US2955988A

US2955988A - Process for carbonizing coal in a laminar gas stream

Info

Publication number: US2955988A
Application number: US715239A
Authority: US
Inventors: John J S Sebastian
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-02-14
Filing date: 1958-02-14
Publication date: 1960-10-11
Anticipated expiration: 1977-10-11

Description

United States Patent PROCESS FOR CARBONIZING coAL IN A, LAMINAR GAS STREAM John J. S. Sebastian, 128 Harden Ave., Duquesne, Pa.

Filed Feb. 14,1958, Ser. No. 715,239

18 Claims. (Cl. 202-) This invention relates to a process for the low temperature carbonization of coal. More specifically it relates to an economical, efiicient and highly versatile process for carbonizing coal of any type, grade or quality to form a highly reactive char or coke, a primary low :temperature tar, and a high calorific-value gas.

Most of the processes for the low temperature carbonization of powdered coals in use at present employ'the fluidized-bed technique, in which the finely-divided coal is suspended in a highly turbulent gaseous medium. All such processes invariably present difficult problems of control due to such factors as channeling and slugging. Another serious problem of the fluidized-bed technique lies in the pronounced tendency of the coal particles to agglomerate when they reach plasticity temperatures at or about 700 F. Certain types of bituminous coals tend to fuse entirely at somewhat higher temperatures. The agglomeration is caused principally by the ceaseless impact between adjacent particles of the coal, which is in violently turbulent motion. This fusion of the particles has either limited the application of the fluidized-bed technique to non-coking or poorly coking coals, and/or has made necessary such measures as pro-oxidation of the coal or the introduction of some air into the carbonizer during the process to destroy the agglutinant in the coal, the primary cause of agglomeration. Such oxidation procedures possess the disadvantage of destroying or degrading the primary nature of the tar produced, thereby reducing its value for the recovery of desired chemicals or their conversion into motor fuels, and of adulterating the evolved: gases, thereby reducing their fuel value.

. The-object of this invention is to provide a'process for the low temperature carbonization of coals of any type, including low grade bituminous coals.

, Another object is to provide a coal carbonization process which yields a highly reactive, smokeless char or semicoke fuel for the generation of electric power or for domestic heating.

- Still another object is the production of primary lowtemperature tars which are unadulterated and substantially undegraded and from which many valuable chemicals, gasoline, Diesel oil and high quality lubricants can be produced. Anotherobject is the formation of a high B.t.u. fuel gas.

. Still another object is the provision of a process which permits a high degree of control both of process variables and of finished products. Other objects and advantages will become obvious from the following detailed description and the drawings.

Fig. l is a diagrammatic view, partly in section, illustrating a preferred mode of carrying out the process of the present invention.

Fig. 2 is a horizontal cross-sectional view taken along line 2- -2 of Fig. 1.

Broadly speaking, my process comprises the thermal steam-distillation of finely divided coal while entrained in substantially laminar or streamlined flow througha tube by means of super-heated steam which functions as slippage between the particles and gas molecules.

an entraining, heating and distilling medium. Preferably also, the gaseous entraining vehicle includes recycle gas, namely the volatilized gaseous distillation products of the thermally treated coal, consisting primarily of hydrocarbon gases,such as methane, and hydrogen. The thermal treatment is carried out at relatively low temperatures, namely at temperatures up to about 1500 F., so that no gasification reaction occurs between the steam and the carbon.

By laminar or streamlined flow as employed in the specification and claims is meant entrainment of the finely divided, solid coal particles in the gaseoum medium in such a way that the carrying gas and solid particles flow insubstantially straight lines at substantially the same velocity and in the same direction, with very little, if any The smooth pattern of flow is not disturbed by turbulence, such as eddy currents. The entrained particles remain dispersed in thegaseous vehicle at a relatively substantial distance from. each other, which generally remains constant. There is, therefore, little or no impact between particles and, consequently, substantially complete freedom from agglomeration.

