Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
  • D21D5/18—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force
  • D21D5/24—Purification of the pulp suspension by mechanical means; Apparatus therefor with the aid of centrifugal force in cyclones
• • 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
  • D21C7/00—Digesters
  • D21C7/06—Feeding devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
  • B04C—APPARATUS USING FREE VORTEX FLOW, e.g. CYCLONES
  • B04C5/00—Apparatus in which the axial direction of the vortex is reversed
  • B04C5/24—Multiple arrangement thereof
• • 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
  • D21C11/0007—Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for

Definitions

• the present invention relates to a problem caused by separating and removing harmful material in the fiber line of a chemical pulp mill during production of chemical pulp, for the reason that if this material is not removed, it can cause disturbances in the process and damage the equipment.
• Comminuted cellulosic fiber material treated in a conventional pulp production process e.g. wood chips, typically contain non-cellulosic harmful material, such as sand, dirt, stones, different pieces of metal (e.g. nails, pieces of metal wire or bolts and nuts), chips of metal or other heavy cellulosic materials (e.g. knots) or non-cellulosic materials.
• the density of this harmful material is typically at least 10% higher than the density of the cellulosic material being treated (e.g. at lest 50% higher).
• a very great part of this material can be re- moved during chips production, but part of the material will anyway be passed into the digester feed system and an optional impregnation vessel and to the digester itself.
• this material is separated from the chips in the feed system by means of some separator. This kind of separator is described in US patent 6,315,128. Harmful material, such as sand, can also be removed from a liquid stream, such as from liquids used in pulp production, cooking and washing liquors.
• a conventional sand separator removes sand and other particles from the cooking solution that is circulated via a chips conveyor arrangement at the digester plant.
• US-patent 4,280,902 describes a cyclone-type separating device for removing undesirable materials, especially sand and corresponding, from the liquid stream of the feed system.
• a sand separator typically comprises a tangential inlet into a cylindrical container. Sand and other heavy particles swirl downwards in the container into a separating hopper, through which the sand and the particles travel into a collecting vessel. An outlet for the cleaned solution is located in the upper part of the cylindrical chamber.
• the digester feed system typically the return circulation
• An object of the present invention is to further intensify and improve the functioning of the feed systems for cooking processes. Especially the object of the invention is to improve the removal of non-desired material, specifically sand, from the digester feed systems.
• An object of the invention is also to provide an arrangement that can be used for removing non-desired material consisting of small particles also in a post-digester pulping stage, such as from low-consistency fiber suspension in screening.
• An object of the present invention is especially to provide a method and an arrangement capable of separating also the finest sand particles from the return cir- culation in the digester feed system more efficiently than before. It is just the finest sand particles that cause wearing of the arrangement. If they cannot be separated from the circulation they can accumulate in the process, which disturbs the process and deteriorates the functioning capability of the apparatuses.
• the present invention relates to an arrangement for separating harmful material, especially sand, from a liquid stream or from low- consistency fiber suspension in a chemical pulping process, said arrangement comprising a cyclone-type separator comprising a vertical chamber, the upper part of which is provided with a tangential inlet for generating a swirling motion for a stream being cleaned and an accept outlet, and a conical lower part, the bottom of which is provided with a reject outlet.
• the invention is characterized in that the arrangement comprises two or more cyclone-type separators that are connected in parallel, whereby their inlets open into at least one feed channel having at least one inlet, and their accept outlets open into a common discharge channel having at least one out- let, and their reject outlets open into a common discharge channel having at least one outlet that is connected to at least one auxiliary separator having conduits for discharge of accept and reject.
• the arrangement according to the invention is provided with successively ar- ranged first step having two or more separators and second step having typically one separator that typically is of cyclone-type.
• the accept is a cleaned fluid or suspension and the reject is a fraction into which harmful material accumulates in the separation.
• Fiber suspension at low consistency is a fiber suspension produced in a digester and having a consistency of less than 1.5%, typically 1.2-1.5%.
• Knot separation in a screen room of a fiber line at a chemical pulp mill comprises knot washing, after which sand is separated from this fiber suspension flow. Sand is removed from the reject of fine screening of the screen room before washing of the reject.
• the present invention can be applied in connection with these sand separations.
• the cyclone-type separators are arranged in a common housing so that the accept discharge channel, the feed channel and the reject discharge channel are located vertically one upon the other.
