JP2001040366A - Cooling method for mixed gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make long continuous operation possible while preventing the accumulation of a heavy hydrocarbon component in a heat exchanger by cooling with a vertical heat exchanger in a temperature range wherein a heavy hydrocarbon component contained in a mixed hydrocarbon gas condensates. SOLUTION: Preferably, the cooling of the mixed gas in a high-temperature range is conducted with a horizontal heat exchanger E-1 and then the mixed gas is cooled with a vertical heat exchanger E-2 having heat exchange planes installed in the vertical direction. For example, a hydrogen-containing mixed hydrocarbon gas at 650-750 deg.C obtained by the heating and hydrodealkylation in a benzene plant and supplied from a reactor R-2, is cooled to 350-570 deg.C, preferably with a horizontal heat exchanger E-1, and then cooled to 90-250 deg.C with a vertical heat exchanger E-2. A heavy component condensed in the vertical heat exchanger E-2 is separated by distillation from products, such as benzene, and light gas distillates at the downstream-side refining steps. Preferably, the vertical heat exchanger E-2 is a shell-and-tube heat exchanger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cooling a mixed gas, and more particularly to a method for cooling a hydrocarbon mixed gas containing heavy hydrocarbons.

[0002]

2. Description of the Related Art In a process in which a cracked gasoline produced from an ethylene plant is distilled, hydrodesulfurized, and hydrodealkylated, a hydrogen-containing hydrocarbon mixed gas is cooled, refined, and a product, benzene, is obtained. , The mixed gas passed through the hydrodealkylation step is passed through a horizontal heat exchanger for 700
A method of cooling from about ℃ to about 250 ℃ is known.

[0003] In this method, a cracked gasoline produced from an ethylene plant is distilled, and a hydrogen-containing hydrocarbon mixed gas obtained by hydrodesulfurization is heated in a heating furnace, led to a reactor, and the hydrogen-containing hydrocarbon gas is reacted in the reactor. A hydrogen-dealkylation reaction of the alkyl aromatic component in the hydrogen mixed gas to form benzene, and a non-aromatic component hydrogenated and pyrolyzed to methane and ethane, ie, a mixed gas, are mixed in a horizontal heat exchanger at 70 ° C.
It cools from about 0 ° C to about 250 ° C.

[0004]

However, in the above-described method, aromatic hydrocarbons are polymerized in the reactor into hydrocarbon heavy components, that is, the mixed gas sent to the cooling step has a high boiling point in the hydrocarbon heavy components. , Heavy hydrocarbons condense during the cooling process and adhere to the inner wall of the horizontal heat exchanger,
There is a problem in that the heat accumulates and the heat exchange efficiency is reduced to cause an operation failure. Therefore, it is necessary to open and clean the heat exchanger at a certain frequency in order to remove the accumulated heavy hydrocarbons, and it has been difficult to continuously operate the heat exchanger for one year or more.

The present invention has been made in view of the above circumstances, and has as its object a method for preventing accumulation of heavy hydrocarbons in a heat exchanger, suppressing a decrease in heat exchange efficiency, and achieving long-term continuous operation. Is to provide.

[0006]

As a result of intensive studies to solve the problems of the prior art, the present inventors have found that a conventional horizontal heat exchanger having a small load due to installation and maintenance when cooling a mixed gas. By using the vertical heat exchanger in the temperature range where the heavy hydrocarbons in the mixed gas condense when used, the adhesion of heavy hydrocarbons to the inner wall of the heat exchanger is reduced, and the inside of the heat exchanger is reduced. It has been found that unexpected effects can be obtained, such as preventing the contamination of the heat exchanger and enabling the continuous operation of the heat exchanger, and suppressing the decrease in the heat exchange efficiency to contribute to the reduction of the fuel consumption of the heating furnace. Reached.

That is, the present invention relates to a method for cooling a hydrocarbon mixed gas containing a heavy hydrocarbon by a heat exchanger, wherein the vertical mixed heat is used in a temperature range in which the heavy hydrocarbon contained in the mixed gas is condensed. The present invention relates to a method for cooling a mixed gas, characterized by cooling using an exchanger.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention can be applied to a hydrocarbon mixed gas containing a heavy hydrocarbon component, and more generally to a mixed gas containing a high-boiling substance. The temperature of the mixed gas is usually 400 to 750 ° C. For example, a cracked gasoline produced from the above-described ethylene plant, which is a preferred embodiment of the present invention, is distilled and hydrodesulfurized. A hydrogen-containing hydrocarbon mixed gas is heated in a heating furnace, guided to a reactor, and hydrogenated carbonized in the reactor. A process in which the alkyl aromatic component in the hydrogen mixed gas is subjected to a hydrodealkylation reaction to form benzene and the non-aromatic component is subjected to hydropyrolysis into methane and ethane is usually 650 to 75.
0 ° C., preferably 700-730 ° C.

