US2313764A - Method of operating coke ovens - Google Patents

Description

March 16, 1943. c. OTTO METHOD 0F OPERATING COKE oVENs 2 Sheets-fSheet l Filed March 12," 1941 lNvENToR H2L 07'70 Match 16, 1943.

C. CTTO METHOD 0F OPERATING oKE ovENs Filed March 12', 1941 INVENTOR 2 Sheets-Sheet 2 CAeL 07'7'0 ATTORNEYV Patented Mar. 16, 1943 METHOD OF OPERATING COKE OVENS Carl Otto, New York, N. Y., assignor to Fuel Relining Corporation, Dover, Del., a corporation of Delaware Application March 12, 1941, Serial No. 382,902

" Y 2 Claims.

The general object of the present invention is to provide an improved method of operating coke ovens of the horizontal regenerative type employed in the production of metallurgical coke and adapted to be heated by the combustion of blast furnace or other lean fuel gas.

Most coke oven batteries built at the present time and in recent years for use in the produce tion of coke of the kind used in blast furnaces and for other metallurgical purposes, are alike in that they comprise horizontally elongated coking chambers extending transversely of the battery and alternating along the length of the battery with heating walls formed with vertical heating flues, and such coke oven batteries com- DTSB regenerators extending transversely of the battery below the coking chambers and heating Walls. Customarily, such ovens are so-called combination ovens, because they are adapted to be heated, at the option of the operator, either by the combustion of coke oven gas or other relatively rich fuel gas which does not require regenerative preheating, or by the com bustion `of blast furnace gas or other relatively lean gas which requires regenerative preheating. In combination coke oven batteries, all of the regenerators are used in preheating combustion air in operation with rich fuel gas, and in operation with a lean fuel gas some, usually half, of the regenerators are used in preheating combustion air, and the other regenerators are used vin preheating the lean fuel gas.

Modern lcombination coke oven batteries cus"- tomarily have coking chamber dimensions and coking times which fall within certain standard limits. Thus, for example, in such a modern coke oven battery, the horizontal length of each cokingr chamber is usually betweenv vforty and forty-five feet, the height of the coking chamber is usually not less than eleven feet and not more than fifteen feet, and the average width of the coking chamber is customarily not less than fourteen inches and not more than twenty inches, and such coke oven batteries are ordinarily designed for operation with coking times varying widely as the demand for coke varies and with minimum Vcoking times varying inversely with their widths. 'Quite usually, such ovens are designed for operation, when heated by the combustion of coke oven gas, withY a normal coking time of about one hour for each inch or" average coking chamber width, and for operation safely and with reasonable efficiency during considerable periods of time, with a lower coking time of one hour or a little less for each inch and a quarter of average oven chamber width, and for operation with much higher coking times during considerable periods in which the demand for coke is relatively low. t

Heretofore it has been considered impossible in actual practice to operate such ovens when heated by the combustion of lean gas with coking times not appreciably higher than are customary when the same ovens are heated with coke oven gas.

I have discovered, however, that by introducing blast furnace gas and combustion air Yinto the regenerators of such a coke oven battery at suitable pressures, appreciably higher than have been customary heretofore, it is practically possible to heat the battery by the combustion of blast furnace gas at the rate required for operation with a coking time about as low as is practically feasible when the battery is heated by the combustion' ofcoke oven gas. Furthermore, I may obtain this advantageous reduction in the minimum practical coking time with blast `Ifurnace gas heating of suitably constructed coke oven'batteries of any of the types now in general use. In particular I may employ my inventionin the operation of coke oven batteries having either so-called hairpin flues, elongated upper horizontal flues, or cross-over connections between the upper ends of vertical heating flues in adjacent vertical heating walls, provided the resistance to gas flow through the heating systems of the ovens is not high enough to create objectionably large pressure, or draft, head loss in operation with non-regeneratively preheated rich fuel gas.

, -In accordance with the present invention .I supply blast furnace gas and combustion air to coke oven battery regenerators for preheating therein at suitably related pressures which vary inversely with the desired coking time and each of which is-in excess of the pressure of the 'atmospherewhen the battery is being operated with a relatively low coking time.

