Guide to chimney engineering design and construction budgeting?

It is true that "the higher the chimney, the better the smoke exhaust capacity" and "the higher the air pressure, the smaller the smoke exhaust capacity", but the higher the chimney, the better the smoke exhaust capacity. It is definitely not caused by the higher air pressure. If this is really the case, don't say that the air in the chimney will flow up by itself, even the air on the ground will run up, haha! Let me explain to you why. Any object in the atmosphere (including air itself) will be subject to buoyancy from the air, but why can the air keep balance (regardless of blowing phenomenon) and not float? This is because air is not only affected by rising buoyancy, but also by its own gravity. Usually, the upward buoyancy of air is equal to its own downward gravity, so it is balanced.

But the smoke from the chimney is hot air with high temperature. The higher the temperature, the more expansion and the smaller the gravity per unit volume. Because the buoyancy remains unchanged, the gravity of hot air becomes smaller, so the smoke floats up and rushes up. After the temperature cools for a period of time, the smoke spreads laterally. If you stand on the mountain in the countryside and look at the windless ravine (preferably in the morning and evening), why should the chimney be made very high? Because the higher the chimney, the more hot air, the greater the total buoyancy, the greater the pressure generated by buoyancy, and the stronger the smoke exhaust ability. (from: www.fdcew.com) Can you make the chimney bigger instead of higher? Of course not. If only the chimney is made larger and not higher, the buoyancy of the flue gas will also increase, and it is proportional to the increased cross-sectional area, but the pressure = pressure/stressed area, and the pressure and area increase in direct proportion, so the pressure will not actually change, and the suction at the lower part of the chimney will not increase. This is because the head of the pump is only related to the vertical height of the water pipe, and has nothing to do with the horizontal distance for the time being.

In addition, the chimney is tapered only because of the needs of the building, which does not help the smoke extraction ability. The higher the chimney, the better. The chimney has an optimum height, which depends on your smoke discharge and chimney diameter. It is meaningless to increase the height of the chimney after it exceeds a certain height under the condition of fixed smoke discharge and chimney diameter. The height of the chimney has an effect on the smoke extraction capacity, but this is not the key. The key is that the chimney should be made into a cone with a small top and a large bottom. Only in this way, the air pressure in the chimney can be much greater than that outside the chimney, thus making the chimney have better smoke extraction ability. When the chimney is built high, it can form a better temperature gradient and the air thermal expansion effect is better.

Product summary index: 1. High temperature resistance: 250℃. 2. Dilute acid (sulfuric acid, nitric acid, hydrochloric acid) with a concentration of 5% and a temperature of 80℃: 12 days; Resistance to 30% sulfuric acid: no change at 80℃ 15 days, no change at room temperature for 30 days. 3. Water resistance: soaked at room temperature for 90 days without change. 4. Stripping resistance: (rapid cooling and rapid heating at 250℃/repeated water cooling cycle) has no change after 50 times. 5. Anti-aging index: there is no change after 500 hours of damp-heat resistance test. 6. Maximum service life: 13 years. 7. Duration: 20-30 days. Single-pipe old chimney is transformed into lining desulfurization (new chimney lining treatment) and acid-proof and anti-corrosion treatment scheme for the inner side of steel chimney;

(1) Reconstruction of old chimney lining and treatment of new single-tube chimney: 1. Treatment methods and procedures: dust removal (there is no such procedure for new chimneys), brushing OM interface agent, scraping OM putty in batches, brushing OM-4 primer twice, and finally brushing OM-5 chimney high temperature, acid and corrosion resistant coating twice (glass fiber cloth 1-2 times can be added in the middle). 2. Construction period: 20 days (210-240m chimney).

