EP1444395A1 - Process for leaching electrical filter ash from a recovery boiler - Google Patents

Process for leaching electrical filter ash from a recovery boiler

Info

Publication number
EP1444395A1
EP1444395A1 EP02751936A EP02751936A EP1444395A1 EP 1444395 A1 EP1444395 A1 EP 1444395A1 EP 02751936 A EP02751936 A EP 02751936A EP 02751936 A EP02751936 A EP 02751936A EP 1444395 A1 EP1444395 A1 EP 1444395A1
Authority
EP
European Patent Office
Prior art keywords
electrical filter
leaching
filter ash
leaching tank
slurried
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP02751936A
Other languages
German (de)
French (fr)
Other versions
EP1444395B1 (en
Inventor
Martin Wimby
Lars Olausson
Mikael Eriksson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Power AB
Original Assignee
Kvaerner Power AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kvaerner Power AB filed Critical Kvaerner Power AB
Publication of EP1444395A1 publication Critical patent/EP1444395A1/en
Application granted granted Critical
Publication of EP1444395B1 publication Critical patent/EP1444395B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
    • D21C11/063—Treatment of gas streams comprising solid matter, e.g. the ashes resulting from the combustion of black liquor
    • D21C11/066—Separation of solid compounds from these gases; further treatment of recovered products

