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j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262

www.jmrt .com.br

riginal article

nalysis of synthetic natural gas injection into charcoallast furnace

lisa Pinto da Rochaa, Vagner Silva Guilhermea, José Adilson de Castroa,∗,asushi Sazakib, Jun-ichiro Yagi c

Post-Graduation Program in Metallurgical Engineering, Universidade Federal Fluminense, Volta Redonda, RJ, BrazilEnvironmental Metallurgy Laboratory, Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang,outh KoreaTohoku University, Sendai, Japan

r t i c l e i n f o

rticle history:

eceived 7 January 2013

ccepted 1 February 2013

vailable online 2 August 2013

eywords:

ynthetic natural gas injection

odeling

harcoal blast furnace

a b s t r a c t

Recently, the synthetic natural gas (SNG) has been available for large consumers in the

Brazilian domestic market. The SNG is a suitable fuel with potential use to several pro-

cesses and facilities of the steel industry. This paper investigates the injection of SNG into

charcoal blast furnaces as a substitute for granular charcoal charged from the top and pul-

verized charcoal injections with potential increase of productivity and decrease of specific

CO2 emissions. In order to study the effect of replacement of granular charcoal and injection

of pulverized charcoal the well known Blast Furnace Five Fluid Model (BF-FFM) is applied to

describe detailed phenomena within the process. This model treats the blast furnace as a

five-phase reactor, accounting for gas, lump solids (raw iron ore, sinter, pellets and granular

charcoal), hot metal, pulverized charcoal, and molten slag. The model is based on conser-

vation equations for mass, momentum, energy and chemical species numerically solved

based on the finite volume method (FVM). The SNG has high amount of H2 and strongly

affects the inner conditions of the reactor and only a comprehensive model with detailed

chemical reaction rates can properly predict the inner parameters of the process and hence

furnish useful information to design smooth operational conditions. The simulation results

obtained in this study indicated that smooth operations using SNG up to 25 N m3/t of pig

iron could be achieved simultaneously by increasing the productivity up to 58% and with a

decrease of 40 kg/thm on the granular charcoal charged.

© 2013 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier

of the charcoal blast furnace is a reality for the pig iron pro-

Este é um artigo Open Access sob a licença de CC BY-NC-ND

. Introduction

he main route to produce hot metal in the steel industrys based on the blast furnace-BOF processes using coke and

∗ Corresponding author.E-mail: adilson@metal.eeimvr.uff.br (J.A.d. Castro).

238-7854 © 2013 Brazilian Metallurgical, Materials and Mining Association. Puhttp://dx.doi.org/10.1016ste é um artigo Open Access sob a licença de CC BY-NC-ND

pulverized coal as reducing agent. In Brazil the technology

duction with comparative advantages to furnish pig iron forEAF route. The charcoal blast furnace used to produce pigiron has received special attention due to its intensive use

blished by Elsevier Editora Ltda./j.jmrt.2013.02.015

256 j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262

Table 1 – Characteristics of the raw materials used in this study.

(Mass %) Granularcharcoal

Pulverizedcharcoal (PCH)

C (fixed) 72.2 70.83Volatile matter 22.5 25.80Humidity 2.1 0.01SiO2 1.61 1.10Al2O3 0.15 0.11CaO 1.10 1.58S 0.001 0.0022P (P2O5) 0.01 0.170K (K2O) 0.32 0.40Ash 3.20 2.96

Volatile matterC 75.3 72.00N 6.50 7.35H 14.4 16.50O 3.75 4.15Average particle diameter (�m) – 120True density (kg/m3) 1345 1150Effective particle porosity (−) 0.65 0.85Effective pore tortuosity (−) 0.7 0.9Effective thermal conductivity (W/mK) 0.6 0.6Calorific value (kJ/kg) 31,274 30,162

Synthetic natural gas (SNG) (vol %)

Propane n-Butane Isobutane Propene Trans-butene-2 Isobutene Cis-butene 2 Others

31.8 28.2 13.2 12.8 4.4 3.8 2.8 3.0

Iron bearing sources sinter + slagging agent (%)

Fe2O3 FeO SiO2 Al2O3 CaO MnO MgO H2O

82.6 3.2 4.9 1.2

of biomass as the main energy source. The so-called greenpig iron, however, depends strongly on the international mar-ket, logistics and raw materials costs. Therefore, tremendousefforts have been made in order to reduce the reducing agentrate of the blast furnace, or at least, replace the granular char-coal consumption by less precious materials injected throughthe blast furnace tuyere [1–6] and hence, improve the processefficiency.

