RU2313053C1 - Method for steam-chemical cleaning of internal surfaces of boiler pipes from precipitations - Google Patents

Abstract

FIELD: heat engineering, possible use for steam-chemical cleaning of internal surfaces of boiler pipes from precipitations of both operational (salt) and atmospheric corrosion (ferrioxide) products.

SUBSTANCE: method includes blowing surfaces being cleaned with overheated steam with dosed injection of chemical reagent into steam. As chemical reagent, water solutions of complexions are used at concentration in steam-chemical environment ranging from 0,1 to 5,0% of mass, and cleaning is performed under steam pressure 0,2-0,7 MPa and temperature of boiler pipe surface heating in interval of 130-170°C.

EFFECT: increased efficiency of cleaning.

3 cl, 1 dwg, 3 app

Description

The invention relates to heat engineering, and in particular to a steam chemical cleaning of the internal surfaces of boiler pipes from deposits of both operational (salt) and atmospheric corrosion products (iron oxide).

A known method of cleaning the inner surfaces of boiler pipes from deposits by washing them with an aqueous solution of a chemical reagent, which is used as a substance from the class of complexones [1] - analogue. The disadvantages of this method are the high costs of the water-chemical solution in an open loop (up to 300 t / h) and low specific cleaning ability (not more than 0.05 g per 1 kg of solution).

There is also a method of cleaning the inner surfaces of boiler pipes from deposits by blowing them with superheated steam with a dosed supply of a chemical reagent [2] - prototype. Moreover, oxygen is used as a chemical reagent according to [2]. The method is carried out at a temperature of superheated steam of more than 175 ° C and a vapor pressure of more than 0.8 MPa. The disadvantages of this method are the low specific cleaning ability (not more than 0.3 g per 1 kg of steam) and the limitation of the cleaning ability by the initial specific amount of iron oxide deposits (up to 200 g / m ² ).

The achieved result of the invention is to increase the efficiency of cleaning the inner surfaces of boiler pipes from deposits.

This result is ensured by the fact that in the method of cleaning the inner surfaces of boiler pipes from deposits by blowing them with superheated steam with a metered supply of the chemical reagent according to the invention, aqueous solutions of complexones are used as a chemical reagent at a concentration of 0.1 to 5 in the vapor-chemical medium, 0 wt.%, And cleaning is carried out at a steam pressure of 0.2-0.7 MPa and a heating temperature of the surfaces of boiler pipes in the range of 130-170 ° C.

Moreover, for the purification of magnesium and calcium compounds, aqueous solutions of complexones are used, which create a pH of the parochemical medium from 7 to 11, and for the purification of compounds of copper, divalent and ferric iron, aqueous solutions of chelators are used that create a pH of the parochemical medium from 1 to 6, followed by neutralization waste environment.

When using complexones as a chemical reagent at a temperature of the vapor-chemical medium from 130 to 170 ° С, all removed impurities will be bound to complexones, forming complexonates. At the same time, they will only be in a dissolved state, and with a decrease in the temperature of the vapor-chemical medium along the cleaning path, the repeated precipitation of complexonates on the heating surfaces will not occur.

As complexons, it is preferable to use ethylenediaminetetraacetic acid (EDTA) and its salts. The main advantage of EDTA and its salts is their versatility, i.e. ability to complex with all cations present in the water of heat power plants. Moreover, the strength of the formed complexonates is significantly greater than for complexonates formed with anions of other organic acids.

In the temperature range 130–170 ° С, the formation of complexonates proceeds at maximum rates, and the corrosion losses of pure iron are minimal. At steam parameters with a temperature below 130 ° C, the efficiency of the steam chemical cleaning is insufficient. At temperatures above 170 ° C, the corrosive loss of pure iron increases sharply. At a temperature of 240 ° C and above, conditions are created for the reverse process, namely, thermal decomposition of the formed complexonates and their precipitation on the inner surfaces of the tract being cleaned.

The vapor pressure in the range of 0.2 ÷ 0.7 MPa provides the corresponding regime of the vapor-chemical medium in terms of temperature, speed and reagent consumption. At a vapor pressure of 0.2 MPa, the saturation temperature is 119.6 ° C. At a pressure of 0.7 MPa, the saturation temperature is 164.2 ° C. The maximum efficiency of steam chemical cleaning is provided when the steam overheats no more than 10-15 ° C. At a pressure of less than 0.2 MPa, a sufficient mass flow of the vapor-chemical medium is not ensured, and at a vapor pressure of more than 0.7 MPa and a temperature of more than 170 ° C, the corrosion losses of pure iron increase.

The concentration of aqueous solutions of complexones in the vapor-chemical medium is from 0.1 to 5.0 wt.%. This is due to the fact that at a concentration of less than 0.1%, the cleaning efficiency decreases, and the production of a vapor-chemical medium with a concentration of more than 5.0% is limited by the solubility of the complexones.

