DE1302036B - Method for breaking down a gas mixture consisting of methane and high-boiling hydrocarbons, in particular natural gas, by means of rectification - Google Patents

Description

1 2

Natural gas is available in large quantities at certain tightly sealed, cooled by heat exchange, isenthalpic locations. From there it is - partially expanded and in a separator in a gas-conveying intermediate connection of the liquid transport - migen and is broken down into a liquid part. A part of the liquid part reaches the consumer centers via pipeline systems as return liquid. The pressure in the long-distance line is generally back in the rectification column. Other backslides in the range of 30 to 70 ata. continuous liquid consisting of C ₁ +, obtained by High quality natural gas contains in addition to the Hauptkom- partial condensation of the to be fractionated natural gas component methane in more or less large con- In this method must therefore first an concentrations condenses the heavy paraffinic hydrocarbons, larger amount C ₁ + if you want to achieve _{a high yield of C 2} + their separation from io for various reasons. May be in we-interest. On the one hand, this process can therefore consist of a two-stage partial condensation of the heavy hydrocarbons, the calorific value, of which the condensation of the natural gas is adjusted to a desired value, which is then separated by distillation. In contrast, a partial condensation is often dispensed with in the process of the invention in favor of the calorific value. Further- 15 not necessary.

len the heavy hydrocarbons a starting The invention is based on the object of a decomposition

to create the basis for a petrochemical process of the type mentioned adjacent to the pipeline, welmische Industry or for the liquid market. Ches not with the above mentioned restrictions

A method has become known which has disadvantages and disadvantages. One was found chem the heavy hydrocarbons through par- 20 process for the decomposition of one from methane and tial condensation deposited and existing by two-higher boiling hydrocarbons stage partial evaporation are concentrated. Gas mixture, in particular natural gas, by means of rectification This process is the degree of separation of the cation in a stripping column, which may be higher hydrocarbons determined by the inlet a stripping column for demethanization (escape concentrations, the separation pressure and 25 methanization column) of the bottom liquid from the the separation temperature, so it is not freely downstream of the stripping column, which can be selected regarding the individual components. A is characterized by that the return for the The disadvantage of this method is z. B. when stripping column at least partially due to low heat yields of ethane, but high yields exchange with bottom liquid from the Abtriebsan Propane and all higher-boiling hydrocarbon columns are generated in a reflux liquefier are desired. Evaporated to a certain extent, but more evenly, under reduced pressure. If the if there is limited leeway, on the other hand, stripping columns offer a demethanization column in which the natural gas is connected in several stages at, the evaporation of the sump separates Temperatures is partially condensed. liquid expediently only driven so far,

A method is also known in which a 35 that one in the demethanization column without Liquefied natural gas gets by in the middle part of a separating reinforcement part.

introduced column and in this in a high-boiling The method according to the invention offers special

Sump liquid and a methane-rich head gas decomposer when decomposing are under high pressure is, with the return for the upper part of the natural gas special advantages because of the separator Column by partially liquefying the degree of topping of the heavy hydrocarbons at gleigases is generated with cold natural gas. This amount of liquid tends to be higher than with procedures driving is based on natural gas supplied in liquid form. through partial condensation. Furthermore, the effort is

Another method for natural gas separation makes for the return generation less, provided one of also starts from the separation by rectification of gaseous natural gas, and the use of demethane and consists in the fact that the cold to reduce the heavy hydrocarbons is easier Run generation to be carried out by at least partial expansion, because this is carried out under reduced pressure tion of the methane-containing head gas carried out in a vortex with more favorable relative volatilities pipe is applied. The bottom of the stripping section is.

the column is heated in this process. The- At extremely high natural gas pressures, it can

This process is disadvantageous if it is expedient to achieve a favorable separating effect The amount of methane accruing from the expansion does not negate the natural gas to be decomposed before it enters the Application is available under reduced pressure and the column is performing work or isenthalpic to depressurization Methane e.g. B. only NEN again on the pipeline pressure. It is not redensified with regard to the invention must become. significantly whether this relaxation at high temperatures

In another method for natural gas separation 55 temperature for the purpose of energy production or at low temperatures the fractionation column is below the head temperature for the purpose of refrigeration, an intermediate fraction withdrawn and so highly compressed. An extensive concentration of the heavy ones

tet that it can heat the column sump, where- hydrocarbons can ultimately be obtained they partially condensed. After that, it will be enough to relax the stripping and demethanizing and as a liquid-vapor mixture back into the 60 rectifying column, an isobaric rectifying column downstream of the top of the column directed. Here it gives off cold; who switches.

The liquid part serves as the return liquid. In the drawing, to explain the

Method is quite a fiction for generating return, exemplary embodiments of the same in schema-complexity required, because a special cycle of table form is shown, namely shows with a compressor, an aftercooler and a 65 F i g. 1 a facility for limited separation or two heat exchangers is required. of ethane and for almost complete separation

Finally, there is a natural gas separation process for all hydrocarbons that boil higher than ethane known, in which the entire top gas is made up of natural gas and in two stages

F i g. 2 shows an excerpt from FIG. 1, whereby in contrast to FIG. 1 the natural gas before it enters the Column is relaxed and then fed into the middle of the column.

