KR900005091B1 - Pyrolysis heater - Google Patents

Abstract

Pyrolysis heater for the pyrolysis of hydrocarbons comprises radiant heating chamber with tubular processing coils having first and second-half for processing fluid in heating chamber, plus radiant burners for heating the tubular processing coils, tubular processing coils within at least portion of the first half only, and extended heating surface for increasig the adsorption of radiant heat. The heating surface comprises heating surface attached to and extending outwardly from external surface of tubular processing coil.

Description

Pyrolysis heater

1 is a simplified schematic diagram of a thermal decomposition diagram applied to the present invention.

2 is a schematic diagram of a tube arrangement in one coil of a pyrolysis furnace applied in the present invention.

3 is an end view of a tube with studs of the present invention.

4 is a cross-sectional view of a tube having pins or ribs extending longitudinally around the inner circumference.

5 is a graph showing the form of temperature compared to the coil of the prior art compared to the coil of the prior art.

* Explanation of symbols for main parts of the drawings

11, 12: outer wall 13, 14: inner wall

15: end wall 16, 17: floor

20, 21: heating area 31, 32: traveling coil

46: line 46: first pass

47: 2nd pass 48: 3rd pass

51: 6th pass

Light olefins (ethylene, propylene, butadiene and butylenes) and related aromatics (benzene, toluene, ethylbenzene, coylene, styrene) products are usually carried out by thermal cracking of the hydrocarbon feed material in the presence of steam. This process is known as steam pyrolysis of hydrocarbons for the products of olephines.

The hydrocarbon feedstock is used as the product of certain bonds and olefins arranged from almost pure ethane to vacuum gas oil. Hydrogen and methane are impure in transport. The process consists of a pyrolysis portion and a recovery portion. Feedstocks, steam pyrolysis coils and agitators that preheat the system to cool the coil effluent are included in the pyrolysis portion of the plant. Many transfer preheating systems and pyrolysis coils are contained in pyrolysis furnaces or reactors. The chemical reaction of the process takes place in a pyrolysis coil without a catalyst.

About 30 to 40% of the total plant capital investment is required in the pyrolysis section. In addition, the economics of the process, i.e. feed material consumption and by-products made for the ethylene product, are determined by the design of the pyrolysis section. Thus, in practice, improvements in the design of the pyrolysis part of the plant have a dramatic effect on the economics of the steam pyrolysis process. The pyrolysis furnace consists of a convection part, a radiating part or any combination thereof. The hydrocarbon transfer is first preheated in the convection portion of the furnace. Dilution steam is then added and the steam hydrocarbon mixture is preheated in the mixed preheating coil of the convection portion. Dilution steam is then added and the steam hydrocarbon mixture is preheated in the mixed preheating coil of the convection portion. In some designs, the dilution vapor is preheated before it is added to the hydrocarbon. The mixture is preheated to the transition temperature which requires pyrolysis in the spinning part. The temperature is identified as the connection temperature between the convection and the radiating part. The temperature varies with the type of feed material and the particular coil design.

For the liquid hydrocarbon feedstock, the evaporation of the transfer takes place at the mixing preheating coil and / or the point where the dilute vapor is injected. In some designs, evaporation of the feed material is outside the convection portion coil to avoid potential coke storage. In addition, the boiler feed water, saturated steam and dilute steam are also heated in the convection section. It is noteworthy that the above description is typical. As with their position and size in the convection portion of the pyrolysis furnace, the requirements for heating repair described above are in accordance with the specifications of each plant requirement.

Pyrolysis coils in which hydrocarbon transfer is pyrolyzed in the presence of dilution steam are included in the pyrolysis furnace or in the radiated portion of the reactor. Many pyrolysis coils for the radiating part are a function of the required ethylene capacity for the pyrolysis furnace, the required pyrolysis yield, coil shape and dimensions, feed material type such as coil outlet pressure and terminal operating conditions. A transmission line exchanger, accompanied by direct quenching with oil, is used to cool the effluent from the coil. Fixed ethylene capacity for the furnace, pyrolysis yield, feed material form and terminal operating conditions, pyrolysis coils than those based on large diameter tubes. It is based on a diameter tube less than the capacity for the coil. Therefore, many pyrolysis coils for small diameter tubes required to meet a particular ethylene product for the furnace are much larger than coils for many required large diameter tubes.

It includes three basic forms implemented that are commonly used in the design of pyrolysis coils. The first version uses a small tube diameter (2.54-10.16 cm) as appropriate for a single tube for the pass and one or more passes for the pyrolysis coils 1-8. The second form also uses a large tube diameter for a single tube for the passage and several passes for the coils 2 to 12. The third form is a combination of small and large tube diameters (2.54 to 17.38 cm) and multiple tubes for passing towards the front end of the coil and several for single tubes and coils 2 to 12 for passing towards the rear end of the pyrolysis coil. Used as a combination of passes.

