DE1252711B - Process for the rectification of olefins from olefin-rich gas mixtures using the cold supplied by liquefied methane gas - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

F 25 j

German class: 17 g -2/01

Number: 1252711

File number: H 518391 a / 17 g

Filing date: February 26, 1964

Opening day: October 26, 1967

The invention relates to a process for rectifying olefin, in particular ethylene, from an olefin-rich gas mixture at low temperatures, with gaseous methane in a first stage is removed from the gas mixture in a methane extraction tower and that as a bottom fraction Accruing gas mixture in a second stage in gaseous olefin and accumulating as bottom fraction Residual gas is decomposed, with part of the gases obtained in both stages after liquefaction in each case is returned as a return to the corresponding stage and that as a return to the first The methane used in this stage runs through a refrigeration cycle with a compressor and expansion valve, using the cold content of externally supplied liquid methane.

The main aim of the invention is an economic exploitation of the liquefied methane gas available standing amounts of cold, especially with favorable adaptation to the requirements of olefin separation.

Methane gas has recently been transported in liquefied form in tankers and tankers, temporarily stored in storage tanks and finally suitably heated and vaporized and then used as fuel or as a raw material for the chemical industry. This forms the appropriate Utilization of the liquefied methane gas (hereinafter also abbreviated as L. M. G.) contained cold for other functions one for the profitability of the use of liquefied Methane gas is an important factor.

A problem that arises in the practical use of the cold of the liquefied methane gas is that that of 1 Nm ³ (calculated on the basis of a gaseous body at ⁰ ° C. and 760 mm Hg) of liquid methane by evaporation at the boiling point under atmospheric pressure, ie at -161.6 ° C, supplied refrigerant is 88 kcal, while in the temperature range between - "are submitted 161.6 ° C and ambient temperature, ie 2O ⁰ C, 65 kcal"cold; there is therefore no great difference between the latent or evaporation heat and the amount of cold corresponding to the product of specific heat and "warm-up temperature difference" (hereinafter referred to as "intrinsic heat").

With regard to the utilizability of these amounts of cold, however, there are great differences, since only the proportion corresponding to the latent heat is available at a very specific (low) temperature while the heat corresponds to the

Process for rectifying olefin from
olefin-rich gas mixtures with utilization
that supplied by liquefied methane gas
cold

Applicant:
Hitachi, Ltd., Tokyo

Representative:

Dipl.-Ing. R. Beetz and Dipl.-Ing. K. Lamprecht, Patent Attorneys, Munich 22, Steinsdorfstr. 10

Named as inventor:

Kiyoshi Ichihara, Hitachi-shi (Japan)

Claimed priority:

Japan February 26, 1963 (8531)

corresponding cold is distributed over a temperature range of more than 180 ° C.

Therefore, in order to be able to effectively evaluate the cold corresponding to the inherent heat, an additional a heat pump system with a compressor and a heat exchanger can be provided. For this The reason is that the cold in the inherent heat component close to the ambient temperature has not yet been evaluated and in most cases uselessly wasted. According to the invention therefore becomes a reasonable one The aim is to utilize the cold contained in the liquefied methane gas by utilizing the same for rectifying olefin (mainly ethylene). To make an externally supplied cooling effective evaluate, this is generally the hardest advantageous used in a section with the lowest possible temperature. So you use liquefied Methane gas in an olefin rectification plant as a refrigeration supplier, it appears to be extremely desirable the cold to generate reflux liquid for the upper section of the methane extraction tower should be used, as this is where the lowest temperature occurs.

But this is not easily possible, for the following reason: Because the so-called liquefied Methane gas is not pure methane, but a small fraction of its components with a high Boiling point, as it contains ethane and propane, is located

709 679/197

Boiling point relatively high, namely between -140 and -150 ° C. If the liquefied methane gas is evaporated at atmospheric pressure, the methane extraction tower must have a working pressure of 2.5 atmospheres at an LMG boiling point of -150 ⁰ C and more than 6.5 atmospheres with an LMG boiling point of -140 ° C.