Achievement of a laminar flow pattern is determined by such factors as the velocity of the entraining coal jet, the

a diameter of the distillation tube, the diameter of the coal particles, the density of the entraining gas jet, and its viscosity. The relationship of these factors is given, for example, in the equations for the conventional Reynolds number, which is calculated solely for a gas phase, and for the modified Reynolds number, which is calculated for a gas carrying entrained solids as follows: i

D u Re t s a where N is the conventional Reynolds number, D, is the tube diameter in feet, u, is gas velocity in ft./sec., ,1: is gas density in lb./ cu. ft. and u is gas viscosity in lb./ (ft.) (sec.); and

Where Mod. N is the modified Reynolds number, Dg'is particle diameter in feet, V is the superficial linear velocity of the gas stream in ft./sec., and is viscosity of the fluid stream in lb./(ft.) (sec.). Thus the laminar or streamline flow requisite for my purpose can be obtained by adjustment of such factors as particle size, velocity of the entraining gas stream and the pressure. Pressure is an important factor because of its effect both on the density and viscosity of the entraining gas stream. Both density and viscosity increase with increasing pressure. The density of the entraining gas stream, however, generally increases at a greater rate with increasing pressure than does viscosity, so that the. Reynolds number, both conventional and modified, increases with increasing pressure.

The foregoing factors can be adjusted at will toobtain laminar flow in a carbonizer tube of a given. size. Other features, such as the internal diameter of the reactor tube and its length, are factors which are predes termined when designing the equipment for given types of operation. The diameter of thetu-be determines its carbonizing capacity, and its length determines the residence time of the coal-entraining gas stream at different velocities.

Calculation of the Reynolds numbers, both conventional and modified, can be employed for a preliminary. rough evaluation as to whether a given set oficonditions will result in the desired laminar flow. Generally speak? ing a conventional Reynolds number above about 2100 and a modified Reynolds number above about 40 are indicative that there may be undesirable turbulence in the entraining gas stream. However, the modified Reynolds number, which takes into account the presence of entrained solids, and is, therefore, somewhat more pertinent here than is the conventional Reynolds number, gives, at best, a rough approximation of the situation because of difficulties in accurately determining such equation factors as the density and viscosity of the entraining fluid stream. It is, therefore, desirable, after such preliminary approximate calculations indicate the feasibility of a given set of conditions, namely, that the conventional and modified Reynolds values will be respectively below 2100 and 40, to verify achievement of laminar flow by preliminary testing as, for example, visually in a transparent tube. Such a tube can be made, for instance, from heat resistant material such as Vicor glass. Absence of appreciable agglomeration in the test char or coke product also serves to verify the presence of laminar or streamline flow through the carbonizer tube.

To obtain the desired laminar flow, the particles should be small and velocity and pressure should not be excessively high as indicated by the foregoing Reynolds number equations. In general, maximum particle size is desirably about 20 to 40 mesh, preferably smaller. For some agglutinating and swelling bituminous coals, the particle size is desirably as small as 100 to 200 mesh. Maximum pressure in the reactor tube should be about 100 p.s.i.g., preferably about 60 to 75 p.s.i.g. and can be as low as p.s.i.g. Lower pressures are preferable for highly agglutinating coals. Above pressures of about 100 p.s.i.g, the density of the entraining gas stream rises at a greatly faster rate than does the viscosity, with resulting turbulence in flow.

The velocity of the gas stream should be sufiiciently high properly to entrain the coal particles yet sufficiently low to allow the desired laminar flow. The optimum velocity to accomplish this will vary with the size and size-consist of the coal particles and can readily be determined by calculation and testing. In general, it ranges from about 2 to 8 feet per second. The velocity can be changed as, for example, by increasing or reducing the rate of fiow of the entraining fluid-stream into the carbonizer tube, to a level dictated by the desired residence time in the tube, so long as it is not increased to the point where it is so excessive as to cause turbulence. The upper velocity limit is, thus, largely determined by the particular diameter of the carbonizer tube, which is generally chosen for the desired capacity, by the preferred particle size of the coal carbonized, the extent of devolatilization desired, i.e. the required residence time for the coal particles, and by the density and viscosity of the entraining gas stream at the chosen pressure of operation. This combination of the operating conditions for the desired overall results can be determined by calculation and preliminary testing.

If the coal charged is not closely sized, and its sizeconsist comprises both finer and coarser particles than its determined average size, the finer particles are conveyed through the carbonizer tube at about the same velocity as the entraining fluid, but the coarser particles may lag behind and move at a velocity inversely proportional to their size. This drag constitutes no disadvantage if the flow otherwise is sufiiciently laminar, i.e. the Reynolds number is safely below the upper limit. The coarser particles need a slightly longer residence time to give off their volatile matter resulting from the thermal decomposition. Thus, all sizes attain devolatilization to the same equilibrium value in the minimum time, depending upon the velocity of the entraining medium.

