WO2009083227A2

WO2009083227A2 - Method and device for separating off low-boiling components from hydrocarbon mixtures

Info

Publication number: WO2009083227A2
Application number: PCT/EP2008/011049
Authority: WO
Inventors: Johannes Menzel; Sascha Wenzel
Original assignee: Uhde Gmbh
Priority date: 2007-12-28
Filing date: 2008-12-22
Publication date: 2009-07-09
Also published as: BRPI0821955A2; WO2009083227A3; EA201070803A1; US20110041550A1; WO2009083227A9; CN101932368A; KR20100125228A; EP2225007A2; JP2011508031A; ZA201004516B; DE102007063347A1; CA2710776A1; MX2010007195A

Abstract

Method and device for separating a starting mixture into a higher-boiling and a lower-boiling fraction in a distillation apparatus operated in a continuous procedure, which apparatus contains at least one line for the feed of one or more starting mixtures, a take-off for the lower-boiling fraction, a take-off for the higher-boiling fraction, and a heating appliance, wherein the distillation apparatus contains at least two condensation stages each having a different temperature level, wherein the respective condensation stages which are upstream in the direction of flow of the vapours in each case have higher temperature levels than the respective downstream condensation stages, in each case internals having separating activity are connected intermediately of the condensation stages, partial condensations proceed at condensation stages, the sub-quantities which are not condensed in each case are fed to respectively downstream separating internals or condensation stages having respectively lower temperature levels and the condensed sub-quantities in each case are passed via separating internals in the direction of the take-off for the higher-boiling fraction, and essentially vaporous medium occurs at the condensation stage having the lowest temperature level and is partially condensed there, wherein the non-condensed-sub quantity of the medium is recirculated to the take-off for the lower-boiling fraction and the condensed sub-quantity is recirculated to a region of the distillation apparatus which is connected upstream of the condensation stage having the lowest temperature level, and the condensation stage having the lowest temperature level has a temperature of below -40°C.

Description

Process and apparatus for the separation of low-boiling components from hydrocarbon mixtures

The invention relates to a method and apparatus for separating low-boiling components from a hydrocarbon stream, in particular for separating a C ₂ fraction from a target desired C ₃ + fraction, for example, in the dehydrogenation of light hydrocarbons, but also others Separation tasks in the C ₁ to C ₄ range.

Typically, such a separation is carried out by means of a combination of a so-called "cold box" and a distillation column The distillation column is operated as a deethanizer and so designated, since all substances which have boiling points less than or equal to that of ethane in this deethanizer over Head to be separated.

Before entering the cold box, the feed mixture is first cooled to about -25 ⁰ C. The resulting condensate is led directly into the deethanizer. The non-condensed vapors are further cooled within the cold box to about -90 ⁰ C, wherein the resulting product-rich condensate is also passed to the deethanizer after heat exchange. The coldbox thus represents a single-stage coarse separation.

The remaining vapor phase, which contains substantially non-condensable components, for example hydrogen, is, after heat exchange in the stream entering the coldbox, relaxed. Due to the Joule-Thompson effect, the low boilers cool to about -110 ⁰ C from. This temperature level is used to partially condense the stream entering the coldbox. The uncondensed low-boiling components are essentially free of C3 ⁺ components.

All product-rich condensate phases are finally led to the actual fine separation in the deethanizer, in which the other low boilers are separated from the heavier boiling components. For this purpose, a temperature of about -20 ⁰ C at the top of the column is required.

As a coolant for the cooling of the feed mixture before the cold box, for the operation of the cold box and for cooling the deethanizer evaporating propane or propene at -30 ⁰ C can be used. The generation of cold for such a process is extremely expensive. The object of the invention is therefore to provide a method and a device are available in which the refrigeration consumption can be significantly reduced.

The invention solves this problem according to the main claim with a method for the separation of a starting mixture

Into a higher and a lower boiling fraction in a continuous distillation apparatus, comprising at least one line for the supply of one or more starting mixtures, a lower boiling fraction discharge, a higher boiling fraction withdrawal and a heating device,

The distillation apparatus contains at least two condensation stages each having different temperature levels,

Wherein the respective condensation stages upstream of the vapors in the direction of flow of the vapors each have higher temperature levels than the respective downstream condensation stages,

Each separation-effective internals are interposed the condensation stages,

• partial condensation takes place at condensation stages,

• The respectively non-condensed subsets are each fed downstream separation internals or condensation stages, each with lower temperature levels and the respective condensed subsets via separating internals in the direction of the trigger for the higher-boiling

Be guided to the group,

• A substantially vaporous medium is obtained at the condensation stage with the lowest temperature level and is partially condensed there, wherein

• the uncondensed subset of the medium, the deduction for the lower boiling fraction and the condensed subset of one of the

Condensation stage is returned to the lowest temperature level upstream section of the distillation apparatus,

• | [\ v _z i] and the condensation stage with the lowest temperature level has a temperature of below -40 ⁰ C. In embodiments of the invention it is provided that the distillation apparatus contains three to five series-connected, each having different temperature levels having condensation stages.

