US 3440863 A
Description (OCR text may contain errors)
April 29, 1969 L- D. LIVINGSTON ET AL 3,440,863
con'rxuuous FLASH POINT RECORDING Filed July 16. 1965 Sheet I of 2 CONTROLLER FIG. l
1.. o. LIVINGSTON J. K. ROWLAND s. Th. F. CRESPIN MZM THEIR ATTORNEY APril 1969 D. LIVINGSTON ET AL 3,440,863
CONTINUOUS FLASH POINT RECORDING Filed July 16. 1965 7 Sheet 2 of 2 R 53 SPARK FLASH so I B l l l- 1/ 0 I0 20 so 40 so so 10 so so 100 no I20 I50 I40 INVENTORS:
L. D. LIVINGSTON J. K. ROWLAND 3 G. Th. F. CRESPIN MZM THEIR ATTORNEY United States Patent 2 Claims ABSTRACT OF THE DISCLOSURE An apparatus for determining the flash oint of a liquid, particularly a liquid having a flash point higher than about 85 C. The apparatus utilizes a flash chamber having liquid and vapor chambers therein. A heated gas liquid mixture is supplied to the flash chamber, vaporized and ignited. A separate heater is used to maintain the temperature of the vapor space at the flash point of the liquid.
The invention relates to an instrument for determining the flash point of a liquid, more particularly, to an instrument for determining and recording the flash point of a continuous stream of liquid. Further, the invention concerns a method of controlling a process such as a distillation, dewaxing, an extraction or a deasphalting process, on the basis of the flash point of a product of this process.
There are disclosed in the prior art various instruments for determining the flash point of a hydrocarbon liquid, especially a petroleum product. One instrument of the prior art utilizes in combination a flash chamber and means exterior of said chamber for heating a stream of liquid and for heating an oxygen-containing gas (e.g., air). The heated liquid and gas are introduced into the flash chamber, and a pool of the liquid is maintained at a constant or substantially constant level in the said chamber. An ignition spark is supplied to the flash chamber above the level of the pool in the presence of the gas. The temperature of the liquid pool in the flash chamber is measured, and the occurrence of a flash within the chamber is detected. The temperature of the liquid may be measured automatically upon the occurrence of a flash in the vapor space of the flash chamber.
The heating means is designed to progressively increase the temperature of the liquid supplied to the flash chamber with the heating means being regulated by the said flash detecting means. The instrument will thus maintain the temperature of the liquid at least substantially at the level at which flashing occurs. Thus, the flash point temperature of the stream of liquid may be continually measured in a relatively rapidly repetitive way.
The instrument described above is used for measuring the flash points of light petroleum products, such as gasoline and kerosene, with flash points up to about 85 C. It has been found, however, that the known instrument is unsuitable for testing liquids with flash points higher than the said limit, since irregular flashing occurs in experiments carried out with liquids with such higher flash point temperatures.
It is therefore an object of the present invention to provide an instrument which is particularly adapted for testing a liquid with relatively high flash point temperatures, such as a lubricating oil distillate, though it may be used for testing liquids with relatively low flash point temperatures as well.
The present invention provides an instrument for measuring the flash point of liquids that is equipped with im- 3,440,863 Patented Apr. 29, 1969 proved heating means for the vapors generated and/or for the liquid to be tested.
In accordance with the first of the said features the instrument is provided with a separate heating means for the vapor space of the flash or vapor chamber. The vapor chamber is adjacent to and preferably situated above the liquid chamber. The liquid and vapor chambers together form the flash chamber and usually a splash shield (e.g., a tray with a bubble cap) is fixed between the two chambers. In the preferred embodiment of the instrument, control means responsive to flashing detected by the flash detector are utilized for temporarily decreasing or switching off the separate heating of the vapor chamber. The decrease or the switching off may be effected for a predetermined time interval, which may be related (but not necessarily so) to the spark time interval.
The second of the above features concerns the application of a preheater for the incoming liquid stream in combination with control means dependent on the temperature difference across the aforesaid main heating means of the liquid (or liquid and gas, if they are heated together in the main heater). The temperature difference is maintained at a constant or at least substantially constant value. In the preferred embodiment of the instrument both features are present simultaneously.
