Contents

3.1 Basic Cycle

3.1.1 Compression

3.1.2 Combustion

3.1.3 Turbine Power Production

3.1.4 Ancillary Equipment

3.2 Recuperated Brayton Cycle

3.3 Modified Gas Turbine Cycle

3.4 Turbine Performance

3.5 Future Developments

3.6 Controls

3.7 Costs

3.8 Fuels

Additional Reading

Natural gas-fired combustion turbines are the most widely adopted prime movers for new power generation worldwide, based on the aggregated power rating; in the year 2000, over 4000 units were sold or ordered. The benefits of gas turbines in power generation are fivefold: (1) comparatively low installation cost per MW output, (2) increasing availability of natural gas for low fixed-price contracts, (3) explosion of demand for peaking capacity in a deregulated energy marketplace combined with (4) the higher electrical efficiencies of aeroderivative turbines, and (5) the ability to site and install units from 1.7 to 40 MW (and larger) in weeks to months, not years.

Basic gas turbine (GT) technology is mature; performance improvements are incremental. Component efficiency is probably the most important performance factor for GTs. A slight increase in efficiency for one component can have significant impacts on the net system efficiency. Incremental improvements to GT components have increased large system conversion efficiency from 25% (LHV basis) in the 1950s to 35-38% in current models.

3.1 Basic Cycle

Gas turbines consist of a compressor, combustor, and turbine-generator assembly that converts the rotational energy into electrical power output. The standard conditions for the ambient air flowing through the GT are assumed to be at 59°F (15°C), 14.7 psia (1.013 bar), and 60% relative humidity. A simple-cycle single-shaft GT is shown in Figure 3.1. As can be seen, singleshaft turbines are configured in one continuous shaft, and, therefore, all stages of the turbine operate at the same speed. These types of units are typically used for generator-driven applications where significant speed variation is not required.

FUEL BLEED

COMPRESSOR INJECTOR AIR

FUEL BLEED

COMPRESSOR INJECTOR AIR

FIGURE 3.1

Gas turbine cross section.

FIGURE 3.1

Gas turbine cross section.

The low pressure or power turbine rotor can be mechanically separated from the high-pressure turbine and compressor rotor. This feature allows the power turbine to be operated at a wide range of speeds and makes it ideally suited for variable-speed applications. All of the work developed by the power turbine is available to drive the load equipment since the high-pressure turbine exclusively drives the compressor. The starting requirements for the load train are also reduced since the load equipment is mechanically separate from the high-pressure turbine. The simple-cycle GTs are a mature technology based on the thermodynamics of the Brayton (or Joule) cycle with the following paths:

Path 1-2: Compression of atmospheric air

Path 2-3: Heating compressed air via fuel combustion

Path 3-4: Expansion of heated air-fuel mixture through a turbine, rotating the blades Path 4-1: Discharging exhaust gases back to the atmosphere

For electric power applications, the nominal rating is measured at the output terminals of the electric generator to include gearing and generator losses. It does not take into account inlet filter or exhaust silencer losses or auxiliary running loads. Natural gas fuel can give a 2 to 3% higher output and a 1 to 2.2% improvement in heat rate over the same machine burning No. 2 distillate oil. Inlet filter and exhaust losses can be equivalent to around a 2% penalty, while auxiliary running losses add about a 0.6% penalty in available power output and heat rate. If gears are used for speed reduction, gearing losses can be as high as 1.5% depending on the specific design and gear ratios, while the electric generator loss is usually about 2% of the GT shaft power output.

Lower heating value (LHV) efficiencies for this design (compressor, com-bustor, turbine) range from 18 to 35%. The energy losses are consumed by the compressor and other auxiliaries as discussed above. Most of the work produced in the turbine is used to run the compressor, and the rest is used to run auxiliary equipment and produce power.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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