US2131702A

US2131702A - Coal processing

Info

Publication number: US2131702A
Application number: US107336A
Authority: US
Inventors: George A Berry
Original assignee: NAT FUELS CORP
Current assignee: NAT FUELS CORP; NATIONAL FUELS Corp
Priority date: 1936-10-24
Filing date: 1936-10-24
Publication date: 1938-09-27
Anticipated expiration: 1955-09-27
Also published as: FR832966A; GB501374A

Description

Sept. 27, 19.38. l G. A. BRRY l coAL PROCESSING Filed Oc'l'.. 24, 1956 3 Sheets--Sheeil l 4a IN 44 1'" .ww/N@ 4 45 *47 afer/0N 5,2 46 camas/vsn? 55, GH S H54 TFA? 47 la Lz: j I l P INV ENT OR.

ATTORNEY.

sept. 27, 1938. G.

COAL PROCESSING A. BERRY 2,131,702y

ATTORNEY.

l Sept. 27, .1938. G. A. BERRY GOAL PROCESSING Filedoot. 24, 195s lLa Sheets-Sheet 3 l 1NvENToR 6150/5765 Eff?? y, Y

, ATTORNEY.

Patented Sept. 27, 1938 l I l 4i'JNlTED .STATES PATENT OFFICE coAL PitocEssmG George A. Berry, Bound Brook, N. J., assignor to National Fuels Corporation, Bound Brook, N. J., a corporation of New Jersey Application October 24, 1936, Serial No. 107,336

6 claims. (c1. 2oz-ao) The object of this invention is broadly to not limited to the treatment of the` material in transform bituminous coal into a carbonizing briquette form. The degree of grinding whichis fuel resembling anthracite and to recover other necessary will vary with different coals, but valuable products. More particularly, the inshould be suiiicient to permitfoperation without vention is concerned with producing carbonizedswelling under the controlled heating conditions 5 briquetted fuelof high density. Y which will be-described below, so that the ilnal This invention is in part a continuation of my' product will have a high specic gravity. copending application Serial No. 680,026, led The sizes of the coal particles used in form- July 12, 1933. ing the briquettes are also such as will, in the 10 By this invention, very valuable commodities formation of the untreated briquette, permit thel 10 may be recovered from bituminous coal, and attainment of a high initial density' therein particularly from the so-called slack which is which favorably influences the ultimate density produced in large quantities in the mining and of the finished product and favors the productransportation of bituminous coal and which sells tion on the carbonized briquettes of a smooth, for considerably less than the price of prepared clean exteriorgfree. from 10056 particles that 15 sizes of bituminous coal. The invention is not might rub'oil.

limited to the treatment of coal in the form of Different sorts of binder may be used, but slack, but is applicable to run of mine coal and binder Consisting. principally 0f Organic Inaprepared sizes. terial is recommended. It has been .found ad- The solid product of the present invention is vanta'geous to use a binder such as waste liquid. 20

characterized by the following properties: from the sulflte pulp process of paper making,

1. It is hard or harder than anthracite and has commonly known as suliite liquor,- although such a high density that the specic gravity is other binders, such as starch or other carbo- 1.1 or higher so that adequate weight of fuel hydrate material maybe used. With some coals,

can be put in a` fire box of given volume. such as semianthracita bituminous binderssuch 25 2. The product ignites more readily than anas coal tar, pitch, etc. may be used. thracite coal and burns at an even rate. 'Ihe coal briquettes are heated up to final car- 3. The product sustains combustion at tembonizing temperaturesof 700 to 1000 C. and then peratures lower than anthracite andis smokecooled down or `quenched so that they can be less. It will burn uniformly throughout the re discharged into the-atmosphere without igni- 30 bed and does not tend to go out around cooled tion. This heating may be considered as disides as is the case with anthracite. vided into three stages or temperature ranges,

