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Analysis of wear reasons and preventive measures of water wall tube in CFB boiler

Words:[Big][Medium][Small] Mobile Page Two-Dimensional Code 2018-10-15     

Analysis of wear reasons and preventive measures of water wall tube in CFB boiler

1, the preface

Hefei tianyuan heat and power co., ltd. is a subsidiary of hefei heat and power group co., LTD., located in hefei high-tech industrial development zone, is a professional enterprise engaged in urban combined heat and power production central heating.It mainly provides central heating for the high-tech development zone and enterprises and institutions, industrial and civil heat users in the west heat district of hefei city.

2. Overview of boiler

Hefei thermal power co., LTD., 3 #, 4 # doctors graduated circulating fluidized bed boiler (YG - 75/3.82 - M1) was made by jinan boiler group co., LTD. Production of medium temperature and medium pressure boiler, the cyclone circulation combustion system of furnace is membrane type water wall structure, superheater high points and low secondary superheater, intermediate water spray attemperator, shall have a level 3 economizer and tail, secondary air preheater.

The boiler plant of our company has redesigned the return material system of two circulating fluidized bed boilers. The efficiency of cyclone separator of boiler no.4 is higher than that of boiler no.3.The two boilers were put into operation for more than a year, and leakage occurred at the welding joint (elevation 9360mm) between the combustion belt at the bottom of the furnace and the water wall tube transition area. Among them, boiler no. 3 appeared once, and boiler no. 4 appeared three times, causing forced shutdown for maintenance and replacement of water wall tube.

3. Wear mechanism of water wall tube

The wear of boiler water wall tube is mainly concentrated in three areas: the wear of the tube wall in the transition area between the combustion belt at the bottom of the furnace and the water wall tube;Wear of tube wall in corner area around furnace;Wear of pipe walls in irregular areas.

3.1 reasons for the wear of the pipe wall in the transition area between the combustion belt at the bottom of the furnace and the water-wall tube: first, the flow direction of solid materials running along the inner wall of the furnace changes in the interface area, thus causing erosion to the water-wall tube and wear to the water-wall tube;Another reason is that in the transition area, the solid materials flowing down the wall face and the solid materials moving up in the furnace move in the opposite direction, generating vortex flow locally and causing wear on the water-cooled wall tube.

3.2 the wear of the tube wall in the corner area around the furnace is caused by the relatively high density of solid materials flowing down from the inner wall of the corner area, and the flow state is also damaged.

3.3 the wear of pipe walls in irregular areas (such as thermometers, differential manometers, etc.) is mainly caused by the disturbance caused by irregular pipe walls to local flow characteristics.

4. Cause analysis of wear and leakage of boiler water wall tube

The boiler water wall tube appears the leakage, after stopping the boiler, has carried on the inspection and the analysis to the boiler protection burning belt place, the spraying area and the boiler operation record.Through comparison, it is found that the wear condition of boiler no. 4 is more serious than that of boiler no. 3, with more wear areas than that of boiler no. 3.Contact relevant departments of jinan boiler factory and consult relevant materials. The analysis shows that the main causes of wear and leakage of water wall tube at the combustion belt are as follows:

4.1 the boiler guard and combustion belt should be paid attention to avoid the occurrence of “Convex platform & throughout;Including the &ldquo formed by uneven grinding of butt weld of water-wall tube;Convex platform & throughout;And gas with water wall tube castable formation “Convex platform & throughout;cars only

If “;Convex platform & throughout;As a result, the falling ash flow forms an impact Angle with the water-wall pipe, which not only aggravates the wear of welding joints and fins at the butt joint, but also causes serious wear to adjacent pipes.This is because the circulating materials in the furnace change direction when flowing down the water wall through the boss, and directly scour a certain part of the water wall pipe, which causes rapid scour and wear of the water wall, especially the two sides where the water wall pipe contacts with the castable.

4.2. Partial material falls off in the flame spraying anti-wear area of the water-wall tube in the boiler combustion belt, resulting in cutting effect of the water-wall tube and aggravating the wear of the tube wall, as shown in FIG. 1-1:

4.3. The velocity of flue gas in boiler operation is the most important factor affecting the wear of boiler water wall tube.The results show that the wear of boiler water wall tube is proportional to the third power of flue gas velocity.In the actual process of boiler operation, boiler operators worry about poor fluidization, in order to improve the safety coefficient of boiler operation, often run with a large amount of air, resulting in the smoke velocity too fast, seriously aggravating the wear and tear of the boiler, at the same time increase the plant electricity consumption - China heating information network.

