US2983771A

US2983771A - Conversion of hydrocarbons

Info

Publication number: US2983771A
Application number: US700057A
Authority: US
Inventors: John W Begley
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1954-10-18
Filing date: 1957-12-02
Publication date: 1961-05-09
Anticipated expiration: 1978-05-09

Description

May 9, 1961 J. w. BEGLEY CONVERSION OF HYDROCARBONS Original Filed Oct. 18, 1954 4 Sheets-Sheet 2 y 1961 J. w. BEGLEY 2,983,771

CONVERSION OF HYDROCARBONS Original Filed Oct. 18, 1954 4 Sheets-Sheet 3 TO TIMER 7| FIG. 5

'UUUUUUUUUUU 37 H6. 4 INVENTOR.

J.W. BEGLEY A TTORNEYS May 9, 1961 J. w. BEGLEY CONVERSION OF HYDROCARBONS Original Filed Oct. 18, 1954 4 Sheets-Sheet 4 INVENTOR. J.W. BEGLEY A TTORNEVS United States Patent CONVERSION OF HYDROCARBONS John W. Begley, Plainfield, N.J., assignor to Phillips Petroleum Company, a corporation of Delaware Original application Oct. 18, 1954, Ser. No. 462,836. Divided and this application Dec. 2, 1957, Ser. No. 700,057

7 Claims. (Cl. 260-679) This invention relates to the conversion of hydrocarbons. In one of its more specific aspects, it relates to novel regenerative furnaces for use in the thermal cracking of hydrocarbons. In another of its more specific aspects, it relates to a process for the thermal conversion of hydrocarbons. In stillanother of its more specific aspects, it relates to a process for the production of unsaturated hydrocarbons.

This case is a division of Serial No. 462,836, filed October 18, 1954.

During the early years of the petroleum industry, the possibility of producing unsaturated hydrocarbons by the cracking of low boiling hydrocarbons received comparatively little attention. Because of apparatus limitations imposed by the high reaction temperatures involved and the lack of understanding of the best manner of operation, early developments excluded the cracking of low boiling hydrocarbons. Still another deterrent in the development of successful processes was the availability of vast supplies of heavy naphthas which could be cracked by more easily manageable processes to form easily purifiable products in high yield. Recent advancements made in organic chemistry have resulted in such an increased demand for petro-chernical starting materials, such as acetylene and ethylene, that it is no longer possible to rely on the old sources of supply for these materials. The demand for ethylene has reached such proportions that it cannot be supplied from refinery streams without upsetting the balance in the production of motor and aviation fuels, Furthermore, commercial production of acetylene by reacting calcium carbide with water is too expensive and is limited to amounts far too low to satisfy the demand for acetylene as a chemical synthesis starting material. ful processes for producing unsaturated hydrocarbons by the cracking of low boiling hydrocarbons has in recent years taken on added importance.

Various methods for the pyrolysis of gaseous hydrocarbons have been proposed which involve the use of a variety of heat sources, including externally heated tubes, electrical heated resistance elements, and spark or electrical discharges. The lack of cheap electric power has also drawn attention to other possible methods of heating, such as by the combustion of preheated natural gas with preheated compressed air. In such latter processes when utilizing regenerative furnaces, a stream of air and fuel gas is burned in, or hot combustion products passed through, a refractory checkerwork so as to heat it to a high temperature. After the hot gases have heated the checkerwork to the desired temperature, the flow of combustion gases is terminated, and thereafter the reactant materials to be treated are passed through the heated checkerwork in order to bring the materials to reaction temperature.

In a particularly useful regenerative furnace of this type, utilized for the thermal cracking of hydrocarbons, such as methane, ethane, propane or butane, to produce unsaturated hydrocarbons, such as ethylene or acetylene,

Accordingly, the development of successan elongated checkerwork of refractory material is provided at either end of a central combustion chamber. Air is passed in one direction through one of the checkerwork structures while a fuel gas is introduced into the central combustion chambers The fuel gas and air burn in the combustion chamber, and thereafter the resulting combustion gases flow through one of the refractory checkerworks. When this checkerwork has reached the desired temperature, the flow of air and fuel is terminated, and the materials to be cracked or otherwise converted are passed in the opposite direction through the heated refractory where the desired cracking or other reaction occurs.

