US2074456A - Method of revivifying clay - Google Patents

Description

Mamgfi 9 PM CARLETON METHOD OF REVIVIFYING CLAY Filed April 16, 1932 2 Sheets-Sheet l ism N I M W|||||v 7 u, m. w F 5 E 5MP R L a Y W 1% m AU VI l I I l l III II IIIIIII A TTORNE Y.

March 23, 1937. R, A AR ETO 2,074,456

METHOD OF REVIVIFYING CLAY Filed April 16, 1932 2 Sheets-Sheet 2 INVENTOR.

ROBERT A. CARLETON WWI va )flmq ATTORNEY.

' Patented Mar. 23, 1937 UNITED STATES,

PATENT- OFFICE 2,074,456 METHOD OF REYIVIFYING CLAY Robert A. Carleton, Brooklyn, N. Y., assignor to National Electric Heating 00., 1110., New York, N. Y., a corporation of New Jersey Application April 16, 1932, Serial No. 605,704

2 Claims.

.5 suspended in a gaseous or fluid medium to promote some desired reaction, by heating the material and subjecting it to such' supplemental treatment as is necessary to accomplish the reaction. Typical uses for this method and appalO ratus are round in the coking of coal, the refining of filtering materials, and the 'drying and roasting oi cereals and other food products.

in the low temperature carbonizing and pretreatment of coal for use in central stations and other plants where pulverized coal is fired under boilers for the generation of steam, the untreated coal contains many hydrocarbon compounds of relatively low value for the generation of heat but of relatively great value for many industrial and manufacturing uses.

It has been proposed to pretreat the coal to obtain these relatively high value by-products, extracting by means of heat, the oils and other volatile compounds and recovering the carbon in the form of coke to be burned under the boilers. By this means, with the coal and the lay-products at a normal value and market, the value of the recovered by-products in the form of light and heavy oils, various hydrocarbon compounds and high calorific value gas suitable for illuminating gas enrichment and other purposes, will return a value which when credited to the cost of the coal will effect a substantial reduction in the net cost of the fuel burned for steam generating purposes. .The mechanisms heretofore employed for such heat treatmet of coal have not been suitable for carbonizlng the coal in a pulverized form, it being necessary to treat the coal in large and cum- 'bersome brick retorts which are not only'oi high initial cost but for which the maintenance or upkeep and operating-costs are also relatively great, and the space required is considerable; and the coke produced is in large masses and of a hard and refractory nature, requiring special and expensive apparatus for pulverization.=

In such operation, due to the relatively long interval of time, .usually 30 to minutes, that 0 the coal and its distillation products is exposed to the carbonizing temperature, the oils and other volatile compounds are cracked or decomposed by the prolonged heating to too great a degree, converting the more valuable oils and other products 55 into relatively low value gas with the production of lower value pitch or tar, and reducing the amount of coke recovered, and thus lessening the total value of the various products obtained.

The carbonizing retorts, due to their size and weight, require a relatively long time, usually 6 5 to 8 hours, to become heated to the required operating temperature and When shutting them down a large amount of stored heat is lost by radiation, and they are therefore not adapted to an intermittent method of operation. 10

Similar difficulties have been encountered in the burning and recovery for reuse of the clay and other material used for contact filtering and clarifying fluids, such as petroleum products and the like. The filtering material is in a finely ,15 divided state usually passing through a 200 mesh screen, and great difflculty has been encountered because of the extreme fineness of the material and the relatively low dilierential in temperature between theoxidizing point of thecarhon 2 or other materials to be removed and the sintering or structural break-down point of the clay. Due tothe difliculty or impracticability of controlling the temperature and other conditions under which the material is treated, closely enough, 25 the structure and the absorbing efilciency of the recovered material is affected to the point that its reuse is not economically practical.

To overcome these difliculties and provide a satisfactory, economical process, I propose to pass 30 the materials in a fluid suspension, through tubular heating devices directly heated by electrical current. This direct heating is preferably accomplished by passing electric current through the tubes which act as the heating devices and 35 flowing the material to be treated through these tubes in a fluid suspension. The method of heating is especially important to the process -because it may easily be controlled to treat the mat'erial rapidly at a high, but closely controlled 40 temperature which causes the reaction to take place quickly and with a minimum of side reactions upon the products formed. Furthermore, the apparatus required is neither large nor expensive.

