RU2238402C2 - Method for degassing oil in end separation plants and device for realization of said method - Google Patents

Abstract

FIELD: oil extractive industry.

SUBSTANCE: method includes mode for vacuum treatment of flow with possible change of productiveness in broad limits due to bypassing through pressure controller to self, feeding gas through pressure controller after self, and effecting with ultrasound oscillations. Following devices are included: construction of devices for local vacuum treatment, foam destroyer, inner controlled end phase separator, drop-precipitating diaphragms and ribs.

EFFECT: higher effectiveness.

3 cl, 10 dwg

Description

1. TECHNICAL FIELD

In the extraction and preparation of oil for transport, in order to reduce losses from evaporation, oil is subjected to separation in end separation plants under atmospheric pressure (usually at an absolute pressure of 0.105 MPa) before entering into atmospheric tanks. To ensure the possibility of gravity drainage into tanks, end separators are raised above the ground to a height of 10 to 25 m, depending on the type of tanks and the terrain. The separator (s), the overpass for their location, the strapping of the separators form an end separation unit (KSU) in combination with shut-off and control valves.

The present invention is intended for separation plants having a lift of the supply pipe to a significant (more than 10 m) height, because in this case, as a rule, an additional energy source is not required. If there is a supply of energy necessary for vacuum treatment or its source, it is also applicable for the degassing of other liquids.

2. BACKGROUND

Currently, the final separation of oil is regulated by RD 39-0004-90 (VNI-ISPT oil. Guidelines for the design and operation of separation units of oil fields, the selection and layout of separation equipment. Ufa - 1990. - 68 p.).

In the practice of oil preparation distinguish between raw materials and commodity tanks. Accordingly, distinguish between “cold” KSU and “hot”. Cold KSU in the technological chain is preceded by level controls in the separators of the previous stage, hot - pressure regulators in oil sumps. Since the pressure of oil saturation with gas in previous devices is much higher than atmospheric, and in KSU separators it is almost equal to it, somewhere in the way from the regulator to the separators the pressure becomes equal to the oil saturation pressure, that is, conditions are created for gas evolution to begin. If this happens during the passage of the regulators, then the formation of a reversed gas-liquid flow (droplets of oil in the gas flow) immediately at the exit of the regulators is very likely. In this case, as a rule, there are no problems with the quality of oil separation.

Problems begin when the boiling front is located in the section where the oil pipeline rises to the separators (in the riser). Since the gas-liquid flow is lighter than the liquid flow, the pressure at the inlet to the riser depends on the altitude of the boiling front and the amount of gas released in the riser. This provokes the variability of the altitude of the boiling front. In this case, the instantaneous performance of the separator turns out to be variable. The inertia of the fluid increases the buildup. Especially dangerous is the appearance of oscillations during the parallel operation of several separators with a ground-based collector. In this case, overflow of some separators and emptying of others is possible. Naturally, the quality of separation is sharply deteriorating. Moreover, the usually taken measures to increase the uniformity of the distribution of liquid between parallel devices, for example, multiple separation of the supply pipe, are practically useless, since they do not affect the main reason - the variability of the altitude location of the boiling front. It does not guarantee uniform distribution and elevation of the collector to the height of the separators. In this case, as a rule, a slug mode is formed in the supply pipe. The unevenness is enhanced by inertial phenomena that generate waves in the reservoir, the consequences of which are amplified when the hydrostatic pressure necessary for the oil to enter the apparatus decreases. So the buildup of oil in several parallel units is almost inevitable.

In 1990, this situation was observed at the KSU, the largest in the European part of the USSR, at the head structures of the Usinsk-Ukhta oil pipeline (Usinsk, Komi ASSR). Since the pipeline was intended for pumping gas-saturated oil, KSU was designed as an emergency. However, the failure of the attempt to pump oil in a gas-saturated state forced it to be put into continuous operation. The installation, including ground collectors, 6 separators of the previous stage and 4 end separators at a height of 22 m, a gas pipeline along the relief terrain and a drain into the tanks formed a huge self-excited oscillating circuit with periodic oil discharges into the gas pipeline and gas breakthroughs into the tanks. The PecherNIPIneft Institute has developed a project for the reconstruction of the installation, which has been accepted for implementation, but does not eliminate the main cause of the buildup.

The author was unable to find published works on the stabilization of the boiling front in the practice of oil separation at KSU, although this tool has been known in the power industry for a relatively long time (see, for example, Kutepov A.M., Sterman L.S., Styushin N.G. Hydrodynamics and heat transfer during vaporization. - M.: Vysshaya Shkola, 1986, - 448 p.) - this is the installation of throttle washers at the entrance to the lifting section. The role of the throttle washer can perform a simple valve. The author stopped the reconstruction of the aforementioned Usinsk KSU and completely normalized its operation without capital expenditures by simply covering the valves before the oil enters the risers and stabilizing the level in the drain tank. But at the same time, there were problems with switching to the new mode of the last (fourth) separator: the pressure in the manifold when closing the inlet valves on the three separators decreased and was insufficient for the oil to enter the fourth separator. The conclusion to a similar mode of the end separator at the Sergeevsky oil treatment point in the oil and gas production department “Ufaneft” at a height of 12 m took place only after hitting the riser with a wrench. This indicates the need for additional measures to ensure that throttle devices are operational.

There are problems with ensuring the quality of oil separation at KSU, due to which the loss of oil from tanks that are not equipped with a capture system is usually 0.2-0.8 wt.% (There may be much more). Studies of the Giprovostokneft Institute have shown that non-foamy oils of Western Siberia can be separated by heating to 45 ° to the required vapor pressure of 500 mm Hg. only when the propane content in them is less than 2 wt.% (up to 6 wt.% are found).

