US2420647A - Vapor generator - Google Patents

Description

20, w47. L, BOLAND 2,420,647

VAPOR GENERATOR 1NVENTOR. Edward L Boland ATTORNEY May 20, 1947- E. 1 BOLAND k 2,420,647 VAPOR GENERATOR Filed July s. 1942 2 sheetslsheet. 2

ATTORNEY Patente'd May 20, 1947 UNITED STATES PATENT OFFICE 2,420,647 VAPORLGENERATOR Edward L. Boland, East Orange, N. J., assignor to The Babcock & Wilcox Company, Jersey City, N. J., a corporation of New Jersey Application July 8, 1942, Serial No. 450,109

3 Claims.

The present invention relates to marine power plant installations of the geared turbine type having a separate astern turbine or turbine stage for stopping and backing, and more particularly to installations of this type incorporating a steam reheat cycle in which the steam for the astern turbine orturbine stage does not pass through the reheater, and in which under stand-by conditions and in port the installation must be operated to supply saturated o-r superheated steam for the auxiliaries with no flow through the reheater.

The general object of my invention is the provision of a steam generating unit which is particularly adapted for use in a marine power plant installation of the character described. A further and more specific object is the provision of a steam generating unit having high thermal efflciency, an arrangement and proportioning of the superheater surface therein providing a steam superheat temperature within safe operating limits at all times, a capacity for maintaining constant superheat and reheat steam temperatures, and adequate protection of the reheater during periods ci low or no steam ow therethrough` The various features oi novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this speciiication. For a better understanding of the invention, its operating advantages and specic objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. l is a simpliiied diagram of the piping lay-out between the steam generating unit and associated turbines;

Fig. 2 is a sectional elevation of a steam generating unit constructed in accordance with my invention; and

Fig. 3 is a horizontal section taken on the line 3 3 of Fig.v 2.

In one marine power plant installation of the reheat cycle type for which rny improved steam generating unit is particularly adapted, steam is supplied to a high pressure turbine at a pressure of approximately 1250 p. s. i. and temperature of '750 F. The steam is then expanded through the high pressure turbine and delivered to a reheater at an inlet pressure of approximately 230 p. s. i. and then reheated at this reduced pressure to its initial temperature of '750 F. The reheated steam then passes serially through the intermediate and low pressure turbines of the installation. In the use of a reheat cycle in a marine installation certain operating conditions peculiar to marine service must be given special consideration. With a separate astern turbine or turbi -e stage for stopping and backing the vessel, the steam i or the astern turbine is not passed through the reheater. Under such conditions a greater amount 0f fuel is required to be burned in the main boiler furnace for iull speed astern than for normal speed ahead. The resulting increased volume of hot gases' contacting the superheater under such conditions is likely to cause heating of the superheater tubes above the desired superheat temperature and possibly beyond a safeoperating temperature. Furthermore, the generating unit must be operated under stand-by conditions and in port to supply saturated or superheated steam or the auxiliaries with no new through the reheater.

The use of a separate steam heated reheater in an installation of the character described. has been proposed. Steam reheat however, is less eicient than combustion gas reheat because the reheat temperature using live steam as the heating medium is limited to the saturation temperature corresponding to the boiler steam pressure. Due

to this inherent limitation, the full possibilities y of the reheat cycle cannot be utilized, whereas with combustion gas reheat the steam can be reheated to any temperature the materials used will stand, permitting, for example, reheating to the original superheated steam temperature.

The steam generating unit illustrated in Figs. 2 and 3 is in general of the double furnace single uptake type illustrated in the copending application of Edward J. Rooney, Ser. No. 228,734,

tiled Sept. 7, 1938, now U. S. Patent 2,332,534, The unit comprises an upper horizontally elongated steam and water drum lll, a laterally offset bottom supported lower water drum i i connected to the drum IIJ by a vertically inclined main bank of steam generating tubes l2. A second bottomsupported lower water drum I3 is positioned below the drum and connected thereto by laterally spaced groups of Water tubes lil. The space within the setting between the tube groups l2 and lll forms the main furnace chamber l5, in

l the double front of which a pair oi liquid fuel burners I5 are horizontally arranged. The portion of the setting at the opposite side of the tube groups i4 serves as an auxiliary furnace chamber Il which is independently fired by liquid fuel burners I8. The outer side wall of the furnace chamber I1 is coole-d by a row of refractory covered tubes I9 having their lower ends connected to a side wall header Z and their upper porti-ons sloping along the furnace roof and connected to the drum IS.

