Application of LaGaO3 based electrolyte for steam electrolysis at intermediate temperature was studied for the generation of hydrogen and oxygen by using the unused heat energy from steelmaking process. It was found that H2 formation rate was much improved by combination of oxygen ion conducting oxide with NiFe (9:1) bimetallic alloy. In particular, combination with La0.6Sr0.4Fe0.9Mn0.1O3 (LSFM) or Ce0.8Sm0.2O2 (SDC) is highly effective for increasing current density. Impedance plots for cathode were consisted of two semicircles, which could be assigned to a diffusion and an activation overpotential in low and high frequency region, respectively. Comparing with NiFe, mixing with SDC is much effective for decreasing the diffusion overpotential. This might be assigned to increase in three phase boundary and porosity of cathode. Effects of steam partial pressure was further studied and because of slow diffusivity of water in porous cathode, increase in humidity pressure decreased H2 formation rate. Humidity utilization of 56% was achieved by using 81 ml/min (29% PH2O) steam flow rate.
When practical utilization of hydrogen in blast furnace will be tried, mass transfer behavior of hydrogen under the upward gas flow should be correctly understood. The purpose of this study is to clarify that diffusion behavior of several kinds of gases in air flow through packed bed in order to understand diffusion behavior of hydrogen in blast furnace. Cold model experiments at room temperature were carried out to investigate the diffusion behavior of He and CH4 gases in air flow through the packed bed. Experimental results were analyzed by R. W. FAHIEN's method and following conclusion was obtained. Effect of molecular species difference on gas diffusion behavior was appeared clearer in the condition of smaller air flow velocity than bigger one from this comparison. In other words, gas diffusion behavior could ignore difference of molecular species under enough large gas flow condition.
Utilization of heat of slag is key technology for the reduction of CO2 emission in steel industries. While hydrogen production is important for the society of aiming to the sustainable energy system, the green hydrogen must be produced for the actual CO2 reduction. In the present study, methane gas was injected into a molten slag and hydrogen was produced through the thermal decomposition reaction. CH4 = C + 2H2 Kinetic analysis was performed using an graphite crucible both with empty and slag. The rate constants for the graphite crucible, kG and the slag, kS, were obtained separately. The rate constants for graphite surface and slag surface, kG and kS, respectively, are as follows: kG / cm·s–1 = 41.74 × exp(−51741 / RT) ± 0.05 kS / cm·s–1 = 4.053 × 106 × exp(−190310 / RT) ± 0.05 Using the obtained rate constants, the increase of the area of reaction surface during the CH4 injection was estimated. It was found that the slow soaking of the injecting lance could be utilized for the heat of molten slag. In addition, the slag shape can be a powder type through the injection of CH4.
How to produce the green hydrogen is important problem for reducing the CO2 emission. Among many processes on the production of hydrogen, a thermal decomposition reaction of CH4 can produce the pure hydrogen without CO and CO2 gases. When the reaction proceeds by using a waste heat, the obtained hydrogen will be approached to the green hydrogen. The thermal decomposition reaction of CH4 is mainly studied kinetically from several decades ago. CH4(g) = C(s)+ 2H2(g) However, the decomposition reaction on the surface of molten slag was not studied. Authors have studied the kinetics of decomposition reaction of CH4 on the surface of the molten slag in the previous study. The rate constant at 1700 K for the surface of the molten slag was about four times larger than that of graphite surface. In addition to the kinetics of the reaction, the carbon properties precipitated are quite interesting, because the structures of carbon are changed by the conditions such as the temperature and kind of solid/liquid surface which provided the reaction sites. In this study, it was found that two kinds of carbon were precipitated during the decomposition of CH4, when a molten slag existed in the system. The micro- and nano-structures of carbons precipitated were examined using SEM and TEM. The onion type carbon sphere were clarified, which were formed in the gas phase, furthermore, the high oriented graphite film was formed on the surface of molten slag.
