RU2794232C1 - Method for manufacturing highly-emissive sol-gel ceramic coating - Google Patents

Abstract

FIELD: manufacturing highly radiant Solcoat ceramic coating.

SUBSTANCE: invention relates to a method for manufacturing a water-based highly radiant Solcoat ceramic coating and can be used, in particular, in the petrochemical industry, metallurgy, waste incineration processes and other fields. A method of manufacturing a water-based high-emissivity ceramic coating Solcoat by baking liquid paint applied to a furnace lining is that a liquid paint is obtained by mixing Solcoat filler, Solcoat binder and water, a ceramic coating is formed on the surface of the lining by applying the resulting paint to the surface of the furnace lining, after which, at the first start-up of the furnace, water is avalanche-like evaporated by heating the applied paint to a temperature of 120°C at a rate of at least 0.5°C in minute, followed by baking the coating to a temperature not lower than the maturation temperature of the coating 560°C.

EFFECT: technical result of the claimed invention is to increase the efficiency of the coating by reducing the loss of thermal energy in the lining.

1 cl, 1 ex

Description

Technical field

The invention relates to a method for manufacturing a highly radiant water-based Solcoat ceramic sol-gel coating and can be used, in particular, in the petrochemical industry, metallurgy, waste incineration processes and other fields.

State of the art

Highly emissive coatings are coatings that change the emissive properties of surfaces. Such coatings are well known. They are used in various fields, including the iron and steel industry and the petrochemical industry.

The development of modern technology is characterized by an all-round intensification of the processes occurring in various installations and apparatuses. This entails the need to create qualitatively new structures using materials to change and control radiant heat transfer in industrial thermal units. This also applies to heat exchange units, the most common of which are metallurgical furnaces and petrochemical furnaces.

So the efficiency of most metallurgical furnaces is 0.2-0.6. Increase the value of efficiency. furnaces can be achieved by intensifying heat transfer by radiation, which is predominant in most metallurgical furnaces, and in some it is the only possible one.

One of the ways to control radiant heat transfer in industrial thermal units is a directed change in the radiation characteristics of the surfaces involved in it by applying so-called highly radiant coatings to them. These coatings can play both the role of heat transfer intensifiers and catalysts for the reduction of nitrogen oxides formed during fuel combustion in fuel furnaces.

Various refractory materials or steel structures of elements of the working space of thermal units can be used as a substrate for coating.

The main physical property of highly radiant coatings is that their deposition on surfaces involved in radiant heat exchange leads to an increase in the degree of emissivity of the radiating surface.

In the publication [Chernov V.V. Research and development of methods for intensifying radiant heat transfer in metallurgical furnaces by increasing the emissivity of heat transfer surfaces. Thesis for the degree of candidate of technical sciences, Moscow, 2004] an analysis of the effect of the degree of blackness of surfaces on heat transfer was carried out, from which it follows that an increase in the degree of blackness of emitters and heat-receiving surfaces intensifies heat transfer by radiation in direct proportion to the increase in their degree of blackness.

The prior art method of manufacturing a highly radiant water-based sol-gel ceramic coating using the Solcoat™ component /http://www.ctkeuro.ru/index.php?p=Coating/. In this method, a liquid paint is first made by homogeneous mixing of Solcoat™ filler, Solcoat™ binder and water. Then this paint is applied to a previously cleaned, dried and dust-free surface, for example, linings, and during the start-up of the furnace, it is baked, followed by an increase in temperature to a temperature not lower than the ripening temperature.

This method is closest to the claimed.

As a result of this method, a highly emissive Solcoat coating is formed on the surface of the lining.

The Solcoat coating is a heat-resistant, gas-tight ceramic composite (up to 1900°C). It has high corrosion resistance in acid gases and condensates. Solcoat is ablation resistant and prevents scale formation.

Solcoat is used for mineral lining, shotcrete and spraying of ceramics, ceramic insulating refractory bricks, monolithic ceramics, ceramic fibers and stainless steel surfaces.

The Solcoat coating, depending on the composition of the components used in its manufacture, can be in various forms, for example:

- green - with increased corrosion and heat resistance,

- black - with increased resistance to abrasion at lower temperatures - CroMag - with an increased temperature limit of use.

Solcoat is made from a water-based paint obtained by mixing Solcoat components in water.

The maturation temperature is the heating temperature of the coating during its creation, above which the coating acquires highly radiant properties.

The highly emissive properties of the Solcoat coating are formed during the first start-up of the furnace after it has been applied to the furnace lining by raising the temperature in the furnace to at least the maturation temperature of the coating.

