Thursday, February 27, 2020

Steam Reforming and the Production of Hydrogen Gas Essay

Steam Reforming and the Production of Hydrogen Gas - Essay Example About 50% of the global production of Hydrogen is produced by this process( eg. activated carbon filters, pressurisation and depending on the reformer design, either pre heated and mixed with processed steam or directly injected with the water into the reformer without the need for an external heat exchanger. The water is normally demineralised using appropriate water conditioning systems. Two options are available for reforming one option is high pressure reforming at a working pressure upto 16 bar. The other option is to use low pressures (1.5 bar) with increased conversion ratios ( 2.2 Steam Methane Reforming: The process involves the use of high temperature steam (700C) which is reacted with natural gas( primarily methane) to produce Hydrogen. Methane reacts with steam under 3- 25 bar pressure in the presence of a catalyst to produce Hydrogen, Carbon Monoxide and a relatively small amount of Carbon Dioxide. This process is endothermic and hence heat must be supplied to the process to proceed. ( The methane steam reforming reaction is endothermic. Hence this reaction requires a high process temperature to proceed. As the number of moles also changes for the reaction, the reaction is facilitated by as low a pressure as possible to maximise the Methane conversion rate. Another way to shift the equilibrium to the right side is to increase the ratio of steam to methane. Overall, the conversion rate of methane is a function of pressure, temperature and steam/ Methane ratio. The reformer reactor consists of catalyst filled tubes surrounded by a fire box that provides the heat for the reaction as shown in the process flow diagram ( Fig.3) Water Gas shift Reaction: CO + H2O CO2 + H2 (H = - 41.2kJ/mol) (2) The water gas shift reaction is exothermic and needs as low a temperature as possible to proceed. Based on Le Chatelier's principle, the WGS reaction rate: (1) Increases with increase in steam fraction in the inlet gas (2) Decreases with increase in Hydrogen in the inlet gas (3) Decreases with increase in temperature The reactor temperature influences the flame temperature of the reactants. Hence at higher temperature more Methane is converted and less Hydrogen. The presence of a catalyst such as Nickel helps in the formation of Hydrogen rich reformate. The heat required for the first reaction is obtained by the combustion of fuel gas and/ or purge tail gas from the PSA system. Following the reforming step, the synthesis gas is fed into the CO conversion reactor to produce additional Hydrogen. This process occurs in two stages consisting of a High Temperature Shift ( HTS ) reactor at 350C and a Low Temperature Shift ( LTS ) at 190 to 210C.High temperature shift catalysts have an Iron Oxide-Chromium Oxide basis while LTS catalysts consist of Copper Oxide. 3.0 Gas Purification: Hydrogen purification by means of pressure swing adsorption (PSA). The PSA units reach hydrogen

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