I
CARL S. SCHLEA and JOHN P. WALSH E. 1. du Pont d e Nemours & Co., Inc., Savannah River Laboratory, Aiken, S.
C.
De-entrainment in Evaporators Use these data for design of im pinge ment-ty pe deent ra iners Tms
STUDY was undertaken to provide design data for a de-entrainer applicable to evaporators that are used to concentrate radioactive solutions. I n this application, entrainment is detrimental since it causes the condensate to be contaminated with nonvolatile radioactive materials. Entrained liquid from an evaporator in ordinary commercial service is normally about one part liquid per 10,000 parts of the vapor by weight; in radioactive service, less than one part liquid per million parts vapor is often the upper limit to permit the condensate water to be discarded. The experiments in this study were designed to provide controlled data on the effectiveness of impingement caps when used with a natural circulation evaporator. These data can be used to test a design method based on fundamental measurements of size of particles generated by boiling liquids (2, 4), impingement theory of jets (7), and atomization of drops by high vapor velocity (3).
Experimental Studies were made with the natural circulation evaporator shown below. The de-entrainment column was offset and connected to the reboiler with a 6-inch-diameter crossover duct. The dynamic liquid level in the liquid recycle leg was maintained a t two-thirds tube submergence. The de-entrainment column consisted of flanged 12-inch lengths of G-inchdiameter pipe, each section containing one plate and external piping for drainage and reflux as shown. Combinations of these sections were used to make a column with plates a t 12-inch spacing. Reflux and drainage liquid were controlled by valves in the external flow circuit; this allowed any or all of the plates to be operated either wet or dry.
One de-entrainment cap was used on each plate. The caps are shown below. The bubble caps are of a variety normally used in distillation. Uranyl nitrate solutions containing 0.4 to 1.5M uranium were used in all experiments. The uranyl nitrate solutions were batch charged to the evaporator, and the composition of the boiling liquid was maintained constant by returning condensate to the reboiler. Makeup solution was added only to replace samples. Samples of the condensate were taken a t the discharge of the condenser and a t least 30 minutes after reaching steady state, which was indicated by constant analyses over a period of 1 hour. The concentration of uranium in condensate samples was measured by a fluorometric method; the very dilute solutions were concen0.30HCtaaranos Spacer, Both End#
0.15" Clearance Spccer, Bath Ends,
)
eoit to Clornp COP to RISW and Plate,
Notes:
-
P Static Pressur*e Tap
Drain Leqe Bent to Flt Inside Draln Trouqh
It
Note. The Risers Were Flttod over f Wlde Slotr
Addition Line
Cop: 16GO. SST 3"0.R 18 slots
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Riser: 2"Sch.40 Pipe
T
Makeup Water
) Pump Evaporator and de-entrainment column
The impingement cap (top) i s a better de-entraimr than t h e bubble cap (bottom) VOL. 53, NO. 9
SEPTEMBER 1961
695
Summary of De-entrainment Studies Entrainment reaching de-entrainer, 15 to 30 parts liquid p e r million ports vapor by weight. of boiling rate, 20 to 200 pounds of vapor per hour per de-entrainment cap
Nuniberof Plates
Deentrainer Dry caps
~ _ Plate _ _ d r_i angemeiitY _ _ 2
1
-
4
3
Range
Reflux Ratio Kn trainmen t Passing on Wet De-entrainer, Plates, Parts I'm ts Llquld/ Liquid/ Million Parts Vapoi by Parts Weight Vapor
3
DB DB DB
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I
Wet caps
3 3
WB WE
WB WB
WB WB
