JPS5826389B2 - Hydrocarbon pyrolysis method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for thermally decomposing hydrocarbons using molten salt and steam for the purpose of producing lower olefins such as ethylene and propylene.

When producing lower olefins by cracking ethane, naphtha, etc., these raw material hydrocarbons are mixed with steam and fed into a cracking furnace reaction tube.

This mixed fluid is heated and heated by a plurality of burners installed on the wall of the cracking furnace, and is decomposed into gas rich in lower olefin components.

The cracked gas coming out of the cracking furnace reaction tube is quenched in a quenching heat exchanger to suppress undesirable reactions such as polymerization.

One drawback of such equipment is that tar substances, coke, etc., which are by-products during the thermal decomposition of feedstock hydrocarbons, adhere to the cracking furnace reaction tube, the quenching heat exchanger heat transfer tube, and the piping that connects them, a so-called coking phenomenon. wake up

Therefore, if the equipment is operated for a long period of time, they will accumulate on the tube walls, which will increase the tube wall temperature of the cracking furnace reaction tubes and quench heat exchanger heat transfer tubes, increase pressure loss, and reduce heat transfer efficiency. .

For this reason, it is necessary to periodically stop the feedstock hydrocarbon supply and perform operations to remove adhering substances, but when using raw materials containing heavy fractions such as crude oil, heavy oil, and asphalt as the feedstock hydrocarbon. However, in comparison with light hydrocarbon raw materials such as ethane and naphtha, a large amount of deposits such as tar and coke are produced as by-products, making long-term operation of the equipment completely impossible.

Therefore, when using raw materials containing these heavy fractions, in order to suppress or prevent the adhesion of tar substances, coke, etc. in cracking furnace reaction tubes, quenching heat exchanger heat transfer tubes, etc., molten salt should be used as raw material hydrocarbon. There is a method of mixing it with water vapor, decomposing it, and rapidly cooling it.

However, in this method some of the deposited substances, especially coke, are mixed into the molten salt.

It is desirable to circulate and use the molten salt repeatedly, but in the case of long-term continuous operation, the proportion of coke in the molten salt increases, resulting in an increase in viscosity and melting point, making it impossible to circulate and use the molten salt. There are drawbacks.

When the molten salt is an alkali or alkaline earth metal molten salt, it has a strong catalytic effect for so-called water gasification, in which by-product coke and water vapor react, and light hydrocarbons such as ethane and naphtha are used as raw materials. In this case, even if coke is mixed into the molten salt, the amount of by-product coke is small, so
By circulating the coke in the cracking furnace reaction tube, it is possible to treat the coke mixed in the molten salt in the water gasification reaction, but when heavy oil is used as a raw material, there is a large amount of by-product coke, so the amount of coke in the molten salt is Coke accumulates.

Therefore, in this case, the molten salt must be passed through a quenching heat exchanger, separated from cracked gas and steam, and then treated in a separate molten salt coke treatment device.

The present invention provides hydrocarbon heat that can completely treat coke mixed into molten salt when producing lower olefins from hydrocarbons using molten salt and steam without separately installing a special coke treatment equipment. A decomposition method and apparatus are provided.

Other objects of the invention will become apparent from the description below.

The present invention has the following configuration.

That is, the hydrocarbon pyrolysis method of the present invention includes a heating section that heats a mixed fluid of steam and molten salt, and a raw material hydrocarbon mixed with the mixed fluid of steam and molten salt discharged from the heating section, which is then heated to carbonize the raw material. Using a cracking furnace that has a reaction section that thermally decomposes hydrogen, the coke that accumulates in the molten salt is gasified and removed in the heating section before it is fused with the raw material hydrocarbon, and this mixed fluid is further processed into the raw material in the reaction section. This method is characterized by thermally decomposing raw material hydrocarbons mixed with hydrocarbons in a cracking furnace reaction tube.

In addition, the hydrocarbon pyrolysis apparatus of the present invention includes a heating section that heats a mixed fluid of steam and molten salt, a raw material hydrocarbon mixed with the mixed fluid of steam and molten salt discharged from the heating section, and heated. a cracking furnace having a reaction section for thermally decomposing hydrocarbons; a heat exchanger for rapidly cooling a mixed fluid of cracked gas, geothermal decomposition products thereof, steam, and molten salt discharged from the cracking furnace;
and a separator for separating molten salt from the mixed fluid coming out of the heat exchanger.The molten salt separated by the separator can be mixed with steam and circulated to the heating section of the cracking furnace. This is a hydrocarbon pyrolysis device that is characterized by the following.

