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Boiler Systems: Troubles in Operation and Their Causes

Definition of boiler systems

Boiler system is a system that is used to heat water and to generate required steam or hot water.

The boiler system is generally composed of the following units:

(a) Feedwater treatment unit: demineralizer, etc.

In case that the raw water is supplied from a river, a lake and so on, the raw water treatment units (clarifier, filter,etc.) are required. 

(b) Feedwater line,

(c) Deaerator,

(d) Boiler including preheater, superheater and desuperheater,

(e) Steam and condensate line,

(f) Condensate treatment unit,

(g) Wastewater treatment unit,

(g) Chemical injection unit.

Classification of boilers by their structures

(1) Cylindrical boilers (pressure : below 20 kgf/cm2) :

(a) Vertical boilers,

(b) Flue-tube boilers,

(c) Fire-tube boilers,

(d) Fire and flue-tube boilers.

(2) Water-tube boilers :

(a) Natural circulation boilers (pressure : low to high),

(b) Forced circulation boilers (pressure : low to high),

(c) Once-through boilers (pressure : above 75 kgf/cm2),

(d) Mini-circulation boilers (packaged type) (pressure : below 30 kgf/cm2).

A typical structure of a water-tube boiler

 

A typical water flow of boiler system


Troubles in Boiler System Operation and Their Causes

Kinds of
problems

Troubles in boiler system
operation

Causes of troubles

Scaling

Reduction of boiler efficiency, Expansion or bursting of heating tubes by overheating.

Leakage of hardness, silica, etc., from softeners or demineralizers, Inadequate blowdown control, Inadequate chemical treatment.

Corrosion

Corrosion damages of boiler systems including feedwater, steam and condensate lines, Scaling troubles caused by corrosion products.

Insufficient deaeration of feedwater,
Inadequate oxygen scavenger treatment,
Insufficient pH control of feedwater, boiler water and condensate.

Carryover

Reduction of steam quality,
Reduction of turbine efficiency by scaling,
Reduction of product quality treated by the steam.

Excess concentration of boiler water,
Contamination of boiler water with organic substances,
Fluctuation of boiler operation load,
Defects of steam separator.

Carryover: Transferring of dissolved solids in boiler water into the steam line.
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