Abstract
The article presents the solution adopted in an existing blast furnace with only two safety valves to minimize the dust and gas emissions to the atmosphere, in case of emergency relief due to abnormal overpressure during operating issues in the blast furnace process. Before the implementation of the system, several openings of the emergency bleeder valves were observed: These led to sensitive pollutant emissions, also in terms of acoustic and visive events, with high impact on the surrounding environment. The new relief system, in addition to the existing bleeder valves, has been engineered with a Computational Fluid Dynamic (CFD) analysis using Ansys Fluent to find out the most effective solution and to minimize modifications on the plant. Few plant modifications, while guaranteeing the achievement of the target of reducing the bleeder openings, allow to reduce the plant shutdown costs for the modifications themselves and the maintenance costs during plant operation and to simplify the operating logic of the blast furnace overpressure control systems. The new installation increased the safety operation of the blast furnace, and it drastically reduced the bleeder valves openings—4% of the pre-intervention total opening time per year—and the associated emissions in spite of the rise of the pig iron production, as recorded by the monitoring and supervision system.
Highlights
Published: 22 February 2022Blast furnace (BF) technology is currently evolving towards operative regimes involving smaller and smaller quantities of reducing agents in order to limit carbon dioxide (CO2 ) emissions
Each BF gas line is equipped with three emergency valves arranged on the main uprights and at the beginning of the descending section in order to vent any overpressure in the BF throat without propagating to the rest of the line
The first circuit (C1) simulates the original conditions: bleeder valve B1 set to open at BF top pressure equal to 950 mmWC; in case the pressure continues to rise, at 1050 mmWC, bleeder valve B2 opens, too; The second circuit (C2) partially bypasses the cyclones and transfers the gas to the reserve scrubber through a new DN800 emergency pipeline
Summary
Blast furnace (BF) technology is currently evolving towards operative regimes involving smaller and smaller quantities of reducing agents in order to limit carbon dioxide (CO2 ) emissions. Operating conditions characterized by low levels of reducing agents and increasingly large BFs lead to occurrence of undesirable phenomena such as slipping and channeling [1,2]. Since these irregularities in the functioning of BF result in a loss of production and materials and cause variations in the quality of the iron [3,4], the analysis and the prevention of the above-mentioned phenomena is of great interest. A sudden reduction in the overpressure inside the furnace before reaching 3the set value for the top furnace emergency bleeder valves opening; Treatment the gasbefore beforereleasing releasing theatmosphere, atmosphere,with withrelevant relevantreduction reduction. The decommissioning of one of the two BFs resulted in the halving of the originally planned flow rate with the consequent doubling of the redundant units
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