Rotary Kiln Research Articles

Large- and Particle-Scale energy assessment of reduction roasting of nickel laterite ore for Ferronickel production via the rotary Kiln-Electric furnace process

• Mineralogical composition and moisture content govern energy consumption. • Dehydroxylation and drying use around one-third of the energy input. • Energy and exergy efficiencies amount to 66.4% and 32.3%, respectively. • Dehydroxylation, drying, and size define intraparticle temperature gradient. Ferronickel is essential in manufacturing austenitic stainless steels, nickel alloy steels, batteries, electronics, and gas turbines, among other crucial products. The Rotary Kiln-Electric Furnace process is a widely recognized pyrometallurgical route for ferronickel production. This paper focuses on the rotary kiln furnace, an intermediate stage in which partially dried minerals convert into calcine, ready for smelting in an electric arc furnace. This paper uses a unique industrial database that contains operation variables and minerals composition of a 180 t h −1 rotary kiln furnace. As a distinguishing feature, this work incorporates the effects of dehydroxylation reactions and uses intraparticle energy analysis to gain further insights into the reduction roasting process. Goethite and serpentine dehydroxylation reactions consume around 18% of the energy input of the rotary kiln furnace. Flue gases and shell losses represent around 25% and 8% of the energy input, respectively, while the vaporization of free moisture consumes nearly 15% of the energy input. The rotary kiln furnace shows energy and exergy efficiencies of 66.4% and 32.3%, respectively, leaving room for waste heat recovery. Particles with surface-to-center distances lower than 5.0 mm could behave as isothermal, while coarser particles could present significant temperature gradients. These results can assist in optimizing operating conditions and provide insights into the thermal effects of the ore mineralogical composition.

The effect of thermal insulation of the lining on the heat exchange of rotating apparatuses

Rotary kilns are used in many industries to process bulk raw materials. In the building materials industry, rotary kilns are widely used for heat treatment. However, the fuel utilization factor in rotary kilns is extremely low. Thus, the bulk of cement clinker is fired in furnaces, the thermal efficiency of which does not exceed 55-60%. Therefore, the task of increasing the efficiency of such units is extremely relevant. In operating furnaces, heat losses to the environment only through the furnace body reach 20-25% of the total heat of combustion. In this case, one of the main factors determining the thermal efficiency of furnace operation is the value of thermal resistance of lining.
 The aim of the work is to study the evolution and temperature changes in the rotary kiln lining made of shaped refractory to reduce heat losses to the environment and improve the efficiency by increasing the thermal resistance of the lining. The increase in thermal resistance is achieved by changing the shape of the refractory by creating appropriate cells and introducing additional fibrous insulating material into them.
 A mathematical model and software have been developed and numerical calculations have been carried out to determine non-stationary temperature fields in the lining with a thermal insulating element and to substantiate the choice of an appropriate thermal insulating fibrous material.
 Analyzing the calculation results, it is possible to conclude about the expediency of using a lining with increased thermal resistance. The use of this technical solution makes it possible to reduce heat losses through the housing by 18-24%, to increase the amount of transferred material in the working zone by 1.5-8% due to the creation of an appropriate temperature field in the working volume, and to reduce the mass of the lining and the furnace as a whole. and increase the energy efficiency of the thermal unit.
 The presence of cells with additional thermal insulation contributes to the emergence of thermal pulsations having oscillatory character and affecting the intensification of heat and mass exchange processes, which in general contributes to the performance of the thermal unit.
 A significant advantage of this method is also the fact that increasing the energy efficiency of the furnace does not require additional fuel consumption, increasing the temperature or increasing the enthalpy of the combustion products.