Definitions

  • the invention relates to a process for leaching electrical filter ash from a recovery boiler in accordance with the preamble of Patent Claim 1.
  • Chlorides are also supplied to the pulp process by way of make-up chemicals and water.
  • the wood also has a content of chloride, even if this content is normally low.
  • Potassium is another non-process element which is principally supplied by way of the wood. Even low contents of the non-process elements such as potassium and chlorides in the flows entering the pulp process contribute to high contents in the pulp process since the process is becoming increasingly closed. Heavy metals are also supplied to some degree.
  • Potassium and chlorides contribute to clogging of the recovery boiler and to corrosion of heating surfaces. High contents of potassium and chlorides in the dust which is separated off from the flue gases from the recovery boiler have a detrimental effect on the efficiency of electrical filters.
  • the electrical filter ash which is separated off from the flue gases from the recovery boiler principally contains Na 2 S0 4 , it also contains, due to the process being closed, the highest concentrations of potassium and chlorides within the pulp mill.
  • One way of decreasing the content of potassium and chloride in the liquor stock in the pulp mill is to separate off part of the electrical filter ash from the chemical cycle in the mill. The separation can take place by the ash being dumped or by the ash being dissolved in water and then conducted to the water purification in the mill. These types of separation result in the heavy metals which are present in the electrical filter ash polluting the effluent.
  • the loss of sodium sulphate which occurs when electrical filter ash is separated off from the chemical cycle must be compensated for by supplying make-up chemicals.
  • SE,C, 504374 discloses a process in which the electrical filter ash is treated in a pressurized filter, in which process filtration and washing of the filter cake, and any possible leaching, take place in one and the same vessel. This process affords a good result as long as the filter can be kept free from clogging. Methods for cleaning the filter, with the cleaning taking place either during operation or in association with occasional interruptions in the filtration process, are required.
  • US,A, 3833462 discloses another process in which leaching takes place at pH 3-6 and 40-80°C, followed by filtration in a filter.
  • a proposed remedial measure was that of using a larger filter; while such a filter should, per se, extend the period of operation, the filter would have to be cleaned sooner or later. It was stated that it was possible to leach out, from the electrical filter ash, a good 89% of the sodium chloride that was present in the ash.
  • SE,A, 9504281 discloses another method which includes cooling.
  • the leaching is to take place at a pH of less than 10 and at a temperature greater than 20°C, typically at 30°C, after which the total quantity of slurried material undergoes cooling down to a temperature of less than 20 °C.
  • This process involves a need for cooling, with an attendant consumption of energy.
  • SE,A, 9603972 also discloses another method for leaching the electrical filter ash in which the latter firstly undergoes a leaching at at least 32°C, preferably in the vicinity of the boiling point of the aqueous solution, and in which a first substance which has crystallized out is returned, after separation, to the black liquor.
  • the leachate which is obtained from the process then also undergoes cooling down to approx. 10-15°C, after which a second substance which has crystallized out is likewise returned to the black liquor. While this system affords good leaching, it demands a high requirement of energy for the cooling even if the cooling is only required for the relatively small quantities constituted by the leachate.
  • the object of the invention is to obtain an improved process for recovering the useful chemicals, principally Na 2 S0 4 , in the electrical filter ash, which process does not suffer from the disadvantages of the prior art. While the improvement is first and foremost aimed at a lower energy consumption, it is also aimed at an improved degree of recovery of these useful chemicals without these chemicals being accompanied by a high proportion of chlorides, in particular, but also potassium. Another object is to obtain a continuous process which does not include filtrations, which filtration processes give rise to clogging problems and the need to regenerate the filter medium. An optimized process, which ensures favourable particle formation, should not require any filtration apparatus.
  • Fig. 1 shows an apparatus set-up which can be used for applying the process according to the invention when leaching electrical filter ash and subsequently separating off the solid phase.
  • Figure 1 shows an apparatus set-up which can be used in accordance with the process according to the invention.
  • Electrical filter ash, and liquid for leaching, and liquid phase which has been returned from a subsequent separation stage, and any chemicals which may be required so as to ensure that a suitable mixture is obtained are supplied to a first leaching tank 1.
  • the liquid for leaching can expediently be fabrication water from the bleaching department or the pulp drying machine, evaporation condensate or scrubber condensate. Water can also be used.
  • H 2 S0 can be supplied when the electrical filter ash contains high contents of Na 2 C0 3 .
  • the amount supplied is typically around 0.1 kg per 1.0 kg of electrical filter ash, i.e. in proportions of approx. 5-15% by weight.
  • the electrical filter ash can typically have a composition corresponding to the following;
  • the ash which is supplied to the leaching tank contains chloride ions and potassium ions.
  • the chloride content in the slurry is 2.0-7.0% by weight.
  • a pH in the interval pH 8-13, preferably 11-12, and consequently a strongly alkaline environment, is established in the leaching tank.
