US3292424A

US3292424A - Method and apparatus for testing the low temperature pumpability of hydrocarbon oil

Info

Publication number: US3292424A
Application number: US354226A
Authority: US
Inventors: Thomas J Smollett; Seymour H Patinkin
Original assignee: Sinclair Research Inc
Current assignee: Sinclair Research Inc
Priority date: 1964-03-24
Filing date: 1964-03-24
Publication date: 1966-12-20
Anticipated expiration: 1983-12-20

Description

1966 'r. J. SMOLLETT ETAL 3,292,424

METHOD AND APPARATUS FOR TESTING THE LOW TEMPERATURE PUMPABILITY OF HYDROCARBON OIL Filed March 24, 1964 2 Sheets-Sheet 1 //v 77 AV/ ///7 V INVENTORS. THOMAS J. SMOLLETT SEYMOUR H PATlNKlN ATTORNEYS.

T. J. SMOLLETT ETAL METHOD AND APPARATUS FOR TESTING THE LOW TEMPERATURE Dec. 20, 1966 3,292,424

PUMPABILITY 0F HYDROCARBON OIL Filed March 24, 1964 2 Sheets-Sheet 2 FIG. 2

FIG. 3

INVENTORS. THOMAS J. SMOLLETT SEYMOUR H. PATlNKlN MOM 2W ATTORNEYS.

Eo mummm 205 $522 misEm 6 United States Patent 3,292,424 NIETHOD AND APPARATUS FOR TESTING THE LOW TEMPERATURE PUNIPABILITY OF HY- DROCARBON OIL Thomas J. Smollett, Harvey, and Seymour H. Patinkin, Chicago, Ill., assignors to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware Filed Mar. 24, 1964, Ser. No. 354,226 12 Claims. (Cl. 73-61) This invention relates to a method for testing the lowtemperature pumpability of hydrocarbon oils, especially those containing material such as wax, which may solidify at low temperatures and thereby interfere with pumping of the oil. Such materials generally are present in minor amounts and sometimes may cause solidification of the complete sample, although usually the solidification initially results in formation of a slurry. The invention is also concerned with apparatus which can be used to perform this test. In the method of this invention an oil sample is chilled to a point of clouding, that is, a point at which wax or other component crystallizes, gels or sediments. The sample is then pumped through a zone of lower temperature and also of more resistance to flow and observations are made to determine the pumpa-bility of the oil under the conditions imposed.

Hitherto, petroleum technologists have encountered difficulty in determining, for example, the lowest temperature at which certain oils may be pumped without encountering line plugging. While the AST M pour point test and similar tests have been widely used for the purpose of predicting pumpability performance in the field, the results of these tests do not always truly indicate the temperature limits of serviceability. Therefore, many other bench tests have been investigated and reported in the literature but none has received widespread acceptance. In fact, it has become common practice to utilize fullscale pumpability test rigs to conduct studies in this area. When the full-scale rigs simulate large equipment such as the fuel systems on jet aircraft, diesel-powered equipment, or domestic heating plants, these rigs are expensive to build and operate, tests are time-consuming, and test conditions tends to be inflexible. With the equipment and method of this invention, the low-temperature pumpability of hydrocarbon oils can be evaluated with less cost, with more speed and under more versatile test conditions than would be possible or practical with full-scale pumpabili-ty rigs.

The method of this invention is applicable to the entire range of normally liquid hydrocarbon oils and particularly to petroleum distillates with boiling ranges falling primarily within about 250 F. to 750 F. These latter are general-1y known as middle distillates and include diesel fuels, jet aircraft fuels, turbine fuels, and furnace oils. The applicable oils may or may not contain additives such as pour depressants, combustion control agents, dyes, detergents, stabilizers, dispersants, corrosion inhibitors, or others. As mentioned, the oil may not contain wax but be affected in its pumpability by the presence of other solidification-prone materials which can impede flow.

