I/EC A
COSTS
W O R K B O O K
F E A T U R E
by Walter L. Hardy, Foster D. Snell, Inc.
COURTESY RODNEY HUNT MACHINE CO.
COURTESY RODNEY H U N T M A C H I N E CO.
Covered installation of a turbulent film evaporator
Exterior installation of a turbulent film evaporator
Turbulent Film Evaporators In a typical turbulent film evaporator operation, butyl ester product yield was increased 15% over that obtained by conventional evaporation
^ ^ N E of the most interesting pieces of equipment to enter the field of evaporation is the turbulent film evaporator. T h e operation is based on providing a turbulent, thin film of the feed liquor, u n d e r controlled conditions of t e m p e r a t u r e and pressure, to affect m a x i m u m evaporation with m i n i m u m deterioration of the product.. T h e evaporator consists of a cylindrical, steam-jacketed unit, in two sections, with a high-speed rotor m o u n t e d concentrically in the center. T h e speed of the rotor can be varied depending on application. T h e rotor shaft is equipped with blades which rotate within m i n u t e clearance of the heated wall. T h e two sections are for evaporation a n d separation or e n t r a i n m e n t removal.
A d v a n t a g e s over Conventional Evaporation
I n operation, the feed liquor—as a liquid or slurry—enters the feed inlet a n d is whirled by the rotor blades against the heated wall. H e a t is provided by the concentric steam jacket. T h e liquor spins down the wall in a continuous, turbulent thin film. T h e thin turbulent film provides m a x i m u m heat transfer to the liquor with little or no possibility for localized overheating. Exposure of the heating surface lasts only a few ecsonds. T h e product is delivered at the bottom outlet at the desired concentration, with m i n i m u m deterioration. Another advantage is the elimination of an elevation in boiling point, as a hydrostatic head is not possible.
T h e vapor from the evaporating section rises through the separating section, which contains unheated, stationary baffles. Any particles of the liquor spun from the rotor blades, or which are otherwise entrained in the vapor stream, are arrested, or they coalesce, respectively, on the stationary baffles a n d flow back to the evaporating section by gravity. T h e vapor stream leaves the unit from a c h a m b e r above the separating section. Scale formation, which is one of the more serious problems with conventional evaporators, is practically eliminated in the turbulent film evaporator. Any minute quantities of scale which m a y form are immediately removed by the high speed rotating blades. Generally, howVOL. 49, NO. 12
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DECEMBER
1957
53 A
I/EC
COSTS
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A Workbook
Feature
Installation of a pilot plant turbulent film evaporator
ever, as the velocity of the liquor through the unit is high, even the formation of minute quantities of scale will be held to a m i n i m u m . As the feed liquor moves through the unit u n d e r turbulent conditions in a few seconds, foaming and froth ing are rarely a problem in the opera tion of the unit. In recent experi ments with a pilot plant unit (above), the feed liquor contained a sucrose ester detergent a n d was processed without foam or froth problems. A further major advantage of the turbulent film evaporator results from the m i n i m u m a m o u n t of m a terial which is in process at any given moment. I n this unit, the quantity of material in process is approximately 3 0 0 % less t h a n that in a single-effect p a n evaporator, a n d is approximately 1 5 0 % less than that in a single effect of a con
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ventional triple-effect evaporator. T h e heat absorption in the turbulent film evaporator is high, b u t of rela tively short term. T h e turbulent film evaporator m a y be operated u n d e r v a c u u m for evaporation a n d concentration, deaeration, deodorization, a n d for carrying out certain reactions at a higher rate u n d e r continuous con ditions. Heat-sensitive materials— such as food products (citrus juices, soluble coffee, etc.) a n d p h a r m a ceuticals (blood serum, vitamins, etc.)—can be effectively processed with m i n i m u m deterioration in prod uct quality. T h e unit can also b e operated at atmospheric pressure or at pressures above atmospheric. T h e advantages of the controlled, tur bulent thin film process will equally accrue u n d e r these conditions.
uct, a n d condensate p u m p s ; the overhead condenser, feed preheater, and vent condenser; the v a c u u m re ceivers; steam j e t s ; piping; a n d instruments T h e operating costs for the tur bulent film evaporator will naturally vary with the purpose for which the unit is employed. O n l y a typical case can be given here for illustrative purposes. Consider the following operation : Butyl ester feed, 450 pounds, is processed t h r o u g h a turbulent film evaporator on a continuous basis. T h e primary product is stripped off overhead a t a rate of 182 p o u n d s per hour. T h e turbulent film evaporator chosen for the purpose is 12 inches in diameter with approximately 9 square feet of heating surface. T h e operating conditions are :
T h e figure above, at left, shows a pilot plant unit operating on the pro duction of sucrose esters.
Feed Overhead Bottoms
Purchase a n d Operating Costs
T h e average purchase cost of tur bulent film evaporators (fall 1957), which m a y be used for estimating purposes, is shown below as a function of the square feet of heating surface. For capacities in excess of those shown, the units can be con nected in series or in parallel. These costs are for a unit constructed of T y p e 304 stainless steel and include the electric drives. Auxiliary equip ment for a typical vacuum installa tion of a 9-square foot heating sur face unit will cost approximately $6000. This includes the feed, prod-
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50 ?
40
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30
α
20 mm. of Hg, absolute
T h e cost of operation for the unit is essentially the cost of utilities. L a b o r cost is negligible, as the unit, operated on a continuous basis, can be easily a n d inexpensively controlled by instruments. T h e utility costs are: Item Dollars per Hour Cooling water, 774 gallons/hr. at $2.50/thousand eu. ft. 0.240 Electricity, 5 kw./hr. at 1.5 cents/kw.-hr. 0.075 Steam, 785 lb./hr. (100 p.s.i.g.) at Sl.OO/thousand lb. 0.785 Total utilities $1.10 per hour Utility cost per pound of butyl ester product $0.00604
I n this instance, in addition to the low cost of operation, the yield of butyl ester was increased approxi mately 1 5 % over that obtained by conventional evaporation.
„.£-^^-*-*£ ^^
20 e^—
' (0
20
30
4 0 50
70
Heating Surface
100 -
20ΰ
Square Feet
Purchase cost based on square feet of heating surface 54 A
Operating pressure
450 lb. per hr. at 120° C. 182 lb. per hr. of butyl ester at 160° C. 273 lb. per hr. of residue at 162° C.
INDUSTRIAL AND ENGINEERING CHEMISTRY
30ϋ
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