JPH0558412B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for recovering power possessed by methanol vapor at the top of a methanol rectification column.

(Prior Art and Problems to be Solved by the Invention) Crude methanol obtained by the catalytic reaction of hydrogen and carbon oxide generally contains 3 to 30 wt% of water and trace amounts of by-products, such as higher alcohols, paraffin, Contains ketones, ethers, etc., and when trying to obtain high-purity methanol for chemical industrial raw materials or methanol for fuel from a mixed solution of these, it is rectified using a rectification column to obtain the desired purity. It is common to obtain methanol.

In this case, especially when trying to obtain methanol for use as a raw material for the chemical industry, it is necessary to remove trace amounts of impurities, and the required purity tends to become more stringent. The reflux ratio of such a methanol rectification tower is 0.8 to 1.2 for methanol for fuel use, and 1 to 3 for methanol for chemical industry raw materials, and the energy contained in the steam distilled from the top of the rectification tower is enormous. becomes.

A method of combining Rankine cycles is known as a method of recovering power from a low-temperature heat source.

However, the top temperature of a methanol rectification column is usually 64 to 65 degrees Celsius because the column pressure is around atmospheric pressure, and even if the top pressure was increased to 2 to 3 atm, the top temperature would be 80 to 94 degrees Celsius. It is ℃. The Rankine cycle is extremely inefficient economically with a heat source of this temperature, and therefore it is not a good idea to apply this method to a methanol rectification column.

(Means for Solving the Problems) The present invention solves the above-mentioned drawbacks and recovers energy from low-temperature methanol vapor obtained from the top of a methanol rectification column. It operates at a pressure of 2 to 10 atmospheres (absolute), and the methanol vapor distilled from the top of the column is introduced into the expansion turbine as it is or after further heating.
In this method, the methanol vapor is expanded to 0.3 to 1.5 atmospheres (absolute) to drive a turbine and generate power, and the expanded methanol vapor is cooled, condensed, and refluxed to the top of the rectification column.

In the present invention, the top pressure of the methanol rectification column is 2 to 10 atm.

The bottom pressure corresponding to this pressure range is 130℃~183℃
Therefore, when the top pressure is 10 atm or more, a heat source with a temperature of 200°C or less cannot be used as the bottom heat source of the distillation column. Heat sources with a temperature of 200° C. or higher can be recovered more advantageously than by the method of the present invention. Moreover, if the tower top pressure is less than 2 atmospheres, the recovery power of the expansion turbine will be small and it will not be advantageous. The appropriate expansion pressure in the expansion turbine is 0.3 to 1.5 atmospheres. This is mainly determined by the cooling water temperature required for condensation.

In the present invention, the steam at the top of the rectifying column may be directly guided to the expansion turbine, but it is effective to further heat it and then guide it to the turbine. The heating temperature is preferably about 50 to 150°C higher than the saturation temperature.

Next, the present invention will be explained in detail with reference to the drawings.

In FIG. 1, raw material crude methanol is supplied from a flow path 1 to the middle stage of a rectification column 2. A reboiler 3 is provided at the bottom of the tower and heated by a heat source 4. The bottom liquid is introduced into the reboiler through channel 5, and a portion is extracted out of the system through channel 6. A part of the by-product is extracted from the side flow path 7 along with methanol and water. The product methanol is extracted in liquid form from the top of the column or from a tray slightly below the top of the column through a channel 8 to the outside of the system. The methanol vapor distilled from the top of the tower is led to a superheater 10 through a flow path 9, superheated to a temperature higher than the saturation temperature by a heat source 11, and
The fuel is then introduced into the expansion turbine 13 and expanded to generate power.

The power generated by the turbine is transmitted to others via the shaft. The expanded methanol vapor is led to a condenser 15 through a flow path 14, where it is cooled and condensed by a refrigerant 16. The extremely small amount of gas that has not been liquefied by condensation is extracted from the system through the flow path 17. The liquefied methanol passes through the flow path 18 and is refluxed again to the top of the rectification column.

(Effects of the Invention) According to the present invention, the energy possessed by the vapor at the top of the methanol rectification column can be efficiently recovered.

Example Crude methanol containing 20 mol % of water and a trace amount of by-products was supplied to a preliminary distillation column, and the crude methanol from which low-boiling-point by-products had been removed was supplied to a rectification column.

Crude methanol at the inlet of the rectification column contains 22 mol% water.
The amount of methanol is 2.605 Kg-mol/Hr. The pressure at the top of the rectification column is 3.6 atm, and the temperature at the top is 100.
℃ and a reflux ratio of 1.20, the amount of distilled methanol vapor was 5730 Kg-mol/Hr, and 100 molppm each of water and ethanol were entrained. The distillate vapor is then introduced into a superheater and heated to 160°C.
Through the pressure control valve, the pressure became 3.2 atmospheres and was led to the expansion turbine, which drove the turbine and expanded to a pressure of 0.61 atmospheres and a temperature of 74.9°C. During this time, 6330kw/H of power was obtained from the shaft end of the turbine, which was used as circulating power for the synthesis system. On the other hand, methanol vapor exiting the turbine was introduced into the condenser, cooled by cooling water, liquefied, pressurized again, and refluxed to the top of the tower.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of the process of the present invention.

Claims (1)

[Claims] 1 The methanol rectification column is operated at a top pressure of 2 to 10 atm (absolute), and the methanol vapor distilled from the top of the column is introduced into an expansion turbine as is or after further heating, and is then heated to a pressure of 0.3 to 1.5 atm (absolute). A power recovery method for a methanol rectification column, which is characterized in that the methanol vapor is expanded completely (absolutely) to drive a turbine to generate power, and the expanded methanol vapor is cooled, condensed, and refluxed to the top of the rectification column.