CA1153972A - Method for hydrogenating coal liquefaction - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In a method for hydrogenated coal liquefaction, using rubbing oils and hydrogen-containing circulation gas, the non-liquefied solid components are concentrated in a hot separator subsequent to the liquefaction reactor, under similar tempera-ture and pressure conditions as in the reactor. Gaseous and vaporous discharge products from the reactor are condensed in subsequent stages. Non-gaseous and non-vaporous separation products, extensively freed of distillable oils, are removed from the hot separator in still pumpable condition, and relaxed in a subsequent fume extractor. The hydrogen-containing cir-culation gas is conducted through the hot separator in contact with the discharge products from the liquefaction reactor, in an amount greater than 5,000m3, given at standard temperature and pressure per ton of water- and ash-free charge of coal.
Variations include branching off part of the circulation gas before the liquefaction reactor and conducting it directly into the hot separator, preheating this branched-off part of the circulation gas before introduction into the hot separa-tor to temperatures between 300° and 550°C, and recovering rubbing oil in an intermediate separation stage directly following the hot separator.

Description

ilS39~Z

1 The liquefaction of coal is, according to known manners of operation, accomplished in pressure vessels, in which the coal together with an oil usually designated as rubbing oil and together with hydrogen-containing gas, is introduced, and in which at tem-peratures between 300 and 550C and at pressures greater than 100 bar, the decomposition of organic coal substances into mainly liquid products ensues.
In the reaction area, one or more catalytically effective chemical compounds can be present. With the manner of operation known as "sump phase" a catalyst in suspended form together with the coal is led continuously into the reaction chamber, and de-livered together with the reaction products from the chamber. With other manners of operation the catalyst, in the form of pieces, is kept in agitation in the reaction chamber, perhaps by obtaining a "simmering" catalyst layer, or through the use of rotating mechan-isms in the reaction chamber, upon which the catalyst is constantly placed.
The liquid products are composed, as a rule, of light, medium or heavy oils, up to a non-distillable, only in molten con-2Q dition, liquid mass. These components are obtained in different ratio amounts, depending upon the liquefacti~n,l~ conditions.
The discharge product from the liquefactio~,l reactor contains besides products that are essentiallylliquid under normal conditions, formed through the chemical decomposition of the organic coal substances, and for the realization of which from coal, rubbing oil is necessary, also solid substances, insoluble under the reac-tion conditions. These are composed not only of coal substances, that do not become liquefied, but also of components of the coal that are not liquefiable under the conditions of the hydrogenating coal liquefactio~ ("ash"), as well as the non-liquefiable catalysts ~lS3~

1 or catalytically effective additive substances, insofar as these are continuously supplied with the entry material.
Finally, the mentioned dicharge products contain also substances that are gaseous under normal conditions i.e., at standard temperature and pressure. These are on the one hand, essentially inert -- in the sense of hydrogenation -- gases, such as methane, ethane and other hydrocarbons as well as carbon oxides, hydrogen sulfide and ammonia, all of which are formed as byproducts of the liquefaction, and, on the other hand, the hydrogen not consumed by the coal liquefaction. The latter will usually be present in a relatively large excess in the coal liquefaction apparatus for different reasons. The hydrogen is therefore as a rule led in circulation. If necessary, the men-tioned, essentially inert gases, will be removed through ap-propriate measures in a particular treatment stage, i.e., "cir-culation gas cleaning," to such an extent that a sufficiently concentrated hydrogen can be led anew as circulation gas into the reaction chamber.
The separation of very fine, up to colloidally divided solids from the viscous product oil is a problem, possessing critical significance to the economical practicability of the coal liquefaction.
A concentration of solids occurs as a rule in the so-called "hot separator". From there, at temperatures reduced only slightly in comparison to the reaction temperatures, and practical-ly at the operational pressure of the liquefaction reactors, pro-ducts are thrown off at the top which are gaseous and vaporous under these conditions. At the bottom of the vessel, a tarry ap-pearing liquid, the so-called "residue," is withdrawn. This con-tains the total solids and the much greater portion of asphaltsubstance, whereas the liquid recovered from the vapors through 11539~2 l subsequent cooling down, the so-called "stripper oil," a distil-late-like product, is as a rule free of solids. In the stripper o:il there are also contained heavy oils, since these remain vaporous under the conditions prevailing in the hot separator.
These heavy oils arrive at the so-called "cold separator", which is the cooling-down stage mentioned for the vapor leaving the hot separator, mainly as a result of its solubility in the con-densed mixture of gas and vapor. They are advantageously used as components of the rubbing oil.
With regard to the recycling of asphalt, formerely considered as incompatible, a mechanical removal of the solids from the residue was necessary, which must be achieved by means of centrifuging the residue, since filtration, particularly due to the presence of asphalt, could not satisfactorily be operated.
Along with centrifugation a dilution of the residue was required, which could be incorporated since the clear portion from the centrifuge was used as component of the rubbing oil, and was therefore not distilled. With the only moderately effective separation of solids through centrifugation of the diluted resi-due, the rubbing oil going back into the reactor attained yet considerable amounts of solids and also asphalt, ~ich is un-desirable for the liquefaction. The centrifuge concentrate furthermore contained a lot of medium and heavy oil. Since their recovery could not be waived, a technically and economic-ally unsatisfactory carbonization was necessary, but which about 15-20~ oils, relative to the water- and ash-free entry coal, were distilled off for use in hydrogenation, as it were under unfavorable conditions. There were obtained in that manner, though, no chemically valuable distillate. The greatest por-tion of these low-temperature carbonization oils were added to the residue as diluting oils before the centrifugation.