Nuclear hydrogen steelmaking (NHS) and nuclear hydrogen partial reduction steelmaking (NHPRS) systems were proposed using very high temperature reactor, and thermochemical hydrogen production iodine-sulfur process. Heat input and CO2 emissions of these systems were analyzed by heat and mass balance calculation. Total net heat input to the NHS system was 28.4 GJ/t-high quality steel (HQS), including material production, material transportation, and power generation. This value was much larger than that of a blast furnace steelmaking (BFS) system of 17.6 GJ/t-HQS. Reduction of hydrogen consumption in the shaft furnace and electricity consumption in the electric arc furnace were desired for lowering the heat input. Total net heat input of a NHPRS system was 31.9 GJ/t-HQS. Optimization of operation parameters such as the reduction ratio of partial reduced ore (PRO) and ratio of the PRO input to the blast furnace is desired to decrease the heat input. CO2 emissions of the NHS system and the NHPRS system were 9% and 50% of that from the BFS system. Substitution of coal by hydrogen and reduction of transportation weight contributed to the reduction. Steelmaking cost was also evaluated. When steelmaking scale of each system was unified to one million t-HQS/y, NHS was economically competitive to BFS and Midrex steelmaking. And NHS was advantageous at higher cost of resources.
The merit assessment of the nuclear hydrogen steelmaking (NHS) was performed for reduction of CO2 emissions from the steelmaking process which accounts for approximately 14% of the total emissions in Japan. The NHS process is composed of the steelmaking process by hydrogen reduction and hydrogen production process using nuclear energy. As for nuclear hydrogen production, the combination of a very high temperature reactor (VHTR) and the thermochemical water splitting method, namely IS process, can be said to be the optimal, considering economics, safety & reliability, nuclear proliferation resistance and so on. Especially, VHTR has the excellent safety features outstanding as compared with the other nuclear reactors that the reactor can be shut down inherently and cooled down passively using natural heat radiation from outside of the reactor pressure vessel even in a loss of coolant flow accident caused by loss of power and so on. Therefore, hydrogen can be supplied directly to a shaft furnace using piping from VHTR installed near the steelmaking plant. The NHS process with VHTR and IS process can decrease the CO2 emissions by approximately 9% of those of the conventional blast furnace process, and be economically competitive to the blast furnace and the shaft furnace processes.
A new energy transformation system based on carbon recycling has been proposed; it is called the active carbon recycling energy system (ACRES) and has been developed in order to reduce the emission of carbon dioxide (CO2) to the atmosphere. An experimental study based on the ACRES concept for carbon monoxide (CO) regeneration via high-temperature electrolysis of CO2 was carried out using several solid oxide electrolysis cells (SOECs). Experimental results showed that a cell with the structure Pt-LSM cermet|YSZ|Pt-LSM cermet exhibited the highest current density and CO production rates of 0.52 mA·cm–2 and 0.75 μmol·min–1·cm–2 respectively, at 900°C. On the basis of the cell's electrolytic characteristics, the scale of a combined ACRES CO2 electrolysis/iron-making facility was estimated.
A new energy transformation concept based on carbon recycling, called the Active Carbon Recycling Energy System, ACRES, had been proposed for a zero carbon dioxide emission process. A smart ironmaking system based on ACRES (iACRES) was discussed thermodynamically. Efficient regeneration of carbon material from carbon dioxide (CO2) emitted from ironmaking system was a key technology for establishment of iACRES. Carbon monoxide (CO) was the appropriate carbon material in recycling system of iACRES because CO had high enthalpy for reduction of iron oxide. CO regeneration by CO2 hydrogenation was employed for carbon recycling because the regeneration was the most practical technology in regeneration ways. Equilibrium analysis for CO recycling in iACRES was discussed. Effluent gas of an iron making process is generally mixture of CO2 and CO. Effect of concentration of CO2 in gas for reduction on CO regeneration was discussed. CO2 had small negative effect on CO reduction. Then, CO and CO2 separation process for effluent gas from ironmaking process was capable to be omitted in iACRES. The omission of the process would realize simplification and cost-reduction of processes in iACRES. A structure of iACRES using external H2 and high-temperature heat was proposed. It was shown that hydrogen was useful material as reductnat for CO2 reduction in iACRES.
