US3505201A - Separation of coal-oil suspensions - Google Patents

Description

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SEPARATION OF COAL-OIL SUSPENSIONS 3 Sheets-Sheet 1 Filed Jan. 27, 1967 kuaaosm xuukuz umm zommuzmtou zuhuvz mutzommzvgh.

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m bbx United States Patent 3,505,201 SEPARATION OF COAL-OIL SUSPENSIONS Gordon W. Hodgson, George F. Round, and Jan Kruyer, Edmonton, Alberta, Canada, assignors to Research Council of Alberta, Edmonton, Alberta, Canada Filed Jan. 27, 1967, Ser. No. 612,188 Int. Cl. Cg l/02; C10b 49/10 US. Cl. 2088 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to the separation of slurries into their component parts and is particularly concerned with the separation of coal-oil slurries by means of flash distillation techniques, wherein the slurry is injected into a reactor, the oil being flash distilled and oil-free coal char particles being left behind.

The coal-oil slurries may for example be slurries formed as suspensions of pulverised or finely-divided coal in crude oil in order to facilitate transportation of coal by pipeline. The pipelined mixture may be moved to points adjacent the market areas of the respective com ponents and processed at those points to recover the coal and oil constituents.

The invention is particularly concerned with the thermal separation of oil and coal from coal-oil slurries whereby the coal component is upgraded. This is to say, the coal char product resulting from the thermal separation process is superior as a fuel to the coal that was present in the original slurry.

Pumping a solid, mixed with a suitable fluid carrier through a pipeline as a slurry has been used by industry as an economical means of transporting certain material. Experimental investigations with a 1-inch, 45-ft. long pilot-scale pipeline at the Research Council of Alberta have indicated the possibility of transporting granular coal with oil as a carrier. Slurries up to 35% coal by weight could be pumped at velocities up to 19 ft./sec. without causing pressure gradients appreciably greater than those encountered when pumping oil alone. Oil was used in these experiments because it was felt that in actual practice transportation in crude oil obviates the need to move an essentially unprofitable carrier. Both coal and petroleum are found in abundance in Alberta and large quantities of both fuels are required in the same general market area of eastern Canada. If the present cost of pipelining oil, which amount to about 0.2 cent per ton-mile, were applied to a slurry of coal-in-oil, transportation charges for coal would be less than one-third of present railway freight charges. Assuming a 24-inch line With a capacity such as already exists for oil between Alberta and the Lakehead, continuous transportation of a 25 percent slurry would permit some 20 million tons of coal to be laid down in a year.

One of the most important problems associated with pumping of a coal-inoil slurry is the necessity of economically obtaining a clean separation of the two components once the slurry has reached the market locality. Two modes of separation have been investigated, separation by classification in multicyclones and separation by flash va- 3,505,201 Patented Apr. 7, 1970 porization in a heated reactor. Flash vaporization of a mixture of Leduc crude oil and Edmonton coal, using a hot fluidized solids reactor has yielded a dry char suitable as a fuel for thermal power stations and an oil that had undergone little change. The present invention is concerned with this thermal separation of a slurry of coal-inoil.

The term fluidization is used to describe a certain mechanism of contacting granular solids with fluids. Since in this work the applicants are concerned with a coal-in-oil mixture involving contacting coal char particles with coal particles and oil fluids, this system may be used to illustrate the process of fluidization.

The particles being fluidized are granular coal char particles, and the fluidizing gas is recycled process gas. As the gas is passed upwards through the bed, there is a certain flow at which the particles are disengaged somewhat from each other. In this condition the bed behaves as a fluid, hence the name fluidization. In order to maintain gas flow through the bed a finite pressure gradient is required to overcome friction, and to increase the rate of flow a greater pressure gradient is required. When the pressure drop approaches the weight of the bed over a unit cross-sectional area, the solids begin to move. This condition is known as the onset of fluidization.

