Ind. Eng. Chem. Res. 1988,27, 1541-1543
1541
COMMUNICATIONS An Apparatus for Measurement of Multiple-Phase Equilibria at Elevated Pressures Specific requirements are presented for the measurement of multiple-component, multiple-phase equilibria. Details of a n apparatus capable of operation in the ranges of 310-425 K and 60-345 bar are given. T h e apparatus features a moveable probe which permits withdrawal of a sample from any phase within the high-pressure cell. The use of a mercury piston coupled with very small sample sizes (in the l-hL range) allows the study of a given feed composition over a wide range of conditions without reloading the apparatus. Operation is simple, and a typical data point for a binary system, reproducible to *0.5%, can be measured in approximately 1.5 h. Data taken with the apparatus for the binary system carbon dioxide + n-decane, show good agreement with literature values. Details are presented for an apparatus capable of measuring multiple-phase, multiple-component equilibria in the ranges of 310-425 K and 60-345 bar. The apparatus features a moveable probe which permits the withdraw1 of samples from any number of phases for analysis by gas chromatography. A mercury piston, allowing easy pressure adjustment coupled with very small sample sizes (in the 1-pL range), allows numerous measurements to be made a t a given feed composition over a wide pressure range. Operation is simple, and results show that a typical data point for a two-phase system, reproducible to f0.5 mol 70, can be measured in 1.5 h. This apparatus is similar to the one described earlier by Simon and Schmidt (1983). However, the earlier publication lacked sufficient detail to allow construction. A significant improvement is introduced here with the addition of a separate vapor sampling loop which dramatically enhances the accuracy of the vapor-phase measurement.
Table I. Manufacturer and Description of Equipment Shown i n Figure 1
General Description A scheme of the entire apparatus is shown in Figure 1. Nominal 1/16-in.stainless steel tubing is used throughout, except where noted. This provides the required mechanical flexibility to connect the probe outlet to the liquid pump [6] (numbers in square brackets indicate part numbers in Table I and Figure 1). All valves are mounted on stand-offs to minimize heat conduction and are operable from outside the oven. The high-pressure cell consists of a Jerguson liquid-level gauge that is modified according to Figure 2. In practice, any high-pressure cell can be used provided that the required probe length is not too long. In our apparatus, the probe traverses the entire length of the cell, which is approximately 10 in. long. The l/s-in. stainless steel tubing used for the probe [2] is under considerable stress when the cell is pressurized. The system described has performed satisfactorily throughout the temperature and pressure ranges indicated. However, as a standard safety precaution, the apparatus is enclosed in an oven made of 3/16-in.thick steel, and the cell windows are viewed via mirrors and lexan shields. The entire oven is insulated and the temperature is regulated by controllers which operate heating elements located inside the oven. In addition to the probe, the circulating pump [6,7] is also unique. Simple, though not obvious, modifications allow the use of an off-the-shelf item to circulate the phases a t elevated temperatures and pressures without resorting
13 14
~~
no.
description 1 liquid level gage, Model 17-T-40, 316 SS, 345 b a r a t 310 K 2 l/s-in. 316 SS tubing, 0.d. 0.125 + 0.0000, -0.0005-in., 0.d. surface finish, 14 pin., rms 3-5 pressure generator, Model 87-6-5, 60 cm3, 345 bar 6,7 Duplex minipump, Model 2396-31, 16-320 cm3/h, 414 bar 8, 9 sampling valve, 1 pL, 483 bar, 425 K, Model 7410 10 switching valve, 6 port, 483 bar, 425 K, Model 7000 11 rupture disk, 345 bar, 304 SS 12
15 16 17 18
19
3-wire, 100-Q P t resistance thermometer, Model RTS-32-B-100 bridge amplifier, Model BA-500 volt meter 0-250 mV, 0.01-mV resolution pressure transducer, Model TJE, 0-345 bar, amplifier readout, Model 450D temp controller, Model D921, with PID unit, 1 "C resolution high-pressure seal, ring-100-06-GC-1, spring-100-VHB-062,with P-22 backup ring heavy-duty stir-pak stirrer motor, 150-3300 rpm, 25 in. 02. torque, Model T-4558-00 worm and wheel reducer, Model DJ-IO, 6 0 1 reduction
manufacturer Jerguson Gauge I
I
Microgroup, Inc. High Pressure Equipment Co. LDC Milton-Roy Rheodyne, Inc. Rheodyne, Inc. High Pressure Equipment Co. Hy-Cal Engineering Hy-Cal Engineering Doric Scientific Sensotec Omega Engineering Bal-Seal Engineering Cole-Parmer Instrument Co. Precision Instrument Corp.
