RU1770723C - Method of cleaning hot-water boiler - Google Patents

Abstract

Usage: for removing scale deposits or crusts, for example iron oxide deposits, in apparatuses with heating liquids for chemical and physical purposes and can be used for pre-launch and operational chemical washing of water-heating equipment (boilers). SUMMARY OF THE INVENTION: The deposits are treated with a 0.1-0.8% sulfuric acid solution with urotropine at a concentration of 2-6 g / l at 30-60 ° C. The concentration of the acidic solution is restored by the addition of concentrated sulfuric acid. The waste solution is removed. It is treated with a solution containing 1-10 g / l of disodium salt of ethylenediaminetetraacetic acid at pH 2-3.5 with circulation of this solution for 3-8 hours at 70-90 ° C. The waste solution is removed. Neutralization is carried out with an alkali solution of a concentration of 0.5-1.5%, circulating at 90-110 ° C for 4-6 hours. Sodium silicate is introduced into the alkaline solution to a concentration of 0.5-5% and circulated for 6-10 hours at 60-90 °. 2 tab. (L C

Description

The invention relates to the field of removal and prevention of deposits, primarily iron oxide, in apparatus for heating liquids for physical and chemical purposes, and can be used to clean heat power equipment (boilers) used in communal heat supply systems after a certain period of operation.

A known method of cleaning hot water boilers, including removing deposits by washing the boiler with a circulating 4-6% hydrochloric acid solution, inhibited by 3-5% urotropine solution, at 40-60 ° C, after the end of the etching, the acid is neutralized and flushing the boiler with demineralized water followed by preservation of the boiler in a sodium silicate solution.

The method has the following disadvantages:

- removal of deposits by means of inhibited hydrochloric acid with its subsequent neutralization leaves the metal of the internal surfaces of the boiler in a corrosion-active state, which leads to its rapid overgrowth with iron oxide deposits and, as a result, to a reduction in the period between necessary flushing.

- despite inhibition, the corrosion rate of carbon steels in hydrochloric acid is high enough, which leads to

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loss of metal from internal surfaces during flushing and, as a result, shortening the life of the boiler.

The boiler processed in a known manner has been in operation for two years. During this time, he was subjected to chemical cleaning from deposits 10 times.

During the operation of the boiler, the main indicator of the amount of deposits located on the inner surfaces of the screen tubes is the pressure drop between the inlet and the outlet of the boiler unit. The difference increases monotonically from the moment of start-up after cleaning to the moment when the boiler circulation pumps can no longer produce the difference (atm), which ensures the circulation of the heat carrier, after which the boiler must be flushed again. During the control period, on average, chemical cleaning was carried out once in about a month and a half.

In addition, cleaning according to the known method does not contribute to an increase in the inter-washing period of the boiler, and also, due to the large number of acid washings in one season, to an increase in its operation time, since each acid wash reduces the wall thickness of the boiler screen tubes.

The purpose of the invention is to increase the efficiency of the process to increase the inter-flushing period and the life of the boiler. For this, before neutralization with an alkali solution, the concentration of the acidic solution is additionally restored by adding concentrated sulfuric acid to it to remove the spent solution and treated with disodium salt of ethylenediaminetetraacetic acid with a pH of 2.0–3.5, circulating at 70–90 ° С for 3– 8 hours, with the removal of the spent solution, while the acid solution is treated with a 0.1-0.8% sulfuric acid solution with an inhibitor concentration of 2-6 g / l at 30-60 ° C, and neutralization is 0 , 5-1.5% alkali solution at 9 0-110 ° C for 4-8 hours, followed by the introduction of sodium silicate into the solution to its content of 0.5-5.0 wt.% And circulate at 60-90 ° C for 6-10 hours.

The invention compared to the prototype.

-the proposed sequence of processing operations leads to an increase in the time of the inter-washing period of the boiler by 2-6 times;

-using the method makes it possible to extend the life of the boiler by reducing the rate of corrosion of the metal of the internal surfaces during the acid washing process.

The invention is illustrated by the following examples.

PRI me R 1. On the PTVM-50 boiler, which was monitored, after the end of the heating season, cleaning was carried out according to the proposed technology. To control the results before and after cleaning, pipe cuttings were made from the screen and convection parts of the boiler. The results of the analyzes are given in table. 1.

