Regarding the issue of particle temperature rise

Hello researchers, When using the DEM model for simulation, I want the particles to reach the pyrolysis temperature (around 600–700 K), but the rate of temperature rise of the particles is particularly slow and cannot reach the target temperature. What method is there to make the particles heat up quickly?

Excuse me, can someone help me solve this problem? I will appreciate it if this problem can be solved.

How are you heating up particles?

Firstly, an initial background IC temperature of 800K was assigned, followed by an initial bed temperature of 800K and a wall temperature of 800K. No matter how I adjusted the reaction rate, the rate of particle temperature increase was slow and could not reach around 500-650K.

Please attach your files (Main menu/Submit bug report)

Hello, reseachers. This is my main menu/submit bug report.
Best wishes! (4.2 MB)

Excuse me again, researcher. The error report has been uploaded. Can you help me solve the problem of slow particle temperature rise? Thank you very much.

How long did you run the simulation for, and how long do you expect the particles to gain 500 degrees? You need to double check your reaction rates values and heats of formation or heat of reaction.

Hello researcher, I simulated for about 6 seconds and ended the process due to the absence of reaction products. At this time, I found that the particles could not reach the pyrolysis temperature when I checked the particle temperature. I also changed the reaction rate and the heat transfer coefficient between particles, but to no avail. Is there any other solution? Thank you very much.

My guess is it is going to take more than 6 seconds to see any substantial change in temperature. You reactions rates may be several orders of magnitude too small. Your heats of formation and or heat of reactions may be off too. My suggestion is to run a unit cell test case first with some reference data so you are confident your chemistry is right.

Hello, thank you for your reply. I will try again and provide you with feedback on the simulation results.

Sorry, I’m just a little confused here. Isn’t the initial condition setting the solids temp to 773K? Why would the particles be only 500K?

$ grep -i ic_t_s *x
ic_t_s(1,1)     = 773.0
ic_t_s(1,2)     = 773.0
ic_t_s(2,1)     = 773.0
ic_t_s(2,2)     = 773.0

Hello, researcher. The initial bed temperature was set to 773K (in our experiment), and only when the biomass reached 500-700K did it undergo pyrolysis and generate products. From the simulation results, it can be seen that the particle temperature cannot reach the pyrolysis temperature.

Sorry, I still do not understand. If the particles start at 773K, what do you mean by “reach pyrolysis temp. of 500-700K”? Aren’t they already above that temp. range? Am I missing something very obvious?

Hello researcher, I’m very sorry that I didn’t explain it clearly. The initial temperature of the bed (silicon dioxide) is 773K, and the temperature of the incoming biomass particles is 293.15 K.Through heat transfer, the biomass temperature rises and undergoes pyrolysis to produce products. Therefore, it is crucial to increase the temperature of biomass from 293.15K to 500–400K; otherwise, products cannot be produced. Sorry again. Can you understand what I mean when I state it this way?

Thank you, it is clear now. I was looking at the initial condition, not the boundary condition. I felt that I was missing something. Sorry for my confusion.

I suppose you could increase the temperature of the particles at the inlet using the boundary condition settings, but that would be “cheating” (unrealistic).

I don’t have anything to add to Jeff’s suggestion - do a unit cell test to check your heats of formation, thermal conductivity, and reaction rates. Also note that it might take more than 6 seconds for the particles to heat up, with a single cell you will be able to run the simulation much faster.

I’m very sorry, I didn’t understand what you and Jeff.dietiker meant by a single cell simulation. Can you explain it in detail?

A unit cell is a very simple simulation that runs fast and that lets you verify some basic behavior is correct.
Here for example you could set up a simulation with one cell, a few sand particles and one biomass particle (use the particle_input.dat to set the initial particle data). You can turn off the particle position update in cfnewvalues.f so the particles don’t move. This will let you run thousands of seconds of simulation quickly and you can test the reaction rates and see how fast the biomass particle is heating up. Of course you must have a good idea of what to expect so you know your are on the right track.

Thank you very much for your reply. I’ll give it a try now.