US1921300A - Distillation of tar - Google Patents

Description

Aug. 8, 1933. s. P. MILLER DISTILLATION oF TAR 2 sheets-sheet 1 Filed Nov'. 3, 1928 Aug. 8,1933. s. P'. MILLER 1,921,300

DISTILLATION oF TAR Filed Nov. 3, 1928 2 Sheets-Sheet 2 f, INVENTOR v AoRNx-:Yg

UNITEDy iSTATI-:s

oFFlcE- DrsmLA'rxoN or TAR Stuart Parmclee Miller, Englewood, N. J., assignor to The Barrett Company, New York, N. Y., a Corporation of New Jersey Application November V3, 1928. .Serial No. 316,894

1 Claim. (Cl. 202-30) -This invention relates to improvements inthe production and distillation of tar and in the operation of Icy-product. recovery systems of coal distillation plants, particularly coke oven plants. According to the present invention, marketable distillate oils and pitches are directlyproduced in a simple and advantageous manner at coal distillation plants. In the operation of coal distillation plants, such as coke ovens, the production of 'coke is in many cases the primary operation, while in gas plants the production of gas is the primary operation. In both cases, coke and gas are produced, and taris recovered as a by-product. Thetar is recovered by cooling the gasses to con-4 dense and separate the tar therefrom. -f-

l The tar produced at coal distillation plants is to some extent employed as a fuel, particularly where coke oven plants are located adjacent to steel mills, in wh'ch case the tar is extensively employed as a fuel in open hearth and other furnaces. For the most part, however, the tar recovered as a by-product at coke oven and gas plants is shipped to tar distillation plants and there subjected to distillation for the production of distillate oils and pitch residues therefrom.

According to the present invention the tar is not collected as a total tar productat the coal distillation plant, but the tar is collected in separate fractions, one of which is a heavy tar, and another of `which is a light tar or tarryr oil; and these respective heavy and light tars are separately subjected to distillation for the production of distillate oils and pitch residues therefrom.

This distillation of the separate tar fractions is moreover carried out directly at the coal distillation plant; and is advantageously carried out by subjecting the separate tar fractions in direct contact with the hot coal distillationgases, thereby utilizing the heat of the gases` for distilling the tar fractions. A

I In the ordinary by-product coke oven plant, the gases are collected from a number of coke ovens in a collector main and are there cooled by tar, or by ammonia liquor and tar, and a considerable part ofthe tar constituents separated from the gases in the form of a heavy tar.

` etc. canbe more readily Instead of combining the heavy tar and the light tar, I keep these tar fractions separate, and I take advantage of their difference in character by subjecting them separately to distillation, thereby recovering distillate oils and pitches Which differ from each other. 'v

The heavy tar separated. from the gases in the collector main, and which, in coke oven operations, may amount to around or 60% or more of the total tar, is relatively low in oil content, and relatively high in pitch constituents; while the light tar or tarry oils yseparated in the condensers of a by-product coke oven contains a large proportion of oils, and particularly of lighter oils, and a relatively low percentage of pitch constituents.

By separately collecting these heavy lighttar fractions and separately distilling them, there can be directly obtained from the heavy tar fractions a relatively heavy distillate oil, and a large yield of pitch residue with a minimum of distillation; while by separately distilling the light tar or tarry oils, there can be directly obtained a large amount of relatively light oils, with arelativelysmall pitch residue remaining after the distillation.

It is Well known that the distillation of.tar in ordinary externally heated tar stills brings about a considerable decomposition of oil constituents, with resulting decrease in yield of y distillate oils and increase in amount of pitch residue produced, .The amount of distillation required, and particularly the amount of der. composition, can be materially reduced by the process of the present' invention. Oils ofdifferent properties can also be more rea'dily obtained, for example, creosote oils which are relatively high in heavy oils or high boiling oil constituents-can be readily obtained from the heavy tar fractions and lighter carbolic oils, obtainedfrom the light tar fractions.

While Ythe separate distillation of the heavy spraying the tar into the gases, while they are J at a high temperature, approximating that atfwhich they come from the ovens or-retorts,

the gases themselves will be scrubbed and freed to a greater or less extent from their heavy suspended carbon and pitch particles, while the tar fractions themselves will be rapidly distilled with resulting enrichment of the gases in oil vapors. As a result, there will be obtained a pitch residue resulting from distillation of the tar fractions and from such additional pitch constituents as are scrubbed from the gases, and there will also be obtained from the gases by subsequent cooling and condensation clistillate oils which are low in tar content and which may bc substantially free from tar contaminations, that is, the oils may be clean oils and directly merchantable as creosote oils or for other purposes.

