Problem: With ever increasing regulatory requirements, the balance between the declining quality of incoming crude oil and the heavily regulated quality of outgoing products makes refining a very quality- conscious operation. For environmental reasons and its impact on quality, accurate measurement of sulfur content in hydrocarbons is critical during refinery processes as levels are rigorously controlled by both national and international regulations. In addition, as maximum levels for sulfur continue to be lowered, analytical instrumentation plays a pivotal role in complying with these regulations.
Low value, high molecular weight hydrocarbon fractions of crude oils are often converted to higher value blending stock, using catalytic cracking processes. These low value products typically contain high concentrations of nitrogen and sulfur, both of which are detrimental to catalytic performance. Knowledge of the sulfur and nitrogen content of low value distillates is therefore required prior to processing into higher value products.
Traditionally, the introduction apparatus used for combustion-based trace elemental analysis of crude products depends upon the boiling point of the sample. For light hydrocarbons, direct injection using a ceramic syringe or liquids module is most common, while for heavy hydrocarbons, boat inlet introduction is employed. As a result, two introduction modules are required by analysts to cover the range of sample boiling points analyzed. This need has meant that analyses take five minutes for light hydrocarbons and 12 minutes for heavy hydrocarbons per replicate, thus affecting productivity.
Solution: Total nitrogen/total sulfur analysis using direct spray injection provides the capacity to analyze both heavy and light hydrocarbons from ppb levels up to percent levels using a single introduction module such as the Thermo Scientific jetPROTM direct spray injector. It operates by introducing the sample into the furnace as an aerosol of sample droplets. This aerosol process is created via high velocity oxygen jets impacting on the surface of the liquid sample as it exits the sample needle. The gas breaks small liquid droplets from the sample surface which produces both a fine mist of sample droplets and mixes the sample with oxygen. The entire sample plus oxygen is then carried into the furnace by a carrier gas. Once in the hot zone of the furnace, the following reactions take place; RN + O2 → NO + H2O + CO2 and RS + O2 → SO2 + H2O + CO2. The jetPRO direct spray injector is permanently located inside the furnace in an environment with a temperature of approximately 1000°C. The spray head temperature, however, is maintained at a temperature below 100°C. If the temperature of the spray head was higher than this, low boiling point samples would not enter the spray head as a liquid and the injection process would be poorly controlled.
Active cooling of the jetPRO direct spray injector is achieved by advanced heat management. The minimum amount of radiative heat is transferred to the injector by coating it with chromium. The injector itself is made of solid copper and is in thermal contact with a large, fan-cooled heatsink. This heat management allows for the spray head to be maintained permanently in the furnace while being at a low temperature.
The jetPRO direct spray injector in the Thermo Scientific iPRO 5000TM Series Total Nitrogen/Total Sulfur (TN/ TS) analyzer has overcome the requirement to use two introduction modules for the precise analysis of light and heavy hydrocarbons. This has been achieved by directly injecting both high and low boiling point liquids into the furnace using a single, universal injector. This new design of injector module has improved the precision and accuracy of results for the analysis of heavy hydrocarbons compared to the current boat inlet oxidation method, while maintaining ASTM compliance. In addition, the analysis time for heavy hydrocarbons is now one quarter of the boat method analysis time at just over three minutes. For light hydrocarbons, accuracy and precision are maintained while the typical analysis time is also three minutes.
The Thermo Scientific iPRO 5000 Series Total Nitrogen Total Sulfur (TNTS) analyzer.
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