Condensed Water Corrosion in Steam Boiler

Specifications

    Condensed Water Corrosion Inhibitor in Steam Boilers

Introduction for the technology

Technique Principle

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.

Potentiodynamic polarization curve for the steel in water

1.Chelating dissolution

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.

2.Lattice distortion

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.

3. Peptization

Turbidimeter measures the peptization of the BF-30a for the scale in the boiler (Figure 5). The results show that with the absence of the scale inhibitors, the scale in suspension subsides at a faster speed; the turbidity of the supernatant drops significantly and the supernatant within 20h is almost identical with the supernatant without scale. When the supernatant with BF-30a, during the test, the scale keeps in suspension; the turbidity of the supernatant is almost same. Therefore, the BF-30a can make the solids flowing into the boiler with the feedwater or generated in the boiler dispersing in the boiler to prevent the deposition in the heat transfer surface and slow-moving parts. The results also show that this peptization is also non-stoichiometric.

The possible reasons for this peptization is that the BF-30a adsorbs to the surface of the solid particles through the physical and chemical actions and make the particle surface with double layers of electricity, changing the charge state of the particle surface. Under the electrostatic interaction, the particles are mutually exclusive to avoid the particles combining with each other into a deposition, so that the particles remain dispersed in the water.

4. Low-dose effects

The chelation, peptization and the lattice distortion of the BF-30a for the scale are non-stoichiometric. The BF-30a can make the calcium ions more than the amount required by the stoichiometric value stable in the water. It means that the BF-30a has the obvious threshold effect. Therefore, when adopt the BF-30a for anti-corrosion and scaleinhibition, as long as the dosage reaches a certain value or more, the BF-30a can control crystalline growth of the scale ion and show the efficient scale inhibition. And there is no need to add more scale inhibitor than the recommended dosage.

1.3. The advantages of the technology

A large number of performance testing and the application tests of the water boiler prove the characters that this technology differs from the existing technology as followings:

(1) Effectiveness: When the boiler is in the general conditions, the inhibition rate and the scale inhibition rate of the BF-30a for the boiler both are more than 99%, much better than the rates of the existing similar technology, which solves the corrosion problem of the water boiler.

(2) Convenience: When adopt the BF-30a, it need not to run the deaerator operations, softening operations and sophisticated analysis operations. Also it does not need to operate the drainage, dry the boiler, run the regular analysis and replace the drugs. Just operate the chemical dosing according to the requirements;

(3) Consecutiveness: This technology break through the traditional mode of separately dealing with the boiler in operation or in discontinuation. Regardless of the periods of the boiler for operation or discontinuation, the BF-30a can provide continuous long-term effect for anticorrosive and scale inhibition;

(4) Low price: It does not require the expensive deaerator as the investment; it does not need to change the drugs for the boiler operation or the boiler discontinuation. Thus it can save the cost of the boiler application greatly.

1.4. Comparison among the similar products and benefit analysis

Currently, the anticorrosive and scale inhibition methods of the most advanced water boiler system still are softening, deaerator and oxygen scavenger methods. Here are the comparisons among these methods. (Refer to the table below).

2. The application of the BF-30a boiler anticorrosion scale inhibitor

Application: Mainly used for anticorrosion scale inhibition of the water boiler, water boiler heating system, secondary hot water heating systems with heat exchanger, and low pressure steam boiler.

Main ingredients: the PESA HPMA ATMP corrosion inhibitors M, sodium carbonate, sodium nitrate.

Technical data: scale inhibition rate ≥ 99%   Inhibiting rate ≥ 99% Inhibiting rate for discontinuation protection≥ 99%

FAQs:

Q:The dosage for the water boiler:

A: The initial dosage: 400~600g/T (the hardness of the feed water <5mmol/L)

The dosage for the feed water: 300~500g/T (the hardness of the feed water <5mmol/L)

When the hardness of the original water is great than 5mmol/L, add 80~100g of the drug for each addition of 1mmol original water.

Q: The dosage for the steam boiler:

A: The initial dosage: 2000g/T (the hardness of the feed water <5mmol/L)

The dosage for the feed water: 200g/T (the hardness of the feed water <5mmol/L)

When the hardness of the original water is great than 5mmol/L, add 60~100g of the drug for each addition of 1mmol original water.