Kiln Operation Research Articles

Effects of Firing Time and Temperature on Physical Properties of Fired Clay Bricks

Brick is one of the most widely used conventional construction materials throughout the world. The production cost of clay brick is significantly affected by the cost of energy required for firing. The aim of this research is to investigate the effects of different firing temperatures on the compressive strength (CS), water absorption (WA) and saturation coefficients (SC) of fired clay bricks produced around Jimma Town and evaluate the effect of firing processes in brick manufacturing on the properties, color and appearance of the clay brick. During the production process, the effects of different heating rates on physical and mechanical properties of firing standard bricks were analyzed. In this study, different heating rates were used: slow heating rate and fast heating rate. Changes in the physical and mechanical properties of the fired clay brick were assessed with the increase in the firing temperature firing time. The results show that the CS increased with the increase in the firing temperature. On the contrary, WA and SC of the fired clay bricks decreased with the increase in the firing temperature. Increment in the duration of firing slightly increases the CS and lowers both the WA and WA of the clay brick. In the study area, traditional brick producers did not have firing temperature control device or mechanism in the fired clay brick production. The kiln operator decided the firing temperature and duration. The absence of the device frequently results in the over or under firing of bricks greatly affecting the engineering properties of this widely used contraction material. Therefore, the traditional clay brick producers should install the temperature control device on their kiln or at least needs to be trained how to approximately determine the optimum temperature.

The effect of operating conditions on the residence time distribution and axial dispersion coefficient of a cohesive powder in a rotary kiln

While continuous rotary calcination is a widely used thermal treatment in large-scale catalyst manufacturing, the process's heat and mass transfer mechanisms remain a challenge to characterize and to predict. Thus, the goal of this research is to improve fundamental understanding of rotary calcination to aid in the creation of a scientific methodology for process design and scale-up. For successful calcination to occur, the residence time of the particles must exceed the time required for heating and calcination at a set temperature. The optimal residence time therefore depends on both of these competing time scales, each of which is function of feed material properties, kiln geometry and kiln operating conditions. For uniform treatment of the feed, the particles must also exhibit low axial dispersion. In this work, the residence time distribution and axial dispersion coefficient for a dry cohesive fluid cracking catalyst powder were measured in a pilot plant kiln using a tracer study developed by Danckwerts. Results were successfully matched to the Taylor fit of the axial dispersion model and the Sullivan prediction for mean residence time. It was found that an increase in feed rate, kiln incline and rotary speed decreased mean residence time and overall axial dispersion. Such results have been established previously for free-flowing material like millimeter-sized extrudates, but have not been previously reported for the cohesive powders such as the one used in our work. As in free-flowing material, the axial dispersion coefficient was found to vary with kiln conditions. The values of the axial dispersion coefficients were lower for the powder than for free-flowing material, showing a dependency of axial dispersion on material properties as well as bulk flow behavior.

Probabilistic evaluation of the final moisture content of kiln-dried lumber using the bootstrap method

This paper presents a probabilistic method of evaluating the final moisture content (MC) of lumber obtained at the end of the kiln-drying process. The final MC data of three different drying tests conducted in past studies were analyzed using the bootstrap method. Target MC was tentatively set below 20 % in the analysis. Two characteristic parameters representing the final MC were estimated with bootstrap confidence intervals. These parameters were the standard deviation (SD) and the percentage of the population that met the MC requirement of less than 20 % (P 20). The histograms of the final MC and the subsequent goodness-of-fit tests revealed that the final MC data of two drying tests did not follow any classical probability distributions, including Normal, Log-Normal, Weibull, and Gamma distributions, thus indicating the need for nonparametric statistics. The uncertainty of the final MC could be evaluated with the estimated SD and P 20. After deriving the relationships between P 20 and the corresponding probability that P 20 is not achieved, we demonstrated how such relationships could provide a kiln operator with information to facilitate better decision-making in optimizing a drying schedule.