A common heating gas outlet flue 25 for the furnaces I5 and I'I is arranged at the outer side of and above the main tube bank l2. A tubular economizer 26 and air heater 2l are located therein for increasing the thermal eihciency of the unit. The setting is of the double walled type, permitting a flow of combustion air therethrough to the double front of the unit and the air registers of' the fuel burners I6 and I3. Downcomer tubes 28 are arranged within the rear double wall of the setting for supplying water from the drum I5 to the drums I I and I3 and header 25.

In accordance with my invention the steam superheating surface of the unit is divided into two spaced sections, a primary superheater section receiving heat by convection from the auxiliary furnace only, and a secondary superheater section receiving heat by convection from both the main and auxiliary furnaces. The primary section is formed by a group of horizontally looped nested tubes 33 extending between a pair of vertical headers Sil and 35 at the front end of the unit, the header 34 being subdivided to provide a two-pass steam ow through the primary section and steam inlet and outlet connections thereto. The primary section is positioned in the upper part of the vertically elongated space 35 between the groups of water tubes I 4 and supported by plates carried by large diameter water tubes SI extending between the drums It) and I3. The secondary superheater section is arranged within a space 38 within the tube bank I2 and consists of an inclined row of looped tubes 4! extending between a pair of inclined headers lll and 42 extending parallel to the tubes I2 and subdivided to provide a three-pass steam flow therethrough. The tubes do are similarly supported by large diameter tubes 44 extending between the drums Ill and II. The headers 34, 35, (1I and l2 are positioned in the front double wall of the setting so that access thereto is not blocked by the downcomer tubes 28. The upper end of the header Sil is connected to the drum IE). The header il is connected at its upper end to the steam outlet of the header 34, while the lower end of the header 42 is connected to the steam line leading to the high pressure turbine. Where saturated steam is required for the auxiliaries, a branch connection is led from the secondary superheater outlet to a coil within the water space of the drum Ie for desuperheating steam for the auxiliaries, as indicated in Fig. 1.

A steam reheater is also incorporated in the unit and arranged in a location permitting eilicient operation of the unit whenever superheated steam with no reheating is desired while affording ample protection to the reheater during such periods, and in addition providing an accurate control of the reheated steam outlet temperature when the reheater is in operation. The steam reheater is formed by horizontally arranged nested rows of single looped tubes 50 occupying the remaining portion of the space 3S between the tube groups I 4. The tubes 55 have their ends connected to vertical headers 52 and 53, which may be separate or, as shown, integral with the superposed headers 34 and 35 respectively. The header 52 is subdivided to provide a two-pass steam flow through the reheater with a steam inlet connection at the upper end of the header and reheated steam outlet at the lower end. The

tubes are supported from the water tubes 31 in the same manner as the primary superheater tubes 33. The row of water tubes I4 adjoining the main furnace I5 have their lower portions provided with metallic studs and refractory to dene a partition or baffle 55 extending from the drum I3 substantially the full height of the reheater. The partition 55 provides an effective protection from flame radiation for the reheater when the main furnace I5 alone is operated. Such protection is essential during periods of low or no steam ow through the reheater. The partition 55 is also advantageous in tending to confine the flow of heating gases from the auxiliary or reheater furnace I1 to the portion of the main furnace I5 substantially above the level of the fue] burners I6 therein, thus avoiding interference with fuel ignition and combustion in the main furnace chamber. Short tube bales 56 and 51 at the lower and upper ends of the space 5t at the auxiliary furnace chamber side thereof direct the flow of heating gases from that furnace across the primary superheater section and reheater.

