US 3597327 A
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g- 3, 1971 A. M. SQUIRES 3,597,327
PROCESS FOR PYROLYZING A SOLID OR LIQUID HYDROCARBONACEOUS FUEL IN A FLUIDIZED BED Filed April 2, .1969 2 Sheets-Sheet 1 FVEA 6'45 M 4 f/E/l 77/)6 flan/v4 INVENTOR 6 52% 9 17/7790? #1. SdN/l/PES rams FELL 75 Aug. 3, 1971 SQUIRES 3,597,321
PROCESS FOR PYROLYZING A SOLID on LIQUID HYDROCARBONACEOUS FUEL IN A FLUIDIZED BED Filed April z, .1969 2 Sheets-Sheet a my 225 /4/ it "United States Paten 3:1:
3,597 327 PROCESS FOR PYROLYZING A SOLID OR LllQUlD HYDROCARBONACEOUS FUEL IN A F LlUllDIZlED BED Arthur M. Squires, 245 W. 104th t., New York, NY. 10025 Continuation-impart of application Ser. No. 561,551, June 29, 1966. This application Apr. 2, 1969, Ser.
lint. or. con; 49/22 US. Cl. 2tl112 12 Claims ABSTRACT OF THE DISCLOSURE A solid or liquid hydrocarbonaceous fuel, such as bituminous coal or residual oil, is charged to a lower zone of a fluidized bed, this zone comprising coke pellets, wherein the fuel is carbonized or cracked (i.e., pyrolyzed) to form gaseous products and a fresh coke accreting upon the pellets. The gaseous products fluidize a superposed, contiguous, upper zone of the fluidized bed, comprising a solid of smaller size and being fluidized at lower velocity. The velocity of the lower zone is suflicient to prevent the smaller solid from penetrating deeply into the zone. Heat is supplied to the lower zone by heat conduction from the upper zone. The heat is either generated within the upper zone (e.g., by combustion or other chemical reaction or by supply of a hot solid to the upper zone and withdrawal of solid therefrom) or supplied thereto by indirect heat exchange from a heating medium. Alternatively, if the fuel carbonization or cracking is conducted in an atmosphere of hydrogen at a sufficiently high partial pressure, so that the reaction of the fuel is exothermic, heat is withdrawn from the lower zone by heat conduction to the upper zone, and the heat is removed from the upper zone, e.g., by indirect heat exchange to a cooling medium.
BACKGROUND OF THE INVENTION This application is a continuation-impart of my copending applications Ser. No. 561,551, filed June 29, 1966, and to issue as US. Pat. 3,437,561 on Apr, 8, 1969, and Ser. No. 754,226, filed Aug. 21, 1968, now US. Pat. No. 3,481,834.
My aforementioned application Ser. No. 561,551, to become US. Pat. 3,437,561, disclosed a technique for hydrocarbonizing coal in an agglomerating fluidized bed, to form pellets of coke and a gas rich in methane. According to this technique, the agglomerating fluidized bed was to operate adiabatically. Temperature control could be effected by adjusting the rate of supply of the coal and the temperature and pressure of the hydrogen-containing gas which fluidized the bed and optionally by adding methane to the hydrogen to reduce the potential extent to which the hydrogen may react with the coal to form methane in accordance with the quasi-equilibrium which limits this reaction.
My aforementioned application Ser. No. 754,226 disclosed a technique for carbonizing coal or cracking oil by supplying the coal or oil to the lower zone of a fluidized bed, this zone comprising coke pellets at a temperature. such that the coal or oil would carbonize or crack therein to form gaseous fuel products and fresh coke which accretes upon the pellets. The gaseous products along with hydrogen would fluidize a superposed, contiguous, upper zone of the fluidized bed, the upper zone comprising a commingling of the coke pellets and a solid of smaller size containing a substance avid for sulfur from hydrogen sulfide, such as calcium oxide. The upper zone was fluidized at lower velocity than the lower zone, and the velocity of the lower zone was to be suflicient to prevent the smaller solid from penetrating deeply into the zone. Means were provided to effect a commingling of the coke pellets and the smaller solid in the upper zone, and the fresh coke was desulfurized through the cooperative action of the hydrogen and the sulfur-avid solid. Fuel gas and coke, each low in sulfur, were withdrawn from the fluidized bed.
SUMMARY OF THE INVENTION The invention relates to an improved method for carbonizing coal or cracking residual oil under conditions which are agglomerating with respect to the coke product.
An object of the invention is to provide an improved process for converting caking coals or residual oils into a gaseous product and coke.
Another object is to provide processes yielding a methane-rich gas or other fuel gas and coke starting from coal, including bituminous and sub-bituminous coals and lignites, many of which are not ordinarily considered to be caking coals, or from fluid hydrocarbonaceous fuel such as residual oil, bitumen, pitch, tar, kerogen, and the like.
Another object is to provide processes to produce a synthetic fuel gas of pipeline grade according to U.S. standards for such a gas.
Another object is to provide processes to produce liquid fuels from coal or lighter liquids from heavy residual oils.
