US2649079A - Steam generator and superheat-reheat control means therefor - Google Patents

Description

Aug. 18, 1953 J. VAN BRUNT STEAM GENERATOR AND SUPERHEAT-REHEAT CONTROL MEANS THEREFOR Filed Jan. 28, 1949 5 Sheets-Sheet l Reheater Inlet Header Reheat Temperature 90 ,Reeponelve l Reheater I I Header Reheated 35, Steam superheated s h Steam uper ea or 7/ I Outlet Ho I Temperature l Registeri f 70 Meter I l v I I I l FIJQI w I I Fuel 2 I J Fug. I.

\NVENTOR ,8 ,8 John Van Bruni A'ITOR EY Aug. 18, 1953 J. VAN BRUNT 4 v STEAM GENERATOR AND SUPERHEAT-REHEAT CONTROL MEANS THEREFOR Filed Jan. 28, 1949 Sheets5heet 2 o 2' U g 60 Total Superheuter 4 E 2L Shir. Siege s2 9. 40 |& Shir. Stage SI 1' .c 2 Rehealer RH Steam Generator Loading INVENTOR John Van Bru m ATTOR EY Aug. 18, 1953 J. VAN BRUNT 2,649,079

STEAM GENERATOR AND sUPERHEAT-REHEAT CONTROL MEANS THEREFOR Filed Jan. 28, 1949' 5 She ets-Sheet 3 Rehenter Dampers Superheoter Dampers INVENTOR John Van Brunt I BY ATTORNEY Aug. 18, 1953' STEAM GENERATOR AND SUPERHEAT-REHEAT CONTROL MEANS THEREFoi Filed Jan. 28, 1949 Rehemer Dampers Superhcuier Dampers J. VAN BRUNT- S'Sheets-Sheet 4 Fig. 6.

Rcheuied Steam Superheotod Sham F. J smmflfiififil a3 73- 7Q 72 1+1:- ilw g5 84 182/ I Step lj Timer Tilt bl IR DR all; /0 /73 INVENTOR John Van Brunt ATTORNEY Aug. 18, 1953 J. VAN BRUNT STEAM GENERATOR AND SUPERHEAT-REHEAT CONTROL MEANS THEREFOR Filed Jan. 28, 1949 5 Sheets-Sheet 5 Superheater Dampers Reheated Steam superheated Steam INVENTOR John Van Brunt ature of I Temper Steam Passlnq 9| Reheater RH Temperature of Steam Paseln 7| ATTORNEY Patented Aug. 18, 1953 STEAM GENERATOR AND SUPERHEAT-RE- HEAT CONTROL MEANS THEREFOR John Van Brunt, Flushing, N. Y., assignor to Combustion Engineering, Inc., a. corporation of Delaware Application January 28, 1949, Serial No. 73,274

This invention relates to steam generators having superheater and reheater elements organized in the general parallel gas pass manner taught by my oopending application Serial No. 56,381, filed October 25, 1948, for Steam Generator.

An important object of this invention is to provide improved facilities for controlling the temperature of the superheated steam and of the reheated steam taken from such generators.

Another object is to provide regulating means effective to hold both of the named steam temperatures substantially constant (either at the same or at different values) over a wide range of generator loading values.

A further object is to effect such regulation automatically in a manner which is simple, practical and reliable.

A still further object is to provide unique means for protecting the reheater tubes against overheating while the steam generator and its supplied turbine are being started up.

Additional objects will become apparent from the following description of illustrative embodiments of the invention when taken in conjunction with the accompanying drawings, wherein:

Figure l is a sectional view of a steam generator and included superheater and reheater elements together with tilting burner and gas-flow damper facilities plus a simplified representation of the new automatic control means;

Figure 2 is a reduced-scale section on line 22 of Figure 1 showing one satisfactory arrangement of the generator furnaces fuel burners;

Figure 3 is an enlarged vertical sectional view through one of those generator fuel burners showing one arrangement for vertically tilting the streams of fuel and air directed thereby into the furnace;

Figure 4 is a diagram of heat absorption curves illustrating some of the performance advantages which the Fig. 1 generator design makes possible;

Figure 5 is an electrical control diagram showing in the lower portion circuits organized to effect an automatic positioning of the tilting burners in a way which holds the superheated steam temperature constant with changing generator loading, and showing in the upper portion cooperating circuits organized to effect an automatic positioning of the superheater and reheater dampers in a Way which further keeps the reheated steam temperature matched with the superheated steam temperature.

Figure 5a shows illustrative elements for enabling the apparatus of Figure 5 to detect differences between the reheated steam temperature and the superheated steam temperature;

3 Claims. (Cl. 122-479) Figure 6 isa diagram similar to Figure 5 but The illustrated steam generator to be benefited The drawings hereof showmy improvements applied to a steam generator organized in the general manner taught by my aforesaid copending application Serial No. 56,331. As represented (in simplified and partly schematic form) by Figure 1 hereof, such a generator comprises an upright furnace fired by burners Ill and serving to heat a boilerthat includes drums l2!3 and that is equipped with superheaters SISZ plus a reheater RH. This furnace is shown as being lined withsteam generating tubes l5; those tubes iii are connected for circulation of Water (and steam) therethrough to the boilers steam and water drums l2 and IS in suitable manner; and

' the illustrated arrangement utilizes downcomers !6 and I! which conduct the water from drums l2 and 13 to the downtake headers l8 and IQ of the aforesaid tubes l5 lining the furnace.

Above the furnaces combustion zones AB--C some of the steam generating tubes 15a and IE2) are bent inwardly and thence upwardly from opposite walls of the furnace and in their upward extending portions are arranged so as to form two parallel walls 20 and 2! defining the sides of a central passage 22 and generally dividing the space above the furnace into two main parallel passes 24 and 25. These two main passes respectively include first stage superheater S! and reheater RH. Each of these heaters is suitably suspended Within its associated pass and may satisfactorily comprise a plurality of sinuously arranged tubes conducting steam flow downwardly in counterflow to the upwardly rising furnace gases.

At the top of central passage 22 some of the tubes from each wall 20 and 2| are arranged to form over-the superhea'ter pass 24 a roof 26 which serves to separate the flow of combustion gases leaving vpass Zl from the gases leaving reheater pass-25. Extending over the tops of all three passes 24--22 25 is an upper roof 2! spaced from the first roof 26in a way permitting the combustion gases from reheater pass 25 to flow therebetween. v

Said first roof 26 iscontinued at 28 to a frame 3 between first and second groups of dampers SD and RD which respectively lead from superheater pass 24 and from reheater pass 25 into the generator furnaces gas offtake a third damper 29 is shown as being provided at the top of central passage 22; and manipulation of these dampers performs steam temperaturecontrol functions as will later be explained. For recovering heat from the waste gases that leave ofitake 30 use is made of an economizer E having tubes over which those hot gases pass and through which feed water is supplied (via conventional piping not shown) to the steam generator after having been heated in the economizelzz heater shown at 33 extracts from the waste gases still further heat which is returnedto the furnace with the air entering same via fuel burners I 0.

Beneath the first stage superheater' SI and the reheater RH is suspended a second stage superheater S2. Latter extends completely across the inlets of all three passes 24, 22 and 25; it receives from the first superheater SI all steam passed therethrough from the boiler drum [3 (by way of tubes 3i); and it thereupon discharges the finally superheated steam from the generator through main outlet conduit 32 and thence to a point of use.

It will here be assumed that a prime mover (not shown) such as a steam turbine constitutes said point of use; also that steam from an intermediate expansion stage of said turbine passes into the reheater RH by way of inlet header 34, thence through the reheaters sinuous tubing (in generator pass 25), and thereafter out of the reheater at header 35 for-return to a subsequent stage of the prime mover.

Modern steam turbines of high capacity may when so supplied operate under high steam pressures, such as about 1400 pf s. i. and over, and at high steam temperatures, such as 950 deg. F. or above for the steam initially supplied to the turbine from superheater S2 (via conduit 32), and 950 deg. F. or above for the steam returned to the turbine after having been taken from an intermediate expansion stage thereof and passed through reheater RH.

