US2217512A - Steam boiler - Google Patents

Description

Oct. 8, 1940.

E. H. DONLEY STEAM BOILER Filed Nov. 13, 1936 Fig.7

/2s "6 JI 2 Sheets-sheaf. 1

1N VENTOR;

Ear] H Don/8y Eng? m ATTORNEY.

Oct. 8, 194-0. E DQNLEY 2,217,512

STEAM BOILER Filed Nov. 13, 1936 2 Sheets-Sheet 2 1N VENTOR.

Ear] H. Doniey Eam- W ATTORNEY.

Patented Oct. 8, 1940 UNITED STATES 2,217,512 STEAM BOILER Earl H. Donley, Elizabeth, N. J., assignor to The Babcock & Wilcox Company, Newark, N. J., a

corporation of New Jersey- Application November 13, 1936, Serial No. 110,564

11 Claims.

This invention is concerned with improvements in steam boilers.

In modern water tube steam boilers and especially in large boilers of the type used in stationary service to supply steam for turbo-electric generators, recent experience has demonstrated clearly that certain conditions are necessary in order that the maximum of practical efiiciency may be attained, and many of these conditions 10 are difficult to fulfill. Relatively high steam pressures must be used in the interest of eiiiciency, and, for turbine use, the steam must not only be superheated to higher temperatures as steam pressures rise, but it is of considerable im- 15 portance that the total steam temperature shall remain substantially constant over a wide range of boiler loads. This is particularly important in the operation of large central power stations which are subject to daily peak load demands.

20 For the protection of superheater metal against overheating when steam flow is'deficient or absent as, for example, when a boiler is being started up, the superheater must be screened to a considerable extent from furnace radiation. It is 35 therefore, heated mainly by convection from the furnace gases. Such a convection superheater when designed for a safe metal temperature and desired superheat at full boiler load will be deficient in superheating capacity at fractional loads, but the factors which require the desired superheat at :full load are still efiective at fractional loads. f It is an object of this invention to correct this difficulty in a reliable manner.

Modern boiler practice has also demonstrated 35 the advantages of the use of economizers to heat the boiler feed water from feed temperature up toward or to the temperature of the saturated steam, and to provide an economizer installation which, in some instances, may also generate some steam. When full advantage'is taken of such possibilities of good economizer practice, it is unnecessary to interpose any water tubes of the boiler circulating system between the gas outlet from the superheater and the gas inlet to the economizer. Therefore, any' otherwise satisfactory means for keeping the total steam temperature at a substantially constant value must also cooperate with economizers receiving gasesdirect- 50 ly from the superheater and not impair theoperation of the former. It is an object of this invention to provide such means for keeping the total steam temperature at av substantially constant value over a wide range of boiler loads, but

5 maintaining the metal temperature within safe limits in a water tube boiler in which the gases leaving the superheater pass directly into the economizer.

Other objects of the invention will appear as the description proceeds.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings which illustrate preferred forms of apparatus for attaining the desired results.

- In the drawings:

Fig. 1 is a view in the nature of a vertical section of a stoker-fired steam-power installation illustrating the teachings of the invention,

Figs. 2, 3, and 4 are diagrammatic views showing different embodiments of the invention some- What in vertical section. v

The'drawings show the superheater tube surface divided into two sections and connected in series as to steam flow. Fig. 1 indicates the primary superheater section 10 receiving steam from an inlet header 12 connected by a conduit I 6 to the outlet header l8 of the secondary superheater section 20. The latter receives steam from the boiler drum 22 through the conduit 24 and the 25 inlet header 26. The superheated steam passes from the outlet header 28 to a point of use.

The Fig. 1 embodiment also indicates the economizer tube surface as divided into two sections. They are connected in series as to water flow, 0

r and one of the sections may be a steaming economizer section.

As shown, the primary economizer section 30 receives feed water through an inlet 32 and discharges the feed water through its outlet header 34 and a conduit 36 to the inlet header 38 of the secondary economizer section 40. From the latter, water, or water and steam passes through the outlet connections 42 to the water space of the drum 22. Both economizer sections are illustrated having a counter flow relation of water flow and gas flow.

