Integrated two-stage coal liquefaction process

This invention relates to an improved two-stage process for the production of liquid carbonaceous fuels and solvents from carbonaceous solid fuels, especially coal.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the liquefaction of carbonaceous 
solid fuels, particularly coals enhanced with respect to production of 
liquid carbonaceous fuels and solvents. 
Many processes have been proposed for the production of low-sulfur, 
low-ash, carbonaceous fuels and distillate hydrocarbon fuels by solvent 
refining of coal in the presence of a hydrogen donor solvent. Typically, 
such a process includes the heating and liquefaction of the coal yielding 
light gases and a slurry which is further processed by vacuum distillation 
to produce a light distillate product, a recycle solvent, and a heavy 
fraction, including residual solvent, dissolved coal products, undissolved 
coal, minerals or ash materials, and unconverted coal macerals. 
It is well known that further products may be produced by subjecting the 
vacuum still bottoms to a solvent deashing process which is sometimes 
referred to as "critical solvent deashing." Such a process is disclosed in 
U.S. Pat. No. 4,070,268. As indicated in that patent, the products of the 
critical solvent deashing process include a stream (HSRC) which is rich in 
coal products soluble in pyridine, but which is essentially free of ash 
and unconverted particulate coal. A bottom stream is also produced which 
includes insoluble coal products and ash. Finally, an underflow stream of 
LSRC rich in products soluble in benzene or toluene is produced which is 
either recycled as solvent in the SRC process or removed as a product. 
As shown by U.S. Pat. No. 4,164,466, the solvent deashing stage often 
comprises several separation zones, each maintained at successively higher 
temperatures and at high pressure. This patent also discloses a process 
wherein the underflow stream of the second zone in the deashing stage is 
recycled to the entry mixing zone in the deashing stage. 
In the process disclosed in U.S. Pat. No. 4,189,372, a portion of the 
underflow from the third and fourth separators is hydrogenated and 
recycled to the coal liquefaction slurry tank. Substantially all other 
intermediate streams from the second through the fourth separators are 
recycled to the entry mixing zone of the SRC process stage as in the U.S. 
Pat. No. 4,164,466. 
In U.S. Pat. No. 4,119,523, the underflow from the first separator in the 
solvent deashing stage is extracted to separate the resulting ash and 
undissolved coal, and the remaining extract recycled to the coal 
liquefaction stage. 
U.S. Pat. No. 4,298,451 teaches the catalytic hydrocracking of a clean coal 
extract 500.degree. F.+ (260.degree. C.+). The process disclosed uses a 
catalytic ebullated bed hydrocracker maintained at a temperature of 
750.degree.-825.degree. F. (399.degree.-441.degree. C.) and a hydrogen 
pressure of 2000-3000 psi (13793-20689 Kpa). The preferred catalyst is 
NiMo. 
U.S. Pat. No. 4,111,788 teaches the hydrogenation of the total effluent of 
a non-catalytic first stage reaction in an ebullated bed catalytic 
reaction zone which consists of two reactors. The first reactor may 
comprise an ebullated bed of non-catalytic material while the second zone 
is an ebullated bed of catalyst. 
U.S. Pat. No. 4,255,248 discloses a two-stage process for the catalytic 
hydrocracking of coal in which the first stage comprises a catalytic 
reactor operating under hydrocracking conditions. 
In view of this prior art there remains a need for further varieties of 
products and enhancements to an integrated two-stage coal liquefaction 
process. 
It is, therefore, the general object of the present invention to provide 
such products and improved processes. 
BRIEF DESCRIPTION OF THE INVENTION 
The present invention involves a solvent coal refining process in which, 
following liquefaction and light gas separation, the coal slurry is 
subjected to vacuum distillation, the bottom stream of which is solvent 
deashed. This solvent deashing includes a sequence of separation steps at 
elevated temperature and pressure. 
Solvent and the "Light SRC" and "Heavy SRC" are hydrocracked on a second 
stage catalyst bed to yield commercially useful liquid fuels, solvents, 
and gases. The present invention involves an improvement in the process 
wherein substantially all the 500.degree. F.+ hydrocracker flash bottoms 
are recycled as first stage dissolver solvent, and the hydrocracker 
solvent is substantially comprised of 500.degree. F. to EP distillate from 
the first state fractionator. 
The term "Light SRC" or "LSRC" refers to and defines that SRC material 
which is comprised of approximately one-third (1/3) oils, which are 
pentane-soluble, and two-thirds (2/3) asphaltenes, which are pentane 
insoluble, benzene soluble. LSRC has a softening point of about 
180.degree. F. (82.2.degree. C.). 
