CN1015469B - Pyrolysis heater - Google Patents

Abstract

The first half and preferably only the first quarter of a pyrolysis coil for treating hydrocarbons is provided with extended heating surface for increasing the adsorption of radiant heat. The extended heating surface may be on the inside or the outside of the tubes and may be in the form of studes or fins or ribs.

Description

Pyrolysis heater

The aromatic hydrocarbons (benzene, toluene, ethylbenzene, dimethylbenzene and vinylbenzene) of unsaturated olefin (ethene, propylene, divinyl and butylene) and association normally obtains the raw material hydrocarbon thermo-cracking under the situation of injecting steam.The method that adopts the steam pyrolysis hydro carbons in order to produce alkene is well-known.

The scope of hydrocarbon feed family that is used to produce alkene is from being that pure ethane is to vacuum gas oil and their any one mixture substantially.Hydrogen and methane are impurities in raw materials.This production process comprises pyrolysis step and recycling step.In the pyrolysis workshop section of device, comprise raw material preheating system, steam pyrolysis coil pipe and be used for the heat exchanger of flow in the spiral coil cooling tube.The major portion and the pyrolysis coil pipe of raw material preheating system have been installed in pyrolyzer or reactor.Chemical reaction in this process is to take place in the pyrolysis coil pipe under the situation of catalyzer not having.

The consumption that is used for pyrolysis workshop section accounts for 30% to 40% of whole plant investment greatly.And, the economy of technology, promptly raw material consumption and the production byproduct that a certain amount of ethene produced are limited by the equipment of pyrolysis workshop section.Therefore, traditionally the improvement of pyrolysis workshop section in the device has been improved significantly the economy of pyrolytic process.

Pyrolyzer is by convection zone and radiation section or their arbitrary combination and constitute.Hydrocarbon raw material preheating in the convection zone of stove earlier adds dilution steam generation then, and hydro carbons and steam mixture be further preheating in the mixing preheat coil of convection zone.In some device, dilution steam generation also will be preheated before it is added hydrocarbon feed stream, up to mixture being preheating in radiation section till the needed transition temperature of pyrolysis, this temperature is identical with the temperature of the intersection between convection zone and the radiation section, and it becomes with raw material type and special coil arrangement.

Make raw material with liquid hydrocarbon, raw material will evaporate in mixing preheat coil and/or in dilution steam generation injection place.In some device, for avoiding coking, raw material evaporated before entering the convection zone coil pipe.In addition, also can be to boiler water supply, saturation steam and dilution steam generation heating in convection zone.Should be noted that this description only is general description.Above-mentioned required heating installation, and their residing position and sizes on the convection zone of pyrolyzer are according to the concrete needs of each device and fixed.

The pyrolysis coil pipe is installed in the radiation section of pyrolyzer or reactor, hydrocarbon raw material pyrolysis within it under with the situation of dilution steam generation.The pyrolysis coil pipe number of each radiation section becomes as the coil pipe top hole pressure with pyrolysis rate, coil arrangement, size, raw material type and the terminal operating status of every needed ethene amount of pyrolyzer, hope.The transfer tube heat exchanger is added with the direct chilling of oil, is used to cooling effusive fluid in the coil pipe.For nominal ethene amount, pyrolysis rate, pyrolyzer that raw material type is identical with terminal operating status, the coil pipe made from narrow tube is littler than the coil pipe throughput made from large diameter pipe.Therefore, in order to obtain certain ethene amount, the pyrolysis coil pipe number made from narrow tube is more than the coil pipe number with the large diameter pipe coiling.

At present, employed coil pipe has three kinds of base types on pyrolyzer.A kind of is with little pipe to medium caliber (1～4 inch), and every path is with a pipe, and each coil pipe has one or several path (1 to 8).Second type is to adopt large diameter pipe (4 to 7 inches), and every path is similarly a pipe, and each coil pipe has several paths (2 to 12).The third type is that narrow tube and large diameter pipe are mixed use (1-7 inch), and every path of pyrolysis coil pipe front end is the multitube road, and every path is an one-pipe in its back-end, and each coil pipe has several paths (2 to 12).

It should be noted that first and second type, the caliber of whole coil pipe can be a constant, or is routed to the final common path caliber from first and increases gradually.

