JPS6229540A - Pressurized distillation of methanol plant - Google Patents

Abstract

PURPOSE:To reduce the energy consumption of the whole plant, by effectively recovering the thermal energy of a reformed gas obtained by two-stage reforming of a desulfurized hydrocarbon with steam and oxygen. CONSTITUTION:A gas containing a desulfurized hydrocarbon is reformed in two-stage reforming with steam and oxygen to give a reformed gas with a low steam content, and crude methanol synthesized therefrom is distilled under pressure. In the process, the following operation is carried out; (i) An initial distillation column 11 is heated to a temperature (70-115 deg.C) 5-25 deg.C higher than the column bottom temperature with a reboiler 16 for recovering the heat of the reformed gas. (ii) A pressurized distillation column 12 is heated to a temperature (135-225 deg.C) 5-25 deg.C higher than the column bottom temperature with a reboiler 14 for recovering the heat of the reformed gas and a reboiler 17 using steam as a heat source. (iii) An atmospheric-pressure rectifying column 13 is heated to a temperature (110-150 deg.C) 5-25 deg.C higher than the column bottom temperature with a reboiler 15 for recovering the heat of the reformed gas and multiple effect reboiler 18 using the overhead gas of the pressurized rectifying column 12.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a pressurized distillation method for methanol plants, and in particular, to improve the energy consumption of the plant, it is a novel pressurized distillation process for log gas from a reformer. The present invention relates to the above-mentioned distillation method applying heat recovery technology.

(Prior art) From the perspective of improving the energy consumption rate in the distillation process, various processes that utilize multiple effects through pressurized distillation have been studied in recent years (for example, 6.Eng+Ch).
ew, Proceaa DeB, Dew.

1983.22, 175179. Japanese Unexamined Patent Publication No. 55-11
Publication No. 2803, Publication No. 1987-123926, etc.)
.

However, these studies only considered the energy consumption rate within the distillation system, and did not consider improving the energy consumption rate of the entire plant, taking into account the thermal energy utilization of the reformed gas.

In other words, by adopting pressure distillation, the bottom temperature of the pressure rectification column is high and the low temperature range of the waste heat of the reformed gas cannot be recovered in the process, so the high temperature heat is relieved and the overall The process shown in FIG. 5, which is not the best, was often used. In Fig. 3, 12 is a pressure rectification column, 13 is an ordinary pressure rectification column, 14 is a pressure rectification column reformed gas reboiler, 17 is a pressure rectification column steam reboiler, and 18 is a pressure rectification column. The tower is a slack capacitor.

And due to this large amount of excess waste heat, there is a large flow of cooling water.
This increases the power of the air cooler fan and causes a total reduction in energy consumption.

(The labor problem that the invention seeks to solve) The present invention aims to effectively utilize such low-level surplus waste heat to improve energy consumption. This paper proposes a method for effectively utilizing the heat energy of output log gas, completely reducing low-level waste heat, and improving the energy consumption of the plant.

(Means for Solving the Problems) The present invention uses a two-stage reforming process of steam and oxygen at a pressure of 50 atmospheres or more to desulfurized hydrocarbon-containing gas, so that the steam content is reduced to just steam reforming. The synthetic crude methanol is reformed into methanol synthesis raw material gas with a lower water vapor content than that possible through the reaction, and the synthetic crude methanol containing 8 to 50 @ 1% water is produced in the synthesis process and its low content is reduced in the first distillation column. In the methanol process, which consists of reforming, synthesis, and distillation steps, in which boiling-point byproducts are removed and then distilled in a nitrification section consisting of two columns: an ordinary pressure column and a pressurization column, (1) As a heat source for heating the distillation column, the reformed gas has a temperature higher than the bottom temperature of the initial distillation column by 5S25℃ (i.e., 7
(2) As a heat source for heating the pressurized rectification column, the reformed gas is heated to a temperature of 5 to 25℃ above the bottom temperature of the rectification column. (3) The heat source for heating the atmospheric rectification column is the top of the pressure rectification column. The temperature of the gas-based multiple effect reboiler and reformed gas is 5 to 25°C higher than the bottom temperature of the rectification column (i.e., 1
To effectively recover the thermal energy of the reformed gas and reduce the energy consumption of the entire plant, which is characterized by a combination of at least two of the above. This paper relates to a pressurized distillation method for methanol plants that allows for

A gas reformed by a simple steam reformer contains a large amount of H2 due to the reaction of CH4+ H2O-+ CiO+ 5H2. - In the two-stage reforming process in which an autothermal reformer is installed downstream of the steam reformer adopted in the present invention, excess H2 for methanol synthesis is converted into steam by 02i supplied to the autothermal reformer. Since it is possible to perform reforming at high temperatures, it is also possible to increase the reforming pressure. Due to the difference in H20 concentration and pressure, the reformed gas thermal recovery IFy method differs between a method using a simple steam reformer and the present invention which employs a two-stage reforming process.

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

This will be explained below based on a specific example. In addition, the explanation is Ls,
/r (Light-5plit/f(eaz-1nt
The present invention is effective not only for this L S/F but also for all pressure distillation processes.

In addition, LS/F is a system in which the product is supplied to a pressurized column, the product is removed from the top of the column, the bottom of the column is supplied to the next atmospheric pressure column, the product is supplied from the top of the column, water is supplied to the product from the bottom of the column, and water is removed from the bottom of the column to the intermediate stage. The flow refers to a flow in which a side stream is extracted from a column (1st to 5th inspection plate), in which a part of light components (products) are extracted in the first column, and the heat transfer is in the forward direction with respect to the flow of the entire process. Therefore, it is called LS/F.

