US2688589A - Apparatus - Google Patents

Description

Sept. 7, 1954 o. F. CAMPBELL. ET Al. 2,688,589

APPARATUS 2 Sheets-Sheet l Filed July 3, 1951 Sept. 7, 1954 o. F CAMPBELL ET AL 2,688,589

APPARATUS 2 Sheets-Sheet 2 Filed July 3, 1951 kmfam i@ Patented Sept. 7, 1954 APPARATUS Oliver F. Campbell and William H. Decker, Whiting, Ind., assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application July 3, 1951, Serial No. 235,006

2 Claims.

Our invention relates to a new type of furnace for refinery still service including diverse and variable operations such as preheating, cracking, vis-breaking, and the like. More particularly, our invention relates to a furnace of the vertical, cylindrical, all radiant, upshot red type which employs highly preheated air and mechanical draft and in which the various design elements are arranged in a particular manner providing special advantages in the way of flexible operating control, high capacity coupled with high efficiency, controlled heat distribution coupled with simplicity in design, low ring and operating costs and easy maintenance.

One of the basic problems in oil refinery furnace design is the practical limit on increase in capacity through simple pro-ration of the general dimensions of conventional designs due to the diioulty of assuring satisfactory burner operation and air supply together with the difculty of maintaining controlled heat distribution within the furnace cavity. For example, we have operated single burners with a capacity release of barrels of fuel oil per hour or 7,000 pounds per hour which is well above the release rates of conventional burners or furnaces. If a burner capable of higher rates is designed, much higher air supply fan pressures are required and elaborate precautionary measures are necessary to protect the refractory linings of the burner throat. These modications tend to become prohibitively costly from the standpoint of installation expense and operating costs. More critical, moreover,than the problem of adequate throat and burner design is the problem of controlled heat distribution in high capacity furnaces. As the number and length of oil heating tubes in the furnace is increased the problem of assuring complete positive control of the heat distribution patterns in all zones of the furnace is increasingly magnified. The result is that distribution control becomes poorer, particularly in the case of a furnace fired with a single burner, which magnies the danger of overheating and coking within the tubes if the control of the heat flux pattern should be lost at any time during operation. Excessive coking or decomposition may destroy both product quality and if extensive enough may require replacement of the tube metal. Excessive coking also tends to limit seriously the operating cycle of a given unit to too short a period.

We have now devised a furnace which develops the increased capacity of the desirable larger duty furnaces but which retains the advantages of ordinary cylindrical furnaces such as controlled heat distribution, simplicity in design, low firing and operating costs and easy maintenance together with high eiciency and flexibility of control. In accordance with our invention we provide a vertical cylindrical furnace shell, two or more rows of tubes which may be multiple rows arranged concentrically within the shell in a manner providing an annular space between the rows or multiples of rows. Within each of the rows are situated a plurality of vertically disposed interconnected heating tubes. A plurality of burners are arranged within this annular space between the rows and are situated in the lower portion of the furnace so as to iire upwardly between the rows. A refractory cylinder providing a flue gas well is located centrally within the inside tube row, and a flue gas outlet duct is connected to a lower portion of the flue gas well. Oil inlets to the tubes and oil outlets from the tubes are provided in accordance with the particular arrangement of tubes within the rows and the requirements placed upon the furnace. Means are provided for supplying fuel and air to each of the burners and means is provided for withdrawing iiue gas from the outlet duct to a stack. Advantageously, the air supply to the furnace is highly preheated, preferably by exchange with the ue gas eluent in a regenerative type air preheater. I'ihus an induced draft fan may be used to withdraw flue gas through the flue gas outlet duct and through the flue gas section of the preheater while a forced draft may be used to feed air to the air section of the preheater and through an air duct from the preheater to the burners.

In a special aspect of our invention, the air duct is arranged in circular form such that it is in communication with the air section of the preheater and is connected with each burner through an individual windbox, each of which is desirably equipped with a blast gate or damper in the individual air supply duct to the wind box so that the air supply means supplies air in an individually controllable fashion from the air duct to each of the burners.

