US2985151A - Vapor generating and superheating operation - Google Patents

Description

May 23, 1961 P. s. DICKEY 2,985,151

VAPOR GENERATING AND SUPERHEATING OPERATION Filed June 29, 1951 5 Sheets-Sheet 1 ooonoonaoooonnoo as an a g o a a a o o o o o a a a a a a a M an IN VEN TOR.

PAUL S. DICKEY f7 RNEY P. s. DICKEY 2,985,151

VAPOR GENERATING AND SUPERHEATING OPERATION 5 Sheets$heet 2 'wwv' TC-I 000000000 000000 0000000 0 0 00000 0000 0 0 oo 0 0 o 0 000000000 000000 0000000 0 O O O .0 2 3 4 C O D 0 0 T T T T 0000000000000000000004000000 000000 0000000 000 J000 OOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOOOGOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOO SCREEN 3 J 0 May 23, 1961 Filed June 29, 1951 INVENTOR.

PAUL S. DICKEY PRIMARY SUPERHEATER'S FIG. 5

MM IFZ/m A ORNEY FIG. 4

SECONDARY SUPERHEATER -4 gkli May 23, 1961 BURNER TILT FINAL STEAM TEMP. F

P. S. DICKEY VAPOR GENERATING AND SUPERHEATING OPERATION Filed June 29, 1951 CHARACTERISTIO BURNER TILT CURVE 5 Sheets-Sheet 3 REMOVED BY ATTEMPERATORQ DEsIRED FINAL STEAM TEMP. W

I Iooo W x RAISED BY BURNER TILT CHARACTERISTIC CURVE CONVECTION SUPERHEATER 800 g g 4 I o 20 40 so so Ioo BOILER LOAD (PER DENT) INVENTOR.

PAUL S. DICKEY FIG. 6 BY May 23, 1961 P. S. DlC-KEY VAPOR GENERATING AND SUPERHEATING OPERATION Filed June 29, 1951 AIR HEATER O O O O O O O O O ECONOMIZER O 7 ooooo0oo PRIMARY SUPERHEATER SECONDARY SUPERHEATER GENERATING SECTION III GAS FLOW PATH 5 Sheets-Sheet 4 FINAL STEAM TEMP.

STEAM PRESSURE INVENTOR.

PAUL S. DICKEY May 23, 1961 P. S. DICKEY VAPOR GENERATING AND SUPERHEATING OPERATION Filed June 29. 1951 5 Sheets-Sheet 5 CFROM SECONDARY SUPERHEATER 9 2,

STEAM \ZI PRESSURE I 40 50 "/1 I m 22 2e [42 f f GAS SEE/lb TEMF? FUEL 2IA TEMP AND AIR SUPPLY G) (D u (Q1 (45 49\ 48 Lo- (Q) 1 Q .L 58 A .LL.

INVENTOR.

Fae.8

PAUL S DICKEY United States Patent VAPOR GENERATING AND SUPERHEATING OPERATION Paul S. Dickey, East Cleveland, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Filed June 29, 1951, Ser. No. 234,169

2 Claims. (Cl. 122-479) My invention lies in the field of steam power generation and particularly in the control of steam temperature in connection with present day vapor generators. Practically all central station capacity presently being installed, or on order, in the United States has rated steam conditions above 800 p.s.i.g. and 800 FTT; the highest operating temperature being 1050 FTI at pressures from 1500 p.s.i.g. to 2000 p.s.i.g. and rated load of from 500,000 to 1,000,000 lb. per hr., with a large percentage employing reheat surfaces. The problems involved in the generation and close control of the properties of steam are quite different now than was the case at the time of the inventions in this field which are shown in the prior art.

Superheat temperature control is particularly desirable in the generation of steam for the production of electrical energy in large central station power plants. In such plants the upper limit of 'superheat temperature is governed by the materials and construction of the turbine served by the steam. In the interest of turbine efiiciency the temperature of the steam delivered to the turbine should be maintained within close optimum limits throughout a wide range of capacities.

