FI62562C - FOERFARANDE FOER BEHANDLING AV MATERIAL I EN VIRVELBAEDDREAKTOR - Google Patents

Description

ΓΒΤ ^ vAnnouncement

W1A (11) UTLÄGGN I NOSSKMPT 6 2 5 6 2 52¾¾ C Rite: /: -Λ ./3 :::. .... 1. / 13 01 1003 ^ cn; V ^: ~ 0 ^ "(51) K» .lk.3 / lnt.ci.3 D 21 C 11/00 SUOH I - FINLAND (21) IWttlhakuuuiu- 7705 ^ 6 (22) HukumtopPIv · —AnaMcnlnffdaf 21.02.77 (23) Alkuptlvt — Glfclghuttuag 21.02.77 (41) Tullut swan - Mtvlt offuntilf 22.00.7 8 fattnttt ») - 30.09.82 ratani och reglsterstyreheo '' Anaekun uttagd och uti.skrtftun pubimnd (32) (33) (31) Pyrdutty utuolkuu * —Bugird prtodtut (71) A. Ahlström Osakeyhtiö, 29600 Noormarkku, Finland-Finland (FI) ( 72) Folke Engström, Karhula, Suomi-Finland (FI) (? U) Method for treating substances in a fluidized bed reactor -Förfarande för behandling av material i en virvelbäddreaktor (6l)

The present invention relates to a process according to Patent No. 54160 for treating substances in a fluidized bed reactor, wherein the substance to be treated is contacted with solid particles separated from the flue gases of the fluidized bed reactor before being fed to the fluidized bed reactor.

It is an object of the present invention to apply the method to pulp cooking liquor from the sulphite and sulphate cellulose industries so that the cooking chemicals contained in the waste liquor are recovered and a cooking solution is prepared from the obtained chemicals.

In the past, sulphate cellulose broth effluent chemicals have most commonly been recovered by incineration of the concentrated effluent in a recovery boiler, whereby the sodium and sulfur contained in the cooking chemicals are recovered from the melt in the form of sodium carbonate and sodium sulfide. Causticization of the melt solution converts sodium carbonate to sodium hydroxide.

2 62562

The chemicals in the sulphite cellulose broth effluent can be recovered, for example, as disclosed in Finnish Patent 45,880 by separating the carbonate and sulphide sulfur from the soda liquor obtained from the melt in a recovery boiler and reacting the sulphide-containing solution with a bisulphite solution to burn hydrogen sulphide. The sulfur dioxide from the combustion is reacted with the aqueous carbonate solution in the absorption tower to form the bisulfite required for the cooking solution.

Pyrolysis has also been applied to the recovery of cooking chemicals contained in waste liquors, for example in the so-called SCA-Billerud process, in which the sodium salts of sodium sulfite waste liquor are converted to sodium carbonate and the sulfur components to hydrogen sulfide. Hydrogen sulfide is burned to sulfur dioxide and absorbed into sodium carbonate solution. This method is presented e.g. in Finnish patent 44,518.

According to the invention, aluminum hydrate and hot dust containing sodium aluminate separated from the flue gases of a fluidized bed reactor are mixed with the waste liquor of cellulose soup based on sodium and sulfur compounds to convert the sulfur content of the waste liquor mainly to hydrogen sulfide, which is separated before the waste liquor is fed to the fluidized bed reactor.

The invention will now be described in more detail by means of the following examples and with reference to the accompanying drawings, in which Figure 1 shows a process according to the invention applied to a sulphite soup effluent and Figure 2 shows a method according to the invention applied to a sulphate cooking effluent.

In Fig. 1, a mixer denoted by reference numeral 1 is fed into which the concentrated sulphite soup waste liquor 2 is fed. The mixer is fed with the aluminum hydrate 4 separated in the filter 3, which is dried in a dryer 5. It is also fed with the necessary make-up chemicals 6. The effluent from the mixer containing hot dust through line 11. In the pre-reactor, pyrolysis of the waste liquor takes place, whereby gas and water vapor are formed. Air 12 can also be introduced into it, causing partial combustion. Gas which e.g. contains the major part of the sulfur content of the effluent, mainly in the form of hydrogen sulfide, and the steam is removed from the pre-reactor via line 13. The gas and steam generated in the pre-reactor and the air introduced into it cause the mixing of the waste liquor, which can be enhanced by mechanical means. The temperature in the pre-reactor is adjusted to a range of 200 to 900 ° C, preferably about 700 ° C. Alternatively, the gases from the pre-reactor are led via line 14 to the fluidized bed reactor 10 or via line 15 to the afterburner 16, where they join the flue gases of the fluidized bed reactor. In a fluidized bed reactor or afterburner, hydrogen sulfide burns to sulfur dioxide. The heat contained in the flue gases is utilized in the waste gas boiler 17, from where they flow to the flue gas scrubber 18.

