US1826209A - Apparatus for the production of activated carbon - Google Patents

Description

Oct. 6, 1931.

A. GODEL' 1,826,209

APPARATUS FOR THE PRODUC TION 0F ACTIVATED CARBON Fiid Oct. 13, 1926 1 I 4 Sheets-Sheet l Oct. 6, 1931. A. GODEL 0 APPARATUS FOR THE PRODUCTION OF ACTIVATED CARBON Filed Oct. 18, 1926 4 Sheets-Sheet 2 A. GODEL 1,826,209 APPARATUS FOR THEYPRODUCTION OF ACTIVATED CARBON Qct. s, 1931.

Filed Oct. 18, 1926 4 Sheets-Sheet 3 WWW,

Oct. 6, 1931. v

APPARATUS FiIedJOct. 18, 1926 4 Sheets-Sh ee'c 4 aw gmw,

Patented Oct. 6, 1931 ALBERT GOIDEL, OF LAGNIEU, FRANCE, ASSIGNOE T0 socrnrn DE nnonnacnns ET DEXPLOITATIONS rE'rRoLIr'EREs, 0F rams, FRANCE, A rnnno soomcrn ANONYME APPARATUS FOR THE PRODUCTION OF ACTIVATED CARBON Application filed October 18, 1926, Serial No. 142,407, and in France April 15, 1926.

It has frequently been noted that certain embers of wood charcoal withdrawn from beneath a thick layer of ashes possessed'a fairly high absorbent power. A study of this fact, which is quite well known in itself, has'led to the conclusion that it is possible:

(1) to treat carbonaceous substances of'the most varying kinds with a view to their activation;

(2) to obtain all kinds of qualities of ab- The present mvention 1's stances at varying temperatures by gases pr gaseous mixtures of diverse compositions but under very particular conditions which will be enumerated hereafter.

It must be admitted that in any combustion of carbon, there is necessarily formed a certain proportion of activated carbon, and also that this activated carbon is destroyed in proportion to its formation, either'by combustion if excess of air be present, or by becoming fouled with hydrocarbons if the combustion is incomplete.

It is no doubt, for this reason that there has been recommended either a sudden cooling of the incandescent and well coked carbon,

or a'circulation of the carbon andthe combustion gases in counter-current or transversely. This last process which evidently obviates thefouling of the active layers of carbon by'the layers not yet activated or still in distillation, has the serious drawback of necessitating the rigorous control of the composition of the activating'gases; in" default of careful regulation, the proportion of active carbon contained in the final product is insignificant; moreover in spite of all precam" It is to be noted that the composition of the tions that, may be taken to regulate the composition of the activating gases in the bestpossible manner, it is impossible to prevent alteration of this composition in passing through the layer of carbon, which renders the preliminary regulation illusory or partly inefiective. This process therefore does not allow of obtaining carbons having a definite maximum activity or of obtaining high outputs.

sorbent or de-colorizing carbons, having varying degrees of activity. I, T based upon the treatment of carbon or ofcarbonaceous subbest protected from the smoke in the grate by this layer of ashes.

This may be interpreted in the following -way: The speed of combustion of the fragment of carbon has to be regulated in such a way that this speed shall be lower than the speed of formation of active carbon, starting from inactive carbon, in the same conditions; only on this cond1t1on can any active carbon subsist.

However it may be, as regards this hypothesis and the factors adapted to favour the speed of production of activated carbon, it is possible in practice, this being the characteristic feature of the invention, to reproduce the phenomenon by enclosing thecarbon within a cover or casing with slightly permeable walls, fulfilling the function of the ashes in the previous experiment. 7

For example, wood charcoal can be enclosed in a vessel made of porous earthenware having its orifice or orifices well plugged, and the vessel being raised in a furnace to a temperature of about 800 C. At the end of a certain time and after cooling, there can be withdrawn from a vessel a'residue of carbon possessing a very high activity.

1 The very slow gaseous exchanges which have taken place by diffusion through the porous walL of the vessel have produced the activation; the speed of this reaction can be regulated by varying the degree of porosity of the earth-'employeduntil the optimum yield for a given carbon, a given atmosphere and a given temperature of the furnace is obtained.

tion of a proportion of sawdust, cork, etc, with the clay efore burning. It is likewise possible to utilize other porous substances such as special carborundum, silica bricks,

etc., as well as finely perforated vessels or.

covers.

Analysis made upon samples of gas taken: (1) In the interior of the porous vessels filled with carbon;

(2) from the exterior of these vessels, that is to say, simply in the atmosphere of the heating furnace; have show-n that there existed a great difference in the composition of the two gases; the former, being the gases resulting from acti7 vation, are combustible gases,rich in carbon monoxide, while the second, or activating gases, are incombustible gases, rich in nitrogen and carbon dioxide like the ordinary products of combustion from furnaces.

It is evident that this difference of composition between two gaseous atmospheres indicated above is due to the reducing influence of the carbon enclosed in the porous vessels; it is this very slow and controllable chemical action which is the cause of the activation phenomenon in the process according to the present invention. This action is selective, that is to say, it affects only the inactive parts, without destroying at the same time the parts of the carbon already activated.

