Fire training unit diesil recovery plant - recycling and reducing discharge
Annual Conference
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New Zealand Defence Force (NZDF) operates a Fire Training Unit at the Sea Safety Training Squadron at the Devonport Naval Base, Ngataringa Bay, Devonport. The school utilises a fire simulation building in which trainees are required to enter and extinguish fires. To establish the fires, diesel is used as a fire propellant to ignite piles of wood and simulate a smoky fire in an enclosed structure.
While a portion of the diesel is ignited, most of the diesel is washed away with the firefighting water and foam before it can be burned. All fire fighting water is treated on site and recycled for reuse. As part of the water treatment system, the unburned diesel is separated out as an emulsified scum layer along with AFFF foam, water and ash. This scum layer was historically extracted and trucked away for further treatment as a special waste at significant cost to the NZDF. The accumulation of the scum layer in the water treatment plant, between extraction events, was causing contamination issues with the recycled water, limiting the ability to discharge to the sanitary sewer as a trade waste.
The initial project Brief was to improve the quality of the trade waste discharge from the training school, but once engaged by NZDF the effects of the diesel on the trade waste quality and resultant loss of a potential resource was identified and the Brief was changed to designing an improved system to remove and treat the emulsified scum layer and recover diesel for reuse in the fire training unit.
A pilot trial was conducted, using 1000 litre tanks, to establish the efficiency of gravity separation of the scum layer. On the basis of the pilot trial a three vessel fractionating plant was designed.
Tank 1 provides for two phase separation of free water from the scum layer. With a longer hydraulic residency time, Tank 2 allows for three phase separation of water, diesel and impurities (AFFF foam and ash). Tank 3 allows for further diesel purification with further water and scum separation. The refined diesel is then available for reuse. All separated water is returned for reuse and the collected impurities are stored for periodic disposal.
During the design phase, special consideration had to be given to the hazardous nature of the diesel and the hazard management requirements of the Environmental and Risk Management Authority (ERMA) and the internal requirements of the NZDF.
The full scale treatment system was installed and commission in February 2011 and has been providing a high recovery rate of good quality diesel, suitable for reuse in the fire training unit. While it is anticipated that new diesel will occasionally be required, in the six month period following commissioning, no new diesel was necessary for the fire training unit, over a period that would have previously required 10,000L of new diesel.
Overall the project has resulted in a net environmental benefit and has exceeded the initial project objectives in that it is now providing a complying trade waste discharge, while also reducing diesel usage and volumes disposed to special waste.