Technological Progress of Thermal Insulation Coatings

Abstract: heat insulation coating can effectively improve the energy saving effect of equipment and pipeline, reduce energy consumption, and has a good application prospect in petrochemical industry This paper systematically introduces the heat preservation mechanism, performance and existing problems of reflective, radiation and barrier heat preservation coatings Especially, aiming at the problem of insufficient corrosion resistance of thermal insulation coating, this paper mainly introduces the anticorrosion and thermal insulation integrated coating with dual functions of anticorrosion and thermal insulation Finally, the future development direction of thermal insulation coating is prospected Key words: coating; heat insulation; anticorrosion; petrochemical pipeline foreword in the petrochemical industry, the energy loss caused by pipeline heat dissipation accounts for about one-third of the total energy consumption every year, and the corrosion of petrochemical pipeline also brings many safety risks for its production and operation Therefore, anticorrosion and heat preservation are very important for petrochemical industry At present, the traditional porous rock wool and aluminum silicate roll felt are usually used in domestic refining and chemical enterprises to insulate the equipment and pipelines The thickness of the general insulation layer can reach 100-200 mm, the construction process is complex and the cost is high Moreover, the thick insulation layer can cover the damage of the equipment and pipelines, which makes it difficult for petrochemical enterprises to avoid the conventional production risks and safety risks At the same time, the insulation layer of elbow, tee, valve and other special-shaped parts has complex structure, many interfaces and great construction difficulty These parts are often exposed, which is the weak link of equipment and pipeline insulation In particular, traditional porous thermal insulation materials often do not have corrosion resistance Corrosion factors can be easily attached and stored in their pores, and become the medium of heat conduction, which not only greatly reduces the efficiency of thermal insulation of equipment and pipelines, but also shortens the service life of the whole thermal insulation system The thermal insulation coating developed in recent years is a new type of functional coating which can reduce the heat transfer in the substrate from the perspective of heat transfer mechanism Compared with the traditional thermal insulation materials, the thermal insulation coating has excellent thermal insulation effect, and the thickness of several millimeters can achieve the thermal insulation effect of the traditional thermal insulation layer with the thickness of 100-200 mm; therefore, the damage of equipment and pipeline is also easy to be detected, and the difficulty and cost of system maintenance are greatly reduced In addition, the coating construction process is simple, which can fully cover the elbow, tee, valve and other special-shaped parts, effectively reducing the heat dissipation of the pipeline In particular, through the reasonable selection and formulation optimization of film-forming materials, the coating can also have the functions of high permeability and corrosion resistance, effectively avoid the penetration of corrosion factors in the coating, greatly slow down the corrosion rate of equipment and insulation system, and improve its service life Thermal insulation coating provides a new strategy for energy saving and emission reduction in petrochemical industry and prolonging pipeline life This paper summarizes the development of thermal insulation coatings and looks forward to its development trend In the field of thermal insulation coating, the thermal insulation performance of the coating is mainly achieved by increasing the thermal radiation reflection degree of the coating, enhancing the emissivity of the thermal radiation of the coating, and slowing down the heat conduction of the coating According to the different heat insulation mechanism, it can be divided into three types: reflective heat insulation coating, radiation heat insulation coating and barrier heat insulation coating 1.1 reflective heat insulation coating reflective heat insulation coating is a coating (Figure 1) that can achieve heat insulation effect by adding pigments and fillers with high reflectivity to thermal radiation (solar radiation, infrared radiation, etc.) in the system to avoid the absorption of solar radiation by equipment and buildings Pigments and fillers are the key to ensure that the reflective thermal insulation coating has high reflectivity to solar radiation Generally speaking, the lighter the color of the coating, the higher its reflectivity to the solar radiation Therefore, the traditional reflective thermal insulation coatings are mainly white, they generally use TiO2 and ZnO with high whiteness as pigments The reflectivity of this kind of coating to solar radiation can be as high as 80%, and some coatings can even reach 95% Therefore, in summer, the temperature of the outer wall of the building coated with reflective thermal insulation coating is far lower than that of the ordinary building, only slightly higher than the ambient temperature, which greatly reduces the cooling load of the building and obviously saves the power consumption In the petrochemical industry, reflective thermal insulation coating is widely used in the thermal insulation of oil storage tank It can effectively prevent the potential safety hazards caused by the high temperature of the tank and improve the available storage capacity of the tank farm With the development of economy, people tend to paint with rich color Therefore, non light reflective heat insulation coating has been widely studied The main research idea is to prepare color pigments and fillers with high reflectance only to infrared radiation, which can make the coating absorb visible light and present rich color, and reflect infrared radiation with high heat, so as to achieve the purpose of heat insulation At present, the organic pigments of perylene, copper phthalocyanine and azo, the inorganic pigments of chromium, cadmium and rare earth all have better infrared light reflecting ability However, organic pigments are often insufficient in UV resistance and heat resistance, while chromium and cadmium inorganic pigments have the problem of heavy metal pollution Only rare earth inorganic pigments have good overall performance, but the preparation technology of these pigments and fillers is difficult and the cost of raw materials is high Therefore, the color reflective thermal insulation coating needs further study In terms of coating durability, the reflective heat insulation coating is mainly used to reflect solar radiation, so the film-forming resin of the coating is mainly acrylic resin, fluorine-containing resin and other polymers with excellent UV aging resistance Acrylic resin has excellent ultraviolet aging resistance because of its molecular structure without benzene ring, double bond and other structures Moreover, the vinyl monomers are various While