Clinker Production Process Research Articles

Numerical investigation of the impact of coating layers on RDF combustion and clinker properties in rotary cement kilns

The formation of regions of solid coating, where agglomerated clinker material adheres to the refractory lining of the kiln wall, is very common during cement clinker production. While a thin coating layer protects the refractory lining, strong deposit formation can impair the material flow through the kiln. In this study, the impact of these coating layers on the clinker production process within a rotary kiln is investigated with CFD simulations. The fuel injected at the main burner is a mixture of pulverized coal and refuse derived fuel (RDF). Advanced models were developed to accurately describe the trajectories and thermal conversion of non-spherical RDF particles in the gas phase. These models are based on a detailed fuel analysis of major RDF fractions. A blocked-off region approach is used to consider different coating profiles within the simulation domain. The thermochemical processes in the clinker bed of the kiln are approximated with a one-dimensional model that calculates heat and mass exchange with the gas phase, the incorporation of fuel ashes into the bed and the chemical-mineralogical reactions of the clinker. The blocked-off region approach is also employed to account for the clinker bed geometry in the kiln, which greatly depends on the considered coating profile. Two cases, one with a thin and evenly distributed coating profile and one with a thick and locally concentrated coating, are simulated. The resulting impact on RDF conversion, gas phase properties and clinker phase formation are assessed and compared to a reference case without any coating. Results show that the insulation effect of a thin coating profile increases the gas phase temperature in the kiln and helps to reduce the free lime content of the final clinker product. In the case of heavy coating, a temperature shift towards the solid material inlet of the kiln occurs, which outweighs the beneficial insulation effect of the coating in the sintering zone and leads to lower local gas phase temperatures. In combination with reduced clinker residence times, this results in a slight increase of the free lime content in the clinker.

The influence of cyclic water freezing on gas permeability of non-air-entrained concrete

The paper discusses the effect of replacing alite in Portland clinker with the equivalent amount of belite on CO2 emissions in the clinker production process. The emission from the raw material and fuel was compared in the case of belite and alite clinkers. Methods of increasing the hydraulic activity of belite are presented. CO2 emis-sions were also compared for Portland and belite-sulphoaluminate clinker, containing more than 50% belite. It has been shown that increasing the belite content in Portland clinker can reduce CO2emissions by about 10%. On the other hand, CO2 emission in the case of belite-sulphoaluminate clinker, containing 50% C2S and 30% C4A3S̅, is lower than this emission by about 30%.

Energy audit for pyro-processing unit of a new generation cement plant and feasibility study for recovering waste heat: A case study

In this work, firstly the energy audit was performed on the pyro-processing unit of a cement plant in Iran to improve the efficiency of the clinker production process and operating the system. In this plant, fuel combustion is the main source of thermal energy due to generation about 94% of the total heat input energy of system that it used for the clinker production process. The results indicated about 50% of total heat input was consumed for the clinker formation and 48% of it was lost in the form of radiation from the shell of the kiln, grate cooler, preheater, and convection along with exhaust gases from the pyro-processing unit. Also, the thermal efficiency of the pyro-processing unit was 50% that is in the range of modern plants thermal efficiency (50–54%). Secondly, according to the obtained data, the potential of electrical energy production from the exhaust gases of preheater and grate cooler was evaluated through the waste heat recovery power generation (WHRPG) unit. It was found that about 5.2 MWh power can be produced in WHRPG unit. Finally, the economic feasibility showed that the time of return of capital could be about 6.7 years.

A Framework of Exergy Efficiency Analysis for Cogeneration Power Plant in Cement Production

As a major energy consumer, cement production industry generates a large amount of waste heat during the clinker production process. There are also lots of dust and sulfur dioxide and nitrogen oxide emission accompanying with the waste heat loss, which are aggravating the eco-environment. It is necessary to develop new energy-saving technologies and push the waste heat utilization in cement industry to improve the utilization rate of waste heat from cement. In this study, an exergy efficiency analysis was conducted for the cogeneration power plant in cement production process. The results showed that cement production system can achieve heat recovery effectively with the cogeneration system.

