Similarly to how
@VirginiaHops1 describes it--if you're just putting the hops in a keg that isn't purged, it's of no value. Even if it's purged, merely opening the lid will introduce at least some air, and thus some oxygen.
Most of us in this thread who are talking about putting them in a purged keg mean in a keg that is being repurged with fermentation gases.
This pic here shows the process--it's my conical here, but I've done exactly the same thing using my bigmouth bubbler plastic fermenters. You just feed a line off the airlock/blowoff port to the OUT post of the keg, open the PRV (or install just a gas QD if pinlocks), and the fermentation gases go into the bottom of the keg and force out whatever is at the top.
So the idea would be to take a star-san purged keg that contains only bottled CO2, pop the top and drop in the hops, being careful to admit as little air as you can (unavoidable to admit at least a little). Then attach the OUT post to the blowoff, and let those fermentation gases purge that little bit of air out of the keg again.
In the pic below I have the gas coming off the pressure manifold on top (I use that instead of a blowoff cane), feeding into the keg. In this case I've daisy-chained a jumper for I use for transfers. I no longer do the daisy chain thing as I purge the jumper w/ beer, but if you just look at the line it terminates at the keg.
(BTW, this is even a way to purge a keg from the get-go without the hops. Clean the keg, sanitize it, dump the star-san, then close up. If you connect it like the pic, you'll fully purge the keg with ferm gases. Every 2 points of gravity produces about 1 volume of CO2. If you have, say, 50 points of gravity attenuation, that is 25 volumes of CO2. That's enough to purge that keg down to virtually unmeasurable O2, better than what bottled CO2 has.)
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