Nowadays safety in the chemical industry has become a high priority. Considerable progress has been made to reduce the risk of an accident, which nevertheless still happens occasionally.

The large majority of the thermal runaways are due to human factors: in particular mistakes in the loading of the reagents and imperfect maintenance.

However, a very significant number of accidents result from an incomplete knowledge of the process or reagents used. Let us consider for example the Semenov Diagram for the case of a technical problem such as a temperature breakdown or a deposit on the walls of the engine, which would decrease its coefficient of heat exchange.

In these situations, heating related to the reaction is no longer compensated by the system of cooling and hence the temperature can increase thus the reaction can runaway.

The chemical system is then likely to initiate secondary reactions or decomposition. These exothermic reactions runaway as well in their turn. The phenomenon adopts unverifiable proportions causing a thermal explosion.

An important tool to increase the safety of the workers near a chemical reactor could be, for example, the protection provided by Textile Screens that are activated in the situation where the temperature increases in the MTSR domain. This kind of protection falls from the height of the reactor creating a soft but resistant tool against the force of the explosion and eventually protection against projectiles.

There are two fundamental problems concerning this kind of textile screen protection: the first is the texture and the material utilised that depend principally on the local stress; the second problem is the shape of the textile screen which depends on the way in which the stress is diffused.

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M. Magno - ENSEM, INPL Nancy France
R. Postle - University of New South Wales, Sydney NSW 2052 Australia
S. Walter - GSEC ENSCMu, University of Haute Alsace France

For the first problem, we should study which material could give a positive response in terms of absorption of the local stress and resistance to disintegration due to the high energy localised in the projectile. This energy can sometimes be near the fusion point of the fibre. The three principal advantages for using wool at this point are: the cost, the modulus (in wool the dissipation of energy is higher then more rigid fibres like Kevlar), the high point of the fusion.

The texture of the screen textile material in the form of a multilayer, which represents another area for a large quantity of research.

Considering the second problem we include the principal parameters that generate the optimal shape of the textile screen when an explosion takes place. We evaluate, by means of optimisation, the functional derived from the energetic factors and their constraints. Energetic factors during the explosion and the way in which the explosion happens are modelled to find the best answer to the problem.

References

M. Magno, R. Postle, S. Walter, (June 22-24 2004) Industrial Textile Screens for Chemical Safety, World Textile Conference - 4th AUTEX Conference, Roubaix, Dissertation

S. Baffoun, “ Feasibility study of textile protective screens for the prevention of the consequences of accidental explosions of chemical reactors”, directed by J.Y. Drean, S.Walter M. Magno, 2002, Université de Haute Alsace, Mulhouse-France.

M. Magno, J. F.Ganghoffer, R. Postle, A. Lallam (2002) “A mesoscopic wave model for textile materials in large deformation” Composite Structure, 57 367-371

J. F. Ganghoffer, M. Magno (December 1999) “La mécanique des tissus” Pour la Science (French version of Scientific American), special issue on "Fibres textiles et tissus biologiques", pp.78-81.
massimo.magno@tin.it


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