JPS6043390B2 - Low-temperature purification method for hydrocarbon decomposition products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-temperature refining method for hydrocarbon decomposition products, and more specifically to a method for refining hydrocarbon decomposition products in a plant that produces ethylene, etc., by thermal decomposition using petroleum, natural gas, etc. as raw materials. Concerning low temperature purification methods.

By-product light fractions such as hydrogen and methane from hydrocarbon pyrolysis products,
Various methods for separating specific heavy fractions such as ethylene and by-product heavy fractions such as ethane, and methods for separating and refining by-product hydrogen and by-product ethane have been proposed and put into practical use. However, it is very important to prevent specific fractions such as ethylene from being entrained in by-product light fractions and to increase the yield of ethylene, etc. from the viewpoint of reducing operating costs and saving energy. .

FIG. 1 shows a typical system diagram of a conventional separation and purification facility for hydrocarbon decomposition products, such as hydrogen, methane, ethylene, ethane, and other hydrocarbon pyrolysis product gases containing heavy components.

This equipment consists of a feed treatment step 1, a demethanizer step 3, and a hydrogen and methane separation and purification step 2. Separation of ethylene from lighter hydrogen and methane typically requires high pressure, low temperature operating conditions. In the feed processing step 1, cracked gas F containing hydrogen, methane, ethylene, ethane, and heavy fractions compressed and pressurized by a compressor or the like is sequentially heated through lines 8, 9, 10, and 11. sequentially with refrigerant passing through exchangers E-1, E-2, E-3 and E-4 and through lines 4, 5, 6 and 7;
Cool, lower temperature. The condensate containing most of ethylene successively generated by the above temperature reduction is transferred to condensers D-1 and D-2.
, D-3 and D-4, and are sent to the demethanizer step 3 through lines 12, 13, 14 and 15, respectively. On the other hand, the gas containing hydrogen and methane as main components separated in the final stage condenser D14 is sent to hydrogen and methane separation and purification step 5 step 2 via line 16. The demethanizer step 3 receives the condensate supplied from the feed treatment step 1 into the demethanizer T-1, and removes hydrogen remaining in heavy fractions such as ethylene and ethane, which are components of the condensate. Light fractions such as methane are ultimately separated and purified from heavy fractions containing ethylene and higher.

The demethanizer tower T-1 includes a tower body 30 and a condenser 31.
, a reflux system consisting of a reflux drum 32 and a reflux pump 33, and a reboiler 34. Demethanizer tower T-1
A fraction containing residual hydrogen and methane is extracted from the top of the column, while a heavy fraction E such as ethylene and ethane is extracted from the bottom of the column. Next, hydrogen and methane separation and purification step 2
This process separates and refines the mixed gas mainly composed of hydrogen and methane supplied from the feed processing step 1 into hydrogen and methane using the Joule-Thompson effect.

The supplied mixed gas is sequentially supplied from the line 16 to the first stage cooler E.
-5, purified through the first stage separation drum D-5, second stage cooler E-6 and second stage separation drum D-6, and finally high pressure and low pressure methane gas from lines 21 and 22 or 7, respectively. In addition, purified hydrogen gas is taken out from line 23. The refrigerant used in coolers E-5 and E-6 is a low-temperature fluid (lines 21, 22 ) and purified hydrogen gas (line 23) are used. In the conventional cracked gas purification method consisting of the above three steps, ethylene in the supplied cracked gas is separated and extracted from the bottom of the demethanizer rectification column T-1 in the demethanizer step 3, but some of ethylene is separated from the hydrogen separated from condensation drum D-4 of feed processing step 1,
It is entrained in the methane mixed gas and the methane gas from the separation drum 32 of the demethanizer step 3, resulting in a loss.

