Life at the limit: Antarctica’s pumping challenge

Cat pumps are playing a key role in an Antarctic hot-water drilling project that aims to discover the potential origin of life on Earth

Britain’s garden centres represent a disparate contrast to the hostile environs of Antarctica but a meeting in one of these horticultural hubs has enabled plans for one of the most ambitiousdrilling projects ever to take place.

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Over a pot of tea, British Antarctic Survey’s (BAS) Andy Tait and Cat Pumps’ Brian Hubbard sat down to discuss the pumping requirements for a project that will sink a borehole through 3km of ice in order to retrieve water and sediment samples from a sub-glacial lake in Antarctica.

Samples returned from the lake are likely to yield data regarding the potential origin of and constraints for life on Earth. This in turn could inform debate surrounding the evolution of life beyond Earth.

Dr David Pearce, science co-ordinator at BAS, believes that finding nothing will be even more significant because it will define limits at which life can no longer exist on the planet.

BAS’s Lake Ellsworth Programme starts hot-water drilling this December and over three days the team will force a 360mmdiameter borehole through ice resting at -20ºC.

The team will then have 24 hours to access the lake before the borehole refreezes.

To get through the ice, water will be continuously supplied at 90ºC and pumped at a pressure of 2,000lb/in2 using three positive displacement triplex pumps from Cat Pumps with a fourth on standby if required.

Other parts of the system comprise a 5m-long water-sampling probe and percussion-driven piston sediment corer, plus three 30,000-litre tanks that will hold melted ice water, a four-stage filter stage system, a heat exchanger in a 1.5MW boiler and the drilling mechanism itself.

Hot-water drilling is not a new method of boring through ice, but at 3km deep this will be the deepest borehole made this way. Added to the challenge is the requirement for none of the equipment to contaminate the lake, which is why BAS has chosen a four-stage filtration system to filter down to 0.1 micron.

‘Post-filtration we’re using two ultraviolet (UV) units to kill any organisms in the water itself,’ said Tait, hot-water drill project manager. ‘Our starting point is very clean water because we’re using the ice – the ambient ice – that’s around anyway. The amount of contaminants that we expect to find in there… is very small, if anything at all.’

Finding nothing will be even more significant because it will define limits at which life can no longer exist on the planet

Dr David Pearce, BAS

An additional weapon against contamination, designed and developed by Cat Pumps, involves a seal barrier system inside each pump.

‘Andy explained the problem: that they needed to keep the liquid inside the system as sterile as possible so they don’t contaminate the samples they’re removing from the underground lake,’ said Hubbard, general manager at Cat Pumps. ‘We have this facility in our pumps where we can put an isolating liquid between the atmosphere and the liquid that’s actually in the pump. Using an inert or sterile liquid in that space should prevent any cross-contamination from the surface-level atmosphere and the water in the lake.’

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Water for the drilling will be produced in the three holding tanks. The team’s 1.5MW boiler will be used initially to melt ice to form water, which is then drawn from the tanks and passed through the filtration system and the UV. Tait said: ‘The water is then taken from that and fed through a heat exchanger in the boiler, which will then produce water at 90ºC. That is then fed into the bank of Cat pumps and boosted up to 2,000lb/in2.

‘We have water exiting at 90ºC and 2,000lb/in2 at 210 litres a minute and that will be connected to the main hot-water hose, which is 3.4km long. That is then fed to a hot-water drill on the end of the hose that comprises a heavy brass section and… a stainless steel nozzle array. We have a single facing nozzle on the end of the drill and we also have an annulus, so it sprays a curtain of water at 90º to the main jet itself.’

A return system ensures recycling of the water, which is facilitated by the drilling of a secondary hole using a borehole pump with a similar hot-water nozzle arrangement.

‘We drill down 300m from the snow surface and we create a cavity,’ said Tait. ‘That cavity will be connected between the borehole – with the borehole pump in – and the main drill hole itself. The cavity will connect two holes together to allow water to be drawn back up, pumped up through an umbilical back to the holding tanks.

Using an inert or sterile liquid in that space should prevent any cross contamination from the surface-level atmosphere and the water in the lake

‘Once we’ve connected the main hole to the cavity itself we will then start the drilling all the way down into the lake.’

Equipment for the project was delivered 1.7km from the actual drill site in January this year and the pumps will operate from containers at 10ºC ambient. However, the pumps will have also had to withstand temperatures as low as -50ºC while in static storage.

Prior to shipment, Cat Pumps commissioned a cold soak test, which subjected a model 3521 pump to temperatures down to -50ºC for 24 hours.

‘We did the -50ºC test in a cold chamber in a laboratory to make sure the pump could withstand being frozen down to that temperature and then warmed back up again, which it did. Once it had warmed back up again we ran the pump and it was in perfect condition,’ said Hubbard.

Hubbard was also on hand to solve another problem that occurred in Britain.

‘We actually had a reasonable amount of vibration on the system and we had quick-release fittings connecting the water hoses, which had a series of ball bearing on the quick releases,’ said Tait. ‘The bearings were starting to pit around the external fittings. Brian suggested putting damping units onto each of the outlets of the pumps, and that drastically improved the system.’

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