The drawing shows a graphical dependence of the instability constant of the pK complex (removed deposits) on the pH of the medium [3]. From this dependence it is seen that the formation of complexonates of all compounds found in operational deposits depends on the pH of the vapor-chemical medium. Thus, by creating the desired pH value, various deposits can be selectively removed. As can be seen from the graph, it is advisable to use aqueous solutions of complexones, which create a pH of the vapor-chemical medium from 7 to 11, for purification from compounds of magnesium and calcium, and aqueous solutions of complexones, which create a pH of the vapor-chemical medium from 1 to 6. At the outlet of the purification circuit, the spent steam chemical medium undergoes appropriate neutralization.

The selected parameters of the vapor-chemical medium make it possible to increase the specific removal of deposits to 1 g / kg and to purify boiler pipes from atmospheric corrosion products and from the entire spectrum of chemical compounds contained in operational deposits, with their specific amount up to 1000 g / m ² .

Example 1. Superheated steam with a pressure of 0.5 MPa and a temperature of 160 ° C was applied to the cleaned surface of the boiler screen tubes with a flow rate of 12.0 t / h. Pepper by the entrance of superheated steam into the screen tubes from the unit for the preparation and supply of chemical reagents was pumped with a metering pump to an aqueous solution of complexon with the required pH and calculated concentration. The cleaning technology consisted of 5 stages.

Stage number 1. Removal of ferric iron.

Used comprehensively - EDTA.

Parameters of the parochemical environment:

- pH 2.0;

- concentration of chemical reagents 0.2%;

- cleaning time 4 hours.

Stage number 2. Removal of metallic copper and its compounds.

Used complex - monosubstituted salt EDTA.

- pH 4.0;

- concentration of chemical reagents 0.5%;

- cleaning time 4 hours.

Stage number 3. Removal of ferrous iron.

The complexone used is the disubstituted salt of EDTA (Trilon B).

- pH 5.0;

- the concentration of chemical reagents 0.7%;

- cleaning time 4 hours.

Stage number 4. Removal of calcium compounds.

The complexone used is the trisubstituted salt of EDTA.

- pH 8.0;

- concentration of chemical reagents 1.5%;

- cleaning time 4 hours.

Stage number 5. Removal of magnesium compounds.

The complexone used is the tetra-substituted salt of EDTA.

- pH 10;

- concentration of chemical reagents 3.0%;

- cleaning time 4 hours.

The specific contamination of the screen tubes before cleaning was at the level of 384 g / m ² . After cleaning, the contamination decreased to 24 g / m ² . The cleaning time was 20 hours.

Example 2. Superheated steam with a pressure of 0.7 MPa and a temperature of 170 ° C was applied to the cleaned surface of the boiler screen tubes with a flow rate of 15.0 t / h. Before entering the superheated steam into the screen tubes from the preparation and supply unit of chemical reagents, an aqueous solution of complexon with the required pH and calculated concentration was supplied by a metering pump. The cleaning technology consisted of 5 steps specified in the first example.

The specific contamination of the screen tubes before cleaning was at the level of 428 g / m ² . After cleaning, the contamination decreased to 32 g / m ² . The cleaning time was 20 hours.

Example 3. Superheated steam with a pressure of 0.2 MPa and a temperature of 130 ° C was applied to the cleaned surface of the boiler screen tubes at a rate of 7.0 t / h. Before entering the superheated steam into the screen tubes from the preparation and supply unit of chemical reagents, an aqueous solution of complexon with the required pH and calculated concentration was supplied by a metering pump. The cleaning technology consisted of 5 steps specified in the first example.

The specific contamination of the screen tubes before cleaning was at the level of 254 g / m ² . After cleaning, the contamination decreased to 38 g / m ² . The cleaning time was 20 hours.

Information sources

1. Operational chemical cleaning of once-through boilers using simplified technology / A.P. Mamet, G.I. Aleinikov, V.A. Taratuta, V.A. Peskov, G.K. Drobot, I.V. Makarov // Thermal Engineering, No. 10, 1971, pp. 63-66.

2. Copyright certificate. USSR No. 976761, MKI F22B 37/48, 1980.

3. The use of complexones in thermal power / T.Kh. Margulova // Moscow, Energoatomizdat, 1986, p. 15.

Claims (3)

1. The method of cleaning the inner surfaces of boiler pipes from deposits by blowing them with superheated steam with a metered supply of a chemical reagent, characterized in that aqueous solutions of complexones are used as a chemical reagent at a concentration of 0.1 to 5.0 wt. %, and cleaning is carried out at a steam pressure of 0.2-0.7 MPa and a heating temperature of the surfaces of boiler pipes in the range of 130-170 ° C. 2. The method of cleaning boiler pipes according to claim 1, characterized in that when cleaning from magnesium and calcium compounds, aqueous solutions of complexones are used that create a pH of the vapor chemical environment from 7 to 11. 3. The method of cleaning boiler pipes according to claim 1, characterized in that when cleaning from grounded, ferrous and ferric iron compounds, aqueous solutions of vzompleksonov create a pH of the vapor-chemical medium from 1 to 6, followed by neutralization of the spent medium.