After a timed reaction period, the flow of reactant materials is stopped, and air is passed through the furnace in a direction opposite to that of its first introduction. At the same time, fuel gas is introduced into the central combustion chamber to mix with the air and form a combustible mixture which is burned therein to form hot combustion gases to heat the refractory checkerwork downstream of the combustion chamber. When the checkerwork attains the desired temperature, the materials to be converted are passed through the heated refractory.

I have now discovered that when utilizing a regenerative furnace of the type described above, having similar refractory cracking sections, a very close temperature approach exists in the center of the cracking sections. The portion of the cracking sections in which the temperature of the gases, i.e., the combustion gases or the reaction products, and the refractory material, are substantially equal may be termed the pinch section and denotes that portion of the cracking section where substantially no net heattransfer occurs between the gases and the refractories. In a regenerative furnace, it is desirable that the length of the pinch section be as short as possible in order to reduce the overall length of the furnace. Figure l of the drawing illustrates graphically the temperature conditions existing in a cracking section of a regenerative furnace of the type described. Curves 1 and 2 represent, respectively, the temperature of the combustion gases and the temperature of the hydrocarbon reactant material as these materials pass through the refractory checkerwork. The combustion gases enter the checkerwork at a higher temperature and leave at a lower temperature while the hydrocarbons are introduced at a lower temperature and pass therefrom at a higher temperature. That portion of the curves in which the gases undergo substantially no change in temperature is labeled pinch section. which designates that part of the furnace in which there is substantially no net transfer of heat between the gases and the refractory. It is noted that a major portion of the furnace is occupied by the pinch section. In order to decrease the length of the furnace, it is desirable tomaintain the pinch section as short as possible, and in accordance with this invention, means are provided for attaining this result.

When operating a regenerative furnace of the type described, having a single combustionchamber disposed between a pair of refractory checkerworks. l have also found that the conversion rate decreases after passing the middle of the furnace. It is noted that the middle of such a furnace is located at the center of the central combustion section. Figure 2 of the drawings illustrates graphically the conversion along the length of such a furnace. From a consideration of curve 3, it is apparent that the rate of conversion falls off after the gases pass the center of the furnace and that the maximum conversion is reached only at a point well past the center of the furnace. Because of the decreased. rate of conversion, a longer reaction time is required to obtain the desired total conversion, which is undesirable because of the increase in the amount of products consumed in secondary reactions. It would improve the quality'of cracking if the conversion rate remained constant or increased after the gases pass the middle portion of the refractory checkerwork, as shown by broken line curve 4 of Figure 2. As represented by curve 4, the maximum conversion is reached at a point only slightly past the center of the furnace. In accordance with the present invention, a regenerative furnace is provided in which this desirable result is obtained.

The following are objects of the invention.

It is an object of the invention to provide improved regenerative furnaces for use in the conversion of hydrocarbons.

6 Another object of the invention is to provide improved methods for the thermal conversion of hydrocarbons.

Still another object of the invention is to decrease the length of a regenerative furnace by decreasing the pinch section of the refractory masses.

A further object of the invention is to improve the quality of cracking in a regenerative furnace by increasing the conversion rate in the middle portion of the furnace.

A still further object of the invention is to provide a method for freezing the reaction prior to the introduction of thereaction products into the quench section of a regenerative furnace.

'Yet another object of the invention is to provide regenerative furnace which includes means for distributing the gases evenly throughout the furnace so as to prevent channeling of the gases through any one portion of the furnace.

Still further objects and advantages of the invention will become apparent to one skilled in the art upon consideration of the following disclosure.

Broadly speaking, the present invention resides in novel regenerative furnaces and their use in processes for the conversion of hydrocarbons. In one modification of the invention, a furnace is provided which includes refractory masses having different sized openings or passageways therethrough for the flow of combustion gases and reaction products. By utilizing a larger number of smaller openings in a portion of the refractory, an increased surface area is presented to the gases, giving a corresponding increase in the heat transfer rate and thereby permitting a decrease in the overall furnace length. In another modification of the invention, a regenerative furnace is provided which comprises three refractory masses, each separated by a combustion space. By operating with a furnace of this type, it is possible to improve the quality of cracking over that obtainable in conventional furnaces. In still another modification of the invention, quench steam is introduced directly into the furnace at a point where the reaction is complete in order to freeze the reaction and thereby prevent secondary reactions.

