RU2505742C1 - Device for natural gas delivery - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: device contains trunk pipeline, means for delivery of pre-treated gas under pressure and means for additional influence on stream of transported gas which are distributed at pipeline sections. Gas hydrate and water pulp with content of gas hydrate in transported gas up to 50% of its volume is used as pre-treated gas; at that particle of gas hydrate are equal to 3-5 mm. Pipeline has functions to support thermodynamic modes excluding decomposition of gas hydrate. Along the pipeline length there are distributed heating units containing inductors capable to heat pipeline perimetre up to the temperature that ensures heating of stream of gas hydrate and water pulp in its surface layer.

EFFECT: reducing costs for energy, capital costs and current expenditures for gas delivery to consumers, reducing hydraulic friction for movement of gas hydrate.

4 dwg

Description

The invention relates to the gas industry and can be used in pipeline transport of natural gas.

Known methods and devices for transporting compressed gas through single or multi-line pipelines with an initial gas pressure in linear sections of 5.5-7.5 MPa and a compression ratio at KS equal to 1.45-1.50.

The disadvantages of these methods and devices are: increased energy consumption for compression of gas due to the relatively low coefficient of utilization of useful pressure (0.68-0.70); significant unit costs associated with the construction and operation of the compressor stations located over 110-150 km (see E.I. Yakovlev. Gas networks and gas storages. M: Nedra, 1991, p. 46, 47).

It is also known a device for transporting natural gas, containing a main pipeline, a means of supplying a previously prepared gas under pressure to the pipeline, and means of additional impact on the flow of transported gas distributed in the pipeline between pump stations (see RU No. 2183788, F17D 1/02, 2000). An additional effect is reduced to an additional gas pressure in the main gas pipeline, for which gas is taken at intermediate and / or final compressor stations from the main gas pipeline, it is additionally compressed, and then an ejected gas stream is supplied to the intermediate points of the main gas pipeline.

The disadvantage of this technical solution is: increased energy consumption for compression and canalization of compressed gas to the inlet points along the length of the pipeline with high material consumption of additional equipment.

The problem to which the invention is directed is expressed in reducing energy costs for gas delivery to the consumer.

The technical result expected from the use of this invention is to reduce energy, capital and current costs for the delivery of gas to the consumer due to the preliminary compaction of the gas (conversion to gas hydrate form) and lower hydraulic resistance to the movement of gas hydrate material. In addition, the material consumption of the set of equipment is reduced.

The specified technical result is achieved in that a device for transporting natural gas containing a main pipeline, means for supplying a previously prepared gas under pressure to the pipeline, and means for additionally influencing the flow of transported gas distributed in the pipeline sections, differs in that as a pre-prepared gas used gas-water-water pulp with a gas hydrate of transported gas up to 50% of its volume, with the particle size ha he hydrate up to 3-5 mm, while the pipeline is configured to maintain thermodynamic conditions in it, eliminating the decomposition of gas hydrate, while along the length of the pipeline are distributed heating units containing inductors made with the possibility of heating the perimeter of the pipeline to a temperature that allows heating of the surface the flow of gas-water-water pulp to the level that ensures the decomposition of gas hydrate in its surface layer.

A comparison of the features of the claimed solution with the features of analogues and prototype indicates its compliance with the criterion of "novelty."

The features of the characterizing part of the claims solve the following functional tasks:

Signs ... "gas-hydrated-water pulp with transported gas gas hydrate content up to 50% of its volume was used as a pre-prepared gas" provides high pulp mobility and provides the possibility of efficient heat removal (at the stage of gas hydrate particles formation) or cold removal from gas hydrate particles (for stage of decomposition of gas hydrate), which provides either efficient efficient formation of gas hydrate or its decomposition.

The signs “when the size of the gas hydrate particles are up to 3-5 mm” provide the possibility of contacting the gas hydrate particles with a heat flow over a large area, which increases the efficiency of the formation of a “lubricating” gas layer in contact with the inner surface of the pipeline, accelerating the process of decomposition of gas hydrate particles having a small volume.

Signs indicating that “the pipeline is capable of maintaining thermodynamic regimes in it, eliminating the decomposition of gas hydrate” determines the need for the pipeline with the expectation of a sufficiently large internal pressure, which makes it possible to deliver gas hydrate pulp to the fullest extent possible, and to exclude energy costs for preserving gas hydrate in the process transporting it. In addition, this increases the safety of transportation.

