US2012415A - Furnace - Google Patents

Description

E. G. BAILEY FURNACE 2 Shets-Sheet 1 Filed Nov. 6, 1951 LINVENTOR Err/[g1 fial'ley FURNACE Filed Nov. 6, 1931 2 Sheets-Sheet 2 INVENTOR Ervin Bailgy /Y HIS AMTORN Y Patented Aug. 27, 1935 UNITED STATES FURNACE Ervin G. Bailey, Eaaton, Pa", assignor to Fuller Lehigh Company, New York, N. Y., a corporation of Delaware Application November 6, 1931, Serial No. 573,344

2 Claims.

- My invention relates to a furnace, and particularly a. furnace wherein fuel in finely divided form is projected toward a pool of molten material.

' The invention is especially useful in connection I with furnaces in which pulverized coal is used as a fuel, and in which ash in the pulverized coal is deposited in molten form in the bottom thereof.

One object of the invention is the provision of a furnace wherein a pool of molten material radiates its heat upwardly and assists in the ignition and combustion of an entering fuel stream. Another object is the construction of such a furnace in a. manner which will permit reversal of direction by the stream of burning fuel in contact with the pool, to the end that particles of molten, incombustible material may be separated from the burning stream by inertia and change of direction, and by contacting with the sticky surface of the pool. A further object is the collection of unburned carbon particles upon the surface of the pool where they may float and subsequently burn. Still a further objectis to create a high temperature in the pool by direct impingement of the flame thereon. Other objects will be apmrent upon consideration of the present specification.

The invention is shown by way of illustration in. the accompanying drawings in which- Figure l is a vertical mid-section of a furnace constructed in accordance with the invention, and

Fig. 2 is a vertical mid-section of another furnece constructed in accordance with the invention:

In the combustion of fluid fuel, particularly pulverized coal, it is desirable to complete the buming of the fuel in the combustion chamber; that is to say, before the hot gases come in contact with the object which it is desired to heat; for instance, the tubes of a boiler. I have discovered that the radiant surface of a pool of molten material-for example, slag-in the bottom of the combustion chamber may be utilized to give added heat to the stream of fuel entering the furnace and thus accelerate combustion and increase the rate of heat release from the fuel. Combustion of the fuel may thus be completed in the furnace proper, and the size of the furnace may thus be considerably restricted. I have also found that the surface of the molten pool may be employed for giving a secondary mixing to the entering fuel stream and air and for separating incombustible material from the fuel stream.

In the accompanying drawings there is shown a furnace including a combustion chamber ill, a

boiler l l, and a. boiler setting l2 above the combustion chamber. A molten pool i3 is shown in the bottom of the combustion chamber ID, and positioned above this pool is a burner M which is adapted to project an ignited jet of slag-bearing fuel 15 approximately vertically toward the pool and into contact therewith. The burner I4 is preferably a fuel and air mixer, and may be constructed in any known or desirable form. I may employ, for example, a. burner similar to that described and illustrated in my copending application for Fuel burner filed September 27, 1930, Serial No. 484,739. The burner is positioned in the roof it of the furnace above part of the pool l3, and the mixed fuel and. air issuing therefrom is projected substantially vertically, changes its direction of travel in contact with the pool, and passes upward into a gas passage i! above a part of the pool wherein the boiler and water tubes i8 forming a part of the boiler are disposed. The outlines of the fuel stream and resulting combustion gases are indicated very generally by broken lines extending from the burner l4.

As the jet of burning fuel comes in contact with the molten pool and reverses its direction, particles of slag from the fuel together with other unburned or incombustible material are thrown outwardly and into the pool by centrifugal force and gravity. Unbumed particles of carbon coming upon the surface of the pool will float there and, absorbing heat from the pool while being swept by air from the burner, will burn and add heat to the combustion chamber. The resulting combustion gases partially freed from both the incombustible solids and ash, now in liquid form, pass upward among the boiler tubes with less ash than otherwise.

Materiel other than ash or slag may be added to the molten pool. Examples of such material are fly ash, dust, or if necessary, some fluxing material.

It will be apparent that, by using the radiant heat of the pool of molten slag or other material, as indicated, a maximum temperature is given the entering stream of fuel and air, causing early ignition and intense combustion. Contact of the fuel stream with the surface of the molten pool affords secondary mixing of the fuel and air, that is to say, a mixing similar to that which occurs at the turbulent burner. A smaller furnace than would otherwise be required is thereby made possibie.