maintaining good weather resistance, the performance of the coating can also be adjusted according to the monomers, which can be used in different environments The bond energy of C-F bond of fluorine-containing resin is as high as 485.6 kJ / mol, the molecular structure is stable, and in its molecular chain, each C-C bond is tightly surrounded by three-dimensional spiral arrangement of F atoms This kind of structure can protect it from UV and has excellent weather resistance Moreover, the C-F bond also makes the coating surface hard and wear-resistant; the surface energy is low, the handle is smooth, the stain resistance is good, and it is easy to wash and clean with water; moreover, the coating also has many advantages, such as mildew resistance and heat resistance But the reflective heat insulation coating is only a kind of material reflecting heat radiation, it can not hinder the heat transfer of other two heat transfer methods to the substrate Therefore, it is impossible to insulate the high-temperature heat transfer medium (such as high-temperature oil pipeline and industrial boiler), it is only a kind of heat insulation coating applied to the external wall of facilities and buildings In addition, the general reflective heat insulation coating has poor corrosion resistance In the heavy corrosion environment, it is necessary to protect the base material from corrosion by coating with heavy anti-corrosion coating Obviously, it has a good development prospect to further improve the corrosion resistance of the coating and to realize the integration of corrosion protection and heat preservation of the coating 1.2 radiation type heat insulation coating radiation type heat insulation coating is a kind of coating which can actively reduce the heat transfer of substrate in the form of emitting heat radiation It is realized by adding pigments and fillers which can emit heat radiation efficiently in the coating system, or directly sintering these materials into ceramic coating When the coating absorbs the heat, it can radiate the heat back to the environment at a certain wavelength of infrared radiation, so as to achieve the effect of heat insulation and cooling (Figure 2) Radiation packing mainly includes SiC, cordierite (the main component is mg2al4si5o18; it can contain Na, K, CA, Fe, Mn and other elements), transition metal oxides (such as MnO2, Cr2O3, COO, CuO) and other materials After they absorb heat, through the energy of molecular vibration and rotation, they constantly make lattice and bond group collide, and re emit the absorbed heat back to the environment Compared with reflective heat insulation coating, radiant heat insulation coating has the characteristics of "active cooling" That is to say, in the process of heat transfer, the reflective heat insulation coating can only slow down the heat transfer speed, when the heat slowly passes through the coating, the internal space temperature increases; at this time, even if the external temperature of the coating decreases, the heat energy can only be trapped in it However, the radiation type thermal insulation coating can emit the heat in the form of thermal radiation, so as to promote the same cooling rate indoor and outdoor Moreover, the thermal stability of this kind of filler is good, so the radiation type heat insulation coating has strong adaptability to temperature It can not only be used for thermal insulation of buildings and petrochemical tanks in normal temperature environment, but also for thermal insulation of high temperature petrochemical pipelines and boilers in high temperature environment However, according to Stefan Boltzmann law, which affects the radiation emittance of materials, the total radiation power of radiation packing is directly proportional to the fourth power of absolute temperature In the normal temperature environment, the radiation power of the packing is low, but in the high temperature environment, as long as the temperature has a small change, the radiation power of the object will change greatly According to Planck's radiation law, the higher the temperature is, the higher the emissivity is, and the better the heat insulation effect is Therefore, the radiation type heat insulation coating has a more extensive application in the high temperature environment In particular, when it is used for thermal insulation of high-temperature Petrochemical pipes, boilers, etc., because the coating can radiate the heat back to the inside of the facility, it plays the role of thermal insulation and insulation, and has the effect of "secondary heating" to the facility, further improving the utilization rate of energy At present, the radiation emissivity of a large number of radiation type thermal insulation coatings at high temperature has reached more than 85%, and the radiation emissivity of some transition metal oxide system coatings (such as fe2o3-mno2-coo-cuo system, nio-cr2o3-sic system) can even reach 95%, with excellent thermal insulation effect Moreover, the coating can effectively improve the energy utilization rate of high-temperature facilities, generally up to 5% ~ 10%, greatly reducing the heating time, reducing the temperature difference in the facilities, and improving the product quality and production efficiency In addition, the excellent heat insulation effect of radiation type heat insulation coating can also play a good protective effect on the substrate After the protection of radiation heat insulation coating, the service temperature of high-temperature facilities is greatly reduced, and its service life can be extended by 1-4 times; for electric heating elements, its service life can be extended by 50% - 70%, which significantly reduces the maintenance cycle and reduces the maintenance cost In particular, with the improvement of radiation type thermal insulation coating, the durability of the coating is greatly improved, further improving the protective effect of the coating, and extending the service life of the facilities For example, by sintering coating technology, the rare earth silicate coating on the surface of SiC can effectively overcome the problem that the traditional SiC coating is easy to be oxidized at high temperature, resulting in the decrease of infrared emissivity Through the composition compounding of radiation materials, doping of rare earth elements or reducing the particle size of radiation materials to nanometer level, the coating can form a more compact crystal structure, and the thermal shock resistance of the coating is significantly improved, so that the radiation heat insulation coating can effectively withstand high-temperature thermal shock, and prevent the coating from being caused by the mismatch of thermal expansion coefficient in the service process Cracking and falling off At present, the radiation type heat insulation coating is mainly ceramic coating, which needs sintering and forming, and the construction process is complex Moreover, ceramic coating is a kind of brittle material, its fracture work is generally only about 300 J / M 2, and the coating failure caused by the coating brittleness is the main failure mode More importantly, temperature has a significant effect on the coating