Kiln Performance Research Articles

A mathematical model of a twin-shaft parallel flow regenerative lime kiln

ABSTRACT Lime is an important flux used in the iron and steel-making processes. Tata Steel Jamshedpur uses a twin-shaft Parallel Flow Regenerative type kiln to calcine limestone. Previously, the kiln was operated based on the temperature measurement at only three locations. This led to suboptimal kiln performance and difficulty in maintaining lime quality. A thermal digital twin was developed using first principles to address these issues. A set of unsteady-state partial-differential equations representing the thermophysical phenomena is solved numerically using the finite volume method. The model was validated with the measured flue gas temperature and lime temperatures. The model is implemented online with the real-time operating parameters to estimate the temperature profile of solid and gas and the degree of conversion of limestone. This real-time visibility enables the operators to optimize the process and achieve lime conversion up to 94%, resulting in energy savings of 31.8 GJ/day and stable lime quality.

Improvement of a cement rotary kiln performance using artificial neural network

In order to investigate the effect of parameters and system optimization, the processes must be modeled first. Cement rotary kiln systems are complex because of non-linear, time invariant and full of behavioral uncertainty where the mathematical modeling of the plant is impossible. Artificial neural network (ANN) is one of the best tools for improving the performance of such processes. In this study, the operational data from a cement factory are gathered and the relationships between variables analyzed via using ANN via MATLAB toolbox. ANN proposed 2.7 and 865 rpm for kiln and fan motor speed respectively and 4599.7 Ncm/h for total grate flowrate as optimum values. This research shows that using ANN for improving the performance of rotary kiln is effective and by optimization of operational parameters through ANN and applying them in the rotary kiln, higher production in the cement industry is accessible.

Efficiency of charcoal production in Sub-Saharan Africa: solutions beyond the kiln

Le charbon de bois restera une source d’énergie importante en Afrique subsaharienne dans un avenir prévisible, le présent article se concentre sur l’amélioration de l’efficacité de la carbonisation comme contribution à des chaînes de valeur plus durables du charbon de bois. Alors que l’efficacité de la conversion du bois en charbon est souvent considérée comme une question technique de performance des fours, cette étude vise à mettre en lumière le rôle d’un contexte institutionnel favorable et les capacités des acteurs impliqués. Sont d’abord passées en revue les initiatives visant à améliorer la production de charbon de bois dans différents pays d’Afrique subsaharienne. Nous comparons ensuite les données sur les processus de carbonisation dans deux zones en République démocratique du Congo : Yangambi et le Plateau de Bateke. Les principales conclusions sont les suivantes : 1) l’amélioration des techniques de carbonisation permet de réaliser d’importants gains en termes de taux de conversion du bois en charbon, mais le succès dépend en grande partie de l’adéquation des solutions de four en fonction du contexte, de la capacité et de la sensibilisation des producteurs et du contexte institutionnel favorable ; 2) le renforcement des capacités des opérateurs et des autres parties prenantes nécessite des techniques de four efficaces, mais aussi une sensibilisation accrue aux avantages et aux options d’approvisionnement durable, le renforcement des compétences financières et de gestion des organisations de producteurs et l’amélioration du transport, de la manutention et de la commercialisation ; 3) le statut illégal ou informel des producteurs de charbon de bois en Afrique subsaharienne nuit à l’efficacité des processus de production du charbon, tandis qu’un cadre institutionnel adéquat facilite l’accès des producteurs aux permis et au financement, fournit une fiscalité claire avec des incitations pour des pratiques plus durables et relie les exigences techniques en termes de carbonisation aux sources et utilisations finales durables. Le succès ou l’échec des techniques de carbonisation améliorées et les résultats socio-écologiques connexes sont déterminés conjointement par les solutions qui incluent les aspects de renforcement des capacités, d’acceptabilité et d’institutions favorables identifiés dans cet article. La poursuite du développement de ces solutions en partenariat avec les producteurs accroît le potentiel de chaînes de valeur plus durables pour le bois-énergie.