In a further embodiment of the invention it is provided that the condensation stage with the lowest temperature level has a temperature of -120 ⁰ C to -70 ° C at a pressure of at least 2 MPa absolute, preferably at least 3 MPa.

In a further embodiment of the invention it is provided that the mixture, which leaves the distillation apparatus as a lower-boiling fraction, is relaxed, the mixture using the Joule-Thompson effect further cooled and thus to cool the condensation stage with the lowest Temperature level is used.

In a further embodiment of the invention it is provided that the relaxation is carried out with an expansion turbine.

Further embodiments of the invention relate to the use of suitable starting mixtures, with which the method can be applied particularly advantageously for the production of useful products.

In a further embodiment of the invention, the process is applied to starting mixtures which contain substantially hydrogen, hydrocarbons having up to two carbon atoms and hydrocarbons having at least three carbon atoms. At the flue for the lower boiling fraction, a mixture containing substantially hydrogen and hydrocarbons containing up to two carbon atoms is formed which contains substantially no hydrocarbons having at least three carbon atoms. At the deduction for the higher-boiling fraction falls a mixture containing at least three carbon atoms hydrocarbons, which contains substantially neither hydrogen nor up to two carbon atoms containing hydrocarbons.

In a further embodiment of the invention, the method is applied to starting mixtures, each containing less than 2 mol% of carbon dioxide and water or water vapor. In a further embodiment of the invention, a reaction mixture of the catalytic dehydrogenation of hydrocarbons is used as starting mixture.

In a further embodiment of the invention, the segment of the distillation apparatus, via which the condensed at the condensation stage with the highest temperature level subset of the starting mixture is supplied to the trigger for the higher-boiling fraction, as the stripping section of the distillation apparatus before.

In further embodiments of the invention it is provided that starting mixtures are added with relatively low proportion of low boiling point components preferably below the condensation stage with the highest temperature level and starting mixtures with a relatively high proportion of low boiling point components preferably above the condensation stage with the highest Temperature level are added.

In a further embodiment of the invention, the condensation stages are present as capacitors.

In a further embodiment of the invention, the condensation stages are cooled with cooling water, evaporating ammonia, propane, propene and / or by the utilization of the Joule-Thompson effect in the expansion of process gases.

In a further embodiment of the invention, the heating device is operated with external waste heat.

The invention also achieves this object with a suitable distillation apparatus for the separation of a starting mixture, comprising: • one or more lines for the supply of one or more

Starting mixtures,

• a deduction for the lower-boiling fraction,

• a deduction for the higher-boiling fraction,

• at least one heating device, • at least 2 cascaded capacitors, and

• Separating internals, which are interposed between the capacitors. In alternative embodiments of the device it is provided that the distillation apparatus is in the form of a single distillation column or that the distillation apparatus is present as a cascade containing a plurality of distillation columns, wherein in each case capacitors are provided between the distillation columns. In particular, it can be provided that the distillation apparatus 3, 4 or 5 connected in series, each having different temperature levels having capacitors.

So what has been achieved so far in 2 process steps, can be realized using the invention now in one step without upstream cold box, which is an advantage of the invention.

By the use of the process according to the distillation device with several operating at different temperature levels capacitors is achieved that not the entire amount of cooling for the condensation at the lowest temperature level and thus must be provided with the highest cost. Instead, the intermediate capacitors operate at temperatures of about + 45 ° C, +15 ⁰ C and -30 ⁰ C, which is a further advantage of the invention.

The largest part of the in the column, if one is used, ascending vapors is therefore condensed before reaching the top condenser and flows as a liquid down. The cold level required for the operation of the top condenser, about -80 ° C, and the required condensation power can be generated by relaxing the low boilers in the plant itself, which is a further advantage of the invention.

The invention is explained in more detail below with reference to 3 examples:

FIG. 1 shows the process according to the invention, in which the distillation apparatus consists of a single distillation column with several intermediate condensers.

FIG. 2 shows the method according to the invention, in which the distillation device is constructed from a separate stripping part and reinforcing part.