These four elements, the two superheater sections and the two economizer sections, are arranged within gas passes in such a manner as to permit variation and regulation of the rate of 46 gas flow over one section of the superheater and one section of the economizer without changing the rate of gas flow over the remaining economizer and superheater sections, and the primary superheater section II) is shielded from the furnace 44' by a radiant heat screen indicated as a bank of steam generating tubes 46. All of the furnace gases leaving the radiant heat screen flow over the tubes of the superheater section it) at all times, and all of the furnace gases subsequently flow over the tubes of the primary economizer section 30 at all times, that is. at all boiler loads. After the furnace gases have left the primary superheater section III they may flow wholly in one of two paths before they reach the second section 30 of the economizer, or they may divide so as to flow partly in one path and partly in the other. In one of these two paths the secondary superheater section 20 is located, and in the other, the secondary section 40 of the economizer is disposed.

When all of the furnace gases flow in one of these two alternate paths intermediate the ends of the entire gas path, they sweep the superheater section 20, and when divided between these two paths some of the gases sweep over the tubes of the economizer section 40 and some over the superheater 'section 20. In either case the gases are substantially cooled before they reach the economizer section 30.

Regulators 50, only one of which is shown, located at the gas outlet of the superheater section 20, and between that section and the economizer section an, control the flow of gas over the section 20 while similar regulators 52 control the flow of gas through the gas path in which the economizer section 40 is located, At full boiler load the regulators may be so set as to cause all of the furnace gases to flow over the economizer section 40 and none over the secondary superheater section 20, the surface areas and gas flow rates being so related that the desired total steam temperature is maintained and the temperature of the superheater metal kept within safe limits. When the boiler is operating at a lower load the steam temperature will decrease if the same setting of the regulators is .maintained but such a decrease is prevented by changing the setting of the regulators so that a part of the gas stream now passespyer thesuperheater section 20 while the remainder continues to flow over the economizer section 40. Thus, superheat and steam temperature will be controlled by the regulators. Automatic control of regulators in response to changes in total steam temperature and in steam flow may be effected by connecting the regulators with such control apparatus as that indicated in Patent 2,131,058.

It is also to be understood that the apparatus described herein may be so operated that the gases may be divided so as to flow partly over the economizer section 40 and partly over the superheater section 20 at full boiler load, superheat control at lower boiler loads being secured by diverting a larger fraction of the furnace gases over the superheater section 20.

Referring to the embodiment indicated in Fig. 2'of the drawings, one of the superheater sections includes a radiant superheater 53 of the wall tube type. It is shown as receiving its steam from an inlet header 54 and the conduit 56 connected to the outlet header 58 of the superheater section 60. Thelatter receives its steam from an inlet header 62 and the conduit 64 connected to the steam space of the boiler drum 66. Steam flows from the outlet header 68 of the superheater 52 to the inlet header ID of a third superheater section I2 from which the steam is transmitted to a point of use. The gas flow in the embodiment of invention illustrated in Fig. 2 is the same as that described in reference to the Fig. 1 embodiment and the regulators and economizer sections are similarly arranged.

The Fig. 3 embodiment of the invention eliminates such elements as the regulators '14 of the Fig. 2 embodiment and also eliminates any superheater corresponding to the superheater section 60, the superheat being controlled by proportioning gas flow between the gas pass of the superheater section I6 and the economizer section 18, the latter having sufficient tube area so that when the regulators are open that section of the economizer imposes a greater resistance to gas flow than that imposed by the superheater section I6. The superheater section I6 and the radiant superheater section 82 of this embodiment are connected in a manner similar to the manner in which the sections 52 and 12 of the Fig. 2 embodiment are connected.

In the Fig. 4 embodiment of the invention the primary superheater section 84 extends across parallel gas passes 86 and 88 which are divided by the wall 90. tion 92 receives its steam from the section 84 and the former is disposed within the gas pass 86. One economizer section 94 is disposed across the entire gas flow, extending across the outlets of the gas passes 86 and 88, as shown. The second economizer section is located within the gas pass 88 and superheat is controlled by regulators 98 arranged at the outlet of the gas pass 88.

It will be understood that the furnace instal lation shown in Fig. l of the drawings is merely representative, and that the invention is not limited thereto. Other furnaces, such as slag tap furnaces may be used. Fig. 1 indicates a stoker fired furnace including a chain grate is not limited thereto but that it may apply to other tubes or boilers such as bent-tube boilers. The particular sectionalheader boiler shown in Fig. 1 includes the uptake headers IIO connected by circulators H2 to the drum 22. At the opposite ends of the steam generating tubes 46 are the downtake headers II4 connected at their upper ends to the water space of the drum 22 by the downtakes H6.

