US2361812A - Heating of fluids - Google Patents

Description

Oct. 31, 1944. w BARNES HEATING OF FLUIDS Filed Oct. 2:5, 1942 O 0 0 00 0 O O O 0 0 O 0 O 0 0-0 0 O O jQ/IZZ OIE' Patented Oct. 31, 1944 2,361,812

"UNITED STATES PATENT OFFICE HEATING OF FLUIDS Marion W. Barnes, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., 'a corporation of Delaware Application October 23, 1942, Serial No. 463,055

- high radiant heat 6 Claims. (Cl. 122-356) The invention is directed to an improved form of heater of the radiant and convection type which will be found particularly advantageous as applied to heating hydrocarbon vapors, normally gaseous hydrocarbons or other vaporous or gaseous materials to high temperatures. The invention also embraces the improved method of heating which may be conducted in heaters such as herein provided. I

Numerous industrial processes, including, for

flames and nascent hot combustion gases even when employing fuels of relatively low calorific example, operations conducted for effecting the a .energy from flames and hot combustion gases is practically mandatory to obtain quick heating of heavy hydrocarbon oils, gases and vapors to high reaction temperatures due tothe high heat transfer rates required. However, the high heat transfer rates obtainable by radiant heating with fuels of high calorific value cannot be achieved with low grade or diluted fuels due to their low value. Therefore, in the heater herein provided -I employ flue gas recirculation and also employ direct radiation from the flames and nascent hot combustion gases, but limit flue gas recirculation to that section of the heater in which combustion gases which have given up a large portion of heir radiant energy are directly contacted with the fluid conduits through which the material undergoing treatment is passed. In another section of the heater, through which no flue gases recycled, I provide fluid conduits disposed outside the direct path of travel of the flames and freshly generated hot combustion gases and transmit radiant heat directly to these conduits from calorific value and low flameburst temperature.

Consequently, the best types of heaters commonly employed by the refining industry in thermal cracking installations, which were designed to operateon fuels of high calorific value to give *liberation and employing a relatively high ratio of radiant heat surface to convection surface, are not so successful as applied to the present problems/above outlined.

It is the primary object of the present invention to provide an improved form of heater and method of eating which obviate the difficulties above mentioned, permitting the use of relatively providing high rates of heat low grade fuels and transfer from th flames and freshly generated combustion gases which closely approach the maximum rates obtainable with the particular fuel employed.

It is well known that the attainment of high heat transfer rates by convection can be accomplished with flue gasrecirculation. However, the

rates thus obtainable are not as high as those which can be achieved by direct radiation from said flames and hot combustion gases and from refractory surfaces over which the' flames and hot combustion gases are passed before being commingled with the recycled flue gas. radiant. and convection heating sections are maintained separate and rates of heat transmission, closely approaching the highest obtainable with the particulartype of'fuel and type of heating employed, are obtainedln each of these sections.

The features and advantages of the invention will be more apparent with reference to the. accompanying diagrammatic drawing which is an elevational view, shown principally in section, of

one specific form of theimproved heater provided by. the invention.

The heater illustrated in the drawing is of the general type now widely used in the oil refining industry and known as a center-wall updraft" heater. This type of heater, Without the improvements herein provided, is described in U. S. Patent 2,147,662 toL. A. Mekler.

Referring to the drawing, theheater hereillustrated comprises substantially vertical refractory side walls I and 2, refractory end walls, one of which is indicated at 3, a floor l, inwardly sloping refractory side walls Sand '6 which connect the substantially vertical walls I and 2, respectively. with other'vertical refractory walls 1 and v 8 between which is disposed a convection or fluid heating zone 9 of smaller cross-sectional area than the lower portion of the heater. 7 Within the heater a pair of substantially vertical refractory walls III and l I, extending from beneath floor 4 to an elevation substantially corresponding to the base of the sloping walls 5 and 6, are disposed. Walls 10 and II are spaced from each other to provide a fluid passageway l2 Thus, the

therebetween for recycled flue gases and are spaced from the adjacent side walls I and 2 to provide a combustion and radiant heating zone l3 between walls I and I and a similar combustion and radaint heating zone I4 between walls 2 and II. Walls l0 and H are bridged at the top by a refractory wall l5, having a plurality of openings l6 provided therethrough at spaced points along its length through which recycled flue gases supplied to fluid passageway l2, as will be later described, are introduced into the zone I! between walls and 6.

