Introducing the new International Standard for Carbon Dioxide Absorbers and safe use of Soda lime in Hyperbaric systems David Cook (Business Development Manager EMEA) Molecular Products Limited Written by Dr Nurul Alam MRSC & Dr Mike Clarke FRSC. Senior Technical Managers
INTRODUCING THE NEW INTERNATIONAL STANDARD FOR CARBON DIOXIDE ABSORBERS AND SAFE USE OF SODA LIME IN HYPERBARIC SYSTEMS; Soda Lime effectively removes CO 2 from Hyperbaric Systems and Re-breather diving systems The only commercial diving standard is the recently published BS8618:2015 which may be replaced by an European EN standard (if adopted). NATO has introduced the ADivP-03 standard which clearly sets out technical performance testing criteria for CO 2 scrubbing media BS & EN have taken up this standard in a modified format, MPL has been integral to advising BS panel on how this new standard could benefit industry
SAFE LIMITS OF CO 2 EXPOSURE >At rest a person respires 24lts of CO 2 /hr >Under exertion up to 40ltrs CO 2 /hr >How much CO 2 is created by 18 man dive team In Saturation per hour? >assuming 33% dive team at rest/sleeping 33% at normal level exertion and 33% at high exertion work/diving >(24 x 6)+(32 x 6)+(38 x 6)= 564ltrs CO 2 >Soda lime will extract 150-170ltrs CO 2, independent test results suggest >200ltrs/ per kg Sofnolime adsorbed (theoretical capacity about 256 litres) per kg of Sofnolime, therefore a scrubber filled with 20kg of Sofnolime will extract up to 4000ltrs CO 2 and last 7 hours before breakthrough CO 2 levels increase
WHAT IS SODA LIME? BBC TOP GEAR CO 2 REMOVAL VIDEO PROVES THAT JEREMY CLARKSON IS NOT SUCH A BUFFOON Top Gear Soda Lime.MP4 Jeremy Clarkson comes up with a rather novel way of reducing greenhouse gases...attach a greenhouse to your gas guzzling Range Rover! Go to http://www.youtube.com/topgear to see a full list of all high quality videos available on the Top Gear YouTube channel and don't forget to visit http://www.topgear.com for all the latest news and car reviews. Please note the Molecular Products CO 2 Scrubber filter
WHAT IS SODA LIME, WHERE DOES IT COME FROM? The main constituent of soda lime is quarried from naturally occurring Limestone in the UK Soda lime Sofnolime MPL Trademark, is a complex mixture of: Calcium hydroxide (Ca(OH) 2 ) Water Sodium hydroxide (NaOH) in the case of our Sofnolime A water content in the granules must be present for the reaction with carbon dioxide to occur at a usable rate. Sofnolime always contains a significant amount of water
PRODUCTION PROCESS OF SODA LIME Mixing: Water Ca(OH) 2 NaOH (dye) Shaping Heat treatment Water addition Size / grading Performance testing packing Distribution
NEW DIVING SODA LIME STANDARD There is now a British Standard BS 8618:2015 standard for commercial and recreational diving grade soda lime. This is based on the NATO A DivP-03 diving specification established in 2013. This sets minimum requirements for some key performance parameters but does not say how it will perform in your application. For diving rebreathers the whole system, including the soda lime, has to meet the requirements of EN14143:2013. For other applications the scrubber performance will still need to be assessed using a specific grade of soda lime. IMCA & the Subsea Industry should consider setting minimum performance levels for Hyperbaric & Emergency bail out systems
CURRENT EN14143 CRITERIA TESTING FOR REBREATHER SETS - AT DEPTH & LOW TEMPERATURES Test conducted @ Ambient Pressure Diving Helston ANSTI test facility These tests were run using a standard Inspiration rebreather dive set, run at 40 litres per minute breathing rate @ 4 C water temperature (2 litres tidal volume x 20 breaths per minute as per EN14143). The test set was charged with a standard carbon dioxide absorber unit filled with the sample of the soda lime to be tested. Each absorber was weighed and the weight of soda lime used recorded. Each test was run with 1.6 litres per minute of CO 2 added to the circuit (EN14143). The elapse time to the initial CO 2 breakthrough to reach a partial pressure Tested media; Sofnolime 797, CD & L grades and a comprehensive range of competitor products. MPL can assist in suggested test criteria for Hyperbarics
NEW NATO /BS/EN CO 2 SCRUBBING CHEMICAL SPECIFICATION The proposal for the EN carbon dioxide absorbent specification testing would be based on the current NATO STANAG 1411 ADivP-03 but may exclude or add to this as deemed appropriate and agreed by the relevant national committees. The current proposal using ADivP-03 is for specification of four Sodalime grades, this is to be written into the New BS & proposed EN standard, they are ; high and low capacity, large and small particulate soda lime absorbent. With an additional two high and low capacity lithium hydroxide granular material. In reality only 2 of these grades would be suitable for Hyperbaric applications Potassium superoxide and solid matrix absorbents would be excluded from the scope. All standards consider indicator dyes in this process to be unnecessary and a contaminant!