In the operation of a coal distillation plan such as a coke oven plant, the present invention does` not require any substantial change or modification in the by-product recovery system or in the operation of such system, so far as the handling of the gases is concerned, except for the provision of separate collecting means for collectingr and keeping separate the heavy and light tar fractions. Separate storage tanks or collecting tanks may be provided for the heavy tar from the collector main and the-light tar from the condensers, and, where` two or more fractions are obtained in the condensers, separate storage tanks may be provided for the different fractions.

Where the gases from the coal distillation plant are employed for distilling the separate tar fractions, provision must be made for collecting the gases while at a sufficiently high temperature and for bringing the tar into intimate contact therewith to effect distillation of the tar together with scrubbing of the gases.

In coke oven plants, the gases leave the coke oven at a high temperature, around 600 to 700 C. or higher. By drawing off these gases from the ovens into a still without permitting any considerable cooling of the gases, and by bringing the tar into intimate contact with the gases while they are still at a high temperature, the tar can be rapidly distilled and a pitch residue produced therefrom at the same time that the gases are themselves scrubbed and freed more or less completely from suspended pitch particles and at the same time that the gases are greatly enriched in oil vapors by the distillation. Separate stills are provided for the separate tar fractions, and, in connection with these stills, separate condensing systems are provided for the distillate oils resulting from the distillation. In this way, the heavy tar can be distilled to produce relatively heavy oils or oil fractions, which are made up for the most part o f heavy oil constituents, and a large amount of pitch residue. On the other hand, the light tar or tarry oils, or the various fractions of such light tars, will be separately distilled and' the distillate oils separately condensed and will give a large amount of light oil, such as carbolic oils, tar acid oils, or oils rich in naphthalene, etc.

The improved process of the present invention enables an unusually high yield of distillate oils to be obtained from 'the tar, and, moreover, obtained in the form of distillate oil fractions which differ from each other. The conditions which are more favorable for the distillation of the lighter oil constituents of the light tars enable these light oils to be obtained with a minimum of decomposition; whileV the conditions which are required for the distillation of the heavier oils from the heavy tar will enable such oils to be distilled without interference by a large amount of lighter oils such as would be present in a total tar produced by admixing the light and heavy tar fractions before distillation.

The extent to which the distillation of the respective tar fractions is carried can be regulated and controlled, depending upon the character of distillate oils desired, and the pitch residues to be produced. Where the maximum oil yield is desired, the distillation can be carried to the point of obtaining pitch of high melting point, e. g,. around 400 F. or higher. Where pitches of lower melting point are desired, or where the yield of oils is not to be the maximum, the distillation can be regulatedr so that less oil will be distilled and a softer pitch produced. Where, for example, naphthalen and carbolic oils are desired, these can readily be obtained from the light tar by subjecting it to distillation, Without the necessity of heating the entire tar body to effect such distillation. Similarly, where a low melting point pitch is desired, this can readily be produced from the heavy tar, with a minimum of distillation, and without the necessity of heating and distilling a large amount of light oils such as wouldbe necessary in the case of a total tar containing both the heavy and light tar fractions.

The invention will be further described in connection with a by-product coke oven plant of 'the Semet Solvay type but it will be understood by those skilled in the art that the invention is applicable to other types of coke ovens and other coal carbonizaton plants in which various grades of tar are fractionally separated from the gases in the collector main and condensing system of the by-product plant.

In the accompanying drawings,

Fig. 1 is a general plan View, of a somewhat conventional character, showing a by-product coke oven plant provided with separate collecting and handling equipment for collecting and keeping separate the heavy and light tars, and for separately subjecting these to distillation, and

Fig. 2 is an enlarged sectional View through one of the separate short collector mains employed as a still.

Referring to the drawings, 5 indicates a coke oven battery equipped with the usual uptake pipes 6 and collector main 7 provided with center-box 8, from which a cross-over main 9 connects in the usual way with condensers 10. The goose-necks of the uptake pipes and the collector main rI may be sprayed with ammonia liquor, or tar and ammonia liquor, through sprays 11 and 12. The heavy tar and ammonia liquor, which drain from the collector main into the center-box 8 are drawn off through pipe 14 to the decanter 15. Tar and ammonia liquor from the cross-over main may also be drawn off into this same decanter through pipe 16, or may be separately collected, or allowed to run into the condensers 10. The ammonia liquor and tar will be drawn off from the decanter 15 to separate storage tanks 17 and 18.

