US2928718A - Method of burning sulphur containing fuels such as shale - Google Patents

Description

United States Patent METHOD OF BURNING SULPHUR CONTAINING FUELS SUCH AS SHALE Bjorn Erik Anders Berglund, Hagersten, Hans Olof Hormander, Alvsjo, and John Erik Kjell Svenke, Bromma, Sweden, assignors to Aktiebolaget Atomenergi, Stockholm, Sweden, a Swedish company No Drawing. Application June 17, 1957 Serial No. 666,225

Claims priority, application Sweden June 21, 1956 16 Claims. (Cl. 23-4) The majority of shales contain carbon in a greater or less degree and possibly also organic substances rich in carbon. As a rule such shales are combustible and they are often concentrated to large deposits where the total heat capacity may be very considerable from an industrial point of view. This is for instance the case in Sweden. In all, the Swedish deposits have probably a heat content corresponding to no less than 10,000 million tons of black coal, by way of an estimation.

A plurality of various expedients of utilizing these heat contents have been resorted to. Thus alum shale has been used for a long time as a fuel in kilns for burning limestone into lime. By pyrolysis, the content of organic matters in certain shales is transformed, into hydrocarbons which are gasified and may be condensed and recovered as oil products, the heat content of which then being rendered useful in various ways. This is done, for instance, in the so called shale oil industry which also has succeeded to a certain extent in burning the carbon in the residues, the so-called coke, which are left after. the oil has been distilled off so as in this manner to utilize a part of the heat content of the coke.

A simple method of burning completely any combustible contents in shale, shale coke or other shale products would no doubt have very good prospects of being economically applied on an industrial scale for generating hot flue gases for heating purpose, steam or electric power. The use of shale as fuel is hitherto rather moderate due to the fact that procedures employed up to now sulfer from technical imperfections and bring in their train severe inconveniences by sulphur dioxide in the combustion gases causing injury and discomfort, the sulphur dioxide being formed in the.combustion of the shale material whichis rather rich in sulphur.

There is a narrow temperature range within which one has to operate because the spontaneous ignition temperature of the shale is comparatively high, generally well over 600 C., and its sintering temperature is low,

about 1000 C. In a molten state the ash is very viscous within a wide temperature interval. For this reason it has not been possible to use combustion methods conventional for fossil fuels or wood. Thus only by controlling the temperature of the combustion zone by means of indirect cooling has one succeeded in carrying through the combustion in some furnace constructions which are in use in the Swedish shale oil industry. In these constructions a relatively coarse material is burnt and the degree of burning out, that is, the utilization of the heat content of the material, is incomplete as is the case in the methodstated of burning limestone using shale as a fuel.

A more common utilizing of shale material as a fuel is prohibited, however, by the fact that in methods hitherto current the sulphur content, which generally occurs in shale products and is rather considerable, is transformed "ice ' the atmosphere, will cause discomfort and injury. Generally the content of sulphur dioxide in the flue gases,

however, is too low to be economically recovered and utilized.

In a procedure according to the present invention a readily controlled, very complete and fast, combustion of the shale material is attained with a moderate excess of air and with no risks of sintering, at the same time as the main portion of the sulphur is bound in the solid combustion residue. The procedure according to the invention is managed in such a manner that the'shale material, which is finely divided, preferably to a maximum particle size less than 5 mm., and mixed with a quantity.

of finely divided alkaline earth metal carbonate, preferably limestone or dolomite, is burnt in a so called fluidized bed with gas mixtures containing air or oxygen,

the time of stay atcombustion temperature, the quantity" and particle size of the limestone or dolomite and the temperature being chosen in such a manner that the content of sulphur dioxide in the flue gases becomes satisfactorily low at the same time as the shale material is comparatively completely burnt out. The necessary conditions for this will become evident from the discussion an'd'experimental results below. v

A most important factor is the burning temperature which will be seen from the following trial results obtained in an experimental furnace for burning fluidized solids, the furnace having a capacity of about .300 kgs. shale per day. Leach residue material from leach ing of shale with solutions of sulphuric acid for recovering the uranium content of the shale and having a maxi mum particle size of 4 mm. was mixed with 23 percent by weight, calculated on the leach residue material, of so called anthraconite, a bituminous limestone (that is, about theoretical quantity, as the lime content of the limestone isabout 36% CaO and the sulphur content of the shale material about 6%), the limestone being crushed to a particle size less than 2 mm., whereupon the mixture was burnt in said furnace with an oxygen content in the flue gas of about 6%. The rate of feed was chosen so that the average time of stay became about The sulphur contents of the solid residues were their 3-5%. In burning of this shale material under the same conditions but'with no admixture of limestone, the sulphur dioxide content in the' flue gas was 1.0-l.l%.

The sulphur balance renders the, following account of the distribution in the test at 820 C.

Percent of the total amount of sulp hur- in coarse in flue material in dust gas from the furnace Generally a temperature exceeding 850' C., with other conditions varied in different ways, has turned out to give too unsatisfactory results as regards the fixing of sulphur. It should be noted that the temperature thus Patented Mar. 15, 1960 with 1.0% S0 Results in accordance with the table below were obtained.

As shown, addition of compounds containing chlorine in combination with limestone or dolomite has a remarkable efiect on the sulphur content in the flue gases.

