Superheated principle

Steam injection. Steam injection reduces combustion temperature by adding an inert to the combustion process. In principle, water or steam could be injected, but dry superheated steam is usually used. This reduces the furnace efficiency as energy is used to produce the steam, and the latent heat in the steam cannot be recovered. It is only used for moderate NO reduction. Steam injection can also be used in gas turbines. 

An evaporator operating on the thermo-recompression principle employs a steam ejector to maintain atmospheric pressure over the boiling liquid. The ejector uses 0.14 kg/s of steam at 650 kN/m2, and is superheated by 100 K and the pressure in the steam chest is 205 kN/m2. A condenser removes surplus vapour from the atmospheric pressure line. What is the capacity and economy of the system and how could the economy be improved ... 

Replacing sterilizers that operate by one set of principles with sterilizers that operate by another principle (e.g., substituting a gravity displacement steam process with a process using superheated water spray). 

We easily find the dependence of the evaporation rate on superheating by applying the principle of detailed equilibrium. The accommodation coefficient, i.e., the probability that molecules of vapor falling onto the surface of the liquid will stick, we take equal to 1. The number of molecules which evaporate in unit time is equal to the number of molecules which fall in unit time onto the surface at equilibrium pressure which, in turn is equal to the product of half the number n of molecules in a unit volume of vapor and the average velocity cx of the molecules in the direction normal to the surface. 

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). 

Accordingly, a dual control principle is provided that acts independently on both parameters. Two methods currently in use are superheated water spray and steam-air mixture. 

Problem 11.7 Predict the product or products of (a) monobromination of toluene (b) monobromination of p-toluenesulfonic acid followed by treatment with acid and superheated stean . (c) Using the principle of (b), and following the guidelines of S. 11.7, outline a synthesis from benzene of o-dibromobenzene of o-bromochlorobenzene. 

The dehydrogenation of butenes in the presence of steam was developed initially by Esso, Shell and Phillips. In accordance with the operating principles of this type of process, the preheated feed is mixed with superheated steam and then sent to adiabatic reactors containing catalyst beds 80 to 90 cm thick. The temperature, initially 620 C, must be raised progressively as catalyst activity decreases. The latter is regenerated by simple steam treatment The reaction pressure is 0.1 to 0.2.10A Pa absolute, and reaches 0.5. 1C6 Pa absolute during regeneration. 

As noted above, any direct dryer, in principle, can be converted to superheated steam operation (e.g., flash, fluid bed, spray, impinging jet, conveyor dryers, etc.). Thermal efficiencies can be improved and the unit size reduced by supplying a part of the heat indirectly (e.g., by conduction or radiation). Note that the inversion temperature is lowered in the presence of indirect heat supply, which is a further benefit. For example, in the presence of appropriate radiant heating, the inversion temperatnre dropped from 250 C to ITO C for a specific case reported in the literature. 

Biofuels and peat can be dried according to different thermodynamic principles. The most common method is the use of flue gases. Another is the use of superheated steam. Finally, double-effect drying will be discussed. 

FIGURE 36.3 Principle of superheated steam dryer in combination with a boiler. 

Mujumdar, A.S. Superheated steam drying of paper Principles, status and potential. InDrying of solids, Mujumdar, A.S., Ed., International Seienee Pubhsher New York, 1992,... 

Mujumdar, A.S., Superheated steam drying Principles, practice and potential for use of electricity, Canadian Electrical Association, Montreal, Quebec, Canada, Report no. 817 U 671,1990, p. 127. 

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