Steaming potential measurements

In the steaming-out process excess chlorine is used and recycled. The major process conditions that are measured and controlled are temperature, pressure, pH, and oxidation potential. 

Energy Efficiency Measures and Estimated Improvement Potentials for Steam Boilers. 

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

The review of Martynova (18) covers solubilities of a variety of salts and oxides up to 10 kbar and 700 C and also available steam-water distribution coefficients. That of Lietzke (19) reviews measurements of standard electrode potentials and ionic activity coefficients using Harned cells up to 175-200 C. The review of Mesmer, Sweeton, Hitch and Baes (20) covers a range of protolytic dissociation reactions up to 300°C at SVP. Apart from the work on Fe304 solubility by Sweeton and Baes (23), the only references to hydrolysis and complexing reactions by transition metals above 100 C were to aluminium hydrolysis (20) and nickel hydrolysis (24) both to 150 C. Nikolaeva (24) was one of several at the conference who discussed the problems arising when hydrolysis and complexing occur simultaneously. There appear to be no experimental studies of solution phase redox equilibria above 100°C. 

Consider deionized water. This has a K value of about 3 x 10-8. Hence, if r 10-5 cm, ir/K= i. 10 5/3 x 10-8 — 333i. Thus, for ir/K < 0.01, acunent density of as much as 30 pA cm-1 could be measured at an ultramicroelectrode in deionized water current. Correspondingly, ultramicroelectrodes have made possible valid potential electrochemical measurements in the electrolysis of steam (Bond and Fleischmann, 1984). 

T oxic elements are present in trace quantities in coal and other fossil fuels. Since enormous quantities of these fuels are consumed each year, appreciable quantities of the associated, potentially harmful toxic elements are produced. For example, if 600 million tons of coal are burned each year in the U.S. with average concentrations (ppm) of Hg-0.10, Pb-20, Cd-0.4, As-5, Se-5, Sb-4, V-25, Zn-200, Ni-100, Cr-20, and Be-2, the corresponding tonnages of the elements released are Hg-60, Pb-12,000, Cd-240, As-3000, Se-3000, Sb-2400, V-15,000, Zn-120,000, No-60,000, Cr-12,000, and Be-1200. (The concentrations are representative of values measured for coal burned at the Allen Steam Plant.)... 

The stability of MCM-41 is of great interest because, from the practical point of view, it is important to evaluate its potential application as a catalyst or adsorbent. It is known that purely-siliceous MCM-41 (designated here as PSM) has a high thermal stability in air and in oxygen containing low concentration (2.3 kPa) of water vapor at 700 °C for 2 h [1], However, the uniform mesoporous structure of PSM was found to be collapsed in hot water and aqueous solution due to silicate hydrolysis [2], limiting its applications associated with aqueous solutions. After MCM-41 samples were steamed in 100% water vapor at 750°C for 5 h. their surface areas were found to be lower than amorphous silica-alumina and no mesoporous structure could be identified by XRD measurement [3]. In addition, PSM showed poor stability in basic solution [4]. 

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