US2332051A - Method of heating and converting hydrocarbons - Google Patents

Description

Oct. 19, 1943. D. G. BRANDT METHOD OF HEATING AND CONVERTING HYDROCARBONS Filed Nov. 8, 1940 2 Sheets-Sheet 1 OOOOQQOOOOOOOOQ Q0 0 Q0 OOOQQOOOOOO L wowowowowo m r w I 7:: 0 0 o 0 0% $4.12? 0 0 0 0 0 0 0 0 0 0 LL31 fi nnnl h 0 0 0 0 0 \1 HHIHO INVENTOR DAVID G. BRANDT BY Z 2 ATTORNEY Oct. 19, 1943. D. e. BRANDT METHOD OF HEATING AND CONVERTING HYDROCARBONS Filed Nov. 8, 1940 '2 sneets sheet 2 T'IOTOR DAVID 6. BR

INVENTOR AN 01' BY m ATTORNEY Patented Oct. 19, 1943 anaest- UNITED STATES PATENT OFFICE METHOD OF HEATING AND CONVERTING HYDROCARBONS David G. Brandt, Westfield, N. J assignor to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania,

Application November 8, 1940, Serial No. 364,798

1 Claim. (01. 196-9) This invention relates to improvements in method of converting hydrocarbons and. pipe still apparatus therefor. More particularly, the improvements relate to the heating of separate streams of hydrocarbons, the combining of said streams, and the heating of the resulting mixture in the same pipe still furnace.

This application is a continuation in part of application Serial No. 262,627, filed March 13, 1939, for Pipe still furnace and method of heating hydrocarbons, now Patent No. 2,221,469.

The primary object of the present invention is to provide an improved pipe still furnace in which separate banks of tubes may be heated under different conditions.

Another object of the invention is to provide an improved method for heating hydrocarbons to effect their conversion into more desirable products.

These and other objects of the invention are attained by constructing a pipe still furnace with two or more radiant heating chambers of relatively great length compared with their width, providing heating tubes onthe side walls of such chambers, and providing a firing pit opening into the bottom of each chamber and extending sub stantially the entire length thereof. The pipe still furnace is also provided with burners in the bottom of the pits, means for recirculating flue gases from the furnace back through the radiant heating chambers, and for distributing such gases over the tubes in the radiant heating chambers. Provision is also made for utilizing the combustion gases from the radiant heating chambers for heating a bank or banks of tubes mounted in a convection section of the furnace.

The important feature of the operation of the furnace is for example, the heating of one hydrocarbon stock on one side of thefurnace to a very high temperature which may be considerably higher than the temperature used on the other side of the furnace for heating a different stock. While means is provided for individually controlling these temperatures, the temperature in the convection heating section of the furnace is controlled independentlyfor example, by increasing the firing and circulation in oneof the radiant chambers and'at the same time not increasing the temperature in that chamber because of the high recirculation load. This control is particularly advantageous because it permits the use ofthe convection section at the de" sired temperature and the carrying out of an exothermic conversion reaction, since the large quantity of flue gas will act as a buffer to maintain the desired temperature either above or be low that which might otherwise exist in the convection reaction tubes. 1

The invention will'be further described with the aid of the accompanying drawings which show by way of example a preferred form of the invention, it being however understood that the inventionis by no means limited to the specific embodiment illustrated. In the drawings:

Fig. 1 is a verticalrcross sectional view of the improved pipe still furnace taken on the line l-! of Fig. 3, showing the relationship of the heating chambers and positions of the various tube banks.

Fig. 2 is a broken longitudinal vertical sectional view taken on the line 2--2 of Fig. 3.

Fig. 3 is'a horizontal sectional view taken on the line 33 of Fig. 1.

Fig. 4 is an enlarged sectional view of a portion of the burner arrangement shown in Fig. 1.

The improved pipe still furnace of the present invention comprises a masonry structure composed of outside supporting walls secured to steel beams to which is also secured an inside refractory brick lining.

