Rotary Kiln Furnace Research Articles

Research of Reactions on Ferronickel Laterite by Rotary Kiln Furnace Process

Nickel is an important strategic metal, which is mainly used for the production of a wide range in the production of various anti-corrosion steels. Electric furnace, rotary kiln and smelting is currently the world-wide integration process for the production of ferronickel from nickel laterite ore, despite its high energy consumption. In this study, with the aim of providing some meaningful analysis for the production of ferronickel and reactions formed in the rotary kiln. The samples obtained were analyzed under conditions including reducing parameters (temperature and time) and smelting parameters (CaO, Al2O3 and MgO ratios). The metal content as well as the Ni, Fe, S and P content of ferronickel were taken into account. The results showed that Ni-containing ferronickel from a laterite with 0.88 wt. % Ni during the process in the rotating furnace is characterized by different reactions which have been verified by XRD diffraction.

Iridium Oxide Nanorods Supported on Sb-Doped SnO2 As Highly Active Oxygen Evolution Catalysts for PEM Water Electrolysis

With the increasing installation of renewable energy generation systems such as solar and wind power, efficient energy storage devices are required to overcome the problem of fluctuations in the availability of electric energy. In particular, the splitting of water by electrolysis to produce storable hydrogen and oxygen appears to be one of the most promising approaches for large-scale energy storage. Proton exchange membrane water electrolysis (PEMWE) has received a great deal of attention due to its ability to respond quickly to renewable energy fluctuations and to operate at high current densities. However, a key limitation of PEMWE is the high cost associated with the use of high loadings of noble metal Ir catalysts at the anode electrode, which is necessary due to the slow kinetics of the oxygen evolution reaction (OER). Therefore, reducing the Ir loading at the OER electrode is essential to realize large-scale applications of PEMWE. This requires the development of highly active OER catalysts to accelerate the reaction or reduce the overpotential. Herein, we report a remarkably active OER catalyst of Ir oxide with nanorod-like structure supported on antimony-doped tin oxide (Sb-SnO2), showing an order of magnitude increase in Ir mass-specific activity than a commercial IrOx catalyst at 1.5 V vs. RHE. We also investigated the temperature dependence of the OER activity, as a way to elucidate the mechanism of enhanced catalysis, from both experimental and theoretical perspectives.The Sb-SnO2 support material (Sb dopant content 4 at.%) with fused-aggregate network structure was prepared by flame pyrolysis method.1 The as-prepared support powder was annealed at 700 oC for 2 h in air using a rotary kiln furnace. Sb-SnO2 supported IrOx nanorods (NRs) catalyst was synthesized by a colloidal method.2 The obtained IrOx NRs/Sb-SnO2 powder was heat-treated at 350 °C in N2 atmosphere for 2 h and at 150 °C in 1% H2 (N2 balance) for 2 h. The Ir loading was determined to be 49.3 wt.% by inductively coupled plasma optical emission spectrometry (ICP-OES). The OER activity was evaluated in 0.1 M HClO4 at 25 to 80 oC using the rotating disk electrode (RDE) technique.2,3 From Figure 1a, it can be seen that the Sb-SnO2 support particles present an interconnected network structure, which is considered to be beneficial to enhance the electron conduction and gas diffusion in the electrocatalytic reaction. On the support, the majority of IrOx nanoparticles are shown to have coalesced, forming rodlike structures. Figure 1b shows OER polarization curves (iR-corrected and normalized to the Ir mass) of the IrOx NRs/Sb-SnO2 catalyst compared to commercial IrOx catalyst (TANAKA Precious Metals). It is clear that the IrOx NRs/Sb-SnO2 catalyst significantly outperforms the IrOx reference catalyst over the entire potential range, and the OER onset potential of the IrOx NRs/Sb-SnO2 catalyst is lower. At 1.5 V (Figure 1c), the IrOx NRs/Sb-SnO2 catalyst exhibits a mass activity (MA) of 0.40 A mg-1 Ir, which is about 10 times higher than that of the IrOx reference catalyst. This dramatically enhanced activity makes it possible to significantly reduce the Ir loading on the anode of PEMWE. Experimental observations and density functional theory (DFT) calculations suggest that the nanorod geometry and strong metal-support interactions may play an important role in lowering the energy barrier for the crucial first step of the OER, thereby enhancing the OER activity. Acknowledgement This work was partly supported by the JSPS KAKENHI (23H02059) and by the project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

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.