Based on this perspective, the replacement of granularreducing agent by pulverized biomass or gaseous fuels is thespotlight of this technology [3–6]. In this study, the combinedinjection of pulverized charcoal and synthetic natural gas(SNG) is analyzed. The composition of charcoal and SNG usedin this study is presented in Table 1. As observed, the charcoalused in this study has very low ash, sulfur and silica quantities,however, volatile matter is usually high and additional oxygenis used. In addition, the technology for injection of pulverizedcharcoal already got maturity and several blast furnaces havebeen continuously operated with pulverized charcoal ratesover 100 kg/thm. However, there is clear limitation for furtherincreases in the injection rates mainly due to the gas and parti-cles flows in the lower part of the furnace and unburned coal orash that can remain in the raceway, which could deteriorates

the permeability of this region leading to unstable operation,although pulverized charcoal injection technology has enteredinto a stage of high technological development [2–4].

4.8 0.2 1.6 1.5

The injection technology of gaseous fuel with high amountof hydrogen has proven the beneficial effects due to low igni-tion temperature and high combustibility, with the advantageof lower investment cost and potential co-injection of higherrates of pulverized charcoal taking the advantage of symbi-otic effects on the raceway to keep stable flame temperature.SNG has high amount of hydrogen and its combustibility isvery high compared with pulverized charcoal. Therefore, thisstudy is focused on the simultaneous injection of pulverizedcharcoal and SNG on a compact blast furnace aiming to clarifythe in-furnace phenomena and show the feasibility of simul-taneous injection.

Several authors have addressed the multiple injections ofcarbonaceous materials into the blast furnace by theoreticaland experimental analysis [1,4–9]. However, only a detailedmathematical model based on fundamental phenomena isexpected to fully consider the important aspects of simul-taneous injection on the inner variables distributions suchas temperature, phase composition and phase flows. In thispaper a mathematical model of the blast furnace is proposedto simulate the blast furnace operation with simultaneousinjection of pulverized charcoal and SNG. The present modeluses similar approach as those presented by Yagi et al. [10],

Austin et al. [11,12], and Castro et al. [13,14], which appliedmultiphase theory to describe the motion, energy and chemi-cal species of each phase inside the furnace.

j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262 257

Inner view of the process

Mesh generationRaceway sector

a b c

ept f

mttdtnbn

anTncwsoore[

2

2

Itmmrh

Fig. 1 – Blast furnace model conc

Although some hybrid models based on discrete elementethod (DEM) have been recently proposed [15–20], the mul-

iphase theory is considered suitable and accurate enougho describe the actual operation of the blast furnace andemands lower computational efforts with high accuracy onhe chemical reaction rates and inter-phase interaction phe-omena. Therefore, the continuum approach is considered aetter tool to evaluate the performance of the whole blast fur-ace process under multiple injection operation [10–15,20–22].

In the present study a detailed model able to take intoccount particular phenomena and mechanism of simulta-eous injection of pulverized charcoal and SNG is presented.hus, this model aims to address new features of the simulta-eous injection of pulverized charcoal and gaseous fuel into aompact blast furnace and study new operation possibilities,hich could contribute to lower the reducing agent con-

umption and suggest new environmentally cleaner processperation techniques. This model differs from the previousnes [10–15] by taking into account new chemical species andeaction rates representing the combustion and flow phenom-na in the whole blast furnace under simultaneous injection6–9].

