US3182640A - Steam generating unit - Google Patents

Description

May 11, 1965 Original Filed Jan. 23, 1962 E. C. MILLER STEAM GENERATING UNIT 2 Sheets-Sheet 1 INVENTOR. Earrle C. miller -May 11, 1965 E. c. MILLER 3,182,640

STEAM GENERATING UNIT Original Filed Jan. 23, 1962 2 Sheets-Sheet 2 LOW LOAD HRSH LOAD coknec'nou av DESUPERHEATER I M [000 DE3IRD SUPERHEAT TEMPERATURE l SUPER 0 I $253" CORRECTION BY TEMR 0F BY-PAS'S DAMPERS I I 950 I I l I I I l 900 I 0 ruu.

- INVENTOR.

Earle C.77Z1'ZZe'r oney United States Patent '2 (Ilairns. or. 122-479 This invention relates to a steam generating unit and, more particularly, to apparatus arranged to produce steam for use with a turbine in the generation of electricity. This is a continuation of my patent application Serial Number 168,060, filed January 23, 1962, now abandoned.

Among the various methods of controlling the temperature of superheated steam in a boiler, one of the most satisfactory makes use of the concept of regulating the residence time of the products of combustion as they flow through the main combustion chamber; lengthening the period in which the gas remains in the combustion chamber tends to lower the temperature of the gas as it leaves the combustion chamber on its way to convection superheater elements. Since the temperature of superheated steam can be varied by varying the temperature of the gases passing over convection sections, this method of control by varying the residence time has many advantages. One of the outstanding methods used for thus varying the residence time is by use of the so-called tilting burner which, when the burners are pointed upwardly in the furnace, causes the residence time to be short, the temperature of gas leaving the combustion chamber to be high, and the superheat to be high. On the other hand, when the burners are directed downwardly in the furnace, the residence time of the .gases in the combustion chamber is. longer, the temperature of the gases leaving the combustion chamber is lower, and the superheat is lower. When the burners are pointed upwardly, one often experiences considerable instability of ignition. With the use of tilting burners, also, the burners must be located high in the furnace, resulting in an extremely high combustion chamber and one which is, therefore, costly. Furthermore, tilting burners are expensive to build and difficult to maintain. These and other deficiencies of the prior art practice have been obviatedin a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a steam generating unit including a means for controlling superheat, which apparatus is inexpensive to manufacture and to maintain.

Another object of the invention is the provision of an apparatus for the control of superheat whose operation is not detrimental to flame stability and the ability to maintain ignition.

A further object of the present invention is the provision of an apparatus for controlling superheat which can be used for initial adjustments of superheat made necessary by inaccuracies in design andconstruction of'the boiler and is also capable of maintaining superheat at constant temperature, irrespective of changes in load.

It is another object of the instant invention to provide a steam generating unit in which apparatus is provided for the control of superheat in which the mass flow of the steam generating unit is not increased.

It is a further object of the invention to provide an apparatus for the control of superheat in a boiler in which the vertical dimension of the furnace is relatively small.

A still further object of this invention is the provision of apparatus for the control of superheat by controlling the residence time of products of combustion in the com bustion chamber characterized by relatively little slagging,

ice

a relatively short combustion chamber, and high flame stability.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view of asteam generating unit embodying the principles of the present invention;

FIG. 2 is a schematic view of the invention showing the operation at low load;

FIG. 3 is a schematic view of the invention showing the operation at high load; and

FIG. 4 is a graphical representation of the variation of superheated steam with load.

In the specification which follows, the expressions longitudinal, transverse, and the like are used to refer to those directions as applied to a steam generating unit in the ordinary practice in that art, and in general, refer to the direction of flow of gas through the unit.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the steam generating unit, indicated generally by the reference numeral 10, is shown as having a vertically-elongated combustion chamber 11 with a pass 12 connected to the upper end of the chamber. A convection superheater 13 is located in the pass and fuel-burning apparatus 14 is located at the lower end of the chamber for producing a mass of hot gas, the gas passing upwardly through the chamber and through the pass 12 to flow in heat exchange relationship to the convection superheater 13. Regulating means 15 is associated with the fuel-burning apparatus 14 to control the degree of diffusion of the gas across the chamber, the

said regulating means causing the gas to be concentrated adjacent the center of the chamber at low load and causing the gas to be diffused evenly throughout the chamber at high load to aid in maintaining the temperature of superheated steam at a predetermined value.

