This accident occurred because an enormous amount of ammonium nitrate stored in a port warehouse contacted a fire starter, propitiating the conditions and triggering ammonium nitrate decomposition reactions (highly exothermal) which released gases that provoked serial reactions and a great explosion that leveled the surrounding area.
Using a methodology they can identify and limit the safe operation areas in industrial chemical reactors, where there are processes that spontaneously release great amounts of energy that are difficult to control and that produce drastic temperature spikes, which can endanger the lives of personnel.
In a great part of the world industries –such a petrochemical, pharmaceutical, fertilizer, food, water treatment plants, among others– there are chemical reactors which are considered the heart of any chemical plant.
However, these reactors are easily exposed to different violent events that could end in fatalities, such as the case of exothermal reactions, produced by the release of energy due to light or heat in the environment. Most of these reactions are oxidations and when they are violent they can produce fire, like in combustion.
An exothermal explosion occurs when a chemical reaction of this nature is out of control and the cooling system is not able to control it, especially because the amount of reactive material cannot be contained using industrial processes.
An example of this was the disaster in Bhopal (India), which occurred in 1984 in a Union Carbide pesticide manufacturing plant, when close to 80,000 pounds of methyl isocyanate in a storage tank inadvertently entered into contact with a considerable amount of water. As a consequence, an out of control exothermal reaction was produced that overheated the system, due to a failure of the cooling system.
Later there was a change in the liquid-vapor phase of the reactive mixture, releasing a massive amount of toxic gas over the city of Bhopal, causing the immediate death of more than 2,000 people and injuries to close to 200,000. The noxious effects of the gas lasted in time, killing thousands more.
In face of this constant threat, Chemical Engineering Ph.D. Juan Carlos Ojeda Toro of the Universidad Nacional de Colombia (UNal) in Manizales, proposed a methodology that determines some of the critical points and the operation limits in a reactor, through discrimination of safe and unsafe operation regions, which can produce an a priori idea of what to do in the face of the requirements of the cooling system and the conditions that should be avoided in the control system.
“With the methodology proposed, we researched and characterized the behavior of some exothermal reactive systems that have been initiators of grave accidents at an industrial level in different operation conditions,” said Ojeda.
With them and using a mathematical model, we can determine diverse critical points (if they exist) in different conditions, which in turn limit the safe and unsafe operations conditions and discriminate different behaviors in their surroundings.
“First we need to have clarity on the physical-chemical properties of the substances managed by the industry because many reactions of this type are formed by accident and not by the product generation process. For instance, industries should not store great amounts of reactive substances in a warehouse,” said the researcher.
Throughout history there have been accidents that have involved these types of systems; in the Bhopal accident, an excess of temperature provoked the release of highly toxic gas over the city, killing almost 30,000 people.
On the other hand, with the disaster in Kursk (Russia, 2000), the energy released by a spontaneous reaction provoked the explosion of a nuclear submarine torpedoes, causing the sinking and death of 118 marines on board.
The study revised the literature of reactive systems that have not been treated correctly to observe their behavior at different conditions as well as determine the critical operation points, differentiate the safe and unsafe regions, and carry out a threat analysis, among others.
They looked for experimental information of highly exothermal reactive systems such as those of Bhopal and Kursk, and that have been actors of great-scale laboratory or industrial incidents.
The proposal created a mathematical methodology as a predictive tool of this class of behaviors in selected reactive systems and determined the unsafe operation regions to avoid industrial accidents. This methodology may be applied to systems of all nature, including chemical, physical, mechanical, electrical, and meteorological systems, among others that could have stability issues or that could vary in time, and particularly in the chemical industry applying it to any process with exothermal reactions.
To use it, the industry needs to have an experimentally verified kinetic model (used to predict product yield), the characteristics of the reactor, and the normal operation conditions. After they will obtain diagrams that will show the regions that can be thermally controlled according to the system conditions and the regions that should be avoided due to all the changes possible, avoiding atypical behaviors and unwanted phase alterations, such as passing from a liquid to a gas mixture.
Ojeda concludes that the research is a call to awareness and that through risk assessment they can warrant an adequate system operation, protecting not only the integrity of the product, the equipment, and the infrastructure but also the lives of workers and the surrounding industrial plant community.
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