On the Development of Thermochemical Hydrogen Storage: An Experimental Study of the Kinetics of the Redox Reactions under Different Operating Conditions

This work aims at investigating the reduction/oxidation (redox) reaction kinetics on iron oxide pellets under different operating conditions of thermochemical hydrogen storage. In order to reduce the iron oxide pellets (90% Fe2O3, 10% stabilizing cement), hydrogen (H2) is applied in different concentrations with nitrogen (N2), as a carrier gas, at temperatures between between 700 ∘C and 900 ∘C, thus simulating the charging phase. The discharge phase is triggered by the flow of a mixture out of steam (H2O) and N2 at different concentrations in the same temperature range, resulting in the oxidizing of the previously reduced pellets. All investigations were carried out in a thermo-gravimetric analyzer (TGA) with a flow rate of 250mL/min. To describe the obtained kinetic results, a simplified analytical model, based on the linear driving force model, was developed. The investigated iron oxide pellets showed a stable redox performance of 23.8% weight reduction/gain, which corresponds to a volumetric storage density of 2.8kWh/(L bulk), also after the 29 performed redox cycles. Recalling that there is no H2 stored during the storage phase but iron, the introduced hydrogen storage technology is deemed very promising for applications in urban areas as day-night or seasonal storage for green hydrogen.

Effects of Treated Cow Dung Addition on the Strength of Carbon-Bearing Iron Ore Pellets

It is of particular interest to use biomass as an alternative source of fuel in direct-reduction ironmaking to ease the current reliance on fossil fuel energy. The influence of cow dung addition on the strength of carbon-bearing iron ore pellets composed of cow dung, iron ore, anthracite, and bentonite was investigated, the quality of green and dry pellet was evaluated based on FTIR analysis, and the mechanism of strength variation of the reduced pellets was investigated by analysing the phase composition and microstructure using XRD and SEM. The results show that cow dung addition decreased the green pellet strength due to expansion of the amorphous region of the cellulose in the cow dung; however, the dry pellet strength increased substantially. In the process of reduction roasting, it was found that cow dung addition can promote aggregation of iron crystals and increase the density of the pellets, resulting in increased strength of the reduction roasted pellets, while excessive cow dung addition resulted in lower strength.

Improvement of the energy utilization efficiency of the V-Ti-Magnetite reduction process with rotary hearth furnace

In order to improve the energy utilization of rotary hearth furnace (RHF), some methods were raised to solve the problem. Through changing the inlet angle of the nozzle, a higher and more uniform temperature field can be got. Thus, the burden in the furnace can be heated to the reduction temperature in a relatively shorter time. By using multilayer pellets technology, the energy can be utilized as much as possible. However, the top layer pellets would be reoxidized when the middle and bottom layer pellets were reduced. The average metallization of the reduced pellets get the maximum value at 25 min, which is consistent with the reality operation.

Reduction of Composite Pellet Containing Indonesia Lateritic Iron Ore as Raw Material for Producing TWDI

Blast furnace process is still an important process for producing pig iron. The process needs high grade iron ore and coke. The two materials can not be found easily. In addition blast furnace process needs cooking and sintering plant that produces polluted gases. Utilization of composite pellet for pig iron production can simplify process. The pellet is made of iron ore and coal. In addition the pellet can be made from other iron source and coal. This paper discusses the evolution of phase during reduction of composite pellet containing lateritic iron ore. Fresh iron ore and coal were ground to 140 mesh separately. They were mixed and pelletized. The quantity of coal added was varied from 0 %, 20 % and 29 % of pellet weight. Pellets were heated with 10 °C/minute to 1100 °C, 1200 °C, 1300 °C and 1350 °C in a tube furnace and temperature was held during 10 minutes. Heated pellets were analyzed with XRD equipment. XRD of reduced pellets showed that iron phase change with coal and temperature. Lack of coal during heating results the re-oxidation of iron phases. This process is due to replacement of reductive atmosphere by oxidative atmosphere.

Effect of Thermal Charging of Iron Ore Pellets on the Reduction Rate and Compressive Strength in Gas-Based Reduction Process

Burden in gas-based direct reduction process is iron ore oxide pellet, which has experienced oxide roasting and cooling before reduction. However, it would be heated again in the reduction process. This may cause much energy waste and adverse effects on reduction process. In this paper, roasted pellets with and without cooling were charged for gas-based reduction respectively. The reduction rate and compressive strength during reduction were studied to reveal the effects of charging methods. Results showed that there is little difference on reduction rate between the two. However, the compressive strength of reduced pellets via thermal charging improves obviously. And nucleation and growth mechanisms of iron crystal grain in gas-based reduction were investigated by optical microscope (Leica DMRXP). The iron crystal nucleuses firstly form at the interface of grains and edge of wustite, and then gradually grow from surface layer to inner core as reduction proceeds. Thermal charging can promote the migration and accumulation of iron crystal grain effectively.

The Preparation of Porous Materials Using Liquid Metal Impregnation for BSE Characterization with a Scanning Electron Microscope

The infiltration of porous and particulate materials for metallographic examination with low-melting alloys was first described by Rose and DeRoos . The use of Wood's metal to fill porosity in sandstone was reported by Craze , by Dullien , and by Yadev et al. . Changes in pore structure and phase dispersions in iron ore pellets after simulated blast furnace reduction were reported by Shultz et al. , wherein liquid Bi-Sn impregnation was used to prepare cross sections of deformed and reduced pellets for backscatter electron imaging. Steele and Engel also applied the technique to examine the microstructure in commercial boron nitride (BN). In that study porosity formed by leaching the B2O3phase was filled with liquid metal to allow argon-ion etching to expose the BN microstructure. The characterization of cracks and porosity in cement-based materials after filling with Wood's metal has been reported by Nemati et al. . Cracks developed during compression testing of marble were studied byin-situmetal impregnation in Chang et al. .

Reduction of Porous Silica Pellets by Electrodeoxidation in Molten Salts

Direct electrochemical reduction of porous SiO2 pellets in molten CaCl2 salt and CaCl2-NaCl salt mixture were investigated by applying 2.8 V potential. The study focused on the effects of temperature, powder size and cathode contacting materials. Starting materials and electrolysis products were characterized by X-ray diffraction analysis and scanning electron microscopy. Due to reactive nature of silicon, different cathode contacting materials were used to test the extent of reactions between silicon produced at the cathode and the contacting materials. X-ray diffraction patterns showed that silicon produced at the cathode reacted with nickel, and iron in stainless steel to form Ni-Si and Fe-Si compounds respectively. Besides, studies revealed that higher temperature and smaller particle size had positive effects in increasing reduction rate. The results were interpreted from variation of current versus time graphs under different conditions, microstructures and compositions of the reduced pellets.