JPS5826388B2 - Pyrolysis of hydrocarbons - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for thermally decomposing hydrocarbons in feedstock oil.

Conventionally, olefins such as ethylene and propylene have been produced by thermally decomposing light hydrocarbons such as natural gas, naphtha, kerosene, and gas oil using an externally heated tubular reaction tube.

On the other hand, in the case of heavy oils such as crude oil, atmospheric distillation residue oil, vacuum distillation residue oil, etc., if these are thermally decomposed in an externally heated tubular reaction tube, a large amount of coke is generated at that time, so the reaction tube
Cooling pipes etc. become blocked, making continuous operation impossible.

Therefore, when heavy oil is used as a raw material, it is not possible to use an externally heated tubular reaction tube, and other methods such as fluidized bed heat transfer method, moving bed heat transfer method, fluidized bed partial combustion method, gas heat transfer method are used. However, it has not yet been put into practical use as a method for thermally decomposing heavy oil.

Incidentally, although thermal decomposition of feedstock oil using an externally heated tubular reaction tube has the above-mentioned drawbacks, attempts to thermally decompose hydrocarbons using molten salt or molten metal as a heat medium have been proposed, for example, in Japanese Patent Publication No. 39-29824. Official Gazette, Special Publication No. 38-5656
No. 3,252,774 or US Pat. No. 3,252,774.

However, in these methods, the reaction heat necessary for thermal decomposition of hydrocarbons is provided by the sensible heat of molten salt or molten metal, so a large amount of high-temperature molten salt or molten metal is retained in the system. , which is unfavorable from a safety standpoint.

Furthermore, it is necessary to circulate a large amount of molten salt or molten metal between the reaction section and the regeneration section or the heating section, which poses difficulties in device design and operation.

Specifically, Japanese Patent Publication No. 47-19244, Japanese Patent Publication No. 50-8711, and Japanese Patent Publication No. 4941027 disclose measures to prevent coke from adhering to the inner walls of pyrolysis reaction tubes or indirect heat exchangers using molten metal. A method is disclosed.

However, these methods merely consider the wettability of the molten metal, the structure of the molten metal introduction part, and the material of the inner wall.
Moreover, although the amount of by-product coke varies depending on the type of feedstock hydrocarbon, the effective amount of molten metal etc. to be used is not specified, which is unfavorable from economical efficiency, operational performance, and safety points of view.

A basic object of the present invention is to provide a method for thermally decomposing feedstock oil containing hydrocarbons using an externally heated tubular reaction tube, which can be operated continuously without clogging due to adhesion of coke to the apparatus.

Another object of the present invention is to provide a method for thermal decomposition of hydrocarbons that is safe and easy to operate.

The above object of the present invention is to thermally decompose feedstock oil containing hydrocarbons through an externally heated reaction tube in the presence of steam and molten salt, in which the hydrocarbons, steam and molten salt flow in a circular flow or An annular spray flow is formed, and the total amount of raw material oil and steam sent into the reaction tube is 30
~140kg/@-sec, the steam/feedstock ratio is in the range of 0.5 to 2, and the amount of molten salt is 1 to 300 times the weight of Conradson residual carbon in the feedstock. This is achieved by thermal decomposition of hydrocarbons.

In addition, in carrying out the present invention, when the Conradson residual carbon in the feedstock oil is in the range of 0.5 to 3 wt%, the amount of molten salt fed into the reaction tube should be adjusted according to the Conradson residual carbon in the feedstock oil. The range is preferably 1 to 60 times equivalent weight, and when the Conradson residual carbon in the raw oil is 3 wt% or more, 1
A range of 20 to 20 times the weight is preferably used.

The raw material oil used in carrying out the present invention includes natural gas,
Examples include naphtha, kerosene, light oil, crude oil, atmospheric distillation residue oil, vacuum distillation residue oil, etc., but in the present invention, in particular, thermal decomposition of heavy oil such as crude oil, atmospheric distillation residue oil, vacuum distillation residue oil, etc. It is effective for

Further, as the molten salt used in carrying out the present invention, one or a mixed salt of two or more of oxides, hydroxides, and carbonates of alkali metals or alkaline earth metals can be used, and in particular, lithium carbonate, One or more mixed salts of alkali carbonates such as sodium carbonate and potassium carbonate, for example, equimolar mixed salts thereof, are effectively used.

Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram illustrating the process of thermally decomposing raw material oil using an externally heated tubular reaction tube to generate cracked gas containing olefins and the like.

First, raw oil and dilution steam are sent from pipes 5 and 6 to preheating pipes 2 and 3, preheated to a predetermined temperature, and then mixed.

On the other hand, the steam sent from the pipe 7 in the heating pipe 4 becomes superheated steam, and then mixed with the molten salt sent from the molten salt tank 12 by the pump 13, and guided to the mixing section 8.

In the mixing section 8, the raw material oil and diluted steam are sprayed from a nozzle into the mixture of heated steam and molten salt, and the raw material oil,
After the mixing of steam and molten salt is achieved, the decomposition reaction tube 1
will be introduced to

In the decomposition reaction tube 1, the feedstock oil undergoes thermal decomposition to produce cracked gas containing olefins and the like.

At this time, the mass velocity of the gas components of cracked gas and steam is 3
0 to 140 kg/771"-5 ec is preferable, and the amount of molten salt fed is 1 to 30 of the Conradson residual carbon in the feedstock oil.
The 0 times equivalent weight and the steam ratio (steam/raw oil) are used in the range of 0.5 to 2.

In the cracking reaction tube 1, the cracked gas and the gaseous components of the steam and the liquid components of the molten salt form an annular flow or an annular spray flow.

On the other hand, the coke generated during decomposition forms a liquid film on the reaction tube wall, and the flowing molten salt prevents it from adhering to the reaction tube wall. At the same time, the coke is steamed by the action of the water gasification reaction catalyst of the molten salt. It reacts with and is completely removed from the system.

The cracked gas, steam, and molten salt leaving the cracking reaction tube 1 are
After being rapidly cooled by the quencher 9 to a predetermined temperature higher than the melting point of the molten salt, it is sent to a gas-liquid separation device 10 such as a cyclone.

In the gas-liquid separator 10, gaseous components of cracked gas and steam are separated from molten salt, and the gaseous components are sent through a line 14 to subsequent separation and purification steps.

On the other hand, the molten salt passes through the connecting pipe 11 and passes through the molten salt tank 12.
The water is then collected into the mixing section 8 through the pump 13 and circulated again to the mixing section 8.

On the other hand, it is known that the amount of coke generated during thermal decomposition generally increases in proportion to the Conradson residual carbon contained in the feedstock oil.

Compared to when light oils such as naphtha, kerosene, and diesel oil are used as raw materials, a large amount of coke is generated when heavy oils such as crude oil, atmospheric distillation residue oil, and vacuum distillation residue oil are pyrolyzed as raw materials. This is due to an increase in the Conradson residual carbon content in the feedstock oil.

Therefore, during thermal decomposition, the amount of molten salt fed in order to prevent coke generated in the reaction tube from adhering to the reaction tube wall is preferably fed in accordance with the amount of coke generated.

That is, a large amount of molten salt is required for feedstock oil containing a large amount of Conradson residual carbon.

In carrying out the present invention, the amount of molten salt used is 1 to 300 times the weight of the Conradson residual carbon in the feedstock, and particularly 1 to 60 times the Conradson residual carbon in the feedstock oil. Equivalent weight, and Conradson residual carbon is 3w
When the amount is t% or more, it is preferable to use the amount equivalent to 1 to 20 times the weight.

If the amount of molten salt fed is insufficient, a sufficient effect of preventing the produced coke from adhering to the reaction tube wall cannot be expected, whereas if it is too large, it is not only uneconomical but also poses a safety problem.