• a space is provided between the feed channel and the reject channel, which space communicates with the reject discharge channel so that the pressure in said space is the same as the pressure in the reject channel.
• the arrangement comprises two feed circuits and two accept circuits.
• the feed channel is divided by means of an intermediate wall into at least two compartments having separate inlets
• the accept discharge channel is divided by means of an intermediate wall into at least two channels having separate outlets.
• This embodiment is preferable in a screen room downstream of a digester, whereby one compartment preferably treats a fiber suspension from knot washing and the other compartment treats reject from fine screening.
• these sand separations can be performed in one apparatus.
• the accept flows are led to different treatment stages in a way known per se.
• a dilution liquid conduit is provided in the reject discharge channel of the arrangement for diluting the fraction being fed into the auxiliary separator.
• the dilution liquid is a stream to be cleaned. If the consistency of the reject becomes excessive, dilution ensures an optimal separation in the auxiliary separator, which can also be called as a second step. Dilution regulates the counter-pressure, whereby a pressure balance is achieved in the first step.
• the feed channel of the stream being cleaned is provided with a pressure measuring device for regulating the feed pressure by means of a valve located in the feed piping connected to the inlet of the feed channel.
• a pressure difference meas- urement is arranged in connection with the feed channel for the stream being cleaned and the accept discharge channel for regulating the exiting accept stream by means of the measured pressure difference
• a pressure difference measurement is arranged in connection with the reject discharge channel and the accept discharge channel of the auxiliary separator for regulating the exiting accept stream by means of the measured pressure difference
• the feed piping for the stream being cleaned is connected to the reject discharge channel for leading the stream being cleaned as dilution liquid for diluting the reject being led to the auxiliary sepa- rator, whereby the dilution liquid stream is provided with a pressure measuring device for regulating the feed pressure of the dilution liquid by means of a valve.
• a pressure difference measurement is arranged in connection with the feed channel for the stream being cleaned and the accept discharge channel for regulating the exiting accept stream by means of the measured pressure difference
• the feed piping for the steam being cleaned is connected to the reject discharge channel for introducing dilution liquid and for diluting the reject to be led into the auxiliary separator, whereby a pressure difference measurement is arranged in connection with the dilution liquid line and the accept discharge channel of the auxiliary separator for regulating the exiting accept stream by means of the measured pressure difference.
• the arrangement is provided in a side stream separated from the return circulation of the digester feed system at a chemical pulp mill for separating harmful material, such as sand.
• the arrangement is provided in a screen room of a chemical pulp mill for separating harmful material, such as sand.
• the present invention also relates to a method for separating harmful material, such as sand, from a liquid stream in a feed system for cellulose-containing fiber material into a high pressure treatment vessel in a production process of chemical pulp, in the practice of which method
• the method is characterized in that
• the removed liquor is divided into at least a first and a second liquor stream
• - harmful material is removed from the second liquor stream by exposing the stream to centrifugal force in an arrangement comprising two or more cyclone-type separators connected in parallel and arranged in a common housing, in which the second liquor stream is divided into a cleaned liquor stream and a first reject that is led into auxiliary separation for obtaining a second cleaned liquor stream and a second reject, and
• the cleaned second liquor stream is fed into the low pressure fiber material stream upstream of the transfer device.
• the cleaned liquor streams are combined are the combined stream is fed into the low pressure fiber material stream upstream of the transfer device.
• the cleaned liq- uor stream is fed into the low pressure fiber material stream by means of pressure energy contained in the liquor stream.
• the pressure of the return line discharged from the high-pressure vessel is utilized in this, so that the side line does not require separate pumps for conveying the stream, either.
• a pressure-increasing device such as a pump
• the fiber material led into the high-pressure treatment vessel is typically chips.
• the second stream is smaller than the first stream, because the first mentioned is a side stream of the return line of the digester feed system.
• the second stream comprises less than 30% of the volume flow of the first stream (e.g. liter/sec.)
• the feed of the second stream being led into separation of harmful material, such as sand is controlled by regulating the pressure thereof.
• the cleaned stream is con- trolled by means of pressure difference between the feed pressure of the second stream and the pressure of the cleaned stream.
• the second cleaned liquor stream exiting the auxiliary separator is controlled by means of pressure difference between the first reject stream and the second cleaned liquor stream.