Signs indicating that "heating units are distributed along the pipeline, containing inductors configured to heat the perimeter of the pipeline to a temperature that allows heating the surface of the gas-water-water pulp stream to a level that ensures decomposition of gas hydrate in its surface layer" ensure the formation on the inner surface of the pipeline thin gas "lubricant layer" providing a decrease in the coefficient of friction between the walls of the pipeline and the flow of gas-water-leading oh pulp (due to dissociation of gas hydrate particles in the slurry flow being the layer directly in contact with the inner surface of the pipeline).

The invention is illustrated by drawings, where figure 1 shows a process diagram of a complex of equipment for the preparation and transportation of gas-water-water pulp; figure 2 shows a diagram of the formation of gas hydrate; figure 3 shows a state diagram of natural gas hydrate in coordinates PT; figure 4 - shows a diagram of the process of dissociation of gas-water-water pulp under the influence of heat flow.

The drawings show:

- a gas hydrate formation unit, including: a reactor 1, its first 2 and second 3 inputs, a natural gas source 4, an ice-containing pulp storage device 5, first 6 and second 7 reactor exits, a gas-water-water pulp storage unit 8, pumps 9, 10 and 11 respectively, for pumping ice-containing pulp, for pumping a mixture of recirculated water with ice, for pumping brine, a turbocharger 12, an ice generator 13, an ice separator from a brine 14, an ice and recirculating water mixer 15, a source of feed water 16, gas pipelines 17 and 18, slurry pipelines 19-21, respectively Consequently, for pumping gas hydrate pulp, for pumping ice-containing pulp and for pumping ice-containing brine pulp, pipelines 22-25, respectively, for pumping recirculated water, for pumping brine, for pumping feed water and for supplying ice. Shut-off and safety valves, instrumentation and other auxiliary devices necessary for the operation of the gas hydrate forming unit, ensuring the implementation of the claimed method are not shown in the drawings;

- gas hydrate transportation unit, including: pipeline 26 for pumping gas-water-water pulp, pump 27, shut-off valves 28 pump station 29, main pipeline 30, inductors 31 of the heating units.

In addition, the drawings show a gas-water-water pulp 32 and a gas layer 33, a direction 34 for transporting a gas-water-water pulp, a regasification plant 35.

A source of natural gas 4 (for example, a supply gas pipeline) is connected by gas pipelines 17 with a first inlet 2 of a reactor 1 and a gas turbine (not shown in the drawings), which ensures the operation of a turbocompressor 12.

The second inlet 3 of the reactor 1 through the pump 9 with the corresponding pipeline is in communication with the storage of ice-containing pulp 5.

The first exit 6 of the reactor 1 is communicated by a slurry pipeline 19 with a storage unit for gas-water-water pulp 8.

The second output 7 of the reactor 1 is connected by a pipe 22 with an ice and recirculation water mixer 15, the output of which, by a pipe 20 with a pump 10, is connected to the inlet of the ice-containing pulp storage 5.

As the drive ice-containing pulp 5 used insulated tank, the output of which is communicated with the second input 3 of the reactor 1.

As a storage unit for gas-water-water pulp 8, a thermally insulated tank (or several tanks) is used, made with the possibility of maintaining the thermodynamic equilibrium of the gas-hydrated pulp stored in them and equipped with means for shipping the material to the consumer.

As an ice generator 13, a vacuum ice machine, preferably of the IDE Tech brand, is used, driven by a turbocharger 12. Structurally, it is a hollow tank filled with any aqueous solution, aggregated by a turbocompressor, which creates a vacuum in the tank equal to the pressure of the triple point of the solution used (in this case, sea water).

In this vacuum ice maker, the refrigeration coefficient is 12 at a boiling point of -3 ° С and condensation + 6 ° С, while an ammonia refrigeration unit at a condensation temperature + 6 ° С has a refrigeration coefficient of not more than 5, because must have a boiling point of -10 ° C (due to the fact that in the evaporator it is impossible to provide direct contact of boiling ammonia and crystallized sea water). An additional advantage of a vacuum ice maker over traditional ones is the use of a turbocompressor that uses natural gas as an energy carrier, which can significantly reduce energy consumption in the production of gas hydrate pulps.

The input of the ice generator 13 is communicated by a pipe 24 with a source of feed water 16, which is used as a seawater intake of known design.

As a separator of ice from brine 14, a known device of a similar purpose is used, such as a vibrating screen or a vibrating screen, the working surface of which is perforated with holes of the order of 1-2 mm in diameter, the productivity of which corresponds to the performance of the installation.

