Clinker Quality Research Articles

Imaging of Flames in Cement Kilns To Study the Influence of Different Fuel Types

The cement industry aims to use an increased amount of alternative fuels to reduce production costs and CO2 emissions. In this study three cement plants firing different kinds and percentages of alternative fuel were studied. A specially developed camera setup was used to monitor the flames in the three cement kilns and assess the effect of alternative fuels on the flame. It was found that co-firing with solid recovered fuel (SRF) would delay the ignition point by about 2 meters and lower the intensity and temperature of the kiln flame compared to a fossil fuel flame. This is related to a larger particle size and moisture content of the alternative fuels, which lowers the conversion rate compared to fossil fuels. The consequences can be a lower kiln temperature and cement quality. The longer conversion time may also lead to the possibility of localized reducing conditions in the cement kiln, which can have a negative impact on the clinker quality and process stability. The burner design may alleviate some...

Simulated Feedback Mechanism-Based Rotary Kiln Burning State Cognition Intelligence Method

Burning state directly determines the clinker quality index in the rotary kiln sintering process. A simulated feedback mechanism-based rotary kiln burning state cognition intelligence method and a calculating model are explored for the purpose of imitating the human cognition process with repeated comparison and inference. The flame image feature space is optimized progressively using the evaluation of uncertain cognition results with different values of cognition demand to realize the simulated feedback cognition mode from global to local. First, the simulated feedback mechanism-based rotary kiln burning state cognition intelligence method with the coupling operation of the training layer and cognition decision layer is proposed, and the framework of the model is described. Second, the evaluation index system of uncertain cognition results based on the bag of words model, latent semantic analysis method, and entropy theory is constructed. Third, the simulated feedback mechanism based on the evaluation of uncertain cognitive results is established, and a concrete calculation model is given. Fourth, the simulated feedback mechanism-based rotary kiln burning state cognition intelligence system is designed, and the relevant cognition intelligence algorithm is provided. Finally, a simulation experiment is carried out with the collected burning zone flame image of a rotary kiln. An average recognition accuracy of 92.32% is achieved with a minor standard deviation in accuracy. The experimental results show that our method is effective and outperforms other open-loop recognition methods with the global configuration feature of flame image.

Online monitoring of cement clinker quality using multivariate statistics and Takagi-Sugeno fuzzy-inference technique

This article addresses the issue of outlier detection in industrial data using robust multivariate techniques and soft sensing of clinker quality in cement industries. Feed-forward artificial neural network (back propagation, radial basis function and regression neural network) and fuzzy inference (Mamdani and Takagi-Sugeno (T-S)) based soft sensor models are developed for simultaneous prediction of eight clinker quality parameters (free lime, lime saturation factor, silica modulus, alumina modulus, alite, belite, aluminite and ferrite). Required input-output data for cement clinkerization process were obtained from a cement plant with a production capacity of 10000 t of clinker per day. In the initial data preprocessing activity, various distance based robust multivariate outlier detection techniques were applied and their performances were compared. The developed soft-sensors were investigated for their performance by computing various statistical model performance parameters. Results indicate that the accuracy and computation time of the T-S fuzzy inference model is quite acceptable for online monitoring of clinker quality.

ONLINE MONITORING OF SOFT SENSOR PERFORMANCE: A CASE STUDY OF CEMENT CLINKER QUALITY PARAMETERS SOFT SENSOR

The predictive ability of soft sensors deteriorates over time due to changes in the state of the plant and process characteristics. The results from the offline laboratory analyses of samples can be used to determine when a soft sensor requires recalibration; however, this approach is time-consuming. This paper presents a systematic approach in which a reverse model is developed for an online monitoring of the performance of soft sensor, the forward model. The proposed methodology is illustrated using a cement clinker quality parameters soft sensor as a case study. The reverse regression model gave rise to root mean squared error, coefficient of determination and worst case relative error values of 17.436, 0.9999 and 4.59%, respectively. Thus, it was concluded that, instead of the time-consuming approach of taking samples at the kiln exit for laboratory analysis, the developed reverse model can be used to provide plant operators with information about the predictive accuracy of the soft sensor.

