Samson SlurryLab: slurry analysis using MRI technology
According to the Danish slurry technology manufacturer Samson Agro and the Danish sensor specialist NanoNord, MRI scanner technology is better suited for mobile slurry analysis than NIR sensors. Ole Jensen, founder of NanoNord, expects a lot from this latest innovative technology.
In 2005, German slurry technology specialist Zunhammer was the first to introduce a ready-to-use mobile NIR sensor for direct slurry analysis. NIR stands for Near Infrared (NIR) spectroscopy and with this type of light you can determine the ingredients, nutrients and contents of many products such as soil, grass, tubers and bulbs, maize and also slurry and digestate.
Real-time analysis of slurry and digestate
Since then, various manufacturers of slurry application equipment have been working on making the technology suitable and (more) reliable for real-time analysis of slurry and digestate to determine how much dry matter, nitrogen, phosphate and potassium it contains.
NIR spectroscopy
NIR spectroscopy is an indirect measurement method for which calibration curves are required to translate the measurements into concrete values. The more calibration curves that are available, the more reliable the measurements are. And that’s the main challenge with NIR sensor technology. Each type of slurry is different, which makes it challenging to make sufficiently accurate measurements using such a sensor.
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Bolt on NIR sensors
The Danish slurry and muck application specialist Samson Agro also closely follows NIR sensor developments and is able to equip its slurry tankers with the necessary brackets and technology to bolt on NIR sensors if customers ask for it.
“But,” says sales and marketing manager Torben Larsen, “we never wanted to invest in our own NIR sensor because we think the accuracy of the technology is insufficient for documentation of slurry contents for (government) accounting purposes. That is why we started testing with Nuclear Magnetic Resonance (NMR) spectroscopy about three years ago, together with NanoNord.”
NMR: Physical phenomenon
NMR is the abbreviation for Nuclear Magnetic Resonance spectroscopy. Simply put, nuclei spin around their axis (nuclear spin) and, because nuclear nuclei have a plus and minus pole, their spinning / rotation creates a magnetic field. With an external (electro) magnet you can resonate the electrically charged atomic nuclei so that they orientate themselves in a certain direction.
If you then turn off the electromagnet and thus remove the magnetic field, the atoms return to their ground state. While doing so, the atoms emit radio waves with a frequency of 1 to 70 MHz, which can be measured with a coil.
Based on the frequencies measured, and how often you measure those frequencies, you can make very accurate statements about how many — and which — atoms are present in a certain liquid. Now every variation of a certain atom, so-called isotopes, resonates differently and thus every isotope also emits different radio waves. Knowing this, you can even detect different nitrogen isotopes such as 14N and 15N.
The chances are that you yourself have been in contact with NMR sensors, since MRI scanners in hospitals use exactly the same technology. MRI stands for Magnetic Resonance Imaging. Neither technology involves X-rays or other nuclear radiation. MRI scanners usually measure only hydrogen atoms in order to analyse the human body.
“That’s because only the radio waves of hydrogen atoms reach far enough to be measured by the large MRI scanner,” says Ole Jensen of Danish NMR specialist NanoNord. “After all, a human body has to fit in an MRI scanner.”
Cheaper and smaller than MRI
Ten years ago, Ole Jensen, founder, owner and general manager of the Danish NMR specialist NanoNord, who jokingly calls himself a ‘crazy inventor’, and the Danish University of Aarhus came up with the idea of using NMR technology for detecting naturally occurring hard particles (so-called catfines) such as aluminium and sand in heavy fuel oil. These particles cannot be filtered out and are harmful to marine engines, says Jensen.
Nuclear Magnetic Resonance is also at the heart of the MRI scanners used in hospitals but, due to the size, the weight (the large magnet in it), the required computing power and the price of an MRI scanner, it is unsuitable for mobile use.
Jensen and Aarhus University managed to reduce the million-euro MRI technology to a sensor with a 7-kilo magnet and a price of up to € 80,000. After succeeding in producing that, Jensen thought, “it must also be possible to use this technology to determine the composition of slurry.”
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Samson SlurryLab
That was about six years ago, and at last year’s Agritechnica, NanoNord and Samson demonstrated the prototype of their NMR sensor: the Samson SlurryLab. That prototype, the Tveskaeg Flow system, which measures approximately 75 by 40 by 25 cm and weighs 43 kilos, has a slightly lighter brother weighing 35 kilos, which is intended for lab measurements (the Tveskaeg Benchtop).
The current processing time required to reliably measure liquids, the cycle time, is 30 minutes. The next step in the development, which is currently being taken, is to develop a mobile version for Samson slurry tankers that takes less time to determine the contents of slurry.