Upon leaving the heating devices, the material is cooled suddenly if desired and separated from the fluid suspending medium and from any vapors or gases extracted from it. These fluids, vapors, and gases are then appropriately separated and in 50 some instances may be reused as a suspending medium for more of the untreated material. Suitable heat exchange may be made between the hot treated suspension and the cold untreated suspension.

With such a method, the material may be treated under a selected pressure, if desired, the length of time during which it is treated may be closely regulated by adjusting the rate of flow of 5 the fluid suspension, and the temperature closely controlled by thermostats. The fluid suspending medium may contain a reagent which reacts with the material being treated or may contain a catalyst to aid the desired reaction.

The present invention finds particular utility at electrical power stations. In the operation of central electric power stations the load or power demand varies during different parts of the day, being very light during certain hours, such as from midnight until morning, during which time large surplus electric generating capacity is available and electric current may be produced for any desired purpose, at a relatively low cost, as fixed charges and labor are already charged against the plant and the only additional extra cost required for generating the electric current for coal pretreatment is substantially that due to the cost of the fuel required to generate the steam for use in the electric generators.

Preferably, the coal to be used is pretreated during the night or other suitable period when the demand for electric current is lowest and surplus electric generating capacity can be utilized, preparing the coal for the 'next days run. The amount of coal required will vary with the size of the plant, some of the larger city electric generating plants requiring 500 tons or more of coal per day.

Many of the modern electric generating plants 35 utilize steam boilers of several thousand boiler horsepower capacity each and are equipped with coal pulverizing and storage equipment, in which case the pretreatment or low temperature carbonizing of the coal is of particular benefit not 0 only as a means of reducing the net cost of the fuel used, by the sale of the recovered high value by-products, but also due to certain advantages of using pulverized coke over that of untreated pulverized coal, among which is not only the 45 reater combustion speed of. the relatively pure carbon or coke, free from moisture and distillable compounds that usually slow down the combustion speed, but also from the consideration of safety, as there is considerable hazard in storing pulverized bituminous coal due to the formation of explosive gases and the possibility of spontaneous combustion, which condition is not present in the handling and storage of pulverized coke.

55 In burning untreatei bituminous .coal, considerable smoke and gas is discharged from the stacks due to the presence of unconsumed hydrocarbon compounds; with the use of coke the volatile matter left in thecoke is only that required to start combustion and rarely exceeds 6 to 8%, and which together with the relatively pure carbon is entirely consumed, resulting in the substantial elimination of smoke nuisance,

65 and higher furnace efficiency.

The apparatus of the invention may be constructed in-large or small capacities, of simple and rugged construction and arrangement, of metals resistant to the corrosive action of the 70 material being treated and that will be durable in service and operate efficiently and economically, that will not burn out or require replacement from overheating and that can be arranged to operate on any available electric heating current. 75 These and other features of the invention will ,in Fig. 1.'

more fully appear from the following description and accompanying drawings and will be particularly pointedv out in the claims.

For a detailed description and illustration of the preferred form of my invention, reference may be had to the appended drawings and to the following description thereof. The embodiments of the invention, as illustrated in the drawings, are particularly suited for the treatment of solid substances, such as coal and other car- In bonaceous materials, filter clays, and the like, that require a high temperature to obtain -a desired reaction and that may be caused to flow through the heating tubes in a finely divided state, suspended in a suitable gaseous medium, 15

but it will be understood that this invention is not limited to the use of the arrangements shown in the drawings and that they may be readily modified within the scope of the invention to provide an efficient heat treating apparatus for many 20 industrial purposes where the material to be treated may be caused to flow in a fluid suspension through tubular heating means.

Preferred forms of apparatus embodying the invention are illustrated in the accompanying drawings, in which Figure 1 is a plan view of an electric heating apparatus, embodying the principles of my invention.

Figure2 is a side elevation of the device sho Figure 3 is asectionalview on line 3-3 of Fig. 2.

Figure 4 is a sectional view on line 4-4 of Fig. 2.

Figure 5 is an arrangement of apparatus especially suited for treating finely divided coal and illustrates a method of separating and collecting the products distilled therefrom.

