Improving handling efficiency within the coal industry

With use of coal still growing not only as an energy source but also as a key element in the manufacture of countless materials, products and chemicals, so efficient transportation of this vital resource is becoming evermore important. Tony Ingham of Sensor Technology discusses the new technology that is helping to boost transportation and handling efficiency, reduce downtime and minimise costs.

RWT series torque transducerFormed from the remains of plants buried hundreds of millions of years ago and subjected to aeons of heat and pressure, coal is the world’s most plentiful fossil fuel. Even today, when fossil fuel has become something of a dirty word, global consumption of coal continues to increase.

Since 2000, global consumption of coal has grown faster than any other fuel, and last year around 8 billion tonnes of coal were used worldwide, with the biggest users – perhaps unsurprisingly – being China, the US, India, Russia and Japan. As of 2013, coal provided approximately 40% of the world’s electricity.

That might seem to fly in the face of efforts to reduce CO2 emissions globally, with fossil fuels seen as a major culprit. But while coal may not be the cleanest source of energy in absolute terms, modern ultra-clean coal-fired power stations have shown that countries can have coal within their energy mix and still meet emissions’ targets.

It’s not just about energy, however. Coking coal is vital to steel production, and coal is also a key element in cement manufacturing. It is also used in the manufacture of numerous chemicals, pharmaceutical products and paper, while many household products have either coal or coal by-products as components.

According to the World Coal Association, coal is mined in over 50 countries. And while most coal is used in the country in which it is produced, it is traded all over the world, meeting the needs of countries that do not have sufficient resources to cover their own energy and manufacturing requirements.

As with every other industry, there are constant pressures within the coal sector to drive down costs, boost uptime and optimise efficiency, with key areas to look at being handling and transportation. Applications such as conveying of coal or agitation of coal slurry present an extremely harsh environment where breakdowns lead to excessive downtime and reductions in efficiency. With the coal industry being increasingly global, there are pressures to attain ever-greater efficiency standards.

One of the technologies that is helping to drive this improved productivity is non-contact digital torque monitoring. For example, in coal conveying, torque monitoring technology is helping to transform an activity where downtime due to mechanical failure has previously been regarded as a fact of life.

Coal conveyors are, by nature of the product being handled, heavy-duty electro-mechanical systems operating in highly challenging environmental conditions. Starting and stopping under heavy loads, problems with dust and debris, and the nature of electromechanical technology all have implications for long-term reliability, availability and maintenance.

When the goal is simply to keep the conveyor running, there may be little time to consider optimisation of the conveyor control system. And yet, with the application of digital torque sensing technology, the control system can be transformed and the whole conveying process can be made more reliable.

When the conveyor is empty, it requires very little power from the driveshaft to keep it moving smoothly. As coal is added and the conveyor load increases, so more power is needed. Similarly, if the conveyor is run at a higher speed, more power is needed. Controlling conveyor speed accurately helps to minimise shock loads, and so leads to both increased reliability and increased efficiency.

Accurate control of the conveyor comes from the ability to monitor accurately the power being used to drive the conveyor. This information can then be fed into computerised control systems to ensure the conveyor is always moving at optimum speed. Real-time data from the conveyor is collected by having sensors monitoring the critical variables – in this case the torque on the driveshaft, the speed of the motor, and the drive power – and fed back to the control system.

However, torque data can be hard to collect, with traditional technologies introducing as many problems as they solve. Because the shaft is rotating, wires attached to it would wind up and snap, so a special way of monitoring it is required. The traditional solution is to use slip rings, but these are expensive, difficult to set up and far too delicate in use for most coal transportation applications.

Sensor Technology is at the forefront of an important enabling technology. Its TorqSense transducer is based on the patented technology of measuring the resonant frequency change of surface acoustic wave (SAW) devices. TorqSense torque sensors use two tiny SAW devices or SAWs made of ceramic piezoelectric material containing frequency resonating combs. These are glued onto the driveshaft at 90 degrees to one another. As the torque increases, the combs expand or contract proportionally to the torque being applied. In effect, the combs act similarly to strain gauges but measure changes in resonant frequency.

The adjacent RF pickup emits radio waves towards the SAWs, which are then reflected back. The change in frequency of the reflected waves identifies the current torque. This arrangement means there is no need to supply power to the SAWs, so the sensor is non-contact and wireless.

This innovative method of measuring torque can bring distinct advantages to coal conveying, whether in extracting coal from the mine, or transporting it for processing, or as part of subsequent shipping operations. A process that was once regarded as very difficult to monitor can now reap the same benefits as many other industrial processes.

TorqSense technology can also improve on the torque limiters that are traditionally relied on to prevent mechanical damage in the event of a coal conveyor jam. Continually monitoring the torque, the transducer can identify the gradual increases that are indicative of an impending jam condition, so enabling preventive maintenance. This key technology can deliver significantly reduced downtime that might have been caused by breakages to conveyor chain, paddle attachments, or the drive gearbox.

With coal still an important global resource, crucial not only as part of the energy supply mix but also in the manufacture of numerous other products, so the pressure is on to increase the efficiency of handling and transportation, and to drive down costs. In this context, accurate, non-contact, digital torque monitoring technology has an important role to play.