US2623505A - Steam generator with dust separator - Google Patents

Description

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M I O 2 M C 5 T T a. 7 E N m 3 E N l 2 S 8 9 W 6 E S 3 3 D I H 2 m a f m wo o o o Mo 0 w S w n N w J W 2 m m m m P o a o o o U w M] m o M 0 M w o n w w n c m Y 0 0 0 0 0 0 0 0 B A 5 I I L E /l\ W. H. ARMACOST STEAM GENERATOR WITH DUST SEPARATOR Dec. 30, 1952 Filed Feb. 26, 1947 Patented Dec. 39, 1952 STEAM GENERATOR WITH DUST sEPARAToB.

Wilbur H. Armacost, Scarsdale, N. Y., assignor, by

mesne assignments, to Combustion Engineering-Superheater, 1110., a corporation of Delaware Application February 26, 1947, Serial No. 731,086

2 Claims.

This invention relates to improvements in steam generators and in particular to an improved organization of the elements of a steam generating unit and dust separator.

The usual arrangement of the elements of steam generating units, with respect to the flow of products of combustion leaving the furnace, comprises a. furnace followed by heat absorbing surfaces including: some boiler surface serving as a screen for superheater surface, said superhea-ter surface, boiler convection surface, economizer surface and/or air heater surface. Whenever dust separators have been used to remove the fly ash from the flue gases these have generally been placed after the air heater and ahead of the induced draft fan with respect to the gas flow.

When burning certain fuels in a furnace, such as anthracite, it has been found that the fly ash or dust carried by the flue gases flowing through the steam generating unit causes objectionable abrasion of the heat absorbing surfaces and particularly abrasion of the air heater surface. To overcome this objection it has been proposed to locate the dust separator between the main bank of boiler convection surface and the air heater or the economizer, if present, to thereby effectively reduce the abrasion of the air heater and economizer surfaces by delivering dust-free flue gases thereto from the separator.

Furthermore, in the flow of gases through the various elements of the steam generating unit there may be unequal rates of mass flow for (lif ferent portions of the gases over the width of the heating surfaces due to unequal resistance in the flow paths of said different portions. Such unequal rates of flow will in turn cause unequal amounts of heat to be absorbed from the gases by the heat absorbing surfaces over said width resulting in a reduction of the average heat absorption by the apparatus at a given rating of the unit.

In large steam generating units there has been a recent tendency to have the passes through which the furnace gases flow across the heating surfaces of such proportions that the velocity of the gases therethrough are relatively low, result ing in lower resistances through said. passes and a consequent relatively lower power requirement to move the gases through the unit. Such lower resistances will increase the tendency to said un equal rates of gas flow because said unequal resistances will be a proportionately greater influence on the gas fiow compared to the lower total resistance through the unit.

It is an object of this invention to provide an improved arrangement of dust separator in a steam genera-ting unit to reduce abrasion of a large portion of th elements of heating, surface thereof while. providing by said novel arrange furnace A, boiler heating surf-ace B, a superheater C, a dust separator D and a heat exchanger 131.. As shown in Figure 1 fuel may be burnedfwithin the furnace as for example by a spreader. stoker F which delivers the fuel onto a traveling gr-ateG.

Referring to Figures 1 and 2, the furnace A comprises front wall I, side walls 2 and a roof 3 all of which may be faced with cooling tubes 4,

as shown on the front wall and roof. connected into the water circulation of the boiler. The rear furnace wall -5 is formed by a bafiie S mounted on the front row 9 of boiler tubes.

The boiler B proper comprises a lower water drum 1 and .an upper steam and water drum 8 into which the front row 9 of boiler tubes connect. A second row of boiler tubes it! and abank of boiler tubes H connect into. the top and bottom drums B and l as shown. The front iow of boiler tubes 9 extends from the lower drum l in transverse parallel arrangement upwardly to Within a distance from the roof whence every alternate tube is bent forwardly into the furnace to thereby be spaced from the remaining tubes and all of the tubes thus spaced extend upwardly into the upper drum 8. In this manner open lanes are provided between tubes through whi-chthe gaseous products of combustion from furnaceA pass. Bafiling E, which forms the rear wall of no furnace and is mounted on the front row of tubes 9, extends from the bottom drum 7 upwardly to the point at which the tubes are bent apart.

Mounted on the second row of boiler tubes I0 is bame l2 the top and bottom ends of said baffle being spaced from the top and bottom boiler drums 8 and 1 to provide passages therebetween for the gases. Mounted on the front row of the bank of boiler tubes I I is baffle I3 which extends from the upper drum 8 downwardly and has its bottom end spaced from the lower drum 1 to provide a passage L therebetween for the gases. The bottom Ma of battle I3 continues transversely across the bank of boiler tubes H in a generally downward direction and joins the top tube sheet [6 of dust separator D. Bafile I ia divides tube bank H into two portions, a smaller lower portion V and a substantially larger upper portion W. The smaller portion V in exposing to the gases a relatively small section of the boiler heating surface is so proportioned that the velocity of the gases is held relatively low, i. e., in the neighborhood of 40 ft. per second. The larger portion W of tube bank I I on the other hand presents to the gases the major portion of the boiler heating surface, over which the gases are made to flow following a sinuous path defined by cross baffles 13a, which confine the gases to a channel having a considerably smaller flow area than that presented to the gases by the lower tube bank portion V, said sinuous channel being so proportioned that the velocity of the gases flowing over the major tube bank portion W will be in the neighborhood of 65 ft. per second. A partition wall l5 spaced rearwardly from the bank of boiler tubes E l forms the rear wall of the gas pass through the bank of'boiler tubes. The

