Analysis of calcination parameters and the temperature profile in an annular shaft kiln. Part 2: Results of tests (original) (raw)
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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.
Process simulation of lime calcination in mixed feed shaft kilns
2018
Ich erkläre hiermit, dass ich die vorliegende Arbeit ohne unzulässige Hilfe Dritter und ohne Benutzung anderer als der angegebenen Hilfsmittel angefertigt habe. Die aus fremden Quellen direkt oder indirektübernommenen Gedanken sind als solche kenntlich gemacht. Insbesondere habe ich nicht die Hilfe einer kommerziellen Promotionsberatung in Anspruch genommen. Dritte haben von mir weder unmittelbar noch mittelbar geldwerte Leistungen für Arbeiten erhalten, die im Zusammenhang mit dem Inhalt der vorgelegten Dissertation stehen. Die Arbeit wurde bisher weder im Inland noch im Ausland in gleicher oderähnlicher Form als Dissertation eingereicht und ist als Ganzes auch noch nicht veröffentlicht. Magdeburg, den 09.01.2012
Energy and exergy assessments of a lime shaft kiln
h i g h l i g h t s < Is evaluated the energetic and exergetic performance of limestone calcination. < Are described as the main factors affecting the thermal efficiency of calcination. < Fuel combustion and heat & momentum transfer accounts for >40% of irreversibilities. a b s t r a c t Calcium oxide (CaO), commonly known as lime or quicklime, is an energy intensive product. In order to produce lime, vertical shaft kilns are widely used in the lime industry. The objective of this work is to analyze the energy and exergy consumption of the calcination process in vertical shaft kilns, in order to identify the factors affecting fuel consumption. Data on energy and exergy consumption and losses throughout the calcination process are given for two shaft kilns. In the process, the energy efficiency is found to be higher than the exergy efficiency, e.g. 71.6% and 40.8% for the energy and exergy efficiency of one of the kilns. Results also showed that the most irreversible processes taking place in the kiln are the exergy destruction due to fuel combustion and the exergy destruction due to internal heat and momentum transfer both accounting for about 40% of the efficiency loss. Moreover, the main exergy loss through the boundaries of the kiln is the exergy loss with the exhaust gases contributing with more than 10% of the efficiency loss. Improvements on both the energy and the exergy efficiencies can be achieved through a better control of the operational parameters of the kiln (ratio limestone/fuel supply, excess of combustion air, size and size distribution of the limestone fed to the kiln and exit temperature of quicklime flow). The present study proposes a tool for the analysis of energy and exergy utilization of the calcination process in limekilns, and also provides some energy conservation measures.
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.
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.
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.
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.
ZKG INTERNATIONAL
of the fuel in counterflow to the air. In all other types of kiln, and also in firing systems of the energy production industry, combustion of the fuel takes place in co-current flow with the air. In a co-current process, the beginning and the end of the flame are largely predetermined, but in a lime shaft kiln the length and the position of the combustion zone decisively depend on the air excess number and the lump size of the solid fuel. For this reason, the lime shaft kiln must always be operated with air excess numbers of around one, in order to guarantee an adequately long combustion time of the coke.
Determination of optimal burning temperature ranges for production of natural hydraulic limes
Construction and Building Materials
There has been an increasing interest in the reproduction of natural hydraulic limes, as they are considered an appropriate material for conservation and restoration of historic buildings. This study assessed the influence of different calcination temperatures (850–1200 �C) on the mineralogical composition and the reactivity of quicklime, as well as the setting time and the mechanical performance of mortar specimens. The limestone was acquired from a single quarry and contained 8.7% SiO2, 45% CaO. The results of XRPD and slaking reactivity of the produced quicklime confirmed a clear dependency on the calcination temperature. The performance properties of mortars made with the produced lime did not demonstrate a clear relation to the calcination temperature. The experiment confirmed that calcination temperatures from 850 to 1200 �C can be used to produce natural hydraulic lime from the selected limestone. The optimal calcination temperature range from 1000 to 1100 �C is recommended
Calcination thermokinetics of three Brazilian limestones
Cerâmica
Limestone and lime producers inadvertently generate a considerable amount of fine material during their processing, consequently becoming a great environmental liability. As far as the industrial calcination process is concerned, there is still a need for an experimental survey on Arrhenius law parameters, as apparent frequency factor and activation energy, referring to Brazilian limestones. The knowledge of these thermokinetic parameters may contribute to energy saving during the industrial calcination process, as well as for allowing the use of limestone fines in other industrial applications. This study aimed to characterize three Brazilian limestones by focusing on their laboratory-scale calcination using both quasi-isothermal and non-isothermal methods to estimate their kinetic parameters. The non-isothermal method (by thermogravimetric analyses) allowed estimating the activation energy for each limestone through the high calcination rate ranges. However, the kinetic parameters...