JP3447408B2 - Crude oil desalination method - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a desalting method for removing salts and impurities such as NaCl and MgCl from crude oil before atmospheric distillation, and in particular, desalting for effectively removing chlorine content not forming an inorganic salt. Regarding the method.

[0002]

2. Description of the Related Art Crude oil contains water such as mud water and seawater, and therefore contains impurities such as sodium and magnesium chlorides. Such impurities cause corrosion of the distillation column or pollution of the heat exchanger in the oil refining process. Therefore, crude oil is often desalted before atmospheric distillation, which is the first distillation step of refining, to remove these impurities.

As a conventional desalting method, for example, the processes of Howe-Baker and Petreco are known. This involves adding wash water to crude oil and mixing it well to produce an emulsion in which salty water is dispersed in the crude oil. By applying an electric field to this in an electric deionization tank, the emulsion is aggregated / broken, and separated into a desalted crude oil layer and a drained wash water layer. At this time, the crude oil is heated to reduce its viscosity, thereby facilitating the mixing and separation with the wash water. If the emulsion remains in the crude oil, the desalination rate deteriorates, and therefore, an emulsion breaker or the like is used as necessary to accelerate the destruction of the emulsion. By such a process, a salt content of 5 lb salt / 1000 bbl crude oil or less can usually be achieved.

[0004]

However, even if the salt content is sufficiently reduced by the desalting treatment, a large amount of chlorine remains in the steps after the atmospheric distillation. Such residues may be particularly large depending on the origin and production time of crude oil.
Due to this residual chlorine content, corrosion of the upper part of the distillation column tower due to the generation of hydrogen chloride and clogging of the heat exchanger due to the precipitation of ammonium chloride, etc., are a major problem for stable operation of crude oil refining equipment and maintenance of equipment. Cause

The present invention solves the above problems and provides a desalting method for effectively removing the chlorine content remaining in crude oil that cannot be removed by the conventional desalination treatment.

[0006]

Means and Actions for Solving the Problems The present inventors have
Through intensive studies on the mechanism of chlorine content remaining in crude oil, it was found that there is chlorine content (hereinafter also referred to as "chlorine salt") remaining in crude oil that is difficult to extract in the wash water. The mechanism of this residue is not clear, but it binds to polar compounds such as basic nitrogen compounds such as quinolines and pyridines contained in crude oil. It seems that chlorine does not move. Then, as a result of examining the method of removing this "chlorine salt" in the desalting step, the present invention has been completed.

That is, in the method for desalinating crude oil according to the present invention, the chlorine content equivalent corresponding to the total content of alkali metals and alkaline earth metals contained in the crude oil is subtracted from the total chlorine content equivalent in the crude oil ( Hereinafter, the crude water is mixed with washing water containing 0.5 to 2.5 equivalents of an alkali compound (also referred to as metal salt non-forming chlorine equivalent) and separated into an oil layer and an aqueous layer to recover crude oil. The alkali compound of the washing water is alkali metal hydroxide, and the concentration thereof is 0.
001 to 0.01 it is an defined. Or crude oil
Equivalent total chlorine content and alkali metal content in the crude oil
And total alkaline earth metal content are analyzed, total chlorine content
Total content of alkali metal and alkaline earth metal from equivalent
Gold equivalent to the chlorine content equivalent
The chlorine equivalent of non-formation of metal salt is determined, and the chlorine equivalent of non-formation of metal salt is calculated.
Washing water containing 0.5 to 2.5 equivalents of an alkaline compound, and
Recover crude oil by mixing with crude oil and separating into oil layer and water layer
It is something.

The total chlorine content equivalent in crude oil can be optimally subjected to desalination treatment by analyzing the crude oil to be treated before desalting treatment and determining the value. As an analysis method,
Microcoulometric titration of hydrogen chloride generated by burning a sample, a combustion-microcoulometric titration method of measuring hydrogen chloride by ion chromatography, a combustion ion chromatography method, and the like can be used. In particular, the combustion-microcoulometric titration method is preferable because accurate and rapid analysis can be performed.

The main substances contained in crude oil as alkali metals and alkaline earth metals are Na, Mg and Ca. The analysis of alkali metals and alkaline earth metals can be performed with high accuracy by dissolving the ash produced by burning the sample and by ICP (high frequency inductively coupled plasma) emission spectrometry, atomic absorption spectrometry and the like. Usually, the analysis is performed for each refining treatment to calculate the metal salt-non-forming chlorine equivalent, but if it is predicted with sufficient accuracy depending on the crude oil producing place, etc., that value may be used.

