IGNITION OF SINTERING MIX AT SINTER MACHINES OF PJSC NLMK

Abstract

The article presents a retrospective review of research papers devoted to the gas-dynamic mode of ignition of sinter mix. The main technical solutions for throttling the vacuum chambers of the sinter machine under the ignition hearth and the parameters, characterizing the gas-dynamic mode of its operation, are presented. The most crucial requirement for the operating mode of the hearth is maintaining a balance between the flow rates of combustion products of gas from the burners and those sucked through the mix bed. Updated data from previous studies on the throttling of the vacuum chambers in the NLMK sinter machine, which sinter mix not preheated by return, are presented. The results of the first of three stages of new studies of the gas-dynamic mode of operation of the ignition hearth after its transfer from mixed natural and blast furnace gas (12 and 88%) to natural gas are considered. Prior to the study, a dampener-type throttle device was installed in the nozzles of the first two vacuum chambers. Measurements revealed that replacing the mixed gas with natural gas did not increase the excess air coefficient α ≈ 1,0. As a result, gas combustion occurs in the flow of air sucked into the furnace, with a highly uneven temperature distribution across the bed width. Additionally, the dual-line kinetic burners installed in the furnace were designed to completely premix the gas with air. The furnace's operating conditions also meet this requirement. Consequently, gas inflow and outflow balance were not achieved even with a nozzle cross-sectional area of 4.4%. The temperature difference between the center and periphery increased during throttling from 180 to 360 °C. Furthermore, it was discovered that the hearth chamber length is almost 7 m, while the throttled vacuum chambers are 6 m long. There is no seal between the second throttled and third non-throttled vacuum chambers; the gap height is 90 mm. It is recommended to reinstall the seal between these vacuum chambers. It has been established that a cause of the uneven temperature distribution across the bed width is increased gas-dynamic resistance of the bed in the upper half of the pallet sides, which is widened from 4000 to 4400 mm. A gradual replacement of the these pallets with pallets narrowed by 100 mm has been organized. A positive, but minimal, effect has been established from this measure. It is recommended to perform measurements of the air filtration velocity distribution at the bed inlet using an anemometer behind the ignition hearth. It is also recommended to install a vacuum sensor in the hearth to create the balance of gas inflow and outflow.