[laser7848]

Hello gentlemen, I am a student whose current capstone project involves a case study for determining the feasibility of on site oxygen production for CNC laser cutting. The demand in this case is specified @ 5 meters cubed per hour.
So far I have most of what I require for a viable solution but have gotten stuck on a certain data point that I cannot find enough evidence to rectify yet.

It seems that the industry standard for o2 laser cutting gas is rated at ~99.5% or greater in order to provide good, clean, and fast cuts. However many of the on site oxygen generator solutions out there are capped at about 95% purity with the exception of medical grade equipment.

What I would like to know is how much difference does that 4.5% disparity make between cutting solutions? Will 95% o2 purity be unusable in a competitive industry environment? I am trying to find data tables to back up the question but so far have only found this single chart. Does anyone know of better data tables that would help? Tables that might explore down to the 90% range or so?

Edit: link didnt work, here is the table.



Thank you for your time everyone.

[Blackened]

it's not just cutting speed that's a problem. Edge quality will drop off too. Piercing will be less effective and increase the chance of spatter fouling the nozzle and lens. I have operated mild steel O2 cutting where there has been accidental contamination of the O2 due to a faulty solenoid valve in another machine on the same O2 circuit. The contamination occurred elsewhere in the factory, and the air managed to work it's way back towards the O2 source and mess up my cut. I have no idea what % contamination this would work out to be but given the circumstances I expect it would have been only a small amount.

[Eldon_Joh]

Presumably you're talking about oxygen contaminated with nitrogen because it was produced with an oxygen concentrator.

If instead you were to deliver oxygen from electrolysis of water, you would get oxygen contaminated with hydrogen.

5 cubic meters per hour of oxygen would be about 6 kilograms an hour, which would be on the order of 35 kilowatts of electrical power consumption.. is this reasonable? bottling the hydrogen would probably not be cost effective to offset the cost. it could be burned on site to produce heat but that would only offset about a third of the cost, because presumably a heat pump or natural gas are both cost competitive at about 1/3rd the cost of resistive heat.

[laser7848]

Regarding "how reasonable" the cost of producing pure oxygen is, I honestly doubt that there is a cost-effective solution for small scales. From what I see pure industrial oxygen runs at about $40/ ton. I was hoping to find out the absolute minimum purity requirements for o2 laser cutting but finding any empirical data or specific studies on the topic is difficult. I will have to assume that 99.5% as the standard is the standard because of past trial and error. However the cost involved producing such high purity goes up exponentially with small scale systems. +ROI may not be possible under current market technologies. Still, I will see what I can do with this project.

Gentlemen, thank you for chiming in and sharing.

[Blackened]

Have you tried contacting a Laser manufacturer for their data?

[aliciahelfan]

Well this is really informative discussion, never think of oxygen generator. I have been selling oxygen concentrator from years but never think of this ever. Great information, thanks all folks.

[laser7848]

Hello again gentlemen…. Since this community was so very helpful in providing useful information regarding this topic I thought I would share the results of the research (within the constraints that can be done of course….)
The scope…
A laser cutting shop buys 99.99% pure liquid o2 (converted into gaseous form for use in laser cutting)
Is if feasible to produce oxygen assist gas for the purpose of laser cutting mild steel in house at small scale operations?
Short answer: No.
Long answer: It depends.
(Some data has been altered for legal reasons.)

Project constraints

-Demand ~ 40-50M cubed per day @ standard 101.325kpa pressure (standard atmosphere)
-ROI positive within 10-15 years
Process selected must be atmospheric intake (source gas)

Processes

There are currently 3 industrial options available.

1. Cryogenic separation – very high power consumption, highest purity (99.99%) and volumetric output available, suitable for large scale, continuous operations, has long start up times.
2. PSA (Pressure Swing Adsorption) – lower power consumption, lower o2 quality (90% to 99.5%) purity range, easy to maintain, does not require start up sequence.
3. Membrane separation – low power consumption, simplistic design, fragile if using ceramic filters, terrible o2 quality in this case (35-50% purity)

How much o2 purity is required?
https://www.sciencedirect.com/scienc...24013697002240
This above scientific study “The effects of gas composition on the CO₂ laser cutting of mild steel” has a lot of data on the question. For the first 0.5% purity lost (99.5% from 100%) you will see a 30% drop in cut performance. Some degradation of cut quality will also occur. At 98.75% purity you see a 50% drop in cut performance, heavy dross buildup and terrible edge quality. Given that the client wished to remain industry competitive, it was accepted that the absolute minimum purity maintain 99.5% at a minimum.

As mentioned before we have 3 current market technologies available. Membrane separation was at this point eliminated due to the inability of approaching our 99.5% criteria. This left Cryogenic separation and PSA as our two possible options.

Long story short, 2 stage PSA will reach an operating range of 99.1% to 99.3% nominal o2 purity. It can reach 99.5% but not continuously as it depends on your environment. (atmospheric variations or fluctuations for instance)

Results (all prices in united states currency values)

Cryogenic separation (10 hour start up time, entry level machine @ 99.5% to 99.7% purity.

Machine cost - $100,000

Power consumption – 65KW/30M cubed produced

$ per M cubed produced with startup time factored ($2.50/ M cubed)

PSA (2 stage nitrogen/argon processor, 99.1% to 99.3% nominal output)

Machine cost $70,000

Power consumption – 3KW/1M cubed produced

$ per M cubed produced ($1.75/ M cubed)

Membrane separation (N/A)

Recommendation was to stay with current 3^rd party solution as the above options will result in negative ROI. Current solution also provides superior purity @ 99.99%

Future considerations

http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf
SEOS (solid electrolyte oxygen separator) is an experimental form of oxygen separation that can theoretically produce 99.99% + purity at a cost much lower than cryogenic separation can. However, there are currently no commercial models for sale at this time.

[Eldon_Joh]

so the cryogenic separation consumes about twice as much power as would simply electrolyzing water to produce oxygen. it will be contaminated with hydrogen, but does hydrogen contamination matter as much as nitrogen?

[underthetire]

Guess this is partially why CO2 lasers are going away in industry.

Sent from my SM-T813 using Tapatalk

[laser7848]

so the cryogenic separation consumes about twice as much power as would simply electrolyzing water to produce oxygen. it will be contaminated with hydrogen, but does hydrogen contamination matter as much as nitrogen?

Hard to say. Our project was limited to atmospheric gas sources and water electrolysis falls outside of this category. Therefore we did no research on its relevant field. I would assume, given hydrogen's corrosive properties that concern in that area would have to be addressed. Nitrogen is pretty safe as it is mostly inert. As far as the research went, most of the objective evidence came from the co2 laser study cited. However, even that study had limitations. They stated in their abstract that their focus was with pressure and gas mixture ratios limited to helium, nitrogen, argon, and oxygen in their study. They did not address the effects of hydrogen, neon, krypton, co2, or methane which are all parts of atmospheric air. A separate study or additional research would have to address those factors.
As far as I can guess the largest single factor affecting the outcome of the cut is the purity ratio itself, so theoretically the differences between 99.5% oxygen/hydrogen as opposed to 99.5% oxygen/nitrogen would be marginal.