US3401675A - Steam generating unit - Google Patents

Description

p 17, 1963 E. c. MILLER 3,401,675

STEAM GENERATING UNIT Filed Oct. 31, 1966 2 Sheets-Sheet l EARLE C. MILLER INVENTOR.

ZZWJW Sept. 17, 1968 E. c. MILLER STEAM GENERATING UNIT 2 Sheets-Sheet 2 Filed Oct. 51, 1966 FI G. 3

{ UNCONTROLLEDI CONTROLLED FIG. 5

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United States Patent 3,401,675 STEAM GENERATING UNIT Earle C. Miller, Worcester, Mass., assignor to Riley Stoker Corporation, Worcester, Mass, at corporation of Massachusetts Filed Oct. 31, 1966, Ser. No. 590,924 4 Claims. (Cl. 122-479) This invention relates to a steam generating unit and, more particularly, to apparatus arranged to produce steam at a closely regulated temperature by the burning of fuel in suspension.

In the operation of steam generating units for central stations, it is important that the temperature of the steam which passes through the turbine be maintained at a predetermined value within close limits. This is because the turbine is a delicate piece of machinery which is designed for its most efiicient operation at a definite pressure and temperature of steam. Maintaining the steam at the desired design pressure presents no particular problem, but the temperature tends to vary. In most boilers, the steam temperature rises with an increase of load or demand on the unit. Most methods for maintaining the superheat temperature at the predetermined value involve less than the most efficient operation because heat is being wasted. Furthermore, many of them are extremely complicated and involve apparatus which does not work well in the practical operation of a steam generating unit. These and other difiiculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a steam generating unit in which steam may be maintained at a constant predetermined value with apparatus whose use does not represent a great departure from conventional methods of operation.

Another object of this invention is the provision of a steam generating unit including a superheated steam temperature control which is simple in operation, inexpensive to manufacture, and which is capable of constant use over long periods of time with a minimum of maintenance.

A further object of the present invention is the provision of a steam generating unit including superheat control means which makes use to a great extent of apparatus normally found in a conventional unit.

It is another object of the instant invention to provide a steam generating unit having superheated steam temperature control involving a novel concept of operation.

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 front view with portions broken away of a steam generating unit embodying the principles of the present invention,

FIG. 2 is a schematic view of the interior of the unit,

FIG. 3 is a transverse sectional view of the unit taken on the line IIIIII of FIG. 2,

FIG. 4 is a somewhat schematic view of the bottom of the interior of the unit under a different condition of operation,

FIG. 5 is a graphical representation of operation of the unit, and

FIG. 6 is a schematic view of controls forming a part of the present invention.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the steam generating 3,401,675 Patented Sept. 17, 1968 unit, indicated generally by the reference numeral 10 comprises a front wall 11, a rear wall 12, a side wall 13, and a side wall 14 defining a vertically elongated combustion chamber 15. At the lower end of the combustion chamber on the front wall 11 is mounted a horizontal row 16 of burners. Each of these burners is of the constant-velocity type shown and described in the patent to Miller No. 3,203,463, which issued on Aug. 31, 1965.

The front wall 11 is made up of water wall tubes originating in a transverse header 17. At the bottom of the furnace the rear wall 12 is similarly formed of water wall tubes and is provided with a forwardly/extending nose 18 above which extends a rearwardly directed convection pass 19. Lying in the convection pass is a superheater 21 which delivers steam to a superheated steam header 22. The side wall 13 is composed of tubes extending from a lower header 23 to an upper .header 24. The side wall 14 is similarly made up of tubes extending from a lower header 25 to an upper header 26.

The row 16 of burners, for the purposes of illustration, is made up of six burners 27, 28, 29, 31, 32, and 33. Mounted on the outside of the front wall 11 outside of these burners is a wind box 34 having a dividing wall 35 between the burner 27 and the burner 28 and a dividing wall 36 between the burners 32 and 33 This means that the burner 27 resides in its own air chamber as does the burner 33, while the central burners 28, 29, 31, and 32 lie within a single large chamber.

