• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The present invention relates to a process for treating fly ash containing sodium sulphate in a pulp mill soda recovery boiler. This process comprises at least the following steps: a) dissolving the ash in an aqueous solution and adjusting the pH of the solution with alkali to precipitate impurities, b) filtering the solution to remove the precipitate containing impurities, c) crystallizing the sodium sulfate from the solution and separating the crystals from the solution - and for the production of sulfur-containing chemicals or process chemicals.
    公开号:FI20175380A1
    申请号:FI20175380
    申请日:2017-04-28
    公开日:2018-10-29
    发明作者:Keijo Salmenoja；Niko Metsämuuronen；Marjukka Joutsimo；Ismo Reilama
    申请人:Andritz Oy；
    IPC主号:
    专利说明:

    METHOD FOR HANDLING BOILER ASH ASH
    The present invention is directed to the treatment and purification of pulp mill sodium sulphate containing streams, in particular a recovery boiler such as a recovery boiler, fly ash from an electric filter.
    As a result of the operation of the recovery boiler, some of the inorganic component of the black liquor is removed from the furnace furnace together with the flue gases in a solid form, i.e. fly ash through electric filters. Fly ash consists mainly of sodium sulfate (typically 80-90%), sodium carbonate (typically 5-15%), and sodium 10 and potassium chloride. Normally, the ash in question is returned to the recovery circuit via the recovery tank mixing tank. The amount of ash to be recovered depends on the size of the boiler but is usually about 10% of the dry matter incinerated. In some cases, fly ash from the recovery boiler will have to be removed from the recovery cycle to control the sulfur / sodium (S / Na) balance of the pulp mill or to remove excess potassium (K) and chloride (Cl).
    Traditionally, fly ash removed from the chemical cycle has been dissolved in water or condensate and led to a waste water treatment plant. Due to increasing environmental regulations, it is likely that the ash leaching will be banned at some point and alternative methods of controlling the factory S / Na balance, potassium 20 and chloride will be needed. Fly ash, which is composed of sodium sulphate and sodium carbonate as its main components, is very light, so it is not economically viable to transport it elsewhere.
    The pulp mill's sulfur balance is burdened, especially in softwood mills, by sulfuric acid (H 2 SO 4 ) used for the extraction of tall oil, which puts an excess of sulfur up to 5.0 per 25 kg of pulp produced (ADt). This excess sulfur is typically removed by removing some of the fly ash from the recovery boiler chemical cycle. The problem with this process is that it also eliminates a valuable cooking chemical, i.e. sodium (Na), which must be replaced by adding sodium hydroxide (NaOH) to the chemical cycle of the pulp mill.
    Another component of the pulp mill's sulfur balance is the acid salt, known as sodium sulphate (Na 2 SO 4 ), from the chlorine dioxide plant. sodium sesquisulfate, Na 3 H (SO 4 ) 2 , which is usually returned to the black liquor evaporator and through it to the chemical cycle or used for bleaching in pH adjustment, or
    20175380 prh 28 -04- 2017 dissolved in waste water. In total, these sulphate-containing salts are generated in the mill at about 50-60 tonnes per day, or about 30-40 kg / ADt. Sesquisulfate is composed of approx. 1.5 kg each produced klooridioksidikiloa (ClO 2). At some plants, sesquisulfate from the chlorine dioxide plant is leached and diverted to waste water treatment, whereby it does not burden the plant's S / Na balance, but on the other hand increases the plant's effluent emissions. The acid salt of a chlorine dioxide plant is usually neutralized and is also called waste salt or waste acid
    It is an object of the present invention to reduce or completely eliminate the discharge of sodium sulphate containing material streams into mill effluents or other waste streams 10 and to provide a new method for treating them. In particular, the invention relates to the treatment of fly ash from a chemical recovery boiler which has to be removed from the chemical cycle. It is also intended to improve the utilization of the acid salt of the chlorine dioxide plant.
    In the new process, Glauber's salt (sodium sulfate decahydrate, Na 2 SO 4 * 10H 2 O) or anhydrous sodium sulfate is produced from sodium ash (Na 2 SO 4 ) containing ash. These can either be used internally at the plant or commercially and sold off-site, thereby significantly reducing or even eliminating the need for ash extraction and waste streams.
