In this tutorial, we will simulate a runaway reaction scenario, which is a situation where chemical process becomes uncontrollable, leading to a rapid increase in temperature. Understanding the conditions that lead to such a reaction is crucial for preventing dangerous accidents in industrial processes. We will use non-isothermal batch reactor in Softinery web app:

https://tools.softinery.com/nonisothermal_batch

Setting the parameters

First, let’s set the parameters of the process. We will define parameters corresponding to a gas phase in slightly increased pressure. Chosen parameters are the following:

Density: 22 kg/m³(step 1 on the image below)
Specific heat: 1000 J/(kg·K) (step 2)
Reaction enthalpy: -500 kJ/mol (step 3)
Initial substrate concentration: 40 mol/m³ (step 5)
Pre-exponential factor: 0.1·104 1/s (step 4)

The remaining process parameters can be left at their default values. You can decrease process time a little to focus on the initial period. We did not change the default reaction so it is set to A₁→ B₁(see green rectangle in the figure below).

Simulation of a runaway reaction -softinery web app — Interface of non-isothermal batch reactor and steps to obtain runaway reaction

Reaction and Temperature Dynamics

The enthalpy of the reaction indicates that a significant amount of heat is released during the process (negative value represents exothermal reaction). Given the low specific heat capacity of the gas, this could cause a rapid temperature rise if the generated heat is not dissipated quickly.

After setting the parameters, the process simulation is performed automatically. The result shows the concentration and temperature profiles over time (figure below). We can see that the reaction proceeds very rapidly. In just 1.2 seconds, the temperature rose to over 1278°C. Such a rapid reaction process would be very dangerous in a real-world scenario.

Results of a simulation of a runaway reaction - softinery web app — Results of a simulation of a runaway reaction

Importance of Safe Process Design

Understanding the dynamics is crucial for designing safe and efficient processes. Simulating reactions like this can help identify potential hazards before implementing them in real-world industrial settings. If the temperature rise is too rapid, as in the case of this simulation, it indicates that additional cooling or process adjustments are needed.

How to avoid runaway reaction?

Please try to increase values for heat removal, that is heat transfer coefficient and heat transfer area. For sufficiently high values the excessive temperature should be avoided. Another solution is to decrease initial substrate concentration, which in reality can be obtained by decreasing pressure. The figure below shows the results for an initial substrate concentration that is halved and a heat transfer area that is doubled. We observe that the temperature is much lower than before, but it is still very high (over 820°C).

Avoiding runaway reaction by adjusting process parameters - softinery web app — Avoiding runaway reaction by adjusting process parameters

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PhD. Eng. Dsc. Szymon Skoneczny has over a decade of experience in developing software for scientific and industrial purposes. He has worked for renowned companies, including Siemens, Electricite de France, and ArcelorMittal. His expertise also includes teaching and participating in research projects at institutions such as the AGH University of Science and Technology in Krakow and the Cracow University of Technology. He is the author of over 40 scientific publications on computer simulations of bioreactors, which have been published in esteemed international journals. Moreover, he has collaborated on research projects funded by the European Union, focusing on the use of high-performance computing.