Laminar flow, by minimizing or preventing particle impact during the thermal treatment, prevents any appreciable particle agglomeration, event at temperatures between 700 and 1000" P. where the coal normally softens and becomes plastic and, subsequently, fluid. Another factor, which minimizes impact and consequent agglomeration, is the rapid evolution of gases from each of the treated coal particles, the force of which tends to push the particles apart. This effect is aided by the non-turbulent streamline flow which keeps the particles moving in such a way that they are not thrown against each other with sufficient force to counteract that of the evolving gases.

Because of substantial elimination of the impact factors which cause agglomeration of the heated plastic coal particles, my process can be employed for the low-temperature carbonization of virtually any type of coal, including soft bituminous coals which hitherto have either not been processi-ble by known techniques because of their high plastic tendencies, or which have required preoxidation or some oxidation during the carbonization process with resultant degradation of the tars and reduction in the calorific value of the evolved gases.

Absence of particle agglomeration and the substantially laminar pattern of flow produce the same degree of devolatilization in each coal particle. This important feature of my process results from the uniform reaction conditions to which all of the particles are subjected, such as identical residence time for each coal particle under the same pressure and temperature. This is an important advantage since it produces a uniformly devolatilized, highly reactive coke or char. Contrasted with this, the char produced by any of the fluidization processes does not have a uniform composition, i.e. the volatile matter contents of the individual particles differ widely.

The use of superheated steam as a coal-entraining medium possesses a number of important advantages and has a dual function. First, it acts as a distillation-strip ping medium, increasing the rate of devolatilization at any given temperature and, thereby, improving the recovery of the desired volatilizable coal tar constitutents. Secondly, it acts as an efiicient heat transfer medium for the thermal treatment and devolatilization of the coal. As a result, a shorter contact time is needed to achieve equilibrium in devolatilization at a given temperature of carbonization. The superheated steam which envelops each particle of coal also serves to desulfurize the char to an appreciable extent, the finer the particles, the greater being the extent of sulfur removal. After passage through the carbonization tube, the steam can subsequently be condensed and separated from the gaseous effiuent and tars, so that it does not become an undesirable diluent or contaminant.

Recycle gas, namely the gaseous efiiuent produced by the thermal treatment of the coal in the carbonizer tube, is preferably employed as a coal-entraining medium together with the superheated steam. This is not always essential, but is desirable in most cases, since the use of recycle gas results in a fuel gas of higher heating or Btu. value than when steam is used alone. If a gas of high calorific value is not desired, the use of recycle gas can be dispensed with.

The gaseous effiuent produced by the low-temperature carbonization of the coal by my process, consists predominantly of methane, ethane and hydrogen. The specific amounts vary, of course, with the particular coal being treated and the temperature of carbonization. The methane generally constitutes a considerable proportion of the efiluent as, for example 40% or higher. Since the heating value of methane is more than three times greater than that of hydrogen, the higher the proportion of methane in the'product gas relative to the hydrogen, the greater is the fuel value of the gas. Use of the gaseous efiluent as recycle gas produces this desirable result inasmuch as part of the hydrogen reacts with carbon under the temperature and pressure mm aces ps Some of the hydrogen may also combine with the carbon, if the pressure is sufficiently high, to form small amounts of ethane and propane which are characterized by even higher calorific values than methane. The gross calorific values of these hydrocarbon gases in pure state are: 995 B.t.u. for methane (CH 1731 B.t.u. for ethane (C H and 2465 B.t.u. for propane (C H per cu. ft. of gas saturated with waterat 60 F. and 30 inches of mercury pressure.

The relative amounts of entraining recycle gas and superheated steam are not critical. Their volumetric ratio is determined largely by the specific conditions of the process and the results desired as, for example, the desired fuel value for the gaseus elliuent. 7

Maximum carbonization temperature should be about 1500 F. to avoid gassification reactions and excessive cracking and degradation both of the gaseous hydro carbons in the efiiuent gas produced, which reduces its fuel value, and of the organic components in the primary tar recovered. In general, I prefer to employ temperatures of about 800 to 1200 F. At the lower temperatures as, for example, at 800 to 900 F., owing to higher ethane and propane contents, a gas of higher calorific value (90 to 100 B.t.u. per cu. ft.) can be obtained than at temperatures, for example, of 1200" F.

(700 to 800 B.t.u. per cu. ft.).