• the first reject stream being led into the auxiliary separator is diluted.
• Fig. 1 illustrates a solution according to prior art.
• FIG. 2 illustrates a preferred process application according to the invention
• Fig. 3 illustrates a preferred arrangement according to the invention
• Fig. 4 illustrates a detail of the arrangement along line A-A in Fig. 1 ,
• Fig. 5 illustrates a side view of an individual separator according to the invention.
• Fig. 6 illustrates a preferred arrangement according to the invention.
• Fig. 7 illustrates a preferred arrangement according to the invention
• Fig. 8 illustrates schematically a principle for adjusting the arrangement according to the present invention.
• Fig. 9 illustrates schematically a principle for adjusting the arrangement according to the present invention.
• Fig. 10 illustrates schematically a principle for adjusting the arrangement accord- ing to the present invention
• Fig. 11 illustrates the sand-separation capacity of the separators.
• Fig. 1 illustrates a prior art recirculation loop connected to digester or an impregnation vessel, which is known from e.g. Fl-patent application 20010851.
• chips are transferred by means of at least one, preferably two high-pressure suspension pumps 251 , 251' for conveying the chips to the inlet of the digester 11 instead of a high-pressure feeder.
• the chips are introduced to a steaming vessel 221.
• the steaming vessel 221 is preferably a DIAMONDBACK®-steaming vessel described in US-patent 5,000,083, which receives steam through one or more conduits 22.
• the steamed chips leave the vessel 221 into a metering device 223, which may a pocketed rotor or a screw-type device.
• the discharge from the metering device 223 can take place directly into a conduit or chute 226.
• a pressure-isolator such as a pocketed rotor- type isolator device can be arranged between the metering device 223 and the chute 226, which isolating device is presented in dotted line at 224, for instance a conventional low-pressure feeder.
• Cooking liquor is added into the chute 226 (see line 226' in Fig. 1) so that an observable level of chips and liquor suspension is formed (not shown).
• the suspension is discharged from the chute 226 via a curved outlet 250 to the inlet of the pump 251.
• the suspension going to the inlet of the pump 251 is augmented with liquor coming from a liquor tank 253 through conduit 254.
• the pressurized, typically heated suspension is discharged from the pump 251' to conduit 234.
• the conduit 234 conveys the suspension into the inlet of a continuous digester 11. Excess liquor is removed from the suspension in a conventional way via a screen 12. This excess liquor is returned to the feed system 210 via a conduit 235, preferably into the liquor tank 253 to be used for slurrying in a conduit 250 through conduit 254. If desired, the liquor in conduit 235 can be conveyed through a sand separator 237. Said sand separator 237 can be designed for pressurized or non-pressurized use according to the desired operational mode.
• the opening of the valve 58 is controlled so that a predetermined, lowered pressure prevails in conduit 235 downstream of the valve 58.
• the liquor tank 253 can be designed so that it operates as a "flashing tank” so that the hot pres- surized liquor in conduit 235 is quickly evaporated to be used as steam source for the vessel 253.
• This steam can be used e.g. in vessel 221 via conduit 60.
• the pressurized liquor in conduit 235 is used for augmenting the flow exiting from pump 251', through conduit 61 and pump 62 or for augmenting the flow between pumps 251 and 251' in conduit 252 through conduit 63, using or not using pump 64.
• Figure 1 illustrates a one-way (check) valve 65 located in conduit 234, which prevents pressurized flow from returning to pump 251 or 251'.
• conventional automatic (e.g. solenoid operated) isolation valves 66 and 67 are located in conduits 234 and 235, respectively, to isolate the pressurized conduits 234, 235 from the rest of the feed system 210.
• a conventional pressure switch 68 is located downstream of pump 251' in conduit 234. The switch 68 is used to monitor the pressure in line 234 so that should the pressure deviate from a predetermined value, the conventional controller 69 will auto- matically isolate digester 11 from feed system 210 by automatically closing valves 66 and 67.
• an object of the present invention is to further improve the operational functionality of cooking processes, especially removal of harmful material, such as sand, from the digester feed system.
• Figure 2 illustrates a separation of harmful material, such as sand, according to the invention applied in a digester feed system of Figure 1.
• harmful material such as sand
• FIG. 2 illustrates a separation of harmful material, such as sand, according to the invention applied in a digester feed system of Figure 1.
