After more than 80 years of development, China’s calcium carbide industry has become an important basic chemical raw material industry. In recent years, driven by the rapid development of the domestic economy and the growing demand for calcium carbide downstream, the domestic calcium carbide production capacity has expanded rapidly. In 2012, there were 311 calcium carbide enterprises in China, and the output reached 18 million tons. In the calcium carbide furnace equipment, the electrode is one of the important equipment, which plays the role of conduction and heat transfer. In the production of calcium carbide, an electric current is input into the furnace through an electrode to generate an arc, and the resistance heat and the arc heat are used to release energy (temperature up to about 2000 ° C) for calcium carbide smelting. The normal operation of the electrode depends on factors such as the quality of the electrode paste, the quality of the electrode shell, the welding quality, the length of the pressure release time, and the length of the electrode work. During the use of the electrode, the operating level of the operator is relatively strict. Careless operation of the electrode can easily cause soft and hard breakage of the electrode, affect the transmission and conversion of electrical energy, cause deterioration of the furnace condition, and even cause damage to the machinery and electrical equipment. Safety of operator’s life. For example, on November 7, 2006, a soft break of an electrode occurred at a calcium carbide plant in Ningxia, causing 12 workers at the scene to be burned, including 1 death and 9 serious injuries. In 2009, a hard break of an electrode occurred in a calcium carbide plant in Xinjiang, causing five workers at the scene to be burned seriously.
Analysis of the causes of soft and hard break of calcium carbide furnace electrode
1.Cause analysis of soft break of calcium carbide furnace electrode
The sintering speed of the electrode is lower than the consumption rate. After the unfired electrode is put down, it will cause the electrode to break softly. Failure to evacuate the furnace operator in time may cause burns. The specific reasons for electrode soft break are:
1.1 Poor electrode paste quality and excessive volatiles.
1.2 The electrode shell iron sheet is too thin or too thick. Too thin to withstand large external forces and rupture, causing the electrode barrel to fold or leak and soft break when pressed down; too thick to cause the iron shell and the electrode core not to be in close contact with each other and the core may cause Soft break.
1.3 The electrode iron shell is poorly manufactured or the welding quality is poor, causing cracks, resulting in leakage or soft break.
1.4 The electrode is pressed and put too frequently, the interval is too short, or the electrode is too long, causing a soft break.
1.5 If the electrode paste is not added in time, the electrode paste position is too high or too low, which will cause the electrode to break.
1.6 The electrode paste is too large, careless when adding the paste, resting on the ribs and being overhead, can cause soft break.
1.7 The electrode is not sintered well. When the electrode is lowered and after it is lowered, the current cannot be properly controlled, so that the current is too large, and the electrode case is burned and the electrode is softly broken.
1.8 When the electrode lowering speed is faster than the sintering speed, the pasting segments in the shaping are exposed, or the conductive elements are about to be exposed, the electrode case bears the entire current and generates a lot of heat. When the electrode case is heated above 1200 ° C, the tensile strength is reduced to Can not bear the weight of the electrode, a soft break accident will occur.
2.Cause analysis of hard break of calcium carbide furnace electrode
When the electrode is broken, if the molten calcium carbide is splashed, the operator has no protective measures and failure to evacuate in time may cause burns. The specific reasons for the hard break of the electrode are:
2.1 The electrode paste is usually not properly stored, the ash content is too high, more impurities are entrained, the electrode paste contains too little volatile matter, premature sintering or poor adhesion, causing the electrode to hard break.
2.2 Different electrode paste ratios, small binder ratio, uneven mixing, poor electrode strength, and unsuitable binder. After the electrode paste is melted, the thickness of the particles will delaminate, which reduces the electrode strength and can cause the electrode to break.
2.3 There are many power outages, and the power supply is often stopped and opened. In the case of power failure, necessary measures have not been taken, resulting in electrode cracking and sintering.
2.4 There is a lot of dust falling into the electrode shell, especially after a long period of shutdown, a thick layer of ash will accumulate in the electrode iron shell. If it is not cleaned after power transmission, it will cause electrode sintering and delamination, which will cause Electrode hard break.
