The invention relates generally to devices used to measure the conductivity of non-aqueous liquids, such as crude oils, as well as methods for measuring the conductivity of these liquids.
The conductivity of non-aqueous liquids, such as crude oils is an important factor for determining how such liquids must be handled, stored and processed. If, for example, a certain liquid has high conductivity at a particular temperature, it would be important to store that liquid in a manner wherein it is protected from potential electrical discharge. Currently, there are difficulties measuring conductivity of non-aqueous liquids in a safe and effective manner For example, samples can evaporate at the temperatures used during testing. Furthermore, at specific temperatures, the conductivity of crude oil can be grossly miscalculated due to polarization effects, which are typically seen upon application of a DC (direct current) field.
The invention provides an apparatus for the measurement of conductivity of non-aqueous liquid samples or sample blends. In particularly preferred applications, the device is useful for measurement of the conductivity of samples of crude oil, blends of crude oil or other non-aqueous liquids at process temperatures and pressures.
The conductivity meter, or conductivity measurement apparatus, is described which preferably features a conductivity cell for containing a liquid sample, a resistance temperature detector (“RTD”) (alternately called an impedance probe (“IP”) or a variable voltage conductivity probe), a voltage source, a heater mantle/block, a heater controller (preferably cascade heater controller), control and process monitor thermocouples, a pressure control/argon purge system, a pressure transducer, and a data control and acquisition system. The conductivity cell includes a testing vessel which contains the liquid sample to be measured. A resistance temperature detector (RTD) is immersed within the liquid sample of the testing vessel. The resulting configuration is that the liquid sample is resident in the annular region between two concentric cylinders—namely, the RTD and the inner wall of the conductivity cell. In the described configuration, the RTD serves as the first electrode, and the outer wall of the conductivity cell, which is connected to ground, serves as the second electrode. A voltage or series of voltages is/are applied across the first and second electrodes of the conductivity cell by the voltage source. The power source is preferably operable to apply varying levels of voltage to the sample for certain lengths of time. In particular embodiments, DC voltage is applied in sequences of varying levels over short intervals of time, such as 1 second or less. The RTD immersed within the sample detects the current induced through the liquid sample by the application of voltage.
In preferred embodiments for a conductivity measurement apparatus, the conductivity cell is contained within a heater block to control the temperature of the conductivity cell and sample. An external heating controller provides an optimized, heated medium within the interior chamber of the heater block. A thermocouple detects the ambient temperature of the interior chamber. The heating controller can be adjusted based upon the reading of the thermocouple. Preferably, the heating controller is a cascade feedback controller which optimally adjusts temperature in a manner which will attain a desired temperature in a rapid fashion.
Also in preferred embodiments, the conductivity measurement apparatus includes a pressure control system which includes a pressure vessel that is pressurized to provide a pressure blanket for the sample during testing. An inert gas, such as ultrapure argon or nitrogen is preferably used to provide the pressure blanket and maintain an inert, oxygen-free environment for the sample during testing. An exemplary pressure control system includes the pressure vessel, a flow regulator to introduce the inert gas into the pressure vessel, a relief valve to depressurize excess gas and a pressure transducer associated with the conductivity cell to measure the pressure of the sample within the conductivity cell.
In accordance with an exemplary method of determining conductivity of a liquid sample, a liquid sample is placed within the testing vessel and the RTD is inserted into the liquid sample, thereby forming a conductivity cell. The conductivity cell is retained within a heater block and further connected to the pressure control system. The conductivity cell is maintained under pressure using an inert gas pressure blanket, after which the heater block is heated to a desired temperature by the heating controller. A programmable data acquisition system is used to specify the temperatures at which voltage needs to be applied, the type of voltage (DC or AC) that needs to be applied, the desired time duration for which voltage should be applied and the sequence of voltages (usually ranging from 1V-100V) which need to be applied. When the desired voltage is applied to the liquid sample in the annular region of the conductivity cell, a conductivity probe measures the current within the sample as voltage is applied across it. During testing, the temperature of and pressure applied to the liquid sample may be varied, which allows measurement of conductivity in a variety of conditions. In accordance with some embodiments, the voltage (type, magnitude and time duration of application) which is applied to the liquid sample can be adjusted during testing.
