US2660996A - Fluid heater - Google Patents

Description

Dec. 1, 1953 E. J. WASP ETAL 2,660 996 FLUID HEATER Filed July 11, 1950 2 Sheets-Sheet 1 FIGJ IN V EN TORS.

EDWARD J. WASP BY JOHN S. WALLIS ATTORNEY.

' Dec. 1, 1953 E. J. WASP ETAL 2,66Q,996

FLUID HEATER Filed July 11, 1950 F'IG.2

2 Sheets-Sheet 2 INVENTORS. L EDWARD J. WASP 30 BY JOHN s. WALLIS FIG. 3 R. NW

ATTORNEY.

Patented Dec. 1, 1953 FLUID HEATER Edward J. Wasp, Brooklyn, andJohn S. Wallis, New York, N. Y., assignors to Petro-Chem Process Company Incorporated, New York, N. Y., a corporation of Delaware Application July 11, 1950, Serial No. 173,086

3 Claims. v(Cl. 126-109) This invention pertains to heaters for air or other gaseous fluids and more particularly relates to a furnace in which the, heating tubes are arranged in banks radiating from the axis of the combustion chamber, forming a starshaped cross section. The heating tubes connect an inlet'manifold near one end of the chamber to an outletzmanifold near the other end of the chamber, the manifolds and the tubes providing an all-parallel path. for flowof the gaseous fluid being heated from the inlet manifold to the outlet manifold. The manifolds and the heating tubes are in most modifications entirely Within the combustion chamber. Burners are installed on the floor of the chamber between each successive pair :of banks, and additional burners may be'provided in the wall of the chamber at various heights.

Under certain conditions where "the gaseous fluid in the tubes enters the furnace at a lowtemperature such .as for example, 80 F. and leaves the outlet of the tubes at a high temperature such as 1500" F., special alloy steels are desirable'f-or the higher temperature zones While ordinary carbon steel may be entirely adequate for the cooler zone.

An object of the invention is to reduce the pressure drop to a minimum so as to adapt the heater to' 'quickly raise the temperature of very large quantities of air at low pressures.

Another object of the invention is to absorb" large quantities of heat into a gaseous fluid at a maximum rate.

Still another object ofthe invention is to provide a tube having sections each of which is particularly adapted for" the furnace zone where it is located. Such a tube may beformed with about one third at one end of carbon steel, an intermediatethird of .4% -6%7 chrome alloy steel usually called low chrome, and the third at the opposite end of 18%--8%. chrome nickel alloy steel known as 18-8 orfhigh chrome.

Another object of the invention is to provide a uniform heat intensity circumferentially around the heating tubes and a variable but controlled heat intensity vertically up and down the tubes.

' Still another object of the invention is to pro vide for a maximum rate of heat absorption in all sections of the heater under controlled conditions, dependingupon the variation in the fluid temperature as governed by the temperature gradient through the furnace and the type of material of which the heating tubes are constructed.

A further object is to provide a heating surface assembly in which a catalyst may be inserted where an all-parallel flow is desired and pressure drop is not so much of a problem.

Further and other objects and advantages will be apparent from the following description and claims, taken in conjunction with the accompanying drawings, in which:

Fig. '1 is a sectional View of a furnace showing.

one embodiment of the invention;

Fig. 2 is a transverse sectional View taken on line 2-2 of Fig. 1;

Fig. 3 shows a modified arrangement for two of the individual radial banks of tubes;

Fig. 4 shows another modified arrangement for one of the individual radial banks of tubes.

where it is desired to insert a catalyst in the tubes;

Fig. 5 is a top view of the arrangement shown in Fig. 4; and

Fig. 6 is a fragmentary sectional view of the stack. 1

The heater shown in Figs.l and 2 is particularly applicable to heating large quantities of a gas, such as steam, air, hydrocarbons, etc., where it is very important to keep pressure drop to a minimum. The design consists of a vertical, cylindrical combustion chamber 6, having a floor 8, atop it and a stack I12. The stack l2 may be, equipped with a damper l3, but this is optional.-

An inlet manifold M, shaped like a truncated cone, with its smaller end down, is within the chamber 6 and coaxial therewith and is inserted near its top It).

An outlet manifold 6, also shaped like a truncated cone, with its smaller end up, is within the chamber 6 and coaxial therewith and near with the top of the inlet manifold M, and an outlet'- pipe 20 projects into the chamber 6-- through its floor 8 and connects withthe bottom of the outletmanifold it. Other outlet means could be substituted for manifold l6 but we believe that it is preferable to have the outlet maul-3 fold i6 correspond to inlet manifold M with its taper reversed.

The heating surface assembly is made up of heating-tubes 22 which are vertical throughout most of their length. The tubes 22 are arrangedin banks which extend radially from the axis of the chamber 6, forming a star-shaped horizontal cross-section, as best shown in Fig. 2. It is to be noted that each bank is illustrated as including only one row of tubes 22 because this is the preferred arrangement and is the one having the An inlet pipe [8 projects into the chamber fi through the stack l2 and connectsgreatest economy; however, each bank may consist of two or more rows of tubes 22, depending upon the most desirable design for a particular use.