By the 1990s, a concept had developed: the quality of separation requires a quiet input of oil into the units. That this requirement is erroneous is shown by cases of disgusting oil separation when the oil remains in the apparatus for more than an hour: when a hammer hit a separator with such a separator, there is a noise of gas emitted, similar to the roar of starting jet engines.

During the formation of bubbles of evolved gas, a depletion zone is formed around them. The larger it is, the slower the mass transfer. The size of the depletion zone depends on the hydrodynamic situation (in particular, on the Reynolds number). Around the microbubbles at a low rate of their growth, an armor shell may form, which excludes their further growth and ascent. All this indicates that gas evolution is best done under dynamic conditions, gas evolution is in a regime that provides the highest bubble ascent rate.

For the separation of oils with a high content of propane, a transition beyond the boundaries of thermodynamic equilibrium is necessary. Such a liquid separation method is known. This is a method of degassing liquids and a device for its implementation (AS No. 1421363-BI No. 19, prototype). Its essence lies in the fact that the degassing of the liquid is carried out in a cavitating flow, whereby a settled pulsating cavitational cavity is created in it with a part of it periodically tearing off and carried away by the flow, for which the flow is narrowed and then suddenly expanded, while the ratio of pressures after the flow is narrowed to pressure before it is kept equal to not more than 0.15. At the same time, a liquid degassing device such as a Venturi pipe with a cylindrical neck with a diameter of D _cr , a length of (0.6 ... 2) D _cr , and a radius of coupling with the walls of the confuser R = (0.2 ... 0.4) D _{cr is patented here.} , and a diffuser with an opening angle of more than 15 °. In this invention, for the first time, hysteresis of gas evolution and gas dissolution processes is used to go beyond the boundaries of thermodynamic equilibrium under separation conditions. But the direct application of this invention to KSU is practically excluded, because it requires that the pressure at the inlet of the device exceed 0.7 MPa, while at most points the oil is treated under pressure not exceeding 0.2-0.5 MPa.

There are a lot of patents using nozzles with a confuser-diffuser flow channel for degassing liquids. But the author’s known attempts to use such nozzles for oil degassing were unsuccessful due to the instability of the results. So, the separation of foamy oils can cause problems. It is known that foam is best destroyed under dynamic conditions. So, in A.S. USSR No. 1260011 (BI, 1986 No. 36) - (prototype) for the destruction of the foam, a phase divider is used with a series of pipes at different heights for the selection of the gas phase, atomization of the liquid and impact of the spray with gas from the divider, which is unnecessarily difficult. Perhaps a simpler solution.

The technical result of the invention is to increase the efficiency of the method and increase the reliability of the tools used.

The necessary technical result is achieved by the fact that in the method of oil separation at the end separation plants, including lifting oil to the separator along the riser, separating and removing oil and gas, according to the invention, before entering the riser, all or part of the oil is subjected to local vacuum treatment in the mode

P _in ≥ P _out + Δ P (Q) + Δ (Q),

where P _in and P _out - pressure at the inlet and outlet of the device for preliminary vacuum processing of the stream;

Δ P - pressure drop across the device when working with a capacity of Q;

Δ is the width of the zone of unstable operation of the device.

Moreover:

the part of the stream that has not undergone vacuum processing is passed through the pressure regulator “to itself” before being fed into the riser, adjusted to the maximum allowable pressure at the inlet to the device;

gas is supplied to the riser through a bubbler through a pressure regulator “behind itself”, configured to operate at the maximum allowable pressure at the outlet of the vacuum processing device;

with increasing pressure at the outlet of the processing device by a vacuum above a certain limit, the area of least pressure or the base of the riser is subjected to vibration by the ultrasonic vibrations emitter.

The technical result is achieved by the fact that in the device for processing the flow by vacuum, consisting of a pre-chamber, an adjusting needle with a drive, a confuser, a neck length equal to its two diameters and conjugated to the confuser along an arc of radius 0.2 of the neck diameter, as well as a diffuser, according to the invention the confuser is made with a taper angle of 80-120 °, the adjusting needle is with a variable taper from 0 to 10 ° at the base and 20-30 ° at the top of the needle, the diffuser is with a variable taper, varying from 6-10 ° at the neck and up to 30 ° at the end, the pre-chamber in polyene of the tee, and an adjusting needle and the inside of the converging tube and the neck made of viscous replaceable austenitic stainless steel.

The technical result is also achieved by the fact that in the separation unit, including the separator and its strapping, according to the invention, one or more vacuum processing devices with shut-off valves at the inlet and outlet of each are connected to it in the base of the riser, bypass with pressure regulator “to itself”, with shut-off valves of the same diameter and an outlet diffuser designed to pass the maximum flow rate entering the unit with the maximum allowable pressure drop and a fully open valve.

Moreover:

the piping of the bottom of the riser includes either a gas supply line with a pressure regulator “behind itself”, or a vibrator mounted on the neck of the vacuum processing device or on the base of the riser;

the installation has an end phase divider for introducing the vacuum-treated mixture into the separator, partially located in the gas space of the separator with a tray system at the outlet of it, eliminating the fall of the jet onto the free surface of the oil in the separator;

at the end of the oil lifting section, a foam breaker is mounted having a movable shutter for controlling the speed of the gas-liquid jet;

at the outlet of the terminal phase divider, the installation is additionally equipped with a shutter for regulating the liquid level in it;

the inner surface of the terminal phase divider is provided in the gas part with gas turbulators in the form of a part of annular diaphragms arranged with a variable pitch, excluding wave formation of the free surface of the liquid in this phase divider, and its outer surface is equipped with ribs for the intensification of droplet deposition.

