Abstract
The importance of carbon deposition occurring during catalytic fuel reforming is briefly described along with former studies on the process. Thermodynamic fundamentals of modeling the critical conditions of the deposition equilibrium are presented. Computational results of ternary C–H–O diagrams with the threshold lines between the carbon deposition and deposition-free regions are discussed for two new pressure levels of 3 and 30 bar and a temperature range from 200 to 1000 °C. The process pressure does not affect the temperature range typical for the type of deposited carbon allotrope; either graphite, multi-walled carbon nanotubes, or single-walled carbon nanotubes in bundles. However, pressure has a profound influence on the location of the threshold lines for carbon deposition. Three reforming processes of two hydrocarbon fuels are analyzed; catalytic partial oxidation, and wet and dry reforming. Chord lines representing varied compositions of process mixtures are introduced to the ternary diagrams. The intersection points of the chord lines with the threshold lines are used in a novel interpretation of the functions of the oxygen-to-carbon critical ratio against temperature and pressure, which can be used in avoiding carbon deposition in catalytic reforming of natural gas and liquefied petroleum gas.
Highlights
The demand for useful energy is systematically growing as the world aims to improve its standard of living
The diagrams are supplied with chord lines drawn between points representing compositions of two fuels and three oxidants that represent different compositions of reformates
With the results of our former study [12] of ternary diagrams for 1 and 10 bar, those diagrams are used for the interpretation and discussion of the critical oxygen to carbon (O/C) values for the fuel-oxidant pairs in the full temperature and pressure ranges
Summary
The demand for useful energy is systematically growing as the world aims to improve its standard of living. The burning of all fossil fuel forms has serious environmental consequences. A promising alternative of fossil fuels for the future is seen in hydrogen. Energy produced by hydrogen-based fuel cells is characterized as high-quality energy, because of the high conversion efficiency from chemical to electrical energy. The efficiency is almost twice as high compared to internal combustion engines and because of the zero emissions of pollutants and greenhouse gases to the environment, hydrogen fuel cells are currently the promoted form. Hydrogen can be obtained using several technologies: steam reforming (SR) [1]; auto-thermal reforming (ATR) [2]; dry reforming (DR) [3]; or catalytic partial oxidation reforming (CPOX ) [4]
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