Supercritical steam plants

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. 

Currently, supercritical power plants reach thermal efficiencies of just over 40%, although a few of the more plants have attained high efficiency up to 45%. A number of steam generator and mrbine manufacturers around the world now claim that steam temperatures up to 700°C (1290 F) (ultra-supercritical conditions) are possible which might raise plant efficiencies to over 50%, but require the use of expensive nickel-based alloys for reaction equipment and power generators because of the corrosive properties. 

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. 

Therefore, usually subcritical pressure plants have thermal efficiencies of about 36—40% and modem supercritical pressure plants of 43—50% (up to 55%). Steam generator outlet temperatures or steam turbine inlet temperatures have reached a level of about 625°C at pressures of 25—30 (up to 38) MPa. However, a common level is about 535—585°C at pressures of 23.5—25 MPa. Fig. A 1.10 shows possible solutions for carbon dioxide capture and storage (CCS) at thermal power plants. 

But getting an operating steam density of 0.3 g/cm (Fig. 1.59) requires supercritical pressure. This was the start of Super FR and Super LWR studies at the University of Tokyo. The plant system of the supercritical steam cooled fast reactor was an indirect cycle at first [104], but the advantage of the once-through cycle was soon recognized and a report on this was made in 1992 [2, 107]. 

The main components of a Super LWR NPP system include the RPV, containment vessel and internals, supercritical steam turbine system and safety systems. The main specifications of a 1700MWe level Super LWR plant system and the improvements from a 1350MWe-class advanced BWR (ABWR) are listed in Table 3.1 [1]. 

The results of over 1 year of continuous, on-line acoustic emission (AE) structural surveillance of high temperature / high pressure steam headers, gained on 2 M-scale 600MW supercritical multifuel ENEL power units in normal operation, are presented in the paper. The influence of background noise, the correlation between plant operating conditions (steady load, load variations, startup / shutdown transients) and AE activity and the diagnostic evaluation of recorded AE events are also discussed. 

An example of a modem, tangentially fired, supercritical, lignite-fuel furnace is shown in Figure 5. This unit, at maximum continuous ratings, supplies 2450 metric tons pet hour superheat steam at 26.6 MPa (3850 psi) and 544°C, and 2160 t/h reheat steam at 5.32 MPa (772 psi) and 541°C. These ate the values at the superheater and reheater oudet, respectively. Supercritical fluid-pressure installations ate, however, only rarely needed. Most power plants operate at subcritical pressures in the range of 12.4—19.3 MPa (1800—2800 psi). 

The concern by consumers about cholesterol has stimulated the development of methods for its removal. Three principal approaches are in the pilot-plant stages use of enzymes, supercritical fluid extraction, and steam distillation. Using known techniques, it is not possible to remove all cholesterol from milk. Therefore, FDA guidelines identify cholesterol-free foods as containing less than 2 mg cholesterol per serving, and low cholesterol foods as containing from 2 to 20 mg (37). 

Natural Products. Various methods have been and continue to be employed to obtain useful materials from various parts of plants. Essences from plants are obtained by distillation (often with steam), direct expression (pressing), collection of exudates, enfleurage (extraction with fats or oils), and solvent extraction. Solvents used include typical chemical solvents such as alcohols and hydrocarbons. Liquid (supercritical) carbon dioxide has come into commercial use in the 1990s as an extractant to produce perfume materials. The principal forms of natural perfume ingredients are defined as follows the methods used to prepare them are described in somewhat general terms because they vary for each product and suppHer. This is a part of the industry that is governed as much by art as by science. 

The current state of analytical SPE was critically reviewed and no major changes of the technique have been observed. Overviews of the developments of the extraction technologies of secondary metabolites from plant materials refer to three types of conventional extraction techniques that involve the use of solvents, steam, or supercritical fluids. Each technique is described in detail with respect to typical processing parameters and recent developments. Eollowing the discussion of some technical and economic aspects of conventional and novel separation processes, a few general conclusions about the applicabilities of the different types of extraction techniques are drawn. ... 

Power plant boilers are either of the once-through or dmm-type design. Once-through boilers operate under supercritical conditions and have no wastewater streams directly associated with their operation. Drum-type boilers operate under subcritical conditions where steam generated in the drum-type units is in equilibrium with the boiler water. Boiler water impurities are concentrated in the liquid phase. Boiler blowdown serves to maintain concentrations of dissolved and suspended solids at acceptable levels for boiler operation. The sources of impurities in the blowdown are the intake water, internal corrosion of the boiler, and chemicals added to the boiler. Phosphate is added to the boiler to control solids deposition. 

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