Pyrolysis process

Description

BACKGROUND ART
The present invention is directed to a process for producing condensed stabilized hydrocarbons by flash pyrolysis of carbonaceous material.
Fluid fossil fuels, such as oil and natural gas are becoming scarce as these fuels are consumed by a world whose population is continually growing. As a consequence, considerable attention is being directed toward pyrolyzing solid carbonaceous materials such as coal to useful liquid and gaseous hydrocarbon products. Pyrolysis processes vary widely and include transport flash pyrolysis where pyrolysis occurs under turbulent flow conditions. A problem exists in maximizing the yield of liquid hydrocarbons having molecular weights useful for conversion to more valuable end products because of the presence of newly formed volatilized hydrocarbon free radicals in the volatilized pyrolytic vapor.
One of the first steps in the pyrolysis of carbonaceous material is the thermal generation of hydrocarbon free radicals via homolytic bond scission of the coal. These hydrocarbon free radicals will combine with each other to produce undesirable heavy molecules such as heavy viscous tars having high boiling points. These hydrocarbon free radicals will also combine with carbon sites, such as present on char, to form more char or coke.
A technique that has been used to upgrade tar liquids and improve middle distillate tar liquid yield, is the addition of gaseous hydrogen directly to the pyrolysis reactor. By hydrogenating volatilized hydrocarbons with gaseous hydrogen directly in the pyrolysis reaction zone, sulfur and nitrogen are removed as hydrogen sulfide and ammonia. Such hydrogenation directly in the pyrolysis zone also reduces the viscosity and lowers the average boiling point of the subsequently condensed volatilized hydrocarbons by terminating some hydrocarbon free radicals before they are allowed to polymerize to heavy tar liquids.
Processes involving such hydrogenation are disclosed in U.S. Pat. Nos. 4,162,959 and 4,166,786 both of which are incorporated herein by reference. These patents disclose a process wherein a carbonaceous material feed, hot heat supplying carbon-containing residue, and hydrogen gas are reacted in a transport flash pyrolysis reactor. Pyrolysis and hydrogenation of the pyrolysis products occur simultaneously.
The effectiveness of hydrogen gas in terminating hydrocarbon free radicals is directly related to the hydrogen partial pressure. The pyrolysis reactor is preferably operated at pressures slightly greater than ambient, although pressures up to about 10,000 psig may also be used. An increase in hydrogen partial pressure increases free radical termination. High pressures, however, increase both the capital and operational cost of pyrolysis. Therefore, the preferred hydropyrolysis pressure in the pyrolysis zone for economical operation is from about 1 psig to about 1000 psig.
Tar polymerization and cracking occur rapidly at pyrolysis temperatures. To minimize cracking pyrolysis vapors are rapid cooled and condensed by either direct or indirect heat exchange. Rapid cooling and condensation, although preventing some tar from cracking, are still not satisfactory in preventing a significant portion of the tar from polymerizing by free radical recombination in the liquid state.
A pyrolysis process is therefore needed which substantially eliminates undesirable volatilized hydrocarbon free radical reactions early in the formation of pyrolysis products, thereby increasing the yield of desirable lower molecular weight tar liquids having relatively low boiling points and decreasing the yield of undesirable heavy viscous tars having relatively high boiling points.
SUMMARY AND DISCLOSURE OF THE INVENTION
This invention relates to a process for recovery of values produced from a solid particulate carbonaceous material containing bound hydrogen atoms. In general a solid particulate carbonaceous feed material containing bound hydrogen atoms is contacted in a pretreatment zone with a predetermined amount of a first capping agent which is a liquid or vapor at contacting conditions. The first capping agent is sorbed at least in part by the solid particulate carbonaceous feed material and there is formed a premixture comprising first capping agent which has not been sorbed by the solid particulate carbonaceous feed material and the solid particulate carbonaceous feed material containing the first sorbed capping agent. The first capping agent is a liquid or solid at ambient temperature and pressure but a vapor or liquid at contacting conditions.
The premixture is pyrolyzed in the presence of a predetermined amount of a second capping agent under conditions of time and elevated temperature sufficient to pyrolyze the solid particulate carbonaceous feed material. The second capping agent, which also is a liquid or solid at ambient temperature and pressure, has the capability of substantially simultaneously stabilizing the newly formed volatilized hydrocarbon free radicals contained in the gaseous mixture. The second capping agent need not be identical in composition to the first capping agent. Both the first and second capping agent can be tailored to their particular use if desired or advantageous in the pyrolysis of the particular solid carbonaceous feed material used in the process.
The first capping agent, whether sorbed by the solid particulate carbonaceous feed material or not, has the capability of substantially simultaneously stabilizing the newly formed volatilized hydrocarbon free radicals contained in the gaseous mixture. Such free radicals are stabilized by the transfer of hydrogen from the capping agent to the free radicals thereby forming stabilized radicals and a hydrogen depleted capping agent. At least a major portion of the volatilized hydrocarbon free radicals contained in the gaseous mixture stream are stabilized either by the first capping agent or the second capping agent or both.
The pyrolysis products comprise particulate solids and a gaseous mixture. The particulate solids comprise a carbon-containing solid residue produced from the solid particulate carbonaceous feed material. The gaseous mixture comprises pyrolytic product vapors produced from the solid particulate carbonaceous feed material. The pyrolytic product vapors comprise hydrocarbons which comprise newly formed volatilized hydrocarbon free radicals. At least a portion of the hydrocarbons comprise four or more carbon atoms. The newly formed volatilized hydrocarbon free radicals are stabilized by reaction with the first or second capping agents or both thereby producing stabilized newly formed volatilized hydrocarbons which are contained in the gaseous mixture.
The particulate solids are separated from the gas-solid mixture removed from the pyrolysis zone to form a substantially solids-free gaseous mixture stream which is then immediately contacted with a quench fluid to condense at least a major portion of the hydrocarbon vapors having four or more carbon atoms present in the gaseous mixture stream. A gaseous residue and a liquid mixture are then formed. The liquid mixture comprises a hydrocarbon condensate, the quench fluid, any excess first and second capping agent, a hydrogen depleted capping agent and condensed stabilized hydrocarbons. Values are recovered from the gaseous residue. Condensed stabilized hydrocarbons are recovered from the liquid mixture.
This invention therefore relates to a process for recovery of condensed stabilized hydrocarbons produced by flash pyrolysis of solid particulate carbonaceous materials and, more particularly, to a process for terminating free radicals by contacting the solid particulate carbonaceous feed material with a first capping agent so that it is sorbed by the solid particulate carbonaceous feed material prior to pyrolysis. The newly formed volatilized hydrocarbon free radicals are then immediately contacted with the sorbed first capping agent and the second capping agent in a transport flash pyrolysis reactor to form substantially simultaneously stabilized newly formed volatilized hydrocarbons which are then condensed to produce condensed stabilized hydrocarbons.
In practicing this invention, a solid particulate carbonaceous feed material containing bound hydrogen atoms and a sorbed first capping agent, a second capping agent, a transport gas, and a solid particulate source of heat are fed to a transport flash pyrolysis reactor for pyrolyzing the solid particulate carbonaceous feed material. A pyrolysis product stream is formed which contains particulate solids and a gaseous mixture comprising pyrolytic product vapors which comprise hydrocarbons. The hydrocarbons formed include larger hydrocarbons having four or more carbon atoms. The hydrocarbons formed also include newly formed volatilized hydrocarbon free radicals including volatilized hydrocarbon free radicals having four or more carbon atoms.
Substantially simultaneous with the formation of the newly formed volatilized hydrocarbon free radicals, at least the major portion of such free radicals are stabilized in the vapor state. While we do not wish to be bound by theory, the sorbed first capping agent and the second capping agent terminate, i.e., stabilize the newly formed hydrocarbon free radicals by providing active hydrogen atoms to react with and terminate the free radicals as they are formed. In one embodiment the first capping agent is added initially to the pretreatment zone of the system and is regenerated by the process. Make-up first capping agent can be added if required. In another embodiment the second capping agent is added initially to the system and is regenerated by the process. Make-up second capping agent can be added if required. In another embodiment the process produces a first or second capping agent, or both, during pyrolysis and such capping agent or agents are produced from the hydrocarbon product stream.
The pyrolysis product stream passes from the pyrolysis reactor to a separation zone where at least a major portion of the particulate solids are separated from the gaseous mixture, to form a substantially solids-free gaseous mixture stream.
A portion of the separated particulate solids is recovered as char product and a remainder of the particulate solids is recycled, after heating, to the transport flash pyrolysis reactor as the solid particulate source of heat.
The solids-free gaseous mixture stream is then contacted in a quench zone with a quench fluid which is provided under conditions sufficient to condense at least a major portion of the hydrocarbon vapors having four or more carbon atoms thereby forming a hydrocarbon condensate and a gaseous residue. The hydrocarbon condensate in admixture with the quench fluid forms a liquid mixture. At least a portion of the capping agent is partially depleted of hydrogen atoms in the pyrolysis zone and passes with any unconsumed capping agent in the liquid mixture to a liquid product separation zone for separation and recovery of liquid products.