    In the new process, the fly ash of the recovery boiler 20 containing sodium sulphate from a pulp mill is purified. The method comprises at least the following steps:
    (a) dissolving the ash in an aqueous solution and adjusting the pH of the solution with alkali to precipitate impurities,
    (b) filtering the solution to remove any precipitate containing impurities;
    c) crystallizing the sodium sulfate from the solution and separating the crystals from the solution by filtration or centrifugation; and
    (d) the crystallized sodium sulphate is used as a starting material for the production of sodium and sulfur chemicals or as process chemicals.
    The ash is dissolved in an aqueous solution, preferably either deionized water (demi-water) or pure condensate, at a temperature of between 32 and 100 Ό, preferably above 32 to 30 Ό, most preferably between 35 and 50 O.. The pH of the solution is adjusted to a level above 11, preferably above 12, to precipitate inorganic impurities such as magnesium in the ash of the recovery boiler. For adjusting the pH, alkali, typically sodium hydroxide, is used
    20175380 prh 28 -04- 2017 roxidia. The water-fly ash mixture is stirred at a constant temperature above 32 Ό and stirred until the salt has dissolved until uniform. The resulting solution is filtered to remove the precipitate containing impurities and crystallized. The crystallization can be done either by cooling crystallization or by evaporation crystallization.
    The solution which is filtered by cooling crystallization is cooled to below 32.4 Ό, preferably to 10-15 Ό, with stirring, whereby Glauber salt crystals (Na2SO4 * 10H2O) are formed during cooling crystallization at temperatures below 32.4. The crystals formed after crystallization are separated from the mother water either by filtration or by centrifugation.
    Chloride and potassium have a higher solubility in water than the other components and are enriched in the liquid phase which can be removed from the process.
    By evaporation crystallization, the filtered solution is concentrated by evaporation with stirring to give sodium sulfate crystals. Evaporation crystallization affords pure, anhydrous, sodium sulfate. The crystals formed after crystallization are separated from the mother water either by filtration or by centrifugation. In evaporation crystallization, the temperature is preferably above 70 Ό, whereby potassium and chloride remain in the mother water.
    Separated sodium sulfate or Glauber salt can be used as a starting material for the electrodialysis process to produce sodium and sulfur chemicals such as sodium hydroxide and sulfuric acid. For this purpose, the crystals are dissolved in a pure aqueous fraction, such as pure secondary condensate from the evaporator or demineralized water.
    If the Glauber salt is used at the factory as a starting salt of an electrolysis or electrodialysis plant (ED), then a fly ash feedstock is required after leaching the crystals, preferably an ion exchange column, to keep the feed solution calcium below 1 ppm. Calcium can also be separated by lowering the pH of the crystal solution during crystal leaching.
    In addition, the crystals fed to the electrodialysis apparatus must be carbonate-free since the cells used in the electrodialysis apparatus are broken in acidic conditions by the release of carbon dioxide (CO 2 ). The ash may contain 5-15% sodium carbonate. From the Glauber salt crystals, the carbonate can be removed with a suitable acid by adjusting the pH of the Glauber salt aqueous solution to less than 6, preferably
    Preferably, the acid used is an acid salt of a ClO2 plant, which does not require pre-purification and typically contains about 26% sulfuric acid. Alternatively, other acids such as sulfuric acid may be used, but this will increase the use of fresh acid in the factory. The acid can be fed directly into the crystal mixing tank, whereby the pH is lowered and can be adjusted. Calcium precipitates and can be removed as a precipitate. At the same time, the carbonate is released as carbon dioxide, the separation of which can be improved by effective mixing or by introducing air into the solution.
    When calcium is separated in solution with crystals, the ion exchange unit can typically be bypassed, however, the ion exchange unit is a necessary process device because it may be needed as a clarifier.
    The potassium (K) and chloride (Cl) in the ash can be removed with post-crystallization filtration or centrifugation effluent, mother water, without the need for a separate potassium or chloride removal plant.
    In the new process, the ash is removed from the chemical recovery cycle and its sodium sulfate is not returned to the recovery boiler. The ash is typically treated for the amount of ash that has to be removed from the chemical cycle and dumped into the wastewater from the mill. This amount can be tens of tons per day. As a result of this new process, the introduction of sodium sulfate into the plant waste streams can be substantially reduced or even stopped.
    The end product of the crystallization is Glauber salt of the Pro Analysis (PA) grade.
    Sodium sulfate from evaporation crystallization or cooling crystallization can also be used as a starting material or as a process chemical in the pulp mill where it is produced or alternatively outside the mill, in addition to electrolysis.
    The invention will be described in more detail with reference to the accompanying Figure 1, which is a schematic representation of a preferred embodiment for implementing the new process.