The vertically tiltable burners 10 Serving to fire the'steam generator furnace are a group of burners arranged in the lower portion thereof as shown at IU (see Figures 1 and 2) above the hopper 31 and there suitably located such as at or near the furnace corners as indieated in Figure 2. When so arranged the burners may satisfactorily project streams of fuel (pulverized coal, oil, gas or the like) and air into the furnace in directions tangential to the surface of an imaginary cylinder (again see Figure 2) located vertically within the furnace preferably at its center.

These burners ID are of the vertically tiltable type organized in the general manner disclosed by the patent to Kreisinger et al. No. 2,363,875 of November 28. 1944, entitled Combustion Zone Control. In the typical construction shown by the fragmentary sectional view of Figure 3 (taken through one of the burners ID of Figures 1 and 2), air chambers 38 are connected at their sides to an air duct 39. (see Figure 1) for supply of air thereto (as indicated in Figure 2) from a suitable source (not shown). Certain of these chambers 38 supply air alone to deflecting vanes or nozzle tips 40 for passage therefrom into the furnace; others are provided with .a. fuel supply pipe 41 (leadingfromafuel; source not shown) and a conduit portion 42 extending through the duct for conveying the supplied fuel from pipe 4| (in a stream of air in the case of pulverized coal) to a nozzle tip 43 and thence into the furnace where burning takes place. The fuel so supplied may be pulverized coal, oil, gas or the like.

Each of the represented fuel nozzle tips 43 may be rectangular in cross section; it is located between air defiecting vanes 4t lying symmetrically above and below the tip and connected thereto by end plates adjacent the air chamber walls 38 normal to the vanes; it is rotatable vertically on pins in horizontal bearings 45 in the end plates, the pins being mounted on the opposite walls of. fuel conduit 42 adjacent the end of said conduit; and nozzle tip 43 and its supporting conduit 42 are formed at their juncture into a cylindrical socket joint. The represented air nozzle tips 4|] likewise may be rectangular in cross section; each is provided with deflecting vanes shown as supported by end plates normal to the vanes; and each is rotatable vertically on pins in horizontal support bearings 45 carried by end plates, the pins being mounted on the opposite walls of the air chamber 38.

The just described fuel and air nozzle tips 43 44 and 40 when turned upwardly or downwardly direct the issuing fuel and air streams accordingly; the distribution of air above and below the fuel streams issuing from each of the fuel nozzle tips 43 remaining symmetrical for any position of the fuel nozzle tip. By directing said burner nozzles horizontally at intense zone of combustion is maintained at location A of Figure 1; by tilting the nozzles upwardly the zone of intense combustion is lifted to location B; and by tilting the burners downwardly the zone of intense combustion is lowered to location C. The eifect of such tilt adjustment will be more fully considered later; obviously less than all of the fuel and air nozzles in each burner 16 may be so adjusted tiltwise, as the Patent 2,363,875 to Kreisinger et al. brings out.

For transmitting tilting movement to each of the burners represented nozzles 49, 43 i4 use may be made of a positioning rod 4! which is pivoted to an end plate of the nozzle offset with respect to bearing 45, and which has an exterior extension 48 connected with a bell crank 49 that in turn receives nozzle adjustin movement from a vertical tilt rod Ell. Upward movement of rod 58 tilts all of the burner nozzles (48, d3-A l) downwardly around their bearings 55 while downward movement of the rod swings all of the nozzles upwardly with respect to the horizontal.

Such tilt-adjusting movements may be imparted to vertical rod 55 in any suitable manner, as by the aid of a motor represented at 52 in each of Figures 1, 3 and 5. An electric motor is here shown at 52; however, an air motor, hydraulic cylinder or the like obviously may be used in its place. In the arrangement illustrated this burner-tilting motor 52 drives into reduction gearing 53 to rotate arm 54 and thereby move connecting link 55 joined with the lower end of tilt rod 50 as indicated. When arm as has the intermediate position represented all of the burner nozzles ll], d344 are aligned horizontally as Figures 1, 3 and 5 show; clockwise rotation of arm 5A thereupon imparts to each of the burner nozzles an upward tilt (the same for all) above the horizontal; and counterclockwise rotation of arm 54 similarly imparts downward tilt to all of the burner nozzles.

The superheater-reheater organization of Figure 1 In the complete boiler furnace of Figure 1 it has already been seen that the generated steam leaving drum I3 by way of tubes 3! flows through the first stage superheater SI and thence through second stage superheater S2 to outlet 32 for discharge to the point of use; that the steam (as from a prime mover not shown) to be reheated passes from inlet header 34 through reheater RH and thence discharges through header 35 (as for return to a subsequent stage of the prime mover); that the first stage superheater SI and the reheater RH are positioned in two individual passes 24 and 25 through which combustion gases from the furnace therebeneath pass in parallel fiow relation; that all of said combustion gases first pass over the second stage superheater S2; and that if desired a portion (selected by central damper 29) of those gases may flow out of the furnace through central pass 22 without con tacting either the reheater RH or the first stage superheater SI.

The last-named heaters SI and RH within the main or outer passes 24 and 25 are preferably so proportioned that the average amount of heat absorbed by each over a predetermined rating of the steam generator will approach being substantially the same; and provision in the form of the earlier mentioned dampers SD and RD is made for adjusting the relative quantities of gas which fiow from the furnace through the two main passes 24 and 25.

One of said heaters within the parallel passes may require proportionally more heat at low load ratings than the other and may require proportionally less heat at a high load ratings; for in a reheat cycle the amount of heat required for reheating is a varying percentage of the heat required for both superheating and reheating, a greater percentage being required at low loads. When these differences in heat absorption at the limits of the rating range are about equal, the amount of gas to be shifted from one pass to the other to compensate for said differences will be a substantial minimum; also the differences of temperature of the gases leaving the heaters in said parallel passes will be a minimum.

To illustrate the above conditions, assume that the two superheater elements SIS2 absorb about 65%, 60% and 55% of the total heat absorbed by both said superheaters and the reheater RH from the combustion gases at the corresponding steam generator ratings of 100%, 50% and 25%. Such superheater absorbing characteristics are indicated by curve 51 of Figure 4. Under such circumstances the first stage superheater SI may satisfactorily be proportioned to absorb about 45%, 40% and 35% of the total heat absorbed by both superheater stages SIS2 and by the reheater RH from the gases at the corresponding steam generator ratings of 100%, 50% and 25%. Such heat absorbing characteristics by superheater SI are indicated by curve 58 of Figure 4.

Under the assumed set of circumstances the reheater RI-I will at said ratings absorb respectively about 35%, 40% and 45% of said total heat, as indicated by curve 59 of Figure 4; so that at the chosen limits of the steam generator rating range (at 100% and 25%), the difierences in heat absorption from the gases between the first 6 stage superheater SI and the reheater RH is but about 10% of said total heat and the sum (of curves 58 and 59 in Figure 4) approaches a constant amount of about of said total heat, as indicated by dotted curve 60 in Figure 4.

From Figure 4 and the foregoing discussion it will now be evident that the remaining 20% of said total heat absorbed from the gases is furnished by the second stage S2 of the superheater. As already mentioned, this second stage superheater S2 is positioned ahead of the passes 24 and 25 with respect to gas flow in a zone of high gas temperature so as to absorb heat from all of the gases leaving the furnace.

In this example, with but a maximum of about 10% of the heat (or the gases) to be shifted from one pass to the other, the movements of the damper sets SD and RD to control the flow of gases need be relatively small. Said two dampers SD and RD, moving adjacent their wide open positions, with one damper approaching said position while the other departs therefrom, will vary the relative openings between the duct walls and the dampers and therewith the flow of gases therethrough, in substantially inverse proportions.

Such coordinated opening and closing of dampers SD and RD may be efiected in any suitable manner, as by aid of positioning facilities such as are represented in Figure 1. There positioning rods 62 and 63 respectively connected with damper vanes SD and RD are adjustably secured to a common plate 64; from that plate there extends a vertical rod 65 which is caused to move up and down by means of a motor 66 driving the rod through reduction gearing 6.1 and an arm 68 which transmits positioning movement from the motor to the damper.

