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Chemical treatment of make up water increases the TDS levels in the boiler, leading to increased blowdown. Returning condensate reduces the TDS levels and thus blowdown, leading to fuel savings.

Fresh water added to the boiler needs to undergo chemical treatment. Among many other factors, this is necessary to prevent scaling in boiler tubes because of hardness in water and to maintain the pH level. This chemical treatment may either occur in the softening plants or by chemical dosing.

While chemical addition is necessary, it leads to the presence of suspended solids in the boiler. These solids will eventually collect at the bottom of the boiler and will have to be removed by bottom blowdown.

The blowdown water is at the same pressure and temperature as water in the boiler drum and this heat is now drained. As fresh water addition increases, the quantity of chemical in the boiler drum also increases. This raises the boiler TDS, necessitating more blowdowns and increasing the quantity of associated heat loss.

Condensate, being as good as distilled water, can be returned directly to the feed water tank. Doing so maintains water quantity without addition of chemicals. This reduces the TDS levels in the boiler, thereby reducing the frequency of blowdowns. Lesser blowdowns translate to reduced loss of heat energy. Besides reducing the cost of chemical treatment and cost of addition of fresh water into the system, this leads to incremental energy savings.

Illustration: Consider a steam load of 6 TPH, of which 50% (3TPH) is indirect consumption.

TDS of feedwater (soft water): 100ppm

TDS of Condensate: 10ppm

TDS maintained in boiler: 3500ppm.

Case 1

Case 2

Condensate recovered

Nil

3TPH

Avg TDS addition to boiler

100 ppm

(100+10) / 2 = 55 ppm

Blowdown per day

4.2 TPH

2.3 TPH