Kiln Feed Research Articles

Clays to lightweight aggregates: Thermochemical modeling and industrial validation

The creation of thermochemical models to forecast the dependent variables governing the bloatability of lightweight aggregates (LWAs) is the goal of this work. Laser particle size analysis, XRD, XRF, IR, TGA-DTA, SEM-EDX, Laser imaging system, µ-CT, hot-stage microscope and Factsage (8.3) thermodynamic software were used for clays and LWAs characterization in the temperature range 900–1250°C. It was found that the LWAs bloating zone occurs at 1050–1250°C with a minimum bulk density (BD) of (0.74 g/cm3) at 1250°C. During the LWAs pyroplastic state, the crystallization of anorthite from the silicate melt lowers its viscosity due mainly to the alkalis’ uptake into the anorthite lattice. However, the silicate melt is still viscous enough to trigger the reduction of hematite and consequently guarantees the evolution of bloating gases. The simultaneous association of higher evolved gas with less melt content of higher viscosity would promote the LWAs bloatability. The higher the gas that accompanied with low melt of lower viscosity would loosen the LWAs their consistency and sphericity upon their sudden cooling. Based on the LWAs bulk density and lab experimental observations, the production window limits of successful LWAs are ≥40 wt% silicate melt of 103-107 Pa.s viscosity that accompanied with (0.50–4.00 wt%) gas content. This production window has been verified by Liapor industrial kiln feed. The LWAs pyroplastic and post-quenching characteristics are all statistically significant variables (<0.05) for prediction modeling. The forecasting models are statistically verified by the multi-collinearity testing that shows VIF values <10 indicating the absence of any multi-collinearity among the models’ explanatory variables.

Using Response Surface Methodology Approach to Modeling and Optimization of the Combustion Process in Cement Kiln

AbstractIn this study, this process has been modeled and optimized using the design of experiment technique and response surface methodology (RSM). The RSM was employed to optimize the combustion process in the cement kiln. Kiln feed (X1 = 160–190 t h−1), fan speed (X2 = 840–870 rpm), kiln rotational speed (X3 = 2.8–3.4 rpm), kiln fuel rate (X4 = 3800–4150 L h−1), calciner fuel rate (X5 = 5700–6200 L h−1), pressure of kiln inlet (X6 = 98–102 Pa), and limestone saturation factor (LSF) (X7 = 94–95.8 %) as independent variables were investigated. The carbon monoxide and the kiln body temperature in RSM were considered as response variables. The absolute average error in the model predictions for the combustion process in the cement kiln, for the kiln body's temperature, is about 1.6 % and for carbon monoxide is about 15.5 %.

Processing municipal solid waste incineration bottom ash for integration into cement product manufacture

Municipal solid waste incineration (MSWI) bottom ash (BA) contains the elemental composition necessary for cement and concrete production and is a feasible substitute for high-value markets such as cement kiln feed (CKF) and supplementary cementitious material (SCM), providing an opportunity to recycle materials that are typically landfilled. This study explores the physical and chemical properties of individual components of MSWI BA—glass, ceramic, concrete, and slag—for use in cement product manufacture. Elemental oxide data reveals MSWI BA contains a variable composition of elements necessary for clinker formation. For example, MSWI BA concrete has a calcium content (33–40%) similar to that of limestone (64%) used in CKF. Compressive strength of mortar made with MSWI BA glass and ceramic is about 75% that of the control. Elemental analysis and isothermal calorimetry confirm that MSWI BA glass and ceramic fractions have the strength and elemental composition for use as an SCM compared to slag and concrete.

How do mud balls form in lime kilns?

Mud ball formation in lime kilns has been a persistent problem in many kraft mills, particularly for older kilns that are equipped with chains. A systematic laboratory study was conducted to examine how mud balls are formed and the key factors that affect ball formation. The results confirm the general mill experience that high moisture and high sodium contents in lime mud are the main contributing factors to ball formation. The high moisture content allows lime mud to agglomerate and grow to form balls, while the high sodium content helps make the balls hard and retain their shape. A ball formation mechanism is proposed to explain how mud balls form and grow near the kiln feed end.

