The use of the Active Carbon Recycling Energy System in ironmaking (iACRES) has been proposed for reducing CO2 emissions. To evaluate the performance of iACRES quantitatively, a process flow diagram of a blast furnace model with iACRES was developed using Aspen Plus, a chemical process simulator. The CO2 emission reduction and exergy analysis was predicted by using the mass and energy balance obtained from the simulation results. iACRES used a solid oxide electrolysis cell (SOEC) with CO2 capture and separation (CCS), an SOEC without CCS, and a reverse water-gas shift reactor as the CO2 reduction reactor powered by a high-temperature gas-cooled reactor. iACRES could provide a CO2 emission reduction of 3–11% by recycling carbon monoxide and hydrogen, whereas the effective exergy ratio decreased in all cases.
Reducing coking coal consumption and CO2 emissions by application of iACRES (ironmaking system based on active carbon recycling energy system) was investigated using process flow modeling to show effectiveness of HTGRs (high temperature gas-cooled reactors) adoption to iACRES. Two systems were evaluated: a SOEC (solid oxide electrolysis cell) system using CO2 electrolysis and a RWGS (reverse water-gas shift reaction) system using RWGS reaction with H2 produced by iodine-sulfur process. Both reduction of the coking coal consumption and CO2 emissions were greater in the RWGS system than those in the SOEC system. It was the reason of the result that excess H2 not consumed in the RWGS reaction was used as reducing agent in the blast furnace as well as CO. Heat balance in the HTGR, SOEC and RWGS modules were evaluated to clarify process components to be improved. Optimization of the SOEC temperature was desired to reduce Joule heat input for high efficiency operation of the SOEC system. Higher H2 production thermal efficiency in the IS process for the RWGS system is effective for more efficient HTGR heat utilization. The SOEC system was able to utilize HTGR heat to reduce CO2 emissions more efficiently by comparing CO2 emissions reduction per unit heat of the HTGR.
An active carbon-recycling energy system (ACRES) has been proposed to reduce emission carbon dioxide (CO2) emission from industrial energy processes. Application of a smart iron-making system based on ACRES (iACRES) in a shaft furnace is modeled numerically as a new low-carbon process. It was assumed that a proportion of the CO2 in the furnace gas was extracted via gas separation, and reduced into carbon monoxide (CO) by electrolysis, after which regenerated CO was mixed with a reduction gas and recycled continuously in the furnace. The use of a solid oxide electrolysis cell (SOEC) was assumed for the electrolysis process. A one-dimensional model for the shaft furnace was employed for feasibility evaluation of the carbon recycling process. The mixing ratio of electrolysis gas, m [–], was defined as the flow amount of CO2 separated from the furnace gas for recycling (which was electrolyzed into CO/CO2 mixture) relative to total inlet reduction gas for the furnace. Electrolysis degree, ed [–], was defined as CO production yield by electrolysis of the separated CO2. The effects of m and ed on the reduction process in the furnace were evaluated. At ed > 70%, metallization degree of > 90% was maintained at m > 10%. The furnace system was envisaged as a pre-reduction process for iron-ore material. When 70% metallization was acceptable for the pre-reduction process, m of 14% was achievable even at ed of 40%. The value of m is equal to primary fuel saving. It is expected that the shaft furnace with iACRES would have potential as a low-carbon iron-making process.
This paper describes a low shaft furnace as a new model with three capabilities for making (1) a “smart iron-manufacturing system” using scrap, (2) “co-production” of electrical power and iron, and (3) a “smart community” of new local adhesion, promotion of industry, and local supply and local consumption into a process which can respond to local demand. In this study, by the “Iron Technology and History Forum”, the iron-manufacturing experimental results using a low shaft furnace were analyzed by chemical reaction engineering, and it is presumed that transient response control of the heating rate and a partial pressure rise of CO in a low shaft furnace were key factors controlling slag and metal components.