Modeling the dynamic mechanism between cement CO2 emissions and clinker quality to realize low-carbon cement

To devise low-carbon cement clinker product, in-depth knowledge about the variation mechanism of cement clinker CO2 emissions is the prerequisite. The determinants of cement clinker CO2 emissions in Chinese cement industry have been inquired by several researches recently. However, the impacts and abatement effect of clinker quality on cement clinker CO2 emissions have not been identified yet. In technological sense, there lacks an integrated quantitative model that can elucidate the dynamic mechanism between cement clinker CO2 emissions and clinker quality. To fill this gap, this paper devises a CO2 emission accounting framework integrated with optimization model to explore the dynamic mechanism between cement clinker CO2 emissions and clinker quality. Based on survey data of 2 typical cement clinker production lines in China, the accounting framework is validated with measured data. Through numerical simulation within this framework, a set of sensitivity analysis is conducted. The results indicate that if the target KH (lime saturation ratio) of both production lines climb from −5% to +5%, the process CO2 emission factor will give rise to an increase of about 16.4 and 14.8kgCO2/t clinker, respectively. With the same variation, the fuel CO2 emission factors of two production lines will gain 17.2 and 13.7kgCO2/t clinker, respectively. Obviously, controlled decrease of clinker quality can reduce CO2 emission of clinker manufacturing. The results of sensitivity analysis are robust and highlight the remarkable role of clinker quality in both process and fuel emissions. Besides, the integrated framework can provide in-depth investigation into the dynamic mechanism between CO2 emissions and the other determinants. Using this framework, cement plants or industry can develop optimal clinker quality standards on a quantitative basis to achieve low-carbon clinker.

Comparison of temperature field distribution between cement preclinkering technology and cement precalcining technology

Through the comparison of calcination conditions between cement preclinkering technology and cement precalcining technology, we studied the characteristics of temperature field distribution of cement preclinkering technology systems including cyclone preheater, preclinkering furnace, and rotary kiln. We used numerical simulation method to obtain data of temperature field distribution.Some results are found by system study. The ratio of tail coal of cement preclinkering technology is about 70%, and raw meal temperature can reach 1070 °C. Shorter L/D kiln type of preclinkering technology can obtain more stable calcining zone temperature. The highest solid temperature of cement preclinkering technology is higher than 80 °C, and high temperature region (>1450 °C) length is 2 times, which is beneficial for calcining clinker and higher clinker quality. So cement preclinkering technology can obtain more performance temperature filed, which improves both the solid-phase reaction and liquid-phase reaction.

AN OVERVIEW OF INDUSTRIAL WASTES AS FUEL AND MINERALIZER IN THE CEMENT INDUSTRY

The cement industry worldwide is facing growing challenges in conserving material and energy resources. According to the International Energy Agency, the main levers for cement producers are the increase in energy efficiency and the use of alternative materials. This work shows the application of industrial wastes in cement industry as fuel and mineralizer that are found out in many studies of literature. The works showed that the waste fuels are viable but it is necessary to take to account that the burning behavior of most waste fuels differs significantly from the behavior of fossil fuels due to higher particle sizes, material densities and transport characteristics. On the other hand the mineralizer decreases of burning temperature of Portland clinker without altering the clinker quality.

Analysis of MSWI Bottom Ash Reused as Alternative Material for Cement Production

The bottom ash sample was obtained from one of three stably running municipal solid waste incineration plants in Beijing. The major components of bottom ash, i.e. CaO, SiO2, Al2O3, Fe2O3, were similar to that of ordinary Portoland cement, suggesting that bottom ash had the potential for reuse as cement material. In this paper, the smaple was sieved into 8 fractions according to the particle size distirbution. The content of CaO and chloride in the bottom ash almost decreased with the increase of particle size of bottom ash, contrary to the SiO2 content variation in the bottom ash. The Al2O3 and Fe2O3 content were relatively stable in the bottom ash with different particle size. The chloride, which could cause serious corrosion in the cement kiln, in 8 portion of bottom ash were all higher than its allowable limit in raw material for cement production and clinker quality, the dosage of bottom ash used as alternative material for cement production must be stringently controled, and some proper treatment must be used to reduce the corrion caused by chloride. The heavy metals concentration in the bottom ash were relatively high, but met standard requirements for heavy metals concentration in raw meterial. The content of alkaline oxide (K2O, Na2O) and sulphur, also affected cement production, in bottom ash with differernt particle size were all relative high. The bottom ash had the potential to be recycled as alternative material for cement production, but proper treatment measures, such as by-pass system, must be taken to satisfy the cement production, clinker quality and environmental safety.