The term "Heavy SRC" or "HSRC" refers to and defines that SRC material 
which is comprised of approximately equal amounts of asphaltenes which are 
pentane insoluble, benzene soluble and preasphaltenes which are benzene 
insoluble, pyridine soluble with only a trace amount (about 1%) soluble in 
pentane. HSRC has a softening point of about 380.degree. F. (193.3.degree. 
C.). 
In the present invention, coal, recycle solvent, and hydrogen are mixed, 
preheated, and reacted in a first stage dissolver vessel of a type which 
is well-known in the coal liquefaction art. The dissolver effluent, 
comprising a mixture of hydrogen, water vapor, light hydrocarbon gases, 
light oil, solvent, solvent refined coal (SRC), insoluble carbon, and ash, 
is sent to a high-pressure, high-temperature separator to remove most or 
all of the vapor-phase material for recovery as recycle hydrogen and 
condensate products. 
The underflow from the separator is directed to a distillation system for 
recovery of the process solvent and then to a critical solvent deashing 
system for separation of oils and asphaltenes from solids and 
preasphaltenes. The residue stream consisting of unconverted coal, 
minerals, and preasphaltenes is sent to a gasifier system. The Heavy SRC 
product is partially removed as product and partially combined with the 
Light SRC and directed to an ebullated bed hydrocracker and then to a 
separator which allows recovery of process solvents, products, and gases.

DETAILED DESCRIPTION OF THE INVENTION 
For a better understanding of the present invention, reference may be made 
to the detailed description which follows, taken in conjunction with the 
accompanying Figures and the claims. 
Feed coal 4, SRC solvent 79, and approximately 500.degree. F.+ hydrocracker 
flash bottoms 77 are combined to form a slurry in mix tank 5 at 
temperatures from 250.degree. F. to 450.degree. F. (232.degree. C.) in 
ratio of from 2:0:1 to 0.2:1.5:1.0 hydrocracker flash bottoms to SRC 
solvent to MF coal. 
The slurry is then passed via line 8 to preheater 10, where it is heated at 
a pressure of from 500 to 3000 psig (3448 to 20690 Kpa) to a temperature 
of from 600.degree. to 850.degree. F. (316.degree. to 454.degree. C.). 
Hydrogen-rich gas is mixed with the slurry prior to its introduction into 
the preheater via feed line 9. 
The heated and pressurized slurry is then passed via line 15 to dissolver 
18, which may consist of one or more reactor vessels operated in series or 
in parallel. Hydrogen-rich gas may be added to the dissolver via line 17 
if desired. 
The superficial flow through dissolver 18 is generally from 0.003 to 0.1 
feet per second for the gas phase. These rates are selected to ensure 
adequate mixing in the reactor. Hydrogen feed rates are maintained at 
10-40K SCF/TON coal. Residence time in dissolver 18 is greater than 40 
minutes. 
The effluent from dissolver 18 is passed to a gas separation system 26 via 
line 20. Light gases including hydrogen H.sub.2 S, CO.sub.2, NH.sub.3, 
H.sub.2 O, and C.sub.1 -C.sub.4 hydrocarbons are removed via line 24, to 
hydrogen purification system 110. The underflow from gas separator 26 is 
passed via transfer line 27 to distillation system 37. 
Distillation system 37 yields four effluent streams 79, 81, 39, and 40. 
Stream 81 is composed of 400.degree. F.- material (204.degree. C.-). 
Effluent streams 39 and 79 are composed of 400.degree. to 850.degree. F. 
material (204.degree. to 454.degree. C.). Effluent stream 40 contains SRC 
bottoms which consist primarily of 850.degree. F.+ material (454.degree. 
C.+) including SRC, unconverted coal, and ash. Stream 40 is routed to 
critical solvent deashing system 50 for subsequent processing. Stream 79 
is recycled to the mix tank 5 as solvent. 
The critical solvent deashing process is described in U.S. Pat. No. 
4,119,523. Critical solvent deashing unit 50 yields an ash concentrate 
stream 51 which is removed from the system and may be passed to equipment 
for hydrogen generation, preferably a gasifier 100. 
Critical solvent deashing unit 50 also yields effluent streams 52 and 53. 