In this paper we analyse the economic and technical effects of using CO2 rich natural gas in an industrial park. The basis for our work is a technical-economic description the processes in the different plants. A mathematical model is established that enable analysis and optimisation of design and operation of the industrial park. The model optimises maximizes the net present value of the available investment and operation opportunities. The candidate plants that we consider in our case study are; a DRI plant, a steel plant (EAF), a methanol plant, a carbon black plant, a combined cycle power plant and a carbon capture facility. We use Norway as a case study due to the political ambitions of increasing domestic consumption of natural gas to achieve a higher level of innovation and industrial development. Several scenarios are analysed, and the main findings from this case study are that there could be both environmental and economic benefits by using a CO2 rich gas in an integrated industrial park.
Reduction of CO2 emissions is an important object for the iron and steel industry. One feasible method may be the utilization of H2 gas as a reducing agent in the blast furnace (BF). However, for stable BF operation, it is first necessary to understand the effects of high H2, and therefore high H2O, concentrations in the reducing gas on the disintegration behavior of iron ore sinter, because it significantly affects the gas permeability of the upper part of the BF. In the present study, disintegration behavior of a sinter sample at 773 K for 3.6 ks under gas flow of N2–CO–CO2–H2–H2O system was examined. The results showed a remarkable increase in the reduction degree and reduction-disintegration index (RDI) upon the addition of a small amount of H2. However, further increase in the H2 concentration caused these values to decrease gradually. Reduction by CO gas led to the formation of magnetite phases with not only thick and long but also fine cracks near the surface. In contrast, H2 reduction did not lead to formation of a significant number of fine cracks. Image analysis of samples revealed that the crack length density showed the similar trend to RDI value. CO gas reduction mainly proceeds near the surface of sinter particles, while H2 gas reduction tends to proceed inside the particles. Accordingly, reduction of H2 gas gave lower RDI than CO gas to the sinter with same reduction degree.
Composite pellets utilizing iron and carbon bearing process waste materials obtained from the integrated steel mill was reduced in a simulated RHF (rotary hearth furnace) reactor at 1523 K and 1573 K to produce DRI (direct reduced iron) pellets with sufficient size, reduction degree, compression strength, and zinc removal as an iron and carbon substitute for the blast furnace. To obtain DRI sizes of more than 4.75 mm, bursting tests of composite green pellets with moisture were done and found to be dependent on the water content and initial charging temperature into the RHF. Bursting of composite green pellets with water content was dependent on the charging temperature. At a charging temperature of 1273 K and 1473 K, water content at 1 mass% and above resulted in pellet bursting, but at 1073 K, water content only above 5 mass% resulted in appreciable pellet bursting. The compressive strength at various temperatures showed composite pellets containing carbon of 5.3 mass% can achieve blast furnace useable DRI at reduction temperatures of higher than 1473 K, but composite pellets containing carbon of 8.3 mass% required reduction temperatures higher than 1573 K. Optimum carbon of the composite seems to be at 9 mass% with a residual carbon content of less than 1 mass%, which results in a reduction of 80–90% with a compression strength of above 120 kg. This optimum condition has also shown Zn removal for the DRI to be above 85%. Higher (%C)/(%VM) showed lower reduction degrees indicating that increased volatile matter from the carbon source aided in higher reduction.
