22 June 2009
Sensors have been integral to industry since the development of the steam engine. It is easy enough to draw the origins of modern sensors from the temperature and pressure gauges on those ancient machines.
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The plant-wide OneWireless Network, with real-time sensors and equipment health monitoring across the facility, and even on offshore assets. Mobile communication and workers have access to real time process information, asset and personnel tracking, and video monitoring.
Today, the average new car has 50 to 100, controlling fuel combustion, maintaining stability, improving braking, deploying the airbags or just helping you park.
And new applications continue to be developed every day. The Economist recently reported, for example, that scientists at the Massachusetts Institute of Technology have developed a new sensor to distinguish between dangerous chemical agents at concentrations as low as 25 parts in a trillion.
Researchers at the University of California announced they have made a contact lens with embedded pressure sensors, which could enable opticians to monitor glaucoma.
Indeed, in Europe, the UK’s communications industry regulator Ofcom has predicted that medicine will become a major market for wireless sensors. Worn by or implanted in patients, these will help carers monitor vital signs and enable the elderly to live at home for longer.
The next generation of sensors, it seems, will not just be all around us, but also within us.
IN PROCESSING PLANTS
Today, a mid-sized plant of 10,000 sq m is likely to have about 5,000 pressure sensors, 1,000 temperature sensors and 500 flow and level meters—not to mention pH meters, conductivity sensors, oil in water measures, vibration monitors, moisture transmitters, noise and leak detectors, and corrosion monitors.
When it comes to the budget for a plant’s control system, as a rule of thumb a third goes into the control system, a third into the valves, and a third to the sensors.
Their role continues to expand, too. At times, lower costs has meant that the sensor budget goes further, boosting uptake of the available technology. Petrochemical plants and refineries, for instance, have long been well instrumented, but lower-cost solutions are now beginning to see greater use of sensors in the utility systems that support production as well.
These systems, consisting of branched piping networks sending steam, air, water, lube oil, fuel gas, fuel oil and electricity to the process units are all too often only instrumented at the network’s main headers. That leaves many areas unmeasured, so that operators are unable to close the material balance, or identify possible leaks or waste.
Boosting the number of flow measurements throughout can help improve energy consumption and increase efficiency.
At other times, increasing use of sensors is driven by regulatory pressure. Witness, for instance, the huge growth in their use for environmental compliance, monitoring waste water, exhaust fumes and so on.
Mostly, however, the role of sensors has been underpinned by improvements in the technology. Some typical industry solutions that would have been unimaginable in the recent past include
• Pressure transmitters with automatic temperature compensation, accuracy of +/-0.0375%, stability of +/-0.01% a year, and reliability of 470 year MTBF;
• Moisture transmitters that can operate at up to 638 degC and pressures of up to 13,790kPa;
• Explosion proof humidity transmitters; and
• Flow meters with integrated pressure and temperature compensation able to cope with superheated and saturated steam measurement.
Processing industries are now able to use more sensors, in more applications, more reliably than ever before, and further advances are likely to continue to boost their role.
The worldwide MEMS (MicroElectro-Mechanical Systems) market, for instance, is estimated to be worth more than US $6 billion currently and to be growing at 14 per cent annually.
ADDING VALUE
This, of course, is a central point. Because, while it is often taken for granted by the process control industries, improved sensor technology remains a key determinant of a plant’s profitability.
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Left: The SmartCET (Smart Corrosion Evaluation Technology) transmitter
The move from pneumatic to digital controls and the distributed control system that began more than three decades ago has now given everyone the same, almost infinite, precision when it comes to control.
However, in the interface between the phenomenon being measured and the electrical signal—the sensor—there is still room to add precision, and therefore value, to the process.
Increasing the precision of the sensor by a few per cent can potentially lead to a similar rise in a plant’s productivity, and a significant impact on the bottom line. Nowhere, perhaps, is this clearer than when it comes to corrosion monitoring.
REAL-TIME CORROSION MONITORING
Globally, corrosion is estimated to cost process control industries US $50 billion a year—much of it through lost production, as well as health and safety, environmental, and legal liability costs.
The impact of corrosion is difficult to exaggerate: just look at the 2006 spill at Prudhoe Bay, the largest to date on Alaska's north slope, in which 67,000 gallons were spilled. BP put the cost of replacing the corroding pipeline at $100 million, was forced to shut the field for six weeks, and was fined $20 million.
Among chemical plants, meanwhile, a survey in 2004 confirmed that corrosion was easily the most common cause of plant failures, a factor in well over half the cases reported. It has been for more than two decades.
