US3649212A

US3649212A - Pyrolysis furnace and baffle means

Info

Publication number: US3649212A
Application number: US888683A
Authority: US
Inventors: Thaddeus J Oleszko; Lynn P Walker
Original assignee: Marathon Oil Co
Current assignee: Marathon Oil Co
Priority date: 1969-12-29
Filing date: 1969-12-29
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14
Also published as: DE2051437C3; DE2051437B2; DE2051437A1

Abstract

A pyrolysis furnace such as a Wulff furnace having an octagonal baffle in each of the combustion chambers, located so that the longitudinal axis of the baffle is between the fuel inlets of the combustion chamber and the center refractory mass which separates two combustion chambers.

Description

[451 Mar. 14, 1972 United States Patent Oleszko et al.

[54] PYROLYSIS FURNACE AND BAFFLE Hasche m L 66 WE 7/1958 .23/277 X 3/1962 Coberly......................... 23/277 Walker, Burghauser, both of Germany [73] Assignee: Marathon Oil Company, Findlay, Ohio Primary Examiner-James H. Tayman, Jr. [22] Filed: Dec. 29, 1969 Attorney-Joseph C. Herring, Richard C. Willson, Jr. and Jack L. Hummel [21] Appl. No.:

[52] US. Cl........................ ...23/277 R, 23/284, 260/679 R, A pyrolysis furnace such as a wulff furnace having an Int Cl 263/51 263/46 2 3,}: tagonal bafi'le in each of the combustion chambers, located so 58] Fieid 5&5;11111111111.11153755; 284- 260/679 263/50 mgnudinal axis the ham is between the fuel inle's 263/51 264/86 of the combustion chamber and the center refractory mass which separates two combustion chambers.

5.9 3 Dr wi g References Cited UNITED STATES PATENTS 695,822 Moore 1 I :E I I C U I II II I I I I I I I II W II 2 I I F H II I I N m I I F I I I I I I I II II 0 I I I W I I I I I I I I I I I I I I I I I I HI 5 IIIII m I I 5 I I c I I I I I w I I ,w I 6 I I I I II I II I I I D IHI I I III I II Y X I I a E I B 2 I I K 2 L II I A 4 F I 3 I I 2 8 I I I I l I I I I I I I HG I I 0 II I I I I I m I I I I I I I I I II I I I I I I I I I II I I I I II a II I I I I I I I I I I 0 I I I I I II 2 I II 4 ll PAIENTEDMAR 14 I972 3.649.212

SHEET 2 BF 2 Fig. 3

M/VE/VTORS T.J. OLESZKO L.P. WALKER PYROLYSIS FURNACE AND BAFFLE MEANS BACKGROUND OF THE INVENTION 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 20 feet long and contains five major sections. Three of these sections are made of refractory tile (see US. Pat. No. 2,622,864 to Hasche), often called Hasche Tile and are often referred to in the art as refractory masses. Two larger sections of this tile form the right and left end sections of the furnace and are commonly referred to as the end stacks. 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.

Baffles have been used in the combustion spaces of such furnaces in order to promote uniformity in the air-gas mixture which in turn, promotes a more uniform combustion. Baffles are also thought to provide a more uniform flow and distribution of the hot products of combustion through the adjacent refractory mass where the cracking occurs.

DISCUSSION OF THE PRIOR ART US. Pat. No. 3,024,094 to Coberly teaches the use of a wing-shaped baffle attached to one side of the combustion chamber. This baffle arrangement promotes uniform combustion and flow characteristics within the combustion chamber. Other types of baffles have also been set in various different arrangements along the walls of the combustion chambers to direct the combustion gases to the center of the center reaction mass. With these arrangements however, a major portion of the combustion gases go through the middle of the center stack, and create undesirable areas of local overheating in the center stack, and hence the prior art often found it necessary to plaster over large sections of the center stack with high temperature mortar. Since the plastered overarea often comprises about 30 percent of the total area of the end of the center stack, this portion is lost for the purposes of energy transfer in the cracking operation.

The baffle arrangement of our invention represents an improvement over the two forms of the above-mentioned prior art because the new invention reduces the need for plastering over any potential areas of local overheating, improves cracking yields, and reduces fuel consumption.

SUMMARY 1. This invention resides in a substantially solid, truncated octagonal-shaped baffle designed particularly for use in the combustion chamber of a pyrolysis furnace such as the Wulff furnace. The battle extends from the floor to the ceiling of the combustion chamber and may have holes in it to promote relief of thermal stresses. Preferably the baffle is made of alumina or a mixture of alumina and mullite (85 percent alumina, percent SiO Said baffle may be poured in place or prefabricated. In the specification, we describe the geometrical features of our apparatus, how to install it, and, in a preferred embodiment we explain how the apparatus works in a well-known pyrolysis process.

