LNG Vaporizer (ORV) Product

Overview

An open rack vaporizer is the workhorse regasification unit of a baseload LNG import terminal. It converts liquefied natural gas stored at -162 °C back into pipeline-quality gas by exchanging heat with seawater — free, abundant, and warm enough at most coastal sites year-round. A single unit handles 180–200 tonnes of LNG per hour; a terminal lines up several with one or two on standby.

The unit is essentially a wall of vertical heat-exchange panels (Heat Exchanger Panel Bank) hung from a galvanized steel rack (Support Structure). Seawater is pumped to open troughs (Seawater Trough) along the top of each panel and overflows serrated weir plates (Weir Plate) to sheet down both panel faces as a thin falling film. Inside the panels, LNG rises through dozens of parallel finned tubes (Finned Aluminum Tube) and vaporizes against the warm film.

How it works

High-pressure LNG from the terminal's send-out pumps enters through the LNG Inlet Manifold, passing a fail-close ESD Shutdown Valve and a LNG Flow Control Valve before splitting into the Bottom LNG Header of each panel. The fluid is already above its critical pressure (4.6 MPa for methane), so there is no boiling in the ordinary sense: the supercritical fluid simply warms and its density falls smoothly as it climbs the tubes. By the Top NG Header it has become dense gas at 1–5 °C, which the NG Outlet Manifold collects into the send-out pipeline through the Outlet Isolation Valve.

The thermal duty is brutal at the panel bottom, where the tube wall faces -162 °C fluid inside and near-freezing water outside. Ice inevitably forms a thin sleeve on the lower 1–2 m of each tube; the star-fin extrusion profile of the Finned Aluminum Tube is designed so this ice stays thin and non-bridging rather than choking the water film. Heat flux runs around 30–50 kW/m² in the lower zone and tapers up the panel. The spent seawater, chilled by roughly 5 °C, falls into the Collection Basin and returns to the sea through an outfall sized to limit thermal impact.

Materials and corrosion

Aluminum alloy gives the panels the thermal conductivity and cryogenic toughness the duty demands, but bare aluminum corrodes quickly in chlorinated seawater. Every wetted panel surface therefore carries a flame-sprayed zinc-aluminum sacrificial layer (Zn-Al Thermal Spray Coating), typically 150–250 µm thick, renewed every 10–15 years when inspection shows thinning. Marine growth in the troughs and supply piping is held down by continuous low-level chlorination at the Hypochlorite Dosing Point point. Cryogenic piping upstream of the panels is TP304L stainless (Cryogenic Inlet Pipe) under cellular-glass Cryogenic Pipe Insulation; the warm side reverts to low-temperature carbon steel (Gas Outlet Pipe).

Control and protection

The controlling variable is send-out gas temperature. Three Pt100 elements (Outlet Temperature RTD) vote two-out-of-three: the control loop trims LNG flow to hold the setpoint, and a trip at -1 °C closes the ESD valve before cold gas can embrittle downstream carbon steel. Seawater flow is the slave variable, modulated by the Seawater Control Valve so the water leaving the panels stays above 0 °C. Send-out is metered by a multipath Ultrasonic Flow Meter, and four infrared Methane Gas Detector points watch the rack perimeter for methane. All signals marshal through the Local Control Panel to the terminal DCS and safety system.

Blocked-in cryogenic liquid expands ferociously as it warms, so every isolatable section carries a thermal relief valve (Pressure Safety Valve) discharging to the flare or cold vent via the Relief Vent Line. A Nitrogen Purge Connection connection allows inerting before maintenance.

Mechanical design

Cooldown from ambient to -162 °C shrinks each panel by roughly 25 mm, so the panels hang from sliding Panel Hanger fittings rather than rigid mounts, with Panel Stiffener Bar bars restraining lateral bowing. The rack itself (Rack Frame) is designed for the combined panel, water, and seismic loads and is bolted to the basin civil works through cast-in Anchor Bolt Set. Grated Access Platform levels give operators reach to the weirs, whose serrations are individually adjusted during commissioning until the falling film wets each face evenly — uneven wetting shows up immediately as asymmetric frost lines on the panel.

Variants

Where seawater is too cold (below about 5 °C) or intake permits are restrictive, terminals use submerged combustion vaporizers, which burn ~1.5% of the send-out gas, or intermediate-fluid vaporizers using a propane loop. ORVs dominate wherever seawater conditions allow because their operating cost is essentially the seawater pumping power, around 0.1% of the energy throughput.