. Methods

.1. Model principles

n this study the blast furnace process is modeled based onhe transport equations for each phase taking into account

otion, energy and chemical species. The mathematicalodel is three-dimensional and analyses the packed bed

egion within the blast furnace, from the slag surface in theearth up to the burden surface in the throat. Fig. 1 shows

or combined injection analysis.

the modeling concept and in-furnace analysis. Five-phasesare treated: gas (includes SNG species), lump solids (granularcharcoal, sinter, pellets, lump ore), hot metal, slag and pul-verized charcoal. All phases are treated simultaneously dueto mutual interactions, as shown in Fig. 2. Thus, the govern-ing equations of all phases, that form a large set of stronglycoupled non-linear equations, are solved simultaneously. Inthis model, conservation equations of motion, energy andchemical species are considered and coupled with chemicalreactions, phase interactions and physical properties. For thesake of simplicity, all the conservation equations are repre-sented in a compact form, as in Eq. (1).

∂(εi�i�i)∂t

+ div(εi�i�Vi�i) = div(εi��i

grad�i) + S�i(1)

In this equation, � is the dependent variable, expressingthe component velocities for the phase momentum equations,the enthalpy for the phase energy equations and the chemi-cal species for the phase continuity equations, i representsthe phase being considered or the chemical species of eachphase. ε and � are phase volume fraction and density, respec-tively. V and t are phase velocity field and time, respectively.��i

is the effective transfer coefficient which represents effec-tive dynamic viscosity in the momentum equations, effectivethermal conductivity in the energy equations and effectivediffusion coefficient of the chemical species in the chemicalconservation species of each phase. The source terms (S�i

) aredue to inter-phase interactions that can appear through chem-ical reactions, surface interactions and external force [6–22].

2.2. Source terms

The source terms in the conservation equations takeinto account chemical reactions, phase transformations,

258 j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262

Gas

Pulverizedcharcoal

Solid{lump one

+sinter+charcoal}

Hotmetal

Slag

Fig. 2 – Phase interactions considered in this model.

momentum exchange and external forces. The continuityand species conservation equations have mass sources dueto chemical reactions and phase transformations. Enthalpysources arise from inter-phase heat transfer, heat of reactionand sensible heat accompanied with mass transfer due tochemical reactions and phase transformations. The formula-tions for the phase interactions and chemical reactions havebeen published in previous reports [10–15].

This model considers the pulverized charcoal and gaseousfuel injected through a separated lance into the raceway chan-nel. SNG firstly combusts within the tuyere and pre heat thegas stream and particles. The charcoal injected through theblast furnace tuyeres is mixed with the gas stream and, in con-tact with oxygen, combusts partially and the volatile matterevolves in the interior of the raceway and finally almost com-plete combustion in the raceway is achieved. The unburnedpulverized coal or ash continues to react and meltdown whenparticle temperature is higher than the melting temperature.The chemical reaction models for pulverized charcoal andinner particle structure were previously published [6].

2.3. Initial and boundary conditions

The boundary conditions were applied on the boundary of thecomputational domain limited at the bottom by the slag sur-

face, at the top by the burden surface and by the lateral walls.At the top, the gas phase is assumed as fully developed flowwhile solid inflow is modeled assuming no gradient velocity,with the inflow rate given by solid mass consumption due to

chemical reactions and melting. At the tuyere inlet of blast,additional oxygen and pulverized coal are given by their inflowrates.

The blast flow rate is fixed, and pulverized coal and char-coal are iteratively calculated to reach the aimed pulverizedcoal and charcoal injection rates, which are specified at thebeginning of the iterative calculation. The blast temperatureis specified as a fixed value throughout the calculation. Atthe side wall, momentum and mass fluxes across the wallare assumed null while heat transfer is allowed by setting anoverall heat transfer coefficient.

For the gas velocity it is assumed null values perpendicularand tangential to the furnace wall. The solid tangential veloc-ity on the wall surface assumes coulomb attrition law witha specified coefficient of 0.3 and the normal force is calcu-lated using the local solid pressure. The burden distributionis determined by the relative volume fractions of the inletsolids and their average diameter. The numerical method usedto solve the transport equations is based on the finite vol-ume method (FVM) formulated for a general non-orthogonalcoordinate system [23]. The numerical mesh is constructedbased on a body fitted coordinate system which allows accu-rate description of the blast furnace wall shape [23]. To solvethe governing (momentum) equations of continuous phasesthe SIMPLE (Semi-Implicit Method for Pressure-Linked Equa-tions) algorithm is applied on a staggered grid for covariant

projections of the velocities and the numerical coefficients ofthe discretized equations are determined by using the powerlow scheme [15,23–25].