As feed water temperatures progressively increase there is less and less work for the boiler proper, with the result that its convection heat-absorbing surface has disappeared to the point where the modern large utility unit consists of a water-walled furnace, a convection superheater, an economizer and an air heater. Furnace design is now centering around sufficient water cooling surface to absorb the radiant heat and to achieve the required relatively low furnace exit gas temperatures.

With the superheating or resuperheating of the stream in one or more convection type heat exchange surfaces, the size and cost of such surfaces becomes a material factor in the total cost of the unit and any improvement leading to a reduction in the size of superheaters becomes of considerable importance. Usually these surfaces must be made of expensive high-alloy tubing to satisfactorily handle the temperatures and pressures encountered.

It is thus a prime desideratu-m, in the design of such a unit, to proportion the steam generating surfaces and :the steam superheating surfaces to give the desired final steam temperature at rated load. At peak load, in excess of the rated load, the final steam temperature will be in excess of that desired and correspondingly at lower ratings the steam temperature will not equal that desired. It is false economy to design the superheater for desired final steam temperature at peak load, for all loads below that value would then produce steam below the desired temperature. On the other hand,'the design of the superheater to produce the desired final steam temperature at some rating below rated load would require an excessive cost of superheating surface I Thus, usually the heat exchange surface of the superheater is designed to provide the desired total tempera ture of the steam at rated loa and experience has shown that below this load the total temperature of the leaving steam decreases while above this load the total temperature increases. This is because the characteristic curve of a convection superheater is a rising function with load as will be seen in Fig. 6 of the present application.

To reach the desired high superheated steam temperature, but not exceed it, requires exceedingly careful proportioning of the heat absorbing surfaces both for generating steam and for superheating it. But even if the desired superheated steam temperature be just attained initially by very carefully designing at rated load, the superheated steam temperature will vary during operation by reasons of changes in cleanliness of the heat absorbing surfaces. Slag will form and adhere to the heat absorbing surfaces in the furnace thereby reducing the effectiveness of such surfaces and raising the furnace outlet temperature of the products of combustion. Furnace outlet temperature will also change with percentage of excess air supplied for combustion, with the characteristics of the fuel burned, and with the rate of combustion and the corresponding rate of steam generation. All of these things will therefore affect the temperature of the gases leaving the furnace and supplied to the superheater, whether the superheating elements are located in the furnace where they absorb heat by radiation from the burning fuel and products of combustion, or whether they are located beyond the furnace where they absorb heat by convection from the products of combustion only.

With the furnace volume, as well as the vapor generating furnace surface, and the vapor superheating surface, fixed and invariable, the possibility of satisfactorily controlling the final steam temperature lies in controlling the volume and temperature of the gases contacting the superheating surfaces. Total fuel and air supply are varied with demand or rating to provide desired steam flow output. Furnace temperature of the flame and products of combustion does not vary greatly with rating. This leaves the controllable variables the volume and temperature of the gases entering the convection superheating surfaces. The volume, or mass flow rate, has been controlled in the past through by-passing some of the gas flow around the superheater surface. The temperature of the entering gases may be controlled by selecting the amount of generating surface to be contacted by the gases before they enter the superheater. It is also known to have spray attemperators or other heat absorbing means for the excess heat in the final steam before the steam goes to a turbine.

For any given furnace, as load increases, the heat input is increased, but the rate of heat absorption does not increase as rapidly as the rate of heat input; therefore, the furnace leaving temperature will rise. With both the quantity rate and the temperature of the gases leaving the furnace increasing with load, it is apparent that a fixed surface convection superheater will receive a greater heat rate at higher loads than at lower loads and the heat transfer area is usually designed for the volume and temperature of leaving gases at rated load. Any further increase in heat release rate supplies to the fixed superheater surface more heat by gas volume and by gas temperature than it is designed for and a corresponding excessive final steam temperature is experienced. Correspondingly, at operation below the rated load the fixed superheater surface receives less volume "and a lower temperature of gases leaving the furnace with corresponding lowering of final steam temperature leaving the superheater. It is therefore a principal object of my invention to provide an improved: method and apparatus for extraeting excessive heat from the steam at high rating and for supplying additional heat to the steam at low ratings, to the end that the final steam temperature will approximate a uniform value over a range of operating ratings at each side of the rated load value.

