Turbine blades, deposits

Siiica S1O2 Scale in boilers and cooling water systems Insoluble turbine blade deposits due to silica vaporization Hot process removal with magnesium salts adsorption by highly basic anion exchange resins, in conjunction with demineralization distillation... 

Scale in boilers and coofing-water systems. Insoluble turbine blade deposits due to silica vaporization... 

Hard facing of various components in the aircraft gas-turbine engine and in industrial apphcations for textile machinery parts, oil and gas machinery parts, paper-shtting knives, etc, is estimated at 1 x 10 in 1995 with an estimated growth rate of 5% annually. The mix is approximately 45% aerospace apphcations, 55% industrial apphcations. Additionally, repair coatings for gas-turbine blades and vanes is estimated at 500 x 10 . These coatings are primarily deposited by plasma spray, arc-wire, HVOF, and detonation gun techniques. 

Solubility. An important aspect of sihca chemistry concerns the sihca— water system. The interaction of the various forms of sihca with water has geological significance and is apphed in steam-power engineering where the volatilization of sihca and its deposition on turbine blades may occur (see Power generation), in the production of synthetic quartz crystals by hydrothermal processes (qv), and in the preparation of commercially important soluble sihcates, coUoidal sihca, and sihca gel. 

The use of Ni-base superalloys as turbine blades in an actual end-use atmosphere produces deterioration of material properties. This deterioration can result from erosion or corrosion. Erosion results from hard particles impinging on the turbine blade and removing material from the blade surface. The particles may enter through the turbine inlet or can be loosened scale deposits from within the combustor. 

Steam turbine, 53, 146, 282-92, 179 back pressure, 282 blade deposits, 479 condensing, 282 efficiency, 288 extraction, 282 induction-type, 282 paitial admission, 288 rating, 290 reliability, 478 selecuon variable, 275, 285 speed, 278 stage losses, 286 steam temperatures, 284 steam velocity, 288 trip and throttle valve. 479 Step unloading system, 80 Stiffness coefficients, 385 Stodola slip, 153, 155 Stonewall, 186 Straight labyrinth. seal leakage, 532... 

The life of gas turbine blades is improved by platinum and/or rhodium, applied below or above, or co-deposited with, aluminised, thermal-barrier or AfCrAlY-type layers. The performance of modified aluminides was demonstrated in long-term engine trials . ... 

The efficiency of power generation is significantly reduced by any deposits formed on the turbine blades by BW carryover and severe turbine damage may also result. Tiirbine efficiency also is reduced by demands for output that exceed the rated maximum and by extended operation beyond the maintenance period or design life. Additionally, errors in steam flow meters, thermometers, and pressure gauges, and so forth cause the control system to regulate the generation of electricity at some further reduced level. 

Silica leakage (DI). Silica volatilization Deposition on boiler surfaces, superheaters, and turbine blades... 

Apart from the risk of silica problems within the boiler section, at pressures above 400 to 500 psig silica volatilization and distillation occurs, resulting in silica deposition in superheaters and on turbine blades. Under these conditions the maximum concentration of silica permitted in steam is 0.02 ppm Si02. 

As a result of the volatility of silica and its ensuing risks, such as the deposition of hard, amorphous, or glassy silicates in superheaters and on turbine blades, various actions are commonly taken in higher pressure boiler plants to limit silica vapor in steam. The maximum permissible silica concentration in steam is generally accepted as 0.02 ppm... 

Vaporous copper may be particularly damaging because it forms cuprous and cupric oxide deposits on turbine blades. 

Yttrium is also used in other areas of metallurgy notably as a component of certain nickel-base and cobalt-base superalloys of the NiCrAlY and CoCrAlY type.(3) These alloys possess excellent corrosion and oxidation resistance, properties that have attracted the attention of the aero-engine industry where they are used as protective coatings on turbine blades. The alloys, when applied by vapour deposition, form an oxide coating that exhibits remarkable adhesion, a property attributed largely to the yttrium component acting to prevent the formation of voids at the oxide/substrate interface.(4)... 

Alumina, iron, nickel, silica, sodium, and vanadium are examples of compounds which can be found in residual fuel ash. If the vanadium content of residual fuel is high, severe corrosion of turbine blades can occur and exhaust system deposit formation can be enhanced. Vanadium-enhanced corrosion can occur at temperatures above 1200°F (648.9°C). 

For one thing, steam produced from hot-lime-softened water will have some amount of silicates. These silicates tend to deposit on the rotor blades of turbines, which use the motive steam as a source of energy. The silicate fouling of the turbine blades reduces the turbine s efficiency. But, more importantly, from an operator s point of view, the silicate deposits eventually break off of the blades. This unbalances the rotor. An unbalanced rotor is the fundamental cause of vibration, Vibrations lead to damage of the shaft bearings and seals. Eventually, vibrations will destroy the turbine s internal components. 

Spray water for use in a spray attemperator should be of the highest quality. Solids entrained in die spray water enter the steam and can cause troublesome deposits on superheater tubes and turbine blades. 

After short combustion tests in the gas turbine deposits were found in the combustion chamber as shown in Fig, 5, The deposits are of a lacquer like nature and can only be removed mechanically. At present, the deposits in the combustion chamber do not constitute a problem for the operation of the gas turbine. However, there are also slight deposits on the turbine blades. 

Figure 1 from GPS A shows how the silica content of boiler water affects the silica content of steam. For example at l,600psia, 100 ppm silica in the boiler water causes 0.9 ppm silica in the steam. If this steam, were expanded to lOOpsia, following the steam line down (the saturated and superheated curves converge by the time lOOpsia is reached), the solubility of silica decreases to 0.1 ppm. Therefore the difference (0.8 ppm) would tend to deposit on turbine blades. 

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