In a further embodiment of this invention the quench fluid also comprises at least one capping agent for terminating or stabilizing any remaining newly formed hydrocarbon free radicals contained in the gaseous mixture stream which were not stabilized in the pyrolysis zone.
A neutral tar liquid stream which comprises tar liquids and at least a portion of the capping agent and hydrogen depleted capping agent is separated from the liquid mixture in the liquid product separation zone. In one embodiment at least a portion of the neutral tar liquid stream is hydrogenated to upgrade the tar liquids and to regenerate capping agent from the depleted capping agent so that it is suitable for reuse in the process as a first capping agent for contacting the solid particulate carbonaceous feed material in the pretreatment zone or as a second capping agent for introducing directly into the pyrolysis zone, which in either case subsequently terminates hydrocarbon free radicals. In one embodiment of least a portion of the hydrogenated neutral tar liquid stream can be utilized as a first or second capping agent, and in the further embodiment mentioned above as a quench liquid. In another embodiment the regenerated capping agent and any unconsumed capping agent are separated from the hydrogenated neutral tar liquid stream and that combination is recycled as the capping agent used in the pretreatment zone. If this stream is also used as a quench liquid, then the quench liquid will have a higher concentration of capping agent than in the former embodiment.
In still another embodiment at least a portion of the depleted capping agent and any unconsumed capping agent are separated directly from the liquid mixture and hydrogenated to regenerate a capping agent suitable for contacting the solid particulate carbonaceous feed material in the pretreatment zone or for contacting the newly formed volatilized free radicals in the pyrolysis zone and subsequently terminating hydrocarbon free radicals. This stream is then recycled to the pretreatment zone as at least a portion of the capping agent required for sorption by the solid particulate carbonaceous feed material or to the pyrolysis zone as at least a portion of the capping agent required therein. In a preferred embodiment, especially after steady state is reached, the capping agent is principally a liquid produced by the pyrolysis process.
Capping agents useful in accordance with the practice of this invention include hydrogen donor solvents, hydrogen transferring or shuttling agents, and/or free radical trapping agents, mixtures thereof and the like.
Hydrogen donor solvents are those solvents which can donate hydrogen to tar free radicals to prevent recombination or polymerization of tar liquids by free radical mechanisms in the vapor or liquid state. Examples of hydrogen donor solvents are hydroaromatic compounds, such as tetrahydronaphthalene, dihydronaphthalene, partially hydrogenated phenanthrenes, partially hydrogenated anthracenes, alkyl substituted compounds of the above, mixtures thereof, and the like, which comprise multi-ring structures wherein one of the rings is aromatic. Hydrogen donor solvents that have fully saturated aromatic compounds or alicyclics, such as decahydronaphthalene, perhydroanthrancene, perhydrophenanthrene, or alkyl substituted compounds of the above, or mixtures thereof or the like are especially preferred because such capping agents crack during the pyrolysis process to form single ring aromatics such as benzene, methyl radicals and hydrogen atoms. The methyl radicals and hydrogen atoms are useful in terminating other free radicals formed during the process. The cracking of these solvents also increases the yield of light aromatics such as benzene, toluene, and xylene and the like. Furthermore, since the pyrolysis product liquid contains aromatics such as naphthalene and the like which can be hydrogenated to replenish the supply of capping agent, capping agent production by the process can be achieved.
Hydrogen transferring or shuttling agents do not have donatable hydrogen but can accept hydrogen from other sources and transfer the hydrogen to the hydrocarbon free radicals. Examples of hydrogen transferring or shuttling agents are naphthalene, anthracene, creosote oil, and the like.
Capping agents can also be free radical trapping agents, such as thiols, phenols, amines, and the like which can act either as hydrogen donor solvents and/or as hydrogen transferring or shuttling agents.
Regardless of the particular capping agent utilized, preferably a sufficient amount of the capping agent or agents is used and sorbed by the feed solid carbonaceous material and introduced directly into the pyrolysis zone to terminate substantially all of the volatilized hydrocarbon free radicals which will be newly formed during pyrolysis in the pyrolysis zone. By "substantially all of the volatilized hydrocarbon free radicals", it is meant that at least about 90% and preferably greater than about 99% of the volatilized hydrocarbon free radicals newly formed by pyrolysis and contained in the pyrolytic vapor stream are terminated.
In carbonaceous materials such as coal or the like there are many large and relatively stable free radicals initially present before pyrolysis which, it is believed, are not terminated in the process. These radicals, of course, are not newly formed and are believed to be large free radicals that have multiple ring structures, having unpaired electrons which are highly stabilized by resonance and therefore are less reactive with capping agents. Steric hindrance factors in such large radicals can also retard the free radical-capping agent interaction.
As the percentage of volatilized hydrocarbon free radicals that are terminated increases, the average molecular weight of the tar liquid products decreases, providing for a higher yield of the desirable lower molecular weight tar liquids. It takes one reactive hydrogen atom to stabilize each volatilized hydrocarbon free radical produced, for example, decahydronaphthalene can donate ten hydrogen atoms or a combination of light hydrocarbon radicals such as methyl radicals and hydrogen atoms for capping or terminating ten volatilized hydrocarbon free radicals. In one embodiment, at least a molar amount of decahydronaphthalene is utilized in the pretreatment zone which is equal to one tenth the number of moles of newly formed hydrocarbon free radicals which will be formed during pyrolysis. In a preferred embodiment excess capping agent is used.
The pyrolysis product vapors and other gases are separated from the pyrolysis product solids and other solids and the substantially solids-free gaseous stream remaining is contacted with a quench fluid in a quench zone.
The quench liquid, which may or may not contain a capping agent, is introduced into the quench zone at a temperature and at a flow rate which will provide for condensation of at least a major portion and preferably substantially all of the vaporized hydrocarbons having four or more carbon atoms. By "substantially all of the vaporized hydrocarbons having four or more carbon atoms", it is meant that at least about 95% and preferably greater than about 99% of the vaporized hydrocarbons having four or more carbon atoms in the gaseous mixture stream are condensed by direct heat exchange with the quench fluid.
Temperature reduction of the pyrolytic vapors should also be sufficiently rapid to hinder recombination of desirable lighter hydrocarbon molecules into less desirable heavier molecules. Generally, the temperature of the product vapor can be reduced sufficiently rapidly by using a ratio of about 0.1 to about 100 pounds of quench liquid per pound of substantially solids-free vapor mixture. Preferably the ratio is from about 1 to about 10 pounds of quench liquid per pound of vapor mixture.
The temperature of the substantially particulate solids-free gaseous mixture stream is usually in the range of the desired pyrolysis temperature, i.e., from about 1100 to about 1400.degree. F. It has been found desirable to provide the quench liquid at a temperature and flow rate sufficient for rapidly reducing the temperature of the gaseous mixture to less than about 700.degree. F., preferably to less than about 200.degree. F. for substantially eliminating recombination of lighter hydrocarbon molecules.
The solid carbonaceous material from which values may be recovered in accordance with this invention include coals, gilsonite, tar sands, oil shale, oil from oil shale, the organic portion of solid waste and the like. Since the process is especially useful for coals, the process will be described for the processing of coals and particularly agglomerative coals. All the various types of coal or coal-like substances can by pyrolyzed. Coals include anthracite coal, bituminous coal, subbituminous coal, lignite, peat, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the present invention will become better understood with reference to the following description, accompanying drawings and appended claims.
FIG. 1 schematically illustrates the overall process of the invention.
FIG. 2 schematically illustrates the operation of a quench zone.
FIG. 3 is a flow sheet of a unit used to demonstrate features of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION
With reference now to FIG. 1, the coal to be pyrolyzed is introduced into a coal preparation zone 10 where it is initially comminuted to a suitable particle size for pyrolysis. A suitable particle size has been found to be less than about 1000 microns.
When an agglomerative coal is used, preferably the particle size is less than about 250 microns to enable the coal to be rapidly heated through the plastic state of the coal before the coal strikes the walls of a pyrolysis reactor in order to prevent the coal from agglomerating and plugging the reactor. The desired coal particle size will depend on the size and configuration of the pyrolysis reactor. In all cases, however, it is desired that a particle size be chosen so that substantially all the coal particles are rendered non-tacky before they strike the reactor wall as described in U.S. Pat. No. 4,135,982 which is incorporated herein by reference.
In general the coal is preferably comminuted to as small a size as practical for facilitating its rapid heating in the pyrolysis reactor. However, it is important to minimize the production of fines, e.g., particles having a size less than about 10 microns, in order to facilitate subsequent gas-solid separation operations as described later herein. Fines which are produced can be removed in a cyclone separation zone (not shown) designed for separation of the fines smaller than a predetermined particle size. Fine removal minimizes particle carry-over and contamination of pyrolysis liquid products.
The coal can be fully dried or preferably only partially dried thereby allowing steam to be produced in the pyrolysis zone which serves to inhibit active sites on char solids, as will be explained further below. It has been found that a high hydrocarbon product yield is obtained by leaving about 15% by weight water in subbituminous coal feeds. The coal can be dried fully or partially with flue gas, or effluent gas from a flare, or the like. Additional details of the preparation of coal for pyrolysis can be found in U.S. Pat. No. 4,145,274 which is incorporated herein by reference.
