US2203645A - Process for the distillation of tar or pitch - Google Patents

Description

June 4, 1940.

o.' REYJNARD PROCESS FOR THE DISTILLATION 0F TAR 0R PITCH Filed Jan. 27, 19 38 2 Sheets-Sheet l FiGJQ BLOW/19 Col/015N658 FiGZ.

June 4, 1940. Q, nE 2,203,645

PliOCESS FOR THE DISTILLATION 0F TAR 0R PITCH Filed Jan. 27, 1938 2 Sheets-Sheet 2 FIG. 3.

Patented June 1940 t i, i

UNITED STATES PATENT OFFICE PROCESS FOR THE DISTILLATION F TAR i on PITCH,

Otto Reynard, Darlington; England Application January 27, 1938, Serial No. 187,251 In France and Germany July 13, 1937 i Claims. (Cl. 196-76) It is known that if tar, derived from the carcharged, or supersaturated, with distillates in the bonisation of coal, lignite, or other naturally form of vapour and drops in suspension, which occurring fuels, be distilled in a current of air, may be, conveniently alluded to as fog. This its separation into, liquid distillates and residual feature distinguishes the invention from all pro- 5 pitch takes place more rapidly than by ordinary casses in which eificient fractionation and/or 5, distillation. It is also known that such air blow- C de sa n of t e distillates take pl before ing results in an increased yield of pitch with the prope n medium of a Ire-enters the t consequent decreased yield of distillates and still. that the residual pitch has a higher content of There are two natural consequences of the free carbon than ordinary pitch. It is known method of proce of the present inVehtiOn- 10 further that if a gas devoid bi oxygen be used Firs in e here i no co ling of the inert gas for blowing instead of air the distillation is accel: harged Wi h vapours and fog) other than the erated in the same way, withoutincreasing either cooling by radiation of the air condenser or septhe yield of pitch or its free carbon content, o t the p ture of the gas and v p I The object of the present invention is to com Which return, t the still rises p y With the 15 blue the acceleration of tar distillation with a D iVe firihg the still- Secondly, Since considerably increased production of liquid disthe whole syste is enclosed and Provision is til lates, v 1 made that the'system be rigidly gastight and According to this invention, an oxygen-free gas, i h an ap ciable pr sur d p go (which for the sake of brevity will be termed an side the circuit. For instance, if coke-oven tar (inert gas in the following description), is cir or gas tar be the raw material subjec ed to diseulated t a, high Velocity through an ordinary tillation, the maximum temperature to which the pot still in which tar is being distilled, into a tar is e s m y e in h n i hbourhood of 300 relatively large air condenser or separator and 0 330 C-, When it Will be found. that the'tem:

g thence back to the inlet of the totally enclosed perature of the returning gas, V pou and e fan, blower or compressor, which ,may be used is 0V6]? 100 C. and the pressure inside the System to provide the circulation. A suitable inert gas h ri en o apre ure equivalent to from 6 to 14 may be nitrogen, carbon dioxide, coke-oven gas, inches of a mercury e e coal gas, or the like, buttit may be foundcon- Although the treatment of tar by the above 80 venient to use atmospheric air for one prelimidescribedprocess results in the production of an nary charge of tar, since the oxygen which it eonincreased amount of liquid distillates for a resitains israpidly absorbed by the heated;tar,1eavdue of a desired consistency, as compared with ing at the end of a certain period of time nitrogen o i y d stillation to a residue of the same as the only gaseous constituent of the circulating consistency, appreciably greater increases are ob:

medium, tained as followsp After all the oxygen has been removed out of As soon asthe material in the still has assumed the circuit, the oxidised pitch present in thestill the desired consistency, fresh tar is continuously is discharged and a fresh charge of tar isadpumped into the still, while the corresponding ,m into the still, for, t Pu pos Of the presamount offpitch is Withdrawn from it. In such 0 eh invention P p M a continuous modeoi operation, the temperature The Inert gas, In the course of 1 clrculatlon: of the still must be maintained constant at a carries with it in the form of vapoursand minute figure which will generally be from to drops in suspension a relatively large amount of degrees entigrade below the boiling point of the hydrocarbons and other volatile constituents of i i i 5 the tar which is being distilled. Owing to the g$nf Z$ f Whmh desired sudden decrease in velocity of the gas, when it i i issues from the conduit which leads from the still f im actmn i fl Inert charged to the separator, sedimentation as Well as conmp r-H e s d tar mdensation of the distillates which accompanythe i f o t temperature {ndma'ted m 50 gas, partially occur in the separator, .at thebote io ipo h results 111 h production of 50 tom of which the distillates accumulate. It is, from 0 P C more ddistillates than however, an all-essential feature of the present are produced y r y at o to a residue invention that such separation and/or condeneithesame consistency, provided that the vesation are only partial and that the inert gas locitypf the gas and the temperature and inp5 returns to the circulating appliance heavily ,ternal pressure of the system are also main- 5 An important feature of the invention relates .to its application to tars containing water.

Whereas it is found in all cases that the sum of the weights of residue and distillates produced by the invention exactly equals the weight of raw material treated, the weight of water associated with thedistillates produced is less than the Weight of the water present in the raw material.

By the method of the invention, therefore, a certain proportion of the water in the raw material combines chemically with one or more of the constituents of the raw material and, as

a consequence of this chemical combination, the use ,of crude tars will in most cases be preferred to'the use ,of dehydrated tars for the purpose of the present invention.

The most advantageous content of water in tar to be treated according to the present invention is from l'toii per cent. Consequently when a tar is to be distilled which contains less than this amount of water, it is desirable to add sufiicient water to the tarbefore treatment to bring the water content thereof up to from 4 to per cent.

On the large scale a multi-stage fan, capable of circulating from 1000 to 2000 cubic feet of air per minute, may be conveniently used to distil cokeoven tar or gasworks tar in 'a pot still of 3000 to 4000 gallons capacity at a rate of between 1 /2 to 3 tons of tar per hour. Owing to the high temperature 'of the circulating medium and to its content of hydrocarbon and phenolic constituents, both in the form of vapour and of fog, it is advisable to fitsuch a fan withgas and liquid-tight glands, thereby separating the inte'ri'or of the fan from external, artificially cooled bearings.

The temperature'and pressure of the circulating medium depend upon: v (1) The temperature of distillation.

' (2)' The rate'of circulation.

(3) The condensation and cooling effected by the air condenser.

:1 Items (1) and (2) are fixed by the consistency of "the pitch which is being manufactured and the rate at which it is desired to manufacture it. Item (3) depends on the capacity and exposed surface of theair condenser and the conduits leading from the outlet of the still back to the inlet of the fan, and is not greatly afiected by atmospheric conditions in temperate climates, provided that the condensing system be protected from direct sunshine and rain. It is, however, best controlled by using a number of smaller vesselsfin series, instead of only one large vessel for the separation of the distillates.

The-degree of supersaturation of the inert gas with tar-oil vapours and tar-oil fog, so far as hitherto described, is fortuitous depending on the rate of circulation of the gas and the temperature drop of the gas between the point where it leaves the heated tar and the point where it re-enters it.

An important feature of this invention is the means whereby the amount of supersaturation .of the inert gas can be controlled and increased to any extent desired, so that a further increase in yield of liquid distillates can be obtained.

In order to increase the supersaturation of the inert gas, the inert gas is passed from the still through a plurality of small condensers and/or fractionators in series and a desired quantity of condensate, consisting of the lighter constituents of the tar under treatment, or a mixture thereof with heavier distillates, is atomised and injected into the inert gas between the circulating device and the tar still, thereby increasing the supersaturation of the inert gas to any extent required, or is introduced directly into the liquid contents of the still at the discharge openings of the distributor for the inert gas in such a way that the spontaneous formation of a supersaturated mixture of the inert gas with atomised oil takes place inside the liquid contents of the still. The inert gas, charged in this way with a much greater proportion of accompanying taroil fog, sweeps out of the heated tar a correspondingly greater amount of liquid distillates.