25 parts of this industrial limestone is equivalent to 7 parts of sulphur. The shale contains 6 or 7% sulphur and therefore a virtually equivalent quantity of lime was used in the example above. There are considerable amounts of limestone interfused in a plurality of shale-deposits, for which reason the costs for the admixture will be small when treating the shale from these deposits. 2% NaCl corresponds to 0.8 part of Na. In combining into Na SO 0.8 part of sodium correspond to 0.55 part of sulphur. Thus it is evident that the pronounced elfect caused by admixing only 2 parts of common salt is not exclusively due to the fact that a chemical combination between sulphur and sodium is formed. Instead the admixture seems to have catalyzed the formation of calcium. sulphate.

In the example related above of conducting a procedure according to the present invention the efficiency will depend on the conditions prevailing during the trial, i.a. as regards the time of contact between the gas and the material. Thus at a longer time of contact the same effect will be attained with a less addition of halogen compounds than in the example.

The present invention may to advantage be applied to the binning of limestone in the presence of siliceous material for producing a starting material for hydraulic binders. The sulphur content of the siliceous material will partly be retained in the solid material as calcium sulphate. Generally flue gases are obtained, however, being so rich in sulphur dioxide that they very often can not be directly discharged without considerable inconveniences.

When applying the present invention to this burning of limestone a simple and inexpensive way is ofiered of transferring a great part of the sulphur to the solid residue by adding a chloride during the burning, for instance CaC1 whereby the content of sulphur dioxide in the flue gas can be brought down to the desired level.

As a matter of course, the cost for the necessary admixture of limestone will depend on the supply of limestone in the neighbourhood of the place where the shale material is utilized by a method according to the present invention. At the Swedish shale deposits, circumstances in this respect are generally extremely favourable as limestone there overlies the shale or is interfused in the same in the form of so called anthraconite. In mining the shale the necessary limestone can thence be obtained simultaneously at a very low cost.

In combustion procedures using a method according to 7 resulting ash occurs.

6 the present invention the distilled water, for instance, can be used directly for heating by means of hot flue gases, for generating of steam or electric power.

What is claimed is:

1. A method of burning the combustible constituents of sulphur-containing solid carbonaceous shale materials, comprising intimately 'mixing the carbonaceous shale material with an alkaline earth metal carbonate in a quantity large enough for binding as sulphate the main part of the sulphur contained in said shale material, heating the resulting mixture in the presence of a catalyst for the oxidation of S0 to S0 to initiate combustion of said shale material in a combustion zone in the presence of a gas containing free oxygen, and maintaining the combustion temperature at a temperature, below 900 C., at which no substantial fusion of the 2. A method as claimed in claim 1, in which the combustion temperature is maintained below 850 C.

3. A method as claimed in claim l, in which the combustion temperature is maintained at from 700 to amount of halogen substance is not more than 0.2 equivalent halogen per equivalent sulphur.

6. A method as claimed in claim 4, "in which the halogen substance is selected from the group consisting of chlorine, calcium chloride, and sodium chloride.

7. A method as claimed in claim 1, comprising adding combustion air in such an excess that the oxygen content in the flue gas is 3-l0%.

8. A method as claimed in claim 1, comprising add ing combustion air in such an excess that the oxygen content of the flue gas is 58%.

9. A method as claimed in claim 1, comprising carrying out the combustion in a fluidized bed.

10. A method as claimed in claim 9, in which the grain size of the solid materials is below 6 millimeters.

11. A method as claimed in claim 10, in which the grain size of the solid materials is below 4millimeters.

12. A method as claimed in claim 9, comprising retaining the solid materials in the fluidized bed for an average time of stay of at least 20 minutes.

13. A method 'as claimed in claim 1 for burning alum shale containing about 57% sulphur, comprising burning the shale together with 20-30% of limestone.

14. A method as claimed in claim 1 comprising using leach residues from the leaching of shale with sulphuric acid solutions as a shale supply. 7 V e 15. A method as claimed in claim 1, comprising utilizing the heat evolved for generating steam.

16. A method as claimed in claim 1, in which the sulphur-containing solid materials are associated, in the combustion zone, with ison oxide acting as catalyst on the reaction SO /zO SO References Cited in the file of this patent UNITED STATES PATENTS 1,899,808 2,602,019 ODell July 1, 1952 2,830,883

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION- Patent N0e 2,928,718

Bjorn Erik Anders Berglund et March 15, 1960 It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

" read materials Column 6 line 57, for "materials are a same column 6, line is line 58 for -"ison" read iron -3 59 for "'s0 o so read so ez o e-eso Signed and sealed this 16th day of August 1960.

(SEAL) Attest:

KARL H. AXLINE Attesting Officer ROBERT c. WATSON Commissioner of Patents

Claims (1)

1. A METHOD OF BURNING THE COMBUSTIBLE CONSTITUENTS OF SULPHUR-CONTAINING SOLID CARBONACEOUS SHALE MATERIALS, COMPRISING INTIMATELY MIXING THE CARBONACEOUS SHALE MATERIAL WITH AN ALKALINE EARTH METAL CARBONATE IN A QUANTITY LARGE ENOUGH FOR BINDING AS SULPHATE THE MAIN PART OF THE SULPHUR CONTAINED IN SAID SHALE MATERIAL, HEATING THE RESULTING MIXTURE IN THE PRESENCE OF A CATALYST FOR THE OXIDATION SO2 TO SO3, TO INITIATE COMBUSTION OF SAID SHALE MATERIAL IN A COMBUSTION ZONE IN THE PRESENCE OF A GAS CONTAINING FREE OXGEN, AND MAINTAINING THE COMBUSTION TEMPERATURE AT A TEMPERATURE, BELOW 900* C., AT WHICH NO SUBSTANTIAL FUSION OF THE RESULTING ASH OCCURS.