2.5 The power failure time is long, and the electrode working section is not buried in the charge and severely oxidized, which will also cause the electrode to hard break.
2.6 The electrodes are subject to rapid cooling and rapid heating, resulting in great internal stress differences; for example, the temperature difference between the electrodes inserted inside and outside the material during maintenance; the temperature difference between the inside and outside of the contact element is large; uneven heating during power transmission can cause Hard break.
2.7 The working length of the electrode is too long and the pulling force is too large, which is a burden on the electrode itself. If the operation is careless, it may also cause a hard break.
2.8 The amount of air supplied by the electrode holder tube is too small or stopped, and the amount of cooling water is too small, which causes the electrode paste to melt too much and becomes like water, causing the particulate carbon material to precipitate, affecting the sintering strength of the electrode, and causing the electrode to hard break.
2.9 The electrode current density is large, which can cause the electrode to hard break.
Countermeasures to avoid soft and hard electrode breaks
1.Countermeasures to avoid soft break of calcium carbide furnace
1.1 Properly control the working length of the electrode to meet the requirements of calcium carbide production.
1.2 The lowering speed must be compatible with the electrode sintering speed.
1.3 Regularly check the electrode length and soft and hard procedures; you can also use a steel bar to pick up the electrode and listen to the sound. If you hear a very brittle sound, it proves to be a mature electrode. If it is not a very brittle sound, the electrode is too soft. In addition, the feel is also different. If the steel bar does not feel the resilience when it is reinforced, it proves that the electrode is soft and the load must be raised slowly.
1.4 Regularly check the maturity of the electrode (you can judge the condition of the electrode by experience, such as a good electrode showing a dark red slightly iron skin; the electrode is white, with internal cracks, and the iron skin is not seen, it is too dry, the electrode emits black smoke, black, White point, the electrode quality is soft).
1.5 Regularly inspect the welding quality of the electrode shell, one section for each welding, and one section for inspection.
1.6 Regularly check the quality of the electrode paste.
1.7 During the power-up and load-up period, the load cannot be increased too fast. The load should be increased according to the maturity of the electrode.
1.8 Regularly check whether the clamping force of the electrode contact element is appropriate.
1.9 Regularly measure the height of the electrode paste column, not too high.
1.10 Personnel engaged in high-temperature operations should wear personal protective equipment that is resistant to high temperatures and splashes.
2.Countermeasures to avoid hard break of calcium carbide furnace electrode
2.1 Strictly grasp the working length of the electrode. The electrode must be measured every two days and must be accurate. Generally, the working length of the electrode is guaranteed to be 1800-2000mm. It is not allowed to be too long or too short.
2.2 If the electrode is too long, you can extend the pressure release time and reduce the ratio of the electrode in this phase.
2.3 Strictly check the quality of the electrode paste. The ash content cannot exceed the specified value.
2.4 Carefully check the amount of air supply to the electrode and the gear position of the heater.
2.5 After the power failure, the electrode should be kept as hot as possible. The electrode should be buried with material to prevent the electrode from oxidizing. The load cannot be raised too fast after power transmission. When the power failure time is long, change to Y-type electric preheating electrode.
2.6 If the electrode hard breaks several times in a row, it must be checked whether the quality of the electrode paste meets the process requirements.
2.7 The electrode barrel after the paste is installed should be covered with a lid to prevent dust from falling in.
2.8 Personnel engaged in high-temperature operations should wear personal protective equipment that is resistant to high temperatures and splashes.
in conclusion
The production of calcium carbide needs to have rich production experience. Each calcium carbide furnace has its own characteristics for a period of time. The enterprise should summarize the beneficial experience in the production process, strengthen the investment in safe production, and carefully analyze the risk factors of the soft and hard break of the calcium carbide furnace electrode. Electrode safety management system, detailed operation procedures, strengthen professional training of operators, wear case protective equipment strictly according to requirements, prepare accident emergency plans and emergency training plans, and conduct regular exercises to effectively control the occurrence of calcium carbide furnace accidents and reduce accident losses .
Post time: Dec-24-2019