Development of Portable Venturi Kiln for Agricultural Waste Utilization by Carbonization Process

Many types of kiln or carbonization equipment have been developed, but most of them were designed for big capacity and some also having low performance. This research aims to develop kiln, especially portable metal kiln, which has higher performance, more environmental- friendly, and can be used for several kinds of biomass or agricultural waste (not exclusive for one kind of biomass) as feeding material. To improve the kiln performance, a venturi drum type of portable kiln has been designed with an optimum capacity of 12.45 kg coconut shells. Basic idea of those design is heat flow improvement causing by venturi effect. The performance test for coconut shell carbonization shows that the carbonization process takes about 60-90 minutes to produce average yields of 23.8%., and the highest temperature of the process was 441 °C. The optimum performance has been achieved in the 4th test, which was producing 24% yield of highest charcoal quality (represented by LHV) in 65 minutes process at average temperature level 485 °C. For pecan shell and palm shell, design modification has been done by adding 6 air inlet holes and 3 ignition column to get better performance. While operation procedure should be modified on loading and air supply, depending on each biomass characteristic. The result of performance test showed that carbonization process of pecan shell produce 17 % yield, and palm shell produce 15% yield. Based on Indonesian Standard (SNI), all charcoal produced in those carbonization has good quality level.

Improving Rotary kiln performance - A case study

Cement production has been one of the most energy intensive industries in the world. In order to produce clinker, rotary kilns are widely used in cement plants. In this paper the heat balance was calculated, depending on the comparison between the heat input represented by the fuel and heat output. It was found that the maximum losses were being lost through hot flue gas about 21.65 %. Some possible ways to recover the heat losses are also introduced and discussed. The thermal efficiency and the combustion efficiency were calculated according to the data collected on the unit. In addition, the combustion efficiency of mazout was compared with combustion efficiency of natural gas, and the saving also was obtained.

Optimisation techniques to compare various selected drying schedules for larch timber

The paper deals with an investigation of the influence of the method used to assembly a drying schedule for larch (Larix) timber on kiln performance and quality of drying. Ten drying schedules were analysed (six from literature and four from industry) using a simulation tool, which was experimentally validated for larch. First, the methods were compared using various criteria, namely drying rate, drying cost, energy consumption and quality of drying. Second, a multi-criteria analysis was performed using one-factor multilevel-categoric design. The results of this study showed that the kiln performance and the drying quality are influenced by the method applied to assembly the schedule. Currently, none of the analysed methods can completely fulfill the industrial requirements (short time, low cost and high quality). According to a cluster analysis, the results showed that the analysed methods can be grouped into three clusters based on their similarities regarding the kiln performance and quality of drying.

Impact of cofiring biofuels and fossil fuels on lime kiln operation

Lime kilns are used to calcine lime mud to produce lime for reuse in the causticizing plant of pulp mills. With significant increase in fossil fuel costs and the sustained drive to minimize carbon footprint, there has been a great deal of research and development of the biorefinery concept and production of biofuels for use within pulp mills. Several new biofuels will become available, together with traditional mill derived fuels such as tall oil. In considering use of biofuels for replacement of fossil fuels in the lime kiln, each fuel has a different impact on kiln performance. An assessment on kiln performance can be achieved and compared to either heavy fuel oil or natural gas. In most cases, the lime kiln fuels with high oxygen content and moderately low calorific values burn in a similar manner as natural gas; hence, in assessing impact on kiln performance, production and induced draft fan limits together with kiln exit gas temperatures need to be considered.