Solcoat is water based and can be applied by air and/or airless spray.

The use of Solcoat extends the life of the protected lining, reducing downtime, and also reduces the cost of production in which it is used, including capital costs.

Solcoat coating is effective for heat and corrosion protection of industrial equipment such as: incinerators, chimneys, heaters for petrochemical and refineries, chemical process equipment, industrial chimneys, boilers, glass and metallurgy, furnaces, burners, etc.

When applying the Solcoat coating to the lining, its effectiveness is determined by the reduction of heat energy losses in the lining

The disadvantage of this method of manufacturing a highly radiant sol-gel ceramic coating is its insufficient efficiency.

Disclosure of invention

The technical result of the claimed invention is to increase the efficiency of the coating by reducing the loss of thermal energy in the lining.

The technical result is achieved by implementing a method for manufacturing a water-based sol-gel ceramic coating Solcoat by baking liquid paint applied to the furnace lining, which consists in obtaining liquid paint by mixing Solcoat filler, Solcoat binder and water, after which a ceramic coating is formed on surface of the lining by applying the resulting paint to the surface of the furnace lining, an avalanche-like evaporation of water is carried out by heating the applied paint to a temperature not lower than the evaporation temperature of water at a rate of temperature change at the first start of the furnace after applying paint to the surface of the furnace lining of at least 0.5 ° C in minute, followed by baking the coating to a temperature not lower than the maturation temperature of the coating.

The rate of temperature change during baking of the coating should be the maximum allowable for a given oven. The upper limit of the temperature change rate is defined as the highest heating rate allowed by the kiln startup chart.

The advantage over the analog is achieved due to the fact that the surface of the coating has an enlarged expanded re-radiating surface, due to which the re-radiation of the coating increases.

Losses of thermal energy in the lining of furnaces are determined by the following factors:

share of reradiated energy

gas permeability of the lining.

The less thermal energy loss, the higher the reradiation and the lower the gas permeability. In turn, the reradiation is the greater, the higher the reradiation coefficient and the higher the deployed reradiating surface, that is, the greater its roughness.

The highly radiant coating Solcoat, when applied to the furnace lining, reduces the loss of thermal energy in the lining due to the fact that it is gas-tight and due to the fact that the re-emission coefficient of the highly radiant coating lies in the range of absorption of flue gases and, at the same time, over the entire temperature range in the furnace significantly higher than the lining.

To obtain a Solcoat coating on a furnace lining, a special paint is first made by mixing the Solcoat components and water, then applied to the lining and baked during the start-up of the furnace.

An additional reduction in the loss of thermal energy according to the claimed method is provided by an increase in the expanded re-radiating surface due to the avalanche-like evaporation of water during baking of the highly radiant coating.

Avalanche evaporation of water in relation to the evaporation of water from paint to obtain a highly radiant coating during its baking is an avalanche-like boiling process of water homogeneously distributed throughout the volume of the paint, with the formation of many vapor bubbles. The content of this process is the formation of steam inside each isolated microvolume of water (in the paint), that is, the evaporation of water, accompanied by the intense formation of bubbles filled with steam. Many steam bubbles go beyond the coating, making it rough due to the caverns formed when the steam exits. The increase in roughness is the basis for reducing the loss of thermal energy according to the proposed method.

In the production of a highly emissive coating, there are three characteristic temperatures of the coating production process in the furnace start-up process.

This:

Paint manufacturing temperature;

The bake temperature is the temperature at which the free (i.e., non-chemically bound) water is completely evaporated from the paint. This is the temperature at which the evaporation of the water that was added during the preparation of the paint is completed;

The maturing temperature is the heating temperature of the coating, above which the coating acquires a high emissivity (reradiates with a high reradiance coefficient). The acquired high emissivity is irreversible, that is, when the coating is cooled, it does not lose this previously acquired property.

In addition, there are two temperature ranges - the temperature range for evaporating free water from the paint and the temperature range for evaporating chemically bound water from the baked coating.

In the process of starting the furnace (that is, when it is heated), the physical properties of the paint change.

The first change occurs when free water boils and evaporates. This change consists in the fact that the paint applied to the lining becomes baked with the coated lining. At the same time, the Solcoat coating does not yet have highly radiant properties.

Upon completion of the evaporation of free water from the paint, the surface of the coating becomes rough due to the formation of many cavities on the surface of the coating by the evaporation of free water. In this case, the higher the evaporation rate, the more rough the surface of the coating.

