I. Preface Steelmaking industry has been disturbed by steel inclusion and short service life. With the development of steelmaking industry, steel plants adopt slag-splashing for protection of converter, in this case, steel slag is more serious so that service life of nozzle and outer pipe of lance body is reduced. However, coordinated application between seamless taper oxygen lance and forging nozzle can solve completely these problems above, which represent development direction in the field of oxygen steelmaking industry. Average service life of common casting nozzle is 200 heats, casting nozzle has to be abandoned because of water leakage at the center or welding seam, hole is easily deformed, service life of oxygen lance is unstable. After forging nozzle is applied, service life is extended with the progress of oxygen supply and management, average service life is over 600 heats, which is over 3 times more than casting nozzle. When forging nozzle is applied with taper oxygen lance, performance is optimized, service life is over 1000 heats. Taper oxygen lance can fall off steel slag automatically, manual slag removal is released, service life is extended, while forging nozzle is durable, hole is not easily deformed, service life is 800-1000 heats, and can guarantee normal oxygen jet flow and steady blowing. Forging nozzle is replaced according to abandonment plan. When taper oxygen lance is applied with forging nozzle, service life of oxygen lance and nozzle is extended by a big margin, productiveity is increased, replacement frequency is reduced, labor intensity is lightened, steel output is raised, at the same time, energy is saved, consumption is reduced, that is, they serve two purposes at the same time. Though there are many advantages when taper oxygen lance is applied with forging nozzle, however, some good tips are necessary. At present, most steel plants overload in order to increase productivity, but they don’t adjust blowing parameters accordingly in time, as a result, hearth environment is worsened causing splattering and return dry, in the end, slag inclusion is very serious, oxygen lance and nozzle are damaged, in this case, service life is shortened. Therefore, reasonable loading system, oxygen supply system and slag-making system should be controlled in order to exploit advantages of taper oxygen lance and forging nozzle to the full, unreasonable operation is forbidden. II. Operating instructions about integrated taper oxygen lance i. Three kinds of assembling methods about taper oxygen lance Because actual smelting conditions in the steel plants are different, our nozzle products are various. However, there are common characteristics about assembling, which can be summed up the following three kinds of assembling methods: 1. Inner pipe, middle pipe and outer pipe are welded; 2. Outer pipe is welded, inner pipe sliding seal, while middle pipe is intubation (inner intubation and outer intubation are included). 3. Inner pipe and outer pipe are welded, while middle pipe is intubation (inner intubation and outer intubation are included). The following are three kinds of assembling method diagrams: ii. Three kinds of assembling methods about taper oxygen lance 1. Inner pipe, middle pipe and outer pipe are welded; 1.1. Disassembling methods about oxygen lance nozzle A. Oxygen lance is fixed horizontally. B. Inlet oxygen pipe flange is opened. C. Welding seam between nozzle and lance body connector is cut according to the drawings, the cut should be vertical, flat and narrow. D. Special-purpose tool is used to push inner pipe until middle pipe welding seam comes out, at the same time, enough welding length is guaranteed for future assembling. After middle pipe welding seam comes out, welding seam is cut off, and then inner pipe is pushed until welding seam comes out (30-50mm), inner pipe is cut off along the welding seam. 1.2. Assembling process flow about oxygen lance nozzle (horizontal assembling) A. Oxygen lance is fixed horizontally. B. Welding grooves of three-layer pipes are dressed and ground to guarantee vertical and flat end without burr. C. Inner pipe of nozzle is aligned with inner pipe of oxygen lance, wood blocks are put under the nozzle end. Special-purpose tool or other tools is used to strike slightly wood block mat until middle pipe of nozzle aligns with middle pipe of oxygen lance, after middle pipe is welded, wood block mat is continued striking slightly until outer pipe of nozze fits perfectly with outer pipe of oxygen lance, and then outer pipe is welded. D. After inlet oxygen pipe flange is assemblied, 2.5Mpa hydraulic pressure testing is carried out lasting 45 minutes without water leakage. 2. Outer pipe is welded, inner pipe sliding seal, while middle pipe is intubation (inner intubation and outer intubation are included). 2.1. Disassembling methods about oxygen lance nozzle A. Oxygen lance is fixed horizontally. B. Outer pipe is cut off along the welding seam between outer pipe of lance body and outer pipe of nozzle. Cut should be neat, vertical and narrow C. Special-purpose tool or manual operation is used to disassembly nozzle. In the process of disassembling, force should be level along the center line direction against deformation of intubation. 