US2781028A - Controlled circulation boiler with orifice drum - Google Patents

Description

Feb. 12, 1957 w. H. ARMACOST' 1,

CONTROLLED CIRCULATION BOILER WITH ORIFICE DRUM Filed July 5, 1952 5 Sheets-Sheet 1 INVENTOR.

WILBUR H. ARMACOST ATTOR Y.

Feb. '12, 1957 'w. H. ARMACOST 2,731,028

CONTROLLED CIRCULATION BOILER WITH ORIFICE DRUM Filed July 5, 1952 5 Sheets-Sheet 2 INVENTOR.

WILBUR H. ARMACOST ATTOR Feb. 12, 1957 w. H. ARMACOST 2,781,028

CONTROLLED CIRCULATION BOILER WITH ORIFICE DRUM Filed July 5, 1952 5 Sheets-Shget 3' 20 6/ 74 73 74 80 6O I 60 80 FIG 5 0 2617 m INVENTOR.

WILBUR H. ARMACOST BY qi a f Feb. 12, 1957 w. H. ARMACQST 2,781,028 CONTROLLED CIRCULATION BOILER WITH ORIFICEI DRUM FiledLJuly 5, 1952 5 Sheets-Sheet 4 INVENTOR. WILBUR H. ARMACOST ATTOR EY.

Feb. 12, 1957 v w; H. ARMACQST 8 CONTROLLED CIRCULATION BOILER WITH :ORIFICE DRUM FiledJuly 5, 1952 v 5 Sheets-Sheet 5 TOR.

' g8 70 7/ 62 "7 6 6 68 7/ 'ATTPR MACOST I CONTROLLED CIRCULATION BOILER WITH ORIFICE DRUM Wilbur H. Armacost, Scarsdale, N. Y., assignor to Combustion Engineering, Inc., a corporation of Delaware Application July 5, 1952, Serial N 0. 297,267

4 Claims. (Cl. 122-406) My invention relates to steam generating means and has specific reference to steam generators of the controlled circulation type.

By the term controlled circulation is meant a steam generator having a positive or forced circulation through the various steam generating circuits and provided with means to proportion the water supply to said circuits. This proportioning is accomplished by means of orifices at the inlet of said various steam generating circuits.

Although this type of generator has been used extensively in Europe, and to a lesser extent in England, for nearly two decades it has not been until recently that boiler manufacturers in this country have given it serious consideration. In the last few years, however, an intensive study of this type of unit has been carried on by the assignee of this application with a finding of inherent advantages of an exceedingly practical nature.

One of the principal reasons for the current adoption of controlled circulation in this country is the ever increasing demand of utility companies for larger and higher pressure installations.

As is well understood, so called natural circulation is motivated by means of the difference in density between the steam and water mixture in the steam generating tubes and the water in the downcomers. As the pressure within the boiler increases this differential in density becomes less and less until a point is reached at approximately 3,226 pounds per square inch at which the density of steam equals that of water, whereupon said differential becomes zero. It is thus apparent that for very high pressure boilers natural circulation is entirely unsuitable and resort must be had to some type of forced circulation.

It is extremely desirable in boiler design to be able to control and proportion the distribution of water to each of the steam generating circuits and it is for this reason that the controlled circulation type of boiler is being so widely chosen as the forced circulation unit most suitable for modern high pressure utility plants. This is pointedly illustrated by the fact that there are now being built by or on order with the assignee of this application some eighteen large high pressure steam generating units of the controlled circulation type for nine central station installations in this country. All of these units have been ordered in the last two years and range in rated output from 750,000 to 1,450,000 lbs. of steam per hour (the latter being the largest ever built to date) and design pressure from 1,670 to 2,650 pounds per square inch.

In the operation of the controlled circulation unit, orifices are provided at the entrance of each steam generating tube in order to control the quantity of water flowing through said tube; with the aim of the boiler designer being to obtain a substantially equal circulation ratio in each tube.