11539'~Z

1 A concept for removal of the solids from the coal hydro-genation process, diverging from th~s manner of operation, has been disclosed in German Offenlegungsschrift DE-OS 2654635; the portion of medium and heavy oil contained in the residue is ex-tensively removed by relaxing the hot residue in a vacuum ("flashing"), so that a vacuum residue is obtained with about 50%
by weight solids as molten liquid bituminous mass, in which by far the greatest part of the asphalt is bound. This residue is completely led to a gasification; further method steps for the separation of asphalt and solids are thereby unnecessary. With the aid of gasification, one obtains the hydrogen required for the liquefaction of the coal. In this manner of operation the rubbing oil is composed only of solid-free distillate.
The treatment of the residue through distillation or "flashing" involves difficult method steps. The recovery of the heaviest oils cannot be waived--on the one hand, on grounds of efficiency, on the other hand, since this oil decisively influences the characteristics of the rubbing oil.
The invention is therefore based upon the problem of overcoming the disadvantages of the mentioned methods, and to improve the efficiency and practicability of the separation of solid- and asphalt-free, distillate-like oil, whereby a subse-quently employed oil recovery from the residue is made unneces-sary.
The amount of solids in the residue should thereby amount to between about 40-60%, preferably 45-55%. Use of the term "solids" here is understood to mean substances that are insoluble in pyridine.
Through the measures according to the present invention one obtains a hot separator residue freed to such an extent of 1 distillable oils, that a subsequent distillation of the residue, and also a centrifugation or a flashing can be waived, i.e.
that the reaction products are pressure-released down to stand-ard pressure, at minimum.
A lower limit for the solids concentration in the residue of 40% is considered still unsatisfactory. With lower values, too many valuable liquefaction products are lost. It is, however, preferred, to strive for a lower limit of about 45%.
As upper limit, 60% comes into consideration, since with values lying above that, even with favorable chemical composition of the liquid component of the residue, its pumpability is no longer guaranteed. An upper limit of 55% is preferred, since in this case the residue from almost every coal hydrogenation product has been shown to be still pumpable, depending upon the type of species contained therein. In every case, with observance of - the mentioned limits during use of the method according to the present invention, all non-distillable asphalt will be retained in the residue.
It has furthermore turned out that temperatures of between about 440 and 480C in the hot separator are particularly advantageous. With lower temperatures, even with the use of ex-cessively larger amounts of circulation gas, the striven for 40%
portion of solids in the residue is no longer realized. At high-er temperatures the carbonization tendency of the hydrogenation product in the hot separator proves in many cases to be highly unavoidable.
With amounts of circulation gas that are less than 5,000 m3 under normal conditions i.e., given at standard temper-ature and pressure in the hot separator per ton of water- and ash-free entry coal, even with the highest possible temper-atures there, the desired minimum solids portion of 40% in ` 1~53~2 1 the residue is usually no longer attained. This lower limit is merely based only upon pure circulation gas -- thus exclusive of the amounts of fresh hydrogen, which have to be constantly in-troduced into the process, in order to compensate for the con-sumption of hydrogen. The hydrogen concentration of the cir-culation gas therefore amounts, in customary manner, to about 80%, although varying concentrations are also possible. The upper limit for the amount of circulation gas conducted through the hot separator is determined by the maximum portion of solids in the residue. As mentioned, this amounts to about 60~ in order to maintain pumpability.
It has turned out, that with increasing temperatures in the hot separator, and for a pre-determined concentration of solids, less circulation gas is necessary; there is, however, the mentioned lower limit of the circulation gas amount. On the other hand, if it is required that the residue should have a greater portion of solids at a given temperature in the hot sep-arator, more circulation gas is necessary.
It is, however, always necessary that the contact of the discharge product from the liquefaction reactor with the hydrogen-containing circulation gas be as close as possible in the hot separator.
For the solution to the problem according to the present invention it is not necessary to lead the entire amount of circulation gas through the liquefaction reactor before it enters the hot separator; a portion of the circulation gas led through the hot separator can be branched off before the lique-faction reactor and led directly into the hot separator. This last measure can be particularly favorable for the effectiveness of the method.