An electric motor is here shown at 66; however an air motor, hydraulic cylinder or the like obviously may be used in its place. Moreover, each of the damper sets RD and SD may if desired be controlled individually, as through use of separate positioning motors. Still further, in the temperature control systems herein disclosed use of the second-stage superheater S2 is optional, as later description will make evident. When element S2 is omitted the superheater outlet conduit 32 will take steam directly from the discharge end of first-stage superheater SI.

In the apparatus organization here shown the damper 29 for the central gas pass 22 is provided with conventional means, typified by rod 36, for setting the damper in any position desired. When this damper 29 is fully closed all of the furnace combustion gases are compelled to divide between the two outer passes 24 and 25 which respectively contain first stage superheater SI and reheater RH; as damper 29 is progressively opened some of the combustion gases are permitted to leave the furnace by way of central pass 22 without contacting either the reheater RH or the first stage superheater SI; and upon full opening of damper 29 a maximum portion of the furnace gases are so by-passed around said heaters SI and RH. Such by-passing has special utility in starting up the steam generator as will later be explained.

Positioner means 36 for central damper 29 may take the form of the represented rod arranged for manual actuation through member 36 and an intermediate bell crank, or arranged for actuation through those or other comparable linkage elements by a positioner motor (not shown) which is controllable manually (as by 7. pushbuttons) from the instrument board for the steam generator. Description later to follow assumes that central damper 29 may have its position selected and adjusted in same such convenient manner.

The presented problem of steam temperature control In the absence of superheat control means a steam generator equipped with superheaters organized as shown at SI and S2 (when S2 is utilized) in Figure 1 will upon changes in loading vary through objectionably wide limits the temperature of the. superheated steam taken from outlet 32. Convection-superheater apparatus (typified by elements.S.l-S2) has a rising steam temperature characteristic; and in going from light to heavy generator load a total rise in the named steam temperature of as. much as 100 deg. F. may be encountered (in absence of superheat control), while in going from heavy to light load. a temperature drop of similar magnitude will be experienced.

Steam-utilizing requirements of the present day make superheat temperature variation of this wide magnitude unpermissible, especially in thehigh-temperature high-pressure installations which supply turbines (earlier discussed) and other devices whose satisfactory operation (due to carefully chosen materials and limited clearances) requires that steam temperature variations be held within relatively close limits. A first phase of the presented problem therefore is to maintain the steam leaving superheater outlet 32 at substantially constant temperature throughout the widest possible range of generator loading variation.

Considerations similar to those which call for a constant steam temperature at superheater outlet 32 also make it highly desirable that the temperature of the reheated steam leaving outlet 35 of reheater RH likewise be held substantially constant throughout the aforesaid widest possible range of generator loading variation. Accomplishment of the latterv therefore constitutes a second phase of the presented problem.

In accordance with my invention both of the named steam temperatures are held substantially constant over an extended range of generator loading values through the medium of regulating means novel in the art as herein disclosed and shown as to further detail by Figures 5, 6 and 7. Before describing those regulating means it may be observed that the represented (Fig. 1) positioning of the first stage superheaterSl and the reheater RH in the parallel gas passes 24'- and 25 constitutes an arrangement which is highly advantageous, as my copending application Serial No. 56,381 more fully brings out; such arrangement making it possible to maintain both the superheated steamtemperature and the reheated steam temperature constant over a much wider range of steam generator loading than can be done with the customary serial arrangement of superheater and reheater elements.

Thus, for example, with a temperature of 1000 deg. F. superheat and reheat, the here-disclosed steam generator utilizing parallel superheater and reheater elements is capable of maintaining the temperature constant from. full generator load down to about40%-50% of full load, whereas in. the conventional serial arrangement that temperature could be maintained constant, only to about 75%-80.% of full load. At lower steam temperatures the range of load during which: conburner nozzles as indicated by Figure 3.

stant temperatures can be maintained increases. substantially. Thus, for example, at approxi mately 950 deg. F. steam temperature for both superheat and reheat, it is possible to maintain that temperature constant down to about 30% of full load. In the customary series arrangement, this temperature could only be maintained down to about of full load.

Such vertical adjustments of burners l0 and such positional adjustments of dampers SDRD as are required to hold the named steam temperatures constant during changes in steam generator loading may of course be accomplished either manually or automatically. Figs. 5, 6 and 7 hereof disclose novelly organized automatic control facilities which will now be described.

The automatic burner tilting facilities of Figure 5 The demand for constant steam temperature at the superheater outlet 32, over a wide range in generator capacity, has long presented a significant problem. My solution therefore is to effect regulation of the superheated steam temperature through an automatic control of the furnaces tiltable burners l0. Such automatic control may satisfactorily be carried out by the aid of the control apparatus of Fig. 5 (lower portion) and in accordance with the teachings of an application Serial No. 18,338, filed April 1, 1948, in the name of Harvey C. Mittendorf for Steam Superheat Control by Automatic and EX- tended-Range Means, Patent No. 2,575,885.

This burner control apparatus as illustratively shown by lower portion of Figure 5 will now be explained. Responding to and at all times registering the temperature of the superheated steam in generator outlet 32 is a meter represented at ill in each of Figures 1 and 5. The meter may satisfactorily be of a type utilizing a thermocouple H in the stream of superheated steam passing through outlet 32 together with an electrical potentiometer circuit (not shown) and associated means which keep an instrument pointer 12 (of Fig. 5) in a position along horizontal scale l3 accurately corresponding to and registering the superheated steam temperature in outlet 32.

From changes in the position of pointer '12 the tilting of furnace burners H! is governed through facilities exemplified by the electrical apparatus now to be described; but obviously hydraulic, air operated or other equivalent facilities may instead be employed. Carried by pointer 12 is a contact it which moves horizontally therewith. As long as the superheated steam temperature stays at the desired value, contact i4 is disen gaged from both of a pair of cooperating stationary contacts I and D. In the arrangement shown stationary contacts I and D are mounted on a slide 15 settable beneath horizontal scale '33 for e the superheated steam temperature that it is desired to maintain constant. The illustrative setting shown by Fig. 5 is at 950 deg. F.

The positioning motor 52 for the tilting burners it! may satisfactorily be linked with the Each burner may be provided with a separate motor 52 and the motors all energized in parallel, or all four burners may receive tilting movement from only a single motor through mechanical interconnections not shown in detail but readily providable. In the description of Figure 5 which follows the latter arrangement will be assumed; and it Will therefore be considered that the single motor represented at 52 in Figure 5 simultaneously effectsthe same tilting adjustment in all four 9. of the furnace burners which are represented at I!) in Figures 1 and 2.

This burner adjusting motor 52 may be of'comparatively low capacity (fractional horsepower or higher as needed) suitable for energization from the control potential appearing between the two vertically drawn supply conductors designated TI and T8 in Figure 5. The named motor driving voltage may be either direct current (as the 110 volt control potential available in power stations) or alternating current (as 110 or 220 volts, either 25 or 60 cycles).

Current for operating burner motor 52 is at proper times fed thereto from the named source through a conductor 88. Connection (as later described) of that conductor with motor terminal R produces forward rotation which causes arm 54 to tilt the fuel and air nozzles of burners I!) in the upward or flame-raising direction; similarly, connection of conductor 88 (again as later described) with terminal L causes motor 52 to rotate in the reverse direction and tilt (through arm 54) all of the burner nozzles in the downward or flame-lowering direction. In order to prevent motor 52 from moving arm 54 too far in either the upward tilting (clockwise in Figure or the downward tilting (counterclockwise in Figure ,5) direction, use is made of normally closed limit switches 8! and 82 respectively inserted in the raise and lower supply leads for motor 52 as per the diagram of Figure 5.

In the illustrative arrangement here shown, translation of the earlier described temperature change responses by master control instrument 18 into appropriate operations of the burner tilting motor 52 is effected through the medium of the two relays which the diagram of Figure 5 (lower portion) represents at IR and DR. Each 'of these two relays may be of conventional type including the usual operating winding shown as a simple block directly over the relays designation plus the contact shown immediately therebeneath and identified with the winding by a vertical dotted line. In Figure 5 both relay windings are shown de-energized and both relay contacts are shown released or open.

