CA1116639A - Synthetic liquid fuels - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An economical, efficient process is provided employing coal, particularly subbituminous coal, as a fuel source for the production of distillate fuels and methanol.
A hydroliquefier is operated under severe conditions to provide a high net yield of light distillates. The vacuum residue, which is produced above, is transferred as a slurry to a partial oxidation gasifier where synthesis gas is produced as feedstock for methanol synthesis. Gaseous hydrocarbon contaminants are separated and used to generate additional synthesis gas, or to supply other fuel requirements.

Description

~6~3g . BACKGROUND OF THE INVENTION
. Field of the Invention .
There is a continuing interest in the upgrading of fuels, particularly coal, to provide fuels having a wide variety of applications and coming within specified standards, such as environmental standards, physical standards~ and the like. Because of the relatively : large supplies of coal, much attention has been focused on the use of coal to replace oil. Bituminous and subbituminous coal has only limited utility as obtained from mining operation. The coal has substantial sulfur, nitrogen and inorganics, such as calcium salts. In order to fulfill environmental standards, it is necessary to remove substantial amounts of the sulfur and nitrogen. Since . calcium and other inorganics have no fuel value, they . .~

~ 11~6639 1 ¦ act to reduce the heat content per unit weight of coal and

2 are contaminants which must be removed from a combustion

3 zone and may interfere with the proper operation of the fuel

4 combustion. In addition, in many generation operations it ~¦ is desirous to have a liquid, rather than a solid fuel.
61 In any refining of coal to upgrade the coal to an 7 ¦ acceptable fuel, it is essential that the system be economical 8 ¦and efficient and, whenever possible, provide at least a 9 ¦portion of the materials necessary for the processing. In 10 ¦ addition, it is desirable to produce products which have 11 ¦high economic value in comparison to the original coal 12 value.
13 Description of the Prior Art 14 ¦ U.S. Patent No. 3,888,896 describes a liquid phase 15 ¦methanol synthesis process. U.S. Patent Nos. 3,816,322 and 16 ¦ 3,764,547, and patents cited therein, describe a partial 17 ¦oxidizer gasifier.

19 ¦ SU~ARY OF THE INVENTION
20 ¦ A process is provided for the economic and efficient 21 ¦upgrading of coal to a clean, light distillate fuel, a heavy 22 ¦fuel and methanol. Coal is solvent refined under severe 23 ¦conditions, preferably in a hydrogen environment, to provide 24 la substantially liquid product, which is divided in a separa-25 ¦tion zone to a light distillate product, recycle solvent, a 26 ¦heavy fuel, and a vacuum residue slurry. The vacuum residue 27 ¦slurry provides an efficient feed for a partial oxidation 28 ¦gasifier which produces synthesis gas as-a feed for me-thanol 29 ¦production and to supply hydrogen to the above liquefier.

f ~1~6639 -1 ¦ Hydrocarbon contaminants in the synthesis gas feed are 2 1 returned to the gasifier or otherwise processed for conversion 3 ¦ to additional synthesis gas. The heavy fuel may be used for 4 ¦ in-plant fuel requirements. Alternately, the hydrocarbon ¦ gases may be used for in-plant fuel and the heavy fuel 6 ¦ gasified with the vacuum residue.

