Patent Application
20130081399
The invention relates to casings for gas turbine engines. In particular this invention relates to a casing section between the compressor and the turbine.
Conventional industrial gas turbine engines are enclosed by an annular engine casing. Engine casings commonly include a turbine casing, a combustor casing, and a turbine casing bolted together. In a can annular gas turbine engine the combustors are disposed in an annular array about a centerline of the gas turbine engine. These combustors may extend radially outward further than the compressor and turbine components adjacent to the combustors. Consequently, in order to enclose the combustors the compressor casing must bulge radially outward further than the adjacent portions of the compressor and turbine casings. In some designs radially outer ends of combustors extend through the combustor casing and are enclosed with a cap (“top hat”). However, even in casings that utilize top hats, the combustor casing still bulges radially outward. Furthermore, emerging advanced transition designs reposition combustors even further radially outward. Thus there exists room in the art for improved casing design.
The invention is explained in the following description in view of the drawings that show:
The present inventors have recognized that conventional combustor casing designs utilized for can annular combustors can be improved upon when a gas turbine engine utilizes an advanced transition combustion system. One example of an advanced transition design is disclosed in U.S. Pat. No. 7,721,547 to Bancalari et al. Similar to conventional can annular gas turbine engine combustor designs, advanced transition combustion systems comprise an array of combustors disposed annularly about a gas turbine engine's centerline. However, in advanced transition designs a first row of vanes commonly present in conventional gas turbine engines is eliminated. Instead, combustion gasses flow along a straight flow path from the combustor until accelerated up to a speed appropriate for delivery to the first row of turbine blades. In some advanced transition designs the combustion gasses continue on a straight flow path when delivered to the first row of turbine blades. In other advanced transition designs the combustion gasses unite with combustion gasses from adjacent combustors and a single unified flow is delivered to the first row of turbine blades. However, in all of these advanced transition designs the combustors are oriented radially outward to a greater degree to achieve a proper direction of flow for the combustion gasses. Consequently, in order to enclose the combustors utilizing conventional annular combustor casing practices a substantial annular combustor casing would be necessary.
The present inventors have devised a unique casing for a gas turbine engine utilizing advanced transition combustor designs. Contrary to prior combustion casing designs where a compressor casing, a combustor casing, and a turbine casing are formed by bolting sections together, the gas turbine engine casing design disclosed herein essentially eliminates a conventional combustor casing section and replaces it with what will be termed a “compressed air casing” that includes a compressed air annular section and a plurality of combustor assembly covers. (As used herein a combustor assembly is a combustor and the associated ducting necessary to convey the combustion gasses to the first row of turbine blades.) The compressed air section essentially encloses a portion of the gas turbine engine from a last row of compressor blades to a first row of turbine blades. The compressed air section essentially takes a most feasible and direct route between the compressor casing at the last row of compressor blades and the turbine casing at the first row of turbine blades, and simply leaves openings where the combustor assemblies extend radially through. The openings are covered with individual covers, known as “top hats” that enclose the portion of the combustor assembly extending past the compressed air section and seal the opening.
Thus, this design provides for a smaller annular portion (the compressed air section) of the casing surrounding the combustor and more substantial top hats enclosing more of the combustor assemblies than the prior art. Using more substantial top hats to enclose more of the combustor assemblies permits a substantial reduction in the radius of the annular section. Reducing the radius of the annular portion of the casing can allow for a thinner wall and smaller overall size of the annular section. By virtue of their shape top hats can readily absorb forces generated by the compressed air not enclosed by the annular portion. Specifically, as a generally cylindrical shape the top hats can absorb force about their circumference readily, and force on a radially outward end is manageable due to the small area of the radially outward end surface. As a result, several light, relatively inexpensive, and manageable top hats can be used to reduce the wall thickness and overall size of the annular portion.
Turning to the figures,
It can be seen that the compressed air section 40 encloses a decreased volume when compared to conventional combustor casings 16. Specifically, the compressed air section 40 encloses a volume that is radially bounded substantially by the inner surface 52 of the compressed air section 40 as if openings 50 were not present. In other words, a volume enclosed by the compressed air section 40 would have a radially outer surface that would conform to the inner surface 52 of the compressed air section 40 prior to the formation of the openings 50. It is understood that various shapes/profiles may be used by the compressed air section 40 to span the length of the gas turbine engine from the aft end 18 of a compressor casing 20 to the fore end 30 of a turbine casing 32. Whatever profile is chosen, minimizing a radius of the compressed air section 40 (the annular portion of the compressed air casing) at all locations along the length 24 of the gas turbine engine (i.e. a radius profile) is a desirable design factor. This minimize the forces generated on the compressed air section 40 by the compressed air enclosed thereby.
It is further understood that while minimizing the radius profile is a design factor in order to reduce the thickness required (in order to accommodate the forces) and the overall size (to ease manufacturing and shipping etc), other factors may supersede, such as other structural requirements including attachment points, fillet radius control, access etc. Consequently, the design is not limited to a specific radius profile, or volume, or surface area etc. In general terms, the volume enclosed by the compressed air section 40 may be slightly more than would be a volume enclosed by a frustum 54 (indicated by a dotted line) defined at an upstream end by an inner perimeter 58 of the aft end 18 of the compressor casing 20, and at a downstream end 60 by an inner perimeter 62 of the fore end 30 of the turbine casing 32. In some embodiments the volume enclosed by the compressed air section 40 will be roughly equivalent to or less than that enclosed by frustum 54. In various embodiments portions of the inner surface 52 of the compressed air section 40 may comprise a radius greater than that of the frustum 54 while a total enclosed volume may still be less than enclosed by the frustum 54.
In other embodiments the total enclosed volume may be roughly the same or even slightly larger than that of the frustum 54. In some embodiments the radius may always be equal to or less than that of the frustum 54 at the same axial position. However, when compared to the bulge 36 of the prior art, the volume enclosed by the compressed air section 40 will be substantially less. As a result of the reduced radius profile, volume, effective surface area etc, the compressed air section 40 will experience reduced forces from the compressed air enclosed therein, and thus may be much lighter, smaller, less expensive, and easier to transport than the prior art combustor casing.
Another embodiment of the compressed air section 40 is shown in
Yet another embodiment is depicted in
The casing of the present invention enables an annular portion with a significantly reduced radius. As a result the annular section may be made with a thinner wall, which decreases cost and weight. Further, the annular portion may be smaller in overall size which makes for an easier to handle and ship annular portion, which adds to the cost savings. In addition, a smaller casing allows for installing the gas turbine engine closer to the ground, yielding further savings.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention.