Japanese steelworks achieve the world’s highest energy efficiency. However, approaches that seek intra-steelworks optimization alone have limitations when planning further energy conservation. It is thus necessary to establish a system that effectively utilizes energy at the societal level. This study is proposed a hybrid steelworks having functionality that combines steel manufacturing and energy supply, focusing on improving the energy utilization of by-product gas. As the results, the typical hybrid steelworks is able to supply society with low-cost electric power without increasing energy consumption through the use of combined high-efficiency GTCC with the promotions of energy conservation in steelworks such as CO2 and N2 separation in blast furnace gas. Moreover, if the technology of this hybrid steelworks is applied to all steelworks in Japan (84 million t-steel/year blast furnace crude steel), the power generation potential is more than 38 billion kWh/year which is equivalent to 4.0% of gross domestic power demand. Furthermore, a CO2 reduction of 33 million t-CO2/year nationally can be expected; this effect is equivalent to a 23% reduction in steelworks CO2 emissions.
Solid oxide electrolysis cell for electrolysis of CO2 to CO was studied with the cell using LaGaO3-based electrolyte at the intermediate temperature (i.e. 973–1173 K). Various metal additives to Ni were examined for cathode to CO2 reduction and it was fund that Ni added with Fe shows high activity and the current density of 1.5 A/cm2 was achieved at 1.6 V and 1073 K on Ni–Fe (9:1) cathode. Improved electrolysis activity was explained by the expanded reaction site which may be assigned the fine particle of Ni. Furthermore, effects of additives to Ni cathode were studied and it was found that the electrolysis current could be much improved by addition of Fe to Ni. Effects of oxide ion conductor mixing with Ni–Fe were further studied and it was found that mixing La0.6Sr0.4Fe0.9Mn0.1O3 with Ni–Fe bimetal is the most effective for achieving high electrolysis current of CO2 of 2.07 A/cm2 at 1.6 V and 1073 K.
Efficient carbon dioxide (CO2) reduction into carbon monoxide (CO) is required to establish a smart iron-making process based on an active carbon recycling energy system (iACRES). A disk-type solid oxide electrolysis cell (SOEC) was prepared and examined experimentally for application to the CO2 reduction process in iACRES. A SOEC with a cathode|electrolyte|anode structure of Ni-YSZ|YSZ|La0.6Sr0.4Co0.2Fe0.8O3-δ was fabricated. The electrolysis of carbon dioxide was conducted at 800–900°C. A current density of 107.1 mA cm–2 was measured between the cathode and anode at 900°C and at 2.52 V. The production rates of CO and O2 were in agreement with the theoretical values determined using Faraday’s law. Evaluation of iACRES using the experimental results indicated that an estimated 0.73 high-temperature gas cooled reactor units as the primary energy source for CO2 reduction and a SOEC surface area of 0.098 km2 were required for the reduction of 30% CO2 in blast furnace gas emitted from a conventional blast furnace.
Reductions in CO2 emission can be achieved directly through CO2 capture and storage (CCS), a method that is particularly effective when used with large CO2 emitters such as electrical power plants and iron and steel mills. Solid-oxide electrolysis presents an alternative means of reducing CO2 that can use some of the CO2 captured by CCS as a source of electrolysis. In addition, unused heat generated by steelmaking and through renewable sources (e.g., solar and wind) can be utilized for high-temperature electrolysis. This study investigated the effect of applying a high voltage of between 2.5 and 4.0 V to common electrolytic materials (YSZ and Pt), and found that although the initial current density of a new cell is very low, it increases drastically upon application of a high voltage. The results of FE-SEM observation revealed that the interface between the YSZ and Pt electrode moves into the YSZ by about 70 μm, and consists of a nano- and micro-porous structure that reduces the resistivity and gas diffusivity.
