Decomposition of fossil fuels for hydrogen production Nerijus Striugas Lithuanian Energy Institute Laboratory of Combustion Processes

Why the interest in Hydrogen? Hydrogen as an energy carrier: Finite reserves of fossil fuels; Improves energy efficiency. Environment-friendly energy carrier: Reduce Greenhouse Gas Emissions ; Reduce Air Pollution.

Hydrogen production Today, nearly all hydrogen production is based on fossil raw materials Water 4 % Coal 18 % Natural gas 48 % Oil 30 %

Hydrogen production technologies from fossil fuels Steam-methane reforming (SMR); Partial oxidation (POX)/Gasification of coal and other organics fuels; Hydrocarbons pyrolysis; Autothermal reforming (ATR).

SMR – half the hydrogen from water, half from methane The conversion efficiencies in this system can reach 65% - 75% Process chemistry: Steam reforming: CH4+H2O CO+3H2 [ΔH=206 kJ/mol] Water-gas shift (WGS): CO+H2O CO2+H2 [ΔH=-41 kJ/mol] Overall reaction: CH4+H2O CO2+3H2 [ΔH=165 kJ/mol]

POX/Coal and oil gasification The maximum theoretical efficiencies using pure oxygen is 66.7% Process chemistry for methane: 1) CH4+1/2O2 CO+2H2 [ΔH=-35.6 kJ/mol] and/or 2) CH4+O2 CO2+2H2 [ΔH=-319.3 kJ/mol] Process chemistry for coal gasification: 3) C+1/2O2 CO+2H2 [ΔH=-110 kJ/mol] 4) C+2H2O CO2+2H2 [ΔH=90.1 kJ/mol] The effluent gas from the 1 and 3 reaction are processed in WGS reactor for more hydrogen production.

Process chemistry for methane: Hydrocarbon pyrolysis This is the only method that does not produce carbon dioxide providing the material is decomposed at high enough temperatures in the absence of oxygen. Process chemistry for methane: CH4 C +2H2 [ΔH=75.6 kJ/mol] In addition to hydrogen as a major product, the process produces a very important by-product – clean carbon.

Autothermal reforming Hydrocarbons reforming process in which both exothermic partial oxidation and endothermic water-gas shift reaction occur together. Process chemistry: Partial oxidation of hydrocarbons: CnHm + n/2O2  nCO + m/2H2 ; Water-gas shift: CO + H2O  CO2 + H2 ; Overall reaction: CnHm + n/2O2 + nH2O  nCO2 + (n + m/2)H2

Autothermal reforming reactor for organic fuel conversion The aim of our research is the combined heat and hydrogen production process development.

Organic fuel conversion limits in presence of various catalyst

Temperature field in autothermal reactor For the hydrocarbons conversion the reactor temperature must be kept in the range 1200 – 1600 oC

Kinetic simulation results Reaction product concentration versus the reactor length, at 1100 oC α=0.48 and initial products composition in mole fraction are: CH4=0.1175,O2=0.1179, N2=0.4375, H2O=0.3271 Measured H2 concentration at the 1500 mm from reactor inlet is 8.4 % (vol.) Simulation result – 9.2 % (vol.)

Kinetic simulation results Reaction product concentration versus the reactor length, at 1100 oC α=0.32 and initial products composition in mole fraction are: CH4=0.1403,O2=0.0985, N2=0.3615, H2O=0.3997 Measured H2 concentration at the 500 mm from reactor inlet is 9.8 % (vol.) Simulation result – 9.98 % (vol.)

Schematic of the membrane assembly that would be used in our research for separating of hydrogen from the product gas mixture

Conclusions The primary experimental investigation and kinetics simulation of the methane autothermal reforming were performed. The aim of research was to determine optimal process condition for autothermal reforming in order to get maximum H2 concentration in the product gas mixture. Gathered information shows, that the H2 yield increases with decreasing of the air excess ratio and the optimal temperature range in the reactor is 1200 – 1400 oC. The most part of hydrogen (70 – 90%) occurs in the primary reaction zone where the fast exothermal partial oxidation (POX) reaction take place. The remain hydrogen produced in the slow conversion zone where the endothermic water-gas shift reaction occurs.

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