RU2545294C2 - Method of corrosion, deposition and slime protection for inner metal surface of water heating heat power equipment, heating network pipelines and closed heat supply systems - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention refers to inner metal surface protection and conservation in closed heat supply system equipment. Method is implemented by addition of reagent, a mix of solid and liquid paraffin, to heat carrier. Within heat carrier temperature range from 26 to 300°C under operational conditions, the reagent is dispersed in the heat carrier up to colloid particle size. Reagent present in a heat carrier in amount of up to 0.5% vol. of water component of the heat carrier can prevent water component and slime particle reaction with metal surfaces by forming a fluid phase preventing any corrosion types, corrosion scale and slime deposition. Advantages of the reagent include low consumption, low cost, non-toxicity, environmental safety, simple storage, preparation, application and analytical monitoring.

EFFECT: improved reliability and quality of heat supply, higher efficiency of internal metal surface protection in equipment, and operation and repair cost reduction.

Description

The invention relates to a power system and can be used to protect and preserve the metal of the inner surfaces of heat power equipment from corrosion, to prevent the formation of scale deposits and sludge in closed heat supply systems. This type of equipment includes: hot water boilers, network heaters, heat exchangers for hot water supply and fresh air ventilation, pipelines of heating networks, heating systems for residential buildings and industrial facilities, individual heating systems, as well as valves for various purposes and pumping equipment.

The technical result is an increase in the reliability and quality of heat supply, an increase in the efficiency of metal protection of the internal surfaces of the equipment and a reduction in the cost of operation and repair.

The reason for the decrease in the efficiency and reliability of heat power equipment is surface phenomena that spontaneously arise as a result of contact of structural materials with water and its impurities. Being a consequence of thermal, hydrodynamic, chemical and electrochemical processes, these phenomena are cumulative in spite of the dissimilarity of the final manifestations, but, mutually supplementing each other, they exacerbate the consequences of their combined effect, which leads to a change in the structural, mechanical and heat transfer properties of the metal. This is expressed in various types of its corrosion destruction, the formation of primary and secondary corrosion-scale deposits and sludge. These reasons lead not only to a decrease in technical and economic indicators, but also are causes of accidents in heat supply systems.

The main tool to prevent metal corrosion of internal surfaces without introducing additional impurities into the water is the removal of corrosive gases from water by thermal deaeration. But the imperfection of thermal deaeration as a thermophysical process, as well as the problems of the hydraulic mode of operation of the deaerators, do not allow the complete removal of oxygen contained in water. Thus, the residual oxygen content for atmospheric deaerators, according to the standards of technical operation, should be 20 μg / kg, and for vacuum - 50 μg / kg, practically these standards are not maintained.

Therefore, more than 90% of deaeration plants in the housing and communal services system and in the power industry do not provide the calculated quality of deaeration of water and deaeration plants are used as intermediate tanks.

In boiler rooms with hot water boilers, vacuum deaerators are usually used, which operate at water temperatures from +40 to + 90 ° C. Vacuum deaerators have significant drawbacks: significant metal consumption, a large number of additional auxiliary equipment (vacuum pumps or ejectors, tanks, pumps), the need for location at a considerable height to ensure the efficiency of make-up pumps. The main drawback is the presence of a large number of equipment and pipelines under discharge. As a result, air enters the water through the shaft seals of the pumps, valves and flanged joints. In this case, the effect of deaeration completely disappears and even an increase in the oxygen concentration in the make-up water is possible in comparison with the source water.

Known methods of inhibiting scale formation in which the active substance are organophosphorus acids, in particular hydroxyethyl diphosphonic acid, or salts of these acids (ODEF) (patent RU 2304084 C2; US patent 5057228; US patent 5221487; patent RU 2158714 C1).

The main limitations when using phosphonates as scale inhibitors are the hydraulic characteristics of the equipment, the composition of water, the temperature regime, as well as the lack of boiling coolant. For boilers, the outlet water temperature is not more than + 110 ° C, and for heating boilers the outlet water temperature is not more than + 130 ° C. Due to poor circulation and the presence of many stagnant zones, the use of ODEF inhibitors is ineffective for hot-water fire-tube boilers and DKVR boilers switched to the hot water mode.

ODEF recommended for use and their zinc complexes are capable of inhibiting only calcium carbonate scale formation, but they do not inhibit the deposition of sulfates and iron compounds. The content of iron oxides in the composition of the deposits reaches 60 - 90%, moreover, with the presence of iron compounds in water above 0.5 mg / kg, the efficiency of phosphonates is significantly reduced. In addition, the high accuracy of the dosage of inhibitors associated with the phenomenon of a threshold effect when inhibiting the scaling process requires the use of additional expensive equipment.