Atmospheric mercury emissions from two pre-calciner cement plants in Southwest China

China produces the most cement product worldwide, and cement plants (CPs) have been regarded as the largest anthropogenic sources of atmospheric mercury (Hg) emissions in China since 2009. Onsite studies of this source are scarce compare to the huge numbers of CPs in China. Hence, quantifying Hg emissions from more CPs is needed in reducing the large uncertainties existed in the current Hg emission inventories and for assessing subsequent impacts of Hg on human and ecosystem health. In this study, two pre-calciner CPs in Guizhou province of Southwest China were selected for quantifying the emission factor and mass balance of Hg. Results showed that Hg emission levels in the two CPs were obviously different due to the differences in Hg input and circulation in the production system. In cement plant #1 (CP #1), the input and output of Hg reached a dynamic equilibrium condition, the emission factor was 76.1 mg Hg·t−1 clinker, and Hg concentration in the stack flue gas was in the range of 14.46–16.64 μg m−3. In cement plant #2 (CP #2), Hg was in an enriching status because it was a new plant with operation of several months and most input Hg was retained inside the production system, hence with a much lower emission factor of 1.8 mg Hg·t−1 clinker and Hg concentration of 0.15–0.49 μg m−3 in the stack gas. Kiln tail stack was the main output pathway of Hg in the clinker production process. With removal efficiency of 73.06% and 99.95% at kiln tail by ESP in CP #1 and humidifier + ESP-FF in CP #2, respectively, Hg emitted into the atmosphere was mainly in the forms of gaseous oxidized mercury (Hg2+) and gaseous elemental mercury (Hg0). Besides, the operation mode (on or off) of raw mill had great impact on the concentration and speciation of Hg in flue gas and flue gas temperature at kiln tail. In the clinker production system, limestone is the main source of Hg input (41.4–56.4%), followed by the fueled coal (15.3–32.5%). While, in the clinker to cement production process, the additives (mainly gypsum from coal-fired power plants, 83.2–94.4%) was the main source of Hg in the cement because Hg concentration in the clinker was very low.

Solar-driven production of lime for ordinary Portland cement formulation

Cement production is an energy-intensive manufacturing process with potentially large environmental burdens. Among the others, it is one of the largest industrial sources of CO2 emission. Limestone calcination is the stage responsible for most of CO2 emissions and energy requirement. This article aims at supporting the use of solar energy as non-carbogenic renewable source to sustain limestone calcination, with advantages on both the economic and environmental aspects of the process. A directly irradiated Fluidised Bed (FB) reactor was used as limestone precalciner for clinker production. Concentrated solar radiation was simulated with an array of three short-arc Xe-lamps of 4 kWel each, coupled with elliptical reflectors, capable of producing a peak flux of about 3 MW m−2 at the centre of the reactor. The total irradiated power is of approximately 3.2 kWth. Thermocouples and an IR camera were used for the analysis of the FB thermal profiles. Calcination was carried out at a nominal bulk bed temperature of 950 °C, in an atmosphere containing about 70% CO2. The reactivity of lime generated by the solar-driven calcination process has been characterised. Lime produced by the solar-driven process was used together with commercial clay as kiln feed components for the formulation of Portland cement samples. A binary mixture composed by fresh limestone and the same clay as above was employed as a reference. The key focus of the investigation was the assessment of the reactivity of the solar-generated lime toward the main clay components in the clinker production process, as compared to lime from ordinary calcination. An aspect that is specifically scrutinised is whether the different, and possibly more severe, thermal history to which limestone particles undergo during solar-driven calcination in directly irradiated FB reactors may compromise lime reactivity. Portland clinkers were produced by burning the raw meals at 1500 °C for 15 min. Clinkers were mixed with 5% natural gypsum to prepare the related Portland cements, which were then paste hydrated for times ranging from 2 to 28 days (water/cement mass ratio = 0.5, 20 °C, 95% relative humidity). Parameters as lime saturation factor, burnability, phase composition of clinkers and hydration behaviour of cement pastes were taken into consideration. Techniques as X-ray fluorescence and diffraction, and simultaneous differential thermal–thermogravimetry were used to study the materials.

