Exhaust gas duct for gas turbines

Exhaust gas duct for gas turbines, including an axial discharge housing, a deflection piece connected downstream of the axial discharge housing in exhaust gas flow direction, the deflection piece having a substantially horizontal first diffusor section and a substantially vertical second diffusor section, the first and second diffusor sections each having a respective inclined edge facing each other, a grid disposed in the deflection piece for redirecting exhaust gas flow into the vertical direction, a substantially vertical exhaust gas chimney disposed downstream of the deflection piece in exhaust gas flow direction, and a noise suppressor disposed in the deflection piece.

The invention relates to an exhaust gas duct for gas turbines, having an 
axial discharge housing, a deflection piece disposed downstream of the 
axial discharge housing, a grid disposed in the deflection piece for 
redirecting the exhaust gas flow into the vertical direction, and a 
vertical exhaust gas chimney being disposed downstream of the deflection 
piece and containing a noise suppressor. 
Stationary gas turbines with a high power rating usually have an axial 
discharge housing which is connected to an exhaust gas chimney through an 
exhaust gas line. The velocity of the exhaust gas flow, which at the 
outlet of the turbine is of the order of 100 m/s, must be slowed down in 
the exhaust gas line to about 50 m/s, because otherwise the sound absorber 
which is required for reducing noise pollution, can be destroyed. In 
addition, such a reduction of the flow velocity is necessary for reducing 
outlet losses and for avoiding excessive noise at the mouth of the exhaust 
gas chimney. 
However, when using justifiable dimensions for the exhaust gas line, a 
reduction of the flow velocity with low loss raises problems, since the 
very large volume flows necessitate large flow cross sections, and a 
redirection of the exhaust gas flow from the axial to the vertical 
direction is additionally necessary. In conventional exhaust gas ducts for 
gas turbines, the noise suppressor is either disposed axially downstream 
of the gas turbine or is inserted vertically into the exhaust gas chimney. 
In the first case, a very long axial transition piece is necessary for 
lowering the flow velocity to an extent which benefits the noise 
suppressor. If this space is not available, flow resistances must be 
built-in for lowering and equalizing the velocity, which generate 
additional losses. If the noise suppressor is disposed vertically in the 
exhaust gas chimney, new flow irregularities, velocity peaks and 
turbulence are generated which can constitute a danger to the noise 
suppressor. To protect the noise suppressor, built-in components are 
therefore used for equalizing the flow and as deflection aids, or the 
noise suppressor is installed high in the exhaust gas chimney. However, 
the corresponding prior art structures have high losses and can only be 
made at relatively high cost. 
It is accordingly an object of the invention to provide an exhaust gas duct 
for gas turbines, which overcomes the hereinafore-mentioned disadvantages 
of the heretofore-known devices of this general type, and in which the 
exhaust gas line permits a low-loss decrease of the flow velocity while 
requiring little space. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, an exhaust gas duct for gas turbines, 
comprising an axial discharge housing, a deflective piece connected 
downstream of the axial discharge housing in exhaust gas flow direction, 
the deflection piece having a substantially horizontal first diffusor 
section and a substantially vertical second diffusor section, the first 
and second diffusor sections each having a respective inclined or mitered 
edge facing each other, a grid disposed in the deflection piece for 
redirecting exhaust gas flow into the vertical direction, a substantially 
vertical exhaust gas chimney disposed downstream of the deflection piece 
in exhaust gas flow direction, and a noise suppressor disposed in the 
deflection piece. 
In the exhaust gas duct according to the invention, the entire exhaust gas 
line is thus formed by a redirection section which acts through a 
substantially horizontally oriented first diffusor section and a 
vertically oriented second diffusor section and therefore causes a 
low-loss lowering of the flow velocity, dispensing with transition and 
intermediate pieces. The prerequisites for a flow through the deflection 
section without separation and for the effectiveness of the vertically 
oriented second diffusor section is ensured by the grid which in this case 
is disposed in the deflection section, for the uniform deflection of the 
exhaust gas flow. The length of the sections of the first and the second 
diffusor can be chosen at will, so that the exhaust gas line can be 
adapted with little effort to the respective local space conditions. 
In accordance with another feature of the invention, the first and second 
diffusor sections and the edges thereof are formed from a single circular 
conical diffusor having a single inclined or mitered cut formed therein. 
This makes extremely economical fabrication of the deflection section 
possible. 
In accordance with a further feature of the invention, there is provided an 
intermediate piece having an elliptical cross section, the intermediate 
piece being disposed between the first and second diffusor sections and 
being welded to the edges thereof, the grid being disposed in the 
intermediate piece. The intermediate piece with the grid can be fabricated 
before it is welded to the two diffusor sections, which, in particular, 
facilitates the welding of the individual deflection baffles of the grid. 
In accordance with a concomitant feature of the invention, the 
substantially horizontal first diffusor section is inclined relative to 
the horizontal for permitting installation of the deflection piece above 
the level of a floor. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in 
an exhaust gas duct for gas turbines, it is nevertheless not intended to 
be limited to the details shown, since various modifications and 
structural changes may be made therein without departing from the spirit 
of the invention and within the scope and range of equivalents of the 
claims.