Simulation of direct separation technology for carbon capture and storage in the cement industry

This research investigated the application of the direct separation reactor (DSR) to the cement industry to capture a large portion of the process-derived CO2. The case herein assumed a DSR fuelled by natural gas, and downstream rotary kiln with a typical coal- and refuse-derived fuel blend. A range of key performance indicators were assessed with these compared to a baseline plant simulated with identical assumptions. This research found that the DSR has the potential to capture up to 58–68% of CO2, reducing net direct emissions from production to around 0.17–0.21 tCO2/tcmnt. This can be achieved with a minimal penalty to thermal duty (+8%) and modest increase in electrical requirement (+30%). Overall, this work calculated a cost of CO2 capture cost between £39-53/tCO2. Promisingly, these results were achieved without rigorous process optimisation, and there are many avenues to further improve the performance of the DSR.

Eco-friendly belite cement from crude calcareous oil shale with low calorific value

Many countries have resources of calcareous oil shale with low calorific value that are unsuitable for energy production. The chemical composition of calcareous oil shale is similar to that of Portland cement clinker. This study aimed to maximize the replacement of raw materials in clinker production with calcareous oil shale, while maintaining standard quality characteristics. Utilization of calcareous oil shale in raw state can partially replace both fuel and other raw materials. In this research, belite-rich Portland cement clinker was produced and studied in the laboratory. Grinding time and sulfate content were optimized and cement was prepared. The cement was investigated and its compliance with standard requirements was tested. We showed that oil shale can replace up to 76 % of raw materials in clinker manufacturing, which is sufficient for calcination and final burning in a rotary kiln. This means that oil shale can partially replace fuel, reducing CO2 emissions during clinker production.

CFD modeling of petcoke co-combustion in a real cement kiln: The effect of the turbulence-chemistry interaction model applied with K-ϵ variations

Abstract Using alternative fuels (AF) in industry high consuming energy where fossil fuels are largely consumed may be a great solution to decrease CO2 emission and cost production. Or, when using these alternative fuels, the combustion may be difficult to control regarding the different components of AFs compared to fossil fuels. In this case, the use of the computational fluid dynamics CFD tools is a great solution to predict the AFs combustion behavior. This paper represents a computational study of petcoke and olive pomace (OP) co-combustion in a cement rotary kiln burner, established on the commercial CFD software ANSYS FLUENT. This study presents a useful key to choose an adequate simulation model that well predicts co-combustion problems. The performance of the K-ϵ turbulence models varieties (standard, Realizable, and Re-Normalization Group) combined with the hybrid finite rate/eddy dissipation model and the simple eddy dissipation model for predicting the co-combustion characteristics was investigated. The particle phase solutions are obtained using the Lagrangian approach. The performance of the mentioned model was evaluated based on the mesh accuracy, convergence time, temperature shape, and important chemical elements concentration. The predicted values of species concentrations and temperature are compared to the results obtained from the real case study and available literature. The standard K-ϵ model combined with the hybrid finite rate/eddy dissipation model gives the best results and the lower computational resources required for the 2-D model realized.

СЖИГАНИЕ RDF-ТОПЛИВА С ИСПОЛЬЗОВАНИЕ КИСЛОРОДНОГО ДУТЬЯ

The cement industry has unique opportunities to address the issues of utilization of manmade raw materials and municipal waste. The problem of using alternative fuels in the technological process of cement production is usually due to their low calorie content. The above calculations show the possibility of using RDF fuel as part of a mixed fuel when it is burned under conditions of an increased oxygen content in the air. Reducing the volume of combustion products increases the temperature of the torch, which increases the productivity of the cement rotary kiln, mixed fuel can be used in both low – and high-temperature zones of cement kiln units with an optimal ratio of components. There are restrictions on increasing the concentration of oxygen in the air, due to a decrease in the actual combustion temperature of the fuel due to the reverse reactions of the decomposition of combustion products and violations of the high-speed modes of operation of suspension heat exchangers. In addition, an increase in oxygen in the air significantly reduces the thermal efficiency of the clinker cooler as a result of the increase in excess air volumes. The use of RDF fuel in the optimal ratio allows replacing up to 42 % of natural gas.

