Our latest case study focuses on a project we recently carried out for a power station in Angola in central Africa. They were looking to improve tanker unloading at the site, and wanted a diesel fuel skid to help achieve an unloading rate of 1800L a minute, or US 480 gallons a minute.

What is a diesel fuel unloading skid?

Bulk deliveries of fuels, chemicals and liquid food products are usually transported by either road or rail. These are the most cost-effective and seamless ways to bulk deliver essential chemicals needed as part of a process or as raw materials for production.

When tankers arrive on site or at a main depot for filling or refuelling there needs to be an efficient way to load and unload these liquids in bulk – quickly, safely and with little wastage ensuring  containers delivering raw materials are stripped of all fluid.

This is where loading or unloading pumps come in. When these pumps are mounted on a common baseplate along with other accessories such as flowmeters, pressure transducers or switches and a control panel, the whole unit is called a pump skid.

The client in Angola wanted a new diesel unloading pump skid with an unloading rate of 1800L every minute, or US 480 gallons a minute. A diesel tanker can hold anywhere between 20,000 to 44,000 litres of liquid, or 5,500 to 11,600 gallons meaning our new diesel fuel skid would have to be able to empty a tanker in a timeframe of 11 to 25 minutes.

Key factors when specifying a diesel unloading pump skid

A number of different technologies can be used to unload diesel from road tankers. There are critical requirements to consider and these will determine which type of pump technology is best for each particular application.

•  Self priming

This is important if the unit is to be located above the tanker, and helps to ensure that the tanker’s contents are fully stripped.

•  UKCA ‘EX’ and ATEX rated

The ATEX rating system is a set of safety regulations established by the European Union. They ensure the safe use of equipment in areas where there’s a risk of explosion due to the presence of flammable gases, vapours, dusts or powders.

The UKCA 'EX' Certification is essentially the same as ATEX with the major difference that the products are certified to 'UK Designated Standards' by a UK government-appointed body for the 'EPS Regulations' (Equipment and Protective Systems).

Therefore when chemicals or fuels are pumped, the equipment specified needs to be correctly rated for the location for use and if it is to be located in an ATEX Zoned area, it must be able to contain any explosion, or not ignite any fluids or gases that may be present in that area.

• Viscosity handling

A fluid’s viscosity is affected by increases and decreases in temperature. Viscosity decreases with an increase in temperature, and the more viscous the fluid, the more sensitive it is to the temperature change. More viscous fluids will be more difficult to handle, reducing both flow and pressure. This makes it crucial that any pump specified can easily handle the liquid’s viscosity range without any loss of performance in both summer and winter or should changes occur to the fluids blend.

• Centrifugal pump or positive displacement pump

There are advantages and disadvantages to both types of technology. Centrifugal pumps have a lower initial investment cost and can produce high flows at a specified discharge pressure. Their power performance curves are generally a half-moon shape, with the highest pressure producing the lowest flow, and the highest flow giving the lowest pressure.

However, performance will reduce if pressure loss calculations are incorrect. In addition, centrifugal pumps do not normally self-prime unless this type of design is specified early on in the process. If the fluid contains entrained gas, or has a low boiling point – common in some refrigerants or chemicals, a side channel pump which has a low NPSH may be the most effective way of tanker emptying.

In contrast, a positive displacement pump has a higher initial cost, but performance is guaranteed and unaffected by changes in viscosity, temperature or discharge losses. A positive displacement pump performance curve is actually a straight line meaning when viscosity increases so does performance. Unlike a centrifugal pump, positive displacement pump flow is proportional to RPM and doesn’t reduce with pressure.

• System and pump protection

To ensure longevity and reliability, serious consideration needs to be given to system and pump protection. Steps that can be taken include incorporating anti-vibration mounts to prevent shock starts and stops from the units transferring to the connecting pipework.

In addition, integrated relief valves can be fitted to the pump for pump protection, along with pressure transducers or switches to stop pumps operating if discharge pressures exceed set limits.

Our diesel fuel unloading pump bespoke features

At North Ridge Pumps, we’re not tied to just one pump technology. Using our experience, we can specify the best pump for any application based on the lowest lifetime cost. We use our expertise to offer a bespoke solution - not something straight off the shelf.

For this specific diesel unloading pump application, we selected two NRBAL Rotary Vane pumps to be incorporated into the truck unloading skid supported by a range of tailor-made product features for this client. 

Manual or automatic operation

The diesel unloading pump skid we specified can be set for both. With automatic operation it starts or stops according to inputs or set criteria being met. Whereas manual operation means that the operator takes control of all functions.

In addition, both pumps were mounted on a common baseplate with anti-vibration mounts, a set of pressure gauges, integrated strainers and a safety relief valve for pump protection.

Bespoke control panel

Control panels on skid-mounted pumps are often customised to meet the requirements of the system and the application. They are essentially the brains and act as an interface between the pump and any connected pipework, obtaining feedback from inputs or sensors and following a predetermined course of action.

For this project, we designed, manufactured and integrated a 15Kw DOL (Direct Online) bespoke panel with the following specification onto the truck unloading skid:

• Integrated flow meter totaliser giving remote monitoring with hard-wired contacts for pump running, pump fault and flow 4 to 20mA via a splitter

• Phase Failure relay and motor protection to prevent pumps from operating if a phase is down or supply is out of symmetry. Plus an indicating lamp on the door to warn if phase failure has occured

• Two sets of control gear consisting of protection breaker, contactor and overload all rated to 15kw

• A beacon with green and red indicators mounted on top of the panel with green for pump running, red for alarm

• Supply of safety relay and terminals for a Newson Gale Road Truck Recognition (RTR) truck grounding device.

• Low pressure switches in relay logic to stop pump after a timed period

Flow rate totaliser and indicator

This enabled the operator to verify that the pump set was working as required, and it provides accurate measurement of the amount of diesel being transferred into the tanks.

Pressure transducer/switch 

This shows operators the pressure that the equipment is operating under, to ensure that there are no performance issues. 

If you have any application requiring the transfer, circulation or injection of any kind of liquid of any viscosity and aren’t sure which pump to specify, speak to North Ridge Pumps to see how we can help.