US3451896A

US3451896A - Method of cleaning a stream of coke oven gas and apparatus therefor

Info

Publication number: US3451896A
Application number: US629263A
Authority: US
Inventors: Erich F Schon
Original assignee: Otto Construction Corp
Current assignee: Otto Construction Corp
Priority date: 1967-04-07
Filing date: 1967-04-07
Publication date: 1969-06-24
Anticipated expiration: 1986-06-24
Also published as: DE1671346A1

Description

E. F. SCHON 3,451,896 F CLEANING A STREAM OF COKE OVEN GAS METHOD 0 I June 24, 1969 AND APPARATUS THEREFOR Filed April 7, 1967 QD UVEE m9 32min NA KMAOOU mwkss mom xz vm 22E. QZCZQUMQ INVENIOR ERICH KF. SCHON United States Patent Olfice Patented June 24, 1969 US. Cl. 201--15 Claims ABSTRACT OF THE DISCLOSURE Method of cleaning a stream of coke oven gas containing ammonia therein comprising: dividing the stream of coke oven gas into a first stream for subsequent combustion in coke oven heating fines and a second stream for subsequent conversion to waste gases which are vented to the atmosphere, scrubbing the first stream with aqueous media to cleanse the gas and remove ammonia therefrom so as to form aqueous ammonia liquor, and passing the cleansed first stream to the heating lines and burning it therein to provide heat for destructive distillation of coal in the coke oven coking chambers. Method additionally contemplates distilling the aqueous ammonia liquor to form ammonia vapor, admixing the ammonia vapor with the second stream of coke oven gas, and passing the ammonia-rich second stream to a conversion zone and converting the stream to waste gas. Apparatus for effecting the foregoing method is also described.

BACKGROUND OF THE INVENTION Field of the invention Description of the prior art By-product coke ovens of the foregoing type are, of course, well known in the art. The coke oven gas coming from such by-product ovens contains various contaminants, in particular, ammonia, H S, HCN, CO tars, benzols, phenols, and the like. Heretofore, it has been conventional to recover one or more of the foregoing components, e.g., ammonia, and then to sell such recovered product so as to olfset the cost of operating the coke oven. However, the expenses involved in effecting such recovery have been increasing, so much so that as of the present time the recovery costs tend to exceed the commercial value of the products so recovered.

It has been conventional in the recovery of ammonia from coke oven gas, to react it with an acid such as sulfuric acid, phosphoric acid, or the like, so as to obtain ammonium sulfate or ammonium phosphate, which products can then be sold as fertilizers. Here too, the cost of recovery as fertilizers has tended to exceed the commercial value of such fertilizers.

SUMMARY OF THE INVENTION 'In accordance with the present invention, a method is provided for cleaning a portion of a stream of cake oven gas containing ammonia and other contaminants therem,

whereby the cleansed portion is subsequently combusted in coke oven heating fines so as to provide heat for the coking of coal disposed in the coking chambers of the coke oven. The ammonia and other contaminants that are removed from the cleansed portion are passed to the second (uncleansed) portion of coke oven gas, and this portion is converted to waste gases that are essentially non-pollutants, which gases are vented to the atmosphere.

BRIEF DESCRIPTION OF THE DRAWING My invention will best be understood from the following detailed description taken in conjunction with the accompanying drawing, which is a schematic flow sheet of the method and apparatus of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with one aspect of my invention, I have developed a method of cleaning a stream of coke oven gas typically containing ammonia, H 8, HCN, CO tars, benzols, phenols, and other contaminants therein, this gas having been obtained from a coke oven battery cornprising a plurality of spaced apart coking chambers with a plurality of heating walls disposed therebetween, the heating walls each having therein a plurality of heating cues. My method involves dividing the stream of coke oven gas into a first stream for subsequent combustion in the coke oven heating flues and a second stream for subsequent conversion to waste gases which are vented to the atmosphere. The first stream is scrubbed with aqueous media to cleanse the gas and remove ammonia and other contaminants therefrom, thereby forming an aqueous ammonia liquor. The so cleansed first stream is then passed to the heating flues of the coke oven and burned therein so as to provide heat for destructive distillation (coking) of coal in the coking chambers.

My method additionally contemplates distilling the aqueous ammonia liquor to form ammonia vapor, admixing the ammonia vapor with the second stream of coke oven gas, and passing the resulting ammonia-rich second stream to a conversion zone and converting this stream to waste gas that may be vented to the atmosphere without danger of pollution.

Desirably, the amount of coke oven gas employed in the first stream is slightly in excess of the heating requirements for the heating fines of the coke oven battery. Thus, after the first stream has been cleansed, that amount of gas in excess of the heating requirements for the heating flues may be bled oif and admixed with the second stream prior to its conversion to waste gases.

