JPS60120788A - Corrosion-preventive operation of distilling tower of coal liquefying equipment - Google Patents

Abstract

PURPOSE:To remove corrosive substances and reduce the total amt. of a cleaning soln., by washing an oily substance obtained by hydrogenation of coal with an aqueous soln. of alkali before it is led into a distilling tower and washing an oil layer with water after separation of a water layer. CONSTITUTION:An oily substance obtained by hydrogenation of coal is washed by addition of an aqueoud soln. of alkali. The amt. of alkali is set at 1/3 equivalent or higher per equivalent of chlorine contained in the oily substance. After separation of a water layer, an oil layer is washed with water which is used in such an amt. that it makes the total of the water and the above-mentioned aqueous soln. of alkali 30vol% or lower of the volume of the oily substance. The two-step washing makes it possible to remove corrosive substances completely and reduce the total amt. of the cleaning solution including the alkaline water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for operating a distillation column in a coal liquefaction plant to prevent corrosion. In order to operate while preventing the introduction of corrosive substances as much as possible and preventing corrosion of the distillation column, the amount of washing water used is small and the removal rate of corrosive substances is as high as possible, thereby improving the distillation column. This relates to a method for completely preventing corrosion.

Various means and methods have been studied for coal liquefaction, but the method of adding a solvent and then carrying out the hydrogenation reaction is becoming mainstream. In this method, a hydrocarbon solvent is first added to coal powder such as lignite to form a slurry, which is hydrogenated in the presence of a hydrogenation catalyst, and then a raw material oil is obtained by performing treatments such as gas separation. Next, the raw material oil is introduced into a distillation column (atmospheric distillation column or vacuum distillation column), and is distilled and separated to obtain coal liquefied oil such as light oil or heavy oil, and a circulating solvent, respectively.

However, when the above-mentioned coal liquefaction equipment is operated for a long period of time, it is often the case that a portion of the distillation column in a specific temperature range (220 to 280° C.) corrodes and the distillation column must be repaired or rebuilt. This is thought to be caused by chlorine compounds (MgCl, CaCl2, etc.) contained as impurities in raw coal, and according to research in the United States, the corrosion mechanism is determined to be as follows. . That is, the chlorine compound undergoes hydrolysis during the hydrogenation reaction to generate hydrogen chloride. Most of this hydrogen chloride is separated and removed as a gas by decompression operation after the hydrogenation reaction, but some is absorbed into the amines contained in the raw oil and forms the hydrochloride of the amine and the liquid. It is said that it remains in the phase. The hydrochloride is then introduced into a distillation column together with the raw material oil, and heated to around 300° C. in the distillation column, causing thermal decomposition and separation into hydrogen chloride and amines. Hydrogen chloride and amines recombine at a relatively low temperature (220 to 280°C) location in the distillation column, and at the same time the amine condensation temperature (220 to 280°C)
It is believed that the amine hydrochloride condenses at a temperature of 20 to 280°C) and gradually accumulates and concentrates, corroding the inner wall of the distillation column.

Therefore, studies have been conducted to prevent the above-mentioned corrosion of the distillation column, and specific measures include (1) constructing the distillation column with highly corrosion-resistant materials such as stainless steel, Ni-Mo alloy, and Ti; (2) a method of neutralizing acidic substances by adding an alkaline agent such as soda carbonate into the raw material slurry or raw material oil; and (3) a method of washing the raw material oil with water before supplying it to the distillation column. However, method (1) has problems in terms of economy because highly corrosion-resistant materials are expensive, and method (2)
) method, corrosive substances (acidic substances) are neutralized and corrosion of the distillation column is prevented to some extent, but the neutralization product itself is not removed and is discharged from the distillation column along with heavy oil, etc. Not only can it corrode equipment in the refining process, but it can also cause contamination of heavy oil products.

Furthermore, in method (3), the acidic substances in the feedstock oil cannot be completely removed, so corrosion of the distillation column progresses, and a large amount of washing water must be used to remove the corrosive substances. Therefore, there is a problem that a large amount of cleaning wastewater is generated and the cost of wastewater treatment increases.

The present invention was made with attention to this situation, and in order to prevent corrosion of the distillation column, corrosive substances contained in the oily substance produced by the coal hydrogenation reaction are removed by washing with water. The purpose of the present invention is to provide a corrosion-protective operation method for a distillation column in a coal liquefaction unit f1y, in which corrosive substances can be almost completely removed by simply washing with a small amount of washing water.

Thus, the method for corrosion-proof operation of a distillation column of the present invention, which achieves the above object, is a method for corrosion-protection operation of a distillation column that distills and separates an oily substance obtained by a coal hydrogenation reaction, the oily substance being introduced into the distillation column. Before adding and mixing 1 equivalent or more of an alkali-containing aqueous solution to 1 equivalent of chlorine contained in the oil, and after separating the aqueous layer, the total amount with the alkali-containing aqueous solution is 30 volumes of the oil. The gist is that the oil layer is washed with water in an amount of i% or less.

That is, the method of the present invention basically attempts to wash and remove corrosive substances contained in the oily substance, but in the above-mentioned continuous distillation column, corrosive substances are formed at the top of the column due to long-term operation. Corrosive substances in the oil introduced into the distillation column must be washed out as completely as possible because of the accumulation of substances. However, corrosive substances in oily substances are thought to exist as amine hydrochlorides, which are basically water-soluble due to their molecular properties, but cannot be absorbed by amines in the presence of large amounts of amines. It is also oil-soluble when injected. Therefore, although it is possible to remove the hydrochloride to some extent by washing with washing water, it is difficult to completely remove it due to its oil solubility, and the amount of hydrochloride may substantially advance the corrosion of the distillation column. remain in the In addition, if we try to increase the removal rate of hydrochloride in order to suppress corrosion even to the slightest extent, a correspondingly large amount of washing water is required, and as a result, a considerable amount of cost is required to treat the washing wastewater. come.

