Nov-2020

Digitalisation for improved operations

Increased availability of gas analysis equipment through digital transformation can raise levels of operational excellence.

TONY DODD
Servomex

Article Summary

Many industrial production processes depend upon reliable, accurate, and stable gas measurements in order to optimise operations, maintain safety, and meet regulatory requirements. Gas analysis companies continue to innovate in this area. However, they also believe that the solution surrounding the measurement could be improved in the future as technology and digitalisation develop.

In today’s Industry 4.0, economic, competitive, and regulatory pressures combine with the challenges arising from cultural and workforce shifts to spur a change in operations. The focus on operational excellence — seeking the optimisation of processes, assets, and people — is increasing and paying dividends.

Top-quartile performers stand out for safety, reliability, efficiency, sustainability, and financial performance when compared to those at the opposite end of the spectrum. They average three times fewer recorded safety incidents, a 4% increase in operational availability, 50% lower maintenance costs, a 30% reduction in emissions and energy use, and 20% lower operating costs — clearly helpful in maximising profits and margins.

With tougher times ahead, a continued focus on operational excellence could be critical for competitiveness or survival. Gains in operational excellence often result from incremental, thoughtful, and focused digitalisation initiatives. These include finding ways to automate or streamline manual, error-prone, or slow activities, and to improve situational awareness.

Low cost sensing, connectivity, data storage, and processing can be harnessed to enable more informed and responsive operations and maintenance, enabling new levels of optimisation and asset management.

Offline gas analysis and operational excellence
Many industrial processes depend on gas concentration measurements to support their operational excellence objectives. If those measurements become unavailable, the result is increased operational costs, decreased operational revenue, and increased operational risks.

When a gas analyser is offline, operational costs can increase because the process control system has less information on which to base adjustments, leading to the degradation of control. In many cases, a process can continue operating and avoid a shutdown, but it cannot run optimally. This may result in higher energy consumption, increased use of fuel or other resources, potential to impact other assets, and, of course, additional overheads to remedy the offline analyser.

A typical application example is the process for the reduction of NOx emissions in combustion power plants (DeNOx) using selective catalytic reduction (SCR). In this process, ammonia (NH3) is injected into the gas flow from the combustion process; this reacts with NOx in the flue gas in the presence of a catalyst to form H2O and N2. A surplus of unreacted NH3, commonly referred to as ammonia slip, is wasteful and costly, and may also lead to harmful deposition effects which impact the catalyst and potentially cause corrosion of air preheaters located further downstream. 

Operational revenue can also decrease when a gas analyser is offline. The degradation in control capability can result in off-spec product quality, lower product yield, or product scrappage. As an example, during semiconductor wafer manufacture — where ultra-pure gases are required — the smallest impurities can result in major defects, leading to product scrappage.

An offline gas analyser also increases operational risks. Using the ammonia slip example above, harmful emissions increase and can have regulatory consequences.

In addition, some processes depend on accurate gas analysis to maintain safe operation. One example is combustion in control fired heaters, integral to many hydrocarbon processes. These heaters are highly dependent on reliable, continuous measurement of excess air. Efficient operation of larger, fuel-hungry units, such as those on ethylene crackers, involves a delicate balancing act to remain on the safe side of a tipping point from efficient, low emission operating conditions to potentially explosive low oxygen and fuel rich conditions.

Factors that reduce availability
It is clearly important to achieve high availability for gas analysis while balancing cost and risk. However, reduced availability can occur due to a number of factors. Firstly, installation and commissioning issues can impact upon tightly planned and coordinated construction, upgrades, and shutdowns, and may lead to delayed start-up of production. The cost of such a delay can amount to hundreds of thousands of dollars each day, due to lost revenue and the need to reschedule dependent works. Factors contributing to these delays include late delivery, defective materials, poor installation, and limited field access to information.

Exposure to unforeseen process and operating conditions is often detectable by analyser diagnostics, but not in all cases. Depending on the exact nature of the conditions, gas measurements may discontinue while the analyser reports faults or out-of-specification indications to the plant control system. Examples of conditions in this category include ambient or sample gas temperature/pressure/flow levels or rate of change beyond specification, poor power supply, excessive vibration, and electromagnetic interference.

Additional conditions may also be detectable by specific gas concentration measurement technologies. For example, unexpected background gases and high dust or particulate loading in the process gas stream can compromise spectral shape quality required to obtain measurements using tunable diode laser spectroscopy (TDLS) measurements. Some conditions can result in damage and require replacement parts.

Another factor which can lead to degraded performance, and ultimately to an unavailable measurement, is inadequate maintenance. For example, sampling systems and analysers themselves often include filters to protect the gas sensors from foreseen contaminants such as particulates and moisture. These may need to be cleaned or replaced periodically. Even under expected operating conditions, obscuration can build up over time on the optics within analysers, which requires cleaning.

Maintenance activities, such as cleaning or replacing filters, cleaning optics or performing periodic validation of measurement accuracy (and, if necessary, calibration), typically require analysers to be taken offline.

If the analyser is incorrectly operated — for example, through the inadvertent adjustment of critical configuration — it can create effects that effectively render the analyser offline or untrustworthy. Examples of this include disabling or changing the temperature or pressure compensation configuration, modifying assigned behaviour of outputs, or even modifying essential measurement details, such as optical path length of an in-situ installation.

Finally, unexpected component failures typically result in diagnostics identifying the faulty part. The impact this has on the gas measurement and its availability to the control system depends on the nature of the faulty part.