While it has heretofore been customary to -vary the pressures at which blast furnace gas tion air has been drawn into the regenerators from the atmosphere by the draft suction, which customarily is due lto chimney stack action, though sometimes supplemented by the use of exhaust fan means.

Heretofore it has been customarily assumed by designers, builders, and operators of combination coke ovens that in a combination coke oven battery designed for eihcient operation with a suitably low coking time when heated with coke oven gas, it is not practically feasible to burn enough blast furnace gas to approximate the same low coking time in operation ,with Such gas, and that When the draft is increased in an endeavor to significantly lower the coking 'time obtainable with blast furnace gas heating, Vthe heating flue pressures are decreased to such an extent as to vcreate dangerous loven leakage conditions.

By the use of the present invention, however, the desi-red heating 4iiue pressures maybe main..-

tained when operating withblast "furnace gas .as

the fuel gas vand with'a ook-ing time approximately as low as is obtainable 'in .operation with rich fuel "gas, 'by the simple :expedient of maintaining suitably high .pressures 'in -the 'inlet :portions of the regenerators of 'ovens having ,heating systems in Whichlthe flow path resistances to :How are not-unduly large. For afull appreciation of the statement just made and its significance, :accou-ntzshould be taken of thepressure conditions prevailing in v`the .look-ing chambers land in the different portions of lthe heating system of combivnation coke oven ibatteries, land an lanalysis of those conditions may *be `facilitated `by the accompanying drawings in which:

` Fig. 1 isa diagrammatic representation of .a portion of a lcoke oven battery andfits heating system;

Fig. y2 is a diagrammatic illustration of tempera-ture and pressure conditions :prevailing in different portions Vof 'the` coke oven vstructure shown in Fig. il; and

Fig. 3 is a Ydiagram generally similar to -Fig.2 'illustrating.temperature and pressure conditions 'in va battery differing from that shown in Fig. 1 in the manne-r in ywhich the upper ends of the vertical Vheating ues are connected.

AThe coke oven `arrangement illustrated dia.- grammatically by wayvofexample in Fig. 1, comprises a cokingchamber A between heating walls lB", each vformed withpairs-of vertical luesB and "b,the -flues B and Tbof v'eachrpair 'being connected at their upper ends yto collectively forma hair.-

pin nue. The arrows shown in Fig. l indicate the v icondition ,of operation'in'which the direction of heating gas -flow is upward in the -`iiu'e `B and downward in the-flue b, this direction of flow be- -ing periodically reversed, usually at half `hour intervals.

jE-ach hairpin-flue :limbB has 4itslower end connected vbyone connection@ `to an air preheating regenerator D, and by r'a -second connection C to -a regenerator E which Kmay be-used interchangeably -to preheat combustion air or blast furnace `gas accordingly as the coke oven is preheated by `the combustion of rich gas or blast furnace gas. -Similarly, each flue limb bhas vits lower end con- -nected by connection channels C to an air preheating regenerator d and `to a regenerator e which ymay Ibe used interchangeably to preheat f combustion air orl -blast furnace gas, accordingvly as the v'coke oven is preheated by the combustion of Arich gas Aor blast furnace gas. With the `how through the lue limbs in the directions indicated by the arrows, the regenerators D and E are on regenerators supplying preheated combustible agents to the ue limb B, and the regenerators d and e are off regenerators which receive heating gases from the ue limb b and are thereby heated up. Periodically, usually at half-hour intervals, flow through the regenerators and flue limbs is reversed so that the previously "on and oiiregenerators then become oif and on regenerators, respectively.

As shown, each of the regenerators D, d, E and e is provided with a supply connection F through :which the regenerator receives the combustible agent preheated in the regenerator from a suitable source of supply of said agent under pressure. Each of the Aregenerators is also provided with an outlet G through which the regenerator, `vvhen servingas'an off regenerator discharges waste heating gases. customarily and as shown, each of the supply connections Fand exhaust connections G includes a damper or throttling deviceI-I for regulating regenerator flow and pressure conditions.

