RU2088298C1 - Method of stripping hydrocarbon vapors - Google Patents

Abstract

FIELD: petroleum processing. SUBSTANCE: hydrocarbon vapor-air mixture is fed through feeder pipeline into membrane unit where mixture is separated into air stream and hydrocarbon vapor stream. The former is withdrawn and the latter is introduced into absorber to be cooled. EFFECT: reduced power consumption and metal usage with no loss in quality of stripping process. 1 dwg, 1 tbl

Description

 The invention relates to the oil industry and can be used in oil refining, distribution, storage and transportation of petroleum products and other volatile hydrocarbon liquids.

 A known method of topping oil vapor (Umergalina T.G. Hafizova A.R. and others. Technology for collecting low-boiling gasoline fractions from tanks, journal Oil economy N 10, 1989, p.6-9).

 The method involves the selection of the gas mixture from the vapor space of the tanks, mixing the gas mixture with part of the oil in the pipeline, cooling in the refrigerator and separating the mixture into gas and liquid phases.

The disadvantages of the method:
significant losses of light fractions taken from the tanks during their subsequent transportation through gas pipelines;
large harmful emissions into the atmosphere and their negative impact on the environment.

 Closest to the technical nature of the proposed is a method of trapping hydrocarbon vapors, including the selection of the vapor-air mixture from the cargo compartments of the tanker, cooling with refrigerated kerosene and separation of the mixture into gas and liquid phases (R. Bennet Recovery of hydrocarbon vapours from crude oil // Petroleum Review. 1993 , v. 47, N 554 p. 134-135).

 The disadvantages of this method include significant energy costs associated with the need to cool the absorbent kerosene and the pump to pump it, as well as the high metal consumption due to the use of powerful refrigeration equipment and equipment for pumping the absorbent. The steam-air mixture arriving for processing is a mixture of hydrocarbon vapors and air, and the air content can vary widely (for example, for a mixture with gasoline vapors from 30 to 95 vol.).

 The presence of air in the composition of the vapor-air mixture plays the role of unnecessary ballast. As a result of this, in order to achieve the required degree of stripping of hydrocarbon vapors from the vapor-air mixture, an increase in the specific consumption of the refrigerated absorbent is required, which leads to an increase in energy costs for its cooling and pumping. In addition, increasing the specific consumption of absorbent material requires the use of more powerful refrigeration equipment and equipment for pumping absorbent material, which increases their metal consumption.

 The purpose of the proposed method is to reduce the energy costs for cooling and pumping the absorbent, reducing the metal consumption by reducing the amount of absorbent needed to process the vapor-air mixture, without compromising the quality of the vapor treatment from hydrocarbons.

 This goal is achieved by the described method of stripping hydrocarbon vapors, including the selection, cooling and separation of the vapor-air mixture into gas and liquid phases.

 What is new is that the steam-air mixture after separation is separated into air and hydrocarbon vapors, after which the separated hydrocarbon vapors are cooled and separated into gas and liquid phases, and air is removed from the process.

 The drawing shows a schematic flow diagram of the implementation of the proposed method.

 It contains a supply pipe 1, a membrane unit 2 with an air exhaust line 3 and a gas exhaust line 4, an absorber 5 with scattering candles 6, a container for refrigerated kerosene 7, a refrigerator 8, a container for spent kerosene 9, a stripper 10 with an integrated heater 11, a reabsorber 12 and reservoir 13.

 The method is as follows.

 The vapor-air mixture (a mixture of hydrocarbon vapors with air) is supplied (for example, from the gas equalization system of the tank storage tank for oil products or from loading systems) through the supply pipe 1 to the membrane unit 2, where the vapor-air mixture is divided into two streams: air and hydrocarbon vapors.

 Studies have established that the optimal amount of air sampling from the incoming steam-air mixture lies in the range of 0.7-0.9 of the potential. Taking air below this value leads to an increased consumption of kerosene absorbent for treating the vapor-air mixture, which entails an increase in energy costs for cooling, pumping and regenerating absorbent kerosene. With a better separation of the mixture (more than the specified value), it is necessary to make increased demands on the manufacture of the membrane unit, which will lead to a sharp increase in its overall dimensions and an increase in capital costs.