Due to such a high working pressure, the operating temperature as a whole is higher, which means the loss of ethylene increases; In addition, the wall thickness of the rectifying tower must be increased will. As a result of the relative return quantities, when operating such a system the amount of cold required to produce reflux liquid for the methane extraction tower usually a third or a quarter of the cold required for the ethylene tower; so if that while generating methane return, L.M.G. evaporated and passed on to the ethylene separation device is used to compensate or contribute to their cold losses, no great advantage is achieved. You then also have to use the cold of liquefied methane gas for the production of reflux liquid use for the ethylene tower, which evaporates in the process. This way of working is obvious disadvantageous, since the cold of the liquefied methane gas for a function at a relative high temperature (is used and problems with temperature adjustment occur.

The invention aims to improve the previously imperfect utilization of the cold of the liquefied methane gas, and it is based on the principle that the liquefied methane gas through a Pump is compressed, thereby bringing its boiling point to a temperature between -110 and —120 ° C to increase, so that reflux liquid for the methane extraction tower through which the liquefied methane gas emitted up to this boiling point Cold can be generated and evaporation occurs at a temperature suitable for the Production of olefin recycle is suitable.

The method according to the invention is accordingly characterized in that the liquid methane is brought to a higher pressure at which its boiling point is adapted to the production of olefin reflux is, and in heat exchange with the liquefying, compressing methane of the methane refrigeration cycle the first stage heated to about the boiling point, in a further 'heat exchange evaporated with the also liquefied olefin from the second stage and finally in the Heat exchange with a gas introduced into the system from outside is further heated.

The Me ^ resulting at the end of this process thangas is available as a compressed gas in a form in which it can be conveniently used as town gas or in a town gas pipe can be fed. As a particular advantage over conventional olefin separation plants there is a saving of compressor and expansion valve for generating olefin return.

The invention is described below with reference to a schematic drawing of a preferred system explained in more detail for the implementation of the method according to the invention.

In the drawing, reference numeral "1" denotes a methane extraction tower with one installed therein Reboiler 2. Numeral 3 denotes an ethylene tower with one therein arranged reboiler or heater 4. With the ethylene tower 3 are an ethylene liquefier or -condenser 5 and an associated collecting vessel 6 connected; a pump 7 is provided to liquid ethylene from the receptacle 6 through line 8 into the upper portion of the ethylene tower traced back. The methane extraction tower 1 is connected to the ethylene tower 3 via line 9 ίο connected. A heat exchanger 10 is arranged to allow heat exchange between the raw gas and to carry out the gas products coming from the methane extraction tower 1 and ethylene tower 3. The heat exchanger 10 is via a heater 12 with a gas-liquid separator 11 connected. A heat exchanger 13 is provided to further cool the uncondensed To effect gas from the gas-liquid separator 11. In a pipe between the methane extraction tower 1 and the gas-liquid separator 11 there is an expansion or regulator valve 14, while in another, the methane extraction tower 1 via the heat exchanger 13 with the line connecting the gas-liquid separator 11, an expansion or regulator valve 15 is interposed is.

According to the invention, a part of that is supplied from the upper portion of the methane extraction tower 1 Methane through a methane recirculation or refrigeration cycle 21, which is a methane compressor 16, heat exchangers 17, 18 and 19 and an expansion or regulator valve 20, again in the tower 1 returned. Liquefied methane gas (L. M. G.) supplied from the outside is supplied by a Pump 22 is compressed and fed to the heat exchanger 18 in the methane recirculation circuit 21, so that the to liquefy returning methane by cooling by means of the own heat of the L. M. G., after which the liquefied methane gas (L. M. G.) for cooling or generating return for the ethylene tower 3 is forwarded.

This system works according to the invention as follows: Raw gas, from which water, CO ₂ and high-boiling hydrocarbons with 3 or more carbon atoms have been removed, is fed to the system through a line α and passed through the heat exchanger 10 and the heater 12, whereby it is cooled to a temperature of around - 90 ° C by means of separated gases and thereby (partially) converted into a condensate. The condensate formed is separated in a gas-liquid separator 11, while the non-condensed gas b is passed into the heat exchanger 13 through a conduit in which it at a temperature between -130 and - 140 ⁰ C is cooled. The condensate formed in the heat exchanger 13 is returned to the gas-liquid separator 11 via the line c , while the remaining gas, consisting mainly of hydrogen, is passed through a line d to an expansion valve 30, where it is expanded to a pressure close to atmospheric pressure and its temperature is lowered. The gas is then allowed to flow in the opposite direction through the heat exchangers 13 and 10 in order to bring about a heat exchange with the raw gas, whereby it is heated to a temperature between -43 and -45 ° C. and discharged from the system.