2. Utility of the Invention The solid octagonal shaped baffle mixes the air and fuel gases and channels the hot products of the combustion into the combustion chamber toward substantially all the surface area of the center stack reaction mass in substantially uniform proportions. Since there is no need to plaster over any potential at'eas of local overheating, substantially all the refractory mass is available for energy transfer in the center stack during the cracking process. The uniform distribution of heat energy in the center refractory mass tends to prevent the problem of overcracking in one area or undercracking in another. It also reduces the localized overheating conditions and temperature swings which tend to cause failure of the Hasche tile in those localized areas.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of a typical pyrolysis furnace with the baffle means of this invention installed in the reaction chambers.

FIG. 2 illustrates a typical flow pattern through a reaction chamber with the baffle means of this invention installed.

FIG. 3 is detailed plan view of the furnace.

Referring to FIG. 3, a pyrolysis furnace typically has a metal shell consisting of a top 2, sides 4, and a bottom. Said shell enables the furnace to be operated under vacuum conditions.

The shell is lined with firebrick 6 for insulating purposes. Disposed within the channel created by the shell, is a left-end stack ceramic mass 8, a center stack ceramic mass 10, and a right-end stack ceramic mass,14. The center stack is spaced from the end stacks so as to create the left 12 and right 16 combustion chambers. Located in the left combustion chamber 12 is a first baffle means 18 and located in the right combustion chamber 16 is a second baffle means 20 identical with the first baffle means 18. It should be understood that the furnace is symmetrical in that the typical production processes involve a cyclical operation whereby gases are conducted both from right to left and from left to right during various phases of the operation cycle. Thus, the furnace consists of, from end to end, an end stack, a first combustion chamber, a center stack, a second combustion chamber, and the other end stack.

As shown in FIG. 3, extending into the left combustion chamber 12, is a fuel injection means 22 extending through the sides of the furnace. A similar fuel injection means 24, is located in the right combustion chamber 16. The outer ends of these nozzles are connected to a suitable source of fuel (not shown). Each of the fuel injection means 22 and 24 is adapted to deliver a fuel, such as, for example natural gas or off-gas from the process, at a high velocity, preferably at about a velocity which is the velocity of sound in the gas employed. The fuel injection nozzles and the source of the fuel supply are so designed. The ceramic masses may be formed of ceramic checkers as shown in Hasche US. Pat. No. 2,622,864, the checkers have semicircular grooves in their bases and are so arranged that when the checkers are stacked they will form in the ceramic masses longitudinal tubular holes or passages.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The desired products of a pyrolysis furnace such as the Wulff fumace 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. The operating conditions of this patent are as described in US Pat. No. 3,024,094 to Coberly.

The novelty of this invention resides in the shape and location of the baffle means. The shape and position of the baffle are such that the mean length of the path of the gases flowing through the reaction chamber is at least twice as long as it would be without the baffle element in position. When coupled with the high air and fuel velocity injection rate, the long path created by the baffle is important to the mixing of the fuel and air so that when combustion products reach the center reaction mass the temperature of the gases will be substantially uniform and hence the heat transfer to the surfaces of the center reaction mass will be substantially constant. FIG. 2 schematically shows the path of the gases issuing from the left reaction mass flowing around the baffle element and into the center mass during a left-to-right heating step. A similar course would be taken by products of combustion leaving the center mass, passing around the right combustion chamber baffle element and entering the right reaction mass during the left-to-right heating step. During a right-to-left cycle of operation, the lines would flow in the opposite direction. The baffle of this invention is a solid, substantially octagonal-shaped baffle positioned in the center of the combustion space of the pyrolysis furnace. The longitudinal axis of the bafiles is located along the KL and MN centerlines of FIG. 3, while the latitudinal baffle axis extend along the centerline OP. The longitudinal extremities of the baffles are equidistant from the longitudinal midpoint of said baffle. The distances of the longitudinal extremities AB, FE, A'B', FE', from the sides of the combustion chamber are the same. The distances of the latitudinal extremities CD, HG, C'D', H'G' of the baffle from the other sides of the combustion chamber, i.e., the reaction masses, are the same. The height of the baffle is equal to the height of the enclosures. It is understood that the bafile of the left combustion chamber is identically equal to the bafile of the right combustion chamber. As indicated in FIG. 3, the baffle has a latitudinal and longitudinal axes of symmetry. The longitudinal axis of the baffle should be at least 1% times as long as the latitudinal axis. Those ends perpendicular to the longitudinal axis i.e., AB, FE, A'B, F'E', should be at least as wide as those ends of the octagonal figure perpendicular to the latitudinal axis, i.e., CD, HG, C'D', H'G'.

The baffles can be poured in place in the combustion chamber or prefabricated and positioned in said chamber. Typically, such baffles are made of a mixture of alumina and mullite (85 percent A1 percent SiO Holes such as those indicated in FIG. 3, X, Y, etc., are located within the baffle to let out water during the curing process and subsequently to relieve thermal stresses during furnace operation.

