Trickle bed reactor

Trickle bed reactor : definition, design, transport steps, mole balance, applications, adv. and dis adv.

1. Trickle-bed reactor Eng. Tareq Al-Anber

2. How it is work? Trickle bed reactors are solid-liquid-gas contacting devices wherein liquid stream flows downward over a bed of catalyst with pressure difference serving as the driving force, and with a gas stream can either flow concurrent with the liquid or countercurrent to it through the bed . It is named Trickle Bed Reactor, because of its operation in a trickle-flow system. The fluid flows over catalyst particles and forms fine films . Trickle bed reactors are primarily operated in continuous mode but are sometimes used in semi-batch processes .

3. Design Tubular tank tubular tank with a sieve plate or wire mesh near its bottom to support the packed bed. At the top of the bed: Bubble cap. Sieve plate distributor. Fine layer of non-reacting particles.

4. Types Conventional tickle bed reactors R andomly packed beds of porous catalyst particles. Semi structures tickle bed reactors Structured packing catalyst. Lower pressure drop and eliminates diffusion as a limiting factor to the reaction. Micro-tickle bed reactor Micro-channel packed with catalyst particles. Better control of reaction parameters and enhance process safety.

5. Transport steps The transport of species A From bulk gas phase to the gas-liquid interface. Equilibrium at gas-liquid interface. Transport from interface to bulk liquid. Transport from bulk liquid to external catalyst surface. Diffusion and reaction in the pellet. The transport and reaction of species B Transport of B from bulk liquid to solid catalyst interface Diffusion and reaction of B inside the catalyst pellet

6. 1) From bulk gas phase to gas-liquid interface .

7. 2) Equilibrium at gas-liquid interface : concentration of A in liquid at the interface H : Henry's constant  

8. 3) Transport from interface to bulk liquid where liquid-phase mass transfer coefficient, m/s : concentration of A in liquid at the interface, kmol/m 3 : bulk liquid concentration of A, kmol/m 3  

9. 4) Transport from bulk liquid to external catalyst surface

10. 5) Diffusion and reaction in the pellet.

11. Combining Equations The overall rate equation for A

12. Mole balance on species A gives is the overall transfer coefficient for the gas into the pellet (m 3 of gas/g cat . s )  

13. 6) Transport of B from bulk liquid to solid catalyst interface Where and are the concentrations of B in the bulk fluid and at the solid interface, respectively.  

14. 7) Diffusion and reaction of B inside the catalyst pellet. Combining Equations and rearranging, we have The overall rate equation for B

15. A mole balance on species B gives

16. Mass Transfer of the Gaseous Reactant Limiting For this situation we assume that either the first three terms in the denominator of Equation are dominant or that the liquid-phase concentration of species B does not vary significantly through the trickle bed. For these conditions . Is constant and we can integrate the mole balance. For negligible volume change = 0, then   Catalyst weight necessary to achieve a conversion of gas phase reactant  

17. Mass Transfer and Reaction of Liquid Species Limiting we assume that the liquid phase is entirely saturated with gas throughout the column. As a result, C As is a constant. Consequently, we can integrate the combined mole balance and rate law to give k vg , k vl . Catalyst weight necessary to achieve a conversion of gas phase reactant  

18. Advantages Can be used for three - phase reactions. Lower total energy consumption since solids are stagnant, not suspended in slurry. Simple to operate under high temperatures and pressures. Lower catalyst attrition

19. Disadvantages Hot spots may develop due to solvent evaporation. Channeling may occur, leading to inefficiencies. Difficult to control vessel parameters. Lower performance when liquid not uniformly distributed. Difficult to scale up due to dependence on fluid dynamics of system.

20. Usage Examples Trickle beds are used in such processes as the hydrodesulfurization of heavy oil stocks The hydro treating of lubricating oils Oxidation of harmful chemical compounds in wastewater