5, boiler wall tube leakage prevention measures

5.1 in order to avoid uneven grinding of welding seam of gas-fired water-cooled wall tube “Convex platform & throughout;And gas with water wall tube castable formation “Convex platform & throughout;cars onlyThe inspection and acceptance of boiler installation and construction should be strengthened to ensure the construction quality.

It is also possible to improve the castable furnace wall at the water wall tube, and suspend the lower part of the connection of the water wall tube here without pouring, so that the falling ash directly hits the castable.

At the same time, when designing the welding seam of the water-cooled wall tube with wei combustion belt, it can be considered to move up or down to avoid the &ldquo formed in the welding seam.Convex platform & throughout;, causing wear of water wall tube.

5.2 periodically carry out supersonic arc spraying on the water-cooled wall tube with flame belt.Supersonic arc spraying is an advanced spraying method in the world at present, which is more ideal than ordinary arc spraying and flame spraying. Taking arc as heat source, the melted abrasive alloy wire is atomized by high-speed airflow and sprayed to the surface of the workpiece to form a coating.It can delay the wear and tear to prolong the running period of boiler.In order to ensure the quality of supersonic arc spraying, some technical problems in the process of construction technology, management and acceptance inspection should be done well.

5.3. Boiler operation adjustment

5.3.1 strictly control the appropriate amount of air entering the furnace, and adjust the ratio of primary and secondary air reasonably under the condition of ensuring normal fluidization, with the proportion of primary air accounting for 50 ~ 60% and secondary air accounting for 40 ~ 50%, so as to reduce the flow rate of flue gas and reduce the wear and tear of water-wall tube.

5.3.2 control appropriate furnace differential pressure and material layer differential pressure.The material layer differential pressure is high, the fluidized air volume increases, increased the boiler water wall tube wear and power consumption.The high differential pressure increases the ash concentration in boiler furnace, which increases the wear of boiler water wall tube.

5.3.3 special attention shall be paid to the impact of fuel characteristics on wear and strictly control the coal quality and particle size of the coal entered into the furnace.The fluidized bed boiler has a wide range of fuel adaptability, which can burn low-quality coal, but the advantages of the fluidized bed boiler are more obvious when it burns high-quality coal, such as small slag heat loss, low power consumption, high boiler efficiency, and reduced water wall wear.Strictly control the coal particle size into the furnace, try to avoid burning high wear coal and coal ratio control, the coal particle size into the furnace should not exceed 13mm.

5.4. How to find leakage of boiler water wall tube as early as possible

Due to the combustion characteristics of CFB boiler, the existence of boiler wear is inevitable. While measures are taken to reduce and delay the wear of water-wall tube, how to timely find the water-wall tube that has been leaking and avoid the leakage in a larger scope is put forward as follows:

5.4.1 if the difference between boiler feed water flow and boiler main steam flow is abnormally large, check the feed water flow and steam flow meter in time to confirm the correctness of the meter.If there is no abnormality in the meter, this phenomenon can be used as one of the most direct and simple criteria to judge the leakage of water wall tube.

5.4.2 during the operation of the boiler, it is necessary to observe whether the furnace wall near the combustion belt is damp and whether there is leakage sound, etc., to determine whether there is leakage of the water-wall tube.

5.4.3 if the coal quality of the boiler is relatively stable, the leakage of the water-wall tube can be determined by the changes of other meters of the boiler set, such as steam, feed pressure, induced draft fan current, smoke exhaust temperature, and temperature meter of the recharging device.

6, summary

Due to the characteristics of CFB boiler, the wear of boiler water wall tube is one of the most serious parts of boiler heating surface. As the running time of boiler increases, the wear of boiler water wall tube becomes more and more serious.We should take measures to reduce and avoid wear and tear as much as possible, delay the boiler operation cycle, and reduce the number of unplanned shutdown.How to choose the best operating condition between boiler safety and economic operation remains to be analyzed in the future boiler operation process, summarize experience, improve the boiler water wall tube wear control and prevention level, to achieve boiler safety and economic operation.


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