Tuyere Assembly

Abstract

A tuyere for controlling flow through a hole in a flat reactor hearth which utilizes the Bernoulli effect to retain its position. The tuyere is essentially a flat disc with a centering shaft fitting loosely in the hearth hole to prevent sideways movement. Either metal, including sheet metal, or refractory material can be used to form the tuyere, and it can be shaped to completely block backflow or with port grooves to increase gas volume flow.

Description

DESCRIPTION OF THE INVENTION

This invention relates generally to fluidized bed reactors and more particularly concerns an improved tuyere and hearth for such reactors.

A fluidized bed reactor includes a flat, horizontal hearth for supporting a mass of material forming the bed. A combustion chamber beneath the hearth supplies gas which flows through holes in the hearth to reach the bed. Conventionally, tuyeres are placed at the upper ends of the hearth holes to control the gas flow and prevent undesirable downward movement of the bed material. Hearth and tuyeres are formed both of metal, which is more economical, and refractory material, which is suitable for higher reactor temperatures.

A primary aim of the invention is to provide a tuyere and hearth which operate on a principal permitting great performance versatility to result from making minor changes in tuyere configuration. A related object of the invention is to provide a tuyere and hearth as characterized above which allows easy, economical tuyere installation and removal, since no cement or fasteners are required, so that tuyeres of varying characteristics can be readily substituted for one another.

A further object is to provide a tuyere and hearth of the above character which can be readily formed to deliver widely varying gas volumes without altering driving pressures, and to completely eliminate backflow of the bed material upon shutdown when that feature is desired.

It is also an object of the invention to provide a tuyere and hearth of the above kind which is virtually clog-proof in operation, and which facilitates cleaning out the bed material after an operating campaign.

Another object is to provide a tuyere as referred to above which is economical to manufacture, having a basically simple shape, and which, depending upon temperature requirements, can be formed of either refractory material or metal, including economical metal sheet material.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIG. 1 is a fragmentary vertical section taken through a refractory hearth constructed in accordance with the invention;

FIG. 2 is an enlarged fragmentary plan taken approximately along the line 2--2 in FIG. 1;

FIG. 3 is a further enlarged fragmentary vertical section showing a portion of the structure illustrated by FIG. 1;

FIG. 4 is a still further enlarged section similar to FIG. 3 but showing a modified form of the invention;

FIG. 5 shows a plan taken approximately along the line 5--5 of FIG. 4;

FIG. 6 is similar to FIG. 3 but shows a further modification of the invention;

FIG. 7 is similar to FIG. 1 and shows a modification embodying the invention;

FIGS. 8 and 9 are similar to FIG. 3 but show, respectively, further modifications embodying the invention; and

FIG. 10 is similar to FIG. 2 and is taken approximately along the line 10--10 of FIG. 7.

While the invention will be described in connection with a number of preferred embodiments, it will be understood that I do not intend to limit the invention to those embodiments. On the contrary, I intend to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention.

Turning first to FIGS. 1 and 2, there is shown a fluidized bed reactor 10 having a cylindrical metal shell 11 lined with refractory material 12 and being divided by a substantially horizontal hearth 13 which defines and separates a lower windbox 14 and an upper reaction chamber 15. In the illustrated construction, the hearth 13 consists of refractory blocks 16 cut and assembled to create a circular masonry arch having a flat upper surface 17 supported at its periphery by a collar structure 18. The blocks 16 are formed with complementary grooves so that adjacent blocks establish substantially circular openings 19 extending from the windbox 14 through the surface 17 to the reaction chamber 15.

As will be familiar to those skilled in this art, the fluidized bed in the reaction chamber 15 is created by transmitting gas, usually at high temperatures, through the hearth 13 from the windbox 14. By maintaining a vertical gas flow across the entire bottom of the reaction chamber 15 the material in the chamber is fluidized for purposes of the desired reaction.

In accordance with the invention, flow through the openings 19 is controlled by individual tuyeres 20 overlying each opening, each tuyere comprising a substantially flat body 21 resting on the surface 17 which is approximately twice the size of the opening and which has a stop surface cooperating with a portion of the hearth to prevent lateral movement of the body from the opening (see FIG. 3). Preferably, the tuyeres 20 are circular, as are the openings 19, with a lower face 22 contacting the hearth surface 17 and being formed with a recess 23 in the center portion of the surface 22 from which a shaft 24 extends downwardly into the underlying opening 19 so as to define the tuyere stop surface. The pressure of the gas flow from the windbox 14 through the openings 19 will cause the tuyere body 21 to rise slightly above the hearth surface 17 so that gas can escape into the reaction chamber 15 between the hearth surface 17 and the contact face 22 of the tuyere. In the typical operating campaign, measurements indicate that a clearance of about 0.020 to 0.030 inch is created between the surface 17 and the face 22 with there being a small amount of constant fluttering of the tuyere. This latter phenomena has been found effective to keep the gas flow uniform since it avoids accumulated material from the reaction bed plugging up the hearth openings.