Circulation ratio is defined as the weight rate of water fed to the steam generating tubes divided by the weight rate of steam generated therein, and ideal operation is obtained when this ratio is the same (such as 5 or some other selected value) in each steam generating tube. Since the circulation ratio will vary in accordance with the amount of water flowing through the tube as well as with the length of the tube and the rate of heat absorption of the tube, it is apparent that these factors will govern the size of orifice required for each tube.

Heretofore, it hasbeen the practice to provide each steam generating circuit with an individual inlet header of cross section far too small to admit a workman and hence requiring along its length numerous handholes for gaining access to the individual tube orifices, as typically illustrated by the Patterson Patent No. 2,578,831, issued December 18, 1951, and owned by the assignee of the instant application. A complete boiler furnace includes several (four or more) such steam generating circuits each of which is composed of a number of individual tubes so arranged in the furnace that all have substantially the same rate of heat absorption as well as substantially the same length. Thus, the orifice needed by each tube in a single generating circuit is of the same size as is the orifice needed by every other tube in that circuit, wherefore all of the orifices in a single conventional inlet header are identical.

It is a difiicult and expensive task to install the orifices in these conventional headers since it is necessary to provide each such header with the numerous hand hole openings already mentioned together with means for closing said openings after the orifices are properly installed in the individual tubes entering the header. In high pressure units it is found that gasketed hand hole closures are unsatisfactory because of excessive leakage and it is necessary to weld the closure plates of these units in place. During periodic acid wash down, at which time it is necessary to remove the orifice, all of these hand hole closures have to be unwelded and removed, requiring man hours in tremendously large number and prolonging the period of time for which the unit is shut down.

It has also been the practice to arrange the .circulating system for controlled circulation boilers in a manner so that the water leaving a particular region of the steam and water drum through the downcomers is returned to the same general region of said drum through the steam generating tubes. Since this arrangement afiords no mixing of the boiler water from one side of the boiler to the other, concentrations of foreign matter tend to build up at particular locations depending upon the characteristics of the individual unit.

It is the general object of my invention to provide a controlled circulation boiler of improved design, construction and operation that will :overcome the aforementioned difficulties.

A more specific object is to provide a controlled circulation boiler with an orifice drum of suflicient cross section to permit the entrance of workmen thereinto and to establish a slow flow of circulating water through the drum during boiler operation.

Another object is to provide a controlled circulation boiler with an orifice drum which serves a plurality of steam generating circuits.

A further object is to provide a controlled circulation boiler with an orifice drum and a steam and water drum interconnected in such a manner as to effect a mixing of the circulating water from one side of the boiler to the other.

Other and further objects of my invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, my invention comprises an arrangement, construction and combinationembodiment that is shown by the accompanying drawings wherein:

Fig. 1 is a vertical section of a modern high pressure, high temperature controlled circulation steam generator equipped with an orifice drum located at the bottom of the furnace.

Fig. 2 is a sectional view taken generally along line 22 of Fig. 1 showing the connection with this single orifice drum of the tubes which constitute the four steam generating circuits that are respectively identified with the four furnace walls.

Fig. 3 is a view in the nature of a transverse section on line 33 of Fig. 2 through the orifice drum showing the circumferential disposition of the four individual circuit rows of steam generating tubes.

Fig. 4 is a perspective view of the orifice drum and a portion of each of the four rows of steam generating tubes connected thereto.

Fig. 5 is a view of the orifice drum (as from the lower left portion of Fig. 3) with the casing broken away to show the longitudinally disposed strainers which cover the orifices that are provided for the four rows of entering tubes.

Fig. 6 is an enlarged elevational view taken generally along line 6-6 of Fig. 1 showing the connection of the steam and water drum with the circulating pumps and the connection of the pumps with the orifice drum.

Fig. 7 is a longitudinal sectional view of the orifice drum taken generally along line 7-7 of Fig. 8 and showing further details of the strainers earlier represented in Fig. 5.

