SU1613481A1 - Oven for thermal decomposition of gaseous of liquid hydrocarbons - Google Patents

Abstract

Apparatus characterised in that it comprises: (a) a distributor connected to the feed block by a conduit, and to the upper entry orifices of the group of cracking reactors by entry pipes, the interior of these entry pipes being in communication with the free space between the outer and inner pipes of one of the reactors, (b) a manifold connected to a heat exchanger by an exit conduit, and to the upper exit orifices of the group of reactors by exit pipes, the interior of these pipes being in communication with the interior of the inner pipe of one of the reactors, (c) the invention relates to an apparatus for cracking gaseous or liquid hydrocarbons. <IMAGE>

Description

The invention relates to a furnace for the thermal decomposition of a hydrocarbon gas, gas or liquid at normal temperature. The furnace is intended for the process of thermal pyrolysis of hydrocarbons, carried out at relatively high reaction temperatures and with a very short residence time in process tubes for the production of lower olefins, primarily ethylene, or for further hydrocarbons with practical application.

The process of thermal pyrolysis of gaseous or liquid hydrocarbons with a boiling point of up to 360 ° C, as a rule, takes place in the presence of dilution steam in tube furnaces at a temperature of 700-850 ° C and a corresponding retention time of the raw material in the furnace in 0.3-1 sec. The reaction space is in these furnaces, usually a vertical tubular coil, either single or branched, which is heated by radiation heat emitted by flameless burners located in the walls or in the bottom or ceiling of the reaction chamber of the furnace. The inner diameter of the tubular coil is usually in the range of 75-160 mm, the total length of the coil corresponds to the range of 45-120 m.

Flue gases from the radiation chamber enter the convection section, 1 de their heat energy is used to evaporate and preheat the hydrocarbon feedstock, to superheat the dilution steam, or to preheat the combustion air or feed water for high pressure heat exchangers or boilers, in which it is utilized

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the heat of the exhaust gaseous reaction product, i.e. pyrogas to produce high pressure steam or to superheat said steam. The pyrolysis gas - then the pyrogas, immediately after leaving the tubular coils, should be sharply cooled below the critical temperature, i.e. below 600 ° C in order to prevent the occurrence of undesired secondary reactions reducing the yield of the main product. The indicated quench cooling, i.e. Quench is achieved in some of the known types of high-pressure heat exchangers, where pyrolysis gas heat is used to generate steam with a pressure of 12-15 MPa, which can be used, for example, to drive turbo-compressors in the process of low-temperature fractionation of gaseous pyrolysis products.

The main disadvantages of tube furnaces used in the industry are, first of all, that tube coils are very dissected with a large number of bends with fittings and profits that can only be made by static casting, as a result of which they inevitably turn out to be thick-walled, due to which there is no only the total mass of the tubular coil, but also the investment, since high-alloy heat-resistant steels are mainly used for the production of tubular coils.

Significant disadvantages of tube furnaces are that they do not provide the required pre-sets for pyrolysis with a reaction time less than 0.3 s, and therefore they are not able to fulfill the requirements of modern worlds aimed at increasing the production capacity of the furnace and the output of ethylene due to the reaction temperature. while reducing the residence time of the reaction mixture in the reaction tubes.

Known types of tube furnaces proposed for ultrashort or millisecond pyrolysis processes consist of a bundle of straight, upright tubes of relatively small diameter (single hord tubes) passing through the radiosyunniy section only in one passage and directly attached to the own cooling section created , for example, by means of doubled, duplicated cooled pipes, through the cooling jacket of which the cooling medium flows, in most cases water or a steam gauge, and the molten metal ( the Soviet Union № 867922, cl. C 10 G 9/10, 1979).

It is also known a solution in which separate reacting pipes are created to have double pipes (a pipe system in a pipe), the upper end of which is removed from the radiation chamber, and in the space above it or next to it smoothly passes into the heat exchange part. In order to reduce the height of the furnace, the duplicate pipe in the heat exchange part is designed as a twin double pipe, equipped with nozzles for supplying preheated raw material in the outer shell of the double pipe and fittings for the output of the cooled pyrolysis gas in the inner part of the double pipe (patent Czechoslovakia 219211, cl. C 10 G 9/20, 1982).