As aforementioned, maximum permissible pressure in the carbonizer tube is about 100 p.s.i.g, preferably about 60 to 75 p.s.i.g. because of thepossible loss of the laminar flow pattern at higher pressures. The principal advantage of employing higher pressures within this range lies in reduction of carbonizer size requirement for a given level of production with concomitant reduction in space requirements and equipment cost. If the production .of pipe-line gas is a specific object of the process, it is generally necessary to compress the purified gas to 600- 1000 p.s.i.g pressure. Carbonization of coal under pressure in this case constitutes a great cost advantage. For example, if the gas is producedat 75 p.s.i.g, the power required for compression of the gas from 75 to 1000 p.s.i.g. is nearly one-half as much as that needed to compress from atmospheric pressure to 1000p.s.i.g. More accurately, 43.4% of the compression cost of the gas is saved by carbonizing at 75 p.s.i.g instead of working at atmospheric pressure. item in making pipe-line gas. The higher pressures also tend to improve the yield of gaseous hydrocarbons such as methane, ethane and propane. In general, I prefer to employ pressures of about 30 to 75 p.s.i.g because of these practical considerations. As aforementioned, however, it may be desirable in some instances to employ pressures as low as atmospheric, as, for example, in the case of highly agglutinating coals.

The products produced by my process are superior in their properties and are of uniformly high quality. The fuel gas, whose yield may vary from 2500-9000 standard cubic feet per ton of coal carbonized, depending on the process conditions chosen, particularly temperature, is not adulterated with undesirable diluents and possesses a high fuel value which can be increased, if desired, as aforedescribed. The high-B.t.u. gas can be used as a pipeline gas to supplement or to substitute for natural gas; it can be used for process-heating or power generation; or it can be reformed and converted catalytically with steam by conventional methods to industrial hydrogen.

The tars are produced in highyield, generally 20 to 40 gallons per ton of coal, depending on the type of coal carbonized, temperature, pressure and time of carboniza tion, and are truly primary in character, since deep or disruptive cracking to carbon and oxidation productsis This is an appreciable cost hopper.

virtually absent because of thelow temperatures employed, the absence of any degradative oxidation mac tions,the uniform thermal treatment of the dispersed coal partioles andthe presence of excess steam which causes the distillation. of volatile matter at lower tem-. peratures and exerts a so-called stripping effect on compounds in theirv primary state.- The tar can either be refined and fractionated for the recovery of numerous organic compounds and solvents, or most of it converted into motor fuels, such as gasoline, diesel oil and high quality lubricants, depending on existing market condi tionsand demand. In addition to benzene, toluene,

xylene and other solvents, the tar-acid fraction can be.

be subjected to the so-called delayed coking process or to hydrogenation cracking for the recovery of further gasoline products. Pitch-coke obtained by the delayed coking process can be calcined for the manufacture of electrodes which are in demand for use in aluminum production andfor othere'lectrometallurgical processes.

The char is a highly reactive, porous, finely granular coke of uniformly high quality. It is easily ignitible and burns smokelessly and with high heat utilization efiiciency. It can be employed for the generation of electric power, for domestic heating, for the production of synthesis gas, in metallurgical processing, e.g. in the reduction of iron ores, etc. Its yield, depending on the process variables chosen, but particularly on the volatile matter content of thecoal and the temperature of carbonization, may vary from 65-90 percent by weight of the coal carbonized.

Figures 1 and 2 illustrate diagrammatically apparatus suitable for carrying out the process of my invention, which will be further discussed with reference thereto; It will be understood, however, that the operational ele-. ments shown can be modified and certain ones dispensed with or pluralized depending upon such factors as the available raw materials and specific process conditions.

The crushed, finely-divided coal in feed hopper 1 is introduced through conduit 2 and valve 3 into lock hopper 4, where it can be pressurized in a control-led and regulatory manner by means of gas introduced through jcon duit 5. and regulating valve 6. The gas c'a'rib'e any. non-reactive gas, preferably recycle gas. At initiationIof the process, namely before recycle gas is available, pres surization can be accomplished by means of any nonoxidizing gas, such as natural gas. The initiating nonoxidizing gas can be introduced, for example, through inlet tube 11, controlled by valve 12, and conduit 9, from which it passes via pressure line 5 into the lock The pressurizing gas should be relatively cool, preferably not higher than about to 200 F to avoid devolatilization of the coal at this point. The gas is introduced in amounts suflicient to provide the positive pressure required to feed the finely divided coal through conduit 7 and regulatory valve 8 into conduit 9, where it is entrained by the gas which carries it into the carbonizer tube 10. When carbonization is carried out sub-, stantially at atmospheric pressure, it is sufiicientrto provide the lock hopper with a slight positive pressure, so that its pressure is somewhat above that prevailing in the carbonizer tube and conduit 9. An additional regulatory control is provided by lock hopper vent 13. An addi: tional purpose of this valve is the depressurization of the lock hopper prior to filling with fresh coal charge from feed hopper 1. In preferred practice, two inter: mittently functioning lock hoppers may be required so that while one is on stream, the ,off-strearn lock hop per can be filled with coal at. atmospheric pressure, .and

