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Cause Analysis and Countermeasure of Boiler Economizer Leakage

A DG410 / 9.8-6 high-temperature and high-pressure boiler produced by Dongfang Boiler Factory of a certain power plant adopts JI type arrangement and DC burner, and is arranged in four corners to suspend tangentially combustion of pulverized coal. Put into operation in February 1999, the cumulative running time of about 20,000 hours.

The furnace economizer for the non-boiling type, staggered layout, upper and lower two economizers and air preheater cross-layout. The lower economizer is arranged symmetrically in four groups along the depth of the vertical flue and the center line in the width direction. Lower economizer tube a total of 132, 264, specifications for the 32 × 4, the pipe is 20G.

At the beginning of 2004, the furnace has been in the 1 month 4 times the next consecutive occurrence of economizer wear and tear failure, leading to 4 forced shutdown. Inspection revealed that the location of four leaks in the lower economizer B on both sides of the middle U-shaped bend of the wind face. Cracks are longitudinal, the crack wall is thinner, the thinnest is about 1 mm. On the lower economizer before and after the box A side of the first and second layer of all U-shaped pipe windward surface with the thickness gauge detection, U-shaped pipe windward face with varying degrees of wear and tear. Specifically, the wall thickness of less than 2.5 mm of 93, of which less than 2.0 mm wall thickness of 48, the wear is very serious.

1 Analysis of wear and tear causes
1.1 Flue gas corridors exist

There are flue corridors at the U-shaped bends of the lower economizer. The actual U-shaped bending distance is about 80 mm, which is larger than the design value (21 mm). The distance between the economizer and the wall The design value (60 mm) is large. Because the smoke corridor resistance is small, the flue gas velocity is bigger, after the computation, the flue gas velocity in the lower level economizer export is higher than the superior economizer entrance big 30% ~ 40%. As the pipe metal wear and smoke flow rate is proportional to the third power, therefore, in both sides of the U-shaped bend B serious wear and tear. (Wall thickness less than 4 mm), which leads to more wear and tear at the windward face of the economizer elbow.

1.2 The actual fuel properties and coal fineness and design value is different

In the wear and tear play a major role in the flue gas that large particles of fly ash, and the degree of wear and total ash related. The more the total amount of ash, the ash particles on the economizer tube the number of impacts will be more, the more serious wear and tear, and the total ash depends on the fuel ash Ay and low calorific value Qdwy.

(R90) is 22 ~ 28, the actual fineness (R90) is about 30, the average ash content of the coal is about 30%, the average ash content of the coal is 24.26%, the practical ash content is about 39.50% And the design of coal have a greater deviation. Coal coarse, ash will lead to ash particles and incomplete combustion of fuel particles increased, flue gas concentration in the fly ash increased, exacerbated the economizer wear.

1.3 Economizer tube bundle arrangement and installation quality

Flue gas sideways scouring economizer tube, the tube arrangement is different, the tube is not the same by the wear and tear. The wear of staggered tube bundles is more serious than that of parallel tube bundles, the wear of the second row of tube bundles is about 2 times larger than that of the first row, and the airflow flows from top to bottom, and the velocity of ash particles may be greater than that of flue gas Speed, thus exacerbating the impact of wear. The stove economizer staggered layout, and the use of specifications for the 32 × 4 pipe, due to poor rigidity of small diameter pipe, thin wall. Resulting in the actual snake-like pipe arrangement is not complete, coupled with the installation of the reasons, can not guarantee neat uniform pitch and pipe spacing, resulting in economizer pipe row of smoke corridor, the local pipe wall

Metal wear serious.

1.4 anti-wear measures are not perfect

In the lower section economizer B side of the U-bend, only the top of the installation of the anti-wear device (wind board), the lower economizer height of about 3 255 mm, the above anti-wear device on the U- Department of anti-wear no effect, therefore, the lower economizer U-shaped bend at the lower part of serious wear and tear.

1.5 The impact of combustion conditions

Boiler operation in the combustion air flow caused by the General Assembly increased the amount of smoke, leaving the wear rate increases. The calculation shows that when the excess air coefficient in the economizer is increased from 1.2 to 1.3, the wear is increased by 25%.

1.6 Other factors

The furnace capacity of the total plant capacity of 50% of the total boiler capacity, long-term full-load operation during the heating period, so the furnace economizer tube bundle by the wear of a long time, a large amount of wear. At the same time there is air leakage boiler phenomenon, according to the provincial company standards, 410 t / h boiler air leakage rate of 12%, while the actual leakage rate of about 20%, significantly higher. Operating practice has proved that when the economizer air leakage coefficient increased by 0.1, will make the metal wear increased by 25%.

2 Suggestions and Countermeasures

(1) in the furnace overhaul when the economizer to conduct a comprehensive inspection, replacement of all the elbow and the installation of U-type retaining tile. In the two rows of elbows installed between the resistance gate, try to eliminate the lower economizer outlet gas corridor. The economizer pipe spraying anti-wear coating (other furnace overhaul has been used, the effect is good).

(2) to strengthen the boiler combustion adjustment and testing. To ensure the safety and economic operation under the premise of ensuring the appropriate secondary and secondary air ratio and coal fineness, so that the fineness of R90 in the design value of 22 to 28 between. To improve combustion conditions within the furnace and to reduce the concentration of incomplete combustion of fuel particles in the flue gas. Under the premise of ensuring the degree of burnout of pulverized coal, reduce the air volume appropriately. Regular air leakage test, and take measures to reduce the air leakage rate.

(3) as far as possible with the design of coal similar to the fuel.

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