FULL contact internal floating roofs and dome roofs for Methanol storage tanks
In 2007 CTS was contracted to supply 3 aluminium domes and 3 direct contact internal floating roofs for 3 new Methanol tanks under construction at the Odfjell Terminal Rotterdam (OTR).

Requirements of the storage tank industry are getting more and more stringent. To meet these requirements OTR and other tank owners are constantly looking for methods to comply with the increasingly demanding legislation and to safely and effectively operate their tanks. To achieve this OTR has equipped the new Methanol tanks 930, 931 and 932 (tank diameter 42.67m) with aluminium domes and aluminium full contact internal floating roofs supplied by CTS. This where OTR has operated 7 aluminium dome roof tanks already since more than 15 years, where these domes were constructed over than already present steel external floating roof tanks to store water sensitive products in these tanks such as Methanol, Ethanol and MTBE.

This combination of aluminium domes and internal floating roof for the 3 newly built tanks has significant advantages over the more traditional steel external floating roofs or fixed steel roofs covering an internal floating roof.
The main advantages of this tank configuration are:

• Low maintenance cost. Due to the materials used the dome roofs do not require any maintenance such as blasting or painting during their entire service life, which well exceeds a minimum expected lifetime of 40 years
• Lower emissions. The combination of an aluminium dome and full contact internal floating roof will reduce the emission from these tanks with a minimum of 97% compared to a reference tank, as is a mandatory requirement by the most stringent European emission legislation (BREF Storage tanks, by IPPC – 2005) and local authorities
• Eliminate weather influences. By covering the tanks completely the influence of wind, rain and lightning is eliminated. This reduces or eliminates product emissions, product contamination by rain water and the risk of rim fires
• High reliability. As an aluminium dome requires no maintenance, and an internal floating roof configuration has no drain line configuration this tank design is much more reliable than other available atmospheric storage tank designs
• Wide range of products to be stored. The range of products to be stored in these tanks is extended with (bio-)fuel related products such as alcohols, ETBE and MTBE. The used anodised aluminium for the internal floating roofs guarantees product compatibility for a very wide range of products.

Tank emissions:
Reducing emissions of volatile organic carbons is of great importance for modern tank terminals, and OTR is committed to realising a maximum emission reduction for all tanks operated, but definitely for new tanks built. When calculating the emissions for the different tank types, based on 12 turnovers per year the following are the results:

The comparison above is made between the supplied dome and full contact aluminium internal floating roof with liquid mounted shoe plate seal against a standard steel fixed roof tank with no further emission reduction measures in place. Under IPPC BAT requirements reducing emissions significantly beyond initial reductions is becoming more and more important. Using domes with internal floating roofs results in significant emission reductions and is classified as BAT (Best Available Technique) for reducing VOC emissions (calculations were made for Methanol on a basis of 12 annual turnovers).

Building the domes and internal floating roofs
The domes have been built inside the tank by CTS. The domes were completed in less than 4 weeks and lifted on the tanks with a mobile crane with a capacity of 400 tons. The flight of the lift (over 40 meters from crane centre to the centre of the dome) required a large crane. Specialised lifting equipment as owned and mobilised by CTS was used to lift the dome safely onto the tank.

In the weeks immediately after completing the domes the internal floating roof were built underneath the dome, as this enables the construction of the internal floating roof independent from any adverse weather conditions.

Key facts and figures:
Each of these domes in a diameter of 42.67m weigh only 18,778 kg each. The dome frame only weighs 10,886 kg. The panels weigh 7,892 kg. Despite this low weight the domes are designed as per API 650 to withstand a 160 km/hour maximum wind speed and can bear an uniform live load of 25 psf across the full roof (1,197 N/m²), resulting in the dome being able to bear an additional load of 171,171 kilograms (this besides its own weight)!

Construction schedule and materials
Each dome consists of the following parts:
- 420 Struts (representing the dome wire frame)
- 324 Panels (covering the dome frame)
- 420 Battens (securing the dome panels)
- 363 Gusset plates (connecting the struts)
- 6,557 Batten screws
- 14,912 Lock bolts
- 960 Bolts and nuts (conventional bolts)
- 1,978 Rivets
- 108 Tubes caulking

Safety and health during construction:
This project was completed without any safety incidents, or personal injury. This is accomplished by giving full attention and great care to all SHE-related aspects on this complicated project by all involved which include Odfjell and CTS staff. By means of this article we would like to congratulate them on this safe performance, and express our expectations for the project to be realised in a safe way within the time period available and required.