Predictive Model for Cement Clinker Quality Parameters

Managers of cement plants are gradually becoming aware of the need for soft sensors in product quality assessment. Cement clinker quality parameters are mostly measured by offline laboratory analysis or by the use of online analyzers. The measurement delay and cost, associated with these methods, are a concern in the cement industry. In this study, a regression-based model was developed to predict the clinker quality parameters as a function of the raw meal quality and the kiln operating variables. This model has mean squared error, coefficient of determination, worst case relative error and variance account for (in external data) given as 8.96 × 10–7, 0.9999, 2.17% and above 97%, respectively. Thus, it is concluded that the developed model can provide real time estimates of the clinker quality parameters and capture wider ranges of real plant operating conditions from first principle-based cement rotary kiln models. Also, the model developed can be utilized online as soft sensor since they contain only variables that are easily measured online.

Effect of Selected Alternative Fuels and Raw Materials on the Cement Clinker Quality

Abstract The article deals with the study of the effects of alternative fuels and raw materials on the cement clinker quality. The clinker quality was expressed by the content of two principal minerals alite C3S and belite C2S. The additions of alternative fuels ashes and raw materials, in principle, always increased the belite content and conversely reduced the amount of alite. The alternative fuels with high ash content were used such as the meat-bone meal, sewage sludge from sewage treatment plants and paper sludge and the used alternative raw materials were metallurgical slags - granulated blastfurnace slag, air cooled blastfurnace slag and demetallized steel slag, fluidized bed combustion fly ash and waste glass. Meat-bone meal, sewage sludge from sewage treatment plants and paper sludge were evaluated as moderately suitable alternative fuels which can be added in the amounts of 2.8 wt. % addition of meat-bone meals ash, 3.64 wt. % addition of sewage sludge ash and 3.8 wt. % addition of paper sludge ash to the cement raw mixture. Demetallised steel slag is suitable for production of special sulphate resistant cement clinker for CEM I –SR cement with addition up to 5 wt. %. Granulated blastfurnace slag is a suitable alternative raw material with addition 4 wt. %. Air cooled blastfurnace slag is a suitable alternative raw material with addition 4.2 wt. %. Waste glass is not very appropriate alternative raw material with addition only 1.16 wt. %. Fluidized bed combustion fly ash appears not to be equally appropriate alternative raw material for cement clinker burning with less potential utilization in the cement industry and with addition 3.41 wt. %, which forms undesired anhydrite CaSO4 in the cement clinker.

Disposal of historically contaminated soil in the cement industry and the evaluation of environmental performance

Approximately 400000t of DDTs/HCHs-contaminated soil (CS) needed to be co-processed in a cement kiln with a time limitation of 2y. A new pre-processing facility with a “drying, grinding and DDTs/HCHs vaporizing” ability was equipped to meet the technical requirements for processing cement raw meal and the environmental standards for stack emissions. And the bottom of the precalciner with high temperatures >1000°C was chosen as the CS feeding point for co-processing, which has rarely been reported. To assess the environmental performance of CS pre- and co-processing technologies, according to the local regulation, a test burn was performed by independent and accredited institutes systematically for determination of the clinker quality, kiln stack gas emissions and destruction efficiency of the pollutant. The results demonstrated that the clinker was of high quality and not adversely affected by CS co-processing. Stack emissions were all below the limits set by Chinese standards. Particularly, PCDD/PCDF emissions ranged from 0.0023 to 0.0085ngI-TEQNm−3. The less toxic OCDD was the peak congener for CS co-processing procedure, while the most toxic congeners (i.e. 2,3,7,8-TeCDD, 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDD) remained in a minor proportion. Destruction and removal efficiency (DRE) and destruction efficiency (DE) of the kiln system were better than 99.9999% and 99.99%, respectively, at the highest CS feeding rate during normal production. To guarantee the environmental performance of the system the quarterly stack gas emission was also monitored during the whole period. And all of the results can meet the national standards requirements.