Full-scale investigations of initial deposits formation in a cement plant co-fired with coal and SRF

This work investigates the initial (short-term) deposit formation in a cement calciner co-fired with coal and SRF (Solid Recovered Fuel). The main objective was to evaluate and compare the tendencies of deposit formation (i.e. material deposition rate and composition) at different locations (heights) in the calciner system, during different operation conditions. A steel probe was used to collect initial deposits from four different sampling locations: i) in the kiln riser (two sampling locations), ii) in the mid calciner, and, iii) at the outlet from the bottom stage preheater cyclone (C5). After an exposure time of the probe between 1 and 20 min, the collected deposit samples were weighted and characterized by SEM-EDX, ICP-OES/IC, and XRD. Plant operation data, measured gas temperatures, as well as gas phase composition data (i.e. KCl(g) and SO2(g)), supported the evaluation of deposit formation. Due to high particle flux (up to approx. 61,000 kg/(m2·h) in the riser duct), the average net deposit formation rate was around 500 kg/(m2·h) for 1 min exposure time, decreasing to <100 kg/(m2·h) for exposure times ≥4 min (due to spontaneous shedding and erosion). The deposits contained primarily five crystalline phases (CaO, CaCO3, Ca(OH)2, KCl, and SiO2), which is in general consistence with the composition of the admitted preheated raw meal (C4 meal) at measurement locations, with a slight enrichment in KCl, suggesting some condensation of volatile elements from the high-temperature gas phase on the surface of the somewhat colder deposit particles. Further, the deposit samples obtained in the kiln riser had a higher degree of calcination (higher proportion of CaO as compared to CaCO3) as compared to the admitted C4 meal, suggesting carry-over of dust from the kiln feed pipe, or fast calcination of the riser meal due to high temperature.The collected short-term deposits differ significantly from long-term (mature) deposits, which have previously been collected from the site, in terms of chemical and physical properties. Compared to short-term deposits, which had a content of KCl in the range of approx. 3–5 wt%, the content of KCl in the mature deposits increased substantially from around 2 wt% in samples from the kiln riser area to a level of >20 wt% in the calciner and C5 cyclone area, implying significant accumulation of KCl caused by volatile circulation and condensation from the hot gas on surfaces with locally lower temperatures. The most prevalent crystalline phases in the mature deposits were KCl, CaCO3, and the mineral spurrite (Ca5(SiO4)2CO3). The presence of spurrite implied that SiO2 reacts with CaCO3, or with CaO and gaseous CO2, to form spurrite during long-term deposit build-up and maturation.Overall, the results from this work suggest that the short-term deposit formation in the cement calciner is dominated by impaction. The composition of the short-term deposits is quite similar to the composition of the entrained C4 meal particles; while the build-up of mature deposits is influenced greatly by local temperature gradients and long-term fluctuations. I.e. in zones with locally lower temperatures, such as cold area of calciner walls (< ∼850 °C), heterogeneous condensation and/or thermophoresis of KCl from the high-temperature flue gas is facilitated.

ადგილობრივი ნედლეულის გარდაქმნის პროცესები კლინკერის წარმოების მბრუნავი ღუმელის სისტემაში რეაქტორ-დეკარბონიზატორის გამოყენების გათვალისწინებით

