US2869520A - Vapor generating and superheating operation - Google Patents

Description

Jan. 20, 1959 -w. L. PAULISON, JR 7 2,869,520

VAPOR GENERATING AND SUPERHEATING OPERATION I Filed Aug. 24. 1953 5 Sheets-Sheet l COND.

' BURNERS AIR HEATER FIG. I

INVENTOR.

WILLIAM L. PAULISON JR.

Jan. 20, 1959 W. L. PAULISON, JR

VAPOR GENERATING AND SUPERHEATING OPERATION 5 Sheets-Sheet 2 Filed Aug. 24, 1953 3 r m 5 4 a 5 #1.!- P 0 MY .W, WWW, m 5 MH Mn fl mw u m Ci k 1 w T k i M 2 q m w T J 1 mm w 4 w lwflm w n m Q Q 3 M A k g: if Q M V REHEATER SUPERHEATER BY-PASS INVENTOR. WILLIAM L. PAULISON JR.

ATTORN FIG. 2

Jan. 20, 1959 w. L. PAULISON, JR 2,869,520

VAPOR GENERATING AND SUFERHEATING OPERATION Filed Aug. 24, 1953 5 Sheets-Sheet 5 Jan. 20, 1959 Filed Aug. 24, 1953 STEAM TEMPERATURE F w. L. PAULISON, JR 2,869,520

VAPOR GENERATING AND SUPERHEATING OPERATION 5 Sheets-Sheet 4 CONVECTION CHARACTERISTICS O (UNCONTROL.LED)(|)(2)(3) l 50 SUPERHEAT fig REH AT a i E i BALANCED SH-RH O00 DESIRED FTT 65 |0o% LOAD I RH DAMPERS OPEN -T SH DAMPERS z 2 J a) ,Q 4 E BY-PASS DAMPERS I UJ 1 CLOSED O BOILER LOAD INVENTOR. 5 WILLIAM L. PAULISON JR. FIG. B

ATTO EY Jan. 20, 1959 w. L. PAULISON. JR

VAPOR GENERATING AND SUPERHEATING OPERATION I Filed Aug. 24, 1955 I 5 Sheets-Sfiaet 5 m;m L L m m I m w EH A 4/ D 8 PE A/ m L w A B I a s m. y m; & M. M M T A TU H H D I M S H Rm E R L G R mm T mm m ,7 I m m 9 O m: Re I D ww m a L m 5 o O C m m m w FIG. 6

VAPDR GENERATING AND SUPERHEATING OPERATION William L. Paulison, Jr., Ridgewood, N. 1., assignor to Bailey Meter Company, a corporation of Delaware Application August 24, 1953, Serial No. 375,963

Claims. (Cl. 122479) 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. I am particularly concerned with the problems encountered in units rated at 1,000,000 to 1,500,000 lb. per hr., operating at pressures from 1500 p. s. i. g. to 2000 p. s. i. g., and with final total steam temperatures of the order 1000 to I050 F. Modern units of this type may have reheat provisions, taking steam exhausted from a high pressure turbine at say 600-800 p. s. i. g. and reheating this steam to a range of l0001050 F. The problems involved in the generation and close control of the properties of steam in such a unit 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 turbines served by the steam. In the interest of turbine efliciency the temperature of the steam delivered to the turbine should be maintained within close optimum limits throughout a wide range of operation.

I contemplate a unit wherein the furnace chamber is surrounded by walls of closely spaced bare tubes constituting the vapor generating section primarily radiantly heated. The superheating and reheating portions of the vapor flow path are preferably located beyond the gas outlet of the furnace in what is termed convection heating locations and, in the particular embodiment which I will describe, the superheating and reheating portions of the flow path are located in separate and parallel gas flow paths with distribution dampers for regulating the distribution of heating gases between the two vapor paths. I For any given furnace, as load increases, the rate of heat absorption does not increase as rapidly as the rate of heat liberation; 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 receiving the volume and temperature of leaving gases at an expected rated load. Any further increase in the 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. On the other hand, at operation below the rated load, the fixed superheater surface receives less volume and lower temperature gases leaving the furnace with a corresponding lowering of final steam temperature.

