CA1231906A

CA1231906A - Refining of coal

Info

Publication number: CA1231906A
Application number: CA000448311A
Authority: CA
Inventors: Quintin J. Beukes; Cornelis Kleynjan
Original assignee: Sasol Operations Pty Ltd
Current assignee: Sasol Operations Pty Ltd
Priority date: 1983-02-28
Filing date: 1984-02-27
Publication date: 1988-01-26
Also published as: GB2138839A; JPH0579717B2; AU558838B2; GB8403482D0; DE3406845C2; DE3406845A1; AU2482584A; GB2138839B; JPS59166587A

Abstract

ABSTRACT OF THE DISCLOSURE

A method of solvent refining coal to produce normally solid solvent refined coal which can be used for the manufacture of high quality electrode coke, includes a two-step liquefaction process. The process includes contacting coal with a solvent in a first step, thereby to refine the coal partially in a first reaction. Thereafter some of the solvent is removed, and, in a second step, the partially refined coal from the first step is allowed to remain in contact with the residual solvent for further refining of the coal in a second reaction. After the second reaction and separation of undissolved matter therefrom, at least some of the residual solvent is removed, thereby to produce normally solid solvent refined coal as precursor for the manufacture of high quality electrode coke. The invention also provides solvent refined coal when produced by said method.

Description

~ 2 ~ ~3~

THIS INVENTION relates to the refining of coal. It relates in particular to a method of refining coal, and to solvent refined coal (hereinafter also referred to as 'SRC').

According to the invention, there is provided a method of refining coal, which includes, in a two-step process, contacting coal with a solvent in a first step, thereby to refine the coal partially in a first reaction, removing some of the solvent; and allowing9 in a second step, the partially refined coal from the first step to remain in contact with the residual solvent, for further refining of the coal in a second reaction.

The method may include9 after said second reaction, removing at least some of the residual solvent, thereby tQ
produce solvent refined coal.

The solvent may be an oil. The oil may be a coal derived oil-fraction, having a boiling range from about 80C to about 450C, for example about 200C to about 450C.

The oil-to-oil coal ratio in the first step may be from abQut 1:, to about 5:1 (on a mass basis), preferably about 3i~

2:1, so that the oil an~ coal are in the form of an oil/coal slurry in the first step.

The method may include adding a catalyst to the slurry.
The ratio of catalyst to coal in the slurry in the first s-tep, may be about 1:50 (on a mass basis). The catalyst may be a metal-based catalyst.

The contacting in the first step may be effected at a temperature of about 350C tc about 480C, For example about 400C to 450C, and at a pressure of about 5x103 kPa to about 30x103 kPa, for example about 20x103 kPa. The reaction may be effected in a hydrogen-rich atmosphere. The reaction time of the first reaction may be less than 20 minutes, for example about 10 minutes or less.

The removal of the oil may be effected by means of distillation. The volume of oil distilled off may be such that the oil and coal residue are still in the form of a slurry in the second step, and the concentration of the catalyst in the slurry in the second step is at least twice the concentration of the catalyst in the slurry in ~he first step.

The contacting in the second step may also be effected at a temperature of about 350C to about 480C, for example about 400C to 450C, and at a pressure of about 5x103 kPa to about 30x103 kPa, for example ~bout 20x103 kPa. The reaction time of the second reaction may be between about 15 minutes and abou-t 150 minutes.
The invention extends also to solvent refined coal when produced accordin~ to the method hereinbefore described.
Various aspects of this invention are as follows:

A method of solvent refining coal to produce normally solid solvent refined coal which can be used as a feedstock for the manufacture of high quality electrode coke, which includes slurrying pulverized coal with a coal-derived solvent in a slurrying stage to form a solvent/coal slurry;
subjecting the slurry to a first reactior~ in a first reaction step;
maintaining the first reaction temperature at between 350C
and 4~0C, the first reaction pressure at between 5x103 kPa and 30xlO kPa, and the first reaction time at less than 20 minutes, thereby to liquefy substantially all of the coal, and to refine the coal partially;
removing some o~ the solvent in a solvent removal stage to produce a residual slurry which comprises mainly residual solvent and liquefied, partially refined coal, with no cooling of hydrocarbon liquid effluent before or after the solvent removal stage being effected, no hydrocarbon liquid solvent being added to the slurry before or after the solvent removal stage and no residual slurry being recycled back to the first reaction step;
subjecting the residual slurry to a second reaction in a -4a-second reaction step, under hydrogenative conditions;
maintaining the second reaction temperature at between 350C
and 480C with the temperature not being substantially lcwer tllan that in the first stage, the second reaction pressure at between 5x103 kPa and 3nX103 kPa, and the second reaction time at between 15 and 150 minutes to refine the coal further; and removing at least some of the residual solvent, thereby producing, as a bottoms product, normally solid solvent refined coal which is suitable as a coking feedstock capable of being formed directly by coking and calcining into coke having a coefficient of thermal expansion of less than 0,7xlO 6, with none of this bottoms product being recycled to the first step.

A method OT producing a feedstock suitable for the manufacture of high quality electrode coke, which includes slurrying pulverised coal ~ith a coal-derived sol~ent in a slurrying stage to form a solvent/coke slurry, subjecting the slurry to a first reaction in a first reaction step;
maintaining the first reaction temperature at between 350C
and 480C, the first reaction pressure at between 5X103 kPa and 30x10 kPa, and the first reaction time at less than 2Q minutes, thereby to liquefy su~stantially all the coal~ and to refine the coal partially;
removing some of the solvent in a solvent removal stage to produce a residual slurry which comprises mainly residual solvent -4b-and liquefied, partially refined coal~ with no cooling of hydrocarbon liquid effluent before or after the solvent removal stage being effected, no hydrocarbon liquid solvent being added, to the slurry before or after the solvent removal stage and no residual slurry being recycled back to the first reaction stepi subjecting the residual slurry to a second reaction in a second reaction step, under hydrogenative conditions;
maintaining the second reaction temperature at between 350C
and 480C with the temperature not being substantially lower than that in the first stage, the second reaction pressure at between 5x103 kPa and 30x103 kPa, and the second reaction time at between 15 and 150 minutes to refine the coal further~ and removing at least some of the residual solvent, thereby producing a bottoms product which is a suitable coking feedstoc~
capable of being formed directly by coking and calcining into coke having a coefficient of thermal expansion of less than 0,7x10 6, with none of this bottoms product beiny recycled to the first step.

The single FIGURE in the drawing shows a schematic flow diagram of a process for producing solven-t refined coal, utilizing the method of the present invention.

In the drawing, reference numeral 10 generally indicates a process for produçing solvent refined coal.

-4c-The process 10 includes a pretreatment stage 18. Into the pretreatment stage 18 is fed, via a flowline 12, powdered coal (for example, coal containing 36% (by mass) volatiles and 10% (by mass) ash). Into the pretreatment stage 18 is also fed, via flowline 16, 2% (by mass3 Fe203 on coal, as an added catalyst. Finally, to the pretreatment stage 18 is fed, via a Flowline 14 9 ,ecycle solvent (the production of which is described in more detail hereunder) comprising a coal-derived oil fraction having a boiling range of from about 200C to about 420C. Sufficient solvent is added via the flowline 14 to form a slurry having a solvent-to-oil ratio oF about 2:1 (on a mass basis), in the pretreatement stage 18.

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The slurry is fed from ~he pretreatment stage, via a flowline 19, into a first reaction step or stage 20. In the reaction stage 20, the coal is contacted with the solvent in a hydrogen-rich atmosphere for a short period up to 15 minutes at a pressure of about 20x103 kPa and at a temperature of about 425C, to liquefy or dissolve the coal and to refine it partially in a first reaction.

The slurry from the stage 20 is then fed, via flowline 21, to a gas separation stage 22 in which gases (such as, C0~
C02, H20 and C1 3) evolved in the stage 20 are separated from the slurry and removed via a flowline 23.

The slurry is thereafter fed, via a flowline 25, into a distillation stage 24. In the distillation stage 24, sufficierlt solvent is distilled off so that a residual slurry ~comprising mainly partially refined coal, catalyst, undissolved matter and solvent) having a catalyst concentration about three times higher than the catalyst concentration in the slurry fed lnto the stage 20, is produced. The solvent distilled off is withdrawn from the stage 24 and fed, via a flowline 26, into the flowline 14.
Hence, this solvent constitutes part of the recycle solvent to the stage 18.