Figure 6 is an arrangement of apparatus for such operations as the reactivation of finely divided contact filter clays and the like. 40

' As shown in the drawings, an electric heater is provided, comprising tubes H having walls of relatively high resistance metal through which the electric heating current is caused to pass, the tubes thus acting as heating elements as well as containersfor the material undergoing the treatment. One or a'plurality of such tubes may be employed to obtain the desired capacity, the internal cross sectional area of the heater tubes H and the thickness of the metal wall being determined by the desired capacity, the pressure under which the system will operate and the electric heating current available.

Preferably, the internal diameter of the heater tubes is such that the finely divided particles of 5' the material being treated and flowing through the tube will become quickly heated to the desired temperature, partly by direct contact with the heated walls of the tubes, but chiefly by the absorption of the radiant heat discharged from the tube walls. I

The gaseous medium used as a vehicle may be of such a nature that it is neutral to and not effected by the material or it may be of such a nature that it will react with the material under 6,; the influence of the temperature and pressure involved, acting to cause a desired chemical or structural change to take place in the material.

The relative amount or volume of the gaseous vehicle is determined by the weight, size and nature of the material treated, the results desired, the speed of flow, and the amount of dilution required.

The heater tubes II are provided with electric terminals l2 welded or otherwise electrically con- 7 :nected to a point substantially midway between the ends, by means of which the electric heating current is supplied. One end of each of the heater tubes II is connected to an inlet connection plate I3 of a separator I4, and the other end of each of the tubes is connected to a feeding mechanism IS, the members to which the tube ends are connected being grounded. The material which has been treated settles into a hopper 35 at the bottom of the separator and is removed by a screw conveyor 34 through a tube 42.

It will be observed that by so arranging the electric heating circuits the ends of the heater tubes II as well as the separator I4 and the feeding mechanism I5 and outer casing I6 are at ground potential, thereby eliminating any possibility of leakage of the electric heating current or the possibility of electric shock by contact with the apparatus.

Three heater tubes are shown in Figures 1 to 4 and by the use of a three-phase alternating current connected to the terminals I2, the currents m the three tubes being out of phase tend to neutralize the self induction thus increasing the power factor to a maximum.

The heater tubes I I are supported by insulating supports I 'I'of transite, fire brick or other suitable electrical insulating material that will withstand the temperature involved. An enclosing casing I6 of steel plate or other suitable material is provided, the space between the casing I6 and heater tubes II being substantially filled with I :suitable heat insulating material I8 to reduce the loss of heat byradiation.

The feeding mechanism I5 with which the ends of heater tubes II communicate comprises a receptacle of steel or other suitable metal connecting by means of a duct I9 with a supply of pulverized coal. A suitable worm or screw feeding device 20 operated by means of gears 2I and a driving pulley 22 causes the pulverized coal to be delivered to the inlet of heater tubes I I at a regular and uniform rate.

A gas manifold 23 isqprovided, connecting by means of an inlet 24 to the jets 25 placed at the inlet of heater tubes II through which gas or other suitable vehicle in suflicient volume is delivered under the desired pressure, causing the pulverized coal to become intimately mixed therewith and to flow in a form of a cloud through the heating tubes I I. As the heater tubes are of relatively small internal diameter and their surface is heated uniformly to a selected high temperature, the finely divided material suspended in they fluid vehicle is exposed to an' atmosphere uniformly heated, chiefly by radiant heat and is quickly and uniformly raised to the selected reaction temperature. 4

The heater tubes may be supplied in relatively long lengths, and correlated to the velocity of the of heat during the first part of its travelthrough the heater tube, so as to raise it to the desired temperature quickly, thereafter supplying suflicient heat only to maintain it at the selected reaction temperature during the balance of its 15 travel through the heater tube. This may be readily done by changing the wall thickness of the tube at difierent portions of its length or by using a metal having a diiferent electrical resistance, the various sections being welded together. The electric current passihg therethrough in series will cause heat to be generated in each section in accordance with its relative electrical resistance. Alternately, the electric terminals I2 may be connected to a point nearer the inlet end of. the tube, whereby due to the lessened resistance at that end, more heating current will flow through the inlet end of the tube walls and more heat will be generated therein.