It is known to control the primary heat absorption in a radiant furnace by directionally controlling the firing as to the furnace surface in relation to the superheater surface. The known tangentially placed tilting burners allow a control of varying utilization of the furnace heat absorbing surface through the tilting of the burners. It is also known to use tilting burners in systems wherein the excessive heat in the upper ratings is absorbed by spray attemperation or is by-passed around the superheater by means of a by-pass damper; and to increase the heat rate which is directed at the superheater, relative to that which is directed to the generating surface, at the lower ratings. Such controls may be accomplished in sequence, or with, or without, overlap at the normal operating point.

I purposely employ selective distribution of load between vertically tiltable burners proportioning the application of heat as between steam generating surface and steam superheating surface at different loads. I vary the heat release direction and consequently the effective furnace absorption area. In other words, as rating falls I utilize proportionately less of the generating surface and thus tend to maintain the temperature of the gases entering the superheating surfaces more nearly constant than would otherwise be the case. This is accomplished by controllably tilting the vertically spaced, tangentially firing burners to the end of directionally applying the heat of combustion to the generating surface in accordance with rating. I

My present invention has as a primary object method and apparatus for operating, and controlling the operation of, such vapor generating units through the utilization of more advantageous indexes of heat availability to the convection superheater and of operation of the unit as a whole.

So far as I am aware no one has previously used the actual entering gas temperature as an element in method and apparatus for controlling steam final temperature on units of the type under discussion equipped with tangentially firing tiltable burners. Attempts'have been made to ascertain continuously the temperature within the superheater tubes near the entrance, near the exit and at intermediate locations. Attempts have also been made to obtain the temperature of the steam before it enters the convection superheater and to use this temperature measurement in conjunction with the final steam temperature, in controlling spray attemperators, gas by-passes, and the like. These methods and arrangements have not been entirely satisfactory. A considerable time and heat lag occurs in the heat transfer through the films and metal of the tube surfaces, and with rapidly fluctuating heat release loads and temperature effects as caused by slagging or deslagging of the furnace walls with corresponding fluctuating variations in heat absorption of the generating surface as well as flame drift around the furnace, has introduced lags in final steam temperature control systems with corresponding hunting and over-shooting. Through the use of my invention I avoid these inaccuracies and adverse effects by utilizing the actual furnace gasexit temperatures as an element in my control system to maintainfinal steam total temperature.

In the drawings:

Figs. 1, 2 and 3 are somewhat diagrammatic sectional elevations of a vapor generating unit having primarily radiant generating surface and convection superheating surface.

Fig. 4 is a section taken along the line 4-4 of Fig. l in the direction of the arrows.

Fig. 5 is a section taken along the line 55 of Fig. 1 in the direction of the arrows and to a different scale.

Fig. 6 is a graph of characteristic values in connection with other figures of the drawing.

Fig. 7 is a diagrammatic showing of my invention in connection with tilting burners and a spray type atternperator.

Fig. 8 is another arrangement of tilting burner and spray attemperator control.

Figs. 1, 2 and 3 show in somewhat diagrammatic sectional elevation a typical vapor generator in connection with which I will explain my invention. Fig. 4 is asection, to somewhat different scale, along the line 4--4 of Fig. 1, in the direction of the arrows.

The generator is of the radiant type, having a furnace 1 which is fully water-cooled withthe walls 2 of vertical closely spaced plain tubes constituting the vapor generating portion of the unit. Products of combustion pass upwardly through the furnace I in the direction of the arrow, through the tube screen 3, over a secondary superheater surface 4, a reheating section 5 and a primary superheating surface 6. A tubular economizer section 7 follows the superheater 6 and in turn may be followed b an air heater.

While my invention is applicable to generating units employing fuel burned in suspension, such as gas, oil, or pulverized coal, the most prevalent use at present of tilting burners is with pulverized coal.