In the process oil is pumped from a reservoir through a transfer tube of substantially diminished cross-sectional area, say of no more than about one-tenth the crosssectional area of the reservoir. The transfer tube is placed in a zone having a different temperature, usually at least about 1 F. colder, than the temperature zone in which the reservoir is held. The transfer tu'be usually provides an extended flow path in this lower temperature zone to assure cooling of the oil to the lower temperature. Observations, including measurements if desired, are made "ice of the flow characteristics of oil passing through the transfer tube and usually to a collection zone.

The reservoir may be, but is usually not, held at a temperature materially greater than the actual cloud point, that is, the temperature where precipitation of solids begins in the oil. The actual cloud point of the oil may not correspond to the cloud point temperature as determined by ASTM standards, but the reservoir temperature usually does not materially exceed the ASTM cloud point of the fuel under test, eg by more than about 10 F. The procedure will usually include studies made at temperatures lower than the cloud point and may be as low as of interest. While pumping, the transfer tu'be zone is maintained at a lower temperature than the reser voir, say, at least from about 1 F. lower to about 20 F., or to temperatures even more than 50 F. colder than the reservoir. This temperature differential may represent, for example, the maximum expected temperature drop over a relatively short period of time in the field, for example, an overnight temperature drop. In any event, at least one of the reservoir and the transfer tube is at a temperature sufficiently low to cause solidification in the oil. The apparatus of this invention comprises a series of at least two chambers each of which is temperature controlled. One of these chambers contains a sample reservoir and a sample duct leads from this reservoir, through the second chamber, to, for instance, instruments suitable for providing observations of the sample flow. The duct can be associated with means for causing fluid flow and such means may comprise an arrangement for gravity flow or a pump may be employed. The sample will be given a linear velocity in the sample duct analogous to that which will be encountered in use, for example, about 35 to 40 inches per minute in the case of domestic heating oil. Means are also provided for controlling the temperature in each of the two chambers. Also, advantageously, means are provided for circulation of a thermostatic fluid in the chambers and for measuring the temperatures in the chambers.

In preferred embodiments of this invention, the thermostatic chambers may both be contained within a mechanically refrigerated cold chest and the temperature differential may be secured by cooling the second chamber below the cold chest temperature or heating the first chamber to a temperature above that in the second chamber. Alternatively, the first and second chambers, suitably insulated from each other and from the atmosphere, may be independently refrigerated. The chambers may comprise a heat conductive solid such as aluminum, but usually employ a thermostatic fluid which may be gaseous, e.g. air, or liquid. To provide for even distribution of the thermostatic fluid a stirrer is usually provided in each chamber or only in the second chamber if the first chamber has an essentially stationary thermostatic material. As a thermostatic fluid any liquid or liquid mixture may be used which is of sufficiently low freezing point not to solidify at the test temperature and which is of sufficiently low viscosity at the test temperature to be readily circulated. Alcohols such as ethyl and isopropyl alcohol, acetone or even brine may be employed. A mixture of water and ethylene glycol in a ratio, say, of 1:1, is the preferred thermostatic fluid.

The sample duct is preferably joined to a metering pump and is provided with pressure gauges, flow meters, etc., as required. By providing independent temperature controls for the sample reservoir and the duct through which the sample is pumped, experimental versatility is imparted which is advantageous in this invention.

The invention will be better understood by reference to accompanying drawings in which FIGURE 1 is a schematic view of an apparatus for performing the method of this invention using a special cold chest and air as the thermostatic fluid;

FIGURE 2 is an exploded cross-sectional view of another apparatus using a liquid as the thermostatic fluid; and

FIGURE 3 is a graph of some results obtained using the method and apparatus of this invention,

