WO2013076433A1

WO2013076433A1 - Process for treating atmospheric distillation overhead gaseous effluent

Info

Publication number: WO2013076433A1
Application number: PCT/FR2012/052713
Authority: WO
Inventors: Pedro Da Silva; Cyrille Mirgain; Frédéric POULY; Patrick GAUTHE
Original assignee: Total Raffinage Marketing
Priority date: 2011-11-24
Filing date: 2012-11-23
Publication date: 2013-05-30
Also published as: FR2983088A1

Abstract

The present invention relates to a process for treating the overhead gases of atmospheric distillation. The overhead gases of atmospheric distillation consist of fuel gases and liquefied petroleum gases or LPGs. The overhead gases of atmospheric distillation have very little pressure and are either sent to flare compressors then to the fuel gas network, or directly flared. However, LPGs are gases that can be made use of commercially. The process for treating fuel gas resulting from atmospheric distillation containing LPGs proposes to bring the fuel gas into contact with a stabilized absorbent liquid hydrocarbon within a stabilization unit so that a portion of the LPGs present in the fuel gas dissolve in the stabilized hydrocarbon in order to obtain a liquid hydrocarbon enriched in recoverable LPGs.

Description

PROCESS FOR TREATING GASEOUS EFFLUENT AT ATMOSPHERIC DISTILLATION HEAD

Field of the invention

The present invention relates to a process for treating atmospheric distillation overhead gases and to a device for setting up such a method.

Context of the invention

Due to environmental and economic constraints, refining companies have to set up recovery systems for gases emitted in the course of their operations.

The atmospheric distillation overhead gases are mainly of two kinds: the so-called combustible gases, or fuel gas, and the liquefied gases or LPG.

The atmospheric distillation overhead gases have very little pressure and are either sent to the torch compressors and then to the fuel gas network, or directly flared.

When directly flared, burning of gases leads to economic loss as potentially valuable gases are burned. This is also accompanied by a negative environmental contribution due to the CO2 emitted and finally, leads to a deficit in terms of image with residents when the torch burns excess gas.

When they are sent to the fuel gas network, they are directly consumed within the refinery.

GPLs contained in the atmospheric overhead gas are valuable products on the market. They cover propane C3 and butane C ₄ . Their use as fuel is environmentally attractive because it reduces CO2 emissions. As LPG is valuable, it is therefore important to recover a major part of it. There is therefore an environmental and economic interest related to the recovery of LPG.

Systems for processing refinery gases are known. In US Pat. No. 6,428,606 B1 to Membrane Technology and

Research, describes a device comprising means for compressing and condensing LPG from the fuel gas network, coupled to hydrogen recovery units by the use of membranes. ExxonMobil application WO 2007/120490 discloses a principle of recovering LPG from various streams through a multi-membrane recovery process producing a high purity, high purity hydrogen stream and a C3 + LPG stream at the same time. high efficiency with low energy expenditure.

It is known that gas recovery can be effected by the use of a heavier solvent. The so-called absorption principle consists of bringing a gas in contact with a liquid of absorption poor in valued constituents. This principle is described on page 201 of the book Petroleum Refining -2- Processes of separation under the direction of J.-P. Wauquiez, Technip Editions; 1998.

This physical principle has been applied in U.S. Patent 2,358,183 where C 3 and C ₄ gas from a separation unit and of a catalytic cracking unit are compressed, condensed and sent to an absorber. The naphtha from the separation unit is sent into the absorber and once enriched, is sent to the reforming unit. The absorption here allows naphtha enrichment in C3 and _C4 but not the recovery of these gases for recovery.

The principle of absorption can also be applied to an FCC unit. This principle is reported on page 186 of the book The Refining of Petroleum Process Processes, under the direction of J.-P. Wauquiez, Editions Technip, 1998. This method requires the use of a cracked gas compressor for compressing overhead drum of gas and two absorbers for the recovery of C 3 and C _4, which have a chemical composition rich in olefins.

These processes require the use of compressors either from the fuel gas network or at the head of a processing unit. In case of strong degassing, the compressor can be saturated and treat only part of the fuel gas emitted. In addition, compressor failures can limit the effectiveness of the treatment.

