US 3375188 A
Description (OCR text may contain errors)
March 26, 1968 w. J. BLOOMER 3,375,188
PROCESS FOR DEASHING COAL IN THE ABSENCE OF ADDED HYDROGEN Original Filed Nov. 26, 1963 mmNEbJOm INVENTOR W.J. BLOOMER ATTORNEY United States Patent 3,375,188 I PROCESS FOR DEASHING COAL IN THE ABSENCE OF ADDED HYDROGEN Ward J. Bloomer, Westfield, N.J., assignor to The Lummus Company, New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 326,030, Nov. 26, 1963. This application Dec. 19, 1966, Ser. No. 603,053 8 Claims. (Cl. 208-8) This application is a continuation of application Ser. No. 326,030 filed Nov. 26, 1963, now abandoned.
This invention relates to a process for producing useful carbonaceous matter from coal and more particularly relates to the production of substantially ash-free coke from a coal selected from the group consisting of bituminous coal, subbituminous coal and lignite, and is an improvement of the process described in co-pending application, Ser. No. 831,310, filed Aug. 3, 1960, now abandoned.
In accordance with the process described in the aforementioned application, a coal selected from the group consisting of bituminous, subbituminous and lignite is contacted with a high boiling solvent of high aromaticity having an initial boiling point from about 650 F. to about 850 F. to form a coal solution, which is a homogeneous solution of the extractable, carbonaceous material. Solvation or digestion of the carbonaceous material present in the raw coal is effected at a temperature of about 600 to 850 F. at a preferred pressure of from 1 to 5 atmospheres with a solvent to coal ratio of from /211 to 6: 1. Under such conditions, the cyclic three dimensional structures of the components of the coal are thermally depolymerized with the resulting constituents being soluble in the solvent. F-usain and mineral matter or ash are substantially unaffected by the solvent and particles containing such insoluble constitutents are suspended in the coal solution.
The coal solution including undissolved solids while in a free flowing state is filtered at a temperature of from 400 to 700 F. to separate such undissolved solids from the coal solution.
The filtered coal solution is thereafter heated to a temperature above its incipient coking temperature, i.e., a temperature of about 850 to about 1050 F. The heated coal solution is thereafter coked in a delayed coking unit to form a substantially ash-free coke having a range of a volatile matter of from about 4 to 16 percent. The overhead from the coking unit is introduced into a fractionating unit and separated to provide, as tower bottoms, a high-boiling liquid solvent having an initial boiling temperature of from 650 to 850 F. which is utilized to effect solvation of the coal. The fractionating unit is preferably operated at pressures of from 1 to 5 atmospheres.
It is a principal object of my invention to provide an improved method for producing substantially ash-free coke from coals selected from the group consisting of bituminous coal, subbituminous coal and lignite.
It is still a further object of my invention to provide an improved method for producing substantially ashfree coke and' valuable products such as gas, aromatic solvents, oils and ammonia from such a coal.
It is still a further object of my invention to provide an improved closed cycle process for continuously preparing substantially ash-free coke from a de-ashed solution of carbonaceous material whereby a substantially st'oichiometric solution of the extractable carbonaceous matter in the coal is effected.
Still another object of my invention is to provide an improved process for preparing substantially ash-free coke from a de-ashed coal solution whereby higher yields of 3,375,188 Patented Mar. 26, 1968 ice carbonaceous material are recovered from the coal than heretofore obtained.
An additional object of my invention is to provide an improved process for producing ash-free coke from a de-ashed coal solution utilizing a solvent having a boiling range within cutpoints of from about 600 to 900 F., whereby such solvent is highly refractory and is not adversely effected by coking operations, and is substantially completely recoverable for reuse.
Further objects and a fuller understanding of my invention may be had by referring to the following description taken in conjunction with an accompanying drawing in which the figure is a schematic flow-diagram illustrating a preferred embodiment of the invention for producing substantially ash-free coke.
In accordance with my invention, the raw coal is first crushed and ground in conventional crushing and grinding equipment to form particles having a particle size distribution in the range up to 10 mm., however, it is preferable to have a particle size distribution whereby a major portion of the particles will pass through a #100 mesh screen. Thereafter, the raw coal is treated with a high boiling liquid solvent having cutpoints of from about 600 to 900 F., predominantly containing angular polycyclic condensed ring aromatic compounds whereby the carbonaceous material present in the coal forms with such solvent a homogeneous solution of such extractable carbonaceous material (hereinafter referred to as coal solution). The fusain and mineral matter or ash are not effected by the solvent and particles containing such insoluble constituents are suspended in the coal solution.
