US3402595A - Flash testing apparatus - Google Patents

Description

Sept. 24, 1968 s. F. KAPFF ETAL 3,

I FLASH TESTING APPARATUS Filed May 2, 1966 a To Relay .Sysfem 1 For Short/0g //0 1 Temperature Recorder Fig. 2 L v 4 26 22 I I I f 54 540 Fig. 3

Air 52 To Zeroing" Circuit Sample 2 To Decoking Circa/f 8 I44 430 Tempera/ure Recorder INVENTORS.

6 5m Frederic/r Kopff Wendell R Cropper United States Patent M 3,402,595 FLASH TESTING APPARATUS Sixt Frederick Kaplf, Homewood, and Wendell P. Cropper, Olympia Fields, Ill., assignors to Standard Oil Company, Chicago, IlL, a corporation of Indiana Filed May 2, 1966, Ser. No. 546,671 5 Claims. (Cl. 73-36) This invention relates to .apparatus for determining the flash points of liquids. More particularly, this invention is directed to improvements in closed-cup flash testing apparatus.

The American standrad methods for the determination of flash points include the Tag Closed Cup, Pensky- Martens Closed Cup and the Cleveland Open Cup. Each of these methods operates on a batch sample, the sample being heated at a prescribed rate and a test flame or spark passed periodically into the vapor above the sample. The temperature of the liquid at which the vapor from the batch sample explodes is designated as the flash oint.

p In the production of certain commercial hydrocarbon products, it is desirable to maintain the flash point within specified limits and for safety reasons the flash point should be above a prescribed minimum specification. For example, in the marketing of hydrocarbons such as furnace oils, it is important to avoid the presence of more volatile constituents. It is essential, for instance, when a quantity of hydrocarbon liquid has been designated as fuel oil, that there be no inadvertent substitution of a more volatile material such as gasoline. It is, therefore, beneficial to have a rapid and accurate means for ascertaining whether the particular sample comes within the prescribed flash point specifications.

Typically, a closed-cup type of flash point instrument comprises an enclosed vented flash chamber with a spark ignition means within the chamber. The chamber has a vapor space above the sample level. A heater is provided to heat the sample under test to vaporization and the chamber is provided with means for supplying combustion air. The sample is heated and a spark is periodically passed through the vapor spaces until an explosion or flash occurs. The flash is detected by a differential thermocouple within the vapor space. One junction of the thermocouple pair has a relatively large mass and thus a high heat capacity and the second junction has a relatively low mass and therefore a low heat capacity.

Both thermocouple junctions are exposed to the flash and when a flash occurs, one junction is rapidly heated and the second is substantially unaffected by the brief period of heating with the result that a differential in temperature occurs and the occurrence of a flash is indicated by the resulting voltage. The key to the sensitivity of flash detecting instruments of this type, and hence the accuracy of the flash point determination, resides in the differential thermocouple.

Difliculties in maintaining sensitivity in these types of flash testing devices arise from the fact that hard coke-like deposits rapidly build up within the flash chamber. These deposits coat the junctions of the thermocouples and greatly interfere with the thermocouples sensitivity and speed of response to the occurrence of the flash. The speed of response is an important characteristic. This characteristic is particularly important when .a system is under automatic control, as is the case with certain types of flash testing devices.

In addition, the gradual build-up of these deposits causes the thermocouple system to drift. A zero drift occurs during deposit build-up because of the insulating effect upon the differential thermocouple junctions. With both junctions clean the system will be adjusted so that Patented Sept. 24, 1968 there will be no voltage output except during the flash. This balancing corrects for small differences between the unctions which would otherwise produce an output voltage even though the junctions are nominally the same and nominally at the same temperature. These differences may 1nvolve: physical placement of one junction nearer the heated wall with resulting more rapid response as temperatures change; different convection currents around the couples causing temperature differences with cup heating; different surface conditions causing different response to radiant heat as changes occur.

As deposits build on the junctions, the response to the above effects will in general change so that now the pre- VlOllS zero setting will be incorrect. Excessive deposits can cause suflicient output that flash detection may not occur or the system may actuate prematurely. Present instruments of this type have a disadvantage in that they require frequent manual cleaning to remove these deposits, thus greatly increasing the maintenance time required to maintain the accuracy of the instrument,

It has now been discovered that these difficulties which arise from the deposits of this hard coke-like material can be eliminated or sustantially reduced through the utilization of a flash tester in accordance with this invention.

Briefly, this invention provides an improved closed-cup flash testing apparatus having a servosystem means adapted to continually maintain the output of the differential thermocouple at zero until the occurrence of the flash. In addition, this invention provides controllable decoking means adapted to control the heater and the supply of combustion air so that the flash chamber is heated to a suflicient temperature and correspondingly supplied with suflicient air to cause the coke deposits which have formed within the flash chamber to be burned off.

