March 22, 2012

Challenges of Gas Purity Measurements Solved

Hi there. Michael Kamphus here. I’m an application engineer for process gas analyzers here at Emerson and in this blog post I’d like to discuss how the measurement of gas purity plays an important role across multiple gas processing industries and applications, mainly for the purpose of detecting gas impurities across a particular process. For example, in chemical reactions, one has to ensure the gases are free of carbon monoxide (CO) because of the risk of poisoning precious catalysts, oxygen (O2) might oxidize catalysts, and carbon dioxide (CO2) might form carbamates or carbonates which may clog process gas lines and lead to costly repairs.

One of the most important gas purity processes is the production of syngas, which is a mixture of CO and hydrogen (H2) and used as a starting point for H2 or CO generation. Syngas is mostly produced by steam reforming of natural gas. After the initial reformer, different reaction steps are necessary to convert and clean the process gas to achieve syngas in the desired H2/CO ratio. Besides steam reforming of natural gas, other technologies generate syngas from coal gasification or wood/biomass gasification. The fertilizer industry uses syngas to produce ammonia and urea. Additionally, methanol and other hydrocarbons can be synthesized by the Fischer-Tropsch reaction, an access to liquid hydrocarbons independent from crude oil.

In air separation units, the inlet air has to be free of hydrocarbons (HC) and CO2. After separation of nitrogen (N2), O2 and argon (Ar) has occurred, the product gas streams have to be monitored for impurities such as moisture, CO2, HC and O2, to ensure product quality. These gases and gases from other industrial processes are then used for gas bottling. Bottled gasses are needed in the food and beverage industry with the carbonization of beverages, welding and shielding to improve weld characteristics, and even in medical gases.

Emerson Process Management, Rosemount Analytical offers solutions for even the most challenging gas purity applications in refineries, fertilizer plants, steel plants and gas processing facilities around the world. For example:

  • The impurity measurements of CO and CO2 are done with non-dispersive infrared photometer (NDIR) measurements and detect from 0-10 ppm or 0-5 ppm, respectively.
  • NDIR is also used for purity measurements of CO2 and nitrous oxide (N2O) with a max suppressed range of 98-100%. Hydrogen measurements are done with a thermal conductivity detector (TCD) making it possible to measure the H2 purity up to 98-100% or impurities of H2 in CO down to 0-1000 ppm.
  • NOx, meaning the sum of nitric oxide (NO) and nitrogen dioxide (NO2) measurements, are performed with a chemiluminescence detector (CLD) as a standard. These ranges can get down as low as 0-5 ppm.
  • Hydrocarbon impurities are detected with a flame ionization detector (FID) with the lowest range being 0-1 ppm.
  • Oxygen, as low down a range as 0-1%, but also suppressed ranges of 20-22% and 98-100%, can be measured with a paramagnetic sensor (pO2). For O2 ranges down to 0-10 ppm, a trace oxygen sensor (galvanic fuel cell) is used.
  • For H2O an aluminum oxide (Al2O3) based trace moisture sensor is integrated into the analyzer enabling us to deliver measurements on the dew point range from -100°C to -10°C or 0-100 to 3000 ppm.

The integration of different technologies can be combined into one analyzer housing; for example, a suppressed 98-100% O2 purity measurement with a 0-10 ppm CO and a 0-5 ppm CO2 impurity measurement, reducing cost for analytical equipment and making integration of the analyzer into the DCS much easier.

If you have a challenging gas purity application, have a question about process gas analyzers, or would like to share your experiences within the gas purity and process gas industry, we would like to hear from you. Post a comment and let us know!

To learn more about gas purity applications and process gas analyzers, visit