CaO- (0–20 mass%) and SiO2-containing (0–30 mass%) wüstite (‘FeO’) compacts were isothermally reduced at 1273 K under CO and H2 gas. Prior to reduction, the phase of dicalcium ferrite (Ca2Fe2O5) and fayalite (Fe2SiO4) was equilibrated with ‘FeO’ at 1273 K under 50%CO/50%CO2 and identified using X-ray diffraction and scanning electron microscopy. The rate of reduction for CaO-containing ‘FeO’ compacts under both H2 and CO increased up to the vicinity of 2.5 mass% CaO, and then decreased with higher CaO dependent on the formation of an intermediate phase of dicalcium ferrite. For SiO2-containing ‘FeO’, the rate decreased with SiO2 additions. When the dense fayalite is present reduction using CO was limited, while considerable reduction was observed using H2. The reduction was affected by three distinct reduction mechanisms of interfacial chemical reaction, gaseous mass transport, solid state diffusion of oxygen or a combination of these individual mechanisms termed the mixed control. The contribution of each mechanism with the content of CaO or SiO2 affecting the reduction behavior was determined. The compact porosity increased when CaO was added to approximately 2.5 mass% and subsequently decreased with higher CaO, but continuously decreased with SiO2 additions. The ratio of the effective diffusivity (De) to molecular interdiffusivity (D) was highest at the vicinity of 2.5 mass% CaO and thus the maximum reduction rate was obtained when the porosity was highest.
Fossil fuel-based carbon is widely used in iron and steelmaking in a number of forms, and the replacement of these materials with renewable carbon derived from biomass is seen as offering the greatest potential to reduce the greenhouse gas footprint of steel production. Life cycle assessment methodology has been used to estimate the greenhouse gas footprint of charcoal production from biomass, as well as the potential reductions in greenhouse gas emissions from the use of charcoal from biomass in the integrated, mini-mill/EAF and direct smelting steelmaking routes. The results indicated that the use of charcoal in the integrated steelmaking route in likely applications and substitution rates has the potential to reduce the greenhouse gas footprint of steel by 0.69–1.21 t CO2e/t steel (or 31–57%) without any charcoal production by-product (bio-oil and electricity) credits, and by 0.91–1.61 t CO2e/t steel (42–74%) with these by-product credits included. The corresponding reductions for the mini-mill/EAF and direct smelting routes were 0.028–0.056 t CO2e/t steel (5.5–11%) and 0.34–1.70 t CO2e/t steel (16–80%) without by-product credits, and 0.037–0.075 t CO2e/t steel (7.3–14.7%) and 0.45–2.25 t CO2e/t steel (21–106%) with by-product credits respectively. However, the magnitude of the by-product credits depends on the by-product yields in the charcoal retort, which in turn are dependent on a number of factors, in particular, the nature of the pyrolysis process (fast or slow) and the biomass feed composition. Estimates of the potential plantation areas available to grow the biomass required to produce charcoal for steelmaking purposes in a sustainable manner, together with estimates of sources of biomass residues suggest that it is possible that an appreciable amount of the world's steel production can utilise charcoal in place of coal or coke over the coming decades. However, transportation is expected to be a significant issue affecting the cost of charcoal delivered to steel plants in all biomass source scenarios. Other issues such as technical aspects of charcoal use in steelmaking and economics will also play a significant role in the uptake of charcoal from biomass as a source of renewable carbon for iron and steelmaking.
Charcoal use instead of fossil fuel is one of the possible technologies for mitigation of CO2 emission in the steel industry because charcoal can be considered as “carbon-neutral” material. In this study, the possibility of utilization of charcoal as carbon source for carburization reaction was examined; more specifically effects of carbon crystalinity and ash in charcoal on carbon dissolution into molten iron and iron carburization reaction in iron-charcoal composite were investigated. Two kinds of experiments were carried out. One is measurement of charcoal carbon dissolution rate in iron bath. Another is observation of isothermal reaction between iron and charcoal in a composite sample. Several kinds of charcoal with relatively low ash content were applied as experimental samples. Charcoal samples were treated with several heating patterns to control their carbon crystallinity. Additionally, charcoal samples were treated with acid solutions, HCl and HF, to control the ash content in them. From these investigations, following results were revealed. Charcoal heat-treated at low temperature, 1273 K, has advantage for carbon dissolution reaction into iron bath. Charcoal ash strongly prevents the carburization reaction between iron and carbon in the composite sample.