The fuel enters the burner system through a duct 37 while the air enters through a duct 38. The flow of fuel to this system is controlled by a damper 39 which is regulated by a linear actuator such as a hydraulic cylinder 41. In a similar way, the air flow through the duct is controlled by a damper 42 which is regulated by a cylinder 43. The air and fuel are mixed and pass down a main duct 44 leading to the portion of the wind box 34 which includes the burners 28, 29, 31, and 32. From the main duct 44 extends a branch duct 45 which leads to the burner 27 and which is provided with a shutoff damper 46 regulated by a cylinder 47. Similarly, a branch duct 48 leads to the burner 33 and is provided with a shutoff damper 49 regulated by a cylinder 51. The burner 28 is provided with auxiliary passages and vanes operating these passages above and below the central fuel gun, in the manner shown and described in the abovementioned Patent No. 3,203,463. The vanes to these auxiliary passages are regulated by a cylinder 52 so that it is possible to maintain the velocity of the fuel-air mixture through the burner at a constant predetermined value irrespective of load. The burners 29, 31, and 32 are provided, respectively, with cylinders 53, 54, and 55 for accomplishing the same purpose.

The end burner 29 is provided with a cylinder 56 which is capable of maintaining constant velocity of the burner and of shutting the burner off entirely on occasion, and a similar cylinder 57 is associated with the burner 33.

Referring to FIG. 3, in the preferred embodiment, the row 16 of burners is located on a downwardly directed surface of a horizontal abutment 58 formed on the front wall 11 of the furnace. A similar row 59 of burners is mounted on a downwardly directed surface of a similar abutment 61 formed on the rear wall 12 of the furnace. The row 16 and the row 59 of burners are on the same horizontal level in the furnace in opposition with one another and the burners in the row 59 are provided with an operating mechanism and control similar to that associated with the row 16.

Referring now to FIG. 6, it can be seen that the superheater header 22 is provided with a temperature-measuring device 62 from which a signal extends through a line 63 to a main control 64. This main control 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 and pneumatic signals which appear in input lines to output hydraulic signals. 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 unit is provided with an airflow venturi 65 through which the air flowing to the duct 38 passes and from this venturi extends a line 66 which carries a signal indicative of the flow of air or of load on the steam generating unit. The lines 63 and 66, therefore, constitute the input lines to the main control 64. The main control is provided with two output hydraulic lines 67 and 68 leading to the fuel cylinder 41 and with hydraulic lines 69 and 71 leading to the air flow cylinder 43. The main control is also provided with two output lines 72 and 73 causing hydraulic signal to flow to the left and right damper actuating cylinders 47 and 51. Output lines 74 and 75 lead to the cylinders 52, 53, 54, and 55 associated with the burners 28, 29, 31, and 32 or the so-called center burners. Output lines 76 and 77 lead to the left burner cylinder 56 and the right burner cylinder 57.

The operation of the apparatus will now be readily understood, in view of the above description. With all of the burners operating and the unit in conventional operation at a low load, such as would be indicated by the point A on the graph in FIG. 5, the gas will leave the burners in the manner shown in FIG. 2; that is to say, will rise straight up through the furnace with the flow neither directed toward nor away from the side walls 13 and 14, and this will result in a given temperature of gas passing over the superheater 21 and producing a steam temperature which, for the purposes of illustration, may be taken as a design temperature of 1000 F. As shown in FIG. 3, the gas passes through certain convolutions in a longitudinal plane before passing upwardly into the furnace because of the fact that the burners in the row 16 and 59 are directed downwardly and inwardly toward the bottom of the furnace.

Now, if the load is raised to, say, 100% of design value, without adjustment, the superheat temperature will rise in the manner indicated on the curve labeled UNCONTROLLED. In the present case, however, the main control 64 (FIG. 6) receives a signal from the superheater header; that is to say, the signal comes from the temperature-measuring device 62 and passes through the line 63 through to the main control. In a similar way, a signal of load comes from the venturi 65 through the line 66. The main control takes these two signals and, 'by measuring the variation of the superheated steam temperature from a desired value at a given load, it makes adjustments in the output lines 67, 68, 69, 71, 74, 75, 76, 77, 72 and 73. Let us suppose that load is raised suddenly up to 100% load, then the main control 64 sends signals through the lines 77 and 76 to operate the left burner cylinder 56 and the right burner cylinder 57 and shut the dampers on these burners down completely. At the same time, the fuel and air is shut off from these burners by a signal through the lines 72 and 73 which operate the left cylinder 47 and the right cylinder 51 to close the dampers 46 and 49, respectively. The outside burners 27 and 33 therefore, not only have their vanes shut down completely, but also receive no fuel and air through the conduits 45 and 48. Naturally, because of the load being raised, the amount of fuel-air mixture to the furnace must be raised and this is done by signals through the lines 67 and 68 operating the fuel damper cylinder 41 which regulates the damper 39 and the lines 69 and 71 operating the air cylinder 43 which regulates the damper 42. The total amount of fuel-air mixture is raised to a value commensurate with the increase of load to 100% and this flows from the fuel conduit 37 and the air conduit 38 into the main conduit 44 to the burners 28, 29, 31, and 32. At the same time, with the increase in load and the increase in air flow through the four '4 central burners it is necessary to adjust the secondary passage vanes in the manner shown and described in the aforementioned Patent No. 3,203,463 to keep the velocity at the optimum value for good ignition. For this purpose, signals are sent out from the main control 64 through the lines 74 and 75 to adjust the cylinders 52, 53, 54, and 55 which has the net effect of opening .up the secondary passages associated with the burners 28, 29, 31, and 32 to maintain in the velocity of air through I the burner at a predetermined value, irrespective of the fact that more air and fuel is passing through individual burners.