Inasmuch as the pressure and heat content per 1b. of the low pressure steam returned to the reheater from the high pressure turbine exhaust decreases with reduction in load, while the pressure and heat content per lb. of the high pressure steam introduced to the superheater remains vted States Patent 0 C? 2,869,520 Patented Jan. 20,1959

substantially constant with a corresponding variation in load, the customary installation of convection superheater and reheater will give a steam temperature-load graph which will slope downward from maximum load to low load, with the result that de.ivery temperatures from both the superheater and reheater will droop, and the outlet temperature-load graph for the reheater will have a greater slope than the corresponding graph of the superheater. This is clearly shown in Figs. 5 and 6.

The unit is preferably designed so that the final total temperature of the superheated steam and of the reheated steam will equal or exceed that which is desired through the expected operating range and, in the present embodiment, I contemplate that this should be in a range of 65-l00% of capacity. In other words,'the surfaces and passages will be so designed that the uncontrolled characteristic of each 'of the surfaces crosses the optimum final temperature line on the graph at approximately 65% of capacity and lies above the optimum temperature value at all ratings from 65% to capacity. It is to be understood that operation below this design point will produce superheated steam and reheated steam at a final total temperature lower than the optimum and continued low-load operation is not expected.

Due to the uncontrolled characteristic, operation in the range (65100% rating) will find the final total temperature of the superheated steam and of the reheated steam greater than that which is desired with possible danger to the turbine, and it becomes necessary to prevent the steam from reaching the excessive temperature throughout this range ofoperation. Preferably, I accomplish this through by-passing some of the heating gases around the convection heating surfaces when operating through the range 65100% rating.

Due to the difference in slope of the characteristic curve of the superheater and of the reheater it is seen that the two final temperatures may depart from equality or from desired relationship of values and this I correct by proportioning the total heating gases between the superheating and reheating convection surfaces.

In general then, I have provided a method and apparatus for maintaining optimum final temperature of the superheated steam and of the reheated steam for some arbitrary range of operation, as for example 65100% rating, through the agency of gas proportioning over the parallel superheating and reheating surfaces and, where necessary, by-passing some of the heating gases around both of the superheating surfaces.

When, hereafter, I use the term throttled with reference to the postion, or positioning, of a damper, I intend to mean that the damper is in some position between closed and open. If a damper is closed it is theoretically shutting off all flow of gases therethrough. If it is open then it theoretically allows flow of gases therethrough unimpeded by the damper. At any intermediate damper position the gas flow is throttled or impeded as to its free flow and, while it may be more strictly correct to speak of the gas flow as being throttled in different degree at different damper positions, it is not incorrect to say that the damper is throttled or in a throttling position. When the damper is moved in an opening direction or in a closing direction it is still in a throtting position so long as it is not closed or open.

To reach the desired high superheated steam temperature, but not to exceed it, requires 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 careful designing at some rated load, the superheated temperature will vary during operation by reason 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, whether the superheating e ements are located in series or in parallel paths. In other words the theoretical characteristic curves are for ideal designed conditions of operation and, while the general trend of the curve is followed, with rating. the actual final temperature of the superheated steam or of the reheated steam may be above or below the theoretical curve or the optimum value at any time, for different reasons and at different rates of operation. By the method and apparatus of my invention I tend at all times to return final total superheated steam temperature and final total reheated steam temperature toward optimum value, upon departure therefrom, regardless of the cause of such departure, through an operating range arbitrarily chosen in the present embodiment as 65-100% of capacity.

In the drawings:

Fig. 1 is a somewhat diagrammatic sectional elevation of a steam generating and superheating unit of the type contemplated, having convection superheating and reheating surfaces located in parallel gas flow paths, and with a gas flow by-pass.