Computer modeling as tools to estimate the impact of fuel type on the capacity rating of lime kilns

In response to the drop in the price of natural gas, the U.S. pulp and paper industry has switched from using fuel oil to natural gas to fire kilns used to regenerate lime in the kraft process. While being financially attractive, replacing fuel oil with natural gas can be challenging. This is particularity true when the capacity rating is constrained by the temperatures of the gas exiting the kiln. In the worst case scenario, the increase in flue gas temperatures associated with switching from fuel oil to natural gas can significantly de-rate the capacity of the kiln. This paper describes a range of computational modeling tools that can be used to estimate the impacts of kiln geometry, fuel type, operating conditions, and burner design on kiln performance. Data taken from operating kilns is presented, which validates the use of these models. A detailed case study is presented showing how small amounts of torrefied wood can be co-fired with natural gas as a replacement for fuel oil without de-rating the capacity of the kiln. The visualization of the flow fields, temperature distributions, and species concentrations provided by computer models are critical to optimizing kiln operations as new fuels are being considered as replacements for more expensive, carbon intensive fuel oil.

Biomass Powered Natural Convection Kiln for Timber Drying

The design and test performance of a biomass powered natural convection kiln for timber drying is presented. It consists of two sections: the heating section where biomass combustion for inlet air heating occurs and the drying section where the timber is loaded for drying. Inlet air heating is achieved in a heat exchanger of dimension 0.5 m by 0.165 m while temperature stratification in the drying chamber is reduced by letting flue gas from the combustion chamber flow through a space between the side walls of the drying section and the outer housing of the kiln before being expelled. The kiln performance test was carried out for 40 day. Results obtained show that air temperature within the drying section stabilized at 55 -59°C with a minimum relative humidity of 31% (when unloaded) and 45% (when loaded). Timber moisture content reduction from 65 to 30% was achieved in 30 days. Thus it has potential for improved timber drying.

Numerical Simulation of a Solar Kiln Design for Drying Timber with Different Geographical and Climatic Conditions in Australia

A numerical simulation for the modeling of solar kilns for hardwood timber drying with different boundary conditions has been developed in this work. This simulation has been used to predict the key behavior of the wood and the kiln itself under different geographical and weather conditions in Australia. This work, therefore, enables a site to be suggested that is likely to give the best kiln performance both in terms of the productivity and the quality of the end-use product. As test cases, realistic climatic conditions for three representative geographical locations in Australia, including Sydney (latitude 33.86°S), Melbourne (37.81°S), and Brisbane (27.46°S), have been considered in this simulation. Out of the three sites considered in this work, the fastest drying rates (and highest diffusion coefficients) were predicted in Brisbane. The highest level of instantaneous strain in the timber for this location was also predicted to be 0.0075 m/m, which is much less than the failure value (0.02 m/m). The moisture content distribution profile within the boards toward the end of the drying period was found to be almost uniform, which is likely to cause low degrade in the dried timber.

Numerical simulation of three-dimensional unsteady granular flows in rotary kiln

The granular particle motion with rolling mode in rotary kiln is investigated using a three-dimensional mathematical model based on the Euler–Euler two-phase flow and the kinetic theory of granular flow. The mathematical model verified by comparing with the published experimental data is used to simulate performance of an inclined rotary kiln. The angle of inclination and the residence time of particles in rotary kiln are taken into account. The active layer thickness can be calculated by observing the particle velocity change from positive to negative values. The stagnation point at the bottom of the free flowing zone is the interface between the active layer and the passive layer. Simulations show that the active layer of the charge end of the rotary kiln is thin and particle velocity is low. With the increase of axial distance, the active layer thickness and velocities of granular particles increase respectively, the thickness of the active layer and velocities of particles close to the discharge end of the rotary kiln decrease. A fourth-order polynomial velocity profile can be obtained from the numerical simulation results. Apart from providing a computationally efficient tool to simulate kiln performance, the results discussed here will provide a useful basis for the development of comprehensive three-dimensional models of rotary kilns.