Improving the rotary kiln-electric furnace process for ferronickel production: Data analytics-based assessment of dust insufflation into the rotary kiln flame

Ferronickel contains 60–80 wt% Fe and 40–20 wt% Ni and is a feedstock for manufacturing stainless steel and other ferrous alloys. The primary pyrometallurgical route to produce ferronickel from laterite nickel ores is the Rotary Kiln-Electric Furnace (RKEF) process. In the RKEF process, minerals undergo calcination and partial reduction in a rotary kiln. Large amounts of mineral dust leave the kiln entrained in flue gases. Dust insufflation is a potential solution in which dust particles enter directly into the burner flame. The aim is that the insufflated dust softens, agglomerates, and finally joins the minerals stream that goes into the electric furnace. We applied data analytics techniques to a 1-year operation database to assess the operation before and after dust insufflation in an industrial rotary kiln furnace. Bootstrapping revealed statistically significant differences in the operation with and without dust insufflation. Principal Component Analysis (PCA) and k-means clustering were used as exploratory techniques. PCA showed subsets of variables that significantly influence the dataset variance, and k-means allowed distinguishing operation conditions for dust insufflation with encouraging results for the calcine-to-fresh mineral and the natural gas-to-calcine ratios. These results pave the way towards successfully implementing dust insufflation in the RKEF process.

Destruction of decabromodiphenyl ether during incineration of plastic television housing waste at commercial-scale industrial waste incineration plants

To investigate the destruction of decabromodiphenyl ether (decaBDE) contained in flame-retarded plastics, we conducted a series of co-incineration tests of plastic television (TV) housing waste at two commercial-scale industrial waste incinerators in Japan, one equipped with a rotary kiln furnace and the other with a stoker furnace. At the former, crushed TV housings containing 5.9% (59,000 mg/kg) decaBDE were mixed at 3.2 wt% with normal industrial waste and incinerated at 1000 °C; at the latter, crushed housings containing 4.9% (49,000 mg/kg) decaBDE were mixed at 3.6 wt% with normal industrial waste and incinerated at 1100 °C. Destruction efficiencies of over 99.9999% were achieved at both plants, and discharge of brominated dioxins and furans was negligible. More than 70% of the total decaBDE output and 90% of the total bromine output were found in the bottom ash and the fly ash, respectively, suggesting that any undecomposed decaBDE was discharged into the bottom ash and that desorbed bromine was concentrated into the fly ash. Our findings indicate that controlled co-incineration is an environmentally sound method for destruction of decaBDE, but attention should be paid to disposing of the bottom and fly ash in a manner that avoids environmental and human impacts.

Study the kinetics involved in solid state reduction of mill scale with lean grade coal and optimization of process parameters involved in reduction through rotary kiln furnace

Abstract Present investigation envisages kinetics involved in solid state reduction of mill scale surrounded by lean grade coal powder in static and dynamic processes. Research aims to evaluate the reduction potential of economically available lean grade coal from Rajasthan in the reduction of mill scale. Experiments were carried out by mixing equal proportion of mill scale and coal and charging into the rotary kiln furnace. The variables studied are time and temperature. The reduction was done at temperatures ranging from 950 °C to 1050 °C. The degree of reduction of mill scale was calculated at 60 to 240 min. The experiments were statistically designed to assess each variable quantitatively and compared. The results indicated an increase in the degree of reduction with time and temperature. With the increment in temperature up to 1000 °C and holding time 240 min, 77.71% of metallization is achieved. The results showed a definite relation between reduction with time and temperature. Using the technique of empirical relation of transformation, the kinetics involved in solid state reduction of iron is studied for the processes. It is empirically calculated that the kinetics of reduction for the process of reduction in rotary kiln using the experimented setup. The Taguchi method, and analysis of variance (ANOVA) for the selected parameters to investigate the major effects and to assess the optimal process parameters show that, temperature is the most significant parameter amongst all whereas the mill scale size is the least affecting parameter. Based upon the analysis the optimized parameters obtained were temperature (at 1000 °C), mill scale to coal ratio (minimum 1:3), time (minimum 180 min), and mill scale size (minimum 425 to 600 µm). The microstructural characterization (XRF, XRD and FE-SEM. FE-SEM) conforms the formation of porous mass due to the solid state reaction between mill scale and coal.

