JPS63227532A - Apparatus for producing makeup water for humidifying hydrocarbon gas used in synthesizing methanol - Google Patents

Abstract

PURPOSE:To obtain the titled apparatus, having a feeding means for distillation column waste water discharged in distilling crude methanol and feeding means for air, filled with packings therein and capable of decomposing formic acid an in the above-mentioned waste water with oxygen and preventing corrosion of humidifier constituent materials. CONSTITUTION:Waste water from a distillation column discharged in distilling crude methanol in the distillation column is utilized as makeup water for a humidifier used in humidifying natural gas for steam reforming in a methanol synthesis plant. In the process, an apparatus 1 for producing the above-mentioned makeup water, having a feeding means 5 for the afore-mentioned waste waster and a feeding means 6 for air and filled with packings, preferably a catalyst material 2 for decomposing formic acid therein is used to oxidatively decompose and remove strong corrosive formic acid present in the above-mentioned waste water as a product of side reaction of methanol synthesis with oxygen in in expensive air. Thereby corrosion of humidifier constituent materials by the formic acid in the afore-mentioned waste water is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for producing make-up water for a humidifier used for the purpose of humidifying natural gas for steam reforming of methanol synthesis.

[Conventional technology]

When methanol is industrially produced from hydrocarbons such as methane, hydrogen,
- The usual method is to produce a mixed gas containing carbon oxide and carbon dioxide as main components and bring this into contact with a copper-based catalyst to obtain methanol.

The fluid supplied into the reactor tube for carrying out the aquatic fish reforming method is -01.2 to 5 molar ratio to C1 with respect to raw material expanded hydrogen gas whose main component is hydrocarbon such as methane CE4.
The usual method is to mix water vapor in a ratio of . For example, CH41m "K to %OL5m" is added, and the steam reforming method of hydrocarbons uses a very large amount of steam, and the saving of thermal energy for supplying steam has a large impact on the operating cost F of Pufun F. It is something.

In order to save thermal energy, a technology has been developed that uses equipment called a humidifier or saturator to effectively utilize the thermal energy of a low-temperature heat source. (“Mitsubishi (MGC/MHI) Methano-V Procenu” by Takase et al., Mitsubishi Heavy Industries branch axis vol. 2 S, N111,
95 (1986)), the above cited document mentions the use of condensed water from the process of cooling steam reformed gas as a water source to be supplied to the humidifier. However, this condensed water has a small amount of hydrogen, carbon oxide, and other gases dissolved in it, but if the dissolved gases are removed, it is high-purity water that can be used as feed water for high-pressure plants with a pressure of 10 Qatm or more, and is used in methanol synthesis plants. From a water economic point of view, it is not necessarily optimal to use this condensed water to humidify hydrocarbons.

Furthermore, if one attempts to obtain this water vapor from fresh water obtained by purifying river water, etc., there is a drawback that the cost of producing fresh water increases.

Therefore, it is possible to use distillation column wastewater as make-up water for humidifying hydrocarbons, but the wastewater contains formic acid as a side reaction product of methanol synthesis, and formic acid is highly corrosive. However, recently existing formic acid has been neutralized with alkali and supplied to humidifiers using hydrocarbon gas. A method has been proposed. (Unexamined Japanese Patent Publication No. 57-18640) However, in this method, alkaline salts (such as sodium formate) are neutralized by evaporation of water.
However, there was a problem in that the amount of water evaporation had to be limited because of the disadvantage that amine salts precipitated.

[Problem that the invention seeks to solve]

The fluid pressure in the steam reforming reactor tube is widely used industrially at 10 to 40 atm, and the operating pressure of the humidifier is also under the same conditions. H of hydrocarbon gas (also called natural gas NG) whose main component is methane at the humidifying inlet,
0 partial pressure is 1 atm or less, and H! The function of a humidifier is to increase the O partial pressure; for example, when the pressure is 35 at.
In order to increase the partial pressure from 40 atm to 20 atm at an operating pressure of 100 m, it is necessary to raise the water temperature from the saturated vapor pressure of water to 211°C. Under these conditions (assuming that equilibrium is obtained), the hydrocarbon partial pressure is 15 atm, the water partial pressure is 20 atm, and the ratio between the two is 1:1.5.

