Superheated water vapor

Diying with pure superheated water vapor has the advantage that no air must be heated and for this reason heat exchangers are not necessary. For water-moistened goods, the vapor pressure reaches the saturation pressure, so that the evaporated moisture does not move through the pores due to diffusion, but according to the laws of laminar flow. Therefore, drying times can be reduced. Superheated steam... 

It appears that the results of experimental studies presented in this chapter have amply demonstrated the technical feasibility of plasma-assisted drying. The most promising is the use of a plasma and/or superheated water vapor as the heat source and drying carrier. In addition to the advantages inherent to superheated steam drying (see Chapter 7), the use of steam plasmas may offer the following benefits ... 

Pyrohydrolysis is a technique that uses decomposition of the matrix by superheated water vapors. This technique can be used for the determination of halogens, borates, nitrates, sulfates, etc. in various food matrices. 

Property values for superheated water vapor and subcooled liquid water are presented in Appendices B.4 and B.5, respectively. In these regions, T and P are independent, so if we specify both, we constrain the state of the system. The tables are organized first according to pressure, then by temperature at each specified pressure. With T and P specified, values of the other properties (o, m, h, and s) are reported. The data in the superheated steam tables begin with the saturated state, whereas the data in the subcooled water tables end at saturation. The usefulness of the steam tables is that in knowing any two independent properties of water, we may look up the values of any of the other properties to solve engineering problems. 

Superheated water vapor at a pressure of 200 bar, a temperature of SOO Xi , and a flow rate of 10 kg/s is to be brought to a saturated vapor state at 100 bar in an open feedwater heater. This process is accomplished by mixing this stream with a stream of liquid water at 20 C and 100 bar. What flow rate is needed for the liquid stream ... 

Fresh reducing gas is generated by reforming natural gas with steam. The natural gas is heated in a recuperator, desulfurized to less than 1 ppm sulfur, mixed with superheated steam, further preheated to 620°C in another recuperator, then reformed in alloy tubes filled with nickel-based catalyst at a temperature of 830°C. The reformed gas is quenched to remove water vapor, mixed with clean recycled top gas from the shaft furnace, reheated to 925°C in an indirect fired heater, and injected into the shaft furnace. For high (above 92%) metallization a CO2 removal unit is added in the top gas recycle line in order to upgrade the quaUty of the recycled top gas and reducing gas. 

As each kernel is heated, the water within each kernel is also heated to the point that it would turn into water vapor. The shell of the kernel, however, is airtight and this keeps the water as a superheated liquid. Eventually, the pressure exerted by the superheated water exceeds the holding power of the kernel and the water bursts out as a vapor, which causes the kernel to pop. These are physical changes. The starches within the kernel, however, ate also cooked by the high temperatures, and this is an example of a chemical change. 

Cholesterol is a low-volatile compound, but it is more volatile than the major triglycerides of milkfat. Superheated steam can be bubbled through the oil, heating it indirectly, which provides for the latent heat of vaporization of the distilling compounds and prevents steam condensation. Thus, the temperature and pressure can be varied independently. When the sum of the partial vapor pressures of water vapor and the distillates is equal to the total pressure, water vapor and the low-volatile components, such as cholesterol and free fatty acids, distill over. 

Henkel has developed a continuous countercurrent esterification using a doubleplate reaction column. The technology is based on the principle of an esterification reaction with the simultaneous absorption of the superheated methanol vapor and desorption of the methanol-water mixture (15). 

The flue gas is cooled to about 600°F. by passage through a waste-heat steam boiler, and further cooled to 400°F. or lower by injecting a spray of superheated water, before introduction into the Cottrell (234). A 20-25 vol. % concentration of water vapor is maintained in the gas in order to minimize arcing. Injection of a small amount of ammonia, about 0.005% by weight of the flue gas, has also been found beneficial. 

One way to increase the temperature of the vapor is to compress it. Fig. 1 shows how adiabatic compression of water vapor (treated as an ideal gas) increases its temperature. Note that the temperature rises faster with increases in pressure than the boiling point increases. Thus adiabatic compression of a saturated vapor nearly always produces a superheated vapor. When heat is removed from this compressed vapor, it will eventually condense at its boiling point for that pressure. 

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