8 BRIEF DESCRIPTION OF THE DRA~ G
9 Fig. l is a diagrammatic view of a process accord-ing to the subject invention.

12 DESCRIPTION OF THE SPECIFIC EMsoDIMENTs 13 The process of the subject invèntion is concerned 14 with the efficient and economical production of light distillate and methanol or methane. Coal, particularly bituminous or 16 subbituminous coal, and preferably the latter, are employed I7 as the raw material.
18 In carrying out the process, a hydroliquefier is 19 employed, whereby coal is contacted with hydrogen and recycle solven-t under severe conditions to produce high yields of 21 light distillate. The gaseous fraction is taken overhead, 22 and hydrogen recycled to the hydroliquefier. The liquid 23 fraction is transferred to a separation zone and divided 24 into a light distillate fraction, a heavy distillate fraction~
and a vacuum residue slurry. The light distillate fraction 26 is a clean fuel. The heavy dis-tillate fraction may be 27 employed internally as a heat source, may be fed to the 28 gasifier along with the vacuum bottoms, may be further 29 hydrocracked into ligh-t distillates, or stored and used for 1~ 39 ,j 1 other purposes. The residue serves as a feed stock for a 2 partial oxidizer gasifier which provides the synthesis gas 3 feed stock for methanol production. Any hydrocarbon impurities 4 from the methanol may be separated and returned to the gasifier, used as fuel gas, or steam-reformed to make addi-6 tional synthesis gas.
The first stage of the process is the hydroliquefier.
8 The hydroliquefier employs finely comminuted coal and hydrogen 9 donor solvent as a feedstock. Various processes for liquefy-ing coal may be found in a wide varie-ty of patents. See for 11 example U.S. Patent Nos. 3,536,608 and 3,700,584.
12 In the subject invention, various bituminous coals 13 may be employed, but subbituminous coal is preferred, because 14 it provides a high yield of light distillate, which is low in sulfur and nitrogen. The comminuted coal will generaliy 16 be less than about one-quarter inch in diameter, more 17 usually less than one-eighth inch, and generally from about 18 20 to 200 Tyler mesh, more usually about 40 to l00 Tyler 19 mesh. The size of the coal particles is not critical to this invention, and substantial variation is permitted.
21 The hydrogen donor solvent is primarily partially 22 hydrogenated aromatic hydrocarbons. Mixtures of hydrocarbons 23 are generally employed, usually boiling in the range of 2~ about 260-425C. Examples of suitable solvent components are tetralin, decalin, biphenyl, methylnaphthalene, etc.
26 Other types of solvents which may be added to the preferred 27 solvents or may be present as part of the recycle stream 28 include phenols such as phenol and cresol. The solvent may 29 be hydrogen treated prior to introduction into the hydroliquefier to enhance the hydrogen donor capacity.
31 The operating conditions of the hydroliquefier are 32 s~ve e so d o enh~nce the pro~uction oE light distillates.

I ' 1~663~ ', `

1 The liquefier will normally be operated at temperatures 2 between about 700F and 900F, more usually between about 3 825-900F and at pressures from about 200 to 4,000 psig.
4 Reactor space rates will generally be in the range of 5 to 500 pounds oE coal per hour per cubic foot of reactor volume, 6 more usually 5 to 40 pounds of coal per hour per cubic foot 7 of reactor volume. ~hile in some instances, catalysts may 8 be added, such as oxldes or sulfides of nickel, molybdenum, 9 cobalt, and the like, supported on a high surface area alumina or silica alumina bar, normally the process will be 11 noncatalytic.
12 The process may be carried out in the presence or 13 absence of hydrogen. Where hydrogen is employed, the amount 14 of hydrogen will generally vary from about 5 to 50 scf per pound of coal.
16 The weight ratio of solvent to coal will generally 17 be in the range of about 1 to 10:1, preferably 1-3:1, and 18 particularly preferred 1.5-2:1.
19 The gas which exits from the hydroliquefier will be a mixture primarily of hydrogen sulfide, carbon dioxide, 21 water, methane, and hydrogen. By employing conventional 22 scubbing techniqu~os, the hydrogen can be purified of the 23 other gases and recycled to the hydroliquefier.
24 The substantially liquid effluent from the hydro-liquefier will be transferred to a separation zone, normally 26 a distillation section, and preferably, one which includes a 27 vacuum distilla-tion column. The hydroliquefier effluent 28 will be divided into four fractions, light distillate, 29 recycle solvent, heavy distillate, and vacuum bottoms.
Preferably, the separation is carried out in two stages, (- ~:116639 (-¦ where the distillate is divided into two fractions the first 21 fraction boiling up to 650F and the second fraction boiling 3 ¦ between about 650F and 950F. The lower boiling fraction 4 ¦ is then further separated into recycle solvent and light

5 ¦ distillate, The quantity of vacuum bottoms will be such

6 ¦ that when gasified, as described below, will supply a sub-

7 ¦ stantial excess of gas over that which is required for the

8 manufacture of make up hydrogen for the liquefier.