This condition varies depending on the temperature and flow rate (calorific value) of the available heat source fluid and the specifications of the heat transfer structure, so it can be changed depending on the thermal design conditions of the plant, but in this example, the H,0 partial pressure at the humidifier outlet is water vapor. Since the reformer supply gas is insufficient, boiler steam or high-pressure turbine oil is additionally mixed to achieve the proper H! It is necessary to set the ratio to 0/C.

This temperature of 211°C is a severe condition from the viewpoint of corrosion of equipment structural materials, and as is well known from the problem of stress corrosion cracking of stainless steel caused by high-temperature water in Atomic Kaburan F, trace amounts of corrosive substances contained in water are present. Corrosion of structural materials becomes a problem.

An example of the composition of distillation column wastewater is shown in Table 1), which contains hydrocarbons with a small corrosive effect and formic acid and methyl formate, which have a large corrosive effect, as impurities.

Table 1 Example of distillation column wastewater a, o 99.98% by weight formic acid
100 ppm CH, OR100 ppm (4HgOHt8 ppm 2-propanol α1 ppm.-〇,
1! L4 ppm It is well known that formic acid is a highly corrosive organic acid, and its concentration in water I Q O
When it's ppm, it's p! (517.500 ppm means pH
It is 2-82.

Therefore, the most effective means is to remove formic acid from distillation column waste water when it is used as make-up water for a humidifier, but this method has not been available in the past.

As mentioned above, a method of neutralizing distillation column waste water by adding an alkali such as caustic soda has been proposed, but this method also has the disadvantages mentioned above and is not practical.

[Purpose of the invention]

The present invention aims to remove formic acid from the wastewater, which is a problem when distillation column wastewater is used as make-up water for a humidifier used to humidify natural gas for steam reforming in a methanol synthesis plant. The purpose of the present invention is to provide a method for effectively removing water from the air and effectively using it as make-up water for humidifiers.

[Means for solving problems]

The present invention provides a hydrocarbon gas humidifier for methanol synthesis characterized by comprising a distillation column waste water supplying means and an air supplying means discharged when crude methanol is distilled in a distillation column. This is an equipment for producing makeup water.

A preferred embodiment of the present invention is to use a formic acid decomposition catalyst material as a filler in the above structure.

In the present invention, an apparatus for producing make-up water for humidifying hydrocarbon gas for methanol synthesis by decomposing formic acid in distillation column wastewater brings the distillation column wastewater into contact with an oxygen-containing gas, such as air, and converts formic acid vertically according to the following formula (1). It is oxidized and decomposed.

HCOO) (+%0,4 H,O+CO,---
--(1) Naturally, air is the cheapest in industrial terms, so air will be used as a representative in the following explanation.

There is no restriction on the amount of air fed, and it is possible to increase the molar ratio necessary for the reaction of formula (1) in excess. Also this (
It is not necessary to decompose the entire amount of formic acid in the reaction of formula 1), and the object of the present invention can be achieved if corrosion of the humidifying material can be reduced.

Naturally, distillation tower wastewater after formic acid decomposition contains air (oxygen), but the oxygen contained in water is harmful from a corrosion standpoint, so it must be removed using a deaerator. Should.

For the purpose of increasing the reaction rate of formic acid oxidation reaction (1), it is preferable to use a solid formic acid decomposition catalyst as the filler.

Furthermore, the air brought into contact with the distillation column waste water (including decomposition reaction products, etc.) naturally contains steam ash water corresponding to the temperature thereof, and this may be recovered. Furthermore, in the packed column type apparatus of the present invention, depending on the reaction rate,
The decomposer may be increased by increasing the effective reaction time by circulation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus for producing make-up water for humidifying hydrocarbon gas for methanol synthesis according to the present invention will be described below with reference to FIGS. 1 to 4. □ [Example 1] Figure 1 shows an example of the device of the present invention, in which 1
is a decomposer (for formic acid), 2 is a packed bed filled with packing material, S
is the pump, 4 is the air column, 5 is the distillation column waste water supply fin,
6 is an air supply line, 7 is a vent gas discharge fin, 8 is a treated water discharge line, 9 is a treated water circulation line, 10 is a treated water fin, 11 is a Hiro heating medium supply twin, 12 is a degassing tower vent gas discharge fin, i3 is not shown This is the treated water supply line to the omitted humidifier.