    The fly ash from the recovery boiler is introduced through line 1 into vessel 2 where the ash solvent is dissolved in aqueous solution from line 3. The aqueous solution is typically either deionized water (demi-water) or pure condensate. The leaching is carried out at a temperature between 32-100 Ό, preferably between 35-50 Ό, with the aim of producing a saturated or nearly
    20175380 prh 28 -04- 2017 Saturated solution. The pH of the solution is adjusted to a level of about 12 to 13 with a base such as sodium hydroxide to precipitate impurities, mainly magnesium (Mg). The base is added through line 4 to the ash leaching vessel 2.
    The water-fly ash mixture is stirred at a constant temperature above 32 Ό and stirred until the sodium sulfate is dissolved until uniform. The solution is filtered, for example, in a cross-flow filter 5, whereby the magnesium-containing precipitate differs from the sodium sulphate-containing solution. The precipitate is taken along line 6 to a mixing tank at the recovery boiler plant where the recycled ash from the recovery boiler is dissolved in liquor.
    The filtered solution is passed through line 7 to a cooling crystallization vessel 8 where the sodium sulfate is crystallized by cooling crystallization in a manner known per se. Cooling crystallization produces Glauber's salt crystals (Na2SO4 * 10H2O) at temperatures below 32.4 O. Glauber's salt crystals (sodium sulfate decahydrate) are separated from the mother liquor of line 19 by a centrifuge 9. The final product obtained by cooling crystallization is
    Pro Analysis (PA) grade Glauber salt. The crystallization can also be carried out by evaporation crystallization to give pure anhydrous sodium sulfate.
    The potassium and chloride in the ash can be removed with the effluent from the centrifuge, mother water, without the need for a separate potassium or chloride removal plant. The effluent from line 22 is thickened in a clarifier 10, on the basis of which the potassium and chloride-containing solution is led through line 11 out of the mill's chemical cycle.
    Sodium sulfate crystals can be used in the electrode dialysis as a starting material at the factory. The crystals are led from the centrifuge 9 via line 23 to the next process step where they are preferably dissolved in deionized water or pure condensate in mixing tank 12. The water or condensate is introduced through line 18. When fly ash is used as a raw material, after leaching of the crystals, a calcium removal unit, preferably an ion exchange column 15, is typically required to bring the calcium content of the feed solution to a sufficiently low level, preferably below 1 ppm. The aqueous solution of the crystals 30 is led along line 13 to an ion exchange column 15, from which the separated calcium is led through line 16 to the ash mixing tank (not shown) of the recovery boiler.
    20175380 prh 28 -04- 2017
    In addition, the crystals fed to the electrodialysis equipment must be carbonate-free since the cells used in the electrodialysis equipment are broken in acidic conditions by carbon dioxide (CO 2 ) released from the carbonate. From the glauber salt crystals, the carbonate can be removed with a suitable acid by adjusting the Glauber5 salt to an aqueous solution pH below 6, most preferably to a level below 4. Most preferably, the waste acid from the chlorine dioxide plant is introduced along line 20. Other acids, such as sulfuric acid, can also be used, but it increases the consumption of fresh acid at the factory. When the pH is lowered, calcium also precipitates and can be removed as a precipitate from the bottom of the crystal mixing tank 12. This calcium deposit is led along line 21 to the ash mixing tank of the recovery boiler. In particular, since the starting salt of the electrodialysis plant must be carbonate-free, the solution may be effectively mixed or air may be introduced into the solution to release carbon dioxide from the solution. However, when calcium is leached during crystal leaching in the mixing tank 12, the ion exchange unit 15 can typically be bypassed through line 14, however, the ion exchange unit 15 15 is a necessary process device as it may be required as a clarifier.
    The solution containing the Glauber salt is passed to an electrolysis or electrodialysis plant (ED) 17 where it is used as a starting salt for the production of sodium and sulfur chemicals for in-house or off-site use, e.g. fertilizers, 20 detergents, textile dyeing and glass industry needs.
    The operation of the electrodialysis apparatus is based on the potential difference between the cathode and the anode and the resulting ion movement through the ion exchange membranes. When there is an electric field between the cathode and the anode, the ions move on the basis of their electric charge, that is, the positively charged ions (cations) migrate to the cathode and the reciprocally negatively charged ions (anions) migrate to the anode.
    The electrode dialysis unit uses two different membranes / membranes, cationic and anionic membranes. Only positively charged ions (cations) and reciprocally negatively charged anions pass through the cation membrane. The cell of the electrodialysis apparatus consists of a series of ion-exchange coils (cation-anion membranes).
