Bottom loading of petrol tankers was first introduced into North America about 25 years ago as a more environmentally friendly, safer, cleaner and ultimately more economic method of loading road tankers compared to top loading. Bottom loading was introduced into Europe in the mid 1980s and is now the main method used for loading petrol. The spread of bottom loading has continued and now includes countries in South America, the Middle East, Asia, the Far East and Australia.
With the introduction of bottom loading came vapour recovery, in fact, vapour recovery can be looked upon as one of the main factors driving the change to bottom loading from top loading. This is because one of the main benefits is that it makes vapour recovery a far simpler and more effective process to achieve than with top loading.
Vapour recovery is necessary because the hydrocarbon vapours given off by the petroleum products, particularly petrol, are also known as VOCs (volatile organic compounds), and are considered to be pollutants having the following damaging effects:
* As local atmospheric pollutants contributing towards smog and haze that occur over cities.
* As 'greenhouse gases' contributing towards global warming.
* As toxic and carcinogenic substances, causing human health problems.
One of the main driving forces behind the adoption of bottom loading and vapour recovery has been the introduction of environmental legislation in many countries limiting the amount of pollutants such as VOC emissions that may be expelled into the atmosphere.
The European Union in 1996 introduced its own legislation to limit VOC emissions during the storage, loading, transportation and unloading of fuels. This legislation required the phasing in of vapour recovery systems to reduce emissions over a nine year period.
The introduction of the VOC legislation in the European Union was based on the following estimates of the amount of pollution occurring within member states.
* A total of 10 million tons per year of VOC emissions from petrol and solvents.
* 500 00 tons per year of VOC emissions, 5% of the total, occur during storage and distribution of petroleum spirit, the majority in urban areas.
* 200 000 tons per year of VOC emissions, 2% of total, occur during refuelling of vehicles, majority in urban areas.
The target reductions in emissions set by the new legislation in Europe are:
* To reduce the total pollution emissions by 80 to 90% over the next 10 to 15 years.
* To reduce emissions occurring during loading and storage at terminals to 0,01%w/w of the total throughput.
* To reduce emissions during loading and storage tanks at service stations to 0,01% w/w of total throughput.
In order to comply with this new legislation it was necessary for oil companies, terminal operators, transport operators etc. To complete the following tasks before 2004:
* Install bottom-loading arms with vapour recovery systems at all of the distribution terminals.
* Install vapour recovery units or alternative systems to process recovered vapours at the terminals.
* Modify road tankers and rail tankers to be suitable for bottom loading with vapour recovery at the terminal with vapour recovery at the service stations.
Emco Wheaton Bottom Loading Arm Systems has an API 'Dry Break' coupler, which connects onto an API adaptor fitted to the road tanker. All API couplers conform to the API code RP1004 to ensure compatibility ie that they connect, seal and operate correctly.
Emco Wheaton bottom loading systems are designed around the use of 100 mm bore pipes, valves and hoses. Loading rates for bottom loaders can be up to a maximum of 2300 litres per minute for 100 mm bore pipe systems. The maximum loading generation is specified to restrict generation of static electricity during loading.
The most common form of bottom loading arm is the hose loader, which has a simple robust construction that minimises the number of swivel joints required on each arm. The weight of the coupler and hose which are always full of liquid as the bottom loader is a 'wet line' system can be balanced by springs, air cylinders or most simply and commonly by counterweights.
A rack of loading arms can comprise of up to five arms containing different products which when correctly specified and installed will allow the arms to cross over each other for loading multiple products into multicompartment tankers.
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