current location：In Inner Mongolia boiler, the design of the superheater and reheater system is more complex, should be based on the boiler capacity and parameters to consider the pipe wall temperature, system resistance, temperature control mode, steel consumption and other requirements, and should be based on the overall layout of the boiler for comprehensive consideration, if necessary, should be different programs of technical and economic comparison, and then choose a better arrangement system.
Low-pressure small-capacity boilers and medium-voltage boilers generally use pure convection superheaters, and high-pressure and ultra-high-pressure boilers are widely used screen-type superheaters. Large boilers generally use reheater reheat system. Influenced by the structure characteristics of the superheater, reheater, arrangement position, flue gas temperature, blowing method, abnormal operating condition characteristics, the superheater and reheater are highly susceptible to contamination and high temperature corrosion during operation. The principle of staining and high temperature corrosion, prevention and control measures are as follows:
(1) The stain on the hot surface of the on-screen overheating and convection superheaters or reheaters, which are characterized in the upper furnace and in the horizontal flue, usually belongs to high temperature sintered ash. At normal operation, the smoke temperature is about 700-1100 degrees C, which is below the start ingenuity temperature (DT) of the ash, and does not produce slag bonding. However, at this temperature, in the combustion process sublimation of sodium, potassium and other alkali metal oxides are still gaseous, encountering a slightly lower temperature of the superheater or reheater is condensed on the wall of the tube, forming a white thin layer of ash. The reaction of alkali metal oxides condensed on the wall of the tank with sulfur oxide in the flue gas produces sulfates, and then the reacts with iron oxide and alumina in fly ash to produce composite sulfates. The compound sulfates are molten in the range of 500-800 degrees C, which binds to fly ash and continues to form a bond, causing the ash layer to thicken rapidly. When the sulfur and alkali metal content in the fuel is high, it is easy to get more serious contamination in the high temperature superheater or reheater. The molten ash slag layer is sintered at high temperature, forming a dense layer of solid ash with higher mechanical strength. The smoke temperature is about high, the longer the sintering time, the higher the strength of the ash slag, the more difficult it is to clear.
(2) Effects of contamination
High temperature corrosion, causing burst pipe, after staining slag, the flue gas resistance increases, the smoke flow rate decreases, and the smoke air flow rate is increased.
Coupled with the reduction of heat transfer capacity of the contaminated tube, resulting in uneven heat absorption between the tube rows, resulting in a larger thermal deviation, causing the super-temperature of the tank wall at the outlet of the superheater;
After contamination, the ability to absorb heat decreases, resulting in an increase in the temperature of smoke, thus reducing the economy of the unit.
Prevention and control measures for high temperature corrosion:
a) Control the temperature of the pipe wall;
b) Low oxygen combustion;
c) select a reasonable furnace to export smoke temperature;
d) Regularly blowing ash on the superheater and reheater;
e) reasonable organization of combustion, to prevent water-cooled wall slag, flame center skew and other phenomenon caused by thermal deviation, reduce the superheater and reheater pollution slag;
f) The use of special high temperature-resistant coatings for boiler thermal radiation condition improvement and corrosion protection.
For the existing boiler equipment construction, process is difficult to make major changes, the use of special high temperature-resistant coatings for boiler thermal radiation state improvement and corrosion prevention will be more effective, more economical method. Although the new boiler can choose a more suitable material for heat exchanger production, but the increased cost and late efficiency will be a problem, the use of special high temperature coating coating will be a better choice.
Here is particularly recommended Zhisheng Weihua ZS-722 thermal anti-corrosion coating, ZS-811 high temperature anti-corrosion coating for the above equipment brushing, ZS-1061 high temperature far infrared radiation coating for furnace brushing.
Introduction to ZS-722 thermal anti-corrosion coatings:
Product composition and characteristics: This product to Zhisheng Weihua special grafting inorganic - organic high temperature-resistant membrane solution, the membrane solution to silicone resin, passivated aluminum sol chelated into an inorganic modified membrane solution, high temperature resistance, good adhesion, good thermal conductivity, overcome the high molecular membrane solution low thermal conductivity.