The first or increase relay IR is activated bymaster control instrument [8 whenever the temperature ofthe superheated steam in outlet 32 (see Figure 1) drops below the desired value. In such event pointer 12 moves to the left along scale i3 and carries contact 15 into engagement with contact I. This complete for relay IR an energizing circuit extending from the supply conductor 1'! (at the left of Figure 5) through conductor 83, engaged contacts '14 and I, the winding of relay IR, conductor 84, and a step timer B5 to the supply conductor '18 (at the right of Figure 5).

Thus activated relay IR closes contact 86 and completes for burner tilting motor 52 a forward circuit extending from supply conductor TI through conductor 88, relay contact 85, limit switch 8|, terminal R of motor 52, the motors forward driving winding, and conductor 81 to the supply conductor 18. Thus energized motor 52 rotates forwardly causing arm 54 to pull member 50 downwardly and thereby tilt the fuel and air nozzles of all furnace burners II) in the upward direction. Such upward tilting lifts the flame body to a higher position in the steam generators water walled furnace (see Figure 1), shortens the vertical length of furnace wall tubes exposed to intense radiation before reaching superheaters S|S2 and reheater RH, and thus 10 has the effect of flowing the gases across those heaters at. a higher temperature than before. This tends to raise the temperature of both the superheated and the reheated steams The second or decrease relay DR is activated by master control instrument 18 whenever the temperature of the superheated steam in outlet 32 (see Figure 1) rises above the desired value. In such event pointer 12 moves to the right along scale 13 and carries contact 14 into engagement with stationary contact D. This completes for relay DR an energizing circuit extending from the supply conductor 11 through conductor 83, engaged contacts 14 and D, the winding of relay DR, conductor 84, and step timer to the supply conductor 18.

Thus activated relay DR closes contact 88 and completes for burner tilting motor 52 a reverse circuit extending from supply conductor 17 through conductor 80, relay contact 88, limit switch 82, terminal L of motor 52, the motors reverse driving winding, and conductor 87 to supply conductor 18. Thus energized the motor rotates reversely causing arm 54 to push burner member 58 upwardly and thereby tilt the fuel and air nozzle of furnace burners ii) in the downward direction.- Result is to lower the flame body in the generators water walled furnace (see Figure l), expose the combustion gases to a greater length of the vertical wall tubes l5, and pass those gases over the superheaters Si-SZ and the reheater RH at a reduced temperature. This tendsto lower the temperature of both the superheated and reheated steam.

The earlier-mentioned step timer 85 may in the Figure 5 control system be organized as disclosed by the aforesaid Mittendorf application Serial No. 18,337, Patent No. 2,575,885. When so inserted into the pick up circuits (including conductor 84) of relays IR and DR, it serves recurrently to break each of those circuits during repeated offperiod intervals which are separated by intervening on period connections of relay conductor 84 with supply conductor 18. The relay IR or DR activated by control instrument 18 (over contacts 14 and I or 14 and D) thu is picked up only during each timer on period (when conductor 84 is connected with conductor 18) and is released "during each intervening 01f period (when the timer 85 disconnects conductor 84 from conductor 18).

Effect of this step timer 85 therefore is to slow d'own'the speed with which each corrective adiustment of the superheated steam temperature is effected by burner motor 52; This is because each on portion of the timer cycle is during corrective action accompanied by a running of the adjuster motor 52 and each intervening off portion produces a waiting period between'motor operations. Such waiting periods allow each corrective adjustment in burner tilt more fully to produce its ultimate change in superheated steam temperature before further adjustment is initiated; in this way any tendency for the regulatlng' system to hunt by overshooting its corrective actions is effectively cared for.

These burner-adjusting facilities of Figure 5s lower portion function to hold the temperature of the superheated steam (leaving outlet 32) substantially constant over a wide range ofgenerator loading values.

-Th e automatic damper adjusting facilities j of Figure 5 Supp1ement ing and functioning in conjunction withthe burner-adjusting facilities of Figure 5s 11 lower portion are the cooperating facilities of Figure 5s upper portion,.which latter facilities automatically adjust reheater and superheater dampers RD--SD in a way effective to keep the temperature of the reheated steam leaving the outlet 35 of reheater RI-I matched with the superheated steam temperature over a wide range of generator loading values. In the illustrative rganization here shown said adjustment is accomplished by damper positioning motor 66 whose driving circuits are governed through a pair of relays IK and DK by an instrument 90 which is responsive both to the reheated steam temperature and to the superheated steam temperature.

Damper control instrument 9|] may be of any suitable form capable of detecting difierences between the reheated steam temperature and the superheated steam temperature, to which end it communicates through element III with the steam in reheater outlet conduit 35 and through element II2 with the steam in superheater conduit 32. Such communication may involve a placement of thermocouples (not shown) in those two conduits and a comparison by instrument 90 of the temperature-proportional potentials respectively generated, or instrument 90 may be arranged to compare temperature-proportional vapor pressures in the manner here represented by way of illustration.

The named temperature-proportional vapor pressures may be produced in any suitable manner as by the aid of small Vaporizers III and II 2' respectively heated by the steam flowing through reheater and superheater outlet conduits 35 and 32. In the arrangement shown by Fig. 511, each of Vaporizers III and I I2 contains a fluid II3 which is vaporized by heat absorbed from the steam passing through the conduit. This fluid H3 may be mercury, in which case a steam temperature of 950 deg. P. will generate in the confined space above the mercury pool a pressure of about 133 p. s. i. a.; a higher steam temperature of 955 deg. F. will cause the pressure of the confined mercury vapor to rise to about 137 p. s. i. a.; while a lower steam temperature of 945 deg. F. will cause the mercury vapor pressure to drop to about 128.5 p. s. i. a.

In the illustrative apparatus of Figure 5, these temperature-produced pressures within vaporizers I I I and I I2 are utilized to actuate the control instrument 9G, which instrument preferably should be located as close as possible to said vaporizers in order that connections II I and H2 will be relatively short. In the form here shown instrument 9i) employs two diaphragms 39a and Ie9b whose centers are interconnected by rod I I4 and Whose outer surfaces are respectively acted upon by said pressures, transmitted thereto through tubing III and H2 from the Vaporizers II I and H2 within reheated and superheated steam conduits 35 and 32. Superheat responsive diaphragm I091) is shown as being of smaller diameter than reheat responsive diaphragm "19a and a compression sprin -I I5 is shown as assisting the former in opposing the force exerted by the latter; the compression exerted by this spring being adjustable by either advancing or withdrawing thumb screws IIB which through washer iI'I holds spring II5 against the inner side of diaphragm 19a.

Attached to diaphragm tie rod H4 is an arm III) by which a control contact 94 is carried between stationary contacts I and D. Upon proper adjustment of spring I lie balanced relationship between the reheated and superheated steam temperatures (in conduits35 and .32) iwillcause rod I I l to hold contact 94 midway between stationary contacts I and D; but when the reheated steam temperature in outlet 35' rises above the superheated steam temperaturesin'outrlet 32 arm III] will be shifted to the right engaging contact 94 with decrease contact D; and when the reheated steam temperature in'outlet 35' falls below the superheated steam temperature in outlet 32 armIIIl will be shifted .to the left engaging contact 94 with increase contact I.

In order to set the reheated steam temperature for maintenance at some value below the superheated steam temperature it is only necessary to back adjusting screws H 6 away from spring H5, thereby decreasing the intensity of spring compression against diaphragm 109a and allowing a lower vapor pressure from tubing I I I onthat diaphragm to maintain contact 94 in the neutral ordisengaged position. Similarly, the reheated steam temperature may be set for-maintenance above the superheated steam temperature merely by advancing adjusting screws H6 towards spring I I 5, thereby building up the spring compression and requiring a higher vapor pres sure from tubing I II on diaphragm' I-09a to keep movable contact 94 midway between stationary contacts I and D.

From the above mentioned changes inthe position of instrument rod H4 and-arm-III) the positionin of dampers RD-SD is governed through facilities exemplified by the electrical apparatus now to be described; but obviously hydraulic, air operated or other equivalent facilities may be employed in place of the electrical COIlta0tSI'-'-94D' and the electric damper positioning motor 66 controlled thereby.