In FIGURE 1, 9 is the interior of an insulated, nearly airtight cold chest 11 having a source of mechanical or other refrigeration (not shown). Inside this chest are the two

thermostatic chambers

13 and 15, both of which may be contained within the same insulated

outside walls

18, 20, 22 and 25 so long as an insulating partition wall 27 is provided for separation of the chambers. During the test thermostatic chamber 13 is maintained in nearly air-tight condition separated from air or other thermostatic fluid in the chamber 9. Chamber 15 is provided with the fluid inlet 30 in one of its walls and this inlet is surrounded by an additional source of refrigeration. For example, as shown, a holder 33 may be provided for reception of Dry Ice 36, so that air passing into the chamber 15 will be additionally cooled. The temperature with in chest 9 is maintained by control of the mechanical refrigeration system and the temperature in chamber 13 may be equilibrated with the temperature in chamber 9 before chamber 13 is sealed. Thermocouples 39 may be provided at strategic locations throughout the refrigerated portion of the apparatus to keep a check on the temperatures. Fan 42 may be provided to assure circulation of thermostatic fluid within chamber 15.

A preferred system for temperature control in chamber 15 is indicated generally in the drawing as 44. This system comprises an exit duct 48, a connecting duct 50, a return duct 52, a by-pass duct 55, a circulation energizer, for example the pump 58, and a flow controller 60. Flow controller 60 may ideally be a valve actuated by solenoid 63, which is actuated by electrical relay 69 in response to electric current conducted from thermoregulator switch 66 by electric leads 68. i

It will be noted that in this system the connecting conduit 50 is outside the refrigerated portion and therefore the air or other thermostatic fluid passing through this condiut is warmed by indirect heat exchange with the atmosphere. Pump 58 may be operated continuously and when the thermoregulator switch 66 senses that the thermostatic fluid in chamber 15 is at lower than the desired temperature, the valve 60 will connect

conduits

50 and 52 and operation of the pump 58 will result in warming the fluid in chamber 15. When the temperature in chamber 15 becomes warmer than desired, thermoregulator switch 66 will cause solenoid 63 to change the position of valve 60 to connect duct 50 with by-pass duct 55. The resulting increase in pressure. in chamber 9 and the decrease in pressure in chamber 15 will cause thermostatic fluid to enter chamber 15 by way of entry 30, thus subjecting thermostatic fluid to direct heat exchange with the Dry Ice 36 in container 33. Thus this apparatus can maintain the desired temperature dilferentials between

chambers

13 and 15.

A reservoir 70 is provided for the oil sample 72 to be tested. The reservoir has a vent 75 for communication with the atmosphere in chamber 13 and also provides for passage of the duct 77 from near the bottom 80 of the reservoir 70 out of the reservoir 70 and chamber 13 through the partition Wall 27 to the chamber 15. The test sample reservoir may consist, for example, of a two-liter stainless steel beaker equipped with a removable cover, the cover being pierced by the vent and by a centrally- :located, vertically oriented copper outlet tube with an internal diameter of /a inch. The outlet tube may preferably extend from about Vs inch above the reservoir bottom to 1% inch above the reservoir cover. The upper end of the outlet may continue as tubing made of any suitable inert material, for example, rubber or plastic. In chamber 15 the sample duct 77 assumes a configuration suitable for heat exchange with cooler materials in the 1 second chamber. For example, the coil 82 may be used,

which in turn may be connected to the outlet duct 84. A

suitable heat exchange coil is an eight foot length of inch I.D. copper refrigerator tubing shaped into a helical coil with a helix diameter of 5 inches.

Outlet duct 84 leads to the pump 86 by way of the gauge 38 and the sample may then be taken to the oil receiver 90. This oil receiver may be, for example, a 2009 ml. graduated glass cylinder. The drawing also shows the provision of other observation devices besides the gauge 83 which may be, for example, a recording bellows tube vacuum gauge, etc. 93 represents a flow meter; 96 is a filter, for example, a coarse fritted-glass filter. 99

is a capillary tube which forms part of a vacuum system attached to the receiver 90, represented by 101, which may be employed to augment the suction capacity of the metering pump 86. Such a system may also comprise the laboratory-size vacuum pump 103, the vacuum gauge i and the bleed valve 107.

