RU2278727C2 - Method of separating liquid and gas - Google Patents

Abstract

FIELD: separation.

SUBSTANCE: method comprises uniform distribution and supply of gas-liquid mixture to the structurized members with macroscopic and microscopic structures, impregnating the surface of the members with the liquid to be separated, collecting liquid on the surfaces of the structures, and discharging liquid and gas separately. The liquid in gas phase is converted into the liquid phase by reaching the phase thermodynamic equilibrium of the mixture.

EFFECT: enhanced efficiency.

3 cl, 3 dwg

Description

The invention relates to separation technology and can be applied in the gas, oil and petrochemical industries.

A known method of separating liquid from gas, described in RF patent No. 2168356, MKI 7, 01 J 19/32, including uniform distribution and supply of a gas-liquid mixture to structured elements, wetting the surface of the elements with separated liquid, accumulating liquid structures on the surface, followed by separate drain liquid and gas.

The disadvantage of this method is the low efficiency of the separation of liquid from gas, because the separated mixture does not arrive at separation in an equilibrium state due to a decrease in pressure and, consequently, the temperature at the mixture inlet fitting and separation units and plane-parallel motion of the phases to be separated, which leads to liquid accumulation in the outlet pipe when phase equilibrium is reached.

This drawback is partially eliminated in the method according to the patent of the Russian Federation No. 2186617, MKI B 01 J 19/32, B 01 D 3/28, which includes uniform distribution and supply of a gas-liquid mixture into structured elements with volumes of macro- and microstructures, wetting the surface of the elements with a separated liquid accumulation of liquid structures on the surface, followed by separate removal of the liquid and the separated gas, the bulk of the liquid being discharged in a continuous flow through the microstructures.

However, the efficiency of separation of liquid from gas remains low:

- due to the lack of forces for the movement of fluid particles on the surface of structures during plane-parallel motion;

- due to insufficient time for condensation of the liquid during separation.

Due to the insufficient separation efficiency, part of the liquid falls out in the pipeline after the separator when the thermodynamic equilibrium of the phases is reached, i.e. there are irretrievable fluid losses and problems in the pipeline network during transportation of a two-phase mixture.

The objective of the present invention is to increase the efficiency of separation of liquid from gas.

The technical result is achieved by the fact that in the method of separating liquid from gas in a nonequilibrium state of the mixture, with the selected separation parameters, including:

- uniform distribution and supply of a gas-liquid mixture into structured elements with volumes of macro- and microstructures;

- wetting the surface of the elements with a separated liquid;

- accumulation on the surface of the liquid structures with subsequent separate drainage of the liquid and the separated gas,

from the gas phase, the liquid in the gas phase is transferred to the liquid by bringing the mixture to phase thermodynamic equilibrium, providing the required time of its stay in the structured elements, and the liquid phase is discarded on their surface, the liquid is transferred on the surface of the elements by a rotational spiral motion, at least one of the phases, the movement of the phase in a spiral is carried out with an axial velocity equal to 1-1.75 of the radial flow velocity, when moving the phase in a spiral drive its vibrations with a ratio of wavelength to amplitude equal to

Exposure to the required residence time of the separated mixture in the structured elements brings it into a state of phase thermodynamic equilibrium with additional condensation of the liquid from the separated gas stream.

Pressure losses at the inlet fittings and pre-separation units, which are always present, reduce the temperature of the gas mixture immediately before the separation process, upsetting the phase equilibrium. Achieving phase equilibrium provides a complete transition of the condensed liquid from the gas phase to the liquid phase at the selected flow separation parameters (pressure and temperature). This leads to an increase in the volume of the separated liquid, an increase in the diameter of the droplets and their number, which, as a result, increases the efficiency of the process of separating the liquid from the gas with its transfer by the rotational movement of the mixture on the surface of macro- and microstructures.