Also we have found that it is of special advantage to arrange the burners around a common circle of intermediate diameter within the annulus between tube rows. Moreover, multiple tube rows provide exibility in operation by lending the furnace design to staggered, radial or other types of tube flow arrangement. The tubes are in a particular sense of our invention interconnected so as to form a plurality of serially communicating coil sections which provide great flexibility in heating operations. Thus a 4-coil equilateral tube pattern may be selected with the oil entering the bottom of the heater on the inside row, flowing one-quarter of the way around the furnace, crossing over at the top to the outside row, passing back through one-quarter of the furnace and out at the bottom. Our invention however permits a number of different tube arrangements and provides for almost any desired number of coils in the furnace.

Our invention will be further described by reference to the accompanying drawings in which Figure 1 represents a plan view in partial section of a particular furnace design. Figure 2 represents a partially cut away andI sectionalized view of a furnace constructed according to our invention. Figure 3 represents a plan view of a variable tube and coil arrangement based upon the principles of our invention.

In the particular design illustrated in the accompanying drawings, the design is based upon a furnace capacity of 200,000,000 B. t. u. per hour heat release rate at an efficiency of 75% resulting in an absorption rate of 150,000,000 B. t. u'. per hour. The specific service required an overall average absorption rate of 8,000 B. t. u; per hour per square foot, based upon outside tube surface. This determines the number of tubes required for the particular installation in accordance with the desired size and length of tube.

Obviously, however, these datav are not oiered as critical but merely as illustrative since it is possible to select widely varying tube sizes and lengths in accordance with different average adsorption rates for a given furnace duty.

In the drawings, it is seen that a furnace shell I is provided and the tubes II are placed, by way of illustration, in two double rows. The burners I2 are arranged on a common circle of intermediate diameter between the inside and outside tube rows, I3 and I4 respectively. The burners nre upwardly and the flue gases pass up through the annular zone 3| between the rows, ow around the top of the inside tube row and pass downwardly through a circular flue gas well I 5 which is situated centrally in the furnace. The ue gases leave the circular flue gas well I5 at grade elevation and pass by means of flue gas duct IS into a regenerative type air preheater Il. An induced draft fan I8 provides a convenient means for withdrawing flue gases through the flue gas duct I6 and the flue gas section of the air preheater Il to the stack I9.

Preheated air is supplied to the furnace by a separate air supply, advantageously directed to a small secondary windbox 20 for each pair of burners I2. The individual air supply is taken from a large circular duct 2| located below the rst construction platform of the furnace. Thus the duct v2| and the individual windboxes are arranged for complete accessibility to the burners, and provision is made for easy replacement and maintenance by installing a blast gate or damper (not shown) in the connecting air supply ducts from the circular air duct 2| so that any two burners may be isolated for repair even during operation. The blast gate provides for additional control of air supply for supplementary regulation of flame pattern and heat distribution in any part of the furnace. Circular air duct 2| is supplied by means of preheated air duct 22 from regenerative air preheater Il, or other type preheater such as a tubular air heater, which advantageously is located at grade elevation, and by forced draft fan 23. As shown in the drawings a single air preheater and a single set of fans, forced draft and induced draft, are used. The fans may be driven by a common driver with a hydraulic coupling between the forced draft and induced draft for controlled speed regulation. For very large size units, however, it is desirable to install more than one set of air preheaters with more than one set of associated fans using if desired separate drivers for each fan. In this respect, the means for supplying air and easily disposing of flue gases is flexible enough to provide for changes suggested" by operating conditions, furnace capacity and other operating considerations.

In construction, the furnace shell I0 as indicated in Figure 2 is protected by an internal refractory lining 30. The tubes are placed in multiple rows with the burners I2 ring upwardly into the annulus 3|` between the rows. Most advantageously all of the tubes are bottom supported using \-type single plug return bends to simplify and reduce the structural problems and reduce first cost. As shown the burners I2 are' arranged-on a common circle of intermediate diameter between the outside and inside tube rows, III and I3, respectively. The circular ue gas well I5 is of refractory construction in the form ofV a cylinder I5 situated centrally of the inside tube row |3 in a manner conducting the ue gases down through the internal core of the furnace cavity. For convenience in construction the flue gas well may comprise two sections, the lower section of which is indicated by 32 in Figure 2v and communicates with iue gas duct I6. The upper section I5 is high enough to provide an internal well over a substantial height of the furnace, but leaving free space at the top for access of flue gases through the inner row of tubes. Thus in the furnace of our invention, the heating tubes of each tubeV row I3 and I4 are subiected to heat radiation from ythe firing of burners I2- within the annulus 3| separating the tube rows assisted by reflection from the refractory' furnace wall 3u of shell I 0 and the outer refractory wall of flue gas well I5.