It has been found that the lower boilingconstituents of tar are most effective for this purpose and it is therefore advantageous to fractionate' the distillates produced by the process as efficiently as possible. It has been found that very sharp fractionation results from the use of a large number'of small condensing vessels in series, say six or more, of which one or more may contain columns of contact material of the desired form and height, or one or more'may be in the form of 'bubblers. The object of the contact mass being to provide thorough contact between liquids and gases with the minimum resistance to the circulating flow, any' of the ing device, itwill be found that, when coke oven tar is being distilled, vessels l, 2 and 3 contain higher boiling fractions and vessels 4, 5 and 6 contain lower boiling constituents. The distillates containing light oils and/or light creosotes are most suitable for this purpose. In'order to prevent excess of vapoursand fog going to the circulating device, or excess of internal pressure in the system, either or both of the last two condensers and/or fractionators may be artificially cooled, for example by' cold water or cold air.

According to the nature of the tar being treated, light oils from the requisite condensing vessels are run into a small container which may conveniently have a capacity of from 50 to 100 gallons. A suitable small pump of positive action and capable of exercising the necessary pressure, draws oil from this container and forces it through an atomising nozzle into the circulating stream at a suitable point in the conduit leading from the circlulating device to the tar still, or the oil maybe introduced directly into the liquid contents of the still. It may be found desirable to inject or introduce from 10 to 50 gallons or more of the specified light oil and/or creosotes into the circulating stream per hour.

Apparatus suitable for carrying out this invention is shown in the accompanying drawings, in which:

Fig. 1 shows an elevation, in diagrammatic form of a plant using'onlyon'e large condenser andonestill; 1

Fig. 2 is a plan of a system comprising a-pair of stills and six small condensers and/orfractionators in series; x

Fig. 3 shows a sectional elevation of one still and blower and the appliance used for injecting atomised oil into the circulating system; and i Fig. 4 is an elevation on alarger scale of one fractionator.

.As illustrated in Fig. 1, the inert gas passes from the still S into a large condenser C and back to the fan ;F. A vertical partition P may conveniently be fitted inside the condenser to prevent short-circuiting of the stream of gas and vapours in their passage back to the fan inlet.

As shown in Fig. 2, the two stills S1 and S2 are intended for use one at a time, so that each in turn can be cleaned out and prepared for charging, while the other is functioning for a desired period. .A single conduit A connects either still with the fractionating plant, suitable valves VI and V2 being provided to shut off one still while communication is made between the work ing still and the fractionators. In the same way, the return flow of the circulating medium from the blower B is directed by means of valves WI and W2 into whichever still is workingand is shut off from the still which is being rested.

In Fig. 3, S is the still through which the inert gas is directed by the blower B. A pump P draws light oil, or a suitable mixture of light and heavier oils, derived from the condensing system or fractionators I to B, from a reservoir or container R and injects it through an atomising nozzle N into the pipe X leading from the blower B to the still S.

In Fig. 4, C is the contact mass supported on a grid G, D is the perforated pipe or other distributing appliance, OI and 02 are overflow pipes fitted with cocks; the cock serving 02 is closed and the cock serving OI is open for bubbling; the former is open and the latter is closed when bubbling is dispensed with. i

It will be apparent that by suitably regulating the amount of light oil, or light oil and heavier distillates, injected into the stream of the inert gas, it is possible to regulate the amount of supersaturation of the inert gas to the desired extent and that therefore the supersaturation of the inert gas is under complete control, and can be varied at will. i

Whereas it has been found that an inert gas, such as nitrogen constitutes the best vehicle for carrying the tar-oil vapours and tar-oil fog for the purpose of the invention,the process is not materially affected should the gas be wholly or partially replaced by steam and/or tar-oil vapours, so long as these become and remain supersaturated in the same way as is specified for the inert gas.