Thermal co-treatment of combustible hazardous waste and waste incineration fly ash in a rotary kiln

As current disposal practices for municipal solid waste incineration (MSWI) fly ash are either associated with significant costs or negative environmental impacts, an alternative treatment was investigated in a field scale experiment. Thereto, two rotary kilns were fed with hazardous waste, and moistened MSWI fly ash (water content of 23%) was added to the fuel of one kiln with a ratio of 169kg/Mg hazardous waste for 54h and 300kg/Mg hazardous waste for 48h while the other kiln was used as a reference. It was shown that the vast majority (>90%) of the inserted MSWI fly ash was transferred to the bottom ash of the rotary kiln. This bottom ash complied with the legal limits for non-hazardous waste landfills, thereby demonstrating the potential of the investigated method to transfer hazardous waste (MSWI fly ash) into non-hazardous waste (bottom ash). The results of a simple mixing test (MSWI fly ash and rotary kiln bottom ash have been mixed accordingly without thermal treatment) revealed that the observed transformation of hazardous MSWI fly ash into non-hazardous bottom ash during thermal co-treatment cannot be referred to dilution, as the mixture did not comply with legal limits for non-hazardous waste landfills. For the newly generated fly ash of the kiln, an increase in the concentration of Cd, K and Pb by 54%, 57% and 22%, respectively, was observed. In general, the operation of the rotary kiln was not impaired by the MSWI fly ash addition.

Computation of steady state thermochemistry in rotary kilns: Application to the cement clinker manufacturing process

Advanced Gibbs free energy minimization was applied for modeling physical and chemical processes in various industrial rotary kilns. The method is the core of a generic computer program (KilnSimu), used to simulate kiln operations with different multiphase chemistries. KilnSimu combines iterative solution of the balance equations coupled with the Gibbs energy calculation of the kiln thermochemistry, thus providing a detailed quantitative analysis of the chemical and phase transformations as well as of mass and heat flows inside the kiln. Adding reaction rate constraints into the Gibbs energy procedure allows for the necessary reaction kinetics in the simulation. The calculation results are typically given as 1-dimensional steady state axial profiles in the longitudinal direction of the kiln.The presented model was applied to an industrial problem in cement clinker manufacturing. The impact of pure oxygen addition at the main burner on the specific heat consumption of the full process was evaluated.

CFD modeling using PDF approach for investigating the flame length in rotary kilns

Numerical simulations using computational fluid dynamics (CFD) are performed to investigate the flame length characteristics in rotary kilns using probability density function (PDF) approach. A commercial CFD package (ANSYS-Fluent) is employed for this objective. A 2-D axisymmetric model is applied to study the effect of both operating and geometric parameters of rotary kiln on the characteristics of the flame length. Three types of gaseous fuel are used in the present work; methane (CH4), carbon monoxide (CO) and biogas (50 % CH4 + 50 % CO2). Preliminary comparison study of 2-D modeling outputs of free jet flames with available experimental data is carried out to choose and validate the proper turbulence model for the present numerical simulations. The results showed that the excess air number, diameter of kiln air entrance, radiation modeling consideration and fuel type have remarkable effects on the flame length characteristics. Numerical correlations for the rotary kiln flame length are presented in terms of the studied kiln operating and geometric parameters within acceptable error.

Characterization of kiln feed limestone by dynamic heating rate thermogravimetry

Quicklime is a product rich in calcium oxide produced in industrial kilns. The process involves thermal decomposition of minerals with high content of calcium carbonate. The kiln feed properties vary with the geological formation from where the mineral is quarried or mined. Characterization of feed properties is necessary to achieve an optimized kiln production. In this work the decomposition of four different types of calcite ore was investigated by comparing conventional constant heating rate and dynamic heating rate thermogravimetric methods.The conclusion of this work is that the conventional method always “overshoots” the calcination temperature when continuously heating during calcination compared to the dynamic rate method that resembles the kiln by holding temperatures constant during the calcination event. This justifies the used of the dynamic rate method. By a correct experimental parameter setup the dynamic rate method can be adapted for individual kilns and feed fractions, giving new additional value to the kiln operator and increasing the high value use of limestone deposits. This new method to characterize calcination properties of kiln feed materials can be utilized in normal kiln operations and when developing new mixes of different quality limestone. The results show differences when comparing the methods and different materials even though CaCO3 is present only as calcite. In addition, the dynamic rate method is faster than the conventional method. Besides quicklime production the method can also be applied in other industries calcining limestone, such as cement clinker production.