Fig. 2 diagrammatically represents a pneumatic control system for the unit of Fig. 1.

Fig. 3 is a modification of the control system of Fig. 2.

Fig. 4 illustrates a manual control station for regulating the operation of the unit of Fig. 1.

Figs. 5 and 6 are graphs of characteristics of convection superheating and reheating surfaces of a unit like Fig. 1.

Fig. 7 shows a modification of Fig. 2.

Referring now to Fig. l I show therein in quite diagrammatic form, and not to scale, a vapor generating and superheating unit in connection with which I will explain my invention. The furnace 1 of the unit is supplied with fuel and air for combustion through burners 2 (not detailed). Gaseous products of combustion leave the furnace after contacting the fluid heating surfaces thereof. The generator is of the radiant type, wherein the furnace 1 has walls 3 of vertical, closely spaced plain tubes constituting the vapor generating portion of the unit. Products of combustion pass upwardly through the furnace 1 in the direction of the arrow, through a tube screen 4, over a secondary superheating surface 5 and a secondary reheating surface 6, to the entrance of three parallel gas passages SH, BP and RH. In the SH path is located the primary superheating surface 7, while ,in the RH path is located the primary reheat surface 8.

dampers 9, while that through the RH path is regulated by the positioning of dampers 10. by-pass is regulated by dampers 11.

Considering now the vapor flow path, it will be seen that saturated steam from the separation drum enters Flow through the :a header 12, passes upwardly through superheating surface 7 and through a conduit 13 to the secondary superheater 5. The superheated steam then leaves the unit through a conduit 14 to a high pressure turbine 15, exhausting through a conduit 16 to a header 17 entrance to the'reheating surface 8. From the reheater the steam passes through a conduit 18 to the secondary'reheater 6 from which it passes by way of a conduit 19to a low pressure turbine 20 exhausting to a condenser. This, in simplified diagrammatic fashion, is the vapor cycle of .the system; Pressure of the superheated steam in conduit 14 is determined by-a -Bourdon tubedevice 21 While final total temperature S HT of the steam is measured by a device 22. The weight rate of flow of superheated steam through the conduit 14 to the high pressure turbine 15 is continuously measured by a meter 23. In the reheated steam conduit 19 the pressure is determined by a Bourdon tube 24 While its final temperature RHT is determined by the measuring device 25.

My present invention contemplates both a method and apparatus for operating and controlling the operation of avapor generating and superheating unit of the type described, through the positioning of dampers 9, 10, and 11 in accordance with, or responsive to, measurements of variables such as pressure, temperature, or flow of the superheated steam, and pressure, or temperature of the reheated steam. I furthermore contemplate using air flow as a load index, under certain conditions of design or operation, and while such an air flow meter is not shown in Fig. 1, it will be appreciated that the air flow meter would provide a continuous determination of either the fresh air supplied for combustion to the burners of the unit, or of the total products of combustion passing through the unit. In speaking of air flow, I intend to mean the products of combustion and excess air as an indication of rating, and this may well be measured in known fashion by taking the pressure drop across a selected portion of the gas passages of the unit. On the other hand, it may be true air flow by being a measure of rate of flow of air supplied to promote combustion as measured in the duct supplying the burners.

Referring now to Fig. 2 I illustrate therein, in quite diagrammatic fashion, a pneumatic control system for continuously and automatically regulating the final total temperature of the superheated steam and of the reheated steam in connection with units such as that of Fig. 1. At 30 I designate a recorder controller for the superheated steam temperature 81-11 and for the reheated steam temperature RHT. A pneumatic pilot valve 31 may be of a known type as disclosed in the Johnson Patent 2,054,464 establishing in a pipe 32 a fluid loading pressure continuously representative of final total temperature of the superheated steam supplied to the turbine 15. In similar fashion a pilot valve 33 establishes in a pipe 34 a fluid loading pressure continuously representative of the final total temperature of the reheated steam passing to the low pressure turbine 20 through conduit 19. The pipe 32 communicates with the A chamber of a relay 35 while the pipe 34 communicates with the B chamber of the relay.

