Evaporators costs

The heating surface usually determines the evaporator cost and the vapor head the space requirements. The vapor—Hquid separator must have enough horizontal plan area to allow the bulk of the initial entrainment to settle back against the rising flow of vapor and enough height to smooth out variations ia vapor velocity and to prevent splashing directly iato the vapor outlet. Separators are usually sized on the basis of the Souders-Brown expression ... 

Distribution of heating surface between effects versus evaporator cost. 

Materials of construc tion versus product quahty, tube life, evaporator life, and evaporator cost. 

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... 

There are two basic evaporator designs that are typically used atmospheric and vacuum evaporation (Metals Handbook 1987). Atmospheric evaporation principles are similar to those of a heated open tank, with the exception that the heated liquid is sprayed over plastic packing in order to increase its surface area and accelerate evaporation. Atmospheric evaporators on chrome plating lines have sometimes been used simultaneously as evaporators and as plating bath fume scrubbers. Atmospheric evaporators are considerably less expensive than vacuum evaporators. Typical atmospheric evaporator capital costs range from 2500 to 4000, while vacuum evaporator costs can be an order of magnitude or more higher. In atmospheric evaporator systems, however, vaporized water is not recovered, as it can be in vacuum systems. 

Through a series of automatic valves, it is possible to draw off a stream of enriched dextrose, as well as one of enriched fructose. Some consideration must be given to the fact that the higher is the purity of this stream, the lower are the solids and the greater is the evaporation cost. Typical purity of the separated streams of dextrose and fructose is 85% to 90%. The dextrose fraction ( raffinate ) is returned to the front of the system to be reisomerized, while the enriched fructose fraction is blended with a 42% fructose stream to produce 55% high-fructose syrup. The enhanced fructose phase may also be isolated as a separate product stream to make 90% high-fructose syrup or crystalline fructose. 

Equities in accounting, 139 Equivalents, list of 870-871 Erosion, 42-43 Error propagation, 770-771 Estimated variance, 743-744 Evaporators cost of 623... 

The two major costs associated with evaporators, as with any process equipment, are capital investment and operating costs. The best estimate of the installed cost of evaporation systems is, of course, a firm bid from a vendor. The installed cost, however, can be estimated based on the heat transfer surface area, as in Peters and Timmerhaus. Costs taken from published references must be adjusted for changes subsequent to the time of publication. To do this, one may use an index such as the Marshall and Swift allindustry index. The value of this index is published each month in Chemical Engineering, a McGraw-Hill publication. Further information on the use of this and other cost indices as well as their histories are available, for example, in Peters and Timmerhaus and Ulrich.f Variation of purchased evaporator costs with material of construction and pressure can also be found in Ulrich. ... 

These evaporators are necessarily precision machines and therefore are more expensive than other types, particularly so if compared strictly on equivalent heat transfer area. When the performance for a specific evaporation duty is the basis of comparison, the thin-film evaporator is often the more economical choice because the larger heat transfer coefficient and higher driving force mean much less surface is required than for other evaporators (A = Q/U AT). Thin-film evaporator cost per unit area decreases significantly with unit size, and the largest available unit has 430 square feet of active heat transfer surface. 

Figure 7. Domains of glazing layers for solar heat cost Evaporator Cost...

To the evaporator cost must be added the cost of collecting the energy in the solar heat collector. The variation in the water cost for the time of year and... 

Evaporator Costs. With so much variation in evaporator construction, materials, and accessories, manufacturers are reluctant to give standard cost figures. The most reliable method seems to be to estimate the unit cost as cylindrical shells, plates, heads, tubes, fittings, etc., based on the weight of material and the unit material and labor costs. This is the method generally used by fabricators. A published set of cost curves for preconstruction cost estimating is given in Fig. 6-12. 

Because the anolyte and catholyte are both quite concentrated, there are osmotic forces at work to dehydrate the membrane. To some extent dehydration is beneficial, because it increases the ratio of sulfonate to water in the membrane, which in turn improves permselectivity. But eventually the dehydration leads to an increase in membrane resistance. Therefore, raising the NaOH concentration to reduce evaporation costs would Hkely increase electrical power costs. 

Evaporation process design and the characteristics of caustic evaporators are covered in Section 9.3.3. The unit cost of steam is a major factor in deciding the number of effects to be used in evaporation. Costing of steam is often somewhat arbitrary, as when low-pressure exhaust steam is available or when a plant has its own cogeneration system. Reducing the consumption of cogenerated steam (Section 12.3.3) when more electrical energy must be purchased (or less sold) may save very little money. 

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