chamber 11. Water-wall tubes leave the header 22 and extend upwardly to define a rear wall 23 of the combustion chamber, while other water-wall tubes extend from the header 22 to define a front wall 24. The transverse header 22 is connected to longitudinal headers 25 from which water-wall tubes extend upwardly to define side walls 26 of the combustion chamber. The tubes which form the rear Wall 23 also pass under the combustion chamber to provide a bottom wall 27, while the tubes which form the front wall 24 also extend over the top of the combustion chamber to provide a roof wall 28. All of these water-wall tubes eventually are connected to the steam-and-water drum 19 for the release of steam and water. Some of the water-wall tubes which make up the rear wall 23 extend forwardly into the combustion chamber 11 at the upper part thereof to form a nose 29. These tubes are spaced apart adjacent the roof 28 of the combustion chamber to provide a gas off-take 31. The upper surface of the nose 29 and the roof 28 are vertically spaced to define a horizontal pass 32. Because of the presence of the nose 29 and the gas oif-take 31 on the rear wall 23, it has substantially less heat exchange surface than the front wall 24; the side walls 26 have sasaeao by a vertical baflle 33 into a front pass 34 and a rearward pass 35. The lower end of the back pass 13 is provided with a set of dampers 36 which underlie the rear pass 35 and control the flow of gas therethrough, and a damper 37 which underlies the front pass 34 and controls the flow of gas therethrough. The back pass 13 is also provided with a centrally-located by-pass (not shown in the drawings) which is also provided with dampers. All of the gases passing through the back pass 13 eventually go through a dust collector 38, through a regenerative air heater 39, and eventually to a stack (not shown). The side walls of the back pass 13 are provided with water tubes which receive water from a lower header 41 which is provided with water through a downcomer 42 connected to the steam-and-water drum 19. The steam tubes 16 leave the top of the steam-and-water drum 19 and line the back wall of the back pass 35 and the baille 33. These steam lines are connected to the low temperature superheater 13. At the upper end the low-temperature superheater 13 is connected to superheater platens 43 which are suspended below the roof 28 of the combustion chamber and have their lower ends located in the restricted passage between the outer end of the nose 29 and the front wall 24 of the combustion chamber. The outlet of these superheater platens is connected to a high-temperature superheater 44 which lies in the horizontal pass 32 and is connected to a superheated steam header 45. It will be understood that the superheater platens 43 constitute a radiant superheater,

While the high-temperature superheater 44 and the lowtemperature superheater 13 are almost entirely convective.

In the front pass 34 is located a low-temperature convection reheater 46 and at the upper end this is connected to a high-temperature reheater 47 of the platen type located in the horizontal pass 32 between the hightemperature superheater 44 and the gas off-take 31.

The Water-wall tubes which define the rear wall 23 of thecombustion chamber are bent to provide an abutment 48 located adjacent the bottom Wall 27, while the waterwall tubes making up the front wall 24 provide a similar rearWardly-directed abutment 49. The abutment 48 is provided on its downwardly-directed surface with a row of directional-flame burners 51, while the abutment 49 is similarly provided with a plurality of directional-flame burners 52. The lower part of the combustion chamber and the burners 51 and 52 are surrounded by an air plenum chamber 53 which is connected by a duct 54 to the air heater 39. The burners 51 are provided with upper vanes 55, while the burners 52 are similarly provided with upper vanes 56. The burners 51 are provided with lower vanes 57, while the burners 52 are similarly provided with lower vanes 58. All vanes are pivotally mounted for rotation about horizontal axes parallel to the walls in which they are mounted. The burners are of the type shown and described in the patent of Miller No. 2,947,289 and are provided with fuel guns and ignition guns in the usual manner. The upper vanes 55 of each of the burners 51 is provided with its own linear actuator 59 which operates through a control rod to adjust the angularity of the vanes to the horizontal. In a similar way, each of the sets of lower vanes 57 of each of the burners 51 is connected to a linear actuator 61, the upper vanes 56 of each of the burners 52 are connected to a linear actuator 62, and the lower vanes 58 of each of the burners 52 is connected to a linear actuator 63. It will be seen, then, that, although the upper vanes of a single burner move together, from burner to burner the upper vanes may be set at various angles. Similarly, although the lower vanes of a particular burner must move together under movement of an actuator, the lower vanes of other burners are independently adjustable by means of their own linear actuators. The linear actuator 59 is connected to a main control 64 4 by lines 65 and 66. Similarly, the linear actuator 61 is connected to the main control 64 by lines 67 and 68, the linear actuator 62 is connected to the main control 64 by lines 69 and 71, and the linear actuator 63 is connected to the main control 64 by lines 72 and 73.