  • the mixture in the leaching tank should not exceed 1600 kg/m 3 , which thus sets an upper limit to the leaching process. If the consistency becomes too high, something which already begins to become apparent at 1570 kg/m 3 , the mixture then becomes increasingly difficult to pump and agitate with the stirrers. In particular, the initial admixing with the electrical filter ash using the first stirrer 11 is rendered more difficult at these concentrations.
  • a suitable lower concentration level corresponds to a mixture at 1450-1550 kg/m 3 .
  • the temperature should be kept within the interval 65-105°C, with a relatively high temperature within the interval 85-105°C being most favourable for the leaching process.
  • An optimum temperature both from the point of view of the process and the point of view of the apparatus is around 95°C.
  • leaching takes place under these process conditions (pH, concentration and temperature) for a relatively long time, within the interval 1-5 hours, preferably 2 hours, and while agitating gently, favourable process conditions are created for crystal growth of, in particular, a solid phase of Na 2 S0. It has been found that the crystals which are formed are distributed normally around a particle size of about 200 ⁇ m, which is a surprisingly good result which should be compared with what can be obtained using the energy-intensive cooling technique, where a crystal formation with particles normally distributed around 300 ⁇ m can be achieved under optimum conditions.
  • the leaching tank is shaped such that repeated gentle agitation is obtained over the whole volume. An initial agitation preferably takes place using a first stirrer 11 in connection with the electrical filter ash being supplied.
  • the mixture passes through at least one additional agitation zone and preferably two agitation zones.
  • This can be achieved by installing at least one double bottom 13 in the middle of the leaching tank.
  • An intermediate-stage stirrer 12a is arranged in an outlet from this double bottom 13, and a final-stage stirrer 12b is arranged in connection with the outlet from the leaching tank.
  • the dwell time in the leaching tank, between agitations, when the mixture is not subjected to direct agitation, should amount to at least 30% of the total dwell time in the leaching tank.
  • the intermediate-stage stirrer consequently acts on the slurried electrical filter ash when the latter has had a dwell time in the region of 30-70% of the total dwell time in the leaching tank, and the slurried electrical filter ash is subjected to a final-stage stirrer in a lower part of the leaching tank in connection with the outlet from the leaching tank.
  • the agitation should be gentle in order to ensure that particles which have already crystallized out are not broken, and a mechanical blade-equipped stirrer of the propeller type can expediently be used, in each respective position, for the intermediate-stage and final-stage stirrers, with both the stirrers being driven by the same shaft, which latter is driven at a moderate rotational speed in the region of 50-200 rpm, preferably around 80 rpm.
  • the slurry which is obtained in this way is pumped onwards, via the pump 4, to a centrifugation stage, in this present case a decanter centrifuge 2, where particles which have been formed, i.e. solid phase containing Na 2 S0 4 , are separated out as a dry fraction.
  • a decanter centrifuge affords a continuous process which does not require to be interrupted for regenerating the equipment (due to clogging, etc.).
  • the decanter centrifuge comprises, in a known manner, a rotating screw body 20, on which a worm 21 has been formed.
  • a casing 22, which also rotates, is arranged around the screw body 20.
  • the slurry is fed into the decanter centrifuge via the inlet 23 and, due to the rotation of the casing 22, the leached liquid is flung against the inside of the casing, where the heavier solid-particle fraction forms the outer layer 28, due to the centrifugal effect, and the liquid fraction forms the inner layer 29.
  • the liquid fraction leaves the decanter centrifuge via the spillway 25, while the screw feeds the solid fraction out towards the outlet 24. Due to the spillway 25 for the liquid fraction being located at a shorter distance from the axis of rotation than the outlet 24, it will be mainly the solid fraction which is transported by the worm 21 towards the outlet 24 via the conformed outlet of the casing.
  • the solid fraction which is obtained in this way, and which chiefly consists of Na 2 S0 4 , is given, by the decanter centrifuge, a dry substance content, in the dry substance fraction, which is in the interval 58-97%, and is then fed to a slurrying vessel 3, where it is admixed with black liquor/BL, for example, for forwarding to recovery, either via evaporation (not shown) or directly to the recovery boiler 18.
  • the solid phase also contains the greater part of the heavy metals present in the electrical filter ash, such as Ba, Pb, Cd, Co and Mn. The heavy metals are returned to the liquor cycle of the pulp process and are separated off in that section of the process which is most favourable.
  • the liquid fraction with its content of chloride ions and potassium ions, can in part be returned to the leaching tank 1 or in part, 26, forwarded to the effluent for external purification or further working- up.
  • a washing zone can be arranged in the decanter centrifuge. This is shown in the figure by means of a distribution ring 27 for washing liquid, which ring opens up radially inwards towards the layer 28 of the solid fraction which is passing by.
  • the washing liquid which is preferably pressurized, can expediently be the condensate (cond.) which is otherwise added to the top of the leaching tank in connection with the initial slurrying of the electrical filter ash.
  • the washing liquid is advantageously added at a position in the decanter centrifuge at which a separating effect is exerted on the liquid even after the position at which the washing liquid is added.
  • the chlorides are bled out via the liquid fraction from the decanter centrifuge, with 0.77 ton of liquid fraction per ton of electrical filter ash being forwarded to effluent or further working-up.
  • the liquid fraction which is separated off from the decanter centrifuge can typically have a content of 7% by weight of chlorides and 3.5% by weight of potassium, with the possibility of these levels building up in a closed process being avoided.

