RU2427704C2 - Procedure for control of supply of protective gas into compressor module (versions) - Google Patents

Abstract

FIELD: oil and gas production. ^ SUBSTANCE: procedure consists in implementation of compressor module containing case of high pressure with electric engine installed in it and via drive connected to compressor by means of shaft. The shaft is installed in magnetic bearings. Axial packing is arranged around the shaft and it divides the case of high pressure into the first compartment with the electric engine and the second compartment equipped with an inlet orifice and outlet orifice for compressed fluid medium. According to the invention in a storage there is set excessive pressure with consideration of required flow rate of protective gas through axial packing and pressure in the second compartment. Also, supply of protective gas is controlled in at least the first department by means of a control device installed in a supplying line. ^ EFFECT: raised efficiency of procedure. ^ 12 cl, 6 dwg

Description

The present invention relates to a method for supplying a shielding gas to a compressor module for compressing hydrocarbon gases in a flow to a well, and in particular, the invention relates to a compressor module comprising a high pressure housing, a compressor and an electric motor separated by a sealing element. The invention is most suitable for use in underwater compressor modules.

The compressor module is basically an assembly in which the compressor and electric motor are connected by a shaft and are located in a common high-pressure housing. To prevent contamination of the electric motor, a seal is located between it and the compressor. The difficulty is that the gas-filled electric motor is always dry to the extent necessary to prevent corrosion and other problems caused by the deposition of hydrocarbon condensates and liquid water inside the electric motor. It is most important to exclude the presence of water in liquid form, which, together with the content of H ₂ S and CO _2, can form acids and, therefore, cause corrosion. These problems are solved according to Norwegian Patents Nos. NO 172075 and 173197, and also according to Norwegian Patent Application No. 200515199. It is also important to prevent particles from entering and accumulating in the electric motor and in magnetic bearings.

Using standard oil-lubricated bearings or the like. in compressors and their electric motors is most common. The author of this invention has studied the possibilities of reliable use of a high-speed electric motor and magnetic bearings in integrated compressor modules that have a common high-pressure housing: by providing a method of protecting the electric motor and magnetic bearings in the compressor module. In these compressor modules, magnetic bearings have, especially during operation, several advantages. In operation, magnetic bearings are more reliable and less expensive. Especially important is the fact that the use of magnetic bearings eliminates the need for lubricating oil, and therefore eliminates possible problems that may arise for the following reasons: dilution of the lubricating oil with hydrocarbon gases in contact with it, accumulation of hydrocarbon condensates or water in the lubricating oil, or deterioration in quality lubricating oil over time due to the special conditions of its use in compressor modules. The problem that arises when using non-encapsulated magnetic bearings in the compressor module is in many respects similar to the problems related to the use of electric motors: for both, for their reliable and trouble-free operation, a completely dry and inert atmosphere is required for a long time with the most practicable low particle content. Encapsulated magnetic bearings are also known or are being developed. These bearings are able to operate in untreated hydrocarbon gas inflow to the well. These types of magnetic bearings are for them. durability and reliability must be installed and operated in a dry and particle-free atmosphere.

The aim of the present invention is to provide a method for controlling the supply of shielding gas to the compressor module, providing a completely or almost completely dry environment for the electric motor and for magnetic bearings in the compressor module, preventing particles, for example, from the inflow passing through the compressor to the well, from the compressor side to the electric motor and / or magnetic bearings.

According to the invention, a method for controlling the supply of protective gas to a compressor module is provided, comprising a high-pressure housing with an electric motor installed in it, drive-connected to the compressor via a shaft mounted on magnetic bearings, and an axial seal located around the shaft and separating the high-pressure housing into the first compartment with an electric motor and into a second compartment with a compressor and provided with an inlet and an outlet for a compressible fluid, characterized in that based on the required barrier gas velocity through the axial seal and the pressure in the second compartment is set overpressure in storage and carried regulate the supply of barrier gas into at least a first compartment with a regulating device disposed in the supply line.

The control device, made in the form of a flow restrictor, can be adjusted in such a way that the volumetric flow of shielding gas is provided in at least the first compartment, which at least provides the necessary speed of the shielding gas through the axial seal.

The control device, made in the form of a plurality of chokes mounted in parallel, can be adjusted to provide a constant mass flow of shielding gas to at least the first compartment, which at least provides the necessary speed of the shielding gas through an axial seal.

