Enable cost savings and optimise production with real-time sulphur results

The demand for biofuels has increased in recent years, with the EU requiring that 10% of the total transport fuel in its member countries to come from a renewable energy source in 2020.

Evan Thomas

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In addition, the U.S. Energy Information Administration anticipates between 18-55% growth in biofuels production over the next 30 years. While biofuels typically contain little sulphur, they are still required to meet fuel quality compliance specifications either for use in vehicles, or as a blending feed for traditional refinery fuels. As such, biorefineries must measure the sulphur in their product to ensure it is below regulatory limits, typically less than 15 ppmw. In addition to this, due to the variety of feedstocks, online analysis of biofuels can be challenging due to changing sample composition.

XOS’ Sindie® Online total sulphur analyser uses Monochromatic Wavelength Dispersive X-ray Fluorescence (MWDXRF) to continuously and non-destructively measure a sample stream and deliver results at user-defined intervals. The analyser uses a Dynamic Window Module (DWM) to automatically replace the sample window which effectively eliminates any drift and significantly reduces the frequency of required calibrations. This, in addition to the rugged design of the analyser, reduces the time and frequency of required maintenance leading to an uptime as high as 98%.

In August of 2019, a Sindie online total sulphur analyser was installed at the Malchin biofuels refinery of ecoMotion GMBH by 360KAS, XOS’ exclusive distributor in Northwestern Europe. This site is one of the first biodiesel pilot plants built in Germany and has been in operation since 2001. The primary feedstocks for this plant are animal fats, vegetable oils, and used cooking oil. This site produces 10,000 tons of biodiesel annually.

The core process in biodiesel production is transesterification. In this chemical exchange reaction, the glycerine contained in the primary material is replaced with methanol. This leads to the formation of fatty acid methyl esters and glycerine. When converting animal fats and used cooking oil, the production process has two additional steps that are not required in conventional biodiesel production. In the first step—prior to transesterification—the free fatty acids contained in the primary material are esterified. After transesterification, the product is distilled. The result is an extremely pure, crystal-clear, and almost colourless product.

The expectation of this analyser was to continuously measure the sulphur concentration in the final product to confirm the site was producing a product compliant with automotive fuel specifications. Previously this required the site to send samples to a remote laboratory which introduced delays and uncertainty in their production. By installing Sindie online sulphur analyser, the site obtains a measurement every 5 minutes, enabling them to optimise their production, be confident their product is compliant and of high quality, and reduce their gas consumption by 5%.

Almost a year after installation, the site has reported that their expectations for the performance of the analyser continue to be met, the analyser continues to operate without any problems, and the measured values match their laboratory cross-checks.

Ultra-Low Sulphur Analysis in Petroleum Process Streams Using Mwdxrf
Refiners are challenged to produce higher-quality products while trying to maximise efficiency. In the last decade, national regulators in places like the US, Europe, China, and India have implemented or plan to implement requirements for total sulphur in gasoline and diesel levels as low as 10 ppm. Increased hydrotreating and modifying crude slate are some of the levers that can be pulled to help lower sulphur levels in finished products. Simultaneously, there are global initiatives to increase the percentage of biofuels produced using renewable feedstocks. In order to meet these lower sulphur levels, refineries must invest in new or upgraded equipment, modify operations or a combination of both. Regardless, it will increase the cost of producing diesel and gasoline.

In order to meet renewable fuel usage targets, new standalone biofuel refineries have been constructed to produce biofuel from a variety of feedstocks, and some traditional refineries have been upgraded to allow for biofuel feedstocks to be used, or completely converted into biofuel refineries. Biofuels present some interesting challenges from an online sulphur measurement standpoint. Some biofuels naturally have such low sulphur, there are few or no additional procedures or units required to further reduce the sulphur content, while others require typical sulphur removal units such as a hydrotreater. However, all biofuels must meet regulated sulphur specifications such as EN 14214, and must be measured and certified to such specifications before being sold. In addition, it can be very valuable to know the specific sulphur content of a given biofuel being used for blending with traditional refinery fuels in order to reduce sulphur giveaway. Of course, it is also highly profitable to measure biofuels where they need to be treated to remove sulphur. A refiner can use a sulphur measurement to reduce hydrogen gas consumption and optimise catalyst usage. The challenge, then, is how to condition and measure biofuels, especially when the feedstock can change and alter the sample conditioning requirements.

Changing feedstocks will always cause complications, as a given analyser will typically be fine-tuned to operate with certain specifications such as pressure, temperature, flow rate, viscosity, density, composition, and filtration. This becomes readily apparent with analyser that require sample conversion before analysis. XRF analyser offer a unique resiliency to this as it is a non-destructive method that does not require the sample to be combusted, mixed with solvents, or adjusted for density to report ppmw properly. In addition to this, due to the nature of XRF, the analyser is resilient to sulphur concentration changes whether it is 10 ppmw, 100 ppmw, or 1000 ppmw, though a calibration and validation program designed for the measurement range of interest will always improve precision. For such a dependable system, the value the analyser provides then comes from its accuracy and precision.

For every part per million of sulphur removed, a refinery spends significant money on capital, hydrogen, catalyst, and energy. The related downtime to catalyst changeout must also be factored into the equation. Catalyst has a finite life, and that length of time is dictated by how the hydrotreater is operated. By varying temperature, space velocity, and hydrogen partial pressure, sulphur removal and catalyst life are impacted. A refiner may choose to vary the specific feedstocks used in order to reduce the total sulphur content entering a hydrotreater for the purpose of minimising the required use of sulphur removal equipment, though this will come at a cost, either in the form of higher purchase price, or by higher concentrations of other contaminants.

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