The pyrolysis coil pipe is arranged in the fore-and-aft plane of pyrolyzer radiation section, and the pyrolysis coil pipe can staggered arrangement, perhaps is arranged to single row or multiple rows.By means of the burner on the radiation section side wall, or the burner of radiation section bottom (siege), or the combination of side wall and base burning device provides radiant heat energy.

Can find out significantly that every via metal surface-area of coil pipe made from same diameter tube and the ratio of coil pipe volume all keep constant from the initiating terminal of pyrolysis coil pipe to end.In this structure, the approaching straight line of temperature distribution history that pyrolysis coil pipe reaction gases is axial with positive slope.

The pyrolysis coil pipe made from narrow tube, although have heat transfer property preferably, but compare with other two types coil pipe, the throughput of its each coil pipe is less, because it is very fast in the coking speed that cycle period measures, and in operational process, owing to coking on the coil pipe inwall causes the coil pipe internal pressure increase is fallen.And the increase that pressure falls is to the pyrolysis rate of above-mentioned first kind of structure unfavorable (under the material quantity situation identical with working time, reduced olefin yield and increased the fuel oil byproduct).

Enlarge gradually to exit end from inlet end by the caliber that makes the pyrolysis coil pipe, the ratio of its metal surface area and volume reduces gradually along the flow direction of pyrolysis coil pipe inner fluid.Latter half caliber at the pyrolysis coil pipe is bigger, thereby coking speed reduces, and has reduced the influence that coking is fallen coil pipe pressure, and the disadvantageous effect to pyrolysis rate also reduces thereupon.Certainly, thicker pipe finally also makes the throughput of coil pipe increase.The axial temperature distribution curve of reactant gases still approaches to have the straight line of positive slope.The defective of big caliber is that heat transfer coefficient is lower, thereby metallic surface temperature is higher.

Owing to export ratio that caliber becomes big its surface-area of coil pipe and volume gradually from entering the mouth to less than the surface-area of constant caliber coil pipe and the ratio of volume, in order to make every coil pipe higher average ethylene output is arranged, coil pipe must extend.Can become obtain identical substantially output to two kinds of coil design by prolonging the residence time with the method that prevents the hydrocarbon partial pressure minimizing.For the pyrolysis coil pipe that increases from the exit diameter that enters the mouth, a significant disadvantages is that heat transfer coefficient is less, because flow is certain, and heat transfer coefficient and D ^1.8Be inversely proportional to, herein, D is a diameter.

In order to increase the ethylene yield of each pyrolysis coil pipe effectively, thereby reduce required coil pipe number in every pyrolyzer, main target should be to improve the axial gas temperature distribution, as much as possible to utilize available metallic surface on the pyrolysis coil pipe.In general, wish to have recessed temperature distribution history, and as far as possible near isothermal curve, rather than the line of collimation of positive slope, perhaps aforesaid preceding two kinds of coil arrangements resulting " convex " temperature distribution history.Isothermal axial gas temperature distribution history has represented to utilize best the heat of pyrolysis coil pipe metal, just for given output and length of run, and the volume maximum of pyrolysis coil pipe metallic flat weight, thereby the pyrolysis coil pipe is the most cheap.

A kind of design concept is to use and is separated into several spatial combustion zone, and firing system must be subjected to suitable control and reach the combustion zone effect.By this method of design, by heat supply equably on whole pyrolysis coil pipe, perhaps increase heat supply intensity gradually towards pyrolysis coil pipe exit, make beginning with straight line or " convex " temperature distribution history operation operation.Little by little, in operational process or when coking takes place in the coil pipe, make heat supply intensity from the coil pipe exit higher transfer in the coil pipe ingress higher.Best, last to round-robin, coil pipe is pressed isothermal or the operation of recessed axial temperature distribution curve.

This class combustion zone can utilize the bigger throughput of each coil pipe at constant in working time.Because the structure of pyrolyzer combustion chamber and combustion control system are all complicated, this method is not widely used in the industrial production of ethene.In addition, it should be noted that to have only when temperature distribution history during near isothermal curve, the metal of pyrolysis coil pipe just can make full use of, and in this class formation, only appearance waits temperature state in partial operating time.

The third coil pipe that the front was once mentioned will be discussed below, and promptly the inlet part path at coil pipe adopts many parallel thin diameter tube, and adopts the major diameter single tube at coil pipe escape passage place.This structure is referred to as " swaged forging formula (Swage) " coil pipe usually, has used " swaged forging formula " this term here.