The residual slurry is withdrawn from the stage 24 and fed, via a flowline 28, into a second reaction step or stage 30.
In this stage 30~ the partially refined coal is contacted with th~ residual solvent for 60-120 minutes at a temperature of 425-445C and at a hydrogen pressure of about 20x103 kPa, to refine the coal fur~her in a second reaction.

The slurry product from the stage 30 is then fed, via a flowline 31, into a further gas separating stage 32. In the stage 32, further gases evolved in the stage 30, are separated from the slurry product, and removed via a flowline 33.

The slurry product is then fed, via a flowline 34, into a solid remoYal stage 36. In stage 36, undissolved matter is separated from the liquid product, and removed from the process via a flowline 35.

Finally, the liquid product from the stage 36 is fed, via a flowline 37~ into a further distillation stage 40. In the stage 40, further solvent is distilled off and withdrawn from the stage 40 via a flowline 38. A portion of this solvent is routed to the flowline 14 so that sufficient solvent passes along the flowline 14 to the pretreatment stage 18. The remaining solvent is withdrawn from the process via the flowline 42 for external use. SRC (which is a solid pitch-like material under ambient conditions) is withdrawn from the stage 40, via a flowline 44, and can be worked up further (not shown) to produce a superior quality coke for the manufacture of electrodes.

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It is to be understood that, in the stages 24 and 40 a liquid fraction having a boiling range of about 80C-200C is also distilled off (not shown).

The invention will now be described by way of the following non-limiting Examples:

1.1 A bituminous coal, containing 36X (by mass~ volatiles and 10% (by mass) ash, was powdered and slurried with 2 parts (by mass) of a coal-derived oil fraction (solvent) having a boiling range of from about 200C to about 420C. 1500 gms of this slurry was reacted in a S litre autoclave with 2% (by mass) Fe203 on coal as an added catalyst. In a first step, the coal was contacted with the solvent in a hydrogen-rich atmosphere for 10 minutes at a pressure of about 20x103 kPa and a temperature of 425C, to refine the coal partially. Thereafter, sufficient solvent was distilled off until a slurry having a catalyst concentration which was about three times higher than the catalyst concentration in slurry of the first step, remained in the autoclave. The now partially refined coal (i.e. the coal residu2) was allowed to remain in contact with the residual solvent for a further 120 minutes in a second step at a te~perature of 425C and a pressure of about 20x103 kPa, for further refining. The autoclave ~as then cooled down and the contents worked up to recover the solvent refined coal (eg unreacted products removed and distillable oils recovered~.

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1.2 1500 gms of the slurry of 1.1 was gain reacted in a 5 litre autoclave with 2~ (by mass) Fe203 on coal as an added catalyst. The reaction conditions were the same as for the first step in 1.1. However, the reaction time in the first step was increased to 130 minutes, and no solvent was thereafter distilled off, ie the second step was not performed.

A comparison of the products obtained from 1.1 and 1.2 above (calculated as nett mass percentages on dry ash-free coal) is as follows:
Ex~eriment 1.1 Ex~eriment 1.2 C0 + C02 3,1 2,0 H2 8,0 7,2 Cl - C3 8,2 11~7 C4 - ?00C 14 91 25,9 200 - 420~ 16,0 -17~
SRC ~420C plus) 42,2 67,9 Undissolved 2~3 3~2 The SRC obtained from both experiments was coked at 500C ~5 hours heating time and 4 hours coking time) and calcined for 30 minutes at 1 370C.

The coefficient of thermal expansion was determined for the calcined coke by means of the X-ray diffraction method. The coefficient of thermal expansion (CTE) was 0~4 x 10 6 for the calcined coke obtained ~rom Experiment 1~1, and 0~7 x 10 6 for the calcined coke obtained from Experiment 1.2.

From the above resul~s 9 it can be seen that a superior quality coke is obtained from the two-step method of the present invention. Furthermore, -the two-step method is self-sufficient as regards solvent requirements. Experiment 1.2 gave coke of a poorer quality and there was a large deficiency in process solvent.

