RU2798104C2 - Flare separator with cyclone droplet eliminator - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention is related to a gas separation device designed to capture aerosol and fine liquid particles from a gas stream in flare systems, and can be used in oil and gas, oil and gas processing, petrochemical and other industries. A flare separator with a cyclone droplet eliminator consists of a horizontal tank having gas inlet and outlet pipes, a liquid outlet pipe and an external remote cyclone connected in series to the horizontal tank, connected by its inlet pipe to the gas outlet pipe of the horizontal tank through a pipeline. To remove condensate from the cyclone, there is a drain pipe and a drain line, which is installed through the pipe of the horizontal tank and falls below the minimum level of filling of the horizontal tank. An obligatory condition for preventing an unacceptable pressure drop across the device is the equal capacity of the gas flow channels through the entire structure of the claimed invention.

EFFECT: device provides an increase in the efficiency of flare gas purification from dropping liquid while ensuring the safe operation of the flare system.

4 cl, 2 dwg

Description

The invention relates to gas separation apparatus designed to capture aerosol and fine liquid particles from a gas stream in flare systems, and can be used in oil and gas, oil and gas processing, petrochemical and other industries.

The flare system is designed for discharge and subsequent combustion of combustible gases and vapors when emergency discharge devices (safety valves, hydraulic seals, etc.) are triggered, as well as at constant ones, provided for by the technological regulations for the production of vents.

Emergency release devices are provided for technological equipment operating under the pressure of gaseous and liquid media.

In accordance with the requirements of the Rules for the Safe Operation of Flare Systems PB 03-591-03:

- item 3.8. Gases and vapors discharged into the common and separate flare systems should not contain dropping liquid and solid particles. For these purposes, it is necessary to install separators within the boundaries of the process plant;

- clause 5.7. In flare installations intended for combustion of combustible gases and vapors, a separator with a permanent liquid withdrawal should be used;

- clause 5.8 .... The design of condensate collectors must exclude liquid entrainment…

Thus, in order to comply with safety requirements, it is mandatory to install a flare separator, which should ensure not only the collection of emergency discharges of technological, including liquid media, but also the separation and retention of the droplet liquid contained in the gas.

From the prior art, horizontal separation apparatuses and tanks are known that are used as flare separators and condensate collectors and operate on the principle of gravitational separation of phases of different density (Flame gas separators of the FS type. Technical characteristics. Spetsneftekhimmash, https://snhm.nt-rt.ru/ images/manuals/3.pdf).

The disadvantage of the known device is the incomplete separation of gas in the presence of a fine liquid phase in the gas stream in the form of an aerosol. Under such conditions, gravity separators are ineffective, and to achieve acceptable efficiency they require a much larger volume, since, in accordance with the calculation of gravity separators, the efficiency of droplet separation depends on its linear dimensions.

It is also known from the prior art that to increase the efficiency of separation of dispersed systems in the form of aerosols, cyclone installations are successfully used, where the separation of a denser component - the liquid phase is carried out due to the action of centrifugal force, which can be several times greater than the force of gravity used in gravity separators (Zarembo K.S. Handbook on the transport of combustible gases).

Cyclone devices are widely used in separation technology, incl. for capturing dropping liquid from a gas stream. Many designs and layouts of cyclones have been developed for various operating conditions, incl. battery (multi-) cyclones.

The disadvantage of the known cyclone devices is the limitation of their use in the flare system in view of the fact that the function of the flare separator is to collect and remove emergency discharges, including liquid media, and when liquid enters the centrifugal separation device, designed to work with gas, the normal mode is disturbed operation of both the cyclone and the entire flare system, while not meeting the requirements of the Safety Rules for the operation of oil treatment plants at oil industry enterprises, approved. Gosgortekhnadzor of the USSR 16.07.76:

- due to the increase in the density of the working medium in the cyclone, an unacceptable pressure drop occurs on the device, which leads to the excess of the maximum pressure of the flare system and its "locking" - violation of clause 2.13.13. The gas pressure in the common flare pipeline before exiting the flare stack should not exceed 0.5 kgf/cm2 ⁾ ;

- due to the fact that the volumetric flow rate of the dropping liquid is much less than the volumetric flow rate of the gas flow, the liquid phase exit pipe from the cyclone has a smaller diameter than the gas inlet pipe into the cyclone, respectively, the liquid does not have time to be removed from the cyclone and goes directly to the flare stack - violation clause 2.13.7. To prevent condensate from entering the flare, it must be removed from the separators in a timely manner .

The closest technical solution adopted as a prototype for the claimed invention is the "Method of upgrading the gas separation unit and the gas separator" (patent RU 2310497, IPC B01D 45/12, B04C 5/00 publ. Bull. No. 32 20.11.2007), where a gas separation unit is being modernized based on a commercially produced small-sized separator, which contains a housing, inlet, outlet, drain pipes, as well as a vortex (centrifugal) separation device.