4. The ash content is low and the caloriic although, of course, it is not necessary to physi value per unit weight is high. ically separate the stages. Heating and cooling The process of this invention is further chartake place in all stages by contact of the 35 acterized by a high yield of organic vapors conmaterial with a gaseous medium of suitable temdensable at ordinary temperatures and in priperature. The gaseous medium is substantially mary condition; that is to say, substantially of nonreactive with the coal and with the products the same composition as they were when rst which it gives off. The stages are as follows:

evolved from the coal, and hence substantially l. 'I'he I'lrst stage involves heating the coal 40 l unchanged by cracking. Gases uncondensable or briquettes up to a temperature of about 300 to at ordinary temperatures, and having high calor- 350 C. at which temperature tar vapors and con'- ic value are also recovered, and when using one densable hydrocarbons will appear. The upper modification of the invention, a second gas of limit of this first stage or temperature range is i lower caloric value can be separately removed determined by the sort of coal treated. 45

from the process. l 2. The second stage is the low temperature disi These products may be produced from a wide tillation stage and extends'from the 300 to 350 variety of grades or characters of bituminous temperature at the end of the first stage up to coal, of which, for example, the coal fields of 500 to 600 C`. `It is during this stage that most eastern United States afford a practically unof the vapors, condensable at ordinary tempera- 56 limitedsupply. tures are likewise produced.

The process is carried out continuously, pref- 3. The third stage is the final carbonization erably with a countercurrent flow of gases and and extends from theupper temperature limit solids. It is preferred to grind the vcoal and of the second stage up to 700 to 1000 C. Fur- Y form it into briquettes, although the invention is ther amounts of tar vapors are evolved during 55 this stage, together with a permanent gas oi lower caloriiic value, and the briquette shrinks more and more and acquires increased density and hardness. The final temperature will depend on the reactivity and density desired in the final product. A lower final temperature will give a more easily ignitable less hard and dense product which is suitable for re place, brazier and similar methods of heating. On the other hand. a higher nal temperature will give a harder and denser product suitable for furnace firing.

4. The fully carbonized coal or briquettes are then cooled in a current oi nonreactive gas down to a sufficiently low temperature so that they can be discharged into the atmosphere without ignition and can be readily handled.

I have discovered that difficulties which have hitherto been encountered in coking bituminous coal and particularly briquettes madefrom such coal, have been due to the fact that bituminous coal becomes plastic during the second stage referred to above, and that if the heating is too rapid, the vapors evolved in the interior of the lumps or briquettes cannot reach the exterior readily and therefore tend to swell the briquette and produce a porous final product which does not have the requisite density for satisfactory fuel use. I have found that the critical points in carbonizing lie in the second stage. The most critical points do vnot extend throughout the whole'range of this second stage, but are located usually at certain temperatures which vary somewhat with different coals. Thus, in the rst stage the heating may be very rapid, for example, heating increments per minute of 10 C., or even higher, do no harm and the same is true in the third stage. It is only necessary to control the ratel of heating accurately in the second stage and in this control it is not sufficient that the average rate of heating during the second stage be below the critical point. The rate of heating will depend on the coal used and on,the binder used, and to some extent on the iineness of grinding of the'coal where briquettes are made. In general, it will vary from about 114 C. per minute for badly swelling or softening coal, up to nearly 10 C. per minute with certain coals such as Pocahontas and New River coal, which do not swell badly or soften unduly. The proper maximum rate of heating will vary with the nature of the coal, and the average rate of heating throughout the stage will also vary with the amount of heating gas circulated per unit of weight and time which will be brought out in greater detail below in connection with the description of Figs. 2 to 6 of the drawings.

In the process of the present invention, the coal or briquettes pass through the differenttemperature zones or regions, for example, by passing downwardly through a retort .countercurrent to the heating and cooling gas or gases for the various stages. Of course, any other means which will move the coal or briquettes count-ercurrent to the gas stream may be employed an'd the present invention is not concerned with any particular structural details of retort design. In general, the average rate of heating through the critical zone will depend on the rate at which the briquettes pass through the zone, provided the ilow of heating gas and'its heat content are such as to supply the heat required to raise the briquettes to the nal temperature of the zone. The maximum rate of heating occurring at any point in the zone will, however, also depend on other factors, notably, ratio between the weight of heating gas and briquettes.

The invention will be described more particularly in conjunction with the drawings in which: Fig. 1 is a diagrammatic illustration of a plant for carrying out the present invention using a plurality of heating gas circuits; and

Fig. 2 to Fig. 6 are curves of gas and coal temperatures for various gas ratios and coal feeds.