_________ 1500 gms of the slurry of Example 1 was again reacted in a 5 litre autoclave with 2% (by mass) Fe203 on coal as an added catalyst. In a first step, the coal was contacted with the solvent in a hydrogen-rich atmosphere for 10 minutes at a pressure of about 20x103 kPa and a temperature of 425C.
Thereafter, suf~icient solvent was distilled off until a slurry having a catalyst concentration which was about 3 times higher than the catalyst concentration of the slurry of the first step, remained in the autoclave. The temperature of the autoclave was raised to 445C, and the contactins continued for a further 60 minutes in a second step, at a pressure of about 20x103 kPa.

The following product spectrum was obtained (calculated as nett mass percentages on dry ash-free coal):
C0 + C02 2,4 ~ 8,5 ~3~

Cl - 3 13,2 C4 - 200C 20~9 200-420C 14,4 SRC (420C plus) 38,5 Undissolved 2,2 Calcined coke was produced from the SRC in the same way as in Example 1, and was again of high quality, havin~ 2 CTE value of 0,4 x 10 6. This method yielded 35% liquid products in the diesel and petrol boiling range ~C4-200C and 200C-420C
respectively).

_______ 1500 gms of the slurry of Example 1 was again reacted in a 5 litre autoclave with 2% (by mass) Fe203 on coal as a catalyst, under the same reaction conditions as in Example 2, in first and second steps similar to those described hereinbefore with reFerence to Example 2. The only difference was ~hat the reaction time of the second step was increased from 60 to 120 minutes, thereby to increase the production of liquid fuels.

The following product spectrum was obtained (calculated as nett mass percentages on dry ash-free coal):

~ + C~2 2,7 ~2 ~,6 Cl - 3 13,5 ~.~23~

C4 - 200C 20,4 200 - 420C 17,3 SRC (420C plus) 35,3 Undissolved 2,4 The total yield of liquid products was 37,7% while the CTE value oF calcined coke produced from the SRC, was 0~3 x 10 6.

Again, 1500 gms of the slurry of Example 1 was used, and to this was added 2% (by mass) Fe203 on coal as an added catalyst. Both the first and second stPps were effected in a continuous flow reactor. For the first step, a 1 litre autoclave was used, while for the second step a vertical open tube reactor having a 25 mm diameter was used. The reaction time was 15 minutes in the autoclave and 120 minutes in the open tube reactor. The contact temperature and pressure for both steps was 425C and 20x103 kPa respectively. The following produc~ spectrum was obtained (calculated as nett mass percentages on dry ash-free coal):

C0 ~ C02 2,8 ~ 10,0 C1 - 3 8,4 C4 - 200C 19,3 200 - 420C 20,3 SRC ~420C plus~ 37/8 Undissolved 1,4 Calcined coke wi~h a CTE value of 0,4 x 10 6 was produced from the SRC as hereinbefore described.

The 200-420C fraction recovered after the first and second steps can be recycled (ie used to form the slurry for the first step). Excess oil can be used elsewhere, eg it can be up-graded to diesel oil.

The Applicant is aware that SRC, which is a solid pitch-like material under ambient conditions and which has hitherto normally been obtained by direct hydrogenation of coal, can be used as a feedstock for producing coke via a delayed coking process. The so-produced green coke can be calcined and can thereafter be used to manufacture electrodes.

The quality of the electrodes depends to a large extent on the degree of depolymerisation of the original or raw coal used.

The Applicant is aware of methods of depolymerizing coal which comprises solvation of coal with a solvent in a single step. During the solvation, the coal is depolymerised, but coal fragments have a strong tendency to combine with solvent molecules or fragments in side reactions, thus resulting in a shortage in recycle solvent. To prevent or reduce the occurrence of these unwanted side reactions, a good catalyst system and high hydrogen pressure are normally used~ Prolonged reac~ion times, which are necessary to decrease the heteroatom content under these conditions, lead to high yields of liquid and gaseous products and subsequently low yields oF so!id SRC. If, on the other hand, the SRC production is maximised by using short reaction times, this product still contains too high a heteroatom content to make it suitable for the manufacture of high quality electrode coke.

During the depolymerization reaction~ gases such as hydrogen sulphide, carbon dioxide~ carbon monoxide, ammonia and water are evolved which indicates that the heteroatoms sulphur, nitrogen and oxygen are liberated from the coal molecules during polymerization.