The high temperature reheater platens 47 terminate in a reheated steam header 74 which contains a temperature-measuring device 75; this temperature-measuring device is connected by a line 76 to the input side of the main control 64. Similarly, the superheated steam header 45 contains a temperature-measuring device 77 which is connected by a line 7 8 to the main control 64.

Connected to the dampers 36 which control the flow of gas through the back pass 35 is a linear actuator 79 which is connected to the output of the main control 64 by means of lines 81 and 82. The damper, 37, which controls the flow of gas through the front pass 34, is connected to a linear actuator 83 which is connected to the main control 64 through lines 84 and 85. The dampers which control the flow of gas down the by-pass of the back pass 13 are connected to a linear actuator 86 which is connected to the output of the main control 64 by lines 87 and 88. The main control 64 is of the usual type used in temperature control applications and is provided with apparatus which is well known in the art for converting electrical signals which appear in the lines 76 and 78 to hydraulic flow through the lines 65, 66, 67, 68, 69, 71, 72, 73, 81, 82, 84, 85, 87, and 83 leading to the hydraulic linear actuators'associated with the apparatus. Since the main control is not part of the present invention in its detailed form, it is not felt that a specific description thereof is necessary adequately to describe the present invention.

The operation of the apparatus of the invention will now be readily understood in view of the above description. Fuel arrives at the burners 51 and 52 and is mixed with a certain amount of air from the air plenum chamber 53. The fuel and air is projected into the high-temperature cell 89 defined by the abutments 48 and 49 and the bottom 27 'of the combustion chamber. The lines of flow of the fuel and air intersect at an imaginary point in the central part of the furnace a short distance above the bottom 27. The air, of course, enters the burner housing and flows past the pivoted vanes into the furnace. Some of the air is controlled by the upper vanes 55 and 56 and the rest is controlled by the lower vanes 57 and 58. This air blends with the fuel flowing from the fuel guns which extend through the burners; a mass of turbulent fuel and air is thus formed in the portion of the combustion chamber which underlies the noses 48 and 49. It is the nature of this particular design of furnace that combustion takes place below or, at most, only slightly above the horizontal line defined by the abutments 48 and 49. Gases pass from the high-temperature cell 89 up through the combustion chamber 11 and leave the chamber through the restricted passage between the nose 29 and the front wall 24 of the furnace. The gases then fiow through the horizontal pass 32, coming into heat exchange contact with the high-temperature superheater 44 and the high-temperature reheater 47. The gases enter the back pass 12 through the gass ofiF-take 31; the gas flow is then divided between the front pass 34, the rearward pass 35, and the by-pass, the division between these passes being determined by settings of the dampers at the bottom part of the passes.

