RO105982B1 - Cleaning process of energetical high-pressu boilers - Google Patents

Abstract

: The invention is directed to chemical cleaning of the internal surfaces of the boiler piping energy. The process uses, for final pickling, another organic acid (a mixture of oxalic and citric acid) than those known and applied so far with much greater efficiency in the complexation of Fe3 + ions. Existing procedures, consumption of citric acid is much diminished, the efficiency of the method being mantle. The process is applied with the same installation as is currently uses chemical boiler cleaning energy.

Description

The invention relates to a process of chemical cleaning, of energy boilers, such as high pressure, to their commissioning.

the purpose of a good functioning of the energy boilers and of the pipes related to the boiler, is their chemical cleaning. before commissioning.

In general, chemical cleaning methods involve the following steps; mechanical washing, cold, mechanical washing, hot, degreasing, primary pickling with sulfuric acid containing a corrosion inhibitor, final pickling (with organic acids), passivation.

depending on the type of boiler, at present, at the final pickling, various organic acids (including citric acid) are used, which actually achieves a dissolving effect effectively on the inner surface of the pipes.

The citric acid has the disadvantage that it has a high corrosion rate, is expensive, nature is produced! and, at the same time, food.

As a chemistry agent for the final pickling, ethylenediamino-tetracetic acid is also used, which has a relatively high efficiency, but is very expensive, is used in high concentrations (3 ... 5%), is also very eorosive and requires dosing. of corrosion inhibitors in the respective solutions.

Adipic acid is effective for mummies at high temperatures, so difficult to apply. Also, adipic acid is hardly soluble in water.

Phthalic acid (phthalic anhydride) has the disadvantage of being difficult to dissolve in water and the efficiency is quite low.

Formic acid is difficult to handle, being difficult to measure due to the vapors it emits, plus its efficiency is very high.

The chemical cleaning process according to the invention eliminates the disadvantages of the known processes, in that the final pickling is performed by dosing, in the respective circuits, oxalic acid, in concentrations of 1%, I adding citric acid in concentration of 0.1% and ammonia in a concentration of 0,5%, the solution is heated to 60 ° C and recirculated for 4 h, through the installation maintaining the same temperature, followed by the passivation phase, which is carried out in the solution from the previous phase, by raising ammonia to values of

9.5 ... 10 and dosage of 1% sodium nitrite, maintaining the temperature of 00 ° C, the duration of the passivation phase being 12 h.

The process according to the invention has a number of advantages, namely:

- the oxalic acid product is synthetic and easily accessible;

- the solubility in water is high (it does not pose problems in dosing);

- the corrosion rate of the oxalic acid - citric acid mixture is lower than all other stripping agents, used today;

- the concentrations of the oxalic acid respectively, of the citric acid, very low sines (the consumption of citric acid is reduced 10 times) compared to the existing citric acid technologies;

- the working temperature is reduced (60 ° C) compared to EDTA procedures;

- The protective layer, formed, is compact and of very good quality (iron oxalate);

- proceeded! does not require a corrosion inhibitor, in the final cutting phase;

- the corrosion rate of the oxalic acid solution (with the addition of citric acid), according to the invention, is about 25 times lower than in the case of the use of acid.

BAD O '' '' of the citrus fruit;

- The process of chemical cleaning, according to the invention, uses synthetic chemical agents. replacing natural products (citric acid) intended for food consumption:

- the process eliminates the use of water-soluble organic acids (phthalate, adipic acid) and which have a low efficiency:

- the chemical washing installation does not change except by the additional installation of the useful storage tank and neutralization of the oxalate residual solutions:

- the concentration of oxalic acid solution is reduced (1%) compared to 3 ... 5% of ethylenediamine-tetraaeetc acid, for example:

- the temperature of the solution, and the final pickling phase, is very low (60 ° C) compared to 100 ... 150 ° C, for other technologies;

- the protective layer, obtained from chemical cleaning, is of superior quality (compact oxalate with a high degree of adhesion and compactness).

It is given. Hereinafter, an embodiment of the invention.

At an energy boiler of 420 t / h succession of technological phases, at the chemical cleaning of the energy boilers, is the following:

- mechanical washing, cold (with raw water), on each circuit,

- mechanical cracking. hot (with raw water), throughout the washing circuit,

- degreasing - with alkaline solutions containing sodium carbonate (1.5%), 1% Irisodium phosphate, 0.5% Na tripolyphosphate, 0.02% of a surface active agent (detergent),

- primary pickling with mineral acid (usually sulfuric acid with a suitable inhibitor);

- final pickling - which follows as follows: in demineralized water, from the circuit (remaining after rinsing from the previous phase), it is dosed in the oxalic acid circuit in concentration of 1% and citric acid in concentration of 0.1%, as well as ammonia approx. 0.5%. The dosing is carried out with the same installation with which the chemical reagents are dosed, for degreasing. The solution is heated to 60 ° C and recirculated for 4 hours, through the circuit, at this temperature.

During the final pickling, Fe and pH analyzes are performed (the pH value must be between 3 and 4).

After 4 hours, continue with the passive dc phase, which sc achieves, in the same solution, from the previous phase, by raising the pH to 9.5 ... 10 (with ammonia) and dosing of sodium nitrite in concentration of 1%. Passivation time - 12 h, at 60 ° C.

After the passivization is completed, the residual solution is neutralized and diluted to the limits provided and the regulations in force (especially for exalates).

Claims (1)

Chemical cleaning process of high pressure energy boilers, performing mechanical washing, cold, mechanical washing, hot, degreasing with alkaline solutions, primary pickling, with sulfuric acid containing a corrosion inhibitor, final pickling and passivation, characterized by that for the purpose of making a protective film. anficorosive, on the inner surface of the pipes of the energy boilers, the final pickling is realized by dosing, in the respective circuits, oxalic acid in concentration of 1%, with addition of citric acid in concentration of 0.1% and humonia in concentration of 0.5 %, the solution is heated to the temperature ^ BAD at 6O ° C and recirculated for 4 hours, by installing the same temperature, followed by the passivation phase, which is carried out and the solution from the previous phase, by raising 6 with pH ammonia at values of 9.5 ... 10 and dosage of sodium nitrite 1%, maintaining the temperature at 60 ° C, the duration of the passivation phase being 12 h.