Plant operations

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. 

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. 

Steam headers and steamline sections may undergo high rates of temperature / pressure variations during plant operation transients - startups, shutdowns or load transients - and are... 

Different plant operating conditions (steady load, load variations, startups / shutdowns) have been encountered during the monitoring period. Electrical load, steam pressure and steam temperature values vs time have been acquired and stored during the entire period. At the same time, the RMS values of the acoustical background noise were have been continuously checked and stored, thus providing a quick check of proper instrumentation condition and a correlation between variations of plant parameters and the acoustical behaviour of the components. 

The AEBIL acoustic emission monitoring system installed on site has shown a good level of functional reliability no instrumentation failure is to be recorded in over 1 year of continuous in-plant operation. 

The development and improvement of scientific-technical level of NDT and TD means for safety issues is connected with the necessity to find additional investments that must be taken into account at the stage of new technogenic objects designing, when solving new arising problems in social, economic, ecological and medical safety. It is not accidental, that the expenses for safe nuclear power plants operation cover 50% of total sum for construction work capital investments. That is why the investments for NDT and TD have to cover 10% of total amount for development and manufacturing of any product. 

Continuous processes have been developed for the alcohols, operating under pressure with Hquid ammonia as solvent. Potassium hydroxide (206) or anion exchange resins (207) are suitable catalysts. However, the relatively small manufacturing volumes militate against continuous production. For a while a continuous catalytic plant operated in Raveima, Italy, designed to produce about 40,000 t/yr of methylbutynol for conversion to isoprene (208,209). 

Patents claiming specific catalysts and processes for thek use in each of the two reactions have been assigned to Japan Catalytic (45,47—49), Sohio (50), Toyo Soda (51), Rohm and Haas (52), Sumitomo (53), BASF (54), Mitsubishi Petrochemical (56,57), Celanese (55), and others. The catalysts used for these reactions remain based on bismuth molybdate for the first stage and molybdenum vanadium oxides for the second stage, but improvements in minor component composition and catalyst preparation have resulted in yields that can reach the 85—90% range and lifetimes of several years under optimum conditions. Since plants operate under more productive conditions than those optimum for yield and life, the economically most attractive yields and productive lifetimes maybe somewhat lower. 

Nonetheless, production and use of nitric phosphates ia Europe are continuing to grow. In general, nitric phosphate processes are somewhat more compHcated than sulfur-based processes and requite higher investment. In the past, several attempts have been made to estabHsh commercial acceptance of this type process ia the United States, but plant operations have been relatively short Hved because of low sulfur prices and resultant competition from sulfur-based processes. 

Ma.gnesium Oxide. Magnesium oxide behaves in a similar manner to other metal oxides. However, most spars contain practically no magnesium oxide, so it does not affect yield loss or plant operation. 

Orga.nic Carbon. Organic materials interfere with plant operation because these compounds react with sulfuric acid under furnace conditions to form sulfur dioxide. There is a reducing atmosphere in the furnace which may reduce sulfur dioxide to elemental sulfur, which results in sulfur deposits in the gas handling system. 

Chloride. Chloride is known to significantly increase the rate of corrosion in acidic fluoride media. The level of chloride that can be tolerated in the HF process before corrosion hinders plant operation is quite low. 

A rack and frame press uses heavy nylon cloth positioned in a wooden frame inside a rack. A measured amount of apple or other fmit mash is added from a hopper above the frame. The mash is leveled with a hand trowel and the edges of the nylon cloth are folded over the mash to encase it and create a cheese. The frame is removed, and a second rack is placed on top of the first cheese the process is repeated until a stack of cheeses is prepared. A hydrauhc ram then appHes gradually increa sing pressure on the stack and expresses the juice. A high yield of juice (80%) is obtained and no press aid is required. Because this process is labor intensive (17), it is mostly used for small farm and pilot-plant operations. 

In 1976, Ashland Od (Ashland Synthetic Fuels, Inc.) was awarded the prime contract to constmct a 540 t/d H-coal pdot plant adjacent to its refinery at Cadettsburg, Kentucky, by an industry—government underwriting consortium. Constmction was completed in 1980 (112). The pdot-plant operation ended in eady 1983. 

Table 9. Wilsonville Plant Operating Conditions and Yields for ITSL and CTSL Modes ...

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). 

I eon—Helium Separation and Purification. As indicated eadier, neon, heHum, and hydrogen do not Hquefy in the high pressure (nitrogen) column because these condense at much lower temperatures than nitrogen. As withdrawn, the noncondensable stream has a neon—helium content that varies 1—12% in nitrogen, depending on the rate of withdrawal and elements of condenser design and plant operation. 

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

A commercial-scale SNG plant, the Great Plains Plant in North Dakota, was actually built and operated for several years using a scheme based on coal. However, upon termination of the government subsidy, the plant s owner, ANR Inc., found it uneconomical to continue plant operation and shut down the plant in the late 1980s. 

Dehydrogenation. Dehydrogenation of / -butane was once used to make 1,3-butadiene, a precursor for synthetic mbber. There are currently no on-purpose butadiene plants operating in the United States butadiene is usually obtained as a by-product from catalytic cracking units. 

The details of specific plant operations have been well documented (6). 

In apphcation to electric utihty power generation, MHD is combined with steam (qv) power generation, as shown in Figure 2. The MHD generator is used as a topping unit to the steam bottoming plant. From a thermodynamic point of view, the system is a combined cycle. The MHD generator operates in a Brayton cycle, similar to a gas turbine the steam plant operates in a conventional Rankine cycle (11). 

Research nd Development. Eor commodity chemicals, emphasis is on the improvement of plant operation and reduction of production costs. Eor specialty chemicals, emphasis is on assembling a staff capable of quickly identifying and solving a customer problem under the existing plant conditions and operating procedures of the customer. 

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