The main gas pipeline 30 in its design does not differ from the known ones and a priori withstands pressure up to 10 MPa (pipeline of the first category) or up to 2.5 MPa (pipeline of the second category).

In areas laid on land it is advisable to provide it with a heat-insulating coating (not shown in the drawings), for example, with a layer of polyurethane foam, about 100 mm thick. When laying a gas pipeline along the bottom of the sea, taking into account the transportation pressure and water temperature in the bottom layer, thermal insulation may not be required.

The pump 27 is installed on the pipeline 26 for pumping gas-water-water pulp from its storage unit 8 to the pump station 29 and is separated from them by shut-off valves 28.

The pump station 29 provides the injection of gas-water-water pulp into the main gas pipeline 30 under the pressure of transportation.

The heating units 31 are made in a known manner, for example, in the form of ring inductors wound like coils around a gas pipeline and connected by a conductive bus to a current source (not shown in the drawings). The conductive elements are enclosed in a current-insulating sheath made in a known manner (not shown in the drawings). The required heat flow rate is determined by the diameter of the gas pipeline and the flow rate of gas-water-water pulp through its cross section. When the pulp passes through the annular inductor, its part in contact with the surface of the gas pipeline, under the influence of the heat flux, dissociates into free gas and water in the amount m = Q / r,

where Q is the power of the heat flux from the inductor to the pulp, kW;

r is the heat of dissociation of natural gas hydrate (propane -90%, ethane -5%, propane -3%) - 410 kJ / kg;

m is the amount of dissociated gas hydrate, kg / s.

At a flow rate of 50% gas hydrate pulp 1000 m ³ / h through a gas pipeline with a diameter of 0.5 m, at a speed of 2 m / s, an inductor power of about 3 kW is required to dissociate a hydrate layer 1 mm thick at the border with the wall of the gas pipeline.

At a flow rate of 50% gas hydrate pulp 1000 m ³ / h through a pipeline with a diameter of 0.5 m, at a speed of 2 m / s, an inductor power of 3 kW is required to dissociate a hydrate layer 1 mm thick at the border with the wall of the pipeline.

The regasification plant 35 is equipped with a set of equipment that decomposes gas hydrate into water and gas, which are used as tanks (insulated tanks made with the possibility of changing the pressure from pressure close to the transport pressure to less than 10 atmospheres, the outlet of which is equipped with a compressor connected to gas holders - the named equipment is not shown in the drawings).

The products of separation of ice-containing brine pulp into fresh ice and brine are used as follows - gravity ice is discharged by pipeline 25 into an ice and recirculation water mixer 15, and brine, the salt concentration in which is higher than in the original sea water, is either discharged into the sea, or, as shown, the pipe 23 is returned to the ice generator 13.

The formation of gas hydrate takes place on the hydrate formation lines (Fig. 2), which are separated from the equilibrium line of the hydrate-gas-water by zones of a meta-stable state (a-b, g-d, g-h).

In reactor 1 (FIG. 1), a natural gas hydrate (its gas hydrate) is formed from a solution of natural gas (NG: methane-90%, ethane-5%, propane-3%) in water. Points a, d, g (Fig. 2) correspond to the equilibrium state of the "hydrate-gas-water" system, and this state cannot go into the hydrate formation process (a-b, g-d, g-h) until until a certain value of the “driving force” of hydrate formation is applied to the system (Gibbs potential G, chemical potential Δµ, supercooling Δt, supersaturation σ = Δµ / RT). All special cases of the manifestation of the driving force behind the nucleation and growth of a new phase are united by the Gibbs potential, at negative values of which the passage of all phase transitions is possible). It is known that, ceteris paribus, the hydrate formation process begins earlier and proceeds faster if various mechanical inclusions, gas bubbles, or molecular complexes-associates are always in the water, which are always the centers of formation of a new phase, in this case hydrated (heterogeneous nucleation). The beginning of the hydrate formation process coincides with the achievement of the figurative point of the spinodal gas-water system (Fig. 2). The distance from the equilibrium line to the region of the stable state of the hydrate illustrates the increase in the "driving force" of hydrate formation.

In this case, the “driving force” of hydrate formation is represented by supercooling of the gas-water system (temperature gradient of supercooling Δt _OVER = t _a -t _b ; t _g -t _d ; t _w -t _z ) with respect to the equilibrium state (points a, g, g in figure 2). Moreover, it is obvious that when the temperature of the gas-water system decreases to the same value (for example, to - 0.2 ° C), the gradient expressed in supercooling will be different at different pressures. This makes it possible to reduce the pressure and, accordingly, energy consumption in the gas hydrate generator, having a high hydration gradient potential obtained due to interphase heat transfer, which sharply reduces the temperature gradient between the growing hydrate particles and the coolant and, accordingly, increases the supercooling gradient Δt _OVERCOOL .