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  • Processing Of Solid Wastes (AREA)
  • Incineration Of Waste (AREA)
  • Electrostatic Separation (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

The invention relates to a process for purifying electrical filter ash from chlorides, in particular, by means of leaching and subsequently separating off crystallized substance, which crystallized substance is returned to the process for forming black liquor. A good separation of solid phase in the form of crystalline Na2S04 is obtained by means of a repeated gentle agitation of slurried electrical filter ash in a leaching tank with a total dwell time of between 1 and 5 hours, directly followed by centrifugation of the leached electrical filter ash. The solid phase is supplied to the black liquor prior to final evaporation and/or recovery in the recovery boiler. More than 70 % of the chloride content in the electrical filter ash and 70 % of the potassium content are efficiently leached out, and an improved utilization of process chemicals is obtained.

Description

PROCESS FOR LEACHING ELECTRICAL FILTER ASH FROM A RECOVERY BOILER
TECHNICAL FIELD
The invention relates to a process for leaching electrical filter ash from a recovery boiler in accordance with the preamble of Patent Claim 1.
STATE OF THE ART
In the present-day pulp mill, it is desired to minimize the discharges and consumption of chemicals.
Several bleaching processes, in particular those which use chlorine dioxide, form chlorides which are either bound in the pulp or which leave together with used fabrication water. While preference is given to closing the process such that the fabrication water is returned, this leads to the contents of chloride in the process being gradually raised to undesirable levels.
Chlorides are also supplied to the pulp process by way of make-up chemicals and water. The wood also has a content of chloride, even if this content is normally low. Potassium is another non-process element which is principally supplied by way of the wood. Even low contents of the non-process elements such as potassium and chlorides in the flows entering the pulp process contribute to high contents in the pulp process since the process is becoming increasingly closed. Heavy metals are also supplied to some degree.
Potassium and chlorides contribute to clogging of the recovery boiler and to corrosion of heating surfaces. High contents of potassium and chlorides in the dust which is separated off from the flue gases from the recovery boiler have a detrimental effect on the efficiency of electrical filters.
While the electrical filter ash which is separated off from the flue gases from the recovery boiler principally contains Na2S04, it also contains, due to the process being closed, the highest concentrations of potassium and chlorides within the pulp mill. One way of decreasing the content of potassium and chloride in the liquor stock in the pulp mill is to separate off part of the electrical filter ash from the chemical cycle in the mill. The separation can take place by the ash being dumped or by the ash being dissolved in water and then conducted to the water purification in the mill. These types of separation result in the heavy metals which are present in the electrical filter ash polluting the effluent. The loss of sodium sulphate which occurs when electrical filter ash is separated off from the chemical cycle must be compensated for by supplying make-up chemicals. Several different types of leaching process exist for recovering Na2S0 from the electrical filter ash which has been separated off by freeing the latter from potassium and chlorides, in particular. The proposed solutions usually involve filters or constituent steps in which all the dissolved or leached electrical filter ash, or parts of this ash, is/are cooled. Other processes for recovering Na2S0 also exist, in which processes the electrical filter ash is firstly dissolved completely and then crystallized by evaporation in a crystallizer, with subsequent separation of solid phase and liquid.
The filtration technique
SE,C, 504374 discloses a process in which the electrical filter ash is treated in a pressurized filter, in which process filtration and washing of the filter cake, and any possible leaching, take place in one and the same vessel. This process affords a good result as long as the filter can be kept free from clogging. Methods for cleaning the filter, with the cleaning taking place either during operation or in association with occasional interruptions in the filtration process, are required.
US,A, 3833462 discloses another process in which leaching takes place at pH 3-6 and 40-80°C, followed by filtration in a filter.
In Tappi Proceedings, Chemical Recovery Conference 1992 in Seattle, pages 329-350, "'Recycle of Bleach Plant Extraction Stage Effluent to the Kraft Liquor Cycle", B. Blackwell and A. Hitzroth present experiences from leaching processes which have been used. A leaching of the electrical filter ash in water at a dry substance concentration of around 15% by weight, and at pH 5, which low pH was pointed out to constitute a substantial corrosion problem, was performed in a Harmac system. The leached liquid was filtered in a filter (belt filter) and this filter exhibited substantial clogging problems due to small particles of organic material which clogged the filter mesh. A proposed remedial measure was that of using a larger filter; while such a filter should, per se, extend the period of operation, the filter would have to be cleaned sooner or later. It was stated that it was possible to leach out, from the electrical filter ash, a good 89% of the sodium chloride that was present in the ash.
The cooling technique
