Gas Heat Carrier Research Articles

Toward the ultimate efficiency of methane to syngas conversion by partial oxidation: A moving bed reactor with parallel preheating of reactants

The conversion of methane to syngas by partial oxidation combined with steam reforming in a counterflow moving bed reactor is theoretically considered. The conversion proceeds in filtration combustion mode with the non-premixed flows of steam–methane and oxidant gas. The flow of solid granular heat carrier is divided in two subflows used to preheat, respectively, steam–methane flow and oxidant gas flow prior to the reaction. The calculations are performed under assumption of thermodynamic equilibrium established in the reaction products. For the main control parameters – the flow rates of oxidant gas, steam, and solid heat carrier, related to the flow rate of methane – the parametric domain has been determined that provides a highly efficient conversion in the absence of soot in the products. Efficient heat recuperation with the solid heat carrier makes attainable conversion with the oxygen-to-methane molar ratio as low as 0.43. The flow arrangement with separate preheating of the reactants prior to reaction promises a highly efficient method of converting hydrocarbons to syngas or hydrogen.

3D transient CFD study of iron-coke briquettes pyrolysis and quench processes in an optimised gas heat carrier pyrolyser

Iron coke is an emerging alternative material for iron-making blast furnaces. To massively produce iron coke, the industrial-scale gas heat carrier pyrolyser is a suitable reactor, but the present pyrolysis technology requires further improvements to lower energy consumption and CO2 emission. In this study, a transient 3D CFD model is developed to describe the thermochemical behaviours in the industrial-scale pyrolyser. Meanwhile, a DEM model is used to simulate the packing status evolution of ellipsoidal iron-coke hot briquettes in the pyrolyser chamber, which is input as the simulation conditions in the CFD model. The numerical model is validated against the lab-scale and pilot-scale experimental data. The integrated numerical model is then employed to illustrate heating and quenching processes using the recycled pyrolysis gas as the heat carrier. A new concept that utilises recycled pyrolysis gas to quench the hot briquette after pyrolysis inside the chamber is proposed and examined by the numerical model. In addition, the structure optimisation, i.e., adjustment of the gas inlets' layout, is conducted and numerically examined. The simulation results indicate that the present structure of the pyrolyser has some non-uniform temperature zones, such as the upper bed and near-wall areas where the heat is not effectively transferred to the bed like other zones. 10 h of pyrolysis could effectively pyrolysis iron-coke hot briquettes in the chamber, but for the quenching process, 10 h is not able to fully cool down the briquette bed to room temperature. The design of the upper inlet layout could significantly improve the heating and pyrolysis efficiency. It can shorten 14% heating time in comparison with the original lower inlet layout.

Numerical modelling of raw materials atomization and vaporization in a heat carrier gas flow in technical carbon production based on the Euler approach

Previously, the authors of this article proposed a 3D Euler-Eulerian model of raw materials spraying and evaporation in the heat-carrier gas flow in the carbon production reactor. The raw materials' droplets fragmentation and evaporation are considered as the carrier and dispersed phase interaction. The continuous phase is a heat carrier gas whose motion is described by the Navier-Stokes equations. Dispersed phase (droplets of raw material and products of its evaporation) motion is described using a non-uniform convective-diffusion equation for the particle concentration. The model was tested with water as a raw material. In this work, hydrocarbons are specified as raw materials. It is proposed next to solve the inverse problem with the target functional providing zero contact of the unevaporated raw materials with the reactor wall. Then the number of solid coke particles in the final product will be minimal. An analysis is made of the unevaporated raw material area sensitivity to the inlet velocity of the heat-carrier gas flow. This parameter has the most impact on the distribution area of the unevaporated raw materials and is assumed to be varied in the optimization problem.

