Simulating and Optimizing Hydrogen Production by Low pressure Autothermal Reforming of Natural Gas using Non dominated Sorting Genetic Algorithm II
Environmental considerations will probably change automobile fuels from gasoline and gas oil to hydrogen (as fuel cell) in the future. Problems of fossil fuels include producing gaseous pollutants, such as NOx, CO, and even SO2 (from incomplete hydrotreated fuels) which need catalytic converters and greenhouse gas emission (such as CO2, CH4, N2O) from the exhaust with a drastic effect on global warming1. Hydrogen usage in fuel cells generates only harmless water vapor2. Another future promising application of hydrogen fuel cells may be in small power plants without pollutants or greenhouse gas emission. Nowadays, power plants of industrial countries are coal based with high SO2, NOx, CO2, mercury, and fly ash emissions. Flue gas desulfurization of such power plants with CaO (dry method) or Ca(OH)2 (wet method) is a costly process3. In addition, SO2 reaction with lime shows pore mouth closure and incomplete conversion problems due to high molar volume ratio of CaSO4 to CaO4. The environmental preference of natural gas in terms of producing hydrogen over coal is a very interesting issue. Natural gas sweetening is very simple, whereas coal desulfurization is almost impossible. Moreover, the amount of greenhouse gas (CO2) emissions from natural gas based combustion is about 45 of coal based power plants5,6. Industrial hydrogen production plants are usually based on catalytic steam reforming (SR) of natural gas to synthesis gas (CO+3H2) water gas shift reaction for converting CO into CO2, CO2 absorption, and methanation of trace remaining carbon oxides7. Conventional steam reforming is a highly endothermic reaction and needs a big top fired or side fired furnace for external heating of Ni packed tubes8. Steam reforming by methane as the feed stock has been extensively studied in the literature9 12. Another method for producing hydrogen or synthesizing gas from natural gas is partial oxidation method. This method includes a highly exothermic reaction with hot spot, sintering of active catalyst sites, and even run away problems13 15. An interesting alternative for steam reforming is the autothermal reforming method with internal heat generation by oxygen or air injection to the steam reforming system and elimination of its costly furnace16,17. ATR (autothermal reforming) combines thermal effects of partial oxidation and steam reforming reactions by feeding natural gas, water vapor, and air (or oxygen) into the reactor. Steam reforming and oxidation of methane occur simultaSimulating and Optimizing Hydrogen Production by Low pressure Autothermal Reforming of Natural Gas using Non dominated Sorting Genetic Algorithm II