From the dust separator 9, part of the sodium-aluminate-containing dust separated therein can be led through a condenser 19 to a dissolution device 20 to which water 21 is added. As a result of the neutralization, the aluminum precipitates in the form of a hydrate, while the sodium salts remain in solution in the form of NaSO 4, NaHSO 4, Na 2 CO 2 depending on the Na / S ratio and the pH.

The aluminum hydrate is separated from the dissolved sodium salts in a filter 3. To enhance the separation, the suspension 24 is first passed to a ripener 25 where the aluminum hydrate crystallizes before being introduced into the filter. After separation, the aluminum hydrate is returned via line 26 to the waste liquor to be treated in the process for mixing. The solution containing Na salts is removed from the filter via line 27 to the digester.

In Fig. 2, the concentrated waste liquor 28 of the sulphate soup is fed to a mixer 29. The mixer is also fed with aluminum hydrate 31 separated from the filter 30. Pyrolysis gases containing sulfur, mainly in the form of hydrogen sulfide, are introduced via line 36 to an absorption tower 37, to which 38 mm from the settling tank is also led. sodium hydroxide solution via line 39. In the absorption tower, hydrogen sulfide is absorbed to form a solution containing mainly NaOH and Na 2 S, which is fed through line 40 to filter 30. Part of the sodium aluminate-containing dust separated therein is passed through line 41 to dissolution device 42, to which water is added. After dissolution, the aluminum hydrate is separated from the formed sodium hydroxide-aluminate solution in the precipitation tank 38 and passed through line 43 to filter 30. In the filter, the aluminum hydrate is separated back to the process and the solution containing sodium salts is removed via line 44 to the digester.

Example 1.

The effluent from the 24 kg / s sulphite digestion with a dry matter content of 8% was concentrated to a dryness of 36% in a thermocompressor evaporator, followed by evaporation to a dryness of 60% in a flue gas scrubber. The concentrated waste liquor was mixed with 0.60 kg / s of Al 2 O 3, corresponding to a molar ratio of Na 2 O 2 in the mixture. The mixture was pyrolyzed at a temperature of about 700 ° C. The temperature was controlled by changing the amount of hot dust separated from the flue gases. Partial combustion was achieved by blowing air into the pre-reactor. The effluent containing Na-Al salts as well as unburned carbon was fed to a fluidized bed reactor where the Na-Al salts were converted to sodium aluminate at temperatures above 900 ° C. Gases from the pre-reactor containing sulfur, mainly in the form of H2S, non-combustible components such as CO2, H2O, N2 were introduced into the afterburner. Air and oil were fed to the fluidized bed furnace. Combustion in the furnace was slightly reducing and the composition of the flue gases was as follows: O 2 = 1.3%, CO 2 »16.6%, N 2 = 76%, CO = 1.3%, CH 4 = 0.4%, H 2 = 1.4% , H2S = 1.3%.

Residual combustion of the flue gases was performed by adding air, whereby H 2 S was converted to SO 2. The heat was recovered in a waste heat boiler, which reduced the flue gas temperature to 400 ° C. The flue gases were then passed to a venturi scrubber to concentrate the effluent and then to another scrubber to absorb SO 2 with alkaline sodium aluminate solution. The sodium aluminate solution was obtained by dissolving 1 kg / s of dust separated from flue gases in 5 kg / s of water. When SO 2 and CO 2 were absorbed into the solution, Al (OH) 3 precipitated, which was separated from the solution in a filter. The remaining solution, the concentration of which can be adjusted by changing the amount of wash water, which in this case was 5 kg / s, contained 106 g / l Na 2 SO 3 and 38 g / l Na 2 CO 3 and could be used as such in the cooking solution. Al (OH) 3 was mixed with concentrated waste liquor.

Example 2.

0.9 kg / s of water was mixed with a concentrated waste broth from a 2.2 kg / s sulphate broth with a dry matter content of 65%. Dust separated at 1000 ° C from flue gases was added to the mixture in a pre-reactor to effect pyrolysis at 300-900 ° C. As a result of the pyrolysis, the sulfur in the waste liquor was converted to hydrogen sulfide, which was absorbed into a solution containing sodium hydroxide and sodium aluminate. The sodium hydroxide-aluminate solution was obtained by dissolving the 0.9 kg / s sodium aluminate separated from the flue gases in a gas separator and a waste heat boiler in 3.6 kg / s water.

Precipitated Α1 (0Η) 3 is separated before H2S absorption. 0.9 kg / s A1 (0H) 3 was separated from the solution, which was returned to the combustion process for 62562 s, while the solution containing 2.9 mol / s sulfur and 5, 7 mol / s sodium, mainly in the form of NaOH and Na 2 S, was used as a cooking solution.

With the method according to the invention, the sulfur in the waste liquor can be reduced under easily controlled conditions before the waste liquor is incinerated. The cooking broth chemicals are recovered in such a form that they are useful as such in the cooking solution. Depending on the pH of the separated solution, they may also exist in forms other than those shown in the examples. It has been shown experimentally that the amount of sodium aluminate remaining in the solution does not interfere with the cooking.