Effluent stream 52 consists of Light SRC and is directed to hydrocracker 
60 via line 59. Effluent stream 53 consists of Heavy SRC and is partially 
directed to hydrocracker 60 via line 59 and partially removed as product 
via line 58. Distillation system effluent 39 is also sent to hydrocracker 
60 via line 59, comprising less than 50% of the hydrocracker feed. 
Hydrocracker 60 is operated as an ebullated catalyst bed at 1500.degree. to 
3500 psig (10345 to 24139 Kpa) at 700.degree. to 850.degree. F. 
(371.degree. to 454.degree. C.). The effluent stream from hydrocracker 60 
is sent via line 62 to hydrocracker flash unit 70 where recycle hydrogen 
and other light gases are transferred via line 73 to hydrogen purification 
system 110. The liquid product is flashed to separate streams boiling 
above and below 500.degree. F. (260.degree. C.), substantially all of the 
former being directed via line 77 to the first stage of the process where 
it serves as process solvent. The 500.degree. F.- stream (260.degree. C.-) 
is combined with the light distillate stream 81 and sent via line 75 to 
distillation system 80. 
Distillation system 80 produces three product streams 85, 86, and 87. 
Streams 85, 86, and 87 are typically a 350.degree. F.- stream (177.degree. 
C.-), a 350.degree. to 450.degree. F. stream (177.degree. to 232.degree. 
C.), and a 450.degree.+ stream (232.degree. C.+) or any combination 
thereof. 
The following example is an illustration of the integrated two-stage 
liquefaction process of this invention: 
Illinois No. 6 coal is slurried with hydrocracker flash bottoms and first 
stage distillation system effluent, pressurized, and pumped through the 
liquefaction reactor. The liquefaction effluent is flashed to remove light 
gases which are subsequently scrubbed to remove acidic and alkaline 
components. Hydrogen and lower hydrocarbons are recovered and recycled 
after purification to various process stages. Alternatively, these gases 
may be burned for fuel. The flash bottoms are then distilled at 
atmospheric and subatmospheric pressure. A portion of the distillation 
overhead is recovered as net product while the rest of such distillation 
overhead is used as solvent for the hydrocracker stage. 
Vacuum tower bottoms are routed to a Kerr-McGee critical solvent deashing 
unit which characteristically rejects the highest molecular weight 
refractory preasphaltenes along with unconverted coal and ash. Portions of 
the HSRC and LSRC products of the critical solvent deashing unit are 
blended together, mixed with process solvent, pressurized, and preheated 
before being sent to the hydrocracker. The products from the hydrocracking 
reactor are flashed to recover recycle hydrogen and gases which are 
fractionated and purified in the same manner as for the first stage. 
Liquid product from the flash stage is flashed again to separate streams 
boiling nominally above 500.degree. F. and below 500.degree. F. The 
500.degree. F.- stream is collected as product while the 500.degree. F.+ 
stream is recycled to the first stage to be used as process solvent. 
Table I details the process conditions for the calculated example. Table II 
details the yield structure for the calculated example. 
TABLE I 
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PDU Com- 
Process mercial 
Conditions 
Range 
______________________________________ 
SRC Unit 
Coal (MF):1st stage distillate solvent: 
1:1.1:.55 1:1.5:0.2 to 
Hydrocraker flash bottoms, wt. ratio 
1:0.0:2 
Slurry concentration, wt. % MF coal 
37.8 35-40 
Feed gas, scf/lb MF coal 
20 15-30 
Hydrogen purity, mol % 
100 80-100 
Reactor nominal residence time, min 
60 30-120 
Reactor pressure, psig 
2000 1500-2500 
Hydrogen partial pressure, inlet psia 
2000 1000-2000 
Reactor temperature, outlet .degree.F. 
810 750-840 
HTR Unit 
Feed slurry concentration, wt. % SRC 
70.0 50-80 
Space velocity (lb feed/hr) lb cat 
0.25 0.1-4.0 
Recycle gas rate, SCF/lb SRC 
30 20-40 
Hydrogen purity, mol % 
100 80-100 
Hydrogen partial pressure, inlet psia 
2000 2000-2500 
Temperature, .degree.F. 