Preferably, the liquid and the gas streams are heated in a combined heater (saturator) which is close to and integral with the flash chamber. The saturator, which is usually heated inside, e.g., by means of a cartridge heater, may consist of a helical channel that discharges into the liquid chamber.
As already mentioned above, the known instrument for determining the flash point of a liquid is equipped with a. heater arranged for progressively increasing the temperature of the liquid. A control means regulated by the flash detector maintains the temperature of the liquid at least substantially at the level at which flashing occurs.
In a preferred embodiment of the present invention the heating is increased progressively as long as no flashing occurs; as soon as flashing is detected the heating is progressively decreased during the flashing period; when flashing stops the heating is again progressively increased.
When testing or measuring the flash point of liquids with relatively high flash points, the known types of flash detectors have proved unreliable mainly because of the high temperatures occuring in the vapor chamber. A new device has been developed consisting of a housing with a diaphragm, preferably formed of tetrafluoroethylene resin known as Teflon. The diaphragm is subject on one side to the vapor space pressure and on the other to atmospheric pressure.
The occurrence of a pressure wave generated by a flash results in a displacement of the diaphragm, which is utilized, e.g., mechanically optically or electrically, to generate a signal that may be indicated, recorded and/0r transformed into a control signal. Preferably, the other side of the diaphragm affects an electrical circuit, e.g., :by actuating a switch. Normally, the chamber containing the diaphragm is connected to the vapor space by a short line. The use of a short line prevents the diaphragm from being fouled by the products of combustion produced in the vapor space.
The instrument measuring the flash point temperature may be used for controlling a process on the basis of the flash point of a product of that process. A sample stream of the said product is fed to the instrument, the flash point temperature is measured and a signal corresponding to the measured temperature is supplied to a controller. The output signal of the controller is used to control the process in such a Way as to make the product of the process assume at least approximately a constant flash point. Alternatively, the control may be effected to prevent the products flash point from exceeding a given limit. Such a control may, inter alia, be applied in propane deasphalting or asphalt-containing residues and in the extraction, for example, the furfurol extraction, or in the solvent dewaxing of lubricating oils.
The solvents used have to be removed from the several phases in these processes and the flash point of these phases is a sensitive indication of the degree of solvent removal. The stripping of the solvents in the phases may be controlled by means of the present instrument in the way set forth above.
The above features and advantages of this invention will be more easily understood from the following detailed description when taken in conjunction with the attached drawings in which:
FIGURE 1 is an elevation partly in section of one embodiment of this invention;
FIGURE 2 is a schematic drawing of a second embodiment of this invention; and
FIGURE 3 is a graph of the measured temperature and the operation of the heater with respect to time.
Referring to FIGURE 1 the instrument is built up mainly of two parts: a flash chamber 1, and a heater (saturator) 2 which is close to and integral with the flash chamber. The flash chamber consists of a liquid chamber 3 and a vapor chamber 4 situated immediately above the liquid chamber. The vapor chamber is provided with spark ignition means 5 connected at 6 to a source of high tension voltage or spark generator (not shown). The flash chamber is also provided with an outlet for vapor 7. A spark is produced at regular time intervals, e.g. every seconds. Usually a direct current spark is used, but an alternating current spark may be applied instead.
The vapor chamber is also connected via a short line 8 with a flash detector 9. The flash detector 9 consists essentially of a diaphragm 10 acting upon an electric switch 1].. The diaphragm is preferably made of tetrafluoroethylene known as Teflon and may have a diameter of about 5 inches. Shock waves generated by a flash in the vapor chamber are detected by the diaphragm which thereupon actuates the switch 11. The switch 11 may be either opened or closed by the movement of the diaphrgam 10.
The feed inlet of the liquid to be tested is at 12. Normally liquid is supplied at a fixed or metered rate by means of a constant displacement pump or a metering orifice disposed in the inlet 12. A metered flow of the oxygen-containing gas, normally air, is introduced at 13 and mixed with the liquid before heating in the saturator 2 takes. place. In a specific case the rate of flow of the liquid (oil) was about 4.5 liters per hour and the rate of flow of the oxygen-containing gas (air) was about 14 liters per hour. Of course these flow rates may generally vary between wide limits, depending on the nature of the liquid to be tested and of the oxygen-containing gas used.
