Πως παρασκευάζετε το Nitrox - EANx (Enriched Air)
Η αποψή μας
Όλοι οι δύτες -τριες, για τις καταδύσεις μας κουβαλάμε αέρια. Αυτά τα αέρια μπορούν να είναι απλός ατμοσφαιρικός αέρας, εμπλουτισμένος με οξυγόνο αέρας (EANx) ή κι άλλα πιο εξωτικά μείγματα όπως πχ αέρας/ηλίο, υποξικά μείγματα κα. Το κάθε αέριο έχει το σκοπό και τους περιορισμούς του και γι' αυτό θα πρέπει να λάβει ο εκάστοτε δύτης/χρήστης του την κατάλληλη εκπαίδευση για τον χειρισμό και τους περιορισμούς που υπάρχουν στην χρήση του (πχ EANx, Trimix, κλπ).
Η αποψή μας
Όλοι οι δύτες -τριες, για τις καταδύσεις μας κουβαλάμε αέρια. Αυτά τα αέρια μπορούν να είναι απλός ατμοσφαιρικός αέρας, εμπλουτισμένος με οξυγόνο αέρας (EANx) ή κι άλλα πιο εξωτικά μείγματα όπως πχ αέρας/ηλίο, υποξικά μείγματα κα. Το κάθε αέριο έχει το σκοπό και τους περιορισμούς του και γι' αυτό θα πρέπει να λάβει ο εκάστοτε δύτης/χρήστης του την κατάλληλη εκπαίδευση για τον χειρισμό και τους περιορισμούς που υπάρχουν στην χρήση του (πχ EANx, Trimix, κλπ).
"Χωρίς την κατάλληλη εκπαίδευση οποιαδήποτε κατάδυση
με οποιοδήποτε αέριο μπορεί να αποβεί μοιραία"
με οποιοδήποτε αέριο μπορεί να αποβεί μοιραία"
Τα τελευταία χρόνια αρκετοί από τους εκπαιδευμένους δύτες επιλέγουν EANx για τις καταδύσεις τους γνωρίζοντας τα οφέλη αυτών, αλλά λίγοι γνωρίζουν πως παράγονται. Παραθέτουμε ένα σχετικό άρθρο (as is) για να παρει κανείς μια ιδέα για τους τρόπους παρασκευής.
Σημείωση: Υπάρχουν εξειδικευμένα σχολεία GAS Blending για την σωστή εκμάθηση παρασκευής αερίων και τις ιδιαιτερότητες αυτών.
"Το GAS Blending είναι επικίνδυνο χωρίς την κατάλληλη εκπαίδευση"
Λογισμικό
Μερικά από τα πολλά δωρεάν προγράμματα που κάνουν τους απαραίτητους υπολογισμούς μειγμάτων μπορείτε να βρείτε εδώ:
There are three major ways out there to make Nitrox.
They are:
- Partial Pressure Blending (Enriched Air Nitrox - EANx)
- Nitrogen Separating Membrane (De Nitrogenated Air- DNAx)
- Continuous Gas Blending with the Nitrox Stik (also EANx)
There are advantages and disadvantages to each of the systems, here's a quick rundown of their strengths and weaknesses:
1. Partial Pressure Blending
Mixes pure oxygen directly into an empty and oxygen clean certified SCUBA tank, then topped off with with Oxygen Compatible Air (OCA) from banks to create desired oxygen mixture. Depending on the complexity of the blending station, you will spend a couple thousand dollars on the mixing panel and additional filtration system. Bottled oxygen needs to be obtained from your local gas Gas Distributor.
Advantages
- Lowest initial startup cost
- Able to mix any mixed gas percentage
Disadvantages
- Very tedious process - Substantial amount of labor, generally 20-30 min, to fill each SCUBA tank.
- SCUBA tanks and fill system need to be Oxygen Clean Certified - more expensive VIP process.
- Potentially dangerous if oil has been inadvertently admitted to SCUBA tank (diesel effect resulting in explosion)
- Unable to use all Oxygen in O2 Tank unless you have a Booster Pump. Usually send O2 tank back to Gas Distributor with ~400 psi.
