Device for prevention and protection against fire and explosion in the lines of the treatment of inflammable comminuted products

Abstract

According to the invention, the device for prevention and protection against the fire and explosion in a line of treatment of inflammable comminuted products comprises: at least, one detector receiving the infra-red radiation emitted in a section of the line by the products circulating in this line; means sensitive to the level and the duration of the radiation received by the said detector and converting into alarm signals the said level and duration when they exceed a fixed limit; and means of intervention controlled by the said alarm signals and causing, in relation to the said level and duration, the injection of a cooling fluid into the line, then the neutralization of one part, at least, of the said line.

Description

The present invention relates to a device for prevention and protection against fire and explosion in the lines of the treatment of inflammable comminuted products and more particularly, but not exclusively, concerns the lines of production in which are treated ligneous fibers or analogous according to a dry process.

Experience shows that the means now used with a view to the said prevention and protection have not the efficiency required to ensure good working conditions, the primitive causes of fires and explosions being not perfectly controlled. However, the origin of these difficulties or accidents is well localized in the case of the lines of treatment of ligneous fibers and is placed in the drying section of the fibers. However, fire and/or explosion may spread in the other sections of the plant. The possibility of a fire or of an explosion immediately results from the physical conditions due to the drying, the said conditions entailing a potential risk of inflammation owing to the rate of dilution of the fibers and of the combustible dust in the air used for the pneumatic transport and on account of the temperature which necessarily is close to the point of inflammation of the said fibers and dust. The conjunction of both factors, dilution and temperature, determines a mixture of air and fibers close to a detonating mixture.

The present invention intends to remedy this dangerous state of things through means easy to use, which prevent and avoid the said difficulties or accidents, thus ensuring a production free from dangers and their consequences.

According to the invention, the device for prevention and protection against the fire and explosion in a line of treatment of inflammable comminuted products comprises: at least, one detector receiving the infra-red radiation emitted in a section of the line by the products circulating in this line; means sensitive to the level and the duration of the radiation received by the said detector and converting into alarm signals the said level and duration when they exceed a fixed limit; and means of intervention controlled by the said alarm signals and causing, in relation to the said level and duration, the injection of a cooling fluid into the line, then the neutralization of one part, at least, of the said line.

Moreover the invention consists in some other arrangements hereinafter mentioned and used together with the main arrangement above specified.

As a mere example and to facilitate the understanding of the invention is given hereinafter a description of a particular mode of realization of the invention schematically represented, but not limited, to the attached drawing on which:

FIG. 1 represents a diagram of a drying line of fibers by means of hot air, the said line being provided with a device of prevention and protection according to the invention; and

FIG. 2 shows a unit for detection and intervention pertaining to the said device.

Referring to the drawing, in the example that has been chosen, the device is applied to the prevention and protection against fire and explosion of a line of treatment of inflammable comminuted products, namely a line of drying of ligneous fibers by means of hot air. The said line essentially comprises a generator 1 for hot gas, a first cyclone separator 2 from which the wet fibers to be dried are coming out, a ventilator 3 ensuring the pneumatic transport of the fibers along the line and a second cyclone separator 4 receiving the dried fibers and separating such fibers before sending them to the place of their utilization. With the exception of the first cyclone separator 2 and of its connecting pipe 5, all the points of such drying line 6 coming from the generator 1 and ending at the second cyclone separator 4 are at high temperature, varying from about 240.degree.C when leaving the generator to 82.degree.C in the cyclone separator 4. Incandescent particles which may come from the combustion chamber of the generator and the punctual self-ignition of fibers which may occur all along the line, one understands that the latter containing a mixture of hot gas and comminuted matter particularly inflammable, represents an important risk of fire and explosion against which it is absolutely necessary to be protected.

For this purpose and according to the invention, line 6 is provided with a prevention and protection device characterized by at least one arrangement defining a unit for detection and intervention comprising a detector 7 of the infra-red radiation emitted in a section of the line 6 by the products circulating in this line. Such detectors, working electrically, are well known and offer sensitiveness and precision required for the said application. The electric signals, emitted by te detector in relation to the intensity of the measured radiation, are amplified by an amplifier 8 and are sent to a device 9 comparator of the level of such signals, the device emitting electric alarm signals utilizable for the control of the means of intervention when the level of the signals introduced in the comparator 9 exceeds fixed limits. More precisely, a signal only exceeding the lower alarm limit and caused, for example, by the passing of one or of a few fibers or particles the temperature of which is too high actuates a valve 10 with an electric control, placed after the detector 7 and injecting in line 6 a cooling fluid, such as wet vapor of water for instance, while a signal exceeding a higher alarm limit causes the neutralization of line 6 by the closing of a diaphragm 11 with electric control, placed after the detector 7 and obturating this line and, eventually, by means of the deviation, before the diaphragm 11, of the line 6 to a collecting chamber by means of a deviation valve 12 with electric control and of a deviation pipe 13. The collecting chamber, not shown, is equipped with a watering system sufficiently efficient to drown the burning products thus deviated. Of course, the diaphragm 11 as well as the injection valve 10 and the deviation valve 12 may be actuated by a fluid under pressure itself being admitted by electro-valves connected to the comparator 9.

The neutralization of the line 6 by the closing of the diaphragm 11 and eventually working of the deviation valve 13 may further result from the existence of a signal only exceeding the lower alarm limit but with a duration such as, in spite of the low level of the detected radiation, the prolonged existence of this radiation and the raising of the corresponding temperature may entail an apprehension concerning an aggravation of the situation. To that effect, the alarm signal of the lower level is also sent by the comparator 9 to a timer 14 which, at the end of a fixed time and if the alarm signal subsists, sends a closing signal to the diaphragm 11 and, eventually, a deviating signal to the valve 12.

