Blackmer sliding vane pumps for bitumen emulsion transfer duties

For approximately six months of each year, typically from April through to the end of September, the UK's road resurfacing industry steps up into top gear as weather conditions become most suitable for the application of bitumen and emulsion.

For Nynas Bitumen's Eastham plant at Ellesmere Port in Cheshire, demands for its road surfacing products soars during this period and the pressure is to provide customers with a steady supply of product increases substantially. Transferring products from bulk holding tanks to road tankers demands pumps that are not only capable of handing the liquid but are also wholly reliable to ensure that products are readily available on demand. And that's where AxFlow's Blackmer vane pumps come into the picture.

Nynas Bitumen's core business is making bitumen emulsion and hot bitumen that has been modified either with polymers or oil to make harder wearing flexible products to satisfy specific requirements that are over and above straightforward bitumen.

In order to capitalise on the changes taking place in the market and optimise its production assets, the plant went over to 24/7 production July 2007. Optimised production has been achieved by effectively slowing down the batch production process so that the blend time in the pots keeps the machines running for 24 hours. Even though running at a slower level per hour Nynas is producing more products over a 24 hour period.

There are two separate companies operating two distinct areas at the Eastham site, these being Eastham Refinery Limited (ERL) and Nynas UK AB. ERL takes the crude oil and processes it to make bitumen and other products. They also load products to vehicles on their own gantry. Nynas takes bitumen from ERL and further process it to make their own range of products which they load on to vehicles at their own gantry area.

When ERL first receives the crude oil product the bitumen content is already at 70%. ERL takes out everything that is not required for the finished product, this process involving distilling the crude using an atmospheric column and a vacuum column to remove the light ends so a heavy residue is all that remains. The Nynas process makes the bitumen emulsion user friendly so that it can be transported to its place of use typically at a temperature of 80-85ºC.

Supplied by AxFlow Limited the Blackmer P Vane pumps were first introduced at the plant in 2001 on the recommendation of Project Design Engineers (PDE), Antrim. Previously, the vehicles at Nynas were gravity loaded, i.e. no pumps were involved. Nynas chemists expressed concern in respect of shearing problems with some of the more complex bitumen emulsion blends, therefore sliding vane pumps were considered. Emulsions do not like shearing as it has an adverse effect on the viscosity of the product.

PDE had previous experience using Blackmer sliding vane pumps on hot bitumen blending and therefore suggested using them for bottom loading of this emulsion at Ellesmere Port. Two Blackmer NP4 sliding vane pumps fitted with packed gland shaft seals were initially installed for transferring emulsion at up to 90ºC and they have worked satisfactorily since installation. Since then two further pumps have been installed on additional loading gantries, one of which is a stainless steel version SNP3 due to the corrosive nature of the product. In order to meet the 24/7 production capability, additional Blacker sliding vane pumps are being installed. The other operates on hot bitumen service.

These pump types feature a number of vanes that are free to slide into or out of slots in the pump rotor. When the pump driver turns the rotor, centrifugal force, push rods, and/or pressurized fluid causes the vanes to move outward in their slots and rub against the inner bore of the pump casing forming pumping chambers. As the rotor revolves, fluid flows into the area between the vanes (pumping cambers) when they pass the suction port. This fluid is transported around the pump casing until the discharge port is reached. At this point the fluid is squeezed out into the discharge piping. AxFlow reports that these pumps are designed to handle clean, non-corrosive industrial liquids and petroleum products and typical applications include fuel oils, lube oils, aviation fuels, edible oils and a variety of solvents and thinners.

Nynas uses one Blackmer sliding vane pump in the finished bitumen products loading area and it has a role to play in loading the road tankers. A further two are used on a fixed mill application taking the bitumen product from the large tanks through a meter for loading onto road tankers. There is currently one hot binder loading system with a pump drawing from three tanks. All the operator has to do is to select the tank required and enter the volume required. At the end, the operator reverses the pump.

The added benefit of the pumps is that they can be reversed for a short period, enabling Nynas to clear the pipeline work. Reverse pumping the products back through the lines prevents the swivel joints on the loading lines from seizing up. In addition, where the single pump is taking separate product from three different tanks, product in the lines can be pumped back into the tanks thereby reducing the possibility of product cross-over.

Currently there are three emulsion loading systems on the site, each fitted with one pump. Two of these systems draw from three separate tanks, with the third drawing from one tank.

For the three emulsion tanks the loading line was initially equipped with one on-line pump, but an additional pump is scheduled for installation in order to meet a requirement for increased capacity and to act as a standby pump unit. Although the earlier pumps were fitted with packed glands, for the hot binder pump it was decided to trial a flushed mechanical seal for higher integrity. This has proved successful and all future pumps will be fitted with similar seals.

The installation of the emulsion loading facilities led to the introduction of sliding vane pumps for bulk liquid transfer at the plant and these have proved to be a successful answer to what can be a challenging duty, given the nature of the products. The design of the pumps means that maintenance is low and operators at the plant only need to carry out vibration and sealing gland checks. At the end of the production season the pumps are given a short flush and steam clean before shutting down for the winter.