• a side stream 236 is separated from the digester return line 235 to the digester feed system.
• the return line 235 is in con- nection with the present invention the main return line and the side line 236 a side return line.
• the pressure of return line 235 is utilized, which typically is approximately 10.4 - 27.6 bar, so that no separate pumps are needed in the side line for conveying the stream.
• the separation of side streams from a main stream requires a pressure-increasing device, such as a pump, in the side stream, because the pressure in the main stream is not adequate for conveying the side stream.
• the side stream feed pressure is typically approximately 4-6 bar.
• the side line 236 is provided with sand separation equipment 260 according to the invention for removing sand and corresponding particles from the return circulation. This allows removing also the finest fraction that otherwise would be accumulated in the digester feed system and would cause most wearing of e.g. the pumps 251-251 " used for transferring chips, thus impairing their working characteristic.
• the main return line typically receives a white liquor feed via conduit 269.
• the liquid in the main return line 235 is conveyed through heat exchanger 268 for heating the liquid in said line or for cooling prior to feeding it into chute 226. This may be desirable when the liquor in this line is at a temperature that exceeds the flash- ing temperature corresponding to the pressure in conduit 226, so that the flashing in conduit 226 can be minimized.
• the liquid is led via the liquor tank into conduit 226 for slurrying the chip suspension.
• Steam is introduced into the steam vessel 221 via conduit 265.
• the liquor cleaned in the sand separation arrangement can be directed to various points of the feed system as required to the suction side of the pumping arrangement 251-251" (or the high pressure feeder). These are marked with x, in an exemplary way.
• the cleaned liquor is typically directed to steam vessel 221 via conduit 264 or to conduit 226 for slurrying the chip suspension together with other fractions being introduced to the feed system from conduits 263, 266 or conduits 261 , 267.
• the flow from black liquor fiber filter is introduced in conduit 267.
• Some of the cleaned liquor in conduit 236 can also be directed to the main return channel via conduits 262, 270.
• the sand separation system is preferably used in connection with a continuous digester 11 , it can also be used in connection with other vertical pressurized (with a pressure of typically at least approximately 10 bar overpressure) treatment vessels, such as in connection with an impregnation vessel.
• Figs. 3, 4 and 5 illustrate a sand separation arrangement according to the invention in more detail.
• the arrangement 300 comprises a number of cyclone-type separators 30 that are connected parallel with respect to the substance to be cleaned.
• An individual separator is illustrated in close view in Fig. 5.
• An individual separator 301 comprises a vertical chamber 302, the upper end 303, i.e. the feed end, of which is provided with a tangential inlet 304 for generating a swirling motion for the stream to be cleaned.
• the upper part 303 of the chamber is also provided with a discharge pipe 305 for cleaned liquid, i.e. accept, which pipe is positioned concentrically with the vertical central axis of the chamber.
• the bottom of the conical lower part 306, i.e. reject part, 307 is provided with an outlet 308 for frac- tion containing sand and corresponding particles, i.e. reject.
• the arrangement 300 comprises two or more cyclone-type separators 301 connected in parallel.
• the tangential inlets 304 for the liquid to the cleaned located in the upper part 303 of the chambers open into a common feed channel 309.
• the feed channel 309 is provided with an inlet 310, through which the liquid being cleaned in the separators is led into the arrangement.
• the feed channel 309 surrounds the upper part 303 of the vertical chambers.
• the end of the accept pipes 305 located outside the chamber are provided with ac- cept outlets 311 that open into a common accept discharge channel 312. It is located in the vertical direction above the chambers 302 and provided with at least one outlet 313 for discharging the accept, i.e. the liquid or fiber suspension cleaned in the separators, out of the arrangement 300.
• the reject outlets 308 of the chambers open into a common reject discharge channel 314 located essentially below the vertical chambers. This discharge channel 314 is provided with at least one outlet, through which the reject is removed.
• the discharge channel is operationally connected to at least one cyclone-type auxiliary separator 316 for further treatment of the reject.
• the reject outlet is connected to the inlet 315 of the auxiliary separator.
• the auxiliary separator 316 has a conduit 319 for discharging accept and a conduit 318 for discharging reject.
• the in-series connected cyclone-type separators 301 are located in a common housing 320 so that the accept discharge channel 312, the feed channel 309 and the reject discharge channel 314 are located in the vertical direction one above the other. Between the feed channel 309 and the reject channel 314 a space 321 is formed that surrounds the conical lower parts 306 of the separators.
