US2296668A - Pulverulent fuel - Google Patents

Description

Patented Sept. 22, 1942 UNITED STATES PATENT GE FE'QE PULVERULENT FUEL William Hennicke, Mannheim, Germany; vested in the Alien Property Custodian No Drawing. Application August 31, 1938, Serial The present invention relates to a process of improving pulverulent fuels.

Pressure extracts of mineral or brown coals, which are to be used as pulverulent fuels and motor fuels, frequently have the objectionable property of softening even by slight heating and this results in deposits and stoppages in the supply pipes and nozzles and in the cylinders of motors and engines.

I have now found that the softening point of the said pressure extracts is raised by treating them with oxygen or gases containing the same at elevated temperatures but below their ignition point. The temperatures to be used depend on the nature of the substances to be treated or reacted and the nature of the treatment and may be between 100 and 600 C., for example in the case of the action of hot combustion gases which still contain oxygen on a pressure extract of mineral coal a temperature between 300 and 500 C. is suitable. The procedure may be that a suitable fuel, as for example illuminating gas, is burned, the necessary temperature established by the addition'of further air and the mixture of combustion gases and air brought into contact with the material to be treated. As a reaction vessel it is suitable to use rotary tubes, tubes provided with conveyor means, tower-like wide vessels in which the material is whirled up by the gas containing oxygen, or apparatus of a similar kind. By the said treatment, the oxygen content of the fuel is appreciably increased and its softening point reduced to such an extent that fuel dust treated in the said manner remains entirely pulverulent until its combustion and does not give rise to trouble by reason of stoppages or soiling of the conveyor or distributing means. The nitrogen content is not increased and the ignition point is not lowered or only lowered to a negligible extent. A more marked. lowering of the ignition point may only occur in some cases when prolonged for a very long time.

When the height of the ignition point is of no importance in the subsequent use of the fuel, as for example in the case of a dust firing, the said treatment is sufiicient. On the other hand, for example when the fuel is to be used in a dust motor, if the fuel still ignites at too high a temperature, there may be carried out, in addition to the treatment with oxygen, also a treatment with nitric acid or nitrous gases, as for example according to the copending application Ser. No. 163,386 now U. S. Patent 2,208,514 dated the oxygen action is:

July 16, 1940. This treatment may be carriedout before or simultaneously with the oxygen treatment but preferably after the same. The heat imparted to the powder by the treatment with oxygen may be utilized if desired for the aftertreatment with nitric acid. In some cases it may also be preferable to cause the oxygen to act in only so. mild. a. manner that the softening point is not brought completely to the desired value, as for example only to 350 C., the softening point and ignition point only being changed in the desired manner by a subsequent nitric acid treatment. In any case considerably less nitric acid is required than in the case of a fuel not previously treated with oxygen.

Another modification of the treatment with a view to increasing the softening point and reducing the ignition point consists in treating part of the pulverulent pressure extract with oxygen or gases containing the same at elevated temperature, and another part with nitric acid or oxides of nitrogen and mixing the resulting products with each other. The height of the ignition point is dependent on the mixing proportions. For example an addition of from 25 to 30 parts of a fuel of low ignition point which has been treated with nitric acid or oxides of nitrogen to parts of a fuel of high ignition point which has been treated with oxygen is sufiicient to obtain a mixture having a useful ignition point. Similarly a part of the residues remaining in the distillation of brown coal pressure extracts with steam or in the treatment with selective solvents may be treated with nitric acid and another part with gases containing oxygen and the resulting products mixed with each other in suitable proportions. It is also possible to prepare mixtures of mineral coal extracts treated with oxygen and distillation residues of brown coal pressure extracts treated with nitric acid. The ignition point of the part of the fuel which has only been treated with oxygen is reduced to a specially marked degree by incorporating therewith fuel treated with nitric acid directly after treatment and while still in the moist state, the mixture then being dried. Apparatus known for the purpose may be used for the mixing, as for example spirals, drums, ball mills and the like.

