US2458515A - Method of heating coking retort ovens with enriched mixtures of fuel gas - Google Patents

Description

Jan. 11, 1949. w. o. KEELING 2,453,515

EETHOD OF HEATING SOKING RETORT OVENS WITH ENRICHED MIXTURES OF FUEL GAS Filed June 24, 1943 IIIIII-llll I N" AWN INVENTOR. R/nunn 0. Khulna.

Patented Jan. 11, 1949 METHOD OF HEATING COKING RETORT OVENS WITH ENRICHED MIXTURES OF FUEL GAS William 0. Keeling, Pittsburgh, Pa., assignolgby mesne assignments, to Koppers Company, Inc., a corporation of Delaware Application June 24, 1943, Serial No. 492,083

Claims. 1

The present invention relates in general to improvements in the heating of such combustion apparatus as coke ovens, and is more particularly concerned with the heating of those coke ovens which, by reason of their design, construction. or provided features of equipment, are restricted for their effective heating solely to fuel-gases ofrelatively higher calorific values; for example cokeoven gas, or its equivalent.

In the heating of coke ovens that do not belong to the so-called combination" class, in consequence of their lacking, for example, either regenerators or combustion-media flow-passageways adequate to supply, to the heating flues, fuelgases of low calorific values at-a rate requisite for their efiective heating, or merely lacking equipment for distributing fuel gas of low calorific value to existing regenerators, circumstances frequently arise making it not only desirable, but urgently necessary, to heat such coke ovens, if

only periodically for a limited period, with an extraneously derived fuel-gas that, by reason of the above-recited limitations of the coke ovens, must belong to those characterized by their relatively high calorific values. An instance where, for example, such circumstance can become particularly critical is in those populous districts where coke-oven gas serves as the exclusive source of industrial and domestic heating. If the cokeoven installation for supplying such district constitutes solely coke ovens of the above-stated type and there is only a limited capacity of productive reserve, serious situations can arise when gas-distribution demands reach or exceed for any considerable period the daily or seasonal demands the coke ovens are adapted to meet. Since the distributed gas must be kept, relatively constant in respect to such properties as, amongst others,

calorific value and specific gravity, because the usual appliances, or the existing settings thereof throughout the district for burning the gas, are relatively limited in their effective tolerance of fluctuations in these characteristics, the utility of any of the usual low calorific value fuel gases, such as produceror blast-furnace gas, for meeting the increased demand is, even in the event there were a source of supply, thus precluded either for purposes of oven heating or for any extensive dilution of the coke-oven gas to be distributed because, for the latter purpose, it is so radically different from coke-oven gas in respect of calorificvalue and specific gravity. In view of the foregoing, there is in the art obviously a need of a flexible method and means whereby coke ovens not of the combination type can be cheaply former said gas, with its requisite physical properties, for delivery to the district to be supplied.

An object of the present invention is the provision of cheap, novel, and effective method whereby coke ovens requiring for any reason a fuel gas of high calorific value for their effective underfiring can be easily and quickly converted from a heating with coke-oven, gas itself to a heating with an extraneously derived fuel-gas of the same or equivalent heating characteristics, thereby releasing for useful purpose the coke-oven gas otherwise requisite for their heating.

Natural gasoline is a liquid petroleum product consisting of the heavier hydrocarbons present in natural gas and extracted therefrom by such meansv as compression, absorption, and other processes. One of the grades of natural gasoline ,available, for example, on the market in ample supply at a relatively reasonable price is a socalled 37-70 natural gasoline. It contains as important ingredients quantities of aliphatic hydrocarbons containing from five to seven carbon atoms in their molecular constitution. These substances have at ,F. individually in pure form, respectively, a partial pressure less than atmospheric and of from about one-half to seven pounds per square inch absolute. They are thus rather volatile but are easily storable even in the hottest summer weather in containers having walls of moderate thickness. When they are dissolved in hydrocarbons having higher molecular weights. their pressures are accordingly reduced. They are per se, however, of relatively limited utility in the usual hydrocarbon markets, being to limited extent employed to lower flash-points of motor fuels for winter use but are usually disposed of by their extensive chemical alteration; for example, by polymerization.