Referring to Fig. 1 of the drawings, the furnace comprises two radiant heating chambers; 6 and 8 arranged in symmetrical manner, although a greater number of chambers may be employed if desired. These heating chambers arerelative- 1y long and narrow and'provided withinside and outside rows of wall heating tubes for the heating of hydrocarbon stock to be converted. For example, a hydrocarbon stock such as gas oil, kerosene, naphtha or butane, may be supplied to the furnace at the desired pressure through a valved supply line Ill from which it passes through aseries ofrpreheated tubes 12 comprising the right half of the lower bank shown in Fig. 1. The hydrocarbon stock is then conducted by :a connecting line l4 through an inside wall tube bank [6 mounted in the heating chamber 6, a connecting line l8, a side wall tube bank 20 and then through a roof bank of tubes 22, all heated by radiant heat in the chamber 6. i

In accordance with the features of the invention a different stock from that heated in chamber 6 is supplied to the other side of the furnace at the desired pressure through a valved inlet line 24 and passed through preheating tubes 28, from which the stock is conducted. through a connecting line 28, a wall tube bank 30 mounted in the heating chamber 8, a connecting line 32, an outside wall tube bank 34 and a roof bank 3'0. The tube banks 30, 34 and 3B are heated by radiant heating in the chamber 8 and such heating may be to a higher or lower temperature than that to which the stock is heated in the tube banks of chamber 6. All of the tubes of the chambers 6 and 8 are supported in metal tube brackets or supports as shown in the drawings.

The hydrocarbon products passing through the tube banks 22 and 36 are mixed in a connecting line 38 and then distributed into a large convection tube bank 40 arranged between and separated from the heating chambers 6 and 8 by refractory bridge walls 42 adjacent the wall banks I6 and 3D. The mixture of products in the line 38 and preferably distributed as shown into parallel tube arrangements so that hydrocarbon vapors for example may be heated for a relatively long period of time in the tube bank 40, which extends the full length of the furnace and in which the tubes are supported by tube sheets 44 (also used to support tubes l2 and 26). The products heated in the "tubes of the tube bank 40 are collected in a line and discharged from the furnace for further treatment.

The wall and roof tubes mounted in each of the radiant heating chambers '6 and iii are supplied with radiant heat from long firing pits 48 which extend substantially the full length of the heating chambers. These ':pits are lined with high temperature refractory material and are preferably constructed with :upwa-rdly diverging side walls as shown which may have a smooth slope or may diverge by steps. The pits "48 are of substantial depth and the walls convergedown to a series of burner units which. are preferably made up in section as :shown in Fig. 3. The

individual bumersare preferably constructed as shown in Fig. =4, iiuel :being supplied thereto through pipes 52, and air for combustion being supplied to the passage way below the burner units'or sections through air "ducts iil.

As shown inEig. 3, the burner for supplying combustion gases to the bottom of the pits 88 are divided into-three sections, 56, 58 :and 130. These sections are preferably supplied with fluid fuel such as combustible gas '01 oil under separate control, so that :the heating efiected by any section may be increased or decreased as desired.

Each burner section 56, 58 and Til) includes a plurality :of burner openings t! into which fluid dfuel is injected and air iinduced. In each o'f'the burner sections there is also a plurality of openings B4 for the admission of secondary air to the space above the burner section proper. The

structure of the burner units is shown more in detail .in the broken sectional view of Fig. 4 in which the burner is shown as comprising a steel supporting plate SB containing the proper holes corresponding to the-openings G2 and 84, the lower portion of the openings 52 being'iormed by short flaring tubular sections of cast iron 68 set in the holes in the steel plate 65. "The burner sections are then formed by filling in around the cast iron elements 68, and removable cores set in openings 64,with plastic refractory material to form the flaring :outer :portion :of :the :openings 62. The whole :unit :or section-of the :plate -66 which may be .-from 4 to 8 feet in length, is cast, dried andifired.

Fluid fuel and air for combustion is supplied to the lower portion of the openings .62, the former from the fuel pipe 2, by means of :branch pipes which terminate in burner tips =7 2, which in turn are provided with braces 14 ,for positioning the burner tips with respect to the openings 62. As combustion take place in the pits 48, the combustion gases expand into the increasing cross sectional area of the burner pits, the diverging walls of which permit the expansion of the gases during combustion without substantially increasing their velocity.

The high temperature combustion in the pits 48 heat the diverging walls thereof to extremely high temperatures so that they constitute radiant heating surfaces which reflect upon the tubes of the wall banks 16, 20, and 34 and of the roof banks 22 and 36. It will be noted that the walls of the combustion pits are so arranged that the wall tubes closest to the pit are exposed to a smaller .area of the radiant pit walls than are the .tubes at greater distances. This arrange ment prevent overheating of th tube closest to the combustion pits and at the same time provides adequate radiant heating surface for the tubes at greater distances. The radiant surfaces may be actually arranged :so that all wall tubes as well .as :the roof radiant tubes will -be heated toappro-ximately thesame degree.