For instance, the plant may be purged with steam for the removal of air, and distillation which is required but will generally supply more The water naturally present in, or purposely added to, crude tar will not only maintain all the steam than is required, so that it may become necessary to condensethe excess, together with some of the other vapours, before passing the circulating stream back to the circulating device. This condensation is easily effected, for instance as already described, by showering either" or both of the last two vessels, 5 and 6, with jets of cold water and regulating the amountof cooling water so used to maintain the relative amounts of water vapour, tar-oil vapours and tar-oil fog so as to yield optimum conditions for the purpose of the invention. i

A small flow of water sufiices to give. the necessary condensation and it has been found that from 100 to 300 gallons per hour of water at atmospheric temperature will maintain the desired composition of the circulating medium when 2 tons of crude coke oven tar are treated hourly.

It should be noted that this method of cooling the circulating medium for regulating its composition before its return to the circulating device is highly sensitive and capable of exact adjustment.

By this means, not only the desired proportions of vapours and fog are regulated, but also the internal pressure of the system. is controlled, which might otherwise become excessive.

The present invention is furthermore applicable to any other system of tar distillation in the form of an additional unit. All that is necessary in such cases is to work the, tar in. the first system to an intermediate stage, such as refined tar or soft pitch, and to allow the residue of this first system to overflow continuously or periodically, by pumping or otherwise, into the additional unit which is in all respects similar to the plant hereinbefore described. This process can also be used if the still is charged with pitch, which has been treated by means of other processes, and a furtherquantity of liquid distillates can be obtained therefrom without altering the physical properties of the pitch as regards consistency and melting point.

I claim:

1. Process of distilling tar or pitch, which consists in circulating at a high velocity an inert gas,

supersaturated with tar vapours, through the material being treated, said material being contained in a still, and through a plurality of condensers in series, atomising a desired quantity of condensate from the condensers and injecting it into the circulating medium at a point between the circulating device and the still, the condensers being maintained at such temperature that the amount of vapours condensed therein does not relieve the supersaturation of the circulating medium.

2. Process of distilling tar or pitch, which consists in circulating at a high velocity an inert gas,

supersaturated with tar vapours, through the material being treated, said material being contained in a still, and through a plurality of condensers in series, and introducing a desired quantity of the condensate from the condensers directly into the liquid contents of the still at points suitable for effecting the spontaneous formation of a supersaturated mixture of gases, vapours and fog.

3. Process of distilling tar or pitch, which con-.

sists in circulating at a high velocity an inert gas, supersaturated with tar vapours, through a still containing the material being treated and a pluof which contains a column of contact material of the desired form and height, atomising a desired quantity of the condensate from the conrality of small condensers in series, at least one densers and injecting it into the circulating medium at a point between the circulating device and the still.

4. Process of distilling tar or pitch, which consists in circulating at a high velocity an inert gas, supersaturated with tar vapours, througha still containing the material being treated and a plurality of small condensers in series, at least one of which is in the form of a bubbler, and introducing a desired quantity of the condensate from the condensers directly into the liquid contents of the still at points suitable for the efiecting the spontaneous formation for a supersaturated mixture of gases, vapours and fog.

fog.

5. Process of distilling tar or pitch, which consists in circulating at a high velocity an inert gas, supersaturated with tar. vapours, through a still containing the material being treated and a plurality of small condensers in series, at least one of which is in the form of a bubbler and contains a column of contact material of the desired form and height, and introducing a desired quantity of condensate from thecondensers into the circulating stream, at a point suitable'for the formation of a supersaturated mixture of gases, vapours and O'I'I'O REYNARD.

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