Next, the mixed gas is subjected to a cooling step using a heat exchanger. The initial cooling, that is, cooling in a high-temperature region, is performed by a normal heat exchanger. A horizontal type is usually used as a heat exchanger. This cooling is performed to a temperature near the temperature at which the heavy hydrocarbon components contained in the mixed gas start to condense.

[0010] Conventionally, heavy hydrocarbons are condensed at the condensing temperature and accumulate on the inner wall of the heat exchanger to block the heat exchanger. Therefore, in the present invention, in the step of cooling the mixed gas, from the vicinity of the temperature at which the heavy hydrocarbons contained in the mixed gas begins to condense to the vicinity of the temperature at which condensation is completed, that is, the vertical heat exchanger is used to cool the condensing temperature range. By adopting, the condensate drops by gravity, and the liquid cools further, condensing the light components and washing away the condensed heavy components. It enables continuous operation of the heater and contributes to fuel reduction in the heating furnace because the heat transfer efficiency does not decrease. The temperature at which heavy components condense is typically 200
To 480 ° C, preferably 280 to 450 ° C.

The vertical heat exchanger referred to here may be any as long as a heat exchange surface for performing substantial heat exchange is provided in a vertical direction, and a liquid dirt component falls. Examples of the type include a multi-tube type, a flat-plate type, a double-tube type, a spiral type, a spiral type, and the like. Any type of heat exchanger may be used, regardless of the type of heat exchanger.

The cooling temperature in the vertical heat exchanger is usually about 250 to 90 ° C. at the outlet temperature. After this heat exchange step, it is further subjected to heat exchange if necessary. This cooling is performed in the same manner as the heat exchange performed from the high temperature region to the vicinity of the temperature at which the heavy hydrocarbons condense, and a horizontal heat exchanger is usually used.

The steps before and after the hydrodealkylation reactor of the benzene plant, which is a preferred application of the cooling method of the present invention, will be described with reference to the accompanying drawings. FIG. 1 is a process flow diagram illustrating an example of a preferred embodiment of the present invention. This process mainly consists of heating furnace (F-1), first stage reactor (R-1), second stage reactor (R-2), horizontal heat exchanger (E-
1) Consists of a vertical heat exchanger (E-2).

As the raw material gas, at least hydrogen, methane, ethane, and C6 to C6 such as toluene and xylene are used.
A hydrogen-containing hydrocarbon mixed gas containing 8 hydrocarbons is used.

The raw material gas is supplied at 300 to 350 ° C. on the tube side of the vertical heat exchanger (E-2) and at 50 ° C. on the body side of the horizontal heat exchanger (E-1).
0 to 580 ° C, and then in a heating furnace (F-1).
Heat to 80-630 ° C. The heated raw material gas is successively led to the first-stage reactor (R-1) and the second-stage reactor (R-2), and hydrogen-dealkylation-reacts the alkyl aromatic components in the raw material gas to benzene. At the same time, the non-aromatic components are hydrothermally decomposed into methane and ethane to facilitate the separation by distillation from benzene. In addition, a condensation reaction of a benzene ring occurs as a side reaction, and heavy hydrocarbons having a high boiling point are generated.

The composition of the reaction product, that is, the hydrocarbon mixture gas containing the heavy hydrocarbon component is usually 45 to 60 mol of hydrogen.
%, Preferably 49 to 54 mol%, methane is 25 to 35 m
ol%, preferably 27-29 mol%, ethane 1-15 m
ol%, preferably 3 to 12 mol%, benzene is 5 to 20 m
ol%, preferably 8 to 14 mol%, toluene
2 mol%, preferably 0.4 to 1.2 mol%, and hydrocarbon heavy content of 0.02 to 0.3 mol%, preferably 0.1 to
It is a mixed gas containing 0.2 mol%. Here, the hydrocarbon heavy fraction has a boiling range of 280 to 450 ° C. and a carbon number of about 1
Means 2 to 30 hydrocarbons.

