US3189006A

US3189006A - Apparatus and method for starting a vapor generating power plant

Info

Publication number: US3189006A
Application number: US238885A
Authority: US
Inventors: Jr Edward L Kochey
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1962-11-20
Filing date: 1962-11-20
Publication date: 1965-06-15
Anticipated expiration: 1982-06-15
Also published as: GB1005172A; BE640156A; DE1271723B; CH442360A; ES293653A1

Description

J 1.965 E. KOCHEY, JR 3,189,006

APPARATUS AND METHOD FOR STARTING A VAPOR GENERATING POWER PLANT Filed Nov 20 1962 .Y 2 m W m B ML A m F D m w D E m B Z 5 .F 6 M llllll ll 9 6 0 3 6 United States Patent 3,189,006 APPARATUS AND METHOD FOR STARTING A VAPOR GENERATlNG POWER PLANT Edward L. Kochey, Jr., Colebrook, Conm, assignor to Combustion Engineering, Inc, Windsor, Conn, a corporation of Delaware Filed Nov. 20, 1962, Ser. No. 238,885

8 Claims. (Cl. 122406) The invention relates in general to a forced flow oncethrough vapor generating power plant, and more particularly to an improved apparatus and method for starting operation of the vapor, for instance, steam generator and turbine associated therewith.

It is known when starting up a forced flow oncethrough vapor generator .to separate the vapor superheating and turbine portion from the vapor generating port-ion by a so called boiler throttling valve. Such separation permits the use of auxiliary vapor in the superheater portion for the. purpose of starting up the turbine, while the vapor generating portion at the same time is brought up to the desired temperature and pressure; or in other instances the fluid in the vapor generating portion after having been raised to a high pressure and temperature can be expanded through the boiler throttling valve to form a vapor and liquid mixture at lower pressure, with such vapor, after having been separated from the liquid in .a vapor and liquid separator and superheated, then being used for starting up and rolling the turbine; or in still other instances, the temperature of the high pressure fluid can be raised to such a value that only dry vapor is produced when the fluid is expanded through the boiler throttling valve to the lower pressure, with such vapor then being superheated and utilized to heat and roll the turbine.

In employing these above-mentioned procedures, however, costly additional apparatus is required including vapor and liquid separating vessel and associated valves and piping, which equipment is only being used during start up and shut down operating periods. The considerable investment represented by this equipment is therefore not economically employed. Furthermore, during an initial phase of the start up procedures as hereinabove described, a turbine by-pass line must generally be made use of, such line leading from a point between the superheater and the turbine shut-off valve to a low pressure region, for instance the hot well of the condenser.

While the present invention still makes use of the boiler throttling valve, it discloses an improved apparatus and method for starting a forced flow once-through vapor genorator which does not require start up apparatus such as separating vessel with associated valves and iping, nor does it make use of a turbine by-pass for raising the temperature of the vapor to a temperature suitable for rolling the turbine.

The objects of the present invention accordingly include an improved apparatus and method for starting a vapor generator of the forced flow once-through type with only vapor entering the finishing superheater; with such object being obtained without the use of auxiliary vapor for starting the turbine; without the use of a separating bottle or vessel and associated valves and piping; without the necessity of providing a turbine bypass for starting up purposes; and without the requirement of adhering closely to given pressure and temperature conditions in the vapor generating portion before the high pressure fluid in said portion canbe expanded to the lower pressure prevailing in the vapor heating portion of the vapor generator, so that only vapor is produced therein.

Other objects and advantages will become apparent as the description of illustrative embodiments of the invention proceeds. The novel features which are considered characteristic of the invention are set forth with particu- 3,1893% Patented June 15, 1965 larity in the appended claims. These claims as well as the following description of the invention will best be understood when read in conjunction with the accompanying drawing in which:

FIG. 1 is a representation of a vapor power plant system in the form of a flow diagram incorporating one em: bodiment of the present invention as characterized by pressure differential means being provided tor maintaining the liquid level in the convection superheater at a desired elevation.