(1) Comparison of two processes (conventional method and method of the present invention) Figures 1 and 2 show the recovery flow of the reformed gas calorific value in pressurized distillation in the method of the present invention and the conventional method.

FIG. 2 shows a flow in a process that requires the least heat load from outside the distillation system (that is, the energy consumption unit for distillation is the least).

This heat recovery flow is a flow often used in conventional pressurized distillation, and is hereinafter referred to as "conventional method".

In the conventional method, the heat source of the pressurized rectification column 12 is provided by the reboiler 14.17 using the reformer outlet gas and steam, and the heat source of the atmospheric rectification column 1S and the initial distillation column 11 is provided by the pressurized rectification column 12 due to multiple effects. Rectification column 12 Reflux condenser 18゜1
8 is given.

FIG. 1 is a flowchart showing an example of the present invention. According to the method of the present invention, the amount of heat required for rectification is increased compared to the conventional method, but the energy consumption of the plant is reduced due to the increase in lower heat recovery.

Hereinafter, this will be referred to as Method 1 of the present invention.

In the method of the present invention, the heat source for heating the initial distillation column 11 is provided by the boiler 16 by the waste heat of the reboiler outlet gas, and the pressurized rectification column 12 is supplied with the waste heat of the reboiler output gas and steam from the reboiler 17. The heat source of the atmospheric rectification column 13 is provided by a reboiler 18.15 using the top gas of the pressure rectification column 12 and the reformer outlet gas by multiple effects. Note that 20 in FIG. 1 indicates the amount of gas-liquid separator metal.

(2) Total energy consumption: 2 500 t/2,500 t/unit using the waste heat of the reformed gas at 55 atm flowing out from the two-stage reforming process of steam and oxygen as part of the heat source.
Taking the LS/F distillation process of methanol as a specific example, the conventional method (FIG. 2) and the method of the present invention (FIG. 1) will be compared in terms of energy consumption.

The reboiler heat amount of each distillation column 11 to 13 and the reflux condenser 18 heat of the pressure rectification column 12 which is used for multiple effects tt
Table 1 shows this.

The mark Δ in Table 1 gives heat to one process (negative heat consumption: tit)
”It shows that it is gold.

As is clear from the table above, when comparing only the heat load from outside the distillation system, that is, the energy consumption of distillation, the distillation process of the present invention and the conventional method are 10.9 MMKcal.
/h is better.

However, the heat amount of the reformed gas reboiler and steam reboiler of each distillation column, the heat amount of the deaerator feed water preheater 19 installed downstream of the reformed gas reboiler, and the surplus energy of the reformed gas that is not recovered in the process are shown in the second column. As is clear from the table, in the method of the present invention, the low-temperature waste heat of the reformed gas is effectively utilized, so that the amount of heat in the steam boiler is 17.
9 MMCcal/hr is decreasing. Furthermore, with the method of the present invention, the amount of heat that was conventionally not recovered as surplus waste heat is reduced by 18.8MM K ca 1/hr.
This results in lower cooling water requirements or lower air cooler fan power.

As shown in Table 2 and above, although the method of the present invention is inferior to the conventional method when only the distillation consumption rate is compared, overall the reformed gas heat -t
It can be seen that it can be effectively recovered and is an energy-saving process.

In the above comparison, all settings were made to recover heat from the reformed gas at 55 atm, but as the reforming pressure decreases, the dew point also decreases, so the amount of surplus heat in the low temperature range increases. The degree of improvement in energy consumption by the law will continue to increase.

The flow shown in 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 controlled 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 one.

[Brief explanation of drawings]

FIG. 1 is a flow diagram showing an example of the distillation process of the present invention, and FIGS. 2 and 3 are diagrams showing an example of a flow commonly used conventionally in pressurized distillation using multiple effects.

Claims (1)

[Claims] A two-stage reforming process using steam and oxygen at a pressure of 30 atmospheres or more is carried out on desulfurized hydrocarbon-containing gas so that the steam content is lower than that possible through a simple steam reforming reaction. Synthetic crude methanol containing 8 to 30% by weight of water produced in the synthesis process is reformed into methanol synthesis raw material gas with low content, and its low-boiling byproducts are removed in a first distillation column.
In the methanol process, which consists of reforming, synthesis, and distillation steps, which are then distilled in a rectification section consisting of two columns, a normal pressure column and a pressurization column, (1) As a heat source for heating the initial distillation column. In this case, the temperature of the reformed gas is 5 to 25 °C higher than the bottom temperature of the initial distillation column (i.e., 70 to 25 °C).
(2) As a heat source for heating the pressure rectification column, the reformed gas is heated to a temperature 5 to 25C higher than the bottom temperature of the rectification column (i.e. (135 to 225℃) and a reboiler that uses steam as a heat source. A combination of at least two of the above, in which the reformed gas is supplied with a reboiler whose heat is recovered to a temperature 5 to 25 degrees Celsius higher than the bottom temperature of the rectification column (i.e., 110 to 150 degrees Celsius). A pressurized distillation method for a methanol plant that can effectively recover the thermal energy of reformed gas and reduce the energy consumption of the entire plant.