Boiler Section [Weekly Topic] Summary Post (continuously updated since 2014)
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This post was last edited by A Dai A Mu on 2013-12-30 at 17:33. 1. Topic: Soliciting descriptions of phenomena, cause analysis, and handling methods regarding economizer leakage accidents. Topic link: http://bbs.hcbbs.com/viewthread.php?tid=337909&highlight=%C3%BF%D6%DC Start date: 2008-12-4 Number of replies: 6 ------------------------------------------------------------------------------------------------ 2. Topic: Into how many stages is the formation process of saturated water vapor divided? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=341101&highlight=%C3%BF%D6%DC Start date: 2008-12-7 Number of replies: 38 ------------------------------------------------------------------------------------------------ 3. Topic: Discussion on the reasons for wear and corrosion in the rear heating surfaces. Topic link: http://bbs.hcbbs.com/viewthread.php?tid=347431&highlight=%C3%BF%D6%DC Start date: 2008-12-14 Number of replies: 27 ------------------------------------------------------------------------------------------------ 4. Topic: What is thermal deviation in superheaters, and what are the two causes of it? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=354039&highlight=%C3%BF%D6%DC Start date: 2008-12-21 Number of replies: 27 ------------------------------------------------------------------------------------------------ 5. Topic: What are the management systems for boiler rooms? And specify one of them. Topic link: http://bbs.hcbbs.com/viewthread.php?tid=390980&highlight=%C3%BF%D6%DCDate posted: February 16, 2009
Number of replies: 13
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6. Topic: How is the material balance in a circulating fluidized bed boiler calculated? And how should it be adjusted during normal operation? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=396037&highlight=%C3%BF%D6%DC Start date: 2009-2-21 Number of replies: 1 ------------------------------------------------------------------------------------------------ 7. Topic: How should the cross-sectional area, volume, and height of the furnace change? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=797883&highlight=%C3%BF%D6%DC Start date: 2011-2-12 Number of replies: 4 ------------------------------------------------------------------------------------------------ 8. Topic: What are the items for random inspections of the welding quality on site in boilers? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=800898&highlight=%C3%BF%D6%DC Start date: 2011-2-19 Number of replies: 1 ------------------------------------------------------------------------------------------------ 9. Topic: What causes pitting corrosion in the image? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=825937&highlight=%C3%BF%D6%DC Start date: 2011-4-12 Number of replies: 19 ------------------------------------------------------------------------------------------------ 10. Topic: Questions regarding the fabrication of test plates for coal-fired steam boilers? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=829223&highlight=%C3%BF%D6%DC Start date: 2011-4-18 Number of replies: 2 ------------------------------------------------------------------------------------------------ 11. Topic: What factors should be considered when determining the furnace width? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=834287&highlight=%C3%BF%D6%DC Start date: 2011-4-29 Number of replies: 3 ------------------------------------------------------------------------------------------------ 12. Topic: What are the requirements for boiler materials when water is in a critical state? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=837254&highlight=%C3%BF%D6%DC Start date: 2011-5-7 Number of replies: 9 ------------------------------------------------------------------------------------------------ 13. Topic: Why are there regulations regarding the time and temperature at which water should be added before starting a boiler? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=840236&highlight=%C3%BF%D6%DC Start date: 2011-5-12 Number of replies: 9 ------------------------------------------------------------------------------------------------ 14. Topic: What phenomena occur when the steam consumption of a boiler exceeds its critical load? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=844395&highlight=%C3%BF%D6%DC Start date: 2011-5-20 Number of replies: 7 ------------------------------------------------------------------------------------------------ 15. Topic: How to solve the problem of frequent thinning at the elbow where the outlet pipe of the secondary economizer connects to the steam drum? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=848777&highlight=%C3%BF%D6%DC Start date: 2011-5-29 Number of replies: 12 ------------------------------------------------------------------------------------------------ 16. Topic: What process steps are involved in lifting and positioning water wall components? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=852842&highlight=%C3%BF%D6%DC Start date: 2011-6-6 Number of replies: 8 ------------------------------------------------------------------------------------------------ 17. Topic: What is the impact of the boiler’s flame center position on its operation? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=855601&highlight=%C3%BF%D6%DC Start date: 2011-6-12 Number of replies: 13 ------------------------------------------------------------------------------------------------ 18. Topic: How can one avoid the situation where the oil gun retracts on its own? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=859990&highlight=%C3%BF%D6%DC Start date: 2011-6-21 Number of replies: 4------------------------------------------------------------------------------------------------ 19. Topic: What requirements should the furnace wall structure of coal-fired boilers meet? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=862630&highlight=%C3%BF%D6%DC Date of posting: June 26, 2011 Number of replies: 8 ------------------------------------------------------------------------------------------------ 20. Topic: At which locations should temperature measurements be taken for boilers? What is its purpose? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=865980&highlight=%C3%BF%D6%DC Start date: 2011-7-3 Number of replies: 10 ------------------------------------------------------------------------------------------------ 21. Topic: Why is it necessary to establish a normal water circulation as soon as possible during boiler startup? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=869373&highlight=%C3%BF%D6%DC Date of posting: 2011-7-9 Number of replies: 5 ------------------------------------------------------------------------------------------------ 22. Topic: Some matters that need attention when installing pipes. Topic link: http://bbs.hcbbs.com/viewthread.php?tid=873241&highlight=%C3%BF%D6%DC Date of posting: 2011-7-17 Number of replies: 5 ------------------------------------------------------------------------------------------------ 23. Topic: What are the requirements for the combination and installation of boiler smoke, air, and coal pipes? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=876837&highlight=%C3%BF%D6%DC Start date: 2011-7-24 Number of replies: 3 ------------------------------------------------------------------------------------------------ 24. Topic: How to align the header when assembling the heating surfaces? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=884161&highlight=%C3%BF%D6%DC Start date: 2011-8-7 Number of replies: 2 ------------------------------------------------------------------------------------------------25. Topic: What are the differences between metal inspection and boiler inspection tasks? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=786881&highlight=%C3%BF%D6%DC Date of posting: January 9, 2011 Number of replies: 2 ------------------------------------------------------------------------------------------------ 26. Topic: What are the methods for ensuring the quality of boiler feedwater? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=892614&highlight=%C3%BF%D6%DC Start date: 2011-8-23 Number of replies: 7 ------------------------------------------------------------------------------------------------ 27. Topic: Talk about the interesting events that have taken place around you this week. Topic link: http://bbs.hcbbs.com/viewthread.php?tid=899453&highlight=%C3%BF%D6%DC Date of posting: September 5, 2011 Number of replies: 5 ------------------------------------------------------------------------------------------------ 28. Topic: What should be taken into consideration in the anti-corrosion design of chimneys and flues? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=896989&highlight=%C3%BF%D6%DC
Date posted: August 31, 2011
Number of replies: 3
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29. Topic: Share stories from your work.
Topic link: http://bbs.hcbbs.com/viewthread.php?tid=907715&highlight=%C3%BF%D6%DC
Date posted: September 22, 2011
Number of replies: 5
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30. Topic: Talk about things that happen at your workplace.
Topic link: http://bbs.hcbbs.com/viewthread.php?tid=919524&highlight=%C3%BF%D6%DC
Date posted: October 21, 2011
Number of replies: 3
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31. Topic: Discuss safety precautions when performing maintenance on boilers.
Topic link: http://bbs.hcbbs.com/viewthread.php?tid=923187&highlight=%C3%BF%D6%DC
Date posted: October 29, 2011
Number of replies: 7
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32. Topic: Discuss methods for saving fuel during boiler ignition.
