New process to obtain unslaked lime through microwave hybrid heating and its fluid dynamics computational modeling

This study aimed to analyze the advantages of limestone calcination through a conventional microwave heating technique. For such a purpose, the microwave was merged by hybrid heating and a refractory ceramic internally coated with copper oxide was used with a conventional muffle furnace. It has also been analyzed the behavior of calcining limestone with different masses and variations in retention time using a muffle furnace and microwaves, both with and without using the refractory ceramic. Afterwards, the process has been modeled so as to analyze temperature versus retention time. As a result, calcination using a microwave susceptor with the refractory ceramic substance proved to be a process that takes 35% less time than conventional methods. Furthermore, there has been a reduction in 66.1% of energy expenditure. It was also observed that the new procedure offers advantages in reduced greenhouse gases emissions on account of the release of only a single substance, ease of air treatment in industrial environments and being a more economically viable process for limestone calcination, which can be further utilized by companies belonging to such a sector. Its patent deposit number BR 202018073002-4 U2 in INPI.

Еfficiency increase of powdered coal application at hot metal production and limestone calcination under unstable technology conditions

Operation of Ukraine ferrous metallurgy under conditions of dependence on import and instability of energy carriers supply, shortage of investments in modernization of production equipment, make the matter of cooperation between steel-works and research organization particularly actual. Basic results of cooperation between Z.I. Nekrasov Institute of Ferrous metallurgy, NAN of Ukraine and Dnepr steel-works in 2017–2019 on blast sfurnace operation pefection and technology of powdered coal injection into rotating limestone calcination furnaces. Results of the finding of the powdered coal optimal consumption shown, which ensure a high efficiency of the coke substitution, reaching of maximum possible blast furnace productivity as well as satisfactory utilization degree of the reducing gas ability. Results of implementation of a complex of measures presented, which ensure a rational distribution of the powdered coal by BF air tuyeres for making the heat conditions of the tuyere zone even by the blast furnace circle. Efficiency of application of technology of joint injection the powdered coal and natural gas was shown, which is achieved by improving the powdered coal combustion conditions in case of increase their mixing degree. Recommendations quoted for blast furnaces starting-up after their idling for a period exceeding the permissible one, without tapping the plug hot metal. The recommendations ensure an accident-free putting a blast furnace into operation followed by reaching planned parameters. Results of usage sensors information, measuring temperature of gas flow above the charge surface presented. The results allow to prove the correction of blast furnace charging mode by an expert module, generating correction impact to support control actions by technological personal. A complex of measures formed to prevent a disturbance of a blast furnace running in case of powdered coal injection in an amount exceeding 140 kg/t of hot metal and without application of special washover materials. The results of efficiency of the mastered technology, envisaging application manganese-bearing materials at a constant base, were shown. Results of diagnostics of workability of the facility for powdered coal injection into rotating limestone calcinating furnace presented, followed by elaboration recommendation on correction parameters of injection facility operation.

Aproveitamento dos rejeitos das indústrias de calcinação de calcário na porção setentrional do estado do Ceará com foco na reparação de dano ambiental

Os resíduos gerados no processo de calcinação dos calcários formam pilhas que se constituem em fontes de degradação do meio ambiente e obstáculos ao bom andamento das atividades das unidades produtoras. O aproveitamento desses rejeitos pode gerar benefícios ao meio ambiente, bem como melhorias ao trabalho dos operários, além de ser mais uma fonte de renda para as indústrias de calcinação locais. Este estudo foi desenvolvido no sentido do aproveitamento racional e econômico desses materiais residuais na pavimentação de estradas e na construção de obras de aterro que exijam solo estabilizado e, consequentemente, de boa consistência. Inicialmente, foram coletados resíduos de três províncias produtoras de cal na porção setentrional no estado do Ceará, sendo uma localizada entre os municípios de Coreaú e Sobral; outra em Forquilha; e uma terceira em Quixeré. As amostras foram misturadas com um solo argiloso, constituindo amostras compostas de solo-rejeito com proporções de resíduo de 0% (zero), 20, 30, 40, 50, 60, 70 e 80%. Ensaios geotécnicos foram realizados para determinação de suas granulometrias e respectivos índices de suporte Califórnia (CBR), de plasticidade (IP) e de grupo (IG). Como resultado, verificou-se aumento da resistência física do solo mediante a incorporação do rejeito nas amostras, constatando que um solo argiloso com características físicas não recomendadas para o uso na construção de estradas poderá se tornar útil para essa finalidade se estabilizado com os resíduos das indústrias de cal, promovendo a reparação de dano ambiental na área das unidades produtoras e uma destinação racional para os rejeitos. Use of tailings from the limestone calcination industries of the state of Ceará with a focus on repair of environmental damage A B S T R A C TThe residues generated in the limestone calcination process form piles sources of degradation of the environment and obstacles to the good progress of the activities of the producing units. The use of these tailings might generate benefits to the environment, as well as improvements to the job of the workers, besides being another source of income for the local calcination industries. This study was developed in the sense of the rational and economic use of these residual materials in the paving of roads and in the construction of landfills that require stabilized soil and, consequently, good consistency. Initially, waste was collected from three producing provinces of lime in Ceará, one of which is located between the municipalities of Coreaú and Sobral; another in Forquilha; and the third in Quixeré. The samples were mixed with a clay soil, consisting of soil-reject samples with residue ratios of 0% (zero), 20, 30, 40, 50, 60, 70 and 80%. Geotechnical tests were performed to determine their granulometry and respective California (CBR), plasticity (IP) and group (IG) indices. As result, soil physical strength increased by incorporating the reject in the samples, noting that a clay soil with physical characteristics not recommended for use in road construction could be useful for this purpose if stabilized with the residues of lime industries, promoting the environmental damage repair in the area of the producing units and a rational destination for the wastes.Keywords: paving; damage mitigation; environmental sustainability; lime.

Numerical Investigation on Multiphase Reacting/Combusting Turbulent Flows: Aerodynamics, Kinetics, Heat and Mass Transfer Inside a Cement Kiln Precalciner

This paper reports the modeling work to develop a computational fluid dynamics (CFD) engineering application, based on an appropriate 3D mathematical model able to perform the thermo-fluid dynamic numerical simulation of multiphase reacting/ combusting turbulent flows within a precalciner of an industrial four-stage cyclone preheater/precalciner cement kiln. In the precalciner furnace the hot micron-sized limestone (calcite/dolomite) meal, held in suspension, is quiet completely converted to quicklime (CaO(s)), and the CO2(g) by-product is driven-off during calcination process. Since, the thermal decomposition mechanism is a very endothermic reaction, the necessary heat is balanced by pulverized petcoke combustion. These major physical and chemical processes inside the precalciner are properly described by the 3-D Favre-averaged Navier-Stokes equations with the species transport equations, the energy equation and the state equation, to be solved by an Eulerian-Lagrange approach. The CFD solver employed in this study is the commercial CFD code ANSYS Fluent R18.2. The used built-in models/sub-models include turbulence models and near-wall treatment, model of traditional air-pulverized petcoke combustion, pulverized-limestone calcination model, as well as the sub-models for radiation heat transfer and turbulence-chemistry interaction. They are used to formulate the closures of the unclosed terms in the PDEs system. In summary, the trends of predicted results of limestone calcination and petcoke/TDF combustion processes in an industrial precalciner furnace are reasonable fair in confront to operation data measurable in the harsh environment conditions, typical for the pyroprocessing systems. The developed CFD engineering application can be used as an effective design tool for preliminary examination of the global effect of thermal-flow aerodynamics and turbulence on the precalciner processes.