US1594994A - Treatment of certain fuels to improve their calorific value - Google Patents

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Aug. 3 1926` W. A. BONE TREATMENT 0F CERTAIN FUELS TO IMPROVE THEIR CALORIF'IC VALUE Filed July 5, 1919 yid/7b .L fw// Il... .T lumi? d Patented Aug. 3, 1926.

UNITED STATES I 1,594,994 PATENT OFFICE.

'WILLIAM .ARTHUR BONE, 0F LONDON, ENGLAND..

TREATMENT OF CERTAIN FUELS T IMPROVE CALORIFIC VALUE.

Application illed July 5, 1919, Serial No. 308,812, and in Great Britain July 30, 1918.

I have discovered that when brown coals and lignites, which have been completely freed from mechanically held water b drying them at temperatures below 110. are heated to higher temperatures which are below that at which destructive distillation Y begins, they undergo a chemical change that begins to be important accompanied by any evolution of hydrogen,

, `H y 'A The technically important result of this chemical change is that it is accompanied a valuable increase in the caloric value i of the fuel.

My invention is based on the foregoing vdiscov'eryand consists in heating brown coal or lignite at temperatures between 250- 400 C. until evolution of gases andwat'er' for the purpose of enhancf cable when the process is conducted as a vapours ceases in the calorilic value of the material.

ince the tem rature in questionfdoes not exceed 400 (f. and inthe case of some ligntes is not above 37 5 0., the o or operations necessary for raising t e grade of such fuels according to this invention is or areof comparatively low cost.` The material may be treated in externally heated retorts or chambers by any known continuous or intermittent procedure; but inasmuch as the vapours and gases expelled or produced by the heating are of comparatively little value, it is economical to use internal heating, that is to say, to'pass hot vapours or gases through the retort or chamber containing the material, particularly asthe temperature required is gene-rally below that of flue gases or like waste gases from boiler 00H H0090- i eration plexes of which the coal substance is now I0 generally admitted to consist. The charactor of such condensation may be symbolized as follows:

4 +m+cotm al furnaces, gas retort settings or the like.

Such gases areapplicable, provided that they are chemically inert, or substantially so, towards the material at the said temperature, or that their content of reactive oxygen Vis low enough to avoid exothermic oxidation suiciently vigorous to raise the temperature of the material above the desired limit. For this reason air alone is seldom. applisingle operation. Sometimes, however, it is profitable first to expose the material to eated air at a temperature below that at which exothermic oxidation becomes vigordus, and then to substitute heated gas or vapour sufficiently free from constltuents :which can react with the material at the higher temperature to whichit is heated.

` In any case the operation of heating) the material by hot gases or vapours may e on the counter-current principle, and whatever the mode of heating 1t may be conducted in more than one stage.

The invention maybe illustrated by reference to the effect of the rocess on the Morwell brown coal from pVictoria, Australia. Thismaterial contains 48 per cent of water and 52 per cent of coal substance (including ash 4 per cent). Its calor'lic value is only 5853 B. t. u. per lb. When heated at 105 C. it loses the` aforesaid water and then has a calori-c value. 10,060 B.t.u. per lb. l

On continuing to heat the drled materlal so as to raise its temperature gradually above 105 C. certain chemical changes occur in the coal substance at temperatures between 250 C. and 375 C. whereby more water is expelled together with a small uantity of non-infiammable gas composed c iefly of carbon dioXide. Oil first appears as a product of the heating when the temperature is about 380 C. 4

Hence the preferable mode of applying the present process to this brown coal consists in heating the coal at a temperature about 375 C. until elimination of water and gases at that temperature has substantially ceased In this manner 100 parts by weight of the coal dried at 105 C. yield 88 parts of a coal the calorifc value of which is 11,460 B. t. u. per lb. i

From the foregoing data it may be calculated that 100 arts by weight of the raw coal, 52 parts of) the dried coal and 45.73 parts of the treated coal have the same heating value. It follows that the potential energy of the raw coal can be concentrated by this process before transport.

