Regarding a steam methane reforming reaction for hydrogen production three reactions are choosen for study.
CH4 + H2 → CO + 3 H2
CO + H2O → CO2 + H2 ( Water gas shift reaction)
CH4 + 2 H2O → 4H2 + CO2 (direct reforming)
In modelling what the rate constants to be provided in fluent window? As in figure attached..
Its the order of reaction i think. For each species rate constants are needed. As iam only looking towards only the f orward reaction, the products rate exponents are zero. What rate constants I need to input for each species in the reactants for the three equations?
I am new to this chemical reaction / species transport area. If anybody have previous experience in setting this for methane steam reforming please help me in solving this.
Thank you
Rick Manner Thank you for your reply sir. I will Include.
And Sir, what regarding the rate exponent values (order of each species/reaction). Any information regarding that.
Thank you
The first reaction is wrong. The sum of the correct first reaction and the second one gives the third. From a stoichiometry point of view, a third reaction is unnecessary. Two conversion degree, and therefore two mass balance equations, are also sufficient.
Dear Professor Miroslaw, first equation is
CH4+ H2O > CO +3H....by mistake I put H2 instead of H2O.
I will eliminate the third reaction.
Professor, any information regarding the order of the reaction/ species in the above equation.
Thank you for your suggestion regarding the discussion.
Ajith Krishnan Rohini, The order of the reaction depends on the type of reaction and catalyst. The reaction may also has no order. In order to answer the question, it is necessary to perform kinetic studies and use them to determine the kinetic equations. You can also try to search in the literature.
Ajith Krishnan Rohini At commercial conditions. The water gas shift reaction goes to equilibrium - or very near it in the SMR (Fe catalyst ~1500 F) the HT (700 F) shift reactor and the LT Shift reactor (400 F)
www.topsoe.com/processes/hydrogen
Ajith Krishnan Rohini this reaction is heterogeneous (mixed phase) reaction-solid catalyst and gaseous species. You can consider Eley Rideal kinetic model
I presume the direct reforming reaction will be first order in CH4 and zero order in steam (H20)
-r = kOa
-roverall= kKaPaPb/(1+KaPa+KcPc+KdPd)
k-reaction rate constant, a-CH4, b-H2O, c-H2, d-CO2, Oa-surface coverage of species a (CH4) on the catalyst active sites , K-langmuir isotherm constant
Rick Manner at high temperatures (700F) the kinetics of the water gas shift reaction is dependent on pressure k(T,P). The reaction mechanism is more intricate as multiple completing pathways from activated complex (transition state) to product water gas exists-complicated kinetic model
However, at 1500F thermodynamic (Gibb's) equilibrium will determines the amount of water gas produced in practical conditions
If you use catalyst the water gas shift reaction will go to equilibrium at 400 F
Before we consider one or another kinetic equation based on one mechanism or another, or even want to use empirical equations based, for example, on the Hougen-Young concept, we must first perform kinetic tests. It is also worth remembering about the reversibility of reactions.