Relay 35 is a differential standardizing relay of the type described and claimed in the Dickey Patent 2,098,913 and provides an output pressure in a pipe 36 from the D chamber of the relay. Such a relay provides a proportional control with reset characteristics from a comparison of, or differential between, the value of SHT and RHT. It provides for the differential or discrepancy between these two final total temperatures a floating control of high sensitivity superimposed upon a positioning control of relatively low sensitivity. A function of the adjustable bleed connection 37 between the D and C chambers is to supplement the primary control of the pressure developed in pipe 36, as representative of the differential between the pressures in pipes 32, 34, with a secondary control of the same or of a different magnitude as a follow-u or supplemental action to prevent overtrave! and hunting.

The output of relay 35, in pipe 36, is available to a manual-automatic selector station 38 which is preferably of the type disclosed in the patent to Fitch 2202,48). The selector station 38 provides the possibility of remote manual, or automatic, control of the SH dampers 9 and the RH dampers 10, together but in reverse direction, by virtue of a reversing relay 39. The output fluid loading pressure from station 38, available in a pipe 40, is subjected upon the B chamber of reversing relay 39 and directly uponthe A. chamber of calibrating relay 41.

' motive means 45 for positioning the dampers 9. The

output of the relay 41, effective in a pipe 46, acts through a selector station 47 upon the motive means 48 for positioning the reheat dampers 10. Thus a signal, in the pipe 40, calling for a change in the proportioning of the gas flow over the superheating and reheating surfaces, will act upon both devices 45, 48 but in reverse direction.

The air flow meter 5t positions the movable element of a pilot 51 establishing in a pipe 52 a fluid loading pressure continuously representative of the load index air flow. The pipe 52 joins the A chamber of a relay 53 whose C chamber is joined by a pipe 54 subjecting upon the C chamber a fluid loading pressure established in accordance with the total of the final superheated steam temperature and the final reheated steam temperature.

A branch of pipe 32 joins the A chamber of a totalizing relay 55 while pipe 34 joins the C chamber of the relay, the two fluid pressures acting in the same direction to totalize and the relay 55 produces in a pipe 56 a fluid load ing pressure continuously representative of such total. Pipe 56 joins the A chamber of a relay 57 which may be a simple relay, or a standardizing relay, according to the action of the solenoid valve 58 in the bleed connection between the D and C chambers of the relay. Solenoid valve 58 is connected by cable 59 with contacts 608 of the meter 3 and the contacts 60B are closed at and above the optimum final temperature SHT of the superheated steam. Thus, when a rating of approximately 65% is reached, as indicated by final superheat steam temperature reaching optimum value, the solenoid valve 58 opens the bleed connection between chambers D and C whereby the relay 57 provides a standardizing action between the pressure in pipe 56 and that in 54 leading to the C chamber of relay 53.

Fig. 7 shows a possible modification of Fig. 2 wherein the valve 58, connecting the C and D chambers of relay 57, is bellows actuated responsive to loading pressure in pipe 56 and thus is sensitive to total (Fig. 2) or average (Fig. 3) of the SHT and RHT values; rather than to one only of the temperatures.

The output of relay 53, available in a pipe 60, controls the positioning of motive means 62, through a manualautomatic selector station 61, and thus the position of dampers 11. At the same time the control fluid pressure in pipe 60 joins a calibrating relay 63 whose output, available in a pipe 64, joins the B chamber of each of relays 41, 42.