The well-known "Method of operating heating systems" (patent RU 2323391 C1), which provides for the use of natural water as a coolant without preliminary treatment (softening and deaeration). It is proposed to protect the metal of internal surfaces from corrosion and accumulation of deposits by dosing surfactants in water in the form of an aqueous emulsion of octadecylamine (ODE) at a temperature of + 80 ° C

The use of octadecylamine in this case cannot provide sufficient protection of the metal, which is associated with the temperature regime of the heating systems and the melting point of octadecylamine, which is ~ + 53 ° C. When introduced into the coolant, the temperature of which is lower than the temperature of the aqueous emulsion of octadecylamine, the aggregation state of the emulsion will change and it will be converted into a suspension.

The well-known "Method of protecting the surfaces of hydraulic systems from corrosion and accumulation of deposits" (patent RU 2439204 C1), in which, in order to eliminate the disadvantages inherent in the aqueous emulsion of ODA, it is proposed to prepare a solution of octadecylamine in ethanol (ethanol) at a temperature of +45 ÷ + 60 ° C and dosing of this substance in the coolant. However, this method will also be ineffective, because and in this case, the aggregation state of octadecylamine will change due to the unlimited solubility of alcohol in water and the transition of the liquid-phase state of octadecylamine to the solid state state under the influence of the coolant temperature. In both cases, this will be related to the temperature schedule of the heat supply system.

The temperatures of the coolant at which the melting point of octadecylamine is lower than the coolant temperature is 30% of the duration of the heating season and is in the range +53 ÷ + 32 ° C.

When using quality control in heat supply systems, this value of the coolant temperature falls on the autumn-spring period (with an average daily outside temperature of + 4 ° C) and the winter period (with an average daily outside temperature of -5 ° C), therefore any interactions between metal and octadecylamine excluded. Therefore, in these periods, both the formation of deposits and corrosion of the metal of the internal surfaces of the equipment will occur.

Due to the fact that in closed systems, water leaks are possible in emergency situations, through equipment leaks and with the possible unauthorized removal of water from heating systems. The use of toxic phosphonates, film-forming amines and other substances that can have a direct or indirect harmful effect on the human body and the environment for the treatment of heating water make-up is undesirable. Most of these substances belong to the third hazard class according to GOST 12.1.007 - 76 and SanPiN 2.1.4.1074 - 01, therefore, they require special safety measures, which complicates their use, storage and disposal.

Non-reagent methods for preventing the formation of scale and sludge are also known, which include the methods of acoustic, magnetic and electromagnetic effects on the water coolant, as well as various combinations of these methods (patents RU No. 2312290 C2; RU 2420362 C2; RU 2273682 C1). The proposed methods are characterized by low efficiency associated with the variability of the seasonal quantitative and qualitative composition of the impurities of make-up water, depending on meteorological conditions, insignificant volumes of treated water, as well as one-sided action, i.e. not able to prevent metal corrosion.

The well-known "Method of protecting the internal surfaces of a steam boiler" (RF patent No. 2378562 C1), the application of which allows the metal of the internal surfaces to be protected from corrosion and deposits when solid paraffin with a melting point of +54 ÷ + 56 ° C is used as a reagent. However, a significant difference in temperature parameters, namely, the lower value of the operating temperatures of the coolant, does not allow the effective use of this method for the full protection of hot-water heating equipment, heating networks and heating systems. The heat carrier temperature in heat supply systems depends on the outdoor temperature. At outdoor temperatures from -5 to + 10 ° C, the temperature of the coolant in the return line, regardless of the temperature schedules used, is within +53 ÷ + 30 ° C, i.e. below the melting point of solid paraffin. Under these conditions, solid paraffin is not able to go into a liquid-phase (molten) state and disperse in a coolant.

The task to reduce the melting point of solid paraffin can be solved by preparing a reagent consisting of a mixture of solid and liquid paraffin, based on the condition of the liquid-phase (molten) state of the reagent in the coolant. The preparation of the reagent is carried out by mixing its components when heated in a certain proportion so that the melting temperature of the reagent is 4–6 ° C lower than the lowest working temperature of the coolant in the return line.

This circumstance is dictated by the operating conditions of the heating systems, in which, regardless of the temperature schedules used, the temperature of the coolant in the return line of the heating systems is + 32 ° C, and when using hot water water heaters + 30 ° C, thus, the reagent solidification temperature must be within 24 - 26 ° C.