SE,A, 9504281 discloses another method which includes cooling. In this case, the leaching is to take place at a pH of less than 10 and at a temperature greater than 20°C, typically at 30°C, after which the total quantity of slurried material undergoes cooling down to a temperature of less than 20 °C. This process involves a need for cooling, with an attendant consumption of energy.
SE,A, 9603972 also discloses another method for leaching the electrical filter ash in which the latter firstly undergoes a leaching at at least 32°C, preferably in the vicinity of the boiling point of the aqueous solution, and in which a first substance which has crystallized out is returned, after separation, to the black liquor. The leachate which is obtained from the process then also undergoes cooling down to approx. 10-15°C, after which a second substance which has crystallized out is likewise returned to the black liquor. While this system affords good leaching, it demands a high requirement of energy for the cooling even if the cooling is only required for the relatively small quantities constituted by the leachate.
The problem with the known solutions is that they suffer from one or more of the following disadvantages;
- are energy-intensive, resulting in high operational costs;
- require expensive and complicated apparatus/systems;
- involve filters which easily become clogged and render continuous operation more difficult;
- do not afford a sufficiently high degree of bleed-out of chlorides and potassium from the process liquid which is returned, or
- do not afford an equally high degree of recovery of Na2S0 from the electrical filter ash.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to obtain an improved process for recovering the useful chemicals, principally Na2S04, in the electrical filter ash, which process does not suffer from the disadvantages of the prior art. While the improvement is first and foremost aimed at a lower energy consumption, it is also aimed at an improved degree of recovery of these useful chemicals without these chemicals being accompanied by a high proportion of chlorides, in particular, but also potassium. Another object is to obtain a continuous process which does not include filtrations, which filtration processes give rise to clogging problems and the need to regenerate the filter medium. An optimized process, which ensures favourable particle formation, should not require any filtration apparatus.
This object is achieved by means of a process in accordance with the characterizing part of Patent Claim 1.
Other features and aspects and advantages of the invention are evident from the subsequent patent claims and from the detailed description of some embodiments of the invention which follows.
BRIEF DESCRIPTION OF THE FIGURE
Fig. 1 shows an apparatus set-up which can be used for applying the process according to the invention when leaching electrical filter ash and subsequently separating off the solid phase.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Figure 1 shows an apparatus set-up which can be used in accordance with the process according to the invention. Electrical filter ash, and liquid for leaching, and liquid phase which has been returned from a subsequent separation stage, and any chemicals which may be required so as to ensure that a suitable mixture is obtained, are supplied to a first leaching tank 1. The liquid for leaching can expediently be fabrication water from the bleaching department or the pulp drying machine, evaporation condensate or scrubber condensate. Water can also be used. H2S0 can be supplied when the electrical filter ash contains high contents of Na2C03. The amount supplied is typically around 0.1 kg per 1.0 kg of electrical filter ash, i.e. in proportions of approx. 5-15% by weight.
The electrical filter ash can typically have a composition corresponding to the following;
Component % by weight (w%)
Na2S04 86
Na2C03 5
NaCl 2
KC1 7
The ash which is supplied to the leaching tank contains chloride ions and potassium ions. The chloride content in the slurry is 2.0-7.0% by weight.
In order to achieve an optimal leaching process, a pH in the interval pH 8-13, preferably 11-12, and consequently a strongly alkaline environment, is established in the leaching tank.
The mixture in the leaching tank should not exceed 1600 kg/m3, which thus sets an upper limit to the leaching process. If the consistency becomes too high, something which already begins to become apparent at 1570 kg/m3, the mixture then becomes increasingly difficult to pump and agitate with the stirrers. In particular, the initial admixing with the electrical filter ash using the first stirrer 11 is rendered more difficult at these concentrations. A suitable lower concentration level corresponds to a mixture at 1450-1550 kg/m3.
The temperature should be kept within the interval 65-105°C, with a relatively high temperature within the interval 85-105°C being most favourable for the leaching process. An optimum temperature both from the point of view of the process and the point of view of the apparatus is around 95°C.
