Chemistry | Chemical Analytics | Analysis and Quality Determination of Saline Solutions in Fertilizer Production
For plants to thrive they need sunlight and water as well as various minerals, which are also known as the inorganic nutrients. Among the most important of these minerals are compounds based on Nitrogen, Potassium, Phosphorous, Magnesium, Calcium and Sulfur. Mineral fertilizers contain these additives mostly in the form of salts that may be sourced from mining, be manufactured or adapted through chemical processes to produce both simple and complex fertilizers; such as Ammonia and Potassium Nitrate, or specific formulas of Nitrate, Phosphor and Potassium with other mineral nutrients. One of the most well established processes in this field is the Haber-Bosch method for producing Ammonia; that has the highest Nitrogen level of any fertilizer.
Healthy plants on rich soil
As not all soil has an optimal nutrient content and different plants have different needs, high-quality fertilizers are decisive for good yields in modern agriculture. Fertilizers contribute greatly to the food supply of the steadily growing world population; which is expected to reach over nine billion people by 2050. According to the Food and Agriculture Organization of the United Nations (FAO) the pressure of this rise in population means that an additional 60 percent of food must be made available by then. Since around 70 percent of the earth is below sea level, less than 30 percent of the surface can be used for agricultural purposes. Consequently, the available agricultural land must be used to its fullest extent, but at the same time in a sustainable and resource-saving way.
Sustainable agriculture requires a high level of commitment, innovation, knowledge and creativity. Currently hydroponics, cultivation in greenhouses, and vertical farming in cities is trending and paves the way for efficient and space-saving agriculture, while the advanced technologies of Precision Farming introduce the latest innovations for increasing yields. Today, as well as in the agriculture of the future, the use of fertilizers, whether in the field, greenhouse or in high-tech showcases, is imperative.
Today over 33 million tons of Potassium fertilizers are produced worldwide; while the market demand for high-quality products continues to rise. On-going success in the fertilizer market requires the ultimate in process reliability, at the same time the full potential of the fertilizer production plant must be realized and be fully exploited by continuous optimization. Online measurement and control is the ideal route to tune the fertilizer manufacturing process to operate economically and at maximum productivity. Efficiency and cost savings are always important factors for manufacturing companies to consider and one of the main ways to obtain better products at competitive prices is to improve the production performance. For this reason automated systems and custom solutions for quality assurance and production process control are in great demand by manufacturers.
Reliable Results in Challenging Process Conditions
In the production process for many fertilizers high temperatures and pressures are required and under these conditions the saline medium can have a very corrosive effect on the materials it contacts. The components of any measurement system in contact with the materials being processed need to be able to withstand this impact, while any such system must also be easy to integrate into existing process plant and be suitable for the ambient conditions of this tough environment. In this situation process monitoring is not an easy task, but will be essential for improving the quality and reliable production of the fertilizer.
A particular challenge in this context is the creation of a suitable method that forms the basis for the analysis to be carried out. Uncontrolled processes and inaccurate composition of substances can lead to poor quality and waste. Therefore, production managers, quality managers and process engineers are looking for a solution to make the process more reproducible and transparent, while less prone to human error.
Many of the raw materials for fertilizer manufacture are extracted by physical mining or solute mining, where hot water is pumped underground into seams containing the required element to dissolve it. When this solution is returned to the surface the water is evaporated and the crystals recovered. Whichever method is used many harmful impurities must be removed by further processing; finally by mixing the various purified chemicals a balanced fertilizer conforming to a specific formula can be produced. To purify the raw materials will always involve processing hot salt solutions containing impurities and various solids. With the help of NIR online measurement technology, element determination, purity and concentration can be monitored in these highly saline solutions so process control and hence product quality can be improved.
Manufacturers integrating an online NIR measurement in the process, instead of performing the required analysis in the laboratory, can transfer sample solutions as they are being processed, directly into a by-pass measurement cell or other suitable point in the process. The optical signal from this cell is transferred to a spectrometer through optical fibers. The spectrometer can instantly interpret changes in the optical signal due to the very short measurement times of NIR spectroscopy, and so rapid correction and hence optimal process control can be achieved.
Salt phosphate fertilizer in fertilizer plant
The spectral range of the “near infrared” wavelength band, within the electromagnetic spectrum, can be found between the spectral ranges of the “visible” (VIS) and the “mid infrared” (MIR) range. Vibrational combinations and overtones of the bond stretching and deformation are a characteristic of this range; so the NIR spectrum contains a large amount of analytically relevant information. In addition, as an optical process, this technology is generally characterized by a high degree of precision and reliability.
Using NIR spectroscopy makes a precise examination of salts and aqueous salt solutions possible. In the "near infrared" spectral range (780-2500 nm), the ionic combination of salts does not give rise to resonance, but water-containing salts generate clear, individual NIR spectra in this range. Due to the strong interactions between different ions and water- molecules specific shifts occur that can be monitored. Although optical measurement using NIR spectroscopy is usually used for organic molecules, indirect mineral phase determination is also possible. It is important as well to know, and record for reference, the changes over time during a production batch, so that problems and trends can be quickly identified. This should enable those responsible for the process to intervene almost instantly to any unwanted changes.
Hellma Excalibur FCP Messzelle
The Measurement Set-Up
The installation of an online NIR measurement system requires the correct metrological structure and the right combination of measuring principle, location, instrumentation, software and chemometrics. The use of measurement cells or immersion probes enables the direct analysis of large-scale processes. The spectroscopic information is securely transmitted via optical fibers from the cell, over distances of up to 100 m and more, to the measuring instrument. The measurement technology can thus be integrated into the production process and allows for timely monitoring, regulation and intervention to optimize the process. The Hellma Excalibur HD FCP Process Cell is installed inline, connected to a spectrophotometer via fiber optic cables and thus continuously delivers results of the condition of the aqueous saline solution during processing.
The measurement cell must withstand adverse process conditions such as high temperatures and pressures and is therefore made of Hastelloy, which has a high chemical resistance and, depending on the model, is equipped with a removable inspection window for cleaning. The built-in fiber optic cables transmit the spectral information in real time to the NIR spectrometer where the measurement signals are sequentially recorded and evaluated.
Simple Technology – Great Benefit
NIR spectroscopy gives access to a high level of analytical information and simple procedural handling. The NIR spectrum contains a lot of analytically relevant information. The use of NIR spectroscopy results in very short measuring times and both accurate and precise measurement of the materials under process conditions.
This technology makes use of the fact that the quartz glass used in the fiber optic cables has almost no absorption in the NIR range and thus transports the signal without loss even over long distances. With the spectroscopic process data collected in this way, composition and concentration of substances can be identified in real time, while trends and process deviations can be detected immediately. Based on this, process understanding can be significantly improved, the quality of the product can be monitored in a targeted manner and corrective action can be initiated more quickly.
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