Fig. 8 is an enlarged transverse section of the orifice drum which corresponds generally to the smaller representation of Fig. 3 and which is taken on line 8-8 of Fig. 7 to show the internal construction of said drum (including the strainers and tube orifices) in further detail.

Fig. 9 is a sectional view taken generally along line 9--9 of Fig. 8 showing the arrangement for retaining the orifices in place at the inlet ends of the steam generating tubes.

Fig. 10 is an elevational end view taken along line 1010 of Fig. 9 showing the orifice retaining means for a number of steam generating tubes.

Fig. 11 is an enlarged sectional view taken generally along line 11-11 of Fig. 10 showing a typical mounting for the orifice at the inlet of a steam generating tube.

Fig. 12 is a sectional view showing how the tube inlet orifice of Fig. 11 appears when viewed from line 12-12 with the cooperating mounting parts therefor omitted.

The illustrative steam generator benefited Referring to the drawings, wherein like parts are designated by like reference characters, the high pressure, high temperature steam generator represented by Fig. 1 comprises a vertically disposed furnace 2 of generally rectangular cross section communicating at its upper end with a horizontal gas pass 4 which in turn communicates with the upper end of a vertical gas pass 6 leading to air preheater 14. Furnace 2, by way of example only, is

disclosed as fired by a plurality of burners 8 that are supplied via conduits 12 with fuel in the form of pulver ized coal from pulverizers 10. Preheated air is introduced into said furnace under pressure via a suitable force draft fan (not shown) which passes the air through prehcater 14 and ducts 16 and thence into the furnace at a plurality of vertically spaced points; such introduction insuring complete burning of the fuel supplied through said burners 8.

Furnace 2 is of the water cooled type and for this purpose has its walls as well as the floor and ceiling lined with steam generating tubes 13. In the steam generator here illustrated adjacent tubes 18 are welded one to another (through small spacer rods not shown) to form a rigid pressure resistant metallic interior surface for the furnace; the wall or casing construction used being disclosed and claimed by co-pending application Serial No.

4 317,520, filed October 29, 1952, under title of Welded Water Wall Construction. Obviously however, the invention of the present application also is useable with boiler furnaces wherein the tubes 18 are not so welded together but instead are organized into walls of various other types and constructions.

Said steam generating tubes 18 are connected at their lower or inlet ends with orifice drum 20 and at their upper or outlet ends with headers 22. Headers 22 are in turn connected via conduits 23 to steam and water drum 24 positioned adjacent the top of the furnace. A plurality of downcomers 25a, 25b, 25c and 25d (see Fig. 6) depend from steam and water drum 24 and are connected at their lower ends to the inlets of circulating pumps 26, 27 and 28 which in turn have their outlets connected to orifice drum 20 thereby completing a fluid circuit through which the pumps are efiective to circulate the boiler water in the following manner: from steam and water drum 24 downward through downcomers 25a, 25b, 25c and 25d, through pumps 26, 27 and 28 into orifice drum 20, through steam generating tubes 18 into headers 22 and through conduits 23 back into steam and water drum 24.

The illustrative steam generator of Fig. 1 includes an economizer 29 in vertical gas pass 6, a low temperature superheater 30 also positioned in said vertical gas pass, a high temperature superheater 32 positioned in horizontal gas pass 4 and a steam reheater 34 also positioned in said horizontal gas pass 4 but down stream (relative to the flow of hot combustion gases) of said high temperature superheater 32. Economizer 29 receives feed water through header 31 and is etfective to raise the temperature of said feed water to a desired point before discharging it upwardly through tubes 29a into header 33 and thence into steam and water drum 24 via conduits 35. Low temperature superheater 30 receives, through suitable conduits 36 and headers 38a, 33b and 380 saturated steam from steam and water drum 24 and discharges this steam through conduits 40 (only one of which is shown) at a superheated temperature into high temperature superheater 32 where the degree of superheat is increased to a predetermined value, after which the steam is conveyed to points of use by suitable piping such as 42 and 44. Reheater 34 receives, through conduits 46 and 48, steam from which a portion of the energy has been removed, reheats this steam to a desired temperature and pressure and thereafter discharges it to desired points of use through suitable piping such as 50 and 52.

