US2387998A - Vapor generation - Google Patents

Description

Search Room I h I-IYUIL! llLfta U10 CROSS REFERENCE 4?; VAFORFZ S,

G. w. KESSLE R VAPOR GENERATION 3 5 Oct. so, 1945.

Filed July 15, 1942 2 Sheets-Sheet 1 IIIIIIIIIIII/I/I zzvmvroa George'Wifessler A TI'ORNE Y UHUSS REFERENUI: bfifii'C'ii h0g3? z; var-{Trim Oct. 30, 1945. e. w. KESSLER VAPOR GENERATION Filed July 15, 1942 2 Sheets-Sheet 2 I N V EN TOR. George W/ ess/er -A ITORNE Y Patented Oct. 30, 1945 VAPOR GENERATION George W. Kessler, New York, N. Y., asslgnor to The Babeoclr 8r Wilcox Company, Jersey City, N. .L, a corporation of New Jersey Application my 15, 1942, Serial No. 450,964

6 Glaims.

The present invention relates in general to the construction and operation of tubular vapor generating. units incorporating a plurality of.independently fired furnaces and. a'vapor superheati'ng device arranged for effective control oi vapor superheat temperatures over a relatively wide load range, and more particularly, to the construction and operation of water tube steam. boilers of the character described for use in the marine field.

The main object of my invention is the provision of a steam generating. unit of the character described. having a plurality of independently controllable furnaces connected to a common heating gas outlet and particularly characterized by an improved construction and airrangement of the steam generating and superheating, surface of the unit relative to the furnaces and gas outlet which aflord an effective controI of superheat temperatures over a wide load range, adequate protection of the steam superheater at starting-up and. low Ioad periods, heating gas temperatures at the. superheater permitting the use of carbon steelor the lower grades of heat resisting alloy steel for the superheater tubes, a substantial reduction inthe size of superheater, a low pressure dlfierential between the furnace chambers, a high overall thermal ethciency, and a reduction in size, weight and. cost for a given capacity unit.

The various features of. novelty which characterize my invention are pointed outwith particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should. be had. to the accompanying drawings and descriptive matter in which I have fuel burners. are located. The pressure parts of the unit include an upper horizontally arranged steam and. water drum 20, a laterally offset lower water drum 2t connectedto the drum 20 by an inclined, bank. of steam generating. tubes 22, and a second lower water drum or header 23 horizontally arranged below the drum. 20 and connected thereto by a substantially vertical. bank of steam generating. tubes 24; A row of water tubes 25 extends downwardly from the drum 20 along the roof section [B and side wall. I to a horizontally arranged wall header 25 at approximately the level of the. drum 23.

The described spaced groups of steam generating tubes, in coniunction with the front and rear inner walls, define a main furnace chamber between the. tube banks 22' and 24, and an auxiliary furnace chamber 3| between the tube groups. 26 and 25. The fornace chambers 31! and 3| are independently fired by separate groups oi liquid fuel bumers 33 and 3E respectively arranged, to discharge horizontally through corresponding, burner ports formed. in the front wall l0. As shown, the four burners 33 are arranged in the lower part of the furnace wall "I, three being in arow parallel to the inclination of the tube bank 22,, while the four fuel burners 34 are arranged in. supe p sed relation in. a row parallel to the tube bank 24 and illustrated and described a preferred embodiment of my invention 0f the drawings:

Fig. I is a sectional elevationoi a marine steam generating unit embodying my invention; and. FlFigI. 2 is a section taken on the line 2-2. of

