Evaporation plant

Film deposition by evaporation and condensation is, with few exceptions, generally performed by evaporating the coating material from sources mounted at the ground plate and by condensing the vapour on substrates mounted in holders at the top of the chamber. The sidewards evaporation is very seldom applied, but an inverted arrangement to the simple bottom to top deposition direction is sometimes 

Special coating unit to metallize large astronomical mirror blanks 

With metallizing decorative plastic parts and automobile plastic reflectors, a good film quality is required but also important and decisive are low expenses of the coating process. Metallization of such parts is often done in horizontal cylindrical coaters with the evaporation sources in the cylinder axis and the substrates arranged around them on planetary axes as can be seen in Fig. 64. 

Ring shaped glow discharge cathode and electrodes for the spiral shaped Al-evaporators mounted at the top of the metallizing plant. 

Reversing calottes for coating both sides of a substrate in bell jar coaters. 

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SQM Nitratos (Chile) operates two sodium nitrate plants in northern Chile Pedro de Valdivia and Mama Elena, about 30 km distant from one another. The caUche is mined in open-pit areas. A solar evaporation plant, Coya Sur, Hes in between. A flow sheet of the processing operations for sodium nitrate production is shown in Figure 2. 

One physical method that has attracted some commercial interest is evaporation several evaporative plants were installed in Japan in the early 1970s, nearly all followed by incinerators for the sludge produced (60). They are, however, expensive in both capital and operating costs. The most recent evaporation systems use a process known as vapor recompression, which has the claimed advantage of much lower operating costs than the eadier evaporative processes used in the wool industry. Capital costs of these processes are still high. 

In the pulp and paper industry, the main gas emissions are from the pulp production. The main sources of emission are in the soda recovery boiler, lime kiln, evaporation plant, and bark combustion boiler. 

The synthesis of 1 kg of dry plant biomass requires the evapotranspiration of about 300 L of water, although smaller amounts of water are needed by some plants such as desert cacti. Approximately one-third of the annual continental rainfall (100 cm/yr) is returned to the atmosphere by evapotranspiration. Although it accounts for only about 10-15% of global evaporation, plant evapotranspiration can play a major role in local climates. For example, a molecule of water falling on the upper Amazon Basin is recycled on average five times during its eventual return to the Atlantic Ocean. 

Stripping and reuse of the condensates from the evaporation plant... 

Sufficient capacity of the black liquor evaporation plant and the recovery boiler to cope with the additional liquor and dry solids load... 

Payer80 states that the UNSAT-H model was developed to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. It addresses soil-water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow as one-dimensional processes. The UNSAT-H model simulates water flow using the Richards equation, water vapor diffusion using Fick s law, and sensible heat flow using the Fourier equation. 

In practice, as the evaporation plant size changes (for constant Q), the ratio of the stage condenser area cost to the unit evaporator cost remains essentially constant so that the number 0.184 is treated as a constant for all practical purposes. Equation (/) can be solved for nK for constant P... 

A thermodynamic analysis of the energy requirements of desalting processes is presented, to clarify the conditions under which such calculations are valid. The effects of departure from isothermal operation, finite product recovery, differential as opposed to single-stage operation, and salt concentration in the feed are examined. A comparison shows that there is essentially no difference between the energy requirements for a distillation and a freezing process. The minimum heat consumption and maximum number of efFects for a multiple-effect evaporation plant are calculated. The above analysis leads to the conclusion that efficiencies in the range 10 to 20% will be very difficult to achieve. 

Table I. Capital Cost of 17,350,000-Gallon-per-Day Combination Thermocompression-10-Effect Sea Water Evaporation Plant...

Table I shows a detailed breakdown of the operating cost for this plant. The cost of steam represents about half of the water cost for the optimum plant. The capital charges for the evaporator plant, which includes amortization, interest on working capital, and real estate, represent about 30%. The remaining 15 to 20% is equally divided between the cost of chemicals for scale control and all the other costs. The converted water is estimated to cost approximately 42 cents per thousand gallons. This water cost represents a realistic figure for a large-capacity multistage flash evaporator that could be built today when the energy in the form of steam costs between 35 and 40 cents per million B.t.u.

Erected cost of complete evaporator plant including intake facilities, reservoir, and site development. 

Pumps for the evaporation plant must stand up under the hot glycerol-brine solution and are also generally of the centrifugal design. Cast stainless steels (CP8M alloy) are often used for this application, but a superior material for pumps is a chromium-nickel-copper-molybdenum stainless steel known as CD M, which should be considered when choosing the pump material. The extra cost is usually not significant. 

In the evaporation plant especially, glycerine can be carried out with the vapor during evaporation and lost in the vacuum system s condensing of water. The amount of carryover can be minimized in several ways ... 

The progress made in membrane-based desalination has lead to the substitution of evaporation plants with RO systems in different part of the world. For example, the United States holds the second position in worldwide desalination capacity (15.2% of the world production) and the 78% of their production come from RO treatments. Mediterranean countries, including Spain, Malta, Cyprus, and Israel, have also reverted from traditional multistage flash (MSF) to RO during the past two decades. The water production by reverse osmosis desalination plants passed from 36% of the global desalting capacity in 1996 to 42%... 

Cole, J. (1984) Chem Engr, London, No. 404 (June) 20. A guide to the selection of evaporation plant. 

Prepare a block diagram for the material flows in a methane evaporation plant. The following blocks can be used in addition to those shown in Fig, 5.9a evaporator, tank, boiler. 

It is evident that one of the principal points to be considered in the construction of an evaporating plant is that the products of combustion should be used to the greatest advantage, that is, that as large a surface as possible of the evaporating vessel should be exposed to their action hence, the surface of the vessel should be a maximum with regard to its volume. The... 

Tertiary treatment processes are used only to eliminate materials which are not amenable to secondary treatment. A treatment method for wool scouring effluent has been developed, consisting of evaporation and incineration plant in combination with a biological plant [56]. The resulting condensates from the evaporation plant and the incineration residues are recycled so that the water, ammonia and scouring aids are returned to the production plant [57]. 

All evaporators remove a solvent vapor from a liquid stream by means of an energy input to the process. The energy source is most usually dry and saturated steam, but can be a process heating medium such as liquid or vapor phase heat transfer fluids (Dowtherm or Therminol), hot water, combustion gases, molten salt, a high temperature process stream, or, in the case of a solar evaporation plant, radiation from the sun. 

Hollow fibers and spiral wound modules have been constructed for this application. A module 18 inches in diameter and 5 feet long can produce up to 1,500 GPD. Plants now exist in the Florida Keys, the Bahamas, and the Cayman Islands ranging in size from 10,000 to 60,000 GPD. They have the highest capacity per unit volume for evaporation plants now in existence. It is claimed that these plants are more cost effective than multiple-effect evaporators, but in the author s view, it is doubtful they can compete with reverse osmosis. 

Figure 1. Simplified flow diagram for spray evaporation plant...

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