SE448102B - PROCEDURE FOR PREPARING COOKING CHEMICALS FOR CELLULOSAMAS PREPARATION - Google Patents

Description

_44s'1o2 2 In the production of cellulose according to the so-called Bulfat- In the process, wood chips are boiled with cooking liquor, the active parts are sodium hydroxide (NaOH) and sodium sulfide (Na2S) ¿ These are oxidized during cooking to carbonates and sulphates.

During cooking, 50% of the wood also goes into solution. mainly lignins and hemicellulose, but also the minerals found in the wood. In a ' ' The heat content of the lye is utilized, after concentration 4 J 1 evaporator, in the aoda boiler, where the lye is burned. e The ash melt of the sodium salts flows out of the recovery boiler to a melt solvent, where it is dissolved with weak liquor. From it thereby formed green liquor1similar ~ solid particles (impurities) usually by sedimentation in a so-called; green liquor cleaner.

Gröniween: eeaen was used for eläeking possibly burnt kenr, which is added in excess to a so-called extinguisher. This is also happening here a separation of lime particles, which are not allowed to suspend in the green liquor, but falls to the bottom and is removed. via eläekningen bila-ae ikeleiwnhyareriq, ce (oH) 2, eem with sodium carbonate, Na2CO5, (green liquor), forms sodium hydroxide, NaOH (cooking cloth); and calcium carbonate, CaCO5 (mesa). This _ reaction is commonly called caustic.

To balance the reaction between sodium carbonate and burnt lime must be able to settle, a certain time is required, why the reaction is allowed to proceed in quench vessels and causticizing vessels about 1-1% up to 2 hours.

The lye and potassium carbonate ¿mesane, after reaction the ion is separated, which takes place in white liquor clarifiers or through filtration. The lye is stored after separation of the mesa and is therefore pumped to tanks, from which the latter is dosed for boiling. i i '_ Mesan goes on to recausticize, whereupon one sounds residual excess air reaction react with green liquor, Hereby weak liquor is obtained, which is used in the former the dissolution of ash melt. e _ e e _ The mesa is dewatered on vacuum filters, which increase the dry content : 111 between so een 709% een wash on fiivtren with the crank, 4.:? 448 102 - 3 before being transported into the rear (cold) end of the mea fl oven.

In the oven, the mesa is dried and burned to lime underneath release of water vapor and carbon dioxide. For heating fired usually oil or gas with burner directly into 1 oven.

The chemical processes are fi oily. IN 0 Reaction in the recovery boiler; Na_S0 _ red._atnosiär gNa 2 4 S + 202 2 Reaction in the extinguisher and caustic vessels; CaO (s) H2 (-; _-_ :) Ca (OH) 2 (s) 1 ce (oH) 2 (fl) + 0032 "¿; r ~ :, ceco3 (e) + 2oH * Reaction in the oven; O 1000 C CaCO 3 (s) g '[-> - CaO (s) + CO2 (s) (a) Today, undesirable compounds come in with lime make-up The wood (round wood - well-sorted wood chips) and the process water. I fab- 'kingdoms that use annual plants (grass, reeds, straw, bagass), bamboo or other tree species, which contain large amounts undesirable compounds, cooking chemicals can hardly be be used without being dumped instead.

Solid fuel heating has become relevant in lime kilns in eenbena ned higher energy prices een neirräaentnyttjerne, .Hel- tree utilization has also meant that the quality of the chips deteriorated, ie the content of undesirable compounds has increased.

When using solid fuels and / or whole wood chips in lime kilns will have similar problems, as then annuals plants etc. are utilized.

The undesirable compounds are the sauce si, AL, -Mn, Mg, Fe and Pr, are enriched in all process streams, depending on the degree of efficiency in the system.

The levels: occurs une qeee an equilibrium 1 the system is reached.

Usually there are no bleeding sites other than with cellulose, green liquor sludge and lime gravel. _448 1Û2j you The enrichment of undesirable compounds entails a number of problems;: * t t ai g ' - Increased propensity to incubate, especially sodium- aluminosilicates on heat transfer surfaces such as g in the evaporator, soda fi another and the cooker. Aluminum content is the controlling factor. when precipitating sodium * aluminosilicates. _ g. _. . t - Increased deposits in pipes and appliances with low currents rates mainly due to poorer sedimentation_ and filtration properties of mesa; t 1 I 7 f - Increased energy consumption, partly to inert in e.g. lime' v must be heated unnecessarily, partly to keep the dry matter on the mesa filter has been lowered as before. _ W Poorer capacity of the facility due to impact according to above. e f I "g When extinguishing the burnt lime, dosing is required amount of carbonate solution (green liquor) only to the extinguisher or alternatively in several streams eg -for the caustic and / or the reconstitution, M t ~ Extinguishing releases large amounts of energy. In order to to get a quick reaction it is required that the temperature is between 90-100 ° C.