Measuring conductivity of crude oil is non-trivial, especially at elevated temperatures where lighter blends of the crude oil tend to evaporate and in turn change the composition (and resultant conductivity) of the crude oil blend. The evaporation potential is reduced by application of a pressure blanket that is maintained at a pressure that is sufficiently higher than the vapor pressure of the liquid sample to prevent any of the samples from escaping via evaporation. A pressure transducer attached to the conductivity cell and the data acquisition system helps monitor the pressure of the sample.
For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like or similar elements throughout the several figures of the drawings and wherein:
A resistance temperature detector (RTD) 40 is inserted through the central opening 36 and into the liquid sample 28. The resistance temperature detector 40 presents a conductive distal end 42 which extends into the liquid sample 28 and is operable to function as a second electrode for the conductivity cell 12. In addition, the resistance temperature detector 40 also has the capability of measuring current flow through the liquid sample 28 passing between the first electrode 38 and the second electrode provided by the distal end 42. The distal end 42 therefore also contains a conductivity probe. Preferably also, the resistance temperature detector 40 is capable of detecting the temperature of the liquid sample 28.
A heating controller 72 is operably interconnected with the thermocouple 52 and is operable to supply heated medium via conduit 50 into the interior chamber 48 of the heater block 44. The heating controller 72 maintains the temperature within the interior chamber 48 in accordance with temperature feedback provided by the thermocouple 52. In preferred embodiments, the heating controller 72 is a cascade feedback controller, of a type known in the art, which can provide optimized heating by attaining a desired temperature in a rapid manner.
The first and second electrodes 38, 40 are operably associated with a voltage power source 74 which are capable of supplying a voltage potential across the electrodes 38, 40 of the conductivity cell 10. The applied voltage might be an AC or a DC voltage. In preferred embodiments, the voltage power source 74 is capable of applying a constant DC voltage, such as 3V DC, for a predetermined length of time. In further preferred embodiments, the voltage power source 74 is capable of applying a variable range of DC voltages to the electrodes 38, 40. For example, the voltage power source 74 might be able to apply voltages within a range from 0-1000 V DC and be programmable to change between voltage levels in accordance with a predetermined scheme. A conductivity/resistance detector 76 is also operably associated with the conductivity probe of distal end 42 and is operable to detect the conductivity between the electrodes 38, 40 when a voltage is applied across them. The voltage source 74 and the conductivity/resistance detector 76 may be combined in a single device, as
In accordance with preferred embodiments, the voltage source 74 is used to specify the temperatures at which voltage needs to be applied to the conductivity cell 10, the type of voltage (DC or AC) that needs to be applied, the desired time duration for which voltage should be applied and the sequence of voltages (usually ranging between 1V-100V). Further, the conductivity/resistance detector 76 preferably serves as a programmable data acquisition system which records or acquires the temperatures of the sample at which voltage is applied. Additionally, the conductivity/resistance detector 76 records or acquires the time duration for which a voltage is applied (i.e., one second or lower), the sequence of voltages applied, the resulting current in the sample 28 that is detected by the RTD 40, and the pressure measured by the pressure transducer 69.
In accordance with particular embodiments, the conductivity measurement apparatus 60 includes a cold gun 78 for rapidly cooling down the heater block 44 and conductivity cell 10 as a safety measure.
The conductivity measurement apparatus 60 is useful to measure the conductivity of a sample 28 of non-aqueous liquid, such as crude oil. In operation, a sample 28 is placed within the liquid sample chamber 16 of the testing vessel 14 and cap 30 is affixed to the testing vessel 14. The resistance temperature detector 40 is inserted into the liquid sample 28 and the first electrode 38 is inserted into the electrode cavity 18. The conductivity cell 10 is then inserted into the conductivity cell sleeve 46 of the heater block 44 and the measurement apparatus 60 further assembled in the manner depicted in
Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.
Number | Date | Country | |
---|---|---|---|
62270621 | Dec 2015 | US |