A more complete understanding of the invention may be obtained by reference to the following description and the drawing, in which:

Figure 1 is a graph illustrating the pinch section existing in a conventional regenerative furnace;

Figure 2 is a graph illustrating the conversion along the length of a conventional regenerative furnace having one combustion section;

Figure 3 is an elevation, partially in section, of a regenerative furnace in accordance with another modification of the invention;

Figure 4 is an end view of refractory tiles suitable for use iii the regenerative furnace of this invention;

Figure 5 is a cross sectional view taken along line 88 of Figure 3; and

Figure 6 is an elevation, partially in section, of a regenerative furnace in accordance with still another modification of the invention.

Referring to Figures 3 .and 5 of the drawing, there is shown the regenerative furnace of this invention which comprises a shell 11 lined with insulating materials 12 and 13. The inner layer 13 of insulating material is formed of a more refractory material than outer layer 12. Refractory masses 56, 57 and 58, disposed within insulated shell 11, are spaced apart so as to provide combustion spaces or sections 59 and 60. Refractory masses 61 and 62, identical in construction with one another and shorter in length than main refractory masses 56, 5-7 and 58, are positioned within combustion spaces 59 and 60. Refractory tiles, similar to those shown in Figure 4, are utilized to form refractory masses 56, 57 and 58 and provide longitudinal passageways 63 therethrough. Refractory masses 61 and 62 are each provided with longitudinal passageways 64 and have, in addition, tubes 66 extending therethrough perpendicular to the axes of and disposed between passageways 64. Conduits 67 connect passageways 64 with tubes 66, which are in turn connected to a header member 68, as shown in Figure-5. Header member 68 is connected to fuel inlet line 69 containing a valve 71. Refractory, masses 61 and 62 and their associated passageways 64, tubes 66, conduits 67 and header member 68 each constitute fuel introduction means, one of which is provided for each combustion space 59, 60. A timer'72 is operatively connected to each of the valves 71 contained in fuel inlet lines 69 associated with each of the fuel distribution means and to three-

way valves

43, 46 and 50, to provide alternate regeneration and process cycles. A timer suitable for use in controlling the cycles of operation is manufactured by Taylor Instrument Companies, Rochester, New York.

Plenum chambers

38 and 39, connected to either end of the regenerative furnace of Figure 3, provide means for introducing reactant materials into the furnace. Each of the plenum chambers may be provided with a perforated distributor plate 41 to insure even distribution of the reactant materials across and through the cross-sec attach oxidant conduit 49 to conduit 44 and, thence, to

conduits 47 and 48, as determined by the setting of valve 46. Conduits 47 and 48 are also selectively connected by a three-way valve 50to an effluent conduit 51 which leads to a product recovery system 52, or other disposal, as desired. Timer 72, which is operatively connected, as previously mentioned, to flow control means 71 contained in fuel inlet line 69, is also operatively connected to threeway

valves

43, 46 and 50, thereby providing the means for sequentially changing cycles of operation of the regenerative furnace.

In still another modification of the invention as shown in Figure 6, regenerative furnace 72 comprises an insulated shell 11 having four spaced apart

refractory masses

73, 74, 76 and 77 disposedtherein. Elements similar to those described in conjunction with Figure 3 are desig nated by identical reference numerals.

Refractory masses

73, 74, 76 and 77 are provided with longitudinal passageways 78 formed by the placement of refractory tiles similar to those described in conjunction with Figure 4. Refractory masses 79, 81 and 82, shorter in length than the principal refractory masses, are disposed within spaces 83, 84 and 86. The shorter refractory masses are similar in construction to those described in conjunction with Figures 3 and 5 and include longitudinal passageways 64,

82 are connected to steam inlet lines (not shown) while the header member associated with refractory mass 81 is connected to a fuel inlet line (not shown); It is to be understood that lines 47 and 48 connected to plenum

chambers

38 and 39 can be further connected to a supply of oxidant and feed material through a valve system, as shown in Figure 3, and that a timer can be used in conjunction therewith to control the cycles of operation.