In operation, both the main and auxiliary furnaces are capable of generating steam and providing superheat. Reheating is provided by the operation of the auxiliary furnace alone. When reheating is not required, such as in startingup or port operation or movements of the vessel astern or during maneuvering, the main furnace l5 alone is used. The reheater section of the unit is normally put in service after approximately one-fourth power has been reached and steady operation or increased power is expected. The reheat temperature is gradually built-up to avoid undue strains in the piping and turbines. The amount of fuel required in the main furnace for full astern operation. is approximately one and one-half times that required for normal speed ahead in the same furnace. The subdivision of the superheating surface into two sections and the location of th'e primary section out of the path of the gases from the main furnace prevents a total rise in the superheated steam temperature under such maximum operation of the main furnace alone above a predetermined value, such as 750 F., and thereby prevents the steam temperature to th'e astern turbine stage from exceedinga safe operating limit. In the full power ahead condition appreciably less fuel is burned in the main furnace, so that the resulting temperature of the steam heated in the secondary superheater section alone would be well below '750 F. The controlled operation of the auxiliary furnace under such conditions for heating the primary superheater section and reheater insures the delivery of superheated steam to the high pressure turbine and reheated steam to the intermediate pressure turbine at the desired temperatures.

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:

l. A steam generating unit comprising a setting, an upper steam and water drum, a laterally oiset lower water drum, an inclined bank of steam generating tubes connecting said drums, a second lower water drum below said upper drum, a vertical bank of steam generating tubes connecting said upper drum and second water drum, said tube banks defining opposite sides of a main furnace chamber therebetween, means forming an auxiliary furnace chamber at the outer side of said vertical tube bank, means for independently firing said furnace chambers, a heating gas outlet at the outer side of said inclined tube bank for receiving all of the heating gases from both of said furnace chambers after flowing over the tubes of said inclined tube bank, a primary superheater section arranged in the upper part of said vertical tube bank, a secondary superheater screened from said main furnace chamber by tubes of said inclined tube bank and arranged to be traversed by heating gases from both' of said furnace chambers, a steam reheater arranged in the lower part of said vertical tube bank, and means forming a partition extending between said reheater and main furnace chamber and arranged to shield said reheater from flame radiation from said main furnace chamber.

2. A steam generating unit comprising a setting, an upper steam and water drum, a laterally offset lower water drum, an inclined bank of steam generating tubes connecting said drums, a second lower water drum below said upper drum, a vertical bank of steam generating tubes connecting said upper drum and second water drum, said tube banks defining opposite sides of a main furnace chamber therebetween, means forming an auxiliary furnace chamber atl the outer side of said vertical tube bank, means for independently firing said furnace chambers, a heating gas outlet at the outer side of said inclined tube bank for receiving all of the h'eating gases from both of said furnace chambers after flowing over the tubes of said inclined tube bank, a primary superheater section receiving steam from said upper drum and having looped tubes arranged in the upper part of said vertical tube bank, a secondary superheater in series with said primary sectionrand screened from said main furnace chamber by tubes of said inclined tube bank and arranged to be traversed by heating gases from both of said furnace chambers, a steam reheater having looped tubes arranged in the lower part of said vertical tube bank, a common tube support for said primary superheater and reheater looped tubes, and means forming a partition extending between said reheater and main furnace chamber and arranged to shield said reheater from flame radiation from said main furnace chamber.

3. A steam generating unit comprising a setting, an upper steam and water drum, a laterally offset lower water drum, an inclined bank of steam generating tubes connecting said drums, a second lower water drum below said upper drum, a vertically extending bank of steam generating tubes connecting said upper drum and second water drum, said tube banks defining opposite sides of a furnace chamber therebetween, means forming a, second furnace chamber at the outer side of said vertical tube bank, means for independently ring said furnace chambers, a heating gas outlet at the outer side of said inclined tube bank for receiving all of the heating gases from both of said furnace chambers after flowing over the tubes of said inclined tube bank, a superh'eater section receiving steam from said upper drum and having looped tubes arranged within the upper part of said vertical tube bank, a separate steam reheater having looped tubes arranged Within the lower part of said vertical tube bank, a common tube support for said superheater and reheater looped tubes, and means forming a partition positioned between said reheater and rst named furnace chamber and arranged to extend from said second lower water drum to substantially the fullheight of said steam reheater so as to shield said reheater tubes from flame radiation from said first named furnace ch'amber.

. EDWARD L. BOLAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS l Number

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