Page 273 - Chemical Process Equipment - Selection and Design

240 DRYERS AND COOLING TOWERS
EXAMPLE 9.4-(continued)

R = 1, moist air R = 5, moist air

W W TS 1 I Rate

18 ! Example 9.4. Belt conye::It:tr
r
~j y i t'r '3 148 IF ABSCK~T)<=.00BBI THEN 168
28 H=l ! chan~e o t- o t he r case5 158 GOTO 78
f
38 INPUT W 160 PRINT USING 170 j WITJ~JRI !
48 H1=(1551.4*~:H+1?+97.4+1480%< Subst R2 for R1 when 1.1<.58
W- . 1 :) > z'7796, C R+ 1 :I 1 7 0 I MAG E D . DD r 25 .* DDD . DD ,2X, D . D D
45 ! H1=(97,4*(R+1~+1488$(W-.l? DD
)~7798/<R+l> ! Replace line 175 GOTO 30
40 rdith this when no recycle 188 END
is used. 288 ! SR for 5at temp
58 C=.24+.45XH1 210 P=EXP(11.9176-7173.9,(T+389.
68 T=128 ! Trial sat temp 5))
78 GOSUB 288 220 H=.621SP,Cl-P) ! sat humidit
sa Y~=Y Y
98 T=1.0801*T 23@ Y=178-T-9B8*(H-H1 >./E
100 GOSUB 268 249 R1=34.15Y~R+1?*.#~CH-H1~
1 10 'i'Z=Y 2.56 R2=6e.33*CR+l)^.8*(H-Hlj*(~-
120 K=.0881*T*Yl~<Y2-Y1) .814)
138 T=Ti'l.6681-K ! Newton-Raphso 260 RETURN
n 278 END

PRODUCTS COSTS
More than one kind of dryer may be applicable to a particular Differences in thermal economies are stated in the comparisons of
product, or the shape and size may be altered to facilitate handling Table 9.2 and other tables. Some equipment cost data are in
in a preferred kind of machine. Thus, application of through- Chapter 20. When the capacity is large enough, continuous dryers
circulation drying on tray or belt conveyors may require prior are less expensive than batch units. Those operating at atmospheric
extrusion, pelleting, or briquetting. Equipment manufacturers know pressure cost about 1/3 as much as those at vacuum. Once-through
the capabilities of their equipment, but they are not always reliable air dryers are one-half as expensive as recirculating gas equipment.
guides to comparison with competitive kinds since they tend to Dielectric and freeze driers are the most expensive and are
favor what they know best. Industry practices occasionally change justifiable only for sensitive and specialty products. In the range of
over a period of time. For example, at one time rotary kilns were 1-50 Mtons/yr, rotary, fluidized bed and pneumatic conveying
used to dry and prepare fertilizer granules of a desired size range by dryers cost about the same, although there are few instances where
accretion from concentrated solutions onto the mass of drying they are equally applicable.
particles. Now this operation is performed almost exclusively in
fluidized bed units because of economy and controlability of dust SPECIFICATION FORMS
problems.
Typical examples of products that have been handled A listing of key information relating to dryer selection and design is
successfully in particular kinds of dryers are listed in Table 9.4. The in Table 9.5. Questionnaires of manufacturers of several kinds of
performance data of later tables list other examples. dryers are in Appendix C.