Equal Life Optimization of Shells Based on Kiln Axis Alignment

The crack of kiln shells was seen regularly due to axis deflection and asymmetric load distribution. It will be helpful to improve kiln performance if the remaining life of kiln shells can be kept the same. For this the formulae of stress spectrum and fatigue life of kiln shells are obtained. Taking the aligned values of axis deflections as design variables, equal fatigue life of shells and maximum axis deflection as the objective function, considering the fuzzy factors during axis alignment, the fuzzy optimization model of kiln axis alignment is set up. The results indicate that kiln axis can be aligned as direct as possible, and life expectancy of kiln shells can be optimized to keep near the same. Accordingly, the valuable production time of kiln can be increased greatly by such aligned method.

Mathematical Model for Heat Transfer Simulation of Rotary Alumina Kiln

According to kiln structure and material movement features, considering convective, radioactivity, conductivity and various phase change and chemical reactions, a series of comprehensive models are built for quantifying the thermal fluxes from the gas to the material bed and the heat loss from outer shell to the atmosphere in the rotary alumina kiln. The results show that the temperatures of outer shell accord with test results; the temperature distribution rule of gas is the same with that of materials, but the gas temperatures are higher; it is feasible to use the model to improve alumina kiln performance.

Alternative Fuels for use in Cement Kilns: Process Impact Modelling

The manufacture of Portland cement is an energy intensive process. It produces significant pollution and uses large amounts on non- renewable resources. With increasing pressures to reduce greenhouse gas emissions due to cement manufacture, research and development of fuel alternatives and their effect on the manufacturing process has become an industry focus. The inherent properties of sintering cement in a rotary kiln allows for a large number of fuels to be burnt which are normally prohibited for use as fuel in other processes. To examine the suitability of a fuel, process modeling and simulation can be undertaken to predict the final impact of that fuel on kiln performance and greenhouse gas emission. With an accurate model and sufficient data, it is possible to conduct simulations for a wider range of alternative fuels. This paper discusses and summarizes the simulation results of three alternative fuels, namely spent carbon lining, used industrial lubricants and used tires, for identifying the most effective fuel source among these three. Among the selected fuels used, industrial lubricant is found to be the best option regarding the CO2 emission, while the spent carbon lining is the worst one. In contrast, feed material requirements can be reduced by up to approximately 15% by using spent carbon lining. Further research is recommended to justify the findings.

In-Line Moisture Content Measurement of Kiln-Dried Lumber for Process Improvement

The in-line moisture meter at the planer measures the moisture content of every board. This information is often not used for process improvement because of difficulty in linking the moisture information to a point in the process and reliable statistical methods for analyzing the data. Test programs in which the moisture contents measured at the planer were used to create process charts for kilns and to identify kilns or zones within kilns with high moisture content or moisture content variability were established in four mills. Tagging units, either with bar codes or with alphanumeric tags, to identify their location in a kiln was a practical and effective way to diagnose kiln performance when the moisture content information collected at the planer was associated with location. Wet areas and dry areas could be identified, and the consistency of moisture content from charge to charge could be evaluated, as could the variability within charges. The latter items can be accomplished without knowing the location of a unit in the kiln if the kiln from which the lumber came is known at the time of planing. The methods developed also allow other factors, such as operator decisions and the performance of in-kiln moisture meters, to be evaluated.

CFD modeling of rotary cement kilns

AbstractRotary cement kilns are widely used to convert calcineous raw meal into cement clinker, and are key components in the cement industry. In this article, we report a comprehensive computational fluid dynamics (CFD)‐based model to capture key transport processes in rotary cement kilns. Separate but coupled computational models were developed for the bed and the freeboard regions of the rotary kiln. The complex swirling airflow produced by kiln burners, coal combustion, gas‐phase combustion of volatile matter and radiative heat transfer in the freeboard region were modeled. The clinkerization reactions in the bed region were modeled assuming solids as pseudo fluids. Coating formation in cement kilns (for both bed and freeboard regions) was considered. Appropriate source and sink terms were developed to model transfer of CO2 from the bed to the freeboard region due to calcination reaction in the bed region. The developed bed and freeboard models were coupled by mass and energy communication through common interface. These coupled computational models were able to quite satisfactorily predict the available data from industrial kilns and previously published results. The computational models were also able to capture the intricacies of the burning zones of rotary cement kilns for changing burner‐operational parameters like axial to swirl ratio and oxygen enrichment. The developed approach, computational models and simulation results will not only help in developing better understanding of cement kilns but also provide quantitative information about influence of burner design and other design parameters on kiln performance. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

