Clinker Rotary Kiln Research Articles

Advanced Process Control for Clinker Rotary Kiln and Grate Cooler

The cement industry includes energy-intensive processes, e.g., clinker rotary kilns and clinker grate coolers. Clinker is obtained through chemical and physical reactions in a rotary kiln from raw meal; these reactions also involve combustion processes. The grate cooler is located downstream of the clinker rotary kiln with the purpose of suitably cooling the clinker. The clinker is cooled through the action of multiple cold air fan units as it is transported within the grate cooler. The present work describes a project where Advanced Process Control techniques are applied to a clinker rotary kiln and a clinker grate cooler. Model Predictive Control was selected as the main control strategy. Linear models with delays are obtained through ad hoc plant experiments and suitably included in the controllers' formulation. A cooperation and coordination policy is introduced between the kiln and the cooler controllers. The main objectives of the controllers are to control the rotary kiln and grate cooler critical process variables while minimizing the fuel/coal specific consumption of the kiln and the electric energy consumption of the cold air fan units within the cooler. The overall control system was installed on the real plant, obtaining significant results in terms of service factor and control and energy-saving performances.

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.

Chemical exergy influence in the exergetic analysis of a real clinker rotary kiln

The most energy demanding process in the cement industry is clinker production, carried out in a rotary kiln. Thus, rotary kiln energetic and exergetic analyses are useful tools to reach cement production process improvements. Energetic analysis is based on the first law of thermodynamics and allows one to calculate the heat uses and losses. On the other hand, exergetic analysis is based on a combination of the First and Second Laws of Thermodynamics and allows quantifying process irreversibilities. Some rotary kiln exergy analyses neglect the mass flows chemical exergy in the exergetic analysis, considering only the fuel chemical exergy. In this work, chemical exergy impact on this analysis was evaluated. Pre-calcination effect was also studied. Rotary kiln classical and modern exergetic efficiency considering all the chemical exergy contributions were 55.5% and 41.8%, respectively, while considering just the fuel chemical exergy were 38.2% and 22.6%, respectively. The results showed that it is inadequate to neglect the mass flows chemical exergy, since their contribution in the exergetic analysis was relevant. Furthermore, it was observed that the method adopted in the process efficiency evaluation affects the system interpretation. Considering the modern exergetic efficiency, results showed that, the higher the pre-calcination, the higher rotary kiln efficiency.

Industrial calcination of kaolinitic clays to make reactive pozzolans

This paper presents the results of an industrial trial for the production of calcined clay to be used as pozzolan in cement manufacture. For the trial, a wet-process clinker rotary kiln was modified to process on dry basis the low grade kaolinitic clay used as raw material. The kaolinitic clay deposit was chosen through a screening based on geologic, chemical and mineralogical criteria, and a confirmation of reactivity with an experimental protocol at lab scale. During the calcination trial technological parameters such as rotation speed, fuel pressure and outer temperature of calcined clay were measured and coupled with the reactivity of the samples tested, thus, preliminary estimations of operational parameters can be made. The trial proved that it is possible to produce a reactive pozzolan at industrial scale by implementing small conversions on existing equipment of a typical clinker plant.

Trend modelling with artificial neural networks. Case study: Operating zones identification for higher SO3 incorporation in cement clinker

Instantaneous measurements of process variables are usually not representative of the process effects as a whole when defining the condition of an output sample mainly in case of laboratory analysis. Moreover, process data have considerable dispersion. This leads to uncertainty in input–output time alignment and in variable relationship. This work employs a trend data-based approach to overcome the negative effects of these uncertainties in both tasks variable selection commonly supported by correlation analysis and model identification. Two real case studies using a clinker rotary kiln from a cement plant and a chemical recovery boiler from a pulp mill were used for illustration purposes. More reliable data-driven system representation enhances the comprehension of the underlying system phenomena supporting a more rational basis for decision making.

Real-Time Modelling of Dynamic Behaviour for Clinker Rotary Kilns: <i>Learning from Experiment and Theory</i>

The authors’ objective is to estimate a dynamic behaviour of Clinker Rotary Kiln when the state variables of the process can be measured only at a few locations. These variables (gas, clinker temperatures and clinker mass distributions) are elaborated with the help of heat, pressure and mass balance partial differential equations. The resulting state model, decomposed into five phenomenological zones of CRK, is used as a first step to define a set of Basic Operating Functions. A second step is used to identify a set of Operating Functions. These OFs have also been decomposed into longitudinal distributions of CRK to replace the constant, unknown or unmeasured parameters. Based on the feature of each zone, the OFs are obtained by solving the steady-state model using the standard Newton-Raphson procedure. The CRK is thus characterized by the state variables and intelligent software of the Numerical Estimated Operating Functions and method is proposed to reevaluate the set of the state variables, in adequate space step-size. Consequently, the state variables profiles are linked with the corresponding OFs, which have a direct influence on submitted disturbances for calibration.

Phenomenological Approach to Model a Clinker Rotary Kiln

The objective of this paper is to provide a modeling of parameters of a phenomenological model regarding the dynamic behaviour of the clinker rotary kiln. The study offers a mathematical platform with respect to the process control. For doing so, a general and complete description of the parameters based on phenomenological and dimensional analyses has first been specified. Secondly, a calibration procedure has been set up to find a better way of dealing with the kiln operating parameters. Finally, an application of this approach has been performed from a stationary state of the system.

Modelling of a clinker rotary kiln using operating functions concept

AbstractModelling and parameter identification of complex dynamic systems/processes is one of the main challenging problems in control engineering. An example of such a process is clinker rotary kiln (CRK) in cement industry. In the prevailing models independently of which structure is used to describe the kiln's dynamics and the identification algorithm, parameters are assumed to be centralised and constant while the CRK is well known as a distributed parameter system with a strongly varying dynamic through time. In this work, the kiln's dynamic is described in the form of a state‐space representation with three state variables using a system of partial differential equations (PDE). The structure is chosen so that it can easily be embedded in classical state‐space control algorithms. The parameters of the PDE system are called operating functions since their numerical values vary with respect to different operating conditions of the kiln, to their position in the kiln, and through time. A phenomenological approach is also proposed in this paper to identify the operating functions for a given steady‐state operation of the kiln. The model is then used to perform a semi‐dynamic simulation of the process through manipulating main process variables.

CAD Versus Self-Tuning Control of a Clinker Grate Cooler

A study has been reported on computer identification and control of a Puller clinker grate cooler pilot plant cooperating with a wet-process clinker rotary kiln. Having briefly described the cooling process, its different experimental models have been analysed, both deterministic and stochastic ones. Offline and on-line versions of popular parameter estimation schemes have been applied, i.e. the least squares, correlation, generalised least squares and maximum likelihood methods. A CAD control algorithm based on a constant process model has been firstly inspected. Next, a simple adaptive control strategy based on self-tuning regulation philosophy has been more successfully applied. Taking finaly into account some emergency situations also, we have found that best solution is to properly compromise between the CAD and self-tuning control.