9 Based on the coal (dry ash free basis~, the yield of light distillates will be in the range of about 15 to 45, 11 usually in the range of about 17 to 40 weight percent, and 12 the stream of vacuum bottoms will be in the range of about 13 40 to 80, usually in the range of about 44 to 75 weight 14 percent.
Without any further processing, the residue from 16 the separation zone is employed as a feedstock for a partial 17 oxidizer gasifier. This type of gasifier which produces 18 synthesis gas has been described extensively in the patent 19 literature. ~arious special techniques may be employed as described in U.S. Patent Nos. 3,528,930, 3,816,332 and 21 patents cited therein. Therefore, only a brief description 22 of the process will be provided.
23 The residue, containing ash, is fed to the partial 24 oxidizer and reacted with oxygen and steam in a closed reaction zone at an autogeneous temperature within a range 26 of about 1,800F to 3,000F, usually about 2,20QF to 2,800F.
2~ The residue and steam are generally preheated to about 28 500F, usually at least 600F. The reactor zone pressure is 29 generally about 600 to 1,000 psig, although a pressure of 3 ~ u to 3,00 psiy s pos-ible.

~1 iL116~39 ( I
1 ¦ The products from the gasifier are carbon mono~ide 21 and hydrogen, containing small amounts of carbon dioxide, 3 ¦ methane and entrained carbon. The entrained carbon may be 4 ¦ removed by conventional methods and the gas stream transferred 5 ¦ to a methanol synthesizer.
6 ¦ The hydrogen-to-carbon monoxide ratio of the above 7 ¦ gas will be shifted to increase the proportion of hydrogen.
8 The means for doing this are conventional and will be apparent 9 to one skilled in process engineering design. The acid gases will be removed.
11 In the shift process, the synthesis gas is 12 contacted with water under conditions where carbon monoxide ~3 reacts with the water to produce hydrogen and carbon dioxide.
14 The hydrogen rich stream is then split, a portion employed for make-up hydrogen for the liquefier and the remaining 16 portion combined with the gasifier stream to provide at 17 least the stoichiometric requirements for methanol or methane ~8 production, 2 and 3 molar proportion respectively.
19 ~hile various processes for the synthesis of methanol may be employed, the preferred process is found in 21 U.S. Patent No. 3,888,896, which is illustrative of me~thanol 22 production from synthesis gas. The specific process carries 23 out the methanol synthesis in 2 liquid medium. Br1efly, 24 polyalkylbenzenes are used as a liquid medium and boil from about 100C to 250C, although other liquids may also be 26 included. The reaction temperature employed ranges rom 2~ about 200F to 950F, usually from about 400F to 750F, 28 with pressures ~rom about 200 to lO,000 psia, usually from 29 about 500 to 3,500 psia. ~lormally, hydrogcn will be in excess 31 .

,' ~1 ~. ~f 1 of the stoichiometric requirement, usually not more than 5, 2 more usually not more than 4 times stoichiometric. The flow 3 ¦ rate of reactants will generally be from about O.l to lO
4 1 pounds of feed per pound of catalyst per hour more usually ~ ¦ about 0.5 to 5 pounds of feed per pound of catalyst per 6 hour.
7 Any conventional methanol forming catalyst may be 8 employed, for example, a copper, chromium and zinc catalyst 9 as described in U.S. Patent No. 3,326,956.
The methanol stream which exits from the methanol 11 synthesizer will generally be contaminated with low molecular 12 weight volatile hydrocarbons. These may be readily separated 13 from methanol and the hydrocarbons returned to the gasifier.
14 Alternatively, where the stoichiometry does not provide for complete reduction of the carbon monoxide, the unconverted 1~ reactants in the exiting gas stream may be employed directly 17 for generation of elec-tric power or for fuel. Alternatively, 18 a side stream may be taken from the gasifier effluent to be 19 used for the direct generation of electric power. In addi-tion, the hydrocarbon purge from the methanol unit may be 21 steam reformed to make synthesis gas, which may be then 22 cycled to the methanol synthesis unit, rather than recycling 23 the hydrocarbon purge to the gasifier unit.
24 The methanol produced from excess gasification products will generally be in the range of about 35 to 80, 26 usually 40 to 60% of the total heating value of the fuel 27 ducts.

