Superheated steam tube

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. 

A good summary of the behavior of steels in high temperature steam is available (45). Calculated scale thickness for 10 years of exposure of ferritic steels in 593°C and 13.8 MPa (2000 psi) superheated steam is about 0.64 mm for 5 Cr—0.5 Mo steels, and 1 mm for 2.25 Cr—1 Mo steels. Steam pressure does not seem to have much influence. The steels form duplex layer scales of a uniform thickness. Scales on austenitic steels in the same test also form two layers but were irregular. Generally, the higher the alloy content, the thinner the oxide scale. Excessively thick oxide scale can exfoHate and be prone to under-the-scale concentration of corrodents and corrosion. ExfoHated scale can cause soHd particle erosion of the downstream equipment and clogging. Thick scale on boiler tubes impairs heat transfer and causes an increase in metal temperature. 

Internal Regenerator Bed Colls. Internal cods generate high overall heat-transfer coefficients [550 W / (m -K)] and typically produce saturated steam up to 4.6 MPa (667 psi). Lower heat fluxes are attained when producing superheated steam. The tube banks are normally arranged horizontally in rows of three or four, but because of their location in a continuously active bubbling or turbulent bed, they offer limited duty flexibdity with no shutdown or start-up potential. 

In this design, the secondary circuit FW is again on the shell side, but recirculation takes place within the steam generator, resulting in the formation of a steam-water mixture that covers the top of the inverted U-tube bundle. Saturated (but not superheated) steam passes through high-efficiency moisture separators and from here is again distributed to the turbine. 

Saturated or superheated steam flows on the shell side and FW on the tube side. Closed FW heaters are so called because the steam and water do not come into contact with each other. Most are of a horizontal design although vertical FW heaters are manufactured. 

For superheated steam, the sample points should be designed and installed to permit correct isokinetic sampling. A modified multiport nozzle design ensures that the velocity of the steam entering the sample nozzle is the same as the velocity of steam in the header. The design incorporates a small, high-quality water delivery tube, used to inject water and remove superheat before sample extraction. 

Substances which volatilise only with very great difficulty are distilled with superheated steam. The superheating takes place in a copper tube (Fig. 22) wound in a conical spiral, interposed between... 

Estimate the volumetric expansion rate if the tubing is exposed to 500 F superheated steam. 

The steam enters through the top of the channel head of the reboiler. Any superheat in the steam is quickly lost to the tubes. Superheated steam does very little in increasing heat-transfer rates in a reboiler. Actually, when considering the temperature difference between the steam and the process fluid, it is best to use the saturated steam temperature, as the real temperature at which all the heat in the steam, is available. For example, assume the following steam flow to a reboiler ... 

Ethylene is made by pyrolysis of hydrocarbon vapors in tubes of 50-100 mm dia and several hundred meters long with a reaction time of several seconds heat is supplied by mixing with superheated steam and by direct contact of the tube with combustion gases. 

Typically, the tubing in the convection zone is placed in a hairpin fashion or series of connected U bends and is suspended horizontally. The steam that will be used as a diluent is also heated in the convection zone in other tubes. This superheated steam and the gaseous hydrocarbons are... 

Fig. 23. (a) Laboratory apparatus for distilling with superheated steam 1, steam generator 2, water trap with vertical safety tube 3, superheater 4, distillation vessel in oil bath 5, condenser with wide tube 6, device for pushing out solid material collecting in the condenser 7, receiver for distillate 8, gas line 9, cooling water. 

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