'FIG. 2 is a diagrammatic illustration of the pressure indicating means in the form of diaphragms.

FIG. 3 is a portion of a vapor power plant similar to that illustrated in FIG. 1, however, including mechanical means for indicating the liquid level in the convection superheater and maintaining said level at a desired location.

Referring now to the drawing in which like reference characters are used throughout to designate like elements the diagrammatic representation of FIG. 1 discloses a forced flow one-through vapor generator 10. A feed pump 12 is organized to supply Working fluid to vapor generator 19 from a working fluid source 14 by way of conduit 16. To control or shut-oil? the flow of working fluid a feed valve 18 is provided in conduit 16. The working fluid passes serially through economizer 2t), conduit-

s

21 and 22, vapor generating tubes 24 lining the wall-s of furnace chamber 25, tubes as, header 23, conduit 39, convection superheater 32, conduit 34, finishing vapor superheater 36 and conduit 38, to a point of use such as vapor turbine 40. A valve 42 is provided in conduit 38 to shut ofl the flow of the working fluid to turbine 40. After having given up the major portion of its thermal energy in turbine 44] the working fluid vapor is condensed in condenser 14 and returned to the vapor generator via feed pump 12.

Fuel and air for combustion are supplied to vapor generator It) by way of burner 44 in any conventional manner. The hot combustion gases produced by the burning of the -fuel pass in heat exchange relation over the heat absorbing surfaces of the vapor generating tubes 24, final superheater 36, convection superheater 32 and economizer 20- To maintain a minimum safe velocity in the vapor generating tubes 24 during .start up and low load operation a recirculating circuit 46 is provided for returning a port-ion of the fluid that is leaving header 28 for passage to convection superheater 32 through conduit 30, to the inlet of vapor generating tubes 24 by way of mixing vessel 48 and recirculating pump 50. A valve 52 permits control or stoppage of the flow of fluid recirculating through circuit t6. As an alternative to recirculation during start-up or low load operation, excess fluid can be discharged to waste through drain line 54 for the purpose of maintaining a minimum velocity in furnace tubes 24. To control flow through conduit 54 a boiler extraction valve 55 is provided.

As earlier mentioned hereinabove it has been found of advantage in starting up once-through vapor generators to make use of a shut-oft and throttling device for separating the vapor generating portion 25 from .the

vapor superheating portion

32 and 36. In practice this device comprises a shut-off valve 56 and a throttling valve 57 arranged in bypass relation with valve 56. The purpose of bypass valve 57 is to obtain throttling with high pressure drop and small flow quantities, while the main shut-off valve 56 is designed for relatively low pressure drops and large flow quantities.

By employing

boiler throttling valves

56 and 57 it is possible to commence start-up operation of the superheating and turbine portion without much delay after the startup procedure for the vapor generating portion has begun. To accomplish this, however, superheated vapor must be furnished to the turbine by the finishing superheater 36 long before such vapor could be produced by the vapor generating tubes 24 at normal operating pressure and tempera-ture. Furthermore, while a large amount of heated gases are released in furnace chamber 25 for bringing the operating fluid up to operating pressure and temperature,

the radiant heating surface of finishing superheater 36 must be protected from the heat of these gases during the final period ofthe start-up operation ofthe vapor generating section. Since it is undesirable to utilize operating fluid in the liquid state for this purpose vapor must be available for cooling the finishing superheater 36 long beforethe vapor. generator is capable of furnishing such vapor at normal operating temperature and pressure.