In its broader aspects, the present invention is not concerned with the particular nature of the heating and cooling gas used so long as it is substantially nonreactive with thelcoal or with its distillation products, although in the preferred embodiment which will be described below in connection with Fig. 1 of the drawings, the evolved gases themselves are used as nonreactive gases and different gas circuits are used for the diierent stages in'order to recover the high caloric, permanent gas separate from the lower caloric gas produced'in the final carbonizing zone or stage. While this preferred lembodiment represents important practical advantages because of the higher price which can be obtained for undiluted, high caloric, permanent gases, the invention is broadly not limited to this procedure. If desired, a nonreactive gas stream may flow countercurrent to the coal throughout the whole length of the retort. -In more specic aspects, of course, the preferred embodiment constitutes a part of the present invention.

The heating gas performs two functions; First, it is a very uniform heating medium, contacting the surfaces of all of the lumps or briquettes, and secondly, the large volume of gas which is, of course, `necessary because of the low specific heat per unit volume, sweeps or scrubs off the vapors reaching the surface of the coal. The partial pressure of the evolved vapors is therefore very low and they remain volatile at temperatures far below their boiling point at atmospheric pressure, and hence do not show any tendency to condense or precipitate on cooler coal which they encounter in passing countercurrent through the stage. y

Since the vapors do not encounter solids at higher temperature, there is practically no tendency for the vapors to crack after evolution. (This is a very important feature of the present invention and one which can not be achieved by other means of heating such as external heat, radiant heat, and the like, because there the vapors distilling out from the coal or briquettes distillv at atmospheric pressure or a little below and, therefore, when they encounter cooler coal they tend to condense on the surface, which leads to serious difficulties, or the vapors encounter the hot source by heat and crack. The partial pressure of the evolved vapors will, of course, vary with the nature of the coal. Usually very high volatile coal will evolve more vapors for a given amount of heating gas and therefore will exhibit a slightly higher partial pressure than a lower volatile coal. 'I'he pressures are, however, very low, even for high volatile material, and are of the order of magnitude of 20 mm. .of mercury or less.

This second function of the gas, namely, the rapid sweeping away of vapors evolved by the coal and under partial pressures much lower than the atmosphere, is one of the most important factors in the present process. Internal gas heating is therefore in no sense thev equivalent of other forms of heating. It is thus possible to avoid swelling of briquettes when heating is by means of a gas stream, even though this rate is suii- 2,131,7oa clently high so that the briquettes would swell if Y the heating took place by other means which would not permit removal of the evolved vapors at a lower partial pressure.

From an economic and practical standpoint, the relative amount of gas used in heatingl is vital. This is clearly shown in Figs. 2 to 6oi' the drawings which represent curves,-the abscissae being temperatures and ordinates time.

Fig. 2v showsthe ideal and preferred operating conditions of the present invention. 7,lin this figure the weight of heating gas circulated per unit of time multiplied by its specific heat is exactly equal to the weight of coal or briquettes multiplied by their apparent specific heat. The expression apparent specific heat is used because the amount of heat absorbed by a unit weight of coal or briquettes in passing through the second stage' does not necessarily correspond exactly to the actual specific heat'of the material multiplied by the ltemperature rise. The reason for this is that there are other phenomena taking place.

such as cracking, distilling of vapors and the like, Y

which reactions may be either endothermic or exothermic Vand which will vary in amount and to some extentV in nature with' different coals. Thus, the amount of heat required to bring a givenv initially-introduced weight of briquettes from -the entering temperature up rto'- the exit capacity, the weight of gascirculated per hour must be 3Allahs the weight of the briquettes passing through the zone. In such a case, when the entering gas is approximately at the exit temperature for the zone, the curves for gas temperature and coal temperature will be two parallel straight lin'es displaced by the small difference required for the heat head to transfer heat from 'the gas to the solid. It will be apparent that the rate of heating at all points is the same and is defined by the slope of the curve with respect to the abscissa or mathematically expressed, is equal to the first derivative of the curve.

Fig. 3 shows the conditions which obtain when the ratio of gas to solids is decreased. In order to introduce the same total quantity of heat to bring up all of the briquettes to the exit tem-` perature of the zone, it is, of course, necessary to introduce the gas at a higher temperature. It

` will be apparent from a consideration of the curves which are no longer straight lines that the rate-of heating in the upper part of the zone is lessV than the average andthe rate of heating in the lower part of thezone is greater than the average; and that as compared to Fig. 2 a given temperature is reached at a later time, which means in the case of a vertical retort at a lower point. Assuming that for a given coal the ratev of heating shown in Fig. 2 is the maximum permissible, it will be obvious that if conditions are changed as shown in Fig. 3 the rate oi' heating'v in a portion of the stage will exceed the permissible maximum. lIn other words, the process will 3 sequently, of course, the total rate of flow of the gas, is`greatly decreased which is Ishown by a vlonger time for the cycle appearing as a higher -rate set by the conditions in Fig. 2. Thus, vas

far as rate ofl heating. is concerned, Fig. 3 shows that it is possible to obtain the required rate of heating without balancing the heat capacity of the gas and solids accurately but this is obtained only at the sacrifice of output because in order to keep the maximum heating rate within the permissible limitation, the average. heating rate, which determines thev output of the must be greatly reduced.

