Boiler Feed Processing (Pengolahan Air Umpan Boiler)

DUNIAPEMBANGKITLISTRIK.COM - In boiler feed water can contain minerals that can cause precipitation, corrosion and carry over. Precipitation of the material can result in a decrease in the effectiveness of heat transfer thereby causing the use of fuel to be wasteful, high-temperature metal can even cause damage.

Sedimentation is also the most serious problem in Boilers, it can also cause problems in the system before and after Boilers. Where the purpose of feed water treatment in a boiler, are:
- Avoiding crust formation.
- Prevents corrosion in equipment
- Avoid carrying unwanted compounds into steam (carry over)

Boiler water treatment method : 

- Mechanical and physical pretreatment, such as: clarification water, demineralization, thermal daerator.

- Chemical processing (chemichal use)

- Blowdown System: Definition Blowdown is the disposal of a small amount of boiler water with a view to maintaining the maximum level of dissolved and deposited solids at the permitted level. For example if water with a dissolved solid content of 100 ppm is then evaporated as much as 50% of the water, the concentration of the solid becomes 200 ppm. This can be written mathematically:
Kg Blowdown

Blowdown is divided into 2 (two) types :

1. Continuous Blow Down: which is installed close to the surface level of the water on the steam drum, intended to maintain the level of solids on the Steam drum, is carried out continuously.

2. Intermitten Blow down mounted on the bottom of the boiler is intended to remove the settling solids.

Continuous Blowdown is the most economical and consistent way to control Total Dissolved Solid (TDS)

Corrosion (rusting) not only causes disturbance in rusty areas, but can also produce metal oxyda contaminants which at serious levels can occur elsewhere. Because everything is related to water treatment, if the formation of deposition (deposit) and corrosion must be corrected and prevented in order to achieve satisfactory results.

The cause of corrosion is due to the presence of oxygen (O2) dissolved in water. The mechanism of corrosion is that metals which come in contact with the following reaction will occur:

Boiler Feed Processing

Dissolved oxygen in water forms Cathodic reactions

Boiler Feed Processing

From Equations (1) and (2) can be obtained:

Boiler Feed Processing

Boiler Feed Processing

The result is ferro hydroxide which settles in solution, this compound is not stable in a solution that still contains O2, so it will oxidize.

Boiler Feed Processing

Ferric hydroxide is known as rust.

To get rid of compound O2 (oxygen) in water to prevent corrosion can be done in several ways including the following:

- Deaerator, the function of this tool is to remove dissolved gases and heat water by contacting directly between low pressure steam with water. if the water temperature rises, the oxygen solubility decreases because it comes out through venting.

- Addition of Hydrazine (N2H4) reaction as follows:

Boiler Feed Processing

At temperatures above 270 C the hydrazine will turn into Ammonia (NH3) and Nitrogen

Boiler Feed Processing

This reaction is slow if the amount of Hydrazin is small, but conversely it will be fast if the Hydrazine is large.

To ensure that the dissolved O2 was depleted, he determined that Hydrazine must be excess (rasidual Hydrazine). In general, for Boilers whose operating pressures are less than 40 kg / cm2G, the N2H4 residuals range from 0.1 ~ 0.3 ppm (parts per million = per million), for pressures of more than 40 kg / cm2 G, around 0.05 ~ 0.1 ppm

- Volatile Treatment or Zero Solid Treatment. Is the use of volatile chemicals, such as ammonia / morpholine or cyclohexyl amine. To control the pH ... This material is injected into the Boiler water which serves to maintain the pH of the Boiler water, so it is high enough to prevent corrosion.

- Injection (PO4) and Alkali (NaOH) is carried out directly into the kettle, the intention is to avoid precipitating Calcium Posphate, Magnesium Silicate, Calcium Carbonate salts, etc., early on the system.

Boiler Feed Processing

Boiler Feed Processing

Boiler Feed Processing

Boiler Feed Processing

The precipitate above can corrode feedwater pipes where there is no method to remove it, whereas in the kettle we can dispose of these deposits by conducting blowdowns. Alkali (NaOH) is injected at the minimum required to raise the pH sufficiently to control corrosion, the material is put with POSPHATE into the boiler.

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