In accordance with the invention this is accomplished f by operating the primary or convection superheater 32 as a vapor generator, producing vapor at a pressure initially considerably lower than the pressure normally at,-

tained in the vapor generating portion 24 ofthe gen erator. I c To maintain a desired'liquid level 58 in the convection superheater 32 when operating it as a vapor gen- V finishing superheater 36 for "for being superheated therein.

cooling the tubes thereof and After a suitable pressure and temperature has been reached in conduit 38 as indicated by pressure sensing device 74 and temperature sensing device 76 valve 42 is being opened to admit superheated vapor to turbine 40 l for rolling and heatingiof the same. a v

q As the liquid in convection superheater 32 is being evaporated, superheated and conducted to the turbine additional. fluid is being admitted by'way of valve 57 .in response to a lowering of the liquid level 58. As

earlier described herein this can be accomplished by the pressure differential indicating device 60 receiving pressure impulses through

diaphragms

64 and 66 as illustratively shown in FIG; 2, or receiving an indication of the liquid level elevation by'means of float 68 and lever systom 65? as shown in FIG. 3. I

7 With turbine. 40 thus being provided with a source of superheated vapor, while the temperature of the fluid in'the, vapor generating portion is being ,raised to the normal temperature necessary for generation of vapor,

tion superheater 32 can be allowed to evaporate.

a'point in thestart-u'p operation of the unit will eventually be reached when all of the liquid in the convec- The temporary function of superheater 32 of evaporating liq uid is thereby gradually replaced by thenormal function 67 and float 68 are shown for indicating theliquid level' 58 and for conveying such indications to transmitter 70. Other conventional apparatus, for indicating the location of the liquid level may housed in connection with the present invention.

According to the invention the start-up operationiof' the vapor generator includes the following steps:

With

valves

56 and 57 closed, working fluid is pumped through economizer 20 and furnace tubes 24 and dis charged through conduit 54 to a point of lower pressure.

ing the'heating of the fluid in tubes 24 recirculation of fluid isestablished through these tubes bymeans of re-,

circulating pump 50, with the recirculated flow being such that a minimum safe velocity is always maintained in,

tubes 24. Obviously, but in a less economical manner such safe velocity could also be maintained by discharging a suificient quantity. of the Working fluid byway of conduit 54 and valve 55. a V, a

The above mentioned predetermined fluid temperature measured atpoint 72 usually correspondsto atempera-i ture of the combustion gases flowing over finishing superheater 36 at which it becomes unsafe to operate-the unit without flowing a cooling medium such as vapor through the tubular heating surface of "finishing superheater-36.

57 is gradually beingwopened permitting high pressure fluid to flow into convection superheater' 32, with tur g bine valve 42 controlled to maintain a desired lower pressure therein. Pressure indicating devices 73 are provided to show the pressure drop across valves 56 and57.

Because of the lower pressure prevailing in superheater 32 and 36 a portion of the high pressure fluid flashes into vapor with'the remaining liquid establishing a liquid level 58. Convection superheater 32accordingly now operates as a vapor generator absorbing heat from the combustion gases flowing thereover. The saturated'vapor thus produced by flashing and evaporation flows into ing point.

After this so-called clean-up operation, valve 55 1 is closed or set to open at a predetermined high pres- Accordingly, at this point of theoperating procedure valve thereof of superheatingithe vapor. in vapor generating portion 25 increases, a greater pro- As] the temperature portion of vapor is being produced by flashing, with the liquid level insuperheater 32 receding to the vanishing point. Or, as the pressures in'vapor generating portion 25 and superheating

portions

32 and 36 approach equality, less and less of the total vapor is'being produced by flashing and moreand. more by evaporation in tubes 24 as the liquid level in superheater 32 recedes to the vanish- As soon as substantially equal pressures are established ,across

valves

56 and 57 as'observedby pressure sensing device 73 these valves will be fully opened and the vapor generator operated under normal operating conditions and control. V The present invention of amethod and apparatus for starting up, a once-through vapor generating power plant accordingly offers the'following important advantages:

While heretofore it was deemed desirable if not essential toemploy a' vapor and liquidseparating vessel with associated-valves and piping between the

boiler throttle valves

56,57 and superheaters 32,136, such auxiliary equipment is not required when starting up a once-through vapor generator in accordance with the teaching of the present invention. v

While some start-up procedures as heretofore practiced required inlieu of a vapor and liquid separating vessel the adhering to very critical conditions of pressure and temperature of the fluid in the vapor generating section 25, before this fluid could be expanded through the

boilerthrottling valve

56, 57 so that only dry steam would result from such expansion, the present invention does not require adherence to such critical conditions of pressure and temperature. 7 c

Whilein the majority of start-up procedures ofoncethrough forced flow vapor generators the use of a turbine by-pass is' a dominating feature essential for successfubstart-up of the power plant, such turbine by-pass can be eliminated when starting up a power plant of the above-named type in "accordance with the present invention.