Chemical processing technologies included the following operations:

-filling the boiler with water;

-water-air flushing for two hours with the supply of air to the circulation circuit. After washing, water is discharged from the boiler;

- filling the boiler with a solution of sulfuric acid at a concentration of 0.5% (5 g / l) with an inhibitor (urotropin) content of 4-5 g / l at 40-50 ° C (with a volume of the container for preparing solutions - 18-20 m3), the amount of acid is 40 kg of 98% H2S04;

- circulation of the qi solution through the boiler for three hours;

enriching the circulating solution by introducing sulfuric acid with urotropine in concentrations of 0.5% (5 g / l for sulfuric acid) and 5 g / l (for urotropin);

- circulation of the qi solution through the boiler for three hours;

- enrichment of the solution by introducing sulfuric acid with urotropine in concentrations up to 0.5% (5 g / l for sulfuric acid) and 5 g / l (for urotropin);

-circulating the solution through the boiler for three hours. Additional acid was introduced in 90 L over a period of 14 hours about 7 times. A total of 630 L of concentrated sulfuric acid was added. Acid consumption is monitored by the pH value determined by titration. Upon reaching pH 5-6, the acid administration was repeated;

-after the last cycle of sulfuric acid administration, when the pH of the washing solution reaches 7.0, 200 kg of Trilon E in the form of a washing paste and 15 l of concentrated sulfuric acid were added to a pH of 2.0 and was circulated for 7 hours at 80 ° C;

- displacement of the washing solution from the boiler with water;

-conducting neutralization of the solutions contained in the boiler and boiler surfaces with a sodium hydroxide solution with a concentration of 1%, circulating the solution for 4 hours at 100 ° C;

- adding sodium silicate to an alkaline solution to a concentration of 5 g / l;

-circulating the solution for 6 hours at 80 ° C;

-removing solutions from the boiler;

- putting the boiler into operation.

A total of 31 hours was spent on processing. 1900 kg of iron in the form of oxides were washed, of which about 600 kg in dissolved form and 1300 kg in the form of suspensions. Residual pollution on internal surfaces is 305 g / m2. The pressure drop across the boiler is 1.7 atm.

After cleaning during further operation of the boiler, the pressure drop increased much more slowly than after washing according to the prototype method. You can see that the processing of the boiler according to the proposed method increases the inter-flushing time by at least two times. An extrapolation to a pressure difference of 7 atm shows that the time between the flushing periods of the boiler is increased by about 6 times, which is confirmed by the results of further operation.

Experience in chemical cleanings according to the invention has shown that at a deposit density of up to 1700 g / m2, the treatment step involving Trilon B can be excluded without compromising the beneficial effect (increase in the inter-flushing period). This reduces the cost of chemicals.

Laboratory studies were carried out (Example 2).

This example shows the results of laboratory experiments to justify the concentration limits of the acid reagents used in the proposed method. The experiments were carried out on samples of steel 20, which is used in hot water boilers; the corrosion rate was determined by the gravimetric method. The results are shown in table. 2.

Thus, laboratory studies show that the use of an acid solution can reduce the corrosion rate of the base metal of the boiler circuit by at least 10 times. Reducing the corrosion rate of the metal of the circuit during acid cleaning can extend the life of the boiler.

Using the invention will allow

to increase the economic characteristics of the operation of boilers by reducing fuel consumption and energy consumption for operational needs. Fuel burnout occurs due to the thermal resistance of the deposits. Power overruns are associated with the cost of overcoming the hydraulic resistance of the circuit due to

deposits. In addition, the cost of chemical treatments is reduced by reducing the amount thereof.

Claims (1)

The claims A method of cleaning a boiler, including treating it with a circulating acidic solution of mineral acid inhibited by urotropine, neutralizing it with an alkali solution and treating with a solution of sodium silicate, the process being carried out under heating, characterized in that, in order to increase the efficiency of the process to increase the interwashing period and life of the boiler , before neutralization with the alkali raster, the concentration of the acidic solution is additionally restored by adding concentrated sulfuric acid acid removal the spent solution and treatment with disodium salt of ethylenediaminetetraacetic acid with a pH of 2.0-3.5, circulating at 70-90 ° C for 3-8 hours, with the removal of the spent solution, while the acid solution is treated with 0.1-0.8% sulfuric acid solution with an inhibitor concentration of 2-6 g / l at 30-60 ° C, and neutralization with a 0.5-1.5% alkali solution at 90-110 ° C for 4-8 hours, followed by the introduction of sodium silicate into the solution to its content of 0.5-5.0 wt.% and circulate at a temperature of 60-90 ° C for 6-10 hours. Table 1 Characteristics of iron oxide deposits on the inner surfaces of the pipes of the PTVM-50 boiler before and after chemical treatment according to the invention The results of comparative corrosion testing of acid solutions of the prototype and invention table 2