US2197387A - Furnace - Google Patents

Description

April 16, 1940. I w. H. ROWAND 2,197,387

FURNACE Filed July 23, 1938 2 Sheets-Sheet 1 Fig] INVENTOR.

Vl ill H Ron and ATTORNEY.

April 16, 1940. w H. ROWAND FURNACE Filed July 23, 1938 2 Sheets-Sheet 2 R. m m ma W DA H Ila ATTORNEY.-

Patented Apr. 16, 1940 PATENT OFFICE FURNACE Will H. Rnwand, Jersey City, N. J., asaiznor to The Babcock & Wilcox Company, Newark, N. 1., a. corporation of New Jersey Application July 23, 1938, Serial No. 220,833

7 Claims. (Cl. 122-336) The present invention relates to the construction and operation of furnaces for burning pulverized fuel in suspension, and is particularly designed and especially useful for a furnace in a steam generator of the integral furnace type, 1.12., a steam generator having its furnace chamber laterally adjoining a vertically disposed bank of steam generating tubes. In steam generators of this type the furnace chamber and space containing the tube bank are usually separated except at one end and the fuel burning means located at the opposite end of the furnace chamber. With pulverized fuel burners so located, it has been found that a substantial quantity of ash is carried out of the furnace by the heating gases and passes through the boiler and out of the stack.

It is believed that the percentage of the ash carried out of the furnace depends in part upon the gas velocities through the furnace chamber and the size of the pulverized fuel particles, but also on the direction of gas flow and on the furnace temperature. A fuel particle must be of suflicient size after being subjected to oxidation or sufficient particles must be heated above their ash fusion temperature during oxidation and subsequently collide and adhere to each other, to form particles which are of suflicient size not to be carried out of the furnace by the gas stream. In the relatively cold furnaces which have heretofore characterized this type of steam generator, the fuel particles do not have as much chance to adhere after collision during the short period when they are above the ash fushion temperature as would be the case in a furnace where the temperature is considerably higher. In most steam boiler furnaces the pulverized fuel is introduced in such a manner that the stream of burning fuel and products of combustion will make a or a turn and then rise vertically a considerable distance in the high temperature zone before entering the boiler tube bank. The greatest opportunity for the ash particles to collide and adhere to each other occurs during the turbulence created in making an abrupt turn in the furnace chamber and any subsequent vertical travel after the turn provides an opportunity for the large particles formed by this adhesion to settle out in a relatively low velocity zone, or to fall back into the turbulent zone of the turn to collide with and adhere to other ash particles. Where however, as in the integral furnace type boiler, the fuel stream is projected horizontally and makes a 90 turn horizontally as it enters the boiler tube bank, the ash particles do not have the same opportunity to pass through a high tem-- 'perature zone after the turn has been made. In

an integral furnace boiler furnace, however, the gases and entrained ash particles usually enter the relatively low temperature zone of the tube bank immediately after making the turn and are chilled below their ash fusion temperature, thus substantially eliminating any possibility of the ash particles adhering to each other or settling back into the turbulent zone of the turn. Furhermore, the gas velocities through the tube bank space are generally higherthan in the furnace chamber, thus making it possible for larger ash particles to be carried. These high gas velocities tend to keep the ash particles in suspension and the only opportunity for the particles to.

settle out occurs on impacting with the tubes and tube bank ballles.

The main object of my invention is the provision of a steam generator, and more particularly a steam generator of the integral furnace type, with an improved construction of the furnace chamber for effecting an increase in the portion of .the ash separated from the burning fuel stream in the furnace chamber. A further object is the provision of a furnace chamber construction of the character described in which a more effective mixing of the fuel and air is provided, while maintaining a compact construction having low floor space and headroom require- 30 terize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operatingagvantages and specific objects attained by its use,- reference should be hadto the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is a sectional elevation of asteam generator embodying my invention, the section being taken on the line I-l of Fig. 2;

Fig. 2 is a horizontal section taken on the line 2-2 of Fig. 1;

Fig. 3 is a vertical section taken on the line 3-3 of Fig. 2; and

Fig. 4 is an enlarged detail of a portion of the target wall shown in Fig. 2.

l3, and a roof l4. A lower drum I5 is horizontally arranged along the lower part of the side wall 13 adjacent the bottom of the furnace chamber. A steam ahd water drum It extends parallel to the drum l5 along the roof H at a location inwardly offset from the drum l5. The

wall l2 and portions of the end walls in and II and roof l4. The walls H and I2 and roof H are fluid cooled. the fluid cooling provisions comprising rear wall tubes having their upper ends bent laterally into the upper drum l6 and their lower ends connected to a header (not shown) which is connected to the drum l5. The side wall I2 and roof l4 are cooled by a row of tubes 23 extending from a lower side wall header 24 to the upper drum IS. The bottom of the furnace chamber is defined by an outwardly inclined fluid cooled floor 25 formed by a row of block covered tubes 26 extending from the header 24 to the drum 15.