When the gas velocity is only slightly above that required for the onset of fluidization, a state known as a quiescent fluidizing bed results. In this state the particles in the bed display little or no mixing, interparticle heat and mass transfer in the bed are then at a minimum. As the fluid velocity is somewhat increased, the bed expands and the solids tend to mix readily. This state is known as a turbulent fluidized bed and causes a slight increase in pressure gradient. Further increase in gas mass velocity causes a further increase in pressure gradient across the bed. If the gas velocity is considerably increased, the bed expands greatly and a condition of great solids dilution is created. The solids are then entrained in the fluid and are carried upwards. This state is known as the dilute fluidized phase. However, with a bed containing a wide range of particle sizes dust is carried upwards even at low gas flow rates.

Gas-solid systems are notorious for possessing nonhomogeneous and labile pore textures. This is largely due to the formation of aggregates of particles. When aggregates are present in the bed, the process is called aggregative fluidization in contrast with particulate fluidization where the bed has a homogeneous pore structure. Whereas in particulate fluidization the onset of fluidization is marked by a gentle oscillating motion of some of the particles constituting the bed, in aggregative fluidization, the fluid literally begins to bubble through the solid bed in a manner identical to the action observed in bubbling a gas through a liquid. The bubbles of fluid rise through the bed and break up at the surface of the bed, splashing a few particles of the solid upwards. As the fluid velocity is increased, the bubbling action becomes more and more violent, streamers of solids being ejected to considerable distances above the bed before returning. These phenomena have been visually observed in a preliminary study of a gas coal system in an unheated glass column. In this case it was noticed that the streamers were very marked and started at about four times the gas mass velocity necessary to obtain onset of fluidization.

A fluidized system may be used to effect a separation of mixtures of substances some of which are essentially volatile, and the other, non-votatile. The volatile components on being introduced to a hot bed of fluidized particles rapidly absorb the heat of vaporization and join the fluidizing gas stream passing through the bed while the non-volatile components remain with the fluidizing particles in fluidization reactor. Thus in the case of slurries of coal in oil, the oil components tend to pass out of the reactor while the coal components remain with the coal char particles in the reactor. One of the main features of the invention is that at the temperatures required to effect such a separation, the coal char product resulting from the thermal separation process is superior as a fuel to the coal that was present in the original slurry, having picked up non-volatile components of the oil. The loss of these components from the recovered oil is balanced off by the production of volatile substances from the coal during the process. These become part of the oil product and process gas stream.

Laboratory experiments have been carried out to illustrate the essential features of the process.

In the following detailed description of the process reference will be made to the following drawings:

FIGURE 1 represents a flow diagram;

FIGURE 2 is a detailed diagram of a fluidization reactor, and

FIGURE 3 is a flow diagram showing a possible commercial modification of the apparatus of FIGURE 1 following the reactor.

The apparatus shown in FIGURE 1 comprises a feed reservoir 1 designed to contain coal-oil slurry which is conveyed to slurry-pump 2 which pumps the slurry into reactor 3 through conduit 4. The crude oil may be augmented with an admixture of heavy crude oil and/or asphalts and petroleum residuums.

Initially the entire apparatus is purged with an inert gas such as nitrogen supplied under pressure from source 5, the'nitrogen flow being controlled by valve 6. Once the apparatus has been purged the gas used is recycled from the system.

The nitrogen and/ or the recycled gas is delivered to the bottom of reactor 1 through preheater 7, and enters the reactor via conduit 8 and maintains the bed of solids in a fluidized state indicated at 9, the bed being supported mechanically by a foraminous metal plate 10 seated immediately above conical section 11 of the reactor. The reactor is heated by means of electrical heaters indicated at 12.

It will be noted that the upper section 13 of the reactor is of larger cross-section than the lower section 14. The larger cross-section at the top of the reactor causes a reduction in gas pressure and velocity in that area which facilitates separation of char and dust from ascending vapors.

Most of the heat necessary for the flash vaporization of the oil and the carbonization of the coal to a char is supplied by heating wires 12 through the temperature of the gas entering the reactor is a factor in controlling the bed temperature. As shown in FIGURE 2 the reactor may be covered with a layer of asbestos cement 15 in order to reduce heat loss.

It is also contemplated as part of the invention to rely on the combustion of the products of the reactor, the process gas and the char product, as a source of heat for the reaction.