In the first two forms, the tube diameter increases from the first pass to the last pass of the pyrolysis coil or is constant through the coil.

The pyrolysis coil is located in the longitudinal plane at the radiating part of the pyrolysis furnace. Pyrolysis coils may be interlaced or placed in a single row or in a complex row. The radiant heat source is provided by igniting one of the burners both from the side wall of the radiating part or from their combination or the floor of the radiating part.

In the design for a single diameter tube through the coil, the ratio of metal surface to coil volume to passage remains constant from beginning to end of the pyrolysis coil. In this design, the axial temperature profile of the gas in response to the pyrolysis coil approaches a straight line with a positive gradient.

Pyrolysis coils with small diameter tubes have good heat transfer characteristics but due to the coke deposited on the inner wall of the coil during operation, due to the small capacity for the coils when comparing the two designs with each other due to the fast coke ratio to be observed during the cycle Increase the pressure drop in the coil. This increase has a detrimental effect on the pyrolysis yield produced by the first design mentioned above, which increases fuel oil by-products and decreases olefin output with a constant feed material converted at cycle time.

By increasing the diameter of the tube from the beginning to the end of the pyrolysis coil, the surface-to-volume ratio also decreases along the direction of flow in the pyrolysis coil. The larger tube diameter in the second half of the pyrolysis coil reduces the coke ratio and has a detrimental effect on the pyrolysis yield. Also, larger tubes ultimately result in larger capacity coils. However, the axial temperature profile of the reactant gas approaches the plus gradient in a straight line. A drawback of larger diameter tubes is lower heat transfer coefficients due to higher metal temperatures.

Since the surface for the volume ratio of the coil with the enlarged tube diameter towards the outlet is smaller than the coil with the constant diameter, the coil must be lengthened to obtain higher average ethylene product for the coil. Both coils will be designed to achieve essentially the same yield by trading increments within the residence time against a decrease in hydrocarbon partial pressure. The obvious limitation to the expansion of the tube diameter towards the outlet portion of the pyrolysis coil is that the coefficient of heat transfer is low, so for a given production the coefficient is inversely proportional to D ^1.8 with diameter D.

The ultimate goal is to reduce the number of coils required for the pyrolysis furnace to significantly increase the ethylene product for the pyrolysis coils in the form of an axial gas temperature that maximizes the use of the metal surface available in the pyrolysis coils. . In general, the target temperature form is reduced to concave and the first two coil designs mentioned above are either raised in the form of blocks or as close to the plus gradient as possible in the form of nearly straight lines. The isothermal axial gas temperature form represents the optimum heat utilization of the metal in the pyrolysis coil, i.e. the given output and working length, the maximum capacity for the unit weight of the pyrolysis coil metal, and the inexpensive pyrolysis coil.

One design approach would be to use local lighting where several partitions required the bulkhead of the firebox in. In addition, the ignition system will be properly controlled to achieve local ignition effects. The principle of operation after the design approach is to initiate the cycle in a concave or straight line with a temperature profile, either by varying the intensity of the ignition further towards the outlet portion of the pyrolysis coil or by constant ignition through the pyrolysis coil. Occurs during the progress of the ignition operation or during the coking of the coil and the ignition changes more intensely from the outlet portion of the coil to the inlet portion of the coil. Ultimately an axial temperature form that is rounded or concave towards the end of the cycle is used to operate the coil.

The approach of local ignition allows the use of higher capacities for the coils at constant operating times. However, this approach is not widely dealt with in the industrial production of ethylene, due to the structure of the firebox into the pyrolysis furnace and the complexity of the ignition control system. In addition, the metal in the pyrolysis coil will occur during a small amount of operating time when the temperature form is isothermal.

The three coil types mentioned above use a small diameter in the passage of the inlet portion of the coil, and a large diameter of a single tube in the passage of the outlet portion of the coil, which will be mentioned next. The design is often followed by a cast iron coil and the word is used in lan.

Fluor coil design approaches have been used in a number of world-class ethylene plants since the seventies. Instead of a complex firebox and complicated and expensive ignition control system, it relies on the coil geometry to get down the axial temperature gas form during the complete run time. Because of this effective use of metals in pyrolysis coils, the coils are characterized by greater production capacity at average yield and constant operating time. The cast iron coil has higher capacity and lower coke ratio due to longer operating time for the cycle.

