A typical beer barrel or beer keg weighs around 30 lbs and is usually made of aluminum so you'd get 30 cents per lb here for the scrap aluminum if it was clean.
At 30 cents per lb that 30 lb beer barrel or beer keg would be worth $9.00 in scrap value but if you sell it as unclean aluminum for 5 cents per lb it would only be worth $1.50
Some scrap yards though may not even take the beer keg or beer barrel but if you can find the beer company they might give you a deposit back on the beer barrel or beer keg which is more than scrap value.