The condensate collected in the gas-liquid separator 11 is drawn off through line e and expanded through the expansion valves 14 and 15 to a gas pressure of 0.5 kg / cm ² . The condensate expanded in the expansion valve 15 is passed through the heat exchanger 13, evaporates while cooling the raw gas and is fed to the methane extraction tower 1, while the condensate expanded in the expansion valve 14 is fed into the methane extraction tower 1 in liquid form. Methane from tower 1 is passed through a line / to methane compressor ^{16, where it is compressed to a pressure of about 20 kg / cm 2.} It is then passed through the heat exchangers 17, 18 and 19 to be cooled therein, then expanded to a pressure of 0.5 kg / cm ² through the expansion valve 20 and returned to the methane extraction tower 1 again.

In this tower 1, the methane collects in the upper section, while ethylene and ethane occur as soil fraction in the lower section. A part of the methane component is, as already stated, passed through the line / to methane compressor 16, while the remaining part or the methane product is passed via a line g in the opposite direction through the heat exchangers 13 and 10 in order to exchange heat with the raw gas heated to a temperature between -43 and -45 ° C and then discharged from the plant. The ethylene and ether components separated at the bottom of the tower 1 are fed to the ethylene tower 3 through the line 9 under a pressure drop.

The type of rectification in the ethylene tower 3, which is operated at a working pressure of 0.3 kg / cm ² , is similar to that of the methane extraction tower 1. In the ethylene tower 3, the ethylene collects in the upper section and the ethane in the lower section. The ethylene component is passed through a line k, the ethylene condenser 5, the ethylene receiving vessel 6 and a line h to the heat exchanger 10, which it passes through for the purpose of heat exchange in countercurrent to the raw gas, and so heated to a temperature of -43 to -45 ° G and then is released from the system. The Äthankomponente is ί through a conduit in the heat exchanger 10 guided that they also pass through for the purpose of heat exchange in countercurrent to the crude gas and then heated to a temperature from -43 to -45 ⁰ C and is then discharged from the plant.

The heat supply in the lower sections of the methane extraction tower 1 and the ethylene tower 3 and the cooling for the generation of return liquid takes place as follows: Liquefied methane gas (LMG) is let into the system through a line / and in the pump 22 to a pressure of 15 kg / cm ² compressed. Then the compressed liquefied methane gas (LMG) is sent to the heat exchanger 18 for heat exchange with methane, which was compressed in the methane compressor 16 and flows back through the methane recirculation circuit 21 and - 120 ⁰ C, and it is then passed through the line 23 to the ethylene condenser 5. The liquefied methane gas supplied to the ethylene condenser 5 causes the liquefaction of a major part of the ethylene which was drawn off from the upper section of the ethylene tower 3 and brought into the ethylene condenser 5 through the line k. (The amount of ethylene to be liquefied corresponds to a required amount of return liquid. If an ethylene product is to be obtained in liquid form, the total amount is liquefied. In this case, the ethylene product is then drawn off via the line / directly from the system.) the heat exchange evaporated LMG is passed through the line m into a heat exchanger 24, carries out a heat exchange with compressed ethylene which has been returned to the heat exchanger via the line r after it has been used as a refrigerant for other purposes; LMG is the heated to a temperature of -45 to - 50 ⁰ C is heated and then discharged from the plant.

Ethylene liquefied in the ethylene condenser 5 flows into the receptacle 6, from which a major part of the liquefied ethylene is fed through the line η to the pump 7, through which it is returned via the line 8 to the upper section of the ethylene tower 3. Part of the liquefied ethylene is passed through a line ο to a pump 25, in which it is compressed to a pressure of more than 3.5 to 4 kg / cm ² , for example to a pressure of 10 kg / cm ² , and is then heated to a certain level by heat exchange with compressed liquid ethylene at a relatively high temperature, in order to be passed into the heater 4 of the ethylene tower 3. Liquid ethylene under a pressure of 10 kg / cm ² , which is liquefied by giving off heat to the ethylene tower 3, is brought through a line ρ to a pump 27, which by its pressure reduces the pressure loss due to the friction during the flow in the pipes and the liquid ethylene is fed through a line q for other functions that require cooling. The cooling temperature available for other functions depends on the working pressure of the heater 4 in the ethylene tower, but in the present example is approximately -45 to -50 ° C.

