Gas Pressurizes The Keg And Beer Is Forced Through a Cooler & Out The Tap...
Keg is stored in a fridge
Advantage is a longer shelf life, but once keg is finished it takes a while to cool the next keg.
Ice is placed on a coil or a cold plate (aluminium casing with stainless steel coils molded into it)
a Stainless steel coil on its own works fine for low volumes of 5-10 Litres per hour while a cold plate can produce very high volumes.
A flash cooler uses electricity to cool the beer. Cold beer on demand but volume depends on the size of the cooler and the cost of the flash cooler can be a disadvantage.