The illustrated motor 66 for positioning generator dampers RD.SD is shown as being linked thereto through elements 62-6364-65 earlier described in connection with Fig. 1; other linkage arrangements are of course usable and if desired automatic positioning movements may be transmitted to only one of the two damper sets. This motor 66 may satisfactorily beef-comparatively low capacity (fractional horsepower or higher as needed) suitable'for energizationfrom the control potential appearing between the earlier-described conductors l1 and '18. 'In the illustrative electrical system ofFigure 5 current for operating the damper motor 66 is at proper times fed thereto through a conductor 99.

Connection (as later described) of that conductor with motor terminal R produces forward rotation by motor 66 which causes arm'68 to-move positioner 6'5 downwardly thereby imparting opening adjustment to reheater dampers RD and closing adjustment to superheater dampers SD; similarly, connection of conductor 99 (again as later described) with terminal L: causes motor 66 to rotate in the reverse direction and by moving (through arm 58) positioner -65 upwardly thereby impart closing adustment to reheater dampers RD and opening adjustment to superheater dampers SD. In orderto prevent motor 66 from moving arm 68 toofar in either the first named (clockwise in Figure 5) or the second named (counterclockwise in'Figure 5) direction use is made of normally closed limit switches I06 and Iill respectively inserted in the raise and lower supply leads of motor 66 as per the Figure 5 diagram.

Translation of the .earlier described temperature-change responses-by control instrument into appropriate operations of the damper adjusting motor 56 may be effected in any suitable manner as through the medium of two relays shown at IK and DK in Figure 5. These relays may be similar to devices IR and DR (lower portion of Figure 5) and both are shown with windings de-energized and contacts released.

The damper motors first or increase relay IK is activated by master control instrument 90 whenever the temperature of the reheated steam in reheater outlet 35 (see Figure 1) drops below the desired value. In such event arm H moves to the left and carries contact 94 into engagement with contact I. This completes for relay IK an energizing circuit extending from supply conductor 11 through conductor I02, engaged contacts 94 and I, the winding of relay IK, conductor 99, step timer 85' and a switch I93 to the supply conductor I8.

Thus activated relay IK closes contact I04 and completes for damper adjusting motor 66 a forward circuit extending from supply conductor 11 through conductor I05, the motors forward driving winding which ends in terminal R, limit switch I99, relay contact I04 and conductor 99 to the supply conductor I8. Thus energized motor 66 rotates forwardly causing arm 68 to lower positioner rod 65 and thereby effect an opening adjustment of reheater dampers RH and a closing adjustment of superheater dampers SD. This, in turn, causes more of the furnace combustion gases to flow through pass 25 over reheater RH (see Figure l) and less to flow through pass 24 over first stage superheater SI. Efiect thus is to correctively raise the temperature of the reheated steam that leaves reheater outlet 35.

The damper motors second or decrease relay DK is activated by control instrument 99 whenever the temperature of the reheated steam in outlet 35 raises above the desired value. In such event arm Ilil moves to the right and carries contact 94 into engagement with contact ,D'. This completes for relay DK an energizing circuit extending from supply conductor 71 through conductor I02, engaged contacts 94 and D, the winding of relay DK, conductor 98, step timer 85', and switch N13 to the supply conductor I8.

Thus activated relay DK closes contact I06 and completes for damper adjusting motor 66 a reverse circuit extending from supply conductor TI through conductor I95, the motors reverse driving winding which ends in terminal L, limit switch Illl, relay contact I06 and conductor 99 to the supply conductor I8. Thus energized motor 66 rotates forwardly causing arm 68 to elevate positioner rod 65 and thereby effect a closing adjustment of reheater dampers RH and an opening adjustment of superheater dampers SD. This, in turn, causes less of the furnace combustion gases to flow through pass 25 over reheater RH (see Fig. 1) and more to flow through pass 24 over first stage superheater SI. Efiect thus is to correctively lower the temperature of the reheated steam which leaves reheater outlet 35.

The earlier mentioned step timer 85' corresponds to device 85 (lower portion of Fig. earlier described and use thereof in the manner shown may be found desirable. as shown into the pick up circuits of damper control relays IX and DK, it serves recurrently to break each of those circuits during repeated off period intervals which are separated by intervening on period connections of relay conductor 98 with supply. conductor 18. The

When insertedrelay IK or DK activated by control instrument 90 (over contacts 94 and I or 94 and D) thus is picked up only during each timer on period (when conductor 98 is connected with conductor l8) and is released during each intervening off period (when timer disconnects conductor 98 from conductor 18).

Eifect of this step timer 85' is to slow down the speed with which each corrective adjustment of the reheated steam temperature is effected b the damper motor 66. This is because each on portion of the timer cycle is during corrective action accompanied by a running of the adjuster motor 66 and each intervening ofi portion produces a waiting period between motor operations. Such waiting periods allow each corrective adjustment in damper positioning more fully to produce its ultimate change in reheated steam temperature before further adjustment is initiated; in this way any tendency for the regulating system to hunt by overshooting its corrective actions is effectively cared for.

Obviously the automatic positioning just described for both sets of dampers RD and SD may if desired be applied to only one of the two damper sets, thereby leaving the other set free for manual or other positioning. With such single-damper control, automatic adjustment of reheated steam temperature will still take place even though the range of such adjustment may be somewhat reduced.

How the complete control system of Figures 1 and 5 operates During operation ofa steam generator such as shown in Figure 1 the firing rate of the furnace fuel is usually regulated (through conventional means forming no part of the present invention and hence not here shown) to maintain a specified constant pressure (such as 1450 p. s. i.) at the superheated outlet 32; moreover, as changes in the demand for generated steam may tend to increase or decrease this pressure the fuel-firing rate is (by the means named) appropriately adjusted to bring the pressure back to desired value. At the 1450 p. s. i. assumed this means that the saturated steam as generated in the boiler and as fed into superheater SI (by way of tubes .3!) has a superheater-entering temperature which stays at or very close to 590 deg. F. regardless of whether the generator loading is high, medium or low.

The manner in which the complete control system of Figure 5 performs its intended functions of holding constant the superheated steam temperature and of keeping the reheated steam temperature matched therewith during changes in generator loading will now be examined in the light of the above.

During initial start up of the steam generator it is of advantage to completely open central damper 29 (as by aid of the earlier described positioner means 3636' of Figure 1) and thereby allow a maximum portion of the combustion gases to leave the furnace through passage 22 without contacting either of heaters SI and RH. Moreover, in order to protect the reheater RH from being overheated by flow of combustion gases thereover during such initial start up, the switch I03 is now placed in its downward position. Such placing disconnects damper relays IK and DK from supply conductor 18 and connects that conductor directly with the limit switch IOI for damper motor 66. Latter connection runs motor 66 in the reverse direction until upward aeaeme 15 movement of damper positioner rod opens limit switch IOI to break the drive circuit. Motor 66 then stops after having closed reheated dampers RD and opened superheater dampers SD.

Under the foregoing conditions (dampers 29 and SD open and dampers RD closed) substantially none of the products of fuel combustion fromthe furnace (supplied by burners l) flow over reheater RH in main pass 25 but instead they leave the furnace by way of superheater pass 2 l'and central passage 22. Damper 29 now being completely open, a substantial portion of said combustion products leave the furnace through central passage 22 without contacting first stage superheater SI and imparting heat thereto. In consequence the gaseous products discharged from the furnace through economizer E and air heater 33 have during the start up period a temperature which is considerably higher than had all of those gases left the combustion chamber by way ofsuperheater pass 24 (or reheater pass 25 in parallel with pass \24). Such elevated temperature during start up is beneficial in that economizer E now heats the feed water more rapidly, and air heater .33 now heats the burner supply air to a higher temperature, and thus shortens the time required to bring the steam generator up to operating pressure.