In order to save high-alloy steels, double pipe can be made from a greater number of sections that will be made from steels with different content of alloyed impurities. Only the section of the outer pipe that is subjected to maximum thermal loads in the radiation zone is manufactured from high-alloy steel.

The savings of capital investments are also considerable, arising from the fact that, with the same cross-sectional area and the same power, the height of the furnace according to the invention decreases

by about 1/3. Due to the fact that the maintenance of the stove is considerably simplified, other things, the operating costs are saved by approximately 25%.

The advantages of the last described arrangement include the fact that favorable conditions have been created for the evaporation and preheating of the hydrocarbon feedstock entering the reaction, namely when using

both the heat of the flue gases leaving off and the heat of reaction of the exhausted hot pyrolysis gas. Thus, the furnace is not limited to only one type of raw material, is universal in nature and can process both gaseous and liquid hydrocarbon raw materials without any structural changes. There is only a change in the technological parameters, for example, the volume of injected CF, its share

in relation to the diluent steam and the inlet temperature or the mixture with the steam.

The pyrolysis furnace of this invention proceeds from the advantage of the last described layout solution, further improving its functionality while eliminating some disadvantages, such as the complexity and laboriousness of the heat exchanger part of the individual reaction parts, elements, i.e. double pipes, and further, among other things, is characterized by an excessively long pipe length and mass due to the gas-gas heat exchange parameters. The total mass of the heat-exchanging part of double pipes in this way often goes out more than the mass of the heat exchanger itself. Also unfavorable

surface temperature distribution along the length of the pipe at which the maximum temperature occurs at the places of maximum mechanical stresses, and moreover unfavorable

This is the temperature profile along the length of the reactor.

A pyrolysis oven of constructional design according to the invention, the reaction elements of which are made

as double pipes, drawn from the upper end of the radiation chamber or chambers, wherein it is characterized by the fact that the inner pipes of the double pipes are connected directly or through

connecting pipes to a minimum of one outlet manifold, which is connected to the inlet of a suitable heat exchanger to use the waste heat, while the outer pipes of double pipes are connected to a minimum of one inlet manifold that is connected to the outlet of the convective section through an inlet pipe. This results in an arrangement in which the reactant mixture is fed into the outer tube and the mixture is reacted out of the inner tube of the linear reaction tube, which improves the heat exchange conditions. This makes it possible to terminate the process of splitting the reaction mixture in the inner tube.

In order to equalize the possible pressure losses that occur in pipes (double pipes) as a result of contamination of pipe walls with coke or inaccuracies in pipe production, it is possible to insert throttle elements, for example, a throttle washer or valve, into some inlet pipelines. This measure will make it possible to achieve that the pressure drop at the inlet pipe is equal to or greater than the pressure loss in the reaction tubes, thereby ensuring uniform distribution of the flux into all the tubes.

The same effect can be obtained with another alternative PII- NII, when the throttle element is replaced by a configuration in which at least part of the length of the inlet pipelines is filled with a narrowed section.

The main advantages of the pyrolysis furnace layout, apart from the high degree of splitting of the raw material while maintaining the reaction time in the inner tube before starting its own cooling in the high-pressure utilization heat exchanger, include the simplicity of the design, as well as the relatively low labor intensity and reduced production costs associated with it. The advantage is also an increase in the equipment's long-term duration, which results from the more favorable temperature characteristics of the heating surfaces.

Since the overall layout of the proposed furnace approaches the layout of the tube furnaces, it makes it possible to quite simply apply the invention in the processes of reconstruction or modernization of existing pyrolysis furnaces with the aim of significantly increasing the yield of olefins while at the same time significantly improving the efficiency of the process. At the same time, the investment economy is very favorably influenced by the fact that the steel supporting structure, convective sections, and above all, the high-pressure steam production unit remain almost unchanged during renovations.