Steam leaves the boiler through the pipe 91 and passes through an orifice 92 so that lines 93 and 94 connected to the input of the main control 64 gives a signal indicative of load. Now, referring to FIG. 2, it can be seen that, when the signal which arrives at the main control 64 through the lines 93 and 94 indicates that a low load operation is being used, signals will pass from the output of the main control through hydraulic lines to give the linear actuators settings such that the upper vanes 55 and 56 are all inclined to angles below the horizontal and toward the imaginary geometric center of the high temperature cell 89. At the same time, the lower vanes 57 and 58 are set at an angle which is approximately horizontal. This results in individual flames from the various burners that are quite narrow and are directed almost directly toward one another resulting in a very narrow flame in the center of the furnace. This results in a very narrow mass flow of gas up the furnace approximately mid-way between the front wall 24 and the rear wall 23. The velocity of the gases in this central core is relatively great and the gas moves through the combustion chamber 11 in a short time and enters the convection passes at an extremely high temperature. The result is a tendency to raise the temperature of superheat and reheat. When the index of load received from the orifice 92 through the lines 93 and 94 indicates to the main control 64 that the operation is in a high load range, the proper hydraulic signal is sent through the lines to the linear actuators to produce the setting of vanes shown in FIG. 3. In this situation, the upper and lower vanes of alternate burners are pointed below horizontal and the upper and lower vanes of the remaining burners are pointed above horizontal to give very broad flames and to cause the gas to be diffused evenly between the front wall 24 and the rear wall 23. For instance, with regard to the burners 51 on the rear walls, the first burner in the row has all of the upper vanes 55 and the lower vanes 57 set above horizontal, as is shown in FIG. 3 in solid lines. In the next burner in the row, the upper and lower vanes will be set pointing below horizontal toward the imaginary geometric center of the high-temperature cell 89; this alternate arrangement takes place across the furnace and across the bottom surface of the abutment 48. Similarly, with regard to the burners 52 on the abutment 49, in the firstburner the upper vanes 56 and the lower vanes 58 are all inclined downwardly toward the center of the high temperature cell, while in the next burner in the row the upper vanes 56 and the lower vanes 58 are pointed in a generally horizontal or slightly above horizontal direction, as shown in dotted line in FIG. 3. The net result is a diffused flame which extends evenly from the front wall 24 to the rear wall 23; this results in the flow of gas being more and more less evenly distributed across the longitudinal dimension of the furnace and results in an integral of flow of gas which is quite low. The passage of the gas through the combustion chamber 11 at a slow rate means that greater residence time is available to permit heat transfer by radiation to the water-walls of the furnace. This results in the temperatures of the gases which move into the convection passes of the furnace being at a lower temperature which means that the tendency will be to lower the temperature of superheat.

As is evident in FIG. 4, if the temperature of superheat becomes higher than the desired value, the temperature of superheat may be lowered by use of the bypass dampers controlled by the actuator 86, by use of the desuperheater 95 which is controlled by a line 96 originating in the output side of the main control 64, or by use of both the by-pass dampers and the desuperheater. As evident from the graphical showing of the operation of the apparatus in FIG. 4, the line labeled VANE SETTING FIG. 3 provides a normal superheat curve which is always above the desired superheat temperature (say, 1000 F.) above load; it is necessary, therefore, to reduce this temperature slightly by use, for instance, of the by-pass dampers under the control of the linear actuator 86. When the load is lowered to a value below 4 load, the vane settings shown in FIG. 2 are used, resulting in the curve labeled VANE SETTING FIG. 2 in the graph, and this results in a superheat curve which is above the desired value all the way from 4 load to /2 load. Between load and load it is necessary to reduce the superheat by use, for instance, of the desuperheater 95. It can be seen, then, that by use of the settings shown in FIG. 2 and FIG. 3 it is possible to obtain a flat curve of superheat from /2 load to full load and above.