(2) Anti-corrosion treatment scheme for the inside of steel chimney: 1. Treatment methods and procedures: After derusting, apply OM-4 primer twice and OM-5 chimney high temperature, acid and corrosion resistant coating twice, with a total dry film thickness of 0.5- 1.0 mm (the design institute shall select the thickness as required) 2. Construction period: 20 days (210-240m chimney). Since the reform and opening up, high-rise buildings have mushroomed all over the country. According to China's national conditions, most high-rise buildings still consider using oil-fired or coal-fired boilers or lithium bromide units as their heat sources. The chimney layout of their computer room, especially the chimney layout of coal-fired boiler room, is often a headache for designers. If independent chimneys are built, because they are all in downtown areas, it is impossible to set them up independently and the cost is expensive. If it is a wall-mounted chimney, mistakes in design or construction will cause irreparable economic losses. For example, the brick chimney attached to the wall of a 28-story residential building in Wuhan was cracked because of some problems in design and construction, and the smoke penetrated into all rooms, so the chimney could not be maintained, so the steel chimney was rebuilt. Causing economic losses of hundreds of thousands of yuan. In the design practice, we learn from others' experience and lessons, make bold innovations, adopt new technologies according to the site conditions, and strictly require the construction unit to construct according to the drawings, thus solving some problems in the chimney design of high-rise buildings. Many projects have passed the completion acceptance of relevant departments, running for several years without problems, and some projects have won the second prize of provincial excellent design (Hubei Construction Bank Office Building and International Finance and Trade Building), which has achieved good economic and environmental benefits.

1. Chimney in the Inner Tube The office building of Hubei Branch of China Construction Bank (also known as Hubei International Finance Building) is one of the first high-rise buildings in Wuhan. The main building of this building has 26 floors and is nearly 100 meters high. Due to the restriction of energy policy at that time, only coal could be used as fuel. However, because the building is located at the intersection of Zhongnan in the downtown area of Wuhan, the environmental protection requirements are particularly high, and the coal-fired boiler is not suitable for the roof, so it can only be arranged on the first floor of the podium. According to the boiler smoke emission standard, the chimney of the boiler room in this project can be designed as 30M (with a total capacity of 5t/h). However, because the height of the building is close to 100M, and there are Zhongnan Commercial Building (about 50M high), the planned Material and Trade Building and Shangzhong Plaza (all built later) around it, the above emission standard also stipulates that "when there are buildings within a radius of 200M around the chimney, the height of the chimney should generally be.

Some people hope that we can design according to 30M, so that the construction unit can save a lot of investment and our design is much more convenient. If we make a fuss about "general" and "should", it is not impossible to ask the environmental protection department to lower the requirements, but we think that from the perspective of environmental protection, from the long-term perspective of urban development, and from the impact of boiler room flue gas on this building-because the boiler room is located in the northwest of this building, the boiler operation time is mostly in winter, and the harm of flue gas to the building (from: www.fdcew.com) is self-evident. However, the real design is very difficult. First of all, this building is one of the first landmark buildings in Wuhan and the office building of Hubei Construction Bank. Urban planning needs luxurious and spectacular external decoration, so in the scheme design, for various reasons, the chimney position 3 meters above the roof is not considered.

If brick chimneys or steel chimneys with walls are considered in the construction drawings, it will not only destroy the image of the building, but also be structurally unsolvable. Secondly, if an independent brick chimney is built, the cost will be as high as one million yuan, and due to local restrictions, it will not be harmonious with the whole building, which will destroy the scenery. Consider sticking it on the podium. What should I do if I can't even reach the minimum 30M? After many consultations with civil engineers, we finally squeezed out a triangular position with an area of about 2.5M2 near the elevator shaft of the main building and decided to set the chimney here. The installation of chimneys in inner tubes is still a new problem in China and even in Asia. First of all, the flue gas has a great influence on the thermal stress of the inner cylinder. Secondly, the boiler room is not on the main floor, but in the podium, with a horizontal distance of tens of meters from the inner cylinder. The flue must pass through several rooms on the standard floor, which will affect these rooms. Especially in winter, boilers generally run more, and the temperature difference between inside and outside the chimney is larger. In order to avoid its influence, the chimney is treated as follows:

1. According to the construction method of ordinary chimneys, the air insulation layer is expanded to 100MM, and the air insulation layer of ordinary brick chimneys is 50MM, which is set to protect the outer wall of chimneys, and the object we want to protect is the whole inner tube of the building, even the whole building. Therefore, we have doubled the air insulation layer to prevent the thermal stress damage caused by the conduction of flue gas heat to the inner cylinder. 2. Masonry the inner wall of refractory bricks with the same height as the chimney, and use red bricks when the flue gas humidity is lower than 500℃. Obviously, the humidity of the outer wall of the chimney is not equal to the room temperature, and the compactness and thermal insulation of refractory bricks are much better than ordinary red bricks, which can effectively prevent the influence of flue gas humidity on the inner cylinder. 3. Expansion joints shall be set at the joint between chimney and flue, and strict thermal insulation measures shall be taken for flue (steel). 4. The outer wall of the chimney (that is, the inner cylinder wall) is poured with refractory concrete, which further eliminates the influence of flue gas. By taking the above measures, the influence of the temperature difference between inside and outside the chimney on the inner cylinder of the main building is completely avoided. If you don't explain, no one knows that the chimney of this building is located near the inner tube aisle of the main building. Several years' operation proves that this method not only solves the problem of installing chimneys in high-rise buildings, but also saves a lot of investment for construction units (compared with independent chimneys, it saves about 700,000 yuan, and compared with wall-attached chimneys, it saves about 1/3, reaching about 300,000 yuan). ) has produced huge economic benefits, more importantly, because the chimney is very high, it has eliminated the pollution of flue gas to the surrounding area and produced more obvious environmental benefits.

2. The chimney attached to the external wall of Jianhua Meida Hotel of Hubei Post and Telecommunications Administration is a large building with 28 floors and a height exceeding 100 meters. The boiler room is located in a four-story podium, and the main flues of three oil-fired boilers are located in a corner of the external wall of the building. We also cut a triangle with an area of about 2M2 on the corner. Because it is on the outer wall, the influence of thermal stress is smaller than that of the inner tube, so the air insulation layer is only 70 mm Other methods are the same as those of Hubei International Finance Building, but after the boiler runs, it is found that the room near the chimney is taller. After analysis and investigation, it was found that when the construction unit laid refractory bricks on the inner wall of the chimney, it did not follow the chimney masonry technology at all, and even the scaffolding holes on the inner wall were not blocked. There are 250 × 200mm big holes and several 20mm wide gaps up to tens of meters. After plugging the leak and taking some other measures, the humidity of the room was reduced to meet the requirements of normal use.

3. The equipment stainless steel chimney with wall is located in Jinbo Town, Zhengzhou, Henan Province, and the boiler room is located on the first floor of the podium, which is connected with the 33rd floor commercial and residential building. The original design office building has 46 floors, and smoke is attached to the office building. However, due to some reasons, only a few floors of the office building have been built, and the commercial and residential buildings have been completed. After research, it was decided to make stainless steel chimneys on the walls of commercial and residential buildings, and the following measures were taken. 1. In order to avoid the high cost of chimney replacement caused by corrosion of ordinary steel, stainless steel was adopted after calculation. 2. In order to reduce the cost, the installation method of short joint flange with less stainless steel is adopted, that is, the distance between two flanges is only 2m, and the chimney is supported on the flange, thus reducing the wall thickness of the lower chimney. According to the calculation, if the weight of the chimney falls on the foundation, the wall thickness of the lower chimney will exceed 10 mm. By adopting the above method, the wall thickness of the upper and lower chimneys will be 4-5mm. The support and fixation are made of ordinary steel that does not contact with flue gas. 3. Take thermal compensation measures for the chimney to prevent the damage caused by thermal expansion between the chimney fixing brackets. The boiler room has been running for several years, and everything is normal.

Four. Several problems in the construction of 1 wall brick chimney. Be sure to invite a professional team to build furnaces or chimneys.

2. The inner wall must be smooth and dense to reduce heat conduction.

3. The width of air insulation layer must be ensured, and two layers of insulation layer are not allowed to be uneven. 4. Building firebricks on the interior wall is absolutely not allowed to build scaffolding on the interior wall, but only on the exterior wall, because the scaffold hole is not tightly blocked. 5. The supervision company must monitor at all times, otherwise there will be endless troubles, such as Ramada Hotel in Wuhan. After the operation, it is very difficult to check because it can't stop the furnace, and it is even more difficult to plug and fill the hole, and the effect is not good. High-rise building is a new thing developed in China in recent years. With the further development of the four modernizations, high-rise buildings have sprung up. Because they are generally built in densely populated cities (from: www.fdcew.com), due to historical reasons, there are few heating centers in cities in China, so boilers are essential. How to solve the problem of smoke exhaust in high-rise buildings (that is, chimney design) is a very difficult topic and cannot be solved.

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