US1500890A - Reclamation of low-melting-point salts from black liquor - Google Patents

Description

' Patented July 8, 1924..

JOSEPH E. PLUMSTEAD, OF WILMINGTON, -DELAWARE, ASSIGNOR TO THE JESSUP 2 MOORE PAPER COL, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF MASSACHUSETTS.

REGLAMATION OF LOW-MELTING-POINT SALTS FROM BLACK LIQUOR.

No Drawing.

To all whom it may concern:

Be it known that I, JosnrH E. PLUM- STEAD, a citizen of the United States, and resident of Wilmington, in the count of New Castle and State of Delaware, ave invented certain newand. useful Improve-- ments in the Reclamation of Low-Melting- Point Salts from Black Liquor, of which the following is a specification.

This invention relates to an improvement in the reclamation of values contained in that waste substance of the paper pulp industry commonly known as black liquor.

The principal object of the invention is the carrying out of a process by which the black liquor is evaporated to dryness in a manner which will prevent fusion of the" low melting point salts contained therein.

This invention contemplates the treatment of black liquor, whether produced by the so-called soda, sulphate or sulphite rocesses, or any other process which pro uces a similar substance which might contain salts of a low melting point, such as those of the soda sulphur type and wherein it is desired to incinerate or otherwise evaporate to dryness and char the material containing these values.

The usual practice in the reclamation of such values is to pass the black liquor slowly into a rotary incinerator of one type or another, which is supplied with heat from a grate fired furnace located at one end. In this way the material being treated is progressively heated as it advances from the cold to the hot end of the incinerator. However, it is the universal experience of those practicing this reclamation process, where the black liquor contains salts of the the cold to the hot end of the incinerator. process is complicated by the fact that these soda sulphur salts have a lower melting point than carbonate of soda which exists in large quantities in this liquor. Tn using a grate fired incinerator, the hottest part of the fire is at the very front of the rotary furnace where the ash is hottest. Consequently there is fusion at the dis charge end. As a result the sodium sulphur salts in melted condition adhere to the brick work of the furnace and form a gummy fluid-like mass which has a tendency to cover up any particles of black ash not yet completely charred. In addition to this Application filed December 15, 1923. Serial No. 681,008.

difliculty, when this mass is placed in the dissolving tanks, the efficiency of the solvent is decreased because of the physical characteristic of this fused mass. It is, therefore, a problem to properly incinerate and char the black liquor containing salts of a low melting point without reaching the points of fusion and volatilization.

I have discovered that in using dried carbon as pulverized fuel, rather than using grate fired coal, I can increase the capacity of the furnace, push the ash through faster, and complete the charring of the black liquor without fusion. The results in a savmg of time, and prevents volatilization of any values in the black ash through fusion, and eliminates the difiiculty in the dissolvmg step.

The pulverized dried carbon may be produced in any desired manner, but I have found it expedient to utilize that material usually produced as a worthless by-product 1n the dissolving step in the treatment of the black ash, such as is described in my Patent No. 1,442,494.

Any desired combustion apparatus may be used which is adapted to burn pulverized or powdered fuel, it being only necessary that the flame produced within the rotary incinerator be such that the incinerator is heated to its highest temperature within the incinerator and at a point between the entry of the liquid black liquor and the point in the incinerator where the charred ash is produced. in this way the incineration of the black liquor is stopped at the black ash and is not carried beyond to the point of fusion.

By practicing this method it will be readily seen that the black liquor before it reaches the point of ash, may be exposed to a heat greater than that which would produce fusion of the black ash. This condition obtains by reason of the fact that when the black liquor is exposed to the maximum heat it is in a fluid or semifiuid state, and by the time the ash has been produced, the hottest part of the furnace has been passed and this ash is exposed to a decreasing degree of heat.

While I have specifically mentioned the utilization of dried carbon as fuel, as this material is most convenient for use among that class of paper pulp plants practicing the soda process, yet it will be evident that any kind of pulverized fuel will be satisfactory. The important point of the process is that the hottest part of the incinerator shall be reached by the material being treated therein before said material reaches the discharge end of the incinerator. This is only possible when pulverized fuel is used, as the flame produced thereby may be inserted into the incinerator to any desired extent. I contemplate the use of pulverized coal, coal dust, pulverized wood waste, and the like, either as substitutes for, or in combination With, the pulverized carbon mentioned above. 4

Having thus described my invention, what I claim is 1. A process of recovering values from black liquor which includes the steps of causing said liquor to pass through heat zones of varying intensity whereby evaporation takes place and black ash is produced, said material reaching the heat zone having the maximum temperature before evaporation is complete.

2. A process of recovering values from black liquor, which includes the steps of passing said liquor through an increasing zone of heat and then through a decreasing zone of heat.

3. A process of recovering values from black liquor containing sodium sulphur salts, which includes the step of passing said material through a heat zone, the temperature of which is above the fusing point of said salts, before said liquor has reached a semi-fluid state, and then through a heat. zone, the temperature of which is below the fusing point of said salts.

4. A process of recovering inorganic values from black liquor which includes the step of passing said material through a heat zone, the temperature of which is above the fusion point of the inorganic values therein, before said liquor has reached asemi-fluid state, and then through a heat zone, the temperature of which is below the fusion point of said values.

5. A process of recovering values from black liquor which includes the steps of passing said liquor through a heat zone at a point inthe heat treatment previous to the formation of black ash, then passing said material through a heat zone, the temperature of which is below the fusion point of the values in the black ash, and continuing the heat treatment until substantially all the black liquor has been converted into black ash.

(i. A process for recovering sodium sulphur salts from black liquor which includes the steps of passing said liquor through a heat zone, the temperature of which is above the melting point of said sodium sulphur salts, at a point in the heat treatment previous to the formation of black ash, and passing said material through a heat zone, the temperature of which is below the melting point of said sodium sulphur salts after the formation of black ash.

7. A process of recovering sodium sulphur salts from black liquor which includes the steps of passing said liquor througl'i a. heat zone, the temperature of which is, above the fusion point of black ash, previous to the formation of black ash, and then passing said material through a heat zone, the temperature of which is below the melting point of black ash, after the formation of black ash.

8. A process of recovering values from black liquor which includes the steps of causing said liquor to pass through heat zones of difi'erent intensity, said material reaching the zone of maximum intensity before black ash is produced.

9. A process of recovering sodium sulphur salts from black liquor which includes the steps of causing said liquor to pass through heat zones of difierent intensity, the zone of maximum intensity having a temperature above the melting point of said sodium sulphur salts, said liquor reaching said maximum heat zone before the production of substantial amounts of black ash.

In testimony whereof, I aflix my signature.

JOSEPH E. PLUMSTEAD.