The unit is fired with pulverized coal from four sets of corner located tangential burners, vertically-adjustable or tiltable through a range of approximately +30 to horizontal to -30. Fig. 4 diagrammatically shows the firing arrangement of the four corner burners at a given elevation or section. I have shown in Figs. 1, 2 and 3 that each corner set has four vertically spaced burners, a total of 16 for the unit. I designate (Fig. 4) thefour vertical sets by the reference characters 10, 11, 12, 13 and in general indicate that the four burners of a vertically spaced set are tiltable together, although it is possible that other combinations of the 16 burners may be had for relative movement.

Figs. 1, 2 and 3 are substantial duplicates except for illustrating the effect upon furnace flame location of burner tilting. In Fig. 1 the burners are horizontally firing or at what I designate a zero tilt position. The general flame location is diagrammatically illustrated.

In Fig. 2 the burners are shown depressed or in a downward tilt of some 25 and it is evident that more of the generating wall surface 2 is contacted than was the case in Fig. 1.

In Fig. 3 the burners are illustrated as having an upward tilt of approximately 25 and it is here evident that a considerable lower portion of the wall generating surface 2 is not directly contacted by the radiant heat of the flame body.

These illustrations show how the flame body can be raised or lowered over a considerable distance to make use of more or less furnace heat absorption surface and thereby proportion the amount of heat subjected uponthe generating surface compared to that subjected upon the superheating surface and thus effecting wide range control over the gas temperatures leaving the furna e at the screen tubes 3. By thus providing control (if furnace heat absorption the effect is similar to that which would be accomplished by the ability to increase or decrease the size of the furnace surface at will relative to a fixed convection superheating surface. I

An upward tilting of the burners tends to increase steam temperature while a downward tilting tends to reduce steam temperature for any given load. The effect of the tilt is to cause the zone of active combustion in the furnace to raise or lower, decreasing or increasing the effective radiant heat absorbing surface in the furnace and to consequently increase or decrease the temperature of the gas entering the super-heater.

I have found that a most desirable index of heat available to superheat the steam is a continuous measure g of the temperature of the gases immediately prior to their contacting the superheating surface. In a unit of the size and type being described the temperature of the gases first contacting the convection superheating surface should be in the neighborhood of 2000 F. for a steam final temperature of 1000 FTT and under different conditions of operation will be in the range of 1700-2300 F. When there is a change in furnace exit gas temperature, for any reason, there is of necessity a time lag of heat transfer and metal temperature stabilization before the gas temperature change is reflected in final steam temperature change. Thus the use of actual gas tempera? tures prior to convection heat exchange as an operating guide or control index anticipates the effect of the gas temperature change upon the superheating of the steam.

I have found it possible to provide a continuous determination of furnace exit gas temperatures by means of a bolometer or other radiation sensitive device as well as bare metal thermocouples or high-velocity thermocouples. In Fig. 1 I designate certain temperature determining locations to which reference will later be made. Representative of furnace exit gas temperature is location A at the entrance to tube screen 3; locationB is the gas entrance to secondary superheater 4; C represents gas entrance to reheat surface 5; D is the location at entrance to primary superheater 6 and E is between the primary superheater and the economizer 7. I expect that the gas temperatures at locations A or B will be in the range 17002300 F. while at location C, D or E the gas temperatures will be in successively lower ranges as the heat of the gases is transferred to the steam.

I preferably employ a radiation sensitive device at locations A and B and will refer to a bolometer as satisfactorily representative. The bolometer of the Rutherford et al. Patent 2,524,478 has been successfully used as a device sensitive to total thermal radiation for producing an eifect representative of the energy level of radiation received. The patent to English et al. No. 2,624,012 dated December 30, 1952 discloses and claims a circuit including the bolometer for actuating a recorder-controller in terms of temperature.

In Fig. 5 I show somewhat diagrammatically a section taken through the unit of Fig. 1,. along the line 5-5, in the direction of the arrows. The locations A, KC and D are not necessarily spot locations but are areas or planes between the various heat transfer surfaces. At 15 I designate a bolometer or other radiation receptive head sighted across A and at 16 a similar head sighted across B. These devices may preferably operate in the range 1700-2300 F. I have also found that bare metal thermocouples or high velocity thermocouples may be used to obtain gas temperatures in locations A and B if proper precautions are taken against the corrosive, and erosive, effect of the gases and entrained solid matter.

