Process simulation of lime calcination in mixed feed shaft kilns (original) (raw)
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Applied Thermal Engineering, 2007
The article discusses experimental measurements of the vertical temperature profile and kiln gas composition in an annular shaft kiln for lime burning. The results obtained confirm that calcination of the limestone in the kiln begins at temperatures between 820°C and 830°C. The average heat transfer coefficient from kiln gases to the stones is determined, as well as the calcination distribution within the kiln. Modeling the calcination process in an annular shaft kiln was performed on the basis of the measured temperature profile. The results of this model are in good agreement with those for samples of partially calcinated stones taken from the area of the lower and upper burners.
Simulation of the limestone calcination in normal shaft kilns
This article presents a mathematical process model to simulate the limestone calcination in a normal shaft kiln. The process model comprises a set of ordinary differential equations derived from the principle of mass and energy balance, coupled with a discrete particle model based on the shrinking core model. With the computed axial temperature profiles of the gas and solid the heat loss through the wall as well as the pressure drop is determined. The simulation was done for a shaft kiln with a solid bed height of 14 m and a product quality requirement of a residual CO2 in lime of 0.3%. The throughput of limestone as well as the particle diameter was changed to show the influence of these parameters on the process. The results of this study can be transferred directly in the praxis for design, operation, regulation and optimization of the normal shaft kilns.
Lime Shaft Kilns: Modeling and Simulation
This study presents a mathematical model to predict the heat transfer in a lime kiln. We assume the reaction is not well-stirred. We prove the existence of unique solution of the timedependent problems. We also examine the properties of solution under certain conditions. The time-dependent temperature profiles are obtained through analytical method. It is discovered that to increase the furnace productivity depends on the parameters involved.
Characterization of a dusting lime kiln û€“ A mill study OPEN ACCESS
Nordic Pulp and Paper Research Journal
The white liquor preparation is one of the main purposes of the recovery cycle in a kraft pulp mill and the lime kiln, being the single unit operation handling bulk solid materials, poses particular challenges in the recovery cycle. In this study, the influence of a dusting lime kiln on the preparation of white liquor was studied. The investigation showed that the dusting lime kiln produced a burned lime with a substantial fraction of fines at the expense of the fraction of granules, whereas a clear lime kiln had virtually no fines and more granules instead. Burned lime from both dusting and clear periods were collected and separated into fines and granules. The different fractions were slaked and causticized in a synthetic green liquor. The study found that the fines always delivered a lower effective alkali in the resulting white liquor, and that the particle sizes of the lime mud were always larger than those originating from the granules, implying that the fines were sintered harder. The industrial consequence is that a dusting lime kiln increases the load on the kiln because the yield of effective alkali is lower; it also introduces a greater dead load into the liquor cycle.
A traditional vertical batch lime kiln: thermal profile and quicklime characteristics.
Full scale calcination of high calcium limestone using traditional methods was performed in the batch process Experimental Lime Kiln (ELK). The ELK is equipped to monitor temperature, air flow and gas compositions and also has significant insulation to ensure minimum lateral energy loss during burning. Internal kiln wall temperatures of up to 550oC, and kiln core temperatures of 850oC, within the range of calcium carbonate disassociation have been achieved for several hours with predictable temperature/time gradients. A mixed feed solid fuel : stone ratio of 1:9 was employed resulting in limestone conversion to quicklime of 75% ± 9. The heat balance efficiency is approximately 45%. However, this may not be a useful indicator of overall efficiency of binder production, especially in a open-top batch process traditional kiln. The hydration behaviour of the low-temperature traditional quicklime is more varied than high-temperature commercially produced quicklime, made from the same stone. The low temperature material hydrates more slowly, reaches a lower temperature and maintains a peak temperature plateau for longer than the high-temperature quicklime. The traditional quicklime also produces as much as 50% non-hydrated residue during the tests. This suggests an origin for “lime inclusion” texture in historic mortars. Mortars produced using traditional hot mixing processes are petrographically similar to historic mortars. The recognition of distinctive quicklime microstructures may also provide a diagnostic tool for quality control in small-scale traditional lime production.
Development of Process Simulation Model for Lime Production
2012
Lime production is a process that entail complex material and energy transport and chemical reaction. Efficient lime production processes are realized via well structured design models approach . Simulation of such process design models essentially provides Information on the attractive features and technical limitations of such processes which serves as guide for normal operations. The choice of appropriate descriptive models forms the basis of a valuable simulation of the process of limestone calcination. This work aim at developing a systematic development of process simulation models for lime production via calcinations of limestones . The various transport phenomena and chemical reaction models prevailing in the conversion of limestone to lime in the kiln are presented in a fundamental and systematic manner. The calcination models which forms a layer model for overall kiln design have been simulated over a temperature range of 900 to 1080’C at varying pressures for Jakura and U...
Thermodynamic aspects of the counterflow lime burning process* (part 2)
Zkg International, 2004
Summary: Due to rising fuel costs, the optimization potential of existing lime kilns has become an important question. In the case of counterflow lime kilns - which are dealt with in this work - a balance calculation of the individual zones is necessary.The exact balance calculation of the decarbonisation zone, described in the first section, is crucial. The high-temperature heat requirement of this zone determines the heat consumption of the overall kiln. Practically usable results can only be achieved if realistic data are employed (wall heat losses etc.).The second section primarily deals with the calculation of important material data, calculation results for shaft and rotary kilns and the most important influencing variables for the specific heat consumption.
In parallel with a wide scale program undertaken at University of Mons in collaboration with the Restoration Directorate of Public Service of Wallonia (SPW) concerning the suitability of mortars formulation for heritage conservation works in the Walloon Region, the authors set up a project to improve the understanding of contemporary and ancient lime as a material. This project involves, in a first step, the experimental on-site reconstruction of five lime kilns and, in a second step, series of lab replications based on data collected along the on-site process. Further than facing constraints encountered by ancient builders, the objective of the research concerns the possibility to outline specificities of ancient limes with regard to their mode of production (and eventual related limitations observed with industrial lime products). For their reconstructions, the authors focus their attention on a " short flame " kiln type used in the Walloon Region between roman and pre-industrial periods. They base their approach on results of archaeological excavations, ancient literature and archives, iconography, recent reconstitutions and experiments with craft kilns as well as ethnographic studies. Several limestones are considered as well as different fuels. Every test is recorded and instrumented (from local and manual temperature picking towards permanent survey in strategic parts of the kilns). The laboratory replication is carried out with computer-piloted electrical furnaces where evolutions of temperature collected on-site may be used as input data for imposing a given heating process to the limestone samples. Preliminary comparisons of products obtained with the on-site and in-lab processes allow outlining interesting results as physical and thermochemical outlooks are considered. Further investigations are in progress, namely considering mechanical aspects, mobilizing lime products that are industrially obtained with given limestones.
Modeling of Rotary Kilns and Application to Limestone Calcination
2009
This paper presents the one dimensional modeling of rotary kilns used for energy intensive production processes. Raw material is fed into an inclined rotating kiln and heated by counter current gas flow. Chemical reactions take place in the bed of raw material as well as in the gas phase. Heat and mass transfer between the bed and the gas phase are implemented. Also the heat transfer to the environment is taken into account. As a benchmark, the process of limestone calcination is chosen. Results are compared with computational fluid dynamic simulations.
Modelling of the Lime Kiln at SSAB, Raahe
Linköping Electronic Conference Proceedings
An OpenModelica model of the SSAB Raahe lime kilns has been developed in order to help in formulation of operation strategies and to choose important parameters to measure and monitor. The model is a dynamic simulation model describing the calcination process of limestone in the lime kiln.