The Design of Life Support Systems for Submarines (Military)
The Customer Issue
DCNS is a major export manufacturer of diesel-electric/hybrid AIP submarines and a major technology driver for Navy submarine manufacture.
During the trials of the boats for the Royal Malaysian Navy in December 2008, the performance of the CO2 removal units was found to be lower than required on this class of submarine.
The data recorded during the trials indicated that the maximum concentration of CO2 allowed on board would be exceeded in typical crew conditions.
Understanding the Issue
The information supplied by DCNS to Molecular Products Ltd included the results of the trials as well as the conditions for use: the total quantity of material used in each of the scrubbers, the internal volume of the submarine, the flow rate of the scrubber fans, standard respiration rate and crew numbers.
The data showed that DCNS had reduced the flow rate through the absorbers to optimize the system. It was their expectation that at lower flow rates the soda lime within the scrubbers would be more efficient.
However, by reducing the flow rate DCNS had increased the circulation time for the air being processed. Thus although the scrubber was working to full specification it was not processing enough air and hence not removing enough CO2 to maintain the levels required.
The Solution
Increasing the flow rate to that required for the specific conditions reduced the CO2 levels to within operating specifications. Molecular Products were able recommend this minimum acceptable rate (to conserve energy and reduce noise) after running their internally developed models.
Molecular Products Ltd supplies the soda lime (Sofnolime® S-grade) used in the life support system for CO2 removal or ‘scrubbing’. S-grade is specially formulated for this application to cope with the particular conditions encountered on a submarine.
The Results
DCNS were satisfied that with the support from Molecular Products technical team and that the CO2 systems supplied were working to full specification and met all their requirements. The boats in question were subsequently delivered to the Royal Malaysian Navy.