Quality improvement in Cleaner Production aspect

The aim of the paper is presented the Cleaner Production (CP) issue in the aspect of the benefits that it gives the company in the competitiveness productivity and efficiency aspect. The research object is a company that is a leader in the Cleaner Production area - cement plant CEMEX. The research was based on a comparative analysis the company’s sustainable development in 2008-2012. It was shown that substitution of alternative fuels (an increase of 43% in 2014 compared to 2010) and the construction the first world’s alternative fuels dryer enabled not only for carbon dioxide reduction, but also hard coal consumption reduction and as a consequence allowed to relieve landfills waste. Thanks to elimination a part of the water contained in alternative fuels up to 8%, the unit heat consumption in the clinker production process is reduced. This is due to avoiding evaporation of water at high temperatures. Analysis the presented data showed that the use of CP not only effectively protects the environment by reducing / minimizing waste streams, but also leads to increased profitability, productivity, efficiency and competitiveness of industry, which in turn leads to economic growth. The paper emphasizes that the CEMEX Rudniki cement plant has saved 132,000 Mg of carbon thanks to the use of alternative fuels over the last 5 years.

Carbon footprint of calcium sulfoaluminate clinker production

Novel cement formulations based on calcium sulfoaluminate clinkers have significantly lower carbon dioxide emissions during production when compared against conventional Portland cement; however, there are no systematic studies of the environmental impact associated in producing these formulations. Previous studies are limited to qualitative evidence that emissions are lower due to a combination of favourable thermodynamics and a reduced usage of limestone. This work evaluates the eco-efficiency of calcium sulfoaluminate clinker production through an analysis of the carbon footprint and costs over the entire clinker production process (cradle-to-gate). Several sulfur sources are considered including calcium sulfate, as both gypsum and anhydrite, and a novel solid-sulfur combustion process in kilns. This latter process has the added advantage of reducing the fuel demand required to reach clinkering temperatures during the manufacturing process. The analysis demonstrates an overall reduction of emissions of 25–35%, which varies largely as a function of the phase composition of the final clinker but is almost independent of the sulfur source. The high aluminium oxide content in the final calcium sulfoaluminate clinker formulation requires the use of alternative raw materials and by-products from the aluminium industry such as high-alumina clays, alumina-rich wastes, or bauxite. Bauxite, which is only abundant in specific regions of the world, is detrimental to the economics of calcium sulfoaluminate clinker production. Despite this, costs of the clinker production remain competitive and the process displays significant potential for improving the environmental impact of cement production.

Thermal Decomposition Characteristics and Drying Process of Municipal Sludge

Using cement kiln dispose sludge from sewage plants can achieve the sludge stabilization, harmless, reduction and resource comprehensive utilization purposes. This is Not only to solve the problem of sludge treatment which is difficult to solve by sewage treatment plant, but also to make full use of the sewage treatment plant sludge to replace part of cement clinker production materials. And it makes full use of sludge incineration emitted in the process of low calorific value. Municipal sludge contains more moisture. It is necessary to dry the sludge outside the kiln before entering kiln process. As cement kiln co-processing, it should be combined with the characteristics of NSP clinker production, it is necessary to not only consider the total energy consumption of the drying process, but also the re-use of dried sludge heat value, as well as consider the total of water into the kiln by drying sludge affecting the whole clinker production process. In this paper, with the initial solid content 20%, dry heating value 3400 cal/g sludge as a research object, the moisture morphology, thermal characteristics, drying technological parameters and composition of water after drying in sludge were analysed. This issue combines sludge drying with cement kiln disposal, which can not only solve the heat and odor problem during the individual sludge drying process, but also provide a theoretical basis for cement kilns co-disposal of municipal sewage sludge to achieve the purposes of sludge stabilization, harmless, minimization and resource utilization.