The saturator is built up of a cartridge heater 14 situated inside a helical channel 15. The heater receives its electrical supply through terminals 16.
The mixture of liquid and gas flow upward through the helical channel 15 and out the exit 17 into the liquid chamber 3. The vapor/liquid separation takes place by gravity. A splash shield 18 prevents liquid drops from carrying over into the vapor chamber 4.
The heated liquid forms a pool in the liquid chamber 3. A constant level of the pool is maintained by providing the liquid outlet through liquid overflow pipe 19 with a weir 20 A temperature measuring means 21, for example, a thermocouple, is located in the saturator outlet 17 to measure the temperature of the test liquid under test conditions. The measured temperature may be displayed on a recorder 22.
According to the invention, the vapor chamber 4 is provided with separate heating means 23. The separate heating means 23 may be a collar heater with terminals 24 for connection with an electrical power supply. In order to compensate for the heat of combustion generated when the vapor in the vapor chamber flashes, the heat supplied to the heater 23 is decreased, preferably switched off, as soon as flashing occurs. When flashing stops the heat input to the heater is restored.
According to another feature of the invention, a preheater for the incoming liquid stream is provided in line 12; this preheater is schematically indicated at 25 and its construction may be similar to that of the saturator, i.e., consist mainly of a housing, a helical channel for the liquid and a cartridge heater mounted inside the helical channel.
Thus only part of the heat input to the flowing liquid stream is provided by the saturator unit 2 with the major part being supplied by the preheater 25. A temperature measuring means 27, for example, a thermocouple, is disposed at the inlet to the saturator unit 2. The measured temperatures at 21 and 27 are supplied to a controller 26. The controller 26 controls the heat input to the preheater 25 to maintain a constant temperature differential across the saturator unit 2. The value of the temperature differential across the saturator unit is set by means of the set point 28 on the controller 26. Normally a 15 to 30 degree Centigrade temperature differential is satisfactory.
In this manner, the work done by the saturator heater is kept very nearly constant and the instrument is capable of dealing in a stable way with large disturbances in condition and properties of the liquid to be heated. This is of special advantage when the liquid stream to be tested shows substantial variations in flash point.
The complete instrument is usually housed in an explosion-proof box, that may, but need not, be temperaturecontrolled.
The instrument so far described may be used for testing the flash point of liquids, e.g. for indicating whether or not a liquid surpasses a certain predetermined flash point temperature. The heating of the saturator may be controlled (not shown in the figure) in this case in such a way that the liquid-gas mixture delivered to the flash chamber is continuously maintained at the said predetermined temperature.
When the device is used for actual flash point measurement, as distinguished from merely indicating whether a flash has occurred below a selected temperature level, the means for heating the liquid are arranged for progressively increasing the temperature of the liquid supplied to the liquid chamber and additional control means for said heating means are provided to maintain the temperature of the liquid at least substantially at the level at which flashing occurs. To this end the power to cartridge heater 14 is decreased or increased, depending on whether the vapor in the vapor chamber ignites or not.
The complete control system of the preferred embodiment of the instrument capable of measuring the flash point temperature is illustrated in FIGURES 2 and 3. In FIGURE 2 the numerical indications correspond to those used in FIGURE 1 although some elements are shown in a simplified form.
The system shown in FIGURE 2 includes all of the elements shown in FIGURE 1 and additional controls for the cartridge heater 14, collar heater 23 and spark 5. The terminal 6 of the spark 5 is connected to a direct current spank source 29. The direct current spark source 29 is controlled by means of a motor 30 that is adjusted to cause the source 29 to energize the spark 5 once every 10 seconds.
The cartridge heater 14 is controlled by a variable transformer 31 driven by a reversible motor 32. The motor 32 should be connected to the variable transformer through a gear train that provides a slow rotation of the transformer control. A suitable speed would be in the range of one revolution every forty minutes. In addition, the motor should be adjusted to normally rotate the transformer control to increase the voltage supplied to the cartridge heater.