In cement and clinker production energy consumption reduction, specific emissions reduction and quality stable increase always has been daily challenge which was addressed in many studies. Nowadays, CO2 emissions are under special focus since the gas is a main contributor in global warming and many other environmental topics. Considering existing challenges, the PhD study is addressing following: Revamping from wet process to the new dry line clinker production process Revamping from the old Kavtiskhevi quarry to new Saskhori quarry Raw meal, kiln feed and clinker quality adjustment after changing the type and amount of the fuel Study of clinkerization process based on the modified design Activation of puzzolanic material – Tuff in the clinker cooler Clinker production process change from wet process to dry process was performed the way that clinker quality was at least the same but grindability of the clinker was increased with relatively lower lime saturation factor. Of course by avoiding drying wet slurry and making heat exchange process more efficient due to more dispersive, powderous material the heat consumption was reduced twice and capacity of the kiln line was doubled. The difficulties caused by switching the Kavtishkevi quarry were solved by using Saskhori limestone as a main source and Dedopsitskaro limestone was used as a sweetener, which contains more than 95% calcium carbonate. This substitution took place in such a way that it did not have a negative impact on the quality of the clinker and on the contrary made it more stable and active. After reducing coal and thus ash by 2 times, raw flour chemistry was recalculated so that the quality of clinker was the same or increased. Appropriate recalculation was done at all stages of trials. The clinker process burning with a new method was studied and optimized. As a result of 20 industrial experiments of raw material and fuel distribution, the best mixes were determined, by means of which the quality of clinker increases or remains the same, while the thermal consumption was reduced as was CO2 emissions from fuel and from raw meal. The most important achievement was the thermal activation of Tuff (Zeolite), which was successfully completed not only in the laboratory but also in the industrial experiment. The origin of the innovative idea was that the drying out of physically bound water makes the puzzolanic material much more active due to created pores. The material usage (with clinker) up to 10% in relation to clinker not only preserves but also increases the strength of this mix compared to clinker. The method of activation of existing puzzolanic material has been studied since the ancient Roman period. However, the activation of the puzzolanic additive requires less thermal energy than the clinker, and therefore also emits additional CO2 emissions. Therefore, the puzzolanic material activated by the standard approach reduces emissions, thermal and other costs relatively less, and also requires an investment of at least 10 million and an installation period of at least 6 months. Based on a complete study of the clinker production processes, a section was identified where the temperature ranges from 600°C to 1200°C and we use ambient air to reduce it. This section is a clinker cooler, where clinker heated at temperatures 1200-1300°C is coming out of from the rotary kiln. The clinker is passing a 30-meter cooler and cools down to about 100°C. The temperatures we wanted were 5 to 10 meters from the hot side. 10 meters away from the hot end, a material discharge chute was arranged, where tuff is supplied with transport conveyors and hopper. The production experiment with a dose of 5% was successful, but it is also possible to increase the proportions to 10% in the following trials. Also, the feeding point on the clinker cooler roof can be moved to the hotter side, which will further activate the tuff and allow us to increase its percentage in the clinker. The most important is that this experiment allowed us to produce 100% clinker with 90% emissions and thermal consumption, which is an incredible result globally, especially for CO2 reduction. The project was implemented with minimal costs (200,000 GEL) and, most importantly, does not include the thermal energy obtained with fuel, which almost cancels the operating costs and emissions. This section of the clinker cooler can be studied to use for drying and heating any other cement additive material.

A machine learning approach for clinker quality prediction and nonlinear model predictive control design for a rotary cement kiln

AbstractCement manufacturing is energy‐intensive (5Gj/t) and comprises a significant portion of the energy footprint of concrete systems. Incorporating modern monitoring, simulation and control systems will allow lower energy use, lower environmental impact, and lower costs of this widely used construction material. One of the goals of the CESMII roadmap project on the Smart Manufacturing of Cement included developing an analytical process model for clinker quality that includes the chemistry of the kiln feed and accounts for critical process variables. This predictive model will be used in nonlinear model predictive control system designed to significantly reduce process energy use while maintaining or improving product quality. In the cement manufacturing plant used in this study, the kiln feed (meal) is tested every 12 h and used to estimate the mineral composition of the cement kiln output (clinker) using the stoichiometry‐based Bogue's model and the expertise of the plant operators. During kiln operation, kiln output (clinker) is sampled and tested every 2 h to measure its chemical and mineral composition. The predicted and measured values of the clinker composition are used by the plant operators to adjust the kiln input stream and the production process characteristics to maintain stable operation and uniform product quality. However, the time delay between prediction and testing, along with inaccuracies inherent in the Bogue's model have made any process changes designed to minimize energy use problematic, especially in‐light of potential clinker quality issues that process changes often pose. A new analytical model that integrates quality information and process operation information has been developed from data collected from 2 years of production from an operating cement facility. To make the model fuel‐type‐independent, consumed heat energy was computed in the model instead of fuel type and amount. A Feedforward Network was trained and tailored from collected data. Many data‐based simulations were conducted to quantitatively evaluate the proposed model and the 5‐fold cross‐validation procedure was used to test the models. The resulting predictive model was shown to have a low root mean square error (MSE) with respect to the estimated clinker mineral composition compared to that using the industry standard “Bogue’ model”. The end goal of this work was to develop a single machine learning tool that allows the use of quality control data and process control variables to improve energy efficiency of the process in a continuous fashion. The proposed nonlinear model predictive control system (NMPC) can generate predicted kiln production characteristics based on manipulated variables in manner that accurately follows the target product quality values. Simulation results also show that the proposed model produced accurate predictions of kiln outputs that fell within the required constraints, while manipulating control variables within typical operational ranges.