All of the foregoing heat exchange devices as well as steam and Water drum 24, furnace 2, including steam generating tubes 18, and orifice drum 20 are supported from above by means of suitable hangers, designated generally 54, which derive their support from building framework 56, preferably fabricated of steel and concrete. This method of support reduces relative movement of the various elements of the generator since the direction of expansion of said elements due to changes in temperature will be the same.

In normal operation of the generator, pumps 26, 27 and 28 are effective to circulate the boiler water as aforesaid. The hot gases of combustion produced by burning of the fuel supplied by burners 8 travel upwardly within furnace 2 contacting the inner surface of steam generating tubes 18 thereby giving up a portion of their heat to the water flowing therethrough and converting a portion of said water into steam which is collected in the upper portion of steam and Water drum 24 and delivered to superheater 30. From furnace 2 the hot combustion gases pass laterally through gas pass 4 and downwardly through gas pass 6 and air preheater 14 into a suitable stack (not shown) giving up a further portion of the heat contained therein to the various heat exchange devices encountered in passage from said furnace 2 to the stack.

Some idea of the tremendous size of the boiler furnaces here dealt with may be gained by comparing the overall height of the steam generator shown by Fig. l with that of the workman pictured to scale at 19 (whose height is six feet). In this Fig. 1 installation the structural steel framework 56 has an overall height of 132 feet (equivalent to 13 stories of an oflice building); the vertical distance between center lines of the lower drum 20 and the upper drum 24 is about 87 feet; and the main combustion chamber of water walled furnace 2 has a height of approximately 80 feet, a depth of 22 feet from front to rear, and a width from side to side that is dependent upon the steaming capacity desired.

In one commercial unit now being built by applicants assignee this width dimension is approximately 40 feet (from left wall tubes 18b to right wall tubes 180 in Fig. 2) and the furnace is equipped with a central water tube partition wall (not here shown) that divides said total 40 foot furnace width into two adjoining combustion chambers each of which has the general proportions depicted by Fig. 2. Said commercial unit involving the double or divided furnace just referred to (and having the other dimensions shown by Fig. 1 hereof) has a rated generating capacity (at 100% full load) of 1,055,000 pounds of steam per hour; a rated operating pressure of 2650 pounds per square inch; and a rated superheated steam temperature of 1100 F. together with a rated reheated steam temperature of 1050 F.

Such cited values are obviously illustrative rather than restrictive; for as the description proceeds it will become evident that the orifice drum improvements of this invention also are useable with boiler furnaces of other capacities, characteristics and designs.

The orifice drum 20 As previously pointed out it has been the practice in controlled circulation boilers to employ a separate inlet header for each steam generating circuit, said headers being located adjacent the bottom of the furnace and each being relatively small wherefore numerous hand hole openings have been required to aiford access to the individual tube orifices therein. One example of this construction is illustrated in the aforementioned Patterson Patent No. 2,578,831.

Through the use of orifice drum 20 the need for these numerous headers with their attendant limitations and disadvantages is eliminated. Said drum 20, here shown as composed of two semi-cylindrical shells integrated by welds 21 (see Fig. 8), is disposed adjacent the bottom of furnace 2 and has the tubes of all steam generating circuits of the generator connected thereinto. This arrangement may best be seen in Figs. 2 and 4.

Since all the tubes lining a single side of a furnace have approximately the same rate of heat absorption and are approximately the same length it will be assumed, for purposes of explanation, that these tubes comprise a steam generating circuit as hereinbefore defined. The steam generator of Fig. 1 when of the single combustion chamber design of Fig. 2 therefore has four steam generating circuits, viz: (a) tubes 18a, lining the front wall of furnace 2, comprising one such circuit; (b) tubes 18b, lining one side wall of said furnace 2, comprising another such circuit; tubes 18c, lining the other side wall, comprising the third such circuit; and (d) tubes 18d, lining the rear wall of the furnace, comprising the fourth such circuit.

