Supercritical “steam

For applications involving steam pressures that exceed 3200 psig (supercritical steam applications), it is again best to contact the SRV manufacturer for assistance in sizing and selection. Both sizing and, in particular, material selection at these extreme high ratings become critical, and not all manufacturers carry valves for this kind of application. 

Oka Y, Kataoka K. (1992) Conceptual design of a fast breeder reactor cooled by supercritical steam. Ann NuclEnergy 19 243-247. 

In a very early study Patat (1945) investigated the hydrolysis of aniline to phenol in a water-based acidic solution in near-critical and supercritical water (Tc = 374.2°C, Pc = 220.5 bar). Phosphoric acid and its salts are used as the catalyst for this reaction. The reaction proceeds extremely slowly under normal conditions and reaches equilibrium at low conversion levels. For these reasons, Patat chooses to study the reaction in supercritical water to temperatures of 450°C and to pressures of 700 bar in a flow reactor. He finds that the reaction follows known, regular kinetics in the entire temperature and pressure space studied and the activation energy of the hydrolysis (approximately 40 kcal/mol) is the same in the supercritical as well as in the subcritical water. He suggests that the reaction is catalyzed by hydrogen ions formed from dissolution of phosphoric acid in supercritical steam. Very small amounts of phosphoric acid and the salts of the phosphoric acid are dissolved in the supercritical steam and are split into ions. Patat lists several dissolution constants for primary ammonium phosphates in supercritical steam. In this instance, the reaction performance is improved when the reaction is operated homogeneously in the mixture critical region and, thus, in intimate contact between the reactants and the catalyst. 

In order to perform NMR studies on compressed supercritical steam, which exhibits a number of unusual properties, de Fries and Jonas developed an NMR probe working in the temperature range 25-700 °C and at pressures up to 200 MPa. The design of this probe, consisting of two high-pressure bombs, is given in Fig. 4.29. Both bombs have a 76 mm outer diameter and a 38 mm inner diameter and are made of IMI-680 titanium alloy (Imperial Metal Industries). The primary bomb at the top contains a furnace, the RF coil and two thermocouples. The sample extends from the ceramic tube in... 

Antal, M.J., Jr. and X. Xu, "Hydrogen Production by the Total, Catalytic, Supercritical Steam Reforming of Wood Sawdust", 216th American Chemical Society National Meeting, Boston, August 23, 1998. 

Tilliette, Z.P. Modem Energy Conversion System and Nuclear Energy, Utilization - of a European, Commercial, Supercritical Steam Cycle, - of an Advanced Hypercritical Steam Cycle, - of Combined Gas-Steam Cycles, American Nuclear Society 1993 Winter Meeting, San Francisco, California, U.S.A., Nov. 14-19, 1993. 

Surprisingly, the first molecular computer simulation of supercritical steam (Beshinske and Lietzke 1969) was published almost simultaneously with the first ever MC simulation of liquid water (Barker and Watts 1969). However, until the last decade, molecular simulations of supercritical aqueous fluids remained relatively scarce (O Shea and Tremaine 1980 Kalinichev 1985, 1986, 1991 Kataoka 1987, 1989 Evans et al. 1988 Mountain 1989 De Pablo et al. 1989, 1990 Cummings et al. 1991). Several reviews have already been published which summarize the state of this field of research by the early 1990s (Heinzinger 1990 Belonoshko and Saxena 1992 Fraser and Refson... 

Walrafen GE, Hokmabadi MS, Yang WH, Piermarini GJ (1988) High-temperature high-pressure Raman spectra from liquid water. J Phys Chem 92 4540-4542 Walrrfen GE, Chu YC (1995) Linearity between structural correlation length and correlated-proton Raman intensity from amorphous ice and supercooled water up to dense supercritical steam. J Phys Chem 99 11225-11229... 

Table 13.1 whereas Table 13.2 reports the properties of significant streams in the plant. The size of the plant has been selected in order to fit with the large size, 50-Hz, heavy-duty gas turbine available on the market. The resulting performance is summarized in Table 13.3. Power output is 367.4 MW with a45.2% efficiency (LHV basis). This value poses the IGCC plant at about the same efficiency level of a pulverized coal boiler, ultra-supercritical steam cycle. Although the latter has higher sulfur oxide and parficu-late matter (PM) emissions, it currently represents the reference technology for large-scale power generation fi om coal given than its investment cost is at least 30% lower than an IGCC plant.

New designs and new types of advanced nuclear power plants (e.g., supercritical steam) present the same need for in-depth understanding of corrosion processes and the associated means to control corrosion s detrimental effects. Indeed, for new plant concepts, knowledge gained from current R D should be used prescriptively (rather than remedially and reactively, as in earlier generations of plants) in the design of components and control systems to avoid operational problems from... 

Improved efficiency, fossil-fuel power generation through the use of ultra-supercritical steam-cycle plants, integrated gasification combined cycle coal plants, and natural gas combined cycle units. 

Fixed bed with supercritical steam as coolant. The concept of a direct cycle reactor operating at supercritical pressure is attractive for radically improving the thermal efficiency. Such reactor could combine the fixed bed concept with the idea of using a direct cycle reactor operating at supercritical pressure, for example, as proposed in [XII-8], Supercritical steam is used as the reactor coolant. The critical pressure of water is 221 bar. When the reactor operates at 250 bar, the supercritical water does not exhibit a change in phase, and the phenomenon of boiling does not exist. The water density decreases continuously with temperature. 

Cycle type Indirect cycle Supercritical steam Rankine cycle steam conditions at turbine inlet p=24 MPa, T=810 K... 

The once-through heat recovery steam generator design is ideally matched to very high temperature and pressure, well into the supercritical range. Moreover this type of boiler is structurally simpler than a conventional one, since no drum is required. A specific mathematical model has been developed. Thermodynamic model has been implemented to suit very high pressure (up to 240 bar), sub- and supercritical steam properties. We illustrate the model use with a 180 bar once-through boiler (0TB). 

Pellegrini LF, Jdnior SDO, Burbano JC (2010) Supercritical steam cycles and biomass integrated gasification combined cycles for sugarcane mills. Energy 35 1172-1180... 

The pressurized water-cooled reactor operating at 160 bar with inlet/outlet temperatures of 290 and 326 C respectively will have an efficiency of about 33%, but the reactor cooled by supercritical steam may have an efficiency of more than 40%. 

Supercritical steam plants operating above the water critical temperature (375°C) and pressure (22 MPa) have the same mechanical components as conventional steam plants. Major differences are greater wall thicknesses to withstand the pressure, more corrosion resistant materials, and lower dissolved solids in the water and steam. 

Almost all of the components in a supercritical steam plant are made of austenitic stainless steels of the 18-8 variety, for example, S30403 or 31603. These materials are employed to minimize corrosion products and their transport through the system. The steam temperature is no higher than in an ordinary superheater, but the pressures are such that many chemicals and corrosion products may show appreciable solubility in the steam. 

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