By way of example I illustrate in Fig. 5 four bare metal thermocouples TC-l, TC-Z, TC-3 and TC-4 spaced across the area A in front of the screen tubes 3. These are preferably spaced across the screen tubes 3 and are connected in series with each other in a measuring bridge network to obtain an average of the temperatures to which they are subjected. Preferably the thermocouples are suspended downwardly through the roof of the unit until the thermocouple ends are in a line across the entrance to the screen 3 at about location A of Fig. 1. The thermocouple itself is encased in a thin wall protecting tube. to' protect it against the erosive and corrosive action Such possible construction where the thermocouplesTO-lo; TC-20, TC-30 and TC40 are projected through, and horizontally from, the rear of the unit assembly on supporting pipes which additionally act as protectors of the lead wires.

Regardless of the type of temperature sensitive device, or its mode of installation, the result is to obtain the actual temperature of the gases rather than any metal temperature or steam temperature in the various locations.

The temperature of the gases entering the steam super heating surfacesis an index of the heat available for superheating the steam. "Many factors may contribute to variation of temperature of the gases entering the convection heating surfaces. Change in demand, with consequent increase or decrease in fuel-air admission rate will change the gas mass flow as well as its velocity and temperature. For steady state demand, the furnace exit gas temperature may vary from such causes as flame waver resulting in varying generating surface absorption, slagging or \deslagging' of generating surface, burnability of the fuel, etc. Regardless of the cause of the variation, the fact remains that a variation in such temperature may cause an undesired deviation in final steam temperature from the desired value.

The temperature of the gases at the entrance to the superheating surface is therefore a cause index materially in time advance of any effect index such as metal or steam temperature of the superheating surfaces. By utilizing such cause index I may anticipate its effect upon the final steam temperature and provide an initial coarse adjustment to be verniered by final steam temperature toward the desideratum.

In Fig. 6 I show the characteristic curve of such a convection superheater designed for final steam temperature of 1000 FTT under rated load operation. From Fig. 6 it will be seen that desired control operation is to remove the possibility of excessive steam temperature at the higher ratings and to raise the deficient steam tem perature at lower ratings. In general I accomplish this by removing excessive heat through'spray attemperation at the higher ratings while, at the lower ratings, I raise the characteristic temperature through proportioning the generating and superheating surfaces by tilting the fuel burners.

Referring now to Fig. .7 I show therein in very diagrammatic' form a typical steam generator to which my invention may be applied and which shows the relation of the gas flow path to the different heat exchangesurfaces. The arrangement shown includes a primary superheater 6 and a secondary superheater 4 between which sections is disposed a spray type attemperator 42. The steam generator may be provided with a reheater section such as illustrated in Figs. 1, 2 and 3 this being immaterial so far as my invention is concerned.

At 20 is shown a control drive arranged to tilt the set of four vertically spaced burners 10, preferably through an angle :30 from the horizontal. In this figure I have shown only a single vertically spaced set of burners'10 as representative of the four corner sets previously mentioned and shown in Fig. 4. It will be appreciated that the showing of Fig. 7 is diagrammatic and the control drive 20 may be considered as simultaneously adjustably tilting all four sets of burners 10, 11, 12 and 13.

The attemperator 42 located in the fluid flow path between the primary superheater 6 and secondarysuperheater 4 is preferably of the type described in the patent to Fletcher et' al. No. 2,550,683 wherein the superheated steam conduit has therein a Venturi acting as a part of a thermal sleeve to protect thezconduit against thermal stresses. Forwardly of the entrance of the Venturi is a spray nozzle in which water, introduced through pipe 41, is atomized in a conical spray which is enveloped by the high velocity superheated steam. The nozzle is thus disposed in a relatively low velocity zone so there is a low pressure lossthrough turbulence created by the this cone being within the entrance surfaces of the Venturi.

of an attemperator such as shown at 42 is to prevent the final steam temperature rising above the desired value at loads above rated load when the final steam temperature is beyond the control range of the tilting burners.

