Numerical simulation of heat transfer during production of rutile titanium dioxide in a rotary kiln

Ding

et al. 2021

Metals

The reduction process inside the ore pre-reduction rotary kiln involves a series of physicochemical reactions, and in-depth understanding of the reduction behavior is helpful to improve the product quality and productivity. This paper reports a three-dimensional steady state mathematical model based on computational fluid dynamics, which considers heat transfer, mass transfer and chemical reactions inside the rotary kiln. A user-defined functions (UDFs) program in C language is developed to define physical parameters and chemical reactions, and calculate the heat and mass transfer between freeboard and bed regions. The model is validated by measurement data and is then used to investigate the detailed information inside the rotary kiln. The results show that there is a temperature gradient in the bed, which is maximal near the kiln tail and decreases gradually as the reduction process progresses. The result also confirms that the reduction of FeO to Fe is the limiting step of the whole reduction process because this reaction requires a higher reduction potential. Furthermore, the influence of C/O mole ratio and fill degree are analyzed by comparing the average bed temperature, reduction potential and metallization ratio.

Section: Numerical Methods and Boundary Conditionmentioning

confidence: 99%

Numerical Analysis on Characteristics of Reduction Process within a Pre-Reduction Rotary Kiln

Ding

et al. 2021

Metals

“…However TiO(OH)2, TiOSO4•H2O and TiOSO4 do not, so they have to be user defined. Density and specific heat capacity values available in the literature [35] are incorporated into the present model for the components participating at Reactions R1-R5. Two RGIBBS reactors have been implemented for the simulation of the kiln [27], hence assuming that all components involved in the reactions reach equilibrium.…”

Section: Development Of a Process Model For Rutile Tio2 Production Using The Sulfate Methodsmentioning

confidence: 99%

Process Simulation and Life Cycle Assessment of Ceramic Pigment Production: A Case Study of Green Cr2O3

Alifieris¹,

Katsourinis²,

Giannopoulos³

et al. 2021

Processes

This study presents a combined process modeling—Life Cycle Assessment (LCA) approach for the evaluation of green Cr2O3 ceramic pigments production. Pigment production is associated with high calcination temperatures, achieved through the combustion of fossil fuels. Therefore, it is necessary to evaluate its environmental impact with regards to energy requirements and CO2 emissions. Initially, a process model is developed to simulate the final calcination stage of the traditional pigments production process. It is validated against titanium dioxide (TiO2) white production industrial data and adjusted for Cr2O3 production. Three alternative processes are examined: two for pigment grade (PIGM1, PIGM2) and one for metallurgical (MET) Cr2O3. Heat demand and CO2 emissions computed by the developed process models are used as input in the LCA along with upstream data from the literature using a cradle-to-gate approach. The implementation of the LCA has resulted in calculated Global Warming Potential (GWP100) ranging from 7.9 to 12.8 CO2-eq and fossil Primary Energy Demand (PED) between 91.4–159.6 MJ-eq (all referring to 1 kg of pigment production). It is depicted that the biggest part of the emissions originates from the upstream production and transportation of raw materials (contributing up to 96% of total CO2 emissions) and other sources (electricity, production plant, etc.), rather than the examined calcination stage (contributing from 1.3 to 3.5% of GWP).

“…By contrast, in many metallurgical applications the chemical reactions of interest are endothermic, and heat-exchanging counter-current flows are used to provide energy for endothermic chemical reactions. For instance, the production of rutile titanium dioxide in a rotary kiln (Agrawal & Ghoshdastidar 2017), the pyrolysis of aluminium (Marias, Roustan & Pichat 2005), the production of cement (Spang 1972) and the production of silicon in a submerged arc furnace (Schei, Tuset & Tveit 1998) all involve endothermic chemical processes in which heat required for the reaction is provided by a counter-current flow. In these endothermic processes, heat is removed from the system by the reactions.…”

Section: Introductionmentioning

confidence: 99%

“…These effects fundamentally change the behaviour from the classical counter-current exchange studied by Mitchell & Myers (1968). For instance, it is observed by Agrawal & Ghoshdastidar (2017) that once the reactant reaches a critical temperature in the rotary kiln, the energy transferred to it by the counter-current flow is used for the chemical reaction, and the reactant remains at or close to this critical temperature. Similar behaviour is seen in cement production (Spang 1972; Mujumdar & Ranade 2006; Stadler, Poland & Gallestey 2011), with distinct regions of the domain in which different chemical and heat-transfer processes are seen to dominate, and there are critical temperatures at which certain reactions become important.…”

Section: Introductionmentioning

confidence: 99%

Modelling and analysis of an endothermic reacting counter-current flow

Luckins

Oliver²,

Please³

et al. 2022

J. Fluid Mech.

We study the endothermic reaction and flow of a granular solid reactant, where energy for the reaction is provided by a counter-current flow of hot gases through the porous reactant bed. Research into reacting flows typically focusses on exothermic combustion processes. However, endothermic processes are common in the metallurgy industry, including the production of cement, silicon and rutile titanium dioxide. Several common features are observed in experimental and numerical studies of these processes, including critical temperatures of the reactant at which the chemical reaction begins, and regions of the reactor with uniform reactant temperature. Motivated specifically by the processes in a silicon furnace, we analyse a model of endothermic, reacting counter-current flow using the method of matched asymptotic expansions. Assuming the Péclet number in the solid is large, we explore the full range of values for the dimensionless inter-phase heat-transfer rate, finding six distinguished limits. In all limits, we find a diffusive boundary layer in which there is a fast chemical reaction rate due to the high temperatures, analogous to exothermic flame fronts. Outside this region, the counter-current flow is crucial to the chemical processes. For intermediate values of the heat-transfer rate, we find the same qualitative properties as those observed across the metallurgy industry, and we quantify the dependence of these properties on the flow rate and heat-transfer rate. In the limit of large heat-transfer coefficient, we derive the single-temperature limit, in which the solution structure is dependent on the direction of net heat flux through the domain.