Experimental validation of multiphysics model simulations of the thermal response of a cement clinker rotary kiln at laboratory scale

AbstractAn increasing demand for buildings, transportation systems and civil infrastructure development has driven expansion of cement consumption world‐wide, producing a significant increase in related global energy demand. With approximately 7% of the world‐wide industrial energy consumption (10.7 exajoules [EJ]), the cement industry is the third most energy intensive industrial processes and a key component for concrete, the most consumed composite material in the global construction industry. In cement manufacturing, the cement kiln accounts for most of the energy consumption in the production process. As the heart of a cement plant, the cement kiln is where the kiln feed primarily containing calcium oxide (CaO), silica (SiO2), alumina (Al2O3), and iron (Fe2O3) are thermally and chemically transformed into clinker minerals. The presented work developed a multiphysics model, designed and built a laboratory‐scale rotary cement clinker kiln, and produced cement clinker at laboratory‐scale. The model was developed to study the interaction between the various thermal, fluid dynamic and chemical interactions involved in the sintering process used to form Portland cement clinker in an effort to reduce energy use. The analytical model was validated through experimental testing using a unique laboratory‐scale rotary cement kiln developed during the investigation. Also demonstrated was the feasibility of producing clinker at laboratory scale. This modeling and lab scale tests were designed to better understand the clinker sintering process so that operational and quality decisions can be made to optimize energy consumption without compromising cement clinker quality. The computational fluid dynamics modeling was developed in COMSOL Multiphysics 6.0. The characteristics of the combustion fluid flow, concentration of species, temperature and heat transfer were studied for a turbulent flow of methane (CH4) gas and oxygen (O2). Theory suggests that heat transfer impacts the cement production process but the multiphysics model more accurately describes the convection, conduction, and radiant heat transfer in the kilning process and thus allows for a better understanding of the energy exchange driving the chemical reactions that produce Portland cement. Clinker minerals were formed because of appropriate burning conditions implemented during experimental model validation.

New Method of Materials Flow Calculation for Double-String SLCI Type Cement Plant (Part 2: Suspension Preheater and Calciners)

In many industries, energy auditing is important as the basis for controlling processes and designing additional equipment or modifying an existing plant. However, it requires detailed data of the materials flow, which often cannot be determined easily by direct measurement due to high-temperature limitations. This paper presents the second part of an integrated study to perform energy auditing in a separate line and in-line calciners (SLC-I) type cement plant. The second part of this study, as presented in this paper, focused on the materials flow calculation for eight separate cyclones and two calciners. The least square method was employed for solving the obtained overdetermined system equations. Using the operation data from Part 1 of the study, calculation of the detailed materials flow in each cyclone was executed. The results showed that the separation efficiency of cyclones 1A, 2A, 3A, 4A and 1B, 2B, 3B, 4B was 93.86%, 89.80%, 84.41%, 81.98% and 93.96%, 88.70%, 88.53%, 80.72% respectively and the estimated calcination percentage of kiln feed coming out of the ILC and the SLC was 85.3% and 56.3%, respectively. These values are impossible to be measured directly in the cyclones and calciners during plant operation.