    The novel process of the invention provides the following advantages:
    - Sodium sulphate-containing ash no longer needs to be fed to the mill's waste streams, but can be used to produce chemicals for in-house or off-site use or to use sodium sulphate as a process chemical per se;
    - the waste acid from the chlorine dioxide plant can be re-used and thus further reduce the waste stream from the mill.
    权利要求:
    Claims (12)
    [1]
    Claims:
    A method for treating fly ash containing sodium sulphate in a pulp mill soda recovery boiler, comprising at least the following steps:
    (a) dissolving the ash in an aqueous solution and adjusting the pH of the solution with alkali to precipitate impurities,
    (b) filtering the solution to remove any precipitate containing impurities;
    c) crystallizing the sodium sulfate from the solution and separating the crystals from the solution by filtration or centrifugation; and
    (d) the crystallized sodium sulphate is used as a starting material for the production of sodium and sulfur chemicals or as process chemicals.
    [2]
    Process according to claim 1, characterized in that the pH of the solution is adjusted with an alkali to remove magnesium to a level above 12 in step a).
    [3]
    Process according to Claim 1 or 2, characterized in that the sodium sulfate is separated by cooling crystallization or evaporation crystallization.
    20175380 prh 28 -04- 2017
    [4]
    Process according to one of Claims 1 to 3, characterized in that the ash is dissolved in step a) at a temperature of 32 to 100 Ό, preferably 35 to 50 O..
    [5]
    Process according to claims 1-4, characterized in that the process further comprises the step e) of removing calcium from the sodium sulfate crystals,
    20 c).
    [6]
    Process according to claim 5, characterized in that the sodium sulfate crystals are dissolved in an aqueous solution and the pH of the solution is lowered with an acid, whereby calcium precipitates.
    [7]
    Process according to Claim 6, characterized in that the acid used is an acid salt of a chlorine dioxide plant.
    [8]
    Process according to Claim 5, characterized in that the calcium is removed by an ion exchange column.
    [9]
    Process according to one of Claims 1 to 8, characterized in that the process further comprises the step f) of removing the carbonate from the sodium sulfate crystals.
    30 after step c).
    [10]
    Process according to one of the preceding claims, characterized in that the sodium sulfate in step d) is in the form of the sodium sulfate decahydrate (Glauber salt) or anhydrous sodium sulfate.
    [11]
    A process according to any one of the preceding claims, characterized in that the separated sodium sulfate or Glauber salt is used as a starting material for the electrodialysis or electrolysis process to produce sodium and sulfur chemicals.
    [12]
    Process according to one of the preceding claims, characterized in that the separated sodium sulfate is used inside or outside the pulp mill.
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    同族专利:
    公开号 | 公开日
    CL2019002952A1|2020-03-13|
    CA3057573A1|2018-11-01|
    FI129103B|2021-07-15|
    SE1951194A2|2020-05-12|
    US20200181841A1|2020-06-11|
    WO2018197753A1|2018-11-01|
    SE1951194A1|2018-10-29|
    引用文献:
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    SU996582A1|1981-09-28|1983-02-15|Всесоюзное научно-производственное объединение целлюлозно-бумажной промышленности|Method of reconditioning spent liquor of sulphate pulp production|
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    CN112174375A|2020-09-28|2021-01-05|北京石油化工学院|Method for extracting sodium sulfate from phenol-containing wastewater|
    CN112792099A|2020-12-29|2021-05-14|江苏智诚达环保科技有限公司|Method for removing pollutants in fly ash and recycling pollutants|
    法律状态:
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    优先权:
    申请号 | 申请日 | 专利标题
    FI20175380A|FI129103B|2017-04-28|2017-04-28|Method for processing fly ash of a recovery boiler|FI20175380A| FI129103B|2017-04-28|2017-04-28|Method for processing fly ash of a recovery boiler|
    SE1951194A| SE1951194A2|2017-04-28|2018-04-26|Method of treating fly ash of a recovery boiler|
    US16/609,006| US20200181841A1|2017-04-28|2018-04-26|Method of treating fly ash of a recovery boiler|
    CA3057573A| CA3057573A1|2017-04-28|2018-04-26|Method of treating fly ash of a recovery boiler|
    PCT/FI2018/050302| WO2018197753A1|2017-04-28|2018-04-26|Method of treating fly ash of a recovery boiler|
    CL2019002952A| CL2019002952A1|2017-04-28|2019-10-16|Method for treating fly ash from a recovery boiler.|
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