Furthermore, in the apparatus of the present invention, the reaction section of the cracking furnace is composed of a tubular reaction tube, and the reaction tube is decomposed into any path and the flow rate control is capable of controlling the supply of raw material hydrocarbon to the reaction tube of any path. A device can be provided, and the raw material searching section of the reaction tube of the cracking reaction section can be changed depending on the properties of the raw material hydrocarbon.

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

The figure is a system diagram for explaining one embodiment of the present invention.

First, the raw material hydrocarbon is preheated to about 400° C. in the convection section 18 of the cracking furnace 1, accompanied by atomized steam from the pipe 8 to the pipe 9, and sent to the reaction tube 12 of the reaction section.

Further, the diluted steam is similarly preheated to about 400° C. or higher in the convection section 18 from the pipe 7 and sent to the mixing section 15 with the molten salt.

On the other hand, the molten salt is sent from the tank 4 by the pump 5 through the molten salt transport vibro to the mixing section 15, where it is mixed with preheated diluted steam in the mixing section, and reacted in the reaction tube 12 in the sub-side section 17 of the cracking furnace 1. The coke introduced into the reaction tube 12 from the tube port 20 and mixed in the molten salt is converted into water gas.

In addition, the preheated raw material hydrocarbon and the sprayed steam sent from the pipes 8 and 9 are transferred from the reaction tube raw material inlet section 21 to the reaction tube 1.
2, where it is mixed with the molten salt and the water-gasified gaseous substance, and thermal decomposition of the feedstock hydrocarbon is carried out there.

The reaction temperature is preferably 700 to 850°C.

The reaction tube 12 is heated by using fuel sent from the pipe 10 and combusted in the burner 11, and combustion waste gas is extracted from the waste gas outlet 19 of the cracking furnace 1.

The cracked gas etc. that exited the reaction tube 12 are immediately led to the quenching heat exchanger 2 and cooled to 350°C in order to suppress secondary reactions of the cracked gas.
It is cooled to a temperature of ~650°C.

Boiler water is fed into the heat exchanger 2 from a pipe 13, and high pressure steam generated here is extracted from a pipe 14 for heat recovery.

The mixture of cracked gas and molten salt is then led to a molten salt separator 3, where the molten salt is separated from the cracked gas.

The cracked gas is extracted from the pipe 16 and guided to a cracked gas purification process, and the molten salt is led to the tank 4 and recycled while containing coke produced by the thermal decomposition.

Further, the diameter of the reaction tube 12 is preferably 1/2 to 8 inches, particularly preferably 2 to 6 inches.

The length of the reaction tube 12 is arbitrarily determined depending on the amount of heat supplied from the burner, the residence time of the cracked gas in the reaction tube, the amount of coke mixed into the molten salt, etc.

Feedstock hydrocarbons used in the practice of this invention include naphtha,
There are kerosene, light oil, crude oil, heavy oil, asphalt, etc., and the apparatus of the present invention is particularly effective for raw materials containing heavy fractions such as crude oil and heavy asphalt.

The molten salt used in carrying out the present invention may be any salt as long as it has the above-mentioned functions, but for example, alkali metal or alkaline earth metal salts, particularly carbonates, are preferably used.

Examples of alkali metal carbonates include lithium carbonate, sodium carbonate, and potassium carbonate, and in the present invention, two or more of them may be used as a mixed salt.

Next, the features of the present invention will be explained.

In the present invention, the molten salt separated from the cracked gas and steam in the molten salt separator is directly guided to the reaction tube of the cracking furnace by a pump, and is heated in the presence of steam for about 50 to The temperature is raised to 900°C to turn the coke in the molten salt into water gas.

In other words, a part of the reaction tube of the cracking furnace is used as a coke regeneration system to gasify and remove coke.

The water gasification reaction here is an endothermic reaction. C+H20→ CO+H2 It is indicated by.

The mixed fluid here is further mixed with the raw material hydrocarbon, and the raw material hydrocarbon is thermally cracked in the cracking furnace reaction tube.