The temperature of the mixed gas is usually 650 due to the heat of reaction.
To 750 ° C, preferably 700 to 730 ° C. The mixed gas that is a reaction product from the reactor (R-2) exchanges heat with the raw material gas on the barrel side at the tube side of the horizontal heat exchanger (E-1), and is usually cooled to 350 to 570 ° C. The body side of the vertical heat exchanger (E-2) exchanges heat with the raw material gas on the tube side and is usually cooled to 90 to 250 ° C. The type of the vertical heat exchanger used here is a multi-tube, flat-plate, double-tube, spiral or spiral heat exchanger, preferably a multi-tube heat exchanger. The heavy fraction condensed in the vertical heat exchanger is separated by distillation from products such as benzene and a light gas fraction in a downstream purification step.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 Hydrogen-dealkylated hydrocarbon-containing gas mixture obtained by distilling and hydrodesulfurizing cracked gasoline produced from an ethylene plant, and is a hydrocarbon mixed gas comprising 49.6 hydrogen
mol%, methane 27.8 mol%, ethane 10.6 mol%,
A hydrocarbon mixed gas containing 11.4 mol% of benzene, 0.5 mol% of toluene, and 0.1 mol% of hydrocarbon heavy components (condensation temperature: around 300 ° C.) is cooled from 720 ° C. to 500 ° C. by a horizontal heat exchanger. Then, it was cooled from 500 ° C. to 100 ° C. by a vertical heat exchanger. As a result, the outlet temperature of the vertical heat exchanger was maintained at 100 ° C. two years later, and no decrease in the heat transfer coefficient was observed. After continuous operation was continued for two years, when opened, no remarkable dirt was observed.

COMPARATIVE EXAMPLE 1 Instead of using both the horizontal heat exchanger and the vertical heat exchanger, the same gas as that of the embodiment was used in one horizontal heat exchanger at 720.degree.
After cooling to 0 ° C at a stretch, the temperature at the outlet of the horizontal heat exchanger rose to about 400 ° C after one year, the heat transfer coefficient decreased by about 40%, the operation was stopped, and opening and cleaning were required.

[0021]

According to the present invention described above, contamination in the heat exchanger is suppressed as compared with the conventional method, so that it is not necessary to stop, open and clean the operation, and continuous operation can be performed for a long period of time. Become. In addition, since contamination in the heat exchanger is suppressed, a high heat transfer coefficient can be maintained, and performance of the heat exchanger can be maintained, thereby improving production efficiency.

[Brief description of the drawings]

FIG. 1 is a process flow diagram illustrating an example of a preferred embodiment of the present invention.

[Explanation of symbols]

 E-1: Horizontal heat exchanger E-2: Vertical heat exchanger F-1: Heater R-1: First stage reactor R-2: Second stage reactor

Claims (6)

[Claims] 1. A method for cooling a hydrocarbon mixed gas containing a hydrocarbon heavy component by a heat exchanger, wherein a vertical heat exchanger is used in a temperature range where the hydrocarbon heavy component contained in the mixed gas condenses. A method for cooling a mixed gas, comprising cooling the mixture. 2. The cooling method according to claim 1, wherein a horizontal heat exchanger is used before or after cooling by the vertical heat exchanger. 3. After cooling the hydrocarbon mixed gas in a heat exchanger to a temperature higher than a temperature range in which heavy hydrocarbons are condensed, the temperature is reduced from a temperature range in which heavy hydrocarbons are condensed in a vertical heat exchanger. The cooling method according to claim 1, wherein cooling is performed to a low temperature. 4. The hydrocarbon mixed gas is cooled to 350 to 570 ° C. by a horizontal heat exchanger, and is cooled to 90 to 2 ° C. by a vertical heat exchanger.
The cooling method according to any one of claims 1 to 3, wherein the cooling is performed to 50C. 5. The hydrocarbon mixed gas is a mixed gas obtained by hydrodesulfurizing a fraction obtained by thermally decomposing a paraffinic hydrocarbon and hydrodealkylating the same. 5. The cooling method according to any one of items 1 to 4. 6. The cooling method according to claim 1, wherein the temperature range in which the heavy hydrocarbons contained in the hydrocarbon mixed gas condense is 200 to 480 ° C.