Safely measuring bulk materials

23 October 2016

Throughout plant operations at Lafarge Tarmac, process instruments gives the instrumentation needed to operate safely and efficiently.

From its quarries across the UK, Lafarge Tarmac  extracts sand, hard rock and gravel that are used to produce a range of products for the construction industry including ready-mixed concrete, asphalt, cement and lime.

Siemens has worked with Lafarge Tarmac to help it control and standardise the management of material deliveries, storage, usage, and reordering of materials. Most importantly, this system also ensures the highest level of safety and efficiency when measuring bulk material levels.

Ingredients for asphalt production include filler dust and fibre pellets: the former helps reduce moisture in the mix, while fibres increase the stability of the asphalt, increasing its lifespan. 

Tankers regularly deliver these materials to the plant. On arrival, the drivers check the relevant panel displays for the amount of filler or fibre to be loaded. Once authorisation is granted from the plant control room, the driver connects the hose from the silo to the delivery tanker and use air to blow the light fibres into the storage silo. 

The process is similar for filler. Both require close monitoring to ensure that safe filling practices are met. This procedure is aligned with Mineral Products Association (MPA) guidance ‘to prevent over-pressurisation of storage silos during the delivery of (non-explosive) powders in the cement, concrete and quarrying industries.

Tanker drivers and operators need to know exactly how much of each material enters the storage silo. They need to ensure that the production facility has enough of each additive so that asphalt production isn’t slowed down or halted. However, they must also control the pneumatic filling process so that the silos are not overfilled – which could result in a potentially dangerous situation.

To keep materials at an optimal level, operators keep a close eye on the display panel mounted at the base of each silo. This reading is also retransmitted and simultaneously shown in the control room for the purpose of monitoring and reordering material. 

Each panel comprises a Sitrans RD200 display, warning LEDs, siren with flashing beacon and a Siemens LOGO PLC. The PLC is connected to a Sitrans LR560 radar level transmitter that is located at the top of the concrete vessel. The radar device continuously tracks the level in the silo, and has two alarm points - high & high-high. A third level, called the ultimate high level, is monitored by a Pointek CLS300 capacitance level switch. A LOGO PLC also handles the panel sequence control.

All of these devices and processes are closely monitored by a dedicated Siemens service engineer who takes care of routine maintenance and the onsite calibration.

Automation throughout production
Elsewhere in the plant a Simatic S7 PLC and SCADA control system operate the plant’s primary and tertiary crushers, and level process instrumentation plays an important role in keeping operations running smoothly. A Sitrans LR300 radar device, for example, measures levels of hot bitumen reaching temperatures of 170 °C, a  Sitrans LC300 capacitance level transmitter tracks levels of hot stone bins and a Sitrans LR200 radar transmitter continuously measures finished asphalt levels in the storage silo

In conclusion, Paul Bishop, electrical engineer at the Lafarge Tarmac Bayston Hill Quarry, said: “Siemens level and remote display instruments help us keep track of our production and make our processes safe for workers and equipment.” 

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