Electrochemical reduction of carbon dioxide using a gas-electrolysis cell reactor was studied. A new electrocatalyst has been screened and Co-phthalocyanine (Co–Pc) supported on carbon support was found to reduce CO2 to CO. Effects of reaction conditions on a formation rate of CO and a selectivity to CO corresponding to a current efficiency (CE) were studied. Loadings of Co–Pc, kinds of carbon materials as a support, reaction temperatures and cathode potentials strongly affected the performance of the electroreduction of CO2 to CO. A maximum CE to CO formation was achieved to 70% with 14 mA cm–2 by use of 0.1 wt% Co–Pc supported vapor-grown-carbon-fiber (VGCF) electrocatalyst at –0.90 V (Ag/AgCl) and 273 K. The reaction model of electroreduction of CO2 was proposed in this work.
CO2 gas is decomposed to CO and C by the molten salt electrolysis using CaCl2–CaO and solid state electrolyte, zirconia, as the anode. Partially CO2 gas dissolves to form CO32– and it is electrochemically decomposed to carbon. The other portion of CO2 gas bubbles reacts with metallic Ca electrochemically deposited near the cathode, and forms C or CO gas. By increasing the flow rate of CO2 gas to the reactor, a high concentration of CO gas is generated. By increasing the concentration of CO2 gas in the initial gas, a large amount of CO gas was produced in the exhaust gas, and its rate approached to 3.32×10–8 m3/s in our experimental setup. These experimental evidences reflect the electrochemical decomposition of CO32– in the molten salt.
Suppression of CO2 discharged from iron and steelmaking companies is an example of the biggest issues for the protection of global environment and sustainable growth of steelmaking industry. One of the efforts made to decrease the emission of CO2 in ironmaking process is blowing of hydrogen gas into blast furnace. Hydrogen gas can reduce iron oxide and form harmless H2O. Cementite (Fe3C) may be formed by introduction of hydrogen into blast furnace and play an important role on carburization and smelting behavior of reduced iron. In the present work, Fe3C sample was held at 1200 K under various CO–CO2–H2 gas mixtures to clarify the stability of Fe3C phase. It was confirmed that metastable Fe3C phase will decompose into Fe and C, and FeO will form under high CO2 partial pressure. Also, it was found that existence of H2 will suppress decomposition of Fe3C. It was confirmed that CO2 gas will be continuously converted into CO by C formed by decomposition of Fe3C.
Dissolved carbon in molten iron can be decarburized by CO2 gas instead O2 gas commonly used in a basic oxygen furnace, in which CO2 gas is reduced to CO gas. Produced CO gas can be returned to ironmaking process and as a whole carbon works as energy transfer medium. However, the precise control of the process is required to utilize the decarburization reaction by CO2–O2 gas mixture because of its significant endothermic reaction. The present study has focused on the decarburization reaction of molten Fe–C alloy by CO2–O2 or H2O–CO2–O2 gas mixtures and the effects of gas composition and temperature on temperature change of molten alloy and exhaust gas compositions were studied by means of thermodynamic calculation. Repeated equilibrium calculations between existing molten alloy and newly introduced reacting gas enabled the estimation of molten alloy temperature and exhaust gas composition changes. Results were discussed in terms of molten alloy temperature change and conversion ratio of CO2 to CO or H2O to H2.
During conventional iron making, the temperature exclusively determines the oxygen potential in a blast furnace hearth because of carbon saturation. Consequently, impurities such as phosphorus are reduced and remain in the iron because of the excessively low oxygen partial pressure, which can be controlled using gaseous reductants such as hydrogen and carbon monoxide to produce solid iron because of the low carbon content. We previously investigated the equilibrium distribution of phosphorus between the solid iron and molten slag at 1623 K by varying the oxygen partial pressure and the basicity of the slag, and the phosphorus content in the solid iron was sufficiently low under the experimental conditions. In this study, the phosphorus distribution behavior was investigated when solid iron was obtained by reducing Al2O3–CaO–FetO–MgO–SiO2 molten oxide, and the system was evaluated based on Fe loss.