If the relative amounts of gas and solids are unbalanced in the opposite direction, that is to say, if the amount of gas is greater than that corresponding to the heat capacity'of thel briquettes, acondition obtained as shown in Fig. 5.

Here, again, the gas and solids temperature curves are no longer straight lines but instead of the rate of heating being lower than the average in the upper portion of the zone, and higher than the average in the lower portion of ther zone, it is higherl in the upper portion of the zone and lower in'the lower portion. In this case, again, if the conditions of; Fig. 2 represent the maximum permissible heating `rate, the maximum rate in the upper partof the"zone as shown in Fig. 5 will exceed this figure and therefore again the process will notfworkand the coal will swell. l

Fig. 6 shows how it is possible to compensate Y'. for the unbalan'ce in Fig. 5 v and again the unbalance is compensated for by "decreasing the rate of flow of briquettes and gas in the same proportion and therefore decreasing the average rate of heating to a point sumciently low so that the maximum rate does not exceed the permissible figure. Again, as in Fig. 3, the compensation is obtained at the expense vci? a longer time cycle "and greatly decreased output for a given piece of equipment. 1

The compensation shown in Fig. 3'is further complicated by the factthat there isv another factor involved ,in the practical carbonization of briquettes by the present process, and this is the factor of head load which the briquettes can sustain. As the coal reaches its point of maximum plasticity or fluidity, there lis a tendency for the briquettes to become 4deformed or stick together and for any given coal and any given binder briquettes will stand a certain maximum -head load at the point of greatest plasticity.

The reason for avoiding any considerable deformation'of any Vsticking together of the briquettes lies in the necessity for subjecting the surface of the briquettes during the carbonization cycle to free and uniformcontact with the heating gases. If briquettes are not deformed excessively andv do not stick together, they roll suflicieritly in passing through the retortso that the points `of contact between the briquettes are constantly shifted.

In general, 1the plasticity increases as the briquette passes through the critical zone reaching equipment. y

a point of maximum and then again decreases.

If we assume apoint of maximum plasticity occurring at a certain temperature on the curve in Fig. 2, andl where the preferred practical design of vertical retort is used this represents a certain depth', there will be a corresponding head load at this point. If Fig. 2 is compared with Fig. 3, it will be apparent that the same temperature is reached at a lower point because the rate of heating is slower in the upper portion and faster in the lower portion, and all temperatures are therefore displaced downwardly in the column of coal`or briquettes. If Fig. 2 represents the maximum permissible head load at the point of greatest plasticity, it will be obvious that Fig. 3 will cause failure because the head load will be increased and reduction in the rate of flow which is used to compensate in Fig. v4 will not help because the briquettes will merely flow more slowly but still the same temperature will be reached at the same height in the column. It

pensation becomes necessary, therefore, where the gasbriquette ratio is unbalanced by having too little gas, to modify the design of retort by increasing its horizontal dimensions in order to permit comfor gas-solids unbalance. Other means for decreasing head load may lalso be used. a

From the above, it will be apparent that the balancing of gas to solids in the critical zone is of the lgreatest practical importance and that where the balance is perfect, operation can take place at maximum output. The control is best at perfect balance because slight variations will have less effect than under conditions shown in Fig. 3 for the reason that there gas temperature and solids temperature do not run along parallel lines and there is greater heat he'ad which per- 7 mits considerable fluctuations in the rate of therefore not .limited to obtaining perfect gassolids balance, and a certain amount of unbalance can be tolerated if the output is kept sufficiently low.

Another advantage of the preferred specic embodiment of the present invention represented by Fig. 2 is that the heat head between gas and solids is kept at a minimum. Both Figs 3 and 5 show at one or other ends of the curves, a much larger heat head or heat difference between gas and solids. There is thus greater danger of cracking or carbonization of vapor evolved at the surface of the coal when encountering the much hotter gas at levels of the zone where the gas temperature and solids temperature curves diverge widely.