• the intermediate space 321 is in connection with the reject discharge channel via an opening 322 surrounding the reject end 307 of the cone, so that the pressure in the intermediate space 321 is the same as the pressure in the reject discharge channel 314. Thus, reject pressure prevails also outside the conical part 306. Locating the separators 301 in a common pressure vessel 320 improves the safety and performance of the arrangement 300.
• the auxiliary separator 316 is preferably located in the same housing 320. Should the conical part 306 of an individual separator wear out and be broken, the operational capacity of the arrangement would not be essentially decreased, and no emergency situation would occur, because the other separators would be operating and the liquid stream being discharged from the broken separator would remain inside the pressure vessel and enter the intermediate space 321 and the reject discharge space 314.
• the return circulation of the digester feed system typically has one cyclone-type separator with a relative large diameter (e.g. 800 mm). It has to have an adequately high capacity to continuously treat the whole return circulation stream. Due to adequate size also wearing and thus damaging is decreased. However, due to the large size the separation ca- pacify of the apparatus is weaker and it may result in accumulation of harmful sand and corresponding material in form of fine particles in the digester feed system due to the return circulation.
• Fig. 4 illustrates a cross section A-A of the arrangement of Figure 3, i.e. separators 301 seen from the above at the feed channel.
• the separators are preferably located staggered, but other positioning with respect to each other is also possible.
• the liquid being cleaned flows in the feed channel 309 and is passed, as shown by arrows 323, into the tangential inlets 304 of the separators for generating a swirling stream in the chambers of the separators.
• a discharge pipe 305 for the cleaned liquid, i.e. accept, is located in the center part of the separators, which pipe leads to the discharge channel 312 for cleaned liquid located above the feed channel.
• Fig. 6 illustrates the arrangement of Figure 3, but provided with a dilution liquid conduit 324 and dilution liquid opening 325 in the reject discharge channel 314 for dilut- ing the reject.
• the consistency of the fraction being fed into the auxiliary separator 316 can be regulated as desired in the reject discharge channel 314.
• the dilution liquid is the liquid fed into the arrangement. If the consistency of the reject becomes excessive, dilution ensures an optimal consistency for the auxiliary separator, i.e. the second step.
• Fig. 7 illustrates an alternative embodiment for the arrangement of Figure 3.
• an intermediate wall 326 is arranged in the feed channel and accept channel so that these channels are divided into two spaces, a first 309 ' and a second 309" feed channel compartment and into a first 312 ' and a second 312" accept channel compartment.
• Both feed channel spaces are provided with an inlet 310 ' , 310" for feeding the stream to be cleaned into the arrangement.
• both accept channel compartments have outlets 313', 313" for leading the accept out of the arrangement.
• a first set of separators 301 ' receive their feed through the first feed channel compartment 309' and the second set of separators 301 " receive their feed through the second feed channel compartment.
• the accept In the first set of separators 301 ' the accept is led into the first accept channel compartment 312' and in the second set 301 " the accept is led into the second accept channel compartment 312". From both sets of separators the reject is discharged as a single stream via the reject channel 314 into the auxiliary separator 316, wherein the accept A 3 is formed and reject separated, which reject is removed via conduit 318.
• This embodiment is suitable especially for sand separation in the knot removal of the screen room and the sand removal from reject in fine screening, whereby these sand removals can be performed in the same arrangement.
• Knot separation discharges a stream F 2 and the reject from the screen room is a stream Fi and respectively the accept streams are A 2 and
• the feed channel compartments and the accept channel compartments are of the same size or of different size depending on the amount of material to be treated.
• the accept streams A 2, A ⁇ nd A 3 are led to further treatment.
• FIGs. 8-10 illustrate schematically a principle for adjusting the arrangement according to the present invention.
• the arrangement according to Figure 3 is connected to the side stream of the return circulation of the digester feed system.
• the feed line (in channel 236 according to Figure 2) is provided with feed pressure regulation, which is performed using a pressure regulation valve 331 and a pressure detector PF in channel 236. It is essential that the cleaned liquid from the accept channel 312 is fed into a space devoid of counter pressure, to the suction side of the pumps 251 -251 " to a desired location of the process. Opening of valve 331 located in the feed pipe line 327 connected to the inlet of the feed channel of the arrangement is controlled so that a predetermined decreased pressure prevails in line 327 downstream of valve 327.