3. SUMMARY OF THE INVENTION

3.1. Stabilization of the KSU

To stabilize the regime, first of all, it is necessary that there is practically no free gas in front of the throttle mounted before entering the riser, and it would undoubtedly be behind the throttle. The latter requires the fulfillment of additional conditions, so that the pressure behind the throttle would be less than the pressure of oil saturation with gas, and during throttling, a fluid velocity of at least 6 m / s would be achieved (see IFZh, 1971, vol. XX, No. 2, pp. 262-267 )

But such a throttling only stabilizes the high-altitude location of the boiling front, without protecting the supply pipe from fluctuations in the separation pressure. To protect against this source of oscillation, it is necessary to reduce the minimum pressure in the throttle to a value determined by the dynamic tensile strength of the liquid. The necessary local pressure reduction can be achieved by converting potential energy (pressure) into kinetic energy, and then by reversing the conversion of kinetic energy into potential energy, for example, in a device such as a venturi. The Venturi pipe, like any other hydraulic device, has a hydraulic characteristic that displays the relationship of flow and the required pressure drop across the device. But it is limited by the condition of continuity of the flowing fluid. With the appearance of the gap, the pattern is violated. In this case, the type of characteristic begins to depend on how the pressure drop across the device changes: due to a change in the inlet pressure with constant back pressure or vice versa. If in the course of the experiments it is agreed that the minimum backpressure is equal to atmospheric, then the pressure drop at this limit mode is equal to the overpressure at the inlet:

Δ P = P _in -P _out = P _{in abs} -P _atm = P _inh .

The resulting device characteristic is presented in figure 1. The OS curve represents an unbroken branch of the device characteristic. It does not depend on the method of its receipt. Lower case letters a, b, c, ... denote characteristics recorded with at varying but constant inlet pressure equal to _Rin and P, P in _Rin, P ... respectively _Rin with changing pressure in the range ≤ P _atm P _O ≤ P _in . Moreover, Δ P≥ 0. These characteristics consist of three sections: vertical (above the curve A'D), transition (between the curves AC and A'D) and continuous, coinciding with the curve of the continuous characteristics of the OS device. The vertical section indicates the independence of the flow from backpressure (pressure at the outlet of the device), which is required. The combination of the upper points of these sections (Pout = P atm) form a curve AB — a curve of the pressure at the inlet of the device versus flow, that is, a discontinuous branch of the device’s characteristics independent of backpressure. It can also be obtained by increasing the pressure at the inlet of the device after the onset of the gap. The set of lower points of the vertical sections forms the curve A'D, bounding the region of unstable modes from above. The transition section corresponds to the region of unstable boiling of the liquid with significant fluctuations in the measured pressures, and its accurate display is quite difficult.

Shown in figure 1, the characteristic is convenient for its removal (experimental receipt), but does not allow to answer the main question about the necessary pressure at the inlet to the device to provide a locking mode at a given backpressure.

The curve P _{in h} (Q) in the area of a stable gap does not depend on backpressure. Since the characteristics Δ P = P _in- P _out as a function of the flow rate on the discontinuous branch also do not depend on the specific value of the components, entirely determined by their difference, it can also be converted to P _{in bh} = Δ P + P _{out huts} and bring Fig. 1 to other coordinates (see figure 2). Since the region of unstable boiling is determined mainly by the strength of the liquid and its local velocity, it can be assumed that there is a weak dependence of the differential Δ (σ) on the back pressure. In this case, the region of regimes with stable boiling of a given liquid for this device is displayed by a portion of the curve A``B, and the condition for stable operation of the device in the gap

P _{BYXmax Rin} ≥ P + Δ F (Q) + Δ (Q) ,

where P _output - the maximum allowed value of backpressure;

Q - performance.

The pressure at the inlet to the throttle is equal to the pressure in the previous unit minus the pressure loss on the way to the throttle. Inequality can be applied in two ways: either to determine the minimum required inlet pressure at a given maximum back pressure, or - to determine the maximum permissible outlet pressure at a given inlet pressure.

3.2. Separation quality

The quality of separation is characterized by the achieved pressure of saturated vapors of the separated oil, the amount of residual excessively dissolved and free gas in it, as well as the content of droplet liquid in the separated gas.

For degassing, first of all, you need a place where gas will be released, that is, nuclei of gas bubbles. Each embryo has a critical size. It is believed that the fate of the embryos is less than critical — disappear, with sizes larger than critical — grow until equilibrium is reached with the environment or removed from the liquid as a result of the ascent. The most acceptable hypothesis is the constant formation and disappearance of nuclei at a pressure above the saturation pressure as a result of fluctuations. As long as the size of the bubble does not exceed the volume occupied by the liquid with the amount of gas originally dissolved in it, not less than the amount of gas in the bubble, the bubble can grow spontaneously at a rate limited only by the inertia of the fluid being expanded. Further bubble growth is due to the diffusion of gas from the surrounding fluid bubble. Moreover, according to the law of mass transfer, the total gas flow into the bubbles is proportional to the mass transfer area and the driving force. The proportionality coefficient - the so-called mass transfer coefficient - depends on the hydrodynamic situation. In the turbulent regime, it can twice exceed the coefficient in the laminar regime, and interfacial turbulence can increase it by 10 times. The mass transfer area of a given amount of gas from the liquid surrounding the bubbles depends very much on the degree of dispersion of the gas, that is, on the number and size of the bubbles, and can reach tens of thousands of m ² / m ³ , that is, it can vary hundreds of times depending on the conditions. The driving force of the gas evolution process is the degree of supersaturation of the liquid with gas. Theoretically, equilibrium is achievable only in an infinitely long period of time, since its driving force is constantly reduced with degassing. The driving force, depending on the conditions, can also change tens of times.