If leaching takes place under these process conditions (pH, concentration and temperature) for a relatively long time, within the interval 1-5 hours, preferably 2 hours, and while agitating gently, favourable process conditions are created for crystal growth of, in particular, a solid phase of Na2S0. It has been found that the crystals which are formed are distributed normally around a particle size of about 200 μm, which is a surprisingly good result which should be compared with what can be obtained using the energy-intensive cooling technique, where a crystal formation with particles normally distributed around 300 μm can be achieved under optimum conditions. The leaching tank is shaped such that repeated gentle agitation is obtained over the whole volume. An initial agitation preferably takes place using a first stirrer 11 in connection with the electrical filter ash being supplied. After that, the mixture passes through at least one additional agitation zone and preferably two agitation zones. This can be achieved by installing at least one double bottom 13 in the middle of the leaching tank. An intermediate-stage stirrer 12a is arranged in an outlet from this double bottom 13, and a final-stage stirrer 12b is arranged in connection with the outlet from the leaching tank. The dwell time in the leaching tank, between agitations, when the mixture is not subjected to direct agitation, should amount to at least 30% of the total dwell time in the leaching tank. The intermediate-stage stirrer consequently acts on the slurried electrical filter ash when the latter has had a dwell time in the region of 30-70% of the total dwell time in the leaching tank, and the slurried electrical filter ash is subjected to a final-stage stirrer in a lower part of the leaching tank in connection with the outlet from the leaching tank. The agitation should be gentle in order to ensure that particles which have already crystallized out are not broken, and a mechanical blade-equipped stirrer of the propeller type can expediently be used, in each respective position, for the intermediate-stage and final-stage stirrers, with both the stirrers being driven by the same shaft, which latter is driven at a moderate rotational speed in the region of 50-200 rpm, preferably around 80 rpm.
The slurry which is obtained in this way is pumped onwards, via the pump 4, to a centrifugation stage, in this present case a decanter centrifuge 2, where particles which have been formed, i.e. solid phase containing Na2S04, are separated out as a dry fraction. Using a decanter centrifuge affords a continuous process which does not require to be interrupted for regenerating the equipment (due to clogging, etc.). The decanter centrifuge comprises, in a known manner, a rotating screw body 20, on which a worm 21 has been formed. A casing 22, which also rotates, is arranged around the screw body 20. The screw body is imparted a rotation Rl and the casing a parallel rotation R2, with typical rotational speeds being Rl = 3400 rpm and R2 = 3350 rpm; consequently, a somewhat higher rotational speed is imparted to the screw, thereby contributing to the worm 21 of the rotational body slowly feeding the crystallized particles towards the outlet 24.
The slurry is fed into the decanter centrifuge via the inlet 23 and, due to the rotation of the casing 22, the leached liquid is flung against the inside of the casing, where the heavier solid-particle fraction forms the outer layer 28, due to the centrifugal effect, and the liquid fraction forms the inner layer 29. The liquid fraction leaves the decanter centrifuge via the spillway 25, while the screw feeds the solid fraction out towards the outlet 24. Due to the spillway 25 for the liquid fraction being located at a shorter distance from the axis of rotation than the outlet 24, it will be mainly the solid fraction which is transported by the worm 21 towards the outlet 24 via the conformed outlet of the casing. The solid fraction which is obtained in this way, and which chiefly consists of Na2S04, is given, by the decanter centrifuge, a dry substance content, in the dry substance fraction, which is in the interval 58-97%, and is then fed to a slurrying vessel 3, where it is admixed with black liquor/BL, for example, for forwarding to recovery, either via evaporation (not shown) or directly to the recovery boiler 18. The solid phase also contains the greater part of the heavy metals present in the electrical filter ash, such as Ba, Pb, Cd, Co and Mn. The heavy metals are returned to the liquor cycle of the pulp process and are separated off in that section of the process which is most favourable.
The liquid fraction, with its content of chloride ions and potassium ions, can in part be returned to the leaching tank 1 or in part, 26, forwarded to the effluent for external purification or further working- up.
In order to further leach out chlorides from the solid fraction, a washing zone can be arranged in the decanter centrifuge. This is shown in the figure by means of a distribution ring 27 for washing liquid, which ring opens up radially inwards towards the layer 28 of the solid fraction which is passing by. The washing liquid, which is preferably pressurized, can expediently be the condensate (cond.) which is otherwise added to the top of the leaching tank in connection with the initial slurrying of the electrical filter ash. The washing liquid is advantageously added at a position in the decanter centrifuge at which a separating effect is exerted on the liquid even after the position at which the washing liquid is added.
By means of the process according to the invention, success has been achieved in separating chloride and potassium from the electrical filter ash and returning the useful process chemical Na2S0 to the process. In one application, which is based on an electrical filter ash having the following composition;
Component % by weight
CI 8.1
K 4.0
Na 30.4
S04 57.0
C03 0.5
success has been achieved in recovering up to 80% of the Na content in the electrical filter ash and 85% of the S0 content in the electrical filter ash. The chlorides are bled out via the liquid fraction from the decanter centrifuge, with 0.77 ton of liquid fraction per ton of electrical filter ash being forwarded to effluent or further working-up. The liquid fraction which is separated off from the decanter centrifuge can typically have a content of 7% by weight of chlorides and 3.5% by weight of potassium, with the possibility of these levels building up in a closed process being avoided.
By means of the process, it is possible to separate 70% of its chloride and potassium content from the electrical filter ash.