More specifically, the invention relates to an improved method for supplying heat to (or removing heat from) a fluidized-bed zone in which coal or oil undergoes carbonization or cracking (i.e., pyrolysis) under conditions which are agglomerating with respect to the coke product. The improved method provided by the instant invention greatly enlarges the range of applicability of the broad idea disclosed in my aforementioned application Ser. No. 561,551, to become US. Pat. 3,437,561, for carbonizing coal in a manner such that the coke product is produced in form of agglomerated coke pellets. In my earlier disclosure, the bed was operated adiabatically. Ac cordingly, the range of suitable variables such as hydrogen pressure, temperature, and coal feed rate was relatively narrow. If the bed could be operated non-adiabatically, with either supply or withdrawal of heat, the range of these variables could be appreciably broadened without departing from conditions which are otherwise operable. Providing heat-transfer surface within the agglomerating fluidized bed of the earlier disclosure is not an attractive idea, since the surface would be subjected both to fouling conditions on account of the stickiness of the reacting coal and also to large mechanical stresses on account of the rapid movement of large masses of coke pellets which are fluidized at a relatively high. fluidizing-gas velocity, advantageously 5 or more feet per second (ft/sec.) on the superficial basis according to my earlier disclosure.
In examples described in the specification of my aforementioned application Ser. No. 754,226, heat was supplied to an agglomerating fluidized-bed zone of the above-described type by direct conduction of heat from a superposed, contiguous fluidized-bed zone. In other words, this disclosure indicated a way whereby the agglomerating bed could be operated in a nonadiabatic manner.
According to the instant invention, there is provided method and apparatus for pyrolyzing a solid or liquid hydrocarbonaceous fuel. The fuel is charged to a first zone of a fluidized bed, this zone comprising pellets of coke at a temperature suflicient to cause pyrolysis of the fuel to occur with production of fuel gases and a coke product adhering to and accreting upon the pellets. Heat is imparted to a second zone of the fluidized bed, or heat is withdrawn therefrom, to maintain the temperature of the fluidized bed substantially constant, this second zone being superposed on the first zone and contiguous therewith and receiving fluidizing gas therefrom. The second zone is fluidized at lower velocity than the first zone, and the solid of the second zone comprises particles of sizes smaller than the coke pellets. The first zone is fluidized at a velocity high enough that the smaller solid is substantially prevented from sinking deep within this zone. The aforementioned heat flows by conduction between the first and second zones. Fuel gas is withdrawn from the second zone, and coke pellets are withdrawn from the fluidized bed.
The term solid or liquid hydrocarbonaceous fuel as here used embraces, as a first category, solid fuels which when heated either exhibit a softening temperature or begin to decompose with deformation and, as a second category, fuels normally liquid at room temperature and solid fuels which when heated exhibit a melting temperature and can thereafter be pumped.
Suitable fuels of the first category for practice of the invention are to be found among bituminous and subbituminous coals and lignites, including many coals ordinarily considered non-caking when viewed in light of conventional atmospheric-pressure coal-carbonization procedures. To use some of the non-caking coals or lignites successfully, one must operate the process of the invention at a high pressure and provide for presence of a high partial pressure of hydrogen in the first zone. It is to be understood that bituminous and subbituminous coals and lignites may be altered by a partial carbonization or a partial oxidation or a reduction in the intrinsic moisture (as, for example, in the drying of lignites by the Fleissner Process). Suitable fuels of the first category are also to be found among such altered coals and lignites, provided the altered material does not contain more than 91 weight percent carbon on a moisture-and-ash-free basis and display a hydrogen-to-carbon atomic ratio below 0.6.
Fuels of the second category include petroleum fractions from the gas-oil range and heavier, but the greater practical interest lies in application of the instant invention to treatment of fuels of the second category which are generally characterized by high specific gravity, low hydrogen content, a significant aromatic content, and a Conradson carbon greater than about 1 percent, usually greater than 2 percent. Examples of the latter fuels are residual fuel oils, cracked residua, asphalts, asphalt fractions prepared from residua by solvent extraction, heavy coker tars, coal tars, pitches, bitumens, carbonaceous matter from tar sands, gilsonite, kerogens, carbonaceous matter from oil shales, and the like.
A temperature greater than about 900 F. is generally sufficient to bring about some carbonization of a solid fuel or cracking of a liquid fuel charged to the bed of coke pellets. A temperature greater than about 1,000 F. is preferred, and a temperature up to about 1,700 F. is generally serviceable. The fuel is heated almost instantaneously to the bed temperature, and converted almost instantaneously by rapid, initial carbonization or cracking reactions into light gaseous products and a residue of sticky matter which adheres to a pellet of coke. The sticky matter is converted to a thin patch or layer of fresh dry coke by later, slower carbonization or cracking reactions which give rise to evolution of further gaseous or vapor products. In general, the sticky matter has a life on the order of only a few seconds between its formation by the initial reactions and its conversion into a dry coke.
When the combined heat effect of all of the carbonization or cracking reactions which occur in the first, agglomerating zone is endothermic, the process of the invention provides a way to supply heat to this zone, i.e., by conduction from the second zone. A variety of means may be employed for imparting this heat to the second zone so that the temperature of the fluidized bed may be kept substantially constant in time.
Solid may be supplied to the second zone at a higher temperature than the temperature of the fluidized bed, and solid may be withdrawn from the second zone to maintain a substantially constant inventory of solid therein.