The saturated vapor pressure of the separated oil depends on its fractional composition, most strongly on the amount of the lightest gases in it (up to propane inclusive). In the process of degassing in the limit, each component is distributed between the liquid and gas phase in a certain proportion, determined by the equilibrium equation. Moreover, the more this component was dissolved in oil, the more it will remain in degassed oil under the same conditions. The proportionality of the different components is different, and when equilibrium is usually reached, methane, ethane, and non-hydrocarbon gases in oil remain small. But with a propane content of more than 2 wt.%, As already mentioned, there is a problem with providing the necessary pressure of saturated vapors even at equilibrium degassing.

The way out of the emerging “insoluble” situation is as follows.

The foregoing indicates a potential possibility to increase the mass transfer intensity by a thousand and even tens of thousands of times, but for this, first of all, a sufficiently large supersaturation of the liquid, that is, a local significant decrease in pressure, is necessary. Moreover, if the intensity of mass transfer is such that it is possible to approach equilibrium during the time spent at reduced pressure, then with the restoration of pressure, the direction of mass transfer will change - instead of gas evolution, gas dissolution will occur - a much slower process. Again, complete equilibrium is possible only after an infinitely long time, but the liquid remains an unsaturated gas, which is what is required.

A significant local pressure reduction can be carried out in the above-described venturi-type device. In the mode considered in 3.1, the greatest degree of supersaturation of the liquid possible under the given conditions is automatically realized, which can be increased only by changing these conditions. So, oil with a saturation pressure of 0.2 MPa bursts at a measured vacuum pressure of 0.05 MPa, i.e. a supersaturation of 0.25 MPa. In principle, the minimum pressure cannot be measured since inevitably, the effect on the sensitive element of the device through the liquid under conditions of impossibility of its long existence. The calculation of the limiting pressure shows that the absolute pressure at the point of water rupture is less than 0. On oil, due to the high gas content and high viscosity, the calculation of the minimum pressure is fraught with great difficulties. Numerous experimental studies at different KSUs show that with the usually observed gas content of oil (less than 10 m ³ / m ³ ), the minimum pressure is always less than atmospheric. This gives reason to call the proposed device such as a Venturi pipe device for preliminary vacuum processing of the flow, or in short - UPV.

Experimental studies at the semi-industrial stand 1990-1991 and the results of acceptance tests of advanced oil degassing technology using UPV on hot KSU TsPPN No. 1 NGDU “Ufaneft” in 1995 gave the same result: preliminary vacuum treatment allows you to cross the border of thermodynamic equilibrium under separation conditions. At the same time, the amount of gas taken off is approximately doubled, and the gas, mainly due to the deeper extraction of propane, has a density 10% higher than the gas density during conventional separation. Three-day experimental studies with an automated system for monitoring the saturated vapor pressure of separated oil from the Ufa Petroleum Institute at a semi-industrial stand showed that this pressure fluctuates between 220-440 mm. Hg Consequently, a deeper separation is provided than is required by existing standards. If the samples of the separated oil, hermetically taken in a screw sampler with a pressure gauge, during normal separation during the delivery of oil for chromatographic analysis, were under excessive pressure, then after preliminary vacuum treatment they were under vacuum.

Studies with the UODS device of the VNIISPTneft design in the process of passing the acceptance committee technology showed that the usual and tested technologies will be the same in the amount of gas taken if separation with preliminary vacuum processing is carried out under a pressure of 0.04-0.06 MPa large. Obtained indirect evidence of the removal of hydrogen sulfide from oil.

In this case, the pressure at the inlet of the UPV varied within the range of 0.21-0.25 MPA instead of 0.7 for the prototype. So there is no need for high pressure at the inlet, and another restriction of the permissible mode, considered in clause 3.1, is necessary. Due to the significant underloading, the oil was prepared at the aforementioned CPPP No. 1 periodically, with stops for the accumulation of oil in the raw material tanks. At the same time, thanks to the top oil input into the UPV separator, it automatically started up and entered the required mode. However, in the late autumn of 1995, the dehydration system failed, which necessitated the recirculation of hot oil through the feed tank. With the release of degassed oil to the KSU, the pressure in the riser increased and the OLA exited the regime. I had to stop the OLA. This again requires the development of special measures to ensure the operability of the installation in these conditions.

3.3. UPV operating modes and measures to ensure them

To calculate the operating mode of the UPV it is necessary, first of all, the ability to determine:

a) an unbroken branch of the characteristic on a viscous gas-saturated liquid;

b) the size of the transition zone (zone of unstable boiling);

c) the discontinuous branch of the characteristic.

To date, methods have been developed for theoretical (using the theory of the boundary layer) and experimental (using the rules of modeling) determination of the characteristics of any devices on any liquid under the condition of flow continuity.

The initial part of the transition zone is also studied quite well in connection with the task of determining the conditions of cavitation-free operation of hydraulic devices. In particular, it has been shown that in this problem on gas-saturated oils, of particular importance is, in particular, the rate of change of pressure and the residence time of the liquid under reduced pressure. Since the decrease in pressure occurs due to the transition of potential energy into kinetic, the critical speed, if it depends on the size of the device, is weak, and the rate of change of pressure and residence time are proportional to them.

In fact, reaching the critical mode is caused not only by acceleration of the liquid during narrowing of the channel. The very appearance of the gas phase leads to a narrowing of the passage section of the channel, a local increase in speed and a decrease in pressure. Since the intensity of nucleation very much (in terms of degree) depends on the degree of supersaturation, the process of forming a blocking front is in the nature of a chain reaction: the appearance of the gas phase sharply enhances the intensity of nucleation, and this, in turn, leads to an increase in the rate of gas evolution. Any experimenter knows cases of spontaneous access to the cavitation mode with a sharp change in all parameters without any outside interference with sufficient approximation to the critical mode. This process occurs in time and space, but does not depend on the size of the device, and, therefore, can be modeled without complex criteria processing.