The disadvantages of this device is the impossibility of its use in flare systems, since it involves the use of a vertical gas separator, while in flare systems horizontal separators are used, the design and orientation of which creates a sufficient volume to trap emergency liquid discharges.

The technical contradiction between the task of increasing the efficiency of gas separation from the dropping liquid and the task of ensuring the safe operation of the flare system in terms of catching emergency salvo liquid discharges is solved by including an external remote cyclone (cyclones) in the flare separator layout, and the inlet pipe of the external remote cyclone (cyclones) is connected with a branch pipe for gas outlet from the flare tank, which makes it possible to freely collect emergency discharges of process liquids and the resulting condensate directly into the flare tank, thereby ensuring compliance with the safety requirements.

For optimal inclusion of external remote cyclone elements in the layout of the flare separator, the principle of dividing a single gas stream into separate flows with a battery of external remote cyclones can be applied, i.e. the use of a multi-cyclone unit, which will achieve the required efficiency of droplet separation without the formation of an unacceptable pressure drop.

The combination of highly efficient cyclone separation elements outside the flare tank, in comparison with the internal placement of cyclones, does not occupy the usable working space of the separator and allows to reduce the loss of light fractions of the product (oil) and involve them in production, reduce the emission and combustion of greenhouse gases, and reduce the carbon footprint of production.

The invention can be applied both in the design of new and in the modernization of existing flare separators.

The essence of the technical solution is to combine two separation devices in one node:

- a horizontal tank, the purpose of which is to capture emergency salvo volumes of liquid, as well as the accumulation of condensate due to the gravitational separation of liquid droplets from the gas-liquid mixture flow;

- an external remote cyclone, the purpose of which is the effective trapping of liquid droplets from the flare gas due to centrifugal separation.

The connection of these separation devices is carried out sequentially with the phased passage of the gas-liquid flow first through a horizontal tank, where large drops and a free liquid phase are separated, incl. liquid plugs, and then through an external remote cyclone, where a finely dispersed phase is trapped on its inner surface due to centrifugal separation and flows under the action of gravity into a horizontal flare tank.

The technical result achieved by the invention is to increase the efficiency of cleaning flare gas from dropping liquid, while ensuring the safe operation of the flare system, which is expressed in ensuring the reception, retention and removal of volley emergency discharges of liquid media, which contributes to:

- reduction of hydrocarbon losses during gas flaring;

- reduction of opacity of burning of a flame of a torch;

- reducing the carbon footprint as part of the decarbonization of production;

- reduction of harmful emissions from combustion products.

The technical task facing the author is to create a layout of the separation unit of the flare unit, which ensures the efficiency of cleaning the flare gas from dropping liquid while ensuring the safe operation of the flare system.

For this, a flare separator with a cyclone droplet eliminator is used, the design of which is shown in Fig. 1, consisting of a horizontal tank 1 having a gas inlet pipe 2, a gas outlet pipe 3 and a liquid outlet pipe 4. The horizontal tank 1 can be equipped with additional internal structural elements that increase the efficiency of gas separation from condensate drops. In series, an external remote cyclone 5 is connected to the horizontal tank 1, connecting its inlet pipe 6 to the gas outlet pipe 3 of the horizontal tank 1 through the pipeline 7. The gas flow containing small drops is spun in the tangential swirler of the external remote cyclone 5 and due to the occurrence of centripetal acceleration small drops fall onto the inner surface of the cone and flow into the lower part of the external remote cyclone 5. The gas purified from the dropping liquid is removed from the external remote cyclone 5 through the outlet pipe 8. To drain the condensate from the external remote cyclone 5, there is a drain pipe 9 and a drainage line 10, which is installed through the branch pipe 11 of the horizontal tank 1 and falls below the minimum filling level of the tank 1, and through which the separated droplet moisture flows freely from the external remote cyclone 5 and accumulates in the tank 1. The minimum filling level of the tank 1 is maintained constantly due to the nozzle cutting device removal of liquid 4 at a level above the cutoff of the drainage line 10 by an amount determined by the calculation from the condition of excluding the breakthrough of the gas flow into the external remote cyclone 5 by reverse current through the drainage line 10. Separation devices: flare tank 1 and external remote cyclone 5 can have shut-off and control valves , as well as devices for monitoring gas flow, liquid level and pressure in lines and apparatuses that ensure the efficiency and safety of the process (not shown in the diagram). To apply the claimed invention to existing flare separators and tanks, their modernization is carried out by including an external remote cyclone (cyclones) in the existing layout according to the description of the design of the invention, with the possibility of installing an external remote cyclone either directly on a horizontal tank or on a separate base when the condition of free drainage is met drops of condensate by gravity through the drainage line 6, to connect which is used a suitable branch pipe or a manhole of a horizontal tank 1. A prerequisite for eliminating an unacceptable pressure drop across the device is the equal capacity of the channels for gas flow through the entire structure of the claimed invention, namely, the area of the transverse cross-section of the channels for the gas flow of the device must not be less than the cross-sectional area of the supply pipeline.