Heating by means of a gas stream also results in great uniformity and since the critical factor of rate of heating applies to each individual coal lump or briquette it is not sufficient that the rate of heating in the critical stage be low merely for the charge as a wholebecause it is not the average .condition throughout the charge which counts but the condition at the surface of each lump. Gas heating, therefore, gives a uniformity throughout the whole charge which is iinpossible with external heating.

While the present invention usually nds its most attractive economic eld in the carbonizing of relatively cheap bituminous coals, particularly in the form of briquettes, it shouldbe understood that the invention is not limited to treating a uniform material. On the contrary, blends or mixtures of different kinds of bituminous coal or bituminous coal with anthracite, semianthracite,

semibituminous, lignite, semicoke and coke may be used. This is particularly important where fine noncoking refuse is available such as, for example, coke breeze, anthracite fines, for example anthracite nes obtained as the flotation concentrate from the flotation cleaning of anthracite slush culm. These ne materials command a very low price and can be effectively blended with bituminous coal by means of the lpresent invention to produce high grade briquettes having superior burning characteristics.

The operation of the invention will be described in detail in connection with a typical example using Pocahontas or New River coals and using the referred dual circuit heating system of Fig. 1. It will be understood, of. course, that the rates of heating apply only to these coals and will vvary with other coals and for each coal the optimum rates must be determined by experiment.

In Fig. 1 of the drawings the reference character I indicates a vertically disposed, elongated,

heat insulated retort with a .chamber 2 at its upper portion to admit briquettes or lumps of coal without permitting escape `ci! gases, and with'a valve 3 at its lower end to permit discharge ofthe final solid or carbonized product without permitting escape of gases.

The retort I may be regarded as divided into four

sections

4, 5, 6 and 1, acting as preheating, distilling, high temperature, and cooling or quenching sections, respectively.

The high temperature section 8 may be a retort of refractory material or metal and may be surrounded by a heating device 8. A burner or burners 9 are provided for the heating device l. An air inlet for `the burner ls shown at III andra lean gas inlet pipe Il is provided with a valve II' leading to this burner. The products of combustion from the burner or burners pass into an Vannular combustionspace or flue I2 in the heating device 8. Ports I3 lead from the combustion space I2 to the annular space `I4 from which a series of exits -or outlets `I5 for hot yproducts of combustion lead into the lower`portion of the high temperature section 8.

A pipe I6 provided with a valve I6' leads to a manifold I'l at the lower portion of the cooling section 1. A series of openings I1' lead from the 4manifold II into the section' 1.

denser 22 to the suction pump or blower 24 from which a pipe leads to the tar extractor 25 which may be any of the well known suitable types. A pipe 25 lfor gases from which tar has been removed leads from the extractor 25 to the lean gas receiver 26. A valved outlet or vent pipe 21 is provided on the receiver 26. The valved pipes I I and Il4 also are connected to the lean gas receiver 26.

A'pipe 30 leads from the heated side of the heat exchanger 20 to a manifold 3| at the lower portion of the distilling section 5 of the retort I, from which manifold 3l hot gases pass through the openings 32 into the lower portion of the distilling section 5. An outlet pipe 33 leads from the upper portion of the distilling section 5 to the condenser 34 which removes organic liquids that are condensible at ordinary temperatures. A pipe 35 leads uncondensed gases of high caloriflc power from the condenser 34 to the suction pump or blower 36 from the outlet of which pipe leads to the tar extractor 31 of yanyof the well known types suitable for removing tar. A pipe`3'I' for rich gases from which tar has been removed leads from the extractor 31 to the-receiver 33 which is provided with a valved outlet .33 -for surplus rich gas. A valved pipe 40 leads rich gases from the receiver 38 to the heat exchanger 20 where these gases are heated and. pass into the distilling section 5 through the pipe 30. .A valved by-pass 4I around the heat exchanger 2l leads from the pipe 40 to the pipe 50 to provide convenient regulation of the temperature of the rich gases that enter the distilling section 5 through the pipe 30.

