LIQUID METHYL CHLORIDE By KARL S. WILLSON, SALTER O . WALKER, W I L L I A M R. RINELLI, AND C. V . M A R S
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ogfczS 3(8fc=3-*-
Liquid phase
Liquid from supply drum.
-LUI.
,
TYPICAL
ffiV
MEASURING
CHAMBER.
Figure 5 #/ /natch rrrut%.rw ed r « Soar wtMrw*et J»*
Paper msu/otton.
11''
J
height which the methyl chloride must be raised during the transfer. This term is independent of the size of the pipe. For more accurate calculations, the difference in density of the liquid methyl chloride at various temperatures must be considered (see Table V).
Tr tube 'phase* vatve 'quidphase
ralve
Rati heiqhh ar-e soch thai drum\ pitches sh/jhtJj toward u-g/yes) ,-*.
-s~
^
- ^
II.
••«>_
Steam
coil
Thermostat
bttlb.
FRICTTONAL PRESSURE DROP. This
drop in pressure from one end of the pipe to the other is due to friction of the moving liquid and increases with the speed of transfer in a given pipe size or for a given
Figure 4
connections which facilitate weighing. The vessel is filled to the desired weight, or until nearly full, and then the appropriate amount is delivered to the desired point. Pressure vessels fitted with calibrated gage glasses are often used for introducing measured volumes of liquid methyl chloride into batch processes. The size of the measuring vessel depends on the quantity of methyl chloride desired and the accuracy of measurement needed (Figure 5). A. rotameter (Figure 6) is commonly used for continuously measuring the flow of liquid methyl chloride. A rotameter or simple mercury-in-glass flowmeter is suitable for measuring the gaseous form (Figure 7). Pressure Drop in Liquid Methyl Chloride Transfer Lines I n determining the carrying capacities of clean, scale-free pipe or tubing for transferring liquid methyl chloride and the operating pressures necessary, three factors must be considered. VOLUME
Table V . Effect of Temperature on Static Head of Methyl Chloride TEMPERATURE LIQUID HEAD
° F.
Lbs./sq. in.
0 32 40 50 60 70 80 90 100 110 120 140
I.
STATIC HEAD.
0.430 0.416 0.413 O.408 O.404 0.399 0.394 0.390 0.384 0.379 0.373 0.359
Calibrated gloss tube iv/tΛ float
m
This term relates
to the weight of a column of liquid and is involved when the receiver is at a different level than the tank from which the liquid is being transferred. Assuming that the liquid methyl chloride is at the same temperature before and after transfer, approximately 0.4 pound per sq. inch of added pressure will be required in the tank in order to overcome each foot of
2 1, N O . 15 » » A U G U S T
Attach controtl wtnebere —I To point of application,
10, 1 9 4 3
Lift/t'ctor
ROTAMETER
ASSEMBLY.
Figure 6 1259
Table V I . Viscosity of Methyl Chloride Capillary tuba-
VISCOSITY*
TEMPERATURE ° F. ° C. -40 -40 -20 -28.9 0 -17.8 20 - 6.7 40 -1- 4 . 4 60 15.6 80 26.7 100 37.8 120 48.9 140 60.0 160 71.1 180 82.2 200 93.3 220 104.4 240 115.6
Rubber tubing •
Reguiatiag "Yw valve.
J 3/8" Std. pipe thread •* Gas in
3e
3£
1/8"· black'lron pipe
Bulb t o cit-.ch l i q u i d ! i n case of Sw-çteî» -
Vapor Liquid Centipoises 0.0086 0.349 O.009O 0.321 0.0094 0.298 O.O09S 0.279 0.0101 0.263 0.0105 0.249 0.0108 0.237 0.0111 0.226 0.0115 0.217 0.0118 0.208 0.0122 0.200 0.0125 0.193 0.0128 0.186 0.0131 0.180 0.0134 0.175
a For vapor at one atmosphere and satu rated liquid. Pressure coefficients are neg ligible in ranges encountered in refrigerating practice.