The regenerative furnaces of this invention are especially adapted for carrying out processes for the production of unsaturated hydrocarbons, such as acetylene, ethylene, and mixtures of acetylene and ethylene. The reaction temperatures for such processes Will vary in the approximate range of 1250 F. to 2700 F. More specifically, in the acetylene process, the reaction temperature is preferably maintained between about 2200 F. and 2700 F, in the process for the production of acetylene and ethylene, between about 1700 F. and 2200 F., and in the ethylene process, between about 1250 F. and 1700" F. The reaction times for the several processes are in the following aproximate ranges: for acetylene, between 0.0001 and 0.2 second; for a mixture of acetylene and ethylene, between 0.01 and 0.2 second; and for ethylene, between 0.01 and 2 seconds. From this consideration of reaction temperatures and reaction times, it is apparent that the reaction times vary inversely with the reaction temperatures, i.e., the higher the reaction temperature, the shorter the reaction time.

A wide variety of hydrocarbon feed stocks can be used in the practice of the processes of this invention. Those which can be suitably used include methane, ethane, propane, butane and mixtures of these hydrocarbons and/or their corresponding olefins. It is to be understood, however, that any vaporizable or gaseous hydrocarbons can be advantageousiy employed as the feed. It is also within the contemplation of the invention to use a diluent such as steam with hydrocarbon feed in order to reduce the deposition of carbonaceous materials within the furnace.

Oxidants which can be used in the process of this invention include oxygen, air, and oxygen-enriched air. Any suitable fuel, preferably a clean burning fuel, can be utilized in the practice of this invention. Gaseous or liquid hydrocarbons are preferably used as fuels, and process off-gases from the procms of this invention or other processes can be advantageously employed. When using a liquid hydrocarbon, the fuel is introduced into the furnace in vaporized form.

In the operation of the regenerative furnace of Figures 3 and 5, during the

regeneration cycle valves

43 and 46 are so positioned by timer 72 as to admit air into plenum chamber 33 and thence into refractory mass 56. It is assumed that the furnace has been previously brought to operating temperature by utilizing an outside source of preheated air. The air, in passing through refractory mass 56, is heated to a temperature at least as high as the ignition temperature of the fuel gas introduced into passageways 64 of refractory mass 61 through fuel inlet line '69, header member 68. tubes 66 and conduits 67. The air, after passing through refractory mass 56, enters passageways 64- of refractory mass 61 where it mixes with the fuel gas to form a combustible mixture. The combustible mixture so formed burns within passageways s4 and combustion space S), forming combustion products at a temperature in the approximate range of 2500 F. to 4000 F., depending upon the amount of air and the amount of fuel introduced into the furnace. The combustion products pass from combustion space 52 and flow through the passageways of refractory masses 63, 62 and 58, heating the refractories to the desired cracking temperature. The combustion products thereafter flow into plenum chamber 39 and then pass through conduits as and 51 to product recovery system 52.

At the conclusion of a predetermined time interval, as determined by the setting of timer 72, valve 43 is actuated to transfer conduit 44 from its connection with conduit 49 to a connection with conduit 42. The timer also functions to close fuel valve 71 and to reverse the settings of

valves

46 and 50 so that conduit 44 is connected to conduit 48 and conduit 47 is connected to conduit 51. As a result of this movement of

valves

43 and 46, the process cycle commences, and hydrocarbon feed and steam, if desired, now pass through conduit 48 into plenum chamber 39. As previously noted, the combination of the plenum chamber and distributor plate provides for even how of gaseous materials through the refractory masses. On contacting hot refractory masses 58, 62 and 57, the hydrocarbon feed is raised to the desired cracking temperature and undergoes reaction. The cracked hydrocarbon feed thereafter passes immediately into and through refractory masses 61 and 56, which has been previously cooled by passage of air therethrough, for rapid quenching to a temperature in the range of about 400 F. to 1000 F. The reaction products then flow into plenum chamber 33, and are subsequently passed through conduits 47 and 51 to product recovery system 52.