Potential of Fly Ash Utilization for the Clinker Substitution in Cement Industry in Thailand

The main objective of this article is to forecast CO2 mitigation from clinker production and to evaluate Fly Ash potential, used Clinker Substitution for CO2 mitigation in cement industry between years 2015-2036 in Thailand following information of the Thailand's power developments plan (PDP2015). PDP2015 forecasts the potential of fly ash in the year 2036 which is estimated at 3.94 M ton and 48.76 M TonCO2 of CO2 emission from 58.01 M Ton of clinker production process. The methodology which is used for potential evaluation of fly ash and amount of CO2 can evaluate from Mae Moh power plant technology. 1 MW can occur 952.3427 Ton and amount of CO2 emission from utilizing is 0.825 TonCO2/TonneCli which is a default value of CSI (Cement Sustainability Initiative).The three different scenarios are used to analysis in this study. The condition of Business As Usual (BAU) scenario is the need of technology, used in 2015 as a base case. The full potential scenario (FP) is represent to the 100% fly ash using. The final scenario is called Zoning scenario (Z scenario) which consists of price rate (270 THB per Ton) and transportation rate (6 THB per kilometer of fly ash). From the result, in 2036 fly ash occur 7.46 M Ton that can mitigate CO2 volume up to 6.15 M TonCO2

Eco innovation strategies for promoting cleaner cement manufacturing

Carbon dioxide (CO2) emissions in cement plants are generated by the decarbonation of raw materials and fuel combustion in the cement kiln during the cement clinker production process and account for 8% of global emissions. This paper presents a mixed integer linear programming (MILP) by considering various mitigation measures, such as co-processing of fuels, kiln improvements and carbon capture and storage (CCS) yields, that can have substantial benefits. The benefits include cleaner cement production with minimum production costs, while satisfying the quality standard, carbon reduction target, and fuels substitution rate. The developed model is applied to a case study in order to demonstrate the applicability of the model. For the base case, the optimal cost for clinker production is USD 90.21/t clinker while CO2 emissions generated from both calcination of raw materials and fuels combustion is 531.68 kg CO2/t clinker and 325.00 kg CO2/t clinker. It was found that the highest possible CO2 emissions reduction that can be achieved by a combination of co-processing, kiln improvements and CCS technology is 79%, with an increment cost of USD 136.46/t clinker.

Predição da composição do clínquer industrial utilizando minimização da energia livre de Gibbs

A existência de processos químicos industriais, com diferentes fases em meio reacional, e a necessidade de conhecer a composição do sistema de interesse é um desafio comumente enfrentado pelos profissionais da indústria. Desta forma, a consideração do equilíbrio químico é uma metodologia comumente empregada por esses profissionais. Uma das principais etapas do processo de obtenção do cimento é a etapa de clinquerização, que ocorre dentro do forno rotativo. Neste estudo, é proposto o uso da técnica de minimização da energia livre de Gibbs para descrever o processo de produção de clínquer. O combustível considerado para o forno é o carvão mineral. Como resultado do estudo, objetiva-se a obtenção de uma rotina computacional que simule a condição de equilíbrio termodinâmico do sistema. Para isto, um problema de otimização não linear restrito é resolvido.

Blended Cements Elaborated with Kaolinitic Calcined Clays

In the clinker production process, the main component of Portland cement (PC), large amount of CO2 are emitted into the atmosphere. The use of calcined kaolinitic clays as supplementary material of cement is an alternative to mitigate the environmental impact. In this paper, the influence of the replacement of PC by two calcined kaolinitic clays (15 and 30%), with high content of metakaolinite and different reactivity was studied. Calcined kaolinitic clays were characterized, the pozzolanic activity usingFrattini test, the compressive strength, rate of water absorption (sorptivity), the assemblage of hydration products and the pore size distributionwere determined at28 days. The results show that the replacement of high percentage (30%) of very reactive clays improves the mechanical behavior and durable parameters compared with those obtained for plain PC

Energy and environmental savings via optimisation of the production process at a Spanish cement factory

With the aim of optimising the production process at the La Robla Tudela Veguín cement factory and improving the characteristics of the final product, a statistical study has been carried out relating kiln parameters with clinker quality. The parameters that most influence the manufacturing process have been identified and correlated with quality parameters. The importance that all these parameters might have with one another has also been shown. Applying the results thus obtained has led to significant energy savings. These findings represent production advantages from both the economic and environmental standpoint, bearing in mind the tons of CO2 which cease to be emitted to the atmosphere.The most important parameters in clinker production have been identified, as well as those that have the greatest influence, using a PLS (Partial Least Squares Projections to Latent Structures) regression program which explains the variability of “kiln” variables (X) with respect to dependent “quality” variables (Y). An analysis of the most important X and Y variables, such as Alite and Free Lime, was carried out. It was found that a decrease in the kiln Sintering Temperature (standardized at 50 °C) yielded produced the same level of quality in the final product. This finding implies a reduction in petroleum coke consumption and a reduction in CO2 emissions to the atmosphere, with the subsequent energy and cost savings at the factory, in addition to contributing to greater sustainability of the clinker production process.

