the outlets of the superheater supply wall tubes of the second gas pass to a position wherein the vapor from the second gas pass superheater supply wall tubes joins the vapor flowing to the first stage of the primary superheater; means conducting the combined vapor flows from the outlet of the first primary superheater stage to the inlet of the second primary superheater stage; a secondary superheater in the second gas pass; means connecting the vapor outlet of the primary superheater second stage to the inlet of the secondary superheater; and means for varying and controlling the heating gas flows through the gas passes.

11. In a high pressure and high capacity steam generating and superheating unit, means including steam generating wall tubes defining a plurality of furnaces, means for independently firing the furnaces, means connecting the steam generating wall tubes of the separate furnaces to a common steam collecting means, means forming separated gas passes conducting gases from the separate furnaces, steam superheating means receiving the steam generated in the wall tubes and heated by the gases in a plurality of the gas passes, a convection steam reheater disposed wholly within one gas pass, and means other than the fuel burning means for varying the flow of gases through the gas passes, the steam superheating means including a convection primary superheater with series connected parts one of which is disposed downstream of the reheater and in its gas pass and the other of which is disposed in another gas pass, said superheater means also including a secondary convection superheater section in the gas pass containing said reheater and arranged to receive steam from said primary superheater, and a second secondary convection superheater section in said other gas pass arranged to receive superheated steam from said first secondary superheater section.

12. In a high capacity vapor generating and superheating unit, upright vapor generating tubes defining the boundary surfaces of a large volume vertically elongated furnace chamber having generally rectangular horizontal cross section with its major dimension much greater than its minor dimension, a pair of spaced and separately walled gas passes extending laterally from the upper part of a longer side of the furnace, convection fluid heat exchange devices arranged in each said gas passes, the

separate gas pass constructions leading from and spaced apart along the longer side of the furnace to permit maintenance access to the adjacent inner sides of the two parallel gas passes, spaced and separate downflow gas pass constructions leading downwardly from said parallel gas passes, said convection fluid heat exchange devices including a first stage of a primary superheater in the downflow part of one of the gas passes, a second stage of the primary vapor superheater disposed within the downfiow gas pass for the other lateral gas pass and connected in series as to steam flow with said first stage primary superheater, a first stage of a secondary convection superheater disposed within the other lateral gas pass, tubular connections conducting vapor from the vapor outlet of the second stage of the primary superheater to the first stage of the secondary superheater, a second stage of the secondary superheater disposed in the lateral gas pass leading to the downflow pass having therein the first stage of the primary superheater, tubular connections conducting vapor from the outlet of the first stage of the secondary superheater to the inlet of the second stage of the secondary superheater, and a reheater disposed in one of said lateral gas passes.

13. In a steam generating and superheating unit, vapor generating tubes disposed in wall formation and arranged to define a hopper bottom furnace of rectangular horizontal cross-section, fuel burner means at a level above that of the hopper bottom effecting the burning of fuel in suspension within the furnace at vary ing rates and directing burning fuel from one vertical furnace wall toward an opposite furnace wall, wall means providing a superheater gas pass opening to the upper part of and receiving combustion gases from the furnace, a convection superheater including a bank of spaced tubes arranged across the gas pass, means conducting steam from the Wall tubes to the superheater, and a gas recirculating system including ductwork having an inlet receiving a proportion of the combustion gases at a position downstream of the superheater and causing such gases to flow into the furnace through the hopper bottom, said hopper bottom having a pair of substantially parallel inclined walls arranged to form an elongated ash discharge throat opening at its upper end to the lower end of said hopper bottom and inclined in a direction intersecting the furnace wall opposite said fuel burner wall at an elevation below the elevation of the fuel burner means, and said gas recirculating system ductwork opening into the lower portion of said ash discharge throat at a point spaced from the upper end thereof a distance suflicient to provide a stream of recirculated combustion gases flowing into said hopper bottom towards said opposite furnace Wall.

References Cited in the file of this patent UNITED STATES PATENTS 1,922,663 Kemnal Aug. 15, 1933 1,931,948 Armacost Oct. 24, 1933 2,334,187 Frisch Nov. 16, 1943 2,677,354 Epley May 4, 1954 2,781,746 Armacost et al. Feb. 19, 1957 FOREIGN PATENTS 503,778 Belgium June 30, 1951 499,583 Belgium Dec. 15, 1950 682,121 Great Britain Nov. 5, 1952 609,674 Great Britain Oct. 8, 1948 523,871 Great Britain July 24, 1940