After a suitable time interval, timer 72 operates to change the setting of valve 43 so that air is now introduced into plenum chamber 39 through line 48. The air flows through refractory mass 58 where it is heated and thence passes into passageways 64 of refractory mass 62. Fuel introduced into passageways 64 of refractory mass 62 through tubes 66 and conduits 67 mixes with the heated air forming a combustible mixture which burns within the passageways and combustion space 60. The resulting combustion products pass through refractory masses 57, 61 and 56, heating these masses to the desired cracking temperature. The combustion products then enter plenum chamber 3 8 and are subsequently passed to the product recovery system through conduits 47 and 51. After a suitable time interval, timer 72 again operates to close valve 71 and terminate the supply of fuel to refractory mass 62. and to reverse the settings of valves E3, 46 and 50, allowing the hydrocarbon feed to enter plenum chamber 38 through conduit 47. The hydrocarbon feed in passing through refractory masses 56, 61 and 57 is cracked and then immediately passes through refractory mass 62 into refractory mass 58, where it is cooled to a temperature between about 200 F. and 1000 F. The reaction products then pass into plenum chamber 39 from which they are removed through conduits 48 and.

51 to product recovery system 52.

It is also within the scope of the invention to introduce steam directly into the regenerative furnace in order to freeze the reaction and thereby prevent secondary reactions. Accordingly, after passing the hydrocarbon feed through the cracking sections of the furnace. i.e., refractory masses 56 and 57 or refractory masses 57 and 58, steam is introduced into the cracked reaction products as they pass through passageways 64 of the fuel distribution means. By operating in this manner, the temperature of the reaction products is lowered immediately upon their leaving the cracking sections of the furnace at which point the total desired conversion has been obtained. By subjecting the reaction products to a rapid quench, secondary reactions, which result in the formation of coke and tar, are prevented. Only sufficient steam to freeze the reaction is introduced into the regenerative furnace since it is not desired to lower the temperature to such a degree that the refractories will be damaged.

By utilizing a regenerative furnace having two combus tion spaces as shown in Figure 3, it is possible to improve the quality of the cracking reaction. In the furnace of Figure 3, the conversion rate remains constant or increases after passing the middle of the furnace as illustrated by broken line curve 4 of Figure 2. Since the total desired conversion is obtained at a point only slightly downstream of the middle of the furnace and the reactionproducts are then immediately passed into the quench refractories or section of the furnace, the amount of product consumed in secondary reactions is reduced to a minimum. Accordingly, a more efiicient cracking reaction is obtainable in this furnace than in conventional regenerative furnaces.

In the operation of the apparatus of Figure 6, during the regeneration cycle air introduced into plenum chamber 38 through conduit 47 passes through

refractory masses

73 and 74. The air in passing through these masses is heated to at least the ignition temperature of the fuel introduced into passageways 64 of refractory mass 81 disposed in combustion space 84. The combustible mixture so formed burns within the passageways and within combustion space 84, forming combustion products which subsequently pass through refractory masses 76 and 77. In the passing through refractory masses 76 and 77, the combustion products raise the temperature of the refractory to the desired cracking temperature. The combustion products then flow into plenum chamber 39 and are subsequently passed to a product recovery system through conduit 48, as described in conjunction with Figure 3.

At the end of a predetermined time interval, the supply of air and fuel to the furnace is terminated, and a hydrocarbon feed is supplied to plenum chamber 39 through conduit 48 to start the process cycle. The hydrocarbon passes through refractory masses 77 and 76 where it is heated to the desired cracking temperature. The ci'acked reaction products then flow through refractory mass 74 and into passageways 64 of refractory mass 79. In passing through refractory mass 74, cooled on the regeneration cycle by passage of air therethrough, the reaction products are partially quenched and then are further quenched by the introduction of steam into passageways 64 of refractory mass 79 in order to freeze the reaction and prevent the occurrence of secondary reactions. The cooled reaction products then flow through refractory mass 73 where they are still further quenched, thereafter passing into plenum chamber 38 from which they are removed through conduit 47 to the product recovery system.

After a suitable time interval, the flow of hydrocarbon feed to plenum chamber 39 is terminated and the regeneration cycle is begun by introducing air thereinto. The air passes from plenum chamber 39'and flows through refractory masses 77 and 76 where it is heated to at least the ignition temperature of the fuel gas. Fuel gas introduced into the passageways of refractory mass 81 through tubes 66 and conduits 67 mixes with the heated air in the longitudinal passageway, forming a combustible mixture. The combustible mixture burns in the passageways and within combustion space 84 forming combustion products which thereafter pass through

refractory masses

74 and 73, heating these refractories to the desired cracking temperature. After a suitable time interval, the supply of air and fuel to the furnace is terminated, and hydrocarbon feed is introduced into plenum chamber 38 through conduit 47 to begin the process cycle. The hydrocarbon feed flows through

refractory masses

73 and 74 and is cracked therein, forming the desired reaction products. The reaction products leave refractory mass 74, passing into and through refractory masses 76 and 82. In passing through refractory mass 82, the reaction products are quenched, as previously described, by the introduction of steam into the longitudinal passageways of this mass. The quenched reaction products then pass through refractory mass 77 for further quenching and thence flow into plenum chamber 39. From plenum chamber 39, the reaction products are removed through conduit 48 and passed to the product recovery system. Thereafter, the regeneration and process cycles are repeated at the predetermined time interval to produce the desired product.

