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11.1 General Concept and Components
11.1.6 Combustion Chamber
A combustion chamber has an outer shell, mostly cylindrical, as in Fig. 11.2,
not exposed to the heat of the combustion, and an inner part which confines
the combustion gas. The outer part has to withstand the pressure difference between the interior of the gas turbine and the external atmosphere. The inner part
is generally called the liner, which means that it functions as a lining or an inner surface. The inner part has to withstand the heat of the combustion and
therefore must be cooled. With large machines, there are two types of combustion chambers. With the can-annular form, as in Fig. 11.2, the inner part is composed of a number of approximate cylindrical cans (16 for the SGT6-5000F
in Fig. 11.2) placed in the outer annular space. The individual liners are connected with tubes so that one liner can ignite another. A second possible form is
annular, which then means that the inner part is annular. The typical fuel for a
gas turbine for electricity generation is natural gas. For this fuel, the cans of
a can-annular combustion chamber typically contain 6–9 burners. The annular combustion chamber has a large number of burners. For instance, the GT26
of Alstom has an annular combustion chamber with 84 burners. A first advantage of the annular combustion chamber is lower friction surface, resulting in a
somewhat lower pressure drop in the combustion chamber. The second advantage is a more homogeneous temperature profile at turbine entrance. The disadvantage is that is more difficult to keep the combustion process stable. Small
or medium size gas turbines often have combustion chambers of can type,
which means a number of cylindrical cans, each with a cylindrical liner. Landbased gas turbines typically have so-called reverse flow combustion chambers. This means that the flow coming from the compressor inverses direction,
as in Fig. 11.2, before it enters the internal parts of the combustion chamber.
The through-flow velocity of the compressor is of the order of 150 m/s (about half
of the blade speed on the mean radius). The allowable velocity at the position of
the combustion itself is of the order of 15 m/s. Realisation of the big velocity reduction is the easiest with a reserve flow chamber. Gas turbines for propulsion always have a straight through-flow combustion chamber, because the frontal area
has to be minimised. The cooling and the heat protection of the liner or liners follow the same principles as with turbine blades. The most common is convection
cooling by air flowing over the exterior liner surface and a thermal barrier coating
on the interior surface. But impingement cooling of cans, requiring then a shell
with holes around the cans, is also employed. With annular liners, other systems
are film cooling of the inner surfaces (see Chap. 12, Sect. 12.6.3) and heat protection by ceramic tiles covering the metal surface.
Figure 11.9 sketches a longitudinal section of a somewhat simplified and
unified version of the burner system used, with some variants, in can-annular
combustion chambers by many manufacturers (Siemens, General Electric, Mitsubishi). A number of equal burners are positioned around a more complex central
11.1 General Concept and Components
11.1.6 Combustion Chamber
A combustion chamber has an outer shell, mostly cylindrical, as in Fig. 11.2,
not exposed to the heat of the combustion, and an inner part which confines
the combustion gas. The outer part has to withstand the pressure difference between the interior of the gas turbine and the external atmosphere. The inner part
is generally called the liner, which means that it functions as a lining or an inner surface. The inner part has to withstand the heat of the combustion and
therefore must be cooled. With large machines, there are two types of combustion chambers. With the can-annular form, as in Fig. 11.2, the inner part is composed of a number of approximate cylindrical cans (16 for the SGT6-5000F
in Fig. 11.2) placed in the outer annular space. The individual liners are connected with tubes so that one liner can ignite another. A second possible form is
annular, which then means that the inner part is annular. The typical fuel for a
gas turbine for electricity generation is natural gas. For this fuel, the cans of
a can-annular combustion chamber typically contain 6–9 burners. The annular combustion chamber has a large number of burners. For instance, the GT26
of Alstom has an annular combustion chamber with 84 burners. A first advantage of the annular combustion chamber is lower friction surface, resulting in a
somewhat lower pressure drop in the combustion chamber. The second advantage is a more homogeneous temperature profile at turbine entrance. The disadvantage is that is more difficult to keep the combustion process stable. Small
or medium size gas turbines often have combustion chambers of can type,
which means a number of cylindrical cans, each with a cylindrical liner. Landbased gas turbines typically have so-called reverse flow combustion chambers. This means that the flow coming from the compressor inverses direction,
as in Fig. 11.2, before it enters the internal parts of the combustion chamber.
The through-flow velocity of the compressor is of the order of 150 m/s (about half
of the blade speed on the mean radius). The allowable velocity at the position of
the combustion itself is of the order of 15 m/s. Realisation of the big velocity reduction is the easiest with a reserve flow chamber. Gas turbines for propulsion always have a straight through-flow combustion chamber, because the frontal area
has to be minimised. The cooling and the heat protection of the liner or liners follow the same principles as with turbine blades. The most common is convection
cooling by air flowing over the exterior liner surface and a thermal barrier coating
on the interior surface. But impingement cooling of cans, requiring then a shell
with holes around the cans, is also employed. With annular liners, other systems
are film cooling of the inner surfaces (see Chap. 12, Sect. 12.6.3) and heat protection by ceramic tiles covering the metal surface.
Figure 11.9 sketches a longitudinal section of a somewhat simplified and
unified version of the burner system used, with some variants, in can-annular
combustion chambers by many manufacturers (Siemens, General Electric, Mitsubishi). A number of equal burners are positioned around a more complex central