Dust control made simple

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The dust produced through materials processing can pose serious occupational health and safety (OHS) and environmental hazards, as well as diminishing the quality of the finished product.

As most processes emit dust as a by-product, including mining, metalworking, food and fertiliser, 'collecting' the dust to purify the air is a key step in meeting modern quality and safety standards.

One company that recently upgraded its dust collection operation is Tasmania's Impact Fertilisers, which operates 24 hours a day, seven days a week, to produce Single Superphosphate (SSP) fertiliser products for Australia's farmers.

The business called on process monitoring and control solutions provider PTronik – which specialises in industrial air filtration and dust collection projects – to update a legacy controller which had fallen below par in monitoring and controlling the plant's 'dust collector' system which was tasked with filtering the dust-laden air produced from the fertiliser component.

Monitor and control

Impact Fertilisers required a control system that could also monitor the dust collector for mishaps, including blockages in the air ducts where the dust entered and the clean air was emitted.

The team at PTronik, including managing director, Robert Bosshard, retrofitted the company's pMCi controller – a system that provides remote monitoring, sensors to detect air pressure loss, air pulsing operation and the ability to monitor the clean air outlet to make sure that there are no dust leaks.

"Dust is everywhere; we estimate that 20,000 dust collector units are operating in Australia – and this is a very conservative figure," Bosshard told PACE.

PTronik engineers installing the pMCi control board to control the dust collector.

PTronik engineers installing the pMCi control board to control the dust collector.

Impact Fertilisers' dust collector is 10 metres high, and incorporates over 350 filter bags. For such a large system, maintenance had become a challenge.

"Maintenance to change the bags is quite time consuming. Our system can indicate the location of the potentially-damaged bags, as well as the state of the air pressure valves – whether they are OK, if they use an open circuit or short circuit coil and which one it is," explained Bosshard.

"When and if the bags have an excess of dust load, the pMCi will detect this state and increase automatically the number of air pulses; then, when the dust is cleaned, it will either slow down or even stop pulsing until there is a need.

"All this is done by constantly monitoring the DP (differential pressure) across the bags; when DP crosses a high level the pulsing starts, and when DP goes below a low level it will stop pulsing. A DP alarm is also available is case there is a blockage."

The pMCi display, complete with programming pushbuttons, driver boards and Ethernet connectivity.

The pMCi display, complete with programming pushbuttons, driver boards and Ethernet connectivity. 

Industrial dust collectors work by employing either tubular filter bags or cartridges to retain fine dust particles, Bosshard explained.

"Dust collectors operate like giant vacuum cleaners with a number of collection bags, called baghouses.
Dust particles are drawn into fabric bag filters and are trapped by the walls of the filter bag. For the bags to filter at an optimal level they must be cleaned regularly.

In order to provide continuous filtered air, dust particles trapped by the filters need to be removed whilst the plant is operating," Bosshard said. "The filters are blasted with compressed air (for example, between every 10 to 30 seconds depending on the type of dust).

"The dust particles then fall from the filters and are collected below in a hopper which is regularly emptied.
"Too much shaking is to be avoided where possible as it can cause unnecessary wear to the filters. The rows of filters are pulsed with high pressure air jets (duration 100 ms) sequentially.

"In the case of the fertiliser plant there are 30 rows divided in five chambers (six rows and six valves per chamber). The first chamber is isolated (no air blowing through) and the first six valves are pulsed sequentially then the second chamber is isolated (all the others are open to air flow) and the next six valves are pulsed and so on."

The solution PTronik installed to the control the dust collector included the pMCi – which acts as the main controller for the system – along with a DS10C Dust Sensor from PCME, and a 8498 Series Pressure Sensor (which operates up to 10 bar) from Trafag.

The dust collector, which receives dirty air (right-hand pipe), and emits the clean air through the pipe on the left. The pMCi controller can be seen at the very top of the dust collector.

The dust collector, which receives dirty air (right-hand pipe), and emits the clean air through the pipe on the left. The pMCi controller is at the very top of the dust collector.

According to Bosshard, as the dust collector's pulse rate is now controlled constantly, compressed air usage has been lowered by 50 percent.

Also, the total energy consumption has been reduced by 40 to 70 percent, and filter bag life by up to 30 percent.
The system also suffers less downtime, and maintenance costs are decreased, he says.

The pMCi system provides: 'on demand' cleaning; broken filter row detection; manual single valve pulsing; electronic fault detection on each solenoid; and mechanical fault detection on each valve.

Data logging; filter state tracking; remote set-up, monitoring and diagnostic control via Ethernet; and wireless control of up to one km are also made possible.

Bosshard says the controller is easy-to-use and, with operation performed using only three push buttons, little or no operator training is required.