After the coal is comminuted to a particle size of less than about 1000 microns, it is contacted in the coal preparation zone 10 with a first capping agent. The first capping agent remains in contact and is sorbed by the comminuted coal prior to feeding it to a pyrolysis reactor.
There are several methods that can be used to contact the comminuted coal with the predetermined amount of the first capping agent. For example, the comminuted coal can be contacted by a liquid first capping agent in a slurry tank to form a slurry of the first capping agent and coal. Alternatively, the comminuted coal can be sprayed with a first capping agent in the form of a fog or mist.
The amount of first capping agent sorbed by the comminuted coal can be adjusted by changing the amount of first capping agent introduced into the fluidized coal feeder or by changing the residence time of the comminuted coal in the fluidized coal feeder. Typically, coal residence times are from a few seconds up to about 1 hour. About 0.1 to about 10 pounds of first capping agent to contact each pound of comminuted coal pyrolyzed is sufficient to terminate substantially all of the hydrocarbon free radicals newly formed by the process. Usually from about 0.2 pounds to about 1.0 pound of first capping agent is sufficient for many feed solid carbonaceous materials.
Preferably the liquid capping agent is heated to a temperature above its boiling point to form a superheated first capping agent vapor which is then used for contacting the coal. This procedure not only heats the coal but also evaporates occluded water from coal particles thereby reducing the heat load for subsequent pyrolysis. The first capping agent can be heated economically with a waste heat stream or the like.
The superheated first capping agent vapor can be introduced into a fluidized bed coal feeder or the like in a coal pretreatment zone of the preparation zone to contact and be sorbed by the comminuted coal. Preferably the comminuted coal is introduced into a fluidized bed coal feeder (not shown in FIG. 1) operating at a temperature of from about 300.degree. F. to about 750.degree. F. in the coal preparation zone 10 of FIG. 1.
Although other gases can be used to fluidize the comminuted coal, it is preferred to use the superheated first capping agent vapor as the fluidizing gas. The super-heated first capping agent vapor is preferably heated to a temperature and provided at a flow rate sufficient to heat and maintain the coal at a desired fluidized bed operating temperature of from about 300.degree. F. to about 750.degree. F. However, in all cases, the coal temperature should be below its softening temperature.
The first capping agent introduced into the coal preparation zone 10, can be a recycle capping agent stream in which the capping agent was formed and continuously regenerated by the pyrolysis process. In another embodiment the first capping agent is added to the system prior to system startup and is regenerated in a hydrogenation zone prior to being recycled. In addition to adding first capping agent at system startup, first capping agent can be added during the process to replenish capping agent losses.
Referring again to FIG. 1, a recycle first capping agent stream 77 is passed through a heater 79 wherein the capping agent stream is heated to between about 300.degree. F. and about 750.degree. F. to form the heated capping agent stream 81a which is introduced into a fluidized bed coal feeder in the coal preparation zone 10 as a superheated first capping agent vapor to contact the comminuted coal. The comminuted coal is heated by and sorbs the first capping agent prior to being transported to the pyrolysis reactor 14 as a coal feed stream.
A heated coal premixture comprising first capping agent and comminuted coal containing sorbed first capping agent is removed from the fluidized bed in coal preparation zone 10 and introduced into pyrolysis reactor.
The coal premixture is combined with a non-deleterious reactive carrier or transport gas and is passed through line 12 to transport pyrolysis reactor 14. By a "non-deleterious reactive carrier or transport gas", herein is meant a gas substantially free of free oxygen, but which may contain constituents which react to upgrade product quality. In one embodiment recycle product gas is used as the carrier gas. Nitrogen could be used as a carrier gas in experimental or developmental studies but nitrogen as a carrier gas in a commercial process is not thought to be economical. The carrier gas can also contain carbon dioxide and/or steam as char deactivators.
The coal premixture is combined, in pyrolysis reactor 14, with a solid particulate source of heat which is preferably a portion of the solid residue of pyrolysis or char product which was heated in oxidation zone 16 by partial oxidation to a temperature sufficient for direct use as a solid particulate source of heat in pyrolysis reactor 14. Pyrolysis reactor 14 is operated under turbulent flow conditions at temperatures from about 600.degree. to about 2000.degree. F. at residence times of less than about 5 seconds and preferably from about 0.1 to about 3 seconds to maximize the yield of volatilized hydrocarbons. Longer residence times at lower pyrolysis temperatures are preferred because cracking of volatile pyrolysis vapors is minimized while the desired degree of devolatilization is still achieved. To effect pyrolysis, the weight ratio of the solid particulate source of heat to the solid particulate carbonaceous feed material, or comminuted coal, will range from about 2:1 to about 40:1. These weight ratios require the temperature of the solid particulate source of heat to be about 25.degree. to about 500.degree. F. higher than the pyrolysis zone temperature. Pyrolysis operations to which this invention is adapted are described in U.S. Pat. Nos. 3,736,233 and 4,085,030 each of which is incorporated herein by reference as well as earlier mentioned U.S. Pat. No. 4,145,274.
The coal or solid particulate carbonaceous feed material premixture feed, the non-deleteriously reactive transport gas, a second capping agent and the solid particulate source of heat are combined under turbulent flow conditions in pyrolysis reactor 14. The second capping agent is at ambient temperature and pressure a liquid or in some cases a solid. Preferably the capping agent is preheated as described below.
As shown in FIG. 1, reactor 14 is preferably a substantially vertically oriented descending flow transport pyrolysis reactor in which the solid particulate source of heat enters a substantially vertically oriented annular fluidization chamber 18 which surrounds the upper portion of a substantially vertically oriented descending flow pyrolysis reactor 14. The fluidization chamber has an inner peripheral wall 20 which forms an overflow weir to a substantially vertically oriented mixing region 21 of the pyrolysis reactor. The solid particulate source of heat is maintained in the fluidization chamber in a fluidized state by the flow of a substantially non-deleteriously reactive gas so that the solid particulate source of heat is discharged over the weir and downwardly into the vertically oriented mixing region at a rate sufficient to maintain the pyrolysis reaction zone at the pyrolysis temperature.
The coal premixture and a substantially non-deleteriously reactive transport gas are injected from a solids feed inlet 22 into the vertically oriented mixing region and form a resultant turbulent mixture of the solid particulate source of heat, the coal premixture, the second capping agent, and the substantially non-deleteriously reactive transport gas. The resultant turbulent mixture is passed downwardly from the mixing region to a pyrolysis reaction zone within the transport pyrolysis reactor in which the particulate coal is pyrolyzed.
The newly formed volatilized hydrocarbon free radicals are substantially simultaneously terminated or stabilized by the first capping agent of the coal premixture and/or by the second capping agent as such radicals are formed. A pyrolysis product stream 24 is formed which contains as particulate solids, the solid particulate source of heat and a carbon-containing solid residue of pyrolysis; and a gaseous mixture comprising the substantially non-deleteriously reactive transport gas and pyrolytic product vapors which comprise hydrocarbons some of which have four or more carbon atoms, stabilized newly formed volatilized hydrocarbon free radicals, and any excess capping agent.
Predetermined amounts of heated first and second capping agents are used to terminate at least a major portion of the hydrocarbon free radicals formed in the subsequent pyrolysis. More preferably, the amounts of such capping agents are sufficient to terminate substantially all of the hydrocarbon free radicals formed. By the term "substantially all" of the hydrocarbon free radicals formed, herein is meant that at least about 95%, and preferably greater than about 99%, of the hydrocarbon free radicals newly formed are terminated. As the percentage of hydrocarbon free radicals that are terminated increases, the yield of the desired lower molecular weight tar liquids is increased.
Due to the turbulent flow conditions within the transport pyrolysis reactor, the various feed streams to the pyrolysis reactor are in intimate contact with each other as the comminuted coal as it is pyrolyzed. The pyrolysis reactor must be operated under conditions which prevent condensation of the volatilized hydrocarbons produced during pyrolysis or the capping agents within the pyrolysis reactor in order to prevent fouling and ultimate plugging of the reactor.
In the embodiment shown in FIG. 1, the first capping agent is introduced into coal preparation zone 10 in recycle first capping agent stream 81a. In this embodiment the first capping agent is formed and continuously regenerated by the process, as will be described below.
In another embodiment, the first capping agent is added to the process prior to startup and is regenerated by hydrogenation of the hydrogen depleted capping agent prior to recycling to the coal preparation zone 10 as a recycle capping agent stream.
In the embodiment of FIG. 1, a portion of recycle capping agent stream 77 is passed through a heater 79 wherein the capping agent stream is heated to between about 300.degree. and about 750.degree. F. It is preferred to limit the heating of the recycle capping agent stream to a temperature that will avoid cracking of the capping agent in the heater. Preferably heated first capping agent stream 81a is introduced into the coal preparation zone as a vapor.
The second capping agent can be fed into pyrolysis reactor 14 along with the coal premixture through feed inlet 22, or it can be injected directly into the vertically oriented mixing region of the pyrolysis reactor, as shown in FIG. 1, or directly into the pyrolysis reaction zone if desired. In this embodiment of this invention, the second capping agent is heated prior to its introduction into the pyrolysis reactor. It is preferred to heat the second capping agent to a temperature greater than about 200.degree. F. and especially preferably to above about 600.degree. F. to reduce the heat requirements in pyrolysis reactor 14.