The amount of molten salt actually fed into the reaction tube should be determined based on the correlation with the flow rate, physical properties, etc. of the gas component that should form the annular flow or annular spray flow. Based on Baker's phase diagram representing the flow state of a gas-liquid mixed flow in a horizontal pipe, Gaughlan's phase diagram representing the flow state of a gas-liquid mixed flow in a vertical pipe, and experiments conducted by the present inventors on water-air systems, etc., The mass velocity of the gas component of cracked gas and steam is 3
It has been found that an annular flow or annular spray flow is formed when the amount of molten salt fed into the reaction tube is 1 to 300 times the weight of the Conradson residual carbon in the feedstock oil at a rate of 0 to 14 okg and 7 m.sec.

At this time, the steam ratio (steam/raw oil) is 0.5 to 2.
The decomposition temperature is in the range of 700-900'C, preferably 750-8500'C.

Incidentally, in the present invention, the preferable amounts of molten salt fed depending on the raw materials are as follows.

Furthermore, the heat transfer test results for steam-molten salt gas-liquid multiphase flow are shown in FIG.

Here, the gas mass velocity (steam) is 34.5! 9/m
-3eC (750'C).

As is clear from FIG. 2, by introducing molten salt into steam, the heat transfer coefficient increases compared to the case of single-phase steam flow.

Also, for the same steam mass velocity, as the molten salt feed rate increases, the heat transfer coefficient also increases.

From the standpoint of heat transfer, it is more advantageous for the amount of molten salt fed into the reaction tube to be large in the annular flow or annular spray flow region.

However, considering the effect of molten salt on preventing coke from adhering to the reaction tube wall, economic efficiency, and safety, the amount of molten salt fed into the reaction tube should be determined based on the amount of Conradson residual carbon contained in the feedstock oil. It is more advantageous if the decision is made accordingly.

Possible methods for supplying the reaction heat necessary for thermal decomposition include a heat medium method, a high-temperature combustion exhaust gas method, and an external heating method, but the heat medium method has problems in safety and operability.

On the other hand, in the high-temperature combustion exhaust gas method, the feedstock oil comes into contact with the high-temperature gas, causing excessive thermal decomposition and generating a large amount of coke, which may not be effective in preventing molten salt from adhering to the reaction tube walls. .

External heating method can avoid excessive thermal decomposition as mentioned above.
Furthermore, the amount of molten salt retained can be significantly reduced compared to the heat transfer method.

In addition, as the molten salt, alkali metal carbonates and the like are used as mentioned above, but for example, Na2CO3- and 2CO
The major difference between using an equimolar mixed salt of 3-Li2CO3 and using the molten metal itself lies in the properties of the water gasification reaction catalyst.

In other words, the coke generated by thermal decomposition inside the reaction tube is decomposed by a liquid film of molten salt formed on the inner wall of the reaction tube.
At the same time, it prevents adhesion to the tube wall, and at the same time reacts with the steam flowing inside the reaction tube to generate hydrogen, carbon monoxide, and carbon dioxide, which are completely processed, thereby preventing coke generation in the quenching heat exchanger. This makes it possible to suppress heat recovery, facilitate heat recovery, and improve the properties of by-produced cracked oil.

According to the present invention, the molten salt forms a liquid film along the reaction tube wall, and the cracked gas and the gaseous components of the diluted steam flow through the liquid film, forming a so-called annular flow or annular spray flow, thereby causing coking problems. can be resolved.

In other words, the molten salt forms a liquid film along the reaction tube wall, which prevents coke generated during thermal decomposition from adhering to the reaction tube wall, and allows heat transfer to the reaction tube without clogging the reaction tube. Good continuous thermal decomposition is possible.

In addition, in the present invention, as described above, as a thermal decomposition method, an externally heated tubular reaction tube is used, and a predetermined amount of molten salt and steam are mixed into the reaction tube together with the raw material oil. By adjusting the flow rates of the gas and liquid components, it became possible to produce olefins such as ethylene and propylene through thermal decomposition using an externally heated tubular reaction tube, which had previously been considered difficult with heavy oil. .

Hereinafter, the specific content of the present invention will be explained with reference to Examples.

Example 1 A thermal decomposition experiment was conducted for the purpose of producing olefins using Minas gas oil as a raw material oil.