In the present embodiment it is desired to have the final superheat temperature and the final reheat temperature both at 1000" F. In certain installations it might be desirable to have the final temperatures different the one from the other, as for example, the final SHT 1050 F. while the final RHT 1000" F. This would be accomplished by a constant bias in the controls wherein they would, in effect, control to the same temperature standard but one would be biased somewhat relative to the other. It is proposed to manipulate the superheat and reheat dampers in sequence to equalize the two temperatures (or in predetermined relation to each other) and control the by-pass to maintain the correct value of the total or average temperatures. It the by-pass damper is wide open and the temperatures are still too high then the superheat and reheat dampers may be somewhat throttled to force more gas through the wide open by-pass. In general the operation of the SH and RH dampers is in sequence with the bypass dampers. However, it is a matter of selectivity rather than true sequence, and the proper combination of damper throttling will be automatically accomplished by the system of Fig. 2 to continually attempt to maintain each of the final temperatures at the desired value throughout a preselected range of operation, in this case, from 65100% of rating.

The over-all operation of the system of Fig. 2 is as follows, reference being had to Figs. 5 and 6. The load index controller (air flow 50) begins to open the bypass damper 11 as the boiler load increases above approximately 65%, by transmitting the loading pressure in pipe 52, through the averaging relay 53, pipe 60, and selector station 61, to the motive means 62. This gradual opening of the by-pass damper, in accordance with load increase, is shown in the lower portion of the graph Fig. 5; the RH dampers and SH dampers being open. Throughout the operating range (GS-%) tne by-pass damper opening is modified as required by the sum or the SHT and RHT controller loading pressures (corresponding to 2000 F.) transmitted from the totalizing relay 55 to the averaging relay 53 by way of pipe 56, standardizing relay 57, and pipe 54. It being understood that throughout this range, as previously mentioned, solenoid valve 58 is open thus allowing a regulated bleed between the D and C chambers of relay 57 making it a standardizing type of relay.

Should the sum of the two temperatures start to in crease above 2000 F. with a wide open by-pass damper, both the SHT and RHT dampers will be throttled together to force the required add.tional gas through the by-pass section. This action is accomplished by an increase in control loading pressure transmitted from pipe 60, through the calibrating relay 63 and pipe 64 and applied to the two calibrating relays 41, 42. Thus, control from boiler load as modified by the sum of the two steam temperatures, will tend to maintain the sum of the two temperatures constant (at 2000 F.) above approximately 65% boiler load.

At boiler loads below 65% the sum of the SHT and RHT temperatures, indicated by the value of the loading pressure in pipe 56, is relayed directly through simple relay 57 and pipe 54, to the C chamber of relay 53. The loading pressure in pipe 54 will, under these conditions,

never exceed a predetermined value corresponding to the total temperature of 2000 F. to be attained at approximately 65% boiler load. When the summation temperature of 2000 F. is reached, at approximately 65% boiler load, not only would the loading pressure of pipe 54, effective in the C chamber of relay 53, tend to exceed the predetermined value, but the contact 60B Will close, thus opening the bleed 58 between the C and D chambers of relay 57, turning it into a standardizing action so that any further increase in the summation of the SHT and RHT temperatures will cause a regenerative amplification of the control pressure in pipe 54 until the condition has been corrected by the by-pass damper and the SH and RH dampers. As previously mentioned, the by-pass damper first opens gradually until it is wide open and, if this has not satisfied, or returned the total temperature to a value of 2000 F., then the signal in pipe 60, acting through the relay 63 and pipe 64, is effective upon both relays 41 and 42 to cause both of the SH and RH dampers to be throttled downward thus forcing more gas through the by-pass.

Referring to the lower portion of the graph in Fig. 5 it will be observed that I have shown the SH dampers and RH dampers throttled in parallel from the load where the by-pass damper is wide open. This is a sequential operation which is accomplished by the system being described. On the other hand, it is possible that there may be some overlap and that actually the SH and RH dampers will begin to be throttled together slightly before the by-pass damper is wide open.