The instantaneous performance of the KSU is rarely stable. Its fluctuations are created by fluctuations in instantaneous productivity above the located links, not compensated by the volume of previous devices. Even with constant performance at the entrance to the previous units, they are provoked by the uneven discharge of settled water in these units. An increase in productivity leads to a sharp increase in pressure at the inlet to the UPV (limited by pressure in previous apparatuses), a decrease to the risk of disruption of the oil lifting effect in the riser with a further exit of the UPV from the operating mode. Since the necessary supply of pressure at the inlet is relatively rare, the question arises of the need for automatic control of the control unit from the condition of maintaining the necessary pressure at the inlet. But this direction has three drawbacks:

1) the introduction of the adjusting needle is associated with an increase in the hydraulic resistance of the device, that is, with a reduction in the working area due to an increase in Δ P (Q) (see figure 2);

2) the adjustable drive of the translational movement of the needle at a cost exceeds the cost of UPV;

3) the zone of effective regulation is limited, because starting from a certain limit, the separated motion of the liquid begins, leading to an increase in the zone of unstable boiling.

In most cases, preliminary vacuum treatment provides deeper degassing than necessary (with the exception of cases of oil purification from hydrogen sulfide). Then it is proposed to vacuum-process not the entire oil flow directed to KSU, but only its part, as a rule, equal to the minimum instantaneous KSU productivity. The rest should be directed to the riser bypass through the pressure regulator “to yourself”. In this case, stability of the inlet pressure is guaranteed, which guarantees the maximum efficiency of the UPV, and the many bubbles created by it serve as a means of intensifying gas evolution from the bypassed stream during turbulent rise of oil to the separator (see paragraph 2 of the claims).

In conditions of limited pressure at the inlet to the KSU, a means to bring the OLA to the operating mode can serve as an artificial decrease in backpressure by enhancing the lifting effect by supplying gas to the base of the riser. The well-known means of deepening the separation, called “blowing” of gases, is used here for a new purpose. To reduce gas flow, the inlet gas pipeline is equipped with a pressure regulator “after itself”. In this case, the gas supply automatically turns on when the backpressure rises above the predetermined value and turns off when the pressure drops below it (see paragraph 3 of the claims).

Pulse processing of the riser contents by ultrasound, for example, by attaching a device used to prevent scale formation in boilers (see, for example, I. Khorbenko, Zvuk, can serve as a means for putting UPV to operating mode in cases when the riser is occupied by gas-saturated oil in a metastable state) , ultrasound, infrasound. - M.: Knowledge, 1986. - 192 p., p.90) (see paragraph 4 of the claims).

Note that when the separator is underloaded, the bottom of the apparatus may also be exposed to the same effect.

3.4. Vacuum Pretreatment Device

The name of the prototype is unsuccessful - gas release is intensified in the device, not gas separation. The main disadvantage of the prototype is its unnecessarily high resistance: Δ Р≥ 5.67 Р _out , while Venturi pipes on water are able to enter the cavitation mode even when the pressure at the inlet is 2-4 m, which corresponds to Δ Р = (0, 2-0.4) P _out (see Bashtata T.M., Rudnev S.S. et al. Hydraulics, hydraulic machines and hydraulic drives. - M.: Mashinostroenie, 1982.- 423 p .; p.116). This mode was necessary to create a pulsating cavity in cavitation conditions. In our case, cavitation is excluded: in the overwhelming majority of cases, the pressure at the outlet from the oil recovery unit is less than the pressure of oil saturation with gas, and if there is more, the gas phase released in large quantities cannot quickly disappear. There will be no phenomena associated with the collapse of the bubbles, that is, cavitation.

The main reason for the increased losses of the prototype is the oversized opening angle of the diffuser (α> 15 °), causing at least a three-fold increase in losses compared to the optimal angle of 6-8 °. For 10 years, the author traveled most of the fields of Bashkiria with UPV models of various configurations, investigated various models in laboratory conditions. At the same time, a great influence of the configuration of the flowing part and the quality of the UPV production on the characteristics was found, but it was not possible to identify the effects of either the configuration or the operating mode when working in the supercritical region (behind the unstable boiling zone) on the quality of oil degassing.

So, from the conditions for the maximum reduction in losses in the diffuser, it is proposed that the initial opening angle be performed within 6–10 °, followed by either smooth or stepwise change to 15–30 °.

An exception is a full-scale experiment in the process of putting technology with adjustable OLA. In this experiment, an attempt to insert an adjustment needle into the mouth of the UPV (before a pronounced adjustment effect appeared) was accompanied by a certain decrease in pressure at the outlet of the UPV, which indicated an increase in the lifting effect, i.e., an increase in gas evolution. With the further introduction of the adjusting needle, this effect quickly disappeared. Apparently, the effect is of the same nature as the introduction of steam generating gratings — an increase in the uniformity of the velocity field. Studies of the created mathematical model will answer these questions in more detail. Here, we note the usefulness of introducing adjusting peaks not only as a means of changing the characteristics of the UPV, but also as a means of increasing the uniformity of the velocity field at the entrance to the diffuser.

Constant taper spikes are usually used to adjust nozzles. But when such peaks are introduced into the cylindrical channel (in the neck), an annular diffuser is formed with an effective opening angle depending on the relative position of the surfaces, i.e., on the course of the adjustment needle. By the effective expansion angle, we mean the expansion angle of an axisymmetric linear diffuser having a rate of change in cross-sectional area equal to the annular one. The study showed that at the recommended taper angles, peaks of 15–20 ° already soon after introducing peaks into the neck, the effective angle cannot guarantee a continuous flow. Reducing this angle sharply increases the size of the peaks, its mass and stroke, which is extremely undesirable due to the placement of peaks on the console and the threat of vibration peaks at the slightest misalignment.