The upper end of each tube 22 is joined to the inlet manifold It by means of a smooth, longradius bend, and the lower end of each tube 22 is similarly joined to the outlet manifold 16 by means of a smooth, long-radius bend. The tubes 22 which are nearest to the axis of the chamber 6 are joined to the inlet manifold I4 nearest its bottom, where its cross-sectional area is smallest, and to the outlet manifold l6 nearest its top, where its cross-sectional area is smallest. The tubes 22 progressively farther from the axis of the chamber 6 are joined to progressively higher points on the inlet manifold 14 and to progressively lower points on the outlet manifold l6. Thus the tubes 22 which are farthest from the axis of the chamber 6 are joined to the inlet manifold l4 nearest its top, where its crosssectional area is greatest, and to the outlet manifold l6 nearest its bottom, where its cross-sectional area is greatest.

The tubes at their ends continue in the plane of the tube bank and leave the heating cells of the furnace unobstructed between banks. A burner 24 is installed in the floor 8 of the chamber 6 between each adjacent pair of banks of tubes 22, and a burner 26 is installed in the wall of the chamber 6 between each adjacent pair of banks. Additional burners may be added if desired.

The burners 24 discharge hot gases upward, parallel to axis defined by the manifolds l4 and IS. The arrangement of the star-shaped tube banks and the burners 24 has the result that'both sides of each bank of tubes can see the flame and hence are exposed to radiant heat. Where each tube bank has only one row of tubes, each tube will be exposed to substantially uniform radiant heat throughout most of its circumference. The combustion products do not pass through and around the tubes and hence there is little or no convection heating.

Furthermore applicants heater is-very efiicient in operation for the reason that the great bulk of the radiant heat gets to the tubes. Only a small amount of heat is lost on the furnace walls. It is true that the walls re-radiate heat, but at a much lower temperature.

The side burners 26 may be omitted, and when they are included they merely supplement the burners 24. The heat supplied by the burners '26 is also primarily radiant.

Each of the tubes is preferably made up of sections welded together, the upper third of the tube where the inside fluid temperature is low is composed of carbon steel, the middle third of the tube is composed of low chrome steel and the lower third of the tube is composed of high chrome steel.

Since the heating elements are fired from both sides by burners in the bottom of the chamber 6 and in the wall thereof, the desired radiant heat adsorption is assured for each tube '22. Thereby, the maximum heat adsorption for a permissible tube wall temperature is attained and by regulating the composition of the tube and the applied heat, the heat intensity and the furnace may be controlled in a vertical direction.

The number of radial banks of tubes is also variable, depending upon the size and design conditions for the unit.

It will be seen that in operation the cold air stock enters the heater through the inlet pipe l8 and passes into the inlet manifold M, where it splits up and passes down through the tubes 22 in an all-parallel flow, being heated enroute. The now hot air then is reunited in the outlet manifold I6, and leaves the heater through the outlet pipe 20.

The combustion gases pass upward from the burners 24 and 26 through the chamber 6 and leave the unit through the stack [2.

It is particularly significant that the tapered shape of the inlet and outlet manifolds l4 and i6 is such as to maintain the air velocity con- :stant, "andhence the pressure drop through the unit is held to a minimum. The fact that the air must make no sharp bends is also conducive to low pressure drop.

In operation, air enters manifold M from above with a definite velocity. Some leaves manifold 14 near its top, some at intermediate levels, and some near its bottom. 'Hence, as the air moves downwardthrough the manifold I 4, it :is progressively diminished in amount. This diminution tends to reduce the pressure of the remaining air (and its velocity as well) and would do so but for the reduction in the cross-sectional area of the manifold M. The reduction in area thus has a marked effect on maintaining the pressure and velocity of the air constant. The air then passes downwardly through the tubes 1'22 and entersman'ifo'ld 16, where the abovedescribed process is repeated in reverse order.

Fig. 3 shows a modified arrangement .of the manifolds and heating surface assembly. The structure is just the :same as in the :unit illustrated in Figs. 1 and 2, as to arrangement of the combustion chamber, the stack, the inlet and outlet pipes and the burners. In'this inodification, a cylindrical inlet manifold 28 is within the combustion :chamber and coaxial therewith and is inserted near its top. A cylindrical outlet manifold 3'0 is within the combustion chamber and coaxial therewith and is inserted 'near its bottom. Horizontal tubular headers 32 and .34 radiate from the inlet :and outlet manifolds 28 and 30 at various angles defining banks of tubes 36 which again presenta star-shaped horizontal cross-section, whichwould look much like .Fig. 2.

In operation the charging stock splits up in the inlet manifold 28, somexentering one header 32, some another. The stock in a given header then divides again, among the various tubes 36 connected thereto. When the header 34 is reached, the stock reunites and passes into the outlet manifold 30.