Pressure and temperature in the apparatus is recorded at desired points in the line and at several levels in the reactor, by means of manometers and thermometers, not shown.

Hot oil vapors and quantities char particles and dust ascend into cyclone 16 mounted in section 13 of the reactor. The particles settle in the cyclone and are removed through cyclone leg or conduit 17 which protrudes through the reactor wall. Quantities of char are removed from the reactor through leg 18, the removal being controlled by solenoid valve 19.

The slurries studied by applicant comprised a mixture of 70% w./w. Leduc crude oil (38.4 API) and 30% w./w. Edmonton subbituminous coal, while others involved mixtures of Lloydminster crude oil and Canmore coal. These were selected to illustrate the process in relation to the pipelining operations for which the process might be used.

The most difiicult fluidized-bed separations are those requiring high heat inputs and those marked by high gas velocities in the fluidized bed. Thus, a fairly dilute slurry of coal-in-oil such as the above 30-70 mixture, and a slurry containing a heavy crude oil such as the Lloydminster oil represent very difficult operating conditions, and any process suitable for such conditions can be readily operated for more favorable conditions of feed. The preferable range of coal concentration in the slurry is thus 30 to 70 or more weight percent. The preferred range for the heavy oil component is from zero to an upper value of or more, a value limited largely by the pipeline flow characteristics of the slurry; the greater the heavy oil content, the greater the enrichment of the coal char product. In the laboratory experiments the mixture of coal in oil, which for example might be a slurry of about l00-mesh coal suspended in crude oil, at a concentration of about 30-40% by weight, is injected into a reactor in which oil is flash vaporised leaving behind the oilfree coal particles in the form of coal char. The slurry is introduced into a fluidized bed of coal char particles, the bed temperature being maintained at about 600 F. to about 1000 F. The vaporized oil is recovered in an overhead stream, and the suspended coal becomes part of the fluidized bed, which is maintained at a predetermined operating inventory level by appropriate withdrawal of the coal particles via leg or char-removal conduit 18.

The temperature of the bed in the experimental studies was varied over a wide range, the operating limits being determined by the failure of the char particles to remain dry and free flowing for the lower limit and by a limited heat input for the upper limit. In the laboratory tests the distillation of oil was incomplete at temperatures below 700 F., with the etfect that the coal char particles tended to agglomerate and thereby prevent proper fluidization. The preferred reaction temperatures are in the 900l000 F. range wherein the gross characteristics of the recovered oil are at least as favorable as those of the oil in the feed slurry, and the heating value of the coal char product approaches a maximum. Thus there is evident an unexpected result which may be attributed to the particular configuration of the system, as will become more evident below.

Slurry to be delivered to the reactor is maintained under vigorous agitation in feed reservoir 1 located above the top of the reactor, falling directly into the fiuidizing bed. The preferred type of pump used to transmit the slurry is a Sigma pump (Sigmamotor, Inc., Middleport, N.Y.). The feed is introduced through the top of the reactor rather than the side with the result that a more complete removal of the oil from the char was rendered possible which in turn, enabled the fluidizer to be operated at a lower temperature than would be possible otherwise. At a reactor temperature of 900 F., for example, the perceutage of benzene-extractibles was reduced from 1.6 to 0.2% by introduction of the feed at the top of the reactor.

Within the reactor a bed of solids composed principally of coal char particles is kept in a constant state of fluidization by means of fluidizing hot gas delivered to the bottom of the reactor from the preheater, and if desired in addition, by means of a stream of inert gas such as nitrogen.

The quantity of solids in the reactor at any given time was indicated by determining the pressure of the bed, and as pointed out above a series of manometers is used for this purpose, the manometers indicating the pressure differential between the top of the reactor and taps (not shown) that may be located on the side of the reactor at appropriate or desired levels. The first tap may for example be placed just above plate 10, the second 3 in. above the first and the third 6 in. above the first. Draw-oh? of char from the bed, to maintain a constant quantity of fiuidizing solids, is accomplished by a pressure-sensitive solenoid plug valve 19, the pressure-sensitive switch 20 (see FIGURE 2) controlling the valve responding to pressure changes in bed height. Entrained dust and char thrown up as streamers from the bed are separated by cyclone 16 as explained above and collected as part of the total char product.