Effects of Furnace Slope and Rotational Speed on the Carbothermic Reduction of Celestite in a Laboratory-Scale Rotary Kiln Furnace

The carbothermic reduction of celestite is the first step in producing many strontium products. The way materials move in the rotary kiln has an essential effect on the carbothermic reduction efficiency as well as the temperature. In this study, the reduction of celestite ore and excess carbon blend in a laboratory-scale rotary kiln was investigated. In the experiments carried out at three different temperatures, the rotational speed and slope of the furnace tube were altered, and their effects on the reaction efficiency were examined. The leachability of the reduced powders and the content of the unburned coke indicated the optimal parameters for the reaction. When the speed was increased to 10 rpm, the powders were more mobile in the stack and could react more easily with the furnace atmosphere. According to the results, celestite can be reduced by carbon at temperatures of 1000–1200 °C, at rates of between 5% and 75%. The maximum reaction yield (75%) was obtained with a slope of 2° and a rotational speed of 6 rpm at 1100 °C.

Beta-glucosidase analysis in dried blood collected on filter paper (DBS), report of a new method applied to the population and patients with suspected Gaucher disease (GD)

Ferronickel contains 60–80 wt% Fe and 40–20 wt% Ni and is a feedstock for manufacturing stainless steel and other ferrous alloys. The primary pyrometallurgical route to produce ferronickel from laterite nickel ores is the Rotary Kiln-Electric Furnace (RKEF) process. In the RKEF process, minerals undergo calcination and partial reduction in a rotary kiln. Large amounts of mineral dust leave the kiln entrained in flue gases. Dust insufflation is a potential solution in which dust particles enter directly into the burner flame. The aim is that the insufflated dust softens, agglomerates, and finally joins the minerals stream that goes into the electric furnace. We applied data analytics techniques to a 1-year operation database to assess the operation before and after dust insufflation in an industrial rotary kiln furnace. Bootstrapping revealed statistically significant differences in the operation with and without dust insufflation. Principal Component Analysis (PCA) and k-means clustering were used as exploratory techniques. PCA showed subsets of variables that significantly influence the dataset variance, and k-means allowed distinguishing operation conditions for dust insufflation with encouraging results for the calcine-to-fresh mineral and the natural gas-to-calcine ratios. These results pave the way towards successfully implementing dust insufflation in the RKEF process.

Respiratory system involvement in Russian patients with mucopolysaccharidosis: Effects of enzyme replacement therapy

Ferronickel contains 60–80 wt% Fe and 40–20 wt% Ni and is a feedstock for manufacturing stainless steel and other ferrous alloys. The primary pyrometallurgical route to produce ferronickel from laterite nickel ores is the Rotary Kiln-Electric Furnace (RKEF) process. In the RKEF process, minerals undergo calcination and partial reduction in a rotary kiln. Large amounts of mineral dust leave the kiln entrained in flue gases. Dust insufflation is a potential solution in which dust particles enter directly into the burner flame. The aim is that the insufflated dust softens, agglomerates, and finally joins the minerals stream that goes into the electric furnace. We applied data analytics techniques to a 1-year operation database to assess the operation before and after dust insufflation in an industrial rotary kiln furnace. Bootstrapping revealed statistically significant differences in the operation with and without dust insufflation. Principal Component Analysis (PCA) and k-means clustering were used as exploratory techniques. PCA showed subsets of variables that significantly influence the dataset variance, and k-means allowed distinguishing operation conditions for dust insufflation with encouraging results for the calcine-to-fresh mineral and the natural gas-to-calcine ratios. These results pave the way towards successfully implementing dust insufflation in the RKEF process.