In the embodiment shown in FIG. 1, the second capping agent is introduced into transport pyrolysis reactor 14 in recycle capping agent stream 81b. In this embodiment the second capping agent is formed and continuously regenerated by the process, as will be described below.
In another embodiment, the second capping agent is added to the process prior to startup and is regenerated by hydrogenation of the hydrogen depleted capping agent prior to recycling to the pyrolysis reactor as a recycle capping agent stream.
In the embodiment of FIG. 1, a portion of recycle capping agent stream 77 is passed through a heater 80 wherein the second capping agent stream is heated to between about 200.degree. to about 1000.degree. F. It is preferred to limit the heating of the recycle second capping agent stream to a temperature that will avoid cracking of the capping agent in the heater. Heated second capping agent stream 81b is introduced into the transport pyrolysis reactor as a vapor at inlet 23.
In the embodiment shown in FIG. 1 the first capping agent, in stream 81a, and the second capping agent, in stream 81b, are the same chemical composition. However, it is to be understood that the recycle capping agent stream 77 can be treated in such a way, for example fractionated, so that the first and second capping agents are not identical in chemical composition but are tailored to suit the needs of the different uses.
In general, the amounts of the first and second capping agents are operative for terminating at least a major portion of the newly formed hydrocarbon free radicals at low pressures, i.e., at pressures near atmospheric pressure. Therefore, the transport pyrolysis reactor may be designed to operate at low pressure thereby reducing the overall process cost.
In several embodiments as described below, the capping agents are hydrogenated neutral tar liquids recovered from the condensate. The capping agents contain at least one regenerative capping agent which is formed during pyrolysis or hydrogenation of liquid pyrolysis products. In another embodiment the capping agents are added initially and when depleted of hydrogen atoms can be regenerated by hydrogenation. In either case it is convenient to add the capping agents to the system at startup. Where the capping agents are produced by the process it can be different than the start-up capping agents in which case the capping agents become essentially process produced capping agents after steady state is reached.
The reactor described herein is especially adaptive to agglomerative coal as it permits the coal to pass through its plastic state before striking the reactor walls. Such a transport pyrolysis reactor is known as an entrained bed or transport reactor wherein the velocity of the transport gas, the solid particulate source of heat, and the solid particulate carbonaceous feed material are essentially the same and in the same direction.
Pyrolysis product stream 24 from pyrolysis reactor 14 is introduced into a separation zone 26. In separation zone 26, which can comprise cyclone separators or the like, at least a major portion of the solids are separated from the gas-solid mixture to form a substantially solids-free gaseous mixture stream 28. It is desirable to separate substantially all, i.e., about 99% or higher, of the solids from the gas-solid mixture to form the substantially solids-free gaseous mixture stream. Removing substantially all of the solids from the gas-solid mixture provides a gaseous mixture stream which can be handled in various downstream equipments without fouling or plugging.
A portion of the carbon-containing solid residue and spent solid particulate source of heat is withdrawn from separation zone 26 and conveyed in conduit 32 to oxidation zone 16 for partial oxidation with a source of oxygen, such as air, to produce a solid particulate source of heat and a combustion gas. Another portion of the separated solids is withdraw as product char in stream 30. The flue gas from the oxidation zone 16 contains oxidation products of the char such as carbon monoxide, carbon dioxide, water vapor and sulfur dioxide. In this embodiment, oxidation of the char, which is exothermic, generates essentially all of the heat required for pyrolysis of the coal in the coal premixture. Other means of heating can be used however.
The hot particulate char is then separated from the combustion gas by means (not shown) such as one or more centrifugal separation stages in series. Preferably, oxidation zone 16 is a cyclone oxidation-separation reactor designed so that the char can be both heated and separated from the gaseous combustion products in a single unit with attendant savings in capital and operating costs.
The separated, heated char particles can then be reacted with steam or with a mixture of steam and carbon dioxide to form hydrogen gas according to the following reactions:
C+H.sub.2 O.fwdarw.CO+H.sub.2 (1)
C+CO.sub.2 .fwdarw.2 CO (2)
CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 (3)
As seen by these reactions, the gas produced comprises hydrogen, carbon monoxide, steam, and some carbon dioxide and is a mixture of water gas and combustion gas. The extent of char gasification to produce hydrogen and carbon monoxide is controlled by the amount of steam used and the temperature and pressure of the hot char steam mixture. The greater the amount of steam used, the greater the amount of hydrogen generated. While we do not wish to be bound by theory, the newly formed hydrogen, or nascent hydrogen, is believed to be very reactive in stabilizing or capping hydrocarbon free radicals, thereby improving the quality of the condensed stablized hydrocarbons produced by this process; or stated another way, the effectiveness of nascent hydrogen permits the use of a lower hydrogen partial pressure for the same degree of hydrogenation.
The heated char is conveyed in char transport line 31 to pyrolysis reactor 14 and utilized therein as the solid particulate source of heat. In this embodiment oxygen is used instead of air as the combustion gas and the flue gas from the oxidation zone is used as the nondeleteriously reactive transport gas which is also introduced into the pyrolysis reactor.
The substantially solids-free gaseous mixture stream 28 from the separation zone 26 comprises the nondeleteriously reactive transport gas and volatilized hydrocarbons. The volatilized hydrocarbons include condensible hydrocarbons having four or more carbon atoms, a portion of which are stabilized newly formed volatilized hydrocarbon free radicals. The condensible hydrocarbons are recovered as condensate in quench zone 34 by direct contact with a quench fluid. The quench fluid, in one embodiment, contains a capping agent to stabilize and terminate any remaining newly formed free radicals which were not stabilized in the pyrolysis zone. Condensation of the condensible hydrocarbons can also be by indirect cooling, such as a heat exchanger. It is to be understood that the volatilized hydrocarbons comprise normally non-condensible gases, such as methane and other lower molecular weight hydrocarbon gases which are not recoverable by condensation means which are not very low temperature or cryogenic. These gases are conveyed through conduit 60 to gas recovery zone 36.
The substantially solids-free gaseous mixture stream 28, which comprises stabilized newly formed volatilized hydrocarbons, is introduced into the quench zone 34 and contacted therein with a quench liquid. Quench zone 34 is a gas-liquid contacting zone and for example can comprise a spray tower, a Venturi contactor, a gas absorption tower, or the like, or combinations thereof.
In one embodiment the quench fluid contains a capping agent for stabilizing or terminating any newly formed volatilized hydrocarbon free radicals which were not stabilized or terminated by the capping agent in the pyrolysis zone. The amount of quench fluid is sufficient to rapidly cool the gaseous mixture stream and to form a condensate which contains the condensed stabilized hydrocarbons and unconsumed and spent capping agent.
Use of a quench fluid causes cooling and condensing of a substantial portion of the hydrocarbon vapors having four or more carbon atoms. This process utilizing a quench fluid increases the yield of lower molecular weight tar liquids by preventing cracking.
In one preferred embodiment a multiple stage quench is used rather than a single stage quench. The advantage of a multiple stage quench is that during pressure upsets or other malfunctions, solids which enter the quench zone can be handled without rendering the quench recirculation system inoperative as is likely to result if only a single stage is used. A two stage quench provides enough system flexibility and time to take corrective action by automatic or manual control procedures. For example in one embodiment the first quench stage is designed so as not to plug with mixtures containing entrained particulates by providing a quench fluid flow rate sufficient to simultaneously scrub and flush out any entrained particulates. This is an important embodiment because the higher molecular weight viscous tars when consensed are sticky and will form an agglomerative mass with any entrained particulates. Examples of a suitable first stage are nonplugging means such as spray wash towers or loose packed towers. However, a wash tower or loose packed tower which is satisfactory for a first stage generally is not efficient by itself as a scrubbing device when high volatile coal is rapidly pyrolyzed with substantial amounts of transport gas as used in the coal pyrolysis process described herein because entrained liquids and aerosols are generally found in the first quench stage effluent. A second stage contacting means therefore is needed to separate and recover any entrained liquids and aerosols. The second stage must have a higher contacting efficiency than normally available in a wash tower. A high efficiency Venturi scrubber is an example of a suitable second stage contactor. A two stage quench system, consisting of a wash tower as a first stage followed by a Venturi scrubber as a second stage, has been found to be effective. The wash tower first stage provides for most of the free radical termination, temperature reduction and removal of the bulk of any entrained solids. The Venturi second stage effectively collects the remainder of the entrained liquids and aerosols.
