Application of thermal spray technology in the field of boiler protection in thermal power plants in my country

       Boiler heating surface tube spray protection



Application of thermal spray technology in the field of boiler protection in thermal power plants in my country



    The boiler is an important component of a thermal power plant. It is a heat exchange device that uses the thermal energy of coal to heat the working medium to a certain temperature and pressure, also known as a steam generator.



1. Composition, operation accidents and causes of boilers



1. The composition of the boiler



The boiler consists of main components and auxiliary devices. The following table lists the main components and auxiliary devices necessary for modern large-scale natural circulation high-pressure boilers.



2. Boiler operation accident



Boiler is a special kind of airtight thermal equipment. It is not only directly scoured by flame and flue gas, but also bears medium pressure higher than atmospheric pressure. Therefore, the safe operation of boiler equipment is directly related to national property and personal safety. Strengthening the maintenance of the boiler is one of the very important links to ensure the safe and economical operation of the boiler.



Common boiler accidents are as follows: drum explosion accident, serious water shortage accident, serious water full accident, co-evolution of soda and water, rupture of heating surface pipe, rupture of economizer pipe, rupture of superheater pipe, rupture of air preheater pipe Cracks and furnace walls crack or collapse, etc.



3. The cause of the accident



my country's power station boilers and industrial boilers are mainly coal-fired. In 1998, the share of electricity produced by coal in my country accounted for about 75%. As the world pays more and more attention to issues such as resources and environmental pollution, although the share of natural gas, nuclear energy and other renewable energy sources in electricity production will increase year by year, it is expected that until 2050, coal As the share of my country's electric energy will exceed 50%. The quality of power coal is relatively poor, with high ash content and sulfur content, which is easy to cause contamination, ash accumulation, corrosion and wear on the heating surface. The analysis data of power plant operation in my country shows that among the equipment accidents in power plants, boiler accidents are the most common. In boiler accidents, "four pipes" (referring to water wall pipes, superheater pipes, reheater pipes and economizer pipes) have the most bursts and leaks. "Four-pipe" explosions account for about 40%-60% of all boiler accidents, or even 70%.



2. Application of thermal spraying technology in the field of boiler protection in coal-fired power plants



Thermal spraying (referred to as spraying) is to use a heat source to heat, melt or soften the sprayed material, and rely on the power of the heat source itself or an external compressed air flow to atomize or push the melt into a spray beam, and spray it to the substrate at a certain speed. A process for forming a coating on a surface.



During the spraying process or after the coating is formed, the metal substrate and the coating are heated, so that the coating melts on the surface of the substrate, and diffuses or melts with the substrate to form a spray welding layer that is metallurgically combined with the substrate, which is also thermal spraying. One of the methods is called thermal spray welding (spray welding for short).



Corrosion starts at the surface, wear proceeds at the surface, and fatigue is significantly accelerated by surface damage. As one of the important branches of surface engineering technology, the application of thermal spray technology in the field of boiler protection is the inevitable result of scientific and technological development.



At present, supersonic flame spraying and arc spraying technology are the most widely used in the field of boiler protection of coal-fired power plants in my country.



The supersonic flame spraying technology is to make the combustion-supporting gas and the combustion gas burn in the combustion chamber to generate a high-pressure flame, and then shoot out a high-speed flame flow through a special nozzle, so as to heat and accelerate the powder material fed into it and spray it to the surface of the substrate to form a coating. method. Liquid fuels such as propane, propylene, hydrogen and acetylene or diesel or kerosene can be used.



The coating prepared by the supersonic spraying process is very dense, with high bonding strength (up to 70MPa) and extremely low porosity (about 1% to 3%). NiCr-Cr3C2 is the most commonly used powder material when using the supersonic flame spraying process to protect the boiler tube wall of the power plant. See Figure 4).



      At present, it is more and more widely used in the field of boiler protection in domestic power plants.