When these adjustments have been made, the burners 27 and 33 are totally closed down and the air flow from the four central burners 28, 29, 31, and 32 takes the pattern shown in FIG. 4. As is evident in the drawing, the gas tends to diffuse outwardly toward the side walls 13 and 14. This causes the temperature in the side walls to rise which is an indication that the side walls are obsorbing more heat from the gas than they had at the previous low load condition. Because of the larger amount of heat absorbed from the gases, their temperature (when they reach the upper part of the combustion chamber and pass into the convection pass 19) is lower than would otherwise be true. Normally, with the increase in load on the combustion chamber, the temperature of the gas passing into the convection pass 19 would be higher and cause the superheat generated in the superheater 21 to rise along the UNCONTROLLED curve. However, in the present case, because of the greater heat absorption from the walls due to the change in difiusion of the fuel in the furnace and the outward flow of the gas toward the side walls 13 and 14, the gas temperature remains the same despite the increase in load which means that the superheat temperature curve is the one indicated in FIG. 5 as CONTROLLED.

It can be seen, then, that by use of the present invention, it is possible to maintain the temperature of superheat at a constant predetermined value despite changes in load. The method that is used involves dropping out the end burners in a row to produce an effect which was totally unexpected; that is to say, the gas flows toward the side walls. This results in greater heat absorption from the gases rather than less, as would normally be expected, if one were to remove the burners closest to the side walls. This method of superheat control takes place, however, without any loss in efficiency of the furnace because it does not necessitate the bypassing of gases around heat exchange surfaces, as is a common practice; nor does it involve desuperheating, which means that cold water is injected into the superheater header to cool the temperature of steam after it has already been raised to a high value. It has an advantage over the socalled gas recirculation method because the mass flow through the surface is not increased; in other words, it does not involve the introduction of colder gas into the furnace with an attendant increase in mass flow which presents the problem of reintroduction of high dust content gas with a subsequent increase in slagging.

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 is:

1. A steam generating unit, comprising (a) front, rear, and side water walls defining a vertically elongated combustion chamber,

(b) a horizontal row of burners mounted on the front wall at the lower end of the chamber,

(c) a convection pass connected to the upper end of the chamber,

(d) a superheater mounted in the said pass, and

(e) means to close down the burners closest to the said side walls to maintain the temperature of superheated steam at a predetermined value, the said means including a main control which receives a signal indicative of temperature of superheat and a signal indicative of load, the main control regulating the total amounts and proportions of fuel and air passing to the burners, separately regulating the amount of fuel-air mixture passing to the said burners closest to the side walls, and regulating the velocity of the fuel-air mixture passing through the burners which are not closest to the side walls.

2. A steam generating unit as recited in claim 1, Wherein a second horizontal row of burners is provided at the same level on the rear wall and wherein the said means is operative in the same manner on the second row of burners as on the first-mentioned row of burners.

3. A steam generating unit as recited in claim 1, wherein each burner provides constant velocity flow of fuel and air irrespective of load.

4. A steam generating unit as recited in claim 1, wherein a horizontal abutment is provided on the front and rear walls at the same level at the said lower end of the chamber and wherein a row of burners is mounted on the downwardly directed surface of each abutment.

References Cited UNITED STATES PATENTS 2,196,377 4/1940 Bailey 122-479 XR 2,905,155 9/1959 Grossman 122-478 2,941,518 6/1960 Firl 122478 XR KENNETH W. SPRAGUE, Primary Examiner.

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