In certain instances, as when treating such materials as filter clays, it is desirable to quickly raise the material to the combustion or oxidation temperature of the carbon or other substance to be removed, then by the admission of air or other medium in controlled quantities, permit the heat of combustion or oxidation to furnish the balance of the heat required to complete the required reaction.

In such operations, it may also be desirable to provide means for cooling the flowing stream of gases and material to control the speed of the oxidation so as to prevent too rapid combustion and the generation of excessive heat that may cause disintegration or injury to the material. This cooling result may be readily obtained by causing the flowing stream of hot material to react by suitable heat exchanging means with the colduntreated material acting to cool the treated or partly treated material and heat the flowing Y stream of the cold material, thereby not only conthe temperature of. the material discharged from the heater tubes and operable directly to so regu-- late the electric heating current supplied the heater tube to maintain the material discharged at a selected temperature. An automatic device 29 is subjected to the pressure of the gas or vapor supplied inlet connection 24 and in the event the pressure of and consequently the volume of the gaseous vehicle supplied the apparatus becomes reduced to a predetermined degree, device 29 acts to open control ci'rcuitjfl and by means of magnetic switch 3I', interrupts the electric heating current supplied the heater tubes.

The apparatus shown in Figure 5 is designed particularly for the treatment of coal. In this apparatus, the treated material is discharegd from heater tube II to separator I4 of the well known centrifugal or cyclone type, where the solid material is separated from the gaseous vehicle and the various reaction products which when distillingcoal will consist of tar and oil vapors, ammonia, and various hydrocarbon gases and compounds, are discharged by means of outlet 33 to suitable apparatus commonly used for the 'separating and utilizing of such distillation products.

In some instances, it may be desirable to quickly cool the gases and solids to terminate the heat reaction, in which event the gaseous material may be caused to flow through a heat exchanger, not

shown, where they are reduced in temperature to the desired degree by heat exchange with a suitable cooling medium which may readily be of the same type of material as that being treated and which flows after being preheated through the heating tube for treatment.

From the separator l t-the distillation products fiow through a pipe 45 to a heat exchanger 66, from there through a pipe to a tar separator 3d and then through a pipe 49 to a fractionating. tower 50. The gas escaping. from the fractionating tower passes through a pipe M to an ammonia scrubber 52 from the outlet of which a part of the gas is returned to the jets 25 at the inlet end of the heater through a pipe 53, a pump 55,

the heat exchanger 46 and a pipe 56. The discharged gases may be passed to any suitable recovery devices (not shown). v

If it is desired to operate the heater under pressure, a weighted valve 51 may be placed at the outlet 33 of'the separator, which valve will retard the flow of fluid so as to allow the desired pressure to be built up in the heater and separator.

Most of the tar, pitch, or other high boiling point compounds are condensed in the heat exchanger and may be removed through a connection 58 in the bottom thereof. The remainder, which pass in the form of a mist into the tar separator 48, are removed therein and pass out through a connection 59. The portions of the vapors which are fractioned outof the tower 56 are discharged through connections fill, 6i and 62 on the tower, and the ammonia is removed by a liquid circulated .through the scrubber by a pump 53 through pipes 64 and 65. The remaining gases are discharged through a pipe 66 from which a portion of the gases are withdrawn for recirculation.

If desired, the coal may be mixed with the ases before they pass through the heat exchanger and also the gases to be discharged may be passed through the heat exchanger before discharging them.

The electric heater described in Figures 1 to 5 being of small mass or weight may be raised to the desired operating temperature and placed in operation withina period of to minutes and when shut down, the amount of heat stored in the apparatus is negligible, thus making it particularly adapted for the intermittent method of operation required in the pretreatment of coal for central station and steam generating plants.

Due to its relatively .simple arrangement and construction, the cost of the electrically heated coal carbonizing furnace is relatively low, being but a fraction of that of the cumbersome brick retorts heretofore employed. The amount of labor required for operation and maintenance is slight and it can be installed in a small area or space, for example, a 50 ton per hour heater of the type shown in Figure 1 requires a floor space of but 3 by 50 feet, whereas the brick retort type of heater of the same capacity usually requires a floor space of approximately'ltl by 100 feet.

