DK142000B - Process for treating waste liquor from a soda-based sulfite pulp preparation. - Google Patents

Description

(11) PUBLICATION NOTICE 1 ^ 2000 DENMARK (ευ int.ci.3 o 21 c 11/02 '(21) Application No 2312/71 (22) Filed on 13 May, 1971 (23) Running Day 1 3 · May 19 11 (44) The application submitted and the o0 submission document published by the AuS * DIRECTORATE FOR.

PATENT AND TRADE MARKET <»» Pnontet desires * from it

May 14, 1970, 371o4, US

(71) SONOCO PRODUCTS COMPANY, Hartsville, South Carolina 29550, US.

(72) Inventor: Donald Robert Sheeley, Route 5, Harley Circle, Hartsville, SC, US: James Henry Rion, 213 Kenwood Drive, Hartsville, SC, US: William Roy £ ook, 300 Warner Drive, Hartsville, SC, US: William Ar = chibald Biggs Jr., Woodland Drive, Hartsville, SC, US.

(74) Clerk of the case;

Scandinavian Patent Bureau v / Prode Larsen._ (54) Procedure for the treatment of waste liquids from a soda-based sulfite = pulp production.

The invention relates to a process for treating waste liquor from a soda-based sulfite pulp preparation, in which the waste liquor is concentrated, mixed with aluminum hydroxide or its hydrate and incinerated to sodium aluminate, treatment of the ash formed with sulfur and aluminum hydroxide formed during combustion. , which is used again.

Known processes for treating waste liquids usually require expensive furnace plants to convert the sodium and sulfur content into a melt. A known method 2 142000 of the disclosed kind in which the solids of the waste liquor are melted to form a sticky mass or melt is disclosed in United States Patent No. 3 * 061,408. In this known process, the waste liquor is added to a reactant containing silica and alumina to the extent that a melt is formed. Evaporation and combustion of the waste liquor can take place in calcination or melting furnaces.

It is an object of the invention to provide a method of the kind indicated, which method can be carried out satisfactorily using cheaper furnace systems. The process of the invention is characterized in that a sufficient amount of recycled sodium aluminate furnace ash from the combustion process is added to the concentrated broth containing aluminum hydroxide or its hydrate, to form solid pellets which are burned at a temperature below the melting point of the sodium aluminate. part of the sodium aluminate being recycled to form new pills.

In this way, the whole waste mass 20 is obtained in a simple manner in the form of non-sticky, separated pills. Further, the pellet form is maintained throughout the combustion reaction process until a final sodium alumina bag, thereby simplifying effective ash recovery. The process can be satisfactorily carried out in such a simple apparatus / or rotary kiln 25 as a multistage hearth. In fact, almost any type of furnace intended for burning solid fuels and for collecting ash can be used in the process, such as charcoal or wood-fired ovens, fluid-bed grills, and destruction ovens.

Furthermore, the portion of the furnace ash which is recycled in the process consists of a large portion of sodium aluminate which acts as an effective absorbent carrier when mixed with waste liquor. This carrier material forms dense, non-clogging particles which are easy to process in said cheap furnace type.

According to the invention, the combustion operation can be carried out at a temperature of at least approx. 538 ° C and preferably between 816 ° C and 1095 ° C. The oven temperature is kept sufficiently low throughout the operation so that the reaction mass does not become plastic or sticky at any time.

According to the invention, such an amount of alumina may be added so that the molar ratio of Na 2 O to Al 2 O 3 is between 1: 1 and 2: 1. This ratio can be raised to 3: 1 in some cases. It is important that the alumina present reacts with sodium in such an amount as to avoid the formation of sodium sulfide and of a sticky mass or melt.

An illustrative example of the method according to the invention as well as the further treatment of the byproducts arising from the various steps of the process will be explained in more detail below with reference to the drawing, which shows a diagram of a plant for carrying out the method according to the invention.

The process is performed in the system shown as follows:

Dilute soda-based sulfite waste liquor is concentrated in multi-stage evaporators 1. The concentrated liquid is passed through a conduit 2 to a continuous mixer 3, where it is mixed thoroughly with recycled hydrated alumina from a conduit 4 as well as with recycled powdered sodium aluminate furnace from a conduit 5. appear as separate pellets passed through a conduit 6 to a furnace 7, such as a rotor furnace, 25 in which the tableted mixture is combusted to convert the sulfur content and organic content into gaseous products such as SO 2, CO 2 and steam and to react the sodium content with alumina to form sodium aluminate.

The sodium aluminate product in the form of a particulate unmelted ash comes from the furnace through a conduit 8, dividing it into two parts, passing an appropriate amount of the ash through a conduit 9 and a crusher 10 back to the mixer 3. The remaining portion of the ash is fed through a conduit 11 to a solvent container 12. Water is supplied through a conduit 13 to dissolve the sodium alumina bag. The resulting solution with very small amounts of insoluble 142000 4 impurities is passed through a conduit 14 to a clarifier 15 where the insoluble precipitate is removed.

The clarified sodium aluminate solution is passed through a conduit 16 to a reactor 17. In the reactor, the sodium 5 aluminate solution is acidified with NaHSO 2 from a conduit 18 to form Na 2 O 2 and precipitate aluminum hydroxide or hydrate. The reaction slurry is passed through a conduit 19 to a continuous filter 20 where the hydrated alumina is removed, leached and recycled 10 through a conduit 4. A portion of the Na2 SO4 filtrate is passed through a conduit 21 to an absorption vessel 22. The residual amount of Na 2 O 2 solution is returned to the pulp plant for recycling through a conduit 23.

The flue gases from furnace 7 containing SO2, CO2, inert gas and vapor are passed through a conduit 24 to a cyclone separator 25 to remove entrained furnace ash particles and recycle to the solvent container or mixer. The purified gas stream passes after the cyclone through a conduit 26 into a waste heat boiler 27, in which the heat is exchanged for the production of steam to the evaporators. The residual gases containing SO 2> are passed through a conduit 28 into the absorption tower 22. In the absorption tower, SO 2 reacts with the Na 2 SO 2 solution of conduit 21 to form NaHSO 2 for use in the acid reaction in the reactor 17.