Preventive measures for coking of the hotpot

2022-07-28
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Preventive measures for boiler coking

boiler coking is a common phenomenon in the operation of coal-fired industrial boilers, which will destroy the normal combustion conditions and reduce the boiler output; Damage to furnace arches and tubes; The normal water circulation will be damaged, resulting in tube explosion accident, affecting the safe operation of the boiler, and in serious cases, the furnace outlet will be blocked and forced to shut down, resulting in safety accidents

I. causes of coking

1 Influence of coal quality

during coal combustion, the ash melting characteristic temperature is expressed by the deformation temperature T1, softening temperature T2 and melting temperature T3. The softening temperature T2 is the main index to judge whether the coal ash is easy to coking. The ash has different melting points due to different compositions: when the content of iron sulfide, ferrous oxide, potassium oxide and sodium oxide in coal is large, the ash has a low melting point and is prone to coking; When the content of silicon oxide, potassium oxide and aluminum oxide in coal is large, the ash melting point is high, and coking is not easy. The ash melting point of coal is generally 1250~1500 ℃ (higher than the design temperature of boiler furnace heating surface with excellent sealing and unparalleled chemical resistance), while the ash melting point of some coal is lower than 1100 ℃. The coal with this low ash melting point is very easy to coking

    2. Overload operation

design, installation and use of too small furnace volume or boiler overload operation, resulting in too high furnace heat load; The layout of radiant heating surface is small, and the distance between water-cooled wall tubes is designed by Donghua technology, which is too large, and the heat absorption is high. These will become the cause of coking during the operation of the boiler

in addition, due to improper operation, the air supply and extraction volume is too large. When the furnace temperature exceeds the ash bonding temperature, high-temperature coking will also be formed. If the air distribution is improper and the coal is not completely burned, a large amount of carbon monoxide, hydrogen and other gases will be produced, which will reduce the iron oxide with high melting point in the ash to iron oxide with very low melting point, reducing the ash melting point (possibly 300~350 ℃). At this time, the boiling combustion boiler is prone to "low-temperature coking", which is why

    3. Standard coke removal

if the coke slag is not cleaned in time, the ash and red fire are mixed together, which will aggravate the formation of coke slag

II. Measures to prevent and remove coking by boiling

1 Compared with developed countries, the purpose of furnace structure transformation is to control furnace temperature and flue gas temperature and prevent coking. Generally, new materials are listed as one of the seven major development directions. The flue gas temperature at furnace outlet is controlled below 50~100 ℃ of coal ash deformation temperature, that is, the best is 900~1050 ℃. To control the flue gas temperature at the furnace outlet, it is necessary to select the appropriate grate heat load and furnace heat load. See Table 1 and table 2 for specific methods

Table 1 heat load data sheet of grate

the level of furnace vessel heat loss also depends on the arrangement of water-cooled walls in the furnace. If there are too few water walls and the heat load of furnace vessel is too high, serious coking will occur. In particular, the slag trap pipe at the furnace outlet shall not be arranged too closely, otherwise it is easy to be blocked by slag. The measures to reduce the furnace temperature and flue gas temperature are to transform the furnace structure, such as changing the concealed pipe in the arch into an open pipe; Add water-cooled walls or anti coking headers on both sides of the furnace

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