Factors Affecting the Upgrading of a Nickeliferous Limonitic Laterite Ore by Reduction Roasting, Thermal Growth and Magnetic Separation

There is considerable interest in the development of new processes to extract the nickel from the oxidic nickeliferous laterite deposits, as the global nickel sulphide resources are rapidly becoming more difficult to access. In comparison to sulphide ores, where the nickel-containing mineral can be readily concentrated by flotation, nickel laterites are not amenable to significant upgrading, due to their complex mineralogy. In this paper, firstly, a brief overview of the conventional techniques used to process the nickeliferous limonitic laterites is given, as well as a review of current research in the area. Secondly, a thermodynamic model is developed to simulate the roasting process and to aid in the selection of process parameters to maximize the nickel recovery and grade and also to minimize the magnetite content of the concentrate. Thirdly, a two-stage process involving reduction roasting and thermal growth in either a tube furnace or a rotary kiln furnace, followed by magnetic separation, was investigated. Thermogravimetric, differential thermal and mineral liberation analyses techniques were utilized to further understand the process. Finally, the nickel grades and recovery results were compared to those available in the literature.

Performance Investigation of an Advanced Robust Biomass Gasifier Operation for Drying Process at Hilly Region in India

This work presents a pilot-scale performance study intended at evaluate the achievability and operatability of biomass gasifier specially designed for hilly regions. The operations were carried out with forest wood blocks with around 35% moisture content. The gasifier was designed for 360 kWth downdraft modes operating with air at 15°C as gasifying agent. The designed gasifier system was installed in a green tea processing factory for supplying thermal energy for panning of green leaves. This system has replaced their conventional open wood firing rotary kiln furnace which was an in efficient combustion due to the ambient conditions. A performance study conducted on the gasifier system for their factory’s thermal demand had shown firewood saving of 35% over conventional panning operation. The economics of installation–cum–operation of the gasifier was also found to be acceptable enough the operation results are discussed.

On the use of alternative fuels in rotary kiln burners — An experimental and modelling study of the effect on the radiative heat transfer conditions

In this work, the radiative heat transfer conditions in a 400kWfuel test furnace were studied. The test furnace is a scaled pilot of a rotary kiln furnace used in iron ore pellet production. In particular, the study focuses on the choice of fuel and the subsequent effect on temperature and radiative conditions in the flame. Several co-firing flames of coal and biomass were investigated and also other fuels such as heavy fuel oil and natural gas. The test furnace was used in the experiments, and radiative intensity was measured with a narrow angle radiometer. Detailed radiation modelling was performed using spectral models for gas and particle properties. The results show that all co-firing flames give a shorter radiating flame length. Based on the radiation modelling, it was also shown that the particle radiation dominates the heat transfer from the flames. Due to the high pre-heating temperature of the combustion air (1100°C), the flame temperatures were generally very high. The flame temperature in the natural gas flame was likely around 2000°C while the coal flame temperatures were estimated to 1500–1600°C. The two coals tested, having almost identical fuel specifications, resulted in a substantial difference in the radiation intensity emitted by the flame. This emphasizes the need of direct radiation measurements to evaluate fuel changes in industrial processes that are highly dependent on the heat transfer conditions.

로터리킬른 반응기 설계를 위한 성능해석 모형

A rotary kiln furnace is one of the most widely used gas-solid reactors in the industrial field. Although the rotary kiln is a versatile system and has different size, approach to the reactor modeling can be generalized in terms of flow motion of the solid and gas phases, heat transfer, and chemical reactions on purpose. In this paper, starting from a zero-dimensional model and extending to higher dimension and comprehensive models, overall procedure of the design development of rotary kiln reactors and considerations are presented. The approaches to performance analysis of the reactors are introduced and examples of application cases are presented.

