US3723067A

US3723067A - Pyrolysis furnace having transverse mixing means in the end stacks

Info

Publication number: US3723067A
Application number: US00111509A
Authority: US
Inventors: L Walker
Original assignee: Marathon Oil Co
Current assignee: Marathon Oil Co
Priority date: 1971-02-01
Filing date: 1971-02-01
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27
Also published as: DE2126632A1; BR7105130D0

Abstract

A regenerative pyrolysis furnace having dual combustion chambers and means for transverse flow in the end stacks of the refractory masses. These means for transverse flow in the preheat and quench tile stacks permit crossflow between the axial flow conduits, thereby minimizing the effects of plugging of these conduits due to carbon formation or shifting of tile.

Description

United States Patent 1 Walker 1 Mar. 27, 1973 541 PYROLYSIS FURNACE HAVING 2,868,855 1 1959 Begley ..23 277 R x TRANSVERSE MIXING MEANS IN THE 2,473,427 6/1949 Hasche 2,936,162 5/ 1 960 Coberly ..263/51 END STACKS Lynn P. Walker, Burghausen, Germany Inventor:

Marathon Oil Company, Findlay, Ohio Filed: Feb. 1, 1971 Appl. N0.: 111,509

Assignee:

References Cited UNITED STATES PATENTS 12/1958 Begley et al ..23/277 R X Primary Examiner-James H. Tayman, Jr. Attorney-Joseph C. Herring, Richard C. Willson, Jr. and Jack L. Hummel [57] ABSTRACT A regenerative pyrolysis furnace having dual combustion chambers and means for transverse flow in the end stacks of the refractory masses. These means for transverse flow in the preheat and quench tile stacks permit crossflow between the axial flow conduits, thereby minimizing the effects of plugging of these conduits due to carbon formation or shifting of tile.

9 Claims, 4 Drawing Figures PATH-HEUumznm SHEET 10F 2 INVENTOR.

L. P. WAL K E R ig. l

PATENWDHARZ 71975 SHEET 2 BF 2 Fig. 2

INVENTOI? L. P. WALKER Fig. 3

SECTION A A' SECTION A-A' (alternate) A T TORNEY PYROLYSIS FURNACE HAVING TRANSVERSE MIXING MEANS IN THE END STACKS CROSS REFERENCES TO RELATED APPLICATIONS 1970, all of which are assigned to the assignee of the present invention, relate to the general field of pyrolysis of hydrocarbons.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of hydrocarbon pyrolysis. Literature relating to this application will be found in Patent Classes 23-277, furnaces for analytical methods; 263-15, heating: with gas furnace heaters; 263-51, heating: checker bricks; 260- 679, hydrocarbons: acetylene; and other related patent classifications.

2. Description of the Prior Art Processes for thermally cracking hydrocarbons into acetylene, ethylene, and other unsaturated gases have been described at length in the literature. (See, for example, the Wulff process described in U.S. Pat. Nos. 1,996,187; 2,037,056; 2,236,534; 2,236,535; 2,236,555; 2,319,679; 2,518,688; 2,526,696; and 2,908,625.) The pyrolysis of methane, ethane, propane, butane and natural gas to form acetylene and ethylene have particularly been studied. (See, for example, Tropsch and Engloff, Industrial and Engineering Chemistry, 27, p. 1,063 (1935) and U.S. Pat. No. 1,983,922.)

Various types of furnaces have been used for hydrocarbon pyrolysis. The well-known Wulff furnace will be used for exemplary purposes herein. This furnace is usually about feet long and contains five major sections. Three of these sections are made of refractory tile (see U.S. Pat. No. 2,622,864 to Has che), often called l-lasche tile, and are often referred to in the art as refractory masses. These refractory masses contain axial flow channels, referred to in this application as longitudinal conduits, through which the process flow stream is transmitted. Two larger sections of this tile form the right and left endsections of the furnace and are commonly referred to as the endstacks. The third smaller refractory mass forms the center section of the furnace and is usually referred to as the center stack. Between the two end stacks and the center stack are two sections known as the combustion zones, one on each side of the center stack. Thus, from end to end, the furnace consists of an end stack, a combustion chamber, the center stack, a second combustion chamber,.and the other end stack. Typically, such a furnace is operated in a cyclical fashion, that is, heating and cracking cycles are carried out in alternate left to right and right to left flow patterns during operations.

The hydrocarbon feedstock is transferred through the end stacks through numerous parallel cylindrical grooves in the tiles which form conduits running longitudinally through the tile stack. This provides proper preheating and quenching before and after the cracking reaction, respectively. However, due to the nature of the cracking reaction, coke is readily formed in these conduits or tubes". This coke plugs certain of the tubes, thereby creating adverse temperature and pressure gradients within the furnace. As this problem becomes more severe, the efficiency of the process is decreased and the furnace must be shut down in order to decoke.

