Chemical Technology August 2015

Chemical Technology • August 2015

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

• 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-

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

DESIGN AND MATERIALS OF

CONSTRUCTION