The raw material oil is sent from the pipe 5 to the preheating pipe 2 which is externally heated by a heater at a supply rate of 15 kg/H.
Preheated to 0°C.

Further, the diluted steam introduced from the tube 6 into the preheating tube 3 which was externally heated by a heater at a supply rate of 2 kg/H became 300° C. steam and was then premixed with the preheated raw material oil.

On the other hand, the 10 kg/H steam supplied from the tube 7 to the heating tube 4 which is externally heated by the heater is 750°C.
After becoming superheated steam, Na 2 C is pumped from the molten salt tank 12 by the pump 13 at lkp/H.
Os-K2COs-Ll2COs was mixed with a melt of the equimolar mixed salt and introduced into the mixing section 8.

At this time, the temperature of the molten salt was 500°C. In the mixing section 8, the premixed raw material oil and steam are blown into the mixture of molten salt and superheated steam through a rough nozzle with an inner diameter of 6. After the raw material oil, steam, and molten salt are mixed, the cracking reaction tube 1 was introduced to.

The decomposition reaction tube 1 is a vertical tube with an inner diameter of 1,671 mm and is externally heated by a heater.

The raw material oil is thermally decomposed in the decomposition reaction tube 1, and the raw cracked gas, steam, and molten salt are rapidly cooled to 550°C by a quench cooler 9, and further, the cracked gas, steam, and molten salt are separated by a cyclone 10. It was done.

The cracked gas and steam pass through the transfer line 14,
The steam was condensed in the cooler and separated from the cracked gases.

The cracked gas was then measured using a gas meter, and its composition was analyzed using gas chromatography.

On the other hand, the molten salt passes from the cyclone 10 through the connecting pipe 11,
It was introduced into the molten salt tank 12 and further sent to the mixing section 8 by the pump 13.

The operating conditions and cracked gas composition are as follows.

The operation was carried out continuously for 150 hours, but no increase in pressure loss inside the reaction tube was observed during the operation, and as a result of the disassembly inspection after the operation was completed, coke was found on the cracking reaction tube wall, quencher, cyclone, and transfer line. No adhesion was observed at all.

(4) Operating conditions Feedstock Minas gas oil Conradson residual carbon in feedstock 0.03wt% Feedstock supply amount
15kg/H dilution steam supply amount
2kg/H superheated steam supply amount 1
0ky/H Molten salt circulation amount 1kg/
H Raw material oil preheating temperature 300℃ dilution steam preheating temperature 300℃ superheating steam temperature
750°C molten salt temperature
500'C decomposition temperature 7
50℃ quenching temperature 550℃ (B
) Cracking gas composition (wt% feedstock oil basis) H21,3 CH48,9 C2H420,8 C2H63,8 C3H,12,9 C3H80゛4 C,+C310,2 C00,2 C024,7 Example 2 Minas crude oil as feedstock Thermal decomposition experiments were carried out for the purpose of producing olefins.

The experimental equipment and flow were the same as in Example 1.

The operating conditions and cracked gas composition are shown below.

Operating conditions Feedstock Conradson residual carbon in Minas crude feedstock 22wt% Feedstock supply amount
15kg/H dilution steam supply amount
3kg/H superheated steam supply amount 12g/H molten salt circulation amount 15kg/H Raw material oil preheating temperature 300℃ dilution steam preheating temperature 300℃ superheated steam temperature
750'C molten salt temperature
500'C decomposition temperature 750
°C quenching temperature 550 °C (B
) Cracking gas group Jff (wt% raw oil standard) H22,
4 CH412,0 C2H426,8 C2H63,5 C3H612,3 C3H80,5 C4+ C58,4 C01,4 CO213,6 The operation was performed continuously for 200 hours, but no increase in pressure loss in the decomposition reaction tube was observed during the operation. There wasn't.

Furthermore, as a result of an overhaul inspection after the completion of operation, no coke accumulation was observed in the cracking reaction tube, quench cooler, cyclone, or transfer line.

Comparative Example 1 A thermal decomposition experiment of Minas crude oil was conducted by discontinuing the feeding of molten salt into the decomposition reaction tube.