In Figure 1, a four-coil equilateral tube pattern comprising separate coils 33, 34, 35 and 36 are provided. It will be noted that 4 coil inlets namely 31, 38, 39' and 4I) are provided together with 4 coi-l outlets 4|, 42, 43 and lili. It will be noted that. the oil advantageously enters the bottom of the heater on the inside row, flows onequarter of the way around the furnace and then crosses over at the topv to the outside row before passing back through. one-quarter of the furnace along the outside row' and out at the bottom.

Our invention lends itself with special advantage to many different tube arrangements as indicated by the 8-coil flow scheme illustrated by Figure- 3. In Figure 3, Various oil inlets 5|, 52, 53, 54, 55, 56, 51 and 53 are provided together with oil outlets 59, B0, 6|, 62, 63, GLI, 55 and 66. Various tube arrangements e. g. staggered or radiant, with inside-outside or outside-inside flow may be employed. The flow pattern illustrated in Figure 3 however provides for moving the oil serially from an inside segment S1 by means of a cross over .63 through an outside coil segment 69 to an outlet, for example 59.

In accordance with our invention, the control of adequate heat distribution is made much easier and the danger of localized overheating or hot spots is reduced by supplying a multiplicity of burners. In the illustrative design, a total of twenty-four burners was found useful, but the number may be varied widely as this is a function of the required heat flux pattern and furnace duty. As the total furnace capacity is increased the number of burners should be increased. The design of the burner opening and attendant windbox is such that any desired type of burner may be used employing either fuel oil or gas. This provides a wide flexibility and choice of any type dictated by operating requirements and available fuel supply. An additional advantage for our arrangement utilizing a large number of burners is the ease with which adequate automatic controls may be set up. For large capacity furnaces, it is usually desirable to install a number of separate coils within the unit so as to avoid excessive pressure drop resulting from the use of only a single coil or even two coils. In the practice of our invention it is a simple matter to provide automatic firing controls for the burners adjacent to each coil so as to insure controlled heating for the selective iiow regardless of variation in fuel quality and variations in inlet temperature and quantity of the stock being heated. Moreover, by mounting the burners at the bottom of the furnace substantially at grade elevation the supervision and adjustment of each burner is simplified and made more positive because of ready accessibility.

Burner design and arrangement according to our invention is important in utilizing to the greatest extent highly preheated combustion air. Preheated air is important in increasing the over-all operating efciency of the unit, generally to an average of around 75% based upon the gross heating value of the fuel. In addition, it improves the combustion conditions within the furnace and materially benets the distribution of heat. The increase in the theoretical flame burst temperature resulting from highly preheated air also tends to equalize the heat iux pattern from the burner flame and increase the rate of absorption of heat by radiation. At the same time, it allows for operation with a lower air requirement with a morey eflicient combustion condition. As noted above, the preheated air is supplied by a separate air supply direct to a small secondary windbox for each pair of burners. The duct and the windbox are arranged for complete and individual accessibility to the burners for easy replacement and maintenance.

