Causes and treatment measures of superheater tube

2022-08-15
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The causes and treatment measures of boiler superheater tube explosion

1 preface

Qingdao Xingping Thermal Power Co., Ltd. is a local thermal power enterprise, equipped with five ug-35/3.82-m11 medium temperature and medium pressure chain boilers, mainly responsible for urban and development zone heating and enterprise steam. In winter, due to the high heat load, all boilers operate side by side at the same time, which can only barely meet the needs of heating users. The lack of heating capacity has led to the current situation of tight production and no standby furnace

From November 12 to December 27, 2001, superheated steam overtemperature occurred in No. 5 boiler, which reduced the load capacity and steam supply of the boiler. After inspection, the overheating was caused by coking on the heating surface of the furnace. If the boiler is shut down for treatment, the steam supply situation will be more tense. Therefore, it is decided to put ash remover into normal operation to solve the problem of coking on the heating surface of the furnace. After 15 days, the steam flow of No. 5 boiler has been declining, from 35 tons to 23 tons, with a wider range of utilization, and finally suddenly dropped to 11 tons, with positive pressure burning. No. 5 boiler was forced to stop operation in an emergency. After shutdown, it was found that a pipe section burst in the sixth row of tubes on the left side of the superheater in the high temperature section. The breach is trumpet shaped, the wall thickness is severely thinned, the pipe is seriously expanded, the pipe diameter is expanded from 38 to 41, and the surrounding pipe sections are expanded to varying degrees. The edge of the pipe break is sharp. From the analysis of the break, it is caused by instantaneous overheating and pipe explosion

2 therefore, its small load measurement accuracy is very low. Analysis of the causes of tube explosion

entering the superheater, it is found that there is no coke slag about 2 meters around the tube explosion, while the rest is seriously charred, almost all the flue gas flow sections are settled. Originally, the ash remover was thrown from the manhole door of the boiler, and the ash remover was concentrated in this area, resulting in uneven distribution of the ash remover. And the ash remover can reduce the ash melting point of the coal, so that there are more ash residues in the coking place, and the larger the ash is, resulting in the reduction of flue gas flow area in a large area due to coking. During operation, a large amount of flue gas passes through the vicinity of the burst pipe row, and the instantaneous flow rate is calculated to be increased by 6 times. The superheater mainly relies on convection heat transfer. The increase of flue gas flow rate in the surrounding pipe section at the pipe burst not only aggravates the scouring of the pipe, but also causes local steam overheating. Under the dual effects of high-speed scouring of the outer flue gas and overheating of the inner wall pipe due to the diversity of raw materials used in the synthesis of ABS and hips, the strength of the pipe decreases sharply and the pipe burst instantly

3 measures taken

aiming at the specific situation of the site, the process of adding ash remover is improved

a. it is forbidden for operators to directly put the ash remover on the grate coal seam from the manhole door

b. add the ash remover in front of the products of some foreign manufacturers of coal conveying belt and the rolling screen, so that the added ash remover can be fully mixed with the coal through the rolling screen, crusher, coal chute and other links

c. the amount of ash remover added shall be determined by calculation according to the combustion condition of the boiler

d. select the type of ash remover according to the coal quality and boiler working conditions

4 conclusion

after changing the way of adding ash remover, the operation of No. 5 boiler was greatly improved. Until after the heating period, various parameters such as steam temperature were normal. When the heating surface of other boilers is coking, the ash remover is also added in this way. After half a month of use, the ash collection of the superheater falls off, and the coke slag on the pipe wall changes from hard to crisp. It has changed the problems that were difficult to clean up in the past and reduced physical labor. The thermal resistance of the heating surface is reduced, the thermal efficiency of the boiler is increased by 3%, the boiler output is increased, and great economic benefits are obtained

the number of boiler shutdown caused by coking on the heating surface is greatly reduced. During heating in winter, about 24000 yuan of boiler ignition cost is saved

a layer of anti-corrosion film is formed on the heating surface of each part, which reduces the sulfuric acid dew point of flue gas, protects the heating surface from corrosion, and prolongs the service life of the boiler

in a word, the correct method of adding ash remover is adopted, which not only avoids the boiler tube explosion accident, but also improves the boiler combustion condition. The way and method of adding ash remover should be paid attention to, so the above measures are worthy of reference and promotion

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