TDS and Its Impact on Boilers

 

TDS and Its Impact on Boilers:

TDS (Total Dissolved Solids) refers to all the inorganic salts and small organic matter dissolved in water — mainly calcium, magnesium, silica, sodium, chlorides, sulfates, etc.

In boiler systems, water turns into steam, but the dissolved solids stay behind and become more concentrated over time. If not controlled, this rising concentration of TDS can severely harm the boiler.

Effects of High TDS in Boilers:

1. Scale Formation:

* High TDS leads to deposits (scale) on boiler tubes and heat transfer surfaces.

* Just 1 mm of scale can reduce heat transfer efficiency by up to 10%, increasing fuel consumption and operating costs.

2. Foaming & Carryover:

* High TDS causes unstable water surfaces and foaming.

* Foam carries water droplets into the steam line, leading to:

a. Wet steam (reducing efficiency)

b. Damage to valves, turbines, and heat exchangers

c. Product contamination in food or pharma applications

3. Corrosion

* Some dissolved solids like chlorides and sulfates are corrosive.

* These can attack boiler metal parts, reducing lifespan and increasing maintenance needs.

Why Blowdown is Essential?

Blowdown is the controlled removal of a portion of water from the boiler to reduce the TDS level

There are two types:

1. Intermittent Blowdown: Done manually at intervals to remove sludge from the bottom of the boiler.

2. Continuous Blowdown: A constant, small flow of water from the boiler's water surface. It helps maintain TDS at a steady, safe level.

What Happens Without Blowdown?

i. TDS will keep increasing.

ii. Scaling, foaming, corrosion, and carryover will become more severe.

iii. Efficiency drops.

iv. Risk of boiler failure or even explosion increases.

Blowdown Rate: The blowdown rate depends on:

* Feedwater quality

* Operating pressure

* Desired TDS limit (usually expressed in ppm

Example:

If a boiler is operating at high pressure (say 20 bar), the recommended TDS may be 3,000 ppm. If feedwater has 100 ppm TDS, then very little blowdown is needed. But if the feedwater has 1,000 ppm, a larger percentage must be blown down to maintain safe limits.

Monitoring and Automation:

* Use a TDS controller to measure boiler water conductivity (which is directly related to TDS).

* Automated blowdown systems can maintain optimal TDS levels with minimal water and energy loss.

TDS control is not just a maintenance task — it is a critical part of boiler operation. Without proper blowdown, a boiler becomes unsafe, inefficient, and costly to run. Monitoring and managing TDS through regular blowdown and proper water treatment ensures:

* Efficient steam generation

* Longer boiler life

* Lower fuel and maintenance costs

* Safe operation