• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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    • 专利摘要:
    Method for producing sodium hydroxide from a waste water stream The pulp production process, which stream comprises organic waste and sodium bound thereto. According to the present method, the waste water stream is concentrated and then burned under oxidizing conditions, in order to break down the organic waste and the sodium compounds. According to the present invention, borate or compounds which form borate are added to the waste water stream, after which the sodium compounds precede an auto-caustic reaction. The reaction is carried out at a temperature high enough to evaporate the sodium and the sodium is mainly in oxide form. The at least partial conversion of sodium carbonate to sodium hydroxide, according to the present invention, improves the usability of the alkali recovered, for example, by using the Alrec process, which in turn reduces the cost of chemicals and reduces energy consumption required for the defibrillation of traflis.
    公开号:SE1250098A1
    申请号:SE1250098
    申请日:2010-08-18
    公开日:2012-02-09
    发明作者:Maija Pitkaenen
    申请人:M Real Oyj；
    IPC主号:
    专利说明:

    The BCTMP factories built in the 2000s by M-real at Jutseno (2001) and Kaskinen (2005) are, in terms of concentrate treatment and recycling of chemicals, integrated with sulphate pulp mills.
    The BCTMP plants evaporate their waste water in a cascade of evaporators to a high proportion of dry matter (2450/0), and from the evaporator section the concentrate is pumped to a mixing zone for mixing with black liquor received from a pulp mill located in the same plant area. After passing through the evaporation unit of the pulp mill, the mixture thus obtained is burned in a soda recovery unit. In the soda recovery unit, the combustion of the material generates carbon dioxide and water (-> CO 2 + H 2 O) and the inorganic ingredients form a melt at the bottom of the recovery unit. This melt is dissolved in water, which produces green liquor (NazCOš + NazS / main products). Consequently, the sodium, which forms part of the alkaline chemicals used in the BCTMP factories, is recycled as part of the process of dissolving the melt (green liquor) in the soda recovery unit.
    The cooking chemicals used in a sulphate pulp mill are sodium hydroxide (NaOH) and sodium sulphide (NaZS). The environment during incineration in the soda recovery unit is reducing, which is why sulfur is recycled directly in the form of a waste. The main components of white liquor are sodium hydroxide (N aOH) and sodium sulfide (NaZS).
    A pulp mill uses a larger part of the green liquor to produce white liquor, but some of the green liquor is oxidized (NazCOä + NaZS -> Na2CO3 + Na2SO4) and led to the BCTMP plant. Oxidation is a way of removing sodium sulfide, which would otherwise cause problems at the BCTMP plant because it consumes hydrogen peroxide, which is used in bleaching the pulp. Sodium sulfate (NazSO 2) is a neutral salt that passes as a "dead weight" through the process at the CTMP plant and ends up in concentrated form back in the soda recovery unit, where it is reduced back to sodium sulfide.
    Sodium carbonate is not an effective chemical for removing equation (ie for delignification) when boiling chemical pulp. Consequently, green liquor is unsuitable for use in impregnation or boiling in the production of chemical pulp. White liquor is produced from green liquor by causticizing with lime. In this process, burnt lime (CaO) is added to the green liquor, and as a result of causticizing reactions, the carbonate precipitates as calcium carbonate, while sodium forms sodium hydroxide. The lime is regenerated by burning (CaCOâ -> CaO) in a lime sludge re-incinerator.
    In the production of chemical mechanical pulp, such as CTMP, lignin is not removed in the step of impregnating wood ice by using alkaline treatment (impregnation), instead the lignin is softened and carbohydrates (hemicellulose) are treated before the next refining step (defibration of wood ice). The pH of the impregnation solution or impregnation liquor is lower (pH 9-12) than in the production of chemical pulp (pH 14). Consequently, it is possible to also use sodium carbonate for the impregnation of wood chips in the production of chemical mechanical pulp.