The modern level of theory and technology of calculations allows you to build a needle profile that meets the requirement of a constant pressure gradient and provides greater resistance to flow separation. Here, in the hope of sufficiency, we restrict ourselves to indicating that the needle should be made with a variable taper, varying from 15-30 ° at the top of the peak to 0-10 ° at the base of the conical part.

The design of the device for preliminary vacuum processing of the stream as a whole is shown in Fig.3. It consists of a nozzle 1, a pre-chamber 2, an adjustment peak 3, and a displacement unit for the last 4.

The nozzle contains a confuser, a neck and a diffuser. The confuser, depending on the available pressure, can be performed in different ways: with its excess - in the form of a truncated cone with an angle at the apex of 90 ° and a smooth transition to the diameter of the precamera, with a lack - in the form of an arc of a circle, as shown in Fig. 3. In the first case, the interface with the neck can be performed with a radius of curvature, eliminating the formation of a vortex zone at the inlet, for example, R = 0.2 Dr, as in the prototype. The neck here becomes a means of limiting the opening angle of the effective diffuser. The great temptation to turn a slightly ascending cone into a throat is hardly justified, since this carries the risk of losing an achievable supersaturation due to a decrease in the rate of pressure change in front of the fracture front. Since the neck extension is associated with an increase in hydraulic losses, we take its length, as well as the prototype, approximately equal to 2 Dr. In this case, the end of the control peaks will enter the diffuser after the main part of the pressure head has already been converted to pressure.

The heaviest load is on the confuser, the neck and the adjustment peak. It is here that a high-speed flow is formed and fluid rupture occurs. In 1996, a water degasser was commissioned for the Cenomanian horizon, which had an initial gas content of 3-4 m ³ / m ³ (almost the same as oil on KSU). The nozzle was made of structural carbon steel. The degree of degassing was evaluated by the feed coefficient of the piston pumping pumps, which was determined with an accuracy of the third significant digit. After a year of round-the-clock operation, the effectiveness of preliminary vacuum treatment decreased. Dismantled the OLA. It turned out that the entire entrance area to the neck at the smallest cross-sectional area, when the adjustment peak was introduced, was ulcerated by deep cavities, i.e., typical cavitation wear was observed (a brilliant confirmation of the hypothesis previously proposed by others that the cause of cavitation destruction of materials is a break in the fluid continuity, and not popping bubbles). The needle, made of viscous austenitic stainless steel, showed no signs of wear. Since then, the manufacture of the confuser and the neck was interchangeable (see Fig. 3) from viscous austenitic stainless steel. Recently, the object was examined after a round-the-clock two-year operation with such an OLA. The effectiveness of his work is fully preserved.

The UPV pre-chamber is best made from a standard tee with a welded adapter to a smaller diameter on the liquid supply side. This design allows you to optimize the fluid intake in the UPV and to avoid significant pressure losses at the inlet (see paragraph 5 of the claims).

3.5. Separation plant

In the process of vacuum processing, 2-4 million bubbles in 1 cm ^{3 of} oil are created. If the oil is not foamy, then the bubbles coagulate quickly and no separation problems arise. The separation of such oils can be carried out in conventional separators (see paragraph 6 of the claims).

If oil has a tendency to pricing, then there is a danger of overflow of the separator with foam with a sharp deterioration in the quality of separation, in particular with a large entrainment of the dropping liquid by gas. At the site of oil recovery to the separator, gravitational forces - the basis of the foam destruction effect - do not work, and micro bubbles suppress the turbulence of the flow. Implementation experience shows that after preliminary vacuum treatment, the liquid rises to the separator quite calmly, without any pressure fluctuations at the inlet to the riser. In this case, an emulsion regime is realized if the amount of gas is insufficient for phase reversal, which immediately passes into a reversed gas-liquid flow, if there is an excess of free gas. However, this will happen if the shear stress exceeds the shear strength of the foam (see Zagoskina N.V., Sokovkin G.M. Determination of flow conditions and destruction of flotation foams. - TOKhT, 2001, t. 35 No. 1. - p.99- 102). If this condition is violated, it is necessary to destroy the foam.

It is best to destroy the foam in dynamic conditions, before it is introduced into the apparatus. With the surface destruction of the foam as a result of rupture of the shells, microdroplets of oil are thrown up, which constitute the main source of gas pollution. The purest gas (cleaner than after the most advanced droplet eliminators) is obtained after passing through properly functioning gas pre-sampling devices or, as they are often called now, terminal phase dividers (CDFs). In this case, the gas passing over the free surface of the liquid in a turbulent mode, self-cleaning due to the capture of the aerosol by the surfaces of the stream. The dimensions of the device to ensure a given degree of purification and pressure loss can be significantly reduced by artificial turbulization of the flow (see, for example, V. Yurchenko. On optimizing the conditions for collecting aerosol on the surface of pipes and channels during turbulence of a gas stream by diaphragms. - TOKhT, 1992. - No. 1 p. 133-137). It can be assumed that the role of turbulizers in a properly functioning depulsator is played by waves formed on the surface of the oil, but waves can also become a source of droplet formation, droplet drop. In conditions of variability of the instantaneous performance of KSU separators for gas and liquid, it is quite difficult to correctly calculate the foam blower. It's much easier to make it customizable.