2.2. Assembling process flow about oxygen lance nozzle A. Oxygen lance is fixed horizontally. B. Inner intubation and middle intubation in the oxygen lance body should be checked against deformation. Rust of low-carbon steel intubation should be removed. C. Inner pipe surface (especially seal loop) is coated with soapy water or cleansing agent for lubrication (Note: grease lubricant is pohibited). D.Special-purpose tool is used to align inner pipes of nozzle and oxygen lance, coaxial angle must be guaranteed. After being clamped and fixed, special-purpose tool is used to push nozzle end surface until outer pipe of nozze fits perfectly with outer pipe of oxygen lance. Or axial force is added after nozzle is aligned with oxygen lance body, meanwhile, nozzle is rotated until outer pipes fit perfectly with each other. Because of high temperature, damp cloth can be used to wrap nozzle in order to prevent seal loop from being burnt, water is poured while outer pipe is welded. After welding is finished, hydraulic pressure testing is carried out without water leakage, which is qualified. 3. Inner pipe and outer pipe are welded, while middle pipe is intubation (inner intubation and outer intubation are included). 3.1. Disassembling methods about oxygen lance nozzle A. Oxygen lance is fixed horizontally. B. Inlet oxygen pipe flange is opened. C. Outer pipe is cut off along the welding seam between outer pipe of lance body and outer pipe of nozzle. Cut should be neat, vertical and narrow. D. Special-purpose tool is used to push inner pipe end surface until middle pipe separates, and then inner pipe is continued pushing until welding seam comes out for welding. Inner pipe is cut off along the welding seam, and cut should be neat, vertical and narrow. 3.2. Assembling process flow about oxygen lance nozzle A. Oxygen lance is fixed horizontally. B. Middle intubation in the oxygen lance body should be checked against deformation. Rust of low-carbon steel intubation should be removed. C. Welding grooves of inner pipe and outer pipe are dressed and ground without cut and burr. End surface is vertical and flat. D. Special-purpose tool is used to align inner pipes of nozzle and oxygen lance, coaxial angle must be guaranteed, at the same time, coaxial angle between nozzle and oxygen lance middle pipe should be taken care. After being clamped and fixed, inner pipe is weld. E. Special-purpose tool is used to push nozzle end surface until middle pipe inserts, and outer pipe of nozze fits perfectly with outer pipe of oxygen lance. And then, outer pipe is welded. F. After welding is finished, hydraulic pressure testing is carried out without water leakage, which is qualified. Note: 1. Lining buffering matter should be added to prevent nozzle from being damaged in the process of pushing nozzle end. 2. Coaxial angle must be guaranteed, which can guarantee unchangeable parameters of oxygen outlet and central axis, it is important to protect furnace lining. At the same time, welding seam quality is ensured, otherwise, deflection and mismatch can make welding seam stress uneven resulting in fatigue fracture and inner intubation deformation so that using is affected because of leakage. III. Operating instructions about integrated taper oxygen lance 1. Operating oxygen pressure Operating oxygen pressure is oxygen pressure at the inlet. There are three kinds of working conditions in the process of actual production, that is, it is higher than design oxygen pressure, equivalent to oxygen pressure, lower than oxygen pressure. A. When operating pressure is higher than design pressure, dynamic stream pressure rises, which is more than energy loss from jet flow caused by shock wave, agitating into the molten bath is guaranteed. Production practice proves that operating oxygen pressure is higher than theoretical design oxygen pressure to some extent, operation is stable, service life is long, nozzle outlet is not easily burnt. B. When operating pressure is equivalent to design pressure, at this time, outlet pressure is equal to environment pressure, stable jet flow is obtained, no shock wave is generated. C. If operating pressure is lower than design pressure, jet flow energy loss is much, operation pressure is low, dynamic stream pressure is reduced, agitating force in the molten bath is weak, at the same time, nozzle sticks easily steel, nozzle outlet is corroded seriously, as a result, service life is reduced obviously. Therefore, normal operation oxygen pressure should be controlled within the range of design pressure, highest operation pressure is not more than design oxygen pressure by 10 percent, is not absolutely less than design oxygen pressure. 2. Angle between nozzle and oxygen lance centerline Generally speaking, overall characteristics of jet flow determines smelting, while overall characteristics of jet flow is influenced by hole angle, and dominated by angle to a large extent. When angle is small, penetration is increased, impact area of molten bath is reduced, when angle is big, penetration is reduced, impact area of molten bath is increased, furnace wall is possibly washed out. Therefore, comprehensive consideration should be taken into according to converter tonnage and furnace profile. 