Measurement and Testing
43
CLORA On-line Analyser
Berry Beumer, XOS Email:
bbeumer@xos.com
Chlorides in crude and process streams pose a significant challenge to the refining industry. According to Te National Association of Corrosion Engineers (“NACE”), refiners have experienced occurrences of extreme corrosion and fouling in crude distillation overheads and/or naphtha hydrotreating units due to severe spikes in chlorides. Most chlorides in crude oil are inorganic (sodium, magnesium, or calcium chloride) and can be effectively removed by a desalter. Te non-extractable chlorides are not removed in the desalter, and can break down from downstream heating and processing to form hydrochloric acid, causing corrosion and fouling problems.
Refiners may actually preclude the use of certain feedstocks due to the risk of unknown chloride levels, i.e., “Some companies called for [a maximum of] 5 ppm, while others called for 0 ppm organic chlorides. Typically, most companies called for from 1 to 3 ppm. From a corrosion point of view, the upper limit of 3 ppm is too high—a more realistic limit is 1 ppm. …. Other companies flatly reject any and all crude oils containing organic chlorides in any amount.” (NACE International Publication 34105)
Chlorides also may arise from process sources including chemicals used in enhanced oil recovery processes; chlorinated solvents used in production; and/or the mixing of crude oil byproducts or other materials with new crude. As the availability of more desirable sources of crude oil is reduced, opportunity crudes are becoming more common, requiring even more diligent elemental composition monitoring.
Technical Innovation – CLORA On-Line Analyser
Any type of on-line chlorine measurement in crude streams or other heavy fuels traditionally presented significant technical challenges.
Most of these flows are “dirty” in an analytical sense, with viscosities not amenable to smooth flows through an analyser. XOS’s introduction of the CLORA On-Line analyser, particularly designed for testing of crude oils, heavy fluids and water streams, is a robust analytic solution for quantification of total chlorine from 0.2 ppm up to 3000 ppm.
The analyser is not sensitive to sample temperature variation and does not require sample conversion, combustion, or associated consumable gasses or liquids. The CLORA On-Line analyser is based on the Monochromatic Wavelength Dispersive X-ray Fluorescence (MWD XRF) analytic platform.
This analytical technique is, for example, widely used in the SINDIE bench-top and on line analysers for the determination of total sulphur in diesel and gasoline fuel. These analysers are known for their ease-of-use and state-of-the-art detection capabilities.
The MWD XRF Technique:
MWD XRF utilises state-of-the-art focusing and monochromating optics to increase the excitation intensity and dramatically improve signal-to-background over traditional XRF instruments. This enables significantly improved detection limits and precision.
A monochromatic and focused primary beam excites the sample and secondary characteristic x-rays are emitted from the sample. A second monochromating optic selects the chlorine characteristic x-rays and directs these x-rays to the detector.
Since MWD XRF is a non-destructive technique it enables the measurement of chlorine in crude and other heavy streams providing key advantages including; (1) The signal / background (S/B) is dramatically improved due to monochromatic excitation of the sample resulting in a LOD of 0.2 ppm in hydrocarbon matrices; (2) superior energy resolution - this eliminates common
interference problems and provides the physical basis for upstream applications; (3) inherent robustness and low maintenance - the analysis engine is low power, compact, with no moving parts, combustion, or consumable gasses; and (4) unprecedented dynamic range, for example, chlorine quantification level up to 3000ppm.
Sample Management – Dynamic Window Module
It is critical to avoid contamination of the analytical cell and the resulting drift caused by such “dirtier” materials as crudes. A specially designed High Viscosity Dynamic Window Module (HV-DWM) is employed for this class of samples ensuring stable and accurate results. The HV-DWM automatically and at preprogrammed intervals positions a new and robust window material in the measurement area. As a result, the measurement is stable and drift caused by contamination build-up is eliminated. The HV-DWM uses an x-ray transparent polyimide film allowing stream pressures up to 80 psi (550 kPa). While the sample stream continuously flows through the HV-DWM, the sample analysis takes place continuously as well as ensuring rapid and highly representative chlorine monitoring.
The CLORA On-Line Analyser can accept most all crude oil streams with a maximum viscosity limitation of 160 cSt at 70º F (1.6 cm3/s at 21º C). More viscous materials can be analysed by increasing sample temperature up to 300º F. The analyser is insensitive to water content or temperature fluctuations of the sample stream. Aqueous matrices can be tested for chlorine concentration in the same fashion as hydrocarbon matrices.
The analyser is a breakthrough analytical solution for the determination of chlorides in crude oil, process streams, water and effluent streams and offers valuable insights in, for example, desalting and refining operations for corrosion management, environmental and process control purposes.
For further information, visit XOS at the Gulf Coast Conference booth 320.
August / September 2011 •
www.petro-online.com
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