Scale Inhibitor For Boiler - China

Anticorrosion mechanism

The anticorrosion mechanism of technology BF-30a is to generate a protective film on the boiler metal surface, which can be confirmed by the electrochemical tests.

Figure 1- Effect of the additives on the electrode potential of 20g steel

From the steel electric potential - time curves (Figure 1), under the different conditions, the steel electrode potential experiences the first severe drop and then the stable process with time changing.

I.E. firstly, the surface natural protective film destructs, and then the corrosion of the substrate take place.

Contrary to the sharp drop of the steel electric potential after the adding of the oxygen scavenger such as sodium sulfite, the steel electric potential after the adding of the BF-30a remains a stable value after a little drop.

This value is higher than the steel electric potential value in the water.

The possible explanation is that the BF-30a has a significantly suppression to the anodic process.

Figure 2 shows the influence of the BF-30a on the anodic process and the cathodic process for the steel corrosion in water.

The BF-30a makes a drastic positive shift of the corrosion potential and a drastic increase of the anodic polarization.

But from the cathodic polarization curves, although the BF-30a makes the oxygen ions potential decrease, the cathodic polarization increases significantly.

Thus the BF-30a not only strongly inhibits the anodic process of steel corrosion, but also significantly inhibits the cathodic of the corrosion.

It is a mixed inhibitor of steel in water.

At the same time, the electrochemical test results are the good evidence to show the high inhibition efficiency of the BF-30a.

Figure 2 - Potentiodynamic polarization curve for the steel in water

1.2.2 - Scale Inhibition Mechanism

1 - Chelating dissolution

The chelating agent can form a stable water-soluble chelate with the calcium ion in water, so that the hard components in water are in the dissolving state.

The typical chelating agent is the ethylene diamine tetra-acetate (EDTA) and the nitrilo tri-acetate (NTA), whose inhibition mechanism is the chelating agent in reaction with calcium ion to blockade the scale cation in its molecule and to prevent the combination between the scale cation and the scale anion.

By this way, a large number of calcium ions are left in water; the solubility of the micro-insoluble calcium in water increases, so that the calcium in the boiler is in the dissolve state.

This chelating agent plays the role as a scale inhibitor.

The chemical reaction runs according the stoichiometry: the hard components like calcium in the 1 mg of CaCO3 / L of requires 3.8 mg / L EDTA tetrasodium.

In order to identify the chelating dissolution of BF-30a, it takes the similar test method as the chelant: put the scale of calcium carbonate solids and calcium sulfate solids into the solution of BF-30a for the chelating dissolution test.

The test results show that the concentration of the calcium ions increase slowly; that means that the BF-30a is with the moderate chelating ability to dissolve the scale.

The main differences between the BF-30a and the EDTA: 1 - EDTA reacts with the calcium ions according to the stoichiometry; while the chelating dissolution of the BF-30a for the calcium ions is not according to the stoichiometry; even in theory, it achieves the stoichiometric value; the chelation is still exit in the BF-30a.

2 - Compared with the strong chelation of the EDTA, BF-30a dissolves the calcium ion gradually from the solid mildly.

In many experiments, there are no the phenomena of scale block splitting and spalling.

These characters are very important for the operation of the boiler.

Because the chelating dissolution is to remove the scale in the boiler to restore a clean surface; but if there are the phenomena of scale block splitting and spalling, it is possible to cause the scale block blocking the pipeline.

In order to identify the inhibition mechanism of the BF-30, observe the morphologies of the calcium carbonate particles with and without BF-30a by transmission electron microscopy.

As the figure 3 and 4 shows that the calcium carbonate particles without BF-30a will generate the inerratic calcite crystals on the heat transfer surface; while when the calcium carbonate particles is with BF-30a, there is only a small amount of loose amorphous calcium carbonate in the heat transfer surface, which can easily be washed out by the water.

Obviously, the BF-30a changes the crystallization type of calcium carbonate and inhibits the crystal of the calcite.

The crystallization type changes of the calcium carbonate and and crystal growth inhibition are for the reason that the BF-30a adsorbs in the crystallization or that the calcium ions on the calcium carbonate crystal interface, with the effect of the chelation, occupy the lattice position for the normal growth of the crystal, which make the crystal cannot normally grow.

It is to say that the crystal distortion takes place.

Company Contact:

• Posted By: Beijing Bidragon Machinery Co., Ltd.

• Phone: 008613027690702

• Address: No.2-1803 Soubao Business Center, No.16 South-West, Beijing , China

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