Faster yet still reliable
In order to determine the contents of slurry, it must flow through the magnet of the NMR sensor. To achieve this, a slurry sample is taken from the tank and sent through the NMR sensor. In order to keep the sensor affordable, comparable to the current price of a NIR sensor, a 30 cm magnet with an internal diameter of 12.5 mm was chosen.
We are currently working with a cycle time of 5 minutes and the ultimate goal is a cycle time of 3 minutes
“The price increases exponentially with a larger magnet diameter,” says Jensen. “At the same time, the accuracy decreases quadratically when you reduce the cycle time because you introduce more noise. We are currently working with a cycle time of 5 minutes and the ultimate goal is a cycle time of 3 minutes,” explains Jensen.
132 measurements of ammonium compared
NanoNord and Samson compared the accuracy of 132 measurements of ammonium (NH4-N) with the Tveskaeg sensor (cycle time of 5 minutes) with lab measurements from the Danish Agrolab. A total of 95% of the Tveskaeg measurements deviated by a maximum of 10% from the lab measurements, while the accuracy of all measurements deviated by a maximum of 25%.
The measurements are done in ‘parts per million’ (ppm) and Jensen indicates that currently in 95% of the cases, the measured amount of nitrogen deviates a few hundred ppm (slurry commonly contains 700 to 4,000 ppm N) with a cycle time of 3 minutes. For P-total, it is a 100 ppm deviation from 200 to 2,000 ppm P-total in slurry.
“With PO4, phosphate, the accuracy is already as good as 10 to 20 ppm,” says Jensen. At the same time, he notes that reliable determination of the potassium content currently takes more than 3 minutes.
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Disadvantage compared to current NIR technology
Compared to current NIR technology, the NMR technology developed by NanoNord and Samson still has the disadvantage that it can only analyse a small amount of slurry and that it requires a few minutes to analyse and determine the contents compared to the continuous real-time measurements of NIR sensors.
The number of calibration curves per NIR sensor supplier and thus the reliability is constantly increasing. An NMR sensor is calibrated once by the manufacturer and that is sufficient. NMR’s biggest trump card – no calibration curves required and therefore greater accuracy – must prove itself in practice. Ole Jensen: “I prefer one reliable measurement to thousands of unreliable measurements…”
Samson Agro plans to test prototypes in the next two seasons and to commercialise its SlurryLab technology from 2022 onwards.
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Further research by Nanonord
Currently Nanonord is working on 3 focus areas for measuring slurry with their Tveskaeg sensors, says managing director Ole Jensen. “The first focus area is further developing the technology to make precise measuring of TN and TP possible, while at the same time making sure this can be done within 5 minutes with mobile applications”, Jensen said. He expects all Nanonord commercial mobile versions will comply with the <5 minute measurement requirements.></5>
Robotic test center
The second focus are is more in-depth comparison of the inaccuracies between measurements done in labs and using NMR. “To facilitate this we have build our own in-house robotic test center, capable of using many Tveskaeg sensor on the same slurries. During spring and summer this year we have – in cooporation with a big German laboratory – been measuring over 400 slurries and done more than 30.000 measurements of all sorts with cross data from the labs”, Jensen said.
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According to him, the results are very much in favour of NMR as the perfect precise and reliable mobile NP sensor. Jensen says NMR is the best candidate to replace complicated routines in labs today. The detailed results of this lab-NMR cross comparison will be published in a scienticific paper within a few months.
“We are now teaming up with more partners for an even bigger cross comparison program in Germany to prove that NMR technology is the best solution for mobile/lab NP slurry sensor applications. We will use the results of this study not only in Germany, but also in Denmark, Belgium and the Netherlands”, Jensen said.
The third focus area is the sampling of slurry from bio digestor tanks and for mobile applications. For this, Nanonord has teamed up with Danish specialist Landia a/s (next to Samson SlurryLab) to work on solutions.
From Bluetooth to slurry
NanoNord founder Ole Jensen claims he invented the Bluetooth technology for his company Digianswer, a developer of digital answer phones, more than 20 years ago. He sold this company to Motorola in 1999.
Bluetooth is named after King Harald I (Bluetooth) of Denmark. The Bluetooth logo stands for the initials H and B from the rune script. A son of Harald – also a king – was called Svend Tveskaeg (Sweyn Forkbeard) and NanoNord’s NMR sensor is symbolically named after him.
Compare the Bluetooth logo with the logo of the Tveskaeg sensor to see how much they resemble each other…