32 ;

1 In a further variation, the methanol synthesis 2 unit may be replaced with a methane synthesis unit, so that 3 methane rather than methanol is prepared, which may then be 4 used as a fuel.
31 For further understanding of the invention, the 6 ¦ drawing will now be considered.
7 ¦ Coal (2) and recycle solvent (30) are slurried 8 ¦ together in slurry preparation section (4), the coal being 9 ¦ relatively dry and in finely comminuted form. The slurry is

10 ¦ mixed with fresh hydrogen (82) and recycle gas (23) at the

11 ¦ preheater (6). The heated products (7) flow to the liquefier

12 (8). The liquefier product (9) is separated into vapors (14)

13 and liquids (12) in the hot vapor/liquid separator (10).

14 The liquid product (12) is fed to a vacuum still (13). The vapor products (14) are cooled and flow to a separator (20) 16 wherein the fixed gases (21) are separated from water (19) 17 and condensed hydrocarbons (26).
18 The overhead products (24) from the vacuum still 19 (13) are mixed with the condensed hydrocarbons (26) and these are fed to an atmospheric fractionation section (28).
21 Three products are taken from the atmospheric fractionation, 22 namely: 400 x 950F recycle solvent (30), optional heavy 23 fuel (32) and net clean distillate product (34). The optional 24 heavy fuel (32) may be absent depending upon the desired product slate. The vacuum still may be operated to leave 26 this cut in the vacuum bottoms (i.e., slurry feed (36) to 27 the gasifier (42).
28 The overhead product (21) from the separator (20) 29 is split partially into recycle gas (23~ and purge gas (22).
33l Stream (22), above, will be of such quantity to control 11 ~ ~39 1 the build up of impurities in the liquefier feed gas and 2 provide the desired partial pressure of hydrogen in the 3 liquefier. Stream (22) will contain hydrogen as well as 4 ¦hydrocarbon gases, carbon monoxide, carbon dioxide, hydrogen 5 ¦sulfide and other impurities. This stream may be admixed 6 with the gasifier output (50) or may alternately be used as 7 a source of fuel gas.
8 The vacuum bottoms product (36) and optionally 9 purge gas stream (46) are fed to partial oxidation gasifiers (42) along with oxygen (40) and steam (44). Synthesis gas 11 consisting principally of carbon monoxide, hydrogen and acid 12 impurities (CO2, H2S, COS) is the product (50). The acid 13 gas impurities are removed in section (56). It may optionally 14 be desired to concurrently remove hydrocarbon impurities if a physical absorption system is used for acid gas removal.
16 If this were done, part or all of stream (48) would be 17 removed as a stream from block (56) rather than from the 18 methanol synthesis purge (46). A portion of the clean gas lQ stream (62) is shifted to form relatively pure hydrogen in blocks (68) and (72). An aliquot of the hydrogen (82) is 21 returned to the coal liquefaction section. The remainder of 22 the gas (66) is remixed ~ith unshifted gas to form the 23 methanol synthesis gas feed (76). The split between streams 24 (62) and (64) is chosen to be such that stream (76) has a 2~ molar ratio of H2/CO being approximately equal to 2. The 26 hydrogen and CO are converted to methanol in block (78) from 27 which impurities emerge as stream (~6) and alcohol product 28 as stream (80).
29 In the above description, it should be understcod that the key process steps have been described in their 31 concept, and that one ckilled in the engineering design of 11166;~9 ~ ~