An integrated experimental and numerical study of iron-coke briquettes' pyrolysis and reduction behaviour in an industrial-scale pyrolyser

Iron-coke is a promising raw material for ironmaking blast furnaces for reducing carbon consumption and can be produced by pyrolysers, but the present pyrolysis technologies should be improved to further lower energy consumption and CO2 emission. In this work, an integrated experimental and numerical study is conducted to investigate the pyrolysis and reduction behaviours of iron-coke briquettes in an industrial-scale gas heat carrier pyrolyser. A lab-scale two-stage tubular furnace is first employed to pyrolyze the briquette samples to obtain the recycled gas components. A DEM model is then used to simulate the packing status evolution of ellipsoidal iron-coke briquettes in the pyrolyser chamber. A CFD pyrolysis model is then used to study the pyrolysis and reduction behaviours of coke briquettes and then evaluate the impact of switching the carrier gas from traditional exhaust gas to recycled pyrolysis gas on the pyrolysis and reduction behaviours. The comprehensive in-furnace pyrolysis and reduction phenomena are illustrated. The simulation results also indicate that using the recycled gas as the gas heat carrier is beneficial to the pyrolysis efficiency and progress of ferric oxide reduction, compared to the exhaust gas. This study is useful for gas heat carrier pyrolyser design and optimisation for efficient iron-coke production.

Simulation investigation of the particle flow behavior in the gas full circulation oil shale retort

3D models of the 300 t/d Gas Full Circulation Retort are developed to investigate the flow behavior of oil shale particles in the retorting process using the discrete element method (DEM). The results show that the flow patterns of oil shale particles gradually change from horizontal to waved along the radius direction in the descending process due to the friction between particles and walls. The cumulative contact energies are mainly concentrated at the top of the center pillar and the bottom half of the three support structures. With the addition of the conical structure for gas-oil mixture gathering and the triangular structures for particle distribution, the oil shale particles distribute more uniformly in the retorting zones. The interaction force among particles decreases obviously under those added structures, which is conducive to the enhancing of the convective heat transfer between gas heat carrier and particles. And the cumulative contact energies on the center pillar and three support structures decrease obviously, which could decrease the abrasion of refractory brick structures of the retort.

РОЗВИТОК КОНЦЕПЦІЇ ПІДВИЩЕННЯ ЕНЕРГОЕФЕКТИВНОСТІ ДУГОВОЇ СТАЛЕПЛАВИЛЬНОЇ ПЕЧІ ШЛЯХОМ УТИЛІЗАЦІЇ ТЕПЛОТИ ДИМОВИХ ГАЗІВ ДЛЯ ПОПЕРЕДНЬОГО НАГРІВУ СКРАПУ

An important factor in improving the energy efficiency of the electric arc steelmaking furnace (EAF) is utilization of the flue gas energy to preheat the initial charge. Implementation of the process in existing EAF requires the measures to synchronize with the carbon monoxide post combustion and to prevent of the toxic PCDD/F formation when conventional scrap heating, which is significantly complicated in a traditional scheme of CO afterburning with a single-stage air inflow through a temperature and concentration factors. The technological basics of medium-temperature scrap preheating by EAF flue gas have been developed and substantiated. Numerical study of carbon monoxide burning thermodynamics and kinetics shown that implementation of two-stage inflow of air into postcombustion chamber for stoichiometric combustion of CO and cooling the heat carrier provides a comprehensive solution of mentioned problems. The ratio of primary and secondary flows 1 to 3.5 provides allowable concentration of carbon monoxide in the ducts; obtaining gas mixture with a temperature of up to 500 °C, which prevents PCDD/F formation; acceptable temperature operating conditions of bag fabric filters of the gas cleaning system within 100 °C regardless of scrap preheating. Numerical simulation of the heat exchange process between the charge layer and the gaseous heat carrier reveal that shredder scrap of standard bulk density 0.9 t/m3 and mass of half EAF capacity can be preheated up to temperature of 450 °C in 18-20 minutes. Given value corresponds to the duration of technological period in the EAF heat cycle, characterizing by comparatively stable emission and maximal temperature of the flue gas flow. Reduction of the scrap fragments bulk density and the average size, as well as increasing the ratio of the heating chamber height to its diameter in the range from 0.7 to 2.0, promotes the heating rate magnification. The technology provides specific energy savings within 20-30 kW.h per ton of steel and can be implemented in existing electric steelmaking shop of the mini-mill without additional CO2 emissions. The payback period for a 50-ton EAF with annual productivity of 400-450 thousand tons of steel is 14-18 months.

