US3171389A

US3171389A - Furnace construction for low temperature operation

Info

Publication number: US3171389A
Authority: US
Inventors: John W Throckmorton; John S Wallis
Original assignee: Petro Chem Dev Co Inc
Current assignee: Petro-Chem Development Co Inc; Petro Chem Dev Co Inc
Priority date: 1963-09-05
Filing date: 1963-09-05
Publication date: 1965-03-02
Anticipated expiration: 1982-03-02
Also published as: GB1080232A

Description

March 1965 .1. w. THROCKMORTON ETAL 3,171,389

FURNACE CONSTRUCTION FOR LOW TEMPERATURE OPERATION Filed Sept. 5, 1963 N a 5 V w M M w m MM i N c 0 AT w w w 1 53 Z M a a J a .W II. in;

United States Patent 0 3,171,389 FURNACE CONSTRUOTION FOR LOW TEMPERATURE OPERATION John W. Throckmorton and John S. Wallis, New York, N.Y., assignors to Petro-Chem Development (30., Inc,

New York, N.Y., a corporation of Delaware Filed Sept. 5, 1963, Ser. No. 306,726 1 Claim. (Cl. 122333) Large quantities of natural gas are transported great distances by pipeline, and to take care of peak loads at the point of use, such as for example the city of Boston, it has been proposed to liquefy natural gas, largely composed of methane, at the point of production, for example near Beaumont, Texas, and to ship the liquid methane in specially insulated tanks which are then shipped by steamer to Boston.

At this point of use the liquid methane will be stored at low temperatures, such as below 257 F. until the peak demand arises. It is then necessary to convert the extremely cold liquid to vapor and gas by supplying the necessary heat of vaporization from an external source.

If this heating is attempted to be done in the conventional tubular type of furnace, the tube wall temperature on certain of the heating elements is so low that moisture in the flue gas which is produced from the products of combustion forms a heavy coating of frost or ice.

The formation of frost or ice on the heating elements adversely affects the heat transfer rate and at the same time forms water in the combustion chamber in the furnace. This causes damage to the furnace, reduces the flame temperature of the heater, and under severe conditions may cause the burner to be extinguished, making the furnace inoperative.

Other normally gaseous products such as propane and butane liquefy at cold temperatures which are higher than that required to liquefy methane, and in such cases the problem of icing or frosting is less severe.

One object of this invention is to provide a heater having tubular heating elements with means for insuring an adequate transfer of heat to the tube walls so that either no ice or frost is formed on the tubes or, if some ice or frost is formed, the efliciency of the heater is not sub- \stantially reduced, because the heat transfer means has adequate heating surface spaced at a suflicient distance away from the tube walls to insure this result.

Another object of this invention is to provide fin tubes in which the fins extend to an unusual extent beyond the surface of the walls, are L-shaped in cross section and have a comparatively large surface area substantially parallel to the surface of the tubes.

It should be understood that the use of fin tubes in the radiant section of furnaces is new and is advantageous only for the special purposes above indicated. If the furnace were used for heating oil or water to high temperatures, such as for example 800 F. to 1200" F., the fins exposed to the radiant heat would be destroyed.

Other objects and advantages of the invention will appear from the following description and attached drawings, in which:

FIG. 1 is an elevation of a vertical tube heater in which the primary heating elements are formed to accomplish the purposes above set forth.

FIG. 2 is an enlarged sectional elevation of a portion of a fin tube constructed totransfer heat inwardly from the outer surfaces of the fin to the walls of the tube on which the fins are formed. In this figure the fins are mounted on the tubes in the form of a helix.

FIG. 3 is a cross-sectional elevation on a large scale of a heating tube having fins similar in formation to those shown in FIG. 2, but arranged longitudinally of the tubes.

" 3,171,38 9 c6 Patented Mar. 2, 1965 FIG. 4 is a cross-sectional elevation on a large scale of a tube having fins of similar cross section but attached to the tube in the form of rings.

Referring specifically to FIG. 1, a well known type of vertical heater is here shown composed of a vertical cylindrical furnace chamber 10 having a concrete bottom 11 in which one or more upshot burners 12 are located and a single row of vertical tubes 13 which are spaced a short distance inwardly from the walls of the furnace chamber 10 and are located in a circular pattern. The tubes are interconnected in a series or parallel arrangement as desired by the use of the usual return bends 14 at the top and bottom of the tubes. A vertical extension 15 of the furnace chamber is smaller in diameter than the furnace chamber 14) and has mounted within it a coil 16 which is connected to the main furnace coil made up of tubes 13 by external connector 20.