As an index of demand I show a Bourdon tube 21B sensitive to the pressure of the steam in conduit 21 leaving the secondary superheater and arranged to position a pilot valve 21A to control total fuel and air supply rate. The demand index may be rating, such as steam flow rate or air flow rate and may include a basic tilting of the burners in accordance with demand or load upon the unit. The pilot valve 21A is of a known type as disclosed in JohnsonPatent 2,054,464.

I show at 28 a recorder-controller of final steam temperature arranged toposition the movable element 29 of a pilot valve 30 continuously establishing in a pipe 31 a fluid loading pressure representative of final steam temperature. The air pressure loading line 31 joints the A chamber of a standardizing relay 32 which may be of the type described in Gorrie' Patent Re. 21,804 and whose output communicates with a pipe 33. Such a relay provides a proportional control with reset characteristics, it provides for the final control index (final steam temperature) a floating control of high sensitivity superimposed upon a positioning control of relatively low sensitivity. A

function of the adjustable bleed connection in the relay 32 is to supplement the primary control with a secondary control of the same or a different magnitude as a followup supplemental action to prevent overtravel and hunting.

The output of relay 32, available through the pipe 33 is admitted to the A chamber of an averaging relay 34. The relay 34 may be of the type described and claimed in my Patent 2,098,913. The output of relay 34 is available in a pipe 35 and transmitted to the control drive 20 through a branch 37. A branch 36 of the pipe 35 conducts the-output of relay 34 to a diaphragm operated control valve 40 disposed in the pipe 41 and effective for regulating the rate of fiow of water to the attemperator 42. Positioned in pipes 36 and 37 are manual- automatic selector valves 38, 39 respectively which may be of the type disclosed inthe patent to Fitch 2,202,485 providing As heretobefore explained, the primary purpose available for superheating the steam and under steady state operation it may be assumed that such an increase would cause an undesirable increase in final steam tem perature. Thus I provide that an increase in temperature at'location B will increase the loading pressure value in pipe and within the C chamber of relay 34 and thus in the pipes 35, 36 and 37. Preferably, an increase in pressure in pipe 37 actuates the control drive 20 to tilt the burners '10 downwardly thus increasing the heat absorption of the generating surface and abstracting some of the available heat from the furnace gases prior to their reaching location B. The components of the system may be so adjusted that, after the burners have been direction as an increase in air pressure within chamber C, and as previously explained, results in a downward tilting of the burners 10 and later an opening of the valve 40.

Conversely, a decrease in gas temperature at location B, or a decrease in final steam temperature, results in a closing of the valve 40 and an upward tilting of the burners 10 to decrease the generating surface heat absorption and raise the temperature of'the gases entering the superheating surface thereby causing more heat to be absorbed in the primary and secondary sup'erheater sections.

Assume it is desired to maintain a final steam temperature of 1000 FTT as nearly constant as possible regardless of demand. It will be understood that the generating a possibility of hand or automatic control of the valve 40 ously position the stem 23 of a pneumatic pilot valve 24 to establish ina pipe 25 an air loading pressure repre-. sentative of the average temperature of the gases at lo-- cation B. Pipe. 25 conducts the loading pressure established by pilot valve 24 to the C chamber of relay 34 through an adjustable bleed valve as shown.

The necessary, and known, adjustments are provided in the recorder- controllers 22, 28, as well as in the relays 32, 34, control drive 20-and valve 40 to the end that the tilting burners 10 and Valve 40 may be biased the one relative to the other or may be sequentially responsive to the control indexes. For example, the loading pressure values available in the averaging relay 34, from pipes 33 and 25, may be so adjusted that the tilting burners will be operated through certain ranges and then sequentially the valved-0 will be positioned. The sequence may be a successive one or with an adjustable overlap as will be explained with reference to Fig. 6.

