Patent Application
20090139235
The present application relates generally to gas turbine engines and more particularly relates to a combustor for a gas turbine that is catalytically stabilized.
At temperatures above about 2800 degrees Fahrenheit (about 1538 degrees Celsius), the oxygen and nitrogen present in the air combine to form nitrogen oxides (NO and NO2, collectively known as NOx.) As a result, modem low emission gas turbines generally use a very lean, premixed flame for low NOx combustion. Operational boundaries include “Lean Blow Out” (“LBO”), which may result in a partial or a complete blowout of the flame in one or more combustors. Another boundary is acoustic pressure oscillations or combustion dynamics. These combustion dynamics may influence the operability or durability of the combustion system as a whole. As a result, it may be necessary to tune individually each gas turbine to remain operational while still satisfying emissions controls. Tuning, however, can influence not only the time required for commissioning, but also may be needed to address ambient or load variations.
Both the LBO and combustion dynamics boundaries can be influenced by providing a stable anchoring flame for the combustor. In older low NOx combustors, this anchoring flame may be provided by a piloting diffusion flame. This type of pilot, however, may cause NOx emissions to be higher than desired or permitted. Specifically, the use of a diffusion pilot makes it difficult to reach the desired single digit NOx emissions in modem gas turbines with high firing temperatures.
Thus, there is a desire for a more stable anchoring flame for low NOx combustors. Such a stable anchoring flame should reduce blow out tendency, increased hot section life, relax tuning requirements, and enhance the low NOx operating range.
The present application thus provides a combustor for a gas turbine. The gas turbine combustor may include a central combustion nozzle with a catalyst therein and a number of outer combustion nozzles surrounding the central combustion nozzle.
The present application further provides for operating a gas turbine combustor with a central combustion nozzle and a number of outer combustion nozzles. The method includes the steps of positioning a catalyst within the central combustion nozzle and modulating a fuel-air mixture exiting the central combustion nozzle to a temperature range of about 1000 to about 1500 degrees Fahrenheit (about 538 to about 816 degrees Celsius).
The present application further provides for a gas turbine combustor. The gas turbine combustor may include a catalytic combustion nozzle with a catalyst therein and a number of non-catalytic combustion nozzles positioned about the catalytic combustion nozzle.
These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
The combustor 120 may be a dry low NOx (“DLN”) combustor also available from General Electric Company of Schenectady, N.Y. Specifically, the combustor 120 may be known as a DLN 2.6 combustor. As is shown in
The catalyst layer 250 may include as an active ingredient precious metals, Group VIII noble metals, base metals, metal oxides, or any combination thereof. Elements such as zirconium, vanadium, chromium, manganese, copper, platinum, palladium, osmium, iridium, rhodium, cerium, lanthanum, other elements of the lanthanide series, cobalt, nickel, iron, and the like may be used. The catalyst layer 250 may be applied directly to a substrate or to an intermediate bond coat or washcoat composed of alumina, silica, zirconia, titania, magnesia, other refractory metal oxides, or any combination thereof. The catalyst-coated substrate may be fabricated from any of various high temperature materials. High temperature metal alloys are preferred, particularly alloys composed of iron, nickel, and/or cobalt, in combination with aluminum, chromium, and/or other alloying materials. High temperature nickel alloys are especially preferred. Other materials that may be used include ceramics, metal oxides, intermetallic materials, carbides, and nitrides. Metallic substrates are most preferred due to their excellent thermal conductivity, allowing effective backside cooling of the catalyst layer 250. Other materials and configurations may be used herein.
The catalytic nozzle 240 may be a nozzle sold under the designation “RCL” by Precision Combustion, Inc. of New Haven, Conn. Other types of catalytic nozzles 240 may be used herein. Only a fraction of the fuel may be reacted such that the internal temperature of the nozzle 240 may be kept within an acceptable range. A mixture of air, unreacted fuel, combustion products, and highly reactive partial combustion products may be injected by the nozzle 240 into a combustion stream. The mixture ideally would be in the temperature range of about 1000 to about 1500 degrees Fahrenheit (about 538 to about 816 degrees Celsius). When the stream from catalytic nozzle 240 is injected into the swirling mixture of fuel and air provided by the outer nozzles 180-220, this relatively hot, highly reactive gas stream should provide a stable anchor to the premix flame. The outer nozzles 180-220 thus may be modulated to a lower operating temperature.
The relatively low temperature of the partially reacted gases should produced very little NOx by the pilot flame. The gases from the nozzle 240 are not intended to ignite the mixture within the combustor 230 but only to provide a stable anchor for the flame once ignited. By providing this relatively low temperature anchor, operability may be improved and combustion dynamics reduced without adversely impacting NOx emissions.
Several or all of the outer nozzles 180-220 also may be replaced with the catalytic nozzle 240. This replacement offers the possibility of obtaining significantly lower NOx emission levels beyond that achievable by conventional lean premix combustors. Any number or configuration of catalytic nozzles 240 may be used herein.
It should be apparent that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