By providing the servosystem it is now possible to maintain the output of the flash sensing differential couple at zero while the sample is being heated. As previously mentioned, the output in a nonzeroing system gradually drifted as deposits built up on the couples. Under such conditions it was diflicult to maintain the flash sensing couple in balance. Such a zeroing system, if it were rapid enough, would, of course, interfere with the flash detection. However, the zeroing system is provided with a timeconstant sufficiently long that it remains almost motionless during the rapid unbalance caused by the flash. In addition, by providing a decoking system, which may either operate automatically or manually, the entire flash chamber may be cleaned of the deposits.

Preferably this invention should be utilized with a high temperature instrument, that is, one which determines flash points within a range of about 200 F. to about 600 F., thus correlating to the Cleveland Open Cup value. A flash testing instrument utilizing this invention can indicate, for example, flash points in the lube oil range of 300 F. to 600 F. with an accuracy considerably better than ASTM Standard Test D-92. This test is stated to have :15 F. repeatability and i30 F. reproducibility. Repeatability of an instrument employing this invention for a test has been i5 F. with a reproducibility of 17 F.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

FIGURE 1 is a schematic diagram of the circuit of the zeroing system.

FIGURE 2 is a schematic diagram of the decoking system.

FIGURE 3 illustrates a closed-cup flash testing instrument of the type for automatically determining and recording the flash point temperature of a continuous stream of hydrocarbon.

While reference in the accompanying figures is to a specific embodiment of the flash test instrument, it should be stressed that the present invention may be utilized with other types of closed cup instruments. For the sake of clarity the invention is merely placed in a specific environment.

Referring to FIGURE 1, an imbalance signal from differential thermocouple arises from the slight diflerences in the emf outputs of the two couples. This difference is caused by the gradual build-up of deposits during extended periods of operation, and from slight temperature differences associated with the difference in mass between the junctions.

This imbalance signal is maintained at zero by the action of amplifier 4 driving servomotor 6 which moves potentiometer 8 as necessary. Power supply 10, resistor 12, and potentiometer 14 provide power to bridge resistors 16 and 18, and balancing potentiometer 8.

The output from amplifier 4 drives servomotor 6 and also feeds meter relay 20. During heating of the flash chamber, the action of servomotor 6 and potentiometer 8 keeps the input of amplifier 4 at zero and meter relay 20 at essentially zero. However, when a flash occurs, the temperature imbalance between the junctions of differential thermocouple 2 produces a sudden voltage at the input to amplifier 4. The response of meter relay 20 is much faster than that of servomotor 6, and meter relay 20 closes contacts which actuate other relays (not shown) to short out the temperature recorder (not shown) and begin a new test cycle.

In FIGURE 2, which illustrates the circuitry of the decoking cycle, relay 28 is shown with the contacts in position for running a flash test. Thermocouple 22 is located in the flash chamber and is connected to temperature recorder 26.

To begin a decoking cycle which may be initiated automatically or manually, button 24 is pressed which starts timer motor 30. Locking contacts (not shown) provide power to motor after button 24 is opened allowing the timer to complete a cycle and then stop. Cam 38 allows switch 32 to close causing relay 28 to operate and switch the thermocouple leads from recorder 26 to controller 40. Contacts 34 serve to short the recorder input during this period.

Controller operates heater 36, bringing the flash chamber up to the decoking temperature of about 1000 F. and controlling it there. After about an hour, cam 38 reopens switch 32 returning the system to normal flash point operation.

Other operations which occur during the decoking cycle and which are not shown in order to simplify the circuitry but which nonetheless would be known to one skilled in the art are: (1) increasing the combustion air rate to the flash chamber, (2) draining the flash chamber of residual oil from the last cycle or test, (3) stopping of flash testing operations, and (4) cooling the flash chamber after turning the heater off before new sample is introduced into the cup.

FIGURE 3 illustrates the operation of a typical closedcup flash tester incorporating the improvements in accordance with this invention. The particular system illustrated is one which automatically deter-mines the flash point temperature of a continuous stream of liquid hydrocarbons.

Sample is fed from process stream 42 through line 44 into the instrument by proportioning pump 46 for a sufficient time to flush out the previous sample. The sample enters flash chamber 62 through the sample inlet 48 having drain 48a. The level of the sample within the flash chamber is controlled by weir 58 at oil outlet 60. Flow into the chamber is controlled on a time basis. After flow stops, the sample is heated by means of heater 36. During heating, combustion air is introduced via line 52 into vapor space and a spark is periodically passed through vapor space 50 and above the sample level by means of spark ignition electrodes 54 and 54a. The flash chamber is vented through vent 56. When the sample temperature reaches the flash point, a small flash or explosion will occur when the vapor space is sparked. Differential thermocouple 2 detects the flash. The temperature at which the flash occurs is detected by thermocouple 22 and the temperature is recorded by means of a temperature recorder (not shown).