The operation of Fig. 7 is as follows: It will be understood that the response rate of bolometer 16 and recorder-controller 22 may be adjusted to rapidly fluctuating gas temperatures to produce an averaging effect, if desired. Assuming a steady state of operation, an increase in temperature at location B indicates an increase in heat and'superheating heat exchange surfaces are so designed and proportioned as to give a final steam temperature of 1000 FIT at rated load operation. The characteristics of such a radiant furnace generator with convection heated superheating surfaces predicates a tendency toward excessive final steam temperature at peak loads and a deficiency in final steam temperature for loads below the designrate'd value. curve of such 'a radiant furnace generator with convection heated superheating surfaces designed for a final steam temperature of 1000 FTT at rated load. From Fig. 6 it will be seen that the desired control operation'is to remove the possibility of excessive steam temperature at higher ratings and to raise deficient steam temperature at lower ratings. In general as heretofore explained, I accomplish this by removing excessive heat through spray attemperation at the higher ratings while, at the lower ratings, I raise the characteristic temperature through proportioning the generating and superheating surfaces by tilting the fuel burners.

It will be seen from Fig. 6 that the burner tilt and bypass damper operations may be sequential, with or without overlap. The system may be so adjusted that through prevent hunting from one control to the other if the of the other. In any event the necessary adjustments are A sequence is as may be termed end-to-end or'with a gap between the stopping of one control drive and the starting provided in the various components of the system to provide a smooth transition across the rated load point of Fig. 6. Normally the control is on the tilting of the burn- An increase in air loading pressure in the A chamber of relay 34 acts in the same In Fig. 6 I'show the characteristic 9 ers and it is only when we get to the limit of range that the by-pass damper or attemperator is used.

By way of example only, I illustrate at the upper portion of Fig. 6 a characteristic burner tilt curve where X indicates the crossing of the characteristic curve with the zero tilt position of horizontally operated burners. The pick-up or beginning of movement of the tiltable burners may be shifted to the right or the left (in Fig. 6-) so that I the characteristic curve may be moved to the right or to the left relative to point X and with such movement the effectiveness of the burner tilt upon the final steam temperature.

In Fig. 8 I show in diagrammatic form a control system embodying my invention arranged for application to a steam generator suchas shown and described with reference to Fig. 7 The control ofthe four corner sets of tiltable burners 10, 11, 12 and 13, by way of their separate control drives 20, 20A, 20B1and 200, is conjointly under the dictates of the gas temperature controller 22 and the final steam temperature controller 28, as in Fig. 7. The pipe 37, beyond the manual-automatic selector valve 39, is branched as at 45, 46, 47 and 48 to the four control drives. I may locate in each of the branches a manual-automatic selector valve' 49 and through the agency of these four selector valves I may bias one or more of the vertical sets of burners relative to the other sets or may adjust any of the sets individually by remote manual means.

In this embodiment I introduce a measure of the flow rate of the Water passing through the conduit 41 to the attemperator 42. Positioned in the pipe 41 is an orifice 50 for producing a pressure differential representative of the fluid flow rate and to which pressure differential a water flow rate meter '51' is continually responsive. The meter 51 positions the movable element 52 of a pilot valve 53 continuously providing in a pipe 54 a fluid loading pressure representative of the flow rate of Water to the attemperator 42.

I provide at 55 a differential standardizing relay to the A chamber of which is connected the pipe 35 carrying the output of averaging relay 34. To the B chamber of relay 55 I connect the pipe 54 thus providing that the relay 55 is subjected to the differential action of the loading pressures within pipes 35 and 54 respectively.

The output of relay 55 is available through a pipe 56 to the positioner 57 of control 'valve 40. Each of the control drives 20, 20A, 20B and 20C are provided with positioners 58 and the positioners 57, 58 may be of the type disclosed and claimed in the Gorrie et al. Patent 2,679,829, dated June 1, 1954. Such positioners of the valve 40 and of the burner tilting control drives insure that the valve and the burners are positioned to the actual positions wanted, for the positioners incorporate a characterizatio-n of the characteristic response curve of each of the controlled elements thus correcting for any nonlinearity of such response curves as well as for differences in response friction, capacities, and the like between the different control elements. Adjustments are provided whereby the control elements may be biased one relative to the other if desired.