Displacement of at least one of the phases in a spiral with an axial velocity equal to the value (1-1.75) of the radial velocity leads to an increase in the residence time of the phases in each element and to the appearance and maintenance of transverse components of the forces under which the liquid drops discarded constantly on the surface of macro- and microstructures. This technique leads to an increase in the efficiency of separation of liquid from gas. The process of formation of phase oscillations, while simultaneously moving them in a spiral, with a wavelength to amplitude ratio of 4-8, leads to an additional increase in the residence time of the phases in each element, their additional mixing, and, as a result, to an increase in the efficiency of the process of separation of liquid from gas at practically constant hydraulic resistance.

The applicant and the authors of the current level of technology do not know how to separate liquid from gas, in which the above methods would be applied.

Figure 1 shows three layers of structured elements rotated 90 ° with respect to each other, with a phase diagram in which the macrostructure in the form of inclined channels is formed by two pairs of intersecting surfaces, of which one pair is inclined, and the microstructure is formed by a porous surface material; figure 2 presents a cross section of structured elements; figure 3 is a diagram of the movement of spiral flows in adjacent channels; figure 4 - corrugated surface of the elements and the movement of spiral flows along it.

In the structured elements 1 with volumes of macro-2 and microstructures 3, a nonequilibrium gas-liquid mixture 4 is uniformly fed, because the pressure in the pipeline and the inlet fitting is always greater than the pressure in the separator by about 0.03-0.05 MPa. The surfaces of elements 5 and 6 are wetted with a liquid. The liquid 7 accumulates on surfaces 5 and 6 and is discharged separately from the gas phase 8. Two or three layers of structured elements are sufficient to divert the free liquid from the gas; more layers are required for condensation and subsequent separation. Adjacent (adjacent two pairs) surfaces 5 and 6 (FIG. 2) form inclined channels — volumes of macrostructures 2 of elements 1 along which the separated gas stream moves. At least one of the surfaces 5 or 6 is made of a porous material or of a sheet material with a porous coating. The porous material or coating forms a developed interfacial contact surface - the microstructure of 3 elements 1 and a drainage system, through which the condensed liquid is discharged.

In the lower two or three layers of elements 1, liquid is separated from the gas, the liquid remaining in the gas mixture is condensed from the separated gas by bringing it to phase thermodynamic equilibrium at actual separation pressures and temperatures, ensuring the required residence time in them.

The residence time of the separated gas in the structured elements is ensured by the length of its passage, and the rotational spiral motion of at least one of the phases, for example gas, is provided inside the macrostructure 2, of each element 1, the transfer of condensed liquid droplets on the surface of the elements, for example by gas flow 9 (Fig. 3), droplets of liquid are transferred on surfaces 5 and 6, which simultaneously increases the length of the passage of the mixture, and therefore, the residence time of the phases. The spiral movement of the phases is provided by swirlers placed before entering the structured elements or made directly in the channels of the macrostructure, for example, blades 10, which can be stamped, i.e. bending at an angle of part of the surfaces 5 and (or) 6. In the channel of the macrostructure 2 stream 4 is divided:

- to the stream 11, taken through the holes 12 of the surface 5 (and / or 6), at an angle upward into the adjacent channel of the macrostructure 2;

- into the remaining stream 13, into which through the opposite openings 14 of the surface 5, flow 15 is fed at an angle upward.

The selection of the gas stream 11 from the macrostructure in one direction and supplying it with a displacement of the stream 15 in the other direction creates a torque that provides a spiral motion, for example, gas - stream 9. The selection of a part of the stream from the macrostructure 2 and the flow of part of the stream from it located opposite macrostructures help to equalize their concentrations through mixing.

The movement of the phase in a spiral is performed with an axial speed equal to 1-1.75 of the radial speed, which depends on the angle of inclination of the blades 10, with an angle of inclination of the blades of 45 ° the axial speed is equal to the radial.

When moving phase 7 and (or) 8 in a spiral (to further increase the mass transfer efficiency between gas and liquid flows and increase the length of the path), it oscillates with a ratio of wavelength to amplitude of 4-8, which is ensured by corrugation of surfaces 5 and (or) 6 with the corresponding ratio of the step of the corrugation to the height of the corrugation (figure 4).

