DESIGN IMPROVEMENT AND OPERATION MODELING OF EAF GAS EXHAUST SYSTEM OF A FOUNDRY SHOP

Abstract

As a result of a survey of gas exhaust systems of low-tonnage electric arc furnaces (from 3 to 10 tons) operated in the foundries of machine-building enterprises, the bottlenecks were identified, due to which a large amount of gas-dust emissions gets into the production rooms and pollutes the air in the working areas. First of all, it occurs due to the design schemes imperfection of the evacuation systems of gas and dust ejected from the furnace cavity through the outlet channel, the working window, gaps between its body and the roof, between edges of the holes in its upper part and the electrodes lowered through them. In particular, joint units of the rotary collection hoods with the gas exhaust pipelines in these systems do not provide proper sealing of movable joints. In this regard, the authors have proposed an improved design of rotation mechanism of the furnace collection hood, which involves the use of two sand gates. These gates eliminate the possibility of harmful emissions release between movably connected elements of the system into the environment. To begin designing of the industrial sample of a modernized mechanism, a method for calculating the energy-power parameters of its drive has been developed. A preliminary validation of the correctness of the taken technical decisions and of the obtained calculating dependencies was performed on the operating model of the investigated system manufactured on a 1:10 scale relative to the industrial sample. For the model research an instrumentation complex that included strain gauge transducer, AC amplifier, analogto-digital converter and computer was used. During this research the load acting on the model drive of the collection hood rotation mechanism when it was transferred from the working position to the parking one and back was fixed. At the same time, the load was measured for two cases: in the absence and in the presence of sand in the gates which ensure sealing of the movably joint elements of the investigated mechanical system. It was established that the portion of resistance forces arising in two sand gates during relative rotation of the moving element is 20 – 26 % of total load on the mechanism drive depending on angular velocity of the cantilever with collection hood. Similarly, this indicator calculated from obtained theoretical dependences was in the range of 17 – 23 % for the rotation mechanisms of collection hood of arc furnaces with a tonnage of 3 to 10 tons. Video filming of the smoke movement patterns, which flows from the furnace model through the existing gaps between its body and roof during the steelmaking process imitating, confirmed the reliability of the sand gates that provide complete sealing at the joint units of the moving parts of the collection hood rotation mechanism. Practical use of the proposed technical solution allows increasing of efficiency of evacuation of the harmful gas and dust emissions from the working zone of smelting furnaces used in the foundry.