Control and Optimization of a Triple String Rotary Cement Kiln using Model Predictive Control

Abstract Pyro processing is one of the most important stages in cement manufacturing process. Control of pyro-processing is vital in improving the energy efficiency and enhancing the production assuring good quality. The complex nature of cement kilns with longer time constants, changing raw material characteristics, non-linear dynamics make them very difficult to control, in addition to that inclusion of various alternative fuels in burning makes the process more complex as the fuel characteristics remain inconsistent throughout the kiln operation. This paper describes a novel way of optimizing a triple string calciner kiln in a real plant using model predictive control and a fuzzy based real time optimizer. Compared to the conventional controllers the MPC handles the disturbances better resulting in improved productivity, lesser energy consumption and better quality.

THE IMPACT OF BRICK KILN OPERATION TO THE DEGRADATION OF TOPSOIL QUALITY OF AGRICULTURAL LAND

Brick kiln is a big environmental issue for the agriculture of Bangladesh as it was observed that the agricultural production in the soil close to the brick kiln was lesser than the same soil far from brick kiln. The study was conducted to assess the impact of brick kiln operation to the degradation of topsoil quality at Singair of Kalihati upazila in Tangail, Bangladesh, during the period of July to December 2013. The Soil was collected from areas close to the brick fields and far from the brick fields at a depth of 0-15 cm. The Electrical Conductance (EC) was found almost double in the soil samples close to the brick field than the soil samples far from brick field. The organic mattter content in the soil sample close to the brickfield was significantly lower than that of the far soil sample. The mean values of total N, available P and S were also significantly lower in the soil samples close to the brick kiln, 0.05%, 12.4, and 8.36 ppm respectively in the close soils, while 0.06%, 24.6, and 11.7 ppm respectively in the far soil. There were no significant changes observed in the other elements.

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.

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.

Levantamento das emissões atmosféricas da indústria da cerâmica vermelha no sul do estado de Santa Catarina, Brasil

<p>Os principais contribuintes antropogênicos para a contaminação do ar são as emissões veiculares e industriais. Santa Catarina é um estado com setor industrial desenvolvido. Destaca-se não apenas pelo número, como também pela diversificação de atividades fabris. Dentre essas atividades, há a de produção de peças cerâmicas vermelhas (tijolos e telhas - as olarias). Há uma concentração representativa dessas empresas no sul desse estado. Suspeita-se que as emissões atmosféricas das olarias comprometam a qualidade do ar, de forma danosa a saúde da população. Entretanto, quase não foram realizados estudos aprofundados, nem da qualidade do ar, muito menos das emissões do setor. Esse trabalho visa verificar como é tratada a questão das emissões atmosféricas por parte das olarias. Tal levantamento foi realizado por duas maneiras: aplicação de questionários e levantamento de informações de licenciamento ambiental. Nos questionários, notou-se que apenas 13% das olarias afirmaram manter os seus equipamentos de tratamento de efluentes atmosféricos ativos durante todo o período da queima dos fornos. Na análise de documentos vinculados ao licenciamento ambiental, averiguou-se que uma grande parcela das olarias não realiza laudos de emissões, como também não verifica o adequado funcionamento dos seus equipamentos de controle de poluição atmosférica. Apesar dos laudos de emissão indicarem compatibilidade com os limites legais de emissão, a concentração dessas empresas em um espaço geográfico restrito indica que provavelmente haja impacto significativo na qualidade do ar.</p>

Recognition of Working Condition in Cement Rotary Kiln Based on Generalized Dimensions

There has been a tight correlation between the change of the cement rotary kiln carrent and operation conditions, such as the kiln thermal condition, the thickness of the crust, the kiln tyre collapse and so on. Considering the different fractal characteristics that cement rotary kiln current signal exhibit in different conditions, this paper has study on the generalized fractal dimension of kiln current signal under different working conditions as the characteristic parameter. The levels and trends of rotary kiln current and working condition will be identified by computing the maximum correlation coefficient according to the generalized fractal dimension of detected signal and of cement rotary kiln current under different working condition.

