US2895456A

US2895456A - Method for generating vapor

Info

Publication number: US2895456A
Application number: US476943A
Authority: US
Inventors: George E Tate
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1954-12-22
Filing date: 1954-12-22
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21

Description

G. E. TATE METHOD FOR GENERATING VAPOR July '21, 1959 y 2,895,456

Filed Dec. 22, 1954 \\\\\\\\\\v\\\ywwv 5 -Y l INVENTOR G50/Paf E. 4 72172' ATlvl-INEY United StateSqPatent O `2,895,456 METHOD FOR GENERATING VAPOR George E. Tate, Summit, NJ., assignor to Foster Wheeler Corporation, New York, N.Y., al corporation of New York i This invention relates to vapor generators and more particularly to a method for generating vapor under rapid start-up conditions.

In some instances it is desirable to provide for rapid start-ups of a vapor generator from a shut-down or cold condition but such start-ups have adverse elfects on the Vapor generator. Foriexarnple, numerous startups and shut-downs cause failure of the pressure parts, such as superheater tubes and boiler tubes, which failure is due to overheating of the parts and consequent fatigue and loss of rupture strength in the tubes.

It is an object of the` present invention to provide a novel method for generating vapor under rapid start-up conditions and for tiring a vapor generator at highrates immediately after light-ott and throughout the wholestart-up period. x

The present invention, therefore, contemplates a novel method wherein a liquid, under pressure, lis provided in the vapor generating tubes and superheater tubes during light-oli of the vapor generator and throughout thewhole start-up period.

The above and other objects and advantages ofthe presentinvention will appear more fully hereinafter from a detaileddescription which follows, taken ,together with the accompanying drawing wherein thesingle figure thereof illlustrates a diagrammatic transverse section of an em.- bodiment of the invention. i

Referring to the drawing, the apparatus of the present invention is disclosed as embodying a vapor` generator 11 which comprises a setting 12 having avapor 4andliquid vessel 13 disposed'in the upper portion thereof, and a furnace. or combustion chamber 1 4 fired by `a plurality `of burners 15. A plurality of boiler or vapor generating tubes 16 are arranged in setting 12 in three spaced banks:

17, 18rand 19,; banks 18 and 19 having a baflle20 therebetween. The upper ends of the vapor generating tubes. of each bank are connected to vapor .and liquid vessel 13 while thelower ends ofthe tubes of` bank17fare `connectedto a liquid header 21 anda liquid drum22, and

those or" banks 18 and 19 yare connected to drum 22.

, A superheater 23,` comprising substantially Ufshaped;

superheater tubes 24, is disposed between banks 17and 18 and is providedwith a superheater inlet'header 25` and a superheater outlet header 26. A vapor conduit 13A is connected at one end to the upper portion of vessel 13 and at the other end to inlet header 25 to provide the latter with vapor during normal operation of the vapor An economizer 27 is disposed in a substan tially vertical gas passage 28 which discharges combustion generator.

gases from the setting. Economzer 27 comprises a tubular coil 29 which has an inlet 30 and an outlet 31.-A

feed pump `32is connected` to a `source of liquid `(not.

shown), as for example water, and at its'discharge side is connected to inlet 3i) of `economizer 27 by a conduit 33.`

Outlet 31 of economizer 27 is connectedto vessel ,13by a conduit 34 to provide the vessel with water. A valve 35i`s provided in conduit 33 tocontrolothe tiovv Jofwate, to economizer 27.` A bypass conduit 36 isY connected at' 4Patented July 21, 1959 nected at its other end to conduit 13A. A valve 37 is connected in line 36 to control ilow of water to inlet header 25. A superheater outlet conduit 38 is connected to outlet header 26 of superheater 23 and communicates the latter with a turbine 38A. A turbine shut-oit valve 39 and a throttling valve 40 are connected in outlet conduit 38 for controlling the flow and the pressure, respectively, of the superheated steam to the turbine. A bypass conduit 41 is connected to conduit 38 and at its other end to the condenser 41A. A valve 42 is arranged in line 41 and serves as a pressure controller during start-up of the vapor generator, as will be presently set forth hereinafter. A blow down conduit 43 is connected to the lower portion of vessel 13 and the line is provided with a valve 44 to control the ilow of liquid therethrough.