Typically, in the type of instrument described the heating stops when a flash occurs and a fresh sample is pumped into the cup. During heating of a sample the temperature is continually recorded until the occurrence of a flash. The recorder is then driven down scale and held there until the next sample has been pumped in and the cup cooled. The temperature record thus consists of a series of spikes spaced about three to four minutes apart with the maxima representing the flash points.

Differential thermocouple 2 and thermocouple 22 are connected respectively to the auto-zeroing system and decoking system as illustrated in FIGURE 1 and FIGURE 2 and operate as described in the explanations accompanying these figures.

Having thus described the invention, what is claimed is:

1. A closed-cup flash testing apparatus having a flash chamber, means adapted to supply test liquid to said flash chamber in communication with the flash chamber, heating means adjacent said chamber adapted to heat said test liquid, means adapted to supply combustion air to said flash chamber communicating with the chamber, spark ignition means within said flash chamber, differential thermocouple means within said flash chamber adapted to sense the occurrence of a flash, temperature recording means electrically connected to the thermocouple means in said chamber and adapted to continuously indicate the temperature of said test liquid, means actuated by said detection means after the occurrence of said flash adapted to drive said temperature recorder downscale, the peak temperature recorded being an indication of the flash point of said liquid, said means having servosystem means connected to said differential thermocouple means adapted to continually maintain the output of said differential thermocouple at zero until the occurrence of said flash.

2. The apparatus of claim 1 wherein said servosystem means is further adapted to short out said temperature recorder and begin a new test cycle after the occurrence of said flash.

3. A closed-cup flash testing apparatus having a flash chamber, means adapted to supply a test liquid to said flash chamber in connection with said chamber, heating means adjacent to the chamber adapted to heat said test liquid, means adapted to supply combustion air to said flash chamber communicating with the chamber, spark ignition means within said flash chamber, differential thermocouple means within said flash chamber adapted to sense the occurrence of a flash, temperature recording means electrically connected to the thermocouple means in the chamber and adapted to continuously indicate the temperature of said test liquid, means actuated by said detection means after the occurrence of said flash adapted to drive said temperature recorder downscale, the peak temperature recorded being an indication of the flash point of said test liquid, provided with controllable decoking means adapted to control said heating means and said means adapted to supply combustion air whereby said flash chamber is heated to a suflicient temperature and correspondingly supplied with suflicient air for a time suflicient to cause coke deposits formed within said flash chamber to be burned off.

4. The apparatus of claim 3 wherein said controllable decoking means is further characterized by a second thermocouple located within the flash chamber and connected to said temperature recording means and switching means adapted to switch said thermocouple from said temperature recording means to controller means adapted to control said heating means and said means adapted to supply combustion air whereby when said decoking means is actuated said second thermocouple will switch from said temperature recording means to said controller means.

5. The apparatus of claim 1 further characterized by controllable decoking means adapted to periodically control said heating means and said means adapted to supply combustion air whereby said flash chamber is heated to a sulficient temperature and correspondingly supplied with sufficient air for a time sufiicient to cause coke deposits formed within said flash chamber to be burned off.

References Cited UNITED STATES PATENTS 2/1961 Jacobs et al. 73-36 8/1964 Thompson 73-36 FOREIGN PATENTS 1,060,987 11/1953 France.

JAMES J. GILL, Primary Examiner.

R. S. SALZMAN, Assistant Examiner.

Claims (1)

1. A CLOSED-CUP FLASH TESTING APPARATUS HAVING A FLASH CHAMBER MEANS ADAPTED TO SUPPLY TEST LIQUID TO SAID FLASH CHAMBER IN COMMUNICATION WITH THE FLASH CHAMBER, HEATING MEANS ADJACENT SAID CHAMBER ADAPTED TO HEAT SAID TEST LIQUID, MEANS ADAPTED TO SUPPLY COMBUSTION AIR, TO SAID FLASH CHAMBER COMMUNICATING WITH THE CHAMBER, SPARK IGNITION MEANS WITHIN SAID FLASH CHAMBER, DIFFERENTIAL THERMOCOUPLE MEANS WITHIN SAID FLASH CHAMBER ADAPTED TO SENSE THE OCCURRENCE OF A FLASH, TEMPERATURE RECORDING MEANS ELECTRICALLY CONNECTED TO THE THERMOCOUPLE MEANS IN SAID CHAMBER AND ADAPTED TO CONTINUOUSLY INDICATE THE TEMPERATURE OF SAID TEST LIQUID, MEANS ACTUATED BY SAID DETECTION MEANS AFTER THE OCCURRENCE OF

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