CO 2 SCRUBBING UNITS WITHIN THE HYPERBARIC DIVING SYSTEM
HOW CAN WE DEFINE THE CO 2 CAPACITY OF SODA LIME? Theoretical capacity the maximum CO 2 capacity available from the chemistry not attainable in practical systems. (256 litres CO 2 per kg SL at 15% water) Intrinsic capacity the CO 2 capacity of the exhausted used part of the absorber not dependant on the size of the absorber (about 170-200 litres CO 2 per kg for Sofnolime depending on grade & breakthrough conc.) Usable capacity the CO 2 capacity of the absorber up to the point that an unacceptable CO 2 level appears at the outlet dependent on the size of the absorber, the reaction rate and the flow rate. (about 120 litres CO 2 per kg at surface in 2.2 kg absorber in a well designed rebreather dive circuit)
FACTORS THAT EFFECT RATE & CAPACITY OF CO 2 ADSORPTION Temperature of the gas stream and in the scrubber reaction zone Level of CO 2 concentration - at inlet Quality / grade / size of the soda lime granules Water content - of absorbent before, during and at end of use this is controlled in the manufacturing process, not by adding to it! Size of the absorber bed (size does matter!) Quality / grade of the Sofnolime particle size, composition and morphology. Amount of water present, within the inlet gas stream and in the absorber Rate of reaction effects size (vol.) of reaction zone. Although we can talk about and measure capacity and rate separately they are always linked.
HOW DOES A CO 2 ABSORBER SYSTEM WORK Inlet Fresh Part Exhausted Exhausted dry Reaction zone absorber Unused Exhausted Zone of dried Sofnolime outlet 4 3.5 3 2.5 2 1.5 1 0.5 0 % CO2 at exit 1 2 3 4 5 6 7 8 9 10 11 Time 16-20% water absorber
NOT ENOUGH WATER CONTENT & TOO MUCH WATER HAS AN IMPACT At Molecular to best demonstrate this we ran a series of tests using very dry air (<1 %RH) through the normal media at 25 C and a high flow rate to 0.5% CO 2 breakthrough. Sofnolime tube test run = 90 litres CO 2 per litre of soda lime (cf. 136 litre CO 2 per litre @ 70%RH max theoretical = 233 l) Usable capacity reduced by 33 % with dry air The same volume of material was used in each case and the same run conditions. In contrast a very high water content will flood the scrubber stack and force the gas stream to the outer edge of the absorber. Gas will take the path of least resistance and CO 2 will breakthrough much quicker (potentially after only 1-2 hours in similar test conditions) as shown in this example 14
MOVEMENT OF WATER THROUGH SOFNOLIME Inlet Fresh dry Part Exhausted Exhausted Reaction zone absorber Unused Exhausted Zone of dried Sofnolime outlet % CO2 at exit 4 3.5 3 2.5 2 1.5 1 0.5 0 1 2 3 4 5 6 7 8 9 10 11 Time 16-20% water absorber dry absorber
TOO MUCH WATER.. CAUSES, Over wetting then flooding Gas takes line of least resistance Over wetted or flooded volumes are lost so do not contribute to capacity Leads to break through
ALL SODA LIMES ARE NOT THE SAME Diving Grade: 1.0-2.5mm size high CO 2 5kPa, at high pressure in cold water for long durations at high breathing rates. High activity small particle Medical Grade: 2.5-5.0mm high CO 2 5%, at 1 atm. Warm ambient temps at low breathing rates small absorbers. Low activity larger particle Submarine /refuge Grade: 2.0-5.0mm low CO 2-1 kpa, 1 atm but very high flow rates. Industrial Grade: 3.0mm large scale absorber (tons) for use in hydrocarbon streams. Dimensions and shape