Solid and liquid paraffins, being related compounds with the same structure, belong to the representatives of the same homological series of terminal alkanes of normal structure and have the general formula C _n H _{2n + 2} . The difference in their state of aggregation, the method of production, and physical constants (molecular weight, melting points, boiling points, decomposition, etc.) does not affect the physicochemical properties that are manifested under the influence of operating conditions during operation of heat supply systems. These properties, which are due to the peculiarities of the molecular structure, include: lack of solubility in water, wetting ability, dielectric properties, hydrophobicity, restoration of properties after transition to a solid state, ability to disperse in water, thermochemical stability, i.e. resistance to carbon deposits and coke formation. Other hydrocarbons, in particular mineral oils, ceresins, paraffins with a fine crystalline structure, which have a polycyclic molecular structure, are subject to thermal decomposition and oxidation.

Since the temperature characteristics of homologues of paraffin wax of normal structure are strictly dependent on the melting temperature, the indicated temperature will determine the boiling point and decomposition of the reagent, in this case they will respectively be +310 ÷ + 320 ° C and +440 ÷ + 450 ° C.

Thus, the temperature range in which it is possible to use a reagent without changing its phase state and signs of decomposition will be within +26 ÷ + 300 ° C.

This makes it possible to use a mixture of paraffins as a reagent to protect the metal of internal surfaces, not only in the entire range of operating temperatures in the used heating schedules when operating hot water equipment and heat supply systems, but also in cases when it is necessary to increase the temperature parameters of the coolant for technical and economic reasons . For example, in order to increase the range of heat transportation or when using a coolant for technological purposes, etc.

The reagent is introduced into the coolant through a dispenser-displacer installed on the return pipe of the heating network (suction line) of the circulation pump. In this case, the pump is additionally used as a “colloid mill”, in which the reagent is dispersed with intensive mixing and under the influence of the temperature of the coolant to the size of colloidal particles of equal fractional composition, the particle size of the reagent is less than 100 nanometers (0.1 μm). As a result, a free-dispersed system is formed consisting of two liquid immiscible phases, water and a reagent. Dispersed systems of this type are positioned as emulsions, this gives the coolant new qualitative properties, due, on the one hand, to the molecular and supramolecular structure of the reagent, which characterizes it as a surfactant with respect to water, on the other hand, the coolant acquires thermophysical properties, affecting the heat transfer rate. The reagent content is up to 0.5% of the volume of the water part of the coolant, contributing to the uniform distribution of the reagent in the water part of the coolant without the addition of emulsifiers with a high degree of aggregate stability.

The specific surface of one cubic centimeter of a reagent dispersed in water is about 600 m ² , which increases the likelihood of contact and the interaction rate of reagent particles with the surfaces of solids, without affecting the hydrodynamic characteristics of the coolant. This state of the reagent in the coolant creates the conditions for the formation and preservation of the protective layer on the surfaces of solids, as well as its restoration in case of destruction at any point in the circulation circuit of the system.

The interaction of the reagent with solids is physical in nature and does not depend on the composition and state of aggregation of impurities in the coolant and the type of metal equipment. Paraffins, having the lowest surface energy among organic compounds, are able to wet any solids.

A significant difference in the values of the surface energy of the reagent, water, available deposits and metal promotes physical adsorption and the formation of an interphase surface in the form of a liquid phase layer on the surfaces of solids with a minimum value of its thickness (3-4 nm).

As a result, the surfaces of solids, characterized by electrochemical heterogeneity, hydrophilicity, etc., acquire properties that are characteristic of paraffin properties, which is manifested in equipotentiality and hydrophobicity, with high dielectric capacity and thermochemical stability.

Thus, the contact interaction of the surfaces of solids with the water part of the coolant and its impurities in a colloidal-dispersed and dissolved state is prevented, which excludes any kind of surface phenomena regardless of the reasons for their occurrence.

This allows you to prevent corrosion processes, reorient scale formation processes at the stage of formation of slurry particles as a result of their crystallization under the influence of operating conditions and to obtain a fine slurry that is not capable of aggregation and secondary scale formation. At the same time, one cubic centimeter of reagent is capable of covering a surface of about 300 m ² , which, with the layer thickness indicated above, cannot have a practical effect on the thermal conductivity of heating surfaces and the heat transfer of heating devices.

In addition, the use of a reagent makes it possible to ensure a non-scale and corrosion-free regime of water-tube boilers in cases of wall boiling associated with a local increase in the temperature of the coolant to +180 ÷ + 200 ° C in individual coil coils of packages, as well as in bends, horizontal sections of pipes and stagnant areas. The liquid-phase state of the layer excludes its destruction under the action of alternating loads during thermal deformation of the equipment metal and erosion from mechanical stress from the coolant during its movement.

The safety of the reagent layer on the surfaces of solids is determined by the action of the force field of these bodies and the surface strength of the layer (tensile strength) of the reagent, which is two times higher for paraffins than for water.

These circumstances eliminate the causes that can affect the throughput of pipelines, the thermal and hydraulic conditions of heat exchange equipment, heating networks and heating systems, and ensure the operability of shut-off and shut-off and control valves. The absence of scale deposits on the heat transfer surfaces of hot-water and heat-exchange equipment gives fuel savings of up to 5%.