    In integrated BCTMP processes, oxidized green lye from the pulp mill and lye (NaOH), which are typically purchased from external suppliers, are used in the impregnation of hardwood. The alkali used in the peroxide bleaching is lye. Sodium sulphite is primarily used for impregnation of softwood.
    In addition to using an integrated solution, it is also possible to perform a separate recycling of sodium chemicals at CTMP factories. According to one embodiment, namely the one known as the Alrec process ("alcali recovery process"), the waste liquor which is concentrated to a high proportion of dry matter of about 65% is incinerated using drop burning under oxidizing conditions (oxygen supply). ) and at a temperature of 1000-1200 ° C.
    In Alrec incineration, in contrast to incineration in a soda recovery unit, the conditions throughout the combustion chamber are oxidizing (excess oxygen). In Alrec combustion, the proportion of oxygen in the combustion gas is 4-6 vol ° / o. During combustion in a soda recovery unit, the combustion conditions are regulated by introducing air, in phases, into different parts of the unit in such a way that the conditions in the stack, for example, are reducing. Therefore - COD (dissolved organic material) is destroyed (-> CO2 + H 2 O), and - sodium from the waste disposal is recovered as sodium carbonate (NazCOâ).
    It is possible to recycle the sodium carbonate to be used in impregnating the traflis and in bleaching the CTMP mass, where it can also be used, in addition to lye, as a cold to alkali.
    In the high temperature process described above, the sodium in the waste water concentrate, which is bound to the organic material, evaporates to its gas phase, where it is present partly in the form of Na 2 O and partly as elemental sodium (boiling point of sodium is 883 ° C). The delay of the residence time in the Alrec process is only a few seconds at a combustion temperature of 1000-1200 ° C, after which period the combustion gases from the combustion chamber are rapidly cooled to 600 ° C. In this case, the gaseous sodium compounds are sublimed directly as solid powdered sodium carbonate. This prevents the creation of sticky narrow sodium carbonate and thus possible contamination of the cradles.
    The solid sodium carbonate (ash) formed in the process is dissolved in water, impurities are removed by filtration and the Na 2 CO 3 solution is recycled to the impregnation of traflis and the bleaching of pulp.
    The process described above is reported in more detail in the published international patent application number WO 2005/068711 (Rinheat Oy).
    There are limitations in the known technology. In our experiments we have discovered that when lye (sodium hydroxide) is replaced during the impregnation step with sodium carbonate, the pH value of the impregnation solution decreases and impregnation and softening of leaf litter decreases, which tends to increase the specific energy consumption during refining. If the specific energy generated during refining increases, it limits the usefulness of the recycled alkali in the impregnation step, i.e. the 100% sodium carbonate solution. Our test runs suggest that the effect of carbonate on the specific energy in refining depends at least on the quality of the CTMP pulp to be produced (technical grades for paper) that is desirable and possibly on the proportion of different types of wood (aspen).
    The sulfite in sodium sulfite (N aZSO 3), which is used in softwood CTMP production, oxidizes during the above-mentioned oxidizing Alrec combustion process to a neutral sulfate compound (N aZSO 4). Sodium sulfate is a neutral salt and is not suitable as an alkaline chemical for impregnation or bleaching. Thus, the Alrec process is not suitable for the recovery and recycling of sodium sulfite, but separate procedures for the regeneration of sulfite.
    There are also limitations associated with the use of sodium carbonate as the alkali in peroxide bleaching. Without the presence of lye, the pH values remain low and the bleaching effect is reduced.
    The object of the present invention is to provide a completely new solution for the recovery of alkali in chemical mechanical and mechanical pulp production. Another object of the present invention is, for example, to extend the usefulness of alkaline chemicals recovered using the Alrec process.
    The present invention is based on the concept of producing sodium hydroxide from a waste stream or effluent of a pulp production process. The stream used typically includes organic waste and sodium and sodium compounds bound to the waste. Thus, borate or a corresponding boron-bearing material (hereinafter referred to as a "boron compound") is added to a waste stream or impregnation solution.
    The addition of the boron compound makes it possible to generate sodium hydroxide, which is formed by sodium and sodium compounds, by a borate autacousticization reaction and subsequent hydrolysis.