Kinetic analysis on premixed oxy-fuel combustion of coal pyrolysis gas at ultra-rich conditions: Selective combustion and super-adiabatic flame temperatures

Oxy-fuel combustion of coal pyrolysis gas has recently been proposed to serve as internal heat source of a vertical low-temperature pyrolysis furnace, in order to make the output pyrolysis gas nearly free of nitrogen and widely useful. To keep the pyrolysis temperature and the heat carrier gas volume unchanged from air combustion to oxy-fuel combustion, the equivalence ratio has to be increased up to 8. To explore the flame temperature and species variation at this ultra-rich condition, freely propagating premixed oxy-fuel flames of a typical coal pyrolysis gas at equivalence ratios of 0.5–10 are numerically studied with detailed chemistry. It is found that super-adiabatic flame temperatures (SAFT) occur at equivalence ratios larger than 3 for the considered pyrolysis gas and the SAFT magnitude is 294 K at equivalence ratio of 8. Due to the high H2 mole fraction (46%) in the pyrolysis gas, preferential diffusion plays a negligible role in the SAFT feature. Global net production of CO and H2 by the rich combustion only occurs at moderate equivalence ratio ranges, which are 1.5–8 and 3–5.5 respectively for the two species. At equivalence ratio of 8, the three fuel components are all net consumed following the mole ratio of CH4:CO:H2 = 1:0.07:0.84. Kinetic analysis reveals three factors responsible for the reaction mechanism change with the increase in equivalence ratio. Firstly, the lack of H-radical and the decrease in temperature result in the disappearance of the H2 production peak in the initial stage. Secondly, HO2 attack to CO prevails and hence contribution of CO oxidation in the initial stage increases. Thirdly, the long lasting OH attack to CO and H2 leads to the weakened CO and H2 production rate in the final stage.

ОСОБЕННОСТИ РАСЧЁТА ТЕПЛОЭНЕРГЕТИЧЕСКОГО БАЛАНСА ДЛЯ ОБЖИГОВОЙ КОНВЕЙЕРНОЙ МАШИНЫ

The work examines the chemical and energotechnological processes of pellet production from fine apatite-nepheline raw materials: moisture removal, carbonate dissociation, taking into account the thermal and technological features of the functioning of roasting conveyor machines. It was established that the same physicochemical processes differ in quantitative characteristics in the process zones of heating, roasting and recovery. The need of the charge for the heat carrier gas for the corresponding zones, the content of carbon dioxide, iron oxide and carbon in dry pellets, which depend on the chemical composition, the degree of carbon dioxide release, iron oxide oxidation and carbon combustion are taken into account. According to the results of the experimental data and depending on the composition of the charge the following characteristics are calculated for each of the zones: heat consumption for limestone decomposition, specific volume of carbon dioxide, heat output during the oxidation of iron oxide, oxygen flow for iron oxide oxidation, heat introduced by carbon dioxide, initial and final heat of heat carrier gas. The mathematical description of heat and power peculiarities of functioning of roasting conveyor machines is proposed. It is based on energy-balance mathematical models and takes into account thermally activated chemical-energotechnological processes, which take place in apatite-nepheline technogenic raw materials during heating

Power and Resourse Efficient Envoronmentally Safe Technology for Processing Dumps of Technogenic Waste From Ore-Dressing and Processing Enterprises


 
 
 This research proposes a systematic approach for the analysis of volumes, physicochemical, granulometric, lithologic and thermal characteristics of waste from ore-dressing and processing enterprises stored in the dumps (tailing dumps) of ore-dressing and processing plants to assess the economic potential of its use in the system of complex power and resource efficient environmentally safe processing including palletizing machines, conveyor indurating machines and ore–thermal furnaces. The obtained results allow the authors to formulate the basic engineering, technological, economic and environmental requirements for complex chemical and power engineering systems of processing technogenic waste from ore-dressing and processing plants, these results make it also possible to define the degree of variability for the characteristics of the waste lots from various dumps. The paper describes the developed intensional and mathematical formulations for the multiscale problem of optimizing chemical and power engineering processes of technogenic raw materials processing in a complex chemical and power engineering system as a problem for discrete dynamic programming. The distinctive feature of this problem is to take into account the spatio-temporal multistage processing in a moving multilayer mass of pelletized raw material, the intensity of the process of internal moisture transfer and the variables for the control flow of the heat carrier gas. It allows increasing power efficiency by intensifying heat and mass transfer processes of multilayer drying, calcination and sintering. The criterion of the efficiency is the minimum cost of electric and thermal energy spent on processing. The obtained results were used to calculate power efficient environmentally safe processing of technogenic waste from ore-dressing and processing enterprises dumps. It was defined that heat and mass transfer processes are intensified, power consumption is reduced and the quality of the finished product is increased in the conditions of optimal power and resource efficient operation for the processing system.
 