From the worldwide most of ethylene units of the seventies, adopt " swaged forging formula " coil pipe, and do not adopted baroque combustion chamber and very complicated and expensive combustion control system.This " swaged forging formula " coil pipe relies on the structure of coil pipe can obtain recessed axial temperature distribution curve in the whole service time.Because effectively utilized the metal of pyrolysis coil pipe, the characteristics of this coil pipe are to have bigger throughput in working time at identical average pyrolysis rate and constant." swaged forging formula " coil pipe has bigger throughput and lower coking rate, thereby each round-robin is longer working time.

Outlet section surpasses the relatively poor shortcoming of its heat transfer characteristic with major diameter thermal decomposition tube superiority technically.The planner once attempted by insert being installed in outlet pipe and/or at the outlet pipe outer wall thermal conductivity that column or longitudinal rib improve pyrolysis coil pipe outlet section being installed, with the little defective of compensation heat transfer coefficient.The pyrolysis situation is more violent at the latter half of coil pipe.In the raw material pyrolytic process, the coke showed increased that the coil pipe latter half forms, and be deposited on the inwall of thermal decomposition tube.This coking phenomenon causes going into operation several days metal temperatures with regard to rising.Because pyrolysis coil pipe first half degree of pyrolysis is lighter, the coke growing amount is wanted much less than coil pipe latter half in the inlet region, therefore, in the inlet region of coil pipe, is moderate because of coking on wall causes the rising of metal temperature.

Because the characteristic of above-mentioned pyrolysis coil pipe wishes to be arranged in the insertion body of outlet pipe at the centronucleus of pyrolytic process for the increase of formation coke.Like this, employing is inserted its length of run of body than expecting that length of run is short in this district, and pressure falls bigger than what expect, condition of reproduction variation, and olefin yield obviously reduces.

In principle,, it should be noted that and utilize enlarged surface, promptly column or fin are set in the coil pipe exit portion thereby make because equivalence heat transfer coefficient in the outside of outlet pipe is lower than inboard heat transfer coefficient.Because coking on the inwall of this part causes the tip temperature of column or fin to limit length of run, therefore utilize the column enlarged surface not have effect in the coil pipe exit.

What the present invention relates to is that inlet part at the pyrolysis coil pipe is provided with enlarged surface, so as to make the axial gas temperature distribution history than at present in the alkene industrial production temperature distribution history that adopted, that even distribution heating reached in the pyrolysis coil pipe more near thermoisopleth.So just make that the throughput of pyrolysis coil pipe unit weight is higher, and can keep the pyrolysis rate of hope, and prolong the production time between the decoking twice.Each coil pipe of the present invention can prolong production time and/or improve ethylene yield slightly under the situation of identical ethylene yield conversely speaking.The present invention also proposes the forebody at coil pipe particularly, and preferably preceding 1/4th zones of coil pipe are provided with enlarged surface, and preferably uses column or vertically straight fin keel or rib, and they are installed in the medial and lateral of pipe inboard or the pipe outside or pipe.

Fig. 1 is the rough schematic view of pyrolyzer of the present invention;

Fig. 2 is that the pipe of one group of coil pipe of pyrolyzer of the present invention is arranged synoptic diagram;

Fig. 3 represents to have a bit of pipe of column of the present invention;

Fig. 4 illustrates the cross section that has the pipe of vertical fin keel or rib in pipe on week;

Fig. 5 is the temperature distribution history of existing coil pipe and the comparison of temperature distribution history of the present invention.

With reference to figure 1, the invention provides a vertical cast pyrolyzer, it is supported on the steel structure frame 10.Pyrolyzer is made up of outer wall 11 and 12, inwall 13 and 14, end wall 15 and furnace bottom 16 and 17.Outer wall 11 and 12 is arranged essentially parallel to inwall 13 and 14, and outer wall 11 and 12 height surpass the height of inwall 13 and 14.The high-level radiation pipe burner 18 of some arranged verticals be installed in outer wall 11 and 12 and inwall 13 and 14 on.Furnace bottom 16 and 17 is in respectively between outer wall 11,12 and the inwall 13,14.Furnace bottom 16 and 17 is equipped with base burning device 19, and burner 19 is flame type preferably.