I From the point of view of cost savings, it can be stated that the main positive contribution of the proposed pyrolysis furnace is that good prerequisites have been created for the evaporation and preheating of hydrocarbon feedstock fed into the reaction in order to achieve the shortest possible residence time of the feedstock in the reaction pipes, lower pressure loss, greater depth of use of raw materials, a long working cycle, which is the result of a low degree of contamination of pipes with coke and fast cooling the product of the pyrolysis while maintaining the cleavage path in the inner pipe-pipe system i.e. double pipe.

Figure 1 shows a vertical section through a pyrolysis furnace with one radiation chamber, a high pressure heat exchanger located above the radiation chamber and with a non-axially located convection section; figure 2 is a vertical section of one double pipe; on fig.Z - section aa on figure 2 (double pipe).

The proposed furnace consists of a radiation chamber 1 of rectangular cross section, on the side walls of which there are flareless radiation burners 2. On the longitudinal axis of the radiation chamber 1 in the same row are reaction tubes 3 and 4, the upper part of which is removed from the radiation chamber 1. Flue gases transferring a part of their heat to raw materials flowing in pipes 3 and 4 are removed from the upper part of the radiation chamber 1 with a rather high enthalpy in

convection section 5. Here, the remaining heat energy of the flue gases is utilized in section 6 for heating feedwater, section 7 for preheating the hydrocarbon feedstock fed to the reaction and section 8 for heating the mixture of preheated raw materials and diluted steam. The nutrient medium, hydrocarbon feedstock and its mixture with dilution steam flow in the tubes of the convection sections in countercurrent to the flue gases that leave the convective part through the chimney 9.

A preheated mixture of hydrocarbon gas and dilution steam from convection section 8 is fed to one of several 10 inlet manifolds, from which it is fed through inlet pipe 11 to the upper parts of double pipes 3 and 4. The number of inlet collectors 10 is selected depending on the number of convection strokes . The fresh mixture enters the annular space between the outer tube 3 and the inner tube 4 and passes through this space in a downward direction, and at the same time it is heated both by the radiation heat emitted by the wall-mounted burners 2 and by the heat of the reacted pyrolysis gas flowing in countercurrent through the inner tube 4 to the temperature at which the splitting of hydrocarbons occurs. When passing from i of the outer tube 3 to the inner tube 4, the reactive mixture is rotated by means of the device 12.

The reacted pyrolysis gas, partially cooled already, in the radiation space of the pyrolysis furnace with a countercurrent relatively cold mixture entering the reaction, leaves the inner tube 4 through its outlet part 13, which is outside the radiation chamber 1 and directly brought to the output collector 14. When contact with a relatively cold raw material supplied by the inlet pipe 11 to the outer pipe 3, further cooling of the pyrolysis gas occurs up to a temperature of less than 750 C. Cooling eff kt fresh mixture fed to the output 13 of the pipe system nestable amplified ohlgik- dagatsim Niemi affect surrounding environment.

Partially cooled pyrogas comes from the output collector 14 to the corresponding utilization heat exchanger 15, where it gives its thermal energy to the steam-and-water mixture supplied to the heat exchanger 15 from the cold branch

Q steam drum 16, fed by water, preheated in the convection section 6. The number of output collectors is determined by the number of process tubes and the number of heat exchangers. The high-pressure steam absorbed in the heat exchanger 15 along the hot branch of the (steam) steam drum 16 is discharged for further use. The cooled pyrolysis gas that leaves the pipe

the space of the heat exchanger 15 is supplied for further processing or for subsequent cooling in irrigation refrigerators, where it cools for 5 s in direct contact with the cooling oil.

The method of circulating the reaction mixture in the reaction tubes 3 and 4, the creation and function of the device 12 for turning the flow, as well as the method of tangential exit of the inlet pipeline 11 to the housing of the outer tube 3 are well understood from FIG. The cross section of the pipe shows the location

. centering partitions 17, which are not shown in FIG. 2 in order to achieve greater consistency. Centering partitions 17, for example, can be performed as a single or multi-pass,

0 crimped or unscalable screw elements, the screw rise along the length of the mixture flow can vary in a straight line Depending on the temperature of the flowing reaction mixture.