Without wishing to be bsund by theory, the Applicant believes that heteroatoms in the molecular structure of a coking feed hinder the graphitisation thereof at higher temperatures, by increasing the viscosity and decreasing the plastic range of the mesophase (J Dubois, C Aquache and J L White - Metallography 3 (1970) 337-360. Hydrocracking is then needed to decrease the hetero atom content of the solvent refined coal as far as possible.

In US Patent 4 210 517 of the Mitsui ~ining Company Limited and the Mitsui Coke Company Limited, the ratio of N___S___0 is correlated with the quality of the calcined coke and ~2~

it was shown that the lowest values correspond with the better quality coke. This shows again that the hetero atom content or the basic 'pitch' must be low and the carbon content high.

In the methods known to the Applicant, either a low yield of good quality SRC or a high yield of poor quality SRC is obtained.

The Applicant believes that in the two-step method provided by this invention (in which said side reactions are minimized or reduced as a result of the removal of some of th~
solvent of the first step), the reaction conditions can be chosen so that (i) a high yield of high quality SRC (ie low hetero atom content), and self-sufficiency as regards solvent requirements, can be obtained, or (ii) a lower yield of high quality SRC with a high yield of liquid products9 can be obtained. The SRC will be suitable for thc manufacture of high quality electrode coke.

The Applicant further believes that large quantities of high quality SRC and self-sufficiency as regards solvent requirements can be obtained by means of the two-step method of the invention, ~ithout the use of the added metal-based catalyst (ie utilizing only the natural catalytic activity present in the coal). However9 subs~antially equally large quantities of high quality SRC and a similar degree of self-sufficiency as regards solvent requirements can be obtained when a metal-based catalyst is used, in which case a higher reaction temperature and shorter ~15-reaction time can be utili~ed to obtain a similar product spec~rum. By using a metal-based catalyst and altering the reaction conditions in the first and second steps, the amount of liquid products obtained can be varied.

This process also has the advantage that a lower initial catalyst concentration can be used (as compared with known processes), resulting in lower overall catalyst usage than is possible with said known processes.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of solvent refining coal to produce normally solid solvent refined coal which can be used as a feedstock for the manufacture of high quality electrode coke, which includes slurrying pulverized coal with a coal-derived solvent in a slurrying stage to form a solvent/coal slurry;
subjecting the slurry to a first reaction in a first reaction step;
maintaining the first reaction temperature at between 350°C
and 480°C, the first reaction pressure at between 5x103 kPa and 30x103 kPa, and the first reaction time at less than 20 minutes, thereby to liquefy substantially all of the coal, and to refine the coal partially;
removing some of the solvent in a solvent removal stage to produce a residual slurry which comprises mainly residual solvent and liquefied, partially refined coal, with no cooling of hydrocarbon liquid effluent before or after the solvent removal stage being effected, no hydrocarbon liquid solvent being added to the slurry before or after the solvent removal stage and no residual slurry being recycled back to the first reaction step;
subjecting the residual slurry to a second reaction in a second reaction step, under hydrogenative conditions;
maintaining the second reaction temperature at between 350°C
and 480°C with the temperature not being substantially lower than that in the first stage, the second reaction pressure at between 5x103 kPa and 30x103 kPa, and the second reaction time at between 15 and 150 minutes to refine the coal further; and removing at least some of the residual solvent, thereby producing, as a bottoms product, normally solid solvent refined coal which is suitable as a coking feedstock capable of being formed directly by coking and calcining into coke having a coefficient of thermal expansion of less than 0,7x10-6, with none of this bottoms product being recycled to the first step.

2. A method according to Claim 1, wherein the solvent is an oil fraction having a boiling range from about 80°C to about 450°C, at least a portion of the solvent removed after the first and/or the second reaction steps being recycled to the slurry stage so that the solvent required for the slurry comprises only recycled solvent.

3. A method according to Claim 1, wherein the solvent-to-coal ratio in the slurry formed in the slurrying stage is from about 1:1 to about 5:1 (on a mass basis).

4. A method according to Claim 1, which includes adding a metal-based catalyst to the solvent/coal slurry, the ratio of catalyst to coal being about 1:50 on a mass basis.