An outlet pipe 44 leads from the upper portion of the preheating section 4 to the suction pump orv blower 45, from the outlet of which a valved pipe 46 leads to a condenser 41 Afrom which a pipe 41' leads uncondensed gases to the heater 48. The gas heater may be heated by combustion of lean gases taken from the receiver 26 through the valved pipe 49 to a. burner 50, air for combustion purposes being admitted through the inlet 5I. The hot products of combustion from the burner 50 after heating the gas heater 48 are lead by the pipe53 into the lower. portion of the preheating section 4. A valved pipe 54 leads from the lean gas receiver 26 to the pipe 44 to supply any needed make up gases for the preheating section. l

The volumes of the gases and the amount of the gas made in the several sections of the retort depend upon the type of coal being treated, although the difference between coals from the standpoint of gas volumes required for heat transfer purposes-from the gas to the coal is small. However, diie'rences in coals will affect to a considerable extent the amount of .gas produced in the several sections of the retort and the weight of the iinished product for a given weight of raw coal treated.

For example, coal containing approximately 20% of volatile matter will produce amounts of gas and will require rates of gas circulation and temperatures as follows:

When 2000 lbs. of such coal is treated by this invention approximately 26,000 cubic feet of lean gas from the receiver 26 will be required in the quenching or cooling section 1. This lean gas will have a temperature of approximately 900 C. when it reaches the lower portionof the high temperature section 6, which is approximately the r temperature section 6.

treated in this section, thus making approximately 49,000 cubic feet of gas leaving the high The gas entering the quenching section from the pipe I Blowers the temperature of the solid productspassing out` through the valve 3 to about 50 C. The gas entering the high temperature section 6 from the combustion flue I2 is taken from the lean gas receiver' 26, and is caused to undergo a sufcient amount of .combustion to bring the temperature of the mixture to slightly above '900 C., the volume being about 13,300 cubic feet. The temperature of the gas leaving the upper portion of the hightemperature section 6. through the pipe II is about 100 higherthan the solid products at this point in the retort I.

About four-muis cr the gas passing through.

the highv temperature section .6 may pass out throughv the pipe I3 to the heat exchanger 20, condenser 22, tar extractor 25 and into the receiver 26. About one-111th or 9,700 cubic feet of the gases passing -through the high temperature section 6 may pass into the lower portion of the distilling section 5 at a temperature of about 600 C. and be joinedb'y heated rich .gas entering this section throughy the pipe 30. By means of the vent 21 on the lean gas receiver 26 the amount of gas that passes from the high temperature section-6 to the distilling Section5 can be regulated,

thus varying the amountot lean gas that is blended with the distilling zone gas so that the heating value of the surplus rich gas that is produced in the distilling zone can be controlled to suit the use to which this rich surplus gasis to be put. Y

. When it is desired Vthat the gases evolved in the distilling section 5 be not 'contaminated with gases from the

sections

6 and 4, the process can be readily operated to prevent` this.- Gas tight .gatesto permit passage of the coal may be located at theends of the section 5 for -this purpose. As already explained, a portion of the lean gas from the receiver 26 may be used for combustion purposes in the gas heater furnace 5 0 and some of' it may be passed through the pipe-54 and used .to augment the gas circulated through the preheating section 4. 1,

When treating a ton per hour of the coal mentioned above containing about 20%, of volatile matter,.approximately 34,000 cubic feet .of gas v is introduced into the lower portion of the distilling section 5 and is augmented.y by approximately 4,000 cubic feet evolved from thematerial being treated sothat approximately 38,000 cubic feet of gas leaves theupper portion ofthe dis-` tilling section 5. The rich gas which is made in `the distilling section 5 and recirculated by being caused to enter through the pipe 30 is heated to a predetermined temperature which depends upon" the upper limit of temperature at vwhich the coal being treated is no longer in aplastic condition and has lost its tendency to swell if heated at a rapid rate. 'Ihe gas entering through the pipe 30 augmented bythe lean gas from the high temperature section 6 and also .by the gas evolved from the material inv this section should be just suiiicient in quantity to transfer its heat to the material being -treated in this section and raise its temperature to within a i'ew degrees of the temperature of the gas entering through the pipe 30, which is approximately 500 C. The amount of gas passing through the -distilling section and the material .being treated passes through at such arate that a temperature gradient of a straight line order is produced so that there is a practically constant increase in temperature per unit of vertical length so that the temperature rise per unit` of time is not .so great in this section as to produce. swelling of the material, or deformation and sticking.

The rich gas of high B. t. u. value is drawn off through the pipe 33 and is passed through the (or part of it through the by-pass 4I) back to the lower portion of the distilling section 5.. The

desired amount through the pipe 4|.

