Mar-2021

Trends and developments in gas analysis

Technical and digital developments are modernising the way gas analysers are built and used.

STEPHEN B HARRISON, sbh4
STEPHEN GIBBONS, ABB

Article Summary

Technical developments to improve equipment functionality and an array of digital innovations are transforming the landscape of gas analysers and instrumentation in the oil and gas sector. These trends and developments are resulting in significant benefits for operators: reduced capex, simpler operations, and a lower cost of ownership.

Gas analysers are used for process control applications where repeatability and speed of response are essential. They are also mission critical for monitoring emissions to the air, a highly regulated area where data must be reported and a high level of gas analyser uptime is critical. Technical and digital developments in these areas are modernising the way gas analysers are built and used. The fundamental applications of level, temperature, and pressure measurement are also benefitting from the transformation that is taking place.

Low maintenance hardware
The right gas analysis hardware can make a big difference. Simplicity is a key driver for change. Combustion optimisation and continuous emissions monitoring systems (CEMS) in a steam methane reformer (SMR) producing hydrogen for hydrotreating in the refinery is a relevant example to consider. The supply of hydrogen to these processes is essential to produce clean-burning, low-sulphur fuels and biofuels. Existing solutions often bundle together all the gas analysers that a refinery would need for SMR safety control and emissions monitoring with a single module which results in improved simplicity. Nowadays, the oil and gas industry is equipped with selective catalytic reduction (SCR) for NOx removal. One way to monitor the effectiveness of the flue gas cleaning process is to monitor ammonia slip as a performance indicator of SCR process control. Ultimately, that translates to reduced operating and capex costs.

Furthermore, analysis of the total oxides of nitrogen (NOx) in emissions from a steam methane reformer is an area where the trend for gas analyser hardware is simplification. It has been common in the past to use the chemiluminescence analytical technique (CLD) to measure NOx. The instrument needs an ozone generator and a catalytic converter operating at 300°C to oxidise NO to NO2 because the CLD technique cannot speciate between the two. That is a lot of technology to pack into an instrument intended for use in rugged industrial applications.

To meet modern NOx measurement requirements, a solution based on ultraviolet spectroscopic analysers is emerging as an attractive option. This kind of gas analyser ensures that NOx measurement is simple, using robust UV gas analysers that can speciate between NO and NO2. At present, this gives an even greater level of visibility of environmental emissions than is generally required but, as legislation shifts, the purchase of a gas analyser which can perform at this level can be considered as future-proofing the investment.
Direct read IR gas analysers are ideal for the measurement of carbon dioxide (CO2) and carbon monoxide (CO) for combustion control and CEMS applications. The levels of CO, CO2, and oxygen in combustion exhaust gases are tell-tale indicators of whether the system is operating at maximum energy efficiency. Simultaneous measurement of CO and CO2 is achieved by a non-dispersive infrared sensor (NDIR) type gas analyser. In contrast to the types of gas analyser that might alternate between measuring CO and CO2, with NDIR sensors both gases are continuously measured. This means that essential process optimisation information is continuously available to feed into the DCS process control loops, resulting in improved hydrogen conversion yields and better energy efficiency.

UV and IR gas measurement technologies can also provide valuable information for combustion process control and optimisation of energy efficiency. Oxygen measurement is also essential for this application. Three main types of gas analyser are suitable for monitoring oxygen in the flue gases from a refinery process heater or steam boiler burner. With an extractive paramagnetic type analyser that features precision and appropriate sample conditioning, the set-up can tolerate difficult process sample streams. A zirconium oxide probe provides accurate and rapid reading. Also designed for continuous, in situ measurement, the laser-based analyser type offers fast response to process changes.

Measurement of flue gas oxygen concentration is an essential process control parameter to ensure stoichiometric combustion and full utilisation of energy contained in the fuel. Where an extractive system is preferred, the use of a paramagnetic oxygen analyser for combustion process control has been common for decades. Recent developments feature a solid state electronic ‘microwing’ to replace traditional gas-filled dumbbell oxygen sensor technology (see Figure 1). The result is higher accuracy and less drift, resulting in reduced calibration frequency. These factors feed through to improved process optimisation and reduced maintenance costs.

Whilst the extractive paramagnetic type analyser claims a reduced calibration interval, IR and UV gas type analysers have self-calibration features that eliminate the need for manual calibration. The gas analysers are fitted with cells that are filled with gas mixtures of known concentrations. These enable automated calibration without the need for external gas cylinders. This means the instruments can be maintained with low cost and complexity.

Digitalisation of hardware
Guided wave radar is well established as a measurement technique. The equipment is robust, the technology is mature, and primary application niches have clearly emerged. However, the instrumentation has developed a reputation for being difficult to install. But digital algorithms embedded into the latest devices mean that the chances of getting the installation right the first time are increased.

The innovations are tapping into two trends: digitalisation and the scarcity of skilled labour. Modern devices with guided wave radar level measurement instrumentation are designed to provide fast installation times. Recently developed gas analysers and instrumentation can be installed by instrument technicians in a fraction of the time that previous models required and with the confidence that they will work from day one. This is especially important when fitting out a tank farm with four or six tanks because the instrument technician will want to complete the installation within a day and return to base.

The guided wave radar level measurement principle relies on the radar wave partially reflecting from the upper crude oil layer and partially penetrating to the oil-water interface, where it is then reflected from the water layer. Leveraging this phase boundary detection is a common application in crude oil storage tanks at remote oil well locations. These tanks receive a mixture of crude oil and water from the well-head and perform an initial physical separation between the two liquids.