Returning Electrostatic Precipitators to the Fe-Ni Production Process

Abstract in English The process of frying the Fe-Ni charge in rotary kilns inherently produces large amounts of process dust, which rotary kilns clean out through the use of electrostatic precipitators [1]. One kiln contains two sections of electrostatic precipitators as a safety mechanism [1]. Electrodes installed in the sections produce electric fields when electricity passes through them, and ionize the dust. The timing of the process must be coordinated carefully, and these electrodes are struck with hammers and occasionally shaken, generating quantities of dust which are then collected in a snail dust conveyor, then returned to the production process and recycled. In addition, a smaller amount of dust is derived from the gas chamber, which returns to production without entering the cleaning process in the electro filters. The difference between the two types of dust is their granulation size [1]. We conducted the research during the years from 2017 through 2020, calculating the components of the rotary kiln process. Here, we present a linear equation as a result of the ratio of calcine and electrofilter dust.

Combustion Condition Recognition of Coal-Fired Kiln Based on Chaotic Characteristics Analysis of Flame Video

Keeping combustion stable and detecting unstable states in time is crucial for coal-fired furnaces such as rotary kilns, boilers, and oxygen furnaces. Because of the interference and complex conditions in the industrial field, recognition of combustion conditions by vision analysis is difficult. In this article, we propose a robust nonlinear dynamic system analysis-based approach for combustion condition recognition by extracting chaotic characteristics from a flame video. We first discover chaotic characteristics in the intensity sequence extracted from a flame video of coal-fired kilns, and then we further find that the underlying chaos rules differ between combustion conditions. Based on this finding, we design a set of trajectory evolution features and morphology distribution features of chaotic attractors for combustion condition recognition. After reconstructing the chaotic attractors from the intensity sequence of a flame video by phase space reconstruction, the quantified features are extracted from the recurrence plot and morphology distribution and put into a decision tree to recognize the combustion condition. The experimental results on real-world data show that the proposed method can recognize the combustion condition in coal-fired kilns effectively and promptly. Compared with other methods, the recognition accuracy is improved more than 5%.

Numerical prediction of rotary-kiln foundation temperature at an early age

The hydration heat confined to the core of the mass concrete during the hydration reaction causes a temperature rise and irregular temperature distribution in the concrete. High temperatures in concrete cause Delay Ettringite Formation (DEF) that cause damage several years after pouring, especially if the concrete is in an acidic environment. The uneven temperature distribution causes thermal stresses that can initiate cracks in the concrete surface. This article discusses a prediction of temperature distribution inside a mass concrete used as a rotary kiln foundation. We measure the heat of hydration of the concrete sample using an adiabatic calorie meter and derive the heat of hydration equation from the measurement data. The hydration heat was used in numerical calculations to obtain the temperature distribution, maximal temperature and temperature differential. The numerical calculation shows that the maximum foundation temperature was 64.01 0C. This temperature is still below the limit temperature for the occurrence of Delayed Ettringite Formation (DEF). The core region has the highest temperature, while the surfaces have the lowest temperature. The difference between the highest and lowest temperatures is 37.40 0C. However, the temperature differential exceeds the safe limit, 20 0C, so heat treatment to prevent cracking needs to be done.

Numerical simulation of pulverized coal combustion in rotary kilns with different oxygen concentrations

ABSTRACT In the present study, CFD were used to investigate the effect of a new type of rotary kiln on the velocity field, temperature field, material component distribution, and NOx concentration distribution in poor oxygen (18% O2), normal oxygen (21% O2), oxygen-enriched (24% O2, 27% O2, 30% O2) and full oxygen (100% O2) combustion conditions. The reliability of the simulations was demonstrated by grid independence and the thermal calibration data of the cement plant. The results revealed that the dual recirculation zone could strengthen the burner’s stabilizing effect. The local low-temperature zone near the burner could prolong the burner nozzle’s service life. Furthermore, the increase in oxygen concentration would change the flame length; the flame length under oxygen enrichment and full oxygen were significantly shorter than that under oxygen depletion. The highest temperature in the kiln was directly proportional to the oxygen concentration. The average temperature changes were relatively smooth, resulting in poor combustion uniformity in the kiln. The maximum temperature of poor oxygen combustion below 1730 K is not conducive to the intensified production of clinker. Full oxygen combustion can maximize the combustion temperature in the kiln and is accompanied by a significant increase in CO2 and thermal NOx concentration. As the oxygen concentration increased from 21% to 27%, the temperature in the kiln rapidly increased, and NOx slowly increased; when the O2 concentration was greater than 27%, the temperature slowly increased, and NOx rapidly increased. Therefore, oxygen-enriched conditions should be controlled by 27%, and the NOx emission reduction effect would be more obvious.