Therefore, in the present invention, there is no need to separately install a molten salt regeneration reaction tank, and furthermore, if the operation is temporarily stopped while supplying steam and molten salt while temporarily stopping the feedstock hydrocarbon supply, the cracking furnace reaction tube It is also possible to remove coke adhering to the quenching heat exchanger heat exchanger tubes, connecting pipes, etc. without turning off the burner of the cracking furnace.

For example, in the case of a cracking furnace with an annual production capacity of 30,000 tons of ethylene, the reaction tube is divided into 8 to 12 passes, although this varies depending on the raw material properties and cracking conditions.

Therefore, if the feedstock hydrocarbon supply to one pass is stopped and the operation is continued while supplying to the other pass, the ethylene production amount per unit time will decrease by 1/8 to 1/12. Therefore, the decrease in ethylene production for the entire plant will be very small.

A method is adopted in which the supply of raw material hydrocarbon is temporarily stopped for each group of reaction tubes connected to the quenching heat exchanger.

Furthermore, the amount of by-product coke varies depending on the properties of the raw material hydrocarbon, and the amount of coke mixed into the molten salt also varies.

Therefore, any feedstock can be treated by changing the feed position of the feedstock hydrocarbon into the reaction tube, and no separate coke treatment equipment is required.

For example, in the above-mentioned drawing, the length of the reaction tube population 20 of the reaction tube 12 and the length of the reaction tube raw material inlet section 21 are made relatively small to process raw materials containing light fractions with a small amount of coke by-product, and By making the length relatively long, it is possible to process raw materials containing heavy fractions with a large amount of coke by-product.

In carrying out the present invention, it is possible to divide the reaction tube into arbitrary passes and provide an arbitrary flow rate control device capable of controlling the supply of raw material hydrocarbons to the reaction tubes of arbitrary passes, thereby controlling the decomposition reaction. The position of the raw material feeding part of the reaction tube can be changed depending on the properties of the raw material hydrocarbon.

According to the present invention, by-product coke can be treated without installing a separate reaction tank for molten salt regeneration, decomposition treatment is possible even if the raw materials have different types and properties, and operation and management are easy. Coke removal is possible without significantly reducing olefin production.

[Brief explanation of the drawing]

The figure is a system diagram explaining one embodiment of the present invention. 1... Decomposition furnace, 2... Rapid cooling heat exchanger,
3... Molten salt separator, 4...-tank,
5...pump, 6...--pipe, 7...
...pifumi 8...pipe, 9...
・・・Pipe) 10・・・Pipe, 11・・・・・・
・Burner 12...-Reaction tube, 13...
Pipe, 14...Pipe, 15...Mixing section, 16...Pipe, 17...Sub-side section, 18...Convection section , 19... Waste gas outlet, 20... Reaction tube inlet, 21... Reaction tube raw material feeding section.

Claims (1)

[Claims] 1. A heating section that heats a mixed fluid of steam and molten salt, and a raw material hydrocarbon mixed with the mixed fluid of steam and molten salt discharged from the heating section, which is then heated to thermally decompose the raw material hydrocarbon. The coke accumulated in the molten salt is gasified and removed in the heating section before it comes into contact with the feedstock hydrocarbon, and this mixed fluid is further mixed with the feedstock hydrocarbon in the reaction section. A hydrocarbon thermal decomposition method characterized by thermally decomposing raw material hydrocarbons in a cracking furnace reaction tube. 2. A heating section that heats a fluid mixture of steam and molten salt, and a reaction section that mixes raw material hydrocarbons into the fluid mixture of steam and molten salts emitted from the heating section and heats it to thermally decompose the raw material hydrocarbons. a cracking furnace, a heat exchanger that rapidly cools a mixed fluid of cracked gas, its geothermal decomposition products, steam, and molten salt that comes out of the cracking furnace, and a separator that separates the molten salt from the mixed fluid that comes out of the heat exchanger. 1. A hydrocarbon pyrolysis apparatus basically consisting of the following, characterized in that the molten salt separated in the separator can be mixed with steam and circulated and supplied to the heating section of the cracking furnace. 3 The reaction part of the decomposition furnace consists of a tubular reaction tube,
3. The apparatus according to claim 2, further comprising a flow rate control device capable of dividing the reaction tube into arbitrary paths and controlling the supply of raw material hydrocarbon to the reaction tube of the arbitrary paths.