By reason of the earlier stated closure of dampers RD (efiected through switch I03) reheater RH is protected against overheating until after the steam generator has been so started up and the prime mover (such as a turbine not shown) supplied thereby has been placed in operation to send part of its steam'back into inlet 34 and through reheater RH for return to the prime mover by way of outlet 35. When the latter conditions have been realized the central damper 29 may be at least partially closed and switch I03 is thereupon returned to the upward position (shown by Figure in which damper motor 66 is restored to automatic control by instrument as through relays IK and DK. Dampers RD and 'SD then move to positions appropriate for holding the steam temperature in reheater outlet 35 substantially constant, as .will now be explained.

Assume first that the burner control instrument it of Figure 5 is set for a temperature of 950 degxl fl; next that the furnace dampers RD and SD occupy intermediate positions such :as represented; and finally that the furnace burners H3 have their nozzles in a substantially horizontal fuel-and-air-fiow position as Figures 1, 3 and 5 indicate.

The foregoing conditions accompany some intermediate value (such as say 50% full rating) of steam generator loading. Due to theuntilted positioning of burner nozzles the burner fuel'and air streams have a horizontal direction into the furnace and cause the main flame body to center itself at about A (see Figure 1) in the waterwalled combustion chamber. The water =wall length (vertically) contacted by the flame gases prior to leaving furnace offtake passes .24 and. then is such that the gases flowing oversuperheaters S2-S! (and reheater RI-I) have a temperature proper for imparting to the steam passing through those superheaters just enough heat to maintain the superheated steam leaving outlet 32 at the desired total temperature of 950 deg. F. (assuming 590 deg. saturated temperature of the steam entering superheater Si plus 360 deg-l5. added to that steam during passage through the superheaters) Burner control instrument H1 now holds contact *M' between stationary members I-and D and burner-tilting motor -52 is accordingly inactive. Moreover, damper control instrument has through contact -94 and relays IK-DK caused motor 66 to adjust furnacedampers RD-SD into positions thatg-ive a proportionment of combustion gas flow through parallel passes 2d and 25 which establishes the steam temperature in reheater outlet-35-at the 950 deg. F. desired value matching-the superheated steam temperature in outlet 32.

Assume now-that the demand for generated steam builds-up thus increasing'the steam generator loading to some higher value (such as rated) at which a considerably greater quantity of fuel is supplied to burners It for combustion the furnace. The furnace flame body now burns with increased intensity and the tem-perature'ofthe furnace'gases is accordingly raised. The resulting stepped-up transfer of heat to-superheaters 62-8! (and to reheater R-H) elevates the total steam temperature in superheater outlet 32 to-some value above the 950 deg. F. desired.

This temperature raising is at once registered by burner control instrument "ID which in moving indicator 'l2 to the'rig-ht engages contact 14 with contact Dto initiate an appropriate decrease adjustment in the superheated steam temperature. Inrcsponding (as earlier explained) relay DR closes its contact 88 thereby completing for burner tilting motor -52 the reverse circuit earlier traced to cause a downward tilting of the fuel and air nozzles of furnace burners I ll as previously described.

Such downward tilting inclines the fuel streams below the horizontaland thereby drops the flame body to a lower position (such as C of Figure l) in the water walled furnace; such dropping increases the vertical length of furnace wall tubes l5 exposed -to-intense radiation from the combustion gases before reaching superheater S2 and olftake passes -24'2-5 and thus has the effect of flowing the gases across superheaters S2Sl (and'across reheater RH) at a lower temperature than before; and the resultant cutting down of heat transfer to elements S2Sl lowers the temperature'of superheatedsteam at outlet 32,

In responding to this corrective decrease burner -control instrument 7!! moves pointer 12 to the left. When-this movement reaches the desired 950 deg. F., contact'l'd separates from contact ill-relay DR becomes deenergized and opens contact: 88,and motor 52 discontinues its tilt lowering adjustment of the fuel and air nozzles of furnace burners #0. This completes the correct1v e lowering of superheated steam temperature occasioned by the earlier assumed rise in steam se tonoi tput.

'Mfianwhilesaid described rise in steam generator output (from 50% to 100% full rating) has tended to ,bring the steam temperature in reheater outlet 35 somewhat above the 950 deg. F. obtaining at the lower generator loading (50% rull rating) ially assumed. Such tendency is ind cated-by;E1gure4 which shows that at the msherngenerator loadings the reheater RH requires relatively less heat absorption to hold propersteam temperature than at the lower loading values. Any resultant rise in reheater steam temperature is at once re istered by damper controlnstrumentasfl'which in moving arm I H) to the right'engages contact-94 with contact D to in- 1Z7 ltiate an appropriate decrease adjustment in that temperature.

In responding (as earlier explained) relay DK closes its contact I06 thereby completing for damper motor 66 the reverse circuit earlier deg. F. temperature of the superheated steam,

contact 94 separates from contact D, relay DK becomes de-energized and opens contact IE6, and motor 66 discontinues its adjustment of dampers RDSD. This completes the corrective lowering of reheated steam temperature occasioned by the earlier assumed rise in steam generator output.

It will be understood that the burner tilting and the damper-positioning adjustments, just described as accompanying rises in steam generator loading, proceed simultaneously; that each is to an extent affected by and hence dependent upon the other; and that both are essential to the desired holding constant of the reheated steam temperature and the superheated steam temperature as the generator loading increases. servations, moreover, apply to corresponding burner and damper adjustments which accompany decreases in steam generator loading.

Thus, assume that the steam generator loading now falls off to some reduced level such as 50% of the generators full rating. Less fuel is then supplied to the burners IE) and the temperature of the furnace gases passing over superheaters Sb-S! (and over reheater RH) is correspondingly lowered. Less heat is now transferred to the steam passin through the superb-eaters, and this is reflected by a lowering of the superheated steam temperature in outlet 32. Burner control instrument l registers this, brings contact '54 into engagement with contact I and picks up (as earlier explained) increase relay IR to effect closure of its contact 86. That closure completes for burner tilting motor 52 the forward circuit earlier traced to cause an upward tilting of the fuel and air nozzles of furnace burners it as previously described.

Result of this upward tilting is to bring the flame body to a higher location (such as A of Figure 1) in the water Walled furnace and to cause exposure of the combustion gases to a lesser length of the vertical wall tubes [5 (see Figures 1-2) before reaching superheater S2 and offtake passes 2425. In consequence the gases flowing over superheaters S2--Sl (and over reheater RH) now have a higher temperature than before, and the transfer of heat therefrom to the steam passing through the superheaters is correspondingly stepped up. This in turn increases the temperature of the superheated steam in outlet 32 and causes burner control instrument It to move its indicator T2 to the right.

When the superheated steam temperature has thus been corrected back to the desired value of 950 degrees F., contact 14 disengages from contact I, relay IR. is die-energized, the accompany- Similar ob- 18 ing opening of contact 86 disconnects motor 52 from its energizing source, and tilt raising adjustment of the burner fuel and air nozzles is thereupon discontinued.

Meanwhile said described drop in steam generator output (from 100% to 50% full rating) has tended to bring the steam temperature in reheater outlet 35 somewhat below (see Figure 4) the 950 degrees F. obtaining at the higher generator loading (100% full rating) earlier assumed. Any resultant drop in reheater steam temperature is at once registered by damper control instrument 90 which in moving arm I l 0 to the left engages contact $4 with contact I to initiate an appropriate increase adjustment in that temperature.

In responding relay IK closes its contact I04 thereby completing for damper motor 66 the forward circuit earlier traced to cause a downward movement of positioner member 5'5 which imparts opening adjustment to reheater dampers RD and closin adjustment to superheater dampers SD. Result is to step up the flow of combustion gases through reheater pass 24 and to cut it down through superheater pass 25'; in consequence of the increased heat absorption by reheater RH the temperature of reheated steam leaving outlet 35 is correctively raised. In registering this corrective increase, damper control instrument 99 moves arm Hi) to the right. When this movement reaches the matching 950 degrees F. temperature of the superheated steam, contact 94 separates from contact I, relay IK becomes de-energized and opens contact [E54, and motor 66 discontinues its adjustment of dampers RD SD. This completes the corrective raising of reheated steam temperature occasioned by the just described drop in steam generator output.

