Automated process control technology helps optimize chemical plant operations. By providing precisely measured values over the entire production process, near infrared spectroscopy helps to bring plant capacity to full utilization, thereby minimizing waste and downtime.
The much-celebrated boom in U.S. oil-and-gas production is shaking up the chemical industry in two key ways. First, the feedstock used to produce chemicals has changed in some plants from crude oil to natural gas. Second, lower energy costs resulting from increases in the supply of both oil and gas mean that producing chemicals in the United States has become profitable again. As a result, new and retrofitted plants are coming online expeditiously.
NIRS Provides Higher Level Control
NIRS technology is being used to help existing and new plants operate more profitably and achieve a return on investment in a shorter period of time. With precise measured values over the entire production process, the technology helps to bring plant capacity to full utilization, thereby minimizing waste and downtime.
The technique can be used for measuring liquids, solids or gases, including powders, tablets and different monomers and polymers. Typical applications include the control and regulation of distillation, polymerization and drying processes.
Offering repeated precise measurements at many stages, the NIRS can be used for:
Even reactions with hazardous substances like hydrazine and hydrazine hydrochloride can be analyzed and monitored. Online measurement procedures ensure that physical samples do not need to be collected manually, which increases occupational safety.
For example, the technology was used to improve quality and reduce energy consumption for a fluidized bed granulation process. Probes were attached at the bottom of the container that measured the spectra (figure A). The measurements then were analyzed, yielding exact data on the moisture content. The curve, which seems to tail off asymptotically, lets operators follow the moisture content exactly and identify when the end point of the drying process is reached and the product is properly granulated. Measurement takes place nearly in real-time. When the display shows that the drying process has finished, the processing of a new batch can begin. The use of inline NIR spectroscopy led to a tangible improvement in utilization of plant capacity.
Bringing older plants online may require investment in up-to-date measurement technology to ensure efficient production and capacity to meet product demand. Many of these existing plants previously used little or no automation technology. They relied on controlling the processes manually — taking samples, analyzing them in the laboratory and using the data to control the process. Or, they used measurements of single physical parameters like temperature, pressure and flow to control the process automatically. For some processes, using simple indicators cannot directly show what is happening in the reactor and leave the operators with no direct control over the process. In some cases, poor process control meant that complete batches had to be discarded or reproduced.
To meet modern demands for efficient production, chemical production plants and their operators need a higher level of process control.
Process Analyzer Technology Brings Efficiencies
Process analyzer technology (PAT) provides real-time measurement of the composition of the chemical substances being processed.
With previously used semi-automation methods, one could determine a substance’s temperature and volume but not its qualities. With PAT, operators continue to measure temperature, volume and level parameters, but they also can take a look into the reactor and pipeline. Put more precisely, they can evaluate the actual concentration of the different substances present and the state of the reaction. This is the most direct control that it is possible to have over a reaction.
A range of online-capable process analysis technologies can be used to measure the parameters in question. For the kind of substances most frequently analyzed in chemical production, the two most frequent PAT technology types are near infrared spectroscopy (NIRS) and gas chromatography (GC).
These two methods are comparable in that each can measure the concentration of substances in a process (table 1). A direct comparison of analytical methods in process analysis technology highlights some of the advantages of NIRS.
With the gas chromatography method, the sample must be extracted and slowly run through a GC column before reaching the analyzer. This presents a safety concern when handling toxic substances. Processing the sample through the GC column extends the time it takes for the sample to be analyzed and results obtained. Also, the sample system is a high maintenance method. Sample lines can plug, and the GC columns must be exchanged over time because they wear out. Finally, although NIRS and GC have similar acquisition costs, GCs involve additional expenses for operating materials, including carrier and reference gases, as well as the cost of new columns.
By comparison, near-infrared spectroscopic methods are non-intrusive and do not extract any samples. They are also faster, measuring process values within seconds and providing an immediate result. This allows subsequent control technology to react swiftly and optimize the process cycles.
Over the past decade, NIRS has established itself as a suitable tool for the quantification of chemical compositions. Its advantages include a combination of multiplexing capability, inline measurement and ease of installation in hazardous areas.
Using NIRS to Ensure Optimum Plant Operation
Chemical processing plant operators have one all-important question on their minds at all times: How can the existing plant perform to its optimum? This aim is referred to as a high space-time yield.
The key factor in optimizing chemical production is knowing the chemical composition of materials in the plant — anywhere, at any time and for all incoming materials and catalysts. Also necessary is the ability to track chemical conversions and use tools to provide quality assurance of the final product. NIRS is a useful tool for these purposes because it can be used to take online measurements in various process stages.
In the spectrum of electromagnetic waves, the near-infrared range is just above the range of visible light in frequency. Each different molecule absorbs certain fractions of the electromagnetic radiation that shines on or through it. This therefore allows conclusions to be drawn about each molecule’s structural composition. The detected absorption spectrum can then be represented in a diagram (figure 1).
Instead of individual wavelengths, a whole spectrum is considered. This provides a volume of information that allows for a safe interpretation of the measurement results — even after changes in the substance matrix.
With NIRS, a dense network of NIR measuring points means precise data and thus better control and greater plant efficiency. For example, take a chemical processing plant in which several educts and raw materials are reacted with a catalyst, perhaps in a solvent. To function properly, such a process requires making precise measurements at many stages.
At the beginning of the process, the quality of the incoming material is checked. Does it fulfill the requirements in terms of all its characteristics, especially identity and purity? Is this also true of the necessary secondary components?
During the reaction, the chemical conversion — the progress of the reaction — must be monitored, for both safety reasons and to ensure that the production process runs perfectly. Process monitoring includes the concentration and condition of residues and byproducts.
To control something, you have to measure it first. The demands on the measurement technology vary considerably. Batch processes — closed processes that run with all ingredients in one vessel — call for prolonged measurement of all concentration ranges. The mixture of substances to be measured is constantly changing. By contrast, continuous processes are involved substances that usually occur in similar concentrations at the same stage of the process.
Knowing about everything going on in a chemical processing plant is important, and a dense network of NIR measuring points gets operators close to optimal exploitation of plant capacity.
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