Reduction of CO2 Emission from Off-Gases of Steel Industry by Dry Reforming of Methane

Hydrogen Production and Carbon Capture by Gas-Phase Methane Pyrolysis: A Feasibility Study

Using natural gas and sustainable biogas as feed, high-temperature pyrolysis represents a potential technology for large-scale hydrogen production and simultaneous carbon capture. Further utilization of solid carbon accruing during the process (i. e., in battery industry or for metallurgy) increases the process's economic chances. This study demonstrated the feasibility of gas-phase methane pyrolysis for hydrogen production and carbon capture in an electrically heated high-temperature reactor operated between 1200 and 1600 °C under industrially relevant conditions. While hydrogen addition controlled methane conversion and suppressed the formation of undesired byproducts, an increasing residence time decreased the amount of byproducts and benefited high hydrogen yields. A temperature of 1400 °C ensured almost full methane conversion, moderate byproduct formation, and high hydrogen yield. A reaction flow analysis of the gas-phase kinetics revealed acetylene, ethylene, and benzene as the main intermediate products and precursors of carbon formation.

Soot Formation in Methane Pyrolysis Reactor: Modeling Soot Growth and Particle Characterization

Methane pyrolysis is a very attractive and climate-friendly process for hydrogen production and the sequestration of carbon as solid material. The formation of soot particles in methane pyrolysis reactors needs to be understood for technology scale-up calling for appropriate soot growth models. A monodisperse model is coupled with a plug flow reactor model and elementary-step reaction mechanisms to numerically simulate processes in methane pyrolysis reactors, namely, the chemical conversion of methane to hydrogen, formation of C-C coupling products and polycyclic aromatic hydrocarbons, and growth of soot particles. The soot growth model accounts for the effective structure of the aggregates by calculating the coagulation frequency from the free-molecular regime to the continuum regime. It predicts the soot mass, particle number, area, and volume concentration, along with the particle size distribution. For comparison, experiments on methane pyrolysis are carried out at different temperatures and collected soot samples are characterized using Raman spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS).

Hydrogen Recovery from Coke Oven Gas. Comparative Analysis of Technical Alternatives

The recovery of energy and valuable compounds from exhaust gases in the iron and steel industry deserves special attention due to the large power consumption and CO₂ emissions of the sector. In this sense, the hydrogen content of coke oven gas (COG) has positioned it as a promising source toward a hydrogen-based economy which could lead to economic and environmental benefits in the iron and steel industry. COG is presently used for heating purposes in coke batteries or furnaces, while in high production rate periods, surplus COG is burnt in flares and discharged into the atmosphere. Thus, the recovery of the valuable compounds of surplus COG, with a special focus on hydrogen, will increase the efficiency in the iron and steel industry compared to the conventional thermal use of COG. Different routes have been explored for the recovery of hydrogen from COG so far: i) separation/purification processes with pressure swing adsorption or membrane technology, ii) conversion routes that provide additional hydrogen from the chemical transformation of the methane contained in COG, and iii) direct use of COG as fuel for internal combustion engines or gas turbines with the aim of power generation. In this study, the strengths and bottlenecks of the main hydrogen recovery routes from COG are reviewed and discussed.

Oxidative Coupling of Methane over Pt/Al2O3 at High Temperature: Multiscale Modeling of the Catalytic Monolith

At high temperatures, the oxidative coupling of methane (OCM) is an attractive approach for catalytic conversion of methane into value-added chemicals. Experiments with a Pt/Al2O3-coated catalytic honeycomb monolith were conducted with varying CH4/O2 ratios, N2 dilution at atmospheric pressure, and very short contact times. The reactor was modeled by a multiscale approach using a parabolic two-dimensional flow field description in the monolithic channels coupled with a heat balance of the monolithic structure, and multistep surface reaction mechanisms as well as elementary-step, gas phase reaction mechanisms. The contribution of heterogeneous and homogeneous reactions, both of which are important for the optimization of C2 products, is investigated using a combination of experimental and computational methods. The oxidation of methane, which takes place over the platinum catalyst, causes the adiabatic temperature increase required for the generation of CH3 radicals in the gas phase, which are essential for the formation of C2 species. Lower CH4/O2 ratios result in higher C2 selectivity. However, the presence of OH radicals at high temperatures facilitates subsequent conversion of C2H2 at a CH4/O2 ratio of 1.4. Thereby, C2 species selectivity of 7% was achieved at CH4/O2 ratio of 1.6, with 35% N2 dilution.

Reduction of CO2 Emission from Off-Gases of Steel Industry by Dry Reforming of Methane

In a novel process, CO₂ and CH₄ from the off‐gases of the coke oven and blast furnace are used in homogeneous reforming of those greenhouse gases to valuable syngas, a mixture of H₂ and CO. Synthetic mixtures of the off‐gases from those large apparatuses of steel industry are fed to a high‐temperature, high‐pressure flow reactor at varying temperature, pressure, residence time, and mixing ratio of coke oven gas (COG) to blast furnace gas (BFG). In this study, a maximal reduction of 78.5 % CO₂ and a CH₄ conversion of 95 % could be achieved at 1350 °C, 5.5 bar, and a COG/BFG ratio of 0.6. Significant carbonaceous deposits were formed but did not block the reactor tube in the operational time window allowing cyclic operation of the process. These measurements were based on prior thermodynamic analysis and kinetic predictions using an elementary‐step reaction mechanism.