Referring now to FIG. 2, a preferred system includes wash tower 38 as a first quench stage, having a condensation section 40 and a liquid collection section 42. A first quench fluid stream 44, which may or may not comprise a capping agent, is introduced into the condensation section 40 of the wash tower. The substantially solids-free gaseous mixture stream 28 of FIG. 1 comprising stabilized volatilized hydrocarbons having four or more carbon atoms is also introduced into the condensation section 40. The first quench fluid stream 44 contacts the substantially solids-free gaseous mixture stream 28 in the condensation section, thereby condensing at least a major portion of the larger hydrocarbons which contain four or more carbon atoms per molecule in the gaseous mixture stream. Preferably the first quench fluid stream is introduced into the quench zone at a temperature and at a flow rate sufficient to reduce the temperature of the substantially solids-free gaseous stream to less than about 700.degree. F. and especially preferably to less than about 200.degree. F. A condensate is formed which comprises the stabilized and terminated hydrocarbon free radicals. A gaseous residue stream 46 then remains which comprises those portions of the gaseous mixture stream 28, such as non-condensible gases, lighter hydrocarbons, which have not condensed, the lighter molecular weight portion of the quench fluid which has been vaporized and entrained liquids, and aerosols. The condensate and the bulk of the first quench fluid flow down into liquid collection section 42 of wash tower 38 and combine to form a first liquid mixture. Any remaining tar free radicals that were not terminated in the gaseous state but were condensed will be terminated by contact with the capping agent in the quench fluid in liquid collection section 42. The liquid mixture containing the condensate is removed from the wash tower and conveyed in conduit 48 to a solids removal zone 50.
A residual gaseous residue stream is removed from the top portion of the condensation section of the wash tower and conveyed in conduit 46 to Venturi scrubber 52. A second portion of the quench fluid stream is introduced into the Venturi scrubber through conduit 54 and contacts the residual gaseous residue stream 46 to terminate any remaining volatilized hydrocarbon free radicals and to scrub entrained hydrocarbons in the form of aerosols or vapors from the gaseous residue stream. The scrubbed gaseous residue stream and the second portion of the quench fluid are combined and removed from the Venturi scrubber through conduit 56. The remaining gas phase is separated from the liquids by introducing stream 56 into separator vessel 58. The separated gas is removed through conduit 60.
The second portion of the quench fluid and the separated entrained tars are removed from separator vessel 58 as a liquid mixture in conduit 62 and combined with the liquid mixture in stream 48 to form a combined liquid mixture in stream 64. Combined liquid mixture stream 64 is conveyed to liquid product separation zone 66 of FIG. 1.
A portion of the volatilized hydrocarbons produced by pyrolysis of coal comprise heavy tars having boiling points above the boiling points of middle distillate tar liquids. These heavy viscous tars have a high carbon-hydrogen atomic ratio and frequently contain heterocyclic compounds such as organic sulfur and nitrogen compounds. By hydrogenating volatilized hydrocarbons in the pyrolysis reaction zone using hydrogen gas, the value of the volatilized hydrocarbons can be increased by sulfur and nitrogen removal as hydrogen sulfide and ammonia. Vapor phase hydrogenation with hydrogen directly in the pyrolysis reactor will also reduce the viscosity and lower the average boiling point of the volatilized hydrocarbons by terminating some free radicals, but hydrogenation at pyrolysis temperatures is not as effective in stabilizing and terminating volatilized free radicals as contacting with a capping agent as described herein. Nevertheless, since some free radicals can be terminated in the pyrolysis zone by treatment with gaseous hydrogen, and some coal sulfur and nitrogen converted to hydrogen sulfide and ammonia, in this embodiment the gas produced from the heated char which comprises hydrogen is introduced into pyrolysis reactor 14 along with the solid particulate source of heat to assist in terminating the newly formed volatilized hydrocarbon free radicals directly in the pyrolysis zone. If desired, a hydrogen containing gas stream can be fed separately into the pyrolysis reactor for this purpose.
The pyrolysis reaction zone is preferably operated at pressures slightly greater than ambient, although pressures up to about 10,000 psig may also be used. An increase in pressure increases the hydrogen partial pressure in the pyrolysis zone and increases the hydrogenation of the volatilized hydrocarbons by reaction with gaseous molecular hydrogen. However, as the pressure in the pyrolysis reaction zone increases, the capital and operating costs of the process also increase. Therefore, in one embodiment the operating pressure range for the pyrolysis reaction zone for economical reasons is from about 1 psig to about 1000 psig. In a further embodiment pressures near atmospheric are employed. At pressures near atmospheric very little of the newly formed volatilized hydrocarbon free radicals are terminated by reaction with gaseous molecular hydrogen, but rather are terminated due to the use of the capping agents as described herein.
It is known that the char produced by rapid heating of coal, as in pyrolysis, is very porous, has a large or open pore volume, and a high surface area. These characteristics result in a higher char reactivity than chars produced by slow heating. High reactivity of these chars is largely attributed to their high internal surface area. The char produced from pyrolysis of coal, as described herein, is also very reactive.
It has been determined that the presence of carbon dioxide and steam in the pyrolysis zone increases the yield of condensible hydrocarbons by neutralizing active sites on the char produced during pyrolysis. Char which has not been so neutralized tends to catalyze the formation of high molecular weight hydrocarbons by promoting polymerization and/or cracking at such active char sites.
While not wishing to be bound by theory, it is believed that the hydrocarbon vapors produced by pyrolysis of coal occupy the reactive sites on the hot char used as a heating medium and are polymerized to heavy tar liquids, char, or coke by free radical mechanisms. This has the result of reducing the yield of middle distillate tar liquids, a desired product. It is also believed that the char reactions with CO.sub.2 or steam involve an oxygen transfer step from these gases to the char, followed by a gasification step in which the oxygen-carbon complex is released as CO. These reactions are believed to take place on the reactive sites on the char, and in so doing reduce the availability of these reactive sites for tar adsorption, polymerization, and cracking. Therefore, hydrogen, steam, carbon dioxide, or mixtures thereof introduced into the pyrolysis zone or used as a carrier gas for hot char, in combination with pretreating the feed solid carbonaceous material with a sorbed first capping agent prior to pyrolysis and introducing a second capping agent directly into the pyrolysis zone increases the yield of lower molecular weight hydrocarbons, decreases the average molecular weight of condensible liquid product, and minimizes hydrocarbon yield loss.
Referring again to the combined liquid mixture stream 64 of FIG. 1, which comprises the liquid mixture from the first stage of the quench zone and the liquid mixture from the second stage of the quench zone, is sent to a liquid product separation zone 66.
In the embodiment shown in FIG. 1, which is particularly useful when the feed coal or solid carbonaceous feed material has a high oxygen and nitrogen content, at least several liquid hydrocarbon fractions are recovered from the combined liquid mixture stream in liquid product separation zone 66. These fractions are the light low boiling hydrocarbon fraction comprising C.sub.4 's to C.sub.8 's, tar acids comprising phenols, tar bases comprising amines, and a neutral tar liquid fraction comprising C.sub.9 's and higher and the heavy tar product.
The neutral tar liquid fraction comprises hydrocarbon liquids which comprise consumed and unconsumed capping agents. The neutral tar liquid fraction can be upgraded by hydrogenation. A fluidized or fixed bed hydrogenation process is useful for this prupose. A suitable hydrogenation process comprises hydrogenating at least a portion of the neutral tar liquid stream to produce a hydrogenated neutral tar liquid stream comprising a regenerated capping agent capable of terminating free radicals. The hydrogenation process in the embodiment shown in FIG. 1 involves the removal of contaminants, such as sulfur as hydrogen sulfide and nitrogen as ammonia, from the liquid, thereby resulting in a more environmentally attractive fuel product. Water is also removed. Conventional processes may be employed for these removal steps. This embodiment will enhance the chemical stability of the product and form products with improved handling and storage characteristics. In another embodiment at least a portion of the liquids are hydrocracked to form lower molecular weight hydrocarbons suitable for use in such products as gasoline.
Suitable hydrogenation conditions are a hydrogenation temperature from about 700.degree. to about 900.degree. F., hydrogen partial pressures of from about 1000 to about 3000 psia, a hydrogen volume between about 1000 to about 5000 standard cubic feet per barrel of feed of neutral tar liquid to be treated, and an amount of catalyst of from about 0.2 to about 3 volumes of neutral tar liquid per hour per volume of catalyst. Suitable hydrogenation catalysts are for example metals in the sulfide form, such as nickel, molybdenum, tungsten, and cobalt which can be supported on alumina or silica-aluminum base. Hydrogenation can also be conducted at elevated temperatures and pressures in the absence of a catalyst.
As shown in FIG. 1, neutral tar liquid stream 68 is introduced into hydrogenation zone 70 and contacted with a stream hydrogen gas introduced into the hydrogenation zone through conduit 69. A portion of the hydrogenated neutral tar liquids thusly produced is then conveyed through conduits 72 and 74 to heater 79 where it is heated to a temperature above about 300 preferably above 600.degree. F. to form a superheated first capping agent vapor. Another portion of the hydrogenated neutral tar liquids is heated in heater 80 to a temperature above about 200 and preferably above about 600.degree. F. to form a heated second capping agent stream for introducing directly into pyrolysis zone 14. In the embodiment shown in FIG. 1, another portion of the capping agent is recycled to quench zone 34 through conduit 76 as the quench fluid. Before introducing the recycled hydrogenated neutral tar liquids into the quench zone, they are first cooled in cooler 78. Another portion of the hydrogenated neutral tar liquids may be removed from the system as product if desired.
