Water, cycle

Modem practice is to maintain the white water system as closed as possible, ie, as much water as is compatible with efficient machine operation is recycled. The loss of fibers and inert furnish components, particularly clay, has been gready reduced. Eiber losses, however, stiU occur into the white water, and greater economy of operation may be achieved if these fibers could be recovered. Thus, it is common to design a fiber-recovery system into the white water cycle. The three general types of save-all fiber recovery are based on filtration (qv), dotation (qv), and sedimentation (qv). If these are operated efficiendy, the net fiber loss can be less than 1%. 

Fossil Fuel-Fired Plants. In modem, fossil fuel-fired power plants, the Rankine cycle typically operates as a closed loop. In describing the steam—water cycle of a modem Rankine cycle plant, it is easiest to start with the condensate system (see Fig. 1). Condensate is the water that remains after the steam employed by the plant s steam turbines exhausts into the plant s condenser, where it is collected for reuse in the cycle. Many modem power plants employ a series of heat exchangers to boost efficiency. As a first step, the condensate is heated in a series of heat exchangers, usually sheU-and-tube heat exchangers, by steam extracted from strategic locations on the plant s steam turbines (see HeaT-EXCHANGETECHNOLOGy). 

Rhenium exhibits a greater resistance than tungsten to the water cycle effect, in which lamps and electron tubes become blackened by deposition of metal. This phenomenon involves catalysis by small quantities of water that react with the metal in a hot filament to produce a volatile metal oxide and hydrogen. The oxide condenses on the surface of the bulb and is reduced back to the metal by hydrogen. 

E. K. Berner and R. A. Berner, The Global Water Cycle Geochemistry and Environment Prentice-HaH, Inc., Englewood Cliffs, N.J., 1987. 

AH stacks and vents attached to the process equipment must be protected to prevent environmental releases of hexavalent chromium. Electrostatic precipitators and baghouses are desirable on kiln and residue dryer stacks. Leaching operations should be hooded and stacks equipped with scmbbers (see Airpollution control methods). Recovered chromate values are returned to the leaching-water cycle. 

This water cycle—the process of moving water from oceans to streams and hack again— is essential to the generation of hydroclcctricity. Moving water can be used to perform work and, in particular, hydroelectric power plants employ water to produce electricity. The comhination of abundant rainfall and the right geographical conditions is essential for hydroelectric generation. 

Also, corrosion may result in contamination at some downstream point in the steam-water cycle. For example, iron and copper ions often may be present as corrosion products in steam and condensate and consequently will reduce the purity of the steam. This may render the steam unsuitable for certain industrial processes or applications where live steam injection is required. 

It also is likely that when considering the steam-water cycle, expenditure on water conditioning equipment at the front end will result in savings in chemical treatments, fuel, and loss of good-quality hot water at the back end ... 

The sulfoxidation of normal Cl4-CI7 paraffins with sulfur dioxide, oxygen, and water is performed under UV radiation in parallel reactors (1 in Fig. 3). The reaction enthalpy is dissipated by cooling of the paraffin in heat exchangers. The 30- to 60-kW UV lamps are cooled by a temperature-controlled water cycle. The reaction mixture leaving the reactors separates spontaneously into two phases in 2. The lighter paraffin phase is recirculated to the reactors. The composition of the heavy raw acid phase is shown in Table 5. 

Berner, E.K. Berner, R.A. Global Water Cycle. Prentice-Hall Englewood Cliffs, NJ, 1987, 178. 

Many hydrologic reservoirs can be further subdivided into smaller reservoirs, each with a characteristic turnover time. For example, water resides in the Pacific Ocean longer than in the Atlantic, and the oceans surface waters cycle much more quickly than the deep ocean. Similarly, groundwater near the surface is much more active than deep reservoirs, which may cycle over thousands or millions of years, and water frozen in the soil as permafrost. Typical range in turnover times for hydrospheric reservoirs on a hillslope scale (10-10 m) are shown in Table 6-4 (estimates from Falkenmark and Chapman, 1989). Depths are estimated as typical volume averaged over the watershed area. 