It has now been demonstrated in the practice that these Cato C1 aliphatic hydrocarbons are themselves of important economic value, when in dispersion in a carrier gas, for the underfiring of coke ovens. Sufiicient quantity thereof are dispersible in an inert carrier gas or in combustion media of low calorific value, to form a fuel gas having a calorific value equal to and even greater than coke-oven gas, without their dewpoint at such calorific values being reached during distribution of the resultant gaseous mixture, under ordinary operating conditions, to the coke ovens. As a carrier-gas, there may be employed 3 blast-furnace gas and producer-gas, which normally require preheating to at least about 1700" F. for effective coke-oven heating. and air, combustion-products, or the like, can be also used for the purpose.

Ordinarily, it is preferred to buy the said hydrocarbons in the form of a solution; for examples, the above-mentioned 31-70 natural gasoline, or a 26-70 natural gasoline, wherein they are present in major proportion; these natural gasolines are common refinery products and are readily available 0.1 the market; they are preferred principally because of ease of storage and relatively low transport risk, the said C to C1 hydrocarbons being then removed from their said solution at the coke-plant site by simple fractionation, and thereafter directly used.

For the present purpose it has been found practical to remove the said C5 to C1 hydrocarbons by a continuous fractional distillation of the employed natural gasoline, the C5 to C1 hydrocarbons being removed as overhead vaporous product and, while not necessarily, they are, for obtaining all advantages of the present improvement, in such vaporous form immediately admixed with the chosen carrier-gas in that proportion which produces a mixed fuel-gas having the preferred calorific value. It is in this wise relatively simple continuously to produce the novel fuel-gas of the present invention with a substantially uniform calorific value that can be even considerably higher than ordinary cokeoven gas without normally exceeding the dewpoint of the C5 to 01 components thereof. The resultant novel fuel-gas is then distributable to the usual fuel-gas distribution system of the coke ovens wherein it can be employed in the usual fashion of fuel gases that do not require regenerative preheating for their efiective combustion therein. All coke-oven gas produced in the coking chambers is thus released for other commercial uses.

The required equipment-by which the said C5 to C7 hydrocarbon fraction can be separated from the natural gasolines, is simple and requires a relatively small investment especially in view of the greater economic value of the coke-oven gas which can be released for other purposes.

In the accompanying drawings forming a part of this specification and showing for purposes of exemplification a preferred apparatus and method in which the invention may be embodied and practiced but without limiting the claimed invention specifically to such illustrative instance or instances:

Fig. l is a diagrammatic elevational view of apparatus for practicing the present invention, and showing also in vertical section crosswise thereof, a coke-oven battery wherein the present improvement can be advantageously practiced; and

Fig. 2 is a vertical section taken longitudinally of the battery along line II-II of Fig. 1.

The same characters of reference designate the same parts in each of the views of the drawings.

Referring now to the drawings, particularly to Fig. 1, tank I l serves as a storage container for the natural gasoline received at the plant and for the reserve supply of said gasoline to the hereinafter described separating plant and the subsequent gas-mixing apparatus. Because of the relatively low vapor pressure of the said natural gasoline at normal atmospheric temperatures, the said storage tank II can be of the strength usually employed for gasoline storage, and a high-pressure tank is not required. Connected to said storage tank II is a discharge pipe I2 through which a predetermined flow of the said natural gasoline is withdrawn by a metering pump l3. The natural gasoline is pumped by the said metering pump, through pipe I4 and column-inlet pipes l6 and I6 which are equipped with thermostatically controlled automatic valves l8 and I9, respectively, into fractionatlng column 20. Inlet pipe l5 connects into the said column 29 at a point near the bottom thereof. and inlet pipe I6 is connected at approximately the middle of said column. The inflow of natural gasoline can thereby be directed into either the middle section or the bottom of the column, or, in predetermined ratio, to both, the rate of flow thereto being automatically controlled by a thermostat 2| that is connected to both said automatic valves l8 and I9, and is located at approximately the midpoint of the column. By such proportioning of the charge to two points in the column the relative quantities and the range of molecular weights of the hydrocarbon constituents of the over-head fraction and bottoms residue can be closely controlled.