What is new is that in the layout of the flare separator, an external remote cyclone or a battery of cyclones is sequentially used, which increase the effective trapping of dropping liquid from the gas stream after passing through the horizontal flare tank, which ensures the safety of the flare system by receiving, retaining and removing volley emergency discharges of liquid media.

What is also new is that the exclusion of an unacceptable pressure drop across the device is ensured by organizing an equal throughput of the device channels for the flow of flare gas through the entire design of the claimed invention.

What is also new is that for accumulation and degassing, the condensate is drained into a horizontal tank by gravity below the level of the minimum filling of the horizontal tank, which does not require the use of additional tanks and a pump.

The claimed device does not require major interventions in existing and operating equipment, can be adapted to existing processes and applied to existing flare installations.

The set of features of the implementation of the proposed flare separator with a cyclone droplet eliminator increases the efficiency of separating the droplet liquid from the gas stream, while maintaining the safety of the flare system.

The listed features are essential and interconnected with the formation of a stable set of essential features sufficient to obtain the specified technical result.

The comparative analysis of the proposed technical solution with the identified analogues of the prior art showed that it differs from the known analogues, therefore the claimed invention is new. The claimed distinguishing features of the invention do not explicitly follow from the prior art, are not obvious to the average specialist in the design and operation of flare systems, and therefore, the claimed invention has an inventive step. Taking into account the possibility of using the device in production, the invention is industrially applicable and allows us to conclude that it meets the patentability criteria.

The present invention is illustrated by a specific example of the use of a flare separator with a cyclone mist eliminator, which clearly demonstrates the possibility of obtaining the specified technical result. Various modifications and improvements are permitted without departing from the scope of the invention as defined by the appended claims.

One application of the invention is described below based on the operation of the flare system (FIG. 2) of an oil treatment unit (OTU).

Flare gas, as a result of continuous or periodic discharge from the separation stages of the OTP, enters the collection header 1 of the flare system of the OTP, where natural gas cooling and condensation of water vapor and hydrocarbons contained in the flare gas can occur. Thus, a gas-oil mixture in the form of an aerosol and/or foam, as well as an oil emulsion periodically enters the collection manifold 1 after the emergency discharge devices (safety valves of separators and settling tanks) are activated, and then to the inlet of the horizontal tank 2 of the flare separator, where the enlarged drops of condensate and oil emulsion are deposited due to gravity on the bottom of the horizontal tank 2, the liquid is accumulated, degassed and, when the maximum level is reached, it is pumped out by pump 3 for disposal for preparation at the “head” of the OPF process. The flare gas, freed from the oil emulsion and large drops of condensate, leaves the horizontal tank 2 and is directed through the pipeline 4 to the external remote cyclone 5, where the fine phase of the condensate is captured from the flare gas flow, which is freely removed by gravity from the body of the external remote cyclone 5 through the drainage line 6 at the bottom of the flare tank 2 under the minimum liquid level. The gas cleaned from drops leaves the external remote cyclone 5 and is discharged through the flare collector 7 to the flare riser 8 for combustion.

The efficiency of capturing droplet liquid when using the claimed invention with respect to known designs of flare separators is achieved due to the fact that, in addition to the capacitive equipment that ensures the safety of the flare system, an external remote cyclone device is connected, which obviously has a high separation efficiency of fine systems in the form of aerosols.

The use of a flare separator with a cyclone droplet eliminator makes it possible to effectively clean the flare gas from dropping liquid, while ensuring the safe operation of the flare system.

Claims (4)

1. A flare separator with a cyclone droplet eliminator, having a body, inlet, outlet, drain pipes and containing a centrifugal-type separation device, characterized in that the body is made in the form of a horizontal tank, for the gravitational separation of free liquid from the gas-liquid mixture flow, and the centrifugal separation device is represented an external remote cyclone for centrifugal separation of liquid droplets from the flare gas, while the external remote cyclone is connected in series to the horizontal tank by a pipeline connecting the inlet pipe of the external remote cyclone with the outlet pipe of the horizontal tank. 2. A flare separator with a cyclone droplet eliminator according to claim 1, characterized in that the exclusion of an unacceptable pressure drop across the device is ensured by organizing an equal throughput of the channels for the flare gas flow. 3. A flare separator with a cyclone droplet eliminator according to claim 2, characterized in that for accumulation and degassing, condensate is drained into a horizontal tank by gravity along the drainage line to the level of the minimum filling of the horizontal tank, which is constantly maintained by the cut device of the liquid outlet pipe at a level above the cut the drainage line by the value determined by the calculation from the condition of excluding the breakthrough of the gas flow into the external remote cyclone by reverse current through the drainage line. 4. A flare separator with a cyclone droplet eliminator according to claim 3, characterized in that the installation of an external remote cyclone is possible both directly on a horizontal tank and on a separate base when the condition of free drainage of condensate drops by gravity along the drainage line is met.

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