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Separation Process Principles- 2n - Seader & Henley - Solutions Manual

Can a spouted bed dryer be used does the use of air

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Unformatted text preview: -transfer areas: 7,388 ( 958.8 ) Q1 A1 = = = 377 ft 2 U1 ( Ts − T1 ) 400 ( 47 ) A2 = (16,860 − 11, 380 ) ( 988.5) = 292 ft 2 Q2 = U 2 ( 273 − T2 ) 350 ( 53) Because the areas are far apart, make another iteration. To do this, adjust the ∆Ts, as follows: Assume the heat duties from above will still hold. That is, Q1 = 7,388(958.8) = 7,084,000 and Q2 = 5480(988.5) = 5,417,000, both in Btu/h. Then, for equal Areas, A: A(400)(230 – T1) = 7,084,000 and A(350)(T1 – 130) = 5,417,000 Solving these two equations, T1 = 176.6oF, compared to 183oF in the first iteration. Iteration 2: Solve (4) for the new temperatures: (5) (16,860 − m1 ) ( 992.4 ) = ( m1 − 5, 620 ) (1117.7 ) + 5, 620 ( −17 ) - m1 ( 82 ) Solving, m1 = 11,400 lb/h, which is very close to the value of 11,380 lb/h Thus, essentially no change in these flow rates from iteration 1 and the problem is converged. Now, solve for the heat-transfer areas: 7,388 ( 958.8 ) Q1 A1 = = = 332 ft 2 U1 ( Ts − T1 ) 400 ( 230 − 176.6 ) A2 = (16,860 − 11, 400 ) ( 988.5) = 327 ft 2 Q2 = 350 (176.6 − 130 ) U 2 ( 273 − T2 ) (c) The area of each evaporator = 330 ft2 (a) The pressure in the first effect is that corresponding to 176.6oF. From steam tables, 7 psia. (b) Evaporation in the Effect 1 = 16,860 – 11,400 = 5,460 lb/h of heating steam. Therefore, percent of total evaporation in the first effect = 5,560/11,240 = 0.495 or 49.5 % (e) Heating steam required for Effect 1 is obtained from a revision of (3), ms(958.8) = (16,860 – m1)(1136.8) + m1(82) – 16,860(6) Solving, ms = 7,340 lb/h Economy = 11,240/7,340 = 1.53 or 153%. Exercise 18.1 Subject: Selection of dryer for removal of surface moisture from 0.5 mm crystals of NaCl without breakage. Find: Suitable type continuous, direct-heat dryers. Highest gas feed temperature. Analysis: Applicable dryers are tunnel dryer or belt dryer. Inlet gas temperature can be high, to say 1400oF, because of the high melting point of NaCl. Exercise 18.2 Subject: Batch drying of 100 kg/h of a toxic, temperature-sensitive material of 350 mm size. Find: Suitable dryers. Analysis: Select a rotating, double-cone vacuum dryer. Exercise 18.3 Subject: Drying of a thin, milk-like liquid to produce a powder Find: Suitable continuous, direct-heat dryer that will restrict temperature to less than 200oF. Analysis: Select a spray dryer. Exercise 18.4 Subject: Selection of dryers from conditions of the feed, temperature sensitivity, and form of the dried product Find: Suitable batch or continuous dryers for different cases. Analysis: (a) A temperature-insensitive paste that must be maintained in slab form. Select a batch tray dryer or a continuous belt dryer. (b) A temperature-insensitive paste that can be extruded. Select a continuous through-circulation belt or band dryer, or a batch, agitated pan dryer. (c) A temperature-insensitive slurry. Select a continuous spray dryer. (d) A thin liquid from which flakes are to be produced. Select a continuous drum dryer. (e) Pieces of lum...
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