The technical advantages of large diameter pyrolysis tubes at the outlet portion are worth more than having low heat transfer properties. The designer endeavors to improve the heat transfer rate at the insertion and / or installation studs or part of the pyrolysis coils inside the outlet tube and to compensate for this drawback by the installation of longitudinal pins on the outer wall of the outlet tube. However, thermal decomposition conditions become more intense in the last half of the coil. The coke forms prominently at this position of the coil during thermal decomposition of the feed material so that the coke precipitates on the inner wall of the pyrolysis tube. Coke precipitation should be responsible for the increase in metal temperature on the day of the flow. In the first half of the pyrolysis coil, coke formation is less than the next half of the coil due to the weak pyrolysis conditions. The increase in metal temperature due to coke deposition on the wall in the inlet region of the coil is appropriate.

Because of this property of the pyrolysis coil, an insertion located inside the outlet tube is expected to act as a nucleus for the growth of coke formed during pyrolysis. Thus, the use of inserts in this region results in shorter than the desired running length, higher than the desired pressure drop, and weakly operating the regeneration of conditions and losses that are important in olefin yield.

In principle, the equilibrium external heat transfer coefficient of the outlet tube is lower than the internal heat transfer coefficient, and attention is drawn to the use of a surface extending to the fin in the form of a stud or at the outlet portion of the coil. However, the use of an extended surface at the outlet position of the coil is not effective and the temperature of the stud or fin lip will limit the running length as a result of coke deposition on the inner wall of this portion of the pyrolysis coil.

The present invention relates to a surface extending on the inlet portion of a pyrolysis coil to produce an axial gas temperature form that is closer to an isothermal form than to achieve a constant ignition in a pyrolysis coil commonly used in the olefin production industry. will be. This allows for higher production capacity relative to the unit weight of the pyrolysis coil while maintaining the flow start time and the desired pyrolysis yield between cycles without coking. Conversely, constant ethylene production for pyrolysis coils in the present invention allows for longer flow start times and / or somewhat higher styrene yields. More specifically, the present invention involves the use of studs or longitudinal straight pins or ribs on either the outside or the inside or both positions of the tube and the position of the face extending in the first quarter and the first half of the coil. It includes.

According to FIG. 1, a vertical tubular pyrolysis heater supported on a structural steel bone, indicated by 10, is provided in FIG. The heater comprises an outer wall 11, 12, an inner wall 13, 14, an end wall 15, and a bottom 16, 17. The outer walls 11, 12 are substantially parallel to the inner walls 13, 14 and the height of the outer walls 11, 12 extending above the heights of the inner walls 913, 14. In the outer walls 11 and 12 and the inner walls 13 and 14, a plurality of vertical rows of high intensity radial burners indicated by 18 are provided. The bottoms 16, 17 extend between the outer walls 11, 12 and the inner walls 13, 14, respectively. The bottoms 16, 17 are provided in the bottom burner, indicated by the appropriate flame type 19.

The outer wall 11, the inner wall 13 and the bottom 16 together with the end wall 15 form a radiant heating zone indicated by 20, while the outer wall 12, the inner wall together with the end wall 15. 14 and bottom 17 form a second radiant heating zone, indicated 21. The end wall 15 is U-shaped converted by allowing the opening area 22 which allows the shaft to the burner 18 installed in the inner walls 13 and 14.

The inner roof 25 is horizontally positioned and installed on the inner walls 13 and 14. An upper roof 25 installed on the outer wall 11 and the end wall 15 is positioned horizontally inward from the outer wall 11 and extends. Similarly, the upper roof 27 extends inward from the outer wall 12 and is positioned horizontally and is installed on the outer wall 12 and the end wall 15. Top walls 28 and 29 are provided on the top walls 26 and 27, where the convection zone indicated by 30 forms the upper extension of the end wall 15. All walls, floors and roofs are of a suitable refractory material.

A plurality of vertical tube forming traveling coils 31, 32 are provided in the radiant heating zones 20, 21 suitably installed from the support structure 10 by a hanger 33. The traveling coils 31, 32 are positioned in the middle of the outer walls 11, 12 and the inner walls 13, 14, respectively. The formation of the traveling coil will be described in more detail later. Conduits arranged horizontally are provided in the convection zone 30. The conduit 35 is in fluid communication with the advancing coils 31, 32 via an intersection 36. Also located within the convection portion 30 is a second portion of the horizontally placed conduit, indicated 38. Inlet and outlet manifolds 38A, 38B are in fluid communication with conduit 38.

Burner 19 supplies fuel from line 40 through a plurality of manifolds 39. Fuel is introduced into manifold 39 through manifold 41 under control of valve 42. The flow of fuel into the burner 18 will change in the vertical row by the described violent ignition of the traveling coils 31, 32. Each burner will adjust the flow of total fuel by valve 44 in line 40 to a heater controlled by valve 45. It will be appreciated that the burners installed between the outer walls 11, 12 and the inner walls 13, 14 are similar to the manifold devices not shown. Similarly, line 46 delivers fuel to the bottom burner.