Therefore, the inventors of the present invention have conducted repeated research on methods for cleaning corrosive substances, and as a result, they have arrived at the method of the present invention shown in the above configuration. That is, in the method of the present invention, first, an alkali-containing aqueous solution (hereinafter simply referred to as alkali aqueous solution) is added to the raw material oil.
Add and wash.

In the present invention, it has been found that the amount of alkali contained in the aqueous alkali solution must be 1/3 equivalent or more relative to 1 equivalent of chlorine contained in the oil.

If the amount of alkali is less than 1/3 equivalent, the removal rate of corrosive substances will be lowered, and a large amount of water will be required for subsequent cleaning, making it impossible to achieve the objective of reducing the amount of waste water for cleaning. On the other hand, there is no particular limit on the upper limit, but it is not preferable to add more than 2 equivalents to 1 equivalent of chlorine contained in the oil, as this will not only result in the alkali being used in vain, but also cause contamination of the oil by the alkali. . There are no particular restrictions on the type of alkali to be used, and examples include sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, ammonia, and the like.

After separating the oil layer and the water layer, the oil layer is washed with washing water in an amount such that the total amount with the alkaline aqueous solution is 30 volumes or less of the oil volume. In the present invention, the above sum is 30
It is unnecessary to use washing water that exceeds the capacity of water, and the burden on wastewater treatment equipment is approximately the same as that of the conventional method (3) [cleaning using only washing water], which defeats the purpose of implementing the present invention. . Note that the washing water does not have to be of particularly high quality, and for example, wastewater discharged from a coal liquefaction plant may be used.

By the two-stage cleaning described above, corrosive substances can be almost completely washed away, and the total amount of washing water including the alkaline aqueous solution and washing water can be kept to a small amount.

Although the reason why such outstanding effects are obtained in the present invention has not necessarily been clearly elucidated, it is presumed as follows. That is, first, an alkaline aqueous solution is added to the raw oil and washed to neutralize and separate the acidic group portion of the amine hydrochloride, which is a corrosive substance. The separation of corrosive substances at this stage is by neutralization, and since only the hydrochloric acid portion of the amine hydrochloride is separated from the oily substance, it is much more efficient than the water washing removal method, which separates the entire amine hydrochloride from the oily substance. Separation of corrosive substances is often carried out. Next, the remaining amine hydrochloride is separated and removed from the oil by adding washing water to the oil after separating the aqueous layer for washing. It is thought that this will increase the overall removal rate of corrosive substances.

When the raw oil is washed with an alkaline aqueous solution and the aqueous layer is separated, some alkali remains in the oil layer.
The alkali is also washed away by washing with washing water in the latter stage, and an oily substance having a high degree of cleanliness is obtained.

The present invention is constructed as described above, and the main part of the corrosive substances in the oil is removed by first washing the oil obtained by a coal hydrogenation reaction with an alkaline aqueous solution before introducing it into a distillation column. Furthermore, by washing the residual oil with washing water, the corrosive substances remaining in the oil can be almost completely removed, so corrosion of the oil distillation column can be almost completely eliminated. You can completely eliminate it.

In addition, although the removal rate of corrosive substances could be increased in this way, the total amount of alkaline aqueous solution and washing water was 30% of the oily substance capacity.
The capacity can be as small as less than 1, and wastewater treatment after cleaning can be done economically. Further, since the oil is neutralized with an aqueous alkali solution and then washed with washing water, no alkali remains in the oil, and clean coal liquefied oil can be obtained.

Next, the present invention will be explained in detail.

Experiment 1 Solvent used for slurry formation (0.8 in d) 11 to 0.
A strongly corrosive simulating liquid was prepared by adding 75% by weight (0,046 mol) of ayunone hydrochloride. After treating the steel under the following conditions, carbon steel and stainless steel (SUS316
) were introduced into the simulated distillation columns manufactured in Table 1 and the corrosion rate was measured. Corrosion could not be sufficiently prevented. Further, as shown in Nu 4 to 7, when cleaning was performed by increasing the number of times of cleaning with a small amount of water according to the cleaning theory, the corrosion rate was slightly slowed down, but a satisfactory corrosion prevention effect was not obtained.

On the other hand, as shown in N[18,9, when the method of the present invention was applied, a sufficient corrosion prevention effect could be obtained even with a small amount of cleaning liquid.

Experiment 2 Solvent used for slurry formation 11VcMgC]2 Aqueous solution was added and stirred, and water was distilled off by heating to prepare a strongly corrosive simulating solution [Chlorine content: 114 liters (0,032 m
olA) :]. After this was treated with the following properties, the corrosion rate was measured in the same manner as in Experiment 1, and the results shown in Table 2 were obtained.

Table 2 When cleaning was performed with only cleaning water, the corrosion prevention effect was not sufficient even if the amount of cleaning water was increased, as shown in Nn1l+12. On the other hand, as shown in Nn13+14, when the method of the present invention was used, a satisfactory corrosion prevention effect could be obtained even with a small amount of washing water.

Applicant: Kobe Steel, Ltd.

Claims (1)

[Claims] A corrosion prevention operation method for a distillation column that distills and separates an oily substance obtained by a coal hydrogenation reaction, wherein before introducing the oily substance into the distillation column, 1/1 of the amount of chlorine contained in the oily substance is
After adding and mixing an aqueous solution containing an alkali of 3 equivalents or more and separating the aqueous layer, the oil layer is washed with water in an amount such that the total amount with the aqueous alkali solution is 30 volumes or less of the volume of the oily substance. Corrosion prevention operation method for distillation column in coal liquefaction equipment.