j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262 259

1

0.8

0.6

0.4

0.2

0.5 1.5 2.5 3.5210

1

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00 3

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0.5 1.5 2.5 3.5210 3

Lump ore + Sinter Lump ore + Sinter

Granular charcoal

Lump ore + Sinter

Granular charcoal

Granular charcoal

Lump ore + Sinter

Granular charcoal

Vol

ume

frac

tion

(–)

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Blast furnace radius (m) Blast furnace radius (m)

Blast furnace radius (m) Blast furnace radius (m)

Base Scenario 2

Scenario 4Scenario 3

a b

c d

for t

3

Iaccccaiopsridio

ibtpww

fsdo

Fig. 3 – Burden distribution patterns

. Results and discussions

n this section, the model is applied to investigate new oper-tional conditions with higher injection rates of pulverizedharcoal (PCH) and SNG in order to compare with a basease considering only injection of pulverized charcoal. In thealculation procedure the oxygen injection and the granularharcoal charged are adjusted aiming at obtaining stable oper-tion of the blast furnace. For all cases the oxygen enrichments adjusted to maintain the thermal condition of the lower partf the blast furnace which guarantee smooth operation com-atible with the base case (actual operation conditions). Thecenarios were selected to simultaneously increase the gasate injection and decrease the amount of granular charcoaln the burden with consequent increase in the productivityue to replacement of the burden volume of the charcoal by

ron bearing granular source and the increase of the oxygenn the blast.

The iterative procedure is carried out by smoothly chang-ng the burden pattern until stable operation is achieved. Finalurden distribution pattern is presented in Fig. 3. The opera-ional parameters calculated in these iterative simulations areresented in Table 2. For the base conditions, the model agreedith the actual operation data for a blast furnace of 850 m3 oforking volume.

As can be observed, the productivity of the compact blasturnace process can be largely increased (about 58%) for the

cenarios analyzed. The raceway temperatures are increasedue to the high combustibility of the SNG and larger releasef heat compared with pulverized charcoal, since the SNG is

he scenarios analyzed in this study.

composed of hydrocarbons, as shown in Table 1. It is observedalso in Table 1, that the blast rate could be decreased by replac-ing air with oxygen and as consequence; the total blast ratewas decreased for all cases considered. The total amount ofcarbon consumed by solution loss reaction taking place onthe granular charcoal increased for all scenarios. This behav-ior is explained by the higher concentration of the CO2 gasin lower region of the furnace due to the combustion of theSNG injected. For all cases the hot metal saturation in carbonwas achieved and the silicon content was dependent upon thelower blast furnace conditions with the general trend showingincreases with the temperature of the raceway but decreasingfor the highest productivity due to lower residence time of thedripping liquids in the elaboration zone of the furnace.

The specific carbon emissions increased as a general trendbut for the highest productivity recovered to the base caselevel, however, it is worthy to mention that most of the carbonemissions are renewed source based on biomass plantationwhich confer to these operations to be classified as cleantechnology and depending on the SNG prices can be used asflexible operation symbiotically implemented with the char-coal technology. Fig. 4 shows the gas temperature patternsof the SNG injection compared with the base case. As canbe observed, the lower part of the compact blast furnaceincreased the temperature for the scenarios simulated andenhanced the heat transfer in this region although the upperpart of the reactor remains almost unchanged.

The solid motion and cohesive zone shape are importantparameters for assure feasible operation conditions of theblast furnace. Thus, Fig. 5 shows the descending solid pat-tern and cohesive zone shapes for the scenarios simulated.

260 j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262

Table 2 – Operational parameters for the scenarios analyzed in this study.