The replacement of coal-based fuels by renewable fuels such as charcoal is an attractive way to reduce net greenhouse gas emissions from the integrated steelmaking route. Our previous studies have indicated that the potential for savings in net CO2 emissions ranges from 32 to 58 percent, with use as a BF tuyere injectant being the largest application. The current study considered the combustibility of four types of charcoal in comparison with PCI coal under simulated BF raceway conditions. The major findings were that burnouts under standard conditions (air-cooled coaxial lance, O/C = 2.0) were comparable or better than that of the high volatile matter PCI coal studied, and a comparison with the trend line for burnout with injectant volatile matter previously established for coals, indicated that the hardwood charcoals studied had burnouts 40% (abs) higher than those of equivalent coals, and the softwood charcoal studied was higher again. A study of the effects of oxygen enrichment indicated that small increases were effective, and particularly so for the least combustible charcoal. Overall, the burnout results indicated that higher-than-coal injection rates should be possible in industrial practice, and in combination with the previous heat and mass balance results, they indicated the potential for increased BF productivity. The brief study of the combustion of coal-charcoal mixtures indicated good combustibility and predictable burnouts. The microscopic examination of both the charcoal injectants and their combustion chars indicated that there was significant fragmentation of the charcoals during combustion, boosting their already high surface areas and combustibility.
Hydrogen gas is one of key materials for promotion of the utilization of energy with low environmental load. Ironmaking and steelmaking processes produce enormous thermal energy during steel production, most of which are not used before final dissipation to natural environment. In the present study, the environmental-friendly H2 gas production process by converting H2O gas with FeO and thermal energy in steelmaking slag has been proposed, and physicochemical properties of reaction between FeO-containing steelmaking slag and H2O-containing gas have been estimated by applying thermodynamic calculation. The effects of slag temperature and compositions, gas temperature, and partial pressure of H2O on production behavior of H2 gas have been investigated.
Hydrogen itself is not a primary energy and needs an energy for its production, which means that CO2 will be exhausted during the production process, more or less. However, when a Green Hydrogen can be produced, it is a best way to use the hydrogen instead of carbon. In this study, two kinds of iron ore were reduced and melted both under hydrogen and carbon atmosphere. The obtained iron metal under hydrogen atmosphere was quite pure one. The impurities in the metal were chemically and thermodynamically analyzed. The characteristics and benefits of hydrogen reduction were discussed in comparison with the carbon reduction. The content of silicon in the metal under hydrogen atmosphere was one tenth to the iron obtained by carbon reduction. Manganese was about one third to one tenth against the carbon reduction. However, phosphorus in the hydrogen reduction was almost the same level to the carbon reduction. Sulfur content became half in the hydrogen reduction. Moreover, the content of hydrogen in the metal was the same level between the hydrogen reduction and the carbon reduction. It was found that the rate of hydrogen evolution from a molten metal during solidification was fast significantly. The activities of elements in the metal were calculated through the thermochemical data, and the relationships among those elements were elucidated. From the thermodynamic analysis, a high oxygen activity in the metal obtained under hydrogen atmosphere caused to a low content of impurities and high activity of oxides related.
Recent years various trials to decrease carbon dioxide emission from iron and steelmaking industries have been made. One of these trials is utilization of hydrogen in blast furnace process, and this study performed numerical simulation of blast furnace operation with hydrogen injection through tuyere. The simulations were carried out under the conditions of constant bosh gas flow rate, adiabatic flame temperature and hot metal temperature. The simulation results showed that the temperature level in the stack part was decreased with increase in the hydrogen injection ratio. This resulted in the lowering of the top gas temperature and retarded the reduction of iron oxide especially one of magnetite. The injection of the hydrogen remarkably decreased the coke rate. The converted reducing agent rate, that is sum of coke rate and six times (molecular weight ratio of carbon to hydrogen gas) as hydrogen rate showed small change. Although this decrease in coke rate deteriorated the permeability of the burden materials in the furnace, pressure drop in the furnace was reduced. Since the molar flow rate of the reducing gas was kept constant, the decrease in the gas density due to the increase in the hydrogen content was mainly considered to lead the decrease in the pressure drop. The water gas shift reaction played an important role in the generation of the field of gas composition, thus this reaction has to be carefully discussed for further utilization of hydrogen in blast furnace.