1 process plants would recognize engineering alternatives for 2 carrying out the same process steps. In particular, it will 3 be important to the overall economics of the process to 4 efficiently recover energy (heat) from streams being cooled and to utilize this energy to offset other process require-6 ments. The particular choice of such items will be apparent 7 to one skilled in the art.
8 In the subject process, coal is transformed into 9 a number of high quality fuels and chemicals by means of an economical and efficient process. Rather than using the 11 coal directly in a gasifier to produce carbon monoxide and 12 hydrogen, the process first hydroliquefies the coal under 13 severe conditions, so as to give a high yield of light 14 distillate fraction. In addition, the process provides hydrogen for the hydroliquefaction of coal and fuel for 16 operation of the plant. The vacuum residual, which is a I7 pumpable slurry at elevated temperature, is employed for the 18 production of synthesis gas anc utlimate production of 19 methanol. Alternatively, the process can be easily modified to produce methane rather than methanol. A key feature of 21 the process is the coproduction of distillates and methanol 22 (or alterna-tely methane) in significant hish yields.
23 The process can easily acco~!odate an increased 24 yield of methanol if this is desired. The slurry feed to 2~ the gasifier (36) is capable of accepting additional solid 26 hydrocarbons, such as coal, while still maintaining its 27 slurry character. A substantial quantity of coal, equal to Z8 30~ or more by weight of stream (36), may be added. This is 29 demonstrated in Example 4, below.

~ 6639 1 The subject process demonstrates how the hydrogen 2 and carbon values of coal can be upgraded to provide useful 3 fuels and chemicals. The various products derivable from 4 coal are integrated into a single system to produce a ~ ¦ spectrum of products, which either may be used in-ternally or 6 ¦ provide high grade fuels or raw materials for further 7 ¦ processing.
8 ¦ For purposes of illustration, the following 9 ¦ examples demonstrate the operation and benefits of the 10 1 subject invention.
11 ¦ Example l - Hydroliquefaction 12 Subbituminous coal( ) from the Wyodak Mine 13 located in Campbell County Wyoming ~Wyokak - Anderson 14 Seam) was liquefied in a continuous apparatus with conditions and yields as follows: -16 Coal Analysis ~7 Moisture, W% 6.4 18 Proximate, W% (dry) 19 Ash 7.0 Volatile Matter 46.5 21 Fixed Carbon 46.5 22 Ultimate, W% (dry) 23 Carbon 67.8 24 Hydrogen 5.0 Nitrogen 0.8 26 Sulfur 0.8 27 Ash 7 0 28 Oxygen (by difference)18.6 29 Heating Value (dry basis) ll,480 Btf/pound.
(l)Johanson, Edwin, So]vent Refining of Wyodak, Illinois 6, and Black Mesa Coals, EPRI RP389 (vol. 2), Electric Power Research 31 Institute, Palo Alto, California, February 1976 (Data quoted are Run 177-114) lZ

~ fi.~

21 Run Conditions 3 ¦ Coal Space Rate lb of dry coal 32 32 4 ¦ hr - Ft 5 ¦ Recycle Solvent to Coal, wt ratio 2 2 6 Temperature, F 840 835 7 Pressure, psig (pure H2 feed gas)2500 2000 8 ¦- Type of reactor Perfectly mixed flow 9 ¦ Yields, Wei~ht % of MAF(l)Coal 0 l CO2 8.25 5.84 11 I CO .61 1.77 12 I Cl x C3 9.10 5.70 13 ¦ C4 x 350F 8.23 8.28 14 ¦ 350 x 650F 11.53 8.81

15 ¦ 650 x 950F 10.01 13.08

16 ¦ + 950F Residuum Oil 36.99 34.94

17 ¦ MAF Unconverted Coal 7.38 13.19

18 ¦ H2O 10.66 10.66

19 ¦ NH3 .24 .13

20 ¦ H2S 50 47

21 ¦Total (100+ Hydrogen reacted) 103.50 102.87

22

23 )Molsture and ash free.

32 l3 I f-1 ¦ Properties of Produets, W%
2 C 4 x 350 F
3 ~ Sulfur 0.09 ~
4 ~ Nitrogen 0.06 - -~1 6 ¦ 350 x 650F
7 ¦ % Sulfur 0.40 8 ¦ % Nitrogen 0.30 10 ¦ EXAMPLE 2 - GASIFICATION OF HYDROLIQUEFACTION VACUUM

12 Vacuum bottoms slurries from hydroliquefaction 13 processing Wyodak Coal (2) were gasified in a 14 Texaco partial oxidation gasifier. Summarized results are as follows:

17 Cold Gas Efficieney - 85 18 (Gross heating value of the 19 synthesis gas as a fraetion of gross heating value of 21 the feed) 22 SCF of Oxygen 23 Oxygen Consumption --270 SCF of 2