Recessed t o r^seive bulb.
pressure drop and thus c a n be omitted without serious error. Leak Detection
Bottom rest
Figure 7 rate. T h e frictional pressure drop is greater the smaller the pipe. Pressure drop m a y b e calculated, w i t h satisfactory accuracy, by means of t h e formula: gd where, / «β .rictiion factor, no units L = length of straight pipe, in feet, plus equivalent length due t o bends, valves, e t c . Ρ = fluid density in pound per c u . foot = 6 2 . 3 X ( s ) u = average velocity of the fluid in feet per second =* discharge as cu. feet per second cross section in s q . feet g « 3 2 . 2 feet per second per second d = actual inside diameter in feet Δ Ρ = pressure drop in pound per s q . foot D = actual inside diameter, inches « = specific gravity, no units Ζ — viscosity relative to water a t 6 8 ° F . , centipoises (Table V I ) 1260
/ is determined from a- grapfa plotted in terms of the factors J)ms/i referred to asF). In the case of drawn «copperr pipe or its equivalent, for values o»f e laager than 0.14 t h e fluid flow is turByulcnt and the value off is taken from TabOe VII - Values for iron pipe differ but sligBttly from those given, the pressure drop being slightly higher but the difference is of litfcJe impor tance for practical purposcs. For streamline flow, minor irregularities in the surface are of even Hessinaportance and for values of F less "than ©.14, / is calculated from the equation 0.00207
III.
for all types of p i p e .
VELOCITY
HEAD-
Thus
term
corresponds t o t h e pressmre required to convert the stationary liquid t o moving liquid. It is independents of Length of pipe a n d for most flow ractes cit>ed in the previous section is negligible IFor some of the higher rates, the p&ressur=e drop is about 1 to 2 pounds and h*enco i s of little consequence compared witEh the zfrictional
CHEMICAL
Methyl chloride in large concentrations in air forms a mixture which m a y be flammable (see Table I) and also hazard ous to health (Table IV). T o determine whether an explosive mixture is present, a special hot wire combustion test appara t u s is available. This type of instrument m a y also be used to detennine hazards due to toxic quantities of methyl chloride for short exposure. When nonexplosive atmospheres have been assured by adequate tests or b y thorough ventilation, the actual leak m a y be readily located by use of special leakdetecting halide torches, such a s are customarily used by refrigeration service engineers. These torches use alcohol cr acetylene a s a fuel, normally producing a colorless flame which turns t o green when the leak-detector tube picks u p very minute concentrations of methyl chloride, and to a brilliant blue with stronger con centrations. T h e space where the torch is being used should be well ventilated t o prevent possible harmful effects of break down products. A soap solution applied at the suspected point indicates t h e leak in many instances b y the formation of bubbles. Hazards D u e to Leaks Methyl chloride has a slight, n o t u n pleasant odor which is not irritating and m a y pass unnoticed. Consequently, i t provides no definite warning in case of leakage unless a warning agent, such a s sulfur dioxide or acrolein, is added. Where quantities of methyl chloride are being handled, possible hazards d u e t o ruptured lines, broken gage glasses, leaking joints, etc., must b e considered. Suitable gas masks should be provided and competent employees instructed i n their use. Care should be taken that t h e g a s
AND ENGINEERING
NEWS
mask is kept in proper working order and contains a fresh charge of suitable absorbent in the canister.
