JPH0692332B2 - Pressure distillation method for methanol plant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pressure distillation method for a methanol plant, and more particularly to a novel heat treatment in the pressure distillation process of a refiner outlet gas in order to improve the energy consumption rate of the plant. The present invention relates to the above distillation method to which a recovery technique is applied.

(Prior Art) From the viewpoint of improving the energy consumption rate in the distillation process, in recent years, various processes utilizing multiple effects by pressure distillation have been investigated (for example, Ind.Eng.Chem.Pro.
cess Des. Dev. 1983, 22, 175-179, JP-A-53-112803, JP-A-56-123926, etc.).

However, these are only studies on the energy intensity of the distillation system, and no study has been made on improving the energy intensity of the entire plant in consideration of the utilization of the heat energy of the reformed gas.

That is, by adopting the pressure distillation, the bottom temperature of the pressure rectification column is high, and the low temperature region of the waste heat of the reformed gas cannot be recovered in the process. Often a non-optimal process such as FIG. 3 is utilized. In FIG. 3, 12 is a pressure rectification column, 13 is an atmospheric rectification column, 14 is a pressure rectification column reforming gas reboiler, 17 is a pressure rectification column steam reboiler, and 18 is a pressure rectification column. It is a tower reflux condenser.

This large amount of excess waste heat also increased the flow rate of cooling water or the power of the air cooler / fan, which also caused a reduction in the energy consumption rate.

(Problems to be Solved by the Invention) The present invention is intended to improve the energy consumption rate by effectively utilizing such a low-level surplus waste heat. In the pressure distillation process of a methanol plant, the refiner outlet is used. The present invention proposes a method for improving the energy consumption rate of a plant by effectively utilizing the thermal energy of gas and reducing low-level waste heat.

(Means for Solving Problems) The present invention is a method for producing a desulfurized hydrocarbon raw material by steam.
A gas containing carbon oxide, hydrogen and methanol obtained by catalytic reforming at a pressure of 8 atm or more is pressurized by a compressor to be a raw material gas (reforming gas) for methanol synthesis, and in a methanol synthesis step. The low-boiling-point by-product of the synthetic crude methanol containing 8 to 30% by weight of water is removed in the initial distillation column, and then the rectification is composed of two columns, an atmospheric column and a pressure column. Reforming, synthesis, such as distillation by part
In the methanol process including the distillation step, (1) As a heat source for heating the initial distillation column, the reformed gas is at a temperature 5 to 25 ° C. higher than the bottom temperature of the initial distillation column (that is, 70 to 11).
(2) As a heat source for heating the pressurized rectification column, the reformed gas is a temperature 5 to 25 ° C. higher than the bottom temperature of the rectification column (that is, 5 ° C.). ,
It is covered by a reboiler that recovers heat up to 135 to 225 ° C) and a reboiler that uses steam as a heat source. (3) As a heat source for heating the atmospheric rectification column, multiple effects by top gas of the pressurized rectification column The temperature of the condenser and the reformed gas is 5 to 25 ° C. higher than the bottom temperature of the rectification column (that is, 11
It is covered by a reboiler that recovers heat up to 0 to 150 ° C) and, if necessary, a reboiler that uses steam as a heat source. At least two of the above are combined and the reformed gas flows from a tower with a high bottom temperature to a tower with a low bottom temperature. The present invention relates to a pressurized distillation method for a methanol plant capable of effectively recovering the thermal energy of the reformed gas and reducing the energy consumption of the entire plant, which is characterized in that they flow in series.

According to the present invention, it is understood that adopting a distillation process that minimizes the heat load from outside the distillation system does not necessarily minimize the energy consumption rate of the plant.

Hereinafter, this will be described based on a specific example. The explanation is LS / F
Although it is based on the (Light-Split / Heat-integration-forward) process, the present invention is effective not only for this LS / F but also for any pressure distillation process.

In addition, LS / F is supplied to the pressure tower, the product is removed from the top of the tower, the bottom liquid is supplied to the atmospheric tower, the product is supplied from the top, and the water is supplied from the bottom to the intermediate stage. A side flow is extracted from the column (see Figs. 1 to 3), and a part of the light component (product) is extracted in the first tower, and the transfer of heat is in the forward direction with respect to the flow of the process fluid. Therefore, it is called LS / F.

(1) Two Processes to be Compared (Conventional Method and Present Invention Method) FIG. 1 and FIG. 2 show recovery flows of the reforming gas heat quantity in the pressure distillation in the present invention method and the conventional method.

FIG. 2 is a flow in the process in which the heat load from the outside of the distillation system is the smallest (that is, the energy intensity of distillation is the smallest). This heat recovery flow is a flow often used in conventional pressure distillation, and will be referred to as "conventional method" hereinafter.

In the conventional method, the heat source of the pressurized rectification column 12 is covered by the reboiler outlet gas (that is, reformed gas) and steam by the reboilers 14 and 17, and the heat sources of the atmospheric rectification column 13 and the first distillation column 11 have multiple effects. The refraction condenser 18,1 of the pressure rectification column 12
Given by 8.