.As .diagrammatically illustrated, the vgas pressure .in the coking chamberA may be .regulated by throttling the outlet A for distillation gases. In van .actual battery of the type illustrated, ,the gas Jpressure in the oven rchambers is customarily regulated indirectly `by regulation of the 'pressure in the fgas c ollectingimainto which the different gas .outlets of vthe .battery are connected.

`In practice, a ycoke oven 'battery having .the 'features vof construction illustrated diagram- .matically in Fig. 1,-Will ordinarily have each of its .different regenerator .chambers provided with :two connection :channels C, one running lto :a flue in one, :and `the second to a flue in the .other of two adjacent heating walls. .Each re- ;generator chamber, moreover, may extend continuously for the full or the half Vvvidth of the battery, and lbe connected by channels C dis- -tributed along its vlength to correspondingly distributed heating wall flues, or, as shown in my prior Patent 2,216,983, each regenerator maybe .divided .to form as many separate regenerator cells or chambers as there vare hairpin Iiues in :each `heating wall, with each such cell or cham- -ber connected to a single limb of a single 'hairpin flue in each of .the two adjacent heating walls. `In practice also, each regenerator is ordinarily :provided with a sole channel beneath the checker brick containing the .chamber or chambers. When each regenerator comprises a plurality of regenerator chambers, the regenerator outlet regulating means, corresponding in function lto rthe dampers` H in the outlets G of Fig. 1, `may 'be `vdevices throttling the passages through-which "the different regenerator chambers communicate with the corresponding Isole channel, as is shown for .examplein my prior Patent 2,216,983. When Leach Yregenerator comprises a single regenerator chamber, thedischarge therefrom of waste heat- .ing gases mayibe regulated by a damper in the regenerator 4sole channel outlet at one or each side of the battery. In general, also, the regenerator supply and oifta'ke connections are alternately closed and open by the use of corresponding reversing Valves.

As those skilled in the art will understand, however, the various regenerators features and characteristics mentioned in the preceding paragraph are all Well known, and their particular ty-pe and form constitute no part of he present invention, and hence they need not be further referred to herein. The type of oven battery shown in Fig. 1 includes rich fuel gas supply and burner means which may be of various forms one of 'which is shown in my prior Patent 2,216,983, but to simplify Fig. 1, no such means are shown therein. i

In Fig. 1, the numbers l-8, inclusive, respectively designate points at the bottom and top of the regenerators D, at the bottom and top of the upow hairpin flue limb B, at the top and' bottom of the downilow hairpin flue limb b; and at the top and bottom respectively of the regenerator d. Similarly. the numbers 9 and Ill designate points at the top and bottom respectively of the oven chamber. In the Fig. 2 diagram, the points I- .9 are arranged along the horizontal base line lei-8 of the diagram at scaled distances, the scale being such as to make the distance between the 'points 3 and 4, i. e., the height of each flue limb B, nine feet and ten inches, and to make the height of the oven chamber eleven feet. Inthe Fig. 2 diagram the draft gage pressures at the points I-IU, inclusive, are respectively indicated by the distances of the points P-P1 from the horizontal line 0-0 passing through the zero point of the scale at the side of the diagram, the scale Aunit being a millimeter of water. Assumed normal temperatures at the points l, 2, 3, 6, l, and 8, and average flue temperatures are shown in Fig. 2 in degrees Fahrenheit. The difference between the top and bottom oven chamber pressures P9 and P10 shown in Fig. 2 is of normal value with the oven temperatures prevailing at the end of the coking operation.

The temperatures and pressures assumed in Fig. 2 are typical of those obtainable by the use of the present invention in the operation of a modern underred regenerative hairpin flue coking oven having the above mentioned dimensions and heated by the combustion of 90 B. t. u. blast furnace fuel gas and coking an ordinarily good coking coal having about 25 per cent volatile matter, with a coking time of about one hour for each inch and one-sixth of the average coking chamber width.