 
 
 Keywords: tecnhogenic waste, waste processing, ore-dressing and processing plant, power and resource efficiency, optimization, system analysis, environmentally safety
 
 
 
 
 

Environmental technology for processing waste from mining and processing plants

This research proposes a system approach for the analysis of volumes, physicochemical, granulometric, lithologic and thermal characteristics of waste from ore-dressing and processing enterprises stored in the dumps (tailing dumps) of ore-dressing and processing plants to assess the economic potential of its use in the system of complex power and resource efficient environmentally safe processing including palletizing machines, conveyor indurating machines and ore–thermal furnaces. The obtained results allow the authors to formulate the basic engineering, technological, economic and environmental requirements for complex chemical and power engineering systems of processing technogenic waste from ore-dressing and processing plants, these results make it also possible to define the degree of variability for the characteristics of the waste lots from various dumps. The paper describes the developed intensional and mathematical formulations for the multiscale problem of optimizing chemical and power engineering processes of technogenic raw materials processing in a complex chemical and power engineering system as a problem for discrete dynamic programming. The distinctive feature of this problem is to take into account the spatio-temporal multistage processing in a moving multilayer mass of pelletized raw material, the intensity of the process of internal moisture transfer and the variables for the control flow of the heat carrier gas.

Research of New Cross-Flow Technology with a Gas Heat Carrier for Lignite Pyrolysis.

The adaptability of the gas heat carrier cross-flow pyrolysis process to Huolinhe lignite (0–80 mm) and the influence of the temperature of the heat carrier and moisture of the raw materials on the yield and properties of the pyrolysis products were studied using a 30 t/d cross-flow pyrolysis pilot plant with a gas heat carrier. When the temperature of the gas heat carrier was increased from 750 to 850 °C, the volatiles (Vdaf) produced from the char decreased from 16.81 to 10.57%, the yield of tar (Tard) increased from 73.81 to 81.1% of the Gray-King (G-K) tar yield, and the yield of gas decreased from 1312 to 1205 Nm3/t. When the temperature of the gas heat carrier was constant at 850 °C and the moisture content (Mt) of lignite was reduced from 12.49 to 7.14%, the Vdaf of char declined from 10.57 to 6.59%, the yield of gas was reduced from 1205 to 805 Nm3/t, the calorific value of gas increased from 3.88 to 4.68 MJ/m3, and the Tard increased to 81.56% of the G-K tar yield. The light tar content (boiling point below 360 °C) was more than 60%, and the ash content was less than 0.04%. The cross-flow pyrolysis moving bed could effectively treat full-size lignite, afforded continuous and stable operation, and provided a high oil and gas yield, which provides basic data for further industrial design.

Development and application of a complex model of titanium diboride plasmosynthesis

An integrated multifactor mathematical model of plasmosynthesis of titanium diboride was developed. The model includes 3 submodels: “Plasma generation”, “Evaporation of raw materials”, “Boride formation”. The model provides the implementation of multivariate research and engineering calculations of plasma processing technological indicators of various types of titanium-containing raw materials, industrial products and waste. The convergence of the predicted and practical results for various types of raw materials is 10.4-12.9%. In all cases, lower values of practical data are noted in comparison with the calculated ones, which is due to the influence of non-isothermal heat carrier gas.