As the material being treated is exposed to the heat reaction for but a short interval of time which may, if desired, be less than one. second, it-may safely be exposed to much higher tempera; tures than would be practical when using methods involving relatively long exposure to the heat, and as the coal is in a finely divided state, usually 85% passing through a ZOO-mesh screen, the distillation reaction is practically instantaneous and as the distillation productspass from the heating temperature, secondary cracking of the vapors and the conversion of the more valuable primary products such as light oils into the less valuable gas,,tar, etc., is substantially reduced, and as the controlling elements of time, temperature, and pressure may be readily and closely controlled, the maximum yield of the desired products may be had on the most economic basis, that is, the balance between yield of coke, light and heavy oils, and gas may be easily and quickly adjusted to suit the available market or demand.

The volume of gas used is such that the mixture of gas and pulverized coal will flow readily, with suitable separation between the particles of coal, so that during the heating and distillation operation the particles of coal will not coalesce but will be delivered in substantially the same finely divided state; the amount of gas required will vary, depending upon the type of coal, its volatile content, velocity of flow, temperature, and. other determinable factors but'will usually be at least 2 to 4 times the volume of the coal.

The section of the heater tube 31 adjacent to the inlet end may be heated to a greater degree than the remainder of the tube so as to quickly gaseous vehicle will not coalesce or stick together I as it goes through the softening period prior to distillation, the vapors leaving the coal particles and converting it into coke.

It is desirable to retain a certain amount of volatile matter in the coke to facilitate ignition and rapid combustion in the furnace and therefore the temperature and other conditions controlling the distillation operation are so adjusted that the coke, as delivered, will retain the desired amount of volatile matter, usually 6 to 8% being a suitable amount.

Under certain conditions, it is desirable to maintain the material under pressure during the reaction period, as I find that at certain pressures the secondary reactions may be better controlled and the yield of light oils and saturated compounds increased and that of gas reduced, and that under other pressure conditions the yield of unsaturated compounds and gas may be increased.

It is therefore evident that by correlating the pressure to the temperature and duration of time the coal is under treatment that the proportions and kind of products obtained by the distillation operation may be readily adjusted to suit the economic conditions or requirements -of the period and the location of the plant. For instance, if a larger production of gas is desired, a longer period of heating at a greater temperature at relatively low pressure would be used, the gas being produced at the expense of and by degrading or cracking the light oils and other distillation products. By the use of a shorter heating period at a greater pressure, the secondary reactions may be reduced and a greater yield of light liquid products obtained with the consequent reduction in the amount of gas formation.

Figure 6 illustrates an arrangementof apparatus for treating solid materials in a comminuted or finely divided form, such as contact filter clay, cement, etc., where the material may be caused to flow suspended in a suitable gaseous medium through the tubular heater, the operation being somewhat similar to that described in Figure 5 except the heat treatment is primarily intended for the'purpose of effecting a structural change in the material rather than the recovery of distillable compounds.

I have found that by heating such material in the type of tubular heater described, that due to the very exact and automatic control of the temperature, the duration of time and the condition '1 of the atmosphere in which the reaction takes place, that the carbon and other impurities can be oxidized and removed without substantial injury to the structure of the clay or other filter material. I

20 I further, find that by treating the clay under pressure with superheated steam in a slightly oxidizing atmosphere that the temperature required to oxidize the carbon is reduced and that the material may be delivered ina satisfactory con- 25 dition suitable for reuse.

As shown in Figure 6, the relatively dry filter clay isdelivered to the feeding mechanism"!!! of the type described in Figure l where it is mixed with asuitable volume of gas supplied under a suitable pressure by means of a blower, the

finely divided clay suspended in the gaseous vehicle passing through a preheater 12, which comprises a double tube construction, the material passing through the annular space 13 provided 35 between the outer tube '14 and the inner tube through which the hot material from the heater tube '86 is flowing, the cold untreated material serving to reduce the temperature and control the heat reaction of the material in the inner or 40 reaction tube to a suitable extent; itself becoming preheated and passing by way of a connection TI and an insulated conduit 18 to the inlet iii of the.

heater tube 16.