As shown in the drawings, Figs. 3 and 4, the tubes of these four circuits ab-cd are connected into drum 20 in four longitudinal rows circumferentially spaced as indicated, and in order to avoid interference tubes 18b, 18c and 18d are first directed upwardly from drum 20 and then at different respective elevations (best shown by Figs. 3 and 4) horizontally to their various furnace walls. Tubes 18d in extending from drum 20 to the rear wall of the furnace form a water cooled bottom for said furnace and are arranged to provide an access opening 58 in said bottom for the extraction of ash and the like. Tubes 18d and 18a are directed inwardly along the inner surface of the top of furnace 2 to approximately the center thereof at which point they are connected to a suitable header 22, said tubes thus forming a water cooled surface for the top of the furnace.

The here disclosed connection of all of the steam generating tubes 18a-bcd into the common drum 20 is accompanied by a making of said drum considerably larger in cross section than the customary individual headers into which the several tube circuit groups have heretofore been individually connected, thereby providing sufficient space within said drum to maintain a relatively slow velocity of water therethrough during operation of the generator and to permit the entrance of workmen (one of which is indicated at 19 in Fig. 1) therewithin through manholes 60 provided at either end thereof (said manholes being normally closed by covers 61). Obviously, however, the same advantages also can be realized when fewer than all of the steam generating tubes 18 are connected to said drum 20. With workmen able to enter the drum it is unnecessary to provide numerous handhole openings in the drum wall in order to gain access to the individual tube orifices 66; instead the only openings necessary to provide the needed access to the drum interior can advantageously be limited to the two end manholes 60 as here illustratively shown.

In the installation here shown this orifice drum 20 has an inside diameter of 36 inches (however diameters either smaller or larger also may be practicable); the wall thereof has a thickness of 3 3 inches; and each of the end manhole openings 60 therein has a diameter of 16 inches (large enought to admit a man). The overall length of this represented drum 20 is about 40 feet when the Fig. 1 furnace has the double chamber design earlier referred to and somewhat shorter when it has the simplified single chamber design illustratively represented by Figs. 2 and 4; each of the represented four tube rows 18a, 18b, 18c, 18d entering the drum includes over individual tubes 18; and each of these tubes 18 has an inside diameter of inch and a wall thickness of inch giving an outside diameter of 1 /2 inches. More than 400 tubes 18 (with orifices 66 therein) accordingly enter drum 20 when the Fig. 1 furnace has the single chamber design shown by Figs. 2 and 4, and when it has the double chamber design earlier referred to the number of tubes 18 entering this drum 20 is even larger.

Said drum 20 receives the discharge of pumps 26, 27 and 28 through a plurality of conduits 26a, 26b, 27a, 27b, 28a and 28b arranged in a cross-over manner (see Fig. 6), for a purpose hereinafter explained, and conveys this discharge water into the steam generating tubes 18abc--d projecting thereinto.

The interior construction of orifice drum 20 The longitudinal rows of tubes 18a, 18b, 18c and 18d project radially through the wall of drum 20 to a predetermined distance within the drum with each tube being welded to the drum and provided at its inner extremity with a restrictor in the form of an orifice such as is shown at 66 in Figs. 11 and 12.

Referring further to Fig. 11 said inner extremity of each tube 18 is counterbored to snugly receive annular bushing 62 therewithin which bushing in turn receives orifice adaptor 64. Said adaptor 64 and bushing 62 have passages therethrough corresponding to the passage through the steam generating tube 18. Adaptor 64 is provided with a radially extending annular flange 67 inwardly of which projects a cylindrical boss 65 counterbored to receive, with a force fit, orifice member 63 having an orifice 66 (see Fig. 12) of predetermined size formed therein.

