Figure 1-... Tu.o-annular com.ustion cham.er for aircraft-type .as tur.ines.
mounted on a rollaway section to facilitate cleaning， repairs， or coil replace-ment after a long period of use.
A horizontally fired burner is located at one end of the heater. The flame extends along the central longitudinal axis of the heater. In this way the wickets are exposed to the open flame and can be subjected to a maximum rate of radiant heat transfer. The tubes should be sufficiently far away from the flame to prevent hot spots or flame pinching.
The air from the compressor enters the inlet manifold and is distributed through the first wicket set. A baffle in the inlet prevents the air flow from continuing beyond that wicket set. The air is then transferred to the return

Figure 1-... Annular com.ustion cham.er.
header and proceeds further until it encounters a second baffle. This arrangement yields various passes and helps to minimize the pressure drop due to friction. The air is finally returned to the end section of the inlet manifold and exits to the inlet gas turbine.
The burner should be designed for handling preheated combustion air. Preheated combustion air is obtained by diverting part of the exhaust from the gas turbine. The air from the turbineisclean， hot air. To recoveradditional heat energy from the exhaust fluegases， a steam coil is placed

Figure 1-... A typical sin.le can side com.ustor.
in the convection section of the heater. The steam is used for steam injection into the compressor discharge or to drive a steam turbine. The flue gas temperature exiting from the heater should be around 600 0F (316 0C).
Fuel Type
Natural gas is the fuel of choice wherever it is available because of its clean burning and its competitive pricing as seen in Figure 1-30. Prices for Uran-ium， the fuel of nuclear power stations， and coal， the fuel of the steam powerplants， have been stable over the years and have been the lowest. Environ-mental， safety concerns， high initialcost， and the long time from planning to production has hurt the nuclear and steam power industries. Whenever oil ornatural gas is the fuel of choice， gas turbines and combined cycle plants are the power plant of choice as they convert the fuel into electricity very

Figure 1-.9. An external fired com.ustor with four passes.
efficiently and cost effectively. It is estimated that from 1997-2006 23% ofthe plants will be combined cycle power plants， and that 7% will be gas turbines. It should be noted that about 40% of gas turbines are not operated on natural gas.
The use of natural gas has increased and in the year2000， has reached prices as high as US$4.50 in certain parts of the U.S. This will bring other fuels onto the market to compete with natural gas as the fuel source. Figure 1-31 shows the growth of the natural gas as the fuel of choice in theUnited States， especially for power generation. This growth is based on completion of a good distribution system. This signifies the growth of combined cycle power plants in the United States.
Figure 1-32shows the preference of natural gas throughout the world. This is especially true in Europe where 71% of the new power is expected tobe fueled by naturalgas， Latin America where 73% of the new power isexpected to be fueled by naturalgas， and North America where 84% of the
7 6 5 4 3 2 1 0

NATURAL GAS COAL DIESEL OIL CRUDE HEAVY FUEL OIL LNG Uranium TYPE OF FUEL
Figure 1-.0. Typical fuel costs per million BTUs.
new power is expected to be fueled by natural gas. This means a substantial growth of combined cycle power plants.
The new gas turbines also utilize Low N0x combustors to reduce the N0xemissions， which otherwise would be high due to the high firing temperature of about 2300 0F (1260 0C). These low N0x combustors require careful calibration to ensure an even firing temperature in each combustor. New types of instrumentation such as dynamic pressure transducers have been found to be effective in ensuring steady combustion in each of the combustors.
　
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