Demolition of towering tubular steel structures by linear concentrating cutting technology

The five crude benzene towers of the coking plant of Xinyu Iron and Steel Co., Ltd. were built in 1970. They were discontinued in 2001 and have been in use for more than 30 years. The internal and external corrosion is serious. If they are not removed, there is a danger of collapse at any time.

However, the bottom of the crude benzene tower has precipitates such as benzene, naphthalene and tar residue. The tower contains flammable and explosive mixed gases such as benzene, naphthalene and gas, and the surrounding environment is quite complicated. The coking plant is a special fire-proof unit with very high safety requirements. Once accidentally caused to cause burning and explosion, the entire coking plant was shut down, and the loss of one day was nearly 10 million yuan. If the traditional segment-by-stage cutting disintegration method is adopted, a large amount of inert gas washing is required to reduce the concentration of the inflammable and explosive mixed gas, and then the sling lifting and discharging is performed from top to bottom, but this method is expensive, has a long construction period, and has poor safety. . Due to the thin wall thickness, drilling (internal charge) blasting cannot be used. If conventional external charge blasting is used, the amount of the drug is large, and the air shock wave is too harmful. Entrusted by the new steel, it was decided to use the energy-cutting technology to carry out blasting demolition, and the related technology was studied, and the practical application effect was very good. According to the new search, the blasting is the first time at home and abroad to use the energy-cutting technology to remove the tall tubular steel structure by directional blasting. It is also the first time to remove the tubular steel structure by blasting in a flammable and explosive environment.

2 Project Overview 21 The five crude benzene towers to be demolished in the surrounding environment are located in the recycling tower of the coking plant. The distance is 2530m. The south side is 165m away from the gas pipelines and water pipes, 25m away from the plant road and 45m away from the 3 coke oven. The west side of the laboratory is 46.5m, the bicycle shed is 40m; the north side is the gas pipeline, water pipes and other overhead pipelines; the east side is 65m away from the waste factory.

Schematic diagram of the explosion area (unit: m) 22 Structure Overview The five crude benzene towers to be removed are two benzene-washing towers, one final cooling tower and two naphtha towers (15 towers from north to south).

The five towers are all vertical cylindrical structures with auxiliary equipment such as partitions. The tower body is made of A3 steel, of which the washing tower is 34 6m high, the final cooling tower is 35m high, and the naphthalene tower is 22 55m high. 3 The lower wall thickness is 10mm, the upper wall thickness is 68mm, and the top of the tower is connected by a bridge. The benzene tower weight 54t final cooling tower weighs 36 489, t wash naphthalene tower weight 54.692t bottom has benzene, naphthalene and tar residue and other sediments, the tower contains benzene, naphthalene and gas and other flammable and explosive mixed gas.

3 blasting overall plan The blasting, first, the surrounding environment is very complicated, second, the blasting object is very complicated, the five towers contain inflammable and explosive mixed gas, and the new steel coking plant is a special fire-proof unit, the removal is very difficult. After analysis and research, it was decided to adopt the following blasting scheme: a large amount of steam is used inside the tower to wash the paint, reduce the density and content of the flammable gas in the tower; cut the interconnection between the tower bodies and affect the collapse of the pipeline, support, etc.; The cutting technology can form a gap in the appropriate part of the tower body, so that the tower body is unstable and collapsed westward. The lower edge of the incision is filled with water at a certain height along the ground 101 from the ground, so that the blasting range is fully isolated from the dangerous gas, and the water pressure is simultaneously The generated thrust is beneficial to the detachment of the detachment from the cylinder; the use of the underwater medicinal package to generate shock waves in the water breaks the uncut portion of the joint and the corner and breaks the rupture of the dent from the cylinder to ensure the formation of a gap.

4 Determination of blasting parameters 41 blasting incision form and parameters 411 incision form General blasting demolition of general tubular high-rise structures The shape of the blasting cut is trapezoidal, rectangular, figure-shaped, herringbone, lip-shaped, etc., but with a linear shaped energy cutter Demolition of the metal cylinder by blasting, the cutter must be closed to form a ring by continuous connection. When determining the form of the slit, it is also necessary to consider the blasting performance when the condenser cutter is connected at different angles...