The necessary hydrodynamic situation in the CDF is determined by the degree of initial destruction of the foam and the gas velocity. The latter depends on the degree of filling of the CDF. Therefore, the most appropriate controlled effect on these values. The first can be done if, at the end of the lifting section, for example, an angular defoamer with a height-adjustable entrance slit is installed, the second - if an adjustable damper is installed at the end of the KDF. And in order to solve the problem of placing CDF at a height of up to 25 m, place it inside the separator, above the surface of the liquid. The fact is that the mudguard is determined by the specific load - the amount of gas released through a unit area. This forces an increase in the area of the mirror in the separator, i.e. fill it in about half. Dropping is also determined by the surface area of the deposition. Consequently, modern separators, having a deficit in the surface area, at the same time have an excess volume of gas space. The proposal will address both of these shortcomings. In addition, the problem of heat loss in the winter is solved.

3.6. Justification of the claims

All claims form a unity of the type “one for the implementation of the other” and meet the requirements of the unity of the inventive concept. The main distinguishing feature of the first paragraph is that local vacuum processing is carried out before entering the riser. It can be carried out in any device - valve, gate valve, throttle washer or in a special device. This allows you to use the lifting effect to reduce back pressure, which, in turn, provides the possibility of vacuum treatment in a special device without an additional pressure source. Experience shows that Δ P (Q) and Δ (Q) in this case in total do not exceed the lifting effect, so that it is possible to introduce vacuum treatment on several parallel separators one by one without disturbing normal separation in other devices.

In the second paragraph, the main distinguishing feature - pressure control “to oneself” guarantees the bypass is turned on at the best operation of the air-tightness, and for the bypassed gas, the gas released as a result of vacuum treatment will serve as a well-known means of intensification of gas separation - the “blow-off” means. But, unlike classical light gas blowing, the gas released is heavier, and, therefore, light components will be “blown away” first of all, as required.

In the third paragraph, the main distinguishing feature is the supply of gas through the pressure regulator “to oneself”, the implementation of which will reduce gas losses by blowing and reduce the removal of gasoline fractions into the gas phase (the main disadvantage of “blowing”).

Paragraph four replaces the aforementioned blow with a wrench or sledgehammer, which is not permissible from a security point of view (unless the wrench or sledgehammer is copper-plated).

In the fifth paragraph, the main distinguishing features are the parameters of the flow part, which allows to reduce the value of Δ P (Q), which is included in the restrictive formula by two to three times in comparison with the prototype and to ensure the replacement of the most worn parts, opening the way for serial production of individual products and making the deadline The design service as a whole is almost unlimited.

In points from the sixth to the tenth, one invention is divided into components, each of which can be used independently and has novelty (to our knowledge). So, for example, the 6th item allows you to group the entire piping at one end of the tank and double the path of degassing the liquid. Therefore, it can only be used for these purposes.

4. The list of drawings:

Figure 1. Hydraulic characteristic of UPV.

Figure 2. Performance characteristics of UPV.

Figure 3. Preliminary vacuum treatment device (UPV) (A).

Figure 4. Installation of the device (UPV).

1. Nozzle

2. The pre-chamber

3. Adjustment peak

4. Drive

Figure 5. Separation unit (general view)

6-10 details of the separation unit

Figure 5-10 indicated:

5. The unit of preliminary preparation for separation

6. Riser

7. Node preliminary phase separation

8. Inclined section of the end phase divider

9. Separation tank

10. Tray

11. Drive plate

12. Plate

13. Corners

14. Half-apertures

15. Rib

16. Damper actuator

17. Damper

18. Rib rib

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

Separation plant

A general view of the separation unit is shown in FIG. It consists of a unit for preliminary preparation of oil for separation 5 (for more details, see Fig. 4), a riser 6, a unit for preliminary separation of a gas-liquid mixture 7, adapters connected to a pipe connected to KDF 8 located inside the separator 9.

The preliminary separation of the gas-liquid mixture (Fig.6-10) externally is a thickening of the top of the riser with a side outlet. Inside it are two circular rows of inclined corners around the central end of the riser. The first row cuts the radial flow into streams falling into the grooves formed by the second row. Above the exit from the riser with a slightly flared end, a movable plate is installed with a drive similar to the valve actuator. The bottom surface of the plate has a conical surface, which creates a conoidal radial outlet with a flared end of the pipe. When moving the plate will change the speed of the outgoing stream, the intensity of its impact on the corners and, therefore, the degree of destruction of the foam. The optimal position of the plate during operation is determined by a simple selection.

The inclined section of the KDF is calculated using RD39-0004-90 (Guidelines for the design and operation of separation units of oil fields, the selection and layout of separation equipment: Ufa: VNIISPTneft, 1990, 68 pp.) And the recommendations of the article by Yurchenko V.I. On optimizing the conditions for collecting aerosol from the surface of pipes and channels during turbulization of a gas stream by diaphragms. - TOKHT, 1992, t. 36, No. 1, pp. 133-137. The latter - with the introduction of the hydraulic radius and a new criterion - the degree of restriction of the flow by the diaphragm, equal to the ratio of the areas of the passage with the diaphragm and without it.

Due to the reduction of the particle path to deposition, a partially filled section is better than an unfilled section, so the recommendations of this article can be used with confidence. It should be borne in mind that the regular step of the diaphragms can contribute to wave formation on the surface, so it is better to make it irregular within the recommended values there.

Finally, the last node is the node regulating the degree of filling of the CDF. The location of the KDF inside the separator relieves from worries about the tightness of the assembly, but it gives rise to new ones - coupling the outgoing jet with a free surface, in the general case, with a variable distance to it. Regulation can be performed, for example, with an ordinary flat heavy damper capable of sliding along a shear plane inclined to the axis of the pipe. In this case, the outer surface of the damper serves as a tray for the jet to swell, and the cut-off angle should be chosen taking into account this circumstance. But reducing the angle below a certain limit is unreasonable - the size of the flap and friction forces are too large. Therefore, an additional tray system is inevitable (see Figure 5.3), which is the intersection of two inclined planes symmetrical with respect to the longitudinal axis of the separator with a cutout to accommodate the shutter and a longitudinally inclined plate intersecting edge.

