Biomass as Fuel in Small Boilers (PDF 6.4 - APO Asian Productivity ...

Biomass as Fuel in Small Boilers
Table 3-1 Boiler treatment processes
S.No Process Treatment
1. Ion-exchange
process
(softener plant)
The hardness of water is removed as the water
passes through a bed of natural zeolite or
synthetic resin.
2. Demineralization Demineralization is complete removal of salts by
using cation resin, which exchanges the cations
in the raw water with hydrogen ions, producing
hydrochloric, sulphuric, and carbonic acid.
Carbonic acid is removed in degassing lower than
water is passes through an anion resin which
exchanges anions with the mineral acid (e.g.
sulphuric acid) and forms water.
3. De-aeration In de-aeration, dissolved gases such as oxygen
and carbon dioxide are removed by pre-heating
boiler feed water with steam before it enters the
boiler.
4. Reverse osmosis This process is used where the TDS level of feed
water is very high. Normal small fire tube boilers
do not use this system because the limit for TDS
level in the boiler drum is high.
Treatment of boiler feed water is essential even from the point of view of
boiler safety. The degree of treatment of boiler feed water is dependent on
the pressure of the steam which is generated. The higher the pressure of the
steam to be generated, the greater is the degree of treatment required. Table
3-2 gives the recommended boiler water limits for different levels of pressure.
Table 3-2 Recommended boiler water limits
Factor Up to 20 kg/cm2 21–40 kg/cm 2 41–60 kg/cm 2
TDS, ppm 3000–3500 1500–2000 500–750
Total iron dissolved
solid ppm
500 200 150
Specific electrical
conductivity
1000 400 300
Phosphate residual
ppm
20–40 20–40 15–25
pH at 25 ºC 10–10.5 10–10.5 9.8–10.2
Silica (max) ppm 25 15 10
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