RU 2335523 proposes that the overhead gases from the first atmospheric distillation column and the second vacuum distillation column be absorbed by a diesel fraction extracted from the second column. The absorber operates at a pressure between 8 and 9 bar that is to say at a pressure where the C3 and _C4 remain in the liquid phases. As described, the use of the diesel fraction as an absorbent liquid requires the enriched mixture to be ironed again in the atmospheric distillation unit.

The principle of absorption is also used in US3907669A, which describes a low energy consumption process for separating and recovering liquid and gaseous components of a charge. The process described consists in treating a feedstock containing liquid and gaseous hydrocarbons in an absorption unit in which the feedstock is brought into counter-current contact with a lean oil which will absorb a portion of the constituents gaseous charge. The lightest gases not absorbed in the absorption unit, such as ethane and methane, are recovered for recovery. The rich oil stream, containing the liquid constituents of the feedstock, the lean oil and the gaseous components absorbed, leaving the absorption unit is stripped to separate the absorbed gases contained in this stream. These gases are then returned to the inlet of the absorption unit in admixture with the charge. The stripped liquid stream recovered is returned in part to the absorption unit to serve as a lean oil and partly to a fractionation unit. In this fractionation unit the liquid stream is separated into a liquefied hydrocarbon gas and a liquid hydrocarbon. The liquid hydrocarbon is then returned in part to the absorption unit in admixture with the stripped liquid stream recovered to form the lean oil. This process thus processes a feed containing both gases and liquids, and requires a stripping unit and a fractionation unit downstream of the absorption unit, for the recovery of an absorbent hydrocarbon used in the unit. absorption.

There is therefore a need to recover upgraded gases at the top of the atmospheric distillation by the implementation of simple processes requiring low running costs and investments. Summary of the invention

The object of the present invention is to obtain a practical process capable of treating a gaseous effluent from atmospheric distillation in order to recover valuable LPG.

To solve the problem, the present invention provides a gas treatment process containing gaseous light hydrocarbons characterized in that the gas from atmospheric distillation is brought into contact with a stabilized liquid hydrocarbon absorbent so that a part of gaseous light hydrocarbons present in the gas are dissolved in the stabilized hydrocarbon to obtain a liquid hydrocarbon enriched gaseous light hydrocarbons consisting of a fraction containing C 3 and C _4.

For example, light gaseous hydrocarbons that can be dissolved in the stabilized hydrocarbon are C ₄ C ₄ gases.

The gas and the stabilized absorbent liquid hydrocarbon are contacted within an absorption unit. The gas contains combustible gas or fuel gas containing Ci and C2 and LPG containing C 3 and C _4.

Advantageously, the gas may contain or consist of 80 to 100% by weight of Ci + C2 + C3 + C _4, for example from 85 to 99% by weight, preferably from 90 to 95% by weight.

By way of non-limiting example, the contents of the gas to be treated in C1 / C2 may be of the order of 15% to 60% by weight and the contents of the gas to be treated C3 C ₄ may be of the order of 0.5% to 60% by weight.

The gas to be treated may optionally further contain C ₅ entrained, in very low levels, less than 2% by weight relative to the total weight of gas to be treated.

These traces of C ₅ contained in the gas to be treated can optionally also be dissolved in the stabilized hydrocarbon during the treatment of the gas in the absorption unit.

Optionally, the gas to be treated may also contain one or more other gaseous compounds, such as H ₂ S, in contents of less than 2000 ppm by weight, N ₂ and CO ₂ , in contents of 1 to 2% by weight, and / or CO in contents of less than 0.5% by weight.

In particular, the gas resulting from atmospheric distillation in charge of the treatment process according to the invention may be the gas contained in the effluents of an atmospheric distillation column in which a hydrocarbon feedstock, for example a crude oil, is treated.

These effluents are a mixture consisting of a liquid hydrocarbon and a gas and possibly water, for example stripping water from stripping in the atmospheric distillation column or water contained in the feed treated in the atmospheric distillation column. These effluents are for example recovered at the top of the atmospheric distillation column.