Claims

PATENT CLAIMS
1. Process for purifying recovery boiler electrical filter ash from chlorides and potassium, in particular, by means of leaching and subsequently separating off a solid phase, which solid phase is returned to the pulp process, with the process comprising a first leaching stage, where the electrical filter ash is firstly slurried in a leaching tank at a temperature in the interval 65-105°C, preferably around 95°C, and at a pH in the interval 8-13, preferably pH 11-12, and where the pH can be adjusted by adding H2S04 and suitable process liquid, with a slurried electrical filter ash having a dry substance level in the interval 15-40% by weight being obtained, characterized in that the process comprises the slurried electrical filter ash passing through, and being treated in, the leaching tank in at least two agitation zones, preferably at least three agitation zones, in which agitation zones the slurried electrical filter ash undergoes repeated gentle agitation in the leaching tank at a total dwell time in the leaching tank, between the first and last agitation zone, in the interval 1-5 hours, preferably approx. 2 hours, and in that the slurried electrical filter ash is not subjected, between agitations, to direct agitation under a period of time amounting to at least 30% of the total dwell time in the leaching tank, after which the electrical filter ash, which has thus been leached, is fed to a separation stage in which the leached electrical filter ash undergoes a separation of crystallized substance by means of a centrifugal separation, from which centrifugal separation a fraction of dry substance and a fraction of liquid are obtained, with the resulting dry substance being reintroduced into the liquid cycle or to an additional leaching stage, with subsequent separation of solid phase from the liquid phase, and with part of the liquid fraction being conducted back to the leaching tank and part being conducted away from the process.
2. Process according to Claim 1, characterized in that the centrifugal separation takes place in a decanter centrifuge having the capacity to obtain a dry substance content in the dry substance fraction which amounts to a level in the interval 58-97%.
3. Process according to Claim 1, characterized in that the repeated gentle agitation is obtained by means of the slurried electrical filter ash passing a first initial stirrer, which is arranged in the upper part of the leaching tank and which mixes the electrical filter ash with the liquid which has been supplied, and an intermediate-stage stirrer in a central section of the leaching tank, after the slurried electrical filter ash has had a dwell time in the region of 30-70% of the total dwell time in the leaching tank, and in that the slurried electrical filter ash is subjected to a final- stage stirrer in a lower part of the leaching tank in connection with the outlet from the leaching tank, with the intermediate-stage stirrer and the final-stage stirrer each being a mechanical blade-equipped stirrer of the propeller type which is driven at a moderate rotational speed in the region of 100-200 rpm, preferably about 80 rpm.
4. Process according to Claim 2, characterized in that the decanter centrifuge comprises a washing zone which acts on separated dry substance fraction, with washing liquid being supplied to the layer of solid fraction which has been formed and leaching out additional chlorides and potassium before the solid fraction is fed out from the decanter centrifuge.
5. Process according to Claim 2 or 3, characterized in that the leaching tank is located in a closed circuit which includes, in series, the leaching tank, which receives electrical filter ash, a pump for forwarding to the separation stage, a decanter centrifuge for separating off solid phase, a mixing vessel for mixing solid phase and black liquor, a recovery boiler for combusting the black liquor having a content of solid phase, an electrical filter for separating off electrical filter ash from the flue gases from the recovery boiler, together with separation of the electrical filter ash from the electrical filter for returning it to the leaching tank, and with condensate and H2S04 for the leaching being supplied to this closed circuit for forming the mixture for the leaching, and with waste water, containing potassium and chloride-rich liquid, being bled out from the circuit.
EP02751936A 2001-08-14 2002-07-23 Process for leaching electrical filter ash from a recovery boiler Expired - Lifetime EP1444395B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE0102717 2001-08-14
SE0102717A SE517587C2 (en) 2001-08-14 2001-08-14 Procedure for leaching electric filter ash from a soda boiler
PCT/SE2002/001405 WO2003016616A1 (en) 2001-08-14 2002-07-23 Process for leaching electrical filter ash from a recovery boiler