The overpressure in the storage can be kept constant, and the control device is adjusted based on the reduction in pressure in the calibrated opening.

The flow restriction can be kept constant, and the overpressure in the storage is controlled by a change in pressure in the second compartment.

The overpressure in the storage can be kept constant and the control device can be adjusted based on the measured pressure drop in the control device.

According to another embodiment of the invention, a method for controlling the supply of shielding gas to a compressor module is provided, comprising a high-pressure housing with an electric motor installed therein and connected to the compressor by means of a shaft mounted on the first magnetic bearings and on at least one second magnetic bearing on the opposite side of the compressor with respect to the first magnetic bearings, an axial seal located around the shaft and separating the high pressure housing and the first compartment with an electric motor and to the second compartment with a compressor and equipped with an inlet and an outlet for a compressible fluid, and an additional axial seal mounted around the shaft between the compressor and the second magnetic bearing and forming a third compartment, characterized in that based on the required speed shielding gas through axial seals and pressures in the second compartment sets the overpressure in the storage and regulates the supply of protective gas to at least the first compartment at power control device in the feed pipe.

The control device, made in the form of a flow restrictor, can be controlled in such a way that the volumetric flow of shielding gas is provided into at least the first compartment, which at least provides the necessary speed of the shielding gas through axial seals.

The control device, made in the form of a plurality of chokes mounted in parallel, can be adjusted to provide them with a constant mass flow of protective gas into at least the first compartment, which at least provides the necessary speed of the protective gas through axial seals.

The overpressure in the storage can be kept constant, and the control device is adjusted based on the reduction in pressure in the calibrated opening.

The control device can be kept constant, and the overpressure in the storage is controlled by a change in pressure in the second compartment.

The overpressure in the storage can be kept constant and the control device can be adjusted based on the measured pressure drop in the control device.

Embodiments of the invention are described below with reference to the accompanying drawings, in which the following is shown:

figure 1 depicts a block diagram of a device according to the invention;

figure 2 is a block diagram of one embodiment of a device for regulating a protective gas;

figure 3 is a block diagram of an alternative implementation of a device for regulating a protective gas;

4 is a block diagram showing the speed of the shielding gas and the transfer of shielding gas through an axial seal;

5 is a diagram of a device for regulating a protective gas.

6 is a mechanical device for regulating the supply of protective gas, providing a constant supply at constant pressure, _and in front of the regulator and temperature, when the regulator is surrounded by water.

1 shows a compressor module according to the invention, comprising an electric motor 1 and a compressor 2 connected by a shaft 8 and installed together in a common high-pressure housing 3. A stream essentially being a hydrocarbon gas, but also containing liquids and particles (hereinafter referred to as the “fluid”), is discharged from their storage (not shown), preferably through a liquid separator and line 17 to the compressor module through inlet 4. At the previous the side (inlet side) of the compressor 2, the fluid has a suction pressure p _s , which in the inflow compression system to the well will slowly decrease over time along with a decrease in storage pressure. On the downstream side of the compressor, the fluid has a discharge pressure p _a . When the compressor is running p _d , there will be more than p _s . The fluid exits the compressor module through the outlet 5. When the compressor does not work and does not work, the inlet 4 is closed by the valve 41, and the outlet is closed by the valve 51, and the pressure in the compartments of the compressor module will equalize and become the same. With the bypass valve 61 closed, the pressure in front of the valve 51 may exceed the pressure after the valve 61. The maximum restriction on the increase in pressure due to leakage through the valves at the wellhead is the pressure in the idle well (closed wellhead pressure - DZUS). When the compressor does not work and the bypass valve 61 is open, the pressure before the valve 51 and after the valve 61 is equalized to the pressure of the idle well. If then the production will be stopped for a longer period, the valves in the receiving terminal will be closed, and the pressure in the transporting pipeline through the compressor module may increase to DZUS. In both mentioned cases of an inactive compressor, the pressure in the compressor module therefore, due to a leak in one of the valves 51 or 61, or from both, can increase to the DZUS. To prevent fluid from entering the compressor module, which can cause condensation, corrosion, and particle buildup when the compressor module is idle, it is advisable to adjust the pressure to increase in the compressor module to a pressure slightly higher than the pressure in pipelines outside valves 51 and 61 , or, as an option, slightly higher than DZUS.

