Submarine survival technique

A technology that removes carbon dioxide from air in submarines without the use of power could help save lives in an emergency.

A technology that removes carbon dioxide from air in submarines without the use of power could help save lives in an emergency.

Reactive polymer curtains (RPCs), thin polymer sheets that use a chemical reaction with lithium hydroxide to remove CO2, would be hung around the submarine when the power had been shut down. Usually mechanical extraction units would be used for the job.

Fluid mechanics specialists at Frazer-Nash Consultancy recently evaluated the technology for the MoD. George Tebbutt, project leader, said the chemical used in the RPCs has worked in numerous other applications before submarines.

‘It’s an existing technology that is used for diving applications and mining,’ he said. ‘It’s what NASA uses to control CO2 on space ships.’

Tebbutt said the company was asked to use its expertise in computational fluid dynamics (CFD) to map patterns of airflow throughout compartments of the submarine and predict whether RPCs would effectively remove CO2.

The RPCs were first tested by the MoD in a dive chamber and specialists at Frazer Nash took those tests results and verified them with CFD. ‘In a subsequent project we created a CFD model, which placed the RPCs into a submarine compartment,’ he said. ‘The model included the crew, so their respiration and the energy they produced were taken into account.’

The benefit of the models, Tebbutt said, was they were able to identify where CO2 levels were likely to build up and fall depending on the position and quantity of RPCs. He said this information will be useful for drawing up guidelines on the use of RPCs in emergencies.

Current carbon absorption units remove CO2 by constantly circulating air through a scrubber system filled with soda lime. The system is DC powered from the submarine’s main battery. If the main battery dies, seawater-activated batteries provide back-up power. These batteries use seawater as an electrolyte.

Tebbutt said the Royal Navy was interested in finding a passive system that did not require power. ‘When reviewed by the MoD, this new product showed it had better performance, usability and portability,’ he said.

The CFD models have validated RPCs based on a T-class submarine compartment and Frazer Nash is preparing to carry out a similar study for Vanguard class submarines. ‘The research is an important step forward for the development of submarine safety systems, helping to improve the efficiency of a vital piece of survival equipment,’ said Tebbutt.

‘If called upon in an critical situation, RPCs could provide a valuable lifeline for submarines, ensuring breathable air by effectively removing CO2.’ He added: ‘Having developed and validated this new approach to simulate the CO2 concentration and chemical reaction, we now plan to use this to assess further situations and similar scenarios in the future.’

Siobhan Wagner