The boiler indicated in Fig. 1 also includes circulators I28 which support the wall I22 separating the gas pass of the superheater section II] from the gas pass of section 20. The tubes I20 are connected at their upper ends to a header I24 supported by circulators I28 which establish communication between the drum 22 and the header I24. Fig. 1 also discloses an air heater I30 through which the furnace gases pass from the economizer section 30 on their way to the final outlet flue.

Under some operative conditions and with certain proportioning of the tube surfaces in the be employed to prevent the cooling of theffurnace gases below the dew point when moisture deposits on the economizer tubes and takesrpart in chemical reactions which cause tube-damage.

"Without proper control of furnace gas tempera- 'tures such 'damageifrequently occurs at-low boiler f loads.

It is to be'understood thattheinventionisnot necessarily limited to boilers which include 'economizers, nor is it .limited to superheaters which are shielded from furnace :radiation. BID some instances, water tubes of the boiler circulating system may replace the economizertubes in wholeor inpart without'changing the'eifece .tiveness of the control .of isuperheat. "E'fiective control of superheatmayalso :be'obtained when the first section of the superheater is partly tor wholly directly exposed to .furnaceradiation. .It is also to be understoodthat the-'relative-pos'itions of the different sections of the :heating surfaces may be widely varie'd solong'asthe illustrative sequential flow conditions are:maintaine'd. The invention .is also applicable to the maintenance .of superheat'control under various circumstances. For instance, the invention may be employed to compensate for a decrease inisuperheat capacity caused by tube deposits 'resulting'from long continued operation, or from undesirable feed water conditions.

I claim:

1. In .a steam boiler, axfumace, a steam generating :section including a bank of tubes "exposed tothe heat of the furnace, aprimary superheater ina'position which isremotefromthe steam generating section, a primary :economizer section,

means providing a'plurality of gas passes arranged-in parallel between-said superheater and said "economizer section, a secondary economizer section .in one of saidparallel gas passes, a secondary superheater in another of said parallel gas passes, andmeansfor proportioning the total gas flow between said parallel gas passes for .maintaining a predetermined superheat over a pparallel gas passes, :and means for connecting the superheaters so that steam flows from the pri- .mary superheater to the secondary superheater.

3. .In asteam'boiler, a steam generating section including abank oftubes extending across a'gas pass, a primary superheaterincluding tubes beyond the steam agenerating section, a primary economizer section, :means providing a plurality of gas passes arranged in parallel between said superheater and said economizer section, a sec- .ondaryeeconomizer section in oneof said parallel gas passes, asecondary'superheater in another of said ,parallel :gas passes, :means for proportioning the total gas'fiow between saidjparallel gaspasses,

:means connecting the :superheaters for the series flow of steamtherethroug'h, and means similarly connecting the economizersifor the series flow of water therethrough'tolthe steam generating sec- .tion.

4'. In asteam 'boiler, -a steam generating section including tubes extending across a gas pass, a {primary superheaterincluding tubes beyondthe steamgenerating section, a primary economizer section,'meansproviding a plurality of gasipasses arranged in parallel between :said superheater "and said economizersectionca second-economizer section in one o'isaidparallel gas-passes, a second superheaterrin. another of 'saidparallel gas-passes,

and regulators 'at the gas inlets of the primary" "economizer for proportioning the total gas now between said parallel gas passesin order thatthe superheat may be maintained at substantially the same values over' a wide range of boiler load variation.

