RU2018331C1 - Method for supply of liquid nitrogen to fire-hose barrel and device for its realization - Google Patents

Abstract

FIELD: fire-fighting equipment. SUBSTANCE: part of liquid nitrogen is taken from reservoir and heated in evaporator (gasified), returned vapors are passed through layer of fluid and simultaneously supplied to reservoir gas hollow. Pressure in gas hollow exceeds the pressure of saturation, fluid proves to be nonheated fully - it does not boils, and, having large density at evaporator inlet, fills it better. In this case, hydrostatic head for bubbling also rises to assist fluid heating in the entire volume owing to condensation heat of separate bubbles up to saturation state, without fear of pressure drop during fluid shaking in transportation. Device for supply of liquid nitrogen to fire- hose barrel includes isothermal reservoir with liquid nitrogen mounted on vehicle, evaporator connected with the help of pipelines supplying fluid and returning vapors to reservoir and dispensing pipeline. Pipeline for returning vapors has two end branch pipes, one of which is lowered to reservoir bottom part and provided with perforated collector (bubbler) and the other is communicated with reservoir top and has cutoff valve. EFFECT: higher efficiency. 2 dwg

Description

 The invention relates to fire extinguishing installations.

 A known method of supplying liquid nitrogen from an isothermal tank to a fire barrel, including self-charging the tank by heating the entire mass of liquid to a saturation state and supplying it under equilibrium overpressure along the guide shaft to the fire source.

 A device for implementing this method is known, including an isothermal tank with liquid nitrogen on a vehicle, an immersed electric heater and a guide barrel, the entrance of which is in the volume of liquid nitrogen (French application N 8711299, CL A 62 C 1/14, 1987).

 The disadvantage of this method and device is their complexity and limited use due to the presence in the tank of electrical circuits, the need for an external power source.

 Closest to the proposed, taken as a prototype is a method of dispensing cryogenic liquid to a consumer, including self-charging of the reservoir by taking part of the stored fluid to the evaporator, returning the generated vapors to the gas cavity (on the "pillow") of the reservoir, and then dispensing the product to the distribution piping.

 It is also known a device for implementing the method, containing an isothermal tank and an atmospheric evaporator connected to the tank through pipelines for supplying liquid and returning steam and a distribution pipe, the inlet of which is immersed in liquid (Cryogenic equipment. M: TsINTIkhimneftemash, 1985, p. 91).

 This method of distributing cryogenic liquid to consumers by self-pressurization, as well as the device, are simple and autonomous. However, when the vapors generated in the evaporator are returned to the gas cavity (“pillow”) of the tank and accumulated, the upper layer of the cryogenic liquid warms up, the temperature of which exceeds the mass average. There is a temperature separation of the liquid, which is not a stable state. When starting to extinguish a fire extinguishing due to fluid oscillation, its “cold” and “warm” parts are mixed, leading to a drop in boost pressure and, consequently, a drop in the pressure of the fluid displacement onto the fire barrel, which reduces the quality of the flowing stream — its range, vapor content, droplet sizes, etc.

 The proposed method for supplying liquid nitrogen to the fire barrel involves self-pressurizing the tank by taking liquid nitrogen to the evaporator, returning the generated vapors to the tank and displacing the liquid into the guide barrel, the returning vapors being passed through the liquid layer and simultaneously fed into the gas cavity (“pillow”) mainly up to working pressure, after which this steam supply line is turned off, and further self-pressurization is carried out by passing vapors through a liquid layer.

 The proposed device for supplying liquid nitrogen to the fire barrel includes a tank with liquid nitrogen on the vehicle, an evaporator connected to the liquid withdrawal and steam return pipe to the tank, and a distribution pipe, the inlet of which is immersed in the liquid, the steam return pipeline contains two end pipes, one of which it is lowered into the bottom of the tank and is equipped with a perforated collector (bubbler), and the other is connected to the top of the tank ("cushion") and is equipped with a shut-off valve.

 The essence of the proposed method is as follows.