The partition 30 separating the furnace chamber from the tube bank space is formed by a row of tubes l'la forming the front portion of the innermost row of the tube bank. The tubes Ha are partially studded to support refractory closing the intertube spaces throughout their 'extent. The partition 30 preferably extends from the front wall ID for about two-thirds the length of the furnace chamber.

The tube bank space is advantageously divided into a plurality of serially connected gas passes by a plurality of transverse vertical baffles 3| and 32. The baflie 3| extends downwardly throughout the height of the tube bank and laterally from the partition 30 to a point short of the side wall I 3. The second baffle 32 is positioned forwardly of the baffle 3| and extends from the side wall l3 partly across the tube bank. The partition, baffles and furnace walls thus divide the tube bank space into three serially connected gas passes 35, 36, and 31 connecting the furnace chamber to a. gas outlet opening to the gas pass 31.

The portion of the tube bank I! in the first gas pass 35 is formed by a small number of rows of tubes Ilb of larger diameter than the remaining tubes in the bank. The tubes l'lb in the innermost row are spaced and arranged as shown in Figs. 1 and 2 to provide a slag screen across the entrance to the first pass 35. The remaining portion of the gas pass 35 is occupied by a group of inverted U-shaped superheater tubes 40 connected to headers 4| and 42, the header 4| being connected to the steam space of the drum 6.

A pulverized fuel burner is mounted in a fuel burner port 46 in the front wall l0 which is symmetrically arranged relative to the furnace chamber cross-section area. The fuel burner 45 is arranged to discharge a substantially horizontal stream of pulverized fuel and primary air longitudinally of the furnace chamber and suit able air conduit provisions are connected to the burner port 46 to discharge a stream of preheated secondary air through the burner port around the fuel stream. With this arrangement a stream of burning fuel will be caused to travel longitudinally of the furnace chamber and the heating gases generated make a 90" turn to enter the first gas pass'35 still flowing horizontally. The heating gases pass successively across the heating surface in the gas passes 35, 36 and 31 to the stack connection.

In accordance with my invention the furnace chamber is advantageously constructed to cause separation of agreater proportion of the ash in the furnace chamber. For this purpose the furnace chamber is provided with an impact baille or target wall in the path of the fuel stream at a point about two-thirds of the furnace length from the front wall. As shown, a row of transversely spaced water tubes 50 extend vertically above the furnace floor with their upper portions bent laterally and connected to the drum IS. The lower ends of the tubes 50 are connected to a transverse horizontally inclined header 5| connected to the side wall header 24 and drum l5 by tubes 52 and 53 respectively. The tubes 50 are fully studded, as shown in Fig. 4, for an intermediate portion of their length to support suitable refractory material 54 for closing the intertube spaces and covering the front side of the tubes. As shown in Figs. 1 and 2, the tubes and refractory thus define a fluid cooled refractory faced target wall extending transversely of the furnace chamber and spaced from the furnace bottom side wall 12, roof I4, and partition 30. As indicated in Fig. 1, the target wall is arranged with its center slightly offset from and above the axis of the fuel burner port 46 and burner nozzle 45, so that substantially all portions of the fuel stream will impinge on its front side as there is a tendency for the hot stream to rise.

With the target wall construction and arrangement described, the furnace chamber will be divided into front and rear sections. The refractory faced construction of the target wall and front portion of the side wall aids in the maintenance of relatively high temperature conditions in the front furnace chamber section, and particularly on the face of the target wall. The fuel stream will impinge on the target wall while the ash particles in suspension are in a fused or molten condition causing the'ash particles to separate out, lose velocity and adhere to the target wall or drop out of the fuel stream onto the front section of the floor or into the ash pit 55 formed by omitting floor tubes in front of the header 5|. The target wall also causes a substantial eddying in the burning fuel stream, promoting mixing of the unburned fuel and air therein and thereby improving combustion conditions. The burning stream flows through the intertube tube row 50 above and below the target wall and around the sides thereof into the colder rear chamber, and thence into the tube bank space. The ash collecting on the target wall will run down the tubes 50 as a molten slag, and drop into the ash pit 55. The ash collecting on the rear section of the furnace floor can be swept into the ash pit in any suitable manner and the collected ash and slag sluiced out of the ash pit.