. then pressurized. For the purpose of feeding the poster a constant, uniform rate, a special feeding device 48"rnay be required below valve 8, such as the well-known Bailey feeder, or the Fuller-Kinyon pump for conveying powdered solid materials. q

The finely divided coal fed into conduit 9 is picked up by an entraining stream of gas, preferably recycle gas, although it may be dry steam or, at initiation of the process, a non-oxidizing gas such as. natural gas. Entraining gases other than recycle gas. can be introduced, as shown, through inlet tube 11 into conduit 9. Where recycle gas is used in the process, a portion of the efliuent gas resulting from carbonization of the coal, after separation of char, tar and oil vapors, can be piped into conduit 14 from condenser 15. The purified gas which is now relatively cool, is passed through blower compressor 16, where it is. raised to the desired pressure, thence. into conduit 9, where it can be preheated, if desired, by passage through preheater 17, such as a multi-tubular heat exchanger, up to a temperature of about 400 to 500 F. before entraining the finely divided coal from lock hopper 4. The gas entraining the coal for injection into the carbonizer tube should not exceed a temperature of about 400 to 500 F. to avoid plasticity and any thermal decomposition of the coal particles with resultant evolution of gas prior to injection into the carbonizer. The temperature of the entraining gas can be considerably lower, as for example, ordinary atmospheric temperature. For better heat efiiciency and operation in the carbonizing zone, it may be desirable to preheat the gases, since the coal particles will then more quickly come to devolatilization temperature when admixed with other high temperature gases introduced into the carbonizer tube both for heat transfer and entraining purposes, as will subsequently be described. This, in turn, will reduce the time required for carbonization, i.e. the residence time in the carbonizer tube, and, therefore, the required length of the tube.

The high velocity gas stream conveying the coal through conduit 9 is passed into carbonizer tube through the central feed-jet 18 and is injected in such manner that it streams up through the carbonizer tube in essentially straight line, vertical flow, substantially parallel to the longitudinal axis of the tube, as shown.

In a preferred embodiment, steam and additional quantities of recycle gas preheated to sufiiciently high teme perature, carry the requisite heat for direct internal transfer to the coal particles flowing in entrainment in the carbonizer tube. To achieve this objective, the simple arrangement described below was found to be effective and flexible.

A portion of the coal recycle gas flows from conduit 14 into conduit 19 where it is joined by dry saturated or slightly superheated steam, flowing into conduit 19 through inlet line 20 controlled by valve 21. The temperature of the steam introduced at this point may range from 500 to 600 F. However, since part of the enthalpy of the steam is transferred to the cool recycle gas, the steam-gas mixture enters heat exchanger 22, which may be of any suitable conventional type, at a temperature of about 300-400 F. The mixture of steam and recycle gas is heated in exchanger 22 to the temperature required for the transfer of sufiicient heat to the coal flowing. in entrainment in the carbonizer. The heat requirements of the heat exchanger can be provided in any suitable manner as, for example, by combustion of producer gas made from part of the char produced. The hot mixture of superheated steam and recycle gas passes from heat exchanger 22 into conduit 23. Steam line 24 can be employed if additional superheated steam is desired for regulatory or other purposes.

If the amount of recycle gas employed to entrain the coal in conduit 9 is adequate for the particular process conditions, and intensive superheating of the process steam to higher temperatures is not required,

conduits

19 and 23 can be shut off entirely by means of

valves

25 and 26 and all of the direct internal heating require mentsin the carbonizer may in this case be provided by superheated steam entering through conduit 24 into conduit 27.

Conduits

19 and 23 andtheir appurtenances such as steam line 20 and heat exchanger 22 can also be by-passed or eliminated entirely by passing recycle gas from conduit. 9 through valve .28 and conduit 29 directly into superheated steam line 24, providing that the heat requirements of the process are satisfied by the enthalpy of the superheated steam entering through line 24.