5 Two examples of a specific solution of the pyrolysis furnace according to the invention are given together with the calculated values of the operating parameters.

Example 1. A model device was made and tested with the ability to process up to 100 kgch of raw materials at a reaction time of 1 s. The device consists of a reactor tube in a tube, the outer tube has a diameter of 57x5 mm, the inner tube has a diameter of 3 x x x mm. The length of both pipes is (v- 6000 mm. A mixture of raw materials and steam with a temperature of 500-650 seconds in the upper part of the double pipe is introduced into the annular

the space through which flows downward, and is heated to a controlled, controlled temperature, at which the raw material splits into a mixture of hydrocarbons, after which the working medium through the inner tube is discharged into the outlet pipeline, heating is fresh in the annular space .

Outer diameter

tubes57x5 mm

Diameter of internal 30x3 mm

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Max. 100 KHZ 0.5-07 from raw materials

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her pipe

Raw material consumption

Steam consumption

Temperature

mixtures at the inlet of 500-650 С

Temperature

turn the device into j mixes

Neither flow 820-920 С

Outputs 11-13 wt.X CH4

25-34 Mac.Z p. 25 14-17 wt.X

Raw Gasoline Exposure Time 0.1 s

Example 2. Radiation amer with a capacity of 11200 kgh as a raw material — gasoline feedstock with a distillation interval of 50–180 ° C. Was chosen as an example of potential operational equipment. J

Outer diameter

pipes102 mm

Diameter of an internal pipe is 60 mm

Pipe length c. 40

Hume radiation zone

Number of pipes

in radiation

camera 32 pcs.

Raw material consumption 45

through one pipe 350 kgch

Raw material consumption

in radiation |

camera 11200 kgch

JQ steam consumption

one tube 175

Steam consumption in

radio radar

5600 kgch camera

Normative theme- ,,

Pyrolysis temperature880 С

Temperature

raw materials at the entrance

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to the convection section 6O with the temperature of the mixture at the outlet of the convection section 620 with the temperature of the pyrolysis gas at the exit from

heat exchanger 350-450 С Temperature of gases at the exit from the furnace space

Flue gas temperature in chimney 190 С Excess air 1,, 1 Temperature of pyrolysis gas at the exit from the reaction element

Fuel consumption 1380 kgch Teplova kiln capacity19.1 MW

Heat consumption of radiation 8.4 MW When solving the problems of designing new Lirolysis furnaces using reaction elements, it is possible to adapt the performance of the entire furnace in a wide range by selecting the required number of reaction elements, i.e. reaction tubes through a pipe system in a pipe in a radiation chamber. You can change the overall layout of the radiation furnace, as well as the distribution and layout of the convective section or sections.

The reaction tube can be made from a larger number of sections with different steel grades differing in different content of alloying additives.

It is recognized as an invention according to the results of the examination carried out by the Office for Invention of CSFR.

Claims (3)

1. A furnace for the thermal decomposition of gaseous or liquid hydrocarbons, containing one or more radiation chambers with vertical reaction tubes connected to one or more heat recovery heat exchangers located above 1-161 a radiation chamber or adjacent thereto, and a convection section connected to the pipe for exhausting flue gases from the radiation chamber or chambers, the reaction tubes being filled out from the outer and inner pipes in the type of pipe in the pipe, the upper ends of which are removed from the radiation chamber or chambers, characterized in that, in order to increase the efficiency of the process, the outer tubes of the reaction tubes are connected to the tubes of the convection section by means of an inlet tube The lecturer and the inlet pipes and the inner pipes of the reaction pipes are connected to the inlet of the heat exchanger by means of the inlet manifold and connecting pipes. 2. Furnace according to claim 1, characterized in that one or several inlet pipelines are provided throttle valves 3. Furnace according to claim 1, characterized in that one or several inlet pipelines for part of the length are made with a narrowed section. .G 72 WITH fl-fl TA Phage.Z