Stage II Vapour Recovery
Petrol contains volatile organic compounds (VOCs), which evaporate inside the fuel tank of a vehicle and fill the air space above the liquid fuel. When a vehicle is refuelled, these vapours are forced out from the fuel tank by the incoming fuel and, unless controlled, escape into the atmosphere through the filler neck of the fuel tank.
Under EU Directives, the UK Government has committed the UK to reduce emissions of VOCs as they contribute to the formation of low level ozone, a major air pollutant, in both the UK and Europe. These targets are already being met.
So called 'Stage I' vapour recovery has been in place for a number of years at storage terminals and at filling stations, to recover vapours that would normally escape into the atmosphere during the filling of storage tanks. This and other measures have reduced VOC emissions from the distribution of oil products by 70% between 1990 and 2006 (Source DEFRA). This downward trend is continuing. Under the UNECE Gothenburg Protocol and the EU National Emission Ceiling Directive the UK has to reduce emissions of VOCs to less than 1.2 million tonnes per annum in 2010. UK emissions in 2006 were well below the target at 0.91 million tonnes per annum and have been on a downward trend since 1989. The emission of VOCs from the distribution of oil products was 3.6% of the UK total in 2006 and will continue to decline.
The introduction of Stage II controls will capture the majority of the VOCs emitted during vehicle refuelling with petrol at filling stations and, under the UK programme, is applicable to those sites with petrol sales greater than 3.5 million litres. These sites are are required to implement Stage II Vapour Recovery by 1st January 2010 (2012 in Scotland).
The European Parliament has adopted at first reading, on 5th May 2009, the proposal for a Directive on Stage II Petrol Vapour Recovery during Refuelling of Passenger Cars at Service Stations. The proposal had been agreed by Member States prior to the vote.
The new Directive will require the installation of Stage II petrol vapour recovery systems to be fitted to new sites, and those undergoing major refurbishment, with sales of petrol above 0.5 million litres per annum.
It will also require retrofitting of existing stations with an annual throughput above 3 million litres by 31st December 2018; along with new sites, and those undergoing major refurbishment, with sales of petrol above 0.1 million litres per annum situated under permanent living quarters or working areas.
The Directive also requires that capture efficiency limits be equal to or greater than 85%. Member States are required to comply with this Directive by 1st January 2012.
In addition, the in-service petrol vapour capture efficiency of Stage II petrol vapour recovery systems must be tested at least once per annum either by checking that the vapour/petrol ratio under simulated petrol flow conditions is in conformity with the provisions in the legislation or by any other appropriate methodology.
Please click here for a detailed briefing paper on Stage II Vapour Recovery during refuelling of passenger cars at service station.
Vapour recovery systems
The system likely to be introduced at filling stations in the UK is the Active Vapour Recovery (AVR) system.
Active Vapour Recovery system
When petrol enters the vehicle tank, the AVR system uses a vacuum pump to suck a corresponding volume of vapours back into a storage tank. Traditional AVR systems consist of a modified nozzle (series of small holes or annulus near the handle), a coaxial hose (fuel supply in the inner hose and vapour return in the space between the inner and outer hose), a vacuum pump (usually in the dispenser) and pipework to return the petrol vapour collected to the underground bulk petrol storage tank. Petrol vapour in the vehicle fuel tank headspace is drawn under negative pressure from the vacuum pump through the holes in the nozzle and up the gap between the outer and inner nozzles. From there it is returned to the site fuel storage tanks via the return pipework at the same time as petrol is dispensed.
Components of an open AVR recovery system include:
- A vapour recovery nozzle with an inner petrol nozzle as now surrounded by a second shorter pipe though which the vapours are collected
- A hose through which the collected vapours are returned to the pump (usually coaxial with the fuel supply line in the middle)
- A pipe through which the vapours are returned from the pump (this may be separate from the fuel line or may be inserted into the fuel line)
- A vacuum pump
- A system to control the ratio of the volume of vapour recovered to the volume of petrol dispensed into the vehicle tank.
Passive Vapour Recovery system
The Passive Vapour Recovery (PVR) system is essentially the same as the active system but with no vacuum pump in the vapour return pipe. This system relies on the petrol entering the tank to force the vapour displaced back to the underground site storage tanks. A rubber bellows/boot is used to provide a seal between the vehicle and the nozzle. This requires a good seal around the filler nozzle and the filler neck and a more cumbersome nozzle than in active systems, which adds considerably to the weight of the nozzle. This disadvantage makes the process of refilling vehicles less acceptable to the motorist and introduces a significant human error into effective performance of the system. Another disadvantage is the reported lower filling rate of fuel. The lower efficiency of these systems is not likely to make them the preferred choice.