The temperature and pressure of the superheated steam or steam-recycle gas mixture passing through conduit 27 into the carbonizer is determined largely by the operating temperature and pressure conditions desired in the carbonizer. For example, if a carbonization temperature of about 1200 F. is desired, the heat-carrying gas is introduced at a temperature ranging approximately from 1400 to 1600 F., depending on the quantity and temperature of the coalconveying stream introduced through line 9 and jet 18 into the carbonizer tube. The heatconveying gas stream and the coal-conveying gas stream are introduced at pressures which will provide the desired pressure level in the carbonizer tube. If operating pres sures of about 30 to 75 p.s.i.g., for example, are desired in the carbonizer, the gas streams are introduced into the tube through the respective jets at slightly higher pressures. The operating pressure in the carbonizer tube and subsequent apparatus can be regulated by means of pressure control valve 44 on product gas outlet pipe 41.

The high temperature steam or mixture of steam and recycle gas passes from conduit 27 into manifold 30 whence it is injected into the carbonizer tube through a plurality of ducts 31, and jets 45, disposed peripherally to the coal injection jet. The heat conveying steam or steam and gas surround the entrained coal streaming up through central jet 18, in essentially straight-line, vertical flow, substantially parallel to the longitudinal axis of the carbonizer tube. The heat required for the process is efiectively transferred chiefly by radiation from the steam to the coal.

The expansion zone formed by the conical bottom of the carbonizer tube, as shown, does not cause any appreciable turbulence if the slope of expansion is very gradual, as, for example, at an angle of at least 75 to to the horizontal plane. The manner of injection of the entrained coal and gases can be varied as desired so long as it is accomplished in such a. way that the requisite streamlined, laminar flow is obtained.

The inside diameter of the carbonizer tube is determined by the desired capacity and is limited to particular minimum and maximum values depending on certain operational factors of the process for which the equipment is designed, such as coal particle size, velocity and pressure. The appropriate selection and combination of these factors for any given tube diameter must permit the desired laminar flow. In general practice, the internal diameter of the carbonizer tube may vary from about 2.5 to 8.0 inches, or more. The length of the tube is determined largely by the desired residence time. In typical practice, the length can be approximately 15 to 30 feet, though this can be varied substantially, depending on such operating factors as the velocity of the gaseous medium which must keep the coal particles in entrainment, the size and size-consist of the coal, the pressure, and the degree of devolatilization desired.

In the internally heated carbonizer tube the finely divided coal particles entrained in laminar flow are quickly brought to devolatilization temperature by the direct transfer of heat from the entraining hot steam or steam and recycle gases. Devolatilization is both rapid and uniform because of the small particle size of the dispersed coal, absence of agglomeration and the stripping effect provided by the superheated steam. As aforementioned, the carbonization temperature may be as high as 1500" F., and is preferably about 800 to 1200 F. Maximum racemes g pressure is desirably about 100 p.s.i.g., preferably about 60 to 75 p.s.i.g. In preferred practice the pressure is in the range of about 30 to 75 p.s.i.g.

In case highly swelling coal of unusually high plasticity is to be processed, it may be desirable to recycle a small amount, as, for example, about to of the char produced in the carbonizer tube as an additional measure to prevent agglomeration. Although this is rarely necessary, provision for such recycling is shown in Figure l, where a small portion of the unpurified gas, together with its char-dust content passes out the top of the carbonizer through conduit 32 controlled by valve 33 into the-coal-entraining gas stream in conduit 9. Since the recycle char and gas are substantially at the relatively high temperature prevailing in the carbonizer, they are cooled prior to entry into conduit 9 by passage through a conventional heat exchanger 34. Saturated steam can be used as a cooling medium, entering heat exchanger 34 through inlet 35 and exiting through outlet tube 36 1 as superheated steam, which can be employed in other portions of the process as, for example, as the source of steam entering conduits 20, or, under certain conditions 24.

The entrained char, tar vapors and gases exit from the carbonizer tube through conduit 37, pass through conventional knock-out and

cyclone chambers

38 and 39, of which several (not shown) may be employed to separate the char, and into a conventional condenser, such as spray-cooler 15, where the tar vapors are condensed. The-condensed primary tar is removed through outlet tube 40 and the water-oil emulsion overflow through outlet tube 46. A portion of the efliuent gases is recycled into the system through conduit 14, the recycle ratio being controlled by valve 43. The remainder is piped oif through conduit 41 for further purification from all traces of tar-fog and fine dust still remaining in the gas. Conventional equipment (not shown), such as a Pelouze- Audouin tar extractor or a Cottrell electrostatic precipitator, can be used for this purpose, the latter being preferable. As the final stage in purification, all hydrogen sulfide and organic sulfur compounds can be removed from the gas by the most suitable conventional procedure. The product gas thus purified can then be compressed to the required pressure (600-1000 p.s.i.g.) for pipe-line transmission to points of consumption.