to the construction of a specialized pump (see, for example, Capps et al. (1975)). Because of their unique nature and versatility, the probe and pump modifications will be described in detail. Pump Modifications The pump used on this apparatus has two pump heads, one used for circulation of the liquid phase [6] and the other for circulating the vapor [7]. Each pump head operates by a reciprocating plunger movement. The plungers, driven by the same motor, operate 180° out of phase so that cell volume and pressure remain constant while
0888-588518812627-1541$01.50/0 0 1988 American Chemical Society
1542 Ind. Eng. Chem. Res., Vol. 27, No. 8, 1988 PIPE NIPPLE
I
, I HIGH PRESSURE BLOCK
PROBE
I I
I I
I
19
&'a
U (
/OVEN
,
.
-
-
K
C
CLAMPING BLOCK
rLtoU'o
k
RETURN
l
/-TEFLDN TVAPOR
TENSIONING SCREWS.
5 PLACES
PROBE A GUIDE B
Y Y Figure 1. Scheme of the apparatus. Heavy lines and shaded parts indicate that they are traced with heating tape.
\ \
1
CIRCULAR LEAD HUB --,
WASHER
WITHDRAWAL
MWNllffi HOLE,
REDuCEhY
q(1
G EINPUT AR SHAFT
Figure 3. Probe guide assembly.
TENSIONING SCREW
8
1
I
PROBE GUIDE BACK TENSIONING STRIP
FRONT PIECE
-
K L T HOLE, 14 PLED EWALLY SPACED
\
at
i8
0 50 0 63
m 0 63
'\
'-0WINCH
NPTPIPE TAP
Figure 2. Modified Jerguson gage, shown without bolts, windows, and window supports.
pumping. The total internal volume of the pump heads and sampling lines is less than 3% of the total apparatus volume. A very simple modification allows placement of both pump heads inside the air bath. The procedure starts by disconnecting each pump from the central gear reducer at the flexible couplings, and then each pump is rotated 180' so that the pump head is farthest away from the motor. The pumps are reattached to the mounting channel by the original bolts. Two holes, one in each pump, are drilled for this purpose. The pump heads are now upside down and must be inverted as described in the operator's manual. Experience has shown that operation above 373 K or in the vicinity of a critical point requires two additional modifications. For high-temperature operation, the plastic used for the ball guide and ball stop in the check valve cartridges is unacceptable. Copies of each part were made in aluminum, with all edges contacting the sapphire ball checks deburred. The pump is supplied with two ball checks in each cartridge, but for this application only one is needed; therefore, the second ball check has been omitted and replaced with a single piece of aluminum tube
Figure 4. Section through the probe guide showing assembly of the three-piece way and tensioning strip.
of the same overall dimensions. To allow operation near a critical point, the original fxed speed motor was replaced with a Bodine variable-speed dc motor and controller (Model 032 and 827). As originally supplied, significant cavitation in the pump head was caused by rapid plunger movement. Continuous adjustment from 60 to 1725 rpm is now possible, permitting fast pumping for mixing or slow pumping for sampling.
Probe Guide Assembly The probe guide assembly consists of three main sections: the high-pressure head, the probe guide, and the drive mechanism. The high-pressure head connects the entire assembly to the equilibrium cell and houses the high-pressure seal. The probe guide supports the probe and allows a smooth linear movement of the probe through the seal. The adjustability required to mount the drive motor outside the oven is provided by the drive mechanism. Details of the assembly are shown in Figures 3 and 4. The high-pressure head is composed of three parts, each fabricated of type 316 stainless steel. Its precise construction is critical to ensure proper operation and a good seal. Connection to the equilibrium cell is by a 1/2-in.NPT
I n d . E n g . C h e m . Res. 1988,27, 1543-1545
half nipple. The prethreaded nipple is press fit into the seal housing and secured by a 1/4-in. fillet weld. The opposite side of the seal housing is then spot faced to a depth of 0.50 in. This spot face allows accurate alignment of the backup plate and the high-pressure seal. The backup plate, which is 0.75-in. thick and approximately 2.00-in. diameter, must fit snuggly in the spot face. The clearance between these parts must not exceed 0.001 in. The backup plate is secured by six 1/4-in.class 8 machine screws, on a 1.25-in. bolt circle. Proper alignment of the probe passage in the backup plate and seal cavity is provided by drilling the assembled parts on a lathe. An undersized l/&. pilot hole is drilled and then reamed to size. The backup plate is then removed, and the seal cavity machined. The seal cavity requirements can be found in the Bal-Seal Design Manual. Performance of the seal is excellent without chrome plating on the seal cavity or probe provided good surface finishes ( ~ 1 pin. 4 rms) are maintained. Of great importance is the mounting of the high-pressure