Using sewage sludge as a denitration agent and secondary fuel in a cement plant: A case study

The influences of sludge feed rate, feed point, feed method, and air-staged combustion were systematically investigated in a Chinese cement plant with emphasis on NOX removal. Results indicate that the use of sludge as a secondary fuel is conducive to NOX reduction, which depends primarily on the feed rate and feed point. Moreover, both feed method and air-staged combustion influence NOX removal to some extent. Nonetheless, these factors have little effects on CO removal. When the sludge feed rate is 9t·h−1 in a precalciner reburning zone in the combustion temperature range from 850 to 1000°C, NOX removal reached 75.82% in the air-staged combustion condition. The NOX concentration easily met the national emission standards. Finally, the use of sludge as alternative fuel does not affect clinker quality negatively. This method utilizes sludge effectively and reduces NOX emissions; hence, the application of sewage sludge as a denitration agent and secondary fuel in cement production is a worthy option.

From Coal to Natural Gas: Its impact on Kiln Production, Clinker Quality and Emissions

In the North American energy market, natural gas (NG) prices have been gradually decreasing during the past several years, primarily due to advances in shale gas extraction techniques. The availability of cheaper NG, while seen as an attractive short-term fuel switching option, is viewed with caution by most cement plants due to long-term procurement concerns. Also, due to traditionally higher NG prices, cement plants have invested heavily into solid fuels, including storage, grinding, handling, and dosing systems—often achieving high thermal substitution rates (TSRs) of solid alternative fuels and raw materials (AFRs). As a result, a wealth of knowledge has been acquired on firing solid fuels, including some of the more difficult ones, e.g., higher sulfur petcoke and bigger size AFRs, where operational issues such as build-ups, emissions, and production losses have been and are being minimized. Switching to gas firing, however, requires readaptation of combustion and process guidelines for a fuel which, although in principal, is easier to burn, but has relatively lower radiative heat transfer and sharper burning characteristics than coal. As such, the plants, which have switched to NG firing, have observed inconsistent trends in production, energy, and emission performance, mainly due to the lack of sufficient information on combustion/process interactions of the two fuel types required for cost-effective optimization. An NG flame ignites earlier, releases intense heat but lacks dissipation of heat as compared with a solid fuel flame, thereby requires plant specific adjustments. This paper presents actual results of NG firing trials at selected cement plants along with mineral interactive computational fluid dynamics (MI-CFD) predictions, subsequent to validation from the plant data, on four kiln and four calciners. Recommendations are also made to improve and optimize NG firing by taking into considerations of the combustion and mineral interactions.

Technical benefit and risk analysis on cement clinkering process with compact internal burning of carbon

This article demonstrates the potential technical benefit and risk for cement clinkering process with compact internal burning of carbon, a laboratory-phase developing technique, from 9 aspects, including the heat consumption of clinkering and exhaust heat utilization, clinker quality, adaptability to alternative fuels, the disposal ability of industrial offal and civil garbage, adaptability to the raw materials and fuels with high content of chlorine, sulphur and alkali, the feasibility of process scale up, the briquetting process of the coal-containing cement raw meal pellet, NOx emission and the capital cost and benefit of conversion project. It is concluded that it will be able to replace the modern precalciner rotary kiln process and to become the main stream technique of cement clinkering process in low carbon economy times.

OVERALL INCREASE IN EFFICIENCY IN RAW MEALS

This paper deals about the quality improvement in Raw Mill – 2. In order to increase the efficiency of production and greater quality of cement, table feeder is replaced with weigh belt feeder. The weight belt feeder helps to weigh the amount of raw material composition and to maintain the constant TPH which is feed to the raw mill. This load cell transfer electrical signals to the electronic unit which is proportional to the load pressure exerted by the raw material. The replacement of existing coin burner with multi channel burner result in increased clinker quality. It is observed that the flame geometry is improved with new burner. Also there is enhanced nodulization and improved strength. Hence a thorough investigation was done on the problems relating to raw mill – 2 and quality improvement is carried out. This dissertation work reports the successful completion and implementation of the same.