Cost Saving of the Explosive Waste Incineration Process via an Optimal Heat Exchanger Network.

Explosive waste is very dangerous, and it should be incinerated under safe conditions. Currently, a rotary kiln is used to incinerate explosive waste; however, it creates air pollutants such as NOx more than the government regulation (90 ppm). To this end, the fluidized bed was suggested, and previous study showed that it could be a new-generation incineration method since it creates NOx less than regulation. Despite impressive results and many approaches to reduce NOx emissions, it is still insufficient to apply the explosive waste incineration process. This is because this process has been studied only for NOx emissions so far. Therefore, in this study, the heat exchanger network (HEN) was grafted and optimized to save the energy used in the process as much as possible based on the operating condition from previous study, which can emit the minimum NOx. As a result, it was possible to save 44% of the total cost compared to the existing method without changing the operating conditions. This result is meaningful in that it is important not only to optimize the design condition of the reactor but also to apply the HEN which will be effective to save the process cost.

Sustainable Systems for the Production of District Heating Using Meat-Bone Meal as Biofuel: A Polish Case Study

The developed production of heat (steam) by Farmutil Company enables use of renewable energy from biofuel meat-bone meal which is incinerated in rotary kilns utilising vapours and odours from its production, instead of natural gas, to ensure Farmutil’s own needs for heat. The transformation of existing district heating in Piła city (currently using coal) into a fourth generation district heating system was proposed, predicting the use of heat (hot water) after combustion of biofuel meat-bone meal as district heating in the city of Piła. The maximum possible surplus amount of heat that can be produced at Farmutil exceeds the needs for the district heating demands of the city of Piła (860,200 GJ/y) by 53.2% at a meat-bone meal burning scale of 150,000 t/y. The use of 52,000 t/y of meat-bone meal for district heating production also results in an increase in incomes through the sale of hydroxyapatite ash from its combustion, amounting 1.638 million EUR/y. The closure of the coal-fired heating plant eliminates the consumption of 44,000 t/y of coal and the need to pay CO2 emission permits amount to over 5.588 million EUR/y.

Development of Ammonia Emission Factor for Industrial Waste Incineration Facilities Considering Incinerator Type.

In this study, the emission factor and concentration of ammonia from industrial waste incineration facilities were analyzed through actual measurements. The ammonia emission factor was calculated and the difference in ammonia emission factor for each type of incineration was confirmed through the Mann–Whitney U test. As a result of analyzing 279 samples, the NH3 emission factor of the SNCR facility of stoker types was 0.012 kgNH3/ton, and the NH3 emission factor of the SNCR facility of the rotary kiln methods was 0.014 kgNH3/ton. Additionally, the NH3 emission factor of this study was higher than the NH3 emission factor (0.003 kgNH3/ton) suggested by Kang’s study (0.009 kgNH3/ton) and EMEP/EEA (2006). There is a need to develop an NH3 emission factor that takes into account the characteristics of Korea, since it is largely different from the NH3 emission factor of EMEP/EEA. As a result of statistical analysis of the stoker type and the rotary kiln method, the null hypothesis that there is no difference between each type was adopted (p-value > 0.05), indicating that there was no statistical difference in the ammonia emission factors of the stoker type and the rotary kiln type.