As previously stated, the pressures P', P2, P3, etc., shown in Fig. 2 are the gage pressures at the points I, 2, 3, etc., respectively, i. e., they are the pressures which would be shown by a gage measuring the difference between the pressure at each such point and the pressure of the external atmosphere at the level of said point. As is well known, the absolute pressure of a fluid owing along a path must progressively diminish as a result of the frictional resistance to the flow as the distance along the path from its inlet end increases. The effect Osuch variations in the absolute pressure of the fluid flowing along the path of flow between the points I and 8 shown in Fig. 1, is masked in Fig. 2 by the eiTect on the gage pressures at different levels of diiTerences between the densitt7 of the heated fluids flowing through the regenerators and the flues of the coking oven, and the density of the cooler, external atmospheric air.

Since the density of a gas is inversely proportional to its absolute temperature and since at the same temperature the density of blast furnace gas is about the same as the density of air, and the density of the products formed by the combustion of blast furnace gas is only a few per cent greater than the density of the air, the density of the upowing gases in the flue B 'of Fig. 1 at a temperature of 2550 F. will be only about one-sixth ofthe `density of air at usual atmospheric temperatures and pressures. Except for the effect of the small pressure drop in the flue B required to maintain the ow through the flue, the excess of the pressure at the point 3 over the pressure at the point 4 would thus be only about one-sixth of the excess of the external barometric pressure at the level at the point 3 over that at the level of the point 4.

With normal atmospheric temperatures and barometric pressures at the relatively low elevations above sea level at which coke oven plants are customarily located, the external barometric pressure will diminish by an amount of slightly less than .375 of a millimeter of water per foot of increase in elevation above sea level. In consequence with the point 4 above the point 3 by a distance of nine feet and ten inches, the external barometric pressure at the level 3 will exceed the external barometric pressure at the level of the point 4 by about 3.69 millimeters of water. With no flow in the flue B, the difference in the absolute pressures at the points 3 and 4 would thus be but a little greater than .61 millimeter of water, and if the gage pressure at the point 4 is zero, for example, the gage pressure at theV point 3 would be about 3.08 millimeters of water.

The effect of the pressure drop due to flow between two points at different levels is to diminish the diierence between the gage pressures,

at the two points when the flow is upward, and to increase the gage pressure difference when the flow is downward.

The pressure drops due to now in the flues B and in the ilue b are relatively quite small, and in Fig. 2 the assumed excess of temperature in the upflow ilue B over that in the downflow flue b happens to be that required to make the difference between the gage pressures at the top and bottom of the ilue approximately the same for each of the flues B and b.

In the regenerators the average temperatures are much lower and the flow resistant-,es and pressure drops are much higher than in the flues, and under the operating conditions assumed in Fig. 2 the gage pressure at the point l is slightly positive although the gage pressure at the point 2 is about 21/2 millimeters of water negative, while the gage pressure at the bottom point 8 is about six millimeters of water more negative than the gage pressure at the point 1.

As is well known, furnaces made of rebrick and subjected to high temperatures are in" practice not gas tight, but will pass air or gas when significant pressure differentials exist between the opposite side surfaces of the wall. Because of this fact it is customary to operate coke ovens in such manner that the gas pressure within the coking chamber varies from a pressure at the top of the chamber somewhat above the pressure cf the atmosphere at the same level, to a pressure at the bottom of the oven chamber which is somewhat below the atmospheric pressure. Thus, as indicated in Fig. 2, the gage pressure at the oven chamber point 9 may well be abouty +1.5 millimeters, and the gage pressure at the point l0 about 2.l millimeters. With such oven pressure conditions, tendency to leakage of the pressure differences should be so related that Y any leakage which may occur should be in the least harmful direction, which ordinarily is from the oven chambers into the ues, rather than in the reverse direction. pressure is about .1 of a millimeter below the oven chamber pressure at all levels, and the pressure in the downflow flue increases relatively to the oven pressure as the bottom of the flue is approached, becoming approximately equal to the oven pressure at the level of the bottom of the flue. lTor purposes of analysis and ready comparison, I have shown in dotted lines at the left-hand side or Fig. 2 the pressure variations between the points 5 and S by a dotted line curve P60 and Poa'nd have shaded the area between that curve and the curve P-P3. The vertical distance between any point on the curve P-P2 and the subjacent point on the curve PSL-P60, is a measure of the pressure difference tending to create leakage at the level of said points through the wall separating an on regenerator from an adjacent oiT regenerator. To prevent such leakage, metallic leakage barriers may be incorporated' in the masonry regenerative division walls as disclosed in my prior Patent 2,216,983, granted October 8, 1940. The vertical distance etween the points P and P80 directly represents the difference in the absolute pressures at the points l and 8 and hence represents the draft loss and leakage producing between those points.

