Blending role for compact pump

Blackmer sliding vane pumps supplied by AxFlow have been given the thumbs up for a bio-ethanol blending application at sites in the Midlands and South East



At the start of 2010 fuel suppliers in the UK became obliged to ensure that a certain percentage of all fuel sold on their forecourts contains a minimum of 5% biofuel. In the run up to this deadline, most suppliers were forced to upgrade their handling, storage and blending terminals in order to cope with changes in fuel blends.



In 2008 AxFlow was invited by Stopford Projects, specialist in engineering design and project management in the processing industries, to recommend pumps to be used in tank offloading, blending bio-ethanol into gasoline, and road tanker loading in the upgrade of terminals at customer's sites across the Midlands and South East.



The original briefing called for rotary twin screw pumps.



These would have been the final choice had AxFlow not pointed out the work it had undertaken on a similar project where Blackmer sliding vane pumps were proving successful.



AxFlow explained that its Blackmer X and MLX positive displacement pumps had an international track record for completely offloading tankers and could dry run for short periods in a hazardous area. Also, because it is a compact pump which uses a small motor it lends itself to the confined space allocated to the blending and loading terminals. The Blackmer pump is widely used in the petroleum industry for handling clean, low viscosity fluids and will satisfy low net positive suction head (NPSH) requirements.

For the bio-ethanol blending part of the project, Stopford projects needed pumps that could provide a flow of between 7 and 67m3/h and be capable of providing 5% ethanol for the accurate blend. The bioethanol is injected in front of the gasoline stream header and because the gasoline line pressure does vary it is important to keep a differential between the ethanol injection pressure and the gasoline. To maintain a higher pressure, the Blackmer pumps were set to operate at 11 bar. Once blending has taken place, the fuel is transferred to road tankers for distribution.



To optimise performance and resources, tank off-loading, blending and tanker loading is normally performed on demand and with all operations being undertaken in a single area. This is because Ethanolblended fuel contains properties that make it difficult to transport and hold in storage.



Carrying out the blending operation as close to the loading rack as possible minimises the risk of the blended fuels being contaminated and prevents them from going out of specification. As a result of this, physical space for the pumpsets is limited making compact pumps that are capable of handling the poor viscosity products without premature wear an attractive proposition.

The Blackmer sliding vane pump operates by means of a number of vanes that slide into or out of slots in the pump rotor when the pump is rotating. Vanes move outwards from the rotor and ride against the inner bore of the pump casing, forming pumping chambers in the process. As the rotor revolves, fluid enters the pumping chambers from the suction port and is circulated around the pump casing until it reaches the discharge port where it is forced out into the discharge piping. This type of design is said to virtually eliminate slippage, so the pump's high volumetric efficiency is maintained at all times.

Because the self-adjusting sliding vanes continuously adjust for wear, sliding vane pumps are able to maintain their near original efficiency and capacity throughout the life of the pump.

The pump speed does not need to be increased over time, making the pump energy efficient.

Once set up, the Blackmer X and MLX pumps should not need adjustments for many years.

Following presentations from AxFlow, Stopford projects and its customer elected to go with the Blackmer sliding vane pump for all the sites and applications. Centrifugal pumps were also supplied for adding denaturant bio-ethanol at one of the sites. In order to comply with the requirements for IP15 rated ATEX zones, AxFlow offered a design modification for the Blackmer pumps which matched the original specification for a double mechanical seal arrangement.



AxFlow has now supplied Blackmer MLX and X series pumps for off-loading, blending and loading in a variety of sizes to satisfy the varied requirement of all the sites. The pumps are run intermittently according to the demands of each site. Stopford Projects reports that tanker loading will typically take 30min, depending on how many loading arms are being operated at the same time.

Initial feedback indicates that all the pumps are providing the levels of performance required on all the applications.



Maurice Worthington of Stopford says: "AxFlow was able to bring Blackmer's international experience in bio-ethanol to the table and it was this which helped to convince us, and most importantly, our client as to the suitability of the pumps."