As has been indicated above, the flame impinges upon the slag pool before turning upwardly and passing to the boiler tubes, The pool thus plays a part in the reversal of the flame direction. The combined distance of the burner from the slag pool and the distance from the slag pool to the boiler tubes is such that the flame temperature has time to reach a sufficiently high point to melt the ash and to burn away or gasify the combustible material in the fuel. At normal feed substantially all of the ash is melted before the flame contacts with the poolfittnd the upstream from the pool to the boiler is a gaseous flame.

The functions of the pool, therefore, are to re fiect and radiate heat toward the burner, and the incoming mass of air and burning fuel, and

cause more rapid and complete ignition of the fuel stream entering the furnace, to shorten the flame, to aid in the reversal of the flame, to aid in mixing the air and fuel, thus acting as a secondary mixture after the primary mixing which occurs in the burner, and to separate from the fuel stream incombustible materials which are brought in contact with the sticky surfaces of the pool as the fuel stream reverses its direction.

Since the slag pool l3 extends horizontally beyond the roof it and beneath the water tubes is, it will be obvious that the slag pool also acts to promote heat absorption, by radiation to the boiler tubes. Heat absorption by the boiler tends to freeze the slag pool, while the flame projected by the burner tends to keep it molten. Projection of the flame downwardly into contact with the pool insures its molten state for lower boiler rating than other forms of firing. In the construction illustrated in Figure 2, a somewhat difierent type of furnace is illustrated. This construction shows the application of the invention to a furnace in which the distance from the roof through which the fuel is projected to the furnace floor is somewhat greater than that in the furnace illustrated in Figure 1. Furthermore, Figure 2 shows a furnace wherein the roof it has a greater slope than the roof it in Figure 1. The fuel jet I5 in this construction is also illustrated as having a slight angle to the verticalas contrasted with the direction of the fuel jet E5 in Figure l which is approximately vertical.

From the above, it will be apparent that in each of the modifications disclosed, a relatively high heat release per cubic foot of furnace volume, per unit of time, is made possible. The vertical distance from. the slag pool to the burner tip is suflicient to permit substantial coking of the fuel particles, yet is short enough for the fuel stream to impinge against the slag pool and to provide the advantageous secondary mixing of the fuel stream which aids in accelerating combustion so that it may be completed within a relatively small distance of flame travel. The slag pool provides an effective target for the fuel stream and aids in the provision of a higher furnace temperature and an early ignition of the incoming fuel. The fuel and air mixing type of burner aids also in the acceleration of the combustion process. It will be observed that in each modification the aoiacis has been particularly described as a boiler fur-- nace, it will be recognized that the invention is equally applicable to other fuels in fluid or finely comminuted form, and to furnaces other than boiler furnaces. Furthermore, the description here given and the furnaces illustrated in the drawings are merely presented as examples of how the invention may be applied. Other forms of the invention will readily suggest themselves to those dealing with combustion problems, which do not depart from the invention or the proper scope of the appended claims.

With this understanding, therefore, I claim:

1. In the method of operating a downwardly fired pulverized fuel furnace, the steps consisting of maintaining over the floor of said furnace a molten slag pool having a horizontal dimension greater than the vertical distance from said slag pool to ariginlet for pulverized fuel and air, mixing a stream of pulverized fuel with sumcient air to cause complete combustion thereof, igniting and driving said stream downwardly toward the slag pool for a distance sufiicient to cause substantially complete coking of the fuel particles prior to contact of the stream with the pool, deforming the stream by impact with the molten pool, and spreading the stream along the aforesaid horizontal dimension over the molten slag pool for a distance greater than the vertical distance between the stream entrance and the slag pool; and thence directing the burning fuel stream upwardly through an outlet.

2. In a slag-tap furnace, the combination of upwardly-extending side walls defining a combustion chamber having a gas outlet in the upper portion thereof; a furnace bottom extending across the lower end of the chamber and constructed to sustain a pool of slag thereon; and burner means spaced from the gas outlet and at one side of the furnace for introducing downwardly toward the adjacent side of the slag pool a turbulently-mixing stream of pulverized fuel with suificient air for supporting combustion thereof; the burner means being spaced from the slag pool a distance sufiicient to effect substantial coking of the fuel in suspension, yet close enough to cause the stream to impinge against the slag pool; the slag pool having a horizontal dimension greater than the distance between the slag pool and the burner means so as to eflect a thorough secondary mixing of the fuel and air and to provide ample space for the stream to turn upward toward the outlet.

ERVIN G. BAILEY.

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