Palletised Cask Filling System

Fill to level bottle applications achieve accurate and consistent fill levels using a nozzle comprised of two concentric pipes. A filling nozzle with a concentric exterior return pipe on is inserted into the vessel. A slight negative pressure is created by the return pipe being vacuumed. Filling begins at maximum flow, when the liquid level reaches the return pipe the excess liquid is removed from the vessel and returned to the pre-filling holding tank filled a later point [6]. When the return pipe is extracting an equal volume as is being filled the process is stopped. This process leads to consistent fill level for high flow rate filling and due to the vacuum seal created the fill level can be set very close to the opening as overfilling is not possible. Applying this solution to cask filling would solve issues of splashing caused by fast filling however the volume filled according to the flow meter in series with the filling head would no longer equate to the filled volume. Measuring the volume extracted by the vacuum line would be inaccurate due to the pipe only being partially full [19] and weighing individual casks after filling is not possible due to the pallet. This inaccuracy in the filled volume is unlikely to satisfy HMRC requirements as mentioned. Due to the risk of the system being noncompliant and the complex control system required; excess liquid return systems will not be considered further.

 

Since fixed volume filling would not provide optimal cask usage, the cask fill completion will be dictated by liquid level in this system.

 

The issues experienced using pressure sensors as mentioned are to be eliminated as part of this design. The alternatives being investigated further are ultrasonic, guided radar and capacitive. Float and servo systems are unsuitable due to mechanical complexity, and unguided radar performs poorly when measuring through obstructions [20] such as cask ends.

 

Ultrasonic level sensing systems have been developed to monitor bottle fill level in vacuum systems similar to that described at the beginning of this page [21]. The advantage of the use of ultrasonic level sensing is the ability to measure the liquid level through a container wall [22] however for an accurate measurement good surface contact between the sensor and the container is required [23], given the irregularity of cask ends contact between the sensor and cask would be unreliable; cask ends are constructed of plank sections resulting in joints and some can be coated in flaking paint as coloured cask ends were previously used as a method of cask type identification. However an ultrasonic sensor which measures the fill level of sample casks after fill completion could be utilised to verify the liquid level is within the required distance of the cask end, and to optimise target fill level continuously after installation by minimising this air gap incrementally through control system feedback.

 

A capacitance level gauge requires specific calibration to the liquid which it is measuring. Given the system will fill both malt and grain whisky which have different capacitances the level sensor would require two calibration points and an ability to alternate between them. This would be complex and a potential source of error and inaccuracy it would also double the time taken for the calibration task during routine maintenance.

 

As a result the trial will be conducted using a guided radar gauge. Radar was excluded initially due to the large pobe diameters but a new sensor released by Siemens has a 21 mm diameter probe which is similar to capacitive gauges. Using radar also means the lance material will not affect the measurement accuracy as with capacitance there was a fear a conductive lance material could potentially interfere with the measurement accuracy.

 

If constant level measurement of both fluids is not possible with a guided radar probe a return to point measurement will be considered. However a cappacitive point sensor will be uses as the dielectric change associated with immersion form air to malt and air to grain is similar enough that a lower threshold setting would trigger effectively for either liquid.

 

Capacitence level sensing offers an attractive solution as the probes could potentially be integrated into the exterior surface of the filling lance [24] [25] this would allow continuous fill level monitoring and an infinitely adjustable fill completion level. However the requirement of seperate set points makes guided radar the most attractive. 

 

The completion level adjustment will be implemented through the control system logic by increasing or decreasing the distance from the probe end at which the filling system is given the completion command. This will allow continuous system optimisation post commissioning.