Heat may also be generated in the second zone by a variety of chemical reactions, such as:
1) a chemical reaction between a constituent of the fluidizing gas and the aforementioned hot solid supplied to the second zone; for example, the solid might contain CaO and the fluidizing gas might contain CO at a partial pressure greater than the equilibrium decomposition pressure of CaCO at the temperature of the fluidized bed, or the gas might contain CO and steam as well as CO the combined partial pressure of the CO and CO exceeding the aforementioned equilibrium decomposition pressure and the CO and steam being converted to CO and H in the fluidized bed;
(2) a combustion reaction supported by the fuel gases entering the second zone from the first zone and by air or other gas containing oxygen injected into the second zone, the oxygen in the air or other gas being preferably supplied at a rate below the stoichiometric for complete combustion;
(3) a reaction between a hydrocarbon of aliphatic character or containing aliphatic groups and hydrogen arising from the carbonization or present in the fluidizing gas to the first zone or arising from conversion and CO and steam to CO and H in the fluidized bed, the reaction yielding methane.
Heat may also be supplied to the second zone by indirect heat exchange from a fluid heating medium, such as helium or liquid sodium.
If the hydrogen partial pressure in the fluidizing gas to the first, agglomerating zone is sufficiently great, the
combined heat effect of the hydrocarbonization or hydrocracking reactions which occur therein can be exothermic. In this circumstance, the process of the invention provides a way to remove heat from this zone, i.e., by conduction to the second zone. This heat may be withdrawn from the second zone by indirect heat exchange to a fluid cooling medium, such as water. Heat may also be withdrawn from the second zone by injecting a vaporizzable liquid therein.
Both the coke pellets and the smaller solid should be present in a range of particle sizes, preferably a range such that substantially the largest particle in each solid is at least about five times larger than substantially the smallest particle in the solid. The largest particle in the smaller solid should preferably be less than one-half the diameter of the smallest of the coke pellets.
The preferred way to ensure that the second zone is fluidized at a lower velocity than the first zone is to provide a second zone larger in cross-sectional area than the first zone.
It is preferable to Withdraw coke pellets from the bottom of the first, agglomerating zone, but a suitable procedure is to withdraw both coke pellets and the smaller solid from the second zone. The mixture of the two solids can be readily separated on account of their difference in size, either byelutriation or by screening.
The fluidizing-gas velocity in the first zone should preferably be less than 10 times greater than the minimum fluidization velocity of the coke pellets. The ability to select velocity whereby the lower elevations of the first zone are maintained substantially free of the smaller solid may be understood by considering the events which occur when a bed of particle is fluidized by a gas at ever higher velocities. As velocity is gradually increased, the density of the fluidized bed decreases, but the rate of decrease in density with increase in velocity is not marked. Ultimately, however, a critical velocity is abruptly reached at which the density of the bed drops sharply; the bed appears suddenly to thin out. Unless the Vessel containing the bed is extremely tall, the gas will convey most of the bed overhead and away from the vessel. This critical velocity may be termed the dilute-phase transition velocity. An attempt to fiuidize the particles at a higher velocity merely produces a dilute phase having a voidage usually well over 90 percent. If a small particle is injected into a gas-fluidized bed of relatively far larger particles, the smaller particle will tend to rise toward the top of the bed if its size and density are such that its dilute-phase transition velocity, in a bed comprising an aggregation of like smaller particles, is appreciably below the actual fluidizing velocity in the bed of larger particles. The largest particle of the smaller solid employed in the second zone of the fluidized bed of the instant invention should be such that it would tend to rise toward the top of the fluidized bed of coke pellets comprising the first zone.
The smaller solid is preferably fluidized in the second zone at a fiuidizing-gas velocity at least about 10 times greater than the minimum fluidization velocity of the solid. The dilute-phase transition velocity of the smaller solid is preferably not more than about 50 percent larger than the minimum fluidization velocity of the coke pellets taken altogether. The fluidization velocity in the second zone should be less than the dilute-phase transition velocity of the smaller solid.
A wide range of solid substances may be used for the smaller solid of the second zone, but in general materials of lower density will be preferred over materials of higher density. The fluidized density of the solid should be less than the true density of the coke pellets.
Coke pellets will tend to geyser from the lower zone upward into the upper zone. The smallest coke pellet should preferably have a minimum fluidization velocity, in a bed comprising an aggregation of like pellets, above the actual fiuidizing-gas velocity in the second zone, so that a coke pellet ejected from the first zone into the second zone will tend to sink back downward into the first zone.
The circulation of coke pellets between the two zones provides the principal mechanism whereby heat is conducted from one zone to the other. In most applications of the invention, the temperatures of the two zones will differ from one another by at the most a few degrees. If the temperatures differ too greatly, they may be brought closer together by providing means to increase the circulation of coke pellets from the lower zone into the upper zone. For example, a vertical pipe or riser could be provided extending from near the top of the lower zone well into the upper zone, transport gas being supplied to the bottom of the pipe to convey coke pellets upward therein.