Before beginning the carbonization process, it is desirable to preheat the carbonizer tube to the required operating temperature. This can be accomplished, as shown, by passing air into the carbonizer via inlet conduit 42, manifold 30 and ducts 31, to sustain the burning of natural gas or producer gas injected via tube 47 through jet nozzle 18. As soon as the canbonizer tube has reached the required operating temperature, both heating gas and air are shut off as neither of these are needed in the process.

Although the process has been described in terms of an upward flowing coal-entraining gas stream, the direction of flow can also be downward, horizontal or at an incline so long as a laminar streamlined flow pattern is maintained.

If an even higher B.t.u. gas is desired, the hot, highly reactive char can be injected into a second reactor tube where it is entrained in and reacted with a mixture of the elfiuent gas from the first stage carbonizer t-ube plus additional hydrogen at a temperature preferably of about 800 to 1000 F. and at pressures of about 600 to 1000 p.s.ig. Under these conditions, methane, ethane, propane and other high-Btu. hydrocarbon gases are formed to produce a fuel gas having a calorific value as high as 1000 to 1200 B.t.u. per standard cubic foot. Entrainment in this case can be turbulent, or the fluidized bed technique may be used.

It will be seen from the foregoing description that my process is highly flexible since the type of coal used and the products obtainable can be varied by appropriate 1 i0 choice and combination of process variables. The. prod ess, furthermore, is highly economical and readily controlled.

Although this invention has been described with refer: ence to illustrative embodiments thereof, it will be apparcut to those-skilled in the ant that the principles of this invention can be embodied in other forms but within the scopeof the claims.

I claim:

1. A process for carbonizing coal which comprises entraining finely divided coal particles having a maximum sizeofabout 20 mesh in a flowing gas stream substantially free from oxygen and comprising superheated ste'amas an essential component, passing said coal-entraining gaseous stream insubstantially laminar flow through acarbonization zone, the maximumtemper-ature i-n'fsaid zone being about 1500 F., the maximum pressure in said zone being about p.s.i.'g., the maximum gasstream velocity being about 8 feet per second and the maximum diameter of said zone in the plane normal to thel-dir'ectionof gas flow being about 8 inches, said entiaining gas being substantially non-oxidant at said temperatures and serving to heat said coal particles by direct heat transfer.

2. The process of claim 1 in which the maximum particle. size of the entrained coal is about 100 mesh, and the maximum pressure is about 75 p.s.i.g.

3'. A process for carbonizing coal which comprises'em training finely divided .coal particles having a maximum size of about 20 meshin a flowing gas stream substan; tially free from oxygen and comprising recycle gas, and superheated steam, passing said 'coal-entrainin'g' gaseous stream in substantially laminar flow through a carboniza tion zone, the maximum temperature in said zone being about 1500" F., the maximum pressure in said zone being about 100 p.s..i.g., the maximum gas stream velocity being about 8 feet per second and the maximum diameter of said zone in the plane normal to the direction of gas flow being about 8 inches, said entraining gas providing the heat requisite for the thermal devolatilization of the coal, to produce effluent gases predominantly comprising methane, ethane and hydrogen, primary tar, and finely divided char, said recycle gas comprising at least a portion of said gaseous efliuent.

4. The process of claim 3 in which the maximum particle size of the entrained coal is about 100 mesh, and the maximum pressure is about 75 p.s.i.g.

5. The process of claim 4 in which the temperature in the carbonization zone is about 800 to 1200 F.

6. A process for producing high B.t.u. gas, which comprises entraining finely divided coal particles having a maximum size of about 20 mesh in a flowing gas stream substantially tree tirom oxygen and comprising recycle gas and superheated steam, passing said coal-entraining stream in substantially laminar flow through a carbonization zone, the maximum temperature in said zone being about 1500 F., the maximum pressure in said zone being about 100 p.s.i.g., the maximum gas stream velocity being about 8 feet per second and the maxim-um diameter of said zone in the plane normal to the direction of gas flow being about 8 inches, said entraining gas providing the heat requisite for the thermal devolatilization of the coal, to produce efiluent gases predominantly comprising methane, ethane and hydrogen, primary tar, and finely divided char, said recycle gas comprising at least a portion of said gaseous eifluent, then injecting said finely divided char product into a reaction zone and entraining said char in said reaction zone in a mixture of gases comprising said gaseous effluent plus additional hydrogen, at a temperature up to about 1000 F. and at a pressure of about 600 to 1000 p.s.i.-g.