With the technology used today, the conditions for extinguishing difficult to control. Too low a temperature gives poor extinguishing and thus reduced capacity. Too high temperature (energy development) causes the liquid in the extinguisher to boil over and severe women's problems with lime dosing occur. An attempt to master the practical problems of uncontrolled extinguishing entails, has been made by the extinguisher pressurized and built into a closed system; 7 t t The present invention is a solution to the above I said prob1emen «_ - The invention relates to a method which can primarily be applied in factories, where solid fuel, such as bark, wood, shavings, peat and carbon was used in the incinerator, 7 and / or where fiber and chemical The raw materials contain high levels of undesirable substances.

Such raw materials can be wood chips from solid wood use, limestone, water, bagasse, bamboo, reeds, straw and the like. In the event of combustion of the above-mentioned fuels in a blast furnace is added 4.1 vä-a - 'I ß _. 448 102 5 lime in the ash containing undesirable substances, such as Si, Al, 'mg, I-nn, Fe, r n.f1. r_ What characterizes the method according to the invention is that Û, burnt lime. is extinguished in a separate process step in an aqueous solution. so that a suspension of calcium hydroxide in aqueous solution p'ningen occurs. From the aqueous solution is then separated the lime milk thus formed, before causticization takes place by the addition of sodium carbonate. The aqueous solution may pure water, scrubber, purified condensate, alka-p_ water or other process water. The alkalinity can.vid needs are adjusted by a minor addition of e.g. NaOH, vit- Lye, Na2CO3 or green liquor. For the latter two, that applies Na 2 CO 3 is reacted with CaO and forms NaOH sufficient to l adjust the pH to the desired level, ie 12-15. Our accompanying drawings illustrate Fig. 1 previously known and process described above, while Fig. 2 shows the method according to the invention. "k" Particles that settle on quenching, hard-burned lime, stone from the kiln masonry and from lime make-up removed from the extinguisher with scrapers or similar. The the homogeneous suspension is then added according to the invention a separation step, which preferably consists of a filter o but which may also be constituted by a sedimentation device or on a combination of both; -In this case, excess water is separated the solution from the calcium hydroxide, which then suitably wash with clean warm water (or purified factory condensate).

The alkaline solutions a. Can also be used as washing water or Na 2 CO 3 solution for adjusting the pH. The one here extinguished and washed lime is dosed together with green liquor to the causation. The strongly Aikai water solution can be circulated in whole or in part back to the extinguisher l or discharged to the factory's sewer or other water treatment. ~ In the event of large recirculation, the aqueous solution must be purified from released substances, before returning to the extinguisher. Example on purification processes is reduction of the pH value and thereafter “Q 448 102 gl ii ~ gö separation of precipitated substance by centrifugation. filtration, sedimentation or separation of cyclones. preferably aqueous solution is added in excess. ellt igform. of washing water, and 'bleeding' dissolved chemical potassium is formed before the remaining aqueous solution is recycled. g i * i In the process of the invention, several processes have parts frenkemnii '.compare-ifred the technique een giid-igere e used, It has thus been found that a majority of _ _ iere dnervärde substances ilbrändikelk rereligger i naden rer-e i (eådene ieireninger), ett de till eierddel gar i lösning ' at dec when fdreeliegne eläerningerörferenden. speeielli; e important compounds with Al and Si can thus be removed, and incrustation of NaAl-i isilicates in the incubation of lye is avoided. Several other trace elements can also be soaked and 'on thus avoiding, that ide lanrikasgi factory lye- and lime- _: f eï. bike. It has also surprisingly been shown that attisedimenta- filtration and filtration properties of white liquor / weak liquor CaGOÖ. ' (mass) is improved. This means that the white liquor clarification gets : with repeeirer. een ett neeein ken ii-väiiee een. evvetrnee better. High retrore content nos mesain results in reduced fuel consumption use in the lime kiln. Furthermore, control of extinguishing so that constant temperature and thus maximum capacitance, without overcooking can be maintained. Through better dreglering ren thereby: also the conditions of the reneiieering Icon is maintained at optimal levels, giving the highest white liquor. exchange and quality. i i i i i ii ' išxemgel i _ i, _ e i i. en ifebrik envendiei berkpnlver i efällei: för elje .een e i fuel in a lime kiln. The bark powder has an ash content of about 3%.

The box consists of a number of inorganic substances. For example are nelierne ev kieelieeh aluminum 14 resp. 12.2 g / kg neka.

