Heat storage hydrates

Gas leaving the economizer flows to a packed tower where SO is absorbed. Most plants do not produce oleum and need only one tower. Concentrated sulfuric acid circulates in the tower and cools the gas to about the acid inlet temperature. The typical acid inlet temperature for 98.5% sulfuric acid absorption towers is 70—80°C. The 98.5% sulfuric acid exits the absorption tower at 100—125°C, depending on acid circulation rate. Acid temperature rise within the tower comes from the heat of hydration of sulfur trioxide and sensible heat of the process gas. The hot product acid leaving the tower is cooled in heat exchangers before being recirculated or pumped into storage tanks. 

A comparison between structures of calcium(II) chloride hydrate crystals and melts, which can be used as a heat storage material, has been carried out by means of X-ray diffraction (52). The phase diagram of... 

Latent Heat storage at low temperature hydrated salts... 

The heat-storage and heat-release reactions occur at different pressure levels. The low-temperature side has a higher reaction equilibrium pressure. The CHP, as studied earlier, operates as a batch system with a heat-storing step followed by a heat-releasing step. For example, hydration and carbonation reactions can be used on the high-temperature (600 to 1200 K) side reactor. Evaporation and condensation of the reactant media are often used on the low-temperature (273 to 523 K) side reactor. 

Watanabe, Y., Salto, T., Nakal, T. Acceleration effect of a nucleatlon agent on the crystallization of salt hydrate as a heat storage material. In Industrial Crystallization 67 (eds. N lt, J., Z 6ek. S.), p. 141, Academia Prague and Elsevier Amsterdeim 1979... 

Hydrated inorganic salts Melting point rc) Melting heat (kJ/kg) Density (kg/m ) Specific heat capacity (J/(kgK)) Heat storage density (MJ/m )... 

Hydrated salts are the intermediate compounds of water-salt systems. Some hydrated salts (such as CaCl2.6H20, CaCNOs) 6H2O) are good materials for heat storage, and many hydrated double salts(such as alum) are industrial products. The computerized prediction of the formation and stability of hydrated salts and hydrated double salts is crucial for the computerized prediction and assessment of the phase diagrams of water-salt systems. 

Voigt W, Zheng D (2002) Solid-liquid equilibria in mixtures of molten salt hydrates for the design of heat storage materials. Pure Appl Chem 74 1909-1920... 

Figure l.ll Heat flow calorimetry of freshly bagged and artificially aged CEM I 42.5 N (storage at 90% relative humidity for 3 days). In case of the aged cement both the silicate and the second aluminate reaction are retarded, and the measured heat flow is lower compared to that of the fresh sample. Heat of hydration after 72 h is 248 J/g for the fresh cement, and 185 J/g for the aged cement. (Adapted from Winnefeld, F., ZKG International, 61 (I l), 68-77, 2008.)... 

Anhydrous sodium tripolyphosphate is slow to hydrate in contact with the atmosphere under normal ambient conditions and generally remains free-flowing. If the relative humidity is below a critical relative humidity, which is different for both anhydrous forms of STP and dependent on temperature, hydration does not take place. For prolonged storage at room temperature, relative humidities above ca 60% in the air result in water absorption. For shorter periods, high levels of humidity can be tolerated. However, even at higher humidities, the amount of water absorbed is small. The heats evolved from vapor hydration of STP-I and -II have been estimated at 343 and 334 kj /mol (82.0 and 79.9 kcal/mol), respectively (25). 

For off-site transportation, the phosphoms is loaded into railcars for transfer to the sites where it is used directly as a raw material or burned and hydrated to phosphoric acid. During shipping, the phosphoms is allowed to soHdify in the cars. The railcars are commonly double walled with a jacket that can be heated with steam or hot water so that the phosphoms can be remelted on-site for transloading to local storage tanks. For overseas shipping, tanktainers with reinforced superstmcture for safe handling are used. Formerly, full tanker ships were in use. 

The properties of calcium chloride and its hydrates are summarized in Table 1. Accurate data are now available for the heats of fusion of the hexahydrate, the incongment fusion of the tetrahydrate, and the molar heat capacities of the hexahydrate, tetrahydrate, and dihydrate (1). These data are important when considering the calcium chloride hydrates as thermal storage media. A reevaluation and extension of the phase relationships of the calcium chloride hydrates, has led to new values for the heats of infinite dilution for the dihydrate, monohydrate, 0.33-hydrate, and pure calcium chloride (1). 

Values taken from S. Glasstone. Thermodynamics for Chemists. D. Van Nostrand Company Inc., Toronto, p. 443 (1947). The values tabulated in this reference were taken from D. N. Craig and G. W. Vinal, J. Res. Natl. Bur. Stand.. Thermodynamic Properties of Sulfuric Acid Solutions and Their Relation to the Electromotive Force and Heat of Reaction of the Lead Storage Battery", 24, 475-490 (1940). More recent values at the higher molality can be found in W. F. Giauque. E. W. Hornung. J. E. Kunzler and T. R. Rubin, The Thermodynamic Properties of Aqueous Sulfuric Acid Solutions and Hydrates from 15 to 300° K", J. Am. Chem. Soc.. 82, 62-70 (1960). 

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