GB2103644A

GB2103644A - Coal liquefaction

Info

Publication number: GB2103644A
Application number: GB08209901A
Authority: GB
Inventors: Harvey David Schindler
Original assignee: Lummus Co
Current assignee: CB&I Technology Inc
Priority date: 1981-08-05
Filing date: 1982-04-02
Publication date: 1983-02-23
Also published as: JPS5827784A; GB2103644B; AU8211582A; NL8201435A; CA1176196A; BE892761A; FR2511024A1; IT8248160A0; ZA822056B; FR2511024B1; AU546749B2; DE3212407A1; IT1148160B; JPS5945711B2

Abstract

Coal is contacted with hydrogen and a process- derived first stage liquefaction solvent 12 in a thermal liquefaction zone to produce in effluent 14 from which a pumpable stream 25 of insoluble material which includes 850 DEG F+ liquid is separated prior to second stage hydroliquefaction at 52 to produce an effluent 55 from which 850 DEG F+ liquid 58 is recovered. The first stage liquefaction solvent includes a portion 31 of the pumpable stream 25 which contains 850 DEG F+ liquid and a portion of 59 of the 850 DEG F+ liquid 58 and comprises 15-50% of 850 DEG F+ liquid, 50-20% of insoluble material and at least 45% of 850 DEG F- liquid having an initial boiling point of at least 500 DEG F. <IMAGE>

Description

SPECIFICATION Coal liquefaction This invention relates to liquefaction of coal, and more particularly to improvements in a two-stage process for coal liquefeaction.

Coal has been liquifield in a single liquefaction stage comprised of a preheater coil where coal liquefaction is essentially completed, followed by a dissolver, where both liquefaction solvent and coal derived liquids are further hydrogenated.

Recently, there has been proposed a so-called two-stage liquefaction process wherein the first reaction stage is a short contact time thermal liquefaction, followed by recovery of essentially ash free liquid, which is further upgraded in a second liquefaction stage.

The present invention is directed to an improvement in such a two-stage liquefaction process.

In accordance with the present invention, there is provided a process for the two stage liquefaction of coal by contacting coal, a first stage liquefaction solvent and hydrogen in a first stage thermal liquefaction zone to produce a first effluent; recovering from the first effluent an essentially ash free liquid and a pumpable stream of insoluble material including 8500F+ liquid; contacting essentially ash free liquid and hydrogen in a second stage liquefaction to upgrade the essentially ash free liquid and produce a second stage liquid effluent, and recovering 850"F+ liquid from the second liquid effluent, which comprises: said liquefaction solvent for said first stage including a portion of the pumpable stream of insoluble material, including 850"F+ liquid, which is recovered from the first effluent, and a portin of 850"F+ liquid which is recovered from the second stage liquid effluent, said liquefaction solvent being comprised of from 15% to 50% of 850"F+ liquid, from 5% to 20% of insoluble material and at least 45% of 850"F- liquid having an initial boiling point of at least 500"F, with at least 10% of the liquefaction solvent being obtained from said pumpable stream and at least 25% of the first stage liquefaction solvent being obtained from the second stage liquid effluent.

More particularly, the first stage liquefaction is preferably a short contact thermal liquefaction which is operated at an outlet temperature in the order of from 830"F to 875"F, at a pressure in the order of from 1800 to 2700 psig, and at reaction contact times (at temperatures above 600"F) in the order of from 3 to 15 minutes. The coal liquefaction solvent employed in the first stage is preferably provided in an amount such that the ratio of solvent to coal is in the order of from 1.2:1 to 3:1, on a weight basis. It is to be understood that greater amounts could be employed but, in general, such greater amounts are not economically justified. In addition, hydrogen is generally added to the first stage in an amount of from 4000 to 15,000 SCF per ton of coal.

In the preferred embodiment of the invention, after treatment to remove insoluble matter, 850"F+ liquid which is essentially free of insoluble material is liquefied in a second stage to further upgrade the material.

Preferably, the pumpable stream of insoluble material (such as ash, undissolved coal, etc.), which includes 850"F+ liquid (generally at least 45%, and most generally about 45% to 55% of the stream is 850"F+ liquid, with the remainder being insoluble material), which is recovered from the de-ashing, is employed in formulating the liquefaction solvent from the first stage.

Preferably the coal liquefaction solvent which is used in the first stage of the process is comprised of from 15% to 20%, most generally from 5% to 10%, of insoluble material, with the remainder being 850"F- liquid having an initial boiling point of at least 5000F, with the 850"F- liquid being present in the solvent in an amount of at least 45%, and most generally in an amount of at least 50% all by weight. In addition, at least 10% and up to 40% of the liquefaction solvent is preferably derived from the pumpable stream of insoluble material recovered from the first stage de-ashing and at least 25% of the liquefaction solvent is preferably derived from the second stage.