Considering the ranges of fluidizing-gas compositions, temperatures, and pressures which may be encountered, and considering the range of density of materials which are candidates for the smaller solid, I am not able to give precise numerical values covering all circumstances to govern the particle sizes for the smaller solid and for the coke pellets and to prescribe the fluidizing velocities in the two zones. Suitable sizes and velocities can be readily established by experiment. I believe that the experimentation can be usefully guided by the foregoing remarks concerning the critical size of particle which tends to rise or to sink in a fluidized bed of larger or smaller particles respectively. The fluidizing-gas velocity in the first zone is preferably greater than about ft./sec., and a suitable minimum size of coke pellet will generally be found to be on the order of inch or larger. The fluidization velocity in the second zone is suitably between about 0.5 and 5 ft./ sec. and preferably between about 0.8 and 4 ft./ sec. A suitable maximum size of particle of the smaller solid will generally be found to be on the order of 40-mesh (U.S. Standard) or smaller.
Successful operation of the process of the invention depends critically upon commencing the operation with a suitable starter bed of solid present in the first zone. The starter bed should comprise a starter solid displaying a range of particle sizes, preferably at least five-fold, and with a smallest particle not substantially smaller than the minimum size desired for the coke pellets to be made. The starter bed need not be carbonaceous, a solid suitable for use at high temperature and having a density between about and pounds per cubic foot being generally satisfactory.
During operation of the process of the invention, seed particles should be added to the first zone to provide new particles on which coke may accrete. The number of such seed particles added during a given operating interval should be substantially equal to the number of coke pellets withdrawn from the bed. The size of each seed particle should preferably be approximately equal to the size of the smallest coke pellet. Seed particles may be conveniently provided by suitably crushing and screening a portion of the coke pellets withdrawn from. the bed.
Coal or other solid fuel for treatment by the process of the invention is advantageously ground to a fineness substantially smaller than IOU-mesh before it is charged to the first zone.
The coke pellets produced by the process of the invention are an excellent fuel for fluidized combustion either by the technique wherein heat is removed from the combustion to boiler tubes in contact with the fluidized bed or by the technique of Godel [U.S. Pat. 2,866,696 (1958)]. The coke pellets are also a good material for gasification in a slagging-grate gasifier [U.S. Pat. 3,253,906 (1966)], or for briquetting and calcining to produce a coke for metallurgy or for electrodes.
DESCRIPTION OF THE DRAWINGS The invention including various novel features will be more fully understood by reference to the accompanying drawings and the following description of the operation of the alternatives illustrated therein:
FIG. 1 is a schematic diagram illustrating a process and apparatus for carbonization of coal in a manner such that the fuel gas and coke products are substantially free of sulfur. The agglomerating zone is endothermic, and heat is imparted to the second zone both by supplying a hot solid to this zone and by reaction of CaO with CO to form CaCO therein.
FIG. 2 is a schematic diagram illustrating an embodiment of the invention in which fluid matter may be in jected into the second zone. The fluid matter might be air or a gas containing oxygen to produce combustion reac tions in the second zone, or a light naphtha to react with hydrogen exothermically in the second zone to produce methane, or a vaporizable liquid to vaporize and withdraw heat from the second zone.
FIG. 3 is a schematic diagram illustrating an embodiment in which heat-exchange surface, either for supply or withdrawal of heat, is placed in the second zone.
FIG. 4 is a schematic diagram illustrating an embodiment directed toward production of a fuel gas rich in methane and hydrogen as well as coke, the fuel gas being suitable for further processing to produce a gas of pipeline grade according to U.S. standards for such a gas.
The embodiments of FIGS. 3 and 4 are suitable for production of liquid as well as gaseous fuels from coal.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Carbon 80.70 Hydrogen 5.47 Sulfur 3.72
Grinding equipment 2 reduces the coal to a particle size such that substantially all of the coal passes through a IOO-mesh screen (U.S. Standard). Coal is supplied from equipment 2 via conduit 3 to heating equipment 4, where the coal is dried and its temperature is raised to 300 F. The coal is transferred from equipment 4 via line 5 to lock system 6. The coal in line 5 carries 28,456 pounds per hour of intrinsic moisture, and is accompanied by steam at 300 F. and 25 pounds per square inch absolute (p.s.i.a.).
Gas is supplied to the process at 397 p.s.i.a. and 700 F. via line 7. The rates of supply of the several constituents in the gas are as follows, expressed in pound-moles per hour (m./hr.):
A fraction 0.31684 of the gas is supplied via line 8 to lock system 6, where the gas is used to raise the pressure of the coal to 397 p.s.i.a., and the gas and coal are injected together at a substantially constant rate into coal-carbonization vessel 9 via a multiplicity of lines 10 and nozzles 11. For simplicity of the drawing, only one line 10 and one nozzle 11 are shown. The remaining gas from line 7 is supplied via line 12 to gas-heating equipment 13 and thence at 1300 F. to the bottom of vessel 9, to provide (together with gas from lines 10 and nozzles 11) the fluidizing gas for fluidized bed 14 housed in a lower part of vessel 9.
Coal-carbonization vessel 9 houses two regions in which particulate solids are maintained in the fluidized state: fluidized-bed 14 at 1400 F. occupies a lower part of vessel 9, and fluidized region 15 at 1740 F. occupies an upper part of vessel 9. Particulate solids are maintained in the dense-phase fluidized condition in bed 14, and they are maintained in the dilute-phase fluidized condition in region 15. The pressure at the bottom of bed 14 is 350 p.s.1.a.
Bed 14 comprises two superposed, contiguous fluidizedbed zones: a lower zone 16 comprising pellets of coke of a size suitably ranging from about inch in diameter to about /4 inch, and an upper zone 17 comprising a solid derived from naturally-occurring dolomite rock of a particle size suitably ranging from about 40-mesh to about 325-mesh. OlTgases from zone 17 convey the dolomitederived solid across void space 18 and into region 15.