EXAMPLE

Natural gas with a liquid at a pressure of 7.6 MPa and a temperature of minus 20 ° C comes from the pipeline, through the inlet fitting to the separator, in which the separation pressure is 7.57 MPa. Since at the entrance to the apparatus there are changes in the parameters of the separation process, the mixture is in a nonequilibrium state. Natural gas in a volume of 210,000 m ³ / h, with a potential content of liquid condensed under these conditions in an amount of 1,113 kg / h, is fed for separation through two or three layers of structured elements (with a layer height of 150 mm), as a result of which 1050 kg / h of liquid is emitted (the amount can be measured in separators or calculated from the amount of unstable liquid product obtained per 1000 m ^{3 of} gas, or determined by the difference between the potential liquid content in the gas and the amount of liquid in the pipeline after separation). Separated gas containing 63 kg / h of non-condensed liquid:

- served and evenly distributed in structured elements with volumes of macro- and microstructures;

- condense by bringing the mixture into phase thermodynamic equilibrium by holding the residence time;

- twist the mixture with gas streams;

- moisten the surface of the elements with condensed drops of the remaining liquid in an amount of 63 kg / h;

- divert by microstructures 42 kg / h.

The ablation of liquid (loss) in a droplet form with gas is 21 kg / h. The calculation of the required residence time before bringing the liquid and gas into phase thermodynamic equilibrium is carried out according to the well-known dependence:

M = DFΔ _seq τ / δ, kg

 (see A.N. Planovsky, V.M. Ramm, S.Z. Kagan. Processes and apparatuses of chemical technology. Goskhimizdat, Moscow, 1982, pp. 573-574),

where D is the diffusion coefficient;

F is the contact surface of the phases, m ² ;

Δ _SL - change in concentration over the thickness of the layer, kg / m ³ ;

δ is the thickness of the liquid film layer, m;

τ is the time, s;

M is the amount of diffusible substance from one phase to another, kg;

D - 1.28 × 10 ^-9 m ² / s, for the key components water - methanol, to exclude the ingress of water and aqueous solutions into the pipeline after the separation process;

F - 337.5 m ² , for a separator with a diameter of 1.8 m for a capacity of 210,000 m ³ / h with a nozzle layer height of one meter with a specific surface of 135 m ² / m ³ ;

δ - 0.0024 m, for 63 kg of liquid and the specified surface;

Δ _cl - 0.6572 kg / m ^3, the average value of the concentration change in the thickness of the liquid film layer;

M - 63 kg, the amount of diffused substance per hour, incl. key components (water and methanol) 1.23 kg.

For the indicated values, the residence time of the gas in the structured elements in order to achieve thermodynamic equilibrium of the phases should be τ≥5.3 s. Therefore, the height of the structured elements at a working gas velocity of 0.3 m / s should be at least 1.6 m, taking into account the spiral motion of the gas stream at a spiral angle of 45 °, the height should be at least 0.8 m.

Thus, the application of the proposed method allows to bring the liquid-gas system into thermodynamic equilibrium directly during the separation process, to condensate an additional amount of liquid, to separate the condensed liquid and to prevent its entry into the pipeline after the separation system.

Claims (4)

1. A method of separating a liquid from a gas, including uniform distribution and supply of a gas-liquid mixture to structured elements with volumes of macro- and microstructures, wetting the surface of the elements with a separated liquid, accumulation on the surface of the liquid structures with subsequent separate removal of the liquid and the separated gas, characterized in that of the gas phase, the liquid in the gas phase is transferred to the liquid by bringing the mixture to phase thermodynamic equilibrium by ensuring the required time or her stay in the structured elements, and the liquid phase is discarded on the surface. 2. The method according to claim 1, characterized in that the transfer of fluid on the surface of the elements is carried out by a rotational spiral motion of at least one of the phases. 3. The method according to claim 1, characterized in that the phase movement in a spiral is carried out with an axial speed equal to 1-1.75 radial flow velocity. 4. The method according to claim 1 or 2, characterized in that when the phase moves in a spiral, it oscillates with a ratio of wavelength to amplitude of 4-8.

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