In another embodiment, not shown in the FIGS., the hydrogenated tar liquids are separated by conventional distillation into at least a hydrogenated tar product fraction comprising at least a major portion of the hydrogenated heavy tars which were contained in the hydrogenated neutral tar liquids, and a hydrogenated liquid fraction comprising at least a major portion of the regenerated capping agent and any unconsumed capping agent which were contained in the hydrogenated neutral tar liquids. At least a portion of the hydrogenated liquid fraction is utilized as the capping agent for contacting the comminuted coal in the coal preparation zone. Another portion of the hydrogenated liquid fraction is preferably used as the quench fluid stream 76 to quench zone 34. At least a portion of the hydrogenated tar product fraction is recycled to the pyrolysis zone for pyrolyzing to more desirable lighter hydrocarbons. In one embodiment the liquid separations are conducted so that the recycle capping agent stream comprises tar liquids having a boiling point range between about 350.degree. and about 650.degree. F.
In an alternate embodiment at least a portion of the unconsumed and consumed capping agent are separated from the neutral tar liquid stream prior to hydrogenation of the neutral tar liquid stream. The consumed and unconsumed capping agent mixture is then hydrogenated separately to form a regenerated capping agent mixture at least a portion of which is recycled to the coal preparation zone as the first capping agent and at least another portion of which is recycled directly to the pyrolysis zone as the second capping agent.
As mentioned above, in the preferred embodiment of FIG. 1, at least a portion the regenerated capping agent can also be used to comprise at least a portion of the quench fluid which is recycled in stream 76 to quench zone 14.
In the embodiment shown in FIG. 2, recycle quench fluid stream 76a is split to form quench fluid stream 44 and quench fluid stream 54. It is to be understood that stream 44 and 54 do not have to be identical in chemical composition as shown in FIG. 2 but can be tailored to the duty required of each quench zone.
At least a portion of the phenols from liquid product separation zone 66, FIG. 1, can, if desired, be added to the capping agent stream 74 and if desired to the quench fluid as additional capping agent for enhancing the free radical termination ability of the capping agent stream and the quench fluid. Phenols are good solvents for tar liquids and will improve the miscibility of hydrocarbon condensate in combined liquid mixture stream 64. Since phenols are also capping agents their inclusion in the capping agent streams 81a or 81b, or quench fluid stream 76a will improve hydrocarbon free radical termination capability of each of these streams.
At least a portion of the heavier tar liquid products having a boiling point of from above about 650.degree. to about 950.degree. F. can be recycled to the pyrolysis zone for further cracking if desired, or blended with light oil to produce a fuel oil.
The remainder of gaseous residue stream is removed from quench zone 34 through conduit 60 and introduced into gas recovery zone 36 for recovery of light hydrocarbons such as methane, butane, propane, and other low molecular weight hydrocarbons. Preferably sulfur and nitrogen compounds are also removed enabling recovery of hydrogen, hydrogen sulfide, ammonia, and the like. For example gas recovery zone 36 can be a conventional acid gas removal unit where the hydrogen sulfide is separated and removed. After removal of the hydrogen sulfide, the remaining gas can be compressed and utilized in coal preparation operations or as a transport gas. Any surplus gas can be used as a fuel gas, or as a feed gas for conversion to pipeline quality natural gas or ammonia. The hydrogen sulfide-rich stream from the acid gas removal unit can be sent to a Claus unit for sulfur recovery.
EXAMPLE
The following example demonstrates the value of this invention.
The pyrolysis unit shown in FIG. 3 comprises a fluidized char feeder 80 for feeding char through char feed valve 82 to char heater 84. The external wall of char heater 84 is heated by electrical heating elements. Char feeder 80 is also used as a receiver vessel for product char.
Comminuted Wyoming subbituminous coal, having a particle size less than 1000 microns, is fed to a fluidized coal bed feeder 88 at a rate of about 3 lb/hr. A first capping agent, decahydronaphthalene, is passed through a heater (not shown) and is heated to about 600.degree. F. to produce a superheated decahydronaphthalene vapor which is introduced into the fluidized coal feeder 88 as vaporized capping agent stream 89. The superheated decahydronaphthalene vapor is introduced into the fluidized coal feeder at the rate of about 1 lb/hr. The decahydronaphthalene vapor passes upwardly through the bed of comminuted coal particles, thereby causing the comminuted coal particles to become fluidized. The superheated decahydronaphthalene vapor contacts and heats the comminuted coal particles and is sorbed by the coal during the time the coal remains in the fluidized bed coal feeder 88, i.e., during the coal residence time. Carbon dioxide, as a transport gas, is fed to the coal feeder at a flow rate of about 0.3 SCFM (standard cubic feet per minute) to fluidize and transport the coal containing the sorbed decahydronaphthalene through coal transport line 90 and into the pyrolysis reactor 86. A mixture of about 1.7 SCFM CO.sub.2 and about 1 SCFM of steam as a transport gas is introduced into char heater 84 to convey the hot char, at a rate of about 30 lb/hr, into the pyrolysis reactor. The coal containing the sorbed decahydronaphthalene, the hot char, the transport gas for both the comminuted coal and char and a second capping agent are introduced under turbulent flow conditions into the pyrolysis reactor through pyrolysis reactor inlet 85. The external wall of the reactor is heated by electrical heating elements, which in conjunction with the heated char causes the coal to be heated to about 1200.degree. F. thereby effecting pyrolysis of the coal. About 1 lb/hr of the second capping agent is introduced directly into the pyrolysis reactor.
The second capping agent, preheated to a temperature of about 800.degree. F. prior to introduction into the pyrolysis reactor, is injected into reactor inlet 85 as a vapor. Preheating the second capping agent reduces the amount or temperature of the hot char required to raise the coal to the desired pyrolysis temperature.
A turbulent mixture of coal containing the sorbed decahydronaphthalene first capping agent, char, transport gas, and second capping agent passes through pyrolysis reactor 86. The coal is pyrolyzed by the transfer of heat from the hot char to the coal particles and a pyrolytic vapor stream is formed comprising hydrocarbon vapors which comprise hydrocarbons having at least four carbon atoms and volatilized hydrocarbon free radicals. As the volatilized hydrocarbon free radicals are formed, they are in substantially simultaneous contact with the sorbed decahydronaphthalene first capping agent and the second capping agent and are stabilized or terminated by a reactive hydrogen of the decahydronaphthalene or the second capping agent reacting with the newly formed volatilized hydrocarbon free radicals as they are formed.
A pyrolysis product stream is formed comprising as particulate solids the char and a carbon-containing residue of pyrolysis and a gaseous mixture. The gaseous mixture comprises the transport gas, unreacted decahydronaphthalene, unreacted second capping agent, decahydronaphthalene and second capping agent which are depleted to some extent of hydrogen atoms, and pyrolytic product vapors which comprise hydrocarbon vapors including hydrocarbons having at least four carbon atoms including stabilized volatilized hydrocarbon free radicals which have been terminated by the decahydronaphthalene.
The product stream comprising hydrocarbon vapors and solids, is treated in series connected primary centrifugal separator 92 and secondary centrifugal separator 94 to separate solids from gases. Separated solids from the primary separator are dropped into a stand leg 96 and then into char feeder 80. Solids, separated by secondary separator 94, are collected in char drum 98.
Hot gases from the secondary separator are conveyed to quench scrubber 100 and contacted therein with water as a quench fluid. At least a major portion of the pyrolytic product vapors are condensed as liquid product and are collected along the quench liquid in primary quench tank 102. Hot pyrolytic product vapors which are not condensed in quench scrubber 100 and uncondensed gas, containing CH.sub.4, CO.sub.2, H.sub.2, and C.sub.2 H.sub.4, flow from primary quench tank 102 to secondary quench scrubber 104 where it is contacted with more water as a quench fluid. Condensate and quench fluid are collected in secondary quench tank 106. Quench liquid flow rates to the primary and secondary scrubbers are maintained at about 10 gph (gallons per hour) each. The quench fluid temperature is about 30.degree. to about 40.degree. F.
The cooled gases and any condensate in the form of an aerosol are passed from the top of secondary quench tank 106 to electrostatic precipitator 112 to separate and recover the aerosols. The remaining cooled gas at a temperature of about 50.degree. to about 80.degree. F. is then passed through activated charcoal bed 114 to remove remaining trace amounts of light hydrocarbons. The cooled gas is then passed from activated charcoal bed 114 through the vent line 116, flow meter 118, drierite bed 119 for removal of water vapor, and lastly through a flow meter 120 before being vented to the atmosphere.
The condensed liquids are withdrawn from the primary and secondary quench tanks and evaluated for the yield of tar liquids. A tar liquid yield of about 35% or more by weight M.A.F. (moisture-ash-free basis), most of which is light aromatics, is to be expected.
The advantage of this invention is that pyrolytic hydrocarbon liquid product recovered by pretreating the solid particulate carbonaceous feed material with a first capping agent so that the solid particulate carbonaceous feed material contains sorbed first capping agent before it is introduced into the pyrolysis zone, and by using a second capping agent directly introduced into the pyrolysis zone, has a lower average molecular weight than the hydrocarbon liquid product recovered when product vapors are produced in a pyrolysis zone without such pretreatment with a first capping agent and without use of a second capping agent directly introduced into the pyrolysis zone.
Although this invention has been described in considerable detail with reference to certain embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of this invention as described above and defined in the appended claims.