The natural gas separation plant according to FIG. 1 consists of the stripping column 7, the demethanization column 21, the dryers 3 A and 3 B, the countercurrent 5, the reflux condenser 9 and the booster 27. In the system according to FIG. 2, in addition to the booster 27, another booster 37 is provided. The door bead 35 is used for partial expansion of the natural gas.

From the natural gas arriving in the pipeline 1, the part necessary for the decomposition is branched off, fed via 2 to one of the two dryers 3 A, 3 B and possibly further cleaning units not shown here. The purified gas is available to be contributed conventionally, e.g. B. by using a propane-ethane cascade or by cold, which is generated during the pre-expansion of the natural gas, as shown in FIG. 2 is shown.

In the demethanization column 21, the heavy hydrocarbon fraction is freed from methane to the desired degree below 21 ata and fed via 24 to the further separation plant. This fraction, 9021 Nm ³ / h, has the following composition:

0 4 percent by volume CH
₆₂ ' ₇ percent by volume CH
207 volume percent C ² H ⁶
₆ ' ₂ percent by volume C ³ H ⁸ and CH
' ^{4 10} "'"

The heat for the steam is driven on in the demethanization column 21 via two separate ones Heat exchangers 22 and 23 supplied. The use of two heat exchangers allows one i A d ili the

then in 4 in front of the cryogenic system, for example g

instruct below 50 ata, 20 ° C and 191200 Nm ³ / h for 20 more favorable adaptation of the working lines

Available with a composition of equilibrium curve and thus saves energy.

90 9 percent by volume CH ^{The second} methane fraction, 31129 Nm ³ Zh, which is 7 * 2 percent by volume CH compared to the first methane fraction is small and only 16 percent by volume CYi ^{from urs} P ^run g ^ucn in the sump liquid of the output 02 percent by volume C ³ H * ²⁵ column 7 dissolved methane is, is pulled over 25 ab 01 volume percent cV, in the heat exchanger 5 again environ- ' ^"m ambient temperature heated, 26 a Nachver-The natural gas is supplied in countercurrent 5 by heat denser 27, in this compressed to approximately pipeline exchange with the two accruing methane fraction pressure, the first cooled over 12.5 and 14 discharges to about -50 ° C and over 6 in 30 drawn and heated methane fraction mixed in the lower part of the stripping column 7 and fed through 29 In the continuation 31 of the pipeline a methane-ethane mixture escapes via its head 8, which is due to be explained
Heat extraction is further cooled and partially liquefied. This liquid 35 flows through 10
Steam mixture to the separator 11, from which

ih i

The first methane fraction escapes via 12 and is reheated to ambient temperature in the heat exchanger5. In line 14, 151 050 Nm ³ / h methane at 48 ata are then available. There is therefore only a slight pressure reduction in the first methane fraction, corresponding to the flow losses. The reflux of the stripping column 7 runs via 13.

given. When the plant is at a standstill, the natural gas that has not been broken down leaves line section 1 via the valve 30 directly to the line section 31. In the method according to FIG. 2 becomes in amendment of the method according to FIG. 1 relaxes the natural gas before entering the stripping column 7, and although partly doing work via line 34 in the turbine 35 and line 36, partly isenthalpic in the Throttle valve 39. Before it is fed into the pipeline via 29, all of the methane must be in the compressor 37 be redensified. The turbine 35 can contribute part of this compression energy. the central introduction of the natural gas into the output

g g g

The 45 column 7 obtained in the bottom of the stripping column 7 allows a substantial amount of methane separating liquid has a composition of voltage already in this column. The necessary gas

70 9 volume percent CH
2U, d percent by volume C _o H _fi

7 1 percent by volume C "H

10 percent by volume CYi

u, 4 ν omm percent ^ _n Ii _n ,

⁵ ° of heat is supplied via the heat exchanger 38. The residual cold for the return ^{condenser 9 supplies a} partial expansion of the natural gas in the ^{turbine35 The first} methane fraction is returned via the return condenser 9 and gives

In addition to methane, this fraction contains all hydrocarbons in the desired amount. Ethane is available in a small excess because a small part of the separated ethane is lost again with the second methane fraction. The bottom fraction, 40 150 Nm ³ / h, is withdrawn via 15, relaxed in valve 16 and passed on through 17. The cold released in the reflux condenser 9 and thus the liquid-vapor ratio of the bottom fraction on entry into the demethanization column 21 can be adjusted via line 19 with valve 20 and via valve 32. The amount of cold that is given off by the sump liquid in the return condenser 9 depends on the pressure and the flow rate in the line 18

Claims (4)

Claims 1. Process for the decomposition of a methane and heavy-boiling hydrocarbons Gas mixture, in particular natural gas, by means of rectification in a stripping column, which optionally has a stripping column for demethanization (demethanization column) Bottom liquid from the stripping column is connected downstream, characterized in that that the reflux for the stripping column (7) at least partially by heat exchange is generated with bottom liquid from the stripping column (7), which in a reflux condenser (9) evaporated under reduced pressure. 2. The method according to claim 1, characterized indicates that the evaporation of the sump liquid is only driven so far that in the downstream demethanization column (21), the rectifying section can be dispensed with. 3. The method according to claim 1 or 2, characterized in that the natural gas to be decomposed before entry into the stripping column (7), work-performing or isenthalpically relaxed. 4. The method according to any one of claims 1 to 3, characterized in that the heat supply to the demethanization column (21) via two separate heat exchangers (22 and 23). 1 sheet of drawings