The usual stack 21 is supported at the top of the convection section of the furnace and extends upwardly therefrom.

The hot flame from the burners 12 projects upwardly through the center of the furnace and largely gives up its heat to the fluid in the tubes 13 by radiation. The hot gases from the top of the main furnace then bathe the convection coil 16 in the usual manner and pass upwardly out of the stack 21.

To carry out the intended operation, very cold liquid such as liquefied methane is introduced into the coil composed of tubes 13 at the bottom, as indicated by arrow 25, and the vapors and gases resulting from the heating of the liquid escape through the outlet, as indicated by arrow 26.

According to FIG. 2, each of the tubes 13 has a specially constructed fin structure which, as here shown, is composed of a channel 30 having a web section 3-1, a hub section 32 and a flange or parallel extension 33 at the outer end of the web. This channel is wound onto the tube 13 in a helical form with the hub members 32 welded or otherwise securely fastened to the outer surface of tube 13. The turns of the helix are sufficiently close that the flange extensions 33 are close together and form a protective surface around the tube 13. This is clearly indicated in the cross section of FIG. 2.

When very cold liquid such as liquefied methane is introduced into the tubes 13, the radiant heat from the furnace is primarily applied to the flange extensions 33 of the fins. The fins are formed of suitable metal so that the heat is immediately conducted through the fins to the tubes 13, and if frost or ice forms on the exterior surface of the tubes 13, it will not interfere with the continuing transfer of heat from the fin surfaces 33 to the tubes by conduction and to the liquefied methane within.

In this way the liquefied methane is efi'ectively vaporized and the necessary heat of vaporation, which is very large, is adequately supplied from the furnace without danger of burning the tubes.

Referring to FIG. 3, an alternate structure is here shown in which the tube 13 is shown in transverse section and the fins, of substantially the same shape as already described with reference to FIG. 2, are applied. In this case, however, the fin structure is applied longitudinally of the tubes 13, but the flange portions 33 of one fin extend close to the flange portion of the next fin and thus effectively transfer heat from the furnace gases to the tubes 13 regardless of whether there has been frost 0r icing formed on the exterior surface of the tubes.

Another alternative is shown in FIG. 4, in which there are mounted on the tube 13 a series of rings which are close together and are Welded or otherwise attached to the tube by the hub sections 32. The rings in cross sec- 3 V 7 tion correspond to those of the'fins of either FIG. 2 'or FIG. 3. l

It is well known that the quantity of heat'required for vaporization of liquefied gases is high and is usually referred to as the heat of vaporization, For this reason the use of. fin tubes in a radiant section of the furnace, where temperatures are extremely intense, is feasible and ,serves to improveithe transfer of heat from the radiant flames and hot combustion gases in the center of the heater to the liquefied'gases Within the tubes.

Fin tubes are,of course, well known in furnace structures, but the fins are usually formed primarily to increase to a slight or moderate extent the exterior surface of the tube and are normally employed in the convection section of the heater where the tubesare bathed in the hot gases ofthe furnace. On the other hand, according to this invention the fins are applied to the tubes which are subjected to'radiant heat and are arranged and designed in order that they may be peculiarly adapted for their intended purpose, as above described. 7

Other modifications of the shape of the fins may be made without departing from the spirit of the invention,

and only such limitations should be imposed as are indicated in the appended claim; 4

We claim:

methane or other low molecular weight hydrocarbons,

which comprises a plurality of tubes substantially spaced from one another and arranged in a tall, hollow, vertical [2 5 A heater for gasifying cold liquids such as liquefied members and the flange members.

References Cited by the Examiner UNITED STATES PATENTS 2,234,423 3/41 Whittmann 122-367 X 2,419,233 4/47 spender 165 182 X 2,994,307 a 8/61 Throckmorton etal. 1-22356 V FOREIGN PATENTS 584,192 9/59 Canada; 735,384 8/55 Great Britain.

' 7 OTHER REFERENCES I 7 Cryogenic Fluids'Heated With No Ice on Tubes, published in Chemical Engineering periodical, Apr. 16, 1962, vol. 69, No. 8, page 104. V

'PERCY/LLPATRIVCK, Primary Examiner.

KENNETHW. SPRAGUE, ROBERT A. OLEARY,

' Examiners.