Fig. 2 correctly indicates the actual fact that the operation of a coke oven battery of the type shown in Fig. 1, when heated by the combustion of suflicient blast furnace gas to have a coking time approximately as low or short as the lowest coking time readily obtainable when the battery is heated by the combustion of coke oven gas, requires the pressure in the inlet portions of the on regenerators to be above the pressure of the atmosphere at the same level. It is thus impossible to obtain such a desirably low coking time when operating with blast furnace fuel gas, by drawing atmospheric air into the regenerators by chimney stack suction.

VAs those skilled in the art will understand, the regulation ci the distribution of ow into the different on regenerators of the battery requires in practice some throttling of the regenerator inlets F in Fig. 2, and this means that the air regenerator inlets must receive combustion air from a source of such air at a pressure signicantly' higher than the pressure maintained in the on regenerators at their lower ends. It hardly needs to be explained that a reduction in the coking time of the battery below the coking time for which the diagram shown in Figr2 was computed, would require the blast furnace gas and combustion air supply rates to be increased, and that this would require an increase in the pressureY at the on regenerator point I, and a decrease in the pressure at the off regenerator point 3, relative to the pressures at the points i and 5 which are desirably maintained approximately constant as the coking time is varied. When the coking time is substantially lengthened because of a material reduction in the demand for coke, the gage pressure at the point I may be decreased to a negative Value, so that it is then possible, theoretically, at least, to draw into the regenerators combustion air from the atmosphere by means of chimney draft.

Fig. 2 is intended to illustrate conditions in a Acollzeo'ven battery having unobstructed hairpin In Fig. 2, the upow fluev ues with no pressure drop in the connection be-l tween the upper ends of the two limbs of each hairpin flue, and in which no portion of the heating gas flow path between the inlet portion of Such a coke oven battery is inherently capable of operation with a smaller pressure drop due to flow through the heating system, than is possible with other well known forms of coke oven batteries in which the heating system flow resistance is increased in any of the following ways; namely, by the use of throttling devices at theV bottoms or tops of the vertical combustion ilues, or by the use of crossover connections extending over the oven chambers and connecting the upper ends of vertical flues in different heating walls, or in which a group of side by side fluesin each heating wall are connected at their upper ends by an elongated upper horizontal channel which at any one time receives heating gases from a plurality of the ues in the group then serving as upow lues and discharges heating gases into the upper ends of the remaining lues in the group which are then serving as downow iiues.

In a coke oven battery having its inherent ow resistance increased by its inclusion of any of the ways just mentioned, the pressure difference between the points l and 8 in the lower portionsof the connection on and olf regenerators of the battery must be higher than are indicated in Fig. 2 for the same coking time. Furthermore, if the pressure differentials between the coking chamber pressures and the flue pressures are to be minimized, the increased pressure drop between the points i and 8 must result in part from an increase in the gage pressure at the point l, and in part from a decrease in the gage pressure at the point 8, as is indicated in Fig. 3.

The diagram shown in Fig. 3 differs from that shown in Fig. 2 as a result of increases in the flow resistances of the connections between the up and down flow fiues and of the connections C between the lower ends of the ilues and the regenerators. the top of the downow iiue is some three millimeters of Water lower than the pressure P4 at the top of the upow flue, while in Fig. 2 the pressures P5 and P4 are approximately the same. In Fig. 3 also the difference between the pressures P2 and P3 and between the pressures P6 and P7 are greater than they are in Fig. 2. The Fig. 3 pressure drop of about three millimeters of water between the tops of the upilow and downilow ues is a normal drop for a well constructed oven battery of the crossover type operating with blast furnace gas and with a coking time of about one inch per hour. With coke oven batteries comprising elongated upper horizontal ues and regulating provisions including throttling slide bricks at the tops of the vertical flues, the pressure in the top portion of an uplow may exceed the pressure in the top portion of the downowiiue by as much as eleven millimeters of water in some cases. Y