The ignition point of the pulverulent fuels or motor fuels of high melting point thus obtained can be reduced still further and further improvements can be obtained by adding thereto small amounts of liquid fuels.

Among suitable liquid fuels there may be mentioned for example motor fuels, such as gas oils,

of liquid additional substance, but in most cases 7 from 3 to 10 per cent are sufiicient to reduce the ignition point considerably but to retain a state in which the powder can still be conveyed without difliculty, does not stick and form lumps and melts only at such a high temperature that no trouble can occur.

The mixing may be carried out in all apparatus known for the purpose, such as mixing worms, ball mills, drums and the like; the solid substances and liquid substances may be mixed directly with each other, or the solid substances may be sprayed with the liquid substances with the aid of nozzles, or the liquid substances may be vaporized and allowed to condense on the solid substances.

The process is used in particular for extracts of mineral and brown coals obtained under pressure with the use of solvents, more particularly solvents giving oiT hydrogen, if desired with the simultaneous pressure of hydrogen with or without the use of catalysts; furthermore for substances obtained from the pressure extracts for example by distillation, extraction, splitting up by mechanical means or in other ways and having a higher melting point than the original extracts.

The following examples will further illustrate how the present invention may be carried out in practice, but the invention is not restricted to these examples. The parts are by weight.

Example 1 Into one end of a tube provided with a conveyor worm there are introduced per hour 100 parts of a finely powdered pressure extract obtained from mineral coal. At the opposite end such an amount of illuminating gas is burned that the combustion gases, after the addition of 40 parts of air, have a temperature of 450 C. This gas mixture is led over the powdered pressure extract. The temperatures of the effluent gas and the withdrawn mass depend to a large extent on the construction of apparatus used. They may amount to 120 and 240 centigrade. The treated fuel has the following characteristics as compared with the untreated material:

For further lowering of the ignition point, a treatment with nitric acid may be carried out, 4.2 parts of nitric acid (calculated as 100 per cent) being used for 100 parts of oxidized extract. The lower ignition point of the final product then lies at 280 C. An extract not having undergone any pretreatment yields under the same conditions a product which ignites at 260 C, but which softens even at from 380 to 385 C.

Example 2 A part A of a pressure extract obtained from mineral coal is treated according to Example 1 at 500 C. for 20 minutes with combustion gases of illuminating gas containing oxygen. The temperature of the waste gases amounts to 220 C. and that of the withdrawn mass to 200 C. An-

other part B is treated according to application Ser. No. 163,386 with nitric acid (0.40 liter of HNO3 per kilogram of extract with 850 grams of HNO3 per liter of acid) and dried to a water content of 1.2 per cent. Mixtures of the resulting products A1 and B1 are prepared. The ignition points of these mixtures may be seen from the following table:

Mixing proportions Ignition point A] B] Example 3 Mixing proportions Ignition point 7 A] O} Example 4 A finely powdered extract obtained by pressure extraction of mineral coal is treated in a rotary tubular furnace in counter-current with combustion gases of illuminating gas containing an excess of air according to Example 1. The temperature of the introduced gas is 500, that of the outgoing gas is 220 and that of the mass withdrawn is 200 C. The mass is in contact with the gases for 20 minutes. The material withdrawn has a softening point above 500 and an ignition point of 438 C. The resulting product (A) is mixed in various proportions with different liquid motor fuels in a ball mill, the relative proportions and the ignition points of the mixtures being given in the following table:

Parts Ignition Numby Parts by weight of additional point her weight substance of of A mixture 95 90 5 of 316 92 4 of gas oil and 4 of benzene .1 280 94 3 of gas oil and 3 of acetaldehyde 234 95 4 of gas oil and l of paraldehyde.. 268

free oxygen at a temperature below their ignition point and part with a substance selected from the group consisting of nitric acid and nitric gases so that the initial material retains its loose pulverulent condition and nitrogen and oxygen are incorporated into the coal extracts, and mixing the products thus obtained with each other.

WILLIAM HENNICKE.