Investigation into the coal-based direct reduction behaviors of various vanadium titanomagnetite pellets

The reduction behaviors of fired vanadium titanomagnetite (VTM) pellets must be fully ascertained for the effective utilization of VTM concentrates via the coal-based rotary kiln direct reduction-electric furnace smelting process. This paper investigates the effects of the reduction conditions on the reduction behaviors of three types of fired VTM pellets, i. e., Pellets 1, 2 and 3 assaying 13.02%, 11.70% and 5.25% TiO2, respectively, as well as the differences among their reduction behaviors. The results indicate that the highest metallization degree of Pellets 1, 2 and 3 increases sequentially when fully reduced at high temperature for long duration. Pellet 1 shows a good resistance to volume swelling under any reduction conditions, while both Pellets 2 and 3 exhibit the abnormal volume swelling during reduction, with the maximum volume swelling up to 43.78% and 36.45%, respectively. The compressive strength of reduced pellets of Pellet 1 is about 1000N/pellet, whereas below or only close to 500N/pellet for Pellets 2 and 3. Mechanism analysis shows that the minerals compositions and microstructure of fired VTM pellets have great effect on their reduction behaviors. Moreover, the reduction behaviors of fired VTM pellets can be improved by addition of ordinary magnetite in the pellet feeds.

The Aerodynamics of an Iron Ore Pelletizing Rotary Kiln

This paper summarizes more than a decade of systematic studies of the flow field in an iron ore pelletizing rotary kiln using computational fluid dynamics (CFD) on simplified models of a real kiln. Physical, laser-based experiments have been performed to validate part of the numerical results. The objective is a better understanding of the kiln aerodynamics and, by extension, its effect on the combustion process. Despite all of the simplifications regarding the models studied in this project, the results show the importance of correctly predicting the flow field in order to optimize the combustion process. Combustion simulations revealed that the heat release from the flame does not affect or change the flow field in any significant way; the flow field, however, governs the flame propagation and affects the combustion process by controlling the mixing rates of fuel and air. Using down-scaled isothermal water models for investigating kiln aerodynamics in general and mixing properties in particular is therefore justified. Although the heat release from the flame cannot be accounted for in isothermal models, valuable implications regarding the real process can still be gained. To better model the actual process numerically, more advanced submodels for both the combustion and especially the flow field are needed. The complex flow field in this type of rotary kiln requires a careful choice of turbulence model to obtain accurate simulation results.

The effect of strengthening thermal fragmentation by rotary kiln on sulfur distribution of fragmentation char with low-rank coal

Thermal fragmentation of low-rank coal was generally viewed as a negative effect. Actually, the thermal fragmentation had a positive effect on the pyrolysis desulfurization of low-rank coals, and it is expected to be a new way to realize the desulfurization of large-size char. A fixed bed pyrolysis device and rotary kiln pyrolysis device were used to investigate the effect of pure thermal action and thermo-mechanical action on the sulfur distribution in thermal fragmentation char of lignite and sub-bituminous coal at 300–900 °C. The intervention mechanism of thermo-mechanical strengthen thermal fragmentation on low-rank coal with different coalification degrees was obtained. For lignite, the non-sulfur components were more fragmented than the high-sulfur components due to thermo-mechanical action at the low-temperature stage. Fragmentation of high sulfur components dominated thermal fragmentation at the high-temperature stage. For sub-bituminous coal, conjoined structures and plastic layer hindered the fragmentation of sulfur-containing components by pure thermal action. The thermo-mechanical action under rotary kiln pyrolysis was helpful for the fragmentation of the conjoined structure and the separation of the char and plastic layer, thereby reducing the Fe-S minerals and organic sulfur content of the large-size char. The difference in organic sulfur caused by thermo-mechanical action is mainly due to the fragmentation of sulfone components.