By adding an alkaline compound in the range of 0.5 to 2.5 times the equivalent of chlorine without metal salt formation to the wash water, the chlorine content remaining in the crude oil moves to the wash water layer with high efficiency. The range is 0.75 to 2.2 times, and particularly preferably around 1.0 (0.8 to 1.5). As the alkali compound, hydroxides, carbonates and the like of alkali metal hydroxides, alkali metal carbonates, alkaline earth metal hydroxides, alkaline earth metal carbonates and the like can be used, but they are easily available and inexpensive. Preference is given to using alkali metal oxides, especially sodium hydroxide. In this case, the concentration of sodium hydroxide added to the wash water before mixing with the crude oil is 0.00 because the chlorine content remaining in the crude oil can be effectively reduced.
1 to 0.01 normal, especially about 0.005 normal (0.
002 to 0.007) is preferable. Deionized water and distilled water are preferable as the washing water, but they are expensive, so industrial water, tap water, and other process waste water can be practically used. The smaller the amount of impurities, the more preferable, and the one containing no chlorine ion is preferable.

After adding the above-mentioned washing water to the crude oil and mixing,
It is divided into crude oil desalted by phase separation in the desalting tank and drained wash water. Usually, in order to facilitate mixing and separation, crude oil is heated to 110 to 140 ° C. to reduce its viscosity. It is preferable to use the wash water in an amount of 5 to 10% by volume of the crude oil, and it is preferable to form an emulsion in order to increase the contact surface between the crude oil and the wash water during mixing. Further, at the time of phase separation, it is preferable that the emulsion is broken in order to prevent the emulsion from remaining in the crude oil and decreasing the desalination rate. In the desalination tank, it is preferable to apply a high electric field to break the emulsion and promote separation.
An emulsifier may be added.

[0012]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples. In the following examples, the total amount of chlorine contained in crude oil was measured by a combustion-microcoulometric titration method. In this method, a crude oil sample is burned in a closed tube, chlorine contained therein is converted into hydrogen chloride, and the resulting product is introduced into a coulometric titration cell to quantify the generated hydrogen chloride. The amounts of Na, Mg, and Ca contained in crude oil were determined by ICP (high frequency inductively coupled plasma) emission spectrometry. As a pretreatment, the ash obtained by burning the crude oil sample was dissolved in acid.

FIG. 1 shows a schematic flow of the desalting apparatus and the atmospheric distillation apparatus used in the examples. The crude oil is heated by the heat exchanger 1, mixed with washing water in the mixing valve 2, and then injected into the desalination tank 3. To wash water before mixing,
Sodium hydroxide solution is injected. In the desalination tank 3, it is divided into desalted crude oil (desalted crude oil) and washing water (washing drainage) which becomes waste water. The desalted crude oil extracted from the upper portion of the desalination tank 3 is heated in the heating furnace 4 and then supplied to the atmospheric distillation column 5. The cleaning wastewater extracted from the lower portion of the desalination tank 3 is treated as wastewater. In this example, the Middle Eastern crude oil with a total chlorine content of 14 ppm by weight was subjected to 85,000 BSD treatment, and 1% was used for desalting.
Heated to 30 ° C. As the wash water, 6% by volume of industrial water based on crude oil and distillate condensed water of an atmospheric distillation unit were used. The desalination tank 3 is a Howbaker type electric desalination tank, and a voltage of about 3 kV was applied to the electrodes in the tank.

FIG. 2 shows changes in the dechlorination rate with respect to the amount of NaOH added. The dechlorination rate was shown by the ratio of the total chlorine content after desalting contained in crude oil to the total chlorine content before desalination. The amount of NaOH added is the amount of NaOH added by the sodium hydroxide solution injected into the wash water, and is normalized by the amount of metal salt non-forming chlorine contained in the crude oil before desalting. This metal salt non-forming chlorine amount is the amount obtained by subtracting the chlorine content equivalent corresponding to the content of Na, Mg and Ca before desalting from the total chlorine amount before desalting. As is clear from FIG.
When the amount of NaOH added is 0.5 to 2.5, a dechlorination rate of 70% or more, and when it is 0.75 to 2.2, a dechlorination rate of 75% or more is obtained. ) Is preferable.