The steam generating unit illustrated has a setting of substantially horizontal rectangular cross-section formed. by a double-walled casing including inner and outer front walls [0 and H respectivehp inner and outer rear walls [2 and 13 respectively, and inner and outer side walls M and I 5 respectively with upper inclined roof portions. l6 and l T. respectively. The opposite side of the unit is defined by inner and outerwalls 58 and [9 respectively. The spaced walls of the setting serve as flow passages for combustion air entering one or more air-inlets 2'! in the rear portion of the setting, the air flow cool-- ing the walls andbeing preheated during its passage to the double front of the unit where the the. lower part of the tubes 25. In all cases the burners. are spaced a-suihcient distance from the steam generating tubes to prevent. flame impingement thereon and permit stable ignition and combustion conditions regardless of the number of fuel burners in operation. The number of fuel burners provided and their relative location is dependent upon the load and total steam temperature requirements. The upper portion of the setting at the. outer side of the tube bank 22 is provided with a. beating gas outlet 411 through which flow all of the heating gases generated in the unit. Auxiliary heating surface, such as an economizer or air heater 41, is positioned in the gas outlet M1 at approximately the level oi the drum 2!]. The described arrangement of the furnaces, steam generating parts and heating gas outlet is particularly adapted; for marine service in view of the adaptability or such units for arrangement in pairs and the permissible compact arrangement of the deck openings for the stack connections (not shown).

The steam generating surface is constructed and arranged to provide a maximum thermal efliciency and a low draft loss tor the unit In one embodiment of the invention having a total evaporation at full power rating of approximating 122,500 pounds of steam per hr, the outboard row of tubes 25 is formed. by 2" 0.. D. studded tubes on 3 /1." centers covered refractory material 3. The vertical tube bank 24 is formed by two outer staggered rows of tubes on each side of 2" O. D. on 3%," centers and six inner staggered rows of 1" 0. D. tubes on 1 /2" centers. Thetube bank 22 isformed by four staggered rows of 2" O. D. tubes on 4%" centers along its furnace side and fifteen staggered rows of l" O. D. tubes on 1 /2" centers outwardly spaced therefrom. The upper ends of the generating tubes 22, 24 and 25 are bent t enter the bottom of the drum 20 radially and are distributed over substantially the entire exposed surface of the drum, insuring proper ligament strength and adequate protection of the exposed section of the drum. The exposed portions of the drums 2| and 23 are similarly protected. The circulation requirements of the unit are supplied by downcomer tubes from the drum 20 psitioned in the air spaces between the front and rear double walls, the downcomers 44 serving the side wall header 26, downcomers 45 serving the drum 23, and downcomers 46 serving the drum 2|. The wall tubes 25 can be extended to the drum 23, if desired, eliminating the necessity for the header 26 and downcomers 44.

The bottom of each of the furnace chambers 30 and 3| is closed by a trough-shaped refractory floor 58, the inclined sides of which are extended upwardly to the corresponding drums and header. Additional exposed refractory surface for the furnace 30 is provided by a short vertical partition wall or baflle 59 extending from the drum 23 to approximately the center line of the uppermost burner 33. The baflle is formed by studding the corresponding portion of the adjacent tube row 24 and applying initially plastic refractory to the studded tube portions. The baflie 59 serves in operation to deflect heating gases from the furnace chamber 3| away from the main ignition and combustion section of the furnace chamber 30, while its restricted height provides a substantial amount of gas flow area across the tube bank 24 for the gases from the furnace 3|, lessening the gas pressure differential across the tube bank 24.

In some steam generating units of the general character described the steam superheating has been accomplished by superheating surface positioned within the tube bank 24 in the space occupied by the small diameter tubes. A substantial amount of superheating surface will be required in such a location, since only the heating gases from the auxiliary furnace chamber traverse the superheater, i. e. only a portion of the total heating gases generated in the unit. In such installations it is usually necessary to use high grade heat resistant alloy steel tubes to insure protection from the high temperatures to which the superheater tubes are liable to be exposed in this location. Such a superheater location is also objectionable in installations where the auxiliary or superheater furnace is liable to be operated intermittently and allow condensate to an undesirable extent in the superheater tubes.