An axial seal 31 is located between the compressor 2 and the electric motor 1 and separates the high pressure housing into the first compartment 10 and the second compartment 20. It is well known that the purpose of the axial seal 31. is to prevent particles, moisture and other contaminants from coming into contact with the electric motor and other electrical equipment. But the axial seal is not completely tight. To ensure a dry and clean atmosphere in the first compartment 10, it is important that the pressure in the first compartment 10 (in which the electric motor is installed) exceed the pressure in the second compartment 20 (in which the compressor is installed), i.e. inert gas passes from compartment 10 through the seal into compartment 20. In FIG. 1, this is shown by the fact that the pressure in the first compartment 10 (and in the additional third compartment due to the equalization piston) is equal to p _a , + Δ _p .

The shaft 8 is mounted with the possibility of rotation on magnetic bearings 11, 21 of figure 1. If the magnetic bearing 21 is said encapsulated type bearing, then an axial seal 32 is not necessary. The axial seal 32 is therefore optional if the magnetic bearing is an encapsulated bearing.

Figure 1 shows the gas supply line 7, one end of which is connected to the first compartment 10 and the other end of which is connected to the gas storage 6, in which the gas is located under pressure p _a and temperature T _a . The gas storage 6 (as an option) may be in fluid communication with another supply source via the supply line 9. That is, the gas supply line 7 can be supplied to the first compartment 10 from the storage 6. This gas will be a dry hydrocarbon gas or a dry inert gas 8 (third-party gas), also without particles. This gas will come from a separate gas source, or dried hydrocarbon gas may be used. Regardless of the source, the gas supplied to the compressor module through the supply line 7 and through the supply line 7 ′ described below is hereinafter referred to as “shielding gas”.

Due to friction losses and, therefore, due to heat generation in the electric motor, which needs to be cooled, for example by heat exchange with surrounding sea water in a heat exchanger (not shown), it is advisable that the supplied shielding gas has the lowest possible molecular weight and therefore the lowest possible density at given pressure and temperature, since friction decreases with decreasing gas density. To ensure minimal friction and maximum efficiency, the use of methane (CH ₄ with a molecular weight of 16) will therefore be preferable to nitrogen (N ₂ : molecular weight 28). Hydrogen (H ₂ : molecular weight 2) will be most preferred in terms of reducing losses. The hydrogen density will be only about 10% of a typical natural gas mixture (molecular weight 20). The density of hydrogen at a pressure of 100 bar will therefore correspond to the density of natural gas only at a pressure of 20 bar with a corresponding decrease in friction in the electric motor, cooling and increased efficiency of the electric motor.

The side of the compressor on which the motor is located is usually called the “drive end” (PC) of the compressor module, and the other side is usually called the “non-drive end” (NPK) of the compressor module. It will be clear to a person skilled in the art that in a practical embodiment, the magnetic bearings of the compressor PC may be located in the clutch housing between the electric motor and the compressor, in which case the seal will be between the clutch housing and the compressor. The clutch housing and the motor form a substantially common compartment with a common clean atmosphere filled with inert gas. If the magnetic bearings are encapsulated type magnetic bearings, and the operating conditions and / or the gas composition in the inflow to the well (fluid) are such that these bearings can work directly in the inflow gas to the well, then only the electric motor will need protection, and the PC magnetic bearings compressor can therefore be located on the compressor side of the seal.

As mentioned above, provided as an option, the axial seal 32 can subdivide the second compartment 20 into another, third compartment 30, in which the magnetic bearings of the NPK compressor module can be installed. An optional supply line 7 ′ or 7 ″ for supplying protective gas from the storage 6 to this third compartment is shown in FIG. 1. If the magnetic bearings are encapsulated type magnetic bearings, the operating conditions and / or the composition of the inflow gas to the well (fluid) are such that these bearings can be used directly in the fluid and protection is required only for the electric motor. In this case, the seal 32 is optional.

To prevent the entry of contaminants into the second compartment 20, in which the compressor 2 is located, and through the axial seals 31, 32, and into the first or third compartment, the linear velocity of the protective gas through the axial seal must exceed the speed of the fluid and particles in it in the second compartment 20 , or be equal to this speed, and have a direction opposite to this speed.