Installation work

If the normal operation of the system for maintaining the level in the separation tank is guaranteed, it is not necessary to fill the installation before start-up. Unlike other cases of use, the device for preliminary vacuum processing of the flow during oil separation gives some kind of effect in any mode, therefore, under normal conditions, when there is enough dissolved gas in the incoming oil, it starts up automatically: the greater the flow rate, the more emitted gas, the lower the back pressure and the closer to the nominal mode. If there is not enough water in a degassed liquid, then in the operating mode there is no sound of bursting liquid in the UPV. Therefore, the mode is judged by the pressure at the inlet and outlet. A sign of the output of the UPV to the mode is a rapid decrease in pressure in the base of the riser at a constant pressure at the inlet of the UPV. At the first start-up, the pressure at which this decrease begins and its final result should be remembered. It is useful to measure the separation pressure at the same time. This will allow you to calculate the effect of lifting. In the proposed separation unit, the inlets and outlets of oil and gas are located nearby. It is useful to equip all pipes with gauges so that the normal course of the process can be monitored. The increased trapping of dropping liquid onto a hot KSU is accompanied by a warming of the wall of the exhaust gas pipeline, therefore, when warming occurs, it is necessary to adjust the operation of the KDF either by changing the position of the inlet throttle plate or by changing the position of the outlet damper. In the process of bringing the installation to operating mode, it is necessary to find their optimal position and find out the nature of its influence on the quality of separation.

The preliminary passage of KDF and thin-layer sedimentation during discharge from KDF to the surface leads to the fact that the oil in the separator can contain only gas trapped by the jet when draining from KDF to the surface of the liquid. This gas is quickly enough separated from oil without polluting the gas space. Therefore, during normal operation of the entire complex, there is no need for special drop separators: the gas must be clean - cleaner than after the most advanced CDFs (due to the additional effect of expansion in the tank).

With a decrease in gas content of oil, the UPV regime may exit the working area. In this case, at the base of the riser, the pressure rises sharply, giving an impulse to turn on the blowing mechanism or to start the ultrasonic emitter. Both of these methods lead to a decrease in pressure at the base of the riser and the release of the OLA to the operating mode, after which the gas supply to the blow-off or ultrasonic irradiation is stopped.

According to the results of industrial tests, the technology doubles the amount of gas taken off, deepening the degassing of oil, and serves as an ideal means for uniform distribution of oil between parallel separators and for breaking the oscillatory circuits.

Claims (11)

1. The method of oil separation at the end separation plants, including lifting the oil to the separator along the riser, separation and removal of oil and gas, characterized in that before entering the riser all or part of the oil is subjected to local vacuum treatment in the mode P _in ≥ P _out + Δ P (Q) + Δ (Q), where p _I and P _o - pressure at the inlet and outlet of the preliminary vacuum processing device; Δ P - pressure drop across the device when working with a capacity of Q; Δ is the width of the zone of unstable operation of the device. 2. The method according to claim 1, characterized in that the part of the stream not subjected to vacuum treatment is passed through the pressure regulator “to itself”, adjusted to the maximum allowable pressure at the device inlet, before being fed to the riser. 3. The method according to claim 1 or 2, characterized in that gas is supplied to the riser through the bubbler through the pressure regulator “after itself”, configured to operate at the maximum allowable pressure at the outlet of the vacuum processing device. 4. The method according to claim 1 or 2, characterized in that when increasing the pressure at the outlet of the processing device by a vacuum above a certain limit, the region of least pressure or the base of the riser is subjected to vibration by the ultrasonic vibrations emitter. 5. The device for processing the flow by vacuum, consisting of a pre-chamber, an adjusting needle with a drive, a confuser, a neck length equal to its two diameters and conjugated with a confuser along an arc with a radius of 0.2 neck diameters, as well as a diffuser, characterized in that the confuser is made with an angle taper 80-120 °, adjusting needle - with variable taper from 0 to 10 ° at the base and 20-30 ° at the tip of the needle, diffuser - with variable taper, varying from 6-10 ° at the neck and up to 30 ° at the end , the pre-chamber is made of a tee, and the adjustment needle and the inside of the confuser and the neck are interchangeable from viscous austenitic stainless steel. 6. Separation unit, including the separator and its strapping, characterized in that at the base of the riser one or more vacuum processing devices with shut-off valves at the inlet and outlet of each are connected to it, a bypass with a pressure regulator “to itself”, with shut-off valves the same diameter and the diffuser at the outlet, designed to pass the maximum flow rate entering the installation with the maximum allowable pressure drop and a fully open valve. 7. The separation unit according to claim 6, characterized in that the piping of the bottom of the riser includes either a gas supply line with a pressure regulator “after itself”, or a vibrator mounted on the neck of the vacuum processing device or on the base of the riser. 8. The separation unit according to claim 6 or 7, characterized in that it has an end phase divider for introducing the vacuum-treated mixture into the separator, partially located in the gas space of the separator with a tray system at the outlet of it, eliminating the jet falling onto the free surface of oil in separator. 9. The separation unit according to claim 8, characterized in that at the end of the oil lifting section a foam breaker is mounted having a movable damper for controlling the speed of the gas-liquid jet. 10. The separation unit according to claim 8, characterized in that at the outlet of the terminal phase divider it is additionally equipped with a shutter for regulating the liquid level in it. 11. The separation unit according to claim 8, characterized in that the inner surface of the end phase divider is provided in the gas part with gas turbulators in the form of a part of annular diaphragms arranged with a variable pitch, excluding wave formation of the free surface of the liquid in this phase divider, and its outer surface is provided ribs to intensify the precipitation.

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