1 The branched off portion of circulation gas led direct-ly into the hot separator can be introduced there not only through admixing to the discharge products of the liquefaction reactor, but also through feeding in to the sump of the hot separator. In any case, a feeding in of a portion of the cir-culation gas directly to the hot separator is particularly pre-ferred, since the liquefaction reactor will only be incompletely used under certain circumstances on account of a too high loading with gas, and it can even dry up. By pre-heating the portion of circulation gas introduced directly into the hot separator to a temperature between about 300 and 550C one obtains, among others, the advantage that, on the one hand, the pumpability of the residue is influenced in the actually desired manner, and, on the other hand, the temperature in the hot separator can be better controlled.
After relaxation to normal pressure in the fume ex-tractor, the residue, as already mentioned, is freed of oil products to such an extent, that a further extensive oil extrac-tion, also with regard to economy, is generally unnecessary.
Nevertheless, it is possible in the course of a thermal decom-position, such as low-temperature carbonization or coking, to extract still further hydrocarbon products from the residue, or to produce the fresh hydrogen necessary for the process by gasi-fication.
According to the method of the present invention, it is presently not, as was earlier, necessary, to withdraw from the residue the oil necessary for coal slurry preparation; it can rather be obtained in a controlled, particularly economical manner in the condensation stages following the hot separator, whereby ` it is particularly advantageous according to the invention to 11~3~2 1 undertake ~he extraction of rubbing oil in an intermediate separator stage provided specifically for this purpose subsequently to the hot separator. In this manner, the best industrial process engineering results can be obtained: namely, that in the hot separator the entire~-at best yet utilizable through thermal decomposition or gasification--residue of the liquefaction reaction is yielded; the entire amount of rubbing oil necessary for the process (but not in excess amounts) is extracted in the intermediate separator under known choice of temperature and pressure conditions; and finally, the entire, solids-free product oil is yielded exclusively in the cold separator.
The novel features which are considered as characteris-tic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construc-tion and its method of operation, together with additional ob-jects and advantages thereof, will be best understood from the following description of specific embodiments when read in con-nection with the accompanying drawings.
FIG. l illustrates a flow scheme for the process varia-tion involving use of a distillation stage subsequent to the cold separator.
FIG. 2 is a flow scheme of the process variation where-in an intermediate separator is used, without a subsequent dis-tillation stage.
The broken lines in FIG. l indicate that with respect to the addition point 14 for fresh hydrogen in the gas circulation and also for the addition point 17 when only a partial stream of circulation gas enters the liquefaction reactor while some is led directly into the hot separator, various places are possible 115~7~2 1 within the scope of the invention.
In FIG. 1, coal 1 and rubbing oil from distillation stage 18, across conduit 19, are introduced into mix container 2.
The mixture formed from these components is then introduced across pulp pump 3 and pulp pre-heater 4 into liquefaction reactor 5.
The reaction products are admitted from there into hot separator 6, in which they are separated into residue and gaseous and vaporous products. From there the residue is introduced into fume extractor 7, from which the concentrated residue 7a and the relaxed gas 21 are withdrawn. The gaseous and vaporous portions separated at 6 are then led across conduit 8 into cold separator 9, where they for the most part are condensed. The condensate is relaxed in a gas separator 10 and freed of gas ~released gas 22), after which it is led into distillation stage 18, from which the rubbing oil across conduit 19 and the product oil across conduit 20 are withdrawn. The gas not condensed in cold separator 9 is led across conduit 11 to a perhaps necessary gas purification 12, whereby the gas components not desired for the remaining in the process are removed. The so purified and to the desired hydrogen-content concentrated gas is then led as process circulation gasacross condenser 13. An amount sufficient for the li~uefaction process gets admitted thereby across conduit 15 and pulp pre-heater 4 into liquefaction reactor 5, whereas the remaining por-tion is admitted directly into hot separator 6 across circula-tion gas heater 16.
E'IG. 2 is distinguished from FIG. 1 in that an inter-mediate separator 31 for the exclusive recovery of rubbing oil is inserted between hot separator 6 and cold separator 9. This intermediate separator operates at temperatures below those in the hot separator. The rubbing oil recovered in intermediate separator 31 is then releaxed in fume extractor 32 and admitted across con-llS3~'~Z