When the SHT control pressure (in pipe 32), and the RHT control pressure (in pipe 34), are equal, and the standardizing relay 35 into which their control pressures terminate is balanced, an increase in reheated steam temperature above superheated steam temperature transmits a change in output of the standardizing relay 35 through the pipes 36, 40 in a direction that throttles the 7 reheat control dampers 9. If the SH damper is Wide open itwould not move. If it is not wide open it might tend to open while the RH damper tends to close. A decrease in reheated steam temperature below superheated steam temperature reverses the dire, .on of the differential standardizing relay output go and causes the reheat damper to tend to open while the superheat damper tends to close. Should the re ater steam temperature remain lower than the su temperature, the differential standardizing put would continue to change in the same :1 and cause the superheater damper to throttle (leaving the re heat damper wide open) as required to equalize the =nperatures. The output of the difierentlal s relay 35 is applied to the SH and dan r odrives through selector valves, reversing and can't; relays as indicated. Thus, the superheat and re dampers are positioned to maintain equal superb rated and reheated steam temperatures. At boiler load nere the sum of these two temperatures of 2000" F. is available each will be controlled at 1000 F.

Referring to the lower portion of the Fig. 5 will be understood that this is d'agrammatic in SH and RH dampers may not start to close rating shown or the by-pass dampers becom at the rating shown. The three sets of dam all moving at the same time but in proper direction to satisfy the desideratum of op superheated steam temperature and optima. rcheated steam temperature at whatever boiler load is had between 65% and 100%. It will be appreciated that, while certain sequential or selective actions between the control mechanisms and the damp tors, this goes on simultaneously and continuously upon any departure of the two final temperatures from their desired value. The actual positioning of the dampers is one of precedence where the pro" is operated in the proper direction so t shift of gas flow between the three parallel paths is the right direction to cause the final steam temperature to approach the desired values.

In the upper portion of the Fig. 5 gr ph have indicated a normal design wherein the uncontrolled convection characteristic (1) for the superheating surface is substantially similar to the uncontrolled convection c acteristic (2) for the reheat surface except that the l falls off somewhat more rapidly upon decrease in For a design where these curves are spaced in sub tial parallelism, the balance or average of final temperature value at 65% boiler load. su design, throughout the control range 65lG" be: the total of SHT and RHT m :hi well be 261?? F.

the reheat temperature and call for the reach. gas flows over the reheat and superheat surfi.

explained.

Fig. 6 shows how these graphs might loo-l: if the dcsign were such that the uncontrolled convection characteristics actually crossed exactly on he desired temperature 1000" F. at 65% bo'ler rating. in tnis condition the reheat curve would tend to be above curve for the range (SS-100% rating and the 4.

relative to the. other, that both the high pressure and reheat steam will be at exactly 950 F. even though the total of the two is only 1900" F.

Under certain conditions it may be desirable that one a or the oi-rer of the SH and RH dampers will always be wlile the other dampers are adjusted to throttle T is is to prevent the possibility of both .13 drifting toward their closed position.

of Figs. 5 and 6 do not show this neverability of such sequential operation exists )ll of the various relays and other devices Under this particular adjustment either the or the SH dampers are throttlcd while the -aintained in a wide open position although, temperature is above that which is desired ..ctor enters into the system to tend to throttle 1 RH and SH dampers and force some of the heat over the by-pass. Provisions may be sup- .f d a ainst the possibility of both dampers ever reachi ed position by remotely actuated pneumatic SLi l mit the damper throttling, unless under in; uation through the selector stations.

D the lower graphs of Figs. 5 and 6 it is not t ale to show the inter-action of all three sets of all loads, both above and below 65%. For simplicity I have shown the SH and RH n to a loft-d where the by-pass dampers are upon an increase in load). From what has con said, however, it will be apparent that below 65%, either, or both, the SH may be throttled to equalize the SH aturcs regardless of whether the total or the average 1000 F. This is not plot because it may be that the SH damper with the RH damper open, or the RH damper 'lli SH damper open, or both tbrottled in 3 show a portion only of the system of Fig.

g therefrom in that the load index in this instance is superheat steam ilo v rate measured at 23 (Pig. ll and the contacts 613A are actuated at approximately '65 31? of 1g rather than from the attainment of pre- "e ed temperature value as was the case in Fig. 2. the relay 55A is indicated as an averaging than as a totalizing relay.