EXAMPLE The following data is based on tests conducted to compare the performance of a Wulff furnace with the baffle means of this invention, with the baffle means taught in the prior art.

Mixed Gas 20% CN 36.57 34.95 Mixed Gas Mixed Gas 30.03 29.92 Mixed gas 38.90 7313 Mixed Gas 36.45 Mixed Gas 20% CN 30.23 3145 Mixed Gas 20% CN 36.82 32.85 Mixed Gas 20% CN 39.21 36.08 Average Yields 35.69 34.71 33.73

Table I shows that the octagonal baffle of this invention effects about a 20 percent decrease in fuel consumption over the rior art.

able II shows the octagonal baffle also effects a small improvement in yields over the prior art.

What is claimed is:

1. In a pyrolysis furnace characterized by: two end refractory masses into which air is introduced for preheating; and, adjacent to and terminating the refractory masses, two combustion spaces having substantially vertical sides, fuel injection points in the said substantially vertical sides; for injecting fuel into said combustion spaces and a center refractory mass separating the combustion spaces wherein combustion gases are cracked; the improvement of positioning a substantially solid octagonal-shaped figure having both a longitudinal and lateral axis of symmetry is in the combustion chambers in such a manner that the longitudinal extremities are substantially equidistant from the longitudinal midpoint of the baffle means and substantially equidistant from the sides of the combustion chamber, the latitudinal extremities are substantially equidistant from the longitudinal axis of symmetry and the said longitudinal axis is located between said fuel injection points and said center refractory mass.

2. The apparatus of claim 1 wherein the baffle has an elongated octagonal shape, wherein the longitudinal axis is the longer axis and is at least 1% times as long as the shorter latitudinal axis with both axes being axes of symmetry and wherein the baffle means is positioned with the longitudinal axis substantially transverse to the major axis of said furnace.

3. The apparatus of claim 1 wherein the two sides perpendicular to the longitudinal axis of symmetry are at least as long TABLE I- Fuel Consumption Comparison A Ratio Mole n Steam Air Feed Fuel C Hl/ Kg. Feedl KgJI-lr. Nmfl/I-lr. KgJI-lr. Nmfi/Hr. C1114 C,

KgJHr. Nm./I-lr. KgJI-Ir. NmP/Hr. C1114 CZH; C2112 Nm. Fuel Standard furnace actual data 12202 12832 3761 1055 8.83 8.86 1.02 3.56

Data adjusted to common base 12100 12500 1.67 3.99

Diamond bafile actual data 12075 12196 3894 809 13.09 7.82 1.67 4.81

Data adjusted to common base*.. 12100 12500 1.67 4.80 Wing. baffle actual data 12059 13007 3776 993 14.14 9.15 1.54 3.80

Data adjusted to common base*.. 12100 12500 1.67 3.90 Standard furnace actual data 12122 12480 3950 978 15.18 8.73 1.75 4.04

Data adjusted to common base 12100 12500 1.67 3.96

1 Data generated by flow over a 15 day period.

*Data adjusted to uniform operating conditions (pressure, etc).

TABLE H as the side perpendicular to the latitudinal axis of symmetry, i.e., those sides of the baffle parallel to the face of the center Yield Comparisons of Baffles stack reaction m3ss Hume" 4. The apparatus of claim 1 wherein holes are located Baffle Type Standard 10 4 ocmaona wing Furnace throughout the baffle means to let out water during cur ng of Feed Material Baffle Bafile with no bafi'le the baffle and to relieve thermal stress during the operation of the furnace. CokerNaphlha 33.01 39:19 5. The apparatus of claim 1 wherein the baflle is made of a I'Ieavy Naphtha 36.66 35.50 36.08 material selected from the group consisting of alumina and a Mixed Gas 35.27 35.38 mixture of a1 umina and silicone oxide.

Claims

2. The apparatus of claim 1 wherein the baffle has an elongated octagonal shape, wherein the longitudinal axis is the longer axis and is at least 1 1/4 times as long as the shorter latitudinal axis with both axes being axes of symmetry and wherein the baffle means is positioned with the longitudinal axis substantially transverse to the major axis of said furnace.
3. The apparatus of claim 1 wherein the two sides perpendicular to the longitudinal axis of symmetry are at least as long as the side perpendicular to the latitudinal axis of symmetry, i.e., those sides of the baffle parallel to the face of the center stack reaction mass.
4. The apparatus of claim 1 wherein holes are located throughout the baffle means to let out water during curing of the baffle and to relieve thermal stress during the operation of the furnace.
5. The apparatus of claim 1 wherein the baffle is made of a material selected from the group consisting of alumina and a mixture of alumina and silicone oxide.