Advantageously, the first stream, prior to the scrubbing step, is spray cooled with ammoniacal liquor so as to remove some or all of the tars and water vapor to thereby form tar-containing aqueous ammonia liquor. Such liquor may then be admixed with the aqueous ammonia liquor obtained as a result of the subsequent scrubbing step. My method also provides for removing any tars contained in the aqueous ammonia liquor obtained by virtue of the aqueous spray cooling, prior to the admixing of such aqueous ammonia liquor with the aqueous ammonia liquor obtained from the scrubbing step.

Referring to the second stream of coke oven gas that is ultimately converted to waste gases, it is desirable that this stream be heated prior to the admixing therewith of the ammonia vapor obtained from. the first stream, the heating being to such temperature that upon admixing, any water or tars that may be present in the ammonia vapor do not condense.

Referring to the drawing, reference numeral 10 designates the coke oven battery, which includes a plurality of spaced apart coking chambers with a plurality of heating walls disposed therebteween, the coking chambers and heating walls generally designated by the reference numeral 12. Coke oven regenerators 14, for preheating air prior to its introduction into the combustion chambers, are disposed beneath the coke oven chambers and heating walls 12 in conventional fashion.

As coal in the coking chambers is coked, coke oven gas is evolved. The coke oven gas is conducted, via conduit 16, through cooling chamber 18 to juncture 20, wherein it is divided into two streams, a first stream S typically 45% by volume of the coke oven gas, which stream is to be cleansed and then utilized as fuel in the coke oven heating flues, and a second stream S typically 55% by volume, for subsequent conversion to waste gases.

The first stream S is passed via conduit 24 into spray cooler 26 for removal of some of the tars and water therefrom as described hereinafter. The cooled gas stream S now passes via conduit 28 to tar filter 30. The tar filter, which desirably is electrical, effects separation of any residual tars. These tars are drawn off via conduit 31 and passed to decanting tank 50. The gas stream S is then passed via conduit 32 and blown by exhaust fan 34 through conduit 36 into scrubber 38. Fresh water is fed into spray head 40 of the scrubber via pipeline 42. The spray scrubber 38 serves to remove ammonia from the coke oven gas.

The cleansed gas stream S is then passed via conduit 44 into gas distribution channel 46 of the coke oven 10. Air is introduced to the regenerators via conduit 47 for preheating and is then admixed with the cleansed gas in conventional manner for combustion in the coke oven heating flues. The thus combusted gases pass from the regenerators through conduit 49 to stack 51 and are vented to the atmosphere.

Referring again to spray cooler 26, this serves to remove some tars and water from the first stream S of the coke oven gas. The bottoms water, which contains therein tars and ammonia, is divided into two portions. One of these portions is drawn off the bottom of spray cooler 26, passed through conduit 59, cooled by cooler 61, and recycled through spray head 63.

The other portion is removed via conduit 48 and pumped into flushing liquor tank 118.

Ammonia-containing water (flushing liquor) is drawn from tank 118 via conduit 120 and pumped through spray nozzles 122 into conduit 16 (stand pipe) and into cooling chamber 18. Chamber 18 collects the gases from the individual coking chambers and hence serves as a gas collecting main. As the hot gases contact the flushing liquor some of the liquor will evaporate, thereby cooling the hot gases. The rest of the flushing liquor together with the gases flows through conduit 19 and passes via conduit 124 to tank 118. Solid particles settle to the bottom and are removed from the liquor (not shown).

The surplus of ammonia-containing water and tars, representing the quantities produced in the coking chambers, is removed via conduit 1% and passed to decanting tank 50. Tars are removed from the bottom of tank 50 via conduit 52, and may either be pumped via conduit 54 to steam boiler 56 for ultimate conversion to waste gas or, alternatively, may be passed through conduit 58, collected, and sold.

Aqueous ammonia liquor is collected from the top of decanting tank 50 and pased through conduit 60 to a suitable dephenolizing apparatus 62, e.g., an extractor, with the separated phenols being collected via conduit 64. The phenols may be readily extracted in dephenolizing apparatus 62 by means of benzene or other appropriate solvent.

Aqueous ammoniacal liquor from the bottom of dephenolizing apparatus 62 is passed via conduit 66, along with aqueous ammoniacal liquor from the bottom of scrubber 38 via conduit -70, to distilling column 72. Heat is supplied to distilling column 72 in the for-m of steam from steam boiler 56 via conduit 74. Ammonia vapor coming off the top of distilling column 72 is rectified by indirect cooling in rectifier 76, the cooling water to the rectifier being suplied via conduit 78 and being returned via conduit 80. Dephenolized waste water is withdrawn from the bottom of column 72 via conduit 82 and may be discharged.