This is principally because throughout that time industry has tended to rely on the analysis of data from ultrasonic inspection of components, electrical resistance measurements by probe elements and, above all, mass-loss readings, using coupons.
The limitations of these methods are various. For a start, they tend to rely on readings taken over relatively long periods of time, and fail to give an accurate picture of the peaks that occur in corrosion rates.
They also accumulate only historic data regarding corrosion, which can prove worthless, given the changes in feed, process conditions and control limits that occur in modern plants.
Furthermore, because these methods rely on measuring corrosion after the fact, the issue has come to be seen by engineers as best managed through repair and regularly scheduled maintenance and replacement. In short, corrosion is all too often considered an unavoidable cost of doing business.
Yet modern sensor technology can reduce the cost of corrosion by up to 20% by moving from a reliance on historic corrosion records to online corrosion monitoring. This can provide plants with real-time data on corrosion as it happens and can even, with SmartCET transmitters, measure the localised corrosion that accounts for between 70 to 90 per cent of all corrosion-related equipment failures.
By bringing corrosion measurement into the control system, it can be viewed in the context of the operating conditions to gain a better understanding and early detection of the process conditions that cause peaks in corrosion.
It also frees up staff time spent manually collecting the data.
Most importantly, though, because it is real-time data being collected, the operator can have an influence on it: mitigating the rate of damage and striking the correct balance between maximising production and protecting the plant’s assets.
A WIRELESS FUTURE
The greatest scope for further expanding sensors’ role in industry, however, is likely to come from wireless technology.
Wireless transmitters have the potential to dramatically enhance the available data to process controllers by enabling measurements that would not have been economically viable or even possible with wired sensors. Integrated into a total wireless solution, the technology has the scope to be the most important development in process control since the development of the distributed control system.
The applications are manifold:
• Temperature measurement on rotating equipment such as kilns, where wireless technology not just avoids costs of US $40 to $160 per metre for wiring to the control room, but allows for the inclusion of additional measurement points to improve product quality;
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Honeywell’s XYR 6000 wireless transmitters
• Improved measurement of exhaust gases through sensors at the top of chimneys, where again wiring costs were previously prohibitive;
• Leak detection—wireless transmitters can operate effectively over a range of 6 miles when used with high-gain antennae, enabling measurements over a far greater area;
• Level measurements in dispersed areas such as tank farms—real time tank level monitoring can show an ROI (return on investment) in three months or less;
• Fire and gas detection in remote areas; and
• Safety showers, where wireless can lower costs by as much as 90 per cent.
Developments in low energy transmitters and energy harvesting will only keep adding to this list.
Through such applications, wireless can increase safety by reducing the need for manual measurement in hazardous areas and cutting the wiring available to produce a deadly spark.
It can also reduce maintenance and increase reliability by extending the scope of equipment health monitoring and corrosion control.
And it can increase efficiency by improving the quality of data available to controllers, as well as cutting wiring costs and installation times, and freeing workers for other tasks.
Despite these advantages, and while it is widely applied by businesses’ IT, facilities management and even distribution operations, industry has been slow to adopt wireless technology when it comes to process control. Its penetration in the oil and gas industry, for instance, is currently estimated to be less than 10 per cent.
This is largely due to concerns about safety, security, and reliability. However, through application in less critical functions and the development of industry standards such as ISA SP100, these concerns are being addressed.
Honeywell alone has now supplied and implemented wireless solutions for more than 500 clients, and the global growth for wireless in manufacturing is expected to be 26 per cent a year for the next five years.
FULL SCALE WIRELESS
The real potential of wireless sensor technologies, though, will not be achieved with piecemeal upgrades or additions to improve safety or efficiency—any more than real time corrosion measurement alone without its full integration as a process variable into the control system brings all the available benefits.
Instead, the future for such sensors lies in their integration as part of a wider solution: a full-scale wireless mesh network deployed across an entire site to handle multiple applications.
In such a framework, the enhanced reach of wireless sensors can combine with a range of other technologies, including handheld devices to give mobile workers access to real-time process information; asset tracking that will further boost productivity by enabling workers to locate equipment quickly and easily; and video monitoring that can be programmed to automatically focus on areas where sensors detect intrusions or process upsets.
Location tracking for personnel through sensors on their identification tags will also greatly improve safety, particularly in the event of an emergency. Fundamentally, a single plant-wide wireless network will enable operators to take full advantage of the flexibility that wireless technology offers, adding and changing wireless devices as their needs and process changes require.
Given the understandable caution of industrial users, the fully wireless plant is still far from being a reality. However, the limits are no longer technological, and in ten years we may see some smaller plants going down this route. For now, though, wireless sensors are taking a lead and, as ever, indicating the way ahead.
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