CASE STUDY

Effective Heat Recovery In Flash And Condensate

Industry

Paper

Background

As condensate recovery potential is above 80 % venting of flash steam was observed at feed water tank end. Sometimes vibration in case of steam trap passing.

Highlights
  • Venting of flash steam in feed water tank
  • Vibration in case of steam leaking through traps
Energy Conservation Measure
  • Utilize condensate and flash steam in process
Estimated savings $36,000 USD per annum
  • Boiler Capacity – 4TPH @ 10.5 barg
  • Fuel – Furnace oil
  • Payback – 6 months
Explanation

In these kinds of plants where the indirect steam usage is 100%, expected feed water temperature is > 100 deg C. The estimated feed water temperature in your case is 165 Deg C. However, in feed water tank technically heat above 100 Deg C cannot be contained. The heat will get lost in the form of flash steam. This is what precisely happening in your case. Additionally, steam getting lost by passing steam traps appears in the form of live steam loss from the tank.

Installing flash vessel and steam operated condensate pump along with atmospheric Deaerator head will not solve this problem, as after complete condensate and flash recovery by this system, steam still will be getting lost from top of the feed water tank due to excessive heat recovery.

It is proposed condensate from all the drying cylinders will be pumped under pressure, to an intermediate pressurized vessel. The condensate from this vessel will then be pumped directly to boiler shell using high temperature electrical condensate pump. The system will be provided with required control instrumentation for smooth operation.

Expected temperature of condensate that will be pumped is about 165 deg C. The advantage of this system is as below

  • No flash steam loss in this system
  • Even if the steam trap starts passing the steam is not lost to atmosphere
  • The operating capacity of boiler is improved (with this arrangement the operating capacity will be f
    & @ 165 deg C)
  • Saving in furnace oil consumption as mentioned below
Flashing observed in vented feed water tank due to pressurized condensate
Flash Steam & Condensate Recovery
Average Condensate Quantity 1400 Kg/hr.
Pressure of incoming Condensate 6 Kg/cm2g
Enthalpy of water @ 1.5 kg/cm2g 165 kcal/kg
Pressure of Flash Steam 0.5 Kg/cm2g
Enthalpy of water @ 0.5 kg/cm2g 110 kcal/kg
Latent heat of vaporization @ 0.5 kg/cm2g 532 kcal/kg
Enthalpy of steam @ 0.5 kg/cm2g 642.2 kcal/kg
Fuel GCV (Coal) 9650 kcal/kg
Cost of Fuel (Coal) 45 Rs/Kg
Boiler Efficiency 84.3 %
Operating hours per year 4680 20 Hrs./Day
% Flash Steam Generated 10.34 %
Flash Steam Quantity 145 Kg/hr.
Equivalent fuel savings 11 Kg/hr.
Annual Savings from Flash Steam recovery 2408565 Rs. /year
Quantity of condensate recovery 1255 Kg/Hr.
Present condensate recovery 1200 Kg/Hr.
Present condensate wastage 55 Kg/Hr.
Proposed fuel savings by eliminating wastage 0.408 Kg/Hr.
Monetary savings by condensate recovery 85840 Rs. /year
Total savings by flash & condensate recovery 24,94,406 Rs. /year
Relation between Condensate Recovery % and Feed Water Temperature
Relation between Condensate Recovery % and Payback for
Pressurized Condensate Recovery System
Menu