SU1733817A1 - Method for cryogenic pipeline shutoff - Google Patents

Abstract

The invention relates to mechanics, in particular to pipes used in cryogenic engineering. The purpose of the invention is to increase reliability by reducing water hammer - by non-condensing gas being blown into the flow of cryogenic fluid before the pipeline closes and creating a volumetric gas content in the range of 0.25 ... 0.70, at which the speed of sound in the flow is 4 .. .6 times less than in a stream of continuous liquid. Then shut off the pipeline, reducing the magnitude of the water hammer. 2 Il.

Description

The invention relates to mechanics, in particular to pipes used in cryogenic engineering.

There is a known method of shutting off a cryogenic pipeline, based on a mechanical blocking of the flow area with valves, gate valves, etc. locking elements.

The disadvantage of this method of blocking the cryogenic pipeline is the low speed due to the inertia of the moving elements of the locking bodies. Moreover, with an increase in the diameter of the overlapped highway, the overlap delay time increases. The speed of the valve is associated with a quadratic increase in the force effect on the moving parts of the valve, which follows from the ratio

kg, G

but

thatҐ, gp t / 21T, ifTp -

and where tp is the time of movement of fixed

valve parts;

h is the amount of valve lift (for full-lift valves);

h 1 / 4d, where d is the diameter of the pipeline to be blocked;

a - the acceleration of the moving elements of the valve;

k is the speed increase factor.

The total delay time of the overlap is the sum of the travel time rd and the time delay of the movement of the valve T3d, i.e. gp td + g3d. The latter is made up of the response time of the EPA (electropneumatic valve) tapk and the actual delay time of the PGK (pneumo-hydraulic valve) tpgk, i.e. road tzdpk + gpgk.

The delay time of the NGL (gpgk) movement is determined by the parameters of pneumatic drives connecting the EPA and NGL, and the gas volumes of the IGF control cavities.

The actual response time for existing EPAs is 0.1 s, and - NGL 2-3 s for pipeline DN 150 mm.

VJ GJ iCJ | 00

VI

In this case, a consequence of an increase in the speed of the NGL is the occurrence of hydraulic shocks and a significant increase in the force of the impact of the valve on the seat, which, apart from the possible destruction of the pipeline, may lead to an explosion, for example, in oxygen pipelines.

Improving the speed of overlapping cryogenic pipelines during their destruction is necessary to reduce the amount of emissions of cryogenic explosions and flammable liquids, leading to a worsening of the emergency situation.

The problem of increasing the reliability and speed of emergency shut-off is especially relevant when developing large-scale pumps with large diameters of inlet and outlet pipelines.

There is also known a method of emergency shutdown of a cryogenic pipeline, based on the injection of condensing gas into a stream of cryogenic liquid, followed by filtration of the condensed phase.

The mechanism for shutting off the cryogenic pipeline by supplying easily condensing gas to it is as follows. The gas, mixing with the cryogenic liquid, partially condenses, evaporating the liquid, and clogs the filter pores with the resulting crystals. The non-condensed part of the gas, which is throttled in the pores of the filter, condenses and crystallizes directly in the pores of the filters. The vapor gap formed as a result of gas injection and evaporation of a cryogenic liquid contributes to a sharp decrease in the mass flow rate of cryogenic liquid in the pipeline at the initial moment of shut-off. In addition, it eliminates the formation of water hammer in the pipeline.

The disadvantage of this method lies in the low reliability associated with the destruction of the filter element material and the ingress of its pieces into the pump cavity. As a rule, the main requirement for the material of the filter element on a cryogenic liquid (i) is low hydroresistance, i.e. It should operate at a slight pressure drop.

When the pores of the filter element are clogged with crystals of the condensed phase, the pressure drop increases dramatically, significantly exceeding its operating range. In this case, the strength of the filter element is broken and the filter element pieces that fall into the pump path (the rotor of which rotates in the stop mode), wedges the rotating blades, causing the pump to collapse. In addition, even before the filter breaks, a portion of the gas can pass through the filter element without condensing. If condensation of this part occurs after the filter, it is obvious that the crystals that form, entering the high-speed pump, can cause its destruction.

The aim of the invention is to increase reliability by reducing water hammer.

This goal is achieved by the fact that in the method involving blowing gas into a stream of cryogenic liquid, according to the invention, a non-condensing gas is blown to a volume content of the gas phase of 0.25-0.7, and then the pipeline section is mechanically closed.

FIG. 1 shows a stand for the implementation of the proposed method; in fig. 2 - dependence of the speed of sound in a gas-liquid stream on the volumetric gas content,

The bench on which the proposed method is implemented contains a pipeline 1 for supplying a cryogenic liquid from a source (not shown) connected to the test pump 2. A volumetric gas content sensor 9 and valve 3 are installed in the pipeline in front of the pump. openings 5, surrounded by a manifold 4 outside the pipeline, connected by pipeline 6, on which valve 7 and throttle 8 are mounted, with a balloon battery 10 with non-condensable gas (helium or nitrogen Britain pump for liquid oxygen).