As already stated the heating operation may be conducted in any suitable manner but preferably by passing hot products of| combustion through a column or layer of the fuel, whether vertical, horizontal or inclined. I have found that Iboilerflue gases having a temperature of 400 C. and containing 1012.5 per cent; of CO2, when passed over the raw coal in question, contain suflicient heat to dry the fuel and to raise its temperature to 375 C. without any danger of exothermic oxidation sufii-` ciently vigorous to raise the temperature of the material higher than this; that is to say without danger of ignition of the coal. This is also true if the gases be passed over the coal which has been dried (at 105) as a separate operation, but not, in any case, if the content of CO2 in the gases falls much below 10 per cent. Since, in a properly fired boiler (which may consume the coal in question after it has been treated by the process) it is easy to obtain iiue gases containing 10 per cent of CO2 and to let down the temperature of these gases (if necessary) by means of an economizer, or otherwise, to 400 C., the process becomes a valuable adjunct to a power station consuming the coal. A

Apparatus for heating such fuels in this manner will readily be designed by the chemical engineer. ,4

A suitable apparatus for this purpose is shown in the accompanying drawing which represents' a vertical section through thefurnace chamber a 'of a water-tube boiler having a well known mechanical Stoker b. As usual, the furnace gases pass from the chamber a .to the chimney through a port chute is continued outside the uptakeby an'` 'l I,

upper extension c and a lower extension 7.A

That part of the'chute which is within the uptake is constructed of bars d which preferabl extend transversely of the uptake so t at the gases can pass freely between said bars. Y

The brown coal passes from the chute d into the hopper g of the mechanical Stoker, at substantially thesame rate at which the Stoker feeds the fuel to the furnace. Thug'I p the chute d constitutes a partition inV the. uptake through which the furnace gases, or a portion thereof, which enter take through the 1port It must pass twice ontheir way to t e compelling this course.: p For the better regulation of the temperature to which the brown coal is heated, there is a second damper-controlled port k for passage of furnace gases intovthe uptake, above the baille z', so that any desired proportion of the gases, determined byA controlling the dampers in the ports h and k, may pass to the chimney without passing4 through the chute. Y f f v What has been said with reference to the Morwell brown coal applies to other fuels of the upi the kind here in question, it bein under?` l stood that the composition, calorihc values Y and temperature of heating vary with each particular fuel. For instance, certain Italian lignites (containing 21.5 per cent.

of water) when dried at.y 105 C. and heated,

Having thus described the nature of the said invention and the best means I know of carrying the same into practical effect, I claim i 1. A process whereby the caloriiic'value of brown coals or lignites may be increased,l ywhich consists in relatively moving in contact with each other the coal or lignites and flue gases having a temperature between 250 CA., and 400 C., until evolution ofi t. gases and water vapour from the material 130 ceases.

Q. A process whereby the caloric value of brown coals or 1i nites may be increased which consists in reatively moving in oontact with each other the coal or vlig'nites and flue gases containing not less than 10 per cent. of carbon dioxide and having a temperature between 250 C. and 400' C. until evolution of gases and water vapour from the material ceases.

3. A process whereby the calorific value of brown coalsor lignites may be increased, which consists in relatively moving in contact with each other the lignite or coal and the flue gaseswformed by combustion of said lignite or coal, the carbon dioxide content of which uegases is not below 10 percent, and at a temperature not exceeding 400 C.

Vvalue of browncoals or lignites by causing the evolution of water vapor and carbon dioxide substantially free from hydrocarbons and uncombined hydrogen, which consists in heating the material at such a rabe and at a temperature not substantially in excess of 400 C. that such evolution takes place, and continuing the heating of the material at a temperature not substantially above 400 C. until such evolution ceases.

In testimony whereof I have signed my name to this specication.

y WILLIAM ARTHUR BONE.

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