    Autacoustication is a reaction described in the literature as early as the 1970s (see Jan Janson, “The Use of Unconventional Alkali in Cooking and Bleaching - Part 1. A New Approach to Liquid Generation and Alkalinity”, Paperíja Pm; 59 (6-7 ), pp. 425- 430 (1977), “The Use of Unconventional Alkali in Cooking and Bleaching - Part 2.
    Alkali cooking of Wood with the use of borate ”. Paperíja Pm; 59 (9), pp. 546-557 (1977) and U.S. Pat. 4,116,759.
    According to Jansson's observations, a separate causticization using burnt lime can also be avoided completely during sulphate boiling by adding borate to the cooking liquor, which by the causticizing reaction generates sodium hydroxide in connection with the dissolution of the melt, i.e. the production of green liquor. However, factory tests performed by Enso Gutzeit in 1982 did not confirm initial expectations about the profitability of the process.
    About 20 years later, Honghi Tran re-examined autobaustic reactions with borate and showed that the exchange of lye from borate was double that described by Janson. According to the reaction formulas presented by Tran, one mole of tetraborate (N a2B4O7) gives 8 moles of lye (NaOH), instead of 4 moles as Janson assumed. (Tran, H .; Mao, X .; Cameron,].; Bair, CM., Pnåzb and Paper Canada 1999, 100 (8), 35-40).
    This finding had a substantial effect on the profitability of autocaustion with borate, as it showed that only half of the original dose of borate was needed. Trans studies have resulted in autocaustion with borate being used in part at certain sulphate pulp mills.
    In an article entitled “Borate autocausticizing: a cost effective technology” (Pnéb d Paper Canada 103: 11 (2002), pp. 16-22, MA Hoddenbagh et al. Describe two factory tests performed 15 years after the Enso test and in which an auto-caustic reaction is used in both the recovery and bleaching of chemicals.Based on the results, alkali produced using the auto-caustic process with borate may be used in the bleaching of CTMP pulp and replace sodium hydroxide purchased from external suppliers.
    Incorporation of borates in a pulping process, for example for the purpose of generating boron-bearing alkaline cooking liquors, has recently been described in the patent literature, as exemplified by published international patent application no. WO 2004/025020.
    That document shows a process in which borate carbonate boiling is integrated with the recovery of chemicals in the production of eucalyptus chemical pulp.
    This solution is based at least in part on auto-caustic, during which some of the cooking chemicals, which are regenerated by using auto-caustic, are used for boiling and / or oxygen delignification or during alkaline bleaching steps, such as peroxide bleaching without conventional caustic. Anthraquinone is used as a catalyst for delignification.
    Published U.S. Pat. 2005/01 55730 describes a high yield process in which core hardwood pulp is produced using quinone catalyst in the wood chip impregnation step, in which the pH value is temporarily below 7, or in a cooking liquor having a low sulphide level and which mainly comprises borate, sodium hydroxide and sodium carbonate. An alkaline cooking liquor is prepared without separate causticization using calcium oxide or calcium compounds.
    Two published international patent applications WO 99/63152 and WO 99/63151 describe how the efficiency of a calcination reaction is improved by the use of borate.
    In the present invention, we have surprisingly discovered that autacoustic reactions occur even during combustion performed under conditions of oxidation and high temperatures, such as under the conditions prevailing during an Altec-type combustion process.
    The solution is implemented, according to the new technology presented, in such a way that the autacoustication reaction is carried out by burning an effluent in a combustion chamber in an oxidizing environment and at a temperature high enough to evaporate at least part of the sodium (boiling point of sodium is 883% ).
    In particular, the operation is carried out at a temperature at which sodium evaporates and is mainly in oxide form (Na 2 O). By subjecting the sodium and its compounds, which during combustion are released from organic material, to a reaction with borate mainly in the gas phase, it is possible to produce sodium hydroxide when the ash, which typically contains sodium orthoborate, during a dissolution step, is dissolved or suspended. in water. The effluent from this reaction can be used as an impregnation solution for example in a BCTMP process or other chemical mechanical defibration, and as a source of alkali in peroxide bleaching.