,A bank l8 of tubular fluid conduits comprising,

in the case illustrated, a single vertical row of horizontally disposed tubes I9 is located in zone l3 adjacent wall I. Another tube bank 20, also comprising, in the case illustrated, a single substantially vertical row of horizontally disposed tubesZI is located in zone l4 adjacent wall 2. Another tube bank 22, comprising a single row of horizontally disposed tubes 23, is located adjacent the sloping wall 5 and another similar bank 24 of horizontally disposed tubes 25 is located adjacent the sloping wall 6. Another tube bank 26 comprising, in the case illustrated, a plurality of superimposed horizontal rows of horizontally disposed tubes 21, is located in fluid heating zone 9.

- A row of burners, one of which is indicated at 2B, is disposed beneath zone [3 in the space 29 provided between floor 4 and sub-floor 30 and a similar row of burners, one of which is indicated at 28', is disposed beneath zone l4 in the space 3| provided between floor 4 and sub-floor 30. Burners 28 and 28 are supplied with fuel through the respective lines 32 and 33 in quantities regulated by the respective valves 34 and 35, and air,

for combustion of the fuel is supplied to zones 29and 3| and to the combustion zones, as will be later described. The burners project the combustible fuel-air mixture through th firing ports 36, disposed adjacent walls l0 and II upwardly against the surfaces of the latter within the respective zones l3 and I4. The resulting flames and nascent hot combustion gases pass upwardly over the surfaces of walls l0 and H, heating the same to a highly radiant condition. Radiant heat is transmitted from the highly heated surface of wall l0 and fromthe flames and hot combustion gases passing upwardly thereover directly to one side of the tubes IS in bank l8 and the adjacent surface of wall I reradiates heat to the opposite side of the tubes l9. In a similar manon these tubes.

tubes of banks 3 and 20 are disposed without the main path of travel of the flames and hot combustion gases through zones l3 and i4 and receive heat predominantly by radiation. In previous heaters of this general type, without the provisions of the present invention for recycling flue gases to zone H, the tubes of banks 22 and 24 may be excessively heated, particularly when a fuel of high calorific value is employed, due to the superimposing of radiant and convection heat In the heater herein provided, when fired with low grade fuel, a considerable portion of the radiant heat energy of the freshly generated hot combustion gases is expended in zones l3 and I4 and, in any event, the gases leaving these zones are commingled with recycled flue gases. Thus, the tubes of banks 22 and 24 receive a much smaller component of radiant heat energy end, although the convective component is increased, are not as susceptible to excessive heating as in previous designs of this type of heater.

The commingled combustion gases and recycled flue gases pass upwardly from zone I! through zone 9 in direct and in intimate contact with the .tubes 21 of bank 26 and transmit fluid heat to ner the heated surface of wall H and the flames and nascent hot combustion gases passing thereover transmit radiant heat directly to one side of tubes 2i of bank 20, and the opposite side of these tubes is heated by reflected radiant heat from the adjacent surface of wall 2.

The combustion gases leaving zones l3 and I4 and entering zone 1 I are commingled with recirculated flue gases which pass from zone l2 through openings l6 into zone II. In passing through zone II the commingled gases transmit most of their remaining available radiant heat energy to the tubes of banks 22 and 24 and these tubes aresalso washed by the-commingled gases passing through zone l1, thereby receiving a substantial component of convection heat.

When the heater is fired, as contemplated by while another regulated quantity of the gases is directed from the zone 38, disposed above zone 9, through duct 39 to a suitable hot gas fan or blower indicated at 40. The blower directs the gases through duct 4| to zone I2 between walls I0 and II and therefrom through openings I6 into zone I 1, thus establishing a flue gas cycle through zones l1 and 9 and increasing the heat supplied by convection to thetubes. of banks 22, 24 and 26 so as to maintain relatively high heat transfer rates in these banks.

As another feature of the invention, I provide, in the case illustrated, for preheating the air employed for combustion of the fuel. This is not to be considered a limiting feature of the invention but is preferably employed when the heater is flred with fuel of relatively low calorific value,

in order to increase the flame temperature and tions separated by the partition 45, each section comprising a plurality of relatively flat metal plates spaced from each other to provide-relatively narrow openings therebetween, alternate openings being open at their top and bottom to permit the passage of flue gases therethrough from zone 38 to stack 31, while the intervening openings are closed at the top and bottonf and are provided with suitable baffles 46. This type of air preheater is well known in theyindustry and a more detailed illustration and description is, therefore, considered unnecessary to arr/understanding of the invention.

