How to Size a High-Pressure LNG Pump for an L-CNG Fueling Station

To size a high-pressure LNG pump for an L-CNG station, start with the station’s required CNG delivery rate, convert that demand into LNG liquid flow, and select a pump that can supply the flow at the required discharge pressure. Then verify the pump’s operating range, suction conditions, motor power, vaporizer capacity, and expected duty cycle as one connected system. The correct pump is not simply the unit with the highest flow or pressure rating: it must meet your peak fueling demand at the actual system pressure.

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For a preliminary calculation, a station needing 300 kg/h of gas and using an assumed LNG density of 430 kg/m³ would require about 0.70 m³/h of liquid flow before design allowance. This is an illustrative calculation, not a universal LNG property or final equipment specification. Actual sizing depends on fuel demand, LNG composition and temperature, process losses, operating sequence, and the station’s pressure requirements.

Key Sizing Takeaways

• Size for the peak simultaneous demand and required fueling profile, not only average daily consumption.
• Convert mass flow to liquid volumetric flow using the project’s design LNG density.
• Confirm that the pump delivers the required flow at the required discharge pressure.
• Check suction conditions, motor power, vaporizer capacity, controls, and operating duty with the pump.
• Treat preliminary calculations as a basis for supplier review, not as a final equipment order.

Step 1: Define the Station’s Peak Demand

Use fueling demand, not just daily gas volume

Begin by establishing how much gas the station must deliver during its busiest operating period. Gather the expected number of vehicles, vehicle storage requirements, fueling window, dispenser count, and likely overlap between fueling events. Average daily consumption helps with operating and storage planning, but it does not by itself establish the pump’s required peak flow.

Where several dispensers may operate at the same time, calculate the combined demand based on the station’s real operating plan. Do not assume that every dispenser will always run at its maximum rate unless that is a defined design case. Conversely, do not size to an average that would leave the station unable to meet planned peak service.

Express demand as a mass flow

Use a consistent design basis, such as kilograms per hour, for the required gas output. If the available demand is stated as a daily total, convert it to an hourly profile that reflects actual fueling hours and peak periods. Include any operating reserve or future capacity only when it is supported by the project’s expansion plan and operating requirements.

Step 2: Convert Gas Demand to LNG Liquid Flow

An L-CNG system pumps LNG as a liquid to high pressure and then vaporizes it before delivery as compressed natural gas. For a first-pass pump calculation, convert the required LNG mass flow to liquid volume using the design density:

Liquid flow (m³/h) = LNG mass flow (kg/h) ÷ LNG density (kg/m³)

For example, if the required output is 300 kg/h and the project uses an assumed LNG density of 430 kg/m³, the calculated liquid flow is 300 ÷ 430, or approximately 0.70 m³/h. If a project team applies a 20% preliminary capacity allowance to this example, the working flow becomes about 0.84 m³/h. That allowance is illustrative only; the appropriate margin must be determined from the station’s demand profile, control strategy, and design criteria.

Use the LNG density specified for the project rather than treating one value as universal. Density varies with composition and temperature, and the pump, vaporizer, and controls should be reviewed against the same design basis. A supplier can check the conversion and operating range once the relevant LNG conditions are provided.

Step 3: Establish the Required Discharge Pressure

Determine the pressure the pump must provide at its discharge so the system can deliver gas at the required station pressure. Account for pressure losses through piping, valves, filters, the vaporizer, and other equipment between the pump and delivery point. Also confirm the station’s operating pressure range and any control requirements that influence the pump’s required differential pressure.

Distinguish between the required process operating pressure and the pressure ratings of the pump and connected equipment. The pump must meet the required duty point, while every component must be suitable for the applicable design conditions under the project’s codes and engineering specifications. Do not select a pump using only a nominal maximum-pressure figure; request its flow-versus-pressure performance for the intended configuration.