In addition, lime make-up is added to the mesa flow, before the mesa ombrännesàiKallsnake-upen contains 1.3 g eAl / kig and 1.4 g Si / ikg. i with the previously used 'eläerningefdrferendei enrilšedee' aluminum. "silicon and other undesirable chemicals in _ E the lye and mesacycle. Compared to oil heating in meisaugnein in v! .in U) gr .._.... ».. ... L., _. A .._.-. E ._-.- .. i --..'- :. _-. . .r ...-.'...-.-... _:, ..; .... 1 '.._'. _. ..- .. «-.- ': .- -“ f-.ß 448 1027 'v 72.1 ' HRS 1 _ 7 increased, for example, the aluminum and silicon content in white liquor from 20 resp. 90 to 180 resp. 220. After installing it The proposed procedure, see Fig. 2, has in the white liquor measured levels 20 mg aluminum / 1 white liquor and 70 mg silicon / l vitlut. In the lime kiln, 23.3 tonnes of mesa / h are burned (Th = 69%) “ and 0.04 tonnes of make-up lime / h to 9 tonnes of burnt lime. the burning requires 3.6 tons of bark / h. The burnt lime.transh transported via a mill to the extinguisher, where the lime is mixed with ' the filter (70 on / n) from a keikmilk filter below a strong -0 0 agitation. In this case, the lime is extinguished during heat generation, 4 .I and the limescale particles are finely divided into a fine sludge. Lime gravel, _ avs. noauler which is not finföraelate (fl aöabräna fl lime, stone äte), - sediments in the sluice and is transported out with a scraper-0 work. This quantity is measured at about 0.050 tons / h. Maintenance the time in the extinguisher is 15 min. From the extinguisher is transported keirmöjiken vid ce 1oo ° c (eiäekt keik een vätska) till the lime milk filter, a drum filter with a diameter of 2.5 and width 4 m, where the slaked lime is filtered from the liquid and dewatered in vacuo. The lime is washed on the filter with a aqueous solution (14 mph), consisting of 1 part NaOH and 10 shares clean water. From the filter the lime is transported, which now has a dry content of 70%, with a conveyor belt to caustic ~ eeringsenneten, where green liquor is added. Fiatrate (75 m3 / n) from the drum filter is pumped through a heat exchanger, where the the liquid is heated to 95 ° C, after which the filtrate is partitioned. The one current is ~ 5 m / h and may go to the sewer, the other the current (70 mph) to the extinguisher. _ _ At one sampling occasion, the following results were obtained: A1 si ash from bark 14000 mg / kg 12200 mg / kg brä flfi lime 2000 "W 2500" vätekeaeien ev keikmjöikenii 364 mg / 1 0 320 mg / 1 festa aeien ev xeikmjöiken 1240 mg / kg 1574 mg / kg the filter from filter 305 mg / l 264 ma / 1 § 44se1o2d 7-7 A Comparison I between oil lining. j barkelaping- pen barkeldning with the new the process part shows the following; d 'j' berxempi fi g med " bark lm bränsleåïšånë. ød d _ dd I 1 zífï * GJ / ton lime .7,9e e e 8¿2 7 ,? _ _ i - '' _ 1-. dry content after d. '_ d' "- mesafilter e e - 63-70 60-65 e sa-'ïof reactivity of the cock v - seconds to achieve d. A ¶- e aximal temperature about '90 d _e .10O ', 180e a vlss amount of lime tlll- d was added to a vlss amount of water of than e temperature of 85 C inerties in km% 1 2.5 1.5 sludge content in garde e e e vi fl ut: ng / m e 50-120 _ 7oo-1o_oo 15o-2oø lf? .get m!

Claims (7)

_L «. V1 i 448 102 P Air ENTKRA v 1.g Process for the preparation of cooking chemicals for cellulose preparation, in which burnt lime from a lime kiln is quenched and the quenched lime is then mixed with green liquor (sodium carbonate), which is causticized to liquor, known as - the result is that the lime is quenched in a separate process step in an aqueous solution and that the lime (Ca (DH) 2) thus formed is then separated from the aqueous solution, before causticization occurs. 2. A process according to claim 1, wherein the pH of the aqueous solution is between 12 and 15. 3.i A method according to claim 1, characterized in that the lime milk separated from the water leach is washed with water before caustication. 4. A method according to claim 3, characterized in that the lime milk separated from the aqueous solution is washed with an alkaline aqueous solution before causticization. 5. A process according to claims 1 and 2, characterized in that the aqueous solution from the step for separating lime milk and aqueous solution is recycled to quenching. s. Procedure according to claim s, characterized in that recycled aqueous solution is purified by adding acid to a lower p value and that precipitated substance is separated from the solution. 7. A method according to claim 1, characterized in that the temperature at quenching is kept between 6D ° and 120 ° C by cooling or heating the aqueous solution.