By utilizing the regenerative furnace of Figure 6, it is possible to immediately lower the temperature of the reaction products to a temperature at which they are comparatively stable. By introducing steam directly into the furnace at points on either side of the combustion section, the steam is introduced at points where the cracking reaction is complete. By providing for an immediate and rapid quench of the reaction products, side reactions are substantially eliminated, thereby cutting down on the formation of coke and tars and concomitantly providing for a greater yield of product. In introducing the quench steam into the regenerative furnace, only sufiicient steam is employed to freeze the reaction, and use of excess steam, which might injure the refractories is to be avoided.

The fuel and steam distribution means of Figures 3 and 6, serve a secondary function in the operation of the furnace in that they provide for the even distribution of gases across the faces of the refractory masses. Because these members facilitate the even distribution of gases through the furnace, channeling of the gases through a portion only of the furnace is prevented. The result of providing for such an even distribution of gases through the furnace is a more efiicient cracking reaction in which overcracking and undercracking of the hydrocarbon feed stock are reduced to a minimum.

A more comprehensive understanding of the invention may be obtained by referring to the following illustrative examples which are not intended, however, to be unduly limitative of the invention.

Example I A regenerative furnace of a conventional type described herein as having similar refractory cracking sections separated by a central combustion chamber is utilized to convert ethane. The hydrocarbonfeed rate is 72,450 pounds of ethane per day, the combustion temperature is about 2200 F., and the combustion gas outlet temperature is about 1040 F. percent of the ethane, refractory cracking sections each having a length of 44 feet are required. A very close temperature approach occurs in the center of the cracking sections, 20 feet being required in the pinch sections.

Example 11 A regenerative furnace similar to the one employed in Example I is utilized to convert ethane. The hydrocarbon feed rate is 72,450 pounds of ethane per day, the combustion temperature is about 2800 F., and the combustion gas outlet temperature is about 1000 F. The average temperature of the hydrocarbon during the cracking reaction is about 1700" F. The desired total conversion of eighty-three percent is obtained at a point about 1.5 feet downstream from the middle of the furnace with the result that the reaction period is greatly prolonged. At higher conversions, the point at which total conversion is obtained is moved even farther downstream from the middle of the furnace, e.g., at a total conversion of ninety-six percent about 3.5 feet. The yield of ethyl ene when 83 percent of the total feed is cracked is 70 pounds per pounds of ethane cracked. Because of the long reaction time required to obtain the desired total conversion, a considerable amount of product is consumed by secondary reactions.

Example III A regenerative furnace similar to the one illustrated in Figure 3 is utilized to crack ethane. The hydrocarbon feed is charged to the furnace at the same rate as in Example II, and the combustion temperature and combustion gasoutlet temperature are also approximately 2800" F. and 1000 F., respectively. The average temperature during the cracking reaction is about 1800 F. By utilizing a furnace having two combustion sections, the conversion rate increases in the middle of the furnace. The total desired conversion of eighty-three per cent is obtained at a point about one-half foot downstream from the middle of the furnace. At a conversion of ninety-six percent, the point is moved only about one foot downstream from the center of the furnace. The reaction In order to convert ninety products then immediately pass into the quench section where they are quenched to a temperature at which they are stable. The yield of ethylene when 83 percent of the total feed is cracked is 75 pounds per 100 pounds of ethane cracked, an increase of 8.3 percent over that in Example II. The amount of product consumed in secondary reactions is thereby reduced to a minimum. Furthermore, because the conversion rate is maintained after passing the middle of the furnace rather than decreasing as with conventional furnaces, the over-all furnace length can be decreased. It is also to be noted that a higher cracking temperature (1800 F.) can be obtained in the improved furnace of Example III than is obtained in the furnace of Example II (1700 F.) at the same combustion temperatures (2800 F.).