Zone 16 is an agglomerating coal-carbonization zone, which preferably has the form of a frusto-conical chamher with a gradual taper and the smaller end at the bottom. The fluidizing-gas velocity is suitably 20 ft./sec. at the bottom of zone 16, and is suitably 15 ft./sec. at the top. Coal entering zone 16 is heated almost instantaneously to substantially the bed temperature, and carbonization of the coal is initiated practically instantaneously. Almost at once, the coal is split into a gaseous fraction, comprising mainly methane and hydrogen, and a sticky, semi-fluid residue. The latter is captured by a coke pellet, sticking thereto to form a smear upon the surface of the pellet. Zone 16 of coke pellets serves as a dust trap for the sticky initial carbonization residue. Further coking reactions, which occur more slowly, transform the sticky smear into dry coke and cause additional gases and vapors to be evolved. However, the residue of carbonization remains sticky for only a time on the order of a very few seconds.
Coke product is withdrawn from zone 16, to maintain the inventory of coke pellets therein substantially constant, via pipe 19 at the bottom. The m.a.f. coke has the following analysis (expressed in weight percent):
8 Carbon 95.92 Hydrogen 1.33 Sulfur 0 .30 Nitrogen 1.43 Oxygen 1.02
The rate of coke production is 333,057 pounds per hour on an m.a.f. basis.
The diameter of zone 17 is appreciably greater than the diameter of zone 16, and the fluidizing-gas velocity in zone 17 is suitably 2 ft./ sec. Heat is generated or developed in zone 17 by mechanisms to be elucidated hereinafter, the heat being communicated or conducted from zone 17 to zone 16 by virtue of the contiguity of these fluidized-bed zones. Coke pellets geyser upward from zone 16 into the middle of zone 17, mingling therein with the dolomitederived solid. The fluidizing-gas velocity in zone 17 is too small for a large inventory of coke pellets to be maintained permanently in this zone, and the coke pellets which enter zone 17 gravitate downward and back into zone 16. The fluidizing-gas velocity in zone 16 is too large for particles of the dolomite-derived solid to sink deep within this zone. The bottom of zone 16, where many of the coke pellets are partially covered with sticky matter arising from the initial carbonization reactions, is substantiallv free of particles of the dolomite-derived solid.
The dolomite-derived solid of zone 17 comprises an intimate intermingling of microscopic crystallites of CaCO CaO, Gas, and MgO. Natural dolomite, the double carbonate of calcium and magnesium, seldom contains these tWo elements in precisely one-to-one atomic ratio, the calcium usually being present in excess. Ideally, however, dolomite may be written CaCO -MgCO Solids derived by half-calcining or fully-calcining dolomite may be written [CaCO -l-MgO] and [Ca0+MgO] respectively, to signify the fact that neither of these solids is a true chemical species, but comprises an intimate intermingling of crystallites of the chemical species included between the brackets. The solid derived by allowing one of these solids to absorb sulfur may be written [CaS+MgO]. The dolomite-derived solid in zone 17 suitably comprises 2 parts CaCO 1 part CaO, 1 part C218, and 4 parts MgO, on a molar basis.
Sulfur in form of H 5 arises in vessel 9 not only as a direct result of carbonization of the coat but also as an indirect result of cracking of tar species and of attack by hydrogen upon coke. Substantially all of the H 8 reacts with the dolomite-derived solid in zone 17, thus:
[CaO-l-MgO] +H S= [CaS+MgO]-]H O (1) The dolomite-derived solid also absorbs CO in zone 17:
[Ca0+MgO] +CO [CaCO |-MgO] (2) The crystallites of MgO in the dolomite-derived solid are catalytic for the water-gas-shift reaction,
H 0+CO=H +CO (3) The solid is extremely effective in promoting the conversion of CO to H by the summation of reactions (2) and (3):
[CaO-l-MgO] +H O+CO= [CaCO +MgO] +H (4) Region 15 is a calcination zone. The flow of materials across space 18, from bed 14 to region 15, comprises (expressed in m./hr.)
C H 391.9 as; a CaO 1,659.2 MgO 6,636.8
CO 6,259.3 H 9,078.1 CO 3,221.1 H O 6,799.5 H S 18.2 COS 0.6 N 19,8117 A 247.1
The gases flowing from the several cyclones 23 are brought together in line 24 and delivered from the process. Fluidizing gas in line 7 represents a return to the process of of this gas.
Solid separated from the gas in each line 22 is delivered from each cyclone 23 to a standpipe 25 fitted with a solidflow-regulating valve 26. The flows of solid through the several valves 26 are suitably regulated so that a return of solid via pipes 25 and valves 26 to the bottom of region 15 produces a loading of solid in the gas rising upward through region 15 and also in each line 22 on the order of one pound or more of solid per actual cubic foot of gas. The effect of cyclones 23, standpipes 25, and valves 26 is to recircualte a large flow of solid from the top to the bottom of region 15. This recirculation of solid serves to maintain the temperature throughout region 15 substantially uniform and thereby to reduce the likelihood of the occurrence of small zones wherein the temperature might rise to a level such that the dolomitederived solid would sinter and lose its chemical reactivity toward H 8 and CO One of the standpipes 25 is fitted with a branch-standpipe 27, which delivers solid via solid-flow-regulating valve 28 to zone 17 of fluidized-bed 14. The solid passing through branch standpipe 27 and valve 28 comprises (expressed in m./hr.):
The flow of solid through valve 28 may advantageously be used as a primary control on the temperature of bed 14, although the temperature of fiuidizing-gas in line 12 and the rate of flow of coal in line 10 may also be used as control variables if desired.