Design of refractory linings for balanced energy efficiency, uptime, and capacity in lime kilns

In this work a computer model is used to examine how refractory linings with both high alumina and basic refractory bricks affect kiln operations. Recommendations are made based on the results to aid mill personnel in designing optimized refractory linings for specific situations. Kilns used to regenerate lime in the kraft process are highly energy intensive. Throughout the 1990s, in response to increasing fuel prices, the pulp and paper industry primarily used backup insulation in conjunction with high alumina brick to line calcining zones of their kilns. The dramatic decline in price of natural gas over the past decade, in combination with mounting pressures to increase production of existing assets, has led many mills to focus more on increasing uptime and capacity rather than on energy savings. To this end, a growing number of mills are using basic (magnesia based) brick instead of high alumina brick to line calcining zones. While the use of basic brick can increase the uptime and reduce the cost to maintain the refractory lining, it can dramatically increase the shell temperatures and heat losses. Tradeoffs, therefore, are created among energy efficiency, capacity, and uptime.

Mill study on improving lime kiln efficiency

Optimization of the lime kiln requires an examination of the entire lime cycle. To increase the energy efficiency of the lime kiln, all auxiliary unit operations must function properly. It is also imperative that the lime and liquor in the system is of acceptable quality. We detail a kiln energy efficiency study performed by MWV Corp.’s Covington, VA, USA, mill. From a recausticizing standpoint, lime quality is much easier to control than liquor quality because liquor passes through many operations that are not under the lime kiln operator’s control. Recausticizing is a fairly closed cyclical process where lime is concerned, so saturation of impurities to the point of operational issues must be considered. Specific cycle performance indicators (e.g., lime mud solids entering the kiln) must be viewed from a perspective that does not exclude their potential impact. To get a true picture of the cost of operating the lime cycle, all inputs must be considered. The four main inputs are power (electrical and fuel), fresh lime, caustic, and water.

Evaluation of leaching of trace metals from concrete amended with cement kiln baghouse filter dust

The production of Portland cement (PC) can result in the release of trace amounts of mercury (Hg) in stack emissions. As a means of controlling Hg stack emissions at Portland cement kiln operations, some facilities have instituted a process known as dust shuttling, where baghouse filter dust (BFD), a partially calcined byproduct, is collected and blended with PC as an inorganic process addition, instead of returning the material to the kiln pyro-process. In response to questions raised regarding environmental impacts of recycling BFD into concrete products, research was performed to investigate the chemical composition of BFD and to assess the potential for leaching of trace metals from concrete products amended with BFD. Leaching of monolithic concrete under submerged conditions was examined as a function of time; concentrations of detected elements were found to be below applicable risk thresholds. Despite elevated Hg in the BFD relative to the PC, no elevated Hg risk was observed. Leachates from raw BFD did exceed risk-based thresholds for Se and V. However, leaching of size-reduced BFD-amended concrete did not show concentrations of these elements above applicable risk based thresholds. The results of this study suggest that the use of BFD as an inorganic process addition, within the percentages currently allowed by US industry standards, does not pose any additional risk with respect to direct human hazard or leaching of trace metals to water supplies.

Modeling and simulation of cement clinkering process with compact internal burning of carbon

This article describes a mathematical model of the thermodynamic process for Cement Clinkering Process with Compact Internal Burning of Carbon. Using simplifying assumptions, results of calculations are presented based on relevant computerized numerical simulation for a set of typical process parameters obtained from the existing cement shaft kiln operation and the electrical furnace test on the mechanical and chemical performance of the compact coal containing cement raw meal pellets. It is revealed that, the carbon internal burning mode, combining fuel combustion and gas solid heat transfer together as well as preheating, calcining, clinkering and cooling of the raw pellets together, is the origin of the process superiority in respect of equipment simplicity, process enhancement, high energy efficiency and low pollution. Important process details are determined, e.g. the features and lengths of the process zones, the material residence time and the burning mode of carbon in each zone, the clinkering reaction course and the maximum burning temperature. It is concluded that numerical simulations could be useful tool for understanding the new process ideas, as well as conducting the technical development and optimizing the process design.