Light tar and tarry oil and ammonia liquor are drawn oi from the condensers 10 to the decanter 20 from which the ammonia liquor and light tar are separately collected in the storage tanks 21 and 22. An exhauster 23 is provided for drawing the gases through the system. Means for recovering ammonia and light oils (not shown)` will be provided beyond the exhauster.. l

In addition to this usual equipment, stills 24 and 25 are provided at the rear of the ovens. Each of these stillsv is adapted to receive hot gases from several of the ovens of the battery 5. By properly manipulating the valv 26 in the goose-necks of the uptake pipes 6, connected with the usual collector main, and in the gooseneclrs 27 of the uptakes 28, which connect selected ovens with the stills at the rear of the ovens,

the gases from those ovens which are connected I with both the usual collector main and one of the stills may be directed to either the usual collector main 7 or one of the stills 24 and 25: By means of these valves the amount of hot gases passing through the stills may be regulated to elfect the desired distillation.

The agitating means shown for bringing the tar into intimate contact with the hot gases in each of the stills comprises a smooth cylinder 29 which dips into the tar in the still to only a slight extent. By regulating the depth of immersion of the roll, the degree and intensity vof spray can be regulated. The motor 30 is provided to cause rapid rotation of the cylinder. Instead of a smooth cylinder, a)corrugated or other cylinder, or sprays, or other means, may be employed for bringing'the tar into intimate contact with the hot gases. Both stills 24 and 25 will be required providing it is desired to distill both light and heavy tars simultaneously.

If simultaneous treatment is not required, one still only need to be installed. l

In operating the apparatus, tarry oil or light tar from the tank 2 is pumped by pump 31 into thev still 25, the a ount being regulated by the valve 32 and bythe pump. By proper regulation of the valves 26 in those uptakes connected to the still, and the corresponding uptakes connected with the usual collector main 7, the amount of gases passing through the still can Abe adjusted. By controlling both the supply the main 36 to cooling means 37. 'I'his cooling means may comprise fractional condensers, or

one total fraction may bel obtained. An ex-A hauster 38` is provided and means for recovering ammonia and light oils may be located beyond this e'Xhauster, and the other exhausters shown, or the gases can be passed to the gas line leading from the exhauster23 and the combined gases then passed through the ammonia absorber, etc.

' Heavy tar from the receiver 18 is supplied through the line 39 to the still 24, Where 'it is distilled to' produce pitch, and one heavy oil or several heavy oil fractions will be recovered in the condensers 40.' The non-volatilized residue` from the distillation, collected in the tank 4l, may be recirculated, at least in part, through `a light tar fraction, subjecting the light tar to dis- .will be distilled in the still 25, and the respective pitches produced as residuespf the distillation will be separately drawn off, while the distillate oills produced will be separately condensed. In this way, a large yield of light oils can be readily obtained from the light tars with a minimum of distillation, While the heavy tars can be separately distilled to give products most readily recovered therefrom.

An alternative operation, Which can advantageously be .carried out, is to subject the light tars to a partial distillation in the still 25, to remove only the lighter oils therefrom, and to produce a heavy tar residue, and then to pass this residue through the line 43 to the still 24 and combine it with the heavy tar from the collector main and subject the combined heavy tars to distillation.A In this method of operation, a separate light oil fraction, ora plurali/ty of light oil fractions, will be obtained from the distillation of the light tar, and heavier oils will be obtained from the distillation of the heavy tar, while the total pitch residue from the distillation of both tars will be produced in the still 24 and will be drawn olf as a total pitch product.

It will thus be seen that the present invention takes advantage of the fractional sepration of the tar in the condensing system of the by-product coal distillation plant by keeping these fractions separate and subjecting `them separately to distillation for the production therefrom of the distillate oils and pitches for which the separate' fractions are particularly adapted. It will further be seen that these operations can readily be carried out at the coal distillationplant so that, instead of producing and shipping tar to be subsequent- 1y aistiued at tar distillation plants, there win 120 be produced only distillate oils of a merchantable character and pitch residues which can be employed as fuel or for other purposes.

While I have described the invention more v particularly in connection with a coke oven 125 plant, it will be understood that it is applicable to coke oven plants of different types, as well as to other coal distillation plants such as retort gas plants, etc. It will also beunderstood that thev fractional separation and condensation of the tar can be carried to such an extent that more than two tar fractions are separately collected and separately distilled.

The improved method of producing distillate 135 oils and pitches from coal tar which comprises fractionally condensing the tar from hot coal distillation gases and thereby producing a ,plu- I rality of tar fractions, including a heavy tar and tillation to separate lightoils therefrom and vto produce a heavy tar or pitch, and combining such heavy tar or pitch Withthe heavy tar fraction and-subjecting the same to distillation for the productionof heavy distillate oils and pitch residues.

S 'IUAR.Tv PARMELEE MILLER. y

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