The fractionating column 20 is a Raschig-ring packed column comprising: an indirect steamreheater 22 with its thermostatically controlled inlet valve 23, a free space 24, which is between a lower section of packing 25 and an upper section 26, and receives the natural gasoline charged into the column through the said pipe l6 for its vaporization; and a set of water-cooled coils 21 disposed in the topmost section of the said column for-controlling reflux therein. Beneath the said lower section of packing 25 and at a level suificient to cover the said reheater 22, there is maintained a constant volume of bottoms fraction by means of a liquid-level control 28, which automatically controls a valve 29 in bottoms discharge pipe 3|]. The said discharge pipe 30 is directly connected to a bottoms pump 3| which pumps the bottoms fraction through pipe 32 into a bottoms cooler 33, that isdisposed in said line 32, whence they fiow into storage tank 34 and from which the bottoms fraction can be directed to any selected use. It is also feasible to employ a spring-operated valve in the said discharge pipe 30, and to set such a valve at a pressure slightly higher than column pressure, in order to prevent bottoms fraction flowing through the said pump 3|.

Any over-head fraction of up to and including C1 hydrocarbons which is separated in vapor phase from the charged crude natural gasoline, by the above-described fractionating means, flows from the top of the column through a vapor line 35 in which is disposed pressure-regulator valve 36 for maintaining a constant pressure on the said column 20. to a Venturi inspirating mixer 31 whereby it is intimately mixed with the employed carrier-gas, which is delivered from appropriate supplying means through pipe 31a.- into gas-holder 38 therefor, whence said carrier-gas fiows through pipe 39 into the said Venturi inspirating mixer 31. The said carrier-gas and vaporous hydrocarbons are delivered into the said Venturi mixer in such relative positions that, irrespective of their relative pressures in said lines 35 and 39, their rapid and thorough mixing is assured.

The resultant novel fuel-gas, comprising said intimate admixture and issuing-from the Venturi mixer 31, is flowed therefrom through pipe 40 into indirect steam-heater means 4| having the conventional steam coils 42 and inlet and outlet steam pipes 43 and 44 respectively. Thence the heated, novel fuel-gas is drawn from the said heater through pipe 45 by a booster pump 46 whereby it is pumped through fuel-gas delivery pipe 41, gas-distribution headers 48 at either coke-oven battery side, and manifold pipes 49, as shown by the arrowed lines, to the heating fiues of waste-heat coke-oven battery 50 of which a vertical cross section, taken longitudinally through an oven, is shown in Fig. 1, and a vertical section, taken longitudinally of the battery, is shown in Fig. 2.

The said waste-heat coke-oven battery 50, illustrated herewith for purpose of example only as representative of the class of combustion apparatus wherein the present improvement can be advantageously employed, is of the type having horizontal heating flues 59 and simple passageways adjacently below the oven soles for recuperatively preheating combustion-air. The

Y fiow of air is indicated on the drawing by simple arrows; it enters the battery structure through tunnel-like longitudinally extending passageways 52, whence it passes into and along subsole flues 53 and at the outlet ends thereof divides and returns in reverse flow at a higher level in those parallel fiues 54, 54, that extend longitudi naliy of the ovens on each side of each of those sole flues 55 whereby combustion-productsare delivered from the oven-heating flues 59 to waste-heat tunnel 65. From each of the parallel fiues 54 the now preheated air rises through uptake fiues 56 which are so branched as to supply such air through ports 58 individually at one end of each of the superposed horizontal heating fiues 59, of adjacent oven-heating walls of adjacent coke ovens 50.