THE DESIGN OF THE SODA LIME GRANULE IS IMPORTANT; DISTANCE TO CENTRE! distance to centre v surface area gas permeable calcium carbonate r < r calcium hydroxide circ.= 2πr r circ. = 3 r unused part used exhausted
DUST FORMATION IN SODA LIME PRODUCTION Zero dust when packed Dust forms from particles rubbing together In supply chain In loose fill absorber During handling and filling More dust is generated from large particle rubbing together than small particles. Dusting can lead to formation of clumps and residue at the bottom of filter stacks Ultimately increases break through time
SHELF LIFE AND SAFE STORAGE Sofnolime is a stable chemical it does not degraded with age or suddenly fail but: If it looses water it reacts slower If it gains water it reacts slower If it gets contaminated it reacts slower Therefore the shelf life is determined by the integrity of the packaging and storage conditions to maintain full capacity. Soda lime in an air tight container under ambient conditions will have a shelf life of up to 5 years
SAFE RESPONSIBLE DISPOSAL OF SODA LIME Used material is a mixture of lime and chalk with small volume of sodium hydroxide. High ph but low solubility Safe in landfill, does not contaminate ground water but check local legislation prior to disposal Also safe in small quantities at sea from moving boat in deep water it disperses easily absorbs CO 2 provides Ca to crustacea and other sea life
POTENTIAL IMPACT OF BS/EN SODA LIME DIVING SPECIFICATION BASED ON NATO ADVICE The original STANAG 1411 standard recognised two S Lime grades; Grade A = (Sofnolime 2050 L grade ) and Grade B (= Sofnolime 1025 D grade ). The new British Standards proposal is to leave the existing manufacturing specifications as they are, for the 1.0-2.5mm & 2.0-5.0mm D and L grade materials, but for manufacturers to rebrand to reflect the link to the later standard(s) for diving applications, and introduce a submarine/ Chamber grade specifically for high flow, low CO 2 concentration applications, as follows; Sofnolime 10-25mm S-H grade - diving (>90 mins; 15 18% H 2 O content) Sofnolime 20-50mm L-H grade - diving (>90 mins; 15 18% H 2 O content) Sofnolime 10-25mm S-H grade - chamber (>90 mins; H 2 O increased water content) Sofnolime 20-50mm L-H grade - chamber (>90 mins; H 2 O increased water content). The proposal is to increase the upper water content specification to allow for high flow, low CO 2 concentration conditions in hyperbaric chambers and Mine safe refuges. This may also require a change to the test gas criteria from high %RH to low %RH.
IN SUMMARY THE NEW BRITISH/EUROPEAN SODA LIME STANDARD WILL SPECIFY Specified grade of soda lime needs to be appropriate to application i.e. 1.0-2.5mm or 2.0-5.0mm size commercial diving grade for hyperbaric/chamber diving. Product compliance testing regimes to meet new NATO ADivP-03 standards Use a highly reactive material to maximise the reaction rate of CO 2 adsorption design high packing density to maximise capacity in Scrubbers The need to control the water in the circuit to maintain absorber efficiency EN/ISO 14143 equipment need to minimise dust, review filling, handling & storage Outlaw use of indication dyes Outlaw use of matrix style absorbers Consistency of batch to batch performance testing
QUESTIONS FROM THE FLOOR? Thank you for listening. Any questions?