As previously noted the size of the orifice 66 for each tube 18 is determined in accordance with a number of factors, with the aim being to obtain a substantially equal circulation ratio in all of the steam generating tubes that are utilized in the complete boiler. The tube circuits 18a, 18c and 18d will therefore require orifice members 63 having difierently sized openings (see Fig. 12); and in order to make certain that each tube 18 entering the drum 20 can receive only an orifice 66 of the particular size that has been pre-selected therefor, the bushing 62 and adapter 64 identified with each individual orifice size are matched or mated in some distinctive way such as is disclosed and claimed by copending application Serial No. 313,202, filed October 6, 1952, now Patent No. 2,694,385, under title of Size Identified Mounting Means for Flow Restricting Orifices.

In order to retain adapters 64 (with their force fitted orifice members 63) in place in bushing 62 during operation of the generator, channel members 68, of sufficient length to span a plurality of tubes in a single row, are suitably bored to receive the cylindrical boss 65 of each orifice adapter 64 in a way permitting the channel member 68 to bear against the flange 67 of each such adapter. Studs 70 (Fig. 9) are welded to the inner surface of drum 20 intermediate certain of said tubes 18 and pass through suitable openings provided in channel members 68. Nuts 71 threadedly received on the end of studs 70 retain said channel members in place.

In order to prevent foreign matter that enters drum 20 from pumps 26, 27 and 28 from clogging the aforementioned orifices, strainers are provided to filter out said foreign matter before it can reach the orifices. In the illustrative form here shown these strainers comprise two generally semi-circular perforate members 72 and 73 extending longitudinally of drum 20 (see Figs. 3 and with member 72 encompassing the inlet ends of steam generating tubes 18c and 18b and member 73 encompassing the inlet ends of steam generating tubes 18a and 18d; the individual perforate openings (see Fig. 7) in these strainer members having a diameter of about inch and thus being considerably smaller than the protected openings in tube orifices 66. Each of the perforate members 72 and 73 comprises a plurality of individually shorter members (actually thirteen in the organization shown, see Fig. 5) provided with abutting flanges 74 secured together with bolts 76 to form an integrated structure.

Angle members 78 are disposed longitudinally of drum and welded to the inner surface thereof. Outwardly turned flanges 79 (see Fig. 8) of perforate members 72 and 73 overlay one leg of said angle members and are secured thereto by any suitable, readily removable, means such as bolts. End plates 80 (most clearly shown by Figs. 5 and 7) are welded to the inner surface of drum 20 at its left and right ends and bolted to the endmost flanges 74 of perforate members 72 and 73 thereby completing the enclosure of the inlet ends of tubes 18a, 18b, 18c and 18d thus forcing all of the boiler water entering drum 20 via conducts 26ab, 27a-b and 28ab (see Fig. 6) to pass through the small openings in said perforated members before entering said tubes.

All of the aforesaid strainer parts are dimensioned for ready entry into orifice drum 20 via either of the end manholes 60 and a similar statement applies to the tube orifices 66 and mounting members therefor.

The interconnection of orifice drum 20 and steam and water drum 24 In controlled circulation boilers it has been the practice to provide each downcomer with an individual circulating pump and to have a particular pump supply a designated group of steam generating tubes through suitable inlet headers. This often resulted in concentration of boiler water impurities at various horizontal locations in the boiler due to the fact that no mixing of the circulating water from one side of the boiler to the other was provided. In the illustrative steam generator of Fig. l specific provision is made to effect a thorough mixing of the circulating water from one side of the boiler to the other.

Downcorners a, 25b, 25c and 25d (best shown in Fig. 6) depend from steam and water drum 24 and are connected at their lower ends to manifold 82. Also connected to said manifold 82 but intermediate the connection of each of the downcomers therewith are the earlier mentioned pumps 26, 27 and 28 with a gate valve 83 positioned in each pump connection for the purpose of isolating the pump should such become necessary. The outlet of each of the pumps 26, 27 and 28 is connected with orifice drum 20 in such a manner that the water handled by each pump is introduced into orifice drum 20 in substantially the reverse longitudinal location from which said water was taken from steam and water drum 24.