In order to permit the rate of flow of solid through valve 28 to be used as a primary control of the temperature of bed 14, it is advantageous that at least one of the standpipes 25 have a diameter suflicient to provide room for a significant inventory of the dolomite-derived solid in the dense-phase condition. Changes in the flow through valve 28 can be reflected by changes in this inventory, so that frequent withdrawals of this solid from vessel 9 or additions thereto may be avoided.
In order to maintain the reactivity of the dolomitederived solid at a high level or to replace losses of solid which pass from cyclones 23 into line 24, it is advantageous to add relatively small quantities of dolomite intermittently from the line 40 to line 27 via valve 41. Line 40 may also be used to add seed particles of coke, suitably of about the same size as substantially the smallest coke pellet in zone 16, at a particle-number rate sub- 10 stantially equal to the particle-number rate of withdrawal of coke product from zone 16 via pipe 19. In addition, line 40 may be used to add a bed of a starter solid to zone 16 prior to starting to operate the process of FIG. 1. A preferred starter solid comprises coke pellets of the aforementioned size range.
Each of the aforementioned reactions (1), (2), (3), and (4) are exothermic. Heat is generated in zone 17 by these reactions, and heat is also developed in zone 17 by the cooling of the solid entering the zone from line 27. This solid is cooled from 1740 F. to 1400 F. in zone 17. Heat is conducted from zone 17 to zone 16 by virtue of the direct contact of these contiguous fluidized-bed zones, the heat serving to furnish the endothermic heat needed for the coal-carbonization process occurring in zone 16.
Solid in the following amount (expresed in m./hr.) is withdrawn from zone 17 via line 29:
CaCO 1,550.0 CaS 775.0
CaO 775.0 MgO 3,100.0
This solid is delivered to sulfur-recovery system 30, wherein sulfur may be extracted from the solid according to the teachings of my US. Pat. 3,402,998 (Sept. 24, 1968). System 30 returns a solid at 1200 F. to zone 17 via line 31, the solid comprising (expressed in m./hr.)
CaCO 2,846.6 CaS 253.4 MgO 3,100.0
If a low-sulfur coal is to be treated, or. if a high-sulfur coal is to be treated but a low-sulfur coke is not required, the operation of the equipment depicted schematically in FIG. 1 can advantageously be modified as follows: Alter the temperature and/or the pressure in region 15 so that CaCO will not decompose therein according to the reverse of reaction (2). This might be done by lowering the temperature and/or by raising the pressure, so that the partial pressure of CO in region 15 is greater than the equilibrium decomposition pressure of CaCO In general, a higher rate of circulation of solid from region 15 via branch-standpipe 27 and valve 28 will be required in order that the cooling of this solid in zone 17 will provide the endothermic heat. necessary for zone 16. In general, according to this modification of the operation of equipment shown in FIG. 1, the sulfur content of the fuel gas in line 23 will be higher than that indicated previously, but may still be sufiiciently low for many purposes which this gas might serve.
Residual fuel oil or other solid or liquid hydrocarbonaceous fuel of types hereinbefore described could be substituted for the coal supplied to vessel 9 via lines 10 and nozzles 11.
If recovery of sulfur is not required, the dolomitederived solid could be replaced by sand or preferably a less dense solid derived from a clay or other solid suitably inert chemically with respect to the gases present in fluidized-bed \14 and fluidized region 15. However, for this situation, a simpler apparatus is provided by the equipment depicted schematically in FIG. 2. In the figure, vessel 109 serves essentially the function of the lower part of vessel 9 in FIG. 1. Equipment items 110, 112, 114, 116, 117, and 119 operate substantially in the manner already described in connection with items 10, 12, 14, 16, 17, and 19 respectively of FIG. 1 (with the exception of the method whereby heat is developed in zone 1117). Heat is generated in zone 117, to be transmitted to zone 116, by the partial combustion of fuel through the agency of air or other gas containing oxygen introduced into zone 117 via a multiplicity of lines 120 and nozzles 121. A fuel gas produced in zone 117 is separated from dust by cyclone gas-solid separator 123, and the gas is delivered via line 124. The solid fluidized in zone 117 is suitably a sand or 11 an alumina or an alumina-silicate or even fine sizes of coke. Make-up solid for zone 117 and seed particles for zone 116 may be added from line 140 via valve 14-1. Prior to start-up to the equipment, line 140 may be used to supply a bed of a suitable starter solid to zone 116.
If a fuel gas undiluted by nitrogen is required, substantially pure oxygen may be supplied to zone 117 via lines 120, and recycle gas from line 124 may be employed as fluidizing gas supplied from line 112.