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Step 4: Match Flow and Pressure to the Pump

Review the complete operating point

Give the supplier the required flow and discharge pressure together, along with the LNG suction conditions. Ask whether the pump can maintain the required flow at the specified pressure and whether the duty point lies within the manufacturer’s recommended operating range. If demand varies substantially, assess the expected low-, normal-, and peak-demand conditions rather than checking only one point.

Confirm how the pump is controlled and how it responds to changing station demand. Start-stop frequency, bypass or recirculation arrangements, and minimum-flow requirements can affect selection and operating stability. These details should be coordinated with the station’s control philosophy rather than added after the pump has been chosen.

Check motor power and electrical requirements

A preliminary hydraulic power check can help identify whether the proposed motor size is plausible. Hydraulic power depends on liquid flow and pressure rise; actual input power is higher because the pump and drive are not perfectly efficient. For illustration, a flow of 0.84 m³/h with a pressure rise of 25 MPa and an assumed overall efficiency of 55% gives an estimated input near 10.6 kW using the hydraulic power relationship.

This example is not a motor recommendation. Final power selection must use the pump’s actual efficiency and operating data, the specified drive arrangement, and applicable electrical design requirements. Ask the supplier to confirm motor rating, starting method, control compatibility, and any project-specific hazardous-area or environmental requirements.

Step 5: Verify Suction Conditions and System Matching

High-pressure performance does not compensate for poor pump suction conditions. Provide LNG storage pressure, liquid temperature, suction pipe dimensions, elevation, fittings, filter arrangement, and any expected changes during operation. The pump supplier should review the available suction conditions against the pump’s requirements and identify any risk of inadequate inlet pressure, flashing, or unstable operation.

Check the pump as part of the complete L-CNG process. The vaporizer must be capable of handling the intended LNG flow and operating conditions, while downstream equipment must suit the required pressure and gas delivery profile. Controls, relief provisions, instrumentation, and shutdown logic also need to be coordinated by the project’s qualified engineering team.

Common Sizing Mistakes to Avoid

• Using daily demand as the pump duty: Daily volume can conceal short peak periods and simultaneous fueling.
• Choosing by maximum flow alone: A published flow figure may not apply at the required discharge pressure.
• Ignoring LNG design conditions: Density and suction conditions affect the conversion and pump operation.
• Adding an arbitrary oversized margin: Excess capacity may complicate control and operating stability; justify allowance against the actual design case.
• Considering the pump in isolation: A mismatch with the vaporizer, piping, motor, or controls can limit station performance.

What to Send a Pump Supplier

To make a supplier review useful, prepare a concise duty specification. Include required gas flow in kg/h, peak and normal operating conditions, target delivery pressure, LNG composition or design density if available, storage and suction conditions, ambient conditions, electrical supply, and the expected operating schedule. Add process drawings or a simplified flow diagram when available, and identify any future expansion requirement separately from the initial duty.

At Dongzhao, we recommend confirming the duty point and system interfaces before comparing equipment options. A supplier should be able to review the requested flow and pressure alongside suction conditions, drive requirements, and vaporizer matching. Ask for the applicable performance information and clarify which project inputs remain assumptions before finalizing a specification.

Conclusion: A Practical Sizing Sequence

To size a high-pressure LNG pump for L-CNG, first define peak gas demand, convert that mass flow to LNG liquid volume using project-specific density, and establish the required discharge pressure after system losses. Then verify pump performance at the combined flow-and-pressure duty point, followed by suction conditions, motor power, control behavior, and compatibility with the vaporizer and downstream equipment. The calculations above provide a screening method, not a substitute for project engineering or supplier confirmation.

Your next step is to assemble the duty specification and operating profile, then request a technical review against the intended station configuration. Dongzhao can discuss your L-CNG pump requirements and help identify the information needed to assess a suitable solution. Share your target capacity, pressure, LNG conditions, and project timeline to begin an application-specific inquiry.