The apparatus of FIGURE 2 shows a more simplified apparatus for bringing the reservoir 70 and the sample duct coil 82 to the temperatures desired for conducting the pumpability test. In this figure, reservoir chamber 113 and sample duct chamber 115 are surrounded and separated by the insulating block or

other materials

118, 120, The tops, and 128 of the chambers may suitably be of heat conducting materials, such as cop- 122, 123, etc.

er or aluminum. As shown, the chambers are supplied with a liquid heat transfer medium, e.g. a water-ethylene glycol mixture, the chamber 113 providing the well 130 for reception of the reservoir 70 and the chamber 115 providing the annular well 133. This form of the apparatus may be provided also with the cover-plate 136' which fits into the

slots

139, 141, etc. in the top 125. This plate preferably also is made of copper or aluminum and when assembled, the heat insulating lid 144 is placed over the tops 125 and 128 and cover 136.

Independent refrigeration systems are provided for

chambers

113 and 115. The fluid heat transfer medium in each chamber may be chilled by use of the

refrigerant coils

146 and 148, respectively, and each may be provided with the

stirrers

151 and 153, respectively. The stirrers 151 may be in constant motion during the test, or their motion may be automatically determined in response to

thermoregulating mechanisms

155 and 157, respectively,

which also control the flow of coolant in the

coils

146 and 148, respectively.

The apparatus shown in FIGURE 2 may be modified to bring about a temperature differential in the two chambers by heating, rather than by cooling. When a cold chest;

is available into which the entire apparatus in FIGURE 2 may be placed, the fluid in

chambers

113 and 115 is allowed to cool to or below the minimum temperature to be employed in the test. Then the fluid heat transfer medium in each chamber may be heated independently by passageof heated fluids through the

coils

146 and 148. until the temperature desired for each chamber is attained.

Alternatively, coils 146 and 148 may be replaced by electric heating elements, the heating current through which may be controlled to give the desired temperature in each ment such as refrigerating devices, heaters, thermostatic.

switches, stirrers, fans, thermometers, thermocouples and others. a

In operation, a test sample of petroleum distillate is cooled in the reservoir to a temperature near, at, or below the cloud point, whereupon wax crystallization, gel

formation, or sedimentation phenomena may occur to the possible detriment of pumpability. Then the sample is drawn at the linear velocity desired by pump suction through the sample duct which is subjected to an environmental temperature still colder than the sample reservoir. Additional wax crystallization, solid state phase transformations, or other phenomena may occur in the transfer tube, tending to plug the tube and restrict How. The test sample is evaluated by making suitable observations while pumping to detect any occurrence of flow failure. These observations are made either visually or with the aid of suitable instruments in the pumping system, or with both.

Practice of the method of this invention by the use of the apparatus described is illustrated by, but not limited to the following specific examples. The apparatus was used to evaluate the pumpability of ASTM No. 2 petroleum fuel oils as follows:

With the entire apparatus of FIGURE 1 at room temperature, the sample system (

elements

70, 77, 82, 84, 86, 88, 93, 96 and 99) was filled with test fuel and then the quantity of fuel in the reservoir was adjusted to 1600 ml. Chamber 13 was opened to permit efficient cooling of the sample by air from the chamber 9.

The mechanical refrigeration system was set to maintain the desired reservoir test temperature, then the refrigeration mechanism was started. Generally, the reservoir 70 reached the test temperature within twelve hours after starting. Fifteen hours after cooling was started, chamber 13 was closed nearly air-tight to insulate the sample. The thermostatic chamber 15 was then set for operation by placing coarse lumps of Dry-Ice in 33, turning on the fan 42, the pump 58, and the solenoid 63, and setting the thermostatic switch 66 to maintain the chamber 15 at the same temperature as the chamber 13.

Sixteen hours after cooling was started the metering pump 86 and the vacuum pump 103 were started. Then the thermoregulator switch 66 was promptly re-set to maintain the air temperature in 15 at a temperature 2 F. colder than the reservoir. The new temperature was established within 5 to 10 minutes. Temperature conditions were maintained constant and a log was kept of the volume pumped, the pump suction at 88, and the flow rate. Each experiment was continued until either the reservoir was emptied or flow failure occurred; the results are given in the table below and in the graph of FIGURE 3.