    It is possible to use the present method for the recovery of alkaline sodium compounds, which are at least partly in the form of sodium hydroxide, and which compounds are suitable for the production process of fibrous pulp.
    More particularly, the method according to the present invention is characterized by what is stated in the characterizing part of claim 1.
    The use according to the present invention is characterized by what is stated in claim 20.
    Significant advantages are achieved with the present invention. Thus, the invention is generally suitable for use in incineration processes in which, typically, waste liquor which is concentrated to a relatively high proportion of dry matter is incinerated under oxidizing conditions (i.e. in excess oxygen). The temperature is preferably at least about 950 ° C. in particular, at least a portion of the sodium carbonate is converted to sodium hydroxide which improves the usefulness of alkali recovered, for example, during the Alrec process. This, in turn, reduces the cost of chemicals and reduces the energy consumption required for defibrating wood ice, which follows impregnation. The usefulness of this alkali in peroxide bleaching is improved.
    The present invention makes it possible to operate an independent (non-integrated) BCTMP plant and a mechanical pulp mill, which is free of waste water, and has means for recycling alkaline chemicals and cost-effective recycling.
    Thermal energy generated during the incineration of organic waste is used as steam in the process.
    In the following, the present invention is examined in more detail by means of a detailed description and the accompanying drawing. The process flow diagram shown in the drawing represents an embodiment of the present technology.
    In the present context, the terms "outflow" and "waste water" will be used largely synonymously to denote a flow / stream containing organic residues and sodium compounds which come from a process for the production of fibrous pulp.
    As described above, in the present technology, autocaustion and high temperature combustion are combined to create a process in which sodium is bound, typically chemically bound, to the organic material of a waste (wastewater), is subjected to, in the gas phase and during oxidizing conditions, a reaction with a boron compound. It seems that under such conditions sodium is at least partially reacted directly with borate, or another boron compound, presumably instead of carbon dioxide. As a result, a mixture of lye (NaOH) and sodium carbonate (N azCO 3) is formed during the dissolution of the ash, which is recovered in the process. It should be noted that the present invention is not limited to this exemplary model described herein.
    According to one embodiment of the present invention, metaborate or compounds forming metaborate are incorporated into the effluent, and the sodium and sodium compounds released during processing are reacted with the borate at a temperature high enough to evaporate sodium which is then mainly in oxide form (N azO). There may also be some elemental sodium. It is possible to incorporate the borate compounds into the effluent by adding them directly to the effluent or by adding them, for example, in an impregnation stream of chememechanical or mechanical defibration, with which they are carried through the process and form part of the effluent from the defibration (i.e. waste water effluent). .
    Preferably, the effluent is first concentrated to a high proportion of dry matter. According to one embodiment, the proportion of dry matter of an effluent which is subject to autocauscitation is at least 45% by weight, preferably at least 55% by weight, preferably at least 60% by weight, in particular at least 63% by weight, or even at least 65% by weight.
    According to another embodiment, the concentrated waste water is dried to a powder, which is fed into the incineration as a dry substance.
    Preferably, an effluent which is concentrated to a high proportion of dry matter of, for example, at least about 60% by weight, especially at least 63% by weight or at least 65% by weight, is burned in the presence of oxygen and borate or a compound which forms borate (a "boron compound"). ), at a temperature of at least 950 ° C.
    Typically, the dry matter of the waste comprises both an organic and an inorganic moiety.
    The weight ratio between it can vary within wide ranges, generally it is about 3: 1. ..1: 1, but these are no absolute limits.
    According to a preferred embodiment, autocaustion is performed at a temperature of at least 1000 ° C, preferably 1000-1250 ° C.
    Has “oxidizing conditions” or “oxidizing environment” means that during the whole or substantially the whole combustion process there is an excess of oxygen with the intention of preventing reducing conditions from occurring in any part of the combustion chamber. The oxygen is in excess relative to oxidizable compounds in the processed stream.