Effective utilization of low grade iron ore (FeOOH) and biomass represents a promising method to reduce the dependency on fossil fuels and decrease raw material costs in the ironmaking industry. A process system diagram was made and a comparison of exergy losses in conventional methods was conducted to evaluate the proposed system, integrated pyrolysis-tar decomposition over a porous ore through Chemical Vapor Infiltration (CVI) process. As the main product, the CVI ore was employed for energy storage based on carbon deposition and pre-reduced ore, Fe3O4 as a product of proposed system that consisted of three units: pyrolysis, CVI, and dehydration-separation. The exergy of CVI ore increased significantly owing to exergy recovery through tar decomposition. In the basis of 3.86%wt carbon deposition (experimental value) and producing of 1000 kg metallic Fe, the exergy loss of the proposed system was found to decrease by about 17.6% compared to that in conventional systems by the recovery of both chemical and thermal tar exergy. The exergy loss decreased drastically to 37.0% when the expected carbon deposition was attained (10%wt). The CVI ore offered great chance to replace the coke breeze as a heat source in sinter plant. With regard to experimental value, the sinter plant could be operated without using additional coke breeze when the CVI ore content was 70% to total input ore. The total enthalpy of CVI ore consisted of the oxidation of deposited carbon and Fe3O4 in the ratio of 60.2% and 39.8%, respectively. Based on these results, the proposed system proffered effective biomass and low grade ore utilization as well as led to decrease in CO2 emissions by the ironmaking industry.
This paper presents a technology to utilize bio-char and bio-tar from the pyrolysis of oil palm empty fruit bunch, EFB. In this study, tar vapor from pyrolysis of EFB was infiltrated within porous bio-char and carbon deposition occurred on the pore surface by chemical vapor infiltration process. For preparation, EFB particles were made into pellets. In the first part of experiments, porous bio-char pellets were produced by slowly heating the EFB pellets in a tube furnace in argon atmosphere to terminal temperatures of 500–800°C. In the second part, the porous bio-char pellets were used as precursor for tar decomposition process to deposit carbon within the bio-char pores. Tar vapor was obtained from the pyrolysis of EFB at 400–500°C at a fast heating rate for tar decomposition to occur. The purpose of this research is to investigate the amount of carbon deposited within bio-char by this tar carbonization process as compared to carbon contents of metallurgical coke. We showed how EFB bio-char was used as the tar filter and in the process to produce carbon-infiltrated bio-char, a useful renewable energy source for ironmaking process.
Latent heat storage using a phase change material (PCM) is a promising method for utilizing the exhaust heat from steelworks. The purpose of this study was to improve the heat release performance of a direct-contact heat exchanger using a PCM and heat transfer oil (HTO). Erythritol (with a melting point of 391 K), which is a kind of sugar alcohol, was selected as a PCM. A vertical stainless steel cylinder with an inner diameter of 200 mm and height of 1400 mm was used as the heat storage unit (HSU). A ring-shaped injector with 18 holes positioned vertically downward was placed at the bottom of the HSU. Each hole in this injector had a diameter of 2.5 mm. We investigated the effects of the height of the PCM in the HSU, the HTO flow rate, and an increase in the number of injection-nozzle holes on the temperature effectiveness and heat exchange rate as indices of the heat release performances. As results, we found that an increase in the number of nozzle holes accelerated the uniform distribution of the HTO in the liquid PCM, prevented the HTO drift flow and adverse solidification of the PCM, and improved the heat release performance under the condition of a high HTO flow rate.