jpa
Use of Gas Masks Canister-type gas masks are unsafe for larger concentrations of methyl chloride and employees should be warned of their possible failure in the event of a really serious rupture. Self-contained oxygen breathing apparatus or a mask with a long air hose and outside source of air may be required under extreme conditions. In general, where serious leaks develop, the person responsible, even when equipped with a suitable mask, should remain i n t h e contaminated area only long enough t o close the necessary valves and make emergency adjustments. Handling Leaks Leaks which might develop are ordinarily not serious and can be readily controlled. Where leaks develop in transfer lines, measuring chambers, etc., the supply of methyl chloride should be cut off by closing the appropriate valve on the storage tank, drum, or cylinder. Leaks at unions or other fittings may often be eliminated b y tightening the connection. If corrosion is indicated, care must be taken to empty the lines before working on them, as a broken fitting might lead to serious loss of methyl chloride before the supply valves could be shut off. While methyl chloride is relatively nontoxic (Table IV), precautions as to ventilation and guarding against leakage must be observed and carelessness prohibited. Exposure to excessive concentrations of methyl chloride results in an attack similar to alcohol intoxication with the characteristic symptoms of drowsiness, mental
VOLUME
a-
f
Table VII. Friction Factors F f 1.80- 1.89 0.0O72 1.90- 2.05 0.0O71 2 . 0 6 - 2.25 0.0O70 2 . 2 6 - 2.40 0.0O69 2 . 4 1 - 2.50 0.0O68
F 1 5 . 1 - 17.5 1 7 . 6 - 20.0 2 0 . 1 - 22.0 2 2 . 1 - 24.5 2 4 . 6 - 26.5
0.OO43 0.OO42 0.OO41 0.OO40 0.OO39
26.633.137.141.047.1-
33.0 37.0 41.0 47.0 51.0
0.OO38 0.OO37 0.OO36 0.OO35 0.OO34
0.0O62 0.0O61 0.0O60 0.0O59 0.0O585
5 2 . 0 - 70.0 7 1 . 0 - 78.0 7 9 . 0 - 85.0 86.O--105.O 106.0-120.0
0.OO33 0.OO32 0.OO31 0.OO30 0.OO29
4.75 5.00 5.30 5.70 6.10
0.0O58 0.0O57 0.0O56 0.0O55 0.0O54
121.O-140.0 140.O-21O.O
0.OO28 0.OO27
6.50 7.05 7.50 8.10 8.80
0.0O53 0.0O52 0.0O51 0.0O50 0.0O49
8 . 8 1 - 9.50 9.51-11.0 11.1 -12.0 12.1 - 1 3 . 2 13.3 - 1 5 . 0
0.0O48 0.0O47 0.0O46 0.0O45 0.0O44
0.14-0.16 0.17-0.20 0.21-0.26 0.27-0.33 0.34-0.37 O.38-0.4O 0.41-0.43 0.44-0.46 0.47-0.54 0.55-0.5S
O.0115 0.011 O.01O5 O.OIO O.00975
2.512.612.762.963.21-
2.60 2.75 2.95 3.20 3.40
0.0O67 0.0O66 0.0O65 0.0O64 0.0O63
0.59-0.68 0.69-0.72 0.73-0.82 0.83-0.86 0.87-0 89
0.009Ô 0.00925 0.0090 O.00S9 O.00S8
3.413.563.764.114.26-
3.55 3.75 4.10 4.25 4.50
0.90-0.92 0.93-0.95 0.96-0.97 0.98-1.OS 1.06-1.14
O.0OS7 0.0086 O.0OS5 O.0OS4 O.0OS3
4.514.765.015.315.71-
1.15-1.20 1.21-1.24 1.25-1.35 1.36-1.42 1.43-1.47
0.0082 0.0081 O.0O80 0.0079 0.0078
6.116.517.067.518.11-
1.48-1.53 1.54-1.61 1.62-1.6S 1.69-1.74 1.75-1.79
0.0077 0.0076 O.0O75 0.0074 0.0073
0.014 0.0135 0.013 0.0125 O.012
/
« valu . e s of, F « .less t^h a n Λ For 0 .,1Λ4 * , / = 0.00207 =—*
confusion, nausea, and possibly vomiting. In any case of excessive exposure to methyl chloride, the patient should be immediately removed t o fresh air and a doctor called. Like other liquefied gases, methyl chloride vaporizes rapidly when it es
2 1, N O . 1 5 » » A U G U S T
10, 194 3
capes and if the liquid comes in contact with the skin freezing may occur. Gradual restoration of temperature, as in frostbite, is followed by treatment as for a bum. I Q the case of serious freezes, or injury t o t o e eyes, a physician should be consulted immediately.
1261