24 SCF of CO ~ H2 2~ EXAMPLE 3 - Integration of Liquefaction and Gasification 26 and Methanol Synthesis 27 Based on the above, Examples l and 2, the follow-28 ing yields are projected for their combination in accord with 29 Figure l (Run 22 of Example l), wherein streams 48 and 54 are null.
31 ( )Robin, Allen M., Hydroyen Production from Coal Liquefaction Residue, EPRI AF-233 Final Report, ~lectric Power Research 32 ~ te ~` 1116639 ~

21 Yields, per 100 3tu net ~lower) heating value of coal.

3 C4 x 350F Distillate 12.8 Btu (LHV) 4 350 x 650F Distillate 17.3 Btu (LHV) 650 x 950F Distillate 15.5 Btu (LHV) 6 Methanol 34.6 Btu (LHV) 7 ¦ Total 80.2 9 ¦ OXYGEN REQUIRED 0.05 SCF
10 l 11 ¦ For comparison, if methanol were produced from coal 12 ¦ directly by partial oxidation, with feed in a water slurry, 13 the products would be approximately 55 to 60 Btu of methanol 14 ~LHV) per 100 Btu of feed coal (LHV), and the oxygen con-sumption would be more than twice as high.
16 In both of the above cases, the internal plant 17 fuel requirements have not been considered. The net plant 18 fuel requirements are about equal for the two cases.
19 The advantages of the subject invention with regard plant efficiency are thus readily apparent.

23 The following data illustrates the fluidity of 24 vacuum bo-ttoms from processing of subbituminous coal and admixtures of that coal with the vacuum bottoms at 600F
26 Vacuum Bottoms - 0.4 poise 27 30% Coal/70% Vacuum Bottoms - 11.0 poise 28 Although the foregoing invention has been des-29 cribed in some detail by way of illustration and example 301 for purposes of clarity of understanding, it will be obvious 1l f- ~11663!9 ~`

1¦ that certain changes and modifications may be practiced 21 within the scope of the invention as limited only by the ~¦ scope of t appended claims.

~2

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A highly efficient method of producing methanol and other valuable products which comprises:
(a) in a hydroliquefaction zone liquefying coal by contacting comminuted coal with hydrogen and a hydrogen donor recycle solvent boiling in the range of 400°-950°F under con-ditions comprising temperatures in the range of 700° to 900°F
and pressures in the range of 600 to 3000 psig to produce a high yield of light distillates boiling below about 650°F, said yield of light distillates comprising from about 15 to 45 weight per cent of the coal, whereby a substantially gaseous effluent and a substantially liquid effluent are obtained;
(b) transferring said liquid effluent to a vacuum dis-tillation separation zone and distilling said liquid effluent into a light distillate fraction, a recycle solvent fraction, a heavy distillate fraction, and a substantial quantity of vacuum bottoms slurry, the quantity of which, when gasified, will supply sub-stantially more gas than is required for producing hydrogen for the hydroliquefier;
(c) pumping said vacuum bottoms slurry into a partial oxidation gasifier and transforming said bottoms to synthesis gas consisting essentially of carbon monoxide and hydrogen;
(d) shifting the hydrogen to carbon monoxide ratio of the said synthesis gas to produce a hydrogen enriched gas and removing the acid gases therefrom;
(e) recycling a portion of the hydrogen enriched gas from said synthesis gas to the hydroliquefier;
(f) reacting the remainder of said synthesis gas to produce methanol or methane;
(g) recycling said recycle solvent to said hydro-liquefaction zone.

2. A method according to claim 1 where the yield of light distillates comprises from about 15 to 45% of the coal (dry ash free basis), and the stream of vacuum bottoms comprises from about 40 to 80% of said coal, and where methanol is produced from excess gasification products and amounts to from about 35 to 80% of the tctal heating value of the fuel products.

3. A method according to claim 2 where the coal is subbituminous coal.

4. A method according to claim 3 where the heavy dis-tillate fraction is included in the vacuum bottoms slurry.

5. A method according to claim 3 wherein the conversion of carbon monoxide and hydrogen to methanol is incomplete, and the unconverted carbon monoxide and hydrogen are burned for the generation of electric power.