tending upwardly through top tube sheet I4 into which it is fastened, and with a dust outlet 34 discharging into hopper 2|. Between the walls of each cyclone 32 and the clean gas offtake 33 there are provided a multiplicity of circumferentially arranged gas deflecting vanes 35 (again see Figure 2). These vanes 35 receive the dust Lladen gas coming from the bottom portion of the bank of boiler tubes I and direct it to a whirl into the cyclone 32. The separated dust flows downwardly into hopper 2| while the clean gas flows upwardly through offtake 33 and thence into the upper portion of the tube bank H.

Figure '3 is similar in arrangement to Figure l excepting that the bank of boiler tubes shown in Figure 1 is omitted and that an additional section of superheater tubes SE is placed on the furnace side of bafiie 6' while a still further group of superheater tubes S is shown as following the dust collector D. A row of spaced boiler tubes .31

- extends into the furnace ahead of said superbottom of partition l5 j0i1ls the top wall N5 of dust separator D.

A hopper I? has a front wall 18 extending downwardly from the rear of lower drum land a rear wall l9 extending downwardly from the bottom tube sheet .29 of dust separator D. The side walls 2 of the furnace extend rearwardly to partition l5 and form a seal with the ends of bafiles 5,, I2, 13 and partition Dust separator D is provided with a dust collecting hopper 2|.

. Above dust separator D is located a heat exchanger E which in this instance is shown as an air heater having a bank of gas conducting tubes 22 fastened into top and bottom tube sheets 23 and 24 and is enclosed by an air chamber defined by rear plate 25, partition l5 and side plates 26 all of which make sealed connections with each other at their meeting edges and with the top and bottom tube sheets 23 and 24. An air intake 2] is provided at the top of the air chamber in plate and air ofitake connections 28 are provided .at the bottom of the air chamber in plates 26. Partitions 27a. and 28a extend across the tube bank 22 and guide the air in three passes thereacross. Top walls .29 and 3f! together with extensions of the side walls 2 form a passage for the gases leaving the bank of tubes l to pass into the top ends of the bank of gas conducting tubes 22. bottom of said bank of tubes 22.

The dust separator D is made about equal in width to the width of the bank of boiler tubes H (see Figure 2) so that the gases leaving the separator and flowing toward the bank of boiler tubes will be substantially uniformly distributed across the width of the bank when entering said upper portion of the bank. The dust separator D herein used for illustration comprises a multiplicity of similar dust separating units in this case small cyclone separators, extending substantially uniformly distributed across the width of separator D and are arranged for parallel paths of gas flow therethrough in substantially equal resistances. The bottom tube sheet 2c is provided with a multiplicity of holes into each of which is mounted one of the cyclone separating units 32.

Each separating unit 32 is provided with a COD- A gas offtake duct 3! is provided at the heater section 35 with respect to gas flow. The bafile IS in Figure '3 now forms the rear wall of the boiler and also forms a front wall for a chamber containing the heat exchanger E which, in this instance, is an economizer. The

rear wall 38 of the chamber for economizer ,E extends downwardly to the rear wall 39 of the dust separator D.

In operation of the apparatus shown by Figures 1 and 2, the gaseous products of combustion flow upwardly in the furnace A, thence across the top of baffle 6, thence downwardly through superheater C while some of the gases may flow downwardly throu h the bypassbetween'bafiles J2 and I3, thence across the bottom V of the bank oi tubes H. In the preferred embodiment of my invention illustrated in Fig. .1 .it :Will he noted that a large cross-flow area is presented to the gases so as to keep the velocity relatively low. In this manner erosion of tube surface by abrasiveflyash entrained in the gases is held within tolerable limits. After having their temperature reduced to a point where oxidation of the dust collectors surface ceases to be a problem, the gases pass through dust collector D wherein the gases are substantially separated from the fly ash. The clean combustion gases then how upwardly over the major portion Wiof tube bank ,II by way-of a sinuous path defined by bafiles 1.3a. The .flow

path over tube bank portion W is so proportioned that the velocity of the gases and consequently the heat transfer rate to the tube bank is high. Since the gases are substantially free of fly ash. abrasion of the tubes or tube cutting is considerably minimized or eliminated and yet high heat transfer and high economy in heating surface is assured. Upon leaving the bank of tubes H the gases pass downwardly through the gas tubes 22 of air heater E to be discharged through offtake 3|.