With a further increase in temperature, gradual evaporation of chemically bound water begins, which occurs due to the breaking of chemical bonds in the coating, leading to a change in its chemical composition and accompanied by the formation of water. Water, turning into steam, leaves the coating, making it porous.

With a further increase in temperature, chromium oxide contained in the coating passes from an amorphous state to a glassy plastic low-viscosity state and in this state fills all the pores that were previously formed during the evaporation of chemically bound water. As a result, the coating becomes gas-tight.

Later, as the temperature rises, starting from the maturation temperature, structural changes in the coating begin, which lead to the appearance of highly radiant properties in the coating.

Thus, the maturation temperature is the temperature above which irreversible changes begin in the Solcoat coating, manifested by the appearance of a high re-emissivity in the coating.

The ripening temperature is 560°C.

The baking of the Solcoat on the surface of the lining takes place at a baking temperature that is below the curing temperature.

The baking temperature is the temperature at which the process of evaporating free water from the paint is completed.

Baking consists in the rigid adhesion of the coating to the surface of the lining and occurs when water evaporates from the paint applied to the lining. Hardening is completed when the water is completely evaporated. Up to this point, the paint remains plastic and hardens as it evaporates.

If the temperature increase occurs smoothly, and is such that the evaporation of water occurs slowly, and not like an avalanche, then the cavities on the outer surface of the coating, which are formed when the vapor bubbles exit, have time to smooth out. In this case, a smooth hardened coating with low roughness is formed.

If the temperature rise occurs relatively quickly, then evaporation occurs like an avalanche and the cavities do not have time to smooth out by the time of solidification, and the hardened coating has a significantly higher roughness compared to the case of a slow temperature increase.

After baking in the temperature range from the baking temperature to the ripening temperature, the Solcoat coating is not highly radiant, but is a so-called cross-linked polymer.

Network polymers (another name is cross-linked polymers, three-dimensional polymers) are polymers, the links of which form a single chemically bound spatial structure. They contain chemical, physical and topological cross-links (branching).

IMPLEMENTATION OF THE INVENTION

The invention can be implemented in furnaces with wall lining and no metal structures (pipes, coils) inside. For example, these are hydrogen reforming furnaces and most metallurgical furnaces. The invention can also be carried out in furnaces with wall lining and containing metal structures inside (for example, radiant convection furnaces).

The source of thermal processes in the furnace is fuel combustion. In furnaces in which the invention can be implemented, their energy efficiency is determined by how large the heat loss from fuel combustion is (that is, how much heat is not used in the process, but is lost (for example, in the walls of the furnace).

Heat transfer can be carried out radiatively (by absorbing radiative heat) and convectively. Both types of heat transfer take place in so-called tube furnaces.

Tube furnaces are devices for high-temperature (over 230 ° C) heating, evaporation and overheating of technological media (liquid and gaseous), as well as for the implementation of destructive transformations of raw materials due to the heat released during the combustion of various types of fuel in the furnace chamber. They are widely used in the oil and gas processing, petrochemical and chemical industries. Structurally, tube furnaces can be radiation, conventional and radiation-conventional.

In radiation-convection tube furnaces, 40-60% of all heat is transferred by radiation, and the rest by convection. This type of tube furnaces has been most widely used in industry due to the variety of designs and good technical, economic and operational parameters.

The implementation of the invention is the same for any furnace with a lining. Including for any tube furnace. However, the implementation of the invention in radiation-convection tube furnaces is the most common case.

The heated hydrocarbon raw material in the radiation-convection tube furnace is supplied from the convection chamber to the radiation chamber by the counterflow of the fuel combustion products in order to make the most complete use of heat.

Since the lining is gas permeable, the Solcoat coating maximizes the amount of thermal energy transferred to the carbon feedstock through the following factors:

- due to the gas impermeability of the coating,

- due to re-emission in the flue gas absorption spectrum (different from the emission spectrum of burners)

- due to a higher re-emission coefficient compared to the re-emission coefficient of the lining (in the temperature range in the furnace)

- by increasing the deployed radiating surface of the coating (provided by the claimed invention).

To implement the proposed method, at the first stage, the surface of the furnace lining is prepared for coating. To do this, the lining is dried from accumulated moisture, cleaned of contaminants and dedusted.

Further, to obtain a coating, the Solcoat components are mixed with water in the proportions recommended by the manufacturer.

In particular, the Solcoat components and water are mixed in proportions:

Two SOLCOAT Part A : One SOLCOAT Part B : One SOLCOAT Part C.