In the system of Fig. 8 I introduce the water flow rate index to take care of feed pump variations, etc.,

which may otherwise affect the amount of water supplied rect amount of water is used for spray attemperation to accomplish the purpose desired.

The relay 55 receives in its A chamber a loading pressure representative of desired water valve positioning called for by the indexes, gas temperature and final steam temperature. To this loading pressure is opposed the loading pressure representative of water flow rate, sub-" jected upon the B chamber of the relay 55, to the end that if the water. flow rate is as desired, the two loading pressures will tend to neutralize each other and no change iii fects in the chambers A and B will be effective to vary the loading pressure within the pipe 56, elfective in positioning the valve 40, until the increased or decreased rate of flow of water through the pipe 41, acting through the flow meter 51 and pipe 54 again brings the relay 55 to a balance condition. I

The control system which I have illustrated and described finds, at the moment, its widest applicability in the burning of pulverized fuel but is equally effective in connection with vapor generating and superheating units adapted to be fired by any fuel burned in suspension including gas or vaporized oil.

While I have described in detail arrangements incorporating a continuous determination of gas temperature at location B through the agency of a bolometer, it will be appreciated that I contemplate the use at location B of any temperature sensitive device or devices which will provide a continuous determination of the temperature of the gases available at the entrance to the superheating surfaces as clearly distinguished from any metal tempera ture or temperature of the steam or other fluid within the heat transfer surfaces. that under certain conditions of operation it may be highly desirable to utilize in my method and control apparatus a determination of temperature of the gas flowing stream at other locations, for example, at A; C, D or B.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion zone with a heating gas outlet in the upper end portion thereof, fired with one or more fluent streams of fuel and air through fixed location in the combustion zone wall spaced vertically downwardly from the heating gas outlet, and having convection vapor superheating surface positioned beyond the combustion zoneoutlet in the path of heating gas flow; the method of operation which comprises varying the total fuel and air input rate in accordance with demands upon the unit, directionally varying the fluent stream upwardly or downwardly into the combustion zone from the fixed vertical location as the temperature of the heating gases leaving the combustion zone outlet to the superheating v rate of attemperator liquid flow increases and vice versa.

2. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion chamber with a heating gas outlet in the upper end portion thereof and having convection vapor superheating surfaces located beyond the combustion chamber outlet in the path of heating gas flow, the-combination of means supplying fuel and air for combustion in fluent form to the combustion chamber, tiltable burner means for the fluent supply located" through the combustion chamber wall spaced downwardly from the heating gas outlet, means continually determining the value of an index of demand upon the unit, control means for the total fluent supply rate responsive to said demand index means, motive means adapted to tilt the burner means from hori- Fnrthermore, I contemplate bustion chamber relative to the heating :gas outlet, an attemperator for the generated vapor, liquid supply means for the attemperator', a flow rate meter for the attemperating liquid, measuring means continuously determining the temperature of the, gases leaving the combustion chamber outlet, second measuring means continuously determining the final vapor temperature, separate control means for the motive means and for the at temperator liquid supply, the control means for the motive means conjointly responsive to both of the temperature measuring means acting to tilt the burner means up- Wardly or downwardly as either of said temperatures decrease or increase respectively, and a regulator for the rate asvsaid gas temperature or final vapor temperature increases or liquid supply rate decreases and vice versa.

References Cited the file of this patent UNITED STATES PATENTS 1,938,699 Huet Dec. 12, 1933 1,949,866 Huet Mar. 6, 1934 2,100,190 Jackson Nov. 23, 1937 2,109,840 Gordon Apr. 1, 1938 2,363,875 Kreisinger et a1. Nov. 28, 1944 2,413,128 Wills Dec. 24, 1946 2,575,855 Mittendorf Nov. 20, 1951 2,575,885 Mittendorf Nov. 20, 1951 2,590,712 Lacerenza Mar. 25, 1952 2,640,468 Armacost June 2, 1953 2,663,287

Armacost Dec. 22, 1953

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