NGL Terminals

Natural gas liquids (NGL) are the hydrocarbons recovered from natural gas during processing: ethane, propane, normal butane, isobutane and natural gasoline (pentanes plus). LPG is a narrower, specification-controlled product made up of propane, butane or their mixtures. That difference drives everything else at an NGL terminal. Two consecutive batches can differ in composition, density and vapor pressure, so a loading or metering setup designed around a fixed LPG grade cannot simply be reused for NGL.

NGL, LPG, LNG and CNG: related products, different engineering

Mixing up the abbreviations can lead to the wrong equipment rating or the wrong calculation standard. From a terminal perspective, the four products compare as follows:

What sets NGL apart from LPG in operation

·         Variable composition: The share of ethane, propane and heavier ends shifts with the source field, the gas plant operating mode and the season. Density and volume corrections cannot rely on a single fixed product definition.

·         Wider vapor pressure range: As ethane content rises, the bubble point pressure of the mix goes up. Pump suction, keeping the meter full of liquid and the tanker design pressure all have to be checked against the lightest expected composition.

·         Raw mix versus purity products: Unfractionated mixed NGL (Y-grade) usually goes to a fractionation plant, which separates ethane, propane, normal butane and isobutane for sale as purity products. A terminal is designed differently depending on which of the two it handles.

·         Component-based accounting: Sales of mixed NGL often settle not only on total quantity but also on how that quantity splits into components. Measured mass is combined with the compositional analysis of a representative sample to get there.

Metering and transfer requirements at the terminal

Established NGL measurement practice centers on mass, because mass handles variable density directly: either direct mass metering with Coriolis meters or inferred mass, where volume at flowing conditions is combined with density at the same conditions. The generalized volume correction tables used for crude oil and refined products exclude NGL and LPG, which have their own correction procedures. Samples of a pressurized liquid cannot go into an open container either; pressurized sample cylinders are needed to preserve the composition.

On the transfer side, closed loading and unloading, joint handling of liquid and vapor lines, emergency shutdown (ESD) and hazardous area classification follow a framework similar to LPG. The difference is that design pressures and safety settings are chosen for the full range of compositions the terminal expects, not for a single product.

Solutions in this section

·         Truck loading: Closed, controlled transfer of high vapor pressure mixes and matching the product to the tanker design pressure.

·         Truck unloading: Product acceptance at the plant inlet, sampling for composition checks and feeding the fractionator.

·         Metering skids: Choosing between mass, volume and component-based measurement and the skid components that follow.

·         Custody transfer metering: Contract-based calculation of quantity and component split, plus verification.

·         Loading and unloading skids: Pressure rating, liquid and vapor arms, ESD and the scope of a pre-assembled package.

·         Propane, butane and mixed NGL transfer: Running several products through shared infrastructure, product changeovers and recipe management.

How TLY Enerji contributes

On NGL projects, TLY Enerji can provide engineering support for selecting the measurement technology from process data, supplying Coriolis meters, density, pressure and temperature instruments, valves and pumps, PLC- and SCADA-based monitoring, and field installation, testing and commissioning. The scope of supply and the composition data behind the design basis are agreed for each project through the technical specification.

Frequently asked questions

Are NGL and LPG the same thing?

No. LPG is a product made of propane and butane and defined by a sales specification. NGL is a broader group that includes ethane, propane, butanes and natural gasoline, and it may be shipped as an unfractionated mix. As a result, NGL density, vapor pressure and composition can vary far more from batch to batch than LPG, and metering and safety design must cover that range.

Can NGL be loaded on a rack built for LPG?

It depends on the composition. A mix with a high share of ethane or other light components can exceed the rated pressure of the piping, the pump, the meter back-pressure setting and the tanker. Volume correction and commercial calculation methods also differ. Before converting a rack, the pressure ratings, safety settings and measurement method should be reassessed against the lightest composition the terminal expects.

Why does an NGL terminal need compositional analysis?

With a variable-composition product, density and vapor pressure cannot be assumed constant, and mixed NGL sales may require the quantity of each component. Measured mass is therefore combined with a chromatographic analysis of a representative pressurized sample. The analysis also shows whether a batch meets the limits for road transport and for the fractionation plant inlet.

Related pages

·         NGL truck loading systems: Where NGL loading departs from LPG: tanker design pressure, vapor line and composition-dependent fill limits.

·         NGL metering skids: Choosing mass, volume or component-based measurement for a variable-composition liquid.

·         NGL custody transfer metering: Component-based invoicing and verification.

·         LPG terminals: Terminal requirements for propane and butane with a tighter product specification.

·         Truck loading and unloading terminals: Fluid-independent overview of loading and unloading solutions.