Design improvement of the hottest tube rack hot wa

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Design improvement of pipe rack hot water boiler

1 problems and reasons

1.1 in recent years, corner pipe rack hot water boiler has been the leading product in Jinan special boiler factory, and most of the products are sold to Northwest China. The original design of this type of boiler has a lower front arch and a shorter and higher rear arch. Two specifications of rear arch pipes are laid in the rear arch. The cooling effect of water in the rear arch pipe makes the temperature of the rear arch low and cannot play the due role of high-temperature radiation. In addition, due to the influence of plateau climate, poor coal quality and low volatile matter, the furnace temperature is low, resulting in adverse consequences such as boiler de ignition, difficult ignition, poor adaptability of coal, incomplete coal combustion and so on

1.2 the cross flow and air leakage of the optimized industrial layout of the chain grate have always restricted the combustion condition of this type of boiler. The chain grate in the original design is composed of more than 4 air chambers. In order to achieve the same sealing and air pressure, all air chambers are separated by diaphragms longitudinally and horizontally, with air supply on one or both sides. Each diaphragm adopts the sealing measures of wired asbestos board. Due to the long-term high temperature environment, the strength and rigidity of the steel wire in the wired asbestos board quickly deteriorate, making the sealing worse, resulting in cross flow and air leakage between the air chambers, reducing the sensitivity of the air regulating device

1.3 the tube burst of the water-cooled wall of the combustion chamber is a major problem perplexing this type of hot-water boiler, especially in some places, the volatile content of coal is relatively high, and some even burn class III bituminous coal. For example, a qxl2 produced by Jinan special boiler factory used in Ezhuang coal mine in Laiwu 7/95/70-a Ⅱ boiler, because it uses the self mining type of the mine (the calorific value is more than 25.08kj), as a result, the front wall water wall tube and rear arch tube burst accidents occurred in less than a heating period. After analysis, one is that the coal is not suitable, the other is that there is thermal deviation, the boiler water distribution is not reasonable, the water flow rate is low, and the outer wall of the water pipe is radiated by the high-temperature flame of the furnace, resulting in the deposition and scaling of impurities in the water on the pipe wall, the water circulation condition is poor, and finally overtemperature tube explosion occurs

1.4 dirt and impurities cannot be effectively discharged during sewage discharge. The lower longitudinal header of corner tube boilers is generally relatively long, and the shortest is more than 4m. The original design has only one blowdown pipe seat. Therefore, the dirt and impurities far away from the blowdown pipe seat cannot be effectively discharged at all; At the same time, because the header is designed to be horizontal, the diameter of the header is very different from the diameter of the blowdown pipe socket. Even if the sewage is discharged quickly, only a small amount of dirt around the blowdown hole will be taken away. If the sewage discharge time is too long, heat loss and increase of make-up water will be caused

2 improvement measures

in view of the problems reflected in the operation of this type of boiler, Jinan special boiler factory carefully listened to the opinions of users and made a detailed analysis, eliminating the rough and extracting the fine, and determined the improved design ideas of improving combustion, improving efficiency, reducing smoke and dust, improving circulation, increasing flow rate and prolonging service life

2.1 its thermoplastic K series products have recently been used by the famous Spanish brand circutor SA to focus on improving the furnace and arch in improving combustion, improving efficiency and reducing soot

in the design of the furnace arch, the form of double folded line furnace arch is adopted. The rear edge of the front arch is higher than the front edge of the rear arch, and the front edge of the rear arch is lower than the middle of the rear arch, causing the whole furnace flame to form a strong turbulent high-temperature flue gas vortex under the action of the blower and induced draft fan, so that the gas in the furnace is evenly and strongly mixed, the residence time is longer, the flame temperature is high, the fullness is good, and the combustion of carbon particles and fly ash in the furnace space is strengthened, It is conducive to the ignition and burnout of coal

in order to solve the problems of air cross flow and air leakage of chain grate, the factory adopts W-shaped air bunker support design, fully enclosed air bunker, isobaric diversion air chamber, fine-tuning air inlet valve and staggered sealing directional push-pull ash falling device. Its operation principle is: one side air supply, and the blast enters the fully enclosed air chamber after fine-tuning the air inlet valve. In order to achieve consistent and balanced combustion of wind pressure in the width direction, the blast enters the equal pressure distribution outlet, and the wind pressure intensity is adjusted uniformly to the grate through the deflector. From the grate gap, it uses non-contact technology to monitor the displacement of the movable magnet, and the ash powder is temporarily stored at the bottom of the air chamber. It is regularly discharged through the staggered sealing directional push-pull ash falling device, and then brought into the front tribal ash hopper with the running chain grate, Basically, the problem of cross ventilation and air leakage is eliminated

2.2 the boiler body has been improved in terms of improving circulation, increasing flow rate and prolonging service life

in the body structure design, the back arch tube is removed, the number of primary rising tubes (513mm) in the furnace ember chamber is reduced, and the heating surface and circulation return of the tail serpentine tube are increased. For example, qxl2 The number of primary riser tubes in the furnace and combustion chamber of 7/95/70 boiler is reduced from 221 to 83, which is 62% less than the original design. The water flow rate is significantly increased from 0.078m/s to 0 26m/s, which ensures the cooling of the pipe wall by the circulating water, and effectively avoids the pipe explosion accident caused by the high heat flux of the rising pipe in the high temperature zone of the furnace. The increase of the heating surface of the tail serpentine tube is conducive to the settlement of flying dust particles, and the dust removal effect is good

increase the blowdown pipes of the left and right lower longitudinal headers from one to two, one in the front and one in the back. According to the boilers of different specifications, the scale collection devices with different design lengths are installed at the bottom of the header to increase the water flow intensity at the bottom of the header (where the dirt accumulates), make full use of the role of rapid sewage discharge and strong water flow, and regularly discharge the accumulated dirt with strong water flow. The gap between the device and the inner wall of the header must be ensured. Too large gap is not conducive to the formation of strong water flow, and too small gap is not conducive to the deposition of dirt. Therefore, it is appropriate to control the gap at 5 ~ 6 mm

in a word, the improved design for the problems existing in the corner tube boiler is to appropriately increase the medium flow rate. The newly designed double fold arch, fast and uniform blowdown device and isobaric air chamber make the boiler stable in combustion, stable in operation, fast in temperature rise, coal saving, strong in overload capacity, good in self-protection effect and safe in operation after power failure. The boiler with improved and optimized design has never failed after a heating period of trial, and users have responded very well. On May 13, 1998, it passed the achievement appraisal organized by Shandong Provincial Science and Technology Commission. Through environmental protection, thermal test and field investigation, it is believed that the output of the boiler has reached the design requirements through computer high-speed sampling, and has 10% overload capacity. The thermal efficiency is 2.6 ~ 3.95 percentage points higher than the standard specified in ZBJ "general technical conditions for industrial boilers" (referring to the five specifications of this series), and the dust removal effect is good

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