The portion derived from the second stage can be the 850"F+ alone or both 850"F+ and 850"F- liquid, with, in most cases, the liquid derived from the second stage being primarily the 850"F+ liquid.

Thus, the liquefaction solvent is preferably comprised of liquid which boils above 500"F, with the liquefaction solvent including 850"F+ material (the full range of material, excluding insolubles, derived from the coal) recovered from both the first and second stages.

In accordance with a preferred embodiment, the first stage effluent is de-ashed by the use of a liquid promoter having a characterisation factor of at least 9.75, a 5 volume percent distillation temperature of at least about 250"F, and a 95 volume percent distillation temperature of at least about 350"F and no greater than about 750"F, as described in U.S.

Patent No. 3,856,675. As described in such patent, a preferred promoter liquid is a kerosene fraction having a 5% and 95% volume distillation temperature of 425"F and 500"F, respectively.

Liquid essentially free of insoluble material (no more than 0.5% ash) recovered from the de-ashing is then treated in a recovry zone to recover promoter liquid, if such promoter liquid is employed in the de-ashing, component boiling below 850"F, which are used in formulating the liquefaction solvent, with higher boiling materials, i.e. 850"F+ material, being employed as feed to the second stage liquefaction. A pumpable stream of insoluble material, which includes 850"F+ liquid is also recovered from the de-ashing and a portion thereof is used in formulating the solvent.

In the second stage liquefaction, the 850"F+ material is contacted with hydrogen, and second stage liquefaction solvent at temperatures in the order of from 7500to 8500F, and at pressures in the order of from 2000 to 3000 psig, with contact times being in the order of from 1 to 5 hours. In the second stage, such contacting is effected in the presence of of coal liquefaction catalyst of a type known in the art. For example an oxide or sulfide of a group VI and group VIII metal, such as a cobalt-molybdenum catalyst, supported on a suitabie support such as alumina or silica-alumina.

In accordance with the preferred embodiment, such second-stage liquefaction is accomplished in an upflow ebullated bed, with such ebullated beds being known in the art.

The effluent from the second stage liquefaction is then subjected to a flashing step to recover lighter components therefrom; i.e. components boiling below about 850 F, with the remaining product being used to provide liquefaction solvent to the second stage, a portion of the liquefaction solvent requirements for the first stage, and net liquefaction product.

An embodiment of the invention is described below, by way of example, with reference to the accompanying drawing, which is a simplified schematic block flow diagram.

Referring now to the drawing, ground pulverized coal, generally bituminous, sub-bituminous or lignite, preferably bituminous coal, in line 10, hydrogen in line 11, and a coal liquefaction solvent, in line 12, obtained as hereinafter described, are introduced into the first stage liquefaction zone, schematically generally indicated as 13 for effecting a short contact thermal liquefaction of the coil. The thermal liquefaction is effected in the absence of catalyst. The first stage liquefaction is operated under the conditions hereinabove described.

Afirst stage coal liquefaction product is withdrawn from zone 13 through line 14, and introduced into a flash zone, schematically generally indicated as 15, in order to flash therefrom materials boiling up to about 500 to 600"F. Such flashed materials are removed from flash zone 15 through line 16. The flash zone 15 is operated primarily for the purpose of flashing material which boil up to the end point of the promoter liquid to be employed in the subsequent de-ashing process.

The remainder of the coal liquefaction product, in line 17, is introduced into a de-ashing zone, schematically generally indicated as 18 for separating ash and other insoluble material from the first stage coal liquefaction product. As particularly described, the de-ashing in zone 18 is accomplished by use of a promoter liquid for promoting and enhancing the separation of the insoluble material, with such promoter liquid being provided through line 19. In particular, the separtion in de-ashing zone 18 is accomplished in one or more gravity settlers, with the promoter liquid and general procedure for accomplishing such de-ashing being as described, for example, in U.S. Patent No. 3,856,675.

The essentially ash free overflow is withdrawn from de-ashing zone 18 through line 22 for introduction into a recovery zone, schematically generally indicated as 23.

An insoluble material-containing underflow is withdrawn from de-ashing zone 18 through line 20, and introduced into a flash zone, schematically generally indicated as 24, to flash materials boiling below 850"F therefrom. The flashing in zone 24 is accomplished in a manner such that there is recovered from flash zone 24, through line 25, a flowable insoluble material containing 850 Ft liquid. The flashed components are withdrawn from flash zone 24 through line 26 for introduction into the recovery zone 23.

A portion of the 850 F+ material in line 31 is introduced into a first stage solvent storage zone, schematically generally indicated as 32, forformulating the first stage liquefaction solvent, as hereinafter described.