ИМИТАЦИОННОЕ МОДЕЛИРОВАНИЕ ПРОЦЕССА СУШКИ ОКАТЫШЕЙ ИЗ ОТХОДОВ АПАТИТ-НЕФЕЛИНОВЫХ РУД

The paper presents a multi-scale mathematical model of a complex multi-level drying process of lumped man-made wastes of apatite-nepheline ores. It takes into account heat-technological peculiarities of the burning conveyor machine, intensity of internal moisture transfer in the shell, negative phenomena of over-wetting of separate horizons of the moving dense multilayer mass of pellets and heat carrier gas. This makes it possible to increase energy efficiency by intensifying heat-mass exchanging multi-layer drying processes. An essential dependence of efficiency of using heat and electric energy from organization of thermal and aerodynamic mode of thermal treatment of pellets from wastes of apatite-nepheline ores on quality of obtained pellets is revealed. According to numerous computational experiments on the developed simulation model, it is shown that when drying a moving multilayer mass of pellets in the drying zone of the burning conveyor machine, moisture is redistributed along the height of the multilayer mass, as a result of which in certain areas the pellets are over-watered.

Pulsation acceleration of drying by means of vibration of the heat carrier gas flow inside the chamber

Pulsation acceleration of drying by means of vibration of the heat carrier gas flow inside the chamber

Vapour-phase conversion of methyl lactate into lactide over TiO2/SiO2 catalyst at the lowered pressure

Now polylactide (PLA) widely use as biodestructive packing material. Usually monomeric lactide produce from lactic acid. Also, methyl (ethyl) lactate could be used for lactide obtaining via its vapour-phase condensation on TiO2/SiO2 catalyst at 2600C in N2 carrier-gas flow. However, at that it is necessary to heat carrier-gas to the reaction temperature. In this communication the results on methyl lactate vapour condensation into lactide with the lowered pressure of 100-150 mbar, without carrier-gas, are presented. Supported TiO2/SiO2 catalyst with 5 wt.% titania content has been prepared by impregnation of silica with Ti(OC4H9)4. After calcination at 5000C prepared catalyst has amorphous mesoporous structure with 335 m2/g surface area and 0.83 сm3/g pore volume. The catalytic experiments were performed in such way. Liquid methyl lactate was dosed into the evaporator (2500C) and further in the flowing reactor (2600C) under pressure of 100 mbar that produced by vacuum pump. Load on a catalyst was varied from 25 to 55 mmol ML/(gcath). Cooled product was analyzed on Agilent 7820A chromatograph and NMR Bruker Avance-400 spectrometer. It was shown that TiO2/SiO2 catalyst provide 74% selectivity towards lactide at 50-53% methyl lactate conversion with lactide productivity of 7.8 mmol L/(gcath) at 2600C/100 mbar. The catalyst stable work is more 80 h. Main impurities are methyl lactoillactate, 1-methoxyethanol and 1,1-dimethoxyethane.

A three-bed six-step TSA cycle with heat carrier gas recycling and its model-based performance assessment for gas drying

To avoid the waste heat exhaust of a gas dryer based on the conventional two-bed five-step temperature swing adsorption (TSA) cycle, we designed and developed a three-bed six-step TSA cycle with heat carrier gas (HCG) recycling. To clarify the impact of the retrofit from the two-bed system to the three-bed system on the gas dryer performance, numerical studies on the three- and two-bed systems were carried out in this work. Firstly, a nonisothermal, nonadiabatic, nonequilibrium mathematical model of the TSA process was established. Secondly, an industrial-scale dryer with electrical HCG heaters was provided for case study, and two concrete cases were studied to examine the effect of regeneration pressure on the energy-saving potential of the three-bed system. Thirdly, the bed profiles and historical curves of the online adsorption and offline regeneration of the two systems were obtained by simulations, thereby the two systems were comparatively analyzed in terms of energy efficiency, drying performance and head loss. Moreover, the economic analysis on the retrofit from the two-bed system to the three-bed system were carried out. In conclusion, the case studies show that, with a comparable drying performance, the three-bed system saved around 40% energy compared with the conventional two-bed system. The economic analysis shows that the additional investment for the retrofit from the two-bed system to the three-bed system is convenient since the payback periods are around one year.

