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Mini Dragon Group (ages 6-7)

Andrew Stewart
Andrew Stewart

Safety And Runaway Reactions _HOT_

Initially, the batch was overheated to almost 50C during NSA addition. The feed was stopped and the batch was cooled to 25C (below the required temperature range). NSA addition resumed, and when complete, the batch temperature could not be controlled by the available cooling methods, exceeding the maximum temperature reportable by the temperature instrument. The runaway reaction overpressurized the reactor and it exploded. The explosion propelled the lower part of the reactor off its supports and onto the building floor. The reactor agitator landed on the roof, and the top of the reactor was thrown about 500 ft (150 m). Fortunately, no one was injured, but the accident cost the company 2 million.

Safety and Runaway Reactions

Before you can handle chemical reactions safely, you must first understand them. In this course, you'll identify potential runaway reactions and tools for sizing relief systems to safely control and contain them.

The SAChE Certificate Program offers working engineers an easy way to access a selection of knowledge about chemical process safety. Originally developed as a supplement to the undergraduate curriculum, these courses serve as an excellent introduction or refresher in chemical process safety for working professionals.

Dr. Burelbach received his PhD in Chemical Engineering from Northwestern University in 1989. Since then he has been a senior staff member at Fauske & Associates, LLC, holding a variety of leadership roles in process safety for the chemical and nuclear industries. This workshop was presented to the Safety Technology for Pharmaceutical can Chemical Processes (STPCP).

Thermal runaway is a chain reaction within a battery cell that can be very difficult to stop once it has started. It occurs when the temperature inside a battery reaches the point that causes a chemical reaction to occur inside the battery. This chemical reaction produces even more heat, which drives the temperature higher, causing further chemical reactions that create more heat.

In thermal runaway, the battery cell temperature rises incredibly fast (milliseconds). The energy stored in that battery is released very suddenly. This chain reaction creates extremely high temperatures (around 752 degrees Fahrenheit / 400 degrees Celsius). These temperatures can cause gassing of the battery and a fire that is so hot it can be nearly impossible to extinguish.

Thermal runaway can occur due to an internal short circuit caused by physical damage to the battery or poor battery maintenance. The same type of scenario could cause an external short circuit which could also kick off the chain reaction.

While the danger of excessive heat may be obvious, the danger of excessive cold may be confusing. The functioning of lithium-ion batteries depends on chemical reactions. Excessive cold can slow or stop those chemical reactions from occurring.

One of the simplest ways to prevent thermal runaway is to store batteries at safe temperatures. The ideal storage temperature for most lithium-ion batteries is between 40-70 degrees Fahrenheit (5-20 degrees Celsius). However, this can differ based on the battery and manufacturer, so consult the label for your specific battery.

There is no doubt that thermal runaway is a serious consideration for all battery systems. But with the proper care and management of your system, you can minimize this risk and enjoy all of the benefits of having battery power available to you whenever you want.

ioMosaic presents a case study on a vapor leak involving a polymerization runaway reaction in May 2020 at an industrial facility in India, sadly leading to several deaths and several hundred injuries. We developed a dynamic model of the incident, which evaluated the effectiveness of monomer inhibitors. We used our model to deconstruct the potential causes that we then compared with actual incident reports. Our article concludes that mixing can lead to hot thermally stratified layers and hence poor cooling in monomer storage tanks, where inhibitor is not mixed effectively to suppress the polymerization reaction. These factors were all found to have contributed to the incident.

A vapor leak involving a polymerization runaway reaction occurred in May 2020 at the M/s LG Polymers Pvt Ltd in R. R. Venkatapurm, Vizakhapatnam district, India. The plant had been closed as part of a national lockdown to prevent the spread of COVID-19. One of the styrene monomer tanks, whilst inhibited, was involved in a runaway reaction spread of COVID-19. One of the styrene monomer tanks, whilst inhibited, was involved in a runaway reaction with several fatalities and many hundreds of hospitalisations.

From our modelling we concluded that the reaction most likely occurred towards the top of the tank within a thermally stratified layer separate from that measured by the temperature probe at the bottom of the tank, which was still measuring 17C moments before the time of the runaway reaction occurring due to insufficient circulation of cooled styrene.We therefore assumed that effective refrigeration unit was lost, or the tank was thermally stratified, on Day 40. This modelled scenario confirms that lower amounts of inhibitor was mixed within these layers and was not well mixed throughout the tank. Our model predicts that for an inhibitor concentration of between 3 and 7 ppm the polymer concentration was consistent with actual measurements as shown in the figure below. This agrees with the conclusions reached in published independent reports on increases in polymer concentration measured at the top of the tank.