    Most appropriate is the amount of boron or other boron compound added to the waste water or impregnation solution before incineration large enough to ensure that the molar ratio Na: B in the waste stream is at least 3: 1. Preferably the molar ratio Na: B is about 3: 1. . _5011, probably about 5: 1. . .35: 1.
    When using borate, at least a major portion of the inorganic borate is added as sodium metaborate or sodium tetraborate or as hydrates thereof. Other housing associations are also possible.
    According to the present invention, the effluent stream to be treated is typically generated as waste water from fibrous pulp production which takes place under alkaline conditions.
    Separately, the wastewater stream comprises the fl fate from an impregnation step, i.e. impregnation, of the raw material for chememechanical or mechanical pulping, or the waste stream from alkaline peroxide bleaching of fibrous pulp, or a combination thereof. Thus, the waste stream may come from the production of, for example, abrasive pulp, pressurized abrasive pulp (PGW / j, refiner pulp or chemical mechanical refiner pulp). Accordingly, the sodium comes from sodium-bearing chemicals used in the impregnation of raw materials or alkaline peroxide bleaching or both, such as sodium carbonate, sodium hydroxide and / or oxidized green liquor or oxidized white liquor coming from chemical pulping.
    According to one embodiment, the combustion treatment is carried out, of an (organic) waste stream comprising borate or to which borate is fed, in two steps, the actual combustion taking place in the first stage under oxidizing conditions and at a temperature of more than 1000 ° C, after which the combustion gases generated during the combustion, which contains sodium in oxide and elemental form, is rapidly cooled to a temperature below 600 ° C, in order to sublimate the sodium compounds from their gas phase directly to the solid phase (sodium carbonate and especially borate compounds, such as Na3BO3).
    The ash, which is generated from the combustion of the waste stream, is recovered and dissolved in water with the intention of producing sodium hydroxide. At the same time, the metaborate (NaBOZ) is regenerated.
    Typically, according to the measures described above, the ash contains a proportion (calculated) of sodium hydroxide which - depending on the organic material and the proportion of sodium in the waste water - is about 1-750 / 0, preferably 5-700 / 0, especially about 10-500 / 0, by weight dry matter.
    Auto-caustic is performed under conditions of excess oxygen, whereby oxidizing conditions apply throughout the combustion chamber. Typically, the proportion of oxygen in the exhaust gas combustion gas is 4-6 vol / o.
    Oxygen is led to the combustion stage as a gas innefatt destiny comprising oxygen, such as air or oxygen-enriched air.
    It is possible to carry out the incineration as droplet incineration, whereby concentrated waste water which is led to autocaustion is dispersed to form droplets. The average droplet size may be, for example, about 0.1-5 mm, preferably <1 mm and more preferably É0.1 mm. It is possible to use the methods described above generally to recover alkaline sodium compounds which are used in the fibrous pulp production process, at least in part as sodium hydroxide.
    In the preparation of chemical mechanical pulp, such as BCTMP, ash, partially causticized in the preparation, is dissolved in water, the insoluble inorganic oxides (precipitate) being removed by filtration or centrifugation, and the alkaline solution generated can be used directly, without further treatment with traditional lime caustic, as a source of alkali for impregnation and peroxide bleaching.
    The present invention can be implemented, for example, in an equipment arranged as shown in the drawing. The equipment comprises a combustion chamber 1 and a cooling chamber 2, which according to the drawing are arranged one below the other in such a way that it is possible to direct the combustion gases, which are generated in the combustion chamber, to the cooling chamber, in which it is possible to cool them by means of cooling gases. , such as cooling air or circulating combustion gas, which is led into the cooling chamber.
    The combustion chamber is equipped with a nozzle 3 for measuring the concentrated waste water to be burned, through which nozzle it is possible to feed the concentrate, for example as a mist which comprises droplets which are dispersed by the use of steam.
    The cooling gas can be led into the cooling chamber 2 through an inlet nozzle 4.
