Every 6oC rise in feedwater temperature reduces the fuel bill by 1%.
Condensate forms at steam temperatures. If it is returned to the feed water tank, every 6oC rise in temperature reduces the fuel bill by 1%.
As steam looses heat, it turns back into water. This water is called condensate and has temperature equal to that of steam.
Returning condensate to boiler feed water tank raises the feed water temperature, improving the steam to fuel ratio. This cuts the fuel consumption thereby reducing the fuel bill.
As a rule of thumb, every 6oC rise in feed water temperature saves 1% on the fuel bill.
Illustration:
Consider 1kg of feed water to be converted to steam at 5 barg.
| Case 1 | Case 2 | ||
| A | Feedwater temp | 400C | 460C |
| B | Amount of energy in feed water | 40Kcal | 46Kcal |
| C | Steam at 5 barg contains | 657.9 Kcal | |
| D | GCV of fuel (Furnace Oil) | 10200Kcal/kg | |
| E | Amount of fuel required to produce steam(C – B) / D | 0.060kg | 0.059kg |
As seen, the fuel required has reduced by 1.6% over the previous requirement.