These effluents leaving the atmospheric distillation column are separated in order to recover the liquid hydrocarbon and the gas. This separation is for example obtained by means of a condenser balloon or reflux balloon. The gas thus separated and recovered may constitute the gas resulting from atmospheric distillation treated by the process according to the invention.

The output of the absorption unit, is thus recovered a liquid hydrocarbon enriched in C3 and C ₄ and the fuel gas (C1 / C2) which is recoverable.

In addition, the liquid hydrocarbon enriched gaseous light hydrocarbon phase (h) consists of a fraction containing C 3 and C ₄ may be returned to the stabilizer column.

The absorbent liquid hydrocarbon may be a hydrocarbon derived from atmospheric distillation of a crude oil. The liquid hydrocarbon is at least the head portion of C 3 and C ₄ in a preferred stabilizing unit and according to one aspect of the invention a fuel in the range of C5 / C10, in particular not containing olefin .

The liquid hydrocarbon may be at least in the head portion of C 3 and C ₄ when it contains less than 0.5% by weight of C3 and less than 4% by weight of C _4.

Advantageously, the stabilized liquid hydrocarbon may contain less than

1% by weight of C ₃ / C ₄ .

The liquid hydrocarbon treated in the stabilization unit may also be derived from the effluents recovered at the top of an atmospheric distillation column. This liquid hydrocarbon may be, for example, the liquid hydrocarbon separated from these effluents, which is stabilized before being brought into contact with the gas to be treated separated from the same effluents.

The stabilization unit may be a stabilizer or debutanizer column. It can in particular separate a head section consisting of all compounds lighter than butane, including this one, a bottom cut called stabilized gasoline. This column can be a column with trays or a column containing loose or structured packing, for example.

Advantageously, the stabilized liquid hydrocarbon can be cooled before entering the absorber, for example at a temperature below 40 ° C but preferably of the order of 25 ° C. Indeed the absorption is more effective at low temperature. The cooling can be provided by coolers, for example, drycoolers, water exchangers or any other known method.

The gas and the liquid hydrocarbon (generally a C5-C10 gasoline) derived from atmospheric distillation can be pretreated in a condenser flask or a reflux flask. This makes it possible to separate the gas from the liquid hydrocarbon, the gas then being returned to the absorption unit, the liquid hydrocarbon being sent to the stabilization unit to form a stabilized liquid hydrocarbon which can subsequently be introduced into the absorption unit as an absorbent.

The ratio between the stabilized gasoline flow rate and the gas mass flow rate, at the inlet of the absorption unit, can be between 5 and 52 for a recovery at least partly of the C3 and C4 _, preferentially between 12 and 25. Such a control of the ratio at the inlet of the absorption unit can make it possible to improve the recovery rate of the light hydrocarbon phase contained in the gas to be treated and constituted by a fraction containing C3 and C ₄ .

The absorption can be carried out at temperatures of the order of 20 to 50 ° C, at a pressure of 0.5 to 5 barg, more particularly between 0.5 and 3 barg.

The invention also relates to a process for the treatment of atmospheric distillation effluents of a hydrocarbon feedstock, for example a crude oil, this process comprising the separation of the effluents into a gas and a liquid hydrocarbon, for example in a reflux flask, this separation being followed by a gas treatment according to the previously described process. These effluents are advantageously the top effluents of the atmospheric distillation.

A gas processing device for the recovery of C 3 and C ₄ comprises at least an atmospheric distillation unit which are from the gas and the liquid hydrocarbon; at least one reflux flask allowing a first separation between the gas and the liquid hydrocarbon; at least one stabilization unit in which the liquid hydrocarbon from atmospheric distillation is stabilized; at least one absorption unit comprising at least one gas injection zone resulting from atmospheric distillation; and at least one stabilized liquid hydrocarbon injection zone derived from atmospheric distillation. The liquid hydrocarbon enriched in C3 and C ₄ can be fed downstream of the reflux drum, to be subsequently sent to the stabilization unit for extraction of C3 and C _4. According to another embodiment, the liquid hydrocarbon enriched in C3 and C ₄ may be reinjected into the reflux drum to be then sent to the stabilizer unit for extraction of C3 and C _4. Brief description of the figures

FIG. 1 represents a refining scheme on which are represented according to the invention: an atmospheric distillation unit 1, an absorber 2, a stabilization column 3, a reflux tank 4, a balloon 5.