As for gaseous pollutants in the H ₂ S, CO ₂ fluid, water vapor and hydrocarbon vapor molecules, there will be some, very small, degree of diffusion within 1 mm / s, as a result of which these components will move in the opposite direction shielding gas flow in the seal. A very small influx (mass transfer per unit time) of the shielding gas into the seal will therefore be sufficient to prevent these pollutants from entering the “clean” compartments, for example, into the first and third compartments.

A very important circumstance is the possible penetration of particles and, possibly, small droplets falling from the inflow to the borehole to seal 32 (for NPK magnetic bearings), for example, if the compressor module is located vertically. These particles may have a vertical deposition rate of more than 0.1 m / s.

Figure 4 shows the possible calculation of the minimum required speed of the shielding gas through the axial seal so that the particles do not fall out through the vertical seal. The shielding gas stream (m) is shown in FIGS. 1 and 4.

The rate of fall is calculated according to Stoke’s law;

v _p = [D _p ² (ρ _p -ρ) g] / 18µ

In the formula and in the drawings, the symbols have the following meanings:

v _p - particle fall velocity into the seal, m / s

v _g is the speed of the shielding gas through the seal, m / s

D _p - particle diameter, m

ρ _p - particle density, kg / cubic meter

ρ - gas density, kg / cubic meter

g - gravity acceleration, m / s ²

µ - dynamic viscosity, kg / m * s

If we assume that the shielding gas is methane (CH ₄ ), the temperature is 20 ° C, the particle density is 2500 kg / cubic meter, then the speed of incidence of a particle with a diameter of 50 μm is 0.25 m / s, and the incidence rate of a particle with a diameter of 25 μm is 0.06 m / s.

Due to the position of the compressor module in the inflow to the well, usually after the liquid separator, very few particles entering the compressor will exceed 25 μm, and there will be almost no particles larger than 50 μm. Theoretically, the upward velocity of the shielding gas above 0.25 m / s through the vertical seal will therefore be sufficient to prevent entry into the seal. For reliability, a significantly higher speed can be used to prevent contaminants. If, for example, such a volume flow of shielding gas is needed so that a speed of 1.25 m / s in the seal is ensured, then a reliability factor of 5 will be ensured. In practice, the final determination of shielding gas supply is based, in addition to the calculations mentioned above , on practical experience. The final choice of shielding gas speed and other required values is based on a balance between the reliability of eliminating the entry of pollutants through the seal in steady and transient conditions, and preventing unnecessary enlargement of the shielding gas supply system. Of particular importance is the choice of the appropriate diameter of the supply pipe (for example, line 9) for shielding gas, for example, component less than 25 mm, and it is also important to eliminate the need for several, not one, supply pipes for one compressor station.

The choice of shielding gas speed between 1 m / s and 5 m / s, depending on the actual operating conditions, usually provides protection against the entry and increase of harmful levels of polluting gases, water condensate, hydrocarbon condensate and particles in the electric motor and in magnetic bearings, s while eliminating the need for an unnecessarily bulky shielding gas supply system. It is the selected speed of the shielding gas through the seal, based on an understanding of the mechanisms that can cause the passage of contaminated fluid through the seals, is the basis for determining the supply values and dimensions of the supply system, and for regulating the supply of shielding gas.

From the formula of Stoke’s law it follows that the particle’s fall rate more or less depends on pressure and temperature. The reason for this is that the gas density, which depends on pressure and temperature, is very small (usually in the range of 40-100 kg / cubic meter relative to the particle density (usually 2500 kg / cubic meter). Therefore, in this calculation, the density gas can be neglected.In addition, the dynamic viscosity varies little in the corresponding pressure limits (usually 50-100 bar) and in the temperature range (usually 50-80 ° C), which means that the supply of protective gas, as mass transfer in time, ( and at the stage when there is a decrease in pressure in flow to the well) can be reduced in proportion to the decrease in pressure at the inlet side of the compressor, p _s , without increasing the risk of particle penetration, since the flow of protective gas through the seal will then be kept constant.