Investigations of the effect of unburnt pulverized coal on the deposit formation mechanism in a rotary kiln for fluxed pellet production

The deposit phenomenon is frequently observed and could prevent the smooth running of the production of fluxed iron ore pellets via the coal-fired grate-kiln process in China. This study investigated the effects of unburnt coal on the deposit formation mechanism in a rotary kiln. The experimental results indicated that the unburnt coal significantly contributed to the deposit formation. The CaO and SiO2 contents of silicates in the deposits increased as the degree of fuel conversion increased, while the content of iron oxides decreased. The locations of the chemical composition of bonding phases in the SiO2-CaO-Fe2O3–10%Al2O3–5%MgO phase diagram moved to a lower melting point. The calculated proportions of liquid phases of the bonding phase showed a trend of increasing as the amount of unburnt coal increased. In summary, the unburnt coal caused a change in the chemical composition of the bonding phases, promoting deposits in the rotary kiln for fluxed iron ore pellet production.

Deeper Understanding of the Lithiation Reaction during the Synthesis of LiNiO2 Towards an Increased Production Throughput

Efficient manufacturing of cathode active materials (CAMs) for Li-ion batteries is one key target on the roadmap towards cost reduction and improved sustainability. This work deals with a two-stage calcination process for the synthesis of LiNiO2 (LNO) consisting of a (partial) lithiation step at moderate temperatures and short dwell times and a subsequent high temperature crystallization to decouple the chemical reactions and crystal growth. The use of an agitated-bed lithiation using the rotational movement of a rotary kiln setup shows beneficial effects compared to its fixed-bed counterpart in a crucible as the lithiation reaction is faster under otherwise comparable conditions. The temperature profile for the agitated-bed process was further optimized to avoid the presence of needle-like LiOH residuals in the intermediate product indicative of an incomplete reaction. The partially-lithiated samples were subjected to a second calcination step at a maximum calcination temperature of 700 °C and afterwards revealed comparable physico-chemical properties and electrochemical behavior compared to a reference sample made by a standard one-stage calcination. In a simplified model calculation, the proposed calcination concept leads to an increase in throughput by a factor of ∼ 3 and thus could embody an important lever for the efficiency of future CAM production.

Static and dynamic characteristics of rotary kiln reactor during processing of biomass and municipal solid waste

The behavior of five types of material (wood pellets, agro pellets, over-sieve fraction (OSF), willow chips and alder chips) in rotary kiln reactor was tested. Basing on the obtained experimental results, the empirical mathematical models were validated to predict mean residence time (MRT). The best fitted correlation generated mean absolute error at level of MAE = 9.4%. Regarding dynamic characteristics, the simplified approach of “first-order + dead time” was successfully applied to model the dynamic characteristic of rotary kiln reactor in terms of solid phase mass flow rate. The characteristic parameters of dynamic model, i.e. τ, min and Θd, min, were determined for every case. Time constant, τ, was in the range of 5.8–34.3 min, whereas dead time, Θd, was in the range of 0.001–73.2 min. Finally, a simplified model to estimate the time (i.e. 3 × τ + Θd) necessary to obtain steady-state conditions in terms of mass flow rate in rotary kiln reactors was proposed.

Thermochemical Modeling Factors in Roasting Pre-treatment using a Rotary Kiln for Efficient Vanadium Recovery

본 연구에서는 Rotary kiln(RK)을 이용하여 바나듐 염배소 전처리시 적정온도를 유지하기 위한 열화학적 모델링 관련 인자에 대해 논의하였다. 관련 모델 메카니즘은 열화학 관련 반응속도모델, 열수지 및 열전달 등이며 이를 통해 rotary kiln내 온도분포를 직관적으로 추정할 수 있다. 이러한 작업을 통해 최적 염배소 온도인 1000 °C(또는 약 1273 K) 근방을 kiln내에서 장기간 유지하는 것이 관건이다. 본 연구에서는 탄화수소(천연가스) 연료연소 및 광석 산화반응으로부터의 발열과 광석으로의 복사열전달 등을 산정하였다. 또한 열화학 측면에서 Rotary kiln내 적정 배소온도구역에서의 온도구배 완화를 위한 방안을 제시하였다.