Modelling of the pyrolysis of low-rank-coal briquettes in an industrial-scale gas heat carrier pyrolyzer

Pyrolysis is an effective coal-upgrading method by converting low rank coals (LRCs) to thermal-efficient and environmentally friendly fuels together with many other valuable products. Compared to wall heat pyrolyzer, gas heat carrier pyrolyzer is expected to be more stable in performance. In this paper, a mathematical model is used to describe the multiphase flow related to the pyrolysis of LRC ellipsoidal briquettes in a gas heat carrier pyrolyzer at industrial-scale. The model is validated against the practical measurements in terms of components distribution of gas products. The comprehensive in-furnace phenomena during the pyrolysis are illustrated, in terms of flow, temperature, gas composition, and pyrolysis characteristics. The simulation results indicate that the opposite-positioned gas inlets lead to weak gas flow along chamber centreline, and results in the non-uniform temperature distribution in the bed. The ellipsoidal briquettes in the lower part of bed show a better pyrolysis performance compared to the upper part because of the stronger interphase heat transfer. Then the effects of particle shape on pyrolysis efficiency are examined by comparing ellipsoidal and spherical particles. It is indicated that in the upper bed where the gas velocity is relatively low, the spherical raw coal particles show better pyrolysis efficiency compared to ellipsoidal briquettes. This model provides a cost-effective way to understand and optimise the pyrolysis practice of gas heat carrier pyrolyzers.

ТЕОРЕТИЧЕСКОЕ АНАЛИТИЧЕСКОЕ РЕШЕНИЕ ЗАДАЧИ О СТАЦИОНАРНОМ ДОКРИТИЧЕСКОМ ТЕЧЕНИИ ГАЗООБРАЗНОГО ТЕПЛОНОСИТЕЛЯ В РАЗВЕТВЛЕНИЯХ ТРУБОПРОВОДОВ ТЕПЛООБМЕННЫХ АППАРАТОВ

The aim of the paper consists in obtaining analytical solutions of the problem on current parameters in the flow bifurcations of a gaseous heat carrier in tubes of heat-exchange equipment used in air-space, shipbuilding and other engineering. The investigation method consists in the solution of the equation system of momentum, continuity and power. In the paper there is substantiated a choice of a theoretical model for a current simulation of a gaseous heat carrier in piping bifurcations of heat-exchange equipment with the allowable degree of proximity to an actual current and complexity of essential computations – a thermo-dynamic model of a subcritical, stationary current of compressible gas. There are obtained analytical solutions of the problem on the current of gaseous heat carrier flows in piping bifurcations of heat-exchange equipment used in different fields of engineering, in particular, in aero-space and shipbuilding and so on, whereas earlier took place only numerical solutions of this problem. In this paper the solutions were obtained without application of special functions used at the solution of non-linear and transcendental equations.

Revealing special features of hydrodynamics in a rotor-disk film vaporizing plant

This paper reports the generalized results of computer simulation of physical processes at a rotor-disk film evaporating plant. Optimization of the operation mode cannot be achieved without establishing patterns in the course of physical processes. We have proposed a computer model of hydrodynamics that accounts for all the features, initial and boundary conditions. The results of computer simulations make it possible to adequately assess the effectiveness of using a rotor-disk film evaporating plant (RDFVP) for the concentration of heat-labile materials. We have established patterns in the course of physical processes within a structure of RDFVP by using computer simulation of hydrodynamics in the programming environment ANSYS and applying a k-e turbulence model. The result of simulation is the derived velocity fields of the concentrated fluid (w max =0.413 m/s) and the gas phase (w max =8.176 m/s), as well as the magnitude of values for shear stress τ=0.94·10 -6 Pa. It was established that the gas heat-carrier is characterized by the highly-turbulent flows with maximum values for kinetic energy TKE max =8.985·10 -1 m 2 /s 2 . The reliability of results is ensured by the correctness, completeness, and adequacy of physical assumptions when stating the problem and while solving it using the computer aided design system ANSYS. It has been established that the proposed structure is an effective alternative to equipment for the concentration of solutions. The data obtained could be used when designing heat-and-mass-exchange equipment for the highly efficient dehydration of thermolabile materials

Study of the pyrolysis of solid organic polymers by their heating with metal melt

The kinetics of the pyrolysis of solid organic polymers by their heating with a gas or a metal melt have been studied. The design features of a small-sized pyrolysis unit for organic polymers have been determined. The pyrolysis process on this unit has been experimentally substantiated. The specifics of the processes of “conventional” pyrolysis in the gaseous heat carrier and the pyrolysis of organic polymers in a lead melt have been revealed. It has been shown that the resulting pyrolysis liquid can be used as a feedstock for the production of the expensive organic solvent limonene or synthetic oil similar in properties to domestic crude oil.