An example of the loss in conventional ethylene separation and purification equipment is shown in Table 1, which shows that a considerable amount of ethylene is lost. The purpose of the present invention is to prevent, as much as possible, loss of specific fractions such as ethylene from being entrained with light fractions such as by-product hydrogen and methane in the conventional separation and purification method of hydrocarbon decomposition products, and to The aim is to increase the profit margin of

In order to achieve the above objects, the present invention provides a feed treatment process for separating hydrocarbon decomposition products into a light fraction and a heavy fraction, and a separation of hydrogen and methane from the light fraction obtained in the feed treatment process. A method for low-temperature refining of hydrocarbon decomposition products, which comprises a step of separating ethylene and other specific fractions from the heavy fraction obtained in the feed treatment step, at least a part of the feed treatment step. The method is characterized in that the method is a rectification step, and the condensate obtained in the hydrogen and methane separation and purification step is used as the reflux liquid in the rectification step.

It is preferable that the overhead gas from the ethylene and other separation and purification process is liquefied as much as possible through an expansion means and used as a cooling refrigerant for the heat exchange means in the hydrogen and methane separation and purification process.

Hereinafter, the present invention will be explained in more detail with reference to the system diagram of the apparatus shown in FIG.

FIG. 2 is an equipment system diagram of equipment for refining ethylene, etc., showing one embodiment of the present invention.

Components that are the same as or correspond to the system shown in FIG. 1 are designated by the same reference numerals. In the figure, this equipment is composed of a feed treatment step 1, a demethanizer step 3, and a hydrogen methane separation and purification step 2, as in FIG. The gas-liquid separation drum (corresponding to D-4 in Figure 1) in the step 2 is replaced by a rectification column (T-2), and one of the condensates mainly composed of methane is The top gas of the demethanizer rectifier T-1 of the demethanizer step 3 is supplied as a reflux liquid to the rectifier T-2 of the feed treatment step 1, and the top gas of the demethanizer rectifier T-1 of the demethanizer step 3 is hydrogen. The difference is that it is supplied as a refrigerant to the hydrogen/methane mixed gas cooler E-5. Hereinafter, this example will be described in detail in the order of steps.

In the feed processing step 1, hydrogen, methane, ethylene, ethane,
Furthermore, the mixed gas F containing the heavy fraction is successively cooled to a low temperature by a refrigerant, and the condensate produced is successively separated from the gas in the same way as in the case of Fig. The mixed cracked gas finally cooled in E-4 is sent to rectification column T-2.
The condensate (D-5) mainly composed of methane from the hydrogen and methane separation and purification step 2 is introduced into the top of the rectification column T-2 as a reflux liquid. The cracked gas and the methane liquid come into countercurrent gas-liquid contact inside the column, and due to the rectification effect, the proportion of the ethylene fraction entrained in the hydrogen and methane mixed gas distilled from the top of the rectification column is reduced. Note that 26 indicates a reflux pump. As the rectifying column T-2, any column used as a rectifying means, such as a tray column or a packed column, can be used. The condensate from the rectification column T-2 of the feed treatment step 1 is then fed to the demethanization rectification column T-1 of the demethanizer step 3 via line 15A;
Due to the rectifying effect of the condenser 31, the reboiler 3 reflux drum 32, and the reflux pump 33, hydrogen and methane contained in the supplied condensate are separated from the ethylene fraction, and the heavy fraction E such as ethylene and ethane is purified. Tower T
On the other hand, the top gas (hereinafter simply referred to as CHi gas) mainly consisting of methane passes through a condenser 31 and a reflux drum 32, and further passes through an expander 40 to separate hydrogen and methane. Cooler E- of purification process 2
5 as a refrigerant, and after recovering its cooling energy, it is discharged from line 21.

The hydrogen and methane mixed gas separated in the rectification column T-2 at the final stage of the feed processing step 1 is supplied to the hydrogen and methane mixture from line 16A.
The methane is supplied to the methane separation and purification step 2, cooled to a low temperature by the first stage cooler E-5, and the condensed methane is separated from the gas by the first stage separation drum D-5, and pumped as described above. Rectification column T- of feed treatment step 1 via 26
2 as a reflux liquid.