According to FIG. 2, it will be appreciated that the design of the traveling coil 31 is shown there schematically and that it is similar to the traveling coil 32. A general form of a pyrolysis heater is shown in US Patent Application Nos. 3, 274, 978. However, the present invention can be applied to pyrolysis heaters that can be installed in other forms of heaters commonly used in the industry.

According to FIG. 2, a schematic arrangement of the traveling coil 31 of the present invention is shown and it will be appreciated that it is similar to the traveling coil 32. The traveling coil 31 is in the form of the previously discussed form of wrought iron and includes the first pass 46, the second pass 47, the third pass 48, the fourth pass 49, the fifth pass 50, and the sixth pass. It consists of a path 51.

As can be seen, the first pass 46 comprises four tubes, and the second pass 47 and the third pass 48 each comprise two tubes. However, the coil is typical and does not limit the invention. The invention is applicable to pyrolysis heaters of any shape and tube dimensions.

The following table describes the details of the coil shape.

As depicted in FIG. 2, the extended heating surface 52 is positioned on the four tubes of the first pass 46. The extended heating surface may be in the form of studs or straight longitudinal pins or ribs. The studs may be cylindrical in any preferred form. The number and size of studs or fins per unit length of the pyrolysis tube will be chosen according to the progress parameters of the particular device. As an example, the stud will be 1.27 cm in diameter with a length in the range of 1.27 cm to 1.905 cm. They will be 8 to 12 studs around the circumference of the tube in any plane. 3 shows a short portion of the stud and the tube. The stud can be applied out of the tube. Straight cell pins or ribs are suitable for the inside of the tube. For example, the fin will be 0.58 cm in height with 6 to 10 fins around the circumference of the tube. 4 shows a cross section of a tube having straight longitudinal pins or ribs around their inner side. An extended heating surface is also installed in the first half of the pyrolysis coil, suitably in quarters. As pointed out, the embodiment shown in FIG. 2 has a stud in the first pass.

The effect of the extended heating surface on the first pass can be seen in FIG. 5 comparing a conventional temperature profile for a pyrolysis coil with the same coil with an extended heating surface. In FIG. 5 it can be seen that the temperature in the first part of the coil increases very much beyond the temperature in the conventional coil but the temperature in the outlet part has only a slight effect. For higher temperatures at the inlet section, thermal decomposition and coil capacity are increased without increasing the maximum outlet temperature or significantly increasing the temperature at the outlet section where coking occurs differently.

The following is a comparison of the calculated propagation characteristics of two different designs incorporating the present invention and conventional mold coil designs. In each case, the coil shape has four tubes in the first pass, two tubes in the second and third pass, and the fourth, fifth and sixth passes each have one tube. Have

Isothermal gas temperature configurations are preferred to make the most effective use of metal in the first half of the coil. Local ignition and the use of prior art form coil designs result in temperature forms close to isothermal. The use of the inner and / or outer extended heating surfaces of the present invention in the first half or quarter of the coil results in a temperature form close to isothermal. The use of an extended heating surface at the end of the coil is away from the isothermal form as well as the previously mentioned coke production. The use of an extended surface at the beginning of the coil is maintained or increased for the duration of the run or cycle time, increasing the ethylene capacity per weight of any combination of them and the tube metal, and selectively maintaining or increasing the thermal decomposition for the olefins.

In Figure 5, the temperature patterns appear very close to each other, but the temperature difference provided to the extended surface and the coil increases within a coil capacity of about 10%. Since the kinematic reaction rate changes exponentially in temperature, small differences in gas temperature have a significant effect on the pyrolysis reaction.

Claims (7)

A pyrolysis heater for pyrolysis of hydrocarbons, the method comprising: a) a heating chamber and b) at least one tubular running coil comprising first and second half for the traveling fluid in the heating chamber, c) A plurality of radiating burners for heating at least one tubular running coil, and d) at least one tubular running coil in a minimum portion of the first half includes an extended heating surface to increase adsorption of radiant heat. A pyrolysis heater characterized by the above-mentioned. The pyrolysis heater according to claim 1, wherein the extended heating surface comprises a heating surface extending and attached outward from an outer surface of the tubular traveling coil. The pyrolysis heater of claim 2 wherein the extended heating surface comprises a stud. The pyrolysis heater according to claim 1, wherein the extended heating surface includes a longitudinally extending heating surface extending and attached inwardly from an inner surface of the tubular traveling coil. 5. The pyrolysis heater according to claim 4, wherein the extended heating surface comprises straight vertical pins or ribs. The pyrolysis heater according to claim 1, wherein the extended heating surface is located in the first quarter of the traveling coil. The pyrolysis heater according to claim 1, wherein the extended heating surface is positioned on the first passage of the tubular traveling coil.

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