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Fighting fire hazards: stopping coal's spontaneous combustion

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When storing or loading large amounts of coal, or even stockpiling it, the issue of spontaneous heating or combustion is and oft forgotten, but crucial one.

When coal is exposed to oxygen its temperature rises and generates heat and in turn promotes further oxidisation, which can cause it to ignite suddenly.

Whether on site or at the port, the issue is ever prevalent.

Earlier this year Glencore saw potential spontaneous combustion issues in the spoil piles at its Collinsville coal mine.

While the legacy issue of the spoil piles igniting was key, the resulting gas emissions from the burning coal also presented a serious problem, not just for the mine but also people living in the vicinity of the operation.

There is also the added problem of airborne coal dust.

As more coal dust rises into the air the chance of a spontaneous combustion rises.

This is in addition to the dangers it presents to air quality on a work site.

This becomes a serious issue at many coal ports, such as Newcastle's Kooragang Island, where tonnes of coal are moved daily, sending a blanket of coal dust into the air.

At one Dutch coal terminal, bulk materials handling company OBA, encountered this problem and worked to develop a unique solution to overcome it.

"Self combustion of coal is something we have to take into account every day," OBA planner Dick Meijer explained.

"To prevent it from occurring at the port we had to take a number of appropriate measures, specifically we would send out an excavator or wheel loader to dig out and spread the suspected area, as well as having dedicated combustion fighting equipment that allows us to compact the area and to release oxygen out of the coal pile," he said.

However the problem with this lies in the fact that the actions are all responsive, instead of proactive, with OBA addressing the issue once combustion occurs or comes close to igniting.

One way it did was by measuring the R70 value [which is a time consuming process and takes more than 16 hours], looking at the increased presence of ethylene CO, hydrogen or ethane.

Reaction time is crucial for the operator, as not only will combustion create costs from energy and quantity loss, it will also have serious safety and environmental impacts.

Because of these ever present issue, OBA looked to a way uncover potential self combustion hazards before they happened.

"In order to minimise those costs as much as possible, we were looking for a way to monitor the temperature of our coal stock before it's loaded on to the barges," Meijer said.

"Thermal imaging turned out to be the perfect technology to do this."

He explained that previously OBA carried out weekly inspections via an external agency, but has now invested more in its own thermal imaging cameras "to be sure that all the coal leaving our site has a temperature that is safe to be transported".

In Europe regulations outline a mandatory coal load temperature of below 60 degrees Celsius, before, during, and after the loading process.

"Therefore, every load of coal that leaves this terminal needs to be back by a valid monitoring certificate; thermal imaging allows us to meet these requirements more easily," Meijer said.

The terminal is now equipped with three ruggedised FLIR A310f cameras to monitor the coal stockpiles and ensure valid monitoring certificates.

"One of the major advantages of thermal imaging compared to other technology is that the cameras can monitor entire areas of the coal stack, so when the coal is on the conveyor belt thermal imaging cameras can read the entire coal mass, not just the surface," Meijer said.

Each camera is positioned on a tower with a wide view overlooking several conveyor belts that deliver the coal to barges.

"This way OBA can detect coals with high temperatures [and] by positioning the thermal imaging cameras as close to the barge as possible it can visualise the entire conveyor belt stretch (up to 900 meters) and monitor the coal temperatures up to the last second before loading, which helps prevent the risk of a combustion incident on board," the company said.

Once the thermal images are taken they are sent over IP to a central control room where they are continuously monitored.

The operators use a software system that provides intuitive colour codes to communicate the real time status of the coal loads, with green meaning with satisfactory ranges, and yellow that the temperature is rising and sitting between 40 and 50 degrees Celsius.

When it reaches the yellow level OBA takes preventative measures such as digging out and spreading the coal.

A code red means that temperatures have risen above 55 degrees Celsius, which prompts an alert that forces the conveyor to stop and in turn prevents the overheated coal from being loaded.

According to OBA it chose the FLIR A310f as it is a highly sensitive, high-speed camera that comes in an environmental housing .

The housing increased the camera's environmental specification to IP66, without negatively affecting its operating capability.

"After thorough consultation and testing with FLIR distributor Rato, we chose the FLIR A310f because it gave us very accurate and consistent results,"" Meijer said.

Along with monitoring coal on the conveyor belt as it's loaded, large stockpiles are also inspected at least once per week.

For this task OBA uses a combined method of temperature probes and a FLIR E6 handheld thermal imaging camera.

"The big difference between both technologies is that a probe will measure pin-point temperature, while the E6 and A310f infrared cameras show temperature patterns and provide measurements for a larger area," he said.

"To put it simply, these thermal images are a good solution we've found to help keep resources and lives safe." 

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