Topic link: http://bbs.hcbbs.com/viewthread.php?tid=927124&highlight=%C3%BF%D6%DC
Date posted: November 7, 2011
Number of replies: 5
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33. Topic: What measures can be taken to prevent low-temperature corrosion of flue gases during boiler operation? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=930549&highlight=%C3%BF%D6%DC Start date: 2011-11-14 Number of replies: 13 ------------------------------------------------------------------------------------------------ 34. Topic: What measures are taken to prevent explosions during the startup and shutdown of the grinding system? Topic link: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=936449 Date of posting: 2011-11-26 Number of replies: 5 ------------------------------------------------------------------------------------------------35. Topic: Prevention of accidents in boiler exhaust fans. Topic link: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=943758 Date of posting: 2011-12-11 Number of replies: 5 ------------------------------------------------------------------------------------------------36. Topic: Precautions to be taken during the operation of gas boilers. Topic link: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=946239 Date of posting: 2011-12-18 Number of replies: 7
This post was last edited by zgj2405 on 2011-7-3 12:12. Topic: Collection of information on the symptoms, cause analysis, and solutions for economizer leakage incidents. Topic link: http://bbs.hcbbs.com/viewthread. ... hlight=%C3%BF%D6%DC Date of posting: 2008-12-4 Number of replies: 6 --------------------------------------------------------------------- Reply from post 4 (*anpangpang: UID 177792) provided a paper on \"Analysis of the Causes of Wear in Boiler Economizers and Corresponding Countermeasures\". --------------------------------------------------------------------- User 6th Floor (coronary: UID 261267) replied by sharing an analysis of the causes and his own experience in dealing with the damage to the economizer at his factory. Let me explain the damage that occurred to the economizer in our factory. Introduction to the economizer: 45 rows, 1-inch coil tubing. Accident discovery: Leakage was found in the ash discharge pipe of the rear furnace chamber. Upon inspection, it was found that tubes 23 and 22 in the last row of the economizer were leaking. Since the water leakage isn’t very severe, after consulting the boiler manufacturer, we decided to keep using it. Half a month later, it was observed that water inflow and leakage had significantly increased. Inspections revealed leaks in 7 pipelines; consequently, the boiler was shut down, and those 7 economizer pipelines were sealed off. The boiler was restarted, but after it had been running for a short time, leaks were detected in other pipelines. The boiler was shut down three times in total; more than 10 economizer pipelines were sealed. Finally, during the shutdown for major repairs, the economizer was replaced. Cause of the accident: 1. The analysis conducted on-site indicated dew point corrosion; indeed, since it was a waste heat boiler, the boilers in the preceding process could not be controlled, and the temperature at the boiler outlet remained low, below 150 degrees. Corrosion must be present. 2. There is another reason for the individual analysis: before the leakage occurred, the entire plant lost power, and it was not possible to determine the water level in the boiler, so the boiler had to be shut down urgently. During this shutdown process, abnormal noises were heard from the economizer, resulting in hidden damage; this damage led to leaks in the economizer’s pipelines during subsequent operations. 3. The damaged pipeline is located at the bend at the boiler outlet; since the flue gas from our plant contains a high level of ash, it is possible that fly ash caused the wear. Lessons learned: 1. In the event of a boiler tube rupture, production must be stopped immediately for repairs; otherwise, under high pressure, the steam or water that escapes will quickly damage the surrounding pipelines. 2. The boiler outlet temperature should be controlled at a high level, as much as possible, based on actual conditions such as the sulfur content, water vapor content, and ash content in the flue gas—for instance, around 180 degrees Celsius—to prevent dew point corrosion. 3. Boiler deaeration must not be taken lightly; oxygen corrosion in the economizer is quite severe.
This post was last edited by zgj2405 on 2011-7-3 12:12. Topic: Into how many stages is the formation process of water vapor at constant pressure divided? Topic link: http://bbs.hcbbs.com/viewthread...hlight=%C3%BF%D6%DC Date of posting: 2008-12-7 Number of replies: 38 --------------------------------------------------------------------- Reply from post 7 (*ngkongwuyu: UID 206682) is quite comprehensive: The process of pressure-controlled formation of water vapor can be divided into the following three stages: 1. The stage of pressure-controlled preheating of unsaturated water; 2. The stage of pressure-controlled vaporization of saturated water; 3. The stage of pressure-controlled superheating of saturated steam. The heat added during the stage of pressure-controlled preheating of unsaturated water is called liquid heat, and it equals the enthalpy of saturated water minus the enthalpy of unsaturated water. It can also be calculated by multiplying the specific heat capacity of water at constant pressure by ts-to. The heat added during the isobaric vaporization phase of saturated water is called the latent heat of vaporization; it equals the enthalpy of dry saturated steam minus the enthalpy of saturated water, and can also be calculated using the formula r=Ts(s”-s’). The heat added during the constant-pressure superheating stage of dry saturated steam is called superheating heat, and it is equal to the enthalpy of the superheated steam minus the enthalpy of the dry saturated steam.