Emission of greenhouse gases from controlled incineration of cattle manure

Greenhouse gas emission is a potential limiting factor in livestock farming development. While incineration is one approach to minimize livestock manure, there are concerns about significant levels of nitrogen and organic compounds in manure as potential sources of greenhouse gas emissions (N 2O and CH 4). In this study, the effects of various incineration conditions, such as the furnace temperature and air ratio on N 2O and CH 4 formation behaviour, of cattle manure (as a representative livestock manure) were investigated in a pilot rotary kiln furnace. The results revealed that N 2O emissions decreased with increasing temperature and decreasing air ratio. In addition, CH 4 emissions tended to be high above 800 °C at a low air ratio. The emission factors for N 2O and CH 4 under the general conditions (combustion temperature of 800–850 °C and air ratio of 1.4) were determined to be 1.9–6.0% g-N 2O -N/g-N and 0.0046–0.26% g-CH 4/g -burning object, respectively. The emission factor for CH 4 differed slightly from the published values between 0.16 and 0.38% g-CH 4/g -burning object. However, the emission factor for N 2O was much higher than the currently accepted value of 0.7% g-N 2O -N/g-N and, therefore, it is necessary to revise the N 2O emission factor for the incineration of livestock manure.

Polycyclic Aromatic Hydrocarbons Formation in Sludge Incineration by Fluidised Bed and Rotary Kiln Furnace

Polycyclic Aromatic Hydrocarbons (PAHs) are typical pollutants arising from incineration. They are produced in any incomplete combustion principally due to inhomogeneities in a combustion chamber. The effects of the afterburning temperature on PAHs formation during sewage sludge incineration are discussed in this paper. Tests were performed inside the area of the wastewater treatment plant of `Bari Ovest' on a demonstrative plant (maximum throughput 250 kg hr-1 of dewatered sludge at 20% solids concentration) equipped with a fluidised bed furnace (FBF) and a rotary kiln furnace (RKF) where sewage sludge was fed, either as it was taken from the dewatering section of the wastewater treatment plant, or previously spiked by different dosages of chlorinated hydrocarbons. Exhaust gases were sampled before the bag filter, where the pollutants can be considered representative of those arising from the process. Parallel sampling of flue gas at the stack was also carried out. In the FBF tests with sludge spiked with high dosages of chlorinated hydrocarbons highest values of PAHs concentrations (>3.9 μg Nm-3) were detected before filtration, when the afterburning chamber was not in use. The operation of the afterburning chamber, at a temperature higher than 900 °C, allows to partially suppress PAHs formation up to values of 0.9—3.2 μg Nm-3. PAHs removal efficiency of the exhaust gas treatment was calculated with a mean value for all the test of 72%.In RKF tests PAHs displayed much lower values before filtration (range 0.04—2.98 μg Nm-3, mean value 0.51 μg Nm-3) probably due to the longer gas residence time in the furnace (>6 s in comparison with values <2 s in fluidised bed furnace). Surprisingly, for RKF tests PAHs removal efficiency of gas treatment appeared quite unstable: some tests evidenced PAHs stripping in the scrubber, where the effluent of the wastewater treatment plant was used. No correlation was observed in RKF tests between PAHs concentration before the bag filter and the temperature of the afterburning chamber.

Dioxins and furans formation in pilot incineration tests of sewage sludge spiked with organic chlorine

The factors affecting polychlorinated dibenzo- p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) formation were studied in sewage sludge incineration tests carried out on a demonstrative plant. The plant includes a circulating fluidised bed furnace (FBF) and a rotary kiln furnace (RKF), operating alternatively. During the tests sewage sludge was spiked with chlorinated hydrocarbons and the operating parameters of the afterburning chamber were varied. PCDD/F were sampled in each test before the bag filter, thus collecting the above contaminants before abatement systems. From the tests it appeared that PCDD/F were always produced in more abundance in the tests carried out by FBF than by RKF. The higher PCDD/F concentrations in the tests by FBF were reached when sewage sludge was spiked with a high dosage of a surrogate organic mixture of chlorinated hydrocarbons and when the afterburning chamber was used only as transit equipment with the burner off. The distribution of the different PCDD/F homologues was compared. P 5CDFs were generally the prevalent fraction, with very few exceptions for the tests by RKF at high temperature of the afterburning chamber. As for FBF tests, it was found that the PCDD/F homologue profile depends on the afterburning chamber temperature.