Outer wall 11, inwall 13, furnace bottom 16 and end wall 15 constitute radiation heating district 20.Outer wall 12, inwall 14, furnace bottom 17 and end wall 15 constitute second radiation heating district 21.End wall 15 is inverted U-shaped, thereby forms an open region 22, can axially be installed in burner 18 on inwall 13 and 14.

Interior furnace roof 25 flatly is arranged on inwall 13 and 14.Last furnace roof 26 flatly extends internally from outer wall 11, and is arranged on outer wall 11 and the end wall 15.Equally, last furnace roof 27 flatly extends internally from outer wall 12, and is arranged on outer wall 12 and the end wall 15.Being positioned on furnace roof 26 and 27 is upper wall 28 and 29, and upper wall 28,29 and end wall 15 stretch upwards part and form convective region 30.All walls, the end and top all are to build up with suitable refractory materials.

Be equiped with many vertical coil pipes in radiation heating district 20 and 21, they form handles coil pipe 31 and 32, and coil pipe 31 and 32 suitably is installed on the supporting structure 10 by suspension hook 33.Handling coil pipe 31 and 32 is arranged in the middle of outer wall and inwall 11 and 13 and 12 and 14.These structure formations of handling coil pipe will be done more detailed description in the back.Being installed in the convective region 30 is horizontally disposed pipeline, has schematically made expression on the figure, and label is 35.Pipeline 35 links to each other with the processing coil pipe by transition conduit 36, and fluid flows through within it.Simultaneously, second section horizontal pipe 38 also has been installed in convective region 30.Inlet header and outlet header 38A, 38B and pipeline 38 communicate.

Many collecting tubules 39 provide fuel by pipeline 40 to burner 18.Under the control of valve 42, by collector 41 with in the fuel introduction collecting tubule 39.According to the heat supply intensity of described processing coil pipe 31 and 32, the fuel that flows into burner 18 can be different in each perpendicular row.Each burner also can be done further to regulate by the valve 44 that is positioned on the pipeline 40, and the fuel total flux that enters stove is regulated by valve 45.As everyone knows, be installed in outer wall 11 and 12, the burner on the inwall 13 and 14 all has similarly but the line equipment of not drawing.Similarly, pipeline 46 is delivered to the furnace bottom burner with fuel.

Fig. 2 has schematically represented to handle the spread pattern of coil pipe 31, and obviously, the arrangement of handling coil pipe 32 is also identical.The pyrolyzer of general type is described in US-PS3274978.Yet the present invention also is applicable to the pyrolysis coil pipe in the pyrolyzer that can be installed in other types, and these pyrolyzer are used in industry at present.

Fig. 2 has schematically represented the layout of processing coil pipe 31 of the present invention, clearly, handles coil pipe 32 and also makes same layout.Handle coil pipe 31 and be generally " swaged forging formula " described above, it is by first path 46, and alternate path 47, the three path 49, the five-way roads 50,48, the four-way roads and the 6th path 51 are formed.As shown in the figure, first path 46 is made up of four pipes, and alternate path 47 and the 3rd path 48 all are made up of two pipes, and path 49,50 and 51 all is made up of a pipe.Yet this coil pipe only is a kind of canonical form, but the present invention is not limited to this type.The present invention also is applicable to the pyrolysis coil pipe of any other structure and caliber.

Following table has at length been represented the structure of coil pipe:

Path sequence number pipe is counted internal diameter (inch)

1 4 3.5

2 2 5

3 2 5

4 1 7.5

5 1 7.5

6 1 7.5

As shown in Figure 2, the heating surface 52 of expansion is positioned on four pipes of first path 46.The heating surface of this expansion can be column or vertically straight fin keel formula fin.Column can be made the shape of any needs, but preferably cylindrical.The size of column or fin and quantity should be decided according to the processing parameter of arbitrary specialized structure on the pyrolysis coil pipe unit length.For example, if the diameter of column is 0.5 inch, then length range is the 0.5-0.75 inch, in arbitrary plane, on the pipe circumference 8-12 column can be set.Fig. 3 has represented to have a bit of pipeline of column.Column is suitable for being arranged on the outside of pipe.It is inboard that vertically straight fin or rib preferably are located at pipe.For example, rib can be 0.2 inch high, and 6-10 sheet fin can be installed on the circumference of pipe.Fig. 4 has represented to arrange the tube section of vertically straight fin or fin on the inside circumference of pipe.Simultaneously, the reinforcement face of expansion should be arranged on the forebody of handling coil pipe, preferably in first 1/4th scope.As indicated such, the embodiment among Fig. 2 only has column on first path.