In accordance with my invention, the steam superheating requirements of the unit are entirely supplied by a convection type superheater located in the space defined between the large diameter or water screen tubes and the remaining portion of the tube bank 22. The superheater is formed by a multiplicity of single looped horizontally extending nested tubes 5| having their ends connected to inclined headers 52 and 53 arranged parallel to the tube bank 22 and positioned between the double walls at one end of the unit. As shown, the headers are located be.-

tween the rear walls I2 and I3 and the corresponding section of the front walls I0 and H is made removable to facilitate replacement of the superheater tubes. The superheater tubes are all supported by plates 54 carried by some of a group of large diameter inclined support tubes 55 positioned within the superheater tube loops and connecting the drums 20 and 2|. The superheater headers are divided by transverse diaphragms to provide a three-pass flow path for the saturated steam entering the upper part of the header 52 and discharging from the lower part of the header 53 to its point of use. The number of passes for the steam in the superheater and the specific arrangement of the same with respect to gas flow is dependent upon the load and total steam temperature requirements. In addition to the main steam outlet 56 on drum 20, an additional outlet 51 is provided for the separate withdrawal of saturated steam directly from the drum.

With the described construction and arrangement of the parts the unit can be started up by the operation of one or more fuel burners in either the main furnace 30 or auxiliary furnace 3|. It is preferable however to use one or more of the auxiliary furnace burners 34 for startingup, due to the additional protection to the superheater afforded by the tube bank 24 in the flow path of the heating gases from the auxiliary furnace. When the main furnace burners are used for starting-up, more care must be exercised in bringing the unit up to steaming pressure and temperature. The presence of the rows of tubes 22 at the furnace side of the superheater adequately reduces the temperature of the heating gases before contacting with the superheating tubes, when the burners 33 are used at startingup. As the amount of steam flowing through the superheater increases, the burners 33 in the main furnace are put into service, as well as additional burners 34 in the auxiliary furnace. Due to the positioning of a substantial amount of convection heated heat absorbing surface between the furnace chambers, the heating gases from the auxiliary furnace 3| are reduced in temperature before entering the furnace chamber 30 and contacting with the generating tubes 22 and superheating tubes 5|.

The superheater is thus screened from the furnace chamber 30 by four rows of tubes 22 and from the furnace chamber 3| by the entire tube bank 24 in addition. By varying the operation of the fuel burners 33 and 34 the effectiveness of convection heat absorbing surface in the path of the gases contacting with the superheater, and correspondingly the temperature of those gases, can be varied over a wide range. Usually during normal operation a major portion of the fuel will be burned in the main furnace chamber 30 and the furnace chamber 3| operated to supplement the steam generating capacity of the boiler or to provide lower temperature heating gases for regulating superheat temperatures. With the dc? scribed capacity for variablefiring of the furnaces and variable heat absorption of the convection heated surface in the path of the heating gases contacting the superheater, a constant superheat temperature can b maintained over the normal range of operating loads.

For limited ratings one or more burners 34 of the auxiliary furnace can be fired and all of the steam generated by the unit removed directly from the drum 20 through the auxiliary saturated steam outlet 51. With only burners 34 in operasamos ation and all of the steam passed through the superheater, substantially saturated steam can be obtained at low ratings. At higher ratings, due to the relatively large amount of heat absorbing surface between the auxiliary furnace and the superheater, very low superheat temperatures can be obtained.

The described relative arrangement of heat absorbing surface and furnaces is also advantageous in permitting a reduction in the amount of the superheating surface required, since all of the heating gases generated in either furnace provide convection heating of the superheater tubes. i. e. approximately 2 to 2 times the amount of heating gases usually contacting with a superheater located within the tube bank 2|. The lower. gas temperatures at the superheater result in a lower tube wall temperature and the permissible use of carbon steel or low grade steel alloy for these tubes. The number of steam passes through the superheater is likewise reduced, thus reducing the pressure drop through the superheater.