Energetic assessment of a precalcining rotary kiln in a cement plant using process simulator and neural networks

Cement production has been increasing rapidly leading to energy consumption, with serious cost implications and environmental challenges. Energy efficiency is a key component required to maintain the cement company’s environmental strategy. In this study, Aspen Plus process model and neural networks are used to assess the energetic efficiency of a precalcining rotary kiln in a cement production process. Aspen Plus process simulator estimated energy efficiency at 61.30 % using the first law of thermodynamic. Further, for the ANN model, kiln feed, kiln gas, calciner gas, clinker cooling air, and primary air were the operation parameters inputs. ANN model is validated and demonstrated it is capable of predicting cement rotary kiln energy efficiency accurately with a correlation coefficient (R2) of 0.991. In conclusion, the Bootstrap aggregated neural network (BANN) was used to search the optimal operational parameters in achieving the lowest mean square error (MSE) of the energy efficiency. The MSE for training, testing, and validation data sets were 3.64 × 10-5, 3.70 × 10-5, and 5.00 × 10-5 for in the estimation of rotary kiln system energy efficiency. To achieve this optimal condition of 61.5 % energy efficiency, the optimal parameters as determined by ANN (BANN) were kiln feed of 205050 kg/hr, kiln fuel gas of 2821 kg/hr, calciner fuel gas of 5648 kg/hr, clinker cooling air of 247463 kg/hr and primary air of 7309 kg/hr. Consequently, it is recommended that ANN should be combined with Bootstrap aggregated neural network (BANN) for effective prediction and monitoring of energy efficiency for precalcining rotary kiln system.

Designing Raw Mix for Manufacturing Portland Cement using Euphrates Formation Marl Instead of Clays

Portland Cement is manufactured by adding 3% gypsum to clinker which is produced by grinding, pulverizing, mixing, and then burning a raw mix of silica, and calcium carbonate. Limestone is the main source of carbonates, while clay collected from arable land is the main source of silica. The marl in the Euphrates Formation was studied as an alternative to arable lands. Nine boreholes drilled and penetrated the marl layer in selected locations at the Kufa cement quarry. Forty-one samples of marl from boreholes and four samples of limestone from the closed area were collected. The chemical content of the major oxides and the hardness of the marl layer was very encouraging as a raw material for Portland Cement as they are SiO2 (17.60), CaO (37.89), MgO (1.94), Fe2O3 (2.47), Al2O3 (4.21), K2O (0.731), SO3 (0.35), and Na2O (0.062). The marl was used in designing a raw material mix suitable for rotary kiln feed and produced a clinker conforming to the approved specifications. The designing a raw mix consisting of 80.30% of marl with 19.70% of limestone. The investment of the marl layer can be used as an ideal alternative to the arable clay giving fit quality to the international specifications, reducing production costs during quarry operations, reducing the energy consumption and equipment wearing.

Improving Kiln Feed Chemistry and Overburden Wasting through Controlled Consistent Quarry Material Mix: A Case Study at Union Bridge Cement Plant

Cement is made by milling clinker with a mix of grinded gypsum. The clinker is produced using a rotary kiln which burns a mixture of limestone, clay, magnesium, silica, and iron with desired atomic percentages. The quarry is the primary source of raw material for the rotary kiln in cement production. The consistency of material feed chemistry, in which the quarry plays a key role, is crucial for optimizing the performance of a rotary kiln. The quarry implemented a six-step methodology that comprised a modified 3D mining software modeling tool, a database computer loop prediction tools, and other tools to improve mining sequencing, optimize raw material usage, and provide consistent chemistry mix material for the kiln. By using overburden as a raw material in the mix, the quarry nearly universally reduces the environmental impact of squandering unwanted material in the quarry. This has a significant environmental impact since it requires less space to manage the overburden waste generated during mining. In addition, raw material usage was optimized for clinker production causing a reduction of 4% in sand usage as raw material, reduction in raw material purchase cost, reducing the variability of kiln feed chemistry, and producing high-quality clinker. The standard deviation of kiln feed LSF was improved by 45 percent, and the variability in kiln feed was reduced by 65 percent.