The coal solution is thereafter filtered and coked in a manner similar to the coal solutions of the aforementioned copending application. A side out having cu points from about 600 to 900 F. is withdrawn from the combination tower and constitutes the solvent utilized for the coal solvation.
It is known that the effective solvents for coal are those that have an angular configuration of the rings, like phenanthene, and that boil above 300 C. (572 F). Non-angular, or linear, condensed ring systems, such as anthracene, to the contrary have a greatly reduced selective solvent action on the constituents of coal that act as binding agents for the inicellar portion of the coal. It is this removal of the binding material that leads to the complete disintegration of the colloidal nature of the coal, and peptization of the micelles in the solvent.
Thus, the angular-ringed phenanthr'ene (b.p., 644 F.) has an extraction efficiency for the coal carbonaceous material of about 95% of the ash-free coal, whereas the linear structure of anthracene yields only an approximate 24% recovery on the same basis.
Coal carbonization crude tar fractions, such as anthracene oil, contain appreciable quantities of both anthracene and phenantlirene, and by virtue of the latter components, are good solvents. This aromatic oil might typically boil between 520 and 750 F. However, I have discovered by utilization of a solvent having cutpoints (converted to one atmosphere) of from 600 to 900 P. which is derived from a coal tar pitch, that efficient solution is effected through use of the higher boiling alkylated homologues of phenanthrene and similarly high boiling polycyclic condensed aromatic ring compounds of angular structure. It will become apparent that the solvent is comprised of materials boiling Within the range of these cutpoints.
One important advantage of the solvent is that extraction eflicie'ncy increases through repeated use of the solvent, since the refractory nature of the solvent is improved with each pass through the process. Additionally, the use of such refractorized solvent also permits complete separation of the original solvent from the coal extract or from the coker cracked total liquids product. The reason for the increases in the extraction efficiency is the increase in the refractory nature of the solvent by a decrease in the undersirable anthracene and higher boiling linear homologues content, thereby resulting in a final, stable, totally recoverable solvent of highest solvency. This improved solvent is now capable of complete recovery from its solution at temperatures of 780 F. and above, free from losses by polymerization of the heavy ends. Further, it is now so completely temperature refractory that it is recovered substantially quantitatively from either the de-ashed coal solution, or from the much more severely cracked liquid product of the deashed coal solution delayed coking operation which is conducted at temperatures of 900 F. and above.
It is understood that other refractory polycyclic aro' matic solvents obtained from petroleum catalytic and thermal cracking operations can also be utilized in the process and that extraction efficiency of such a solvent would similarly increase by improving the refractory nature of the solvent by each pass through of the p cess until a totally recoverable solvent is obtained, of highest solvency.
Referring to the drawing, raw coal, selected from the group consisting of bituminous coal, subbituminous c al and lignite, and/ or mixtures thereof, is crushed and ground in conventional crushing and grinding equipment (not shown). The particle size distribution may range up to 10 mm.', however, a particle size distribution is preferred whereby a major portion of the coal particles pass through a #100 mesh screen.
The ground or pulverized coal is collected in a hopper 1, from which it is continuously distributed at a desired rate by a conveying mechanism 2 into a solutizer tank 3 maintained at a pressure of from about 1 to atmospheres. As illustrated, conveying mechanism 2 is a screw type feeder which introduces the coal into solutizer 3 without loss of pressure therein. Any conventional means of mechanical transfer may suffice, providing the means allows for positive transfer of the coal into solutizer 3 without a substantial loss of pressure therein.
The high boiling liquid solvent having cutpoints of from about 600 to about 900 F. is introduced into solutizer 3 through line 4 at a rate so as to provide a ratio of solvent to coal of from 1/2:] to 6:1. Normally, a solvent to coal ratio of from about 1:1 to about 3:1 is preferred, since effective extraction rates are obtained within this ratio range while minimizing filtration costs. Solutizer 3 is maintained at a temperature of from about 600 to about 850 F., preferably of from 750 to 800 F., and at a pressure of about 1 to atmospheres, whereby substantially all of the extractable carbonaceous matter present in the raw coal is thermally depolymerized. The products of depolymerization are soluble in the solvent and thereby form, with the solvent, a homogeneous coal solution. Insoluble solids including mineral matter or ash mineral charcoal or fusain are suspended in the coal solution. An agitator (not shown) may be provided to agitate the coal-solvent mixture during solvation.