FIG. 3 shows the method according to the invention, in which the distillation device is made up of three sections, the intermediate capacitors being located between the sections. In all three examples, the vaporous feed mixture 1, for example, in an ammonia evaporator 2 are first cooled to 15 ° C. In a further heat exchanger 3 can be further cooled to about 10 ⁰ C against the recovered C2 fraction 4, wherein a portion of the vapor condenses. Vapor phase 5 and condensate 6 arrive separately in the distillation apparatus. Depending on the composition of the starting mixture, the task can also be carried out above the condensation stage with the highest temperature level.

In the example shown in Fig. 1, the liquid in the distillation column 7 flows down and is partially re-evaporated. The non-evaporated part is withdrawn as C3 ⁺ product 8 at the bottom of the distillation column 7. The low boilers rise upwards as vapor and are partly condensed by the two-part first condenser 9, which is located above the feed tray, cooling water and ammonia being used successively as the coolant. Further rising vapors are partially liquefied in the second condenser 10, which is operated with the coolant propane or propene, so that only a small part of the vapors reaches the top condenser 11. The vapors not condensed in the top condenser 11 form the C2 fractions 12 and 13, which is expanded following the condensation in the expander 14, wherein it cools to about -125 ⁰ C. This cooled vapor 15 is used as a cooling medium on the cold side of the top condenser 11, wherein it is heated to about -50 ⁰ C. Subsequently, this C2 fraction 4 passes through the heat exchanger 3 for cooling the feed mixture 1.

In the example shown in Fig. 2, the liquid flows in the stripping section 16 down and is partially re-evaporated. The unevaporated part is withdrawn as C3 ⁺ product 8 at the bottom of the stripping section 16. The vaporous low boilers 17 flow into the two-part design, first condenser 9, where they are partially condensed, being used as a coolant sequentially cooling water and ammonia. Both the condensate 18 and the vapors 19 are added to the reinforcing member 20. A portion of the sump of the reinforcing member 20 is used as a head template 21 of the output member 16. Further rising vapors are partially liquefied in the second condenser 10, which is operated with the coolant propane, so that only a small part of the vapors reaches the top condenser 11. The noncondensed in the top condenser 11 vapors form the C2 fractions 12 and 13, which is relaxed following the condensation in the expander 14, wherein it is about -125 ⁰ C. cools. This cooled vapor 15 is used as a cooling medium on the cold side of the top condenser 11, wherein it is heated to -50 ⁰ C. Subsequently, this C2 fraction 4 passes through the heat exchanger 3 for cooling the feed mixture 1.

In the example shown in FIG. 3, the liquid in the stripping section 16 flows downwards and is partially re-evaporated. The unevaporated part is withdrawn as C3 ⁺ product 8 at the bottom of the stripping section 16. The vaporous low boilers 17 flow into the two-part design, first condenser 9, where they are partially condensed, being used as a coolant sequentially cooling water and ammonia. Both the condensate 18 and the vapors 19 are introduced into the first reinforcing member 22. A part of the sump of the first reinforcement part 22 is used as a head template of the output part 16. Further rising vapors are partially liquefied in the second condenser 10, which is operated with the coolant propane or propene, both the condensate and the vapors are added to a second enrichment part 23. The sump of the second amplifying part 23 serves as a head template of the first amplifying part 22, in this way only a small part of the vapors reaches the top condenser 11. The vapors not condensed in the top condenser 11 form the C2 fractions 12 and 13, which after the condensation is relaxed in the expander 14, wherein it cools to about -125 ⁰ C. This cooled vapor 15 is used as a cooling medium on the cold side of the top condenser 11, wherein it is heated to about -50 ⁰ C. Subsequently, this C2 fraction 4 passes through the heat exchanger 3 for cooling the feed mixture 1.

This last variant has the advantage over the preceding that only the upper part of the second reinforcing column must be carried out at low temperature and equipped with a stronger insulation to prevent heat absorption, which is one of the advantages of the invention.

Although in all three examples, a larger amount of heat to operate the evaporator over the conventional art is required, but this heat is only required at about 75 ⁰ C, which is why waste heat from other parts of a system network are usually used is, which otherwise would have to be dissipated by means of air coolers, which is a further advantage of the invention. In total, more cooling is needed, but it can the heat is dissipated at a more favorable cooling level, which is a further advantage of the invention.

