Drax receives radars from VEGA

Sussex, UK - Electricity generation from biomass is a low carbon technology delivering significant carbon dioxide savings compared to fossil fuel generation.

The biomass co-firing facility enables the power station to receive, handle, store and process a variety of biomass materials. These are directly injected into Drax’s coal-fired boilers where they are burnt alongside coal.

The storage facility for the biomass is a key part of this process, to ensure it is kept at optimum condition before being used.

When compared to coal, biomass is lighter, it has fluctuating handling properties and generally much lower, variable bulk density. It therefore requires larger storage facilities and offers some different process challenges.

The feedstock products vary from forestry residues, or cultivated products such as Miscanthus and Willow, to agricultural by-products like straw.

The storage capacities for these products need to be large and stock rotation/retention time requires careful management, as the products need regular ‘rotation’ to avoid any degradation.

The construction of the silos can also differ greatly, with taller narrower and shorter wider designs, depending on material behaviour and materials handling schemes.

However, even with large silo sizes, the biomass typically only has a retention time of only 24-48 hours, before being sent to electricity production.

An important area of this fuel stock management is the level measurement. A non-contact technology is preferred on site, to mitigate the potential for fouling and wear.

VEGA have installed many non-contact radar level transmitters on biomass level measurements around the world, where they have a proven performance dealing with dust and filling noise.

At Drax, there are two 12,000m3 storage silos, around 27m high and 30m in diameter, and the biomass is brought in by rail. These are centrally filled by conveyor and emptied via rotary screw discharger at the bottom.

The size and throughput means the silos are being frequently fed into and discharged from giving an uneven product surface and the need for long range measurement.

VEGA have installed non-contact VEGAPULS 68 level radars for solids, working over a range of approximately 27m.

Two units are installed on each of these large silos, to give an average reading, as well as for dual redundancy level measurement of the biomass material.

They are mounted towards the centre of the silo, aimed down and slightly outwards, this is to measure at a point approximately at half the radius, to deliver a good average level reading over the surface profile.

Although the conveyor fill point is quite close-by, the units work reliably, regardless of the filling stream. There are no cross-talk issues with VEGAPULS radars, even with multiple units in the same silo.

For more information visit http://www.vegacontrols.co.uk/vegapuls_radar_index.asp