In the normal course of testing the pump 2 with liquid oxygen, it comes from the source and is discharged into the receiving tank or returned to the pump inlet through the jet coolers of the cryogenic liquid stream. In the event of an emergency associated with the destruction of a pump or piping, in order to reduce the release of liquid oxygen, which exacerbates the fire and explosion hazard situation, piping 1 is closed. Opening valve 7 serves non-condensable gas through conduit 6 through a pre-open throttle 8 into the collector 4, and through the openings 5 into the stream of cryogenic liquid flowing through pipeline 1. By adjusting the throttles 8, a gas-liquid mixture is formed at the pump inlet, mask which void fraction is in the range 0,25-0,7. It is known that the speed of sound in a gas-liquid stream with a volumetric gas content of 0.25-0.7 is about 4-6 times lower than the speed of sound in a liquid (see fig. 2). The control over the volume content of the gas phase is carried out by the sensor 9, which issues a command through the control unit (not shown) at p 0.25-0.7 to close the valve 3. The cryogenic liquid flow through the pump 2 is cut off. Because of the smaller the speed of sound in the gas-liquid flow, the magnitude of the surge from closing the valve 3 and its velocity in the pipeline 1 will be 4-6 times less than in the stream of continuous cryogenic liquid. In addition, the presence of a gas phase at the moment of gas injection into the stream of cryogenic liquid begins to block its flow and reduce its mass flow, which reduces the amount of cryogenic liquid pouring out from the pump, i.e. In this method of overlap, there are two positive points: the hydraulic shock is eliminated when the valve 3 is closed, which cannot be done without gas supply; action is provided quickly, since when the gas is blown in, the mass flow rate decreases, i.e. the pipeline is overlapped. In general, this increases the reliability of the overlap due to the absence of mechanical particles of the condensed phase, which lead to jamming of the pump rotor and disabling it.

The method can be implemented by another method. Preliminary for specific flow rates of cryogenic liquid and known valve response time 3, the required flow rate of non-condensable gas is determined, which ensures the minimum time for creating a given volumetric gas content p 0.25-0.7 through throttle 8. Then, the cyclic diagram of valve response sequence 7 is entered into the control unit supplying non-condensing gas and valve 3, which mechanically shut off pipeline 1. This option optimizes the shutdown time of pipeline 1.

obtain a volumetric gas content equal to p 0.25-0.70.

Writing the mass balance equations for a two-phase flow formed by a slightly blowing gas into a liquid in the form Gr Gx prVrpF, SJ C (1-X) / OzhUzh (1-p) F, where G Gr + 6G is the second mass flow rate of the gas mixture and liquids; X Gr / G - mass gas content; p Fr / F is the volumetric gas content;

R - DENSITY;

V is the speed;

F is the cross-sectional area, p RG / RJ, and indices r is gas, W is liquid, and having solved them with respect to X, we obtain the condition that the gas velocity is equal to the velocity of the liquid.

X UR

one

Then for p 0.25, p 2.66 / 1137 0.00234

0.25 -0.00234 1 1 - 0.25 + 0.25 -0.00234

 0.779 10

, w

Gri

Szhh 20-0,779-10

-z

1 x 1 -0.779-10 3 0,0156 kg / s.

Respectively for p 0.70 and P 0.00234

X2 0.00546 Gr2 0.109 kg / s. The pr-in average of the interval is p 0.25-0.70

Gr (Gri + Gra) / 2 (0.0166 + 0.109} / 2 0.0624 kg / s.

For the case of supercritical outflow in 64 holes. with a diameter of 1.5 mm with a flow coefficient of ju 0.7 from the formula

Example. Liquid (oxygen) is pumped by pump 2 with a second mass flow rate equal to 20 kg / s and an inlet temperature to the pump (in pipe 1) equal to 90 K, pressure 0.5 MPa. Liquid density equal to 1137 kg / m. liquids must be blown into the gas stream (non-condensing) to a volume content of the gas phase of 0.25-0.70 and then shut off with valve 3. We use helium as the non-condensing gas. At a temperature of 90 K and a pressure of 0.5 MPa, the density of the gels is 2.66 kg / m. Determine the flow rate of gas that must be blown to

Gr

R / RotvAp

VRTBX

0.0624У494 -ЗПП

/ RotvAp 0.7-0.785 (1.5-10 3) 2-2.15

22.25

17.01-10 3

- 13.1 10 kg / m2 1.31 MPa

Thus, the pressure in the reservoir 4, which supplies the gels with a flow rate of 0.0624 kg / s, is 1.31 MPa. From the known geometrical dimensions of the pipeline connecting the manifold 4 to the gas pressure regulator, the pressure differential AP from the pressure regulator to the collector is calculated. Setting pressure of gas reducer Rred 1.31 MPa + L R. This setting will ensure, when blowing gels, volumetric steam content in a flow p of 0.25-0.7,

The use of the invention will improve the reliability of the overlap of the cryogenic pipeline and thereby reduce the impact of the spilled fire-explosion cryogenic liquid during the destruction of the pipeline.

1

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Claims (1)

Claims A method for shutting off a cryogenic pipeline, including blowing gas into a stream of cryogenic liquid before shutting off the pipeline, characterized in that, in order to increase reliability by reducing water hammer, a non-condensable gas is blown into it, creating a volumetric content of the gas phase in the fluid flow in the range of 0.25. ..0.70, then shut off the pipeline. 0.2 0.4 0.6 0.8 f FIG. 2