Figure 2 shows the evolution of the recovery rate of LPG in absorber 2. Experimental points are placed on the theoretical absorption curves.

Detailed description of the figures

In FIG. 1, the atmospheric distillation unit 1 makes it possible to treat a charge of crude oil. The operating pressure of the atmospheric distillation is set by the condensation conditions of the gas and petrol cut at the top of the atmospheric distillation column 1. At the top of atmospheric distillation 1, the mixture c consists of a liquid hydrocarbon a, a gas b and stripping water or water contained in the charge of the distillation column. This water is discharged through the bottom valve of the reflux tank.

The liquid hydrocarbon a is a gasoline obtained in the range of C5 / C10. The liquid hydrocarbon a is a gasoline containing substantially no olefins. For example, the olefin content is less than 1% by weight.

The gas b is constituted for at least part of a fuel gas or fuel gas g comprising in part Ci and C2, and may also contain hydrogen and impurities such hydrogen sulfide. The content of the gas b in hydrogen is for example less than 10% by weight and the content of the gas b in impurities, such as hydrogen sulphide, is for example less than 2000 ppm by weight. The content of the C2 gas is, for example, of the order of 5% to 40% by weight. The content of the gas b Ci is for example of the order of 5 to 40% by weight. The C1 + C2 content of the gas b is for example of the order of 15 to 60% by weight.

The gas b is constituted for at least another part of propane C3 and butane C ₄ . These two gases constitute liquefied petroleum gases (LPG) and are valuable. The reflux flask 4 receives the mixture c consisting of the liquid hydrocarbon a and the gases b which comes from the top condenser of the atmospheric distillation 1. The atmospheric distillation head condensers can be air-cooled condensers or condensers with water-cooled condensers. 'cooling water. The reflux flask 4 will make the separation between the gaseous phases b and the liquid hydrocarbon a as well as of the aqueous phase. The reflux tank 4 constitutes a reserve of liquid products to ensure a regular flow of reflux and withdrawal.

The stabilizer column 3 will separate the liquid hydrocarbon in a gaseous light hydrocarbon essentially containing e Ci, C2, C3 and C ₄ and stabilized absorbent liquid hydrocarbon of this is to say the head part essentially Ci, C2 , C3 and C _4. Acceptable unstabilized gasoline for an application according to the invention is substantially free of C 3 and C ₄ and mainly comprises hydrocarbons between C ₅ and C 10 (inclusive).

Column 5 can separate i liquefied petroleum gas (LPG), butanes and propanes C3 C ₄ g of the most volatile constituents said fuel gas consisting essentially of methane and ethane Ci C2.

The absorber 2 is a balloon provided with internal allowing the absorption of the C3 propane and butane C ₄ b contained in the gas from the atmospheric distillation 1 by mixing with the absorbent liquid hydrocarbon stabilized d. The internals of the absorber 2 called contactors may be trays or preferably lining. The absorber 2 is placed near the reflux tank 4 and the stabilization column 3. The installation of the absorber 2 is performed on an existing nozzle and can therefore be carried out.

According to one embodiment of the invention, the atmospheric distillation unit 1 has, at the top of the column, a mixture c of gas b and liquid hydrocarbon a. This mixture is injected into a reflux flask 4. Within this reflux flask 4, the mixture c will be separated into gaseous compound b and liquid hydrocarbon a. The liquid hydrocarbon a is sent via a pump 10 to the stabilization column 3.

The stabilizer column 3 will separate the liquid hydrocarbon is in gaseous light hydrocarbons e containing essentially C3 and C ₄ and marginally Ci and C2, and absorbent liquid hydrocarbon stabilized d.

The light hydrocarbon gas e passes through the transfer zone 15 where it is cooled by the heat exchanger 12. The light hydrocarbon gas e is sent to the balloon 5 in which the liquefied petroleum gases (LPG) are separated. The most volatile constituents, called fuel gas, consist essentially of methane Ci and ethane C2. Cs C ₄ i are thus recovered to feed the GPL pool.