If a fuel gas undiluted by nitrogen and rich in methane is required, a possibility would be to employ a fluidizing gas rich in hydrogen and low in nitrogen in line 112 of FIG. 2 and to supply a material to zone 117 via lines 120 capable of reacting exothermically with hydrogen to produce methane. If this possibility is elected, the pressure should be appreciably above atmospheric, suitably atmospheres or greater. A suitable material to react with hydrogen would be ethane or propane or other aliphatic hydrocarbon containing 2 or more carbon atoms. A light naphtha would be a suitable material, as would also aromatic materials containing aliphatic side-chains, such as toluene or xylene or ethyl benzene or the like.
Alternatively, if a fuel gas undiluted by nitrogen is required, the embodiments depicted in FIGS. 3 and 4 may be preferred. Equipment items 109, 110, 112, 114, 116, 117, 119, 123, 124, 140 and 141 in each of FIGS. 3 and 4 operate substantially in the manner already described in connection with these items in FIG. 2 (with the exception of the method whereby heat is developed in zone 117 The fluidizing gas in line 112 is preferably low in nitrogen, and may advantageously comprise at least in part a recycle of a portion of the fuel gas product in line 124.
In FIG. 3, zone 117 houses heat-exchange surface 132, whereby heat is transferred by indirect heat exchange from a hot fluid medium to zone 117, to flow by conduction therefrom to zone 116. Suitable hot fluid mediums are liquid sodium metal and helium gas, for example.
In FIG. 4, vessel 209 serves essentially the function of the upper part of vessel 9 in FIG. 1; and equipment items 215, 222, 223, 224, 225, 226 227, and 228 operate substantially in the manner already described in connection with items 15, 22, 23, 24, 25, 26, 27, and 28 respectively in FIG. 1 (with the exceptions of the methods whereby air, fuel, and solid are introduced into region 215). Air or other gas containing oxygen is supplied as fluidizing gas to the bottom of vessel 209 from line 220. Fuel is supplied to region 215 from a multiplicity of lines 233 and nozzles 234 (for simplicity, only one line 223 and one nozzle 234 are shown in FIG. 4). Solid is transferred from zone 117 of vessel 109 to region 215 of vessel 209 via line 235 and solid-flow-regulating valve 236; the rate of the transfer is regulated to maintain a substantially constant inventory of solid in zone 117. The fuel supplied to region 215 may sometimes advantageously comprise the same fuel as that supplied via line 110 to zone 116 of vessel 109, especially if this is a fluid fuel. Alternatively, the fuel to region 215 may sometimes advantageously comprise either a portion or all of one of the two fuel products from vessel 109, the coke in line 1.19 or the fuel in line 124. Another alternate arises if the fuel gas in line 124 contains significant quantities of condensibles, such as benzene, toluene, etc. In this circumstance, the fuel to region 215 may sometimes advantageously comprise either the gaseous fraction or the liquid fraction arising from the fuel gas in line 123 after it has been cooled.
The embodiment of FIG. 4 may be used to produce a gas rich in methane and hydrogen in line 124 from either a coal or a residual oil feed in line 110. This may be accomplished with a supply of a dolomite-derived solid from line 227 to zone 117, the solid containing either CaO or CaCO along with CaS and MgO. If this is done, a system for sulfur recovery may advantageously be added to FIG. 4, like system 30 of FIG. 1. Alternatively, the solid supplied to zone 117 from line 227 may suitably be a sand or an alumina or an alumina-silicate or a fine coke.
The aforementioned gas rich in methane and hydrogen would be suitable for further processing to yield a synthetic pipeline gas having a heating value on the order of 920 or more British thermal units per standard cubic foot. This further processing might advantageously include an operation in which condensibles in the gas in line 124 are subjected to a hydrodealkylation treatment, which may sometimes advantageously employ hydrogen present in the non-condensible fraction of the gas from line 124.
The embodiments described above in connections with FIGS. 3 and 4 are suitable for modification in direction of greater yield of condensible fuel products and lesser yield of methane or other light hydrocarbons. Such a modification may be brought about by lowering the temperature of bed 114. For maximum production of liquid products, this temperature should be between about 900 and 1100 F.
If a hydrocarbonaceous fuel, such as bituminous coal or residual oil, is treated in the apparatus of FIG. 3 by a gas from line 112 containing hydrogen at a sufliciently high partial pressure, the hydrocarbonization or hydrocracking reactions occurring in zone 116 will be exothermic, rather than endothermic as in the embodiments previously described. This heat may be removed from vessel 109 by providing a cooling medium to heat-exchange surface 132. A suitable cooling medium is water, for example, and the heat transferred from zone 117 to the water may advantageously be employed to generate high-pressure steam. Alternatively, the apparatus of FIG. 2 might be used, and a vaporizable liquid such as water could be added directly to zone 117 via lines 120 and nozzles 121, the latent heat of the water flashing in zone 117 taking up the exothermic heat passing by conduction from Zone 116 into zone 117.
I do not wish my invention to be limited to the particular embodiments illustrated in the drawings and described above in detail. Other arrangements will be recognized by those skilled in the art, as well as other purposes which the invention can serve.