The most favourable activation temperature varies with the nature of the product treated, the porosity of the vessels and the nature of the gases servin for the activation; it is for example approximately 800 C. for ordinary wood charcoal in a normal nonoxidizing furnace atmosphere with good combustion of the fuel. i

It has been; noted as advantageous for obtaining a satisfactory yield of active carbon, to arrange all the fragments of carbon similarl in relation to the porous casing, which can effected by the use of very flat vessels of large surface area.

The difference of chemical composition existing between the two gaseous atmospheres separated by the porous wall, leads to the supposition of a pressure of gas in the interior of the well plugged vessel, analogous to the osmotic pressure which is developed in liquid solutions separated by a semi-permeable diaphragm.

This pressure has been verified and is brought into effective use, according to the invention, in order to extract by natural action the combustible gas arising from the activation of the carbon, which gas can be utilized for the actual heating of the furnace or for any other purpose such as motive power, etc. The pressure above atmosphere amounts to some tenths of a millimetre or to some millimetres of water, according to the.

particular case.

In order to extract the activation gases, it is suflicient to provide a suitable conduit connecting the interior of the porous vessel under treatment to a pipe system arran ed externally of the furnace. By this device, it is even possible to regulate the speed of activation by a factor other than the porosity of the earthenware employed in the construction of the vessel; it is in fact only, necessary to create a slight fall or a slight increase of pressure by the aid of this conduit, in order to'increase or to diminish the speed of the gaseous exchanges through the porous wall.

It will be understood that one of the principal advantages of the ap'paratus according to the invention is the automatic .provision of a gaseous atmosphere suited to the activation, however unfavourable may be the composition of the furnace gases, of too great oxidizing power, for example.

If, moreover, the furnace gases should contain a certain proportion of incompletely burnt hydrocarbons, these being very unfavourable to activation, these same hydrocarbons would be partially decomposed or burnt in their very slow passage through the porous cover or casing at high temperature, by

reason of the well known influence of porous surfaces upon the combustion of gases.

Although the use of porous vessels reduces considerably the impoitance of a precise regulation of the combustion in the furnace, it is not without interest to provide a more particularlysuitable gaseous mixture on the very outside of the vessel, and for this purpose to add or to substitute any gas or vapour ada ted to favour the activation.

Accor ingto the invention, in order to attain this object, it is advantageous to employ smoke gases rich in water vapour, whether this vapour be obtained by the combustion in the furnace of a gas rich'in hydrogen, such as water gas, or whether steam be introduced directly, either mixed with the gases or with pre-heated air.

invention, when smoke gases rich in water vapour are used for the activation, the com position of the gases in the interior of the porous vessels is considerably modified and may contain in particular a larger proportion of hydrogen, this proportion being doubled for example.

The steam or water vapour, being a gas of low density, traverses the porous walls more quickly than the other heavier gases such as carbon dioxide, nitrogen, etc.

This water vapour which passes in a large proportion through the porous walls of the vessel acts selectively upon the inactive carbon so as to ield on the one hand a .residue of active car on and on the other hand hy drogen and carbon monoxide. It is clear that by the action of the porous walls there is produced a filtration in which the gases are classified by density, which is a eat advantage since a large proportion o the nitrogen is arrested during the passage of the activating gases through the porous wall, and that the activation gases are thus at least partially purified from incombustible nitrogen; on the other hand, these gases are rich in hydrogen and in carbon monoxide formed in the interior of the vessel, for example by reaction of the steam upon the carbon.

Advantage of the use of porous surfaces may be taken in the same conditions every time that it isdesirable to create around the carbon an atmosphere comprising any known activating gas, together with steam, carbon dioxide, chlorine, oxygen, etci, such atmosphere having a speed of action which can be varied by the actual dilution-of the gas, so

' that this control or variation is obtained by the use of porous walls of a given porosity.

In the industrial application of the apparatus forming the present invention, it is not necessary that the porous vessel containing the carbon shall be completely closed; it is suflicient that no harmful exchange of gases can take place at the surfaces not provided with porous walls, for example that there shall be no admission of air. It is then possible to carry out continuous activation in retorts with large side surfaces of a porous nature,-at the extremities of which the supply or the extraction of the carbon under treatment is carried out in a continuous manner.

The accompanying drawings represent two modes of practical construction according to the invention.

Figures 1 and 2 show a tubular furnace respectively in vertical section and in horizontal section.

Figures 3 to 5 represent a'furnace with vertical chambers in longitudinal section, in

transverse section and in part-sectional plan.

These two furnaces are constructed in accordance with the invention.

The cylindrical and preferably vertical furnace shown. in Figures 1 and 2, comprises a reaction chamber heated by gas, containing porous tubes 1 arranged concentrically and presenting a maximum possible surface for the volume of the furnace in question. 1

Each poroustube is continued by a metallic cooling tube 2, extending down into a discharge hopper 3, provided with a movable grid 4, indicated diagrammatically.

Wood charcoal or other carbonaceous substances to be treated is char ed into the hopper 5 and descends by gravity into the, tube 12-as far as the level of the grid 4.

