Effect of steam

FIG. 11-106 Effect of steam pressure on steam demand at 38 C condenser temperature (ASHRAE 1983 Equipment Handbook). 

Heat-transfer coefficients in steam-tube dryers range from 30 to 85 J/(m s K). Coefficients will increasewith increasing steam temperature because of increased heat transfer by radiation. In units carrying saturated steam at 420 to 450 K, the heat flux UAT will range from 6300 J/(m s) for difficult-to-diy and organic solids and to 1890 to 3790 J/(m s) for finely divided inorganic materials. The effect of steam pressure on heat-transfer rates up to 8.6 X 10 Pa is illustrated in Fig. 12-71. 

Here n indicates an active surface site, and X— indicates die species X adsorbed on an active site. The first reaction allows for the possibility that methane may occupy more than one active site on adsorption. The dik d and fourth reactions show die observed retarding effects of steam and hydrogen... 

Fraize, W.E. and Kinney. C. (1979), Effects of steam injection on the performance of gas turbines and combined cycles, ASME J. Engng Power Gas Turbines 101.217-227. 

Figure 6-13. Effect of steam pressure on capacity for constant system suction and back-pressure. By permission, R Freneau, [4],...

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

Figure 10-4. Effect of steam/EB, temperature, and pressure on the conversion of ethylbenzene/...

Griskin et reported that there is no apparent effect of steam pressure on the rate of oxidation of Cr-Ni steels at temperatures between 600°C and 650°C at 10.1-20.2 MPa. Similar observations for Cr-Mo and Cr-Mo-V steels between 500°C and 600°C have been made by Wiles" . She compared low-alloy steel samples exposed to 101 kPa steam with power plant components that had operated for up to 150000b in steam at 17.25 MPa and found no significant difference in the oxidation rates (Fig. 7.11). 

In addition to actual synthesis tests, fresh and used catalysts were investigated extensively in order to determine the effect of steam on catalyst activity and catalyst stability. This was done by measurement of surface areas. Whereas the Brunauer-Emmett-Teller (BET) area (4) is a measure of the total surface area, the volume of chemisorbed hydrogen is a measure only of the exposed metallic nickel area and therefore should be a truer measure of the catalytically active area. The H2 chemisorption measurement data are summarized in Table III. For fresh reduced catalyst, activity was equivalent to 11.2 ml/g. When this reduced catalyst was treated with a mixture of hydrogen and steam, it lost 27% of its activity. This activity loss is definitely caused by steam since a... 

Cause-and-effect analysis reveals that steam purity and quality are both reduced by the degree of carryover taking place in a boiler, and carryover is itself a function of the effectiveness of steam-water separation. In turn, the mechanics of separation are a function of three areas, each with its own variables ... 

Testing for steam quality measures the amount of entrained water in dry steam on a weight/weight basis. (Hence the effectiveness of steam separators and reduction in theoretical heat content can be identified.)... 

Rahn, W., Meyer, H. W., Koenig, W.A., Effect of steam treatment on the composition of phenolic components of green and roasted coffee, Z. Lebensm.-Unters. Forsch. 169, 346, 1979. (CA92 40077m)... 

Figure 23.38 The effect of steam levels on heat recovery.

Effect of steam content on product gas composition. (Adapted from Shiying, L., Michiaki, H., Yoshizo, S., and Hiroyuki, H., Energ. Corners. Manag., 46, 869-880,2005.)... 

Doi, S., Kurimoto, Y., Takahashi, M. and Yoshimura, T. (1997). Effects of steaming heat treatment on the stimulation of termite feeding. International Research Group on Wood Preservation, Doc. No. IRGAVP 97-10212. 

MacLean, J.D. (1953). Effect of steaming on the strength properties of wood. Proceedings of the American Wood Preservers Association, 49, 88-112. 

Figure 4.25 IR spectra showing hydroxyl region of H-FAU samples showing the effect of steaming and calcination.

Figure 4.28 Effect of steaming and calcination on Bronsted and Lewis acid site strength distributions of a FAU-type zeolite as determined by pyridine adsorption/desorption IR.

Effects of steaming on the shape selectivity and on the acidity of HZSM-5. React. Kinet. Catal. Lett.,... 

Effect of Steam on Reactants Adsorption over LaFeo.8Cuo.2O3... 

Effect of Steam Treatment. X-ray diffraction analyses indicated that ZSM-5 retained in excess of 90% of its crystallinity after the steam treatment described in the methods section. Unit cell constant of the REY zeolite in Super-D declined from 24.658. to 24.38a due to the steam treatment. Independent measurements... 

The effect of steam treatment of ZSM-5 on its cracking activity and selectivity was measured with experiments using n-hexadecane feed. With the thermally treated ZSM-5 catalyst, concentration of the unconverted n-hexadecane in the product was not measurable while 507e of the feed was unconverted with the steam treated ZSM-5 catalyst (Table II). The lower limit of conversion with the thermally treated catalyst corresponding to detection limit of n-hexadecane is 99.99%. This lower limit suggests at least an order of magnitude reduction in apparent first order rate constant of the ZSM-5 catalyst upon steam treatment. The small reduction in crystallinity upon steaming cannot fully explain the dramatic activity loss. Loss of active sites due to dealumination of ZSM-5 can be postulated to explain the reduction in activity. 

Effect of Steam Treatment of ZSM-5 Catalyst on Product Selectivity During n-hexadecane Cracking... 

The presence of silicon on the deactivated additive raised several questions about the silicon source and how it gets to the additive. The effect of steam was examined first. 

Two sets of experiments were made to show the effect of steaming temperature on stability. In the first set, steaming was done non-interactively. Cerium/alumina additive was steamed (100% steam, 1 atm) for 5 hours in a fixed bed from 1200 to 1450 F. SO2 removal ability was then measured on these steamed samples diluted with cracking catalyst. The data in Figure 14 show that, for steamings done separate from cracking catalyst, losses of SO2 removal ability are small but become more pronounced above 1350 F. 

Figure 8. Effect of steaming temperature on V XANES spectrum of...

Figure 9. Effect of steam treatment on V XANES spectrum of Catalyst B containing 5000 ppm V (from V 0 ) 1450 F steaming (---), 1450 F air calcination (---).

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