To this point, direct human impacts on the hydrosphere have remained restricted to the regional scale. Although they can still be important, particularly in terms of water supply, these direct manipulations of the hydrologic cycle are unlikely to affect the global water balance significantly. However, this is not to suggest that the global water cycle is immune to human influence its close ties to other physical and... 

Berner, E. K. and Berner, R. A. (1987). "The Global Water Cycle." Prentice-Hall, Englewood Cliffs, New Jersey. 

Vorosmarty CJ, Sahagian D (2000) Anthropogenic disturbance of the terrestrial water cycle. Bioscience 50 753-765... 

Sabater S (2008) Alterations of the global water cycle and their effects on river structure, function and services. Ereshw Rev 1 75-88... 

Administrative representatives are often shy about developing water reuse projects. Evaluations of the risks related to water reuse have been twisted so as to be employed in political arguments during election campaigns, which may explain the reluctance of politicians. Examples of failure and success of indirect potable reuse projects in the United States are provided by [13]. Such experiences point out the importance of public education as regards the human interaction with the water cycle and the management of water resources. The population should be aware that... 

Bar, V. (1989). Children s views about the water cycle. Science Education, 73(4), 481-500. 

Berner EK, Berner RA (1987) The global water cycle Geochemistiy and environment. Prentince-Hall, New Jersey... 

The presence of water as solid, liquid, and gas is a feature that makes Earth unique in the solar system and that makes life possible as we know it. The transport of water and the energy exchanged as it is converted from one state to another are important drivers in our weather and climate. One of the key missions is to develop a better understanding of the global water cycle at a variety of scales so that we can improve model forecasts of climate trends,... 

As evaporated water is pure, solids are left behind in the recirculating water, making it more concentrated than the makeup water. The blowdown purges the solids from the system. Note that the blowdown has the same chemical composition as the recirculated water. Cycles of concentration is a comparison of the dissolved solids in the blowdown compared with that in the makeup water. For example, at three cycles of concentration, the blowdown has three times the solids concentration as the makeup water. For calculation purposes, blowdown is defined to be all nonevaporative water losses (drift, leaks and intentional blowdown). In principle, any soluble component in the makeup and blowdown can be used to define the concentration for the cycles, for example, chloride and sulfate being soluble at high concentrations can be used. The cycles of concentration are thus defined to be ... 

Water. Water generally occurs in air in low or relatively low concentrations, mostly in the form of atmospheric moisture. Its importance cannot, however, be overemphasized, since atmospheric moisture, unique to the surface of the earth, is a determining factor in the water cycle (see below) and in living and other processes. Moisture is, therefore, one of the most important and probably the most relevant atmospheric components for the majority of living processes. 

The Water Cycle. The evaporation of water from land and water surfaces, the transpiration from plants, and the condensation and subsequent precipitation of rain cause a cycle of transportation and redistribution of water, a continuous circulation process known as the hydrologic cycle or water cycle (see Fig. 86). The sun evaporates fresh water from the seas and oceans, leaving impurities and dissolved solids behind when the water vapor cools down, it condenses to form clouds of small droplets that are carried across the surface of the earth as the clouds are moved inland by the wind and are further cooled, larger droplets are formed, and eventually the droplets fall as rain or snow. Some of the rainwater runs into natural underground water reservoirs, but most flows, in streams and rivers, back to the seas and oceans, evaporating as it travels. 

The purify of the water changes constantly during the water cycle. As rain falls through the air, for example, the water dissolves some atmospheric gases such as oxygen, carbon dioxide, and in industrial regions also such air pollutants as sulfur dioxide and oxides of nitrogen. Still more carbon dioxide... 

Analysis, Fate and Removal of Pharmaceuticals in the Water Cycle Food Contaminants and Residue Analysis Protein Mass Spectrometry... 

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