Further advantages of the method according to the invention over the prior art method presented at the outset are:

By using cooling water about 25% of the ammonia cooling capacity can be saved, therefore, only a smaller ammonia cooling system is required. The propane cooling capacity is about 55% lower, therefore, the required compressor capacity for the propane refrigeration cycle is about 50% lower, too the compressor can be dimensioned correspondingly smaller

Claims

claims

A process for the separation of a starting mixture into a higher and a lower boiling fraction in a continuous distillation apparatus, the at least one line for the supply of one or more starting mixtures, a deduction for the lower boiling fraction, a deduction for the higher boiling fraction and a heating device, characterized in that

Each separation-effective internals are interposed the condensation stages,

• partial condensation takes place at condensation stages,

The respectively uncondensed subsets are respectively fed to downstream separating installations or condensation stages, each with lower temperature levels, and the respectively condensed subsets are conducted via separating internals in the direction of the withdrawal for the higher-boiling fraction,

The non-condensed portion of the medium is returned to the lower boiling fraction effluent and the condensed portion to a distillation effluent upstream of the condensing stage at the lowest temperature level,

• and the condensation stage with the lowest temperature level has a temperature of below -40 ⁰ C.

2. The method according to claim 1, characterized in that the distillation apparatus contains three to five series-connected, each having different temperature levels having condensation stages,

3. The method according to any one of claims 1 or 2, characterized in that the condensation stage with the lowest temperature level has a temperature of -120 ⁰ C to -70 ⁰ C at a pressure of at least 2 MPa absolute.

4. The method according to claim 3, characterized in that the condensation stage with the lowest temperature level has a temperature of -120 ⁰ C to -70 ° C at a pressure of at least 3 MPa absolute.

5. The method according to any one of claims 1 to 4, characterized in that the mixture, which leaves the distillation system as a lower-boiling fraction, is relaxed, the mixture using the Joule-Thompson effect further cooled and thus to cool the condensation stage with the lowest temperature level is used.

6. The method according to claim 5, characterized in that the relaxation is carried out with an expansion turbine.

7. The method according to any one of claims 1 to 6, characterized in that the starting mixture used is a mixture which contains substantially hydrogen, hydrocarbons containing up to two carbon atoms and at least three carbon atoms, at the deduction for the lower-boiling fraction Hydrogen and hydrocarbons containing up to two carbon atoms obtained containing substantially no hydrocarbons having at least three carbon atoms and at the deduction for the higher-boiling fraction of at least three carbon atoms containing hydrocarbon-containing mixture obtained substantially neither hydrogen nor up to two Containing carbon atoms containing hydrocarbons.

8. The method according to any one of claims 1 to 7, characterized in that a mixture is used as the starting mixture, each containing less than 2 mol% of carbon dioxide and water or water vapor.

9. The method according to any one of claims 1 to δ, characterized in that a reaction mixture of the catalytic dehydrogenation of hydrocarbons is used as the starting mixture.

10. The method according to any one of claims 1 to 9, characterized in that the segment of the distillation apparatus, via which the condensed at the condensation stage with the highest temperature level subset of the starting mixture is supplied to the trigger for the higher-boiling fraction, is present as a stripping section of the distillation system.

11. The method according to any one of claims 1 to 10, characterized in that starting mixtures with a relatively low proportion of components with low Boiling point preferably be added below the condensation stage with the highest temperature level.

12. The method according to any one of claims 1 to 11, characterized in that starting mixtures are added with a relatively high proportion of low boiling point components preferably above the condensation stage with the highest temperature level.

13. The method according to any one of claims 1 to 12, characterized in that the condensation stages are present as capacitors.

14. The method according to any one of claims 1 to 13, characterized in that the condensation stages with cooling water, ammonia, propane, propene and / or cooled by the utilization of the Joule-Thompson effect in the relaxation of the distillation system as a lower boiling fraction leaving mixture become.

15. The method according to any one of claims 1 to 14, characterized in that one or more heating devices are operated with external waste heat.

16. A distillation apparatus for carrying out the method according to any one of claims 1 to 15, comprising a) one or more lines for the supply of one or more starting mixtures, b) a deduction for the lower-boiling fraction, c) a deduction for the higher-boiling fraction, d) at least one heating device, e) at least two capacitors connected in series, and f) separating internals, which are interposed between the capacitors.

17. The apparatus according to claim 16, characterized in that the distillation apparatus is in the form of a single distillation column.

18. The apparatus according to claim 16, characterized in that the distillation apparatus is present as a cascade containing a plurality of distillation columns, wherein in each case capacitors are provided between the distillation columns.

19. The apparatus according to claim 16, characterized in that the distillation apparatus 3, 4 or 5 connected in series, each having different temperature levels having capacitors.