Publications (2)

Publication Number Publication Date
EP1444395A1 true EP1444395A1 (en) 2004-08-11
EP1444395B1 EP1444395B1 (en) 2010-09-08

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EP02751936A Expired - Lifetime EP1444395B1 (en) 2001-08-14 2002-07-23 Process for leaching electrical filter ash from a recovery boiler

Country Status (5)

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EP (1) EP1444395B1 (en)
AT (1) ATE480662T1 (en)
DE (1) DE60237629D1 (en)
SE (1) SE517587C2 (en)
WO (1) WO2003016616A1 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE529103C2 (en) * 2005-09-21 2007-05-02 Metso Power Ab Procedure for the purification of flue gases and treatment of ash from waste incineration
EP1798297A1 (en) * 2005-12-16 2007-06-20 CTU - Conzepte Technik Umwelt AG Process for the treatment of heavy-metal bearing dust
SE530373C3 (en) * 2006-11-22 2008-06-10 Metso Power Ab Apparatus and method for leaching chloride and potassium from electric filter ash
EP2427598B1 (en) * 2009-05-06 2016-01-06 Valmet Aktiebolag Process for improved leaching of electrostatic precipitator ash from a recovery boiler
US9333468B2 (en) 2012-09-24 2016-05-10 Abengoa Bioenergy New Technologies, Llc Soak vessels and methods for impregnating biomass with liquid
FI129103B (en) 2017-04-28 2021-07-15 Andritz Oy Method for processing fly ash of a recovery boiler

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08170288A (en) * 1994-12-15 1996-07-02 Mitsubishi Heavy Ind Ltd Removal of sodium salt and potassium salt from caught ash of soda-recovering boiler
DE19519626A1 (en) 1995-05-29 1996-12-05 Siemens Ag Manual valve
SE9502583D0 (en) * 1995-07-12 1995-07-12 Eka Chemicals Ab Leaching process
SE9603972D0 (en) * 1996-10-31 1996-10-31 Kvaerner Pulping Tech Process for making ash consisting mainly of sodium sulphate from a soda boiler
SE9901453L (en) 1999-04-23 2000-03-27 Kemira Kemi Ab Way to treat ash

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO03016616A1 *

Also Published As

Publication number Publication date
SE0102717L (en) 2002-06-25
ATE480662T1 (en) 2010-09-15
SE0102717D0 (en) 2001-08-14
EP1444395B1 (en) 2010-09-08
SE517587C2 (en) 2002-06-25
WO2003016616A1 (en) 2003-02-27
DE60237629D1 (en) 2010-10-21

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