Another common fault of this furnace is the shifting of some of the tile stacks due to vibration and continual thermal expansion and contraction. This random shifting prevents flow through certain portions of the end stacks, thereby creating a similar problem as that when the spaces become plugged.

SUMMARY General Statement of the Invention According to the invention there are provided conduits for transverse flow among the longitudinal conduits in the refractory mass of each of the end stacks. For example, this may be a space formed by removing a transverse section of the refractory mass. This space can be equipped with baffles or not, as desired.

The resulting tranverse flow alleviates the problem of pressure and temperature gradients developed from the blocking of passages due to coke formation or tile shifting. The existenceof this space provides more evenly distributed flow patterns, resulting in a considerably longer process run forthe furnace, and an increase in product yield.

Utility of the Invention The invention relates to the production of the commercially well-known products of ethylene and acetylene which principally find use as reactants in the synthesis of numerous organic chemicals and as fuels. (See Miller S. A., Acetylene: Its properties, Manufacture and Uses, Vols. 1 and 2).

The transverse mixing zone channels the process gases towards substantially all of the surface area of the inner portion of the end stack in substantially uniform proportions. The uniform distribution of heat energy in the end refractory mass tends to prevent the problem of overcracking in one area or undercracking in another. This results in a higher product yield and longer runs between shutdowns for decoking the furnace.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a detailed plan view of the furnace.

FIG. 2 is a cross-sectional top view of the mixing space, containing a baffle means.

FIGS. 3 and 4 are cross-sectional end views of a refractory mass, illustrating typical arrangements for the interconnection of the longitudinal conduits within the refractory mass.

Referring to FIG. 1, a pyrolysis furnace typically has a metal shell consisting of a top 2, sides 4, and a bottom. Such shell enables the furnace to be operated under vacuum conditions.

The shell is lined with fire bricks 6 for insulating purposes. Disposed within the channel created by the shell are left end stack

ceramic masses

8 and 10, a center stack ceramic mass 12, and right end stack ceramic masses l4 and 16. The center stack is spaced from the end stacks so as to create the left 18 and right 20 combustion chambers. Located between the

end stack masses

8 and 10 is transverse mixing space 22. Similarly, located between

end stack masses

14 and 16 is a transverse mixing space 24. The furnace is symmetrical and the typical production processes employ a cyclical operation whereby gases are conducted from right to left and, alternately, from left to right during the two cycles of operation (when feed' gas is moving from right to left, the right combustion chamber and end stack are said to be operatingon the production or make cycle, while the left combustion chamber and end stack are operating on the product heat transfer or heat cycle. The converse is true when the feed gas moves from left to right).

Extending into the left combustion chamber 18 is a fuel injection means 26 extending through the sides of the furnace. A similar fuel injection means 28 is located in the right combustion chamber 20. The outer ends of these nozzles are connected to a suitable source of fuel (not shown).

The ceramic masses (or refractory masses) may be formed of ceramic checkers as shown in Hasche Pat. No. 2,622,864. The checkers have semi-circular grooves in their bases and are so arranged that when the checkers are stacked they form in the ceramic masses longitudinal conduits. The cross-sectional area of these conduits represents about 20 percent to about 30 percent of the total cross-sectional area of the ceramic masses.

FIG. 2, a cross-sectional top view of the mixing space, illustrates one of many baffle means which may be employed in

transverse mixing spaces

22 and 24 of FIG. 1. The height of these baffles may range from being equal to their widths to being equal to the vertical dimension of the mixing space.

FIGS. 3 and 4, both cross-sectional end views of a refractory mass, illustrate typical arrangements for the interconnection of the longitudinal conduits within the refractory mass. As is readily observed, many variations of these arrangements may successfully be utilized within the scope of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The desired products of a pyrolysis furnace, such as the Wulff furnace, are acetylene, ethylene, or other unsaturated chemical compounds or mixtures thereof, formed by the pyrolysis of a suitable hydrocarbon in the furnace and by the process known to the art. A suitable hydrocarbon" is any hydrocarbon known to the art to be capable when pyrolyzed of forming acetylene, ethylene, or other unsaturated chemical compounds. Methane, ethane, propane, butane, gas oil or other petroleum fractions, and unsaturated hydrocarbons such as ethylene, butylene, and propylene, and gases such as natural gas or refinery gases are among the many hydrocarbons which fall within this definition. Also, both light and heavy naphthas serve as suitable hydrocarbons. The operating conditions of this example are as described in US. Pat. No. 3,024,094 to Coberly, Column 5, line 32 to Column 8, line 29.

