Running a normal Co2 keg on nitro setup

It is possible. It's not good for the beer, but it will pour.

If you're going to sell the beer VERY quickly (a day or two), then it won't do much harm. It will pour OK, albeit with minimal head and likely seem a bit flat.

Any longer than a day or two and the keg is going to flatten out. A nitro system (25/75 CO2 to Nitrogen Blend) doesn't have the CO2 the beer requires to keep it from going flat as the headspace in the keg increases.

An actual nitrogenated beer only has around 1.2 to 1.6 volumes of CO2. If it's not a nitrogenated keg, it likely has somewhere around 2.4 to 2.6 volumes of CO2.

If it's going to be on tap any longer than 2 or 3 days, you need to pour it from a more standard gas blend (60/40 CO2 to Nitrogen)

 

if you are asking the question, and you aren't exactly sure how the nitro faucet works, what different gas blends achieve, how nitro beer is packaged and the vols of different beers, then the answer is don't ruin your beer on the wrong gas and/or faucet.
there are a few lengthy discussions on this forum about how nitrogen works.

@jacewg makes some good points. you asked if a you can run a standard CO2 beer through a nitro system. definitely no. pushing the CO2 through the stout faucet will make a beer milkshake.

Nitro beer through a regular faucet with 100% CO2 will work better, but is also a bad idea. it will be flat until the keg equilibrates. CO2 also adds quite a bit of acidity, and that too is going to mess up the beer.
Cheers.

 

I'm not a Physics guy, so bear with me. I'm assuming that if the headspace is pressurized to, say 11psi, the CO2 would still come out out of solution. Does Dalton's Law of Partial Pressures apply here? Does the relative insolubility of Nitro factor into this?
#knowledgeforknowledgesake

 

the beauty of the mix gas is that you can force the beer through the restrictor plate at high pressure. you need over 30 psi to get the beer through the tiny holes. the restrictor plate strips out the CO2 into tiny bubbles. beer packaged for nitro dispense will have low vols, just enough to create the cascade effect.

so, we need 30+ psi of pressure. but we also need low vols. the N provides the pressure and the 25% CO2 provides the low vols.

if we were to apply 100% CO2 at 30 psi, the vols would quickly go way up. push that amount of dissolved gas through a plate and it will be a solid beer shake. I know this from experience, we eventually got it together and corrected the dumb mistake. lesson learned.

otoh, if you just run Guinness or any other low vol beer that is intended to go through a stout faucet on a regular faucet it will pour just fine. but because it has such low vols it will be quite flat. given enough time at say 12 psi it will eventually gain vols, but that isn't what the brewer intended. Guinness is really flat after the bubbles settle out, which is the main reason it should never be sold as a growler. by the time you get to serving it the gas has settled out and it is quite nasty.
Cheers.

edit-
and all this essentially means that Guinness gas has one distinct job to do. other blends can be used to overcome system resistance much in the same way. N for pushing and reduced CO2 to keep the vols correct.

 

Not all styles are suited to Nitro, IMO. I had an IPA a few years ago that was pushed with Nitro. Interesting mouthfeel, to be sure, but I didn't order a second. Part of the problem is that an IPA really needs CO2 to deliver the aroma.

But that's just my opinion.