3. Requirements about oxygen lance position control We propose that normal oxygen lance position should be 35 times of outlet diameter, basic position fluctuates ranging ±0~200mm. It is necessary to implement minimum position limit in order to avoid the condition that excessively low position does damage to nozzle. However, limit value of lowest absolute position changes with different stages of campaign life because furnace bottom and molten bath change in the process of campaign life, and metal bath surface becomes low. This work is done by section technical staff through modifying and setting lowest limit value in the computer according to liquid level measurement and thickness laser measurement value of furnace lining in different stages in the form of interlock control. If position is excessively low, slag will easily return dry owing to long-time blowing causing metal splattering, service life is shortened. If position is excessively high, splattering is also easily caused, blowing time will be extended. If position is excessively high, while oxygen pressure is very low, serious splashing will be caused, therefore, hanging blowing should be forbidden. Thus it can be seen that improper position control will cause splattering and return dry, and has a bad effect on service life and performance of oxygen lance and nozzle. Therefore, appropriate position is necessary according to work conditions in order to guarantee good performance of oxygen lance and nozzle. 4. Service life In the process of using, nozzle condition should be good, no deformation occurs, oxygen jet flow is stable, (TFe%) content in the slag is normal, each shift should pay attention to checking, nozzle is abandoned in light of actual condition according to regulations. 5. Control requirements about cooling water pressure In practice, cooling water supply is insufficient for various reasons, which will affect cooling performance of oxygen lance and nozzle, as a result, ideal operating conditions of oxygen lance nozzle can not be realized. Water pump, i.e. water supply equipment, should own enough lift, it is better to provide stand-by pump, in case that water pressure is too low or service pump shut down, thus stand-by pump can substitute it and guarantee normal production. Water supply pressure is as followed: If nominal tonnage of converter is under 100T, water pressure should be more than 1.0 Mpa; If nominal tonnage of converter is more than 100T(100T is included), water pressure should be more than 1.2 Mpa. 6. In addition, taper pipe should be lifted upwards softly to avoid collision at the mouth of nitrogen sealing ring because one-end taper pipe is thick, in case of collision, high-temperature taper pipe is possibly deformed, water flow is affected. 7. Attention to safety should be paid in the process of removing slag inclusion, steel slag can fall off automatically owing to taper angle, therefore, slag shoule be dealt with from top to bottom, slag can fall off totally when cracking is opened from one side. IV. Rationalization proposal Taper oxygen lance can not stick slag whose external surface of taper pipe suffers from little hot corrosion, at the same time, servive life can be extended when taper oxygen lance is applied with forging nozzle. However, taper oxygen lance should be operated scientifically, after all, there are slight defects on the surface of taper pipe owing to the long-term operating. We suggest that repairing and maintenance of taper pipe surface should be carried out, e.g. slag inclusion, ripple markings or corrosion parts should be polished, in order to guarantee good slag release and smooth surface after 500-600 heats. In this case, slag release effect can be improved, thus service life of taper pipe can be extend further. V. Concluding remarks 1. When nozzle hole quantity, position and dip angle are determined reasonably, which is favorable to improving slagging, solving spray problem because of overlapping streams, which is also primary condition to ensure service life. 2. In the process of using, it is important to choose some parameters such as oxygen lance position, water flow and operating oxygen pressure and so on, especially oxygen pressure, operating oxygen pressure should be equal to or higher than theoretical design oxygen pressure to some extent, in addition, lowest position limit is adopted in the process of production management, which is favorable to service life. If choice is not appropriate, nozzle will be corroded rapidly, service life is reduced obviously. 3. We would like to supply high-quality products, excellent technical support and first-class services to you, and create values for you to realize win-win! 4. In the process of compiling this operating instructions, we take proposals from large and medium-sized steel plants at home and abroad, at the same time, summarize rich production experience of our company. We offer this instruction to workers and friendsengaging in the steelmaking business for your information, please don’t hesitate to correct our mistakes if any. Oxygen Lance Research Institute Shandong Chongsheng Metallurgical Oxygen Lance Co., Ltd |
