RU2262365C2 - System to provide explosion protection in compartments with equipment working in explosive environment - Google Patents

Abstract

FIELD: fire prevention, particularly for power engineering and transport, to design rooms, compartments and so on characterized by risk of explosive gaseous mixture (air and inflammable gas, combustible liquid vapor) accumulation, namely to protect combustible material storage facilities, power plant rooms, compartments in vehicles and so on.

SUBSTANCE: the essence in the invention is in the following. When combustible gaseous mixture even having stoichiometric fuel-oxidizer ratio ignites detonation wave appears practically immediately. For detonation wave forming some space is needed in which separate compression waves generated by flame are united in common compression shock, namely in detonation wave. The detonation wave unlike the compression wave immediately heats gaseous mixture behind wave front. Because of above heating detonation wave moves with supersonic speed, pressure in wave front is substantially higher than in the case of normal gas burning. Above pressure increase takes place practically instantly at distance equal to several free paths of gas molecules. To take into consideration above processes system has adjusting partitions arranged so that straight distance between any two points in free space does not exceed length of predetonation zone in stoichiometric mixture of above gaseous mixture including oxygen, wherein the mixture is under atmospheric pressure if the volume communicates with atmosphere and is under maximal possible pressure if the volume is closed.

EFFECT: prevention of gaseous mixture detonation.

2 dwg

Description

The invention relates to the field of fire and explosion safety and can be used in energy and transport in the design of volumes (rooms, compartments, etc.) in which explosive gas mixtures (air and combustible gas or vapors of a combustible liquid) can accumulate. Such facilities include storage facilities for combustible substances, premises of power plants, vehicle compartments, etc.

Leaks in equipment working with combustible gases and liquids often lead to the formation of fire and explosive gas mixtures in confined spaces where this equipment is located. The degree of danger of such objects is evaluated by the categories of fire hazard ("PO") and explosion hazard ("VO"), and their operation requires the fulfillment of numerous safety conditions (GOST 12.1.010-76, etc.).

In this case, explosive (“VO”) volumes pose the greatest danger, since detonation can occur there. The loads realized in this case are much greater than in the "quiet" combustion of gases. One of the most common means of ensuring fire and explosion safety (PVB) in such cases is to fill the volume containing the hot gas mixture with inert gas from its separate source along the line with shut-off valves, triggered by a signal from sensors analyzing the composition of gases in the volume. The inert gas is filled up until the concentration of combustible gas in it falls below the minimum ignition limit of this gas [1]. This technical solution is taken as an analog. Its disadvantages include the following:

- the process of filling the volume with an inert gas requires a certain time during which an explosion can occur. This is especially important for large volumes, the filling time of which is long;

- if a combustible gas has wide concentration limits of ignition (for example, hydrogen), a lot of inert gas is required. The inert gas storage system must therefore have a large capacity, that is, either a large volume or a high working pressure, which is not always acceptable, especially in transport;

- for a sealed volume (compartment, rooms, etc.), the pressure of a large amount of inert gas can lead to an unacceptable increase in pressure in this volume and its destruction;

- when filling with an inert gas of a volume with complex internal "architecture" in its separate parts, an explosive gas mixture that is not diluted with an inert gas may remain.

Another close to the proposed solution is a system that prevents the explosion of gases due to ventilation "IN" of the room. Such a system contains means for venting the volume and sensors for dangerous concentrations of gases, the signal of which turns on the ventilation. At the same time, the volume ventilation system must be reliable and guarantee the absence of local accumulations of explosive gas mixture. In this case, specific gases can be released into the environment or burned out in the ventilation system itself. Such a technical solution is taken as a prototype [1]. Its disadvantages include the fact that:

- the development of a complex ventilation system is quite laborious, and its operation requires energy consumption;

- none of these systems guarantees against local accumulations of explosive gas mixtures, especially in emergency situations;

- determination of possible zones of accumulation of explosive mixtures in a room is quite difficult and not always unambiguous (for example, for transport objects that can change their orientation in space);

- during the first explosion, the PVB system and the ventilation system can be damaged, and the subsequent accumulation of combustible gas in the volume will be uncontrolled.

The objective of the proposed technical solution is to develop such a system for ensuring explosion safety, which would exclude the possibility of detonation. Thus, the category of this volume in PVB actually decreases from “VO” to “PO”, although formally it remains the same (since according to GOST the categorization in PVB is determined by the possibility of the formation of a gas mixture with a dangerous concentration of fuel, rather than an explosive wave).

The problem is solved in that the explosion safety of the volume with equipment operating in an explosive gas environment is provided by a system containing devices for monitoring the composition of the gas medium and for ventilation into which the technological partitions are introduced, while the equipment and technological partitions are placed in the volume so that the distance in a straight line between any two points in the remaining free space of the volume did not exceed the length of the pre-knock section in the stoichiometric mixture, the aforementioned gas medium oxygen at atmospheric pressure, if the volume communicates with the atmosphere, and at the maximum permissible pressure for the volume, if the volume is airtight.