From Fig. 5, can see the effect that enlarges hot face at first path.Fig. 5 has compared traditional pyrolysis coil pipe and the temperature distribution history with the identical coil pipe that enlarges hot face.In Fig. 5, can see in the temperature in the first part of coil pipe clearly surpassing temperature in the first part of traditional coil pipe, and the temperature of exit portion is only influenced slightly.Because the temperature of ingress is higher,, can strengthen the throughput of cracking severity and coil pipe not improving maximum temperature out or can not significantly improving under the situation of the temperature that pyrogenic exit takes place.

The estimated value of performance characteristics that has compared the coil pipe of traditional " swaged forging formula " coil pipe and two kinds of different structures of the present invention below.In all these situations, the structure of coil pipe is four pipes in first path, is two pipes in the second and the 3rd path, is a pipe in the 4th, the 5th and the 6th path.

Traditional coil pipe B of the present invention

" swaged forging formula " coil pipe A

Coil pipe

Path length, 31 33 31

(foot)

5.756 7.212 6.577 of every coil pipe

Throughput,

（T.HC/h）

Energy increases % basis amount 24.4 13.5

Thermal load, 16.07 20.1 18.41

MMBTU/hr

Length of run, fate 60 60 60

Ethylene yield Wt%

Once by 28.9 28.7 28.7

The limit 32.9 32.9 32.9

Work coil pipe 30 24 26.3

Additional column increases

The effective surface % that adds

The path sequence number, 1 does not have 50 100

Other paths do not have

In order to utilize the metal of coil pipe forebody most effectively, will do one to gas isothermal distribution curve and describe.

Adopt combustion zone and existing " swaged forging formula " coil arrangement simultaneously, can make temperature distribution history approach thermoisopleth.The present invention utilizes inboard and/or outside expansion heating surface can make temperature distribution history more approach thermoisopleth in first half or first 1/4th zone of coil pipe.Enlarge heating surface at the coil pipe rear portion and will make temperature distribution history further depart from thermoisopleth, but also produce the coking phenomenon.First part's expansion heating surface at coil pipe can keep or prolong length of run or cycling time, and maintenance or raising increase the ethylene yield of metal tube unit weight and the output of their any mixture for the cracking selectivity of alkene.

Although two temperature distribution histories among Fig. 5 are in close proximity to each other, its temperature head is favourable to the coil pipe that enlarged surface is arranged, and makes the throughput of this coil pipe increase about 10%.Change because dynamic response speed is index law with temperature change, the little gas temperature difference can the product remarkable influence to scission reaction.

Claims (7)

1, a kind of pyrolyzer that is used for the pyrolysis hydro carbons, it comprises:

A) radiation heating chamber;

B) at least one is divided into forebody and latter half of tubulose is handled coil pipe, so as in above-mentioned heating chamber treat fluid;

C) some radiant burners are handled coil pipe so that heat at least one tubulose;

It is characterized in that:

D) at least one above-mentioned tubulose handled coil pipe, and the part at its forebody is provided with the expansion hot face at least, so that increase absorbing radiation heat.

2, the pyrolyzer that is used for hydrocarbon pyrolysis according to claim 1 is characterized in that above-mentioned expansion hot face is for handling with tubulose that coil pipe links to each other and from the outward extending heating surface of outside surface of tubulose processing coil pipe.

3, the pyrolyzer that is used for hydrocarbon pyrolysis according to claim 2 is characterized in that described expansion hot face is a column.

4, the pyrolyzer that is used for hydrocarbon pyrolysis according to claim 1 is characterized in that the longitudinal extension hot face of above-mentioned expansion hot face for linking to each other with internal surface that tubulose is handled coil pipe and extending internally from this internal surface.

5, the pyrolyzer that is used for hydrocarbon pyrolysis according to claim 4 is characterized in that above-mentioned expansion hot face is vertically straight fin keel or fin.

6, the pyrolyzer that is used for hydrocarbon pyrolysis according to claim 1 is characterized in that above-mentioned expansion hot face only is positioned at first scope of 1/4th of above-mentioned processing pipe.

7, the pyrolyzer that is used for hydrocarbon pyrolysis according to claim 1 is characterized in that above-mentioned expansion hot face only is positioned at tubulose and handles on first path of coil pipe.

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