Thermodynamic and Environmental Impact Assessment of Calcium Oxide Formation in Clinker Production

In this research, energetic andexergetic analysis of calcium oxide formation, CO2 emissions, andenvironmental effects during the clinker production process in rotary kilnare investigated. First the energy and exergy analysis of rotary kiln were carried out according to the first and second law of thermodynamics based on dead state, respectively. Consequently, the amount of CO2 emissions associated with calcination and fuel combustion processes, improvement potential and sustainability index are determined. In this system, the energy efficiency is calculated to be higher than the exergy efficiency, e.g. 53.4% and 28.6% for the energy and exergy efficiencies. The exergy destruction due to irreversible calcination and fuel combustion processes is determined 33,884 kW which is 40.6% of inlet exergy. Results also shows that 18.4% of exergy input is lost by exhaust hotgases.Thetotalemissions are estimated 157,228 kg/hr, which 31.3 % of it isdue tocalcination and 0.9 % of it is due to fuel combustion. The improvement potential (IP) and sustainability index (SI) are calculated 24,193.176 kWand 1.4, respectively.

Modelagem matemática de um forno rotativo empregado na produção de clínquer

Uma das principais etapas do processo de obtenção do cimento é a etapa de clinquerização, que ocorre dentro do forno rotativo. Em pleno funcionamento, o forno rotativo empregado na produção de cimento é alimentado basicamente de matéria-prima, combustível e ar. As vazões de saída são, basicamente, o clínquer e aos gases de combustão. Neste estudo, o processo de produção de clínquer por via seca é analisado, sendo a alimentação composta por 80% a 95% de calcário, 5% a 20% de argila e por pequenas quantidades de minério de ferro. O combustível empregado neste estudo é o carvão mineral. Os principais fenômenos envolvidos na obtenção do clínquer são a evaporação da água livre residual da matéria-prima, a decomposição do carbonato de magnésio, a descarbonatação, a formação da fase líquida do C3A e do C4AF, a formação do silicato dicálcico e a formação do silicato tricálcico. O objetivo principal deste estudo é a proposta de um modelo matemático que descreve o processo de obtenção do clínquer no forno rotativo. O modelo, composto por equações algébricas, foi desenvolvido por meio de balanços de massa e energia do forno. A modelagem foi implementada em linguagem de programação, empregando-se um programa comercial. A condição operacional considerada representa uma condição média adotada na indústria. O modelo proposto se mostrou satisfatório para a descrição do processo de clinquerização, sendo especialmente útil na realização da análise da demanda energética do equipamento.

Heat recovery from a cement plant with a Marnoch Heat Engine

Abstract This paper examines the performance of a new Marnoch Heat Engine (MHE) that recovers waste heat from within a typical cement plant. Two MHE units with compressed air as the working fluid are installed to recover the waste heat. The first unit on the main stack has four pairs of shell and tube heat exchangers. The second heat recovery unit is installed on a clinker quenching system. This unit operates with three pairs of shell and tube heat exchangers. The recovered heat is converted to electricity through the MHE system and used internally within the cement plant. A predictive model and results are presented and discussed. The results show the promising performance of the MHE’s capabilities for efficient generation of electricity from waste heat sources in a cement plant. The new heat recovery system increases the efficiency of the cement plant and lowers the CO2 emissions from the clinker production process. Moreover, it reduces the amount of waste heat to the environment and lowers the temperature of the exhaust gases.

