Boiler heating surface tube coating protection

Thermal spraying technology application in the field of thermal power plant boiler protection in our country

Boiler is an important component of coal-fired power plants, is the use of the heat of the coal working medium heated to a certain temperature and pressure of heat exchange equipment, also known as steam generator.

One, the composition of boiler, accidents and the reasons

1. The composition of the boiler

Boiler made up of main components and auxiliary equipment.Modern large-scale natural cycle table below necessary main parts and auxiliary device of high pressure boiler.

2. The boiler accidents

Boiler is a special kind of closure of thermal equipment.Not only directly scour by fire and smoke, but higher than the atmospheric pressure of the medium under pressure.As a result, directly to the safe operation of boiler equipment is closely related to national property and personal safety.Strengthen the maintenance of the boiler, is to guarantee safe and economic operation of the boiler is one of the important link.

General common boiler accident has the following kinds: drum explosion accident, serious water shortage, serious accident filled with water and soda teng, heating surface tube rupture accident, economizer tube rupture, superheater tube, air preheater pipe bursts and furnace wall cracking or collapse, etc.

3. The cause of the accident

Power station boiler and industrial boiler is given priority to with coal in our country.In 1998, China produced by coal power share accounted for about 75%.As the world within the scope of the importance of the problems of resources, environmental pollution is increasing day by day, though, such as natural gas, nuclear power and other renewable energy share in the electric power production will increase year by year, but is expected until 2050, coal power in China's share of over 50%.And bad quality of power coal, ash content and sulfur content is higher, easy to cause heating surface contamination, dust, corrosion and wear.The analysis of power plant operation data show that in power plant equipment accident, most boiler accidents.In the accident of boiler, "four pipe" (refers to water wall tube, superheater tubes, reheater tube and economizer tubes) explosive leakage most times."Four tubes" explosive leakage accounted for about 40% of the boiler all accident - 40%, even up to 70%.

Second, in the field of thermal spraying technology in coal-fired power plant boiler protection applications

Thermal spraying (hereinafter referred to as coating) is the use of heat source to heat melting or softening, spraying materials by heat source their own power or with compressed air, will impel the molten droplet atomized or grain beam into injection of grain, and at a certain speed into the substrate surface coating process.

Formed in the process of coating or coating, and coating to metal substrate is heated, the coating on the surface of the matrix, melting, and matrix diffusion or melt, spray welding layer formed in the substrate metallurgical bonding, which is one of the hot spraying method, called the thermal spray welding (welding).

Surface corrosion start, on the surface of wear and tear, and fatigue was significantly accelerated surface damage.As an important branch of surface engineering technology of thermal spraying technology, the application in the field of boiler protection is the inevitable result of the development of science and technology.

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

Hypersonic flame spraying technology is to make the fuel gas and combustion of gas in the combustion chamber to produce high pressure fire, then through a special nozzle injection high-speed flame flow, which will be sent to the powder material heating, to accelerate the jet to the substrate surface coating method.Can use propane, propylene, hydrogen and acetylene or liquid fuels such as diesel or kerosene.

Supersonic spraying technology on preparation of the coating is very compact, high bond strength (can reach more than 70 mpa), has a very low porosity (1% ~ 3%, right).NiCr - Cr3C2 is the use of supersonic flame spraying technology for power plant boiler tube wall of the most commonly used for protective powder material, coating prepared from its microhardness can reach about 1400 hv, has the very good abrasion and grain properties (see figure 4).

At present in domestic power plant boiler protection is more and more widely in the field of application.