Axial compressors blades

Figure 4-15. Axial compressor with fixed stator blades, double-casing design, and forged monoblock rotor. Particularly suitable for compressing nitrous gases. There are no dead spaces provoking buildup of ammonium nitrate salt.

Figure 4-16. Axial compressor with adjustable stator blades, either partially or on all stages. Double-casing design and forged monoblock rotor. This design offers a wide operating range especially in combination with speed control.

As with other types of rotating machinery, an axial compressor can be described by a cylindrical coordinate system. The Z axis is taken as running the length of the compressor shaft, the radius r is measured outward from the shaft, and the angle of rotation 6 is the angle turned by the blades in Figure 7-2. This coordinate system will be used throughout this discussion of axial-flow compressors. 

Inlet startup screens have been recommended for other compressors covereii in the earlier chapters. If the point has not been made yet. n should be with the axial compressors. Considering that most of the cost of the compressor is in the hundreds of vulnerable blades just waiting to be hit by some foreign object, it should be obvious that some protection is needed until the piping has been proven to be clear and clean. 

Axial compressor blades are usually forged and milled. Precision casting has been used on occasion. The most common material used is a 12 chrome steel, in the AISI 400 series, and is also known as 400 series stainless steel. While the stator blades are occasionally shrouded, the rotor blades are free-standing. Lashing wires have been used on rotor blades, but are generally used to solve a blade vibrational stress problem. 

Because most axial compressors are in air service, most are equipped with labyrinth type end seals. There are no interstage seals in the machines with unshrouded stator blades. The balance piston seal, a labyrinth type, is the only internal seal. There is no reason that axials cannot use some of the other seals as described in Chapter 5, such as the controlled leakage or the mechanical contact type, if the gas being handled by the compressor needs a more positive seal. If there is any prob-... 

Figures 12-99, 12-100, and 12-101 show approximate speed-capacity comparisons with the centrifugal machine. Each stage consists of one stationary plus one rotating blade row. Figure 12-101 shows an axial compressor performance handling 100 psia air.

Figure 12-95. Axial compressor Type AV100-16, during erection. Note stationary and rotating blades. Two identical steam turbine-driven machines supply air to blast furnace at steel works. Suction volume = 560,000 NmVh discharge pressure = 6.2 bar power input = 52,000 kW each. (Used by permission Bui. 26.13.10.40-Bhj. Sulzer Turbo Ltd.)...

Figure 12-96. Stator blade control mechanism on four-stage axial compressor. (Used by permission A C Compressor Corporation.)...

Figure 12-100. Pressure-capacity characteristic comparison of an axial compressor with adjustable stator blades with a centrifugal compressor. (Reprinted with permission Lowell, W. O. Petroleum Refiner, V. 34, No. 1, 1955. Gulf Publishing Company. All rights reserved.)...

For a dynamic compressor, a continuous totfUtng element (rotor) js used to increase gas velocity. Then, gas velocity is converted to static pressure at compressor outlet. Dynamic compressor is classified as centrifugal or axial compressor. For centrifugal compressor, the rotating element is an impeller, and gas flow is in either radial or mixed flow direction. For axial compressor, the rotating element is a bladed rotor and gas flow is in the axial directioa... 

The symptoms of surge are pulsating pressure, rapid flow reversals, a drop in motor current and a jump in turbine speed. Continuous, rapid flow reversals can cause severe damage to the compressor. In axial compressors the blades may touch, resulting in instant destruction. However, centrifugal compressors are more mgged, and only seal damage results [15]. 

Tarabrin, A. E, Schurovsky, V. A., Bodrov, A. I., Stalder, J. E, 1996, An Analysis of Axial Compressor Fouling and a Cleaning Method of their Blading, ASME Paper No. 96-GT-363. 

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