FIG. 1 is a flow showing an example of the present invention. According to the method of the present invention, the amount of heat required for rectification is increased as compared with the conventional method, but the energy consumption of the plant is reduced due to the increase of the lower heat recovery. Hereinafter, this is referred to as the “method of the present invention”.

In the method of the present invention, the heat source for heating the first distillation column 11 is covered by the reboiler 16 by the waste heat of the refumeer outlet gas, and the pressure rectification column is used.
Reference numeral 12 designates an atmospheric pressure rectification column 13 which uses heat generated by the reboiler 14 for exhausting the refumeer outlet gas and steam produced by the reboiler 17 as heat sources.
The heat source is covered by the reboilers 18, 15, and 19 using the overhead gas of the pressurized rectification column 12 with multiple effects, the reformer outlet gas, and steam. In addition, 20 in FIG. 1 has shown the gas-liquid separator.

(2) Comparison of total energy intensity A specific example is the LS / F distillation process of 2500 t / d methanol that uses the waste heat of the reformed gas at 15 atm flowing out from the steam reformer as a part of the heat source. The units are compared based on the conventional method (FIG. 2) and the method of the present invention (FIG. 1).

Table 1 shows the calorific values of the reboilers 14 to 17 and 19 of the distillation columns 11 to 13 and the calorific value of the refraction condenser 18 of the pressure rectification column 12 having multiple effects.

A mark indicates that "heat is given to the process (negative heat consumption)".

As is clear from the above table, when comparing only the heat load from outside the distillation system, that is, the energy consumption of distillation, the conventional distillation process is superior to the method of the present invention by 20.3 MMKcal / h.

However, as is clear from Table 2 which shows the reformed gas and steam reboiler calories of each distillation column and the surplus energy of the reformed gas that is not recovered in the process, in the method of the present invention,
By effectively utilizing the low temperature waste heat of the reformed gas,
On the contrary, the calorific value of the steam reboiler is reduced by 18.7MMKcal / hr. Furthermore, in the method of the present invention, the amount of heat that has not been recovered as excess waste heat in the past is reduced by 39.0 MMKcal / hr, which leads to a decrease in the required amount of cooling water or a decrease in the fan power of the air cooler.

As described above, the method of the present invention is inferior to the conventional method when compared with the distillation basic unit, but it is possible to effectively recover the calorific value of the reformed gas as a whole, and an energy-saving process. You can see that

The flow of FIG. 1 is an example of the process based on the present invention, and one of the three reformed gas reboilers 14 to 16 is selected depending on the degree of pressurization of the distillation system, the pressure of the reforming system and the heat recovery method. It is also possible to omit.

Further, in the flow of FIG. 1, a deaerator feedwater preheater (not shown) may be installed on the downstream side of the reformed gas reboiler 16 (that is, on the way to the reformed gas synthesis system). The heat quantity of the preheater is the same in the conventional method and the method of the present invention (for example, in the case of Table 1, both are 15.0 MMKcal / hr).

[Brief description of drawings]

FIG. 1 is a flow chart showing an example of the distillation process of the present invention, and FIGS. 2 and 3 are diagrams showing an example of a flow often used conventionally in pressure distillation utilizing multiple effects.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Morita 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Masaru Murayama 3500 Matsuhama-cho, Niigata-shi, Niigata (72) Inventor Osamu Hashimoto 3500, Matsuhama-cho, Niigata City, Niigata (56) Reference JP-A-53-79807 (JP, A) JP-A-53-112803 (JP, A) JP-A-55-45637 (JP, A) JP-A-SHO 56-123926 (JP, A) JP-B 56-16338 (JP, B1)

Claims (1)

[Claims] 1. A gas containing carbon oxide, hydrogen and methane obtained by contact reforming a desulfurized hydrocarbon raw material with steam at a pressure of 8 atm or more is pressurized with a compressor to produce methanol. The raw crude gas (reforming gas) for synthesis, and synthetic crude methanol containing 8 to 30% by weight of water produced in the methanol synthesis step, had its low boiling point by-products removed in the first distillation column, followed by Reforming, synthesis, such as distillation by a rectification section composed of two columns, an atmospheric pressure column and a pressure column,
In a methanol process consisting of a distillation step, (1) As a heat source for heating the first distillation column, the reformed gas is at a temperature 5 to 25 ° C higher than the bottom temperature of the first distillation column (that is, 70 to
(2) As a heat source for heating the pressurized rectification column, the reformed gas is 5 to 25 ° C. higher than the bottom temperature of the rectification column (ie , 135 to 225 ° C), and a reboiler that uses steam as a heat source. (3) As a heat source for heating the atmospheric rectification column, multiple gas is used by the top gas of the pressurized rectification column. By the effect condenser, and the reboiler in which the reformed gas is heat-recovered to a temperature 5 to 25 ° C. higher than the bottom temperature of the rectification column (that is, 110 to 150 ° C.), and if necessary, a reboiler using steam as a heat source. It is provided that at least two of the above are combined to allow the reformed gas to flow in series from a tower with a high bottom temperature to a tower with a low bottom temperature, which effectively recovers the thermal energy of the reformed gas. The energy consumption of the entire plant can be reduced. Pressure distillation method methanol plants.