The Port of Immingham covers 1,230 acres and is the largest by tonnage in the UK, handling some 50 million tonnes every year. It can accommodate vessels of up to 130,000 tonnes, so maintaining full operation at all times is essential.

Whilst surface water build-up was not a major threat to the port's operations, it was seen as a recurring problem that had to be resolved. In mid-2015, Associated British Ports' (ABP) engineers called on the services of pump distribution and engineering specialist AxFlow Limited, asking them to devise a solution that would eliminate the build-up problem. AxFlow's proposal was to build a surface-mounted pumping station that would drain the interconnecting chambers and pump the water into the dock. 

Figure 1. The pumping station was positioned over the discharge pit.

AxFlow's technical support manager, Mark Redgrove, explains why the company decided on this solution. “The existing drainage system consisted of a series of underground chambers that collected the water which then drained into a main discharge pit on the lock side of the port. From there the water was discharged through the tidal flap located on a mud bank in the estuary. However, the tidal flap regularly silted up and clearing away the silt and mud had to be undertaken manually by divers,” says Redgrove.
Self-priming pumps
The new pumping station is positioned over the discharge pit and comprises two Warman WSP6 self-priming pumps, galvanised mild steel pipework, heated jackets for cold weather protection and a control panel c/w pulsar ultrasonic level control. “The discharge pit is approximately 1m2 so a surface-mounted, self-priming pump was selected as there was insufficient space in the pit to use submersible pumps,” continues Redgrove. “We also had to take into account the issue of pump maintenance, which is much easier with surface-mounted pumps. The decision to use Warman WSP6 pumps was made on the grounds that as the run-off water contains grit and solids that collect on the docks, this pump would easily handle them as they are not affected by solids.”
The Warman WSP6 heavy duty self-priming pump is equally at ease with clean and solids laden liquids due to its open type two-vane impeller. Suitable for applications across a broad spectrum of applications water and wastewater handling, the WSP has a differential head capability ranging from 3 – 42 m and can deliver flowrates from 10 – 700m3/h. The two-vane impeller is manufactured in a choice of cast iron or CD4MCu with the wear plate also made from cast iron and the casings are in ductile iron. It is this build quality that enables the pump to handle both clean and aggressive fluids, plus the solids handling capability is of a high level for this range.
Self-priming pumps are well-suited to any duty with a suction lift where ease of access to the pump is necessary for maintenance purposes. Whereas submersible pumps have the benefit of being primed by the liquid in which they are submerged, access can be difficult when maintenance is required.
The two 6-inch Warman pumps have been installed by AxFlow on the edge of the pit and have suction legs descending 7.5 m into the pit. The run-off water is pumped through 30 m of discharge pipework that takes the water away to a point where it drops into a dummy sluice, which is a small chamber that is parallel to the lock. It is connected to the lock and as the level of the water in the lock rises and falls, so does the dummy sluice. The water run-off passes out of the dummy sluice, into the lock and enters the estuary when the lock gates are opened.
Figure 2. Installing the suction legs into the 7.5 m deep pit.
The discharge pit has the capacity to hold between 6- and 7 m3 of water, and once it is empty it soon fills up as water from the interlinked chambers drains into it. The design flow is 200 m3/hr, which provides the dock with plenty of surplus capacity, with emptying times of between four and five minutes. Once the chamber is empty it can fill up relatively quickly depending on the rainfall. Due to the fluctuations in the volume of surface water run-off, the pumps are not operating continuously. The pumps are on duty/standby configuration so that both pumps share the workload. When one pump has run for a period, the ultrasonic control system will switch operation to the standby pump which then becomes the duty pump. Should there be very high rainfall both pumps can operate at the same time to keep the flowing at optimum capacity.
AxFlow has undertaken a number of pump projects for Associated British Ports over the years. “This is not our first project at the Port of Immingham,” says Redgrove. “Back in 2014 we were asked by ABP engineers to produce a pumping solution for emptying a grit chamber in a settling pit at the coal terminal where the water separates out from the grit. We installed two sets of 4-inch submersible pumps and these have worked very well.”
The new surface water pumping station was commissioned in early 2016 and Mark Redgrove says that initial reports received indicate that the surface-mounted pumping station is working successfully.