Solvation temperatures are maintained in solutizer 3 by withdrawing and circulating a portion of the coal solution and/or coal-solvent mixture through an external heating system. The withdrawn portion is passed through line 5 by pump 6 under the control of valve 7 to heater 8 and thereafter re-introduced through line 9 into solutizer 3. In this manner, solvation temperatures are maintained within solutizer 3 without the necessity of a high pressure heating system which would be the case if the solvent was preheated to a temperature sufiicient to maintain solvation temperatures within the solutizer.
A through-put time of the raw coal of from about 3 to 120 minutes is normally sufiicient to effectively and efiiciently dissolve or digest the extractable carbonaceous matter. Since the solvent has an initial cutpoint (converted to one atmosphere) of 600 F., whereas solvation temperatures may be as high as 850 F., solutizer 3 is provided with vent line 10 under the control of valve 11 to permit the withdrawal of the lower boiling components of the solvent and any volatile matter vaporized from the raw coal. In this respect, it has been observed that the quantity of volatile matter is practically negligible. A substantially uniform coal solution, wherein undissolved and insoluble solids are suspended, which include mineral charcoal of fusain and mineral matter Or ash, is withdrawn through the bottom draw-off 12 and is passed through cooler 13 by pump 14 to a continuous rotary filter 15. Accordingly, I have recovered in excess of 95% of the extractable carbonaceous matter based on ash-free coal.
The coal solution is cooled to a temperature of from about 400 to 700 F. during its passage through cooler 13. Preferably, the rotary filter 15 is precoated with conventional filter aids and is normally operated at a pressure of about 40 to -p.s.i.g. to effect eflicient removal of substantially all of the suspended solids. The filter cake is washed and dried to recover absorbed solvent and is withdrawn from filter 15 through line 16. Precoating the filter substantially improves the separation of undissolved and insoluble particles from the coal solution. Utilizing a precoated filter, we have prepared filtered coal solutions which when analyzed for ash only varied between 0.02 to 0.08 weight percent, irrespective of the ash content of the raw coal which varied from 1 to 20 percent. This indicated that the efficiency of the de-ashing by filtration was a function of the size of the ash particle rather than the ash content. Utilizing filter aids having a high carbon content, the filter cake may be charged to a combustion unit to recover the B.t.u. content thereof.
The sulfur content of low sulfur coals (i.e., about 1.46 weight percent sulfur) has been reduced to values of from 0.3 to 0.6%, which represents an average reduction of about percent. Since the organic sulfur present in the raw coal is partially soluble in the solvent, the quantity of sulfur separated from the raw coal is a function of the pyritic and sulfate sulfur content of the coal, since they are substantially wholely removed by the filtration and thus, the final sulfur content of the filtered coal solution is primarily a function of the original organic sulfur content of the coal. With high sulfur coals, (i.e., about 4.3 weight percent sulfur) the ratio of inorganic sulfate and pyritic sulfur to organic sulfur is normally greater than for low sulfur coals. Consequently, with high sulfur coals, a greater percentage-wise reduction of the sulfur content has been observed, reducing the sulfur content of the filtered coal solution to as low as 0.6 weight percent, which corresponds to an over-all reduc tion of the sulfur content of from 70 to The substantially de-ashed coal solution is passed through line 17 to surge drum 18 from which it is passed through line 19 and pump 20 to heater 21 (a suitable coil heater). The coal solution is heated to a temperature of from about 850 to 1050 F. in heater 21 and is passed therefrom through line 22 to a coking unit maintained at a pressure of about 1 to 6 atmospheres. The coking unit, as illustrated, is a delayed coker and is comprised of coke drums 23 and 24. The heated coal solution in line 22 is introduced through line 22a into coker 23 wherein the charge is decomposed into coke and a vaporous effiuent. Introduction of the solution into the coker may result in some foaming. This may be effectively inhibited by the addition of a small amount of an anti-foam agent, at the point of introduction or at some elevated point in the coker.