Parameters Base Scenario 1 Scenario 2 Scenario 3 Scenario 4

Model Measured

Productivity (thm/day/m3 working vol.) 3.19 3.18 3.85 4.26 4.74 5.08Oxygen enrichment (N m3/thm) 39.5 39 109.4 132.1 149.9 138.5Blast (N m3/thm) 814.7 815 676.5 606.5 551.9 513.3Total blast (N m3/thm) 854.2 854 802.8 753.2 726.4 676.9Blast temperature (◦C) 950 950 950 950 950 950Raceway temperature (◦C) 2115 – 2331 2430 2498 2465Si (%) 0.44 0.45 0.49 0.47 0.48 0.32C (%) 4.79 4.8 4.79 4.79 4.79 4.79Slag rate (kg/thm) 205.4 205 203.5 203.9 201.2 205.5CaO/SiO2 1.01 1.0 1.09 1.10 1.13 1.11CaO (%) 37.8 37.7 38.3 38.5 38.5 38.1MgO (%) 14.1 14.2 16.2 16.2 17.3 17.5Al2O3 (%) 10.5 10.4 10.1 9.9 9.7 9.8Off gas (N m3/thm) 1483.3 1485 1478.4 1443.2 1420.1 1716.6

CO2(CO2+CO) (%) 31.1 32 30.5 28.9 31.0 32.4

Granular charcoal (kg/thm) 399.7 401 398.5 415.1 379.3 358.9PCH (kg/thm) 134.1 134 133.9 134.1 134.3 133.8SNG rate (N m3/thm) 0 – 15.8 14.6 25.8 24.8

Granular charcoal solution loss (kg C/thm) 33.1 –Carbon emission (kg C/thm) 410.2 415

As indicated by the simulated scenarios, as the simultane-ous injection was increased the cohesive zones slightly moved

down. This behavior is attributed to the increase of the pro-ductivity combined with the heat transfer in this region dueto the increase in the gas velocity. Fig. 5e indicated that the

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1

200018001600140012001000

800600400200

Y

Base Scenario 1 Scenario 2

a b c

X

Z

YX

Z

YX

TG

Fig. 4 – Temperature distributions within the char

38.1 42.1 43.2 51.3431.4 444.7 429.7 410.5

scenario 4 restores the positioning and shape of the cohe-sive zone compared with the base case but with very high

productivity, indicating that it is possible to attain high pro-ductivity with low granular charcoal consumption and highrates of SNG injection combined with oxygen enrichment.

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coal blast furnace for the scenarios analyzed.

j m a t e r r e s t e c h n o l . 2 0 1 3;2(3):255–262 261

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Fig. 5 – Solid flow patterns and cohesive zone shapes for the simultaneous injection of pulverized charcoal and syntheticnatural gas–time intervals of 3600 s for the lump solid residence time within the furnace.

Tcicpcr

4

Icfpawih

asoiS

herefore, among the scenarios analyzed, the scenario 4 wasonsidered the best candidate to operate with simultaneousnjection of pulverized charcoal and SNG with compatible spe-ific carbon emissions and inner temperature and solid flowatterns, although all cases shown in Fig. 5 are feasible andould be selected depending on the operational strategy andaw materials cost.

. Conclusions

n this paper a five-phase mathematical model for the char-oal blast furnace has been presented, which can simulate theurnace operation under simultaneous injection of SNG andulverized charcoal. The model considers multiphase inter-ctions for momentum, energy and chemical species coupledith the rates of chemical reactions. The model was applied to

nvestigate feasible scenarios of simultaneous injections andigh productivity for the compact charcoal blast furnace.

The model was applied to a base case of actual operationnd model predictions showed good agreement with mea-

ured data. The model was applied to simulate new scenariosf operation with combined injection. The model results

ndicated that combined injection of pulverized charcoal andNG can be smoothly carried out with effective increase in

the productivity of the actual furnace (about 58%) for the bestscenario and about 40 kg/thm of granular charcoal could bedecreased keeping compatible conditions for the materialsflows in the furnace. Therefore, based on this study, it isrecommended the symbiotic operation of the charcoal blastfurnace with injection of SNG and pulverized charcoal inorder to improve the energy efficiency and competitivenessof this technology to produce green pig iron.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

This study was partially supported by Coordenacão deAperfeicoamento de Pessoal de Nível Superior (CAPES), Con-

selho Nacional de Desenvolvimento Científico e Tecnológico(CNPq) and Fundacão Carlos Chagas Filho de Amparo aPesquisa do Estado do Rio de Janeiro (FAPERJ), Brazil.

n o l

r

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