, While specific embodiments of the invention havebeen shown and described herein, it will be apparent to those skilled in the art that various changes, specifications, substitutions, additions and omissions may be made without departing from the spiritand scope of the invention as set forth in the appended claims.

What I claim is:

1. A method of starting a forced flow once-through vapor generator having a first heating section including vapor generating furnace walls and having a second heating section including a primary superheater and a finishing superheater said heating sections being directly connected and being serially arranged for flow of a vaporizable fluid therethrough; said method comprising the following steps:

(1) maintaining a body of heated working fluid at a predetermined relatively high pressure in said first heating section;

(2) flowing working fluid from said first heating section directly to said primary superheater, while reducing the pressure thereof from said high pressure down to a predetermined low pressure maintained in said primary superheater said low pressure being such that a partial flashing of said fluid into vapor occurs, so as to obtain a body of vaporizable fluid and a body of vapor, and establish a fluid level in said primary superheater;

(3) generating additional vapor from said body of vaporizable fluid in said primary superheater and passing vapor to said finishing superheater for superheating therein;

(4) conducting said superheated vapor to a point of use; and

(5) controlling the fiow of vaporizable fluid from said first heating section to said primary superheater to establish and maintain the fluid level in said primary superheater within desired limits.

2. A method of starting up a forced flow once-through steam generator having a tubular first heating section and having a tubular second heating section including a primary superheater and a finishing superheater said heating sections being directly connected and being serially arranged for flow of water and steam therethrough; said method comprising the following steps:

(1) producing and maintaining a body of heated water at a predetermined 'supercritical pressure in said first heating section only;

(2) flowing water from said first heating section directly to said primary superheater, while throttling it from said supercritical pressure down to a predetermined subcritical pressure maintained in said primary superheater and finishing superheater, said subcritical pressure being such that a partial flashing of water into steam occurs, so as to obtain water and steam in said primary superheater and steam only in said finishing superheater;

(3) generating additional steam from said water in said primary superheater. and passing steam to said finishing superheaters for superheating therein;

(4) conducting said superheated steam to a point of use; and

(5) controlling the flow of water from said first heating section to said primary superheater to establish and maintain a water level in said primary superheater within desired limits, while the steam generated in said primary superheater passes to said finishing superheater and to said point of use.

3. A method of starting up a forced flow once-through vapor generator having a first heating section including vapor generating furnace walls and having a second heating section including a primary superheater and a finishing superheater said heating sections being directly connected and being serially arranged for flow of a vaporizable fluid therethrough; said method comprising the following steps;

(2) recirculating said body of heated working fluid from the outlet of said furnace walls directly to the inlet thereof;

(3) flowing working fluid from said first heating section directly to said primary superheater, while reducing the pressure thereof from said high pressure down to a predetermined low pressure maintained in said primary superheater said low pressure being such that a partial flashing of said fluid into vapor occurs, so as to obtain a body of vaporizable fluid and a body of vapor, and establish a fluid level in said primary superheater;

(4) generating additional vapor in said primary superheater and passing vapor to said finishing superheater for superheating therein;

(5) conducting said superheated vapor to a point of use; and

(6) controlling the flow of vaporizable fluid from said first heating section to said primary superheater to 1 establish and maintain the fluid level in said primary superheater within desired limits.