Influence of organic chlorine on emissions from sludge incineration by a pilot fluidised bed furnace

To demonstrate that sewage sludge incineration could be a safe operation if well conducted and that hazardous compounds could also be disposed of without problems in sludge incinerators plants, a research program has been set up by the Italian Water Research Institute on a demonstrative scale plant where a completely circulating fluidised bed furnace and a rotary kiln furnace can operate alternatively. In this paper results of tests performed by a fluidised bed furnace on sewage sludge spiked with highly chlorinated compounds under different operating conditions are presented. A deep investigation on micropollutants formation has been made at different sampling points: before and after bag house filter, and at the chimney. The experimental data show that concentrations of PCDDs+PCDFs (TE) and of PAHs do not strictly depend on the operation of the afterburning chamber and that a complete compliance with the European and Italian standards on the emissions were always achieved even in the most critical conditions investigated.

Partitioning of Cr, Cu, Pb and Zn in sewage sludge incineration by rotary kiln and fluidized bed furnaces

The behaviour of four metals (Cr, Cu, Pb, Zn) during sewage sludge incineration was studied in eight pilot plant tests performed with a rotary kiln (RK) and a fluidised bed (FB) furnace. To simulate sludge co-incineration with hazardous wastes, in three FB tests feed sludge was mixed with chlorinated organic compounds. Chromium and copper showed similar concentrations both in bottom or cyclone ash and in fly ash, even at high chlorine input and high combustion temperature. In contrast, zinc and lead concentrations in fly ash produced in RK tests are one or two orders of magnitude higher than those in bottom ash. However, not even these two metals showed significant enrichment in FB tests carried out at high chlorine input. The predictive capability of a thermodynamic model was checked by comparing predicted metal volatilisation in the combustion chamber with experimental metal enrichment in the fly ash. Large discrepancies were observed in FB tests carried out at high chlorine content, where Pb, Zn, and Cu are predicted to volatilise in great extent, andin RK tests where zinc volatilisation is not predicted. Likely explanations of these discrepancies are the very short solid residence times in the FB furnace (non equilibrium conditions) and the incomplete mixing conditions in the RK furnace (pyrolysis pockets). From the environmental impact point of view, the pilot tests suggest that sludge incineration with fluidised bed furnace is safer than the one using rotary kiln furnace.

Influence of sludge cake concentration on the operating variables in incineration by different types of furnaces

The influence of cake concentration on fuel consumption, air requirement and flue gas production in incineration of sewage sludge is discussed. Fluidized bed (FBF), multiple hearth (MHF) and rotary kiln (RKF) furnaces are considered as alternatives together with the optional use of an afterburning chamber where exhaust gases are taken at 950°C for 2 s with an oxygen concentration of 6% by volume. It clearly appears that, if an afterburning chamber is used, and total minimum fuel consumption can be achieved at an optimal value of cake concentration (45.9% for FBF and 32.5% for MHF) when autogenous conditions are reached in the furnace and air addition is no longer needed in the afterburning chamber. At higher concentrations, abundant exhaust gas productions, due to the dilution air needed in the furnace, can considerably increase fuel consumption in the afterburning chamber, especially in MHF operation. In the rotary kiln furnace, fuel requirement decreases over the whole range of cake concentration as no conditions for autogenous combustion in the furnace can be achieved.

Nitric Oxide Formation in an Iron Oxide Pellet Rotary Kiln Furnace

ABSTRACT A one-dimensional numerical model was developed to simulate the effects of heat and mass transfer on the formation of oxides of nitrogen (NOx) in a rotary kiln furnace for iron oxide pellet induration. The modeled kiln has a length-to-diameter ratio of approximately seven. The principal mechanism of heat transfer is radiation from the flame, which was described by the net radiation method. The well known Zeldovich mechanism was used to predict thermal NOx generation. Temperature fluctuations in the vicinity of the flame were estimated with a clipped Gaussian probability density function. The thermal energy and mass balance model equations were solved numerically. The model is capable of predicting temperature profiles and NOx production rates in agreement with observed plant performance. The model was used to explore the effects of process changes on the total NOx formation in the kiln. It was concluded that the gas temperature as well as the partial pressure of oxygen in the process gases controls the rate of NOx formation. Lowering the temperature of the kiln gases by increasing the secondary air flow rates requires simultaneously decreasing the pellet production rate in order to maintain the pellet temperatures needed for blast furnace conditions.