1 duit 19 (as in FIG. 1) back to mix container 2, whereas the gasseparated in fume extractor 32 is withdrawn across conduit 33.
The use of intermediate separator 31 makes the distil-lation stage 18 employed in FIG. 1 for the product components condensed in cold separator 9, superfluous.
The manner of operation represented in FIG. 2 is, among other reasons, also particularly advantageous, since the entire product oil 20 yielded behind the cold separator contains oil that is, as is welllkno~n, more valuable, since it is richer in hydrogen, than comparable distillation fractions from the inter-mediate separator 31. The advantage of hydrogen-richer oil resides in particular in that it is more easily processed in catalytic methods.
It will be understood that each of the elements described above, or two or more together, may also find a useful applica-tion in other types of coal processes differing from the types described above.
While the invention has been illustrated and described as embodied in a method of hydrogenated coal liquefaction, it is not intended to ~e limited to the details shown, since various modifications and structural changes may be made without departing in any way fcom the spirit of the present invention.

Claims (9)

The embodiment of the invention in which an ex-clusive privilege or property is claimed are defined as follows:

1. Method for hydrogenated coal liquefaction, using rubbing oils and hydrogen-containing circulating as, in which while a concentration of the non-liquified solid components occurs in a hot separator added subsequent to, and under simil-ar temperature and pressure conditions as in, the liquefac-tion reactor, and the gaseous and vaporous discharge products from said liquefaction reactor are extensively condensed in subsequent stages, the non-gaseous and non-vaporous separation products, extensively freed of distillable oils, are removed in still pumpable condition from said hot separator, and re-laxed in a subsequently added vessel (fume extractor), char-acterized by conducting said hydrogen-containing circulation gas, in contact with the discharge products from said lique-faction reactor, through said hot separator, in an amount greater than about 5,000 m3 given at standard temperature and pressure per ton of water- and ash-free feed coal.

2. Method according to claim 1, wherein the temper-ature in the hot separator is held to between about 440° and 480°C.

3. Method according to claim 1, wherein a part of the circulation gas led through the hot separator is branched off before the liquefaction reactor and conducted directly in-to the hot separator.

4. Method according to claim 3, wherein the branched off circulation gas is conducted into the hot separator together with the discharge products from the liquefaction reactor.

5. Method according to claim 3, wherein the branched off circulation gas is conducted into the sump of the hot separator.

6. Method according to claim 3, wherein the branched off circulation gas is pre-heated before it is conducted into the hot separator to temperatures between about 300° and 550°C.

7. Method according to claim 1, wherein the rubbing oil is predominantly recovered from condensation stages subsequent to the hot separator.

8. Method according to claim 7, wherein the rubbing oil is recovered exclusively in an intermediate separation stage directly following the hot separator.

9. Method according to claim 1, further comprising the step of thermally decomposing the product degassed in the fume extractor to produce hydrocarbons.