5. A method according to Claim 1, wherein the first reaction is also effected under hydrogenative conditions.

6. A method according to Claim 4, wherein the catalyst addition is effected in the first step and wherein the solvent removal is effected by means of distillation, the volume of solvent distilled off being such that the concentration of the catalyst in the residual slurry is at least twice the concentration of the catalyst in the slurry in the first reaction step.

7. A method according to Claim 1, wherein the reaction temperatures and pressures of the first and second reaction are substantially the same.

8. A method according to Claim 1, in which the first reaction temperature is maintained at between 350°C and 450°C.

9. A method according to Claim 8, in which the feed to the second stage is maintained at substantially the first stage effluent temperature.

10. A method according to Claim 1, in which the feed to the second stage is maintained at substantially the first stage effluent temperature.

11. A method according to Claim 1, wherein the solvent is an oil fraction having a boiling range from about 80°C to about 450°C, at least a portion of the solvent removed after the first and/or the second reaction steps being recycled to the slurrying stage so that the solvent required for the slurry comprises only recycled solvent.

12. A method of producing a feedstock suitable for the manufacture of high quality electrode coke, which includes slurrying pulverized coal with a coal-derived solvent in a slurrying stage to form a solvent/coke slurry;
subjecting the slurry to a first reaction in a first reaction step;
maintaining the first reaction temperature at between 350°C
and 480°C, the first reaction pressure at between 5X103 kPa and 30x10 kPa, and the first reaction time at less than 20 minutes, thereby to liquefy substantially all the coal, and to refine the coal partially;
removing some of the solvent in a solvent removal stage to produce a residual slurry which comprises mainly residual solvent and liquefied, partially refined coal, with no cooling of hydrocarbon liquid effluent before or after the solvent removal stage being effected, no hydrocarbon liquid solvent being added, to the slurry before or after the solvent removal stage and no residual slurry being recycled back to the first reaction step;
subjecting the residual slurry to a second reaction in a second reaction step, under hydrogenative conditions, maintaining the second reaction temperature at between 350°C
and 480°C with the temperature not being substantially lower than that in the first stage, the second reaction pressure at between 5x103 kPa and 30x103 kPa, and the second reaction time at between 15 and 150 minutes to refine the coal further, and removing at least some of the residual solvent, thereby producing a bottoms product which is a suitable coking feedstock capable of being formed directly by coking and calcining into coke having a coefficient of thermal expansion of less than 0,7x10-6, with none of this bottoms product being recycled to the first step.

13. A method according to Claim 12, wherein the solvent is an oil fraction having a boiling range from about 80°C to about 450°C, at least a portion of the solvent removed after the first and/or the second reaction steps being recycled to the slurrying stage so that the recycle solvent constitutes at least a portion of the solvent in the slurry.

14. A method according to Claim 12, wherein the solvent-to-coal ratio in the slurry formed in the slurrying stage is from about 1:1 to about 5:1 (on a mass basis).

15. A method according to Claim 12, which includes adding a metal-based catalyst to the solvent/coal slurry prior to subjecting it to the first reaction, the ratio of catalyst to coal being about 1:50 on a mass basis.

16. A method according to Claim 12, wherein the first reaction is also effected under hydrogenative conditions.

17. A method according to Claim 15, wherein the catalyst addition is effected in the first step and wherein the solvent removal is effected by means of distillation, the volume of solvent distilled off being such that the concentration of the catalyst in the residual slurry is at least twice the concentration of the catalyst in the slurry in the first reaction step.

18. A method according to Claim 12, wherein the reaction temperatures and pressures of the first and second reactions are substantially the same.

19. A method according to Claim 12, in which the first reaction temperature is maintained at between 350°C and 450°C.

20. A method according to Claim 19, in which the feed to the second stage is maintained at substantially the first stage effluent temperature.

21. A method according to Claim 12, in which the feed to the second stage is maintained at substantially the first stage effluent temperature.

22. A method according to Claim 12, wherein the solvent is an oil fraction having a boiling range from about 80°C to about 450°C, at least a portion of the solvent removed after the first and/or the second reaction steps being recycled to the slurrying stage so that the solvent required for the slurry comprises only recycled solvent.