With the coal underv considerationv approximately 33,000 cubic feet of gas is passed through the preheating section 4, the gas entering the llower portion of this section through the pipe 55 having a temperature of about 300 C. This gas consists of Sas given of! by the coal while it is being preheated in the preheating section 4 plus some lean gas from the receiver 26, when necessary. Approximately, 5% of4 the total amount of gas in this circuit is caused to pass downwardly into the upper portion of the distilling section 5 to prevent tar-laden gases from this section from entering the preheating section 4 and causing condensing and precipitating tars on the briquettes in this section. The remaining portion of the gas from the gas heater 48 raises the temperature of the raw material to about 300 C. as it leaves the lower ,portion of the preheating section 4 and removes from this raw material any moisture or other material that would be volatilized at the temperature to which the material is subjected in this preheating section.

The moisture and other condensable products are condensed out of the gas leaving through the pipe 44 before it enters the heater 48.

The rich gasl that is produced byctheocoa'l in the distilling section 5 is of very high caloric value. It has been found to be` from 800 to 1000 or more B. t. u. per cubic foot, depending upon the sort of coal that is treated. 'I'his gas is largely methane and higher hydrocarbonslusually called illuminants and a relatively small amount of hydrogen.

In the above example the rate of heating in the distilling section is 2 to 4 C. per minute for the coals specied.

The invention has been described specically in conjunction with a plurality of gas circuits which permit the separate removal of high Acaloriilc gas. It will be apparent that the carbonization, that is to say, theproduction of `the solid product of the invention is not concerned with the characteristics of heating gas so long'as the heating gas is nonreactive with the material. Where it isl not desired to obtain high calorlflc permanent gas separately, a cheaper operation from the standpoint of equipment and operating costs can be effected by permitting the gas stream to flow through the Whole length o f the retort. 'I'his will result in mixing the lean gas present in section E with the rich gas evolved in section 5 and the whole will be diluted with the amount of nitrogen introduced by the combustion of a portion of the gas in the combustion flue I4. Where the gas from section 6 is used as the heating gas for section 5, it is unnecessary and, in fact,

'undesirable for the gas to leave section 6 at a temperature of 100 above that of the solids. On the contrary, it should leave at approximately the temperature of the solids as they emerge from section 5. 'I'his is effected by reducing the volume of gas circulated through section 6 to that which circulates through section 5 when adual system is employed, and also by reducing the proportion of gas burned in the burners 9 because there is no longer any need to compensate for the radiation and other losses involved in the heat 'exchanger 20 and the whole heating gas circuamamos:v temperature may be regulated by by-passing the it is ringot diluted with as much nitrogen and other ne .f

Compromises may also be eiIected, that is to say, distilling section 5 may be partly heated by gases flowing up from the section 8 and partly by gases coming from the heat exchanger 20'. When such a compromise isemployedthe condenserv 22, tar extractor 25, and receiver 26 is reduced in si\z\e by corresponding reduction in the heat losses and in th wer and other operating expenses. The/Wfaken off through the pipe 39 will, of course, be of a caloriiic value intermediate between that obtainable with a full dual circuit operation and that corresponding to a complete single circuit. In every such case, the skilled I engineer will choose a compromise which represents the best economic value for a particular plant using a particulargraw material in a given location. It is an advantage of the present invention that gases of different calorific power can g be produced so as to adapt the process for the different conditions obtaining in different geographic locations.

In the speciiic description of the invention in connection with Fig. 1 of the drawings, reference has been made to zones which in the retort shown --in the drawings are equally physically distinct compartments. It should be understood however that this particular apparatus structure forms no part of the invention and the zones as referred to in the claims are directed entirely to the temperature ranges through which the coal passes. regardless of whether the zones are physically separated or simply temperature ranges in a single moving column. It is, of course, possible to break up the zones into physically separate retorts where the structural design and space requirements make such a construction desirable. ,The invention, of course, coversrthe process-of heating the coal at the rates and with the gas volume specied, regardles of the physical location of the various heating zones.-

The invention has been described in conjunction with the use of gas heating for all stages or zones. This is, of course, the preferred and ideal method, but it should be understood that gas4 moval of evolved vapors are required. It is there-l fore possible, although less desirable, to heat in the first'v or third zones by othermeans than a gas stream and such modifications are included in the broader aspects of the invention. Such modifications are, however, normally less desir-` able and accordingly, the preferred embodiment of the invention which represents the most efflcient practical method of carrying out the principles of thevinvention, utilizes gas heating 'for all three zones.