In Figure 3 where only the upper portion of the furnace is shown, the type of firing may be different from that shown in Figure 1 in that there may be provided means for burning pulverized fuel in the lower portion of the furnace, not shown. The products of combustion 'rise in the furnace A, a portion of which 'pass' upwardly and diagonally across the first superheater section 35. thence across the top of baflie thence downwardly through the second section of superheater C, thence through dust separator D, thence directly upwardly through the third superheater section S and finally through the economizer E to be discharged throuh offtake 40.

If the dust separator D is placed beyond the elements of the steam generating unit with respect to the gas flow it will have a lower resistance to gas flow than when it is placed ahead of certain elements, because of the increase in gas volume and temperature at the latter location. However, I take advantage of this fact and place the dust separator in an advanced location with respect to gas flow, substantially following the first superheater surface and ahead of the main body of boiler convection surface and/or economizer and air heater surf-ace. I use a dust separator of the type whose gas inlet preferably approximates the width of the heating surface with which the gases have last contacted, that employs a multiplicity of similar dust separating units arranged for parallel paths of gas flow therethrough of substantially equal resistance, that discharges the gases at a substantially uniform rate over the entire cross section of its gas outlet, and whose gas outlet approximately equals the width of the heating surface next following the separator.

This arrangement, together with the relatively high resistances through the separator units, has the effect of redistributing any unequal rate of flow of the gases occurring ahead of the separator. The gases leaving the separator are then delivered to the subsequent surfaces in substantially uniform distribution and rate of flow over the width of said surface and will insure a more uniform and improved heat absorption in these surfaces.

By so placing the dust separator, I establish new and useful purposes for it in that it delivers substantially dust-free gases to the subsequent elements of the heating surfaces and serves as a redistributor to deliver gases to said heating surfaces in substantially uniform distribution.

A further advantage of my new location of the separator is that the subsequent heat absorbing surfaces will be kept relatively clean and soot blowers may be dispensed with.

While I have shown and described the preferred embodiment of my invention, it will be understood that changes in construction, combination and arrangement of parts may be made without departing from the spirit and scope of the invention as claimed.

What I claim is:

1. In a steam boiler comprising a furnace from which combustion gases are discharged and boiler heating surface over which said combustion gases flow in heat exchange relationship, the combination of means forming a first channel which includes a relatively small portion of the aforesaid boiler heating surface and which causes that included surface to present a relatively large flow area to the passage therethrough of the aforesaid combustion gases with resulting low gas flow velocity over said included small portion of boiler heating surface; means forming a second channel which includes a remaining substantially larger portion of the aforesaid boiler heatin surface and which causes that surface to present a. relatively small flow area to the passage therethrough of the aforesaid combustion gases with resulting high gas flow velocity over said included large portion of boiler heating surface, said larger heating surface portion being arranged in series to follow the small heating surface portion with respect to direction of gas flow; and a dust separator interposed between the smaller boiler heating surface portion and the larger boiler heating surface portion, said dust separator comprising a multiplicity of similar dust separating units substantially uniformly spaced across the width of the gas stream, whereby the gases with dust therein carried in leaving the low velocity smaller boiler heating surface portion enter said dust separator where said dust is removed therefrom and upon leaving the separator in a cleaned state flow over the said larger boiler heating surface portion at high velocity without damage to that surface.

2. In a steam boiler comprising a furnace from which combustion gases are discharged and fluid heating surface over which said combustion gases flow in heat exchange relationship, the combination of means forming a first channel which includes a relatively small portion of the aforesaid fluid heating surface and which causes that included surface to present a relatively large flow area to the passage therethrough of the aforesaid combustion gases with resulting low gas flow velocity over said included small portion of fluid heating surface; means forming a second channel which includes a remaining substantially larger portion of the aforesaid fluid heating surface and which causes that surface to present a relatively small flow area to the passage therethrough of the aforesaid combustion gases with resulting high gas flow velocity over said included large portion of fluid heating surface, said larger heating surface portion being arranged in series to follow the small heating surface portion with respect to direction of gas flow; and a dust separator interposed between the smaller fluid heating surface portion and the larger fluid heating surface portion, said dust separator comprising a multiplicity of similar dust separating units substantially uniformly spaced across the width of the gas stream, whereby the gases with dust therein carried in leaving the low velocity smaller fluid heating surface portion enter said dust separator where said dust is removed therefrom and upon leaving the separator in a cleaned state flow over the said larger fluid heating surface portion at high velocity without damage to that surface.

WILBUR H. ARMAC OST.

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

UNITED STATES PATENTS Number Name Date 1,943,949 Coghlan et al Jan. 16, 1934 1,972,143 Gordon Sept. 4, 1934 1,972,893 Langvand Sept. 11, 1934 2,065,554 Beers Dec. 29, 1936 2,158,509 Kuhner May 16, 1939 2,189,234 Wagner Feb. 6, 1940 2,213,052 Rosencrants et a1. Aug. 27, 1940 2,263,433 Allen Nov. 18, 1941 2,391,860 Badenhausen Jan. 1, 1946 2,399,509 Rich Apr. 30, 1946

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