In order to reduce the requirements (1) of fresh water, supplied via conduit 42 and (2) of steam, supplied via conduit 74, aqueous ammoniacal liquor leaving dephenolizing apparatus 62 via conduit 66 may be passed, in whole or in part, via conduit '67 and pumped into the liquor recycled via conduit 109, before such liquor passes into cooler 110 (described hereinafter).

The resulting concentrated ammonia-water-vapor from rectifier 76 is passed through conduit 84 into conduit 86, which conduit is of course in communication with juncture 20. Hence, conduit 86 contains therein the second stream S of coke oven gas. Thus, the second stream S now enriched with the ammonia vapor from conduit 84, is passed via exhaust fan 88 through conduit 90 to the steam boiler 56.

It is important that, upon introduction of the concentrated ammonia-water-vapor from conduit 84 into conduit 86, no condensation of water or other vapor occur. Accordingly, provision is made for a heater 92 to heat the second stream S of coke oven gas at a point prior to the injection of the ammonia-water-vapor therein. As shown in the drawing, heater 92 is supplied with steam from steam boiler 56 via conduit 94.

It is to be noted that in accordance with my invention, the amount of coke oven gas separated at juncture 20 and utilized as the first portion S will be slightly in excess of the normal fuel consumption of the coke oven. That is, it will be slightly in excess of the heat requirements for the coke oven heating flues. Accordingly, a bleed-01f line 96 is provided, one end of which communicates with conduit 44, the other end of which communicates with conduit 86. Regulating means, e.g., governor 98, in the bleed-off line 96 automatically bleeds off that excess of gas present in the first stream S so that it is fed into the second stream of gas S in conduit 86.

Steam boiler 56 is maintained under conditions of elevated temperature and pressure, typically at a temperature of at least about 1000 C., and desirably at a temperature of about 1400 C., and at elevated pressures, e.g., of the order of from 40 to 100 atmospheres. Under these conditions, the ammonia present in the second stream S is readily cracked to nitrogen and water, these products being non-pollutant to the atmosphere. In like manner, other contaminants present in stream 8; are converted to relatively inert or non-pollutant products, so that the overall products obtained in the steam boiler 56 may readily be vented to the atmosphere as waste gases via stack 100.

It will be noted that provision is made for a water cooler 102. Make-up water is supplied to the cooler via conduit 104. Cooled water exits from cooler 102 via conduit 106, with warmer water that is to be recooled being returned via conduit 108.

Cool water from conduit 106 is fed into liquor cooler 110 via conduit 112, the heated water being returned to conduit 108 via conduit 114. In the same manner, cool water is fed to cooler 61 via conduit 106, the warmer water being returned to the cooler via conduit 108. And again, cooling for rectifier 76 is provided from cool water via

conduits

106 and 78, the warmer water being returned to water cooler 102 via

conduits

80 and 108.

As will be seen from the drawing, liquid media for the scrubber 38 is supplied not only via fresh water from conduit 42, but also by recirculation of some of the aqueous ammoniacal liquor at the bottom of the scrubber. Thus, a portion of this liquor is withdrawn via conduit 109, cooled by cooler 110, and recycled to spray head 111. Similarly, ammoniacal liquor from flanges 113 and 115 is collected in

conduits

117 and 119, respectively, and recycled to spray

heads

121 and 123.

Considering an illustrative example of the foregoing method and apparatus in actual operation, coke oven gas produced in the coke oven from the coking of coal will generally enter conduit 16 at a temperature of from about 700 to 800 C., the gas having a dew point of about 68 C. As the gas goes along conduit 16 it cools down to about 600 C. prior to entering cooling chamber 18. The spraying of droplets of ammonia liquor from flushing liquor tank 118 into cooling chamber 18 cools the gas so that upon leaving the cooling chamber and passing to juncture 20 the gas is cooled down to a temperature of, e.g., about 90 C., and has a dew point of about 78 C.

The first stream S of the gas thus enters spray cooler 26 at a temperature of about 90 C. Ammonia liquor entering spray cooler 26 through spray head 63 is typically at a temperature of about 35 C. Coke oven gas, after leaving cooler 26 via conduit 28 and passing through tar filter 30 and exhaust fan 34, has a temperature of about 48 C. and a dew point of about 38 C. The gas then passes through scrubber 38 and leaves the scrubber at a temperature of about 40 C. The thus cleansed gas passes via line 44 into distribution channel 46 for combustion in the coke oven heating flues.

