Page 64 - Industrial Plant 2020

Fig. 3 Scheme of the prototype and picture of the equipment on site
(at Verneuil-en-Halatte, France)

Study and results observed, then going back to the initial distance.

of extinguishing tests on a Whenever extinguishing occurred, it occurred within
the first few seconds of the extinguishing powder

prototype flare unit injection (always less than 5 s).
Thanks to this prototype’s modularity, many
In order to carry out this study, Ai Group have parameters can be explored: e.g. gas flow rate,
received financial support from partners across the powder flow rate, powder granulometry, powder
world of oil & gas including from ENTREPOSE, a formulation, propellant gas composition, injection
major player in the design, manufacture and operation location etc.
of oil and gas infrastructures. In view of the results, the mechanism of action of the
Furthermore, the Ai Group have approached INERIS, extinguishing powder in the case of torches is quite
a worldwide recognised institute for the realisation of complex and combines a multitude of parameters.
extinction tests in “realistic” situations.
The injection of powder into the methane stream
An extensive bibliography has shown one of the key changes the density of the flow; the air entrainment
parameters for extrapolating the results would be to capacity of the methane stream is altered, resulting in
maintain the flow rate of methane into the vent. a change in the combustion rate, in a proportion that
Thus, a transparent vertical pipe with a diameter of depends on the size and concentration of the particles
200 mm and a length of 4 m is fed with methane from making up the fire extinguishing powder.
the lower part. The extinguishing system is fitted at Thus, the effect of the powder is, on one hand
the midpoint of the pipe (figure below). The pipe’s mechanical (variable part according to the nature and
open end is equipped with a refractory steel tip (where granulometry of the particles), by modifying the
temperature is measured during the tests). quantity of movement of the discharge (methane +
Once the methane is ignited (the flame is about 15 powder) and on the other hand, thermal via the
metres high above the end pipe), the flame attachment reduction of the combustion speed.
distance (distance from the end of the pipe to the By introducing these hypotheses, the Ai Group and
base of the flame) can be estimated to be about INERIS were able to develop a model, hence
50-70 cm (distance depending on the methane flow calculating the optimal conditions to obtain the
rates). suppression of the flame out of a torch: for a given
Once combustion is established, injection of extinguishing powder granulometry, there is a clear
extinguishing powder into the gas stream is initiated, relationship between the gas flow rate and the
displacing the flame attachment zone. When the powder flow rate. Thus, for a gas expansion rate in
powder flow is not sufficient to achieve extinction, the vent of the order of 100 m/s, the flow of
flame attachment distances of up to 9 m have been extinguishing powder (a fine sodium bicarbonate

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