 The air flow through line 3 is diverted to a scattering candle 6, and hydrocarbon vapors through line 4 are fed to the lower part of the absorber 5, to the upper part of which comes refrigerated kerosene from the tank 7, cooled by the refrigerator 8. In the absorber 5, the vapor of the hydrocarbons is mixed with the cooled kerosene, after which kerosene, saturated with trapped vapors of hydrocarbons, enters the tank for spent kerosene 9, and a small part of the non-trapped vapors of hydrocarbons with air residues is discharged through a dispersion candle 6 into tmosferu. From the tank 9, kerosene saturated with trapped hydrocarbon vapors is fed to the upper part of the stripper 10, in which the trapped hydrocarbon vapors are separated from kerosene by heating, the purified kerosene is returned to the tank 7 for cooling, storage and reuse in a new cycle, and the regenerated ones hydrocarbon vapors are sent to the reabsorber 12, where they dissolve in the circulating stream of oil product (gasoline) coming from the reservoir 13 and again returned to it.

 The use of preliminary separation of the air-vapor mixture into air and hydrocarbon vapors and cooling of the latter reduces the required consumption of absorbent kerosene for processing vapors (with a constant degree of extraction of hydrocarbons from the mixture) and, therefore, avoids additional energy costs for cooling, pumping and regeneration of absorbent kerosene, and also reduce metal consumption through the use of refrigeration and equipment for pumping less power.

When filling tanks containing A-76 gasoline, the steam-air mixture from the tank’s vapor space containing hydrocarbons in an amount of 48% by volume, with a flow rate of 500 m ³ / h and at an overpressure of 70 Pa was displaced into the gas equalization system and then through the supply pipeline 1 entered the membrane block 2 at the beginning of the process. In the membrane block 2, the vapor-air mixture was separated into air and hydrocarbon vapors. Separated air in an amount of 0.7 from the potential (182 m ³ / h) is sent to a scattering candle 6. Vapors of hydrocarbons mixed with air residues in an amount of 318 m ³ / h are fed into the absorber 5, into which cooled2 is supplied to minus 10 ^o C kerosene in an amount of 6.5 m ³ / h. In countercurrent mode, hydrocarbon vapors were mixed in the absorber 5 with chilled kerosene, then a small portion of unsaturated hydrocarbons with air residues in an amount of 114 m ³ / h were removed from the process through a dispersion candle 6, and kerosene saturated with trapped hydrocarbon vapors in an amount of 7.23 m ³ / h fed to the vessel for spent kerosene 9 where collected and flattened on its concentration and further a uniform flow fed to the desorber 10, wherein when heated to +140 ^o C trapped hydrocarbon vapors separated from erosina then kerosene returned for reuse and the regenerated hydrocarbon vapors in an amount of 204 m ³ / h flows into reabsorber 12 where they are mixed in the recycle gasoline stream supplied from the tank 13 in an amount of 10 m ³ / h.

 The results obtained by testing the known and proposed methods are shown in the table.

From the table it follows that with the same degree of hydrocarbon recovery (85%): the amount of absorbent kerosene needed to treat the vapor is reduced from 8.0 m ³ / h (known method) to 6.5 m ³ / h (proposed method); energy costs for cooling absorbent kerosene in the proposed method is less than in the known (21.6 versus 27.0 kW / h); energy costs for pumping and regenerating absorbent kerosene are also less (3.3 versus 4.0 kW / h and 15.4 versus 19.0 kW / h, respectively); the total energy costs for cooling, pumping and regeneration of absorbent kerosene in the proposed method is less than 8e than in the known (40.6 versus 50.0 kW / h).

 In addition, as a result of a decrease in the amount of absorbent kerosene necessary for treating the vapors, and taking into account additional capital investments associated with the introduction of the membrane block, the metal consumption in the proposed method is reduced by 12–15% compared to the known method, depending on the type of vapor recovery unit used hydrocarbons.

 The technical and economic effectiveness of the proposed method of stripping hydrocarbon vapors is due to the reduction of energy costs and metal consumption.

Claims (1)

 A method of stripping hydrocarbon vapors, including the selection, cooling and separation of the steam-air mixture into gas and liquid phases, characterized in that the steam-air mixture after separation is separated into air and hydrocarbon vapors, after which the separated hydrocarbon vapors are subjected to cooling and separation into gas and liquid phases, and air is removed from the process.

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