The stabilized liquid absorbing hydrocarbon d passes through the transfer zone 14 where it is heated by the heat exchanger 11. the stabilized absorbent liquid hydrocarbon at the absorber inlet 2 is adapted to the gas degassing flow rate b at the inlet of the absorber 2. Thus, depending on this flow rate, a portion of the stabilized absorbent liquid hydrocarbon d is sent to a hydrotreatment unit 16, or is injected via the injection zone 7 into the upper zone of the absorber 2 constituted by packing. The gas b is sent into the absorber 2 below the lining of the absorption unit 2 by the injection zone 6. Part of the light hydrocarbon gas charge i present in the gas b will dissolve in the absorbent liquid hydrocarbon stabilized d to obtain a liquid hydrocarbon enriched gaseous light hydrocarbon phase h composed of a fraction containing C 3 and C _4. The gases Ci and C2 g are sent to the fuel gas network or the torch via the exit zone 9.

The liquid hydrocarbon enriched in C3 and C ₄ h is withdrawn from the absorber 8 of the balloon 2. The liquid hydrocarbon enriched gaseous light hydrocarbon phase h composed of a fraction containing C 3 and C ₄ is sent, via the transfer line 13, on the transfer line 17 where this liquid hydrocarbon enriched in gaseous light hydrocarbon phase h goes to the pump 10.

Under certain conditions, it may occasionally happen that the liquid hydrocarbon h, when it is sent on the transfer line 17, forces the liquid hydrocarbon a towards the reflux flask 4. The liquid hydrocarbon h is then sent to the bottom of the reflux flask 4. In this case, on the one hand, the liquid hydrocarbon h brings frigories to the flask 4, which improves the recovery of Cs C ₄ , on the other hand, the training the liquid caused most of the C ₄ C ₄ of the hydrocarbon h to flow to the pump 10.

Examples

Analyzes of from atmospheric distillation gas are carried out upstream and downstream of the absorption unit 2 so as to enjoy the C3 recovery rate, C ₄ and C _5. Each analysis was performed under the following conditions:

• Absorber off

• Flow rate of 5t / h of stabilized gasoline

• Flow rate of 8t / h of stabilized gasoline

• Flow rate 15 t / h of stabilized gasoline

Example 1: The absorber is stopped. It is thus logically found that the composition of the gas (G) is the same at the input as at the output of the absorber. Example 2: A degassing of 0.200 t / h before absorber is coupled to a stabilized gasoline flow rate of 5 t / h. A recovery rate of C3 of 99.1%, C ₄ of 95% and C ₅ of 28.2% is obtained. The ratio between the stabilized gasoline flow rate and the gas flow rate (G) at the inlet of the absorption unit is 25.

Example 3: a degassing of 0.230 t / h before the absorber is coupled to a stabilized gasoline flow rate of 8 t / h. A C3 recovery rate of 99%, C ₄ of 96, 1% and C ₅ of 36% is obtained. The ratio between the stabilized gasoline flow rate and the gas flow rate (G) at the inlet of the absorption unit is 34.8.

Example 4: a degassing of 0.290 t / h before the absorber is coupled to a stabilized gasoline flow rate of 1 5 t / h. A recovery rate of C3 of 99.2%, C ₄ of 96.2% and C ₅ of 69.7% is obtained. The ratio between the stabilized gasoline flow rate and the gas flow rate (G) at the inlet of the absorption unit is 51.7.

In Figure 3, the evolution of the recovery rate of LPG in the absorber can be followed by extrapolation. To be efficient, that is to say to allow a recovery rate of almost 100% LPG, the stabilized gasoline flow must be increased when the degassing rate is higher, as is the case when the temperatures outside are higher. Conversely, a low degassing rate makes it possible to consume less stabilized gasoline and thus to save energy.

In general, the ratio between the stabilized gasoline flow rate and the gas flow rate (G) at the inlet of the absorption unit is between 12 and 52 for at least part recovery of the C3 and C _4, preferably between 12 and 25.