Ethylene, which was used as a coolant elsewhere, flows back into the system in the form of gas through line r , is partially re-liquefied in heat exchanger 24 and passed through line s into the heater 4 of the ethylene tower and the heater 2 of the methane extraction tower . It is clear that the amount of ethylene fed must be determined on the basis of the thermal equilibrium in the plant. Ethylene liquefied by heat transfer to the methane extraction tower 1 in the heater 2 is passed through a line 28 and the heat exchanger 26 to an expansion valve 29, where it is brought to a pressure approximately corresponding to the working pressure of the ethylene tower 3, ie to about 0.3 kg / cm ² is combined with the ethylene return coming from the pump 7 and is fed to the ethylene tower 3.

As described in detail above, according to the invention, the temperature is that for other functions available cooling at the boiling point of ethylene below that in the ethylene tower heater 4 prevailing work pressure, which is free

a value of more than 3.5 to 4 kg / cm ² can be set. According to the invention, the cold content of the liquefied methane gas for the (separation) separation of ethylene and the excess cold is practically used in a very wide temperature range, but the liquefied methane gas is ultimately in the form of gas at a pressure of over 10 kg / cm ^{2 is} obtained.

The liquefied methane gas is mainly used by gas production companies, and these companies also produce oil gas. The use of liquefied methane gas for separation of olefin from oil gas is therefore extremely beneficial, especially if it is after such a process methane gas obtained is obtained in the form of gas, which is easily fed to a town gas system can be.

Furthermore, since the cooling to generate the required Return amount for the methane extraction tower 1 only a third or a quarter of the cooling makes up, which is necessary to generate return for the ethylene tower 3, is of course enough for the generation of methane return, the one that is released when it is heated to the boiling point or the inherent heat corresponding cold of a liquefied methane gas, which is used for the generation of ethylene return is evaporated at a temperature between - 110 and -120 ° C.

Because of the extended temperature range when using the cold of the liquefied methane gas in the methane extraction tower, a methane recirculation or cooling circuit with methane compressor and expansion valve must be provided according to the invention, as in older systems that work without cooling by liquefied methane gas. According to the invention, however, a pressure of about 20 atmospheres is sufficient, while in conventional devices is compressed to 50 atmospheres, since the cooling temperature is relatively low, that is between -110 and - 120 ⁰ C is located. The installation of such a refrigeration circuit is therefore not a disadvantage overall, if one takes into account the increased ethylene yield due to the low working temperature, the effective utilization of the cold of the liquefied methane gas and the other advantageous factors.

The methane compressor can incidentally despite high performance because of the relatively low Pressure of 20 atmospheres can be easily established. This compressor generally has one Labyrinth-like construction, so that mixing of oil with compressed gas is avoided will.

In the context of the invention, a so-called cooling circuit is formed and for the separation of Olefin used to carry a component like ethylene with a higher boiling point than methane a pump or compressor to compress and recycle, taking ethylene through the excess Liquefied cold and the cold produced by the evaporation of the liquefied ethylene used for other functions. So can the

ίο excess cold in the with increased temperature working device and a major part of the derived from the inherent heat of the liquefied methane gas Cold can be used for cooling at a predetermined temperature, creating a high degree of evaluation of this cold can be achieved.

Claims (1)

Claim: Process for rectifying olefin, in particular ao special ethylene, from an olefin-rich gas mixture at low temperatures, at which in a first stage removes gaseous methane from the gas mixture in a methane extraction tower and the gas mixture obtained as the bottom fraction is converted into gaseous form in a second stage Olefin and residual gas obtained as bottom fraction is broken down, with part of the in both Stages obtained gases after liquefaction in each case as a return to the corresponding stage is returned again and the methane serving as the return to the first stage is one Cooling circuit with compressor and expansion valve runs through, utilizing the cold content from the outside supplied liquid methane, characterized in that the liquid methane at a higher pressure is brought, at which its boiling point is adapted to the production of olefin reflux, and im Heat exchange with the liquefied, compressed methane of the methane refrigeration cycle the first stage is heated to about the boiling point, in further heat exchange with the also liquefied Olefin evaporated from the second stage and finally in heat exchange with one of the gas introduced into the system is further heated. Considered publications:
French Patent No. 1,217,272;
U.S. Patent No. 3,058,314;
"Handbook of Refrigeration Technology", Vol. 8 (1957),
Pp. 224 to 226. 1 sheet of drawings 709 679/197 10.67 © Bundesdruckerei Berlin