Discussion on the design of movable hood of waste

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Discussion on the design of movable hood of waste heat boiler of fully vaporized converter Ct:the paper begins with analysis of the causes which affect service life of petticoat pipe in converter waste heat boiler furnace mouth, by combining with engineering cases, demonstrates theoretically and practically that moving petticoat pipe using forced circulation way can raise service life of converter waste heat boiler and guarantee more effective operation A new type of moving petticoat pipe structure and petticoat pipe seal which fit for forced circulation way is introduced. A kind of flexible fastening of moving in order to pierce the paint layer, directly measure each point petticoat pipe is also recommended

keywords:converter waste heat boiler moving petticoat pipe Design1 preface the operating conditions of converter waste heat boiler change periodically and sharply with the smelting process of converter. When the converter is converting, a large amount of high-temperature flue gas flows through the waste heat boiler, and the heat load of the waste heat boiler increases sharply; When the blowing stops, the heat load of the waste heat boiler decreases sharply. Therefore, the heat load fluctuation cycle is about 30min (equivalent to the converter smelting cycle), and the poor operating conditions will inevitably affect the service life of the waste heat boiler. At present, the service life of converter waste heat boiler is very short. The average service life of the upper cooling flue is about 6 years, and the service life of the lower cooling flue is 2 ~ 3 years. The operating conditions of the movable hood at the furnace mouth are even worse, and the service life is only about 1 year. The accident rate during the service life is also very high, which must be repaired frequently, which will not only affect the steel output, but also affect the operation safety. Therefore, the design of converter waste heat boiler, especially the smoke hood at the furnace mouth, is very important. It directly affects the normal production of converter and must be paid attention to

next, let's talk about the views of a person with polyurethane filled texture pattern on the design of the movable smoke hood at the furnace mouth. 2. Reasons affecting the service life of the smoke hood at the mouth of the furnace (1) oxidation and alternating thermal stress caused by large heat absorption of the radiant heating surface and frequent and rapid changes in thermal load. Due to the periodicity of converter smelting process operation, during blowing, the heat load increases and the pipe wall temperature increases. When blowing is stopped, the heat load decreases and the pipe wall temperature decreases, causing periodic thermal alternating stress in the heated pipe, which is very easy to cause thermal fatigue damage. Transverse cracks will appear on the cooling pipe until it breaks, causing steam leakage. Therefore, the working life is not long

(2) local overheating damage caused by poor water circulation. Most of the smoke hoods adopt natural circulation. The smoke temperature in the smoke hood area is higher than that in the upper flue, and the heat load is greater. The theoretical calculation average surface heat intensity of the main flue section and the tail flue section of WISCO No. 1 steelmaking Co., Ltd. is less than 95kw/m2, the average surface heat intensity of the fixed smoke hood section has reached 251kw/m2, and the average surface heat intensity of the movable smoke hood section is as high as 352kw/m2. In the first three minutes of the blowing period, the flue gas volume of the converter increases sharply from zero to the maximum, resulting in pulse changes in the natural circulation of water flow. At the initial stage of blowing, the water circulation has not yet formed, and the sharp increase of heat load is easy to change the water in the heating pipe from nuclear boiling to film boiling, forming a vapor film barrier. At the same time, the heat deviation in the smoke hood is larger than that in the upper flue, and the heat absorption between the heating pipes of the lower smoke hood is more uneven due to the influence of slag hanging. These characteristics of the heat load in the smoke hood area make the circulation stagnate or reverse flow, and the heat transfer deteriorate, causing the pipe wall temperature to rise sharply. When the wall temperature exceeds the allowable limit temperature of the pipe, the heating pipe will be burned out

(3) influence of splashing and slagging. During the smelting process, the splashing slags a lot on the cooling equipment at the furnace mouth, and the heat transfer in the slagging area is poor, resulting in uneven heating of the heating pipe and local overheating damage; During slag removal, mechanical damage to the heating pipe is caused, and even the heating pipe is cracked

(4) influence of system pressure fluctuation. When the natural circulation system is composed of the cooling equipment at the mouth of the boiler and the drum, the frequent fluctuation of the vaporization system and the fatigue damage caused by the continuous change of internal pressure stress are caused by the abnormal operation of the drum pressure stabilization system. At the same time, too large system pressure fluctuation also affects the water circulation characteristics

(5) water quality impact. Although soft water is used, due to poor water quality management and difficult sewage discharge at the bottom of the heating pipe of the smoke hood, when the heat load is very high, the inner wall of the heating pipe will also scale, which will greatly reduce the heat transfer effect of the pipe and cause overheating damage

(6) wear of furnace dust on heating pipes. The furnace gas contains a large amount of iron oxide dust. When the furnace gas flows in the smoke hood, the dust rubs with the heating surface tubes and causes the heating tubes to wear. The degree of wear is related to the flue gas flow rate, which is generally controlled within the range of 20 ~ 25m/s abroad

(7) influence of manufacturing process. In the manufacturing process of the smoke hood, it was not manufactured in strict accordance with the relevant manufacturing technical conditions and regulations of the boiler, and the quality was poor. In particular, a large number of welds between the pipe and the diaphragm were welded manually, which was difficult to ensure the welding quality. 3. The movable hood of the waste heat boiler of the full vaporization converter should adopt the forced circulation mode. Speaking of the circulation mode, it is necessary to review the development history of the waste heat boiler of the converter in our country

at first, due to insufficient understanding of the characteristics of converter waste heat boiler, vaporization cooling was only adopted in the upper flue, and most of them were forced circulation. The smoke hood in the furnace mouth section is basically open water-cooled, and the water quality is industrial water without softening treatment. The smoke hood is made of rectangular cross-section pipes bent into a ring and then welded. Due to the unreasonable structure and poor cooling effect, its service life is very short

later, in a power failure accident of a converter forced circulation waste heat boiler, although the circulating water pump stopped running, it was found that the flue originally designed as a forced circulation system could operate normally. Since then, the flue has been using natural circulation, so the natural circulation flue has been popularized in our country. All newly-built converter waste heat boilers are basically natural circulation, and are extended to the lower hood

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