Referring now to the figures of the drawing in detail, and first 
particularly to FIG. 1 thereof, it is seen that the exhaust gas canal 
begins with a partially illustrated axial discharge housing 1 of a gas 
turbine, from which the exhaust gas flow, indicated by arrows 2, emerges 
in the horizontal direction. The discharge housing 1 is followed by a 
first diffusor section 31 of a deflection piece designated overall with 
reference numeral 3. In the first diffusor section 31, the flare angle of 
which is designated with reference symbol .alpha., a low-loss slowdown of 
the exhaust gas flow is achieved. The first diffusor section 31 is 
directed slightly upwards to avoid the necessity of providing an 
installation below the floor level F. However, the deviation from the 
horizontal, designated by an angle .gamma., must be small because 
otherwise, a flow separation could already occur at the beginning of the 
first diffusor section 31. 
The nearly horizontally oriented first diffusor section 31, the end of 
which is cut at an angle, is followed by an intermediate section 32. A 
grid 321 formed by a multiplicity of deflection baffles for deflecting the 
exhaust gas flow 2 into the vertical direction, is disposed in the 
intermediate section 32. The uniformity of the deflection of the exhaust 
gas flow 2 with minimal deflection losses is ensured by providing a 
sufficient number of deflection baffles for the grid 321. 
The intermediate piece 32 with the grid 321 is then followed by a second 
diffusor section 33 of the deflection section 3, which begins with an 
angle section and is oriented vertically. In this second diffusor section 
33, the flare angle .alpha. of which corresponds to the flare angle 
.alpha. of the first diffusor section 31, a further low-loss slowing down 
of the exhaust gas flow 2 is achieved. 
The second diffusor section 33 is followed by a vertical exhaust gas 
chimney, which is designated with reference numeral 4 and is divided into 
a cylindrical noise suppressor section 41, a conical transition piece 42 
and a cylindrical chimney part 43, as seen from the bottom up. A sound 
absorber 5 which is formed of a number of vertical plates serving as sound 
absorber elements, is disposed in the noise suppressor section 41. 
The individual steps in the fabrication of the deflection section 3 may be 
seen in FIGS. 2 to 4. According to FIG. 2, initially a single circular 
cone diffusor K is divided by a miter cut S into the first diffusor 
section 31 and the second diffusor section 33. The miter angle is 
designated with reference symbol .beta.. The miter cut S gives the two 
diffusor sections 31 and 33 inclined cross-sectional surfaces in the form 
of ellipses, which fit together according to FIG. 3 if the second diffusor 
section 33 is rotated about its axis by an angle of 180.degree.. To 
complete the deflection piece 3, it is only required to weld the 
intermediate piece 32 with the grid 321 into the miter gap between the two 
diffusor sections 31 and 33. 
The partial lengths of the two diffusor sections 31 and 33 can also be 
adapted to local conditions. Since the pressure recovery percentages, the 
flow separation criteria and overall pressure losses of circular cone 
diffusors are also known to be a function of the length and the flare 
angle, the dimensions of the exhaust gas section 3 can be calculated and 
optimized.