PhreeqcUsers Discussion Forum

Kinetics and Equilibrium => Kinetics => Topic started by: Laknesh on March 16, 2017, 05:57:06 AM

Title: ADVECTION with KINETICS
Post by: Laknesh on March 16, 2017, 05:57:06 AM
Hello

I am working on the dissolution of Calcite during the transport of carbonated water. Initially, I modeled it considering EQUILIBRIUM_PHASES only during ADVECTION. Now, I did the same model considering KINETICS of Calcite instead of EQUILIBRIUM_PHASES. The calculation time for the simulation with KINETICS is too long and it never end. Could you please guide me how to reduce the calculation time.
 
SOLUTION 0      
temp 25          
pH 7   
units mmol/kgw             
Water 3.7321e-004   
EQUILIBRIUM_PHASES 0   
CO2(g) -2.0000e-001             10   
SAVE SOLUTION 0          
END              
   
SOLUTION 1-163      
temp 25   
pH 7 charge   
units mmol/kgw          
Water 3.7321e-004   
 
KINETICS 1-163      
Calcite   
-tol 1.0000e-011   
-m0 2.2847e-002   
-m 2.2847e-002   
-parms 1.5929e+006  6.0000e-001   
-bad_step_max 1000   

EQUILIBRIUM_PHASES 1-163   
Quartz 0 1.9035e-005          
END         

Advection    
-cells  163   
-shifts 18460   
-time_step 6.2202e-002 hour    
-initial_time 0   
-print_cells 163   
-print_frequency 1   
-punch_cells 163   
-punch_frequency 1

Thank you

Laknesh


Title: Re: ADVECTION with KINETICS
Post by: dlparkhurst on March 16, 2017, 04:10:12 PM
Your reaction rate is very fast, such that calcite equilibrium occurs in less than 1 second. I think the Runge-Kutta integration method is not working very well for your relatively long time steps and very fast rates. Given the parameters and resulting reaction rates, you could assume equilibrium and use your previous calculations with no loss of accuracy.

SOLUTION 0       
temp 25         
pH 7   
units mmol/kgw             
Water 3.7321e-004   
EQUILIBRIUM_PHASES 0   
CO2(g) -2.0000e-001             10   
SAVE SOLUTION 1           
END             
KINETICS 1
Calcite   
-tol 1e-9
-m0 2.2847e-002   
-m 2.2847e-002   
-parms 1.5929e+006  6.0000e-001   
-bad_step_max 1000 
-step 1 in 100
END

EQUILIBRIUM_PHASES 1
Quartz 0 1.9035e-005         
END 
USER_GRAPH 1
    -axis_titles            "Seconds" "Calcite saturation index" ""
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 graph_x total_time
20 graph_y SI("Calcite")
  -end
    -active                 true
RUN_CELLS
-cell 1
END       
Title: Re: ADVECTION with KINETICS
Post by: Laknesh on March 17, 2017, 02:31:08 AM
Dear David

Thank you for your advice and help. Yes, the reaction is very for the parameters. I will do it with Equilibrium.

Laknesh