Heat Treatment of Firewood for Emerald Ash Borer (<I>Agrilus planipennis</I> Fairmaire): Case Studies

The movement of firewood within emerald ash borer (Agrilus planipennis Fairmaire) (EAB)-infested states and into adjoining areas has been a contributor to its spread throughout the United States and Canada. In an effort to prevent further human-aided spread of EAB and to facilitate interstate commerce, the USDA Animal and Plant Health Inspection Service and cooperating states in the EAB quarantine have established a heat treatment process to be used as a mitigating treatment to allow movement of firewood from EAB quarantine areas. Firewood producers have since been faced with challenges implementing heat treatment processes and meeting the treatment standard for firewood. In this article, we present four case studies, conducted at firewood heat treatment facilities, with the aim of addressing these challenges. Different heat treating strategies were used in each of these facilities to meet the particular needs of operation. A step-by-step operating procedure was developed for heat treatment operation and temperature monitoring of both kiln and firewood samples during the heating process.

0419 Occupational injuries among child labourers: Preliminary results from a study of the brick manufacturing industry in four countries

ObjectivesInternationally, brick kilns employ tens of thousands of children. Due to the extreme poverty facing families who work in this industry, child labour in this sector has been challenging to...

English

Brick manufacturing is the fastest-growing industrial sector in many countries (like china, India, Bangladesh and Pakistan) and among the top three sectors, along with vehicle exhaust and resuspended road dust, contributing to the air pollution and health problems in Dhaka (Bangladesh). The total emissions from the brick manufacturing in the Greater Dhaka region, to produce 3.5 billion bricks per year has been estimated about 23,300 tons of particulate matter having aerodynamic diameter < 2.5 μm (PM2.5), 15,500 tons of sulfur dioxide (SO2), 302,000 tons of carbon monoxide (CO), 6,000 tons of black carbon (BC) and 1.8 million tons of carbon dioxide (CO2). Emission of individual air pollutant from brick kilns varied significantly during a firing batch (seven days) and between kilns. Average emission factors per 1,000 bricks were 6.35 to 12.3 kg of CO, 0.52 to 5.9 kg of SO2 and 0.64 to 1.4 kg of particulate matter (PM). Presently sulphur dioxide (SO2), oxides of nitrogen (NOx) and suspended particulate matter (SPM) are the main issue pertaining to air pollution problems in developing countries, where it contributes both to urban pollution and to regional acid depositions. Among man-made sources, coal combustion in stationary sources accounts for 74%, industries 22% and transportation 2% of the total oxides of sulphur (SOx). and it is considered that SO2 is the chief emission in brick production. On an international basis, 75 to 85% of SO2 emissions are the result of fossil fuel burning. It is predictable that just about 93% of the global SO2 emissions are emitted in the northern hemisphere. It has been revealed that biomass is responsible for the emission of both trace and non trace gases such as carbon dioxide (CO2), methane (CH4) and oxides of nitrogen (NOx) from traditional brick industries and lots of toxic fumes containing suspended particulate matters rich in carbon particles and high concentration of CO and SOx get produced. Studies have shown the average value of particulate matter of size less than ten microns and total suspend particles for the pre-operation time of brick kilns was 0.029 and 0.033 mg/m³, respectively whereas, it reached 0.050 and 0.056 mg/m³, respectively during the brick kiln operation time. Similarly, recent studies on brick kilns in District Budgam of Kashmir valley (India) have shown some major negative impacts on the environment in respect of air quality, human health and vegetation in particular. Key words: Pollution, emissions, environment, industrialization, transportation, brick kiln, human health, vegetation.