The formation of the tube bank between the two furnaces entirely of closely spaced vertical water tubes increases the thermal efficiency, minimizes space requirements for a given steam generating capacity, and affords improved protection for the associated drums; The absence of superheater headers in this location permits a better arrangement of downcomer tubes and reduces the number of downcomers which extend circumferentially around the steam drum.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the'apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. A vapor generating and superheatin unit comprising a setting, an upper vapor and liquid drum, a bank of inclined vapor generating tubes having their upper ends connected to said drum, a second tube bank of substantial depth and open throughout a major portion of the tube height and consisting solely of rows of vertically extending vapor generating tubes arranged to be heated mainly by convection and having their upper ends connected to said drum, a furnace chamber arranged between and having opposite sides defined by said tube banks, a second furnace chamber at the opposite side of said second tube bank, said second tubebank defining the gas outlet side of said second furnace chamber, means for independently and variably firing each of said furnace chambers, the vapor superheating surface of said unit consisting solely of a vapor superheater screened from said first furnace chamher by a plurality of rows of tubes of said first tube bank, the number of tube rows and heat absorbing capacity of said second tube bank being substantially greater than the number and heat absorbing capacity of the tube rows of said first tube bank screening said superheater from said first furnace chamber, a single heating gas outlet for said setting at the opposite side of said first tube bank from said first furnace. chamber, and said furnace chambers, tube banks, superheater and gas outlet being so relatively arranged that substantially all of the heating gases from both of said furnace chambers fiow across said superheater and the heating gases from said second furnace chamber flow across a major portion of the height of the tubes in said second tube bank and through said first furnace chamber prior to flowing across said first tube bank and superheater.

2. A vapor generating and superheatlng unit comprising a setting, an upper vapor and liquid drum, a main bank of inclined vapor generating tubes having their upper ends connected to said drum, a second tube bank of substantial depth and open throughout a major portion of the tube height and consisting solely of rows of vertically extending vapor generating tubes arranged to be heated mainly by convection and having their upper ends extending to and directly connected to the lower portion of said drum over a substantial circumferential area of said drum, a'furnace chamber arranged sublacent to said drum and between and having opposite sides defined by said tube banks, a second furnace chamber at the opposite side of said second tube bank, said second tube bank defining the gas outlet side of said second furnace chamber, means for independently and variably firin each of said furnace chambers, the vapor superheating surface of said unit consisting solely of a vapor superheater screened from said first furnace chamber by a plurality of rows of tubes of said first tube bank, said second tube bank having a heat absorbing capacity at least thirty per cent of the heat absorbing capacity of said first tube bank and substantially greater in number of tube rows and heat absorbing capacity than the number and heat absorbing capacity of the tube rows of said first tube bank screening said superheater from said first furnace chamber, a single heating gas outlet for said setting at the opposite Side of said 4.0 first tube bank from said first furnace chamber,

and said furnace chambers, tube banks, superheater and gas outlet being so relatively arranged that substantially all of the heating gases from both of said furnace chambers flow across said superheater and the heating gases from said second furnace chamber flow across a major portion of the height of the tubes in said second tube bank and through said first furnace chamber prior to flowing across said first tube bank and superheater.

3. A vapor generating and superheating unit comprising a setting. an upper vapor and liquid drum, a bank of inclined vapor generatin tubes having their upper ends connected to said drum, a second tube bank of substantial depth and open throughout a major portion of the tube height and consisting solely ofrows of vertically extending vapor generating tubes arranged to be heated mainly by convection and having their upper ends extending to and so directly connected to said drum as to occupy substantially the entire drum circumferential area between said first tube bank and said setting. a furnace chamber arranged subiacent to said drum and between and having opposite sides defined by said tube banks, a second furnace chamber at the opposite side of said second tube bank, said second tube bank definin the gas outlet side of said second furnace chamber, means forming a baille extending along the lower portion of said second tube bank at the first furnace chamber side thereof, burner means in an end wall of said setting for independently and variably firing each of said furnace chambers, the vapor superheating surface of said unit consisting solely of a nace chamber by a. plurality of rows of tubes of said first tube bank, the number of tube rows and heat absorbing capacity of said second tube bank being substantially greater than the number and: heat absorbing capacity of the tube rows of said first tube bank screening said superheater from said first furnace chamber, a single heating gas outlet for said setting at the opposite side of said first tube bank from said first furnace chamber, and said furnace chambers, tube banks, superheater and gas outlet being so relatively arranged that substantially all of the I heating gases from both of said furnace chambers flow across said superheater and the heating gases from said second furnace chamber fiow across a major portion of the height of the tubes in said second tube bank, over said bafile and through the upper part of said first furnace chamber prior'to fiowing across said first tube bank and superheater.