Air is admitted to the spaces of preheater 42 which are closed at the top and bottom through suitable air inlet ducts 41, in amounts controlled by the dampers 48, and is preheated by direct contact and heat exchange with the gases passing through the preheater from zone 38 to stack 31. The air is directed through the preheater as 7 indicated by the dotted arrows and is directed the preheater passes downwardly through spaces 49 and 50, wherein it is further preheated by contact withthe refractory walls of'the ,heater, and

enters the zones 29 and 3| through suitable ports 52 and 53 provided through the side walls I and 2. The preheated air passes, in part, from zones 29 and 3| through burners 28 and 28 and, in part, directly through firing ports 36 into the combustion and radiant heating zones l3 and I4 wherein it serves to support combustion of the fuel. Air may be drawn through the preheater and through the spaces "and 5|] by the inspirating action of the burners or, when desired, it may be supplied throughducts 41 from a suitable fan or blower, not illustrated.

The present invention is not concerned with the particular flow employed for the fluid undergoing heating in the various tube banks or the particular sequence of the tube banks in the flow. There'are numerous possibilities, some of which are illustrated and described in the aforementioned Mekler Patent 2,147,662, and the particular flow employed may be selected to suit requirements. It is worthy of note, however, that the improved heater herein illustrated retains the advantages of formercenter-wall up-draft heaters in that it permits wide flexibility of operation with respect to the flow of fluid undergoing heating through the heating coil and permits the treatment of two parallel streams of fluid under either substantially identical or different heating conditions or the treatment of a single stream of fluid, passed in series through the various tube banks in any desired sequence, or the treatment of two or more streams in a portion of the heating coil and treatment of a single stream in other portions of the coil.

I claim as my invention:

- 1. A heater for fluids comprising, in combination, spaced substantially vertical refractory walls, other substantially vertical refractory walls spaced from each other to define a passageway for recirculated combustion gases therebetween, the last named walls being disposed between and spaced from the first named walls to define separatle combustion and radiant heating zones, a bank\of tubular fluid conduits disposed-adjacent one of said walls in each ofthe combustion and radiant heating zones, burners disposed adjacent one end of each of said combustion and radiant heating zones to direct flames and hot combustion each of said zones opposite said fluid conduit therein, a fluid heating zon'e disposed adjacent and in communication with that end of the therefrom, a bank of tu ular fluid conduits dis-,

posedwithin said fluid h ting zone in the direct path of travel of combusti n gases passing there gases vertically over the surface of that wall in through from said combustion and radiant heat ing zones, means for discharging combustion gases which have passed through said fluid heating zone therefrom, and means for directing regulated quantities of the last named gases through second named refractory walls, out of direct contact with the flames and hot combustion gases the aforesaid passageway disposed between the passing through said combustion and radiant heating zones, and therefrom into direct contact with the combustion gases passing from the latter zones to said fluid heating zone.

2. A heater such as defined in claim 1, provided with an air preheater disposed within a flue leading from said fluid heating zone to a stack, and means for directing air through said preheater to said combustion and radiant heating zones to support the combustion of fuel supplied to the latter from said burners.

3. A heater such as defined in claim' 1, provided with an air preheater disposed in a flue leading from said fluid heating zone to a stack, a housing spaced from and disposed adjacent the first named refractory walls and means for directing air through said preheater and through means for passing combustion gases from the last-named zone through said intermediate zone and said convection zone, a tube bank disposed in the radiant zone to be heated predominantly by radiation, a tube bank arranged in the intermediate zone for heating thereof by radiation and convection, a tube bank in the convection zone disposed in the path of the combustion gases passing 'therethrough, means for removing the combustion gases from the convection zone and means for introducing a regulated portion there- 1 of to said intermediate zone to commingle therein with the combustion gases from said radiant zone.

5. A fluid heating furnace comprising refrac tory vertical walls forming a radiant heating section, additional vertical walls defining a convection heating section in vertical alignment with r and spaced from the radiant section, the convection section being of smaller cross-sectional area than the radiant section, sloping refractory walls joining the first-named walls with said additional walls, and defining an intermediate'zone in the furnace, heating tubes in said radiant section adjacent the first-named walls and means for applying radiant heat thereto, heating tubes in said intermediate zone adjacentsaid sloping walls, means for passing combustion gases from the radiant. section through said intermediate zone in heat exchange relation with the lastmentioned tubes and then through the convection section, heating tubes in the convection section disposed in the path of travel of the combustion gases therethrough, means for removing the combustion gases from the convection sec tion and means for introducing a regulated portion thereof to said intermediate zone to commingle therein with-the combustion gases from} the radiant section.

6. The furnace as defined in claim 5, further characterized in that said means for a dying radiant heat comprises a refractory pargfi ti bning member disposed in the radiant section between and spaced from the first-named vertical walls and burners arranged to project combustion products in a vertical direction along the opposite sides or said member.

MARION W. BARNES.

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