There is constant formation of gaseous products in the reactor which results in a continuous increase in the amount of gas within the system which necessitates constant removal to maintain the desired operating pressure. During the start-up period the system may be filled with an inert gas such as nitrogen, but after about one hour of operation however, less than 5% of the original nitrogen remains in the system as part of the recirculating gas.

A stream of the vapor formed in the reactor is constantly being diverted into the cyclone where the treated coal char particles settle out and are removed by gravity at removal point 17. Hot vapors formed from the coal and the oil pass overhead from the cyclone through conduit 21 and are delivered through line 22 to a watercooled condenser 23. An oil fog and a liquid product result from the initial condensation and are conducted to cyclone 24. The condensed liquid is passed through water trap 25 and the oil portion collected.

The oil fog from the condenser is preferably delivered from cyclone 24 into a moving-wire electrostatic precipitator 26, the moving wire 27 acting as a self-cleaning electrode. Where a stationary wire is used it is found that the electrode becomes coated with asphalt and entrained dust. The outside wall 28 of the precipitator may be painted with silver conducting paint as indicated at 29 the paint acting as the second electrode. As shown in FIGURE 1 fog enters the precipitator at 30, oil is removed at 31 and gas at 32. The precipitator collects between and 50% of the total oil product, depending upon the reactor temperature. For example, at a reactor temperature of 900 F. approximately five times as much fog oil is produced as is the case at 700 F.

The overhead gas and vapours from the precipitator 26 are passed into a second water-cooled condenser 33, liquid from this condenser being passed to water trap 34 and the oil collected and combined with the condensed oils from the first condenser and the precipitator as a total oil product. Wet gases leaving the condenser are preferably partially recycled via line 35 to maintain the desired fiuidization velocity and pressure within the reactor, the gas to be recycled being compressed in compressor 36. Unrecycled gas is passed through charcoal adsorber 37 where adsorbable components are removed and the dry gas metered and collected. An average recovery of 96% of total feed in the laboratory tests may be accounted for on a mass balance basis; the remainder being accounted for as gas leaks, char dust, and oil in interconnecting lines and vessels.

The gas mass flow rate through the bed was controlled by a compressor and a bypass valve and measured with a rotameter, the rotameter being calibrated for nitrogen at room temperature. Since the fiuidizing gas was recirculated constantly, it soon became very rich in hydrocarbon gases, hydrogen, carbon monoxide and carbon dioxide. This continuous buildup of gases within the system necessitated a constant removal of a portion of these in order to maintain the desired operation pressure. After one hour of operation, as has been indicated, less than 5% of the original nitrogen remained as part of the recirculating gas. A rotameter reading was chosen so that the bed was operating well within the turbulent fluidized region. This reading was found by plotting the pressure gradients in the bed versus rotameter readings. Good mixing of the bed was indicated by equal temperatures at various levels in the bed.

A comparison of the products produced by the carbonibation of Edmonton coal at 500 C. (932 F.) and fiuidization of Edmonton coal with Leduc oil at 910 F. is shown in Table 1.

TABLE 1 Fluidization (Experiment 1Slurry: 30% coal w./w.):

Total ieed= 18.80 lb.

Feed rate 3.8 lb./hr. Pounds Percent Products:

Product, Feed Percent Oil Analysis:

Sediment 0. 45 2. 40 C residue 1. 45 0. 74 Volatiles 98. 15 96. 86

Total 100. 00 100. 00

Percent Char Analysis:

Ash 11.9 18. 5 Fixed 0 69. 6

Total 100. 0

12,440 B.t.u./lb., dry basis carbonization Percent Products:

Total 100. 0 100. 0

11,940 B.t.u./lb., dry basis Table 1 shows a comparison of a typical fluidization experiment at 910 F. with a carbonization at a slightly higher temperature, for the same coal. While an overall quantitative comparison is not possible since the systems are not equivalent, e.g. in carbonization there was no contributing oil and the atmosphere was not inert, it is possible to compare the chars formed on a lb./lb. basis. Fluidization gave a char of better heating value and lower ash content-both desirable features. Water and other volatiles were removed from the coal and petroleum coke was deposited on the char.