805 700-840 
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TABLE II 
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Yield Structure 
______________________________________ 
Yields, wt. % MAF Coal 
Hydrogen consumption 
(3.9) 
Total gases 
C.sub.1 /C.sub.4 13.7 
H.sub.2 S 2.5 
CO.sub.x 1.6 
NH.sub.3 0.6 
H.sub.2 O 6.3 
Net Usable Product 
IBP-400.degree. F. 16.2 
400-500.degree. F. 8.4 
500-650.degree. F. 9.1 
650-EP 12.4 
CSD SRC 11.9 
Ash Concentrate 
SRC 14.6 
Unconverted coal 6.6 
Total 100.0 
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A necessary feature of the process integration scheme of the present 
invention is that the process solvent for the first stage includes 
substantially all of the 500.degree. F.+ hydrocracker flash bottoms. These 
hydrocracker flash bottoms are rich in asphaltenes and preasphaltenes and 
provide a substantially improved solvent quality as compared to the prior 
art. Comparative solvent qualities are illustrated in Table III. 
3 TABLE 3 
Summary of Yield Distribution Data for Kentucky #9 Mulford Coal 
Temperature, (.degree.F.) 800 800 800 800 840 840 840 760 810 810 810 
840 840 840 700 Residence Time (min)* 20 20 + 20 30 + 30 40 + 40 20 20 + 
20 30 + 30 30 + 30 20 40 30 + 30 20 20 + 20 30 + 30 30 + 30 Solvent ARS 
ARS ARS ARS ARS ARS ARS ARS BASE BASE BASE BASE BASE BASE BASE Conversion 
(% MAF Coal) 87.5 91.3 91.4 93.6 78.2 80.1 81.9 92.0 88.4 89.6 91.8 
88.0 89.5 88.2 91.5 H.sub.2 Consumption 1.4 2.1 2.9 3.1 2.0 3.4 4.1 2.0 
1.5 2.0 2.4 1.5 2.6 3.1 2.1 Yields C.sub.1 -C.sub.4 4.9 8.5 9.1 10.2 
10.3 16.2 19.1 3.2 4.4 7.2 9.3 6.3 12.3 14.9 4.9 CO + CO.sub.2 1.4 1.9 
1.7 1.6 1.8 2.3 2.2 1.4 1.5 1.8 2.0 1.6 1.7 2.2 0.5 H.sub.2 S + NH.sub.3 
1.2 1.7 1.7 1.5 1.5 2.1 2.0 1.3 1.6 2.0 2.3 1.4 2.8 2.7 1.0 H.sub.2 O 
2.9 3.1 5.0 4.7 4.5 5.0 5.9 3.8 3.2 3.6 3.0 2.2 4.0 4.9 4.4 Distillate 
12.3 23.9 33.7 39.1 12.5 16.8 25.4 28.5 17.9 20.0 26.9 15.5 20.2 22.6 
25.0 SRC 64.2 54.7 42.7 39.7 49.3 39.0 29.5 55.8 58.4 53.1 48.9 60.3 
49.0 40.9 54.5 Asphaltene 16.2 21.0 19.1 18.2 18.8 11.8 8.7 27.1 31.0 
29.1 25.3 31.0 24.6 23.0 31.2 Preasphaltene 48.0 33.7 23.5 21.5 30.5 
27.2 20.8 28.7 27.4 24.0 23.7 29.2 24.4 18.0 23.3 
Temperature, (.degree.F.) 800 840 760 800 840 760 800 840 760 800 840 
Time (min.) 20 20 20 + 20 20 + 20 20 + 20 30 + 30 30 + 30 30 + 30 70 + 
70 70 + 70 70 + 70 Solvent PRS PRS PRS PRS PRS PRS PRS PRS PRS PRS PRS 
Distillate 35.9 35.1 29.0 42.7 44.3 33.8 47.5 51.6 46.9 62.4 57.0 SRC 
41.9 37.8 53.6 35.0 23.1 45.4 28.8 13.2 32.3 10.8 7.2 Asphaltene 15.1 
11.09 20.4 15.3 10.9 21.4 16.0 8.1 22.5 6.4 7.4 Preasphaltene 26.8 25.9 
33.2 19.7 12.2 24.0 12.8 5.1 9.8 4.3 -0.3 HC Gases 3.0 6.3 2.1 6.0 12.5 
3.5 7.0 16.3 4.7 10.8 20.5 CO + CO.sub.2 1.5 2.0 1.3 2.1 2.5 1.6 2.1 2.7 
1.5 2.1 2.1 H.sub.2 S + NH.sub.3 1.6 1.8 1.4 2.1 2.5 1.6 1.5 2.6 1.9 2.6 
2.5 H.sub.2 
O 3.5 4.9 3.0 3.8 5.7 5.2 5.7 6.0 5.5 6.7 6.1 Coal Conversion 86.2 86.5 
89.2 89.7 87.9 89.2 90.1 88.9 90.5 91.8 90.2 H.sub.2 Consumption 1.4 1.7 
1.4 2.3 3.0 1..7 2.6 4.0 2.4 3.3 5.6 
*Addition of two numbers indicates two reactors in series. 
