According to a 2005 government report, the industrial and mining sectors account for 47% of total end user energy demand in South Africa. Energy remains the second leading cost pressure (behind raw materials) currently affecting most manufacturers. Some of the biggest culprits are incinerators, crackers, process heaters, and other energy intensive combustion-based equipment.
The harsh operating conditions associated with combustion analysis applications can eat up a sensor in no time, resulting in inaccurate and unreliable measurements. This can make it nearly impossible to control these processes adequately. However, new analysis techniques, such as tuneable diode laser spectroscopy (TDLS), can improve efficiency, maximise throughput, reduce emissions and improve safety in combustion analysis applications.
Reduce energy consumption while improving throughput
Most energy intensive operations, such as those found in a refinery or chemical plant, experience considerable variability in energy consumption due to changing operating conditions, equipment degradation, fluctuating market conditions, and inefficient control strategies. As a result, plants typically consume more energy than necessary, yet are unable to improve efficiency due to the inability to collect and analyse real-time performance data. Frequently, the goals of optimising efficiency and maximising throughput are at odds with the need to reduce emissions and ensure plant and personnel safety. Effective energy management is essential for a ‘triple bottom line’ business strategy that addresses social, economic, and environmental concerns. TDLS can contribute to such a strategy by helping increase throughput and reduce energy costs, while supporting safe and environmentally responsible operations.
Advanced process control (APC) systems require sensitive and accurate process measurements in real-time, or near-real-time. APC reduces process variability and inefficiency, improves product quality, and provides for more stable operations. With few exceptions, current process analytical techniques lack the speed, accuracy and sensitivity to provide reliable measurements for APC. On-line optimisation goes beyond advanced control to optimise a process based on an economic objective function.
This is becoming more important in applications where profitability depends upon improving quality, while maximising material utilisation and minimising energy usage.
Historically, obtaining reliable quality measurements in time to impact control has been an issue in combustion control applications. The current best practice utilises a Zirconia sensor for point measurement of oxygen. In applications requiring multiple measurements, point measurement cannot provide a representative sample, making it both error prone and potentially dangerous. Process oxygen measurement requires samples to be extracted and then transported to an analyser for conditioning and analysis. This slows response time, adds cost, and degrades measurement accuracy.
TDLS in combustion analysis
Inefficient combustion can be attributed to the air/fuel ratio. Excess air results in loss of efficiency and increased NOx emissions, while too little air is dangerous. Carbon monoxide measurement provides an indication of fuel-rich conditions, while oxygen measurement indicates air-rich conditions. The optimum control point is the lowest possible excess air value that does not cause the system to enter into an unsafe condition or violate emissions limits.
Tunable diode laser technology is an innovative measurement technique that utilises semiconductor lasers to detect a variety of gases at trace levels in the part-per-million (ppm) or part-per-billion (ppb) range. Tuneable lasers, which enable miniaturisation of transmission and receiving units, provide highly sensitive, quantitative measurements with fast response times without the need for recalibration. The lasers can be tuned to detect specific constituents independent of process gas concentrations.
TDLS enables high performance measurements in real-time, even in challenging process environments. Exact performance specifications may vary somewhat according to supplier; however, the benefits are universal.
To date, the most widely reported application of TDLS has been for combustion control. Energy can be the largest component of a manufacturer’s cost structure with costs expected to trend upward over the long term. A willingness to apply state-of-the-art technologies can have a significant impact on the success of energy management programs. Technologies, such as TDLS, that can improve performance and provide quick ROI can have a significant impact on the bottom line.
For more information contact Larry O’Brien, ARC Advisory Group, (+1) 781 471 1126, [email protected], www.arcweb.com
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