Table 2 shows a comparison of the test coals used in the process as described.

*Uncorrected for mineral matter.

Table 3 shows the results of several fluidization runs at various temperatures, the analytical results being compared with the oil and coal feed materials.

TABLE 3 Run 1 2 3 4 5 Oil Feed Bed Temperature, F 875 780 750 Total Feed, Lb 23. 4 14. 7 17. 9 Feed Rate, Lb./Hr 4. 5 7. 3 3. 6 Oil Analysis:

Gravity, A.P.I 33.0 35. 2 34. 0 Viscosity, cst.:

9. 26 6.32 7. 37 4. 46 4. 17 4. 65 Unsaturates, U, percent 17. 6 15. 8 11. 8 Asphaltenes, percent 0. 46 0. 20 O. 22 Carbon Residue, percent. Sulfur, percent 0. 28 G. 18 O. 24 Sediment, mg./ml 1. 26 4. 11 3. 70

Ash, percent 12. 7 11.0 10.1 10. 7 Benzene Extractibles, percent. 0. 16 0. 33 0. 9S 1. 35 Volatiles (dry), percent 18.4 25. 9 26. 1 Heating Value, B.t.u./Lb.

(Dry Basis) 12, 660 12, 400 12, 170 11, 960 (Dry Ash Free Basis) 14, 500 13,920 13, 550 13,400 Gas Produced, S c f lLb. Feed Total 2. 04 0. 25 Hz.... 1. 20 O. 02 O0 0. 06 0. 06 CO2" CH4 0. 20 O. 03 Other hydrocarbons"--. 0. 58 0. 14

In each instance the oil product compares favorably with the feed and the coal product is markedly improved. It should be obvious that the process herein described is something more than a simple resolution of a two component mixture. It is even more than a simple distillation of the volatile compounds of each component. Chemical changes are taking place, to the benefit of one or both of the slurry components, as indicated by the nature of the gas production, and by the character of the oil. Some or all of these beneficial aspects of the process. may be attributed to the catalytic nature of the surface of the coal char particles at the reaction temperatures involved.

It will be realised that in commercial operation that processing equipment would be modified following the reactor and initial condensation in FIGURE 1. A practical modification is shown in FIGURE 3 wherein the overhead fractions from the existing column would go to a condenser and there would be three liquid fractions produced; one out being taken from the middle of the enriching column, though in commercial practice several fractions might be taken off this column and then go to further processing. As indicated part of the gas stream is recycled for fluidization.

In other words FIGURE 3 shows how vapors produced in a commercial application of the invention might be handled. In this instance the solids-free vapors are introduced into the side of an enriching or fractionating column comprising a vertical chamber with a number of perforated horizontal baifle plates. Cooling of the vapors takes place and substantial portions of the vapors are condensed to liquids which tend to collect on'the plates, the higher plates collecting the light oils, i.e. the lowerboiling components, while the lower collect the heavy, i.e. higher-boiling, components. The temperature balance in the column is controlled by the volume of light components recirculated in the reflux cycle. The enriching fractionating column can be designed to produce a few oily product streams as illustrated in FIGURE 3 or as many more as desired. The uncondensed vapors from the column are led to a condenser where cooling Water or air is used to abstract further heat from the vapors and a light oil product is recovered. The uncondensed vapors are thus separated from the oily constituents and are available as product and/or recycle gas stream for the fluidized reactor.

It will be clear however that while this process may have a different expression in terms of physical process equipment in commercial practice, the principles of the process will remain unchanged. For example, the heat required for the process may be obtained from (a) cooling of the coal char product, (b) condensation of the overhead vapors, (c) combustion of the process gas, and (d) combustion of coal char product. Combustion of the process gas as apart of this invention may take place in a preheater furnace through which the coal-oil slurry is passed prior to introduction to the fluidized reactor. It may also take place in a preheater furnace with the flue gases being used for part of or all the fluidizing gas stream; alternatively, combustion of the fuel gases may take place in the reaction chamber itself through the controlled addition of air or oxygen to the system. Heat may be added to the system by combustion of a part of the char product in substantially the same manner as with the process gas. Further, combustion of char particles to provide process heat may be carried out in a second fluidized reactor containing char particles,by the addition of oxygen to the fluidizing stream. The combustion so sustained raises the temperature of the particles in the reactor, which particles, are recycled to the distillation reactor to maintain the desired temperature in that unit.

