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Author: Subject: High Voltage with High Power for Birkland-Eyde reactor
FranzAnton
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[*] posted on 10-5-2020 at 09:59


@WGTR interesting SIC Mosfet, but with 390pf gate capacity there must be an efficient driver circuit in use the 2153 will be sure not strong enough. If I keep switching freq. below 40kHz the IGBT is a very reliable component. To be honest I have no experiance in unsing SiC designs at all.

The multi arc design you described sounds interesting, but I fear that pumping an air/Nox gas mixture through another arc, some decomposition cannot be avoided.
Some old docs I found describe that using activated oxigen (means some ozone content in the air) will also help to increase the NOx output.

My idea of better cooling is very simple. My arc chamber consists of 2 glass plates in parallel with a distance of 2-3mm. Insive there are the 2 elextrodes as liquid cooled copper pipes (pressed flat) clamped between the glass plates. They are arranged in the form of a ventury nozzle (looks similar to a jacobs ladder)
On the side where the arc starts I inject compressed air, but with a very thin glas pipe so that the air throughput is not so high (8l/min) but the flow keeps turbulent. That helps also to press the gases within the arc zone to the flat glass walls for cooling. (The flat areas of the glass plates will also be liquid cooled)

So I have 2 parameter to adjust the reactor for optimum output. Air pressure and current in the arc by my inverter.
After the inverter I woud inject also air or oxygen (depends if I can get a used medical oxygen concentrator) for oxidation of the NO to NO2.
For this part I planned not a big glas balloon (which I often saw from other users) I will feed the gases in a 200m long PTFE pipe with 10mm inner diameter. This is my "reaction chamber" with the given flowrate nearly 98% of the NO is oxidized to NO2.

For the NO2 absorbtion I have to do some investigation because I read some paper that this is a tricky part where some NOx can easily excape.
My first try would be in that way to absorb the gas in an array of some gas wash bottles (that's not new) but I will fill them with HNO3 of appr. 68%. I tried this long time ago anf found that NO2 is quite good soluble in HNO3 of this concentration. It becomes a real deep green solution if saturated.

Then I will try to find out if this works what I read in a real old chemistry book. It was stated that if oxygen is pressed in that solution with about 30-50 bar. It becomes high concentrated HNO3 so all the water and the solved NO2 will change to HNO3 with the additional oxygen.
I dont know anything about reaction time and if there a further catalyst is needed, but it this really works it would be great.

30-50 bar oxygen pressure on concentrated HNO3 sound pretty difficult at home, but I had a kind of pressure vessel in mind from stainless steel with a flange so that I can put directly a (open) glass bottle inside filled with the acid to keep it away from the steel housing. Then pressurize from an oxygen bottle used for gas welding.
So I estmate that the reaction can be watched if the oxygen pressure is falling so I would repressurize as long as no more oxygen is absorbed.

Can you imagine that this will worke?
If the vessel is not so big, lets say one litre, so the pressure of 50bar and some extra savety should be possible to produce on the lathe at home.

There is an article (in german) which would describe this, but I did not pay for it. Maybe you have an idea how to get it for free....
https://onlinelibrary.wiley.com/doi/abs/10.1002/zaac.1931198...


[Edited on 10-5-2020 by FranzAnton]

[Edited on 10-5-2020 by FranzAnton]

[Edited on 10-5-2020 by FranzAnton]
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Sulaiman
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[*] posted on 10-5-2020 at 11:14


if available, could hydrogen peroxide solution be a viable way to capture NO2 at normal pressure ?



CAUTION : Hobby Chemist, not Professional or even Amateur
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WGTR
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[*] posted on 10-5-2020 at 11:16
Here is the file you requested...




Attachment: klemenc1931.pdf (639kB)
This file has been downloaded 35 times




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FranzAnton
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[*] posted on 10-5-2020 at 23:37


@WGTR: Wow thank you so much for the document you organized for me. I will walk trough a.s.a.p and post a summary of items which may of interest in a private (small scale) equipment area. That's so kind. I was not able to get this doc for free.

Regarding H2O2: Yes, a lot of papers refer that it's helpful also in industrial style to keep the NOx losses in the environment small.

The reason why I am not dealing with that is because H2O2 is extremly limited available in my country and if you get a solution of 10-12% it is stabilized with organic stuff that is not stable against Nox and the related substances which will build up. So H2O2 is hardly available, not cheap and "polluted" with stabilizer...

In homebrew apparatus it's not so the issue of absorbing the NO2, because we are (normally) not dealing with high flow rates and finally the exhaust gas can be absorbed in NaOH soulution.
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FranzAnton
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[*] posted on 11-5-2020 at 01:02


Content of the document about speed of oxygen absorption in a system of
HNO3-NO2-H2O. The experiments were done by Alfons Klemenc and Johann Rupp
in 1930 at university of Vienna.

Important basic parameters:

The experiments were done at temperature 0°C and 10°C (for determination the speed acceleration with higher temperatures)
The oxygen pressure were around atmospheric pressure and max. 0,86 Bar (12,5 psi)
Another parameter was the mixing speed of the liquid system (rpm of the stirrer)

The basic reaction behind:

4NO2(in solution) + 2H2O(in solution) + O2(gas) --> 4HNO3 (liquid)

The examination starts with HNO3 density 1,43 (65%) and ends with
HNO3 D:1,524 (99%-100%)

It's a heterogen reaction (gas-liquid) and one parameter of reaction speed is undoubtedly
the stirring speed.
They tried an apparatus which can stirr so fast (2000rpm) that the reaction speed became
nearly independent from stirring.

So the outcome in short:
HNO3 of lower concentration allows the oxidation of NO2 with H2O and O2 to HNO3 quite faster
(5h reaction time until stop of absorption)
The higher the HNO3 concentration the higher the inhibition of the NO2 oxidation.
The increase of temperature speeds up the reaction but at approx. 79% HNO3 concentration the
reaction can be considered as inhibited.
So under normal O2 pressure you can get max. a 79% concentrated HNO3.

---------------------------------------------------------------------------------
So basically it is possible, but the main topic in that examination was the limited oxigen partial pressure of 12,5 psi.
May statement was (which I found long time ago in the literature-but forgot the source) that this system can be driven to nearly absolute HNO3 by using pressure of 30-50 bar (435-750 psi) and higher temp.

The last days I started to find this source again, but did not succeed until now. So the worst case -it has to be verified by own experiment. This will last several month until I can manage to get the necessaray pressure vessel and the rest of the equipment. Meanwhile I got a used medical oxygen concentrator which can deliver aprox. 90% enriched oxygen from ambient air with 6l/min flow rate. So I am now searching for an high pressure -low volume oilfree pump which allows me to compress that oxigen in a bottel
If anyone has a practical idea of such a pump (not expensive) if it can bring up to 750 psi it would be great :)

A small Linde air condenser would be the lucky shot, but in my region I never saw something like that as used machine available.
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FranzAnton
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[*] posted on 11-5-2020 at 02:01


Here (sorry a little bit off topic) an interesting document dealing with Nox generation and N2 fixing from atmosphere using NTP or DBD plasmas. I mentioned this already in an other "fred" here, but the mains high frequency high voltage power supply which we were talking here is also capable to be used in a non thermal pasma arrangement. (If the surface is big, also for NTP's some energy is needed.

https://www.researchgate.net/publication/324034510_Non-therm...
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