Considering the second stream S of coke oven gas, as previously noted, this stream passes through conduit 86 and then through conduit 90 into the steam boiler 56. Typically, it reaches the steam boiler at a temperature of from about 100 to 110 C. with a dew point of about 80 C.

Referring to scrubber 38, fresh water is fed via conduit 42 and generally is introduced at a temperature of about 35 to 38 C. The temperature of the ammonia liquor existing from the scrubber 38 via conduit 70 is typically about 39 C. That portion of liquor that is to be recirculated through scrubber 38 via conduit 109 is cooled via cooler 110, e.g., to a temperature of 38 C.

Ammonia liquor is also collected from the bottom of spray cooler 26. This ammonia liquor is passed to tank 118, generally at a temperature of from about 40 to 50 C. Part of the ammonia liquor from the bottom of spray cooler 26 is recycled. Thus, it leaves via conduit 59 at a temperature of about 50 C., is cooled by cooler 61 to a temperature of about 35 C., and is recycled through spray head 63.

Tar-free ammonia liquor is passed through conduit 60, generally at a temperature of from about 50 to 70 C., and is introduced to dephenolizing column 62. Upon exiting from the dephenolizing column (through conduit 66) the temperature of such ammonia liquor is generally of the order of about 50 C. Thus, ammonia liquor exiting from the dephenolizing column (conduit 66) and from the scrubber (conduit 70), when combined together typically are at a temperature of from about 40 to 45 C. This stream is passed to distilling column 72. Dephenolized waste water at about 98 C. is drawn ofl from the bottom of the column via conduit 82. Ammoniawater vapor is evolved at the top of the column, typically made up of about 92% water and 8% ammonia at a temperature of about 98 C. The vapor then passes into rectifier 76 for concentration, and emerges from the rectifier with an ammonia concentration of about 10 to and a water vapor concentration of from about 85 to 90%, the temperature being about 95 C.

It is important that when this ammonia-water vapor is admixed with the (uncleansed) second stream S of coke oven gas, no vapor condensation, e.g., of ammonia, water vapor, or the like, occur. Accordingly, heater 92 is disposed so as to preheat stream S prior to the addition thereto of ammonia-water vapor from conduit 84. Steam for heater 92 is provided via conduit 94 from steam boiler 56. Thus, stream S is typically at a temperature of 90 C. (dew point 78 C.) prior to entering heater 92 and exits from the heater at a temperature of from about 110 to 120 C. This effectively prevents vapor condensation when ammonia-water vapor from conduit 84 is admixed with preheated stream S Referring to water cooler 102, it is desirable that the cool water therefrom entering conduit 106 be at a temperature of below 30 C. Thus, water entering liquor cooler 110 via conduit 112 is at about 30 C., the warmer exit water leaving via conduit 114 typically being about 34 C. Similarly, the water entering cooler 61 via conduit 106 is at about 30 C., the exit Water leaving via conduit 108 being at about 45 C. In like manner, water entering rectifier 76 via conduit 78 is at 30 C., the exit water being a few degrees higher. The warmer water returning to cooler 102 via conduit 108 is generally of a temperature of from about 40 to 45 C.

Stream S now passes via conduit to steam boiler 56, typically at a temperature of about to C. (dew point 80 C.). The steam boiler is desirably at about 1400 C. with a pressure of about 100 atmospheres. Accordingly, at these relatively drastic conditions ammonia is readily cracked to nitrogen and water. Other contaminants that would tend to pollute the atmosphere are similarly cracked or converted to substantially non-pollutant materials. The resulting waste gases are then vented to the atmosphere through stack 100. The exit gases are generally at a temperature of about 200 C. (dew point of about 70 C.).

It will be apparent that the foregoing method and apparatus provides means for utilizing a portion of coke oven gas evolved in the coking of coal to satisfy the heat requirements of the coke oven heating filues. The remaining portion of coke oven gas may readily be passed to a steam boiler for conversion of atmospheric contaminants to nonpollutants, e.g., cracking of ammonia to nitrogen and water, followed by venting to the atmosphere, whereby little or no atmospheric pollutants are introduced. My process provides for merely cleaning approximately that portion of the coke oven gas that is needed to satisfy the fuel requirements of the coke oven. The remaining portion need not be subjected to cleaning. Additionally, the objectionable contaminants initially present in that portion of the coke oven gas that is to be cleansed are separated, passed into that portion that has not been cleansed, and then converted to substantially non-pollutant byproducts.