Mixing is carried out at the place of application of the coating, for example, using a screw mixer for 45 minutes. The paint obtained by such mixing can be used within 12-24 hours. The paint is applied immediately to the prepared surface in several, preferably 2-4 layers. The final thickness should be 0.12-0.25 mm. The time between applying the layers can be from 30 minutes to 4 hours.

At the same time, the roughness of the coating depends on the proportion of water contained in the paint and the rate of heating near the boiling point of water. The more water in the manufacture of paint, the greater must be the rate of temperature change when starting the furnace near the vaporization zone to ensure the avalanche evaporation of water.

The resulting paint is applied to a pre-cleaned, dry and dust-free surface of the furnace lining, after which, to increase the expanded reradiation surface, the paint is heated until an avalanche-like evaporation of water from the paint (120°) is achieved.

Avalanche evaporation usually occurs at a temperature change rate of 0.5° C. per minute or more when starting the furnace. However, in order to obtain the highest possible roughness of the coating, the rate of temperature change when starting the furnace in the temperature range of evaporation of free water from the paint should be the maximum possible from the technologically admissible rates for this furnace. Therefore, the heating rate when starting the furnace in this case in the temperature range of vaporization should be at least 30°C per hour.

If, in accordance with the technological regulations for starting the furnace, it is possible to vary the rate of temperature change at start-up, then this rate should be such that an avalanche-like evaporation of water during baking of the coating is ensured (at least 30 ° C per hour).

In furnaces that have metal structures inside the furnace (pipes, heat exchangers), including radiation-convection tube furnaces, if water evaporates to the dew point, this will lead to moisture condensation on the surface of the pipes. This leads not only to the appearance of scale, but also, as a consequence, to a decrease in the thermal conductivity of the pipes.

Therefore, evaporation must take place at temperatures above the dew point.

The task of matching the speed and degree of roughness of the baked coating is a multifactorial one that does not have an analytical calculation model.

However, it is possible to build such a model based on collecting a set of technological parameters (furnace parameters, lining parameters, coating parameters, burner operating modes, technological modes and furnace start-up and drying parameters, etc.) and constructing on their basis empirical data of multi-parameter functions or nomograms, allowing to determine for the implementation of the proposed method:

- the best ph of the paint and the parameters of the technological mode of starting the furnace

- the best ph of the paint for a given technological mode of starting the furnace.

Such a model should take into account that the rheological or mechanical properties of the wet mass have a significant effect on the uniformity of the coating. When water is added to a powder mixture, the cohesiveness of the powder mass increases and this causes higher mixing resistance. Therefore, wet mass torque measurement is consistent with different stages of fluid saturation [R.C. Rowe, G.R. Sadeghnejad, The rheology of microcrystalline cellulose powder/water mixes - measurement using a mixer torque rheometer, International Journal of Pharmaceutics, 38 (1987) 227-229]. There are four phases of liquid-solid interaction, namely pendulum, funicular, capillary and drip phases. When water is added, the torque of the wet mass increases as the saturation with liquid passes through the pendulum phase and the funicular mass phase of the funicular. The maximum torque approximately corresponds to the capillary phase [B. Hancock, P. York, R. Rowe, An assessment of substrate-binder interactions in model wet masses. 1: Mixer torque rheometry, International Journal of Pharmaceutics, 102 (1994) 167-176].

In a known method for manufacturing a highly radiant water-based sol-gel ceramic coating using the Solcoat /http://www.ctkeuro.ru/index.php?p=Coating/ component, which is closest to the claimed one, at a rate of temperature change when starting the furnace At 0.3°C per minute, the roughness was, on average, 71 µm, whereas when the coating of the same composition was heated at a temperature change rate of 0.5°C when the furnace was started, the roughness was, on average, 92 µm. The specified rates of temperature change at the start of the furnace 0.3°C and 0.5°C occurred when heated to 120°C. The measurements were carried out by Elcometer E224C-BS (digital surface profiler with remote sensor).

Claims (1)

A method for manufacturing a water-based high-radiation Solcoat ceramic coating by baking a liquid paint applied to a furnace lining, which consists in obtaining liquid paint by mixing Solcoat filler, Solcoat binder and water, forming a ceramic coating on the surface of the lining by applying the obtained paint to the surface of the furnace lining , after which, at the first start-up of the furnace, an avalanche-like evaporation of water is carried out by heating the applied paint to a temperature of 120°C at a rate of at least 0.5°C per minute, followed by baking the coating to a temperature not lower than the coating maturation temperature of 560°C.