The combustion gases discharged from the combustion pits :48 flow up through the radiant heating chambers 6 and 8 and over bridge walls '32 into the convection heating chamber where they heat the reaction tube bank and the preheating tubes l2 and 25. .A considerable part of the heat in the combustion gases is removed by the tube banks .48, I2 and 25, after which the gases thenflow through end discharge ducts 16 into a passageway 18 (Fig. 3) from which they pass to a stack or to a recirculation flue gas fan 82, or both. The ducts .16 :are provided with control damper 84 which maybe operated by handles F85 to control the proportion of flue gas discharged {through each 'duct.

One of the important features of the present invention is the recirculation of flue gases discharged from :the furnace back into the radiant heating chambers to aid in controlling the heating of the roof 'tubes :and also the convection tubes. The :gases to be recirculated are picked ,up by ,the Ian 82 which is operated by a .motor asshownin Fig-3, andconducted through a main passageway 88, then into distribution headers '90 for the zradiantlheatingchambers 8 and ii. From the headers M the recirculated hot flue gases are passed to distribution ducts on each side of the burner pits which extend beneath the wall tubes I6 22 8, 30 and 3A. The means for distributing the flue gases under each .of the wall tube banks is illustrated in detail in Fig. .2 in which flue {gases :are conducted from each header 9!) through separate distribution ducts 92,114 and 96 which :lead respectively to the front, middle and'farend-sections of the furnace. The proportion of hue gas introduced into each of these ducts is controlled bya @damper $8. The flue gas passed through the ducts 92, 94 and 96 (Fig.2) is distributed directly under the vertical row of wall tubes. through openings sbetween fire brick Hi8 which-are mounted in spaced relation directly below each of the vertical rows of wall tubes 34. Thesame arrangement 'is used :for the otherwall tubes I6, .28 and 30. The dampers 98 for controlling the supply 50f recirculated flue gas to ducts -92, 94-.and I98 for bothsides ofeach of the radiant heating chambers 15 and *8 may, if desired, be operated together by handles I02, as shown in Fig. 3. Thedampers 98 forany vertical tube bank may be operated individually to effect any desired control.

Instead-of dividing the radiant heating chambers lengthwise into three sections with respect to return of the flue gases (which correspond generally to the three- burner sections 56, 58 and 66), each heating, chamber may be :divided into any desired number of sections provided with individual control. The structure as shown provides for the control of the recirculated flue gas introduced into any section of each radiant heating chamber by suitable manipulation of the dampers 98. For example, all of the flue gases returned to one of the radiant heating chambers may be introducedthrough the opposite-passageways 96 or the dampers 98 may be adjusted to exactly proportion the returned flue gases to the whole length of the heating chamber through the passages 92, 94 and 96 which would be impossible if the furnace were not divided into sections for control of flow. The burner sections 55, B and 66 mounted inthe bottom of each combustion pit are preferably operated by sections corresponding to the sections of control provided for the return of flue gases.

In heating the vertical wall tube banks in either heating chamber 6 or 8, the burner sections may be operated for example by supplying most of the fuel to the section 55 and-only moderately firing the burner sections 58 and 6D. In such a case the flue gases returned to the chamber may be introduced to the greatest extent through ducts 92 for that chamber by controlling the dampers 98 thereto. This type of operation will provide adequate protection for the portions of the tubes opposite the burner section 53. The heating of this particular chamber may be further controlled by closing the flue gas outlet nearest the fan 82 in Fig. 3, so that most of the flue gas is discharged from the opposite end of the furnace to that of highest temperature. This will cause a flow of combustion gases longitudinally in the radiant heating chamber and supply more heating gases to thev sections toward the stack end of the convection heating chamber containing tube banks 40, I2 and 26.

Various other modifications may be made in the operation of the burner sections and flue gas return ducts to accomplish any desired result or effect, and one of the radiant heating chambers may be operated to supply considerably more heat or a higher temperature than the other if desired or necessary in carrying out a particular conversion operation.

As an example of the use of the improved pipe still furnace arrangements in the conversion of hydrocarbons to produce a high anti-knock gasoline, a charging stock of straight run gas oil is introduced at a pressure of about 600 lbs. per square inch through the line Iii, preheated in tubes I2, and then subjected to conversion in tube banks It, 29 and 22, so that the products are discharged into the mixing line 38 at a temperature of about 980 F. The heating operation carried out in the radiant heating chamber 6 is preferably such that the gas oil is heated rapidly to an active cracking temperature in the tube bank It and then subjected to conversion in tube banks 29 and 22 to provide a maximum of unsaturated olefinic type hydrocarbons by the time the products enter the mixing line 38.