The commercial operation of my method is advantageous. Thus, considering a typical coke oven, approximately 10,000 tons per day of coking coal are utilized along with approximately 6,500 tons per day of fresh water, the electric requirements being approximately 100 mw.h. per day. The resulting products are coke in the amount of about 7500 tons per day, steam (for power generation) in the amount of about 12,000 tons per day, and dephenolized waste water in the amount of about 2,000 tons per day. All waste gases are passed to the stacks and vented directly to the atmosphere.

Variations can, of course, be made without departing from the spirit and scope of my invention.

Having thus described my invention, what I desire to secure and hereby claim by Letters Patent is:

1. In a method of processing a stream of coke oven gas containing vaporous tars, ammonia, and water therein, said gas having been obtained from a coke oven battery comprising a plurality of spaced apart: coking chambers with a plurality of heating walls disposed therebetween, said heating walls each having therein a plurality of heating flues, comprising:

( 1) dividing the stream of coke oven gas into a first stream for subsequent combustion in the coke oven heating lines and a second stream for subsequent conversion to waste gases,

(2) cooling the said first stream to condense water vapor and tar vapor therein and thereby form aqueous ammonia liquor and tar,

(3) scrubbing said cooled stream with aqueous media to cleanse the gas and remove the ammonia therefrom, thereby forming aqueous ammonia liquor, and

(4) distilling the aqueous ammonia liquors, formed by cooling the gas in step (2) and scrubbing the gas in step (3), to form ammonia vapor the improvement comprising (a) admixing said ammonia vapor with the second stream of coke oven gas and passing the ammonia rich second stream to a conversion zone and converting the stream to waste gas which may be vented to the atmosphere and (b) passing the cleansed first stream to the heating flues and burning the stream therein to provide heat for destructive distillation of coal in the coking chambers.

2. The method of claim 1 wherein the amount of coke oven gas employed in the first stream i slightly in excess of the heating requirements for the heating flues of the coke oven battery.

3. The method of claim 2 wherein prior to passing the cleansed first stream to the heating flues, that amount of gas in excess of the heating requirements for the heating flues is bled off and admixed with the second stream prior to its conversion to waste gases.

4. The method of claim 1 wherein at least a portion of the aqueous ammonia liquor formed from the spray cooling step (2) is employed in the scrubbing step (3).

5. The method of claim 1 wherein distilling step (4) is carried out with steam to form said ammonia-water vapor, said vapor then being cooled to increase the ammonia concentration therein, said cooling being effected prior to the admixing of the ammonia vapor with the second stream of gas.

6. The method of claim 5 wherein said second stream of gas is heated prior to the admixing of ammonia vapor therewith, said heating being to such temperature that upon said admixing, water or tar that may be present in said vapor does not condense.

7- The method of claim 1 wherein the scrubbing step (3) is performed in a plurality of stages and wherein there is employed in the scrubbing (a) fresh water, (b) recycled ammonia liquor from the scrubbing, and (c) ammonia liquor obtained from cooling step (2), the amount of recycled ammonia liquor (b) and ammonia liquor (c) being greater than the amount of fresh water (a) employed.

8. Apparatus for cleaning and combusting coke oven gas comprising:

(a) means for dividing coke oven gas containing ammonia therein into a first stream for subsequent combustion in coke oven heating flues and a second stream for subsequent conversion to waste gases,

(b) means for scrubbing said first stream with aqueous media to cleanse the gas and for recovering ammonia therefrom as aqueous ammonia liquor,

(c) conduit means for passing the first stream to said scrubbing means, and

(d) conduit means for passing the cleansed first stream to coke oven heating flues for combustion therein.

9. The apparatus of claim 8 additionally comprising:

(e) conduit means for passing aqueous ammonia liquor formed in element (b) to a distilling means,

(f) means for distilling the aqueous ammonia liquor and for recovering ammonia vapor,

(g) means for converting the second stream to waste gases and for venting such gases to the atmosphere,

(h) conduit means for passing the second stream to said converting means, and

(i) conduit means for passing the ammonia vapor formed in element (f) to said conduit means defined in element (b) so that such ammonia vapor is admixed with the second stream prior to its combustion.

10. The apparatus of claim 9 additionally comprising:

(i) conduit mean communicating with said conduit means defined in element (d) and communicating with said conduit means defined in element (h), and

(k) means for proportioning the flow of cleansed gas (1) to the coke oven heating flues and (2) through said conduit means defined in element (j) such that that portion of cleansed gas in excess of the heating requirements of the heating flues is passed through said conduit means defined in element (j).

References Cited UNITED STATES PATENTS NORMAN YUDKOFF, Primary Examiner.

D. EDWARDS, Assistant Examiner.

US. Cl. X.R.