The fuel-gas of the present improvement is supplied at one end only of each horizontal flue by a nozzle 6|, the nozzles for the heating flues at one end of each wall being supplied by a manifold pipe 49. The said gas flows under the influence of stack draft along the said horizontal heating flues 59, burns therein with the said adjacently delivered preheated air from airports 58, and the combustion-products for all the flues of the heating walls enter sole fiues 55 through solefluc bull's eyes 63 and leave the battery through passageways 64 and waste-heat'tunnel 65. The flow of collected combustion-products just prior to leaving the battery is indicated in the drawing by circled arrows.

In one example of battery operation in accordance with thepresent improvement, an approximately 127 B. t. u. producer gas, having a 0.9 specific gravity, was continuously mixed in the diagrammatically shown apparatus with the top fraction of a natural gasoline to produce the present new fuel-gas which had an average heating value of 800 B. t. u. per cubic foot under standard conditions. The natural gasoline employed was of the grade which is termed 31-70 natural gasoline, that is, one having a vapor pressure of thirty-one pounds per square inch absolute at 100 F. and of which 70% distills at 140 F, The 31-70 natural gasoline that is available as a commercial product in the market under that designation varies in composition, its A. P. I. gravity, for example, ranging from 83 to 94; it contains variable minor proportions of low-boiling butane, and the like, which are frequently disposed of in these said trade products. Despite such variations it was possible with the i illustrated apparatus simple and continuously to producethe present new fuel-gas with substantially the same heating icharacterlstics at all times.

The above employed natural gasoline was continuously pumped at an average rate of seven allons per minute by adjustable metering pump l3 into the illustrated fractionating column 20 which was operatedmnder a vapor-pressure of approximately 15 pounds per square inch gage. Therein the said gasoline was continuously separated into an overhead fraction that constituted 80% of the charge, over 80% of said fraction comprising aliphatic hydrocarbons having five to seven carbon atoms in their molecular constitution. The bottoms residue consisted substantially only of some heptane with the heavier hydrocarbons. hydrocarbons in the re-boiler 22 in the base of the column was continuously maintained at about 240 F. by thermostatically controlled automatic operation of the supply of steam to I the heating coils therein.

The vapors leaving the top of the column were maintained at a temperature of about 140 F. by

means of the cooling coils 21.

From the top of the column these vapors passed to the Venturi mixer 31 wherein they were admixed with producer-gas from holder 38 in such proportion as to produce the new fuelburned in the heating flues. Hydrocarbon vapors representing about7,600 gallons of liquefied hydrocarbon fraction per day were burned in the oven fines of the illustrated battery. This new gas-released approximately 1,400,000 cubic feet of coke-oven gas per day for other purposes. 4

In a second example of operation wherein two coke-oven batteries of the type described were heated by the fuel-gas of the present improvement, four million cubic feet of coke-oven gas per day were released to consumers use. The fuel-gas was formed by mixing producer-gas and the vaporous hydrocarbons as above described; it had a calorific value of 800 B. t. u. per cubic foot under standard conditions. During winter operation the atmospheric temperature reached 10 F. and yet no hydrocarbon condensate was found in the gas transmission pipes for said gas mixture.

One of the special advantages of the present process resides in the fact that the special'carburant hydrocarbons are continuously prepared as required in vapor form in situ and are immediately introduced, without any condensation step therefor, into the carrier-gas. There is thus no opportunity, after their separation from the natural gasoline, for them selectively to evaporate into the carrier-gas and give a resultant fuel-gas product that varies from time to time in calorific value due to the tendency of lower-boiling constituents preferentially to evaporate. This latter disadvantageous circumstance is especially apparent in any procedure where liquid mixed hydrocarbons are vaporized by their contact with a carrier-gas.