General solution to kiln support reactions and multi-objective fuzzy optimization of kiln axis alignment

Based on the analyses of the mechanical features of rotary kiln with multi-supports, a general mechanical model for indeterminate kiln with variable bending rigidities, arbitrary supports and complex loads is established. From this model, the equations of the rotational angle and the deformation are deduced, the general matrix and procedure are developed. The correlation between the roller forces and axis deflections of no. 2 rotary kiln is derived. To improve kiln performance by kiln axis alignment, taking roller forces equilibrium and relative axis deflection minimum as the optimization goal, considering the fuzzy constraints of axis alignment, the fuzzy optimization model of kiln axis alignment is set up. The optimization model is solved with the max–min approach. The results show that fuzzy optimization alignment of rotary kiln can make kiln axis as straight as possible and can distribute kiln loads equally.

Wet process rotary cement kilns: modeling and simulation

The knowledge of wet process kilns design and operation in the cement industry has not been improved substantially during the last decades since the pre-calcination process has been developed to become the technological standard. In spite of the tendency to replace wet process rotary kilns for cement production by modern dry process kilns with pre-calcination, there are still a substantial number of wet process kilns in operation. Their efficient operation requires an individually designed chain system to enhance the kiln performance. Currently the design of chain systems for wet process rotary cement kilns depends strongly on experience. Systematic theoretical and experimental investigations for the dimensioning of chain systems are not known. Based on a one-dimensional cell model, a simulation program for wet process rotary cement kilns with chain systems has been developed. With the aid of this simulation tool, the influence of chain systems on solid composition and temperature profiles, clinker throughput and fuel requirement is predicted and the design of chain systems can be optimized.

Modeling of Rotary Cement Kilns: Applications to Reduction in Energy Consumption

Rotary cement kilns are used for converting calcineous raw meal into cement clinkers. In this paper, we discuss and evaluate possible ways of reducing energy consumption in rotary cement kilns. A comprehensive one-dimensional model was developed to simulate complex processes occurring in rotary cement kilns. A modeling strategy comprising three submodels, viz. a model for simulating the variation of bed height in the kiln, a model for simulating reactions and heat transfer in the bed region, and a model for simulating coal combustion and heat transfer in the freeboard region, was developed. Melting and formation of coating within the kiln were accounted for. Combustion of coal in the freeboard region was modeled by accounting for devolatilization, finite-rate gas-phase combustion, and char reaction. The simulated results were validated with the available data from three industrial kilns. The model was then used to understand the influence of various design and operating parameters on kiln performance. Sev...

Simulation of Rotary Cement Kilns Using a One-Dimensional Model

Rotary kilns are used to convert calcineous raw meal into cement clinkers. In this paper we present a one-dimensional model to simulate key processes occurring in solid bed of cement kilns. Solid-solid reactions occurring in cement kilns were modelled with a pseudo-homogeneous approximation. Variation of bed height and melt formation in burner zone within the kiln was accounted for. Energy balance (including conductive, convective and radiative heat transfer) was solved based on a quasi-steady state approximation. The mathematical model was first applied to a rotary calciner. The model predictions were verified by comparing them with the published experimental data. The model was then used to simulate performance of three industrial kilns. Numerical experiments were carried out to investigate influence of key operating and design parameters on energy consumption of kilns. The model was also used to explore the possibility of manipulating temperature profile within the kiln to reduce energy consumption in kiln per ton of clinker. Apart from providing a computationally efficient tool to simulate kiln performance, the model and the results discussed here will provide a useful basis for the development of comprehensive three-dimensional models of rotary cement kilns.