This post was last edited by zgj2405 on 2011-7-3 at 12:13. Topic: Discussion on the reasons for wear and corrosion in the rear heating surfaces. Topic link: http://bbs.hcbbs.com/viewthread....hlight=%C3%BF%D6%DC. Posting date: 2008-12-14. Number of replies: 27. -------------------------------------------------------------------- The reply from the 3rd poster (lupg: UID 111652) is very insightful: 1. Wear in the rear heating surfaces 1.1 The extent of wear in these surfaces depends on the properties of the fuel, the velocity of the flue gases, and the arrangement of the heating surfaces. 1.2 For gaseous or liquid fuels, there are virtually no significant contradictions. 1.3 The likelihood of issues arising with solid fuels is relatively high; however, certain measures can be taken during structural design to mitigate or prevent such problems. 1.4 Another factor contributing to wear on heating surfaces is the mutual interaction between wear and corrosion. 2 Causes of corrosion on the rear heating surfaces 2.1 At high-temperature areas, the possibilities of high-temperature sulfidation and high-temperature oxidation still exist, depending on how the “rear section” is defined. 2.2 More commonly, there is sulfuric acid dew point corrosion; in most cases, the temperature in the rear section has dropped significantly compared to that in the radiation section. Nevertheless, when the flue gas temperature is slightly above or below the sulfuric acid dew point, corrosion of the rear heating surfaces intensifies. The accumulation of ash and scale on the heated surfaces lowers the temperature of the metal; even if the flue gas temperature is above the dew point, the metal temperature can still drop below this level, leading to corrosion. In environments prone to dust accumulation, using finned tubes to increase the heating surface is not a good choice; the potential negative effects are more pronounced. --------------------------------------------------------------------- The reply from the user on the 6th floor (Yaoling Mountain: UID 99378) is closer to the standard answer: Since the fly ash particles carried along with the flue gas possess a certain amount of kinetic energy, these particles continuously impact the metal pipe walls over time, resulting in wear and tear of the heat transfer surfaces. Since the fuel used in boilers contains a certain amount of sulfur, sulfur dioxide and sulfur trioxide are generated upon combustion, which then combine with water vapor in the flue gases to form sulfuric acid vapor. When the wall temperature of the heated surface is below the dew point of sulfuric acid vapor, the vapor condenses into acid, which then corrodes the heated surface.
This post was last edited by zgj2405 on 2011-7-3 12:13. Topic: What is the thermal deviation of a superheater, and what are the two causes of it? Topic link: http://bbs.hcbbs.com/viewthread....hlight=%C3%BF%D6%DC Date of posting: 2008-12-21 Number of replies: 27 --------------------------------------------------------------------- Replies from post 3 (jlx518: UID 10739), post 5 (*ngkongwuyu: UID 206682), post 12 (long060: UID 248229), and post 14 (tuy001: UID 87632) are fairly comprehensive, but quite similar: In a boiler, the superheater and reheater have the highest temperatures of the working fluid flowing through them; at the same time, the heat load on these heating surfaces is also quite high. Moreover, the heat release coefficient of steam is relatively low. As a result, the superheater and reheater are the heating surfaces in a boiler where the metal temperature is the highest and the operating conditions are the most severe. In actual operation, due to various factors on the flue gas side and those related to steam, the amount of heat absorbed by the steam—that is, the increase in enthalpy—in each heating surface often varies; this is known as thermal deviation. As a result, their outlet temperatures and tube wall temperatures differ, and at times, temperature excursions and overheating occur. The main causes of thermal deviation in various heated surfaces are thermal non-uniformity and hydraulic non-uniformity. I. Factors affecting thermal unevenness: The uneven distribution of temperature and velocity fields of the flue gases in the boiler furnace and flues is the main cause of thermal unevenness in the superheater and reheater. In the furnace, due to the heat absorption by the water wall and wall-type reheaters, the temperature of the flue gas near these heating surfaces is lower; the flow velocity of the flue gas in the middle of the flue is usually higher than that on the sides. This results in the heat absorption of the pipe located in the middle of the flue being greater than that of the pipes on both sides, leading to a thermal deviation. When improper operation causes the flame and smoke in the furnace to deviate, it can also lead to thermal imbalance on both sides of the flue. In the event of coking on the water wall, the deviation between the temperature of the flue gas on both sides of the convective flue and the temperature of the flue gas at the furnace exit also varies; the flue gas temperature on the side where coking occurs on the water wall is relatively higher. When coking or ash deposition occurs on the heated surfaces of the convective flue, the heat absorption by the tubes in those areas decreases. When local coking occurs