When ASTM No. 2 fuel oil samples were tested as described, two types of flow failure occurred. One type, designated line plugging, resulted from blockage in the transfer tube usually by Wax. The blockage caused starvation of the metering pump, thus line plugging failures were characterized by high suction values at the pump inlet (i.e. at 88) and by low fuel flow rates. Such failures are indicated in FIGURE 3 as L. The other type, designated reservoir, occurred because progressive depletion of liquid from the mixture of solid and liquid fuel in the reservoir resulted in residues which were so viscous that they would not flow to the reservoir outlet at an adequate rate. When this occurred, channels or depressions developed in the pasty mass of fuel in the reservoir, and air was able to enter the reservoir outlet via these channels or depressions. Thus, the demand of the metering pump was partially satisfied by a flow of air partially by a flow of fuel, and these failures were characterized by the presence of much air in the efiluent, by low fuel flow rates, and by low suction values at the metering pump inlet. These failures are indicated in FIG- URE 3 as R.

Two samples of fuel oil, each of which is described in the Table below, were tested in the apparatus of this invention and were also tested in a full-scale pumpability rig, with the following results:

TABLE Fuel A Fuel B Fuel Inspection Data- Flash Point, F. 136 137 Cloud Point, F 16 18 Pour Point, F.. -25 5 Dlstlll'ition Temp 370 371 624 626 F 2. 622 2. 629 Gravity, Deg. API 34. 6 34. 5

FULLSCALE TEST RESULTS Test No. Gold Room Percent Fail. Percent Fail.

Temp. F. Removed Type Removed Type 10 44 Line Plug. 0 48 o 15 99 Reservoir- 10 99 Reservoir.

0 94 Do. 8 51 D0.

INVENTION TEST RESULTS Reservoir Transfer Test No. Temp, Tube Cham- Percent Fail. Percent Fail. F. ber glle mp, Removed Type Removed Type 13 11 Line Plug.

6 d -5 l3 s 13 Reservoir.

6 Do. -5 Do. 13 Do.

There tests show that Fuel A at a temperature between about F. and 15 F. has a marked tendency to plug a fuel line. At reservoir temperatures between about 15 F. and 5 F. Fuel A exhibits good pumpability characteristics, with no tendency to plug fuel lines and only a relatively insignificant tendency to fail by reservoir failure, such failures occurring only after about 99% of the initial reservoir charge has been removed. In contrast, Fuel B exhibits no tendency to plug fuel lines over the entire range of temperatures tested; however Fuel B does exhibit a significant tendency to produce reservoir failures at reservoir temperatures colder than approximately 0 F. At reservoir temperatures between about 0 F. and +13 F. Fuel B exhibits a relatively insignificant tendency to produce reservoir failures, such failures occurring only after about 90% or more of the reservoir charge has been removed.

It is apparent from the graph of FIGURE 3 that a high degree of correlation exists between results obtained using the test method of this invention and the results obtained when full-scale pumping is attempted. Also, as can be seen from the table and the graph, similarity in cloud points of Fuels A and B gives no indication of the line plugging tendencies of Fuel A, which tendencies do not appear to be present in Fuel B. Also the pour point temperature of Fuel A gives no indication of the line plugging which may occur when this fuel is used at temperatures considerably warmer than its pour point. In contrast, the test method and apparatus of this invention reveal these qualities.

It is claimed:

1. A method for testing the pumpability characteristics of a hydrocarbon oil containing material which solidifies at a low temperature, which method consists essentially of passing said oil from a first zone maintained at a first temperature through a second zone of substantially smaller cross-section than said first zone at a second temperature at least about 1 F. lower than said first temperature, and determining the pumping characteristics of said oil under these conditions, at least one of said first and second temperatures being sutficiently low to cause solidification in the hydrocarbon oil.