The target wall construction described not only provides a simple and effective method of substantially increasing the amount of ash separated in the furnace chamber with its consequent advantages, but also materially improves combustion conditions in the furnace chamber by the substantial intimate mixing of the fuel particles and air in the fuel stream. The target wall is also beneficial in substantially reducing the slagspaces of thev ging of the tube bank and preventing the exposure of the front row tubes l'lb in the first pass to excessive furnace radiation.

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 fluid heater comprising means defining a horizontally extending furnace chamber, means at one end of said furnace chamber for discharging a stream of finely divided solid fuel and air longitudinally of said furnace chamber, and means forming a vertically disposed continuous target wall extending across said furnace chamber intermediate its length and arranged directly in the flow path of the burning fuel stream in a position to receive the impact of molten slag particles in suspension in the burning fuel stream.

2. A fluid heater comprising means defining a furnace chamber, means at one end of said furinace chamber for discharging a stream of finely divided solid fuel and air longitudinally of said furnace chamber, and means forming a'vertically disposed fluid cooled target wall extending across said furnace chamber intermediate its length and arranged directly in the fiow path of the burning fuel stream in a position to receive the impact of molten slag particles in-suspension in the burning fuel stream, said target wall including a row of vertically disposed tubes, metallic projections on and extending into the intertube spaces of said tubes, and refractory material closing said intertube spaces.

3. A steam generator comprising upper and lower horizontally elongated drums, a bank of steam generating tubes connecting said drums, means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent one end,

' means for discharging a stream of finely divided solid fuel and air longitudinally of said furnace chamber toward said end, and means forming a vertically disposed continuous target 'wall extending across said furnace chamber intermediate its length and arranged directly in the flow path of the burning fuel stream.

4. A steam generator comprising upper and lower horizontally elongated drums, a bank of steam generating tubes connecting said drums, means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent its rear end, means at the front end of said furnace chamber for discharging a stream of finely divided solid fuel and air rearwardly of said furnace chamber, and means forming a vertically disposed continuous target wall extending across said furnace chamber intermediate its length and arranged to obstruct a major portion of the fiow path of the burning fuel stream. a

5. A steam generator comprising upper and lower horizontally elongated drums, a bank of steam generating tubes connecting said drums, means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent its rear end, means at the front end of said furnace chamber for discharging a stream of finely divided solid fuel and air rearwardly in said furnace chamber, and means forming a vertically disposed fluid cooled target wall extending across said furnace chamber intermediate its length and directly in the flow path of the burning fuel stream, said target wall-forming means including a row of vertically disposed tubes, metallic projections on and extending into the intertube spaces of said target wall tubes, and refractory'material closing said intertube spaces over at least a portion of the length of said target wall tubes.

6. A steam generator comprising upper and lower horizontally elongated drums, a bank of steam generating tubes connecting said drums, means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent its rear end, means at the front end of said furnace chamber for discharging a stream of finely divided solid fuel and air rearwardly in said furnace chamber, and means forming a vertically disposed fluid cooled target wall extending across said furnace chamber intermediate its length and directly in the flow path of the burning fuel stream, said target wall-forming means including a row of vertically disposed tubes having their upper ends directly connected'to said upper drum, a transverse header connecting the lower ends of said target wall tubes to said lower drum, metallic projections on and extending into the intertube spaces of said target wall tubes, and refractory material closing said intertube spaces over at least a portion of the length of said target wall tubes.

7. A steam generator comprising upper and lower horizontally elongated drums, a bank of steam generating tubes connecting said drums; means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent its rear end, means at the front end of said furnace chamber for discharging a stream of finely divided solid fuel and air rearwardly in said furnace chamber, a fluid cooled floor for said furnace'chamber, means forming a vertically disposed fluid cooled continuous target wall extending across said furnace chamber intermediate its length and directly in the flow path of the burning fuel stream, said target wall-forming means including a row of vertically disposed tubes having their upper and lower ends connected to said upper and lower drums respectively, and an ash pit extending transversely of and in front of said target wall.

WILL H. ROWAND.

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