    The bottom of the cooling chamber is equipped with an outlet nozzle 5 for removing carbonate, and with an outlet nozzle 6 for removing cooling gases and cooled combustion gases.
    Outflow which has been removed from a process and which comprises metaborate or boron compounds which form metaborate is evaporated in an evaporation unit as an internal process, preferably with the intention of producing a dry matter content of at least 45%.
    It is then passed through feed nozzle 3 into the combustion chamber 1, where it is burned, for example, at a temperature above 1000 ° C. 13 The combustion process is described in more detail in the published international patent application no. WO 2005/068711 (Rinheat Oy).
    The residence time in the combustion chamber 1, at a high temperature, is only a few seconds and the combustion gas coming from the combustion chamber is rapidly cooled in the cooling chamber 2 to below 600 ° C, the sodium compounds sublimating directly to solid material and can be removed as ash.
    When the ash is dissolved in water, the sodium orthoborate (trisodium borate) reacted with water reacts with the wild sodium hydroxide and, at the same time, the metaborate is regenerated according to formulas (1) and (1) Na fi co, + Naßo, -> Na fi ßo, + co, metaborate orthoborate (2) Na3BO3 + H2O -> ZNaOH + NaBOZ Borates are completely water-soluble compounds and regenerated metaborate is moved in the impregnation solution to the impregnation step and from there on, in the effluent from the impregnation together with waste water, through the evaporator, back to oxidizing combustion. The proportion of boron in the waste water that goes to the evaporation unit is kept at a constant level through additional coverage.
    As previously pointed out, the combustion in the combustion chamber is carried out with excess oxygen, in order to ensure that the combustion conditions in all parts of the chamber are oxidizing.
    It is also possible to carry out the dissolution of the ash in the cooling chamber 2. In that case, water is fed into the cooling chamber via the inlet nozzle 4. The water thus fed can be either pure water or an aqueous solution, such as a solution generated from the recirculation. With the aid of water, an aqueous film can be formed on the surface of the chamber, in which film it is possible to dissolve the alkali metal carbonates contained in the cooled combustion gases. Example A concentrate from an evaporator, which concentrate has a proportion of organic material of 52% and a proportion of inorganic material of 48% of the dry matter, was burned with excess air under laboratory conditions.
    The combustion temperature was 1100 ° C. Prior to firing, sodium metaborate was mixed into the concentrate.
    Table Ash yield Proportion NazCOâ pH value of Titrated proportion 0/0 of ash aqueous NaOH mg / g ash solution of ash mg / g ash Concentrate 43.1 719 1 1.8 40 Concentrate + NaBOZ; Na / B 48.4 109 12.9 385 mol / mol = 3: 1 The proportion of Na 2 CO 3 of ash was determined using a TOC carbon analyzer.
    The proportion of lye in the aqueous solution of ash was determined by titration, which was based on the standard SCAN-N 30:85.
    权利要求:
    Claims (20)
    [1]
    A method for producing sodium hydroxide from an effluent from a mass berm mass production process, which effluent comprises organic waste and sodium bound thereto, according to which method - the effluent is concentrated, - the concentrated effluent is burned under oxidizing conditions to decompose the organic waste and sodium compounds and to produce a combustion residue, and - the residue is dissolved in water to produce sodium hydroxide, characterized by the combination of - incorporating borate or a borate-forming compound into the effluent before said burning, and - the sodium compounds together with said borate or said compound which forms borate is subjected to an auto-caustic reaction which is carried out at a temperature so high that sodium evaporates.
    [2]
    2. A method according to claim 1, characterized in that borate is incorporated into the effluent by adding it directly to a waste water stream.
    [3]
    3. A method according to claim 1, characterized in that borate is incorporated into the effluent by adding it to a chemical solution used in the pulp production.
    [4]
    Method according to one of the preceding claims, characterized in that sufficient borate is added to make the Na: B molar ratio in the effluent at least 3: 1, preferably 3: 1. . _5011 and most preferably 5: 1 ... 35: 1.