Before heating the desalted crude oil in the heating furnace 4, sodium hydroxide was further injected. This injection is
Suppress the generation of hydrogen chloride (HCl) in the atmospheric distillation column 5,
This is done to prevent corrosion around the atmospheric distillation column 5 and the like, especially around the top of the column. In this example, since the total amount of chlorine in the desalted crude oil supplied to the atmospheric distillation column 5 can be reduced,
You can reduce the injection of sodium hydroxide here,
It is possible to reduce the sodium content of the residual oil after the atmospheric distillation step.

In order to examine the dependence of the dechlorination rate on the NaOH concentration in the wash water, an extraction test was carried out when the NaOH concentration was changed. The change in the total chlorine amount after desalting depending on the number of extractions is shown in FIG. Extraction test method is 40m
1 l of crude oil, 10 ml of xylene, and 50 ml of an aqueous solution of sodium hydroxide were mixed and carried out at 83 ° C. by a lubricating oil anti-emulsification tester (JIS K 2520), and then the total chlorine concentration in the crude oil was measured. As can be seen from FIG.
Even if the OH concentration is increased, the total chlorine concentration remaining in the crude oil does not become sufficiently low, and if the concentration is 0.1 N or higher, the total chlorine concentration remaining in the crude oil is high, and the total chlorine concentration is 0.001-0.01 N. It can be seen that the residual concentration becomes low. Especially 0.005
It can be seen that the prescribed level (0.002-0.007) is preferable.

[0017]

As described above, the method for desalinating crude oil according to the present invention has a chlorine content equivalent corresponding to the total content of alkali metal and alkaline earth metal contained in the crude oil from the total chlorine content equivalent of the crude oil. mixing the wash water and raw oil containing 0.5 to 2.5 equivalent of an alkaline compound in an amount obtained by subtracting the state, and are not to recover the crude oil is separated into the oil layer and an aqueous layer, or
In addition, the total chlorine content equivalent in crude oil and the alkali contained in the crude oil
Analyze the total content of Li metal and alkaline earth metal,
Chlorine content equivalent to alkali metal and alkaline earth metal
Of chlorine content equivalent to the total content of
Corresponding metal salt non-forming chlorine equivalent is determined, and the metal salt non-forming salt is calculated.
Washing with 0.5 to 2.5 equivalents of alkaline compound
Purified water is mixed with the crude oil and separated into an oil layer and an aqueous layer to produce crude oil.
Is to be collected.

Therefore, the residual chlorine content can be reduced after the atmospheric distillation step, and it is difficult for corrosion of the distillation column and clogging of the heat exchanger to occur, so that the crude oil refining apparatus can be operated stably. There are few problems in equipment maintenance.

[Brief description of drawings]

FIG. 1 is a schematic flow diagram of a desalting apparatus and an atmospheric distillation apparatus used in Examples.

FIG. 2 is a graph showing changes in the dechlorination rate depending on the amount of NaOH added.

FIG. 3 is a diagram showing changes in the total chlorine amount after desalting according to the NaOH concentration.

[Explanation of symbols]

1 heat exchanger 2 mixing valves 3 desalination tank 4 heating furnace 5 Atmospheric pressure distillation column

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-132507 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C10G 19/00-19/08 C10G 31 / 00-31/11 C10G 33/00-33/08

Claims (2)

(57) [Claims] The method according to claim 1 Total chlorine content equivalent and the total content of alkali metals and alkaline earth metals contained in the raw oil in the crude
Analyze and analyze the total chlorine content equivalent from alkali metal and alkali
Subtract chlorine equivalent equivalent to total earth metal content
The equivalent amount of metal salt-free chlorine which has not been formed is calculated.
Washing water containing 0.5 to 2.5 equivalents of salt- free chlorine equivalents and the crude oil are mixed and separated into an oil layer and an aqueous layer to recover crude oil. Salt method. 2. The amount of chlorine contained in crude oil is calculated based on the total equivalent chlorine content of the crude oil.
Total content of alkali metal and alkaline earth metal
0.5-2. Of the amount obtained by subtracting the chlorine-containing equivalent corresponding to.
Mixing the crude oil with washing water containing 5 equivalents of an alkaline compound
Desalination of crude oil to recover crude oil by separating into oil layer and water layer
In the method, the alkali compound of the washing water is an alkali metal hydroxide, and the concentration thereof is 0.001 to 0.01.
A method for desalinating crude oil, characterized by being stipulated.