Claims

1. A process for producing condensed stabilized hydrocarbons from a solid particulate carbonaceous material comprising:
(a) contacting a solid particulate carbonaceous feed material in a pretreatment zone with a predetermined amount of a first capping agent under conditions of time and elevated temperature sufficient to sorb said first capping agent on or in said solid particulate carbonaceous feed material thereby forming a premixture comprising said solid particulate carbonaceous feed material containing sorbed first capping agent, wherein said first conditions will maintain said first capping agent in a liquid or gaseous state, and wherein said first capping agent is a liquid or solid at ambient conditions;
(b) rapidly heating said premixture from said pretreatment zone in the presence of a predetermined amount of a second capping agent in a pyrolysis zone to pyrolyze said solid particulate carbonaceous feed material of said premixture and to produce from said solid particulate carbonaceous feed material a char product and pyrolytic product vapors which comprise newly formed volatilized hydrocarbon free radicals and substantially simultaneously stabilizing at least a major portion of said volatilized hydrocarbon free radicals by reaction with said sorbed first capping agent and said second capping agent to form stabilized volatilized hydrocarbons;
(c) removing from said pyrolysis zone a gas-solid mixture which comprises gases which comprise said stabilized volatilized hydrocarbons and solids which are entrained in said gases and comprise said char product, and separating at least a major portion of said solids in said gas-solid mixture from said gases in a separation zone;
(d) cooling said gases separated from said solids in said separation zone by contacting said gases with a quench fluid in a quench zone to form condensed stabilized hydrocarbons which are formed from at least a major portion of said stabilized volatilized hydrocarbons; and
(e) recovering at least a portion of said condensed stabilized hydrocarbons.
2. A process for producing condensed stabilized hydrocarbons from a solid particulate carbonaceous material comprising:
(a) contacting a solid particulate carbonaceous feed material in a pretreatment zone with a predetermined amount of a first capping agent under conditions of time and elevated temperature sufficient to sorb said first capping agent on or in said solid particulate carbonaceous feed material thereby forming a premixture comprising said solid particulate carbonaceous feed material containing sorbed first capping agent, wherein said first conditions will maintain said first capping agent in a liquid or gaseous state, and wherein said first capping agent is a liquid or solid at ambient conditions;
(b) rapidly heating said premixture from said pretreatment zone in the presence of a predetermined amount of a second capping agent in a pyrolysis zone to pyrolyze said solid particulate carbonaceous feed material of said premixture and to produce from said solid particulate carbonaceous feed material a char product and pyrolytic product vapors which comprise newly formed volatilized hydrocarbon free radicals and substantially simultaneously stabilizing at least a major portion of said volatilized hydrocarbon free radicals by reaction with said sorbed first capping agent and said second capping agent to form stabilized volatilized hydrocarbons;
(c) removing from said pyrolysis zone a gas-solid mixture which comprises gases which comprise said stabilized volatilized hydrocarbons and solids which are entrained in said gases and comprise said char product, and separating at least a major portion of said solids in said gas-solid mixture from said gases in a separation zone;
(d) cooling said gases separated from said solids in said separation zone by contacting said gases with a quench fluid in a quench zone to form condensed stabilized hydrocarbons which were formed from at least a major portion of said stabilized volatilized hydrocarbons, thereby forming a gaseous residue and a liquid mixture comprising said condensed stabilized hydrocarbons, and a hydrogen depleted capping agent;
(e) separating said liquid mixture from said gaseous residue;
(f) hydrogenating at least a portion of said liquid mixture, after separation from said gaseous residue, to produce a hydrogenated capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals;
(g) utilizing at least a portion of said hydrogenated capping agent as at least a major portion of said first capping agent used in said pretreatment zone and as at least a major portion of said second capping agent used in said pyrolysis zone; and
(h) recovering at least a portion of said liquid mixture which comprises at least a portion of said condensed stabilized hydrocarbons.
3. A process for producing condensed stabilized hydrocarbons from a solid particulate carbonaceous material comprising:
(a) contacting a solid particulate carbonaceous feed material in a pretreatment zone with a predetermined amount of a first capping agent under conditions of time and elevated temperature sufficient to sorb said first capping agent on or in said solid particulate carbonaceous feed material thereby forming a premixture comprising said solid particulate carbonaceous feed material containing sorbed first capping agent, wherein said first conditions will maintain said first capping agent in a liquid or gaseous state, and wherein said first capping agent is a liquid or solid at ambient conditions;
(b) rapidly heating said premixture from said pretreatment zone in the presence of a predetermined amount of a second capping agent in a pyrolysis zone to pyrolyze said solid particulate carbonaceous feed material of said premixture and to produce from said solid particulate carbonaceous feed material a char product and pyrolytic product vapors which comprise newly formed volatilized hydrocarbon free radicals and substantially simultaneously stabilizing at least a major portion of said volatilized hydrocarbon free radicals by reaction with said sorbed first capping agent and said second capping agent to form stabilized volatilized hydrocarbons, some of said pyrolytic product vapors comprising a product agent suitable for use as a capping agent either directly or after hydrotreatment of said product agent;
(c) removing from said pyrolysis zone a gas-solid mixture which comprises gases which comprise said stabilized volatilized hydrocarbons and said product agent and solids which are entrained in said gases and comprise said char product, and separating at least a major portion of said solids in said gas-solid mixture from said gases in a separation zone;
(d) cooling said gases separated from said solids in said separation zone by contacting said gases with a quench fluid in a quench zone to form condensed stabilized hydrocarbons which were formed from at least a major portion of said stabilized volatilized hydrocarbons, thereby forming a gaseous residue and a liquid mixture comprising said condensed stabilized hydrocarbons, a hydrogen depleted capping agent, and said product agent;
(e) separating said liquid mixture from said gaseous residue;
(f) hydrogenating at least a portion of said liquid mixture, after separation from said gaseous residue, to produce a hydrogenated capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals, at least a major portion of said hydrogenated capping agent being produced from said product agent;
(g) utilizing at least a portion of said hydrogenated capping agent as at least a major portion of said first capping agent used in said pretreatment zone and as at least a major portion of said second capping agent used in said pyrolysis zone; and
(h) recovering at least a portion of said liquid mixture which comprises at least a portion of said condensed stabilized hydrocarbons.
4. A process for producing condensed stabilized hydrocarbons from a solid particulate carbonaceous material comprising:
(a) contacting a solid particulate carbonaceous feed material in a pretreatment zone with a predetermined amount of a first capping agent under conditions of time and elevated temperature sufficient to sorb said first capping agent on or in said solid particulate carbonaceous feed material thereby forming a premixture comprising said solid particulate carbonaceous feed material containing sorbed first capping agent, wherein said first conditions will maintain said first capping agent in a liquid or gaseous state, and wherein said first capping agent is a liquid or solid at ambient conditions;
(b) rapidly heating said premixture from said pretreatment zone in the presence of a predetermined amount of a second capping agent in a pyrolysis zone to pyrolyze said solid particulate carbonaceous feed material of said premixture and to produce from said solid particulate carbonaceous feed material a char product and pyrolytic product vapors which comprise newly formed volatilized hydrocarbon free radicals and substantially simultaneously stabilizing at least a major portion of said volatilized hydrocarbon free radicals by reaction with said sorbed first capping agent and said second capping agent to form stabilized volatilized hydrocarbons, some of said pyrolytic product vapors comprising a product agent suitable for use as a capping agent either directly or after hydrotreatment of said product agent;
(c) removing from said pyrolysis zone a gas-solid mixture which comprises gases which comprise said stabilized volatilized hydrocarbons and said product agent and solids which are entrained in said gases and comprise said char product, and separating at least a major portion of said solids in said gas-solid mixture from said gases in a separation zone;
(d) cooling said gases separated from said solids in said separation zone by contacting said gases with a quench fluid in a quench zone to form condensed stabilized hydrocarbons which were formed from at least a major portion of said stabilized volatilized hydrocarbons, thereby forming a gaseous residue and a liquid mixture comprising said condensed stabilized hydrocarbons, a hydrogen depleted capping agent, and said product agent;
(e) separating said liquid mixture from said gaseous residue;
(f) separating said liquid mixture, after separation from said gaseous residue, into at least neutral tar liquids comprising at least a major portion of said hydrogen depleted capping agent and said product agent, and a residue liquid mixture comprising at least a portion of said condensed stabilized hydrocarbons;
(g) hydrogenating at least a portion of said neutral tar liquids, after separation from said residue liquid mixture, to produce hydrogenated neutral tar liquids comprising a hydrogenated capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals, at least a major portion of said hydrogenated capping agent being produced from said product agent;
(h) utilizing at least a portion of said hydrogenated neutral tar liquids as at least a major portion of said first capping agent used in said pretreatment zone and as at least a major portion of said second capping agent used in said pyrolysis zone; and
(i) recovering at least a portion of said residue liquid mixture which comprises at least a portion of said condensed stabilized hydrocarbons.