In operation, when the vapor generator is to be started up from a cold or shut-down condition, turbine shutott valve 39 and throttling valve 40 in conduit 38 are closed to lprevent ow to the turbine. Valve 44 in line Y 43 is also closed and valve 35 in conduit 33 is opened to provide flow of feed water from feed pump 32 to econo mizer 27. Water from economizer 27 llows into vessel 13 thence downwardly into vapor generating tubes 16 of banks 17, 18 and 19, and header 21 and liquid drum 22,

respectively. When economizer 27, vessel 13 and vapor` generating tubes 16 are completely lled with water, valve is closed to thereby eifect a completely sealed circuit from which the water cannot ilow. Valve 37, in conduit 36, is opened to provide ow of feed water through the following circuit: Feed pump 32, conduit 33, conduit 18l and 19 whence the gases pass' upwardly through gas,v i. passage 28 and in heat exchange relationship with tubular coi1129 of economizer 27.

Shortly after light-oli", the water in tubes 16 reaches a temperature slightly above the boiling-point at the metal- Wall interface. The water boils locally andthe main body of water in the tubes` is heated by condensation of some value, valve 37 yin line `36 and valve 42 in line` 41 closed, and valve 44 in blow down line`43 is openedtd or all the bubbles formed at the metal-wall interface. Sincer the system is completelytilled with water` and is closed, the pressure of `the water causes the latter to be subsaturated `that is, the pressure of-theliquid is in excess of the pressure at which vapor and liquid are in a state of thermo-dynamic equilibrium, so that the steam bubbles formed arenot large enough to cause the tubes to be.

come steam bound land thereby prevent circulation. Steam formed in the tubes `16 and which is not condensed therein flows toA `vessel 13 in r admixture with the subsaturated water the latter where the steam (bubbles) is confA densed to heat the water. Consequently, steam-free water,r flows from the drum into the downcomer tubes 16 away, from the furnace, and enters the heated or riser tubes 16,`

closer to the furnace, to provide for ready circulation `in the system; parts is prevented.` The superheater is also protected from overheating because of flow of fluid therethrough.` The system pressure is utilized to cause a flow of `fluidA through the superheater regulated in amount by valve 42, i to keep the,` superheater metal parts sufficiently cool atthe high initial tiring rate.I

l.When the temperature ofthe'water in the vapor` genL eratingelements reaches the desired or` rated temperature*Y Burners 15 are then ignited at a high firing rate.

Inlthis manner overheating of the boiler,`

decrease the level of the water in drum 13 to the normal l operating level. Valve 35 in conduit 33V is then opened to again provide flow of water to economizer 27 and turbine shut-off valve 39 and throttling valve 40 are also opened Vto permit flow of steam through line 381 and to the: turbiney ESA.

If some. steaming should occur in economizer 27, valve 35 may be opened slightly to provide water to the economizer, or a bypass conduit may be provided to bypass the valve 35 to deliver a small ilow of water to economizer during start-up. In the present description, they feed water pump is disclosed as pressurizing the water in the boiler but it is to be understood that any auxiliary pump, or other means may be employed for such pressurizing purpose.

It will now be apparent that the present invention provides a novel method for generating vapor under rapid start-up conditions to greatly reducel the time necessary for starting vapor generators as compared with conventional arrangements. The positive pressurizing of the boiler parts of the vapor generator causes the bulk of the water therein to be subsaturated under rapid start-up conditions, whereby circulation through the tubes is enhanced by virtue of minimum volume occupied by steam at the pressure maintained on the system. Consequently, overheating of the boiler parts of the vaporv generator is prevented. By providing a constant ow of water through the superheater during the start-up period overheating of the super-heater also is prevented.

inasmuch as various changes may be made in the particular form, location, and arrangement of parts of the apparatus disclosed and in the steps of the method and other sequences disclosed without departing from the principles of the invention, it will be understood that the invention should not be limited excepting by the scope of the appended claims.

What is claimed is:

l. A method for rapid start-up of a vapor generator to raise liquid therein to a temperature and pressure for the production of vapor, said vapor generator incl'uding a circuit containing a vapor and liquid vessel and vapor generating tubes in communication with each other, said circuit having an inlet and an outlet both incommunication with a source of liquid under pressure, the circuit inlet receiving liquid from said source and the circuit outlet being subjected to the pressure of said source and adapted to discharge vapors from said circuit, the steps comprising, conducting liquid from the liquid source to the circuit inlet to ll the vapor and liquid vessel and vapor generating tubes completely with liquid, closing off communication between the source of liquid and the circuit inlet but maintaining communication between the liquid source and the circuit outlet to prevent ilow of liquid from said circuit and to cause the pressure of said liquid source to be impressed upon the liquid in the circuit to thereby cause subsaturation of the liquid during start-up tiring of ther vapor generator, firing the vapor generator during start-up at a rapid rate until the liquid in the vapor generating tubes is raised to the desired temperature and pressure to produce vapor, withdrawing a portion of the liquid from the vapor and liquid vessel to reduce the liquid in said vessel to a normal operating level, cutting off communication between the source of liquid and the circuit outlet to permit discharge of vapors from the circuit, and reopening communication between the source of liquid and the circuit inlet to permit flow of liquid to the latter.