For this purpose conduits 26a and 26b connecting the outlet of pump 26 to orifice drum 20 extend to the right, as view in Fig. 6, so that the water from pump 26, which is taken from the left end of steam and water drum 24 (via downcomers 25a-b), is conveyed to the right end of drum 20; conduits 27a and 27b connecting the outlet of pump 27 to orifice drum 20 extend to the left and right, respectively, so that the water from pump 27, which is taken from the central portion of drum 24 (via downcomers 25bc) is conveyed to the left and right ends of drum 20; and conduits 28a and 28b connecting the outlet of pump 28 with drum 20 extend to the left so that the water from pump 28, which is taken from the right end of drum 24 (via downcomers 25cd) is conveyed to the left end of drum 20. Each of the conduits 26a, 26b, 27a, 27b, 28a, 28b is provided with a check valve 84 arranged to prevent back flow through pumps 26, 27 and 28. By means of this cross-over system of piping intimate mixing of the circulating water from one side to the other side of the boiler is obtained at all times thereby insuring that there will be no concentration of dissolved solids and other impurities at a particular horizontal location in the boiler.

Advantages and summary From the foregoing it will be seen that I have provided a controlled circulation steam generator with an orifice drum 20 which is of suflicient diameter to insure a relatively slow flow of the circulating water therethrough and to permit the entrance of workmen therewithin; and that through this arrangement I am able to obtain a number of significant advantages over previously known types of controlled circulation boilers.

Among such advantages are; provision of a settling chamber (i. e. the bottom of the orifice drum) into which suspended solids can collect in large quantity Without interfering with normal operation of the unit and from which removal can readily be effected through the dmms manhole openings 60; insurance that the chemicals introduced into the boiler water to treat the same have had sufficient time to react and thoroughly mix with said water before it enters the steam generating tubes; provision for better and more rapid accessibility of orifices and strainers both as to replacement and inspection thereby improving the availability of the generator; elimination of the welded hand holes required in supply headers of the prior art type; provision for a more economical design of casing and insulation at the lower part of the furnace, which installation of all tube orifices in the single drum 20 makes possible; and reduction in the problem of support since the single orifice drum 20 is easier to mount than are the numerous headers previously required for the various individual steaming circuits (such as 18a, 18b, 18c, 18d).

It will further be seen that I have also provided a controlled circulation boiler with an orifice drum interconnected with the steam and water drum in such a manner as to insure a positive mixing of the circulating water from one side of the boiler to the other.

While I have shown and described one preferred embodiment of my orifice drum invention and have disclosed same as being applied to a controlled circulation steam generator of a particular design it is to be understood that such showing and application are illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of my invention.

What I claim is:

1. In a controlled circulation boiler of the type described, a generally vertical furnace for receiving and burning fuel; a plurality of contiguous steam generating tubes associated with said furnace for absorbing heat from the fuel burned therewithin having their inlets adjacent the lower portion and their outlets adjacent the upper portion of said furnace; a generally horizontal steam and water drum into which the outlets of at least a majority of said tubes communicate; an orifice drum parallel to said steam and water drum and having the inlets of said majority of tubes connected thereto; restrictor orifices associated with the inlets of the tubes so connected; a plurality of downcomers depending from said steam and water drum and longitudinally displaced therealong; and pump means fluidly connecting each of said downcomers to said orifice drum in substantially reverse longitudinal position with respect to the connection of the downcomers with the steam and water drum, said pump means being effective to circulate water through said orifice drum and said restrictor orifices into said tubes, through said tubes into the steam and water drum and thence through the downcomers back into said orifice drum.