Working mechanism: the coating fillers have silicon carbide, thermal graphite, boron nitride, aluminum carbide, graphite carbon tube, chromium trioxide, aluminum chloride, aluminum tripolyphosphate high temperature grinding synthesis, the formation of a thermal structure internal network, these fillers high thermal conductivity, high temperature resistance, chemical properties stable, long-term acid-resistant, high hardness, long-term wear, long service life.
Long-term temperature resistance: 750 degrees C, heat transfer coefficient 50w/m.k.
Application: Brushing in the water-cooled wall, heat exchange tube outside surface temperature at 750 degrees C heat exchanger surface, play the role of anti-coking, anti-acid dew point corrosion.
ZS-811 High Temperature Anti-corrosion Coatings Introduction:
Product composition and characteristics: This product to Zhisheng Weihua special chelation of silicon-oxygen-carbon inorganic re-modification high temperature solution and ultra-micro inorganic polymer flaky metal oxides and other fillers. The long-term high temperature resistance of the curing coating can be up to 2300 degrees C, the coating dense and wet-resistant heat corrosion effect is outstanding, the high temperature presents the glass state, the coating strength is high, the hardness is large, has a better wear-resistant wipe and impact resistance effect. Paint for pure unit-free division, non-toxic harmless, environmental protection.
Working mechanism: the coating after the hot high temperature solution and filler lattice cross-linking, forming a dense glass state, high temperature Tg phase stability, can effectively prevent the oxidation of the medium and corrosive media ion son invasion, to avoid the destruction of the entire lattice. The coating component contains a large number of corrosion-resistant factors and OH active groups, and the active components in the filler and steel or other materials active surface rapid cross-linking reaction, the formation of a three-dimensional structure of inorganic polymer coating, the coating and the substrate into a whole, forming a high temperature anti-corrosion coating with electrochemical protection and physical shielding.
Long-term temperature resistance: 2300 degrees C, heat transfer coefficient 30w/m.k.
Application: Brushing on high-temperature surfaces such as water-cooled walls, heat exchangers, reheaters, etc., plays an excellent anti-high temperature oxidation, low-temperature acid dew point corrosion and other complex high temperature corrosion conditions.
ZS_1061 introduction to high temperature far-infrared radiation coatings:
Product composition and characteristics: coatings using the company's own research and development of special inorganic silicate composite system as a film material. Add transitional elemental oxides, zirconia oxides, rare earth oxides Y2O3 and other fillers. Curing molding coating film has a good high and stable infrared emission rate, temperature resistance is stable, high temperature radiation rate is strong, corrosion resistance is good, hardness is high, wear resistance is excellent.
Working mechanism: the coating system using transitional elements oxides and zirconia, silicate refractory materials, high temperature doped to form a solid solution, not only increased the impurity energy level, improve the infrared radiation coefficient, but also maintain the corresponding heat resistance, high strength, corrosion resistance, wear resistance and other excellent performance, improve the overall strength and density of the coating. The doping of rare earth element oxides (e.g. Y2O3) can improve the activity of reactants, and is also the preferred material for doping and stabilizing the coating structure.
Long-term temperature resistance: 1800 degrees C, average infrared band radiation rate of 0.9
Application: Painting in the furnace, increasing the thermal radiation function of the furnace, reducing the absorption of heat from the furnace, effectively equalizing the thermal state of the furnace space, improving the state of uneven heat ingress in the furnace tube, improving the thermal efficiency and ensuring safe production.
Over the years, ZS-722 thermal anti-corrosion coating, ZS-811 high temperature anti-corrosion coating, ZS-1061 high temperature far infrared radiation coating is widely used in coal-fired boilers, gas boilers, induction furnace boiler energy-saving transformation field, reliable and stable coating, energy-saving effect is satisfactory.