v For the attainment vof `the full advantages of the present invention, it is essential that the pressure drop, or draft head loss, should be substantially the same in the regenerators used in preheating combustion air as in the regenerators simultaneously used in preheating fuel gas. In

practice this requires that the gas and air pre- In consequence, the pressure P5 atY heating regenerators should be respectively proportioned to the volumes of the preheated gas and air uniting in combustion. This means that in a coke oven battery designed for operation with such a lean fuel gas as 90 B. t. u. value blast furnace gas and having cross regenerators of the usual form, the horizontal cross section of each air preheating regenerator should be about '75% to 80% of the horizontal cross section of the corresponding gas preheating regenerator, since the combining volumes of the gas and combusticn air are in about the ratio of l to 71/2 or 8,

In heating a combination coke oven battery about the same volume of combustion air is required for the maintenance of a given coking time when the fuel gas is coke oven gas or when it is blast furnace gas. Since al1 of the regenerators are used in preheating combustion air, when the fuel gas is coke oven gas, the air velocity through the regenerators will then be less than half as great as it is when the fuel gas is blast furnace gas, if the air regenerators in which all of the combustion air is then being preheated are only 80% as big as the gas preheating regenerators. When account is taken of the fact that the pressure head drop due to flow through a regenerator is approximately proportional to the square of the flow velocity, it is easy to realize Why low coking time operation of a given combination coke oven battery is possible with natural draft when the fuel is coke oven gas and requires forced draft when the fuel is blast furnace gas.

For example, the particular coke oven battery for which the operating characteristics shown in Fig. 2 were computed and assumed When using coke oven gas as its fuel, can be operated With the Fig. 2 coking time and pressures at the tops of the flue, but with a gage pressure of about 3.2 millimeters of Water minus. With the pressure of the atmosphere more then three millimeters above that in the inlet portions of the regenerators natural draft operation is entirely feasible.

As already indicated and as Will be apparent to those skilled in the art, the present invention may be used with advantage in the operation of coke oven batteries differing greatly from one another in type and form,

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention, as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

l. In the operation of a coke oven battery having air and gas preheating regenerators beneath horizontally elongated coking chambers and heating Walls alongside said chambers and including vertical heating flues, each connected at its lcwer end to one air preheating and one gas preheating regenerator and each connected at its upper end to one or more other vertical lues, whereby each of said vertical flues is adapted to serve as an upfloW flue receiving preheated air and gas from the two regenerators connected to its lower end during periods which alternate with other periods in which said flue serves as a downflow fiue discharging heating gases into the last mentioned regenerators, the method which consists in supplying combustion air and lean fuel gas to the regenerators connected to ues then serving as upoW iiues so as to maintain gage pressures in the portions of the last mentioned regenerators adjacent and at the discharge sides of their respective inlets which are positive with a relatively low battery coking time.

2. Inheating a regenerative coke oven battery by the combustion of a lean fuel gas uniting in combustion with substantially less than its own volume of combustion air, in vertical flues in the heating walls at the sides of the Ibattery coking chambers and each connected at its upper end to one or more other flues, Whereby each of said iiues is adapted to serve as an upfloW flue receiving combustion air and fuel gas at its lower end during periods which alternate with other periods in which said flue serves as a doWnoW flue and receivesv products of combustion at its upper ends from the flue or flues connected thereto, the method which consists in passing preheated combustion air and fuel gas into the lower end of each flue, when the latter is serving as an upiioW flue, from corresponding air and gas regenerator chambers similarly proportioned relative to the respective volumes of said combustion air and fuel gas preheated therein, and supplying such fuel and combustion air and fuel to the respective inlets to said chambers for preheating therein at such pressures that the gauge pressures Within said regenerator chambers and at the discharge sides of their respective inlets which are positive when the battery is operating with a relatively low but battery coking time, and diminishing the last mentioned pressures as the battery coking time is increased.

CARL OTTO.

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