The pyrolysis process is usually run with more than one furnace, so as to permit continual production even when a particular furnace is shut down" for maintenance. Proper valve and piping arrangements are well-known to the art. See, for example, U.S. Pat. No. 2,956,864 to Coberly.

the adjacent refractory mass and a width of preferably about 0.01 to about 5, more preferably about 0.1 to

about 3, and most preferably about 0.7 to about 1.5 of

the combustion chamber width.

The transverse mixing space can also be equipped with a baffle arrangement to facilitate the crossflow.

FIG. 2 illustrates a typical baffle arrangement. While the baffle means shown in FIG. 2 provides good mixing, it is not intended that this application be limited to that means. Many conventional means of baffling will also work quite well with the proposed invention, or baffling can be eliminated if desired.

EXAMPLE The results obtained from the practice of this invention on a furnace,the dimensions of which are identical with those given in FIG. 1, indicate an average increase in acetylene-ethylene yield of about 3.5 percent compared to the same-furnace before the mixing space was installed. The mixing spaces used in this example are identical with those illustrated in FIG. 1, and are located so that the front surface of each space is 1,285 mm from end to respective end.

The following table, which provides the process operating conditions which existed during the experimentation, compares the results obtained without the mixing space (trials 1 and 2) with the results obtained with the mixing space (trials 3 and 4):

The furnaces of trials 3 and 4 were also able to remain onstream percent longer than the furnaces of trials 1 and 2.

It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended thereto.

What is claimed is:

1. In an apparatus for hydrocarbon pyrolysis comprising a plurality of regenerative pyrolysis furnaces each comprising a first and a second end refractory mass having longitudinal conduits through which feed gas is introduced for pre-heating and products are exited for cooling respectively; and adjacent to and terminating each refractory mass, two combustion chambers equipped for external injection of fuel therein; and a center refractory mass, separating the combustion chambers wherein feed gases are cracked; the combination therewith of a means for providing transverse flow of gases among at least a plurality of said longitudinal conduits of said end refractory masses, wherein said means for providing transverse flow comprises a transverse space having a longitudinal dimension of from about 0.9 to about 1.1 combustion chamber widths and said transverse space is equipped with one or more baffles.

2. The apparatus of claim 1 wherein the center line of said space is located about three combustion chamber widths from the center line of its respective combustion chamber.

3. The apparatus of claim 1 wherein the cross-sectional area of said space is equal to the cross-sectional area of the adjacent refractory masses.

4. The apparatus of claim 1 wherein said means for providing transverse flow consists of at least a plurality of transverse conduits connecting various longitudinal conduits.

5. The apparatus of claim 1 wherein said means for providing transverse flow consists of various transverse conduits connecting at least a plurality of longitudinal conduits.

6. The apparatus of claim 1 wherein the total crosssectional area of the longitudinal conduits is about 20 percent to about 30 percent of the total cross-sectional area of the refractory masses.

7. The apparatus of claim 1 wherein the longitudinal conduits are cylindrical in shape.

8. The apparatus of claim 1 wherein each longitudinal conduit is substantially equidistantly spaced from each adjacent longitudinal conduit.

9. Apparatus according to claim 1 in which said baffles consist essentially of a plurality of baffles extending from the wall of the furnace toward the midpoint of the furnace in a direction substantially transverse to the direction of flow.

Claims

2. The apparatus of claim 1 wherein the center line of said space is located about three combustion chamber widths from the center line of its respective combustion chamber.
3. The apparatus of claim 1 wherein the cross-sectional area of said space is equal to the cross-sectional area of the adjacent refractory masses.
4. The apparatus of claim 1 wherein said means for providing transverse flow consists of at least a plurality of transverse conduits connecting various longitudinal conduits.
5. The apparatus of claim 1 wherein said means for providing transverse flow consists of various transverse conduits connecting at least a plurality of longitudinal conduits.
6. The apparatus of claim 1 wherein the total cross-sectional area of the longitudinal conduits is about 20 percent to about 30 percent of the total cross-sectional area of the refractory masses.
7. The apparatus of claim 1 wherein the longitudinal conduits are cylindrical in shape.
8. The apparatus of claim 1 wherein each longitudinal conduit is substantially equidistantly spaced from each adjacent longitudinal conduit.
9. Apparatus according to claim 1 in which said baffles consist essentially of a plurality of baffles extending from the wall of the furnace toward the midpoint of the furnace in a direction substantially transverse to the direction of flow.