Typically, the compressor module will be installed horizontally, and then particles / small droplets will not have a falling speed in the direction of compaction. The above-mentioned values of the speed of the shielding gas in the seal at the same time will create effective protection against contamination of the motor and seals in the established operating conditions ("steady state"). This selected speed of the shielding gas will also prevent particles that could be thrown onto the seals by rotating blades or a shaft, as their momentum is quickly taken from them by countercurrent protective gas and the actual physical barrier created by the seal. Even in transient conditions, for example, substantial protection against contamination will be provided when starting or stopping the compressor module, or while shutting down the well. Even if gaseous pollutants penetrate the electric motor for a short time during the transient conditions, they will be so diluted with pure protective gas in the electric motor that harmful levels will not be reached. The same applies to particle accumulation.

In the horizontal position of the compressor module, it is also possible, with the vertical modules described above, to assume that the supply of protective gas can be reduced by a pressure drop on the inlet side of the compressor, since the gas flow rate will be maintained with a lower mass transfer.

Figure 4 shows that the seal 31, 32 forms a ring around the shaft 8. This ring may typically have a size of about 0.3 mm. To determine the required amount of shielding gas, a shielding gas velocity of 2.5 m / s, a shaft diameter of 150 mm, and a gas pressure of 100 bar were selected. Methane was chosen as the shielding gas. Calculations show that the required feed (i.e. mass transfer, m) of shielding gas for compaction is about 0.0068 kg / s. For a compressor module with two seals, where the magnetic seals of the PC and NPK are in a protected and “clean” atmosphere, about 0.02 kg / s of protective gas will be required. Such a small amount of shielding gas will give the appropriate dimensions for the shielding gas supply system, including umbilical pipe, even with several compressor modules in an underwater compressor station.

To protect the motor and magnetic bearings during compressor operation, the present invention is based on the application, in combination, of knowledge of the required speed of the shielding gas v _g through the seal and the measured pressure inside the compressor compartment facing the seals, p _s (usually equal to the suction pressure in compressor), and how this pressure decreases over time.

Knowing the above, the following steps can be performed.

The specific desired overpressure, p _s , can be set in the accumulator 6, which can be installed in the supply line 9 of the protective gas, or the volume in the inlet pipe can form the corresponding accumulator.

An adjustable amount of shielding gas can be introduced into the compressor module (the first and, alternatively, the third compartment) using a flow limiter 71, 71 'in the supply pipe 7, 7', 7 '' between the accumulator 6 and the inlet to the first (as an option, also the third) compartment, in which the electric motor and / or magnetic bearings are located.

The flow limiter is calibrated and / or adjusted to provide a certain volumetric flow of shielding gas to the first (alternatively also to the third) compartment, which at least provides a predetermined minimum speed of the shielding gas through the seal.

The flow limiter can also be calibrated and / or adjusted to ensure consistent mass transfer, i.e. a volumetric flow that increases depending on the drop in suction pressure, p _s , of the shielding gas in the first (and, alternatively, in the third compartment), which gives at least a certain minimum speed of the shielding gas through the seal. Such regulation is practically very easy to carry out in an underwater system, where T _a will be constant (equal to the ambient temperature of sea water), by keeping p _a constant in time regardless of the value of p _s . The flow meter between the accumulator at p _{and the} flow restrictor can then be controlled by a fixed signal, for example, a fixed pressure drop - with the help of an adjustable throttle opening. The mass transfer and speed along the supply pipe 9 will then be constant in time.

Since the speed v _{g of the} shielding gas through the seal is low, the pressure drop in the seal is also small. The pressure inside the motor compartment and the bearing compartment (that is, in the first and third compartments) will be only slightly excessive, Δ _p (approximately in the range 0.02-0.3 bar) with respect to the suction pressure, p _s , of the compressor, and this circumstance is important for choosing the appropriate value for the pressure in the accumulator, p _a , which, for example, can be set to a value of 5-50 bar or more above p _s . The pressure drop in the seal can therefore be neglected with respect to the pressure drop in the flow limiter, and therefore, practically only the flow limiter determines the protective gas flow.

Accumulator 6 need not be a separate container, and may in some cases be the volume of compressed gas in the pipe in front of the flow restrictor 71, 71 '. But in many cases, next to the flow limiter, it is advisable as a drive to provide a high-pressure reservoir having the appropriate dimensions (Fig. 1).