4. A method of starting up a forced flow modified oncethrough vapor generator having a first heating section including vapor generating furnace walls and having a second heating section including a primary superheater and a finishing superheater said heating sections being directly connected and being serially arranged for flow of a vaporizable fluid therethrough; the invention comprising feeding vaporizable fluid to said first heating section only; heating said vaporizable fluid by supplying heat to said first and second heating sections; permitting a first overflow of heated vaporizable fluid from said first heating section to a point of lower pressure for fluid cleanup purposes; discontinuing the feeding of vaporizable fluid to said first section while recirculating said fluid from the outlet of said furnace walls directly to the inlet thereof to maintain the flow velocity in said furnace walls above a predetermined minimum velocity; discontinuing said first overflow and raising the pressure in said first heating section to a predetermined value in excess of that prevailing in said second heating section; permitting a second overflow from the relatively high pressure region of said furnace walls to the relatively low pressure region of said primary superheater said excess of pressure being such that a partial flashing of said fluid into vapor occurs, so as to obtain a body of vapor and a body of vaporizable fluid in said primary superheater and to establish a liquid level therein; generating vapor from said body of vaporizable fluid in said primary superheater and flowing said vapor from said primary superheater to said finishing for superheating therein; conducting said superheated vapor to a point of use; and re-establishing a controlled flow of vaporizable fluid to said steam gtfenerator consistent with the flow of vapor to said point 0 use.

'5. In a forced flow once-through vapor generator having a first heating section and having a second heating section including a primary superheater having a bottom inlet and a top outlet and a finishing superheater said heating sections being directly connected and being serially arranged for flow of a vaporizable fluid therethrough; the combination comprising:

( 1) means for maintaining a body of heated vaporizable fluid at a predetermined relatively high pressure in said first heating section;

(2) means for flowing water from said first heating section directly to the bottom inlet of said primary superheater;

(3) means for throttling said fluid from said high pressure down to a relatively low pressure maintained in said primary superheater with said low pressure being such that a partial flashing of said fluid into vapor occurs, so as to obtain vapor and liquid and establish a liquid level in said primary superheater;

(4) means for generating vapor in said primary superheater;

(5) means for passing vapor from the top inlet of said primary superheater to; said finishing 'superheater;

(6) means for superheating said vapor; (7) means for conducting said superheated vapor to a point of use; .s

(8) means for controlling'the flow of fluid from first heating section tosaid primary superheater' so as to establish and maintain the liquid level in said 'pri mary'superheater within desired limits; and

(9) means for feeding vaporizable fluid to said first heating section in conformity with the flow of superheated vapor to said point of use.

6. ,In a forced flow modified'once-through steam generator having a first heating section including steam generating furnace walls and having a second heating section including aprimary superheater and a finishing superi said waterby supplying a heating medium to said steam generator in heat exchange relation with the heating surfaces thereof including said furnace walls, a primary superheater and finishing superheater; relief valves means for limiting the pressure in said first heating section to a predetermined value and for permitting a first overflow ofheated water'due to expansionvthefreoffrom said first heating section to a point of lower pressure; shut-off means for discontinuing 'the feeding of water to said first. section; means for recirculating said water from a point downstream of the outlet of saidfurnace walls to the inlet thereof to maintain atpredetermi ned minimum flow velocity in said furnace walls;'s hut-'oif means for discontinuing said; first .overflow;'throttling means for heater said heating sections being directly connected and 7 beingserially arranged for flow of water and steam there through; the combination comprising: s means for maintaining a body of'heated water at a predetermined supercritical pressure in said'first heat,- ing section; 1

means for recirculating heated Water from the putlet' of said furnace walls directly to the inlet thereof; smeans for flowing water from said'first heating section directly to said primary superheater;

means, for throttling said water from sald supercritical pressure down'to the subcritical pressure maintained in said primary superheatersaid low pressure being such that a partial flashing of water'into steam occurs, a so as to obtain waterand steam and establish a water 7 level in said primary superheater; means for generating steam in said primary superheater; meansfor passing steam to'said finishing superheater; 7 means for superheatingfsaid steam; r means for conducting said superheated steam to a point of use; I i