The collar heater 23 is connected to a source of power by means of normally closed contacts on relay 33. The relay 33 is energized by the flash detector 9 to open the normally closed contact and remains energized for a period of 9 seconds. The 9-second period is controlled by a switch 34 that is actuated by the motor 30. The motor 30 closes the switch 34 at the same time that it actuates the spark source 29. The relay 33 also contains a second set of contacts that close when the relay is energized. The second set of contacts serve to reverse the direction of rotation of the motor 32. When the motor 32 reverses the voltage supplied to the cartridge heater 14 will be reduced.
A direct current spark is generated in the vapor chamber 4 once every seconds by means of a spark generator 29 connected to terminal 6. If the test liquid is below its flash point, no ignition occurs and the heat input to the cartridge heater 14 is gradually increased by the variable transformer 31. As soon as flashing starts the flash detector 9 energizes a relay 33. This relay is held in the energized state for a period of 9 seconds, determined by a switch 34 actuated by the same motor 30 which initiates the spark generator. The relay 33 carries contacts which for the said period of 9 seconds reverse the variable transformer drive motor 32 and switch off the heating of the collar heater 23. After the period of 9 seconds the relay is de-energized, the collar heater is switched on and the variac drive is reversed. One second later a new spark is generated and, if another flash should occur, the process just described will be repeated.
FIGURE 3 shows a horizontal time scale 35 running from 0-140 seconds. It is assumed that the first six and the last two sparks give rise to flashing (indicated by short vertical lines).
The two lines under the time scale represent schematically the condition of the vapor chamber collar heater 23 (upper line 36) and of the cartridge heater 14 (lower line 37) respectively.
The heater 23 is either in the on or in the off position. From the 60th to the 130th seconds the heater is continuously on.
Line 37 shows the movement of the variable transformer drive motor; from the start to the 60th second the variac output voltage is decreased continuously with the exception of the one-second periods at the end of each time interval of 10 seconds between two successive sparks.
From the 60th to the 130th second the output voltage is continuously increased.
The temperature as measured by the thermocouple 21 and recorded on the recorder 22 will be the flash point of the liquid being tested. By continuously obtaining a large number of flash points of the liquid and the average temperature can be determined. The average temperature will acurately reflect the true flash point of the liquid.
We claim as our invention:
1. An instrument for measuring the flash point of a liquid comprising:
a flash chamber including a liquid chamber and a vapor chamber adjacent to and situated above the liquid chamber;
a spark means disposed within said vapor chamber;
flash detecting means in communication with the flash chamber for detecting a flash occurring within the flash chamber;
aliquid supply means for said flash chamber, an oxygen containing gas supply means, said oxygen supply means communicating vvith said liquid supply means to supply an oxygen liquid mixture to said flash chamber;
a preheater means, at least said liquid supply means passing through said preheater;
a first heating means, said oxygen liquid mixture passing through said first heating means, said first heating means discharging into the liquid chamber of said flash chamber;
a first temperature measuring means, said first temperature measuring means being disposed to measure the temperature of the oxygen liquid mixture at the inlet to said first heating means;
flow control means communicating with said liquid chamber for maintaining a constant liquid level in said liquid chamber;
a second temperature measuring means, said temperature measuring means being disposed to measure the temperature of the liquid in said liquid chamber;
a first control means, said first and second temperature measuring means being coupled to said first control means, said first control means being coupled to said preheater to maintain a constant temperature rise across said first heating means;
a second heating means, said second heating means being disposed to heat the vapor in said vapor chamber;
a second control means, said second control means being coupled to said flash detecting means, and said first and second heating means, said control means being responsive to said flash detecting means to control said first and second heating means to maintain the liquid in said liquid chamber and the vapor in said vapor chamber at substantially the flash temperature of the liquid.
2. The instrument of claim 1 wherein said second control means progressively decreases the heat input to the first heating means in response to flashing detected by said flash detecting means.
References Cited UNITED STATES PATENTS 2,746,285 5/1956 Greanias 73-36 2,746,286 5/1956 Greanias 7336 2,971,370 2/1961 Jacobs 7336 3,186,213 6/1965 Donnell 73--36 3,293,905 12/1966 Ratway et al. 7336 JAMES J. GILL, Primary Examiner.
50 R. S. SALZMAN, Assistant Examiner.