7. A process 'for carbonizi-ng coal which comprises introducing into an elongated carbonization zone a mixture of finely divided coal particles entrained in recycle gas, said coal particles having a maximum size of about 20 mesh, separately introducing into said elongated carbonization zone gas comprising superheated steam at substantially higher temperature than said coal-entraining recycle gas mixture, said tcoal-entraining recycle gas and said higher temperature gas comprising superheated steam being substantially free from oxygen and being introduced in such manner that they stream in admixture through said elongated carbonization zone in substantially laminar flow, the maximum temperature in said zone being about 1500 F., the maximum pressure in said zone being about 100 p s.i.g., the maximum gas stream velocity being about 8 feet per second and the maximum diameter of saidzone in the plane normal to the direction of gas flow being about 8 inches, said higher temperature gas providing the heat requisite for the thermal devolatilization of the coal, to produce efiluent gases predominantly comprising methane, ethane and hydrogen, primary tar, and finely divided char, said recycle gas comprising at least a portion of said gaseous eflluent.

8. The process of claim 7 in which the maximum temperature of the recycle gas mixture conveying the entrained coal is about 500 F. prior to introduction into the carbonization zone.

9. The process of claim 7 in which a small amount of char is introduced together with the coal particles into the carbonization zone.

10. The process of claim 7 in which the higher temperature gas includes recycle gas in addition to said superheated steam.

11. The process of claim 10 in which the maximum temperature of the recycle gas mixture conveying the entrained coal is about 500 F. prior to introduction into the carbonization zone.

12. The process of claim 10 in which a small amount of chat is introduced together with the coal particles in the carbonization zone.

13. The process of claim 7 in which the maximum particle size of the entrained coal is about 100 mesh, and the maximum pressure is about p.s.i.g.

14. The process of claim 18 in which the temperature in the carbonization zone is about 800 to 1200 F.

15. The process of claim 14 in which the maximum temperature of the recycle gas mixture conveying the entrained coal is about 500 F. prior to introduction into the carbonization zone.

16. The process of claim 14 in which a small amount of char is introduced together with the coal particles into the carbonization zone.

17. The process of claim 14 in which the higher temperature gas includes recycle gas in addition to said superheated steam.

18. The process of claim 17 in which the maximum temperature of the recycle gas mixture conveying the entrained coal is about 500 F. prior to introduction into the carbonization zone.

References Cited in the file of this patent UNITED STATES PATENTS 1,924,856 Heller Aug. 29, 1933 2,038,657 Hillhouse Apr. 28, 1936 2,285,276 Hemminger June 2, 1942 2,590,219 Stephanoif Mar. 25, 1952 2,623,011 Wells Dec. 23, 1952 2,662,007 Dickinson Dec. 8, 1953

Claims

1. A PROCESS FOR CARBONIZING COAL WHICH COMPRISES ENTRAINING FINELY DIVIDED COAL PARTICLES HAVING A MAXIMUM SIZE OF ABOUT 20 MESH IN A FLOWING GAS STREAM SUBSTANTIALLY FREE FROM OXYGEN AND COMPRISING SUPERHEATED STEAM AS AN ESSENTIAL COMPONENT, PASSING SAID COAL-ENTRAINING GASEOUS STREAM IN SUBSTANTIALLY LAMINAR FLOW THROUGH A CARBONIZATION ZONE, THE MAXIMUM TEMPERATURE IN SAID ZONE BEING ABOUT 1500*F., THE MAXIMUM PRESSURE IN SAID ZONE BEING ABOUT 100 P.S.I.G., THE MAXIMUM GAS STREAM VELOCITY BEING ABOUT 8 FEET PER SECOND AND THE MAXIMUM DIAMETER OF SAID ZONE IN THE PLANE NORMAL TO THE DIRECTION OF GAS FLOW BEING ABOUT 8 INCHES, SAID ENTRAINING GAS BEING SUBSTANTIALLY NON-OXIDENT AT SAID TEMPERATURES AND SERVING TO HEAT SAID COAL PARTICLES BY DIRECT HEAT TRANSFER.