2. A method of rapid start-up of a vapor generator to raise liquid therein to a desired temperature and pressure to provide vapor, said vapor generator including a circuit containing a vapor and liquid vessel and vapor generating tubes in communication with each other, said circuit having an inlet and an outlet both in communicationy with a source of liquid. under pressure, the circuit i inlet receiving liquid from said source and the circuit outlet being subjected to the pressure of said source and adapted to discharge vapors from said circuit, and a superheater having an inlet in communication with the circuit outlet and with the source of liquid and having an outlet in communication with a vapor operated turbine, said superheater. outlet also being in communication with a condenser, the steps comprising, conducting liquid from the liquid source to the circuit inlet to till the vapor and liquid vessel and the vapor generating tubes completely with liquid, closing off communication between the source of liquid and the circuit inlet but maintaining communication between the source and the circuit outlet and superheater inlet to prevent ilow of fluid from said circuit and to cause the pressure of the source of liquid to be impressed upon the liquid in the circuit to thereby cause subsaturation of the liquid during start-up tiring of the vapor generator, cutting oif communication between the superheater outlet and the vapor operated turbine but maintaining communication between the superheater outlet and condenser to provide a ilow of liquid through the superheater and into the condenser during start-up, ring the vapor generator during start-up at a rapid rate until the liquid in the vapor generating tubes is raised to the desired tempera-l ture and pressure toproduce vapor, withdrawing a por-y tion of the liquid from the vapor and liquid vessel to reduce the liquid therein to a normal operating level, cutting off communication between the source of liquid andthe circuit outlet to permit discharge of vapors from the circuit, closing off connnunication between the superheater outlet and the condenser, reopening communication between the superheater outlet and the vapor operated turbine, and reopening communication between the source of liquid and the circuit inlet to permit flow of liquid to the latter.

3. A method for rapidi start-up of a vapor generator to bring liquid in the latter to a desired temperature and pressure for the production of vapor, said vapor generator including an economizer in communication with a feed liquid pump, a circuit containing vapor generating tubes and a vapor and liquid vessel in communication with each other, said circuit having an inlet in communication with the economizer and an outlet in communication with the feed liquid pump, the circuit inlet receiving liquid from said economizer and the circuit outlet being subjected tothe pressure of said feed liquid pump and adapted to discharge vapors from said circuit, and a superheater having an inlet in communication with the' circuit outlet and with the feed liquid pump and having an outlet in communication with a vapor operated turbine, said superheater outlet also being in communication with a condenser, the steps comprising, delivering liquid from the feed liquid pumpv to the economizer, passing the liquid from the economizer to the circuit inlet until the vapor and liquid vesselland the vapor generating tubes are completely lled with liquid, closing olf communication between the feed liquid pump and the economizer but maintaining communication between the feed liquid pump and the circuit outlet and the superheater inlet to prevent ow of iluid from the circuit and to cause the pressure of the feed liquid pump to be impressed upon the liquid in the circuit to thereby cause subsaturation of the liquid during start-up tiring of the vapor generator, cutting olf communicationJ between the superheater outlet and the vapor operated turbine but maintaining communication between the superheater outlet and condenser to provide a ilow of liquidv through the superheater and into the condenser duringl start-up, tiring the vapor generator during start-up at a rapid rate until the liquid in the vapor generatingA tubes is raised to the desiredA temperature and pressure to. produce vapor, withdrawing a portion of the liquid from the vapor and liquidY vessel to reduce the liquid therein. to a normal' operating level, closing olf communication between the feed liquid pump and the circuit outlet and superheater inlet to permit ow of vapors from the circuit outlet to the superheater inlet, cutting ofI" communication between the superheater outlet and the condenser and reopening communication between the superheater outlet and the vapor operated turbine, and reopening communication between the feed liquid pump and the economizer to permit [flow of liquid through the economizer and the circuit.

References Cited in the le of this patent UNITED STATES PATENTS FOREIGN PATENTS Switzerland Oct. 15, 1933