A jet 8B is provided, by means of which a se- 4 lected volume of superheated steam is supplied theflowing stream of finely divided clay and gas, and by means of a jet iii a determinate volume of air or other oxidizing medium is likewise supplied, the amount of steam and air admitted 50 being that required to complete combustion of the carbon and other combustible matter in the clay, at such a rate that complete combustion will take place while the clay is passing through the heater l6 and the .reactor tube 15, but not 55 sufllcient to cause too rapid a rate of combustion so as to raise the temperature of the clay to the sintering or melting point.

The mixture, with the combustible matter partly or wholly consumed, passes from the end of 60 the heater tube 16 to the reactor tube 15 of the heat exchanger 12 where the combustion of the carbon is completed, being gradually cooled by heat exchange with the cooler untreated material passing through the annular space 18 and is then discharged to a suitable separator 82, preferably of the usual centrifugal type, where the solid material is removed by means of screw device 83 and a discharge pipe 84, the gas and products 70 of distillation and combustion passing to a suitable scrubber 85 and to the gas recovery system,

not shown. v

A jet 88 at the entrance to the reactor tube 15 is. provided, whereby additional air or other oxi- 75 dizing medium may, if necessary, be added to accelerate or continue the combustionof the carbon.

As in the treatment of pulverized coal described in Fig. 5, due to the relatively high temperatures involved, the thermal reactions are extremely rapid and it is very essential that the elements of temperature, time, pressure, and atmospheric conditions, all of which factors influence the condition in which the material is delivered and its value for reuse, be properly correlated and closely controlled.

Due to the relatively small mass and weight of the heater tube 16 the walls of which comprise the heating elements, it responds very quickly to any change in the value of the heating current supplied, and by means 0! the sensitive pyrometer controlling device 81 and the voltage regulator 88, may be readily and automatically maintained within a variation of approximately 2 Fahr. of the selected operating temperature. The pressure under which the reaction proceeds is automatically regulated by a loaded valve 51 and as the clay or other material to be treated is supplied in a uniform and regular manner, after the apparatus is once adjusted to suit the required operating conditions, it will thereafter operate with but slight further attention.

The electric heating current may be supplied from any suitable source, either direct or alternating but the drawings show the heater c n nected to a 3-phase electric power circuit; a d

the connections and controls being similar \to those shown in Figure will not again be described.

While but a single heater tube is shown in Figure 6, it is obvious that any desiredplurality of such tubes may be employed, in a. manner substantially as shown in Figure 5, and'that while the heater tubes are shown in relatively long straight sections, they may readily be constructed in a spiral or other desired form or arrangement.

When treating certain materials, it may be desirable to introduce into the flowing stream of such material a suitable reagent, which may be in a gaseous form as hydrogen or compounds that liberate hydrogen at high temperatures, these constituents being introduced alone or combined with any suitable liquid or solid substance to effect a desired reaction in the material being treated. Such a catalyst or substance may be readily introduced into the flowing stream by means of a suitable mechanism such as a pump or measuring device by way of inlets 80, H, or 86.

While the invention has been described particularly with reference to the treatment of finely divided coal and filter clays, it is obvious that its use may be extended to other fields in which it is desired to treat and process various forms of material that may be caused to flow throu h tubu; lar heating means in a fluid suspension.

It is also obvious that many other embodiments of the invention may be made by those skilled in the art, and it will be therefore understood that the particular devices and arrangements shown and described are of an illustrative character and are not restrictive and that various changes in form, construction, arrangement in parts and methods of use may be utilized within the spirit and scope of the following claims.

What I claim is:

1. The method of continuously purifying comminuted filter clay contaminated with carbons;

ceous material, whichcomprises suspending the material in a gaseousmedium, which issubstantially non-oxidizing at operating temperatures,

flowing the suspended material in a closely confined stream, subjecting each increment of the said stream to the influence of radiant heat for a period of less than a few seconds, subjecting 5 said stream to the influence of a gaseous medium introduced to pass in the direction of flow to cause oxidation of the carbonaceous material at operating temperature, removing the said stream from the heating influence and separating the solid 10 from the volatile products of said reaction.

2, The method of continuously purifying comminuted filter clay contaminated with carbonaceous material, which comprises suspending the material in a gaseous medium which is substantially non-oxidizing at temperatures between 950 and 1200 F., flowing the suspended material in a solid from the volatile products of said reaction.

ROBERT A. CARLZE'I'ON.

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