Pilot-scale cement production using treated waste incineration bottom ash: physical and environmental performance

The use of washed municipal solid waste incineration (MSWI) bottom ash as a kiln-feed material for cement production provides an opportunity to recycle materials which are traditionally landfilled. The impact of MSWI bottom ash as a kiln feed material on cement performance is still poorly understand and industry feedback suggests that robust pilot-scale data sets are needed to address operator concerns prior to widespread implementation. This work contributes to the knowledge based as it reports the results from three discrete pilot-scale trials where washed MSWI bottom ash was used to replace typical kiln feed material at 0%, 1% and 2% by mass to manufacture portland cement. The resultant elemental and mineralogical composition were equivalent for each of the three cements. A detailed analysis of mechanical performance parameters indicate no significant differences in grindability, workability, hydration kinetics, or strength properties of the three cements. A screening assessment of direct exposure and leaching risk indicate no meaningful differences in constituents of potential concern. Air emissions monitored during each trial indicate no differences in concentration for monitored pollutants. The results support that modest incorporation of washed MSWI bottom ash into full-scale portland cement production is a safe and feasible means of replacing traditional raw materials.

Techno-commercial Assessment of Concurrent Municipal Brown Field Reclamation Procedures: A Pivotal Case study of Jawahar Nagar Dump Site

Techno-commercial Assessment of Concurrent Municipal Brown Field Reclamation Procedures: A Pivotal Case study of Jawahar Nagar Dump Site

Washed waste incineration bottom ash as a raw ingredient in cement production: Implications for lab-scale clinker behavior

Municipal solid waste incinerator (MSWI) ash has a similar chemical composition to traditional cement kiln feed components, making it a potentially viable replacement for traditional materials in the absence of deleterious components invariably present in ash. This supposition should be confirmed by lab-scale experimentation prior to full-scale implementation. This study explores lab-scale cement manufacturing using varying replacement percentages of unwashed and water-washed MSWI bottom ash. The use of unwashed MSWI ash as a kiln feed is associated with a considerable decrease in tricalcium silicate content. Each replacement percentage of washed bottom ash incorporation resulted in an approximate tricalcium silicate content of 45%, while unwashed bottom ash specimens had tricalcium silicate contents of approximately 35%. Aluminate concentrations in ash-amended clinkers were considerably higher than reference clinkers, which may require additional gypsum to ensure proper setting. The effects of mineralogical differences were reflected in cement reactivity. Unwashed MSWI ash-amended specimens should be monitored for chloride and alkali content. Results of this study highlight the simultaneous impact of washed and unwashed MSWI bottom ash addition as kiln feed on clinker formation, and the special considerations for clinker production and behavior. The addition of MSWI ash as cement kiln feed is beneficial provided it is washed and appropriately controlled below 8% to reduce deleterious phase composition.

Reducing unplanned downtime using Predictive Maintenance (PdM)

Maintenance is one of the essential aspects that contribute to keep production process continue to operate and reduce unplanned downtime. In the cement industry, especially kiln area, unplanned downtime can cause not only low availability but also high maintenance costs due to unplanned demand for spare parts and the need for labour to complete unplanned downtime, hence the right method of maintenance is needed. One of the strategic maintenances could be applied is Predictive Maintenance (PdM). Among others maintenance strategy, PdM provides more accurate task due to real time condition monitoring of equipment based on sensors obtained from server data. In this paper, Mahalanobis-Taguchi System (MTS) is applied to provide reliable multisensory analysis and real-time decision making. MTS includes 1) fuses data from multiple sensors into a single system level performance metric; 2) extends MTS by providing a single tool for fault detection/diagnostic, isolation, and prognostic; and 3) offers a systematic way to determine the key parameters following with fault reducing analysis. Multi-sensor data in the kiln used in this research are speed motor main drive, Pfister Coal feed, kiln feed, speed motor IDFAN1, speed motor IDFAN2, speed motor EPFAN. Based on the MTS calculation, the normal data values are obtained from each sensor data. This method is also used to detect, identify, and classify failures based on tests from scheme data. The proposed diagnostic and prognostics scheme from this paper are useful for guiding the company to predict the failure as well as the maintenance schedule then it will increasing the availability from 80% to 90% by reduce the unplanned downtime.

