Fiber Optic Process Spectroscopy

nir spectroscopy May 18, 2020

Whether it be Raman, Ultraviolet, Near Infrared or Infrared spectroscopy, spectroscopic measurements via fiber optic coupling to a remote sample cell has some unique advantages. These include:

  • Measurement close to the process sample point
  • Simplified sample systems
  • Custom analyzer shelter / building not required
  • Toxic or combustible process fluid not transported back to a space where people are expected to work

The combination of the above benefits can provide better measurement, reduced maintenance (operating costs), reduced capital investment and improved safety for process monitoring in gas plants, refineries and chemical plants. Here's how !

Taking the measurement out to the process point has some great potential advantages. The first is that the cell or measurement point (it could be a fiber coupled probe) will often operate at the same conditions as are in the process pipe. By that, I mean the same temperature, pressure and phase (be it gas or liquid). This is important because many of our problems in process analysis arise because the sample changes phase on the way to the analyzer. If it is a gas phase phase analyzer measuring BTU content and heavy hydrocarbons condense out due to Joule Thompson expansion through a regulator, we miss measuring these compounds and are biased low. If it is a liquid phase analyzer measuring vapor pressure or propane content in condensate and bubble escape, the analysis is biased again. Close coupled optical cells operating at line pressure and temperature get around these issues by ensuring the fluid measured is under the same conditions and measured as in the process pipe. Below is shown a simple installation on a flowing natural gas pipe - operating at 40 C and 1000 psig.

As seen above, there is very little in the sample system. This is significant as it is well acknowledged in the industry that more than 80% of all analyzer installation problems are not with the analyzer itself, it is in the sample system. With a spectroscopic solution, we can often minimize or even eliminate the need for regulators, filters, bypass loops and flow control valves in a well designed installation. Even in cold climates like Canada, the complete system can be installed close to the process pipe in a small heated enclosure. The panel below includes an optical flow cell connected by fiber to a remote analyzer, as well as pressure, temperature, and flow transmitters. Also included are lab sample points, low point drain, flow interruption valves and other features. Installed in the Canadian north near Grande Prairie, Alberta by one of our expert field representatives, Nathan Ward.

When we think of a process analyzer installation, we often think of a large complex analyzer building with multiple levels of infrastructure around it. Typically, an analyzer shelter installation will include trenching to run power, civil engineering for a pad, the shelter itself, cabling, explosion proof air conditioning and electrical panel boards, elaborate sample conditioning systems to prepare the sample for the analysis, calibration standards and samples, as well as a safety system to ensure that toxic or flammable gases in the confined space are detected. Often the infrastructure around the process analyzer far exceeds the cost of the analyzer itself. Figures below are from: Improving analytics to meet process industry demands.

Since fiber optically coupled spectrometers do not bring any process fluid back to the analyzer, there is no need for a complex analyzer enclosure. In mild climates, the analyzer may be installed outside, while in more severe climates it is recommended to be protected from the elements by a simple building such as an MCC building, control room or metering skid shack. See for example this post Hythe Install, where the picture below is discussed.

Since process fluid never leaves the process connections (in a close coupled or in-situ system), no fluid is brought back to the analyzer or analyzer building. This eliminates the need for a sample recovery and disposal system and also mitigates risk to both infrastructure and personnel. In a conventional installation, toxic and combustible fluid is brought back to the analyzer shelter. While all efforts are taken to ensure that such systems are safe (explosion proof equipment, chemical sensors for gas detection), these are not always sufficient to prevent damage or personal harm. For example, unusual situations may arise during startup or shutdown, as described in this report. Using online spectroscopy, the close coupled sample cell returns directly to the process and is not in a confined space when a human works on it.

In summary, online process spectroscopy can improve analytical measurement and analysis by better maintaining sample phase during the measurement process. It can dramatically reduce maintenance requirements and improve reliability of the measurements due to the simplified sampling requirements. Such analyzers can eliminate the need for complex analyzer buildings and reduce the capital installed costs, while at the same time providing improved safety for facilities and personnel.

Insight Analytical Solutions provides automated sampling panels, composite samplers, and real-time process analytical solutions for the hydrocarbon processing industry. For more information, visit us at our Webpage.

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