Expansion turbines application

Agahi, R. and Ershaghi, B., Expansion Turbine in Energy Recovery Applications, XVIIIth International Congress of Refrigeration, August 1991. 

Expansion Turbine, 296-300 applications, 300 condensation, 299 operating limits, 297 power recovery, 297 refrigeration cycles, 298 reliability, 480 types. 206 Experience... 

Expansion turbines are related in many design features to the centrifugal compressor. The key exception being that the turbine receives a high pressure gas for expansion and power recovery to a lower pressure and is usually accompanied by the recovery of the energy from the expansion. For example, applications can be (1) air separation plants (2) natural gas expansion and liquefaction (for gas let-down in pipeline transmission to replace throttle valves where no... 

Expansion Turbines for Energy Conversion and Cryogenic Applications, Atlas Copco, Bui. 2781005601, pub. date not known. 

Application of liquid and gas expansion turbines can recover mechanical work (e.g.,... 

In 1973, Hastelloy S was developed for gas turbine applications requiring oxidation resistance, good alloy stability, and a low thermal expansion. The chemical composition will be foimd in Table 15.19. Its composition is similar to that of alloys C-4 and C-276, and it has similar corrosion resistance. However, the carbon content may prevent its use in some aqueous media in the as-welded condition. After 10,000 h of aging in the temperature ranges encoimtered in this application, the alloy S welds exhibited 80% of their original ductility. 

Expanders have not been the essence of reliability. It is not that the expander design in itself has any significant problems. The problems for the most part seem to be related to the application. Most of the failures have been the result of the expander ingesting foreign substances, such as the catalyst in a catalytic cracking unit heat recovery application. Unlike the expansion section of the gas turbine, the inlet temperature is not as high, therefore, temperature is not a significant factor in reliability reduction. 

Carbide-based cermets have particles of carbides of tungsten, chromium, and titanium. Tungsten carbide in a cobalt matrix is used in machine parts requiring very high hardness such as wire-drawing dies, valves, etc. Chromium carbide in a cobalt matrix has high corrosion and abrasion resistance it also has a coefficient of thermal expansion close to that of steel, so is well-suited for use in valves. Titanium carbide in either a nickel or a cobalt matrix is often used in high-temperature applications such as turbine parts. Cermets are also used as nuclear reactor fuel elements and control rods. Fuel elements can be uranium oxide particles in stainless steel ceramic, whereas boron carbide in stainless steel is used for control rods. 

Cyclic Oxidation In many industrial applications it is particularly important for the component to be resistant to thermal shock for example, resistance-heating wires or blading for gas turbines. Chromia, and especially alumina, scales that form on nickel-base alloys are prone to spalling when thermally cycled as a result of the stress build-up arising from the mismatch in the thermal expansion coefficients of the oxide and the alloy as well as that derived from the growth process. A very useful compilation of data on the cyclic oxidation of about 40 superalloys in the temperature range 1 000-1 I50°C has been made by Barrett et... 

The main application for this cycle is the air-conditioning and pressurization of aircraft. The turbines used for compression and expansion turn at very high speeds to obtain the necessary pressure ratios and, consequently, are noisy. The COP is lower than with other systems [15]. 

Balanced research of oxide and non-oxide materials on their specific life-limiting characteristics appears to be necessary because neither class of materials can satisfy design and service life requirements for all of the anticipated applications. For example, SiC-based materials have the high thermal conductivities and low thermal expansion coefficients essential for some components, particularly in high performance turbines for which oxides are inadequate. Conversely, in some corrosive environments (e.g., hot gas filters in coal-fired power systems), oxides provide necessary corrosion resistance. 

Porous aluminum titanate DMO has both a low thermal expansion coefficient (nearly zero at least up to 600°C) and a low thermal conductivity, suggesting possible applications in thermal barriers and abradable seals for turbine rotor shrouds [116] and automobile exhaust port liners and gas desulfurization nozzles [117]. Other possible thermal applications of silicon carbide reinforced DMO include heat exchangers [117] and flaps and seals in the afterburners of jet engines [119]. In addition, SiC particulate-reinforced DMO could serve as a lossy insert for high powered microwave tubes, withstanding temperatures up to 1000°C in ultrahigh vacuum. 

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