Effect of Wet Steam

Wet steam erodes the ejector nozzle and interferes with performance by clogging the nozzle with water droplets [16]. The effect on performance is significant and is usually reflected in flucluadng vacuum. 

Applied Process Design for Chemical and Petrochemical Plants 

I suppose it may seem strange that creating more condensation of the motive steam could allow more useful work to be extracted from the steam. But it was this particular observation that led James Watt to vastly increase the efficiency of the steam engine almost 200 years ago. On the other hand, moisture in the motive steam supply itself is bad. As the steam is expanded to a lower pressure, the moisture in the supply steam will evaporate and cool off the steam, thus reducing the amount of sensible heat that could be converted to steam velocity. 

A useful way of summarizing the concepts I have just related is to think about momentum. That is  

When we operate a steam turbine, we are trying to provide a certain amount of horsepower to drive our pump, or compressor, or generator. If I want to provide this power with less mass of steam, I need to increase the velocity of the steam. And this is done by extracting more sensible heat from the motive steam, and more importantly, more latent heat from the motive steam. 

You can see quite clearly that it is not the pressure of the steam that is driving a turbine. Place a pressure gauge on the turbine case of a single-wheel machine. The pressure on the turbine case will be quite close to the exhaust steam pressure and certainly not the motive steam pressure. 

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Effect of Wet Steam. Steam turbines should not be operated with wet steam. The manufacturers will not guarantee performance when the moisture is greater than 3%. 

Air/water vapor mixture, chart, 364,365 Air/water vapor, 359 Capacity at ejector suction, 369 Capacity for process vapor, 362 Evacuation time, 371, 380 Load for steam surface condenser, 367 Non-condensables, 362, 363 Size selection, 371 Steam pressure factor, 373 Steam requirements, 372 Steain/air mixture temperature, 361 Total weight saturated mixture, 362 Capacity, 358 Discharge, pressure, 358 Effect of excess steam pressure, 358 Effects of back pressure, 359 Effects of wet steam, 356 Inter-and-after condenser, 351 Load variation, 370 Materials of construction, 347 Molecular weight entrainment, chart, 360 Performance, 358, 370, 375 Relative comparison, 357... 

The effect of small amounts of copper in steel on erosion resistance is controversial. Some tests indicate a benefit, while others reveal no effect on wet steam erosion resistance. Some researchers use the equation R = 0.61 + 2.43 Cr + 1.64 Cu + 0.3 Mo to estimate the relative resistance of carbon steel to... 

For pressure turbines, the area of the annulus at the low-pressure end is an index to the steam flow. About two-thirds the area may be effective, the remainder being used up by the bucket thickness. The velocity to be considered is that normal to the disc, or the steam velocity multiplied by the sine of the exit angle of the buckets say by sin 20°. The specific volume is that of wet steam at the exhaust pressure, say about 275 cu. ft. at 28 in. vacuum. Then at a maximum steam velocity of 900 ft. per second, if the diameter of the (single) low-pressure drum is d in. and the blade height (last row) is h in., the weight of steam discharged per hour is bS.Sh (d -f h) lb. Thus for d = 25, /i = 5, the weight of steam is 8,820 lb. per hour. 

Equation (16.85) possesses the advantage that it is independent of efficiency calculations. Hence p criii/PoT may now be computed off-line from the main simulation in all cases where y i constant. The only exception is the case of wet steam, where the effective value of y depends on the dryness fraction, x. 

It can be seen that the end point of the expansion (point 2 ) is in the area of wet steam. Thus small droplets of condensate will form in the motive jet. In the motive nozzle, combined with the decrease of pressure, the temperature will also decrease. In the wet steam region the steam is cooled to the boiling point temperature corresponding to the pressure. When the motive steam expands to a pressure lower than 6mbar, the corresponding temperature is below 0°C, thus ice will form. Steam jet vacuum pumps for such applications are often heated at the mixing nozzle and sometimes also at the motive nozzle, to prevent the ice crystals from adhering to the internal wall. This would cause a constriction of the cross-sectional area and adversely effect the flow. 

Liquid pyridine and alkylpyridines are considered to be dipolar, aprotic solvents, similar to dimethylformarnide or dimethyl sulfoxide. Most pyridines form a significant azeotrope with water, allowing separation of mixtures of pyridines by steam distillation that could not be separated by simple distillation alone. The same azeotropic effect with water also allows rapid drying of wet pyridines by distillation of a small forecut of water azeotrope. 

A method [62] has been described for the determination of down to 2.5ppb alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. These workers considered the possible interference effects of clay, humic acids, and sulphides, all possible components of river sediment samples on the determination of alkylmercury compounds and inorganic mercury. 

Extending this concept, we now consider those experiments which led to molten aluminum-water explosions without the presence of a wet, solid surface. In all of these there was an external shock applied to the system—usually in the form of an exploding wire or a detonator. As presumed by the investigators, these artificial shocks could be very effective in collapsing steam films. 

If the water were to be injected into a cold engine cylinder, the flash steam would immediately condense and there would be no pressure rise. To overcome this problem, the cylinder head and walls are heated and supply additional heat to the wet steam entering the cylinder. The atomised water droplets experience extremely high collision rates with the cylinder walls because of the explosive effect of the flash process. The tiny size of the droplets, coupled with high collision rates ensure rapid absorption of heat allowing them to be quickly converted to steam which is then heated further to superheat. 

A number of physical tests have been proposed for the estimation of catalytic activity, but except for purposes of control in catalyst manufacture none of these is an acceptable substitute for direct cracking tests. In general, such tests as the measurement of the selective adsorption of an aromatic hydrocarbon from a standard binary mixture of aromatic and paraffinic components (Scheumann and Rescorla, 19), or the measurement of the heat of wetting with methanol (Mills, 20) merely reflect the extent of available surface. With a given catalyst composition, these methods may have some utility in following the decline of activity due to the effects of temperature or steam (but not of sulfur) or as a rapid and approximate control method in the manufacture of a catalyst. 

Effect of Temperature and Steam Rate. Gasification experiments similar to the standard tests were conducted in unit A except that the reaction temperatures were varied from 650° to 950 °C and steam rates used were 1.16 and 5.8 grams/hr. The catalyst used was flame-sprayed Raney nickel 65% activated. Also, tests were conducted at 750°C and 1.16 grams/hr steam rate with sprayed Ranel nickel activated and charged wet and at 850°C and 5.8 grams/hr steam rate with sprayed Raney nickel unactivated. 

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