The waste water discharged from the bottom of the distillation column (not shown) is fed to the fin 5.
It is fed into the decomposer 1 and flows down the packed bed 2. On the other hand, the air fed through the fins 6 below the packed bed 2 rises up the packed bed 2 and comes into contact with the gas and liquid in countercurrent flow.

This packed bed 2 is filled with a filler such as a Raschig ring or a Lessing ring. This filling is 810g,
k140B, Ti01. Fegog, Fe10
4. It is preferable that it contains either of the following, but it is not limited to this. Any material that accelerates the reaction of formula (1) may be used.

The formic acid-containing waste water from the distillation column that is dispersed and flowed down from the upper part of the packed bed 2 is oxidized by oxygen in the expanded air, causing the reaction of formula (1), but this packing accelerates the reaction rate (
catalytic effect).

The cracked gas generated by the reaction of equation (1) rises in the decomposer 1 together with air, and is discharged from the vent gas discharge fin 7 at the top of the decomposer. In this case, the air also functions as a carrier gas for transporting the decomposed gas.

If the reaction amount in equation (1) is small after passing through the packed bed 2 only once, and the formic acid concentration in the treated water from the treated water discharge line 8 does not decrease sufficiently, the treated water circulation twin 9 It is preferable to pass through the packed bed 2 multiple times.

The treated water with reduced formic acid concentration is sent to the deaerator 4 through the treated water line 10, heated by the heating medium supplied to the heating medium supply fins 11, and dissolved oxygen etc. in the water are removed through the pent gas discharge line 12. The water is released and transferred to a humidifier (not shown).

[Example 2] In Example 1, the distillation column waste water and air are brought into contact with each other in an alternating current, but as shown in FIG. 2, they may be brought into contact in a parallel current. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts as in FIG. 1, so the explanation will be omitted.

[Embodiment 3] In the embodiment shown in Embodiment 3, a heater 14 was provided in the treated water circulation line 9, and other aspects were the same as in Embodiment 1.

In the apparatus shown in FIG. 1, the vent gas and the steam equivalency corresponding to the temperature of the decomposer 10 and the vent gas discharge line 7 are
, O flows out. In other words, a temperature drop corresponding to the latent heat of vaporization of this outflowing water vapor occurs. In order to maintain this temperature at an appropriate level, this embodiment is provided with a stove heater 14.

Naturally, this heater can also be provided on the treated water circulation fins 9 of the apparatus shown in FIG.

[Embodiment 4] Fig. 4 shows that the packed bed 2 in the decomposer 1 is made into two stages, and the vent gas from the vent gas discharge line 7 of the decomposer 1 is cooled by the cooler 15 and condensed in the steam separator 16. This system separates water and vent gas and recovers the water. In Figure 4, 1 to 13 are the same as in Figure 1, 6! >, 1y is a vent gas discharge fin of the steam/water separator 16, and 18 is a condensed water discharge line of the separator 16.

FIG. 4 shows an example in which the vent gas discharge fins 12 from the degassing tower 4 are connected to the lower part of the filler 2 of the decomposer 1. The condensed water may be collected and collected independently from the vent gas.

〔Effect of the invention〕

In a methanol synthesis plant, in order to produce 111,000 tons of methanol, approximately 100 tons of fresh water (generally ion-exchanged pure water) is sent to a distillation column for extractive distillation, but this water is used as distillation column wastewater. becomes. This distillation column waste water can be used as make-up water for humidifying hydrocarbon gas for synthesis of large metatools according to the present invention, and its industrial effects are enormous.

[Brief explanation of drawings]

1 to 4 are diagrams for explaining the present invention in detail.

Claims (2)

[Claims] (1) For humidification of hydrocarbon gas for methanol synthesis, characterized in that it is equipped with means for supplying distillation column waste water discharged when crude methanol is distilled in a distillation column, and means for supplying air, and is filled with a filler inside. Makeup water production equipment. (2) The manufacturing apparatus according to claim (1), wherein the filler is a formic acid decomposition catalyst material.