2. The method of claim 1 in which said second zone has a cross-sectional area no greater than about one-tenth the cross-sectional area of said first zone.

3. The method of claim 2 in which wax solidifies in the hydrocarbon oil.

4. An apparatus for determining the flow characteristics of a hydrocarbon oil containing material which solidifies at low temperature which comprises two chambers, means for maintaining a constant low temperature in each chamber, means for maintaining the low temperature in the first of said chambers above the temperature of the other of said two chambers at the same time, a liquid sample reservoir in the first of said chambers and a sample duct of substantially less cross-section than said reservoir leading from said reservoir through the second said chamber and means for causing fluid flow from said reservoir through said duct.

5. The apparatus of claim 4 in which the means for causing fluid flow comprises a metering pump having a vacuum pump and capillary tube associated therewith.-

- 6. The apparatus of claim 4-in which the means for maintaining a constant low temperature comprises a cold fluid, and a refrigeration means for the thermostatic fluid, said refrigeration means being operable independently of each other, a liquid sample reservoir in said first chamber and a sample duct of substantially less cross-section than said reservoir leading from said reservoir through said second chamber in heat exchange relationship with said thermostatic fluid, and means for causing fluid flow from said reservoir through said duct.

8. The apparatus of claim 7 including a temperature control means cooperating with said refrigeration means for individually controlling the temperature in said first and second heat-insulated chambers.

9. An apparatus for determining the flow characteristics of a hydrocarbon oil containing material which solidifies at low temperatures which comprises first and second heat-insulated chambers, eachcontaining a thermostatic fluid, a cold chest surrounding said chambers and communicating with said second chamber and containing;

a thermostatic fluid, means for refrigerating said thermostatic fluid within said cold chest, a liquid sample reservoir in said first chamber and a sample duct of substantially less cross section than said reservoir leading from said reservoir through said second chamber in heat exchange relationship with said thermostatic fluid, means for causing fluid flow from said reservoir through said duct, and

temperature control means for controlling the temperature in said first and second chambers, said temperature control means including an exit duct for withdrawing thermostatic fluid from said second chamber, a connecting duct for exposing said fluid to indirect heat exchange with the atmosphere, and a return duct for returning said thermostatic fluid to said second chamber.

10. The apparatus of claim 9 including a by-pass duct communicating with said return duct and said cold chest,

and valve means responsive to temperature regulating means in said second chamber for directing said thermostatic fluid from said return duct through said by-pass duct to said cold chest and into said second chamber.

11. The apparatus of claim 10 wherein the first and I second heat-insulated chambers contain a means for ci'r-.

culating the thermostatic fluid.

12. The apparatus of claim 11 wherein an additional cooling means is provided where the cold chest communicates with the second heat-insulated chamber.

References Cited by the Examiner UNITED STATES PATENTS 3,187,557 6/1965 Holbourne 7317 3,222,916 12/1965 Davis 73-15 I DAVID SCHONBERG, Primary Examiner.

Claims

1. A METHOD FOR TESTING THE PUMPABILITY CHARACTERISTICS OF A HYDROCARBON OIL CONTAINING METERIAL WHICH SOLIDIFIES AT A LOW TEMPERATURE, WHICH METHOD CONSISTS ESSENTIALLY OF PASSING SAID OIL FROM A FIRST ZONE MAINTAINED AT A FIRST TEMPERATURE THROUGH A SECOND ZONE OF SUBSTANTIALLY SMALLER CROSS-SECTION THAN SAID FIRST ZONE AT A SECOND TEMPERATURE AT LEAST ABOUT 1*F. LOWER THAN SAID FIRST TEMPERATURE, AND DETERMINING THE PUMPING CHARACTERISTICS OF SAID OIL UNDER THESE CONDITIONS, AT LEAST ONE OF SAID FIRST AND SECOND TEMPERATURES BEING SUFFICIENTLY LOW TO CAUSE SOLIDIFICATION IN THE HYDROCARBON OIL.