Dryers 1118 INDEX

As an example, the battery-limits capital cost can be estimated for the production of 10,000 t/yr of ethylene (qv) from ethanol (11). Seven processing blocks, ie, vaporizer, reactor, water quench, compressor, dryer, distillation, and energy recovery, can be identified. The highest temperature is 350°C (reactor), and the highest pressure is about 1.7 MPa (17 atm) (compressor, two towers). If a materials-pressure factor, + of 1.03 is assumed, then for N = 7 0 = 0.87 1/0 = 1 64 and f =0 K = 6.3. This gives the 1981 cost as 4.4 X 10 . The 1991 battery-Hmits investment can be obtained, by updating with the CE Plant Cost Index, as 5.3 x 10 . ... 

If the feed flows countercurrent to the air, as is the case when drying granulated sugar, the exhaust temperature does not respond to variations in product moisture. For these dryers, the moisture in the product can better be regulated by controlling its temperature at the point of discharge. Conveyor-type dryers are usually divided into a number of zones, each separately heated with recirculation of air, which raises its wet-bulb temperature. Only the last two zones may require indexing of exhaust air temperature as a function of AT. 

FIG. 8-57 Product moisture from a cocurrent dryer can be regulated through temperature control indexed to heat load. 

Some materials that are prepared in the molten state are converted advantageously to flake form by cooling a thin layer continuously on the surface of a rotating drum. Another way is to spray cool from the melt, using a spray dryer with cold air. Thus, massive cooling and subsequent pulverizing are avoided. See the Index for details of these other methods. 

Wilson equation, activity coefficients, 374 Wilson-Lobb-Hottel eqiration, 214 application, 219 Winkler process 582 Wire mesh deentrainers, 615 calculation example, 620 disengaging space, 616 kev dimensions, 618 k-values, 615 pressure drop, 616 tvnical installations, 616 Work index, size reduction, 342 Wyssmont dryer, 237,251... 

The whiteness index of softened fabrics depends on the fabric softener treatment, on the number of launderings, and on the fabric type. Dryer softeners significantly improve the whiteness index of cotton [34],... 

These criteria are restrictive, and it is quite unlikely that any solid will satisfy them over an exhaustive range of conditions however, the concept is widely used and often utilized for interpolation and prediction of dryer performance [3,17]. The use of the mean moisture content as an index of the degree of drying contains the implicit assumption that the extent of... 

In some reports, steam drying is claimed to reduce power consumption for milling as the grindability index is increased due to steam drying. At elevated degrees of superheat and prolonged exposure times, some studies have reported a reduction in the sulfur content of coal. This is not necessarily an advantage as the sulfur will then enter the dryer-exhaust steam. Additional data are needed to evaluate this aspect in detail. 

DMC uses a direct, least-squares computational procedure to find the optimum values of future changes in the manipulated variables to match future output responses such that some performance index is minimized [8]. Panda applied DMC to control the fluid-bed dryer as mentioned earlier and proved that DMC gives better control in the presence of measurement noise [19]. The response in the exit-air temperature does not show much oscillation and settles quickly. 

C is the installed cost (US in the year of the M S Index) covering the dryer and auxiliaries, including foundations and erection, but no secondary dust collectors or building... 

FIGURE 65.2 The dependence of dryer cost on evaporation capacity in kg moisture/h and inlet-air temperature in °C, according to Equation 65.3 (M S Index = 1100). 

The fabrication cost of a drying unit besides its size depends also on the material of construction it is the lowest for carbon steel. If the process requires a more chemical-resistant material, a cladding may be applied in some cases. In certain drying operations, optimum design of the equipment as well as product-quality requirements calls for the use of not only more durable but also more expensive materials. In general, drying equipment built of 304-stainless steel typically costs from 1.5 to 1.7 times more than that made of carbon steel and 2-3 times more if built of titanium. The cost depends also on the auxiliary equipment, and this is a reason for some uncertainty in cost prediction from literature sources without vendors data. Figure 65.3 presents, as an example, the purchase cost for several dryers in relation to their capacity that is updated to the year 2000 with the M S Index equal to 1089. 

The process system consists of two long-tube vertical evaporators, a draft-tube baffled crystallizer, a rotary-drum vacuum filter, and a direct-heat rotary dryer. Also, pumps are needed to move the solution from evaporator 1 to evaporator 2, to recycle the filtrate from the filter to the crystallizer, and to move the magma from the crystallizer to the filter and a heat exchanger is needed to heat the recycle filtrate. However, the purchase costs for the three pumps and the heat exchanger are not considered here because examples for these types of equipment are presented in Section 16.5. For the equipment considered here, assume fabrication from stainless steel, with a material factor of 2 for the ratio of stainless steel cost to carbon steel cost. For the process, using the following size factors and the equations in Table 16.32, the estimated f.o.b. equipment purchase costs at a CE index of 394 are included in the following table. 

This book is unique in its extensive cross referencing. Some pieces of equipment are used for many different purposes. For example, fluidized beds are selected, sized and operated as heat exchangers, dryers, reactors, coaters and agglomera-tors. The details are given for each specific application with cross referencing to lead to other uses and rules of thumb. This cross referencing is included in each pertinent section and in the lengthy index. 

Metal plate, squeegee to remove excess ink, conicalshaped transfer pad, indexing device to move parts into printing area, dryers, depending on type of operation. 

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