The essence of the proposed solution is as follows. When igniting a combustible gas mixture, even with a stoichiometric ratio of fuel and oxidizer, the detonation wave does not occur immediately. For its formation in a gas, a certain minimum distance is required at which the individual compression waves generated by the flame add up to a common compression shock — the detonation wave [2]. In contrast to the compression wave, the detonation wave almost instantly heats the gas mixture behind its front. Due to this, it moves at a supersonic speed, and the pressure in the wave front is significantly higher than in the usual gas combustion mode. The pressure increase in the front of such a wave occurs almost instantly, at a distance of several mean free paths of gas molecules.

Thanks to these detonation properties, it is it that represents the main danger during the combustion of gases and thanks to it, major equipment failures and destruction of materials occur. The fact that a certain minimum distance (the so-called pre-detonation section) is necessary for the formation of a detonation wave makes it possible to prevent its formation due to the "crowding" of the volume. This is possible if the distance between any two points in the free space of a given volume does not exceed the length of the pre-knock section (PDU) in the gas mixture filling this volume.

It is known that the main factors determining the length of the remote control is the relative concentration of fuel in the mixture and the pressure of the gas mixture. Both of these determine the distance between the molecules of the reacting gases. An increase in pressure in the mixture obviously reduces this value, and the minimum PDE corresponds to a stoichiometric mixture of fuel and oxidizer [3]. The figure for the oxygen-hydrogen mixture shows the experimental dependence of the length of the remote control on the composition of the mixture, its pressure and temperature. It can be seen that the temperature of the gases practically does not affect the length of the remote control, while the composition of the combustible mixture and pressure are the main arguments for the length of the remote control [3].

Thus, if the maximum distance between any two points in the free space of the volume (not occupied by equipment) is less than the length of the remote control in a gas mixture with a stoichiometric content of fuel and oxygen and at the maximum pressure allowed in the volume, there will be no detonation when the gas ignites in the volume, even if concentration of combustible gas allows this.

For example, as can be seen from the graphs in figure 1, in the volume where oxygen and hydrogen can be, detonation is excluded if the distance between any two points in free space does not exceed ~ 0.7 m (if atmospheric pressure). Moreover, the composition of the mixture does not matter anymore, since such a remote control refers to the stoichiometric composition (minimum on the curve).

Power impulse loads acting in this case will be almost an order of magnitude smaller than those realized during gas detonation. In this case, the dynamic loading of structures will be much more "smooth", i.e. the duration of pressure pulses will be an order of magnitude less. This is a positive effect of this technical solution, since it significantly reduces the strength requirements for the room itself and the equipment in it.

The scheme of the proposed system is given in figure 2, where it is indicated:

1 - volume with equipment operating in an explosive gas atmosphere;

2 - working equipment (for example, gas cylinders are shown);

3 - device for monitoring the composition of the gaseous medium;

4 - volume ventilation device;

5 - technological partitions.

As an example of equipment located in the volume of figure 2, shows cylinders with natural gas (methane). Since there is quite a lot of free space and with the leakage of cylinders this space can be filled with an explosive mixture of methane with air, technological partitions 5 are additionally installed in the volume, which prevent the formation of a detonation wave. Their shape, size and quantity in each case may be different. Thus, the "clutter" of the internal space of the volume with an explosive gas mixture helps to ensure that there is no detonation in the event of a fire. Moreover, for the "crowding" of the internal space, the volume of the equipment 1 placed there may not be enough. In this case, it is advisable to add additional technological partitions 5 inside the volume in order to “select” the excess space. They can be made in the form of hollow sealed (including inflatable) inserts. Similar "inserts", in addition, reduce the total amount of combustible gases in the room. If they are hollow or inflatable, they can be filled with nitrogen or freon, used to suppress the flame.

Thus, the proposed system for ensuring the explosion hazard eliminates the possibility of detonation of the combustible gas mixture in volumes. In practice, the PVB category of this volume is reduced from the “VO” category to the “PO” category.

List of references

1. "Fire and explosion safety of substances and materials and their extinguishing agents." Directory. M., Chemistry, 1990

2. B.C. Setae. The physics of gas combustion.

3. Physics of fast processes. Per. under. ed. N.A. Zlatina, vol. 3, Moscow, Mir, 1971, p. 222.

Claims (1)

A system for ensuring explosion safety in volumes with equipment operating in an explosive gas environment, comprising devices for monitoring the composition of the gas medium and for venting the volume, characterized in that technological partitions are introduced into it, while the equipment and technological partitions are placed in the volume so that the distance in a straight line between any two points in the remaining free space of the volume does not exceed the length of the pre-knock section in a stoichiometric mixture of the above gas medium with islorodom at atmospheric pressure, if the volume communicates with the atmosphere, and at the maximum allowable pressure for the volume if the volume is sealed.

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