The temperature of the heavier In the above-given examples, producer-gas has been employed as the carrier-gas; the present improvement is not however limited thereto and, in fact, it may often be found preferable for the advantages of economy and cleanliness to employ air, combustion-products, or blast-furnace gas, for the purpose. For example, an 800 B. t. u. per cubic foot gas formed by admixing air and the C to C1 natural-gasoline hydrocarbons is a nonexplosive mixture.

The invention as hereinabove set forth is embodied in particular form and manner but may be variously embodied within the scope of the claims hereinafter made.

I claim:

1. In coke-oven operation, heating said coke oven with a fuel-gas, by the steps of: storing in liquid state at the coke-oven site a natural gasoline, withdrawing and fractionally distilling as a product from the stored natural gasoline a vaporous stream of a hydrocarbon mixture comprising the hydrocarbons of the natural gasoline having up to six and seven carbon atoms in their molecular constitution, admixing a stream of a carrier-gas, chosen from the group consisting of air, blast-furnace gas, producer-gas, and combustion-products, with a vaporous stream of the hydrocarbon mixture separated from the natural gasoline as product including hydrocarbons having up to six and seven carbon atoms in their molecular constitution, the rate of said admixing being such as to provide a carrier gas admixture of a calorific value effective to heat said coke oven but insufficient to raise the dewpoint temperature of the so-formed admixture above a temperature point reached therein during its traversal of a distribution system to the heating fiues in said coke oven; applying heat to said admixture to maintain the temperature thereof, during its traversal to said coke oven, above the dewpoint temperature with respect to the condensible constituents of said admixture; and introducing into and burning the so-formed admixture in heating fiues of said coke oven without regeneratively preheating said admixture.

2. A method of operation for the alternative generation of heat required for coking of coke oven charges by the combustion of an extraneously derived fuel gas in lieu of coke-oven gas in the heating fiues of a coke oven battery comprising alternate coking chambers and intermediate walls provided with combustion fiues adapted for heating the coking chambers by com bustion therein of coke-oven gas derived from said coking chambers; said method comprising: storing in liquid state at the coke plant site natural gasoline having a vapor pressure of about one atmosphere and of which only about 70% distills at 140 F continuously withdrawing from said storage and fractionally distilling liquid natural gasoline aforesaid and separating therefrom in vaporous form a stream of hydrocarbon compounds containing substantially all of the hydrocarbons up to, and including also hydrocarbons having, seven carbon atoms in their molecular constitution leaving as residue substantially only heavier hydrocarbons; without-substantial condensation of said vapors, continuously admixing the said hydrocarbon stream with a carriergas having too low a calorific value effectively to supply the heat required for coking without preheating said carrier-gas by heat derived from waste-heat of products of combustion'for effecting coking in said battery, in proportion to provide a fuel gas'admixture having a calorific value at least equal to the coke oven gas but insuflicient to raise the dewpoint temperature of the so-formed admixture above a temperature point reached therein, during-said admixtures traversal of a distribution system therefor to the heating fiues in said coke oven battery; applying heat to said admixture to maintain the temperature thereof, during its traversal to said coke oven battery, above the dewpoint temperature with respect to the condensible constituents of said admixture; continuously flowing the admixture through the gas distribution system for underfiring the heating fiues of said battery with cokeoven gas aforesaid; and continuously delivering said admixture as fuel-gas from the distribution system to heating fiues of said coke oven battery without preheating for combustion for eflecting coking aforesaid and burning the same therein in quantity to generate the heat required for coking charges in the coking chambers of said battery.