The flow restrictor 71, 71 'can be located in close proximity to the inlet of the supply line 7, 7', 7 '', which extends into the compartment for the electric motor and seal, or it can be located many kilometers from it. For subsea compressors, this may mean that under the water and very close to the compressor module there will be a flow limiter and storage capacity, and shielding gas will be supplied through the supply line in the umbilical line from the platform or shore, and under pressure from the gas supply source to create the desired pressure p _a . For transportation over long distances, it is advisable that the flow restriction occur close to the compressor module for supplying shielding gas at maximum pressure with the smallest possible diameter of the supply pipe. In other cases, especially when the distance between the compressor module and the shielding gas source is small, the desired shielding gas flow rate can be supplied under relatively low pressure, only sufficient to overcome friction in the pipe, directly from the shielding gas source, for example, a reciprocating compressor adjusted to deliver the desired volumetric flow rate through the seal, without the use of a drive and flow limiter next to the compressor module, or by supplying the desired volumetric flow rate from the shore or boards ormy if the storage tank and the mass flow controller will be there. The disadvantage of this technical solution is that due to the low gas pressure, i.e. Due to the expanded gas volume, the diameters of the supply pipe must be large, resulting in an increase in the cost of the umbilical cord.

The flow restrictor 71, 71 ′ is generally shown in FIG. 5, according to which the pressure (p _a ) in the storage is regulated in one of the following several ways to the desired pressure in the first compartment (10), i.e. p _s + Δ _p .

Figure 3 shows a variant of the limiter 71; 71 'flow, where the throttle (valve) 79 is regulated by the measured flow. Figure 2 shows another variant of the limiter 71; 71 'stream, according to which use several parallel mounted chokes 79'.

Above, the shielding gas flow is controlled by means of a corresponding restrictor 71; 71 'of the flow in the supply pipe 7, 7', 7 '' going into the compartment (s) for the electric motor and magnetic bearings. This flow limiter restricts, on the one hand, the known pressure, p _s , (currently determined pressure in the storage and pressure reduction to the compressor inlet), and, on the other hand, the desired target pressure, p _a , in front of the flow limiter.

The supply of shielding gas to the “clean” compartments can be practically controlled by the following methods

Constant p _a , constant flow restriction

The pressure p _{a is} left fixed, calibrated, and a fixed flow restriction is set, giving the minimum sufficient supply of protective gas at the beginning of compression (i.e., at start-up, at an early stage of the well), and giving increasing consumption with decreasing pressure in the storage (and also p _s )

The volumetric flow rate of the shielding gas and, therefore, mass transfer increase by the square root of the difference p _a -p _s . This very simple regulation has the disadvantage that the shielding gas supply system, as well as the diameter of the supply pipe, must have dimensions corresponding to this increasing consumption. If, for example, p _s decreases from 100 bar at the beginning of compression to 60 bar at the end of compression, then the size of the supply system will have to be increased by 50%. But in some cases, this may be an acceptable solution for a simple technical design and simple operation.

Regulation p _a together with a decrease in p _s .

Regulate with a decrease in p _and with a decrease in p _s , and accordingly reduce the discharge pressure from the supply source on the shore or on the platform. In this case, the supply of shielding gas to the compressor module at any given time ensures an almost unchanged speed of the shielding gas through the seal. As shown above, the supplied shielding gas mass flow rate can be reduced over time with decreasing p _s , so that the speed of the shielding gas through the seal remains constant, and so that the seal can trap contaminants. With a decrease in p _a and, therefore, a pressure level in the supply line 9, if the mass flow rate remains constant, an increase in the volume of transported gas, which will be approximately inversely proportional to a decrease in p _a , and friction in the pipe will increase as an increase in the volume of gas in squared, i.e. the pressure drop from the shielding gas supply source through the umbilical line to the compressor module is quadrupled. Moreover, the mass flow rate of the shielding gas can also be reduced accordingly and at the same time maintain the desired speed through the seal, and the pressure drop in the supply pipe will remain at an acceptable level. Therefore, a method based on maintaining a given speed through the seal by regulating with decreasing in time: (p _a ) = function (p _s ) with a fixed flow restriction between two pressure levels, it will be advisable, because this regulation is very simple, since the pressure p _s decreases over time slowly. As mentioned above, the supply of shielding gas will be set with a large supply of its gas against the penetration of pollutants. Short-term changes in temperature and pressure, as mentioned above, will not cause unwanted penetration, even if (p _a ) will be regulated with decreasing.