4. A steam generating unit comprising a setting, an upper steam and water drum, a lower laterally offset water drum, a main bank of vertically inclined steam generating tubes having their ends connected to said drums, a second lower drum below said upper drum, a, second tube bank of substantial depth and open throughout a major portion of the tube height and consisting solely of rows of vertically'arranged steam generating tubes arranged to be heated mainly by convection and having their ends extendin to and directly connected to the lower portion of said-upper drum and second water drum, means for bottom supporting said tube banks and drums, a furnace chamber arranged subjacent to said upper drum and between and having opposite sides defined by said tube banks, a second furnace chamber at the opposite side of said second tube bank, said second tube bank occupying the gas outlet side of said second furnace chamber, means for independently and variably firing each of said furnace chambers, the steam superheating surface of said unit consisting solely of a. steam superheater screened from said first furnace chamber by a plurality of rows of tubes of said first tube bank, the number of tube rows and heat absorbing capacity of said second tube bank being substantially greater than the number and heat absorbing capacity of the tube rows of said first tube bank screening said superheater from said first furnace chamber, a single heatin gas outlet for said setting at the opposite side of said first tube bank from said first furnace chamber, and said furnace chambers, tube banks, superheater and gas outlet being so relatively arranged that substantially all of the heating gases from both of said furnace chambers flow across said superheater and the heating gases from said second furnace chamber flow across a major portion of the height of the tubes in said second tube bank and through said first furnace chamber prior to flowing across said first tube bank and superheater to said gas outlet.

'5. A steam generating unit comprising a setting, an upper steam and water drum, a lateral- 1y offset lower water drum, a bank of vertically inclined steam generating tubes having their ends connected to said drums, a second lower water drum directly below said upper drum, a second tube bank of substantial depth and open throughout a major portion of the tube height and convapor superheater screened from said first fursisting solely of rows of vertically arranged steam generating tubes arranged to be heated mainly-by convection and having their ends extending to and directly connected to the lower portion of said upper drum and second water drum for a substantial circumferential sector of said drums, means for bottom supportin said tube banks and drums, a furnace chamber arranged subjacent to said upper drum and between and having opposite sides defined by said tube banks, a second furnace chamber at the opposite side of said second tube bank, said second tube bank occupying the gas outlet side of said second furnace chamber, means for independently and variably firing each of said furnace chambers comprising a group of fuel burners in an end wall of said setting arranged to discharge into the lower part of said first furnace chamber and a group of superposed fuel burners in an end wall of said setting substantially symmetrically arranged relative to said second furnace chamber, the steam superheating surface of said unit consistin solely of a steam superheater screened from said first furnace chamber by a plurality of rows of tubes of said first tube bank, said second tube bank having a heat absorbing capacity at least thirty per cent of the heat absorbing capacity of said first tube bank and substantially greater in number of tube rows and heat absorbing capacity than the number and heat absorbing capacity of the tube rows of said first tube bank screening said superheater from said first furnace chamber, a single heating gas outlet for" said setting at the opposite side of said first tube bank from said first furnace chamber, and said furnace chamber, tube banks, superheater and gas outlet being 50 relatively arranged that substantially all of the heating gases from both of said furnace chambers fiow across said superheater and the heating gases from said second furnace chamber flow across a major portion of the height of the tubes in said second tube bank and through said first furnace chamber prior to flowing across said first tube bank and superheater.

6. The method of generating and superheating steam which comprises burning fuel in a furnace chamber to generate high temperature heating gases, simultaneously burning fuel in a second furnace chamber to generate high temperature heating gases, directing the heating gases from said second furnace chamber over a substantial amount of steam generating surface receiving heat mainly by convection heating and absorbing sufficient heat to reduce the temperature of the heating gases from said second furnacechamber substantially below' the temperature of the heatin gases generated in said first furnace chamber, directing the lower temperature heating gases from said second furnace chamber through said first furnace chamber in mixing relation with the heating gases generated therein, passing all of the steam to be superheated solely over steam superheating surface receiving heat mainly by convection heating, directing substantially all of the mixed heating gase in convection heat transfer relation with said superheating surface, and varying the fuel burning rates in one or both of said furnace chambers to vary the temperature of the mixed heating gases directed to said superheating surface and thereby the final superheat temperature.

GEORGE W. KESSLER.

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