Thus it will be seen that the unit shown in Fig. 3 presents an all-parallel flow with straight tubes 36. The pressure drop is higher than that in the unit shown in Figs. '1 and 2 because the stock must makeseveral'right-angled turns. This reduces velocity. Also, since .the headers 32 and 34 have a uniform cross-sectional area, the velocity of stock flow will decrease the further the stock passes from the inlet and outlet manifolds 28 and 30.

Figs. 4 and 5 show another modification of manifold and heating assembly construction where it is desired to insert a catalyst into a heater having an all-parallel flow. In such a case, it is fruitless to attempt to keep the pressure drop to a minimum, as the presence of the catalyst itself is conducive to a large pressure drop.

The unit illustrated in Figs. 4 and '5 is very similar to that shown in Fig. 3, and is installed in the furnace the same way, with one exception, to be noted later. A cylindrical inlet manifold 38 is within the combustion chamber and coaxial therewith and is inserted near its top. A cylindrical outlet'manifold 40 is Within the combustion chamber and coaxial therewith and is inserted near its bottom. Horizontal tubular headers 42 and 44 radiate from the inlet and outlet manifolds 38 and 40 at various angles, defining banks of vertical tubes 46 which once more are arranged to form a star. The headers 42 and 44 are joined to the tubes 46 by auxiliary tubes 48 and 50, respectively, which make right angles with the headers 42 and 44 and with the tubes 46.

It is to be noted that the tubes 46 are of relatively large diameter. This is so that they can be filled with the catalyst, which is not shown. The tubes 46 extend outside of the combustion chamber, both at its top and at its bottom, and have cover plates 52 and 54, respectively, for inserting and removing the catalyst.

The combustion chamber, the stack, the inlet and outlet pipes and the burners are the same as in the heater shown in Figs. 1 and 2.

In operation, the charging stock enters the inlet manifold 38, flows through the headers 42, which feed all of the tubes 46. The charge then flows downwardly through all of the tubes 46 in an all-parallel flow, passing through the catalyst on the way, and reunites in the outlet manifold 40.

From the foregoing, it will be seen that the invention is one well adapted to attain all of the ends and objects hereinbefore set forth.

Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, we claim:

1. In a heater for gaseous fluid having a combustion chamber, a floor and an inlet pipe: a tapered inlet manifold having its larger end connected to said pipe and defining a vertical axis; a heating surface assembly connected to said manifold to provide parallel paths forv flow of fluid and including a plurality of vertical heating tubes arranged in thin single tube banks which define planes extending radially from said axis, and means connecting one end of each said tube to said inlet manifold, the tubes farthest from said axis being connected to said manifold near its larger end, the tubes closest to said axis being connected to said manifold near its smaller end and the intermediate tubes being connected to said manifold at corresponding intermediate localities; and radiant heating burners discharging parallel to said axis between successive banks of tubes for exposing each tube of said banks to radiant heat from both sides.

2. An air heater comprising a cylindrical ver- 6 tical furnace chamber, a coaxial flue gas outlet of smaller diameter at the top of the cylinder, a large air inlet having a gradually tapering end extending downwardly into the chamber from the top and coaxial therewith, constituting an inlet manifold, a corresponding outlet manifold at the bottom of the chamber having a taper reverse of that of the inlet manifold, a plurality of air heating tubes arranged in radial banks which separate the cylindrical furnace chamber into a plurality of open cells extending throughout the length of the cylindrical furnace, the tubes in each bank being substantially parallel and being curved at each end and terminating in the manifolds one above another, whereby the air velocity at the tube inlets and at the tube outlets is maintained uniform, burners in each open cell for maintaining an end to end flow of hot flame and gases therein, whereby heat is imparted by radiation to the tubes in the radial banks on both sides, said tubes being so disposed in each bank that the entire peripheries of the tubes are exposed to radiant heat.

3. An air heater comprising a cylindrical vertical furnace chamber, a coaxial flue gas outlet of smaller diameter at the top of the cylinder, a large air inlet having a gradually tapering end extending downwardly into the chamber from the top and coaxial therewith, constituting an inlet manifold, a corresponding outlet manifold at the bottom of the chamber having a taper reverse of that of the inlet manifold, a plurality of air heating tubes arranged in radial banks of single tube width which separate the cylindrical furnace chamber into a plurality of open cells extending throughout the length of the cylindrical furnace, the tubes in each bank being substantially parallel and being curved at each end terminating in the manifolds one above another, whereby the tubes are all connected in parallel and whereby the air velocity at the tube inlets and at the tube outlets is maintained uniform, upshot burners located in the bottom of the furnace chamber and discharging flame and hot gases upwardly into the several furnace cells, whereby heat is imparted by radiation to each tube in the radial banks on both sides.

EDWARD J. WASP. JOHN S. WALLIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 373,576 Young Nov. 22, 1887 1,125,758 Stack Jan. 19, 1915 1,342,073 Trinks June 1, 1920 1,647,570 Kling Nov. 1, 1927 2,211,903 McCarthy Aug. 20, 1940 FOREIGN PATENTS Number Country Date 678,302 Germany July 12, 1939

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