The effectiveness of the tuyeres 20 depends upon the Bernoulli effect, that is, the fact that pressure in a stream of fluid is reduced as its velocity is increased. In this instance, the gas flow through the openings 19 from the windbox 14 not only increases in velocity as it escapes between the surface 17 and the face 22 but also expands radially beneath the tuyeres, both factors creating lesser pressures beneath the tuyeres tending to hold the tuyeres onto the hearth surface 17. It has been found that this effect obtains when the tuyere diameter is approximately at least twice the size of the opening which it is controlling. The holding force created by the Bernoulli effect is actually increased upon increasing the gas flow rates through the openings 19. Lateral movement of the tuyeres is prevented by engagement of the stop surface shafts 24 with the sides of the respective openings 19.

Slight modifications to the shape of the tuyeres can be made for achieving certain desired results. For example, gas flow can be greatly increased by forming port grooves in the tuyere hearth contact face. In FIG. 4 there is shown a modified tuyere 20a embodying the invention and having a body 21a, center recess 23a and stop surface shaft 24a together with a plurality of radial port grooves 30. As in the tuyere 20, the tuyere 20a has an unbroken periphery around the recess 23a adapted to contact the hearth surface 17. This eliminates the possibility of backflow from the fluid bed through the opening 19 when the reactor is first shut down.

If even greater gas flow into the bed is desired, the radial ports in the tuyeres can extend through the tuyere periphery, as do the ports 30b in the tuyere 20b shown in FIG. 6. Otherwise, the tuyere 20b includes a body 21b, a center recess 23b and a stop surface shaft 24b corresponding to the similar parts previously described.

An important aspect of the invention lies in the ability to replace the tuyeres readily for an alternate design having slightly differing operating characteristics. For example, it is merely necessary to lift the tuyeres 20 from the reactor 10 and replace them with a set of tuyeres 20a or 20b, with the latter being merely dropped into position. No fasteners, adhesives or cements are required and the hearth is not disturbed. Because of the basically flat shape of the tuyeres, they extend only a short distance into the reaction chamber and an essentially flat surface is presented when it is necessary or desirable to clean out the fluidized bed.

The tuyeres already described are preferably formed in one piece of refractory material for use in a high temperature, refractory lined reactor of the type represented by the reactor 10. The invention is also susceptible of use in lower temperature, and also lower cost, metal reactors of the type represented by the reactor 10b shown in FIGS. 7 and 10. Here, a metal reactor shell 11b surrounded by insulating material 35 supports a flat metal plate hearth 13b on a collar structure 18b, with the hearth 13b being pierced by a plurality of holes or openings 19b for admitting gas from a windbox 14b to a reaction chamber 15b. The tuyeres 20c, made of sheet metal, control gas flow through the openings 19b and include a body 21c formed to define a center recess 23c through which extends a shaft 24c constituting the tuyere stop surface (see also FIG. 8). The tuyere 20c functions as do the tuyeres previously described but it can be appreciated that the sheet metal configuration provides a particularly economical construction.

An alternate tuyere form, (FIG. 9), provides a tuyere 20d of formed sheet material having radial ports 30d for increasing the gas flow. The ports 30d function as do the previously described radial ports.

Claims

I claim as my invention:

1. In a fluidized bed reactor having a wind box and a reaction chamber, the combination comprising, a substantially horizontal hearth separating the wind box from the reaction chamber, said hearth having a flat top surface and an opening extending from the wind box through said flat surface with no peripheral lip, and a tuyere for controlling flow through the opening, said tuyere having a substantially flat body on said surface overlying the opening and being at least approximately twice the size of said opening, said body having a stop surface cooperating with a portion of the hearth to prevent lateral movement of the body from said opening, the flow through said opening and against said body being substantially unimpeded so that said flow after striking said body expands radially and increases in velocity between the body and said flat surface to develop a force holding the tuyere in place.

2. The combination of claim 1 in which said opening and said tuyere body are substantially circular and the face of the body contacting said surface is recessed in its center portion, said stop surface being defined by a shaft on said body extending from the approximate center of said recess down into said opening.

3. The combination of claim 2 in which said contact face includes an unbroken periphery resting on said hearth surface without creating a gap between the tuyere and the hearth.

4. The combination of claim 2 in which said contact face is formed with a port groove extending radially from said recessed center portion.

5. The combination of claim 4 in which said groove extends through the periphery of said body.