P _a fixed, adjustable flow restriction through the valve

p _a remains fixed, and the flow restrictor 71, 71 'is adjustable, for example, in the form of one or more valves that can be operated manually (for example, an operator or a remotely controlled vessel can work with them) to increase the restriction with decreasing p _s . The flow limiter can be adjusted, for example, by the measured pressure drop in the flow limiter.

Or, p _a remains fixed, and the flow restrictor 71, 71 ′ is adjustable, for example, in the form of a hydraulic valve, which can be manually adjusted from the control room to increase the restriction at certain intervals while decreasing p _s .

The flow restriction can be controlled, for example, by measuring the pressure drop in the flow restrictor.

Fixed p _a , flow restriction by measured pressure drop

p _a is fixed and a flow regulator is installed that regulates the flow according to the measured pressure drop in the restrictor in front of the valve. This ensures a constant mass flow, because the pressure p _a and the temperature for the underwater compressor, equal to the temperature of the sea water in front of the valve, have approximately fixed values. Due to the expansion of the gas, the velocity through the shielding gas seal will increase as pressure p _s drops. From the point of view of protection against the penetration of pollutants through the seal, this circumstance is advantageous, and it is not a disadvantage for determining the dimensions of the supply system, which must be determined for the beginning of the compression state, when the mass flow of the protective gas is the highest for the required minimum speed through the seal.

Fixed p _a , flow restriction by measured pressure drop, and pressure and temperature in the motor compartment

p _a is fixed, and a flow regulator is installed, which regulates the flow by measuring the pressure drop in the restrictor in front of the valve, and by measuring pressure and temperature in the motor compartment and in the magnetic bearing compartment, as a result of which the valve provides a fixed volume flow and, thus, fixed desired set speed of the shielding gas through the seal. This is possible, but unnecessarily complicated regulation.

When the compressor 2 is stopped and does not work, it will be isolated from the inlet 4 and the outlet 5 by the corresponding stop valves 41, 51. In this position, the supply of protective gas will be stopped when the entire compressor module 3 (i.e., the first, second and third compartments) the pressure will increase to the pressure p _{a of the} reservoir. It is important that the pressure inside the compressor module 3 in its idle state is higher than the pressure in the inlet and outlet pipes in front of the valves, as a result of which, in case of leaks in the valves 41, 51, the protective gas will leave the compressor module, and not the liquid and contaminated gas into the module . If during operation of the compressor the pressure p _a is set higher than the highest pressure that can occur in the inlet or outlet line during standstill, then protection against inflow during standstill will be automatically provided. This highest possible pressure is usually the wellhead pressure (DZUS). If during operation the pressure p _a will be set lower than the pressure created outside the valves, then the p _a can be adjusted with increasing as necessary, for example, to a pressure of 1 to 5 bar above the pressure in the inlet / outlet pipe on the inlet gas lines from a supply source (on shore or platform).

6 shows a mechanical device for regulating the supply of protective gas, providing a constant mass flow when the pressure and temperature in front of the regulator are constant. This control device comprises a valve body 101 with an inlet 102, through fluid communication with the cavity in the valve body in which the piston 103 is mounted. As shown in this drawing, the piston has a fixed hole 104, or it is made between the piston and the inner wall of the body valve, and gas can flow through this hole. The piston 103 is connected to a spring 105, which in turn is fixed in the channel 109 of the valve body. The piston is also connected to the first pipe 111, which is coaxial with and partially surrounds the second pipe 107. The first pipe 111 is located in a separate channel 108 and is configured (together with the piston 103) to slide back and forth along the second pipe 107.

The second pipe 107 is in communication with the hole 110 in the valve body and with a part of the second pipe 107, which on the side after the piston 103 has one or more holes 106, thereby providing fluid communication between said cavity and said hole 110. Opening 110, in operation connected to the control device described above, an outlet for shielding gas to the motor compartment and the compartment for magnetic bearings.

