Figure 1. Gas analysis is essential to support
operational excellence and competitive performance in many industrial facilities.
Figure 2. A service plan, supported by predictive
condition-based monitoring, increases confidence that unplanned downtime can be avoided.
competitiveness, or even survival. These gains in operational excellence often come from incremental, thoughtful and focused digitalisation initiatives; for example, finding ways to automate or streamline manual, error-prone or slow activities, and improving situational awareness. Low-cost sensing, connectivity, data storage and processing can be fully utilised, enabling more informed and responsive operations and maintenance, and creating new levels of optimisation and asset management.
Offline gas analysis and the impact on operational excellence Gas concentration measurements support the operational excellence objectives of many industrial processes, meaning that if those measurements become unavailable for any reason, operational revenue decreases while operational costs and risks are increased. An offline gas analyser means that the process control system has less information on which to base adjustments, leading to the degradation of control and higher operational costs. A process may be able to continue, thus avoiding a shutdown, but cannot run optimally. The consumption of energy, fuel, and other resources may increase, other assets may be affected, and the operator will incur additional costs to remedy the offline analyser. May 2021 40 HYDROCARBON ENGINEERING
Take the example of the NOX emission reduction process in combustion power plants (DeNOX), using selective catalytic reduction (SCR). Ammonia (NH3) is injected into the gas flow from the combustion process. It reacts with NOX in the flue gas, in the presence of a catalyst, to form H2O and N2. Surplus unreacted NH3 (ammonia slip) is wasteful and costly, and often leads to harmful deposits which impact the catalyst and may cause corrosion of air pre-heaters located further downstream. A gas analyser going offline can also impact operational revenue, since the degradation in control capability can take product quality off-spec, reduce product yield or increase product scrappage. Consider semiconductor wafer manufacture, which relies on ultra-pure gases. The smallest impurities can result in major defects, leading to product scrappage. Operational risks are also increased by an offline gas analyser. In the ammonia slip example above, an offline analyser means harmful emissions increase, and can affect regulatory compliance. Accurate gas analysis is essential to maintain safe operation in some processes, such as combustion in control fired heaters. These are integral to many hydrocarbon processing applications, and depend on the stable, continuous measurement of excess air. Operating large, fuel-hungry units efficiently – for example, those on ethylene crackers – requires a delicate balancing act, ensuring efficient, low-emission operating conditions while remaining on the safe side of a tipping point that leads to potentially explosive low-oxygen, fuel-rich conditions.
Factors that can reduce gas analysis availability While balancing cost and risk, it is essential to achieve high availability for gas analysis. Nonetheless, there are a number of factors that may lead to reduced availability. Issues with installation and commissioning can affect tightly planned and coordinated construction, upgrades, and shutdowns, and could delay the startup/restart of production. Delays can cost operators up to hundreds of thousands of dollars each day, with lost revenue and the need to re-schedule dependent works. Late delivery, defective materials, poor installation and limited field access to information are all factors that contribute to such delays. If an analyser is exposed to unforeseen process and operating conditions, this is often detected by the analyser’s diagnostics, though this is not always the case. Depending on the conditions encountered, gas measurements may stop while the analyser reports faults or out-of-specification indications to the plant control system – for example, changes to the ambient or sample gas temperature, pressure, or flow levels, poor power supply or excessive vibration. Specific gas concentration measurement technologies may also be able to detect additional conditions – for example, tunable diode laser spectroscopy (TDLS) measurements can be compromised by unexpected background gases and high dust or particulate loading in