- Accuracy of Nitrox mix is dependant on the proficiency of the person operating the fill station.
- Need to have readily available supply of Oxygen
2. Nitrogen Separating Membrane
This technology was initially developed by the welding industry to generate Nitrogen. It uses a low pressure air source (or a high pressure air source regulated to low pressure) to force heated air through a special membrane system. There are two outlets from the membrane: one for the nitrogen vent, and one for the permeate (enriched Oxygen mixture) that goes into your high pressure air compressor. There are a couple different variations on this design. The oxygen content is controlled by either adjusting the input pressure to the membrane or adjusting the nitrogen vent. The membrane is unstable initially until it reaches operating temperature (~30 min). Adjustments to the membrane input pressure or nitrogen vent typically take about a minute before their affects stabilize at the oxygen sensor at the inlet to the HP air compressor. The outlet of HP air compressor is either sent directly into SCUBA tanks or a Nitrox Bank. More information about nitrogen separating membranes is available at AirLiquide, and Air Products.
Advantages
- Requires no bottled oxygen, independence from oxygen distributors.
- Can safely make Nitrox up to 40%
- Scuba tanks and fill system do not need to be oxygen clean.
Disadvantages
- Expensive initial procurement cost - typically on the order of $15-20K for a system capable of delivering 36% Nitrox at 15CFM
- System is slow to start up and can be frustrating to operate - difficult to dial in desired oxygen mixture. The heated air fed to the membrane causes the chemical reaction in the oxygen sensor to speed up, significantly throwing off oxygen analyzer calibration.
- Additional costs (electricity/maintenance) associated with running low pressure air compressor to supply air to membrane.
- If HP air banks are used to provide input air pressure to membrane - there is an enormous amount of wasted HP air and associated HP compressor electricity and wear.
- If filters are not frequently changed, membrane can get clogged with dirt particles, requiring its replacement - expensive!
- Membrane is fragile and can be damaged due to carelessness, if over pressurized or not properly heated (making the tubes brittle), you can easily burst the small tubes inside, requiring the membrane to be replaced - expensive!
- Replacement membranes are expensive! If the system is equipped with a LP compressor, a replacement membrane represents about half the cost of the system. If the system uses a HP to LP regulator, the replacement membrane represents about two third's the cost of the system. A replacement 6 foot membrane (used with 15CFM compressors) costs ~$8K.
- System should be constantly monitored during operation.
- Usually the highest cost per Nitrox SCUBA Tank.
3. Continuous Gas Blending with Nitrox Stik
The Nitrox Stik continuous gas blender uses O2 tanks and a patented blending “Stik” to homogeneously mix air and pure oxygen at the inlet of a high-pressure air compressor. Placing the system on service involves isolating the system's air storage bank, bleeding all the air out of the lines on the discharge side of the compressor (this reduces the time it takes to purge the air and replace it with Nitrox), and then while the compressor is running, placing the oxygen tank on service and throttling the oxygen supply to achieve the desired oxygen concentration. Continue bleeding the discharge of the air compressor until the system is purged and the oxygen analyzer monitoring the outlet of the compressor indicates the desired oxygen concentration. The air compressor, associated filters and air lines have now all been purged and he outlet of HP air compressor is either sent directly into SCUBA tanks or a Nitrox Bank. It typically takes between 5-10 minutes to place the system on service and start filling Nitrox SCUBA Tanks.
Advantages
- Moderate initial procurement cost - $2300 for the Nitrox Stik and an additional $2700-$3200 (depending on size of HP compressor) for the Nitrox Controller.
- Can Safely make Nitrox up to 40%.
- Scuba tanks and fill system do not need to be oxygen clean.
- Nitrox Controller allows operator to attend to other matters while filling Nitrox Tanks, reduces labor costs, increases accuracy of Nitrox Mix, and has additional safety features.
- Usually lowest cost per Nitrox SCUBA Tank by far when considering oxygen, labor and operating costs.
Disadvantages
- System should be constantly monitored during operation (unless a Nitrox Controller is installed).
- Need to have readily available supply of Oxygen.
When taking everything into account, the Nitrox Stik with the Nitrox Controller usually makes the most sense.