(a) Schematic diagram of rectangular incision (b) Schematic of hexagonal incision 2 Incision length The main principle of blasting demolition of a cylindrical structure is to blast a certain size of the incision at a certain height at the bottom of the structure, and use the self-weight of the structure itself to cause eccentricity If the pressure is unstable, the material of the end of the other side of the incision is broken or yielded. When the part of the incision is partially crushed or not damaged, the upper part of the incision is deflected in the design direction with no damage at the incision. Dumped. The determination of the chamfer angle is the result of a combination of the structure of the cylinder, the material properties (density), the wall thickness and height of the cylinder, the radius of the incision, and the maximum tensile and compressive strength of the material.

After calculation and analysis, it is more appropriate to retain part of the central angle a. Here, the length of the cut is L=8m. 413 Incision height For the tall tubular structure, the principle of calculating the height of the blasting cut is: when the structure is tilted, the upper and lower edges of the cut are closed. The distance the center of gravity moves should be greater than the outer diameter at the lower edge of the slit, as shown in (b).

When it is poured until the incision is closed, the incision closing angle ah(a) under the incision along the cross section (b) pouring process in the bursting area is calculated according to the above-mentioned offset distance of the center of gravity is larger than the setting of the outer radius of the incision, then there is a body The central angle of the arc length; H is the height of the center of gravity of the structure.

In this project, when the upper and lower edges of the incision are thin (only 10mm) and the upper and lower edges of the incision reach the same horizontal plane, the upper and lower incisions are not completely fitted to form a support, but the upper part is inserted into the lower part to form a support, and the upper part of the incision is larger. The deformation, and thus the same slit height, the inclination angle of the cylinder is large, and the actual slit height can be appropriately reduced. Take the cross section of the condenser cutter (unit: mm) 533 (Q) 113; the yield strength of A3 steel.

Through calculation and analysis, it was determined that the amount of drug in the water was 400g emulsion explosive.

The design delay time of the 432 underwater drug pack extension time is mainly determined by the time when the blasting incision has been formed and the tower body has not been tilted or the inclination is not obvious (that is, when the fragment in the incision is not stuck), the water packet explosion occurs. The shock wave in the water acts just on the fragment inside the incision. According to the experimental and numerical calculations, the process of metal jet intrusion into the cylinder after blasting is completed in about 100 s. After the blasting, the upper cylinder of the incision starts to tilt for about 0510s. For the sake of safety, the extension time range can be 150Ms 100ms. According to the existing equipment, The energy-carrying cutter adopts the instant non-electric detonator detonation. The water-medicine package uses milliseconds and 3 sections of non-electric detonators. The parameters of the 42-energy cutter are generally: the factors affecting the cutting effect are: the type and density of the explosive; The material, thickness, cone angle; the cutting resistance of the cutting object, the cutting resistance of the cutting object mainly depends on the structural form, physical and mechanical properties of the material; According to the actual situation of this project, the company has developed a suitable cutter in cooperation with the state-owned 9904 factory: the R852 explosive is used for the charge; the paint cover is lead-bismuth alloy, 2mm thick, 90 cone angle; the line charge density is (160 best) The height of the single cutter is 2mm. The length of the single cutter is 2m. The schematic diagram of the cross section of the shaped charge cutter is shown in Fig. 43. The parameters of the water in the package 431. The amount of the drug in the water pack can generate a certain thrust to push out the fragments in the incision. Without destroying the remaining part of the wall, the reverse direction is out of control, that is, it meets: explosion.

5 The detonation network design is complex for the surrounding environment of the blasting object. In order to avoid the influence of stray current, RF current and induced current and lightning on the blasting network, the detonating cord and the fuse network cannot be used in this demolition blasting. Only use safe and reliable non-electrical plastic detonator detonators, detonator detonators with four-way dual-connection network. The detonating point of the cutter is at the top of the cutter, and the instant detonator is used to simultaneously detonate the water in the water. The detonation of the water packet is performed in milliseconds, and the end of the network is fired by the electric detonator. The detonating power source uses a military detonator.

6 blasting safety design and measures 61 blasting earthquake control the maximum dose of a single explosion. The maximum dose of a single explosion according to the specific requirements of the environment is determined by the following formula: (m); V is the vibration velocity of the particle (cm/s) K is the medium correction coefficient related to the blasting geology; K The empirical coefficient is dispersed for the charge; a is the seismic wave attenuation index.