Mercury species, mass flows and processes in a cement plant

The aim of the study was to evaluate the behaviour of mercury in the cement clinker production process. Simultaneous measurements of mercury in all important materials and gas streams were performed in three sampling periods on about 300 solid samples and about 80 samples taken from gas streams. Mercury species in flue gases at characteristic parts of the process were measured as total Hg(t), particulate Hg(p), elemental Hg 0(g) and reactive Hg 2+(g) mercury. Based on the results of measurements, mercury mass flows and mass balances of the whole and in certain parts of the process were evaluated. It was shown that the process comprises many mercury cycles which are strongly dependent on the operating conditions and technological specifics. Cycling of mercury causes a significant enrichment of mercury inside the process. In the annual mercury input of about 27 kg, raw materials accounted near by 60% and fuels about 40% (i.e. petrol coke 31%, waste tyres 10% and waste oil 0.4%). The annual emission of mercury represented 40–70% of the inputs, while cement clinker only contained about 10%. The difference between inputs and outputs (11–45%) obtained in the annual mass balance could be assigned to mercury recycling and significant enrichment inside the process, as well as variability between spot measurements. The parts of the process with the highest mercury mass flows and the lowest material/gas flows were identified. Such points represent an opportunity to remove a significant amount of mercury from the process at low material flows and to improve mercury control. Mercury was mainly emitted in gaseous form with 92% (direct mode) or 89% (combined mode) as Hg(g) on average, of which about 2/3 was as Hg 2+(g), and about 1/3 as Hg 0(g). Only a small part (the rest) was emitted as particulate Hg(p). Shares of individual mercury species in the last sampling period were 65.7% Hg 2+(g), 34.0% Hg 0(g) and 0.3% Hg(p) on average. Ratios between individual mercury forms were found to be related to operating modes. The quantities of Hg(t), Hg(g) and Hg 2+(g) emitted were higher when operating with the raw mills off (direct mode). It was seen that the efficiency of Hg removal was strongly related to the dust removal efficiency. Bag filters very efficiently removed all mercury species.

Design and Construction of a Cell to Model the Stabilization of Toxic Waste Solids to Residuals by Means of an Encapsulated Process

The residuals from galvanization processes, production of electronic components, paintings, electroplating, steel production, etc., are considered dangerous due to their high content of heavy metals such as lead and chromium. In this work, we designed and built a quartz cell which is able to resist the high temperatures at which the cement type, Portland, is obtained, with the purpose of exploring the stabilization of these elements when incorporating them into the process of production of the cement, and evaluating various quantities added as ingredients. The influence of this addition in the primary product, the clinker, is evaluated, as well as the retention of the metals and their possible incorporation into the rotational oven. The clinker production process is simulated by coupling the cell built into a laboratory device mounted to model the process. Temperature is controlled and the heating ramps represent the real process of production. Tests of leached material were performed on the product, under the norm governed by the Environmental Protection Agency (EPA), to verify the incorporation and retention of the metals studied in the structure of the clinker. Compression tests were carried out to verify that the addition of the metals does not affect the mechanical properties of the final product. Samples were prepared by additions of from 5 to 20 wt% of each element and the clinkering process was simulated in a laboratory device. Leaching tests were performed with the produced clinker samples in order to verify the incorporation of the studied metals in the clinker structure and the 28‐day compressive strength test in order to verify mechanical properties of the product. Scanning electron microscopic analysis revealed the effectiveness of the encapsulation among the clinker crystalline phases. The results led to the conclusion that additions of up to 20 wt% of lead and up to 5 wt% of chromium to clinker raw‐material are totally incorporated and do not affect the maximum compressive strength.

Effect of burning supplementary waste fuels on the pollutant emissions by cement plants: a statistical analysis of process data

This paper shows how some statistical tools can be applied in the process analysis of real plant data, e.g. in the clinker production process by using alternative fuels (shredded tyres and waste oils) as alternative fuels in clinker kilns of two different cement plants. Statistical Student's t-tests, stepwise linear regression models and factor analysis were employed in the data analysis to evaluate the effect on the atmospheric stack emission of these alternative fuel feeding. Moreover a quite large improvement in the knowledge of the process have been obtained by statistical analysis of the data process that very often suffer of internal correlation among the process variables under investigation. Experimental results statistically analysed have shown encouraging results, if less than 20% of regular fuel is replaced with alternative one: in particular clinker characteristics were unmodified, and stack emissions (NO x , SO 2 and CO mainly) were, in the case of tyres, slightly incremented, but remaining almost always below the law imposed limits; in the case of waste oils, polluted gas emissions were even decreased. Some empirical equations relating the stack emissions with some process data have been also obtained to be used for process analysis purposes.