Regenerating the air in a submarine

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Regenerating the Atmosphere of a Disabled Submarine
Replenishing Oxygen and Removing Carbon Dioxide from a Submarine’s Atmosphere

By Capt. (N) Ryszard Klos
Scientist
Diving Gear and Underwater Work
Technology Department, Naval University of Gdynia
Gdynia, Poland



Air-regeneration for disabled/distressed submarines (DISSUB) occurs under tactical or emergency circumstances in which the DISSUB is not able to emerge on the surface and ventilate her atmosphere.

Regeneration of the DISSUB’s atmosphere consists of oxygen replenishment and excess carbon dioxide removal. In most situations, carbon dioxide elimination is achieved by means of sodalime, which is a chemical used for the removal of carbon dioxide from gases. Sodalime consists of calcium hydroxide, sodium hydroxide (NaOH) and/or potassium hydroxide (KOH). The approximate content of NaOH and/or KOH is two to five percent mass of the solid phase. Sodalime is placed in a separate absorber, which is connected to a suitable ventilation system. An appropriate reserve quantity of sodalime is essential onboard a submarine.

Procedures can differ on every DISSUB, but it is an accepted fact that if carbon dioxide content reaches one percent of its volume, absorption of carbon dioxide should be started. At two percent volume carbon dioxide content, the DISSUB must be ventilated or preparation made to abandon the vessel.

Mean oxygen consumption by one human is assumed to be about 25 dm3 × hour-1. For the average person, it is generally accepted that the emission of carbon dioxide divided by oxygen consumption (respiratory quotient) amounts to 0.8.2. This means that carbon dioxide emission produced by a person during the respiration process is assumed to be about 20 dm3 × hour-1. These values are used to calculate the reserve quantity of sodalime for dealing with DISSUBs.


Sodalime Qualities

Porosity and bulk density are of utmost importance in designing a carbon dioxide scrubber, which is a type of chemical reactor which absorbs pollutants. However, the porosity and bulk density of sodalime are not taken into account by the Polish Industrial Standard or provided by the manufacture (Polish Industrial Standard ZN-2001/DWORY S.A.-70). Therefore, it is necessary that scientists determine porosity and bulk density of sodalime.

Bulk density was measured by weighing the in-air (1,000 ± 100) cubic-centimeters mass of the sodalime bed. The bed mass was (801 ± 20) grams. Buoyancy correction was not taken into account in this case because its value, one gram, is less than the mass measuring error.2 Thus, the bulk density of the sodalime is (d = 0.80 ± 0.02) kilograms × m-3.

Sodalime bed porosity, defined as the free inter-molecular volume of the total volume occupied by the granulated material, was determined by flooding the bed of the volume equal to 500 ± 5 cubic centimeters, which consists of 10,236 granules, with water. This showed the height of the bed to be (l = 75 ± 2) millimeters, and diameter to be D = (90 ± 2) millimeters (the ratio height to diameter l/D = 0.83). As it follows from experiments, the water volume necessary for flooding the bed was Vw = 276 ± 2 cubic centimeters and it gives porosity (0.55 ± 0.02), which is typical for granulates.

Determination of the mean sodalime hydraulic diameter is approximate. It may be different (10 to 20 percent) because sodalime granules are additionally twisted. Mean hydraulic diameter of sodalime can be determined from earlier experiments and is equal to (3.470 ± 0.003) × 10-3.2


Objective

A submarine sodalime scrubber was filled with (18.73 ± 0.02) kilograms of sodalime. The base of internal bed dimensions is about 299 by 278 millimeters and height is 276 millimeters. Calculated bulk density from that is d = 0.82 kilograms × dm-3. This means that it corresponds to the density determined earlier in the laboratory. The total flow resistance (channel flow resistance and bed flow resistance) in the carbon dioxide scrubber is measured with the aid of an attached differential manometer. For air steam, (1320 ± 10) dm3 × min-1 bed resistance was Dp = (100 ± 2) pascals. From these measurements, sodalime qualities can be determined for the shape factor of sodalime particles, which is needed for scrubber pre-design.