1. A process for pyrolyzing a solid or liquid hydrocarbonaceous fuel, comprising:
(a) providing a fluidized bed comprising first and second zones, said first zone comprising pellets of coke, said second zone being superposed on said first zone and contiguous therewith and receiving fluidizing gas therefrom and comprising a particulate solid having particles of sizes smaller than said coke pellets, said first zone being fluidized at a superficial gas velocity sufliciently great as to substantially prevent the substantially largest particle of said solid from sinking deep toward the bottom of said first zone, and said second zone being fluidized at a superficial gas velocity sufficiently small as to allow the substantially smallest pellet of said pellets of coke to sink downward within said second zone and to reenter said first zone,
(b) charging a solid or liquid hydrocarbonaceous fuel to said first zone,
(c) causing heat to flow by conduction between said first and second zones in an amount and direction to maintain a substantially constant temperature in said first zone, said temperature being sufficient to cause pyrolysis of said fuel to occur with production of fuel gases and a coke product adhering to said pellets,
(d) withdrawing fuel gas from said second zone, and
(e) withdrawing coke pellets from said fluidized bed.
2. The process of claim 1 in which said direction of flow of said heat in step (c) is from said second zone to said first zone, and in which heat is imparted to said second zone.
3. The process of claim 1 in which said direction of flow of said heat in step (c) is from said first zone to said second zone, and in which heat is Withdrawn from said second zone.
4. The process of claim 1 including the step of providing seed particles of coke to said first zone having a particle size substantially equal to said smallest pellet, the particle-number rate at which said seed particles are provided being substantially equal to the particle-number rate at which said coke pellets are withdrawn from said fluidized bed in step (e).
5. A process for pyrolyzing a solid or liquid hydrocarbonaceous fuel, comprising:
(a) charging a solid or liquid hydrocarbonaceous fuel to a first zone of a fluidized bed, said first zone comprising pellets of coke at a temperature sufficient to cause pyrolysis of said fuel to occur with production of fuel gases and a coke product adhering to said pellets,
(b) imparting heat to a second zone of said fluidized bed to maintain said temperature substantially constant, said second zone being superposed on said first zone and contiguous therewith and receiving fluidizing gas therefrom and comprising a particulate solid having particles of sizes smaller than said coke pellets, said first zone being fluidized at a superficial gas velocity sufliciently great as to substantially prevent the substantially largest particle of said solid from sinking deep toward the bottom of said first zone, said second zone being fluidized at a superficial gas velocity sufficiently small as to allow the substantially smallest pellet of said pellets of coke to sink downward within said second zone and to reenter said first zone, said heat flowing by conduction from said second zone to said first zone,
(c) withdrawing fuel gas from said second zone, and
(d) withdrawing coke pellets from said fluidized bed.
6, The process of claim 5 including the following steps: feeding a particulate solid having particles of substantially said sizes to said second zone at a temperature greater than said temperature, and withdrawing solid from said second zone at a rate to maintain the solid inventory of said second zone substantially constant.
7. The process of claim 6 in which said particulate solid includes calcium oxide and the fluidizing gas to said second zone contains carbon dioxide at a partial pressure exceeding the equilibrium decomposition pressure of calcium carbonate at said temperature.
8. The process of claim 6 in which said solid includes calcium oxide and the fluidizing gas to said second zone contains carbon monoxide, steam, and carbon dioxide, the combined partial pressure of the carbon dioxide and carbon monoxide exceeding the equilibrium decomposition pressure of calcium carbonate at said temperature.
9. The process of claim 5 including the step of adding air or other gas containing oxygen to said second zone to effect partial combustion therein of said fuel gases, thereby generating heat in said second zone.
19. The process of claim 5 in which said second zone houses heat-exchange surface whereby heat is added to said second zone by indirect heat transfer from a fluid heating medium.
1'1. A process for pyrolyzing a solid or liquid hydrocarbonaceous fuel, comprising:
(a) charging a solid or liquid hydrocarbonaceous fuel to a first zone of a fluidized bed, said first zone comprising pellets of coke at a temperature sufiicient to cause pyrolysis of said fuel to occur with production of fuel gases and a coke product adhering to said pellets,
(b) fluidizing said first zone with a gas containing hydrogen,
(0) withdrawing heat from a second zone of said fluidized bed to maintain said temperature substantially constant, said second zone being superposed on said first zone and contiguous therewith and receiving fluidizing gas therefrom and comprising a particulate solid having particles of sizes smaller than said coke pellets, said first zone being fluidized at a superficial gas velocity sufiiciently great as to substantially prevent the substantially largest particle of said solid from sinking deep toward the bottom of said first zone, said second zone being fluidized at a superficial gas velocity sufliciently small as to allow the substantially smallest pellet of said pellets of coke to sink downward within said second zone and to reenter said first zone, said heat flowing by conduction from said first zone to said second zone,
(d) withdrawing fuel gas rich in methane from said second zone, and
(e) withdrawing coke pellets from said fluidized bed.
12. The process of claim 11 in which said second zone houses heat-exchange surface whereby heat is removed from said second zone by indirect heat transfer to a fluid cooling medium.
References Cited UNITED STATES PATENTS 2,595,366 5/1952 ODell et a1 20136X 2,725,349 11/1955 Cahn et al 201--20X 2,970,893 2/1961 Viles 23-181 3,194,644 7/1965 Gorin et 'al. 48-197 3,320,152 5/1967 Nathan et al. 201-12X 3,431,197 3/1969 Jahnig et a1. 2013 1X 3,443,908 5/1969 Chaney et a1 20112X NORMAN YUDKOFF, Primary Examiner D. EDWARDS, Assistant Examiner US. Cl. X.R.