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Streamlining mixed fuel management and recovery

29 November 2015

Lee Aiken describes a project to maximise the operational efficiencies of remote mixed-fuel tank access and contents management using advanced sensor technologies.

A diagrammatic representation of Temposonics magnetostrictive sensing technology

As the pressures being exerted on the world’s energy reserves continue to increase, the importance of making good use of what is already available and safeguarding against wastage is being further underlined. It is estimated that in the UK alone the cases of motorists incorrectly fuelling their vehicles (filling a diesel vehicle with petrol, or vice versa) results in the generation of approximately 7.5 million litres of contaminated fuel each year. This fuel, along with that claimed back from other places, can be processed and then resold again - thus satisfying a respectable proportion of the market’s ever-growing demands.  

Dealing with several millions of litres of fuel every year, Refuels Limited is the largest mixed fuels recovery business in the UK, with a complement of twenty sites located nationwide. The company is involved in numerous activities that concern the collection and re-purposing of fuel. There are a multitude of different sources of this fuel, such as workshops, garages, car dealerships, end-of-life vehicle centres and roadside assistance units, as well as mobile fuel evacuation operators.

In order to improve its efficiency levels and boost profitability, Refuels recently looked to upgrade its operational support capabilities. Working in collaboration with software provider InfoSoft NI, it set about deploying a fully automated asset management system, which would give the team at Refuels greater visibility of the company’s fuel inventory.

There would be a steady stream of detailed information on the volume of fuel being stored at each site, the quantities being offloaded at a particular time and by whom. All users would need to be authenticated, via a transponder tag, before being able to deposit fuel into one of the company’s tanks. The system would also flag if any of the tanks were reaching full capacity.  

As the storage tanks at Refuels’ decanting depots are generally in remote locations, connection to the power grid simply would not, in many cases, be a viable option. Energy would therefore have to be supplied via battery banks connected to arrays of solar panels. This would ensure that uninterrupted operation was maintained without the risk of system downtime.

By amassing the data from each solar-powered measurement unit, this system would be able to cover the company’s expansive network of facilities across the country, enabling continuous monitoring of the fuel stock in real time. The level sensor apparatus inside the storage tank at every site would be connected by a secure Internet feed to a cloud-based Web portal.

In particular, the specified sensor system had to be exceptionally reliable and offer a high degree of repeatability. Moreover, as it would be situated in hazardous, potentially explosive environments, it needed to comply fully with the ATEX industry standard.

MTS Sensors was chosen to supply the liquid level transmitters - in this case, the company's Level Plus Model MG, as it was deemed to be the most appropriate for this particular application. This high precision level transmitter is optimised for bulk liquid storage applications, proving simple to incorporate into storage vessels of all shapes and sizes.

Specific benefits of the model MG are its high level of accuracy and the ability to provide not only level but also volume and temperature measurement. The accuracy of the level transmitter is important, ensuring inventory and billing records are precise and that each disposal is only charged for its precise volume of reclaimed fuel. Gross and net volume are provided directly from the level transmitter so there is no need for additional conversion electronics that would otherwise contribute to battery drain at these remote locations.

The MG transmitter features a Modbus RTU interface over RS485 that is capable of integrating with most control systems. The transmitter offers ±1mm inherent accuracy for level measurement, as well as ±0.1°C temperature accuracy. It is available with different hazardous area approvals, including ATEX, FM, CSA, KC, INMETRO, CCoE and IECEx.

With product level, interface and temperature measurement all available from a single process opening, multiple items of instrumentation are no longer needed; the associated costs, as well as the time and effort involved in integrating the sensor system are thus significantly reduced. And thanks to the built-in volume calculation function, the quantity of liquid present can be ascertained rapidly without the need for complex algorithms. In this application it was possible to ascertain the contents of 15,000 litre tanks to within a margin of 2 litres.

The model MG level transmitter function is based MTS Sensors’ proprietary Temposonics - an advanced form of magnetrostrictive technology suited to deployment in the most challenging of working environments. Temposonics based sensing devices enable position to be accurately determined through the momentary interaction between two magnetic fields. One of these fields is generated by a movable permanent magnet housed in a float that passes along the outside of the level transmitter, while the other is generated by a current pulse being applied along a ferromagnetic waveguide that runs parallel to the direction in which the permanent magnet travels.

When these two magnetic fields interact with one another a sonic torsion pulse is created. This passes through the waveguide and is detected by the sensing element. By precise measurement of the time period between the current pulse being applied and the torsion pulse being received it is possible to derive an exact value of the distance to the movable magnet. As the output from sensors employing this technology corresponds to an absolute position rather than a relative value, recalibration can be avoided.

Once the asset management system (along with its many constituent MG level transmitters) had been implemented, Refuels was in a position to gauge the ongoing status of its fuel resources with great accuracy. This would in time translate to increased productivity, lower overall running costs, reduced losses and more accurate billing of its customers.

Lee Aiken is with MTS Sensors

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