Steam concentration cell

A stable e.m.f. is also observed when air with different humidities is suppUed to the electrode compartments (cell 3). In this case, the electrode with the higher humidity is the negative pole. This is a type of steam concentration cell using a proton conducting electrolyte. The principle of the steam concentration cell is shown in Fig. 8.6 . The difference in water vapour partial pressure between the electrodes can be a driving force for the following electrode reactions. 

Generally, when gases I and II in the cell include oxygen and water vapour at different partial pressures, the e.m.f E of the steam concentration cell can be given as... 

Fig. 8.6. Prindple of steam concentration cell using a protonic conductor.

Tsurumi et al. have assembled a hydrogen concentration cell using an NH4 /H30 P"/p-gallate ceramic to measure e.m.f. values the results agree well with a thermodynamically estimated value . The group have also assembled a steam concentration cell and claim that the e.m.f. values cannot be explained by means of a simple equation . Both studies found that the large resistance of the electrolyte, which is much greater than expected for the bulk resistance makes the measurement of e.m.f. difficult. 

According to the report by Kumar et al. (1996) the temperature at which the Arrhenius slope exhibits a change corresponds well to the emf measurements, as shown in table 4 the polarity of open circuit voltage measurements changes in steam concentration cells... 

Fig. 32. Mechanism of a steam concentration cell using a solid protonic conductor PHjOCI) > PHjOOI) (Iwahara et al. 1983 a). (Reprinted by permission of the publisher, Chapman and Hall.)...

Fig. 12.2 The ionic (proton and oxide ionic) transport number of SrCe0.95Yb0.05O3 a determined by hydrogen and steam concentration cells P(H2) of 10 Pa and 10 Pa were used for the hydrogen concentration cells under P(H20) = 2.1 X 10 Pa P(H20) of 6.1 X 10 Pa and 2.1 X 10 Pa were used for the steam concentration cells using 1% H2-99% Ar mixture as a base gas...

Tuberculation Tuberculation concentration-cell corrosion may be found in all types of boilers, especially HW heating boilers and LP/HP steam-heating boilers. 

A modern synthesis gas plant can be coupled to a gas/steam combined cycle. The gases could in a future installation be consumed at enhanced efficiency by a hybrid fuel cell/combined cycle plant, notably if the fuel cells were equipped with concentration cell circulators. See Section 5.2.13. 

In the first few years after the introduction of membrane technology, diaphragm cells in several plants were equipped with membranes (retrofit) to reduce the cost of steam for cell liquor concentration, to give a small reduction in electricity consumption and better quality of caustic. This procedure is economic where steam is very expensive [188], [192],... 

Figure 7.20 shows the water steam effect on the detonation cell size in H2 + air at 0.1 MPa and 650 K temperature (H2 concentrations in the mixture are 10%, 18% and 30%). In [17] the cell sizes were measured in a heated tube of 0.27-m diameter and 21-m length. The increase in water steam concentration in the mixture has the effect of increasing cell size at a certain steam fraction, depending on H2 concentration, propagation of the detonation in the tube ceases. 

Phosphoric Acid Fuel Cell. Concentrated phosphoric acid is used for the electrolyte ia PAFC, which operates at 150 to 220°C. At lower temperatures, phosphoric acid is a poor ionic conductor (see Phosphoric acid and the phosphates), and CO poisoning of the Pt electrocatalyst ia the anode becomes more severe when steam-reformed hydrocarbons (qv) are used as the hydrogen-rich fuel. The relative stabiUty of concentrated phosphoric acid is high compared to other common inorganic acids consequentiy, the PAFC is capable of operating at elevated temperatures. In addition, the use of concentrated (- 100%) acid minimizes the water-vapor pressure so water management ia the cell is not difficult. The porous matrix used to retain the acid is usually sihcon carbide SiC, and the electrocatalyst ia both the anode and cathode is mainly Pt. 

The explicit aims of boiler and feed-water treatment are to minimise corrosion, deposit formation, and carryover of boiler water solutes in steam. Corrosion control is sought primarily by adjustment of the pH and dissolved oxygen concentrations. Thus, the cathodic half-cell reactions of the two common corrosion processes are hindered. The pH is brought to a compromise value, usually just above 9 (at 25°C), so that the tendency for metal dissolution is at a practical minimum for both steel and copper alloys. Similarly, by the removal of dissolved oxygen, by a combination of mechanical and chemical means, the scope for the reduction of oxygen to hydroxyl is severely constrained. 

Procedure. A hexane solution of Compound 118 is diluted or concentrated so as to bring the 118 content within a range of 15 to 150 micrograms per ml. In cases where the hexane solution requires concentration, the evaporation is carried out in a beaker on a steam bath with a gentle stream of air passing over the surface. The concentrated or diluted solution of 118 is washed with hexane into a volumetric flask and made up to volume with the hexane washings. One milliliter of the adjusted Compound 118 solution is precisely measured into a spectrophotometer cell, 2 drops of phenyl azide are added, and the dihydrotriazole is quantitatively formed and then treated with diazotized dinitroaniline to produce the red color as in the preparation of the standard curve. A blank, starting with 1.0 ml. of hexane and 2 drops of azide, is run at the same time. 

An ultraviolet spectrophotometric analysis is used to assay pseudoephedrine hydrochloride in tablets. A portion of finely powdered tablets equivalent to approximately 30 mg of pseudoephedrine hydrochloride is placed in a distilling flask which is part of a micro-steam distillation apparatus. Sodium chloride, water, and concentrated sodium hydroxide are added. A minimum of 30 ml of distillate is collected in a volumetric flask containing dilute hydrochloric acid. The flask is made to volume with distilled water and the absorbance of the solution is determined at 257 nm in 1 cm cells and compared to a solution of known concentration of NF Pseudoephedrine Hydrochloride Reference Standard.1... 

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