The use of the reagent is not limited to the chemical composition of the impurities of make-up water, which eliminates the methods of its preliminary treatment, i.e. softening and deaeration, as well as reduce current operating costs and capital costs during the construction of new boiler houses.

The use of the reagent helps to clean the metal of the internal surfaces of the equipment from previously formed deposits, regardless of their type, chemical composition and location, which is associated with the processes that take place during the formation of these structures. Corrosion-oxide layer, deposits and large sludge formation, not being physically and chemically homogeneous, are coherent dispersed systems, i.e. porous bodies with various sizes of cracks and pores filled with water. The mechanism of sediment destruction is associated with the displacement of water both from the surface of solids and from pores and cracks, which leads to mechanical destruction. This phenomenon is explained by the magnitude of the work of the physical adsorption of the reagent, which is a function of the surface tension and the contact angle, as well as the low viscosity of the reagent in the liquid phase state, which is due to the molecular structure and geometry of the reagent molecule.

A significant role in improving the reliability of heat supply systems is played by the preservation of metal on the internal surfaces of hot water equipment and pipelines, in particular peak thermal boilers of thermal power plants, determined by the combined effect of the so-called "parking corrosion" and the duration of metal contact with the coolant. So the inter-heating period for boilers operating in the heating mode is on average 5 months, and for peak boilers - about 7 months, while the corrosion rate is 15 - 20 times higher than the intensity of corrosion that occurs during the heating period. This leads to the accumulation of a large amount of iron oxide deposits in boilers, pipelines of heating networks, heating systems and equipment by the beginning of the heating period.

The properties of the reagent, namely, a change in the state of aggregation associated with a decrease in the temperature of the coolant, i.e. the transition from molten to solid state allows the metal to be preserved on the internal surfaces of the equipment. In order to increase the reliability of conservation before stopping, an additional amount of reagent must be introduced into the coolant. This will guarantee the effective protection of the metal of boilers, pipelines of heating networks and heating systems, heating devices, valves and pumping equipment, etc. for the entire period of the inter-heating period without draining the coolant and the use of additional equipment, which will make it possible to save water. In this case, there is no phenomenon of "freezing" with the formation of traffic jams. The re-preservation of equipment and its commissioning does not require any preliminary measures and occurs only due to an increase in the temperature of the coolant when the equipment is put into operation, which eliminates the need for pre-start and inter-season chemical flushing of equipment and systems.

Control over the content of the reagent in the coolant can be carried out without additional analytical equipment and costs according to the readings of the density of the coolant or by determining the transparency of the sample “by font or ring”.

Advantages of the reagent are low consumption, low cost, ease of preparation, use and storage. Solid and liquid paraffins in significant quantities are produced by domestic oil refineries in accordance with the relevant GOSTs and technical specifications, which ensures their quality, availability and practical applicability. Preliminary preparation of the reagent in the form of a concentrated aqueous emulsion completely eliminates its fire hazard during storage and transportation.

The reagent is not toxic and does not form toxic compounds when used, similar mixtures of solid and liquid paraffins in various proportions are used as dosage forms for external use. These forms are known in pharmacology under the name "artificial petroleum jelly" (vaselinium artificiale) and are registered as a food supplement E 905b.

Application area:

• hot-water water-tube and fire-tube boilers, regardless of the type and type of metal, including DE steam boilers; DKVR; E, etc., transferred to the hot water regime;

• pipelines, heating devices of closed systems of centralized and local heat supply of residential buildings and industrial facilities, regardless of the connection methods and type of materials;

• network steam-water heaters;

• water-to-water heat exchangers, including plate-type and shell-and-tube heat exchangers with heat-exchange surfaces of complex geometry;

• hot water boilers operating according to an independent scheme in open heat supply systems;

• heat recovery boilers;

• heating systems for individual houses;

• pump equipment;

• condensate lines and condensate tanks.

The reagent can also be used as a sealant, in combination with ball float gates, in order to prevent secondary aeration of water in the makeup water supply tanks of closed systems and hot water storage tanks of open heat supply systems, as well as in condensate tanks.

Claims (1)

A method of protection against corrosion, deposits and metal sludge of the internal surfaces of hot water heating equipment, pipelines of heating networks and heating of closed heat supply systems, which consists in using a reagent based on paraffin, which is introduced through a dispenser on the suction line of the circulation pump to ensure the formation of the emulsion of the reagent and its dispersion, characterized in that the paraffin is used in the form of a mixture of solid and liquid paraffins, prepared by mixing its components when heated with ensuring the melting temperature of the reagent 4-6 ° C below the lowest operating temperature of the coolant in the return line of the heating system.