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ABSTRACT
The sulfur recovery unit converts H2S to elemental sulfur by the Claus process. The process occurs during two combustion and catalytic reactions. Alumina (γ-Al2O3) and bauxite (Al2O3H2O) are the main Claus catalysts in crude oils. The volume distribution of micro- and macropores and the parameter of Bethe lattice representing the complex structure of catalyst pellets pores are the most important parameters affecting catalyst performance. This research is aimed at evaluating these parameters impact on effective efficiency of catalyst bed after blocking by liquid sulfur for the second and third reactors. It can be done by considering micro- and macropores as a function of pellet diameter. The results show that pellets with a minimum coordination number or Bethe lattice parameter of 6 are more suitable to use in catalytic reactors. There is a great consistency between the modeling results and the industrial ones. In addition, a catalytic pellet with a diameter of 4.55 mm has the most optimal performance for sulfur recycling processes in industrial crude oil.
Nomenclature
| a | = | Relative capacity of the catalyst |
| Cc | = | Intrinsic heat capacity of the catalyst bed (kJm− 3K− 1s− 1) |
| CP | = | Heat capacity of reaction mixture (kJm− 3K− 1s− 1) |
| CLS | = | Heat capacity of liquid sulfur (kJm− 3K− 1s− 1) |
| CGS | = | Heat capacity of gaseous sulfur (kJm− 3K− 1s− 1) |
| CC0 | = | Reactant concentration (molm− 3) |
| dP | = | Diameter of the catalyst pellet (m) |
| De | = | Effective diffusion coefficient (m2s− 1) |
| Dk | = | Knudsen diffusion coefficient (m2s− 1) |
| DAm | = | Diffusion coefficient of the components in the mixture |
| DAB | = | Bulk diffusion coefficient (m2s− 1) |
| D | = | Average local diffusion coefficient (m2s− 1) |
| E | = | Reaction activation energy (kJmol− 1) |
| f | = | Structural correction factor |
| HG | = | Enthalpy of the reaction mixture (kJm− 3.) |
| KP | = | Claus reaction equilibrium constant |
| ℓ | = | Axial coordinate (m) |
| L | = | Catalyst bed length (m) |
| Ni | = | Mass flux (kmolm− 2s− 1) |
| = | Partial pressure of ith substance near the catalyst surface (Pa) | |
| Pi | = | Partial pressure of ith substance in the gas flow (Pa) |
| Pt | = | The total pressure (Pa) |
| QP | = | Total reaction heat |
| r | = | Claus reaction rate at the catalyst surface (s− 1) |
| r′ | = | The average rate of Claus reaction (s− 1) |
| rmicro | = | Micropore radius (A°) |
| rmacro | = | Macropore radius (A°) |
| R0 | = | Universal gas constant (kJmol− 1K− 1) |
| R | = | Rate of sulfur condensation (s− 1) |
| τ | = | Time |
| T | = | Gas temperature (K) |
| U | = | Gas flow velocity (ms− 1) |
| νi | = | Stoichiometric coefficient for ith component in the Claus reaction |
| Vmacro | = | Macropore volume (cm3/g) |
| Vmicro | = | Micropore volume (cm3/g) |
| = | Mole percent of the components | |
| x | = | Liquid sulfur content (degree of filling of catalyst pellet with liquid sulfur) |
| Z | = | Coordination number |
| ϵc | = | Percolation threshold of capillary porosity |
| ϵmicro | = | Microporosity |
| ϵmacro | = | Macroporosity |
| ϵb | = | Porosity of the catalyst bed |
| ρLS | = | Density of liquid sulfur (kgm− 3) |
| ρGS | = | Density of gaseous sulfur (kgm− 3) |
| α | = | Heat transfer coefficient in the catalyst bed |
| βi | = | Mass transfer coefficient in the catalyst bed (s− 1) |
| θ | = | Catalyst temperature (K) |
| λeff | = | Effective coefficient of the catalyst bed frame heat conductivity |
| γ | = | Heat capacity of the catalyst bed (kJm− 3.K− 1) |