Plant availability

Thermal power plant components operated at high temperatures (>500°C) and pressures, such as superheater headers, steamline sections and Y-junctions, deserve great attention for both operation safety and plant availability concerns. In particular, during plant operation transients -startups, shutdowns or load transients - the above components may undergo high rates of temperature / pressure variations and, consequently, non-negligible time-dependent stresses which, in turn, may locally destabilize existing cracks and cause the release of acoustic emission. 

Make maintenance planning more flexible, by providing, wherever possible, viable alternatives to unplanned shutdowns and to immediate component replace or repair actions. Increased flexibility of maintenance planning, by conditionally running under surveillance components with potential or incipient stmctural integrity problems, means improved plant availability, reduced energy replacement and maintenance costs. 

During its 40-year development, three different si2es of PETROSIX retorts have been operated on a continuous basis a 1.83-m (6-ft) diameter demonstration plant a 5.49-m (18-ft) diameter Prototype Unit (UPI) and a 10.97-m (36-ft) diameter Industrial Module (MI). Within the SIX facihty are numerous pilot plants available for retorting coarse-si2ed oil shale, fines utih2ation, and oil shale upgrading (3,67). 

The problems with jojoba as a commercial crop are the usual ones of domestication and cultivation. It is a slow-growing plant, available only in the wild and therefore has very wide genetic variabiUty. Efforts are underway to select the most promising variants and cultivate these as a crop in the southwestern United States deserts (7). A possible alternative for producing jojoba oil is to culture plant embryos in bioreactors (see Cell culture technology). 

Agronomic Properties and Nutrient Release Mechanism. The conversion of UF reaction products to plant available nitrogen is a multistep process, involving dissolution and decomposition. Materials are slow to enter the soil solution by virtue of their low solubiUty. Longer polymer chain products are less soluble than shorter chains and take longer to become available to the plants. 

Once in the soil solution, urea—formaldehyde reaction products are converted to plant available nitrogen through either microbial decomposition or hydrolysis. Microbial decomposition is the primary mechanism. The carbon in the methylene urea polymers is the site of microbial activity. Environmental factors that affect soil microbial activity also affect the nitrogen availabiUty of UF products. These factors include soil temperature, moisture, pH, and aeration or oxygen availabiUty. 

The calculations for fuel gas savings have been based on an international price of fuel, at about US 2.50 per million BTU (US 2.64 per million KJ). The plant availability was taken at 97%, which is the availability throughout industry for most frame type plants. The cost of sale of new power was based on the average price of US 0.04 per KW-Hr. 

Availability and reliability have a very major impact on the plant economy. Reliability is essential in that when the power is needed it must be there. When the power is not available it must be generated or purchased, and can be very costly in the operation of a plant. Planned outages are scheduled for non-peak periods. Peak periods is when the majority of the income is generated as usually there are various tiers of pricing depending on the demand. Many power purchase agreements have clauses, which contain capacity payments, thus making plant availability critical in the economics of the plant. 

The increase in unit size and complexity together with the higher turbine inlet temperature, and higher pressure ratio has lead to an increase in overall gas turbine efficiency. The increase in efficiency of 7-10% has in many cases lead to an availability decrease of the same amount or even more as seen in Figure 21-5. A 1% reduction in plant availability could cost 500,000/yr in income on a 100 MW plant, thus in many cases offsetting gains in efficiency. 

Plant Availability. A detailed PSA (2) may be used to analyze the effects of test and maintenance on plant jperability through improved scheduling, component reliability improvement, and improved procedures Hie eost-beiiefit of stocking vs warehousing of feed materials and spare parts may be done to find an optimum ... 

Phosphorus (P) is one of the major limiting factors for plant growth in many soils. Plant availability of inorganic phosphorus (Pi) can be limited by formation of sparingly soluble Ca phosphates, particularly in alkaline and calcareous soils by adsorption to Fe- and Al-oxide surfaces in acid soils and by formation of Fe/ Al-P complexes with humic acids (94). Phosphorus deficiency can significantly alter the composition of root exudates in a way that is, at least in some plant species, related to an increased ability for mobilization of sparingly soluble P sources (29,31,71). 

Although iron (Fe) is one of the major soil constituents (0.5-5%), where it is usually present in the oxidized state (Felll), plant availability is severely limited by the low solubility of Fe-(hydr)oxides at pH levels favorable for plant growth. Therefore, plants need special mechanisms foraquiring Fe from sparingly soluble Fe forms to fit the requirements for growth, especially in neutral and alkaline soils, where the availability of Fe is particularly low (151). Mechanisms involved in iron acquisition by plants are also discussed in Chap. 8. 

Humic substances can form complexes with metals, including cationic micronutrients (36), thanks to the presence of electron-donor functional groups in these molecules. It therefore appears evident that due to these properties, humic substances can contribute to the regulation of the chemical balances of metals, thus influencing their solubility (5). With regard to plant availability, the molecular dimension and solubility of humic substances are very important. 

A. Jungk, Soil-root interactions in the rhizosphere affecting plant availability of phosphorus. J. Plant Nutr. 70 1197 (1987). 

The basic classification of CWs is based on the type of flow regime and macrophytic growth. In general terms, two types can be described (Figure 10.3). The selection of the most appropriate option shall be according to various operational factors and to the plants available in the region of... 

As shown in Figure 25.8, an increase in soil thickness from the design thickness (A) by 50% to (B) may result in only a small increase in plant-available water-holding capacity during a single... 

Base the design on reduced plant-available water-holding capacity (e.g., 10% reduction). 

Jin Q., Wang Z., Shan X., Tu Q., Wen B., Chen B. Evaluation of plant availability of soil trace metals by chemical fractionation and multiple regression analysis. Environ Pollut 1996 91 309-315. 

Warden B.T., Reisenauer H.M. Fractionation of soil manganese forms important to plant availability. Soil Sci Soc Am J 1991 55 345-349. 

United States Department of Agriculture. USDA strengthens 2003 permit conditions for field testing genetically engineered plants. Available from http //www.a phis.usda.gov/lpa/news/ 2003/03/ gepermits brs.html... 

Smith, C., K.W. Brown, and L.E. Deuel, Jr. 1987. Plant availability and uptake of molybdenum as influenced by soil type and competing ions. Jour. Environ. Qual. 16 377-382. 

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