The coker overhead in line 25a is passed through line 25 into a fractionating unit. While coker 23 is being filled with coke, coker 24 is being de-coked with product coke withdrawn through lines 26a and 26 for subsequent processing. In normal operation, cooling and de-coking of coker 24 is completed prior to the filling of the coker 23. With de-coking completed on coker 24 and having filled coker 23 to a predetermined level, the coker charge is diverted to coker 24 through line 22b, with the vaporous efiluent in line 25b being passed to the fractionating 6 A heavy middle oil in line 36 is passed to surge tank 37. By properly controlling the temperature level within tower 27, and the aforementioned reflux, the distillate fraction'in line 36 has cutpoints (converted to one unit through line 25. After cooling, coker 23 is de- 5 atmosphere) of from 600 to about 900 F. and reprecoked with product coke being passed through line 26b sents the solvent utilized for dissolving or digesting the and 26 for subsequent processing. The lower limit above extractable carbonaceous matter in the pulverized raw the incipient coking temperature to which the coal solucoal feed. Since the combination tower may be operating tion is heated is dictated by the upper limit of the volaat pressures up to about 1 to 5 atmospheres whereas the tile matter desired in the coke product, normally about 10 solutizer 3 is normally operated at from 1 to 10 atmos- 12 to 16%. The upper limit above the incipient coking pheres, valve 11 in vent line 10 permits both units to be temperature to which the coal solution is heated is dicoperated at diiferent pressure levels. The solutizer may tated by the lower limit of the volatile matter in the be considered to be an extension of the fractionating coke product, normally about 6to 8%, since coke having unit, but it is not necessary to operate both the fracless than 6% volatile matter is extremely hard and is contionating unit and solutizer at the same pressure. Gensequently difficult to remove from the coke drum. erally the overall level of pressure in the solutizer will The coal solution may also be coked in a contact cokbe at some higher pressure than the fractionating unit ing unit (comprised of a reactor having a downwardly because of the normal increase of solutizer temperature flowing bed of a particulate material on which the feed over tower bottom temperature and because of the presis spread and coked) and at higher temperatures so as to 20 ence of some lower boiling coal decomposition products obtain product coke having less than 6% volatile matter. formed in the solutizer. Solvent requirements may neces- Higher temperatures are permissible since there is no sitate a higher pressure on both units to provide more practical limitation of de-coking a drum filled with coke solvent from the fractionating unit by the inclusion of having less than 6% volatile matter. Further, contact light ends normally lost to side streams and/or overhead coking procedures do not require preheating of the coker when operating the fractionating unit at lower pressures. feed to a temperature above its incipient coking tempera- Tower bottoms are withdrawn through line 3 8 and ture since the feed may be heated in the coker to a temmay be passed to heater 21 by pump 39 and coked with perature above incipient coking by the sensible heat the de-ashed coal solution in .line 19. A portion of the of the contact particles. tower bottoms in line 38 may be withdrawn through The cokcr overhead in line 25 is introduced into a line under the control Of valve 41, and passed to storfractionating or combination tower 27 which is provided age and refining units (not shown). with suitable fractionating decks (not shown). The here- Start-up or make-up solvent is introduced into surge inbefore mentioned distillate and volatile matter in line tank 37 through line 42 under the control of valve 43. 10, which are evolved during solvation, are introduced The quantity of solvent necessary to provide a solvent to into the lower portion of the tower 27. 35 coal ratio of from /2 :1 to 6:1 is withdrawn from tank 37 The combination tower overhead products in line 28 through line 44 and passed by pump 45 under the concomprising condensible and non-condensible components trol of valve 46 into line 4. After start-up, should the are passed to conventional processing units to separate quantity of captive solvent exceed solvation requirements, the condensible components from the non-condensible excess solvent may be withdrawn from tank 37 through components. A medium middle oil is withdrawn from 40 line 47 under the control of valve 48. an intermediate point on the tower 27 through line 29 The following examples in tabular form will further ilby pump 30 and is passed through line 31 to refining lustrate the nature of this invention. In Table I, there are units (not shown). A portion of the middle oil in line provided examples setting forth data relative to the com- 29, under the control of valve 32, is passed through position of the raw coal, solvent-ratios temperatures and line 33, waste heat boiler 34, and line 35 and is therepressures of solvation, and analysis of the coal extract after split into at least two portions (lines 35a and 35b) solution. for introduction as reflux into tower 27.
' TABLEI Example N o.