In addition to creating a gradient that ensures hydrate formation in the gas-water system, it is necessary to ensure the removal of hydration heat, which for methane hydrate is 410 kJ / kg.

In the process of hydrate formation, simultaneously with the formation of gas hydrate particles, their dissociation proceeds due to local temperature fluctuations, which always accompany exothermic phase transitions. They arise due to the impossibility of efficient heat removal from each nascent and growing particle of a new phase, due to their remoteness from the heat exchange surface.

In reactor 1, the heat generated by the generated gas hydrate particles is removed from them by a comparable size and located in close proximity to them (including in contact) with ice particles contained in the ice-containing pulp. Moreover, the intensity of interphase heat transfer thus ensured (heat transfer coefficient α, W / m ² * K) between the surface of growing hydrate particles and melting water ice particles of 3 ... 5 μm in size reaches 3000 ... 5000 W / m ² * K, which is comparable in effect with immersion of hydrate particles in boiling Freon-22.

The reason for such a significant effect of the sizes of ice crystals on the rate of their melting, and ultimately on the intensity of heat removal from growing particles of gas hydrate, is that in thermally thin bodies, at a distance from their thermal center to the surface (R) of the order of 5-10 μm , the rate of temperature change inside the object does not depend on thermal conductivity, but is determined by its size (for example, the duration of the process of melting a water ice crystal with a size of 100 microns is 0.2 seconds, and with a size of 5 microns - 4 * 10 ^-4 seconds).

Thus, during the nucleation and growth of gas hydrate particles surrounded by water ice particles, the value of local temperature fluctuations will be practically zero.

In this case, water ice particles simultaneously serve as centers of nucleation of a new phase of gas hydrate. Upon nucleation, the particles of gas hydrate begin to release thermal energy, which is immediately absorbed by the melting particles of water ice that are present directly at the origin of the gas hydrate. The uniform distribution of particles of water ice and gas hydrate is achieved by the constant supply of iced pulp to the reactor and the removal of recirculated water.

An additional factor that increases the efficiency of hydrate formation is the infinitely large heat transfer area between an infinitely large number of thermally thin bodies (hydrate particles and water ice), which is the reason for maintaining high heat flux between growing hydrate particles and melting particles of water ice, with a temperature gradient between almost equal to zero.

When ice is generated, seawater begins to solidify at a temperature of -2 ° С and a pressure of 420 Pa (the boiling - hardening temperature decreases to -3 ° С, when 30% of the solid phase is frozen out of water and, to -5 ° С, when 50% of solid is frozen) phase), while ice is chemically pure water in a solid state of aggregation. The water ice obtained in the cavity of the vacuum ice maker forms an ice-containing brine pulp with the liquid phase of the solution, which is transferred to the ice separator from the brine. After separation of the ice-containing brine pulp into fresh ice and brine, the ice is gravity fed into the ice and recirculation water mixer 15, and the brine is either discharged into the sea or returned to the ice generator 13.

Ice-containing pulp, including dispersed ice (up to 50% of the pulp volume) and fresh water, accumulates in the accumulator 5, from where it is pumped into the reactor 1. Here, water ice particles melt during heat removal from the generated gas hydrate particles and are removed by the pump in the form of recirculated water into the mixer of ice and recirculation water 15.

The finished gas-water-water pulp is accumulated in its storage unit 8, from where it is shipped via a pipe 26 to a pump station 29, which ensures its pumping into the main pipe 30 under transport pressure. Moreover, even at a pressure of 1 MPa and a temperature of the order of + 2 ... + 3 ° C (point 1, Fig. 3), the gas hydrate pulp retains stability sufficient for practical use.

The heat flow supplied from the heater (with the aforementioned gas pumping parameters) dissociates a 1-mm-thick gas hydrate layer. in the confined space of the pipeline an isochoric process takes place, then the gas will take the place of the dissociated gas hydrate minus the volume of water (80% of the volume of the dissociated gas hydrate), which will correspond to the thickness of the gas layer of 0.2 mm.