The operating conditions were the same as in Example 2, except that the molten salt was not fed into the decomposition reaction tube.

Thirty minutes after the start of operation, the pressure loss inside the decomposition reaction tube began to rise, and after one hour, it became impossible to continue operation.

Upon completion of the operation, an open inspection revealed that a large amount of coke had adhered to the cracking reaction tube wall, and only a few cavities were observed in the cracking reaction tube.

A large amount of coke was also found in the quencher, cyclone, and transfer line.

Comparative Example 2 A thermal decomposition experiment of Minas crude oil was conducted with a molten salt circulation rate of 0.15 kg/H.

The operating conditions are the same as in Example 2 except for the amount of molten salt circulated.

One hour after the start of operation, the pressure loss inside the decomposition reaction tube began to rise, and after 10 hours, it became impossible to continue operation.

After the operation was completed, an open inspection revealed that a large amount of coke was generated in the cracking reaction tube, quench cooler, cyclone, and transfer line.

Example 3 A pyrolysis experiment was conducted for the purpose of producing olefins using Arabian Light vacuum residual oil as a raw material oil.

The experimental equipment and flow are the same as in Example 1.2.

The operating conditions and cracked gas composition are shown below.

(4) Operating conditions Feedstock Arabian Light vacuum residue Conradson residual carbon in feedstock 20.8wt% Feedstock feed rate
15kg/H dilution steam supply amount
6 kg/H superheated steam supply amount
12kg/H Molten salt circulation amount 30kg
/H Raw material oil preheating temperature 300'C diluted steam preheating temperature 300'C superheated steam temperature 7500C molten salt temperature
500°C decomposition temperature
750℃ quenching temperature 550
°C (B) Cracking gas composition (wt% feedstock oil basis) H23
,I CH49,I C2H415,0 C2H62,2 C3H67,9 C3H80,3 C4+C55,6 C02,I C0217,8 The operation was carried out continuously for 160 hours, but no increase in pressure loss inside the decomposition reaction tube was observed during the operation. Ta.

Furthermore, as a result of a disassembly inspection conducted after the completion of operation, no coke accumulation was observed in the cracking reaction tube, quench cooler, cyclone, or transfer line.

The following table summarizes the main points of Examples 1.2.3 and further shows the Conradson residual carbon and heat transfer coefficient.

[Brief explanation of the drawing]

FIG. 1 is a system diagram illustrating an embodiment of the present invention in which feedstock oil is thermally decomposed using an externally heated tubular reaction tube to generate cracked gas. FIG. 2 shows the results of a heat transfer test for a steam-molten salt gas-liquid mixed flow, and is a diagram showing the relationship between the heat transfer coefficient and the mass velocity of salt/mass velocity of gas. 1... Decomposition reaction tube, 2... (raw oil) preheating tube, 3...
...(steam) preheating tube, 4...(superheated steam) heating tube, 5...tube, 6...tube, 7...tube, 8...
Mixing section, 9... Rapid cooler, 10... Gas-liquid separation device, 1
1... Connecting pipe, 12... Molten salt tank, 13...
(molten salt) pump, 14... line.

Claims (1)

[Claims] 1. When pyrolyzing feedstock oil containing hydrocarbons through an externally heated reaction tube in the presence of steam and molten salt,
The hydrocarbons, steam, and molten salt form an annular flow or annular spray flow in the reaction tube, and the total amount of raw material oil and steam fed into the reaction tube is 30 to 140 kg/d.
-8eC, the steam/feedstock oil ratio is in the range of 0.5 to 2, and the amount of molten salt is 1 to 300 times the weight of Conradson residual carbon in the feedstock. Pyrolysis method. 2 Conradson residual carbon in feedstock oil is 0.5-3wt
%, and the amount of molten salt fed into the reaction tube is 1 to 60 times the weight of Conradson residual carbon in the feedstock oil. 3 Conradson residual carbon in the feedstock oil is 3 wt% or more, and the amount of molten salt fed into the reaction tube is equivalent to 1 to 20 times the weight of Conradson residual carbon in the feedstock oil, Claim 1 The pyrolysis method described in.