Since the process in the distillation reactor involves catalysis by the char particles, another element of this invention is the recognition of this priciple and the extension of it through the inclusion of catalyst bodies in the reactor chamber to accentuate and direct the desirable effects arising from such catalysis. Thus, the catalytic aspects of the process can be extended and modified through the inclusion of foreign catalyst bodies directly in the fluidized reactor bed of char particles. A typical catalyst body would be free-flowing screen cylinders or fixed wire grids coated with appropriate substances to produce desired eifects such as olefin saturation, aromatics production, hydrocarbon alkylation and general hydrogenation.

We claim: 1. The process of treating coal comprising delivering a "slurry of finely divided coal in crude oil into contact with a bed of fluidized coal char particles in a heated reactor maintained at a temperature of about 600 F. to about 1000 F., permitting interaction between the oil and the coal, flash-vaporizing the volatiles in the oil and coal and conducting them out of the reactor as a vaporous stream, trapping coal-char particles within the reactor and withdrawing them therefrom, separating oily and gaseous components from the vaporous stream by condensation and separately recovering the coal solids, oil and gas products.

2. The process of recovering upgraded oil and char products from a slurry of coal and oil comprising slurrying finely-divided coal in crude oil, introducing the slurry into a fluidized bed of coal char products within a reactor maintained at a temperature of about 600 F. to about 1000" F., flash-vaporizing the slurry and separating it into two principal phases, a hot oil vaporous phase and an oil-free coal-char particle phase, maintaining bedpressure and bed-density at a predetermined level by drawing off char from the fluidized bed, passing the vaporous phase upwardly through a cyclone to separate entrained solid particles therefrom, fractionating and condensing the solids-free vaporous phase to form a plurality of oily phases in an enriching column and condenser, and separating an overhead gas product vapor phase.

3. The process of reacting the components of 'an oilcoal slurry at high temperature and recovering therefrom an upgraded coal-char product of enhanced fuel value, in addition to upgraded oil and gas products, comprising introducing a slurry containing 60-80% crude oil and 4020% finely divided coal by Weight into a fluidized bed zone of coal-char particles within a heated reactor, the temperature of the bed being about 850950 F., the bed being fluidized by means of a gas stream comprising at least one of the group: recycled gas from the reactor and inert gas, the fiuidizing gas being introduced at the bottom of the reactor, heating the slurry within the reactor in order to react the oil and coal components to form a particulate char phase and a vaporous hydrocarbon phase, elements of each phase emanating from both the coal and the oil, predeterm-inining the optimum density of the bed in relation to the pressure in the reactor and maintaining the desired reactor temperature and beddensity by withdrawing solids from the particulate char phase within the bed, removing entrained solids from the vaporous hydrocarbon phase, subjecting the vaporous phase to a fractionating and condensing step to separate it into a plurality of oily phases, recovering the oily phases as oils, and recovering gas from the vapor phase.

4. The process according to claim 3, the crude oil including additionally a composition selected from the group consisting of an admixture of heavy crude oil and asphalts and an admixture of petroleum residuum-s and asphalts, the slurry containing about crude oil and about 30% finely-divided coal by weight, and the temperature of the bed being about 900 F.

5. The process as claimed in claim 3, the fluidized bed containing added catalyst substances.

6. The process as claimed in claim 3, the fluidized bed being heated by combustion of process gas and/or coal char product.

7. The process as claimed in claim 3, the gas product phase being treated as an oil-fog in a precipitator thereby forming an additional oily phase.

8. The process of claim 3 in which the recovered gas is recycled.

References Cited UNITED STATES PATENTS DELBERT E. GANTZ, Primary Examiner V, OKEEFE, Assistant Examiner US. Cl. X.R.

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