Determination of Key Parameters Required to Optimize Calcination Process in Ferrous Metallurgy Heating Plants

Lime is the product of calcination. Its formation is always related to removal of carbon dioxide generated in the course of carbonate decomposition. Ferrous metallurgy, construction material, chemical and food industry companies account for about 90 % of lime produced in the country. Ferrous metallurgy is the major consumer of commercial lime using up to 40 % of all produced lime. Currently, despite occurrence of new binding and artificially produced chemical compounds, lime remains the major chemical compound produced by the industry in terms of output. Various units (shaft, rotary tubular kilns and fluidized bed kilns) are used for calcination. Shaft kilns are used the most widely. Considering continuously growing demand for lime, the need occurs for intensification of the burning process and optimization of the shaft kiln operating conditions. This requires knowledge of calcination physicochemical and heat transfer process mechanisms. Thus, the work deals with the issues related to determination of the optimal specific fuel consumption for burning of limestone from a particular deposit. It may be done only basing on thermal calculations for an operating shaft kiln, what, in its turn, causes the need for determination of the whole set of limestone and lime heat transfer properties. The obtained work results may be used to optimize the operating conditions of not only shaft but also rotary kilns intended for limestone heat treatment.

Regional disparity in clinker emission factors and their potential reduction in China

Detailed analysis the disparity and reduction potential of clinker emission factors at the provincial level is important for regional reduction policies. Using the surveyed data from 185 new suspension and pre-heater (NSP) process lines and 69 Shaft kiln lines, this study firstly analyzed the disparity in emission factors based on production process, production scale, and regional distribution in 2015. We found that the emission factor of the Shaft kiln process (898.24 kg/t) is higher than that of the NSP process (858.59 kg/t), and that small-scale production lines have higher emission factors than large-scale lines both for the two process. China's clinker emission factors increase from the eastern to the western regions. Then we estimated the reduction potential of structural adjustment, raw material substitution, and energy saving and fuel substitution in regional emission factors by 2030. The result shows that emission factors of the surveyed provinces will decrease by 101.41-174.60 kg/t compared to the values in 2015, which is mainly contributes by energy saving and fuel substitution (65.98%), and raw materials substitution (25.72%). And structural adjustment contributes only a small part reduction for most investigated provinces. The national average emission factor is estimated to be 715.33 kg/t in 2030, which indicates a reduction of 16.65%. These results can provide valuable feedback to government officials on the effectiveness of existing measures and also serve as a reference for future decisions on emission reduction polices.

The Influence of Al2O3 Microparticles on the Pore Structure of Fired Clay

Contemporary demand after high-quality ceramics leads to the depletion of raw material deposits. The industry also produces waste secondary materials that cannot be used directly for the desired purposes. It is therefore necessary to find other uses for these materials. It is common practice in the ceramics industry to stockpile fine fractions of refractory clays prior to their firing in a shaft kiln. These fractions have the size of 35 mm and less and when stored in a mound are facing a risk of weathering. Finding a purpose for these unused materials will markedly slow down fresh clay mining and make the production more eco-friendly and cost-effective. This paper seeks a suitable technology of treating fine fractions of BC (Brezina Clay), sometimes called FBC (Fine Brezina Clay), prior to its being fired into grog. The stockpiles hold tens of thousands of tons of these fractions. The properties of the fired clay are determined by the length of time for which the material has been stockpiled, moisture content, of the clay, as well as the briquetting pressure before firing in a shaft kiln. FBC contains approx. 41 % of aluminium oxide. This amount is not high enough for certain applications. The aluminium oxide content can be increased by the addition of bauxite, corundum, mullite, kaolin, clays rich in Al2O3, or technical Al2O3. The experiment described in this paper tested how the addition of technical Al2O3 affects the pore structure of fired FBC, which is later used as a grog in both shaped and non-shaped refractory products. The influence of firing temperature on the material's mineralogy was examined as well

Use of Undersize Fractions of Refractory Claystone for Grog Manufacturing in Shaft Kilns

Refractory aluminosilicate grogs are made by firing refractory clays and claystones. They are fired predominantly in rotary or shaft kilns. Prior to firing in shaft kilns, particles of claystone smaller than 35 mm are separated These fine fractions cannot be processed in a shaft kiln, since they lower the quality and homogeneity of firing. However, these claystones can be briquetted into larger pieces (5 – 6 cm), which can be easily fired in shaft kilns. It is possible to modify the raw material by adding correcting materials or other types of clay. This method can then be used for making special grogs. The paper discusses the possibilities of manufacturing grog with an increased Al2O3 content with undersize fractions of claystone mined in Březinka. The research focused on the influence of raw material water content and compacting pressure on the final properties of fireclay grog, and determining the influence of firing temperature on the properties of the grog.

Energy optimisation of vertical shaft kiln operation in the process of dolomite calcination

The essential part of the refractory materials production on a basis of sintered dolomite as raw material is the process of dolomite calcination. The technology process usually takes place in shaft or rotary kilns, where the dolomite stone, CaMg(CO3)2, is subjected to a high temperature heat treatment. The calcination of the dolomite is highly endothermic reaction, requiring significant amount of thermal energy to produce sintered dolomite (CaO, MgO), generating a large flow of hot gases at the furnace outlet. The objective of this work was to assess the possibilities of utilization of waste heat of exhaust gases from a shaft kiln in order to improve the overall energy efficiency of the technology process. Several different options were analyzed: (a) preheating of a raw material, (b) preheating of heavy fuel oil, (c) preheating of combustion air, (d) preheating of combustion air and raw material with flue gas, and (e) preheating of air for combustion and for drying of a raw material. Option (e) was selected as the most attractive and therefore it was analyzed in more details, showing significant annual energy savings and relatively short simple payback period on the investment.