The suppression of the risk detected by the detector 7 brings back to an inactive state, eventually with a certain temporization as a precaution, the means of intervention: injection valve 10, diaphragm 11 and, eventually, deviation valve 12.

The device for prevention and protection of the drying line 6 preferably comprises several units for detection and invention of the type previously described, distributed along the line. For example, a first unit, with a detector 7a, injection valve 10a and deviation valve 12a, deviation 13a and diaphragm 11a, is placed between the outlet of the hot gas generator 1 and the ventilator 3 for pneumatic transport; after the inlet 5 of fibers to be dried may be placed a second analogous unit with a detector 7b, valves 10b and 12b, deviation 13b and diaphragm 11b and several units each of them only comprising one detector 7c, 7d, 7e or 7f, one injection valve 10c, 10d, 10e or 10f and one obturating diaphragm 11c, 11d, 11e or 11f. The means of intervention, neutralizing, at least, one part of line 6, may also comprise, apart from obturation diaphragms 11 and deviation valves 12, means of stopping or reducing the heating and outflow of the hot gas generator 1 and of the deviation of the fibers coming out of the cyclone separator 4 by a deviation 15, such deviation being commutated by a deviation valve 16. Eventually, the means of intervention placed after or before one or several of the units of the device may be actuated by the detector or detectors of this or these units, if the seriousness of the situation requires it. For this purpose, it suffices to set the necessary connections between such means of intervention, on the one hand, and the comparator or comparators 9 and the timer or timers 14 concerned, on the other hand. The delay of response of a unit of the device, that is to say the time elapsing between the detection of a thermic anomaly and the going into action of the means of intervention, injection of wet vapor, for example, is about 0.1 second. Considering a transport speed of fibers amounting from 12 to 25 meter per second in the line 6, the distance between the detector and the nearer means of intervention which such detector may actuate after itself is about 2.5 meter. Such considerations permit to fix the respective position of various units of the device and of the components of the said units to obtain a complete prevention and protection all along the line 6.

The fractioning of the line by the units of the device not only increases the security, but further reduces at the very least the regrettable consequences which any thermic accident might have on the production. Owing to the said device, such thermic accident remains localized and then is eliminated. Besides such advantages, the device according to the invention permits to guarantee a real protection of the employees and of the machines and thus to respect the clauses prescribed by the safety regulations.

The invention is obviously not limited to the methods of application and realization indicated, it also covers all its variants.

Claims

What is claimed is:

1. A device for prevention and protection against fire and explosion in a line of treatment of inflammable comminuted products, particularly in a line adapted for dry treatment of ligneous fibers or the like comprising: at least, one detector receiving the infra-red radiation emitted in a section of the line by the products circulating in this line; first means sensitive to the level and the duration of the said radiation received by the said detector and converting into alarm signals the said level and duration when they exceed a fixed limit; and second means of intervention controlled by the said alarm signals and causing, in relation to the said level and duration, the injection of a cooling fluid into at least a portion of the line whereby there is achieved the neutralization of a fire or explosion hazard inherent in a sensed condition.

2. A device according to claim 1 wherein said detector and said first and second means define a unit comprising an infra-red radiation detector adapted to develop an electrical signal, amplifying means operatively associated therewith for amplifying the signals emitted thereby, a comparator adapted to emit electric alarm signals when the level of the signals introduced into said comparator exceeds certain limits and means controlled by the said alarm signals.

3. A device according to claim 2 in which the means of intervention of the said unit comprise an injection valve and a diaphragm placed after the detector and controlled by the said electric alarm signals, the said valve injecting in the line of treatment a cooling fluid, such as water vapor, and the said diaphragm neutralizing the said line by the obturating of this line.

4. A device according to claim 2 in which the means of intervention of the said unit comprise a deviation valve controlled by the said electric alarm signals and neutralizing the line of treatment by the deviating of this line to a deviation pipe.

5. A device according to claim 2 wherein the electric alarm signals of a low level control the injection valve and those of the higher level control the diaphragm.

6. A device according to claim 4 wherein the electric alarm signals of a higher level control the deviation valve.

7. A device according to claim 3 wherein the said unit comprises a timer receiving the alarm signals of a low level and sending, at the end of a fixed time and if the said alarm signals subsist, a closing signal to the diaphragm.

8. A device according to claim 4 wherein the said unit comprises a timer receiving the alarm signals of a low level and sending, at the end of a fixed time and if the said alarm signals subsist, a deviating signal to the deviation valve.

9. A device according to claim 2 in which several units for detection and intervention are distributed along the line of treatment.

10. A device according to claim 9 in which means of intervention placed before or after any unit of the device may be actuated by the detector of this unit, the necessary connections being set between the said means of intervention, on the one hand, and each comparator and timer concerned, on the other hand.

11. A device according to claim 1 wherein the line of treatment includes a generator of hot gas and said means of intervention further comprises means of stopping or reducing the heating and outflow of this generator.

12. A device according to claim 1 wherein said means of intervention is adapted to assume an inactive state upon suppression of the fire or explosion hazard.

13. A device according to claim 3 wherein the electric alarm signals of a low level control the injection valve and those of a higher level control the diaphragm.

14. A device according to claim 4 wherein the electric alarm signals of a higher level control the deviation valve.

15. A device according to claim 3 wherein the said unit comprises a timer receiving the alarm signals of a low level and sending, at the end of a fixed time and if the said alarm signals subsist, a closing signal to the diaphragm.

16. A device according to claim 4 wherein the said unit comprises a timer receiving the alarm signals of a low level and sending, at the end of a fixed time and if the said alarm signals subsist, a deviating signal to the deviation valve.