means for controlling the flow of water from said first heating section to said primary superheater so as to establish and maintain the water level in said primary superheater within desired limits; and V 7 means for feeding water to said body of water in conformity with the flow of superheated steam to said point of use. 7. In a forced flow modified once-through steam generator having a first, heating section" including steam. generating furnace walls, and having a second heating section including aprimary superheater and a finishing superheater, said heating sections being serially arranged for flow of water and steam therethrough; the combination comprising valve means for shutting oif flow from i said first to said second heating section; means for feeding water to said first heating section; means for heating means for controlling saidflow'into said primary superheater such as to maintain said water 'level at a desired elevation; means for superheating the steam received from said primary superheater in said finishing superheater and conduct it to a point of use; and meansfor re-establishing a flow of feedwater to said steam generator consistent with the flow of steam to said point of use.

8. The organization defined in-claim 7 wherein said means for indicating the water level in said primary superheater and for maintaining the same at a desired elevation comprises means for obtaining'a static pressure differential between the inlet and the outlet of said primary superheater and means for. regulating the flow from said first heating section to said primary superheater in response to variations in said pressure differential.

References Cited by the Examiner UNITED STATES PATENTS 1,767,714 6/30 Stender 122-406 3,019,774 2 /62 Beyerlein.

OTHER REFERENCES Strohmeyer: Large Sub and SupercriticaI Steam Generator Startup and Control System Integration With The Turbine Generator, reprint of paper presented at American Power Conference, Marchv 1962.; FIGS. 5 and 7 and pages 6-10 in'particular.

PERCY L; PATRICK, Primary Examiner. MEYER PERLIN, Examiner.

UNITED STATES PATENT OFFHHZ CERTIFICATE OF CORRECTION Patent No. 3,189,006 June 15, 1965 Edward L. Kochey, Jr.

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

Column 6, line 50, after "finishing" insert superheater Signed and sealed this 30th day of November 1965.

(SEAL) lkllest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. A METHOD OF STARTING A FORCED FLOW ONCE-THROUGH VAPOR GENERATOR HAVING A FIRST HEATING SECTION INCLUDING VAPOR GENERATING FURNACE WALLS AND HAVING A SECOND HEATING SECTION INCLUDING A PRIMARY SUPERHEATER AND A FINISHING SUPERHEATER SAID HEATING SECTIONS BEING DIRECTLY CONNECTED AND BEING SERIALLY ARRANGED FOR FLOW OF A VAPORIZABLE FLUID THERETHROUGH; SAID METHOD COMPRISING THE FOLLOWING STEPS: (1) MAINTAINING A BODY OF HEATED WORKING FLUID AT A PREDETERMINED RELATIVELY HIGH PRESSURE IN SAID FIRST HEATING SECTION; (2) FLOWING WORKING FLUID FROM SAID FIRST HEATING SECTION DIRECTLY TO SAID PRIMARY SUPERHEATER, WHILE REDUCING THE PRESSURE THEREOF FROM SAID HIGH PRESSURE DOWN TO A PREDETERMINED LOW PRESSURE MAINTAINED IN SAID PRIMARY SUPERHEATER SAID LOW PRESSURE BEING SUCH THAT A PARTIAL FLASHING OF SAID FLUID INTO VAPOR OCCURS, SO AS TO OBTAIN A BODY OF VAPORIZABLE FLUID AND A BODY OF VAPOR, AND ESTABLISH A FLUID LEVEL IN SAID PRIMARY SUPERHEATER; (3) GENERATING ADDITIONAL VAPOR FROM SAID BODY OF VAPORIZABLE FLUID IN SAID PRIMARY SUPERHEATER AND PASSING VAPOR TO SAID FINISHING SUPERHEATER FOR SUPERHEATING THEREIN; (4) CONDUCTING SAID SUPERHEATED VAPOR TO A POINT OF USE; AND (5) CONTROLLING THE FLOW OF VAPORIZABLE FLUID FROM SAID FIRST HEATING SECTION TO SAID PRIMARY SUPERHEATER TO ESTABLISH AND MAINTAIN THE FLUID LEVEL IN SAID PRIMARY SUPERHEATER WITHIN DESIRED LIMITS.