An asphaltene rich solvent (ARS) is defined as a non-integrated SRC-I 
process solvent to which 30 wt% LSRC gas been added. A presaphaltene rich 
solvent (PRS) is defined as the non-integrated SRC-I process solvent to 
which 30% HSRC has been added. The compositions of the non-integrated base 
solvent, ARS and PRS, are illustrated in Table IV. 
TABLE IV 
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Solvent 
Composition, wt. % 
Base ARS PRS 
______________________________________ 
Oils 96 85 74 
Asphaltenes 4 13 16 
Preasphaltenes 0 2 10 
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In each case, Kentucky No. 9 Mulford coal was slurried with each solvent 
and reacted at a range of dissolver operating conditions. These conditions 
and the product yields achieved for each are reported in Table III. The 
yields are graphically represented as FIG. 2. Clearly, FIG. 2 demonstrates 
that recycle of asphaltenes and preasphaltenes to the dissolver stage 
improves distillate yield substantially. 
Several important facets of the integrated two stage liquefaction process 
of this invention are demonstrated by the results achieved in Wilsonville 
Run No. 242 which was reported in "Technical Progress Report Run 242, with 
Illinois #6 Coal," DOE/PC/50041-19. 
Illinois No. 6 coal was slurried with hydrotreated flash bottoms, 
pressurized, and pumped through the liquefaction reactor. The liquefaction 
effluent was flashed to remove light gases which were scrubbed to remove 
acidic and alkaline components. The hydrogen and lighter hydrocarbons were 
recovered and recycled to various process stages or burned for fuel. The 
flash bottoms were then distilled at atmospheric and reduced pressure. 
Some of the distillation overhead was recovered as net product while the 
rest was used as solvent in the hydrocracker. The vacuum tower bottoms 
were routed to the Kerr-McGee critical solvent deashing unit where ash and 
unconverted coal were removed. The HSRC and LSRC products of the CSD were 
blended, mixed with process solvent from the SRC unit, pressurized, and 
preheated before being sent to the ebullated bed hydrocracker. The 
products from the hydrocracking reactor were flashed to recover recycle 
hydrogen and processed gas which were fractionated and purified in the 
same manner as in the SRC area. The liquid product from the flash stages 
was flashed again to separate a stream boiling nominally above 500.degree. 
F. from a stream boiling below 500.degree. F. The 500.degree. F.- stream 
was collected as product, and the 500.degree. F.+ stream was recycled to 
the first stage to be used as process solvent. The process conditions for 
the example are presented in Table V and the yield structure is given in 
Table VI. 
TABLE V 
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Process Conditions for Wilsonville Run 242 
______________________________________ 
Material Balance 242A - 12/10/82 
SRC Unit 
Coal (MF):first stage distillate solvent: 
1:0:0.0:2.0 
Hydrocracker flash bottoms ratio 
Slurry concentration, wt. % MF coal 
36.4 
Feed gas, scfh 3,650 
Hydrogen purity, mol % 90.1 
Reactor coal space, rate, lb/hr-ft.sup.3 
38.5 
Reactor pressure, psig 2,410 
Hydrogen partial pressure, inlet psia 
2,150 
Reactor temperature, outlet .degree.F. 
859 
HTR Unit 
Feed slurry concentration, wt. % SRC 
50.1 
Space velocity (lb feed/hr) lb cat 
1.08 
Recycle gas rate, MSCF/ton SRC 
62.6 
Hydrogen purity, mol % 95.9 
Hydrogen partial pressure, inlet psia 
2,721 
Temperature, .degree.F. 
680 
______________________________________ 
TABLE VI 
______________________________________ 
Yield Structure for Wilsonville Run 242 
______________________________________ 
Material Balance 242A - 12/10/82 
Yields, wt. % MAF Coal 
Hydrogen consumption (3.85) 
Total gases 
C.sub.1 /C.sub.5 4.72 
H.sub.2 S 2.11 
CO.sub.x 1.20 
NH.sub.3 0.76 
H.sub.2 O 8.22 
Net Usable Product 
ibp-350.degree. F. 5.85 
350.degree.-450.degree. F. 
5.70 
450.degree. F.-EP 43.38 
HTR SRC 9.60 
Ash Concentrate 
450.degree. F.- EP 0.72 
SRC 8.36 
Unconverted coal 13.22 
Total 100.01 
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