Each porous tube 1 may with advantage be provided with an inner tube for collect-' ing combustible activation gases, this inner tubebeing arranged axially of the outer one and provided for the whole of its length with any suitable form of perforation.

These inner tubes not shown in the drawbustible coal, suc gases being otherwise wasted or at least returning as a pure loss into the reaction zone or chamber-by diflusion through the lateral walls of the porous tubes 1.

Alternatively, a portion of the activation gases might be drawn oflifrom the hopper 5 in which they collect in spite of the resistance of the very deep layer of carbon con tained in the porous tubes 1.

The operation of the furnace is extremely simple; the material under treatment descends in the tubes 1 in strict proportion to the withdrawals effected by the operation sage through the said porous tubes.

The chamber furnace shown in Figures 3 to 5, is divided into several parts, 6, 7, 8 and v9, etc. and may serve for the simultaneous activation of several qualities of carbon. It comprises essentially a stack of porous -hollow bricks arranged vertically to form walls 31, 32, 33, 34, etc. I

These walls, through which the combustion gases pass, provide between them vertical chambers of very narrow width (a few centimetres, for example) in which the material to be treated descends. The combustion gases serving for the heating and derived from the grate'35, are distributed to thevertical walls by a flue 10 connecting with the horizontal passages 11, 12, etc., at the tops of the walls; the said gases are removed at the base of the walls by other passages 13, 14, etc., which deliver these gases finally to the chimne 16 through a flue 15.

The activatlon gases are drawn off from the mass of carbon by means of extra-porous These flues deliver 'externallyof the furnace! into a collector 23.

The gases thus drawn of." may be conducted to the grate or to anyother point for utilization, being perfectly pure and free from dust. If their natural pressure is insuflicient,

they may be exhausted by a steam injector arranged for example at 24. Moreover there -may be provided an arrangement for tapping off pyrogenous distillation gas from the charging hop rs, if the raw material utilized has not alrea y been distilled, as for example if the activating process is applied, directly to wood, peat, lignite, etc., not already .coked. This arrangement is not indicated in- Figures 3, 4 and 5 of the drawings.

. in the form of an injector exhausting these The carbonaceous material intended for activation is loaded into the hoppers 6', 7', etc. from which it falls naturally by gravity between the porous-brick walls and there undergoes the said activation. The activated carbon is withdrawn in a continuous or a discontinuous manner from other hoppers 25, 26, etc. in which it cools.

In practice, each of these hoppers which forms a downward prolongation of the carbon chambers below the furnace, is provided withtwo grids indicated diagrammatically at 27, 28, having flaps or shutters which when operated separately and at given intervals, form a measuring device for gauging the delive of activated carbon; the activated carbon ischarged from the hoppers is collected a at the outlets 29, 30, etciwhich are hermetically closed in the intervals between tappings in order to avoid any entrance of air.

It is advantageous to inject water vapour into the grate so as to enrich the products of combustion in activating gases and the activation gases in respect of hydrogen and other combustible gases. This injection of water vapour may serve, as has been stated above, to create a fall of pressure assistingthe evacuation of the activation gases if it is arranged gases. Moreover, the combustion gases can be enriched in water vapour by atomization of water from a sprayer at the entrance of the air to a preheater recuperating the waste heat ofthe smoke gases.

It is to be understood that modifications or improvements'may be applied to the above system of activation furnace. For example,

' the furnaces utilized may be either discontinuous or continuous, vertical or horizontal, fixed or movable, with or without counter-current flow, or with transverse current flow, with or without recuperation of the activation gases, etc. These furnaces come within'the scope of the present invention when they utilize. or take advantage of porous or other like vessels behaving in the manner indicated above.

The activation ap aratus described above is applicable to'carlionaceous materials of themost diverse kinds such as wood, wood charcoal, coal, lignite, peat or coke derived from coal, lignite or peat, and waste products of any kind of mineral, vegetable or animal ori 'n, containing a sufficient proportion of car on.

It is applicable to the activation of agglomerated carbon either inactive or presenting already a certain activity, and so on. The products may be ure or mixed with-substances adapted eit er to improve the activation. or ,to provide in the activated product either a physical texture or chemical properties that may be advantageous. The appa-l ratus is applicable likewise to the re-activation of used have become ouled or encrusted; the carbon to be re-activated, purified or crude, can with advantage before being passed into the activating furnace, be coated according to the in vention set out in by pending application Serial No. 74,174, filed December 8th 1925.

The apparatus is also ap licable to the revivification or to the manu acture of decolorizing blacks.

The various activated carbons obtained may in certain cases be utilized without urification, but in other cases it will be a vantageous to free them from foreign matter by suitable washing.

The modes of utilization of the active carbon, crude or washed, are all those well known purposes to which this kind of product is applicable.

What I claim is Apparatus for the production of activated carbon, comprising a plurality of narrow chambers, walls of porous material surrounding said chambers, meansfor feeding carbonaceous material into one end of said chambers, means for dischargin material from the other end of said cham ers, and means for heating said chambers and the enclosed material by an external activating atmosphere having access to said porous walls butexcluded from direct entrance to said chamsignature.

ALBERT GODEL.

anular active carbons which

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