, I5. iIn a steam boiler,:a steam generatingsection including tubes extending across a gas pass,..a primary superheater including tubes beyond the steam generatinglsection, a primary economizer section, means providing a plurality of gas passes arranged in parallel between said superheater and saideconomizer section, a secondxeconomizer sectlonin one of said parallel gas passes, a'sec- 'ond superheater .in another of said parallel gas passes, .andregulatorsat the outlet of each ofthe parallelgas'passes for proportioning the total gas flow between said parallel gas passes to compensate for changes in the boiler load .and maintain .a desired superheat. 6. A water tube boilerhaving-a primary superheater subjected-to the heat of furnace gases in a relatively high temperature zone, a secondary superheater subjected to the .heat of furnace gases but located in aizone of relatively low gas temperatures, meansifor connecting the super- "heaters in series with reference to steam flow,

means to direct all of .the'furnace gases across the primary superheaten'means whereby the fur-' .nace vgasesleaving the primary superheater are dividedso as to flow in the same direction through parallel gas passes in-one of which the secondary superheater islocated, an economizer sectionzin another 'ofsaid parallel 'gasjpasses, means contacted ibythe gases :adjacent the ends of the parallel :gas'passes for :proportioning the flow "of fur- 'nacergases between said parallel gas passes ac- "cording'to the .load imposed on theboile'r, and another economizer section receivingthe flow of :all of the furnace gases after they have passed through one or both of said parallel gas passes.

'72 A-water tube boiler-havingla primary superheater subjected to the heat of fumace gases in a relatively high temperature zone, a secondary superheater subjected to the heat of furnace gases -but located-in a zone of relatively low gas temperatures, means for connecting the superiheatersin :series with reference to steam now, :means to direct all of the furnace gases across "the primary superheater, means whereby the .fumace gases leaving the primarysuperheater are divided so as to flow in the same direction through parallel gas passes in one .ofwhich the secondary superheater is located, an economizer section in another of said parallel gas passes,

means for proportioning the flow of furnace'gases between said :parallel gas passes, and another economizer section receiving the flow of 'alko'i' the furnace gases after they have passed through one or both .of said parallel gaspasses.

8. In a-water tube steam boiler, a steam generating section subjected'to the heat of furnace gases, means .for establishing three separateifluid heating-.zonesarranged serially in .thedirection of gas flow, the first and last of said zones being undivided while "thesecond zone is dividedin-to .a'

plurality of parallel gas passes, a primary superheater section in the first zone, a primary economizer having tubes arranged in the last zone and across the gas flow from both of said passes, the secondary superheater section arranged in one of the gas passes of the second zone, an economizer arranged in the other gas pass of the second zone, and regulators arranged forwardly of the third zone for controlling the proportioning of the gas flows in the parallel paths of the second zone to control superheater and economizer operation.

9. The method of operating a steam boiler and associated superheater and economizer which comprises efiecting heat exchange between high temperature furnace gases and water flowing in restricted and separated paths across the path of said furnace gases, causing said furnace gases to superheat steam flowing in restricted paths across the path of said gases beyond said restricted water flows (with reference to gas flow) and through a superheating zone, utilizing radiant heat of the furnace gases approaching the steam generating zone to further superheat the steam flowing in restricted paths from the first superheating zone, dividing the furnace gases beyond said superheating zone so that they flow in a plurality of paths, eflecting further superheating of the steam by the gases flowing in one of said paths, causing absorption of heat by feed water flowing in restricted paths across another of said paths, effecting a further absorption of heat by the feed water after the furnace gases flowing through said paths have been reunited, and counter-acting variations from a desired superheat temperature by apportioning the percentages of the total amount of gases passing through said gas paths in response to said variations and steam flow.

10. In the superheating of steam, causing a first absorption oi heat from high temperature furnace gases by steam flowing in restricted paths, subsequently dividing the stream of furnace gases so that it flows in a plurality of parallel gas paths, effecting a further superheating of the superheated steam in one of said parallel gas paths, causing an absorption of heat by feed water flowing in restricted paths across the path of the furnace gases in another of said parallel paths, apportioning the percentages of the total amount of gas flow through said parallel paths in response to variations of superheat from a desired value, and causing all of the gases from said parallel paths to pass over feed water of a lower temperature than that in one of the parallel paths, said lower temperature feedwater flowing through the combined gases and thence to the above mentioned restricted feedwater paths.

11. In a water tube steam boiler, steam generating tubes, a primary superheater section, a secondary superheater section in series with the primary section as to both steam and gas flow, a primary economizer section, a secondary economizer section in parallel with the secondary superheater section as to gas flow and in series with the primary economizer section as to waterflow, and means whereby at a given boiler load the gas flow over the secondary superheater section and the secondary economizer section is simultaneously controlled or varied while the gas flow over the primary superheater section and primary economizer section remains constant.

EARL H. DONLEY.

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