Methodology

Scrubber Pre-Design
The calculations of the carbon dioxide scrubber are based on the assumption that the air passes through the laminar trough-fulfilled scrubber; resistance consists of sorbent bed resistance and scrubber body resistance; the scrubber body resistance is relatively small compared to the sorbent bed resistance; resistance coefficient for granulates (for one granulate fraction) can be defined according to the Blake-Kozena definition, particle diameter of the granular bed is determined according to the mean hydraulic diameter of sodalime; the set of the granular particles replaces the equal volume and area spheres; air viscosity is not dependent on temperature and pressure; and -1 dm3 of sodalime approximately bonds 90 dm3CO2.2,3

Carbon Dioxide Emission
Research in carbon dioxide emission was carried out on the Kobben-class submarine. Each bottle was filled with (3.50 ± 0.01) kilograms carbon dioxide and (0.25 ± 0.01) kilograms nitrogen and were prepared for simulating preliminary carbon dioxide concentration into the DISSUB atmosphere. Preliminary carbon dioxide concentration was created by releasing the content of two cylinders into the DISSUB atmosphere. After stabilization of the carbon dioxide concentration (around 10 minutes), stable carbon dioxide content amounts to (1.16 ± 0.05) percent volume carbon dioxide. Further carbon dioxide emission, adequate to maximize its production by the crew while breathing, was simulated by a special simulator.2 Its emission amounts to (10.81 ± 0.05) dm3CO2 × min-1.

Monitoring System
A submarine was equipped with a portable atmospheric monitoring system. The monitoring system consisted of four carbon dioxide gas analysers (Polytron IR CO2), produced by Drägerwerk AG (Lübeck, Germany).4. These analysers were placed in the bow, midship, stern and hydro-cabin. The analysers were connected to a typical personal computer by Advantech data acquisition modules into exchange electronic signals standard RS 485 net. Readouts were recorded every five seconds.


DISSUB Atmosphere Regeneration

The regeneration system scrubber was filled with 13.2 kilograms of sodalime. Regeneration of the DISSUB atmosphere began with simultaneous carbon dioxide emission. Regeneration was carried out until one of the analysers did not show a stable content of carbon dioxide. Preventive time of operation amounts to around two hours.

Dynamic absorbing power was assumed to be around 90 dm3CO2 for one dm3 of sodalime, which is the amount put into the canister (13.2 kilograms corresponds to 16.1 dm3 sodalime), which should absorb around 1,450 dm3CO2.


Conclusions

This experiment proved the simple and effective pre-design of the carbon-dioxide-removing scrubber method. Sodalime, in accordance with Polish Industrial Standard ZN-2001/DWORY S.A.-70, was successfully used for filling the carbon dioxide scrubber in the regeneration system built into a Kobben-class submarine for the purpose of eliminating carbon dioxide from the vessel’s atmosphere. The effective absorbing capacity is guaranteed because the dynamic absorbing capacity of carbon dioxide was 90 dm3CO2 for one dm sodalime.


Acknowledgements

This research was financially supported by contract 20/DPZ/3/OTM/S/WR/MON/2002/706, which was enacted for the Polish navy and sponsored by the Polish Ministry of Defence. /st/

References

1. Klos, R., “Metabolic Simulator Supports Diving Apparatus Research,” Sea Technology 12, 53-56, 2002.

2. Klos, R., “Aparaty Nurkowe z Regeneracja Czynnika Oddechowego,” KOOPgraf Poznan, 2000.

3. Pasternack, A., “Design Principles for Sodalime Cartridges in Respiratory Protection Apparatus,” Dräger Review 61, 26-29, 1988.

4. Klos, R., A. Olejnik and A. Khan, “Monitoring of the Submersible Atmosphere Composition,” Dräger Review 87, 28-30, 2001.

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Capt. (N) Ryszard Klos graduated from the Technical University of Wroclaw, completed his M.S. in physical chemistry in 1984 and started his career as a chemist at the Institute of Low Temperature and Structural Research, Polish Academy of Sciences. In 1985, he joined the army and served as a special forces group commander. In 1986, he joined the navy and served in the Military Diving School and then, in 1988, at the Naval University of Gdynia. Klos completed his Ph.D. in machinery exploitation in 1991.