 Part of the liquid nitrogen is taken from the total mass and subjected to heating in the evaporator (gasified), the return vapors are passed through a liquid layer and simultaneously fed into the gas cavity of the reservoir. The pressure in the gas cavity is higher than the saturation pressure, the liquid is unheated - it does not boil and, having a high density at the inlet to the evaporator, better fills it. At the same time, the hydrostatic pressure on the bubbling increases, contributing to the heating of the liquid throughout the volume due to the heat of condensation of individual bubbles.

 In contrast to the known schemes for bubbling changes in the temperature of a liquid that require a third-party accumulated gas, in the proposed solution, gas for bubbling is taken from the same liquid that is heated, which is achieved in the proposed solution due to the combination of bubbling with pressurization of the "pillow". It has been experimentally found that the bubbler (warm-up) circuit only starts to work efficiently with a certain boost pressure of the “cushion”, due to the structural design and thermal insulation of the pipelines supplying the evaporator.

 In FIG. 1 schematically shows a device; in FIG. 2 - experimental dependence of pressure growth as a function of time to the state of saturation.

 The device consists of an isothermal tank 1 with liquid nitrogen 2 mounted on a vehicle (not shown), a fluid withdrawal valve 3, an evaporator 4, a steam return pipe 5, two end pipes 6 and 7 with a perforated manifold 8 and a shut-off valve 9, valve 10 gas discharge valve 11 of the issue and the fire barrel 12.

 The device operates as follows.

 In the initial position, the tank 1 is filled with liquid nitrogen 2, the gas discharge valve 10 is open, the remaining valves are closed. The pressure above the liquid mirror (in the gas "cushion") is 1 ata.

When the valves 3 and 9 are opened (the gas discharge valve 10 is closed), liquid nitrogen enters the evaporator 4 and is gasified. The resulting vapors enter the reservoir in two ways: through the pipe 6 and through the perforated collector 8 under the liquid layer and through the pipe 7 into the gas cavity (on the "pillow"). In this case, in the gas cavity there is a process of vapor accumulation to the working pressure (points 0-I, Fig. 2), and in the entire volume - heating of the liquid. Deviation of the boost pressure from the worker to a smaller side leads to a decrease in the bubbling efficiency and at a pressure of 1/3 P _slave to its complete cessation. Effective bubbling begins with a pressure of 2/3 P _slave and above, i.e. with the growth of hydrostatic pressure at the entrance to the nozzle 6 bubbling. The run-up of pressure 2/3 P _slave to P _{slave is} determined by the design device and the insulation quality of valve 3 and pipe 5 of the evaporator 4. The deviation of the boost pressure to the larger side is limited by the strength of the tank vessel.

When the "pillow" of the reservoir reaches the working pressure, the valve 9 closes. The 4 pairs returned from the evaporator are supplied only to the perforated collector 8 under the liquid layer to warm it up. The pressure in the gas "cushion" drops to a certain value equal to 0.6 P _slave (points I-II, Fig. 2), followed by growth to saturation (points II-III, Fig. 2), i.e. the pressure in the gas "cushion" increases in accordance with an increase in the temperature of the liquid in the entire mass without fear of a drop in pressure when the fluid oscillates (agitates) while the vehicle is moving.

Claims (2)

 1. The method of supplying liquid nitrogen to the fire barrel, including self-charging the tank by taking the liquid to the evaporator, returning the vapor to the tank and displacing the liquid into the distribution pipe, characterized in that the return vapor is passed through the liquid layer and simultaneously fed into the gas cavity of the tank.  2. A device for supplying liquid nitrogen to a fire barrel, containing a tank with liquid nitrogen on a vehicle, an evaporator connected through pipelines for supplying liquid and returning steam to the tank, and a distribution pipe whose inlet is immersed in liquid, characterized in that the steam return pipe contains two end pipes, one of which is lowered into the bottom of the reservoir and is equipped with a perforated manifold, and the second is in communication with the upper part of the tank using a shut-off valve.

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