I 11 III IV V Coal Pana. Illinois Seacoal Seacoal Raw De-ashed ClP tA1si.s,r tb lit;
ndiiii.flinn ffffinf'ffii 2.69 lvloislfliie-lree Basis 2.75 1.4 1.1 Volatile Matter. 37. 7 33. a 32. 6 38.90 36. 6 86. 6 Fixed Carbon 38.9 56.6 67. 53. 99 66. 6 56. 6 sh 19.66 9.8 0.3 7.11 5.4 5.4 Sulfur. 3. 72 4. 0 1. 0 1.18 1. 46 1. 46 Chlorine 0. 15 0. 003 Solvent:
Boiling range, F.:
Initial About 750 000 000 About 750 600 Final About 1,050+ 900 900 About 1,050+ 900 Refractorized No Yes Yes No Yes Solvent to Coal Ratio- 3-1 3-1 2-1 2-1 3-1 Solution Temperature, F 8G0 800 785 800 800 Solution Pressure, p.s.i.g. 75 75 75 75 75 Residence Time, min. 20 20 3 20 20 Filtration Temperature. 550 625 600 450 600 De-ashed Coal Recovery:
On crushed coal 67.3 On ash-tree coal 83. 8 Sp. Gravity (l100" F.) 1.251s Softening Point, F. (BdzR) 147. Sulfur, wt. percent 0.63 Carbon Residue, wt. percent:
Rarnsbottom 32. 7
Conradson Os Solubility, wt percent itumin.
7 The following Table 11 illustrates the effectiveness of sulfur removed with respect to organic, pyritic and sulfate sulfur of Example III of Table I.
Raw Coal Coal Extract Organic S, percent" v 799 0. 593 Pyritie S, percent... 0.370 Sulfate S, percent. 0. 012
1 Not detected.
Table III is an analysis of a typical high boiling solvent having cutpoints of about 600 to about 900 F. utilized in Examples 11, III, V of Table I.
TABLE III.COAL DE-ASHING SOLVENT BOILING RANGE Vapor Temperature, F. Converted Percent Distilled: to 760 mm. Hg Abs.
Specific Gravity (100/60 F.) 1.1664
It is noted that the solution efliciencies of Examples I and IV (which are presented in the aforementioned application) wherein a different boiling temperature solvent is utilized are substantially less than the efficiencies of the solvent having cutpoints of from about 600 to about 900 F., utilized in Examples 11, III and V.
It is noted that the high-boiling solvent has components which boil between such cutpoints as illustrated in Table III and that the term solvent having cutpoints of is interpreted in the specification and claims to mean a solvent having components boiling between such cutpoints and with a minor portion of components boiling below and above such cutpoints, depending upon the fractionation efiiciency of the combination tower.
Table IV illustrates results of coking a deashed coal solution to form coke in accordance with my invention.
While I have shown and described a preferred form of my invention, I am aware that variation may be made thereto and I, therefore, desire a broad interpretation of my invention within the scope of the disclosure herein and the following claims.
What is claimed is:
1. A process for deashing a coal selected from the group consisting of bituminous coal, subbituminous coal and lignite comprised of extractable carbonaceous matter, fusain and mineral matter, which comprises:
(a) mixing the coal in crushed form in the absence of added hydrogen with a high boiling aromatic liquid solvent having cutpoints, converted to one atmosphere, of from about 600 to about 900 F. to form a solution of said extractable carbonaceous matter wherein solids including insoluble fusain and mineral matter are suspended; and
(b) separating said suspended solids from said solution.
2. The process as defined in claim 1 wherein the mixture is heated to a temperature of from about 600 F. to about 850 F. to form the solution of extractable carbonaceous matter.
3. The process as defined in claim 2 wherein the ratio of solvent to coal is from about /2 :1 to 6: 1.
4. The process as defined in claim 3 wherein the ratio of solvent to coal is from about 1:1 to 3:1.
5. The process as defined in claim 2 wherein the mixture is heated to a temperature between about 600 F. and about 850 F. to form the solution of extractable carbonaceous matter.
6. The process as defined in claim 5 wherein the ternperature is maintained for about 3 to about minutes.
7. The process as defined in claim 6 wherein the mix ture is heated to a temperature between about 750 F. and about 800 F.
8. The process as defined in claim 6 wherein said solution is cooled to a temperature between about 400 and about 700 F. prior to separating the suspended solids.
References Cited UNITED STATES PATENTS 1,904,586 4/1933 Winkler et al. 2088 1,925,005 8/1933 Rose et al. 208-8 2,221,410 11/1940 Mathias 20 88 2,686,152 8/1954 Franke 2088 3,109,803 11/1963 Bloomer et al. 20S-8 FOREIGN PATENTS 457,971 12/ 1936 Great Britain.
DANIEL E. WYMAN, Primary Examiner.
P. E. KONOPKA, Assistant Examiner.