The gas from the separation drum D-5 is further cooled to a lower temperature by the second stage cooler E-6, and most of the methane in the gas is condensed by the lower temperature, and hydrogen is removed by the second stage separation drum D-6. It is separated from the main component gas, and further expander 25
The gas is lowered in pressure and temperature due to the Joule-Thompson effect (hereinafter, this gas is referred to as LPCH4 gas), and is supplied as a refrigerant to cooler E-6 and then to E-5, where its cold heat is recovered. , line 22 and used as fuel, for example. On the other hand, the purified hydrogen gas extracted from the top of the second stage separation drum D-6 is supplied as a refrigerant to the cooler E-6 and then to the cooler E-5, and after recovering its cold energy, it is sent from the line 23. It is discharged as a by-product. In addition,
The hydrogen and methane mixed gas is cooled by the cooler E-5 mainly by the immediate Clll gas from the demethanizer step 3. In the above embodiment, the final separation means of the feed processing step 1 is the rectification column T-2, and a part of the condensed methane liquid from the hydrogen and methane separation and purification step 2 is used as the reflux liquid in the rectification column T-2. By supplying the hydrogen to methane separation and purification step 2, the ethylene fraction entrained in the purified hydrogen gas and methane gas (LPCH4) separated and discharged from the hydrogen methane separation and purification step 2 is reduced, and the ethylene yield is further increased. It is possible to reduce costs and save energy.

In addition, in order to return the condensed methane liquid from the hydrogen methane separation and purification step 2 to the rectification column T-2 as a reflux liquid, the methane from the demethanizer step 3 was used as a refrigerant in the cooler E-5 of the same step. By supplying the column overhead gas (HP), which is the main component (CH4 gas), it is possible to effectively utilize the column overhead gas and to cool the hydrogen and methane mixed gas. An example of operational data of the ethylene separation and purification equipment according to the above embodiment is shown in Table 2.

As is clear from comparing the results in Tables 1 and 2, by adopting the separation and purification equipment of the present invention, the amount of ethylene loss was reduced by 126 gI'/year compared to the conventional method, and the ethylene yield increased. It can be seen that it contributes significantly to

In the above embodiment, the separation and purification of a fraction of ethylene or higher (mainly ethylene) and light fractions of hydrogen and methane was described, but the present invention is not limited to these.
It can also be applied to the separation and purification of hydrogen and methane light fractions from other decomposition products, such as ethane, propane, and propylene fractions.

As described above, according to the present invention, a rectification step is incorporated into a part of the hydrocarbon decomposition product supply treatment step, and the condensate obtained from the hydrogen and methane separation and purification step is used as the reflux liquid of the rectification step. , the required reflux ratio of the rectification column in the demethanization process can be reduced, in other words, the rectification effect of the demethanization process can be enhanced, and the yield of specific fractions such as ethylene obtained from the bottom of the column can be increased. be able to.

Furthermore, when the yield is constant, the number of stages in the demethanizer can be reduced compared to conventional methods, and equipment such as condensers can also be downsized.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are system diagrams of a purification facility for hydrocarbon cracked gas containing ethylene and the like, showing the prior art and the embodiment of the present invention, respectively. 1...Feed treatment step, 2...Hydrogen,
Methane separation and purification step, 3... demethanizer step,
E-1, E-2, E-3, E-4... Heat exchanger for cooling cracked gas, D-1, D-2, D-3, D-4.
... Gas-liquid separation drum, T-1 ... Demethanization rectification column, T-2 ... Rectification column.

Claims (1)

[Claims] 1. A feed treatment step for separating a hydrocarbon decomposition product into a light fraction and a heavy fraction, a step for separating hydrogen and methane from the light fraction obtained in the feed treatment step, and In a method for low-temperature purification of hydrocarbon decomposition products, which includes a step of separating ethylene and other specific fractions from the heavy fraction obtained in the feed treatment step, at least a part of the feed treatment step is a rectification step; A method for low-temperature purification of hydrocarbon decomposition products, characterized in that the condensate obtained in the hydrogen and methane separation and purification step is used as the reflux liquid in the rectification step. 2. The overhead gas from the ethylene and other separation and purification process,
2. The low-temperature purification method for hydrocarbon decomposition products according to claim 1, which is used as a cooling refrigerant in the hydrogen and methane separation and purification step.