One of the particular advantages of our in- 5 vention is that a furnace for almost any desired range of capacity can be designed merely by proper adjustment of furnace diameter. Regardless of capacity requirements, there is no sacrifice in over-all operating eiiiciency. Eiciency is not affected by either a change in fuels or simultaneous operation with two fuels. Thus either fuel oil and/or fuel gas can be red either alone or in combination. The problem of localized over-heating or hot spots even at high capacity is largely overcome. The oil tubes may be kept at reasonable length merely by changing the furnace diameter and because of the tube arrangement the maximum cold fraction is provided in the furnace which improves the heat distribution patterns. Because of the use of vertical bottom supported tubes, the problem of adequate tube supports often encountered in horizontal heaters is avoided. With the burners located at the grade, the supervision of actual firing becomes much better and in addition the lighting-off procedure is both simplified and expedited. Simple automatic combustion and 5 oil temperatures controls advantageously can be set up for the furnace with all such equipment located at grade level for easy accessibility. Because of the use of a plurality of burners and the design of the individual burner windboxes, 10 any one unit can be serviced, repaired or replaced during operation without materially affecting the over-all unit capacity. In an emergency, the fans may be taken out of service for any reason such as power failure and ring may be l5 continued at reduced rates by installation of a manually operated explosion door on the top of the furnace. We claim: 1. An oil refinery heater of the vertical cylindrical all-radiant upshot red type, which comprises a vertical cylindrical shell, a plurality of serially interconnected vertical heating tubes disposed in inner and outer concentric rows within said shell with an annular space between the inner and the outer tube rows, a plurality of burners concentrically disposed in the lower portion of the furnace intermediate said inner and outer tube rows and directed to fire upwardly 'within said annular space between the serially interconnected inner and outer tube rows, a refractory cylinder forming a flue gas well located centrally within the inner tube row communicating at its upper end with the upper interior portion of the furnace, means for passing oil serially through said interconnected inner and outer tube rows, means for supplying fuel and air to each of said burners, and means for withdrawing flue gas from the lower portion of the flue gas well.

2. An oil refinery heater of the vertical cylindrical all-radiant upshot fired type, which comprises a vertical cylindrical shell, a plurality of serially interconnected groups of vertical heating tubes disposed in inner and outer concentric rows within said shell with an annular space between the inner and the outer tube rows and with each serially interconnected group of tubes comprising tubes in both the inner and the outer tube rows within a sector of said furnace, a plurality of burners concentrically disposed in the lower portion of the furnace intermediate said inner and outer tube rows and directed to fire upwardly within said annular space between each of the serially interconnected groups of inner and outer tube rows, a refractory cylinder forming a iiue gas well located centrally within the inner tube row communicating at its upper end with the upper interior portion of the furnace, means for passing oil serially through each group of interconnected inner and outer tube rows, means for supplying fuel and air to each of said burners, and means for withdrawing flue gas from the lower portion of the iiue gas well.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,378,307 Young May 17, 1921 2,081,970 Alther June 1, 1937 2,112,224 Alther Mar. 29, 1938 2,114,269 Moore Apr. 12, 1938 2,216,471 Frame et a1. Oct. 1, 1940 2,221,469 Brandt Nov. 12, 1940 2,332,051 Brandt Oct. 19, 1943

Claims (1)

1. AN OIL REFINERY HEATER OF THE VERTICAL CYLINDRICAL ALL-RADIANT UPSHOT FIRED TYPE, WHICH COMPRISES A VERTICAL CYLINDRICAL SHELL, A PLURALITY OF SERIALLY INTERCONNECTED VERTICAL HEATING TUBES DISPOSED IN INNER AND OUTER CONCENTRIC ROWS WITHIN SAID SHELL WITH AN ANNULAR SPACE BETWEEN THE INNER AND OUTER CONCENTRIC ROWS PLURALITY OF BURNERS CONCENTRIALLY DISPOSED IN THE LOWER PORTION OF THE FURNACE INTERMEDIATE SAID INNER AND OUTER TUBE ROWS AND DIRECTED TO FIRE UPWARDLY WITHIN SAID ANNULAR SPACED BETWEEN THE SERIALLY INTERCONNECTED INNER AND OUTER TUBE ROWS, A REFRACTORY CYLINDER FORMING A FLUE GAS WELL LOCATED CENTRIALLY WITHIN THE INNER TUBE ROW COMMUNICATING AT ITS UPPER END WITH THE UPPER INTERIOR PORTION OF THE FURNACE, MEANS FOR PASSING OIL SERIALLY THROUG SAID INTERCONNECTED INNER AND OUTER TUBE ROWS, MEANS FOR SUPPLYING FUEL AND AIR TO EACH OF SAID BURNERS, AND MEANS FOR WITHDRAWING FLUE GAS FROM THE LOWER PORTION OF THE FLUE GAS WELL.

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