FI85994B - SAETT ATT AOTERVINNA KEMIKALIER UR MASSAAVLUTAR. - Google Patents

Description

1 85994

Method for recovering chemicals from pulp broth

The invention relates to a process for recovering chemicals from pulp effluents, simultaneously utilizing the energy released in the process, wherein the pulp effluents are fed to a reaction zone in the reactor while simultaneously supplying external, combustion-independent thermal energy. another gas and / or carbonaceous material.

The pulp industry seeks to reuse energy and chemicals as far as possible, for both economic and environmental reasons.

15 In principle, these recovery processes comprise four sub-processes, i.e. a sulfur reduction process, a process for the separation of inorganic products, an oxidation process of organic products which releases energy, and the treatment of alkali into a usable form. These processes 20 may be performed as separate sub-processes or may be performed in multiple steps. In a modern alkali recovery digester, the Tomlinson digester, the first three processes are performed in one step, while the base process is performed during the subsequent causticization step.

In general, a recovery boiler is the factor that limits the possibility of expanding and / or increasing the capacity of a pulp mill. The capacity of the soda boiler is limited by the volume of gas flowing through the primary air space 30 of the digester without entraining too much solids or floating particles. Another limiting factor may be a steam-side heat load.

. ·. : The soda boiler can also be limited by chemical or • · * ··. the difficulty of simultaneously optimizing intake and combustion.

35 This means that a certain amount of both alkali and sulfur is released into the gas phase. One solution to this problem- * ♦ ·> ·. · 2 85994 countries are disclosed in SE Patent No. 8,302,245-0, in which the entire recovery process is divided into three stages. The process begins with a high temperature step in which sulfur is reduced and removed in molten form, at the same time gassing both the alkali and the organic material. In the next step, the alkali is condensed and at the same time converted to the desired form, and finally, in the third step, the gas from the organic part is burned to generate energy. The purpose of the above method is therefore to eliminate subsequent alkali treatment.

Another method for recovering chemicals from waste liquors is disclosed in SE Patent No. 7,204,304-5. Here, the melt and the gas are separated in the pre-reactor and the process is completely dependent on the partial combustion of the energy generated to achieve a sufficiently high temperature. In practice, this poses considerable difficulties. If partial combustion is insufficient, the temperature is too low to guarantee a flame, whereas if combustion is excessive, both sulfur and 20 alkali are removed with the gas.

The above-mentioned problems and difficulties can be solved by the present invention.

The invention relates to a process for recovering chemicals from pulp effluents simultaneously utilizing the energy released in the process, wherein the pulp effluents are fed to a reaction zone in the reactor while simultaneously supplying external, combustion-independent thermal energy. and / or carbonaceous material. The process is characterized in that the temperature in the reactor is maintained at 900-1100 ° C and the oxygen potential is adjusted by a controlled supply of oxygen-containing gas and / or carbonaceous material, whereby sulfur in the pulp broth is reduced and substantially all alkali and sulfur are bound to the molten phase, which is separated from the gas phase.

3 85994

According to the present invention, the recovery process is divided into three different steps. During the first stage, the sulfur is reduced and removed with the inorganic part of the waste liquor in the molten phase while the organic part is gasified. This step is optimized to achieve the most complete separation of sulfur and alkali possible. During the second stage, the gas is burned to generate energy. This can be accomplished in a number of different ways and for a variety of purposes, but being completely separate from the recovery step 10, it can be easily optimized separately. The third step is the conventional conversion of the alkali to the desired form.

The gas to be fed is suitably air and forms a carrier for the external heat energy to be fed to the reactor.

Alternatively, the external energy is added as a high-energy gas heated in a plasma generator.

Suitably 96-100% of all alkali and sulfur 20 binds to the molten phase.

The process according to the invention, as well as the process described in SE Patent No. 8,302,245-9, uses a combustion-independent energy source, which thus makes it possible to eliminate the problems previously encountered in the process described in SE Patent No. 7,204,304-5.

In particular applications where a plasma generator is used, it has surprisingly been found that the reaction rate of strong gasification is particularly high, so that the reactor can be specially designed to give maximum separation of the molten phase from the gas phase.

The precise temperature control possibility according to the invention allows the composition of the cooking chemicals to be optimized in relation to the cooking process without the melting point and fluidity of the molten phase causing problems in the recovery step.

4 85994

Example

In the experimental equipment, 9 kg of heavy strong nitrogen was fed to a cylindrical reactor before a plasma generator located tangentially on the cylinder. 270 m3 N of air per hour was fed through the Plas-5 magenerator. In addition, 120 m3 N was introduced into the process via a second tangential inlet.

The composition of the strong liquor was as follows:

Na 20.5% of dry matter 10 S 4.5% H2 3.7% 02 37.0% C 34.0%

Cl 0.3% 15 65% dry matter and calorimetric calorific value 13.89 MJ / kg DS.

The reactor temperature was maintained at 1000 ° C. An additional energy of 1260 kW was required to maintain this temperature, in part to compensate for losses in the reaction vessel. By keeping the swirl number greater than 0.6 and the Reynolds number greater than 18,000, as well as selecting the appropriate reactor dimensions, almost 100% melt phase separation is achieved.

The melt was run continuously throughout the process, .25 and the amount was 147.5 kg / h. The result of the analysis is as follows:

NaOH 2.1%

Na2CO3 64.7%

NaCl 0.7%

Na2S 31.5% '30 Dry matter composition of the resulting gas: CO 16.8% Na 0.03% CO2 13.0% NaOH 0.04%: H2 23.5% NaCl 0.02% N2 46.6% 35 If the amount of air is increased to reduce the increase in energy, Na2S is largely oxidized - which must be avoided at all costs.

Claims (4)

5 85994 A method for recovering chemicals from pulp effluents simultaneously utilizing the energy released in process 5, wherein the pulp effluents are introduced into a reaction zone in a reactor while simultaneously supplying external, combustion-independent thermal energy, the temperature and oxygen potential in the zone being controlled by oxygen-containing gas and / or carbonaceous material, characterized in that the temperature in the reactor is maintained at 900-1100 ° C and the oxygen potential is controlled by a controlled supply of oxygen-containing gas and / or carbonaceous material, reducing sulfur in the pulp liquor and binding substantially all alkali and sulfur to the molten phase, separated from the gas phase. A method according to claim 1, characterized in that the gas to be fed is air and forms a support for the external heat a11e supplied to the reactor. Method according to Claim 2, characterized in that the external energy is supplied as a high-energy gas which is heated in a plasma generator. Process according to one of Claims 1 to 3, characterized in that 95 to 100% of all alkali and sulfur are bound to the molten phase. 6 85994