comparison between economizer and air preheater

comparison between economizer and air preheater  

In terms of Efficiency-
Economizer-Increase the temperature of feed water

Air pre heater(APH)-Increase the temperature of combustion air

In terms of corrosion in boiler-
Economizer-The corrosion in boiler is due to the dissolve oxygen in the water. These dissolve gases will come out of water at higher temperature, which will be taken care in the Economizer automatically. 

Air pre heater(APH)-Corrosion can not avoid just by placing air preheater

In terms of ambient condition-
Economizer-No any effect

Air pre heater(APH)- if atmospheric conditions change than result in to the change in the volume of combustion Air, which will affect the efficiency of system.

In terms of repairing/maintenance Cost-
Economizer-High cost in comparison with air preheater

Air pre heater(APH)-Low cost in comparison with economizer

In terms of heat transfer coefficient -
Economizer-higher 50 to 300 W/m2-deg.C

Air pre heater(APH)- lower 10 to 50 W/m2-deg.C
 

Boiler water parameter, boiler water parameter limit

Boiler Water parameter limit is given below:

Hardness as CaCO3 -- Not detectable

Sodium Sulphite as NaSO3 -- 30 to 70 PPM

Sodium Phosphate as Na3PO4 -- 50 - 100 PPM

Caustic alkalinity as CaCO3 -- 350 PPM min

Hydrazine as N2H4 -- 0.1 to 1.0 PPM

Total alkalinity as CaCO3 -- 1200 PPM max

Suspended Solids-TSS -- 50 PPM

Dissolved solids-TDS-- 3500 PPM max.

Silica as SiO2 -- less than 0.4 of the Caustic alkalinity

Boiler Feed water parameter, feed water parameter quality, feed water parameter limit

Boiler feed water parameter as per British Standard BS - 2486 - 1978.

Feed Water to Boiler:

Hardness CaCO3 -- 5 PPM max.

pH -- 8.5 to 9.5

O2 -- nil

Oil -- nil

Total dissolved solids -- minimum possible to reduce blow down