During this operation in the radiant heating chamber 5 a butane fraction is converted in radiant heating chamber 8. In this operation a butane fraction composed mainly of butane but which may include propane and a small proportion of pentane, is introduced at a pressure of about 600 lbs. per square inch through the products.

line 24, preheatedin tubes 26, and rapidly heated to' a temperature of about 1050 F. in wall tube banks 30 and 34. The temperature of the butane fraction is further raised to about 1100" F. in the tube bank 35, so as to effect substantial dehydrogenation by the time the products enter, the mixing line 38. i

In the line 38 the hydrocarbon products containing' very substantial proportions of unsaturated hydrocarbons, are mixed and then distributed into the tube bank 40 where alkylation and polymerization reactions take place to produce a product boiling within the gasoline range which contains from 25% to of aromatic hydrocarbons. Many of these hydrocarbons have side chains of from 1 to 6 carbon atoms. The temperature in'the tube bank 49 is controlled to substantially maintain the reaction conditions constant at a temperature of about 1925 F. or somewhat lower, depending upon the aromatic content desired in the final product. The high temperature products are discharged from the tube bank 46 through the transfer line 46 into suitable apparatus for segregating the desired Under certain conditions, the high temperature products in the line 46 may be conducted into a reaction chamber for further conversion either with or without a catalyst. In any case, the products discharged through the line 46 are subsequently fractionated in the desired manner to separate out the desired high antiknock gasoline or motor fuel fraction.

In the operation described above, the temperatures maintained in the radiant heating chamher 8 are substantially above those maintained in chamber 6. This may be accomplished by increasing the firing rate of the burner sections for the chamber 8. Flue gas recirculated along the wall tube banks in both radiant heating chambers may be controlled to prevent substantial impingement of high temperature gases from the firing pits. Furthermore the temperature in the convection bank 40 may be controlled independently by increasing or decreasing the firing rate in one of the furnace chambers and increasing or decreasing the flue gas recirculation rate therein. An increase in the circulating flue gas load has its primary efiect upon the conditions maintained in the convection bank All which may be controlled so that the flue gases either act to slightly raise the temperature of the hydrocarbon products under reaction or to actually decrease the temperature of the hydrocarbon products and prevent undue rise in temperature because of exothermic reactions which may take place in the hydrocarbons being treated.

Various modifications may be made in the pipe still furnace and in its operation to carry out the desired conversion reactions without departing rom the spirit and scope of the invention as defined by the accompanying claim.

Having thus described the invention in its preferred form, what is claimed as new is:

A process for converting hydrocarbons for the reduction of hydrocarbons of high antiknock value in a pipe still furnace provided with radiant heating chambers separated by a convection heating chamber, said chambers being provided with tubes for heating the hydrocarbons to be converted, which comprises separately and independently heating relatively low boiling and relatively high boiling stocks in said radiant heating chambers, said stocks being substantially completely vaporizable under the temperature and pressure conditions .maintained :in :the tubes of said radiant heating :chamb'ers, heating the higher boiling stock to :a cracking temperature ffor :a suificient time to convertittoa :productcontaining substantial proportions of unsaturated olefinic hydrocarbons, heating the lower boiling stock to a substantially higher cracking temperature and converting said lower boiling. stock into constituents containing substantial proportions of olefinic hydrocarbons, mingling the conversion products of said heating operations carried out in said radiant heating chambers and conducting the resulting mixture through the tubes in said convection heating chamber and therein interpolymerizing and reacting the hydrocarbon conversion products to produce a substantial proportion of constituents boiling within the motor fuel range :andwhich are of'hig'h antiknock character, maintaining a substantially constant temperature in said convection heating chamber, independently heating the hydrocarbons in said radiant heating chambers 'by radiation from a combustion heating means in each chamber, combining the high'temperature products of combustion from said radiant heating chambers and passing them over the heating tubes insthe convection heating chamber to effect the :desired reactions therein, maintaining a substantially higher temperature in the radiant heating chamberin which the lower boiling stock is heated than in the other radiant heating chamber, and simultaneously and independently controlling the temperature maintained in the convection heating chamber without substantially changing the temperature maintained in said radiant heating chambers and preventing impingement of high temperature combustion gases on the heating -tubes in said higher tempera'ture radiant heating chamber by distributing regulated quantities of relatively cool recycled flue gases over the heating tubes in said higher temperature radiant heating chamber and conducting the flue gases passed over said tubes into'sa'id convection heating-chamber along with the combustion products from said higher temperature radiant heating chamber, whereby a substantially constant temperature is maintained in said convection heating chamber regardless of the high temperatures in saidradiant heating chambers.

DAVID G. BRANDT.

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