in a certain section of the convective flue, the flow velocity and volume of the flue gas in the remaining sections increase, resulting in increased heat absorption by those heated surfaces. If the tubes in the flue are not arranged uniformly, resulting in varying gaps between them, this will also lead to uneven heat absorption by each tube. When there are relatively large gaps between the tubes, a so-called “flue gas corridor” is formed. In this area, the flow velocity and volume of the flue gases increase, thereby enhancing convective heat transfer. Additionally, the thickness of the radiation layer in the flue gas corridor is greater, which increases the amount of heat absorbed by the serpentine tubes located adjacent to it. In the boilers at our plant, the residual rotation of the flue gas at the furnace outlet often causes deviations in both the flow velocity and flue gas temperature on both sides of the gas stream. This, in turn, results in uneven heat absorption by the heating surfaces within the flue ducts on both sides. Due to uneven heat distribution, there is uneven heat absorption in the superheaters and reheaters; the tubes that absorb more heat reach higher temperatures, resulting in a larger specific volume of the steam. This leads to a higher flow velocity and greater resistance, which inevitably results in a decrease in flow rate, thereby further exacerbating the increase in thermal imbalance. II. Factors Affecting Hydraulic Unevenness The steam flow rate in each parallel tube of the superheater or reheater is closely related to the degree of uniformity of the heat load across the cross-section of the flue. In addition, the flow distribution among the parallel pipes is related to the flow resistance of each pipe and the pressure difference between the inlet and outlet manifolds. When multiple parallel tubes located in the same inlet and outlet header are in operation, the way in which the steam inlet or outlet pipes are connected to the header affects the pressure distribution within the header. Due to the uneven pressure distribution in the header, different pressure differences occur at the inlets and outlets of each parallel tube. This causes deviations in the flow rate among various tube rows, resulting in uneven water distribution. The uneven flow rate is often due to the different flow resistances of the fluid in each parallel tube. Factors such as the length of the pipe, its inner diameter and roughness, elbows, and heat absorption amount are often the main reasons for the differences in flow resistance of the working fluid in parallel pipes. When the water quality is poor, scaling occurs inside the pipes; this results in varying resistances within the pipes, which is also a major cause. When the resistances of the various pipes are different, the fluid flow rate in the pipe with higher resistance is low, while the flow rate in the pipe with lower resistance is high. --------------------------------------------------------------------- Floor 19 (wbp: UID 264041) provided a good response with its own analysis: the reasons for the thermal imbalance in the heated surfaces are uneven heat absorption, uneven structure, and uneven flow rates. The inconsistent structure of the heating surfaces affects both the heat absorption and flow rate; therefore, the main causes of thermal deviation are generally attributed to uneven heat absorption and uneven flow distribution. I. Regarding uneven heat absorption: 1. The flue gas temperature and flow velocity vary along the width of the furnace, resulting in different heat absorption rates for tubes at different positions. 2. The flame is not fully filled in the furnace, or the flame center is offset. 3. Local slagging or ash accumulation on the heat-exchanging surface can cause severe uneven heat absorption between the tubes. 4. In convective superheaters or reheaters, excessive differences in tube pitch, or the removal of individual tubes during maintenance without subsequent repair, can create smoke \"corridors\", resulting in increased heat absorption by the tubes adjacent to them. 5. The outer tubes of the screen-type superheater or reheater absorb more heat than other tubes. II. Uneven flow distribution
1. For parallel pipes, due to differences in their actual inner diameters (such as pipe flattening, weld beads protruding at weld joints, or blockages caused by debris), the flow resistance of each pipe varies, resulting in uneven flow distribution. 2. The connection methods between the header and the inlet/outlet pipes differ, resulting in different pressure differences at both ends of the parallel pipes and thus uneven flow. Modern boilers often use multiple tubes connected to inlet and outlet manifolds to ensure that the flow rates in parallel tubes are essentially the same.
1. For parallel pipes, due to differences in their actual inner diameters (such as pipe flattening, weld beads protruding at weld joints, or blockages caused by debris), the flow resistance of each pipe varies, resulting in uneven flow distribution. 2. The connection methods between the header and the inlet/outlet pipes differ, resulting in different pressure differences at both ends of the parallel pipes and thus uneven flow. Modern boilers often use multiple tubes connected to inlet and outlet manifolds to ensure that the flow rates in parallel tubes are essentially the same.