In the above description of operation, the vane settings are either as shown in FIG. 2 (to give high gas temperatures at low loads) or as shown in FIG. 3 (to give low gas temperatures at high load). In practice, however, it may be desirable in the range from /2 load to load to change the vane settings continuously from the condition of FIG. 2 to that of FIG. 3. This will result in a curve which follows the DESIRED SUPERHEAT T EM- PERATURE line, so that no desuperheating is required in this range. To accomplish this, alternate upper vanes are gradually moved from downwardly-directed to upwardly-directed and alternate lower vanes are gradually moved from upwardly-directed to downwardly-directed. When this is done, the flames in the high-temperature cell 89 gradually change from sharp, narrow flames which point horizontally (at /2 load) to broad streams which entirely fill the cell with flame (at /1 load). The gas flow is gradually changed from a concentrated stream located in a vertical plane midway between the front and rear walls (at load) to a broad undifferentiated flow (at load). This gradual change results in high average gas temperature in the convection passes (at /2 load), intermediate average gas temperature (at, say, load), and high average gas temperature (at load). The temperature of superheated steam is, thus, maintained at the desired preselected value.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent 1. A steam generating unit, comprising front, rear, side, roof, and bottom walls defining a vertically-elongated combustion chamber, the side walls having similar amounts of heat exchange surface while the front and rear walls have substantially different amounts of heat exchange surface, a back pass connected to the upper end of the chamber, a convection low-temperature superheater and a reheater located in the back pass, a gas off-take leading from the rear wall at the upper end of the chamber to the back pass, a nose extending into the chamber under the gas elf-take to define a horizontal pass with the roof wall, a high-temperature superheater residing above the nose in the said horizontal pass, opposed abutments extending toward one another from the front and rear walls of the combustion chamber at the lower end thereof to define a high-temperature cell with the bottom wall of the chamber, directional-flame burners located on'downwardly-directed surfaces of the abutments for producing a mass of hot gas, the gas passing upwardly through the chamber and through passes to flow in heat exchange relationship to the convection superheater and reheater, the directional-flame burners having vanes whose angle to the horizontal may be changed, damper means to by-pass gas around the said convection superheater and reheater in the back pass, and regulating means connected to the said vanes to set them at predetermined angles to cause the flow of gas to be concentrated mid-way between the front and rear walls of the chamber at low load and causing the gas to be diffused evenly between the front and rear walls of the chamber at high load to aid in maintaining the temperature of superheated steam at a predetermined value, the concentration of gas at a given load being the same throughout a given vertical plane extending between the side walls in a direction parallel to the front and rear walls.

2. A steam generating unit, comprising a verticallyelongated combustion chamber having a first set of opposed walls of similar heat-exchange characteristics and a second set of opposed walls having substantially different amounts of heat exchange surface, a pass connected to the upper end of the chamber, a convection superheater located in the pass, fuel-burning apparatus located at the lower end of the chamber for producing a mass of hot gas, the gas passing upwardly through the chamber and through the pass to flow in heat exchange relationship to the convention superheater, means to by-pass gas around the said convection superheater, and regulating means associated with the fuel-burning apparatus to control the degree of diffusion of the gas across the chamber, the said regulating means causing the gas to be concentrated adjacent the portion of the chamber intermediate the Walls of the second set at low load and causing the gas to be diffused evenly between the walls of the second set athigh load to aid in maintaining the temperature of superheated steam at a predetermined value, the concentration of gas at a given load being the same throughout a given vertical plane extending between the walls of the first set in a direction parallel to the walls of the second set.

References Cited by the Examiner UNITED STATES PATENTS 2,941,517 6/ 60 Patterson 122478 2,941,518 6/60 Firl 122478 2,947,289 .8/60 Miller l22479 PERCY L. PATRICK, Primary Examiner.

KENNETH W. SPRAGUE, Examiner.

Claims (1)

1. 2. A STEAM GENERATING UNIT, COMPRISING A VERTICALLYELONGATED COMBUSTION CHAMBER HAVING A FIRST SET OF OPPOSED WALLS OF SIMILAR HEAT-EXCHANGE CHARACTERISTICS AND A SECOND SET OF OPPOSED WALLS HAVING SUBSTANTIALLY DIFFERENT AMOUNTS OF HEAT EXCHANGE SURFACE, A PASS CONNECTED TO THE UPPER END OF THE CHAMBER, A CONVECTION SUPERHEATER LOCATED IN THE PASS, FUEL-BURNING APPARATUS LOCATED AT THE LOWER END OF THE CHAMBER FOR PRODUCING A MASS OF HOT GAS, THE GAS PASSING UPWARDLY THROUGH THE CHAMBER AND THROUGH THE PASS TO FLOW IN HEAT EXCHANGE RELATIONSHIP TO THE CONVENTION SUPERHEATER, MEANS TO BY-PASS GAS AROUND THE SAID CONVECTION SUPERHEATER, AND REGULATING MEANS ASSOCIATED WITH THE FUEL-BURNING APPARATUS TO CONTROL THE DEGREE OF DIFFUSION OF THE GAS AROUND THE CHAMBER THE SAID REGULATING MEANS CAUSING THE GAS TO BE CONCENTRATED ADJACENT THE PORTION OF THE CHAMBER INTERMEDIATE THE WALLS OF THE SECOND SET AT LOW LOAD AND CAUSING THE

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