5. A process for producing condensed stabilized hydrocarbons from a solid particulate carbonaceous material comprising:
(a) contacting a solid particulate carbonaceous feed material in a pretreatment zone with a predetermined amount of a first capping agent under conditions of time and elevated temperature sufficient to sorb said first capping agent on or in said solid particulate carbonaceous feed material thereby forming a premixture comprising said solid particulate carbonaceous feed material containing sorbed first capping agent, wherein said first conditions will maintain said first capping agent in a liquid or gaseous state, and wherein said first capping agent is a liquid or solid at ambient conditions;
(b) rapidly heating said premixture from said pretreatment zone in the presence of a second capping agent in a pyrolysis zone to pyrolyze said solid particulate carbonaceous feed material of said premixture and to produce from said solid particulate carbonaceous feed material a char product and pyrolytic product vapors which comprise newly formed volatilized hydrocarbon free radicals and substantially simultaneously stabilizing at least a major portion of said volatilized hydrocarbon free radicals by reaction with said sorbed first capping agent and said second capping agent to form stabilized volatilized hydrocarbons, some of said pyrolytic product vapors comprising a product agent suitable for use as a capping agent either directly or after hydrotreatment of said product agent;
(c) removing from said pyrolysis zone a gas-solid mixture which comprises gases which comprise said stabilized volatilized hydrocarbons and said product agent and solids which are entrained in said gases and comprise said char product, and separating at least a major portion of said solids in said gas-solid mixture from said gases in a separation zone;
(d) cooling said gases separated from said solids in said separation zone by contacting said gases with a quench fluid in a quench zone to form condensed stabilized hydrocarbons which were formed from at least a major portion of said stabilized volatilized hydrocarbons, thereby forming a gaseous residue and a liquid mixture comprising said condensed stabilized hydrocarbons, a hydrogen depleted capping agent, and said product agent;
(e) separating said liquid mixture from said gaseous residue;
(f) separating said liquid mixture, after separation from said gaseous residue, into at least:
(i) neutral tar liquids comprising at least a major portion of said hydrogen depleted capping agent and said product agent, and heavy tars of said liquid mixture, and
(ii) a residue liquid mixture comprising at least a portion of said condensed stabilized hydrocarbons;
(g) hydrogenating at least a portion of said neutral tar liquids, after separation from said residue liquid mixture, to produce hydrogenated neutral tar liquids comprising hydrogenated heavy tars and a hydrogenated capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals, at least a major portion of said hydrogenated capping agent being produced from said product agent;
(h) utilizing at least a portion of said hydrogenated neutral tar liquids as at least a major portion of said first capping agent used in said pretreatment zone and as at least a major portion of said second capping agent used in said pyrolysis zone; and
(i) recovering at least a portion of said residue liquid mixture which comprises at least a portion of said condensed stabilized hydrocarbons.
6. A process for producing condensed stabilized hydrocarbons from a solid particulate carbonaceous material comprising:
(a) contacting a solid particulate carbonaceous feed material in a pretreatment zone with a predetermined amount of a first capping agent under conditions of time and elevated temperature sufficient to sorb said first capping agent on or in said solid particulate carbonaceous feed material thereby forming a premixture comprising said solid particulate carbonaceous feed material containing sorbed first capping agent, wherein said first conditions will maintain said first capping agent in a liquid or gaseous state, and wherein said first capping agent is a liquid or solid at ambient conditions;
(b) rapidly heating said premixture from said pretreatment zone in the presence of a predetermined amount of a second capping agent in a pyrolysis zone to pyrolyze said solid particulate carbonaceous feed material of said premixture and to produce from said solid particulate carbonaceous feed material a char product and pyrolytic product vapors which comprise newly formed volatilized hydrocarbon free radicals and substantially simultaneously stabilizing at least a major portion of said volatilized hydrocarbon free radicals by reaction with said sorbed first capping agent and said second capping agent to form stabilized volatilized hydrocarbons, some of said pyrolytic product vapors comprising a product agent suitable for use as a capping agent either directly or after hydrotreatment of said product agent;
(c) removing from said pyrolysis zone a gas-solid mixture which comprises gases which comprise said stabilized volatilized hydrocarbons and said product agent and solids which are entrained in said gases and comprise said char product, and separating at least a major portion of said solids in said gas-solid mixture from said gases in a separation zone;
(d) cooling said gases separated from said solids in said separation zone by contacting said gases with a quench fluid in a quench zone to form condensed stabilized hydrocarbons which were formed from at least a major portion of said stabilized volatilized hydrocarbons, thereby forming a gaseous residue and a liquid mixture comprising said condensed stabilized hydrocarbons, a hydrogen depleted capping agent, and said product agent;
(e) separating said liquid mixture from said gaseous residue;
(f) separating said liquid mixture, after separation from said gaseous residue, into at least:
(i) light aromatics comprising liquids of from about four to about eight carbon atoms per molecule,
(ii) tar bases comprising amines,
(iii) tar acids comprising phenols, and
(iv) neutral tar liquids comprising at least a major portion of said hydrogen depleted capping agent, said product agent, and heavy tars of said liquid mixture,
wherein at least a portion of said condensed stabilized hydrocarbons are contained in said light aromatics, said tar bases, or said tar acids;
(g) hydrogenating at least a portion of said neutral tar liquids thusly separated to produce hydrogenated neutral tar liquids comprising hydrogenated heavy tars and a hydrogenated capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals, at least a major portion of said hydrogenated capping agent being produced from said product agent;
(h) utilizing at least a portion of said hydrogenated neutral tar liquids as at least a major portion of said first capping agent used in said pretreatment zone and as at least a major portion of said second capping agent used in said pyrolysis zone; and
(i) recovering at least a portion of said light aromatics, said tar bases, and said tar acids, one of which at least comprises at least a portion of said condensed stabilized hydrocarbons.
7. The process of claim 4, 5 or 6 wherein said first and said second capping agents have a boiling point range between about 350.degree. and about 650.degree. F. for about 90 weight percent of said capping agent.
8. The process of claim 1, 2, 3, 4, 5 or 6 wherein said solid particulate carbonaceous feed material is selected from the group consisting of coal, agglomerative coal, gilsonite, tar sands, oil shale, oil from oil shale, and the organic portion of solid waste.
9. The process of claim 1, 2, 3, 4, 5 or 6 wherein the amount of said first capping agent used in said pretreatment zone and the amount of said second capping agent used in said pyrolysis zone are sufficient to terminate substantially all of the newly formed volatilized hydrocarbon free radicals in said pyrolysis zone.
10. The process of claim 1, 2, 3, 4, 5 or 6 wherein the amount of said first capping agent used in said pretreatment zone and the amount of said second capping agent used in said pyrolysis zone are sufficient to terminate 95 percent of the newly formed volatilized hydrocarbon free radicals in said pyrolysis zone.
11. The process of claim 1, 2, 3, 4, 5 or 6 wherein the amount of said first capping agent used in said pretreatment zone and the amount of said second capping agent used in said pyrolysis zone are sufficient to terminate 99 percent of the newly formed volatilized hydrocarbon free radicals in said pyrolysis zone.
12. The process of claim 1 or 2 wherein at least a portion of said first capping agent and said second capping agent are selected from the group consisting of tetrahydronaphthalene, decahydronaphthalene, dihydronaphthalene, hydrogenated phenanthrenes, hydrogenated anthracenes, alkyl substituted tetrahydronaphthalene, alkyl substituted decahydronaphthalene, alkyl substituted dihydronaphthalene, alkyl substituted hydrogenated phenanthrenes, alkyl substituted hydrogenated anthracenes, naphthalene, anthracene, creosote oil, thiols, phenols, amines, and mixtures thereof.
13. The process of claim 6 further comprising adding at least a portion of said tar acids to said hydrogenated neutral tar liquids before said hydrogenated neutral tar liquids are utilized as at least a major portion of said first capping agent used in said pretreatment zone and said second capping agent used in said pyrolysis zone.
14. The process of claim 6 further comprising separating at least a portion of said phenols from said tar acids and adding at least a portion of said phenols thusly separated to said hydrogenated neutral tar liquids before said hydrogenated neutral tar liquids are utilized as at least a major portion of said first capping agent used in said pretreatment zone and said second capping agent used in said pyrolysis zone.
15. The process of claim 1, 2, 3, 4, 5 or 6 wherein said quench fluid comprises a capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals.
16. The process of claim 2 or 3 wherein said quench fluid comprises a capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals, and further comprising utilizing at least a portion of said hydrogenated capping agent as at least a major portion of said capping agent contained in said quench fluid or contacting said substantially solids-free gaseous mixture stream.
17. The process of claim 4, 5 or 6 wherein said quench fluid comprises a capping agent suitable for stabilizing said newly formed volatilized hydrocarbon free radicals, and further comprising utilizing at least a portion of said hydrogenated neutral tar liquids as at least a major portion of said capping agent contained in said quench fluid for contacting said substantially solids-free gaseous mixture stream.
18. The process of claim 1, 2, 3, 4, 5 or 6 further comprising heating said first capping agent above about 300.degree. F. prior to contacting said solid particulate carbonaceous feed material in said pretreatment zone with said first capping agent.
19. The process of claim 1, 2, 3, 4, 5 or 6 further comprising heating said first capping agent to a temperature sufficiently high prior to contacting said solid particulate carbonaceous feed material in said pretreatment zone with said first capping agent so that said premixture will have a temperature above about 300.degree. F.
20. The process of claim 1, 2, 3, 4, 5 or 6 wherein said first capping agent used for contacting said solid particulate carbonaceous feed material in said pretreatment zone is in a vaporous state.

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Entry
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Pyrolysis process

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