As described above, the process for treating gases containing gaseous light hydrocarbons has the following advantages:

- The recovery yield of C 3 and C ₄ is almost 100%

- This recovery limits the releases to the flare and allows a valuation of the products thus recovered

- The installation of the absorber balloon is carried out on an existing quilting and can therefore be carried out in operation - The process is simple and avoids expensive maintenance due to mechanical problems of compressors.

- The introduction of an absorber balloon and power supply and output lines is a very economical realization

Claims

claims

Process for the treatment of gas (b) from atmospheric distillation (1) containing a gaseous light hydrocarbon feedstock (i), characterized in that the gas (b) is brought into contact with a stabilized liquid absorbing hydrocarbon (d) so that a part of the gaseous light hydrocarbon feedstock (i) present in the gas (b) dissolves in the stabilized liquid absorbent hydrocarbon (d) to obtain a liquid hydrocarbon enriched in the gaseous light hydrocarbon phase (h) consists of a fraction containing C 3 and C _4, said absorbent liquid hydrocarbon stabilized (d) being a gas in the range of C5 / C10.

Process according to claim 1, characterized in that the gas (b) and the stabilized liquid absorbing hydrocarbon (d) are brought into contact within an absorption unit (2).

Method according to one of claims 1 or 2, characterized in that the gas (b) contains combustible gas fuel gas Ci and C2 and LPG C ₃ and C ₄ .

Process according to any one of the preceding claims, characterized in that the stabilized liquid absorbent hydrocarbon (d) is a hydrocarbon derived from the atmospheric distillation (1) of a crude oil.

A method according to any one of the preceding claims, characterized in that the stabilized liquid hydrocarbon absorbent (d) is at least in the head portion of C 3 and C ₄ in a stabilization unit (3).

Process according to any one of the preceding claims, characterized in that the stabilized liquid absorbent hydrocarbon (d) does not contain olefins.

Process according to any one of the preceding claims, characterized in that the gas (b) is a gas contained in a mixture (c) resulting from atmospheric distillation, and separated from said mixture (c) in a reflux flask (4) .

8. A method according to claim 7, characterized in that the liquid hydrocarbon enriched gaseous light hydrocarbon phase (h) consists of a fraction containing C 3 and C ₄ is sent to the stabilization unit (3).

9. Method according to one of claims 7 or 8, characterized in that the mixture (c) is a mixture recovered at the head of the atmospheric distillation unit (1).

10. Process according to claim 9, characterized in that the mixture (c) is a mixture recovered at the top of the atmospheric distillation unit (1) in which a hydrocarbon feedstock, for example a crude oil, is treated.

1 1. Process according to one of Claims 7 to 10, characterized in that a gasoline (a) separated from the mixture (c) in the reflux flask (4) is fed into the stabilization unit (3) to form a gasoline stabilized, which is sent to the absorption unit (2).

12. Method according to any one of the preceding claims, characterized in that the ratio between the stabilized gasoline flow rate (d) and the gas flow rate (b) at the inlet of the absorption unit (2). is between 12 and 52 for recovery at least partly of C3 and C4 _, preferably between 12 and 25.

13. gas treatment device (b) from atmospheric distillation (1) for recovery of C 3 and C ₄ (i) and implementing,

at. at least one atmospheric distillation unit (1) from which a mixture (c) consisting of a hydrocarbon liquid at ambient temperature (a) and a gas (b)

b. at least one reflux flask (4) allowing a first separation of the mixture (c) with gas (b) and liquid hydrocarbon at room temperature (a)

vs. at least one stabilizing unit (3) in which the liquid hydrocarbon (a) is separated into a stabilized liquid hydrocarbon absorber (d) and a hydrocarbon gas (e) at least one balloon (5) in which the gaseous hydrocarbon (e) is separated into LPG (i) and gas (g)

at least one absorption unit (2) comprising at least one injection zone (6) of the gas (b), at least one stabilized absorbed liquid hydrocarbon injection zone (7), at least a withdrawal zone (8) enriched in C3 and C ₄ hydrocarbon liquid (h) and a recovery zone (9) of fuel gas (g)

at least one transfer line (13, 17) of the withdrawal zone

(8) to the stabilization column (3).