Page 173 - Handbook Of Multiphase Flow Assurance

Paraffin wax 169

TABLE 5.7 Methods to find the temperature of wax precipitation
Type Method
Optical Visual—deposit in laboratory cold finger or flow loop equipment or in the field separator inlet
strainer, scraper receiver or bypass spool pipe at various temperatures.
Visual polarized light microscopy, atmospheric and pressurized. Polarized light is only applicable to
n-paraffin waxes because these crystals can rotate the plane of light polarization. Amorphous wax
such as from biodegraded crudes cannot be detected by CPM
Infrared or visual light transmission. Infrared light is more applicable to crude oils as crudes are
translucent to infrared light
Heat Differential scanning calorimeter to detect heat released by crystallization of paraffins, atmospheric
and pressurized
The DSC method is applicable to both n-paraffins (macrocrystalline wax) and isomerized paraffins
(microcrystalline and amorphous wax) because heat of fusion is released by both
Mechanical Viscometer to detect transition to non-Newtonian fluid behavior with appearance of solids
Rheometer to detect transition to non-Newtonian fluid behavior with appearance of solids
Pressure Cold filter plug to find onset of wax deposition by measuring pressure drop

TABLE 5.8 Procedure to calculate wax diffusion coefficient from a deposition experiment data such as a
laboratory cold finger
Flux = D (C_WAT − C wall )/L_diff - Assume Fick's law
V_sample, mL 166 Estimated
Depth, in. 2.6 Assume +1 in. from U tube to flask bottom to allow for stirrer
Flask area, cm 2 24.8 = V_sample/depth
Flask ID, cm 5.6 Diameter calculated from area
L_deposit, in. 4 Estimated from image
L_vertical, in. 1 Estimated from image
OD_finger, in. 0.25 Estimated from image
Area_deposit, in. 2 3.14 = pi × OD × L
Circumference, in. 4 to estimate radius of cold finger
R, in. 0.636 radius of cold finger
Stirrer RPM, 1/min 100 estimated
Flow velocity past finger, in./ 400 = 2 × pi × R × RPM 16.9 cm/s
min
Viscosity of stock oil @ 36 °C, cP 40.995 per lab data 0.040995 kg/m s 0.40995 g/cm s
3
Density oil, g oil/cm oil 0.85 850 kg/m 3
2
2
Kinematic viscosity, cm /s 0.482 = viscosity/ 4.82E-05 m /s
density
Viscous sublayer, cm 0.330 = 11.6 × kinem.visc/flow velocity
(Continued)