In the claims the term capable of coking is used to dene coals which pass through a plastic state on heating and are therefore capable of forming an autogenous binder during carbonization. It should be understood that this term is not used in a narrow sense in which the term is sometimes used in the art to designate a type of coal which is capable of practical economical coking in the ordinary ltype of externally-heated by-product coke oven. Wherever the term is used in the claims, it is used in the broader sense defined above and in no other sense.

I claim:

1. A continuous process of destructively distilling coal whichcomprises passing the coal capable of coking in succession through a series of zones, the rst being a preheatlng zone to a temperature at which evolution o! volatile material begins, the second zone being the lfirst dlstilling zone and extending from the softening point of the coal up to a temperature of about 500 to 600 C. in which zone the major portion of the condensable hydrocarbon volatiles are evolved and a third zone extending up to about '700 to 1000 C. in which zone the desired degree of distillation and carbonization is reached, the heating for at least the second zone being by contact with hot gases which are substantially nonreactive with the coal at the existing temperatures in the zones, the volume of heating gas and its speciilc heat in the second zonebeing suilicient so that when introduced at substantially the exit temperature of the coal leaving the zone i t contains suilicient heat to bring the coal passing through the zone up to exit temperature while Abeing itself cooled down to substantially the temperature of the coal at the inlet of the second zone, the rate of heating in the second zone being sufficiently low so that the particular coal will not swell sufficiently. to produce a product having a density as light as high-temperature coke produced from the same coal in a standard by-product coke oven.

2. A continuous process of vdestructively distilling coal capable of coking, which comprises grinding the coal, incorporating a binder with` the ground coal forming it into briquettes having suilicient strength to permit handling and I passing the coal in succession through a series of zones, the rst being a preheating zone to a temperature at which evolution 'of volatile material begins, the second zone being the ilrst vdistill-- ing zone and extending from the softening point of the coal up to a temperature of about 500 to 600 C. in which zone the major portion of the' condensable hydrocarbon volatiles are evolved and`a third zone extending up to about 700 to 1000 C. in which zone the desired degree of distillation and carbonization is reached, the heating for at least the second zone being by contact.` with hot gases which are substantially nonreac- 'tive with the coal at the existing temperatures in the zones, the volume of heating gas and its specic heat in the second zone being suillcient so that when introduced at substantially the exit temperature oi' the coal leaving the zone it contains suilicient heat to bringthe coal and binder passing through the zone up to exit temperature while being itself cooled down 4to substantially the temperature of the coal at the inlet to the second zone, the rate of heating in the second zone being sunlciently low so that the particular coal will not swell sufficiently' to produce a.

product having a density as light as high-temperature coke produced from the same coal 'in a standard by-prcduct coke oven. v

3. A continuous process for destructively distilling coal capable of coking which comprises passing the coal in succession through a series of zones, the rst being a preheating vzone to a temperature at which evolution o'f volatile material begins, the second zonebeing the ilrst distilling zone and extending from the softening point of the coal up to a temperature of about 500 to 600? C. .in which zone the major portion of the .condensable hydrocarbon volatiles are evolved and a third zone extending up to about '700 to 1000 C. in which zone the desired degree of distillation and carbonization is reached, the

heating for all zones being by contact with hot v gases whiclnare substantially nonreactive with the coal at the existing temperatures in the zones, the volume` of heating gas and its specic heat in the second zone being sufficient softhat when introduced at substantially the exit temperature of the coal leaving the zone it contains suiilcient heat to bring the coal and binder passing through the zoneup to exit temperature while being itself cooleddown to substantially the temperature of the coal at the inlet to the zone, the rate of heating in the second zone beinggsuillciently low so that the particular coal will not swell suillciently to produce a lproduct having a density as light as high-temperature coke produced from the .same coal in a standard by-product coke oven.

4. A'process according to claim 1 in which the heating in the third zone is eilected by a gas v stream oi' relatively low caloric value which has been partially burned' and the heatingv in the second zone is effected by the circulation of a gas stream of high caloric value whereby dilution ofthe volatile material evolved in the second zone with gases of low calorinc value is avoided.

5. -A method according to claim 1 in which the heatiig in the preheating zone and in the third Gronau A. maar.