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.

Modelling the cement process and cement clinker quality

This paper presents a recently developed simulation model that can be used as a tool for evaluating sustainable development measures for cement and lime production processes. Examples of such measures are introducing new combustion technologies such as oxy-fuel combustion, using biomass fuel and using alternative materials in the raw material feed. One major issue when introducing process changes is the need to maintain product quality. In some ways, oxygen-enriched air combustion resembles oxy-fuel combustion. The model results were validated and found to be consistent with full-scale operational data for normal running conditions and for a full-scale test with oxygen-enriched air. The model shows, for example, that with an additional 1500 m3/h of oxygen, fuel addition at the calciners can increase up to 108% and the raw material feed rate can increase up to 116% for a process with a raw meal feed of 335·5 t/h.

Minimization of Variation in Clinker Quality

Cement quality is typically assessed by its compressive strength development in mortar and concrete. The basis for this property is a well-burned clinker with consistent chemical composition and free lime. The main reason for the clinker free lime to change in situation with stable kiln operation is variation in the chemical composition of the kiln feed. This variation in chemical composition is related to raw mix control and the homogenization process. To ensure a constant quality of the product and maintain a stable and continuous operation of the kiln, the attention must be paid to storage and homogenization of raw materials and kiln feed. Due to variations in the kiln feed chemical compositions that affect its burnability and the fuel consumption. The raw materials for Portland cement production are the mixture (as fine powder in the 'Dry process') of minerals containing calcium oxide, silicon oxide, aluminum oxide, ferric oxide, and magnesium oxide. The homogeneity of feed chemical composition has an important relationship to fuel consumption, kiln operation, clinker formation and cement performance. In this regard an attempt made to deals with the mixing of raw materials process and estimation of composition of raw mill feed, kiln feed, as well as formed clinker, which were done successfully through various results obtained experimentally and various steps have been taken to reduce these variations in clinker quality.

Development and comparison of neural network based soft sensors for online estimation of cement clinker quality

The online estimation of process outputs mostly related to quality, as opposed to their belated measurement by means of hardware measuring devices and laboratory analysis, represents the most valuable feature of soft sensors. As of now there have been very few attempts for soft sensing of cement clinker quality which is mostly done by offline laboratory analysis resulting at times in low quality clinker. In the present work three different neural network based soft sensors have been developed for online estimation of cement clinker properties. Different input and output data for a rotary cement kiln were collected from a cement plant producing 10,000 tons of clinker per day. The raw data were pre-processed to remove the outliers and the resulting missing data were imputed. The processed data were then used to develop a back propagation neural network model, a radial basis network model and a regression network model to estimate the clinker quality online. A comparison of the estimation capabilities of the three models has been done by simulation of the developed models. It was observed that radial basis network model produced better estimation capabilities than the back propagation and regression network models.

Co-firing of refuse derived fuels with coals in cement kilns: combustion conditions for stable sintering

<title/>Usage of refuse derived fuels (RDFs) in cement clinker processes has grown considerably in the last decade. It has been demonstrated that RDFs can partially substitute fossil fuels without compromising clinker quality. The paper considers RDF properties which are essential for stabilisation of the sintering zone in the clinker burning process. An energy replacement indicator, defined as the RDF thermal input to the fossil fuel thermal input ratio, is used. Comminution of RDF to particle scales of pulverised fuel is economically not yet feasible and RDF is burnt at particle sizes in the order of several millimetres. Therefore, RDF combustion rates are orders of magnitudes smaller if compared to pulverised coal combustion rates. This shifts the flame zone downstream the rotary kiln and flame temperatures are reduced. A simple kiln combustion model has been used to examine the effects of RDF properties on sintering zone temperatures. Refuse derived fuels with calorific values below 20 MJ kg−1 and coarse particle sizes burn at adiabatic temperatures below 2000°C. To compensate for this, the energy replacement ratio has to be increased to 114%. Calculations have shown several options to increase gas temperatures in sintering zones. The most effective would be the comminution of RDFs to pulverised fuel sizes. In this case, a further reduction of the RDF calorific value would be acceptable.