head to, and the construction of, the probe guide. The probe guide is a linear motion device consisting of a three-piece, 45" dovetail way which guides the clamping block. The clamping block holds the bottom end of the probe and is powered by a lead screw. All parts other than the screw were machined from T3-2024 aluminum. The lead screw is of mild steel with a pitch of 24 threads/in. This pitch assured that the screw/block combination would be self-locking under load. To provide smooth movement of the clamping block in the way, a tensioning strip, made of 0.188- X 0.625-in. aluminum bar stock, was mounted in a grove on the base of the way. Tension was adjusted by five equally spaced screws positioned along the back of the probe guide (see Figures 3 and 4). Proper alignment of the head to the probe guide is obtained by using a dial indicator. The head is then bolted in place and reference pinned. This allows future assembly without tedious alignment. The two front pieces of the way are each secured by five machine screws. The front pieces are positioned by use of gage blocks and a dial indicator. When aligned properly the way must allow the clamping block to move parallel to the probe passage in the high-pressure head. To fasten the probe to the clampling block, a 0.125-in. wide slot is milled in the clamping block and the probe is held in place with four screws. The depth and position of this slot are important if the probe is to be concentric with the seal. Careful attention to fitting and assembly is important so that the probe enters the seal squarely and that the two are concentric. Accurate alignment is provided by machining the slot after the block has been
1543
mounted and pinned and the ways assembled. The lowest section of the assembly is the drive mechanism. A gear reducer, made by Precision Instrument Corp. (Model DJ-lo), is positioned on a two-piece angle such that its output shaft powers the lead screw. The angle is mounted on a circular hub with an external snap ring. This allows the angle and the gear reducer to rotate 360°, and alignment of the motor shaft [18] to the reducer input shaft is greatly simplified. A flexible coupling is also used on the input shaft for further protection against shaft failure due to misalignment.
Conclusion The pump and probe assembly presented here allow the construction of a versatile apparatus for the determination of phase equilibria a t high pressure. The apparatus described allows quick and accurate sampling as proven by testing on the C02 + n-decane binary mixture (Kneisl, 1988). This represents a very strigent test of the apparatus since the gas phase is very lean in n-decane and the isotherm studied contained a critical point. The addition of density, surface tension, and viscosity measurements, as outlined by Simon and Schmidt (1983), illustrates the unique capabilities attainable by this sampling technique. Acknowledgment The authors thank the Union Carbide Corporation for several fruitful discussions. Funding for this research was provided by the U S . Department of Energy under Grant DE-FG05-82ER75056 and The Energy Research Center of the State of West Virginia under Grant ST86-CP7-2. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support.
Literature Cited Bal-Seal Design Manual; Bal-Seal Engineering Company: Santa Ana, CA. Capps, E. F.; Eubank, P. T.;Gielen, H.L.; Hall,K. R.; Mansoorian, H.Rev. Sei. Instrum. 1975,46(10), 1350-1351. Kneisl, P. Ph.D. Dissertation, West Virginia University, Morgantown, WV, 1988 (in progress). Simon, R.; Schmidt, R. L. Fluid Phase Equilib. 1983, 10, 133.
Philip Kneisl, John W. Zondlo,* Wallace B. Whiting Department of Chemical Engineering West Virginia University Morgantown, West Virginia 26506
Received for review April 29, 1987 Revised manuscript received March 23, 1988 Accepted April 22, 1988
Entrainment of Ambient Air into a Cylindrical Duct by a Turbulent Jet from a Single Nozzle Measurements were made of the rate of air entrainment induced by a turbulent jet stream from a single nozzle in a semiconfined flow system. A simple correlation was then developed between the rates of air entrainment and jet flow. The correlation agreed with measurements to within f3.1% . This study will prove useful for the design of furnaces, dust collectors, and fluid mixing equipment in the chemical industry. As a jet issues from a nozzle into a stationary medium, it entrains fluid from the surroundings. Albertson et al. (1950) assumed that the sole force producing the deceleration of the jet and the acceleration of the surrounding 0888-5885/88/2627-1543$01.50/0
fluid is the tangential shear within the mixing region. This led to the conclusion that the momentum flux must be constant for all normal sections of a given flow pattern. From this conclusion, an explicit form of the axial velocity 0 1988 American Chemical Society