. l have schematically illustrated certain inrecording instrumentalities useful as a guide remote control of the variable operating facaerations of the unit in accordance with in the conduit 1 leading to the high pressure 5 and provides a visual indication thereof on The indicating devices 22, 25 provide mani- 1.nal superheated steam temperature and steam ter oerature respectively. The air controller 5t] and the superheated steam controller 23 provided not only a visual but permanent continuous record of these The points of measurement of these opmay be widely scattered but I prefer- :neters at a central control location having station Preferably the panelboard each-board type wherein the indicating struments are mounted on the vertical are below.

Upon the bench-board portion of the panel 1 indicate three Forward-Revsrse-Stop push button stations 101 actively controlling. electric motors 45A, 48A and l for rem to manual positioning of the dampers 9, iii, 11.

it will now be clear that my improved methods of oreration of the unit may be manually performed by 75 an operator located at the Station 100, observing the measuring instrumentalities, and selectively remotely activating the motors 45A, 48A and 62A for positioning the dampers 9, 10, ll. Selective and sequential operation may be obtained, as well as proper proportioning of the gases over the superheater and reheater, with or without, the bypass in service.

It is understood in this art that either vapor out-fio rate or air flow rate may be used as an index of output or boiler rating.

While I have chosen to illustrate and describe certain preferred embodiments of my invention, it will be appreciated that the invention may be embodied in other forms, and thus I do not desire to be limited to the specific showings disclosed.

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

1. Apparatus for controlling the operation of a vapor generating and superheating unit of the type having a convection vapor superheater and a convection vapor reheater disposed respectively in divided and separate parallel structurally defined gas flow passages from a common combustion space and having a controllable structurally defined gas by-pass around the said parallel heating passages, including in combination, damper throttling means for the superheater passage, damper throttling means for the reheater passage, damper throttling means for the by-pass, means continuously determining reheat final total temperature, means continuously determining reheat final total temperature, means continuously ascertaining an index of load upon the unit, first control means responsive to both the superheat final total temperature and the reheat final total temperature determining means and producing a control etfect representai0 tive of the total of the two temperatures, means arranged to position the by-pass damper means conjointly responsive to said first control means and said load index means, a second control means responsive to both the superheat final total temperature and the reheat final total temperature determining means and producing a second control effect representative of the diiference of the two temperatures, and means selectively responsive to said second control efiect arranged to throttle the damper of the superheat passage or of the reheat passage whichever temperature is higher while leaving the opposite damper open.

2. The combination of claim 1 including limiting means making ineffective the by-pass damper positioning means for opening said by-pass from closed condition when either the load index is below a predetermined value or the total of the two temperatures is below a predetermined value.

3. The combination of claim 1 wherein the control effect produced by said first control means is representative of the average of the two temperatures.

4. The combination of claim 1 including means responsive to the load index ascertaining means also effective upon the selective means.

5. The combination of claim 1 wherein the control efiects are fluid pressures.

References Cited in the file of this patent UNITED STATES PATENTS 2,298,700 Junkins Oct. 13, 1942 2,519,240 Fellows Aug. 15, 1950 2,526,843 Birchler et a1. Oct. 14, 1950 2,649,079 Van Brunt Aug. 18, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,869,520 January 20, 1959 William L Paulison, Jr

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2', line '70, after "heated" insert ,steem column 8,

line 58, for "provided" read mprovide column 9, line 28, for "reheat" read me super-heat i Signed and sealed this: 8th day of September 1959. i

Attest:

; KARL H AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

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