As a result of receiving thermal energy from the inductor, the surface layer of the pulp stream containing gas hydrate particles increases its temperature to the value T1, while the figurative point of the system from the equilibrium line mixes to point 1, which is on the dissociation line, intersecting the region of the metastable state in which is the restructuring of the system (figure 4). At point 1, the gas hydrate begins to dissociate into free gas and water, while the free gas causes an increase in pressure in the system to a value of P1. As a result of increasing pressure, the figurative point of the system shifts to point 3, at which the dissociation of gas hydrate is no longer possible.

As a result of the release of free gas in the near-wall layer of the pipeline, resistance decreases to negligible values when the pulp moves relative to its surface (λ = 0.001) [Zukoski, EE Influence of viscosity, surface tension and inclination angle on motion of long bubbles in closed tubes, J. Fluid Mech., 25, 1966; Fabre, J., Line, Alain. Slug flow. Termopedia. 2010]. In this case, the pressure jump as a result of the expansion of the system during the dissociation of gas hydrate goes into the kinetic energy of the system, which increases the flow rate. Thus, the inductor, in addition to reducing hydraulic resistance, performs a pumping function.

For the effective application of this method, it is necessary that the working pressure in the gas pipeline equals equilibrium or slightly exceeds it (Fig. 4), because at significant pressures (point 4), too much thermal energy will be required to shift the figurative hydrate point to the dissociation line (point 5).

When the gas-water-water pulp enters the regasification plant 35, it is pumped into receiving tanks (filling them with no more than 80% of the volume), then the pressure in the tanks is reduced below 1 MPa, for which the tank is connected in a known manner through a compressor to a gas tank. Then, by means of a compressor, pumping of the gas cushion from the tank begins, with the transfer of gas to the gas holder. As a result, the pressure in the tank decreases to atmospheric (Fig. 3, process 1-2), as a result, the gas hydrate particles that make up the pulp begin to dissociate into water and free gas (point 3). In order for gas hydrate dissociation to take place continuously, it is necessary to continuously supply thermal energy to its particles from a source, while the pulp itself contains two sources of thermal energy (the heat contained in the particles of the gas hydrate itself and in the liquid phase of the pulp).

Thus, reducing the pressure in the gas-water-water pulp to atmospheric triggers the hydrate dissociation mechanism due to the heat contained within the gas hydrate itself (200 kJ / kg). The endothermic process of dissociation, in turn, leads to a decrease in the temperature of the gas hydrate particles, which will continue until the temperature of its particles reaches equilibrium temperature (point 4, figure 4). However, for the development of such a scenario, it is necessary that the gas hydrate particles be isolated in some way from the water surrounding them. Because gas hydrate particles are part of a finely divided water-gas hydrate system, i.e. pulp, then when the temperature of the gas hydrate is lower than the temperature of the liquid phase of the pulp, heat transfer will begin, resulting in a heat flow from the liquid to the particles of gas hydrate. After gas hydrate reaches a temperature of 0 ° C (point 3, Fig. 4), or rather -0.2 ° C, solidification of the liquid phase of the pulp (i.e. water) will begin, with the release of thermal energy in the amount of 335 kJ / kg. Obviously, after dissociation of the gas-water-water pulp, another pulp is formed in its place - ice-containing, while the number of particles of water ice in the ice-containing pulp will be more than the hydrate particles in the gas-water-pulp because hydrate particles consume more thermal energy during dissociation (410 kJ / kg) than liquid water releases during solidification (335 kJ / kg). At the same time, free natural gas released from the hydrate during its dissociation is removed by the compressor from the tank to the storage tanks.

The ice-containing pulp remaining in the tank after removal of the released natural gas is used in a known manner, either as a source of cold in cooling or conditioning systems, or (after melting) as desalinated process water in various technological processes.

Thus, the dissociation of natural gas hydrate in a regasification plant is possible without supplying thermal energy to the gas hydrate-water pulp from the outside.

Claims (1)

A device for transporting natural gas containing a main pipeline, means for supplying a previously prepared gas under pressure to the pipeline, and means for additionally influencing the flow of transported gas distributed in the pipeline sections, characterized in that gas-hydrated-water pulp containing gas hydrate of the transported gas up to 50% of its volume, with a particle size of gas hydrate up to 3-5 mm, while the pipeline is made with the ability to maintain thermodynamic regimes in it, eliminating the decomposition of gas hydrate, while the heating units are distributed along the pipeline, containing inductors configured to heat the perimeter of the pipeline to a temperature that allows heating the surface of the gas-water-water pulp stream to a level that decomposes gas hydrate in its surface layer.

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