Multistage Muscle: Driving Diesel Transfer with Precision

North Ridge Pumps recently delivered four heavy-duty horizontal multistage pumps to meet diesel transfer operations at 30 bar pressure and 1000 litres/minute flow rate. The heavy-duty pumps were delivered in bareshaft condition for interfacing with customer-installed motors and foundation plates. The installation is part of a bigger plan to switch from heavy fuel oil (HFO) to diesel in a large thermal power station.

This installation emphasises the paramount significance of high-pressure pumps in energy systems, where efficiency and reliability over a long period, and above all, performance are of utmost concern.

How high is 30 bar for pressure?

If a pump is 30 bar, that is high compared to domestic systems, which are below 6 bar. At industrial levels, 30 bar is usually the norm for what is deemed the performance of a high-pressure pump.

All the same, pressure requirements are always relative to the use. Some operations within the chemical, oil and gas sectors, not to mention sophisticated applications like hydro-demolition or waterjet cutting, can call for hundreds or even thousands of bar. Based on that, 30 bar is low, but that is still a significant requirement for diesel transfer operations.

Multistage pumps have no problem reaching and going over this level of performance, depending on the numbers of stages, while gear pumps are typically only in the region of 50 bar.

In what way is HFO different from diesel?

HFO (heavy fuel oil) is a heavy, residual fraction of crude oil distillation. It has a high sulphur content, requires heating for pumping and storage, and has been used historically to fuel large ship and power station engines.

Diesel, by contrast, is lighter processed petroleum fuel with significantly reduced sulphur levels. It is found across much of transport, agriculture and industry, will pour at normal room temperatures and does not require specialist warmed-up storage.

Why would a power station switch from the use of HFO to diesel?

The move from HFO to diesel in power generation can be driven by several operational and strategic reasons:

• Environmental compliance: ULSD reduces sulphur dioxide emissions by more than 99% and particulate matter and CO₂ emissions by up to 70%, both improving efficiency and air quality.
• Fuel cost and availability: While HFO might be cheaper, changes in price or unreliability make diesel the more reliable and cheaper option.
• Operational flexibility: HFO must be preheated to remain fluid and avoid viscosity issues, whereas diesel flows naturally without heating even during low engine loads.
• Engine performance: Diesel allows for more thorough combustion, avoiding cold spots, poor atomisation and incomplete burn which can occur in HFO. This means higher efficiency and dependability.
• Availability: In remote or inland regions, it is difficult to receive a consistent supply of HFO, but diesel is available.

Overall, diesel offers a cleaner, more flexible and more reliable source of fuel for power plants that require efficiency and fewer emissions.

Single-stage and multistage pumps

For the project, four horizontal multistage pumps were supplied by North Ridge Pumps to satisfy the pressure and flow rate required.

• Single-stage pumps consist of a single impeller and are most suitable for lower-pressure applications.
• Multistage pumps consist of multiple impellers in series, with the pressure added at each stage progressively. They are very efficient for applications involving high pressure and flow.

Advantages and applications of multistage pumps

Multistage pumps are specifically designed to create high discharge pressures economically and reliably. Some of the significant advantages are:

• Energy efficiency: They use less energy to deliver high pressure compared to single-stage alternatives.
• Compact footprint: Vertical multistage configurations save valuable floor space.
• Versatility: Can handle varied fluids in a wide range of industries.

Applications include:

• High-pressure fluid transfer in oil and gas, chemical industries
• Pumping water long distances or to high-rise buildings
• Industrial cleaning and high-pressure washing applications
• Supplying feedwater to high-pressure boilers
• Reverse osmosis in desalination plants

Why use horizontal multistage pumps for diesel transfer?

The project brief called for four diesel transfer pumps heavy-duty with 30 bar and 60 m³/h fuel transferring capability. The requirements were clearly defined: efficiency, low maintenance, direct drive by the motor without a gearbox.

Diesel was quite low in viscosity, making horizontal multistage designs feasible for it, which have good pressure capacity handling and convenient maintenance access.

North Ridge Pumps also provided flexibility through:

• Variable speed drives for optimal energy efficiency at different duty points
• Double impeller sizing for top efficiency at the intended operating levels
• Rotatable discharge and suction flanges for ease of installation with existing pipework

A multistage pump with eight ring stages

All four diesel transfer pumps were specified with eight ring stages. These are composed of an impeller, suction and discharge diffuser. Staged in series, these deliver the 30 bar pressure and constant 1000L/min flow rate required.

This design not only meets the client's performance specifications but also guarantees long-term reliability in the adverse thermal power operating conditions.

North Ridge Pumps – engineering know-how

With more than 25 years of experience in industrial pump design and manufacture, North Ridge Pumps brings tested and proven skills to every project. Solutions are tailored to the customer's duty specification with regard to efficiency, reliability and cost of ownership.

For applications such as diesel transfer, our multistage pumps for high-pressure applications provide a robust and adaptable solution, providing reliable performance and reduced downtime.