From the foregoing it will become evident that the burner-tilting and the damper-positioning adjustments, just described as accompanying drops in steam generator loading, proceed simultaneously; that each is to an extent affected 'by and hence dependent upon the other; and that both are essential to the desired holding constant of the reheated steam temperature and the superheated steam temperature as the generator loading falls off.

As the loading of the represented (Figure 1) steam generator is further decreased into the lower output range (as below 30 to 40% full rated), a point may eventually be reached wherein the burners IE3 have been adjusted to the upper limit of their tilting movement. When this happens the main flame body may center at about location B in the Figure 1 furnace, and an attendant'opening of motor 52s limit switch 8| may make it impossible for the flame body further to be raised.

Under this condition still further falling off of the generator loading (with a corresponding decrease in the fuel supply to burners II!) is accompanied by reduction in the temperature of the combustion gases which flow over superheater S2 and through ofiftake passes 2fi-25. Tendency thus is for both the superheated and the reheated steam temperatures to drop. This they both do damper control instrument 9t then continuing to act through relays IKDK and motor 66 to position dampers ED-SD in the manner required to hold the temperature of the reheated steam (passing through outlet 35) in balanced relation to the temperature of the superheated steam (passing through outlet 32) throughout the entire range of generator loading values.

This balanced temperature relationship thus is maintained not only through the range of enerator loadings from 100% rated (or above) down to the lower outputs (as below 30 to 40% rated), but also within those lower outputs even after the burners I have been adjusted to the upper limit of their tilting movement. Under the latter condition still further falling off of generator loading (with a corresponding decrease in the fuel supply to burners I0) is accomplished by reduction in the temperature of the combustion gases which flow over superheater S2 and through olftake passes 2 l2 5.

This causes both the superheated and reheated temperatures to drop; and Fig. s damper control instrument 98 now continues to assure that both of the named temperatures will share that drop equally and thus continue in their balanced relationship.

If desired the justdescribed control facilities of Fig. 5 also may be organized to control burner tilting from the reheated steam temperature (at reheater outlet 35) and to balance the superheated steam temperature (at superheater outlet 32) thereagainst. In such case the thermocouple H from burner control instrument will be transferred to reheater outlet 35 while damper control instrument 9!] and associated relays IKDK will be rearranged (as by transferring contact I04 to relay DK and contact I06 to relay IK) so that damper adjusting motor 66 can respond in temperature balancing manner.

The modified temperature control system of Fig. 6

In Fig. 6 the earlier-described burner control facilities of Fig. 5 have been reproduced without change, while damper control facilities generally corresponding to those earlier shown have been arranged to provide means for maintaining the reheated steam temperature substantially constant throughout a wide range of generator loading values. The superheated steam temperature thus is again governed by control instrument 10, relays IRDR, tilting motor 52 and furnace burners ID (as in Fig. 5).

The accompanying regulation of reheated steam temperature is accomplished in Fig. 6 through the medium of dampers RD--SD adjusted by positioning motor 66 that is controlled through relays IKDK by instrument 90. This instrument 95 generally corresponds to device 99 of Fig. 5 but differs therefrom in being responsive only to the temperature of the reheated steam in reheater outlet 35; it may satisfactorily be of the same type as the earlier described instrument 18 shown in each of Figs. 5 and 6.

As illustrated in Fig. 6 at 99, this damper control instrument utilizes a thermocouple 9| in the stream of reheated steam passing through outlet 35 together with an electrical potentiometer circuit (not shown) and associated means which keep pointer 92 (of Fig. 6) in a position along horizontal scale 53 accurately corresponding to and registering the reheated steam temperature in outlet 35. From changes in the positioning of pointer 92 the positioning of dampers RDSD is governed through facilities exemplified by the electrical apparatus now to be described; but obviously hydraulic, air operated or other equivalent facilities may instead be employed.

Carried by pointer 92 is a contact 94 which moves horizontally therewith. As long as the reheated steam temperature stays at the desired value, contact 94 is disengaged from both cooperating stationary contacts I and D. Latter are mounted on a slid 95 settable beneath horizontal scale 93 for the reheated steam temperature that it is desired to maintain constant. The illustrative setting shown by Fig. 6 is at 950 deg. F.; some other setting, either higher or lower, may of course be chosen.

Instrument acts through relays IK and DK to control damper positioning motor 65 in sub-' stantially the same manner as does instrument 96 of Fig. 5; moreover, the reheater protecting switch I03 is coordinated with damper motor 66s limit switch Illl in the same way as in Fig. 5 and functioning of that switch during initial start up of the steam generator therefore is the same as earlier explained.

Hence, placement of switch H33 in the down- Ward position during generator start up runs motor 66 in the reverse direction to close reheater dampers RD and to open superheater dampers SD; this protects reheater RH from injurious exposure to combustion gases until after the steam generator has been started up and the prime mover (not shown) supplied thereby has been placed in operation to send part of its steam back through reheater RH; and switch IE3 is thereupon returned to the upward position (shown in Fig. 6) in which damper motor 56 is restored to automatic control by instrument 90' through relays IK and DK.

Thereafter, each closure of instrument contacts 94 and D (produced by too high a temperature of the reheated steam) picks up relay DK to drive motor 66 (over contact H36) in the reverse direction. By elevating positioner member 65 this imparts closing adjustment to reheater dampers RD and opening adjustment to superheater dampers SD and thereby correctively lowers the reheated steam temperature (in outlet 35) back to the desired value (as 950 deg. F.). Instrument 90' then separates contact 9 3' from contact D and stops the damper adjustment.

Likewise, each closure of instrument contacts 94and I (produced by too low a temperature of the reheated steam) picks up relay IK to drive motor 66 (over contact I04) in the forward direction. By lowering positioner member 55 this imparts opening adjustment to reheater dampers RD and closing adjustment to superheater dampers SD, and thereby correctively raises the reheated steam temperature (in outlet 35) back to the desired value. Instrument 90 then separates contact 94' from contact I and stops the damper adjustment.

In operation of the complete Fig. 6 system, burner control instrument 1!) acts through relays IR,DR and motor 52 to tilt burners It in the manner required to hold the temperature of the superheated steam (passing over thermocouple H in outlet 32) substantially constant throughout a wide range of generator loading values. The so-held temperature illustratively indicated by Fig. 6 is 950 deg. F.; some other value (either higher or lower) may of course be selected by shifting the position of instrument slide 15.

Meanwhile, damper control instrument 96 acts through relays IKDK and motor 66 to position dampers RD-SD in the manner required to hold the temperature of the reheated steam (passing through outlet 35) substantially constant throughout the aforesaid wide range of generator loading values. The so held temperature illustratively indicated by Fig. 6 is 950 deg. F.; some other value may of course be selected by shifting the position of instrument slide 9.5.

As the loading of the represented (Fig. 1) steam generator is decreased into the lower out- 21 put range (as below 30 to 40% full rated), a point may eventually be reached wherein the burners II] have been adjusted to the upper limit of their tilting movement. When this happens the main zone of combustion may be at about location B in the Fig. 1 furnace, and an attendant opening of motor 52s limit switch '8i may make it impossible for the flame body 'further to be raised.

Under this condition still further falling off of the generator loading (with a corresponding decrease in the fuel supply to burners i) is accompanied by reduction in the temperature of the combustion gases which flow over superheater S2 and through ofitake passes 2425. Tendency thus is for both the superheated and the reheated steam temperature to drop; but Fig. 6s damper control instrument 90 in responding to that drop causes motor 66 to further open reheater dampers RD and to further close superheater dampers SD. This holds the reheated steam temperature up and causes the superheated steam temperature to decrease even more rapidly, a point finally being reached wherein damper motor 88 opens limit switch 100 and thereby discontinues damper adjustment in the direction named.

The further temperature control system of Figure 7 In Figure '7 the just-described control facilities of Figure 6 have been reorganized to provide a system wherein the reheated steam temperature controls the tilt of burners l0 and the superheated steam temperature controls thepositioning of dampers RD-SD. This is accomplished by placing thermocouple 'II in reheater outlet 35 so that burner control instrument it responds to the temperature of the steam leaving reheater RH, and by placing thermocouple iii in superheater outlet 32 so that the damper control instrument 90 responds to the temperature of the steam leaving superheater S2.