To reduce CO2 emission from the iron and steel making process, a novel steam generation system using waste hot water is proposed to use waste heat effectively from the process. This system adopts a direct heat exchange method for the adsorption heat pump to increase the heat transfer rate between the adsorbent and heat transfer fluid. In this study, the performance of the system is evaluated according to the mass of steam generated during the cyclic operation. The regeneration process is first studied taking the transport phenomena in the generator into account. The mass of steam generated is then estimated based on the distributions of water content and temperature in the generator. The results from the model exhibit good agreement with the experimental results. The effect of the operating conditions on the performance of the steam generation process is studied. It was found that there was an appropriate regeneration time to maximize the mass of steam generated during the cycle. For the effective use of adsorption heat, reuse of the water drained from the steam generation process (Drainage Recycling) is proposed. As a result, recycling the drainage water is a practical and helpful method to improve the performance of the system.
New composite materials were developed for application in chemical heat storage (CHS) systems based on the calcium oxide/water/calcium hydroxide (CaO/H2O/Ca(OH)2) reaction. It was found that the mixtures of expanded graphite (EG) and Ca(OH)2 enhance the reaction performance and moldability, which are important factors for the application in a packed-bed CHS heat exchanger. The reaction kinetics was investigated by thermogravimetric analysis. The maximum mean heat output of a mixture containing 11 wt% EG was 1.76 kW (kg-material)−1, which is twice as high as that of the pure Ca(OH)2 (0.85 kW (kg-material)−1). A repetitive dehydration-hydration experiment was carried out and it was confirmed that the positive effect of EG was preserved during the investigated 10 cycles. Therefore, based on our results, these composite materials can enhance the thermal performance of the CaO/H2O/Ca(OH)2 reaction cycle in CHS systems.
A heat recovery system based on thermal energy storage from the iron-making process at medium temperature range (200–300°C) is presented. For an efficient waste heat recovery system the selection of suitable thermal energy storage material is essential. Accordingly, a new candidate for a chemical heat storage material used in a magnesium oxide/water chemical heat pump at medium-temperature was developed in this study. The new composite, named EML, was fabricated by mixing pure magnesium hydroxide with lithium bromide and expanded graphite, which are employed as reactivity and heat transfer enhancers, respectively. The effects of mass mixing ratios w of EG to Mg(OH)2 on dehydration and hydration were investigated by a thermogravimetric (TG) method, with the result that the w of 0.83 was the optimal mass mixing ratio for the EML composite. Thereby the heat output capacities of the EML composite (w = 0.83) were evaluated with varying reaction vapor pressure and hydration temperature. Heat output capacity per unit initial weight of the EML composite (w = 0.83) was calculated as 1168.7 kJ kgEML–1 at a hydration temperature of 110°C and reaction vapor pressure of 57.8 kPa. This value was 1.2 times higher than the corresponding heat output capacity of pure Mg(OH)2 powder (958.5 kJ kgMg(OH)2-1). This result showed that the EML composite has sufficient heat output capacity and mold-ability provided by EG for practical use in a heat exchange reactor. Thus, this composite could potentially be used as chemical heat storage materials for thermal heat storage.
Magnesium oxide/water/magnesium hydroxide (MgO/H2O/Mg(OH)2) heat storage system using a composite material mixed with Mg(OH)2 and expanded graphite (EG), named as EM, was discussed experimentally and numerically. Thermal performance of EM tablet of 10 mm diameter and 7 mm thickness was evaluated by packed bed reactor experiments. Thermal performance of a packed bed of pure Mg(OH)2 pellets (diameter of pellet of 2 mm and 5–10 mm length) was compared with one of EM in the same experimental reactor. It was observed that the higher effective thermal conductivity of the bed of EM tablets contributed on enhancing the heat storage performance of the packed bed reactor. The effect of thermal conductivity enhancement of thermochemical heat storage materials was discussed numerically. The numerical model was utilized for a preliminary investigation on the behavior of a larger system, made of bundles of chemical heat storage units (CHSU), designed as pipes (length of 2 m) containing a packed bed of CHS material. It was shown that CHSU charged with EM tablets was capable to be utilized for recovery waste heat from the cooling down process of continuous casting of steel slabs.