14 Nov 2018

Integrating Process Flow Cells | Spectroscopy Guides

Modern process control benefits from access to real-time updates without time-consuming or disruptive sampling for analytical testing. Fiber optic-coupled process flow cells are a key enabling technology to facilitate the acquisition of continuous online UV/Vis and NIR spectroscopic absorbance process measurements.

an NIR process liquid cella liquid process flow cellan integrated gas process cell

General benefits of using integrated process flow cells include a significant cost saving through process optimization, no requirement to extract hazardous samples for analysis, a reduction in the cost of process sampling and the elimination of sample wastage

How do integrated process flow cells work?

Light is transmitted via an optical fiber cable from the spectrophotometer source to one port of the process flow cell. Collimation optics then direct this light beam through a set pathlength of process stream to a second set of optics which re-focus the beam to a return optical fiber cable attached to the second process flow cell port.

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The return optical fiber cable serves to transmit the light beam back to the spectrophotometer detector. Process flow cells are typically installed as part of the process circuit either directly in the process stream or in a 'by-pass loop'. By adopting the process flow cell in a 'by-pass loop' configuration, the user has the opportunity to isolate the process flow cell from the process cell for routine cleaning, servicing or calibration. Hazardous process flows should be suitably isolated before the cell can be safely removed from the installation.

There is no fixed number of NIR cells on a chemical production facility, this can range anywhere between 1 and 6. The beauty of an NIR system is the option to multiplex between different cells which can be hundreds of metres apart from each other and analyse different process streams. The process streams can have different compositions and physical states (gas and liquid cells on one spectrometer)

How do I ensure my process flow cell is correctly calibrated?

Chemometric analysis provides the user with diagnostic data like residuals and quality of the spectral fitting. Should these increase, it is normally a sign that the user has an issue with the cell (e.g. fouling) or that the composition of the process stream has changed considerably. Therefore the user should check light throughput, residuals and other diagnostics like Mahalanobis distance.

What window material is suitable for NIR process flow cells?

Sapphire windows are used as standard to ensure the highest level of process cell durability. With outstanding thermal characteristics, coupled with exceptional abrasion resisitance (second only to diamond) and strong resistance against corrosive process fluids, sapphire is a clear material of choice for process flow cell windows.

Standard sapphire substrates offer excellent transmission characteristics from the UV to 5 microns. For a specific UV application, UV grade sapphire is available. As sapphire can be polished to a high degree and has a very low friction coefficient, it is less prone to fouling than other lesser materials.

What materials ensure high build quality?

Process flow cells are designed to withstand the rigors of process and environmental conditions while maintaining continuous measurement stability. This often goes beyond the standard operating conditions and includes aggressive cleaning regimes and extreme weather conditions. 

The choice of construction materials is important to ensure material compatibility with a range of substances in the process stream and durability to the temperature and pressures of operation.

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Specac 'ProCell' Process Flow Cells are manufactured from a range of materials, chosen to ensure optimum chemical compatiblity and environmental durability. Typical materials include Stainless Steel 316L, Duplex Stainless Steel, Hastallow© C276, Zirconium or Titanium, but others are available upon request.

Process flow cells contain a seal between the optical and mechanical components and the integrity of this seal is often critical to the reliability of the cell. Speac offers a wide variety of seal options to meet a broad. scope of customer needs.

These include chemically inert perfluoroelastomers (such as Kalrez© or Chemraz©), or gold diffusion bonding for the most demanding applications.

For added peace of mind, perfluoroelastomer seals may be incorporated in a unique dual seal arrangement to guard against the unlikely event of window seal failure. With the aid of complex modelling software, Specac application engineers can predict the behaviour of the seal under a wide variety of conditions that may be experiences during its lifetime.

Coated optical fiber cables

Specac ProCell process flow cells are compatible with a range of optical fiber cables, with core sizes of up to 600 microns diameter. These should be selected by the user to be appropriate for the application. For instance, water-free optical fiber is typically used for NIR applications, while special UV-grade optical fiber should be used if enhanced UV transmission is needed. 

Fiber optic cable for NIR process cell

SMA 905-style connectors for Process Cell optical fibers

Optical fibers should also be appropriately coated for the temperature experienced at the point of connection to the process flow cell: polymide-coated or metal-coated fibers are recommended for higher temperature applications. Specac follows the industry standard by using the widely available and popular SMA 905 style of fiber connector to interface optical fibers with the process flow cell.

Leak warnings and optics guards

A wide range of added features are offered by Specac to further enhance the performance of our ProCell process flow cell product range. 

For instance, seal leak warning ports can be incorporated for additional process security and cells can be specified with a cleaning port to allow easy in-situ cleaning of the windows without the need to remove the cell from the process environment.

Furthermore, protective metal hoods (to I.P. 65 rating) can be fitted over the fiber connections to relieve strain from the fiber connector, to guard against accidental damage at the process cell port and to prevent ingression of moisture and dust/dirt.

Types of process flow cell

There are three main variants of Process Cell  available for in-situ sample analysis. See below for a summary of the options available.

Vortex Flange-Mounted Phase Process Liquid NIR Flow Cell

Vortex Process NIR Cell

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  • flange-mountred cell
  • reliable in aggressive settings
  • easily trace-heated
  • choose body/seal materials
  • selection of sizes
  • cleaning port option
  • up to 300ºC tempeartures
  • factory-aligned optics

Cascade Pipe-Mounted Process Liquid NIR Flow Cell

cascade NIR process cell

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  • pipe-mounted cell
  • UV/Vis and NIR
  • fiber interfaces for 300 to 600 µm
  • choose body/seal materials
  • cleaning port option
  • factory-aligned optics

Typhoon Phase Process NIR Gas Flow Cell

Typhoon NIR Gas Process Cell

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  • reliable in aggressive settings
  • analyze gas/vapour in process
  • choose body/seal materials
  • simple and flexible process integration
  • cleaning port option
  • factory-aligned optics

Contact us for a free consultation

Get in touch for a price estimate and consultation with one of our specialists.

With state of the art design and material modelling tools and over 15 years of process application experience to draw from, Specac's range of process flow cells have a proven track record of reliability and robustness to ensure long-term operation in the most demanding industrial environments.

Computer-aided optical design ensures that our process flow cells have the highest levels of optical throughput to ensure the best quality of spectroscopic data.

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