It will be apparent that many advantages accrue from the utilization of the regenerative furnaces of this invention. Accordingly, by utilizing a furnace which provides for a more rapid heat transfer rate in the central portion of the cracking sections, it is possible to decrease the over-all length of the furnace. Furthermore, by utilizing a furnace comprising three refractory masses separated by combustion spaces, it is possible to improve the quality of the cracking reaction. Still again, by utilizing apparatus of the type described, a rapid quenching of the reaction products within the furnace proper can be effected, thereby substantially eliminating secondary reactions and providing for a greater product yield.

As will be evident to those skilled in the art, various modifications of this invention can be made or followed without departing from the spirit or the scope of the disclosure.

I claim:

1. A regenerative furnace which comprises, in combination, an elongated, closed shell; a first refractory mass disposed in one end portion of said shell; a second refractory mass disposed in the other end portion of said shell; a third refractory mass disposed in an intermediate portion of said shell, each of said refractory masses having passageways therethrough substantially parallel to the longitudinal axis of said shell; a fourth refractory mass positioned between and spaced apart from said first and third refractory masses; a fifth refractory mass positioned between and spaced apart from said second and third refractory masses, each of said fourth and fifth refractory masses having a plurality of passageways therethrough substantially parallel of the longitudinal axis of said shell;

and means for introducing air and material to be converted into the ends of said first and second refractory masses remote from said fourth and fifth refractory masses, respectively.

2. The regenerative furnace of claim 1 in which each said fourth and fifth refractory masses are substantially shorter in length than each said first, second and third refractory masses.

3. A furnace according to claim 1 wherein conduit means are provided for introducing fluid directly into each of said fourth refractory mass and said fifth said refractory mass from outside of said shell.

4. A regenerative furnace which comprises, in combination, an elongated shell; a first refractory mass disposed in one end portion of said shell; a second refractory mass disposed in the other end portion of said shell; third and fourth refractory masses disposed in an intermediate portion of said shell, said third refractory mass being between said first and fourth refractory masses; relatively short fifth, sixth and seventh refractory masses positioned, respectively, between said first and third, said third and fourth, and said fourth and second refractory masses; passageways extending therethrough, and each of said refractory masses being spaced apart from the adjacent refractory masses, said passageways being substantially parallel to the longitudinal axis of said shell; means for introducing fuel from ouside said shell directly into said 10 sixth refractory mass; means for introducing fluid fiom outside said shell directly into said fifth refractory mass and said seventh refractory mass; and means for passing air and material to be converted through said refractory masses.

5. The regenerative furnace of claim 4- in which said means for passing air and material to be converted through said refractory masses comprises first and second plenum chambers each having a conduit attached thereto and each attached to and enclosing one of the ends of said shell.

6. A regenerative furnace which comprises, in combination, an elongated, closed shell; a first refractory mass disposed in one end portion of said shell; 21 second refractory mass disposed in the other end portion of said shell; a third refractory mass disposed in an intermediate portion of said shell, each of said refractory masses having passageways therethrough substantially parallel to the longitudinal axis of said shell; a first combustion section comprising a fourth refractory mass positioned between and spaced apart from said first and third refractory masses; a second combustion section comprising a fifth refractory mass positioned between and spaced apart from said second and third refractory masses, said fourth and fifth refractory masses having passageways therethrough substantially parallel to the longitudinal axis of said shell; fuel introduction means within each of said combustion sections communicating with said passageways of said fourth refractory mass and said fifth refractory mass, said means comprising additional passageways extending through each said fourth and fifth refractor/ masses substantially perpendicular to the longitudinal masses of said shell and between said parallel passageways, conduit means communicating said perpendicular passageways with said parallel passageways; a first header member connected to said perpendicular passageways of said fourth refractory mass for introducing fuel into each of said perpendicular passageways; a second header member connected to said perpendicular passageways of said fifth refractory mass for introducing fuel to each of said last-named perpendicular passageways; and means for introducing air and material to be converted into the ends of said first and second refractory masses remote from said combustion sections.

