It is always advisable to use dry steam for heating applications. Dryness of steam is measured as expressed as dryness fraction. It is advised to use steam with maximum dryness fraction. Steam below the dryness fraction of 97-98% might lead to following disadvantages-
1. Corrosion and Scaling
As steam evaporates from the boiler drum, it leaves back the impurities in the drum. When steam is wet, the water droplets have the impurities dissolved in them. These impurities get carried into the steam network and process equipment. The impurities carried in damage the steam system by corroding it or by scale formation.
2. Water Hammer
Wet steam can increase the chances of occurrence of water hammer. Water hammer is a phenomenon where a lump of condensate travelling at high speed hits the piping or some equipment fitted on the piping. The dryer the steam, the lesser are the chances of water hammer.
3. Reduced heat transfer
If a water film is formed over the heat transfer surface, it will reduce the rates of heat transfer as thermal conductivity of water is much lower than that of steam. This will result in increased batch timings and uneven product heating.
4. Increased load on steam traps
Wet steam implies large quantity of condensate formed. This increases the load on steam traps. Steam Traps are designed to discharge a certain amount of condensate. Wet steam might result in condensate quantities higher than trap capacity; this will result in undesired phenomena such as water hammer and water logging.
5. Damage to equipment
Wet steam damages both process equipment and various equipment fixed on steam lines. Wet steam can damage equipment such as flow meters, control valves etc. Hence, it is advisable to fix a moisture separator before flow meters, control valves etc.