2. In a controlled circulation boiler of the type described, a generally vertical furnace for receiving and burning fuel; a plurality of steam generating circuits associated with said furnace for absorbing heat from the fuel burned therewithin, each of said circuits comprising a multiplicity of contiguous tubes having their inlets adjacent the lower portion and their outlets adjacent the upper portion of said furnace; a generally horizontal steam and water drum into which the outlets of said tubes communicate; an orifice drum having a normally closed manhole in its end for access to the drum interior, said drum being in parallel relation to said steam and water drum and having the inlets of the tubes of a number of said circuits connected thereinto; a restn'ctor orifice associated with the inlets of the tubes so connected; a plurality of downcomers depending from said steam and water drum and longitudinally displaced therealong; and pump means fluidly connecting each of said downcomers to said orifice drum in substantially reverse longitudinal position with respect to the connection of the downcomers with the steam and water drum, said pump means being effective to circulate water through said steam generating tubes into said steam and Water drum and thence through the downcomers into the orifice drum and then through said orifice drum back into said steam generating tubes.

3. In a controlled circulation boiler of the type described having a generally vertical furnace of polygonal transverse section with the inner surface of each of the sides lined with longitudinally disposed parallel contiguous tubes whereby each such side forms a separate steam generating circuit, a generally horizontal steam and water drum adjacent the upper portion of said furnace and operatively connected to the outlet ends of the tubes of each of said steam generating circuits, a plurality of downcomers depending from said steam and water drum and longitudinally displaced therealong, and pump means for circulating water from each of said downcomers through said boiler, the combination of an orifice drum adjacent the lower portion of the furnace in generally parallel relation to said steam and water drum and having the inlet ends of the tubes of each of said circuits connected thereinto in circumferentially spaced longitudinal rows; restrictor orifices associated with the inlets of said tubes for restricting the flow through said tubes in accordance with predetermined factors; strainer means including a plurality of elongated perforated plates fixedly secured longitudinally within said drum in such a manner as to filter the water flowing from the interior of said drum into and through said restrictors; and means fluidly connecting said pump means to said orifice drum in such a manner that water flowing from a particular longitudinal location of the steam and Water drum through a particular downcomer enters the orifice drum at substantially the reverse longitudinal location thereby mixing the circulating water from one side of the boiler to the other, said pump means being effective to circulate the water through the steam generating tubes into the steam and water drum, thence through the downcomers into the orifice drum and then through the strainer plates and orifices back into the steam generating tubes.

4. In a controlled circulation boiler, a plurality of steam generating circuits each of which is composed of a multiplicity of tubes; an orifice drum having a normally closed manhole in its end for access to the drum interior, said drum having the inlets of a number of said tubes associated therewith in a plurality of longitudinal rows along the drum wall; an orifice associated with each such inlet; means for establishing a forced circulation of boiler water through said drum, said orifices, said steam generating circuits and thence back into said drum; strainer means within said drum disposed between the inlet for boiler water into said drum and said inlets of said number of tubes effective to filter the boiler water prior to passage through the orifices, said strainer means comprising a plurality of perforate plates individually admissible through said manhole and assembled within the drum in end-to-end abutting relation so as to form a continuous elongated strainer extending longitudinally of the drum throughout substantially its entire length with said strainer encompassing the said orificed tube inlets in said plurality of tube rows, said perforate strainer plates removably secured to the inner surface of the drum and to abutting strainer plates thereby providing ready access to a particular orifice.

References Cited in the file of this patent UNITED STATES PATENTS 1,988,659 La Mont Jan. 22, 1935 2,357,300 Bailey Sept. 5, 1944 2,578,831 Patterson Dec. 18, 1951 FOREIGN PATENTS 223,858 Great Britain Feb. 19, 1925 414,896 Germany June 16, 1925 427,783 Germany Apr. 14, 1926 535,959 Germany Oct. 17, 1931 450,114 Italy July 8, 1949 651,048 Great Britain Mar. 7, 1951

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