    [5]
    Method according to any one of claims 1-4, characterized in that the causticizing reaction takes place at a temperature of at least 950 ° C, at which temperature sodium contained in the effluent is present in evaporated form, in a gaseous phase of 10 16 reaction, wherein said sodium is mainly in the form of sodium oxide.
    [6]
    Method according to one of the preceding claims, characterized in that the borate is added to the waste water stream or to the chemical solution of defibration, at least mainly as sodium metaborate or sodium tetraborate or as hydrate thereof.
    [7]
    Method according to one of the preceding claims, characterized in that the effluent comprises a waste water flow from the fibrous pulp production which is carried out under alkaline conditions.
    [8]
    Method according to claim 7, characterized in that the effluent comprises an effluent stream from impregnation of raw materials in chemimechanical or mechanical pulping, or the effluent comprises a waste water stream of an alkaline peroxide bleaching of fibrous pulp.
    [9]
    Method according to claim 8, characterized in that the effluent comes from the production of mechanical wood pulp or abrasive pulp, pressurized abrasive pulp, refiner pulp or chemical mechanical refiner pulp.
    [10]
    Method according to claim 8 or 9, characterized in that the effluent contains mainly organic compounds which are dissolved in connection with mass production, and sodium, which is bound to these compounds in connection with the impregnation of raw material or alkaline peroxide bleaching or both parts, and which sodium comes from the sodium-bearing chemicals used, such as sodium carbonate, sodium hydroxide or oxidized green liquor or oxidized white liquor.
    [11]
    Method according to any one of the preceding claims, characterized in that the autacoustication is carried out at a temperature of at least 1000 ° C, preferably 1000-1250 ° C and under oxidizing conditions.
    [12]
    Method according to one of the preceding claims, characterized in that the borate-bearing organic effluent is subjected to a combustion treatment in two steps, the actual combustion taking place in the first stage under oxidizing conditions and at a temperature of more than 1000 ° C, after which the combustion gases generated during the combustion are rapidly cooled to a temperature of less than 600 ° C to sublimate the sodium compounds from their gaseous phase directly to their solid phase.
    [13]
    Method according to one of the preceding claims, characterized in that the borate-bearing organic effluent is subjected to combustion in an combustion chamber and the residence time thereof in the combustion chamber is about 0.1-10 s, in particular about 0.5-5 s. .
    [14]
    Method according to any one of the preceding claims, characterized in that the combustion residue comprises ash generated in the combustion of the effluent which is recovered and dissolved or suspended in water to produce aqueous sodium hydroxide.
    [15]
    Method according to any one of the preceding claims, characterized in that - the autacousticization is carried out in a combustion chamber, and - there is an excess of oxygen to prevent reducing conditions from occurring in any part of the combustion chamber.
    [16]
    16. A method according to claim 15, characterized in that the oxygen is fed into the combustion stage as a gas waste comprising oxygen, such as air or oxygen-enriched air.
    [17]
    Method according to one of the preceding claims, characterized in that the proportion of dry matter of the waste water which is subject to autacousticeiing is at least 45% by weight, preferably at least 55% by weight, more preferably at least 60% by weight, and in particular at least 65%.
    [18]
    18. A method according to any one of the preceding claims, characterized in that the borate-bearing waste water concentrate, which is subject to auto-caustic, is dispersed to form droplets. 18
    [19]
    19. A method according to any one of the preceding claims, characterized in that the borate-bearing effluent concentrate, which is led to combustion, is in the form of a dry powder.
    [20]
    Use of a method according to any one of claims 1-19 for the recovery of alkaline sodium compounds, at least in part in the form of sodium hydroxide, which are used in the fibrous pulp production process.
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    FI20095851A|FI124685B|2009-08-18|2009-08-18|A process for the production of sodium hydroxide from a waste stream for the production of pulp|
    PCT/FI2010/050654|WO2011020949A1|2009-08-18|2010-08-18|Method of producing sodium hydroxide from an effluent of fiber pulp production|
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