If it is used as a control device for the protective gas, the protective gas at a pressure p _a and at a constant temperature (ambient seawater) will flow into the inlet opening 102 and into said valve body cavity. As gas passes through the piston bore 104, the pressure will decrease. This pressure reduction creates a force pushing the piston 103 and the first pipe 111 in the direction of gas flow (to the right in FIG. 6). The spring 105 creates a counteracting force that pushes the piston 103 and the first pipe 111 in the direction of gas flow (to the right in FIG. 6). The spring 105 can be adjusted so that the pressure drop in the bore 104 of the piston remains fixed. Due to the decrease in pressure 110, the flow through the piston bore 104 will increase, as a result of which the piston will be forced to move to the right. Then the first pipe 111 (the accompanying piston) will close the main part of the hole 106 in the second pipe 107, as a result of which the decrease in pressure through the hole 106 will increase, and the decrease in pressure through the hole 104 will be unchanged. On the contrary, the piston will shift to the left if the pressure of the outlet 110 increases so that the pressure decreases and, therefore, the flow through 104 remains unchanged.

If the flow from the outlet 110 is blocked, for example, when the compressor module stops, the piston 103 will be forced to move completely to the left, fully opening the hole 106 in the second pipe 107. As a result, the pressure value in the entire system, including the compressor module, will be equal to p _a .

Claims (12)

1. A method of controlling the supply of protective gas to a compressor module comprising a high-pressure housing with an electric motor installed in it, drive-connected to the compressor by means of a shaft mounted on magnetic bearings, and an axial seal located around the shaft and dividing the high-pressure housing into a first compartment with an electric motor and to the second compartment with a compressor, and provided with an inlet and an outlet for compressible fluid, characterized in that the excess the pressure in the storage, based on the required speed of the shielding gas through the axial seal and the pressure in the second compartment, and carry out a regulated supply of shielding gas to at least the first compartment using a control device located in the supply line. 2. The method according to claim 1, characterized in that the regulating device, made in the form of a flow restrictor, is controlled in such a way as to provide a volumetric flow of protective gas in at least the first compartment, which at least provides the necessary speed of the protective gas through the axial seal. 3. The method according to claim 1, characterized in that the control device, made in the form of a plurality of chokes installed in parallel, is controlled to provide a constant mass flow of protective gas in at least the first compartment, which at least provides the necessary speed of the protective gas through the seal. 4. The method according to claim 1 or 3, characterized in that the overpressure in the storage is kept constant, and the regulating device is controlled based on a decrease in pressure in the calibrated hole. 5. The method according to claim 1, characterized in that the control device is kept constant, and the overpressure in the storage is controlled by a change in pressure in the second compartment. 6. The method according to claim 1, characterized in that the overpressure in the storage is kept constant, and the control device is controlled based on the measured pressure reduction in the control device. 7. A method for controlling the supply of shielding gas to a compressor module comprising a high-pressure housing with an electric motor installed in it, drive-connected to the compressor by means of a shaft mounted on the first magnetic bearings and on at least one second magnetic bearing on the opposite side of the compressor relative to the first magnetic bearings, an axial seal located around the shaft and separating the high-pressure housing into the first compartment with an electric motor and the second compartment with compressor, and equipped with an inlet and outlet for compressible fluid, and an additional axial seal mounted around the shaft between the compressor and the second magnetic bearing and forming a third compartment, characterized in that the excess pressure is set in the storage, based on the required speed of the protective gas through axial seals and pressure in the second compartment, and carry out a regulated supply of protective gas in at least the first compartment using a control device in a movable pipe be. 8. The method according to claim 7, characterized in that the regulating device, made in the form of a flow limiter, is controlled in such a way as to provide a volumetric flow of protective gas into at least the first compartment, which at least provides the necessary speed of the protective gas through axial seals. 9. The method according to claim 7, characterized in that the regulating device, made in the form of a plurality of chokes installed in parallel, is controlled to provide them with a constant mass flow of protective gas in at least the first compartment, which at least provides the necessary shielding gas velocity through axial seals. 10. The method according to claim 7 or 9, characterized in that the overpressure in the storage is kept constant, and the regulating device is controlled based on a decrease in pressure in the calibrated hole. 11. The method according to claim 7, characterized in that the control devices are kept constant, and the excess pressure in the storage is controlled by a change in pressure in the second compartment. 12. The method according to claim 7, characterized in that the overpressure in the storage is kept constant, and the control device is controlled based on the measured pressure reduction in the control device.

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