In this Figure 7 organization thereheater protecting switch I03 is coordinated with damper motor EBs limit switch it]! in the same way as in the system of Figure 6, and functioning of that switch during initial start up of the steam generator therefore is the same as earlier explained.

The Figure '7 organization of those relays IK and DK duplicates that of Figure S-eXcept for an interchanging of relay contacts I04 and 1% made necessary by fact that in Figure 'l the damper control instrument 9i! responds to superheated steam temperature rather than to reheated steam temperature. Undesired temperature rises in the superheated steam flowing over thermocouple iii in superheater outlet 32 (Figure '7) thus are corrected through relay DK and contact I06, while undesired temperature drops in that superheated steam thus are corrected through relay IR and contact [84.

In operation of the Figure 7 system, burner control instrument "it acts through relays IR-DR and motor 52 to tilt burners ill in the manner required to hold the temperature of the reheated steam (passing over thermocouple H in outlet 35) substantially constant throughout a wide range of generator loading values. The so-held temperature illustratively indicated by Figure '7 is 950 deg. F.; some other value (either higher or lower) may of course be selected by shifting the position of instrument slide 75.

Meanwhile, damper control instrument 90 acts through relays IKDK and motor 66 to position dampers RD-SD in themanner required to hol'd'the temperature of thesup'erheated steam (passing over thermocouple 9| in Figure? outlet 32) substantially constant throughout the aforesaid wide range of generatoroutputs. The so-held temperature illustratively indicatedby Fig. 7 is 950 deg. F.; some other value may of course be selected "by shifting the position of instrument slide 95.

Functioning of this automatic temperature regulating system of Figure '7 is therefore substantially equivalent to that of Figure "6 throughout the range of generator loadings from 100% rated (or above) down to the lower outputs (as be1ow30 to 40% rated) of the Figure 1 generator. In approaching those lower outputs a point is eventually reached wherein the burners Ill have been adjusted to the upper limit of their tilting movement. When this happens (the main fiame'body then centering at about location B in'Figurel) an attendant opening of motor 52s limit switch'tl makes further raising of'the flame body impossible.

Under this conditionstill further falling off of the generator loading (with a corresponding decrease'inthe fuel supply to burners H3) is accompanied by reduction in the temperature of the combustion gases which flows over superheater S2 and through ofitake passes 24-45. Tendency thus is for both the reheated and the superheated steam temperatures to drop; but Fig. 'ls damper control instrument in responding to that drop causes'motorfiii to further open superheater dampers SD and to further close reheater dampers RD. This holds the superheated steam temperature up and causes the reheated steam temperature to decrease even more rapidly, a point finally being reached wherein dampermotor '66 opens limit switch llil to discontinuedamper adjustment in thedirection named.

Summary From the foregoing it will be seen that I have provided improved facilities for controlling the temperature of the superheated steam and of the reheated steam as taken from steam generators having superheater and reheater elements organized in the general parallel gaspass manner taught by my copending application Serial No. 56,381, filed October 25, 1948, for Steam Generator; that I have provided regulating means effective to holdboth of the named steam temperatures substantially constant (either at the same or at difierent values) over a wide range of generator loading values; that I have enabled such regulation to be effected automatically in a manner which is simple, practical and reliable; and that I have made provision for protecting the reheater tubes against overheating by the combustion gases while the steam generator and its suppliedtunbine are being started up.

My invention improvements are therefore extensive in their application and hence are not to be restricted to the specific form here disclosed by way of illustration.

What I claim is:

. 1. In a steam generator operating under the reheat cycle, in which apredetermined controlled relationship must be maintained between the superheat and the reheat; a setting providing a combustion chamber and a gas chamber in communication therewith; steam generating tubes lining the walls of said combustion chamber; burners for introducing into said combustion .23- chamber streams of fuel and air which create a mass of burning gas within the chambers tube lined walls; means in the gas chamber providing at least two parallel gas passes through which the products of combustion flow from the combustion chamber out of the setting; a superheater for superheating the generated steam and disposed in one of said two passes; a steam reheater for reheating steam and disposed in the other of the passes; burner tilting means responsive to variations in the temperature of said reheated steam for directing the said fuel and air streams issuing from said burner means either toward the combustion chamber outlet in response to a decrease in reheat and towards the inlet of each of said two gas passes, or away from the outlet of said combustion chamber in response to an increase in reheat and away from the inlet of each of said two gas passes so as to alter the location within the water walled combustion chamber of said burning gas mass with respect to the water cooled walls and thereby change the temperature of the combustion products flowing through the passes over the superheater and the reheater, said gas temperature chang resulting in a disturbance of said predetermined temperature relationship; and damper means cooperating with said superheater pass and with said reheater pass and positionally adjustable in response to variations in the aforesaid predetermined temperature relationship to proportion the combustion gas flow through each of said two passes and thereby re-establish said predetermined temperature relationship between the superheated steam and the reheated steam. 2. In a steam generator operating under the reheat cycle, in which a predetermined controlled relationship must be maintained between the superheat and the reheat; a setting providing a combustion chamber and a gas chamber in communication therewith; steam generating tubes lining the walls of said combustion chamber; burners for introducing into said combustion chamber streams of fuel and air which create a mass of burning gas within the chambers tube lined walls; means in the gas chamber providing at least two parallel gas passes through which the products of combustion flow from the combustion chamber out of the setting; a superheater for superheating the generated steam and disposed in one of said two passes; a steam reheater for reheating steam and disposed in the other of the passes; burner tilting means responsive to variations in the temperature of said superheated steam for directing the said fuel and air streams issuing from said burner means either toward the combustion chamber outlet in response to a decrease in superheat and towards the inlet of each of said two gas passes, or away from the outlet of said combustion chamber in response to an increase in superheat and away from the inlet of each of said two gas passes so as to alter the location within the water walled combustion chamber of said burning gas mass with respect to the water cooled walls and thereby change the temperature of the combustion products flowing through the passes over the superheater and the reheater, said gas temperature change resulting in a disturbance of said predetermined temperature relationship; and damper means cooperating with said superheater pass and with said reheater pass and positionally adjustable in response to variations in the aforesaid predetermined temperature relationship to proportion the combustion gas flow through each of said two passes and thereby re-establish said predetermined temperature relationship between the superheated steam and the reheated steam.

3. In a steam generator operating under the reheat cycle, in which a predetermined controlled temperature relationship must be maintained between the steam leaving a first steam heater and the steam leaving a second steam heater; a setting providing a combustion chamber and a gas chamber in communication therewith; steam generating tubes lining the walls of said combustion chamber; burners for introducing into said combustion chamber streams of fuel and air which create a mass of burning gas within the chambers tube lined walls; means in the gas chamber providing at least two parallel gas passes through which the products of combustion flow from the combustion chamber out of the setting; a first steam heater disposed in one of said two passes; a second steam heater disposed in the other of the passes; burner tilting means responsive to variations in the temperature of the steam leaving said first steam heater for directing the said fuel and air streams issuing from said burner means either toward the combustion chamber outlet in response to a decrease in the aforesaid first heaters steam temperature and towards the inlet of each of said two gas passes, or away from the outlet of said combustion chamber in response to an increase in the aforesaid first heaters steam temperature and away from the inlet of each of said two gas passes, so as to alter the location within the water walled combustion chamber of said burning gas mass with respect to the water cooled walls and thereby change the temperature of the combustion products flowing through the passes over the first steam heater and the second steam heater, said gas temperature change resulting in a disturbance of said predetermined steam temperature relationship; and damper means cooperating with said first steam heater pass and with said second steam heater pass and positionally adjustable in response to variations in the aforesaid predetermined temperature relationship to proportion the combustion gas flow through each of said two passes and thereby reestablish said predetermined temperature relationship between the steam leaving the first heater and the steam leaving the second heater.

JOHN VAN BRUNT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,773,088 Armacost Aug. 19, 1930 2,158,509 Kuhner May 16, 1939 2,298,700 Junkins et al. Oct. 13, 1942 2,363,875 Kreisinger et a1. Nov. 28, 1944 2,471,728 Dickey May 31, 1949

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