• the accept channel is provided with pressure measurement PA1 .
• pressure difference PF-PA1 indicated by pressure detector PDIC and valve 332 located in the accept discharge pipe line 328 connected to the outlet of the accept channel, the flow of the accept can be regulated within a wide range according to each process situation.
• the reject discharge channel 314 is provided with pressure measurement PR1.
• the accept dis- charge channel 329 of the auxiliary separator is provided with pressure measurement PA2.
• the flow of the accept is regulated by means of pressure difference PR1-PA2 and valve 333 located in the accept discharge pipe 330 connected to the accept outlet of the auxiliary separator.
• Fig. 9 illustrates regulation of the flow, when the arrangement illustrated in Figure 6 is connected to the side stream of the return circulation of the digester feed system.
• connection presented in Figure 9 differs from the embodiment of Figure 8 in that dilution 334 is connected to the reject discharge channel.
• the dilution liquid is introduced from the feed line 327 of the arrangement as side stream 334.
• the pres- sure measurement PD is preferably in the reject discharge channel 314.
• Valve 335 is located in the dilution liquid line 334. The opening of the valve 335 is controlled so that a predetermined, lowered pressure prevails in the dilution liquid line after the valve.
• the pressure of the return circulation is typically approximately 10 bar and the pressure in the feed line 327 is decreased typically to approximately 6 bar and in the dilution line 334 to approximately 3-4 bar.
• the flow in said accept line 330 is regulated by means of the pressure difference PD-PA2 between the dilution line 334 and the accept line 330 of the auxiliary separator, using valve 333.
• Fig. 10 illustrates flow regulation when the arrangement of Figure 7 is connected to stream F 2 downstream of the knot washing of the screen room and to the reject stream F1 of the screen room. Then the arrangement is provided with two parallel connected feeds F 2 and Fi for the material to be cleaned, and two accept removals A 2 and
• the feed line is provided with feed pressure regulation, which is effected using a pressure regulation valve and a pressure detector PF1 and PF2.
• the first feed line feeds the first set of separators 301 ' and the second feed line F 2 feeds the second set of separators 301 ".
• the opening of the valve 401 , 402 in the feed lines is controlled so that a predetermined, lowered pressure prevails in them after the valve.
• the flow in the accept lines A2 and A1 is regulated by means of the pressure difference between said feed line and the accept line and by means of a corresponding valve, as in connection with Figures 8 and 9.
• the first and the second set of separators have a common reject channel 314 that leads into the auxiliary separator 316.
• the flow in the latter accept line A 3 is regulated by means of pressure difference between the reject line and said accept line, as already described earlier.
• Fig. 1 1 illustrates the sand separation capacity of separators of different size depending on the particle size.
• the particle size is stated according to ISO Classes, whereby 1 represents the biggest particle size and 5 the smallest.
• the diameter of the separator is 200-300 mm, small particles are much more easily separated than when a separator with essentially larger diameter, typically 800 mm, is used.
• An advantage of the present invention that is worth mentioning is that in connection with the digester feed system the sand separation can be arranged in the side stream of the return circulation, where the flowing is effected by means of digester pressure.
• the cleaned side stream is returned to the suction side of the pumps in the chip feed line, to process locations as required.
• the arrangement according to the invention is compact.
• the sand that has been separated in the whole arrangement is collected into one sand collector that is located in the reject discharge conduit of the auxiliary separator and is periodically emptied.
• the arrangement provides a high separation level for small- particle sand, because the arrangement comprises separators having a small diameter, typically 100-300 mm, preferably 150-300 mm.
• the arrangement typically comprises10-15 separators.
• the connections and regulation devices connected thereto can be arranged compactly. Maintenance and servicing of the arrangement is simple, because the arrangement is easily accessible. The capacity can be changed and optimized simply by changing the number of separators used in the housing of the arrangement.
• the above description relates in more detail to the use of the sand separation arrangement according to the invention in connection with the digester feed system.
• the arrangement can also be used in sand separation of the screen room following the digester room, in sand separation of knot separation and in sand separation of combined knot separation/screen room reject and other corresponding applications.

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• 2010
  • 2010-03-18 FI FI20105269A patent/FI123094B/fi not_active IP Right Cessation
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