Chemical Technology August 2015

DESIGN AND MATERIALS OF CONSTRUCTION

Types of vaporisers Typical types of vaporisers that have been used worldwide for LNG regasification are: • Open Rack Vaporisers (ORV) • Submerged Combustion Vaporisers (SCV) • Ambient Air Vaporisers (AAV) • Intermediate Fluid Vaporisers (IFV) Open rack vaporisers (ORV) and submerged combus- tion vaporisers (SCV) are the most common vaporisation methods in existing regasification terminals, which have generally been located in the subequatorial region. Recent LNG receiving terminal activities have been shifting to the equatorial region where the weather is warmer, and the use of intermediate fluid vaporisers (IFV) is found to be more suitable. Important factors that should be considered in the LNG vaporiser selection process are: • Site conditions and plant location • Availability and reliability of the heat source • Customer demand fluctuation • Emission permit limits • Regulatory restrictions with respect to the use of seawater • Vaporiser capacity and operating parameters • Safety in design • Operating flexibility and reliability

pared to other sources of heat, and is the preferred heat source. The oppositions are concerns about the destruction of marine life within the seawater system and the negative impacts from the cold seawater discharge and the spent chemical disposal. Open rack vaporiser (ORV) An Open Rack Vaporiser (ORV) is a heat exchanger that uses seawater as the source of heat. ORVs are well proven technology and have been widely used in Japan, Korea and European LNG terminals. The common seawater tempera- ture for ORV operation is at least 5 °C. ORV units are generally constructed of aluminumalloy for mechanical strength designed to operate at the cryogenic temperature. The aluminum material has high thermal conductivity which is important for heat transfer equipment. The tubes are arranged in panels, connected through the LNG inlet and the regasified product outlet piping manifolds and hung from a rack (Figure 1). The panels are coated ex- ternally with zinc alloy, providing corrosion protection against seawater. The panel arrangement feature provides ease of access for maintenance. ORVs require regular maintenance to keep the finned tube surface clean. The ORV design is very flexible. The panels can be iso- lated for maintenance and heating duty can be adjusted as needed. The unit can be turned down to accommodate fluctuations in gas demand, gas delivery temperature and variation in seawater temperature. For large regasification terminals, detailed evaluation of the seawater system including future expansion must be

• Capital and operating costs. Seawater (SW) heating

LNG receiving terminals are generally located close to the open sea for ease of access to LNG carriers. Seawater is generally available in large quantities at low cost as com-

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Chemical Technology • August 2015