7. A process for converting hydrocarbons which comprises passing air through a first refractory checkerwork into a first combustion Zone; introducing fuel gas into said first combustion zone, thereby forming a combustible mixture; burning said combustible mixture; passing the resulting combustion products into and through a second and a third refractory checkerwork in order to heat same to a desired temperature; terminating the supply of air and fuel gas; introducing hydrocarbon feed into said third refractory checkerwork; passing said hydrocarbon feed through said third and second refractory checkerworks, thereby cracking said feed; introducing steaminto said reaction products immediately upon their passing from said second refractory checkerwork so as to rapidly cool same; passing the resulting cooled reaction products into and through said first refractory checkerwork, there by further cooling said reaction products to a temperature at which they are comparatively stable; removing said cooled reaction products from said first refractory checkerwork; passing air through said third refractory checkerwork into a second combustion zone; introducing fuel gas into said second combustion zone, thereby forming a combustible mixture; burning said combustible mixture and passing the resulting combustion products into and through said second and first refractory checkerworks in order to heat same to a desired temperature; terminating the supply of air and fuel gas; introducing a hydrocarbon feed into said first refractory checkerwork; passing said hydrocarbon feed through said first and sec ond refractory checkerworks, thereby cracking said feed;

introducing steam into said reaction products immediately upon their passing from said second refractory checkerwork so as to rapidly cool same; passing the resulting cooled reaction products into and through said third refractory checkerwork, thereby further cooling said reaction products to a temperature at which they are comparatively stable; removing said cooled reaction products from said third refractory checkerwork.

UNITED STATES PATENTS V Keeling Aug., 29, 1950 Hasche June 19, 1956 Hasche July 17, 1956 Begley Mar. 12, 1957 Begley et al. Dec. 30, 1958 Begley Ian. 13, 1959

Claims

1. A REGENERATIVE FURNACE WHICH COMPRISES, IN COMBINATION AN ELONGATED, CLOSED SHELL, A FIRST REFRACTORY MASS DISPOSED IN ONE END PORTION OF SAID SHELL, A SECOND REFRACTORY MASS DISPOSED IN THE OTHER END PORTION OF SAID SHELL, A THIRD REFRACTORY MASS DISPOSED IN AN INTERMEDIATE PORTION OF SAID SHELL, EACH OF SAID REFRACTORY MASSES HAVING PASSAGEWAYS THERETHROUGH SUBSTANTIALLY PARALLEL TO THE LONGITUDINAL AXIS OF SAID SHELL, A FOURTH REFRACTORY MASS POSITIONED BETWEEN AND SPACED APART FROM SAID FIRST AND THIRD REFRACTORY MASSES, A FIFTH REFRACTORY MASS POSITIONED BETWEEN AND SPACED APART FROM SAID SECOND AND THIRD REFRACTORY MASSES, EACH OF SAID FOURTH AND FIFTH REFRACTORY MASSES HAVING A PLURALITY OF PASSAGEWAYS THERETHROUGH SUBSTANTIALLY PARALLEL OF THE LONGITUDINAL AXIS OF SAID SHELL, AND MEANS FOR INTRODUCING AIR AND MATERIAL TO BE CONVERTED INTO THE ENDS OF SID FIRST AND SECOND REFRACTORY MASSES REMOTE FROM SAID FOURTH AND FIFTH REFRACTORY MASSES, RESPECTIVELY.

7. A PROCESS FOR CONVERTING HYDROCARBONS WHICH COMPRISES PASSING AIR THROUGH A FIRST REFRACTORY CHECKERWORK INTO A FIRST COMBUSTION ZONE, INTRODUCING FUEL GAS INTO SAID FIRST COMBUSTION ZONE, THEREBY FORMING A COMBUSTIBLE MIXTURE, BURNING SAID COMBUSTIBLE MIXTURE, PASSING THE RESULTING COMBUSTION PRODUCTS INTO AND THROUGH A SECOND AND A THIRD REFRACTORY CHECKWORK IN ORDER TO HEAT SAME TO A DESIRED TEMPERATURE, TERMINATING THE SUPPLY OF AIR AND FUEL GAS, INTRODUCING HYDROCARBON FEED INTO SAID THIRD REFRACTORY CHECKERWORK, PASSING SAID HYDROCARBON FEED THROUGH SAID THIRD AND SECOND REFRACTORY CHECKERWORKS, THEREBY CRACKING SAID FEED, INTRODUCING STEAM INTO