Parametric Studies of Cement Production Processes

The cement industry is one of the most intensive energy consumers in the industrial sectors. The energy consumption represents 40% to 60% of production cost. Additionally, the cement industry contributes around 5% to 8% of all man-made CO2 emissions. Physiochemical and thermochemical reactions involved in cement kilns are still not well understood because of their complexity. The reactions have a decisive influence on energy consumption, environmental degradation, and the cost of cement production. There are technical difficulties in achieving direct measurements of critical process variables in kiln systems. Furthermore, process simulation is used for design, development, analysis, and optimization of processes, when experimental tests are difficult to conduct. Moreover, there are several models for the purpose of studying the use of alternative fuels, cement clinker burning process, phase chemistry, and physical parameters. Nonetheless, most of them do not address real inefficiency taking place in the processes, equipment, and the overall system. This paper presents parametric study results of the four-stage preheater dry Rotary Kiln System (RKS) with a planetary cooler. The RKS at the Mbeya Cement Company (MCC) in Tanzania is used as a case study. The study investigated the effects of varying the RKS parameters against system behaviour, process operation, environment, and energy consumptions. Necessary data for the modelling of the RKS at the MCC plant were obtained either by daily operational measurements or laboratory analyses. The steady-state simulation model of the RKS was carried out through the Aspen Plus software. The simulation results were successfully validated using real operating data. Predictions from parametric studies suggest that monitoring and regulating exhaust gases could improve combustion efficiency, which, in turn, leads to conserving fuels and lowering production costs. Composition of exhaust gases also depends both on the type of fuel used and the amount of combustion air. The volume of exit flue gases depends on the amount of combustion air and infiltrating air in the RKS. The results obtained from the study suggest a potential of coal saving at a minimum of about ṁcoal=1263 kg·h−1, which approximates to 76,126 tons per year at the current kiln feed of 58,000 kg·h-1. Thus, this translates to a specific energy saving of about 1849.12 kJ·kgcl-1, with relatively higher clinker throughput. In this vein, process modelling provides effective, safe, and economical ways for assessing the performance of the RKS.

Critical examination of recycled municipal solid waste incineration ash as a mineral source for portland cement manufacture – A case study

Municipal solid waste incineration (MSWI) ash has the potential to be used as mineral feed for portland cement manufacture but is not currently used in this manner in much of the world. A scoping study was performed using samples and data from Florida, US, to assess the potential magnitude of material that may be recycled to create a viable clinker. Results indicate that MSWI ash possesses the elemental ingredients to serve as a partial kiln feed replacement. Large amounts of MSWI can be used based on mineralogy alone, but chloride and alkali content limitations decrease allowable replacement amounts, especially for fly ash. Average allowable replacement percentages that did not exceed standard chloride and alkali limits were 6.4%, 0.33%, and 1.17% for bottom ash, fly ash and combined ash, respectively. MSWI bottom ash may be the preferred material stream in the absence of pre-processing techniques such as washing. The scoping study found that available MSWI ash could supply a large amount of the current kiln feed demand, and a feasibility and cost assessment supports that both MSWI facility and cement kiln operators have justification to pursue this technology with more detailed evaluations.

Risk and performance assessment of cement made using municipal solid waste incinerator bottom ash as a cement kiln feed

To assess the feasibility of incorporating municipal solid waste incineration (MSWI) bottom ash (BA) as a replacement for traditional raw materials in cement kiln feed, an industrial-scale kiln trial was performed. Leach testing and chemical and physical characterization data from a cement product made at a replacement percentage of 2.8% by mass of kiln feed were comparable to results from ordinary portland cement. The concentrations of constituents of concern in leach tests were generally below risk-based screening levels or of similar or lower magnitude than leachate from control products. Ash-amended cement exhibited greater early age reactivity, and this was reflected in initial mortar compressive strength results; ultimate compressive strength results were higher in the control mortar. The ash-amended and control cements were similar in characteristic, but quantitative x-ray diffraction results reveal differences in alite and aluminate formation during the clinker formation process.

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.