The precise prediction of reaction progresses in adiabatic conditions is necessary for the safety analysis of many technological processes. Calculations of an adiabatic temperature-time curve for the reaction progress can also be used to determine the decrease of the thermal stability of materials during storage at temperatures near the threshold temperature. Due to insufficient thermal convection and limited thermal conductivity, a progressive temperature increase in the sample can easily take place, resulting in a thermal runaway.

Several methods have been presented for predicting reaction progress of exothermic reactions under heat accumulation conditions [1, 8-17, 23-44]. Because of decomposition reactions usually have a multi-step nature, the accurate determination of the kinetics is a key prerequisite for correct describing the progress of the reaction. The use of simplified kinetic models for the assessment of runaway reactions can, on one hand, lead to economic drawbacks, since they result in exaggerated safety margins. On another hand, it can cause dangerous situations when the heat accumulation is underestimated. For strongly exothermic reactions occurring adiabatically, incorrect kinetic description of the process is usually the main source of prediction errors.

Due to the totally different rate of heat exchange in adiabatic conditions the heating rate of the process (called now self-heating rate) cannot be controlled anymore, being dependent now on the kinetics, adiabatic temperature rise and φ-factor. Experimental data collected during investigation of exothermic reactions in adiabatic conditions must be corrected for the effect of sample container heat capacity. This correction factor is called the phi factor or thermal inertia (Townsend and Tou [24]). The heat capacity of the container (test cell) serves to lower the measured temperature of the reaction and increase the time to maximum rate. The thermal inertia is defined as φ= (heat capacity of the sample + heat capacity of the vessel)/ heat capacity of the sample. The phi-factor approaches the value of 1 for large vessels or at genuine adiabatic conditions.

Because the presence of a temperature difference leads to heat transfer, an adiabatic calorimeter constantly attempts to achieve the equilibrium state by keeping Te = Ts. As a consequence there is no driving force for a heat transfer and the chemical reactions run adiabatically. We obtain as before

The adiabatic induction time is defined as the time which is needed for self-heating from the initial temperature to the time of maximum rate (TMRad) under adiabatic conditions. Depending on the decomposition kinetics and ΔTad, the choice of the initial temperature strongly influences the time to runaway and the rate of the temperature evolution under adiabatic conditions. Figure 5.5 presents the dependence of the adiabatic induction time TMRad on the initial temperature.

Some chemicals have the potential to cause fires or explosions, and, as hazardous materials, are handled with appropriate care to minimize accidents. This category of hazardous materials includes a group of chemical substances called reactive or self-reactive chemicals which may initiate exothermic decomposition by themselves. The commonly applied thermal hazard indicator which estimates the hazard probability, especially for packaged materials during transport, and/or storage, is Self Accelerating Decomposition Temperature (SADT). The determination of SADT is based on the monitoring of the temperature of the sample with the mass m, volume V, surface area S, density (or bulk density) ρ, and specific heat capacity Cp, with a uniform initial temperature T0 and packed into a vessel of arbitrary shape. At time t0, the surrounding temperature of the investigated material is increased to Te which initiates the heat transfer between the packaged material and its surroundings, characterized by a heat transfer coefficient h. The SADT, as defined by the United Nations SADT test H.1 [41], is the lowest ambient temperature at which the centre of the material within the package heats to a temperature 6C higher than the environmental temperature Te after seven days or less. This period is measured from the time when the temperature in the center of the packaging reaches 2C below the ambient temperature. The determination of SADT according to UN test H.1 [41] is based on the results of series of large-scale experiments performed with the packaging in an oven at constant temperatures. Each test, performed at a new temperature, (according to the UN recommendations, the step of the oven temperature variations amounts to 5C) requires a new large-scale packaging. This procedure, despite its reliability, is rarely used, because it is rather expensive, material- and time-consuming and, in certain cases, quite dangerous due to thermal safety and toxicity reasons. Another limitation is related to the relatively common situation when only a small amount of the investigated material is available at the early stages of a project. Taking into account all the issues presented above, it seems fully understandable that there is an important need of other reliable, faster, safer and cheaper test methods requiring smaller amounts of reactive materials and applicable at the laboratory scale (mg or g). 041b061a72


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