3. In coke-oven operation, generating the heat for coking oven-charges in a masonry coke-oven battery comprising coking chambers and contiguous heating walls therefor comprising combustion fiues, by the steps of: storing in liquid state at the coke plant site a natural gasolinehaving a'vapor pressure of about one atmosphere and of which about 70% distills at F.; withdrawing from said storage and fractionally distilling the natural gasoline so as to separate therefrom in vaporous form a mixture of hydrocarbon compounds containing substantially all of the hydrocarbons up to, and including also hydrocarbons having seven carbon atoms in their molecular constitution while leaving as bottoms substantially only heavier hydrocarbons; admixing th so-separated hydrocarbon mixture with a carriergas chosen from the group consisting of air, blastfurnace gas, producer-gas, and combustion products, and in proportion to provide a mixture having a calorific value suflicient to generate by its combustion in the combustion fiues in the heating walls of contiguous coking chambers in the masonry coke-oven battery aforesaid, the heat required for coking oven-charges in the oven chambers contiguous to the heating walls but insuflicient to raise the dewpoint temperature of the so-formed admixture above a temperature point reached therein during said admixture traversal of a distribution system therefor to the combustion fiues in the heating walls of said masonry coke oven; maintaining heat in said admixture to maintain the temperature-thereof during its traversal to said coke oven, above the dewpoint temperature with respect to the condensible constituents of said admixture; flowing the admixture through a distribution system therefor to the combustion fiues in the heating walls of contiguous coking chambers in the Mom-- said battery; delivering said admixture as fuel gas from the distribution system to the combustion fiues in the heating walls of said masonry coke-oven battery without preheating for combustion for effecting coking therein; and burning the same therein in quantity to generate the required heat for coking oven-charges in the cok- ,ing chambers contiguous to the heating walls fed lar constitution, and having at 60 F. individually a partial pressure less than atmospheric, in liquid state at the coke-oven plant site in a container of the strength not greater than that usually employed for gasoline storage; withdrawing and introducing the same in measured quantities in vapor form into a carrier-gas of the group consisting of air, blast-furnace gas, producergas, combustion products, in proportion to form a fuel-gas mixture having a dewpoint in respect of the hydrocarbons less than 0., and a calorific value of substantially 800 B. t. u. per cu. ft. effective to generate the coking heat required for coking oven-charges in said oven battery when burned in the combustion flues therefor without substantial preheating of the gas mixture therefor; distributing the fuel-gas mixture to the combustion fiues of the aforesaid oven battery in proportionate amounts required through a fuelgas distributing system therefor comprising headers, manifolds, and nozzles leading to the individual combustion flues that are primarily de-- signed and adapted for feeding solely thereto,

optionally, the proportionate quantities of cokeoven gas that the oven-chambers themselves-generate, and are required to meet the underflring requirements in said combustion fiues; applying heat to said admixture to maintain the temperature thereof, during its traversal ,of the distribution system to the heating lines in said coke oven battery, above the dewpoint temperature with.

respect to condensible constituents of said admixture; and burning said fuel-gas mixture in 'said combustion flues as thus fed thereto in the proportionate amounts required to meet the underfiring requirements of the individual combustion flues.

5. In coke-oven operation, heating said coke oven with a non-regeneratively-preheated fuel gas, by the steps of: Withdrawing from reserve, in liquid state, at the coke-oven plant site and heating to vaporize a mixture of hydrocarbons con- -too low a calorific value effectively to heat said taining up to and including hydrocarbons having seven carbon atoms in their molecular constitution; continuously flowing the heated vaporous mixture of hydrocarbon compounds containing up to and including hydrocarbons having seven carbon atoms in their molecular constitution, into admixture with a producer-gas having heat to said admixture to maintain the temperature thereof, during its traversal to said coke .oven, above the dewpoint temperature with respect to the condensible constituents of said admixture; and continuously delivering said admixture as fuel-gas to heating flues of said coke oven without a regenerative preheating step and burning the same therein.

' WILLIAM 0'. KEELING.

REFERENCES CITED file of this patent:

UNITED STATES PATENTS Number Name Date 1,935,298 Richardson Nov, 14, 1933 1,958,381 Dickey May 8, 1934 2,021,271 Thomas 1 Nov. 19, 1935 2,079;586, I Atwell May 4, 1937 2,134,882 I -Monro Nov. 1, 1938 OTHER REFERENCES Petroleum and Its Products," .by W. A. Gruse,

page 19, found in Div. 64 of this ofllce.

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