This post was last edited by zgj2405 on 2011-8-25 21:06. Topic: What are the management systems for boiler rooms? And specify one of them. Topic link: http://bbs.hcbbs.com/viewthread. ... hlight=%C3%BF%D6%DC Date of posting: 2009-2-16 Number of replies: 13 --------------------------------------------------------------------- The reply from floor 7 (hxl4939: UID 262487) is very useful for reference.
This post was last edited by zgj2405 on 2011-7-3 12:14. Topic: How to calculate the material balance in a circulating fluidized bed boiler, and how to make adjustments during normal operation? Topic link: http://bbs.hcbbs.com/viewthread. ... hlight=%C3%BF%D6%DC Date of posting: 2009-2-21 Number of replies: 1 --------------------------------------------------------------------- Reply from Floor 2 (anship1984: UID 161862) – an article titled \"Methods for Calculating Material Balance and Combustion Efficiency in Circulating Fluidized Bed Boilers\" was uploaded, which can basically address the raised questions.
Topic: How should the cross-sectional area of the furnace chamber, its volume, and its height change? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=797883&highlight=%C3%BF%D6%DC Date of posting: 2011-2-12 Number of replies: 4 --------------------------------------------------------------------- Reply from post 4 (zgj2405: UID 242333) provided the reference answer: For a boiler with certain parameters and capacity, the heat released by the fuel in the furnace per unit of time is constant. Therefore, when qv is large, the furnace volume is small ； If the size is small, the furnace volume is large. If qv is too high, the furnace volume becomes too small; as a result, the coal powder stays in the furnace for a short time, leading to incomplete combustion. Additionally, with a small area for the water-cooled walls, the furnace temperature rises excessively, which can easily cause slag formation. If qv is too low, the furnace volume becomes excessive, resulting in low furnace temperatures, which is unfavorable for combustion. This also increases the cost of the boiler as well as the amount of metal required. The empirical data are shown in Table 5-4. As can be seen from the table, the easier the coal is to burn, the larger the allowable value of qv becomes. With the same furnace volume, the furnace can be designed to be long and narrow or short and stout. The excessively long furnace chamber results in good flame filling, but the burner area suffers from slag formation due to the lack of sufficient water-cooled walls to cool the flue gases. An excessively short and stubby furnace chamber results in low temperatures near the burner, which is unfavorable for ignition; moreover, the flame cannot fill the furnace chamber properly, the coal powder stays in the furnace for a short time, and heat losses due to incomplete combustion increase. The general shape of the furnace chamber is usually determined by both the heat intensity per unit cross-sectional area of the furnace chamber and the heat intensity per unit volume of the furnace chamber. The thermal intensity of the furnace cross-section refers to the amount of heat released per unit time per unit area of the furnace cross-section. When qv remains constant, a higher value for qA results in a smaller cross-sectional area Al, making the furnace longer and slimmer; whereas a lower value for qA leads to a larger cross-sectional area Al, resulting in a shorter and more robust furnace. The empirical data are shown in Table 5-5. After the heat intensity per unit area of the furnace cross-section is determined, the cross-sectional area of the furnace is calculated using equation (5-3); by dividing this value by the volume of the furnace, the average height of the furnace can be obtained. However, the width and depth of the furnace still need to be determined. Given the actual conditions in our country, low-volatility coal tends to be burned using DC burners arranged at the four corners. Such furnaces require that the width of the furnace chamber be equal to its depth; in other words, the width-to-depth ratio should be 1, with a maximum value not exceeding 1.2. Coals with high volatile matter tend to use swirl burners arranged at the front wall or at both the front and rear walls. If the swirl burner is arranged on the front wall, the depth of the furnace chamber cannot be too small, to prevent the flame from reaching the back wall and causing slag formation.