The remaining portion of the material in line 33 may be used as feedstock to a partial oxidation process for producing hydrogen.

The recovery zone 23 may include one, two or more distillation columns which are designed and operated to recover the promoter liquid through line 41 for subsequent introduction into de-ashing zone 18 through line 19, after addition of make up promoter liquid, as required, through line 42.

In addition, there is recovered through a line 43 a stream which boils within the range from about 600O to about 900"F for use in formulating the first stage liquefaction solvent in first stage liquefaction solvent zone 32.

850F+ material is recovered from the recovery zone 23 through line 51 for introduction into a second stage liquefaction zone, schematically generally indicated as 52, along with hydrogen in line 53 and second stage liquefaction solvent in line 54. The second stage liquefaction zone 52 is operated at temperatures, and pressures, as hereinabove described, preferably with the use of a coal liquefaction catalyst of the type hereinabove described.

In accordance with a preferred embodiment, the second liquefaction stage is in the form of an upflow ebullated bed.

The effluent from the second stage liquefaction, in line 55, is introduced into a flash zone, schematically generally indicated as 56, to flash therefrom material boiling below about 850"F, with such lower boiling materials being recovered through line 57. Optionally some of the material in line 57 may be employed in line 62 for formulating liquefaction solvent.

The 850 F+ product recovered from flash zone 56 through line 58 is employed for providing second stage liquefaction solvent through line 54, and for formulating first stage liquefaction solvent through line 59.

The remaining portion is recovered through line 61 as net product.

The first stage liquefaction solvent in zone 32 is thus formulated by combining material boiling within the range from 600"F to 900"F, in line 43, 850"F+ liquid, which includes insolubles in line 31, and 850 F+ material from the second stage liquefaction in line 59. Optionally, some of the lighter material recovered from the second stage may be used in formulating the first stage solvent.

Although the invention has been described with respect to a particular embodiment, it is to be understood that the invention is not limited to only such embodiment. Thus, for example, the de-ashing may be accomplished other than as particularly described. Similarly, the second stage liquefaction may be accomplished other than as particularly described; i.e. other than by use of an upflow ebullated bed.

The present invention is advantageous in that 850"F+ material derived from the coal is used for providing a portion of the liquefaction solvent and a portion of such 850"F+ material is provided from the pumpable stream of insolubles recovered from the de-ashing thereby reducing the amount of material required from the second stage for formulating first stage liquefaction solvent.

Claims

1. A process for the two stage liquefaction of coal by contacting coal, a first stage liquefaction solvent and hydrogen in a first stage thermal liquefaction zone to produce a first effluent; recovering from the first effluent an essentially ash free liquid and a pumpable stream of insoluble material including 850"F+ liquid; contacting essentially ash free liquid and hydrogen in a second stage liquefaction to upgrade the essentially ash free liquid and produce a second stage liquid effluent, and recovering 850"F+ liquid from the second liquid effluent, which comprises: said liquefaction solvent for said first stage including a portion of the pumpable stream of insoluble material, including 850"F+ liquid, which is recovered from the first effluent, and a portion of 850"F+ liquid which is recovered from the second stage liquid effluent, said liquefaction solvent being comprised of from 15% to 50% of 850 F+ liquid, from 5% to 20% of insoluble material and at least 45% of 850 F- liquid having an initial boiling point of at least 500"F, with at least 10% of the liquefaction solvent being obtained from said pumpable stream and at least 25% of the first stage liquefaction solvent being obtained from the second stage liquid effluent.

2. The process of claim 1,wherein a pumpable stream is comprised of from 45% to 55% of 850"F+ liquid and the remainder is insoluble material.

3. The process of claim 1, wherein the liquefaction solvent for the first stage is comprised of from 20% to 40% of 850"F+ liquid.

4. The process of claim 3, wherein the liquefaction solvent for the first stage is comprised of from 5% to 10% of insoluble material.

5. The process of claim 4, wherein the first stage liquefaction solvent includes at least 45% of 850"F- liquid.

6. The process of claim 1, wherein the at least 25% obtained from the second stage liquid effluent is comprised of both 850"F- liquid and 850"F+ liquid.

7. The process of claim 2, wherein no more than 40% of the first stage liquefaction solvent is derived from said pumpable stream of insoluble material.

8. The process of claim 1, wherein the first stage thermal liquefaction is operated at an outlet temperature of from 8500to 8750F, a pressure of from 1800 to 2700 psig and in the absence of catalyst.

9. The process of claim 8, wherein the second stage liquefaction is effected in an upflow ebullated bed.

10. A process for the two stage liquefaction of coal, substantially as hereinbefore described with reference to the accompanying drawing.

11. Any novel feature or combination of features described herein.