=15Qa=L5), R takes the distance of the nearest key protection target (test building), that is, R=465m is substituted into the above formula, and the allowable one-time explosion dose is Q=4Q5kg. No more than 1Qkg, so blasting vibration will not pose any threat to the laboratory and all buildings.

In order to prevent damage to the windows and doors of nearby buildings, remove the sash that can be removed, and do not remove the appropriate amount of adhesive tape (m-shaped) to ensure that the glass will not be broken.

64 ground contact vibration According to the measured data of directional blasting of multiple towering tubular structures, the general rule is that the blasting seismic wave is small, and the grounding vibration of the cylinder is slightly larger. For the effect of the grounding vibration of the cylinder, there is no accurate formula calculation that is accepted by everyone to adapt to various situations, and it is usually determined by previous similar engineering experience. For the most unfavorable situation: rigid structure to rigid ground, the formula measured by the Institute of Mechanics of the Chinese Academy of Sciences is as follows. Some precision instruments in the building can be transported and transported, and it is inconvenient to carry it for anti-shock treatment. The pad is appropriately raised, and the power-on instrument is powered off.

62 The maximum scattering distance of individual scattered objects in the blasting of individual scattered objects is calculated according to the empirical formula in the Blasting Calculation Manual. When the explosion index n=1, V=12m/s; it is the acceleration of gravity.

Use bamboo rafts, straw bags, sandbags, etc. to protect the position of the charge, reduce the scattering of the fragments and the damage of the shock wave to the surrounding environment and the blasting noise. At the periphery of the charge, the double-layer straw bag is used to bundle the occlusion, so that the scattered matter can be completely controlled. Within a certain range, there will be no harm to the surroundings.

63 air shock wave According to a large number of experimental results, when the charge is exploded in an infinite air medium, the peak value of the air shock wave overpressure can be calculated by the following formula: 106 Pa; 0 is the initial pressure in the air, 106 PaC is the charge, kg; For the distance from the blasting heart, it is the proportional distance, m/eg13; r is the distance from the measuring point to the blasting heart, m. After calculation, the charging amount is 6kg and the distance from the blasting heart 46 (wide; m is the cylinder mass, kgH is the center of gravity) Although the object of high blasting is strong overall, it is light in weight, and the speed value of the protected building caused by landing vibration will not exceed 1 7 blasting effect and experience 5 benzene towers with 3 blastings (2 bridges for the first time, 3 4 bridges for the second time, 15 bridges for the third time), the collapse direction is completely in accordance with the design direction, and the collapsed cylinder is still a whole The fragment in the incision is also a whole and is punched out a few meters away. The upper and lower sides of the incision are flattened and deformed along the adjacent cylinder. In the opposite direction of the collapse, part of the base is picked up by about 30 cm. The part of the cylinder is removed except that the 5 tower is pulled from the weld. The remaining four towers are curved and continuous, with no front and back sitting. During the construction and blasting process, the gas in the tower was not burned and exploded. Except for several pieces of glass broken in the abandoned factory building in the east, the blasting vibration and shock waves did not cause damage to surrounding facilities and buildings.

After analyzing and summarizing the successful blasting, the following experience is realized: 1) The linear shaped energy cutter is used to blast the metal cylinder, and the cutter must be closed into a ring shape by docking. When determining the shape of the cut, it is necessary to consider the different angles of the shaped energy cutter. Explosive performance and cutting ability at the corners. Only when the docking angle is greater than or equal to 90*, the blasting performance and cutting ability at the corner can meet the requirements. The corresponding cut form is a rectangle with a rectangle with an internal angle of not less than 90* (generally a hexagon with an inner angle of 120* is preferred) .

Photo blasting before photo blasting Photo tubular steel structure compared with ordinary tubular structure, small self-weight, thin wall thickness (more than one order of magnitude difference), high strength, corresponding blasting incision parameters compared with ordinary cylindrical structures, cutting height Should be smaller, the center angle of the incision should be larger.

The fragment in the blasting incision is a whole, and it is not possible to separate the cylinder from the cylinder and require auxiliary measures such as water blasting. The time for the extension of the drug pack in water needs to be carefully designed.

Blasting in a flammable explosion environment is prohibited. Detonating cords and fuses are prohibited as detonating equipment. Measures should be taken to isolate the metal jets generated by the blasting or Mars from the flammable atmosphere, or to reduce the concentration of flammable substances. Below the danger point.

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