Topic: What are the inspection items for the on-site welding quality of boilers? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=800898&highlight=%C3%BF%D6%DC Date of posting: 2011-2-19 Number of replies: 1 --------------------------------------------------------------------- Reply from Floor 2 (zgj2405: UID 242333) provided the reference answers: (1) Items for random inspection of on-site welding quality: (3 points) ① Random inspection of the quality of weld joint groove preparation (during on-site processing) ； ②Randomly inspect the visual quality of welded joints ； ③Random inspection of the qualifications of on-site welders ； ④Inspect no less than 20% of the negatives, with a focus on those before and after repair, to check the quality of the negatives, the accuracy of defect assessment, and the quality of the welds as shown. For screen superheaters and high-temperature superheaters, the following items should be added: ① Conduct non-destructive testing on no less than 1% of the alloy steel weld joints through random on-site inspections ； ② If necessary, conduct random hardness tests on the heat-treated welded joints and heat-affected zones ； ③ Random spectral analysis of the welded joints shall be conducted, with a sampling rate of not less than 1%. (2) Judgment and correction of errors: (3 points) ① The inspection ratio for the low-temperature superheater is incorrect. It should be changed to: Radiographic or ultrasonic testing of the on-site welded joints of the low-temperature superheater shall be carried out on 25% of the total number of joints ； ② Error. It should be changed to: If the supplementary inspections still show failure, flaw detection tests should be conducted on all butt joints welded by that welder. ③ Error. It should be changed to: The test pressure for the primary steam system (the boiler itself) is 1.25 times the operating pressure of the steam drum: 1.25×18.67=23.34 MPa. The test pressure for the secondary steam system (the reheater) is 1.5 times the operating pressure of the reheater: 1.5×3.8=5.7 MPa. ④ Correct. ⑤ Error. It should be changed to: Before the hydrostatic test, the system undergoes an air pressure test at 0.3 MPa.
Topic: What causes pitting corrosion in the image? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=825937&highlight=%C3%BF%D6%DC Date of posting: 2011-4-12 Number of replies: 19 --------------------------------------------------------------------- Reply from floor 15 (gjn1970: UID 621143) contains an in-depth discussion: I would like to discuss this with the original poster and the forum moderators. I have seen tubes that have suffered from oxygen corrosion; in most cases, after the rust and scale were removed from inside the tube, there were many small pits on the inner metal surface of the tube wall. These pits were generally distributed fairly evenly along the tube wall, and the areas where the corrosion was most severe were the ones where leakage occurred. Another important characteristic of oxygen corrosion is that the inner surface of the pipes is covered with a lot of rust, which is a product of the corrosion process. Moreover, there are small holes in some areas of this rust; these holes are formed as a result of the electrochemical reactions that occur during corrosion (oxygen corrosion being an example of such electrochemical reactions). If you scrape away the rust from those areas, you will definitely find small pits on the underlying metal surface. May I ask the original poster whether you removed the rust before providing the sample tube? If there was no rust, then I believe it definitely wasn’t oxygen corrosion. If the rust was removed, please check carefully again whether there are any small pits on the inner wall of the tube; if not, then it’s not certain whether it was oxygen corrosion or not. In summary, I believe it is possible that there is acidic corrosion on the outer wall of the pipe, with the main cause being the fact that the operating temperature of the outer wall of the pipe in the low-pressure section is below the acid dew point.
Subject: Questions regarding the manufacturing of test plates for coal-fired steam boilers? Topic link: http://bbs.hcbbs.com/viewthread.php?tid=829223&highlight=%C3%BF%D6%DC Date of posting: 2011-4-18 Number of replies: 2 --------------------------------------------------------------------- Reply from the 2nd poster (zgj2405: UID 242333) was quite comprehensive: (1) Products with the same steel grade, welding process, and heat treatment specifications should be grouped together for continuous production (with no interruption in production lasting more than half a year); each batch should contain no more than 10 units, and the manufacturer should select one unit from that batch to use as a welding test piece ； (2) For pressure vessels with a design pressure not exceeding 1.6 Mpa and made of materials in the Q235 series, 20R, or 16MnR, products of the same steel grade shall be grouped together; one product shall be selected from each batch for use in creating welding test plates on a continuous basis every year ； (3) Glass-lined equipment does not require welding plates made of low-carbon steel (except when special requirements are specified). If production is interrupted for more than an hour past midnight, one unit of the product should be selected to create a welding test plate ； (4) For mobile pressure vessels manufactured in batches based on nearly identical design drawings, when produced manually in succession (with production interruptions not exceeding one year), no more than 10 units per batch shall be selected by the same manufacturing unit to be used for preparing product welding test plates. Welding test plates are produced in batches rather than one by one. If one of these test plates fails the inspection, an additional number of test plates must be made for retesting and metallographic analysis. If they still fail, the process must revert to producing welding test plates individually, until 30 test plates made from the same steel grade, using the same welding procedures and heat treatment specifications all yield satisfactory test results.